Volume 15 Issue 8 March 2017

March 2017 Volume 15 Issue 8

If undelivered return to : 8, Jyoti Wire House, 2nd Floor, Off Veera Desai Road, Near Kolsite, Andheri (W), Mumbai – 400 053. India

Contents 3 - President’s Talk - Managing Editor’s Talk - Chief Editor’s Talk - Guest Editor’s Talk

7 - Chapter Chairmen / Secretary

MARCH 2017 Volume 15 Issue 8

- Chapter News - Chapter Focus - Mumbai

12 - About ISNT - ISNT Team

14 - Dr. Baldev Raj, Indian Scientist - IGCAR

16 - High Energy X-ray Flat Panel Imagers And Systems - Automatic Recognition Of Burn-through In Welds Using Digital Radiographic Image Processing Techniques - Understanding Defect Criticality Using Digital Radiography - Digital Radiography Methods And Factors Governing The Imaging Quality - Residual Stress Measurements In Carbon Steel Weld Joints Made By Sequential Welding Passes Using X-ray Diffraction Technique - A Review of Industrial Computed Tomography Standards

45 - Basic Principles of Eddy Current Testing - Codes & Standards of Eddy Current Testing

50 - Product Gallery 54 - NDE 2016 - A Brief Report

The cover photo illustrates

- 15th APCNDT 2017 - Announcement - NDE 2017 - Announcement

63 - About NGC - Meeting Schedule

65 - Training / Exam Schedule

67 - NDE Patents - Crossword Puzzle www.isnt.org.in

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LETTERS

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“I am extremely happy that March 17 issue of NDE Journal will be shortly in the hands of NDT professionals. Tremendous advances in NDT science are taking place all over the world and Radiography is not an exception to this.

The topics covered in this journal on Digital Radiography, X-ray Diffraction, Computed tomography will be of most interest to the NDT professionals. The recently conducted workshop on Digital radiography at Pune organised by Working Group of Digital radiography of ISNT jointly with Pune chapter received overwhelming response which clearly indicates the importance of these topics in todays contest & trends in NDT. The Eddy Current articles in the back to basics will be of interest to young NDT professionals and practising Service providers. I am sure that the experts will also give a fresh look at the basics of eddy current.

The consistently improved quality of NDE journal is receiving great appreciation from many NDT professionals. The efforts are being made that this Journal will reach the important Public and private sector industries which in turn will benet the advertisers to promote their products. I am sure that all the NDT professionals will nd this NDE journal quite useful. “

MANAGING EDITOR Talk

D.J.VARDE president@isnt.org.in

Cheers to the rst Volume of the year 2017. We completed the four editions of last year, which were very well received by our members & Industry. The success of our journal can be measured by the continual demand from advertisers, an important source of revenue.

This Volume we are highlighting the advances in ‘Digital Radiography’, a subject which has immense following in the ndt industry.

We are featuring an interesting interview with our very respected Past President, Padma Shree award winner, former Director BARC, current Director of National Institute of Advanced Studies, Dr. Baldev Raj. I extend my heartfelt gratitude & respect for our March guest editor, Dr. Debasish Mishra for his prompt & persistent support in bringing together the intellectual set of technical papers, Back to Basics on Digital Radiography & the apt contribution for the cover page image. Special thanks to our Past President Mr. V. Pari for conducting an engaging interview with Dr. Baldev Raj, under whom he has fondly worked for our society in various capacities.

A brief report & event highlights on NDE 2016 held in Thiruvananthapuram is worth reading. Not to miss the grand announcement of 15th APCNDT 2017 to be held in Singapore & the ISNT NDE 2017, Chennai – December, which is being organized on a mega scale.

‘JNDE on the Go’/ E-version, is gaining popularity, undoubtedly for the pros of quick & assured access it offers, resulting in increased number of readers now opting only for the soft copy of JNDE. I welcome our readers who also wish to only receive the soft copy of JNDE to feel free & go through the pages to enroll for a subscription to the soft copy of JNDE, instead of the hard copy which we mail.

CHIEF EDITOR Talk

RAJUL PARIKH secretary@isnt.org.in

The NDE 2016 in Trivandrum was extremely well organized and the level of participation from various sectors of the NDE fraternity was heartwarming. The JNDE team congratulates the organizing team of ISNT Trivandrum Chapter for a job well done.

This issue of the JNDE focuses mainly on X-ray methods for measurements and imaging. It also presents a back to basics article on Eddy Current Testing. The face-to-face interview article with the doyen of ISNT Dr. Baldev Raj will open your mind to new possibilities.

As we grow, ISNT has to focus on new possibilities, new avenues of growth, and new business potentials in order to overcome some of the current challenges faced by the industry. We need new technological products to make NDT more accessible, faster and cheaper. We need our practitioners trained in these new tools. We need academia, researchers, service providers, and endusers to work together in this quest for new technologies. We need end-users to recognize the value of home-grown technologies and support such developments. I am condent and hopeful of this.

DR. KRISHNAN BALASUBRAMANIAM balas@iitm.ac.in www.isnt.org.in

Journal of Non Destructive Testing & Evaluation

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PRESIDENT Talk

LETTERS

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GUEST EDITOR Talk Industries are changing fast. Big data, cloud computing, articial intelligence, automation are recent advancement in technologies which is going to change industries quite a bit. With the usage of these technologies all disciplines are going to gain the advantage of digitization. Specically, for inspection and non-destructive evaluation (NDE), what has worked for last several decades may still continue to work, but will not meet the industry expectations unless the community adapts the fast changes and reinvent itself in a complete new look. Inspection and NDE community is doing its bit to stay in this race and meet industry expectations. As we make those changes and leverage the speed of digital evolution a lot of technology intersection is expected. NDE as an area is going to benet in itself due to this extensive collaboration resulting from the technology intersections and digital revolution.

This special issue is focused on Digital Radiography and specialized application of x-ray diffraction. Radiography remains a very powerful modality for inspection. Digital transformation of this technology is not new, users are now feeling comfortable with it and realizing the benets this change is offering to them. New digital radiography standards have now been introduced through various agencies and that will streamline the conversion of lm to digital with a steady pace in the next few years. Digital radiography has opened up several new applications and opportunities for the industries, to mention a few: 3D imaging (computer tomography), advanced image processing techniques, automatic decision making etc. While the hardware transformation of digital has many positive implications there is yet more work to be done to leverage the complete digital revolution in radiography area. Those are mostly in the data management and interpretation area of digital radiography. Digital tools and fusion of digital radiography with advanced modeling and analytics should enable new techniques, better reliability, fast inspection, automation, and overall easier for the operators while improving value for the users.

We have a few interesting articles packaged in this issue. Special thanks to all the authors for contributing their research and experience in this platform. I am hopeful this will be useful to the community. Please share your insights at the email below, this will help in improving the contents of this journal in the future.

MR. DEBASISH MISHRA debasish.mishra@ge.com

CHAPTER SPACE

Ahmedabad Chapter Shri D.S Kushwah (Chairman) C/o. NDT Services, 1st Floor, Motilal Estate, Bhairavnath Road, Maninagar, Ahmedabad: 380028 (Off): 079-25431845 dskushwah@vsnl.net

Kalpakkam Chapter Shri B. Anandapadmanaban (Chairman) Associate Director, QA-FRFCF & Head, QAD, IGCAR, Kalpakkam - 603 102 Ph: 0 9443881190 bap@igcar.gov.in

Shri Rajeev Vaghmare (Hon. Secretary) C/o. Modsonic Instruments Mfg.co. Pvt. Ltd., Plot No.33, Phase III, GIDC Industrial Estate, Naroda, Ahmedabad - 382 330 (Off): 079 - 22811217

Shri G. Kempulraj (Hon. Secretary) Head, Central Workshop Division IGCAR, Kalpakkam-603102 Ph: 0 9444061792 kempul@igcar.gov.in

Bangalore Chapter Shri Vijayaraghavan (Chairman) No.303, Rr Takht, 37 Bupasandra Main Road, Sanjayanagar Extension, Bangalore - 560 094 Cell:0 9980255932 pvrvan@gmail.com

Kochi Chapter Shri C.K. Soman (Chairman) Dy. General Manager (P&U) Bharat Petroleum Corp. Ltd. (Kochi Renery) PO Ambalamugal 682 302, Ernakulam, Kochi Ph : 0 9495001014 somanck@bharatpetroleum.in

Shri Shashidhar P. Pallaki (Hon. Secretary) CEO, Pallakki NDT Excellence Center No-411, A, 4th Phase, Peenya Industrial Area Banaglore - 560058 Cell:0 9448060717 pallakki@pallakkindt.com Chennai Chapter Dr. Krishnan Balasubramaniam (Chairman) Dean & Professor of Mechanical Engineering, Head of Centre for Non Destructive Evaluation, "MEMH/MDS 301, Department of Mechanical Engineering" Indian Institute of Technology (IITM), Chennai – 600 036 Ph.044 – 22574662 / Cell: 0' 9840200369 balas@iitm.ac.in Shri R. Vivek (Hon. Secretary) Managing Partner, Electro-Mageld Controls & Services.

"Plot No.165, Women’s Industrial Park, Sidco Industrial Estate," Vellanur, Kattur Village, Chennai – 600 062 Ph : 0 9840023015 emcs@vsnl.net / r_vivekh@yahoo.com Delhi Chapter Shri Dayaram Gupta (Chairman) Cell: 0'9891841907 Shri T. Kamaraj (Hon. Secretary) 799-Pocket - V, Mayur Vihar Phase - I, Delhi – 110 091 Ph : 9810364515 isntdelhi@gmail.com /inicondt@yahoo.com Hyderabad Chapter Shri P. Mohan (Chairman) Metsonic Engineers ( P ) Ltd No, 63, Ishaq Colony, Wellington Road, Secunderabad, Telangana - 500015 Ph: 0 9490167000, Fax: 040-27840585 metsonic.engineers@gmail.com

Shri V. Sathyan (Hon. Secretary) Bharat Petroleum Corp. Ltd - SM (Project) (Kochi Renery) PO Ambalamugal 682 302, Ernakulam, Kochi Ph : 0 9446086345 sathyanv@bharatpetroleum.in Kolkata Chapter Shri Dipankar Gautam (Chairman) AB 121, Salt Lake, Kolkata – 700 064 Ph. No. 033 23581072 Cell: 98048 13030 / 98302 03223 dgautam1956@gmail.com / dipankargautam@yahoo.co.in Shri Sreebash Chandra Saha (Hon. Secretary) 123, Ramlal Agarwala Lane, Meghdoot Apartment, Block A, Flat No. 2B, Kolkata – 700 050 Ph. No. :0 98300 21818 replndt@cal.vsnl.net.in Kota Chapter Shri Ambresh Bahl (Chairman) CE(QA), RR Site, NPCIL, PO - Anushakti, Via - Kota (Raj) - 323 307 Ph.01475 - 242164; Cell:0'9413351764 abahl@npcil.co.in Shri A. Varshney (Hon. Secretary) Cell:0'9413358365 abhishekvarshney@npcil.co.in

Shri M. Venkata Reddy (Hon. Secretary) Scientist, NDE Division, Defence R&D Laboratory Kanchanbagh, Hyderabad, Telangana, PIN: 500 058 Ph: 040-24583940, Cell: 9440472195 mallu.venkatareddy@gmail.com

Mumbai Chapter Shri Hemant Madhukar (Chairman) Metal Analysis & Services Pvt. Ltd. 219, Busa Industrial Estate, Udyog Bhavan, Tokersey Jivraj Road, Sewri, Mumbai- 400 015 Ph. No. 022-2413 0813/ 2413 1160 Cell: 98191 43936 / 98206 38249 metalanalysis1997@gmail.com

Jamshedpur Chapter Dr. Amitava Mitra (Chairman) Head, BDM Division, CSIR - National Metallurgical Laboratory, Jamshedpur - 831 007 Ph. No. 0657-2345205; Cell: 0'9430717376 amitra@nmlindia.org

Shri Samir K. Choksi (Hon. Secretary) Choksi Imaging Ltd., 4 & 5, Western India House, Sir P. M. Road, Fort, Mumbai- 400 001 Ph. 0 9821011113 choksiindia@yahoo.co.in

Shri Tarun Kumar Das (Hon. Secretary) Sr. Sct., MST Division, CSIR - National Metallurgical Laboratory, Jamshedpur - 831 007 Ph.No: 0 9955465980 tkdas@nmlindia.org

Nagpur Chapter Shri Jeevan Ghime (Chairman) M/s. Becquerel Industries Pvt. Ltd. 33, Rishikesh Modern Co-op. Hsg Society, Ingole Nagar, Wardha Road, Nagpur - 440 005 jeevan@biplndt.com

www.isnt.org.in

Shri Parag W. Pathak (Hon. Secretary) M/s. NDT Solutions Saket - Pruthvi Appt, Plot No. A+ B, Second Floor, Surendra Nagar, Nagpur - 440015 Ph : 0 7709047371 paragwpathak@yahoo.com Pune Chapter Shri M. S. Shendkar (Chairman) Sonal Industrial Services, Sr. no. 415/1B, Manimangal Society, B-103, Near Siddharth Motors, Kasarwadi, Pune-411034.

Ph: 91-982254633 sisndt@yahoo.com / chairman@isntpune.org.in Shri Uday B. Kale (Hon. Secretary) KUB Quality Services, Plot No 55, Scheme No- 4 Sector 21, Yamunanagar, Nigdi, Pune- 411044 Ph: 91-9822246543 anay2000@gmail.com / secretary@isntpune.org.in Sriharikota Chapter Shri V Ranganathan (Chairman) Chief General Manager - Solid Propellant Plant, SDSC – SHAR, Sriharikota – 524124 Ph:- 08623-225525, M : 0 9490471915 vranga@shar.gov.in Shri B Karthikeyan (Hon. Secretary) Sci/Eng. NDT/SPROB, SDSC – SHAR, Sriharikota – 524124 Ph:- 08623-223076,223382 karthikeyan.b@shar.gov.in Tarapur Chapter Shri Elangovan Mudliyar (Chairman) Hon. Secretary-ISNT, Tarapur Chapter Shri D B Sathe (Hon Secretary) Trichy Chapter Shri. Mathivanan (Chairman) General Manager / Quality New Quality Bldg, HPBP, BHEL, Trichy, Tamilnadu, PIN-620014 Ph : 0 9442649140 gmathi@bheltry.co.in Shri V. Deepesh (Hon. Secretary) Deputy Manager/NDTL, Bldg-I, HPBP, BHEL, Trichy, Tamilnadu, PIN-620014 Ph : 0 9489054004 secyisnttry@gmail.com Trivandrum Chapter Shri G. Levin (Chairman) Group Director, PRG/PRSO, TERLS AREA VSSC, ISRO P.O, Trivandrum-695022 zPh : 0 9496050075 g_levin@vssc.gov.in Shri Shanmughavel (Hon. Secretary) SCI/ENGR SE, QCM/QCG/MME, RFF AREA VSSC, ISRO P.O., Trivandrum - 695022 Ph : 0 9249562486 isnttvm@gmail.com Vadodara Chapter Ms. Hemal Mehta (Chairman) 3, Uday Park, Near M Cube Mall, Jetalpur Road, Vadodara-390 007, Gujarat Ph : 0 9825042087 mehtapmet@gmail.com Shri Jaidev Patel (Hon. Secretary) 11/A Sudarshan Society, Manjaipur, Near Jain Temple, Vadodara-390 011, Gujarat.

Ph : 0'9376255166 jaidev@tcradvanced.com Journal of Non Destructive Testing & Evaluation

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CHAPTER Chairmen & Secretary

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CHAPTER News THIRUVANANTHAPURAM - DECEMBER 2016 TO JANUARY 2017 15th December to 17th December 2016 - “NDE 2016”, 26th National Seminar & International Exhibition.

18th January to 19th January 2017 - ISNT Trivandrum arranged two days PUNE - DECEMBER 2016 TO FEBRUARY 2017 2nd January 2016 to 9th February 2017 - ISNT Level III Course and Examination were conducted. Courses for the following methods were conducted and the Course Director was Mr. Sunil V Gophan.

Ultrasonic Testing - Course coordinator Mr. M S Shendkar, Basic - Mr. Uday B Kale, Radiographic Testing - Mr. B B Mate, Magnetic Particle Testing -Mr. Mandar A Vinze, Penetrant Testing - Mr. Kalesh Nerurkar, Eddy Current Testing - Mr. Vivek Kavishwar & Leak Testing - Mr. Chintamani M Khade. (Leak Testing Course is postponed and will be conducted from 15th to 20th March 2017.

13th January 2017 to 15th January 2017 - A Workshop for Degree Students for Annasaheb Dange College of Engineering (ADCET) on “Advanced Ultrasonic Testing” was conducted. This workshop had a blend of theory and practical taken to understand the basic and applications of Ultrasonic testing.

About 42 students attended this workshop.

2nd February 2017 - A Technical Lecture on “NDT in Aeronautics” was conducted by ISNT ADCET Student Chapter.

The lecture was given by Mr. Abinash Behara of Hindustan Aeronautical Limited, Koraput. He explained the various NDT methods used in aircraft overhaul and maintenance. About 120 students attended the lecture. Mr. Kalesh Nururkar, Jt. Secretary coordinated the program.

2nd February 2017 to 3rd February 2017 - An “NDT Awareness Program“ was arranged in Bharati Vidyapeeth Jawaharlal Nehru Institute of Technology, Pune. Mr. Mandar A Vinze was the coordinator and was supported by various EC members of ISNT Pune Chapter.

3rd February 2017 and 4th February 2017 - National Workshop on “Applications and Advances of Digital Radiography Technologies” was conducted jointly by DRWG and ISNT Pune Chapter. The Workshop was held at Hotel Tarawades Clarks Inn and GE India Pvt. Ltd. Pune.

The Workshop was inaugurated by Mr. Vikas Neeraj, Lloyds Register Inspection Services in the presence of ISNT President Mr. D J Varde, President ( Elect ) Mr. R J Pardikar and Past President Mr. V Pari and ISNT Pune Chapter Chairman Mr. M S Shendkar.

This National Workshop was attended by 42 participants who came from every part of India. The Convenor of this Workshop was Mr. Bikash Ghose and was supported by industr y experts from all over India. There was an overwhelming response and it was decided to make this event annual or biannual.

lecture and practical demonstration as part of short term course conducted by College of Engineering, Trivandrum for the faculty of Civil & Mechanical engineering disciplines of Kerala.

21st January 2017 - Closing LOC of NDE 2016 & family get together of team NDE 2016 was arranged. It was attended by around 125 people including family members.

3rd February 2017 - A Technical Lecture and Product Demonstration in the evening was arranged for the members of ISNT Pune Chapter and the participants of National Workshop at Mahratta Chamber of Commerce. The Technical Lectures were based on Advances in NDE and Product display.

The program was sponsored by M/S Topax NDT Solutions, Mumbai and M/S NDTS, Mumbai. About 80 participants attended the program.

INAUGUR ATION OF ISNT STUDENT CHAPTER AT ENGINEERING COLLEGES 13th January 2017 - ISNT Student Chapter at Annasaheb Dange College of Engineering ( ADCET) was inaugurated at Ashta, in the presence of President Mr. D J Varde, Director of ADCET Mr. Kanhai and Chairman ISNT Pune Chapter Mr. M S Shendkar. On this occasion Mr. Kanhai announced an amount of Rs. 50 lakh to be allocated to establish “NDT Centre of Excellence“ with the help of ISNT Pune Chapter. This Is a rst ISNT Student Chapter in India after the approval by NGC and AGM of ISNT held during NDE 2016 in Trivandrum.

11th February 2017 - ISNT Student Chapter of KIT College of Engineering, was inaugurated at Kolhapur. The inauguration was held in the presence of President Mr. D J Varde, Chairman of KIT Mr. Sachin Menon, and Chairman ISNT Pune Chapter Mr. M S Shendkar.

11th February 2017 - ISNT Student Chapter of Sharad Institute of Technology, was inaugurated on at Yadrav, Ichalkaranji. The inauguration was held in the presence of President Mr. D J Varde, Principal Prof. S A Khot, and Chairman ISNT Pune Chapter Mr. M S Shendkar.

It has been observed that Engineering Colleges are interested in forming ISNT Student Chapter in near future. The ones in line are Bharati Vidyapeeth Jawaharlal Nehru Institute of Technology and Government Polytechnic Pune.

14th EC Meeting on 10th December 2016, 15th EC Meeting on 28th January 2017 & 16th EC Meeting on 22th February 2017.

Inauguration of Student Chapter at ADCET

Inauguration Proceedings of National Workshop on (AADRT-2017)”

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CHENNAI - DECEMBER 2016 TO FEBRUARY 2017 30th November 2016 to 10th December 2016 Radiographic Testing Level-II (IS-13805 / SNT-TC-1A) course and examination conducted. Number of candidates attended course was 19 and examination was 20. Mr.P.Anandan was the course Director and Mr.E.Sathya Srinivasan was the examiner.

Faculties were Mr.B.Ram Prakash, Mr.R.Subbaratnam, Mr.M.Manimohan, Mr.R.K.Kannan, Mr.P.V.Sai Surya Narayana, Mr.M.S.Viswanathan and Mr.N.Vasudevan 19th January 2017 to 28th January 2017 - Surface NDT (MT & PT) Level-II (IS-13805 / SNT-TC-1A) course and examination was held. Number of candidates attended the course and examination was 21. Mr. R.Subbaratnam was the course director and Mr.M.Dharmaraj was the examiner. Faculties were Mr.B.Ram Prakash, Mr.M.Manimohan, Mr.S.Sundararaman, Mr.R.Vivek, Mr.R.Subbaratnam Practical session was handled

by Mr.R.Vivek, Mr.M.S.Viswanathan and Mr.S.Velumani.

13th February 2017 to 18th February 2017 - Visual Testing Level-II (IS-13805 / SNT-TC-1A) course and examination was conducted. Number of candidates registered for the course and examination was 8. Number of candidates attended the course and examination was 7. Mr.E.Sathya Srinivasan was the course director and Mr.J.Shanmugam was the examiner.

Faculties were Mr.R.Chandran, Mr.M.Manimohan, Mr.B.Ram Prakash, Mr.S.Velumani, Mr.Mahesh and Mr.Jayaseelan.

13th February 2017 - One day workshop was conducted at Sri Sakthi Polytechnic College, Tiruvannamalai 14th February 2017 - One day workshop was conducted at Rajalakshmi Engineering College, Tiruvannamalai 17th to 18th February 2017 - Two days workshop at MIT, Crompet, Chennai 22nd January 2017 - Executive committee meeting was held.

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CHAPTER News

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CHAPTER FOCUS - MUMBAI HISTORY : ISNT Mumbai Chapter has all along remained at the forefront in the multi-disciplinary profession of NonDestructive Testing because of the unique industrial and application-oriented research environment obtained in the western region of India. In the metropolitan area of Mumbai and nearby areas, there have been various modern sectors including petro-chemical, deep sea platforms, thermo-electrical and nuclear power, shipping and ship-building, chemicals and fertilisers and aeronautical. These sectors and their regulators require latest techniques that may be available in the eld of Nondestructive Testing from the mandatory safety point of view. Thus a plethora of various NDT equipment manufacturers and NDT professionals to operate and maintain the equipments came on the scene. In accordance with the international mandatory regulatory and code requirements, it was necessary that such professionals should be trained, qualied and certied.

Under such circumstances, a technical, professional body, named NDT Society of India was formed and registered at Kolkata in 1972 with the active participation of National Test House and various private and public sector establishments.

Due to the intense technical activities, as mentioned above in the Mumbai region, the headquarters of the NDT Society of India got transferred to Mumbai. This was also facilitated by the active participation of senior technical personnel from BARC who were working on latest NDT techniques and were trained in international programmes. They were participating in international NDT standards being developed at that time for both the procedural techniques and for personnel certication.

Thus they provided the trainer man-power and initiated the NDT personnel training programmes under the auspices of the NDT Society of India. The BARC, in Mumbai, were providing training and certication in gamma radiography as they were equipped to handle radio-isotopes and their cameras. BARC also provided trainers for topics in radiation safety to the certication programme of NDT Society of India.

ACTIVITIES : Apart from the formal educational training and certication programmes, the Mumbai Chapter has all along been active in organising National Annual Technical seminars on advanced topics in NDT with particular emphasis on various industrial sectors in different seminars. The pro-active NDT equipment manufacturers in Mumbai, the NDT service providing organisations, academic institutions like IIT and engineering colleges, research laboratories like Naval Chemical and Metallurgical lab and the QC section of Mazgaon Docks, Air India, RCF, HP, BP,NPCIL, L & T, Reliance, ONGC etc have been providing huge support to the technical activities of Mumbai Chapter.

Mumbai Chapter is very active in NCB of ISNT . Some members actively participate in formulation and revision of NDT standards of BIS. Again, some members are on the panel of assessors for National Accreditation Board for Laboratories (NABL). Mumbai Chapter conducts many programmes for preparing NDT personnel to appear for the examinations of all levels of ISNT and level III of ASNT. MILESTONES ACHIEVED : In 1989, the Mumbai-based NDT Society and Chennai-based IINDIE merged and Indian Society of Nondestructive Testing (ISNT) was formed.

The Mumbai Chapter is one of the most active chapters of ISNT winning the Best Chapter award several times. Many members of Mumbai chapter have received National Awards of ISNT at Annual Technical Meetings. Further, Mumbai Chapter has instituted its own awards to recognise and honour its outstanding members. The awards are conferred in a ceremony to coincide with the Annual General Body Meeting of Mumbai Chapter.

Mumbai Chapter of ISNT maintains strong bonds with sister professional like IIW, NANSO, and NAARRI. Mumbai Chapter has its own well-equipped premises for ofce and has well-appointed rooms for conducting technical courses and managing committee meetings.

Mumbai Chapter has had the privilege of being nurtured by stalwarts like Shri K Balaramamoorthy, Shri Rameshbhai Parikh, Shri Rajoo Bhatt, Shri V. S. Jain and others to develop and bring it to its current eminent position.

RT - I COURSE CONDUCTED AT MUMBAI CHAPTER.

ABOUT ISNT

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ABOUT ISNT

Indian Society For Non Destructive Testing (ISNT) was formed on 21st April 1989 by merger of two societies namely Non Destructive Testing Society of India registered in Calcutta in July 1972 and Non Destructive Inspection Engineering registered at Madras in March 1981. It is a non-prot organization and is registered under the Tamil Nadu Societies, Registration Act, 1975 (Tamil Nadu Act 27 of 1975) Regd. No.49 of 1981.

The Indian Society for Non-destructive Testing (ISNT) is the society for NDT professionals and practitioners which offers invaluable resources, information and linkages for industrial quality development and professional development to its members. The objective of the Society is to promote the awareness of NDT Science and Technology through education, research and exchange of technical information within the country and internationally to its members and other professionals using NDT. The family of ISNT has more than 6000 strong members. It is a diverse and dynamic family of professionals representing NDT technicians, scientists, engineers, researchers, manufacturers and academicians – all dedicated to improve product safety and reliability. These specialists represent virtually every industry and discipline that may benet from NDT technology.

ISNT holds periodic seminars and workshops on topics relating to NDT methods and applications, as well as exhibitions displaying cutting edge NDT products and services.

ISNT has 18 chapters spread all over the country with headquarters at Chennai. In addition to the above, we have two wings.

• National Certication Board - The National Certication Board has been formed for the training and certication of NDT professionals in India and has been periodically conducting Level-I and Level-II courses through ISNT chapters. NCB-ISNT has been recognized by ASNT as the NSO in India and has been periodically conducting Level III ASNT exams right from 1986. NCB-ISNT plays key role in international harmonization of training and certication.

• QUNEST – Quality Through Non-Destructive Evaluation Science and Technology - The QUNEST trust has been formed to : a) Identify NDE issues and thrust areas; b) Foster NDE Science and Technology nationally with international inputs; c) Continuing Education and d) Enhance international standing and make ISNT a global player.

ISNT keeps the members informed about technological advances, new products, certication and training and international linkages.

MEET THE ISNT TEAM

A.SUBRAMANIAN

K. VENKATESWARLU

K. SAVEETHA

S. EABEN RUTH

RACHNA JHAVERI

ACCOUNTS OFFICER & IN-CHARGE OF ISNT HO. In ISNT since 02-01-2012.

Has vast knowledge and experience in Accounts, Taxation & Administration Matters. Managing day to day functioning of Head Ofce, matters connected with statutory compliance, co-ordinates with ISNT chapters and ISNT Chapters and ISNT Ofce bearers, arrangements for Meetings, guiding HO Staff in their respective area of work.

In ISNT since 1-11 2010.

In charge of work

In ISNT since 23-3-2011.

In ISNT since 4-8-2014.

In-charge of work

Coordinate with JNDE

JNDE EXECUTIVE In ISNT since 17-8-2015.

connected with Accounts,

connected with Training

Executive, Correspondence

In charge of sourcing,

Preparation of MIS,

and Certication conducted

with Subscribers and other

Payment of Statutory dues

by NCB-ISNT as per the

institution in connection

maintenance of Accounting

instruction of NCB Ofce

with JNDE Journal.

handling advertisements, Invoicing, payments follow up. Coordinating payments & JNDE related matter with

Records, Preparation of

Bearers. Takes care of

Assisting accounts in-

Monthly Income &

general correspondences

charge in matters

Expenditure Statement and

and other administration

connected with

matters connected with

Authors / Chapters for write

matters of Head Ofce.

preparation of vouchers,

ups & managing contents.

ISNT Membership.

Head Ofce. Correspond & coordinate with Editors /

Assisting of Ofce in charge

Receipts, Tabulation of

Laying out, designing cover

in regular matters.

Service Tax, Data Entry in

page, editing, proof

Ta l l y a n d o t h e r w o r k

reading, taking for nal

assigned from time to time.

print.

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FACE TO FACE

FACE TO FACE

Dr. BALDEV RAJ (BE, Ph.D)

H

e is the Director - National Institute of Advanced Studies, Chancellor - Academy of Scientific and Innovative Research (AcSIR), Distinguished Scientist and Former Director - Indira Gandhi Centre for Atomic Research, Chairman-Research Council of Gas Turbine Research Establishment- DRDO, Past President Indian National Academy of Engineering, Past President International Council of Academies of Engineering & Technological Sciences.

You have the distinction of being bestowed with the coveted Padma Shri Award, how did you feel when you received the award?

“Recognition by way of awards is always a motivating factor.

More so, if it comes from the highest authority”. Being recognized by your country for the work done gives impetus to take more challenges. Much such recognition I received during my career, I would attribute to my colleagues and the team.

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Being recognized by your country for the work done gives impetus to take more challenges.

Talkng about challenges, whom would you give credit to identify a challenge and to surmount it? Was it is responsible for your growth?

My biggest inspiration is ’My Mother’. I come from a humble family. I lost my father at a very young age. My mother took up the responsibility of bringing up me and my four brothers and eldest sister. My mother worked tirelessly to meet

all our basic needs and went on to educate us with the right kind of up bringing. She always insisted that my expectation out of life should and must be based on ethics and the mantra ”You were born to serve the country!” I grew up in that kind of environment. I hold her singularly responsible for all my achievements. That is why, I respect all women and a strong believer that women in our country should be empowered, for our country to progress.

The second most important aspect I would reason for my upward growth is, to identify challenges and device methods to overcome those challenges. I would look around for such opportunities; it may or may not be in my organization. It could be anywhere. The most important core principle of meeting challenges is to choose domains and quantums with diligent care and imagination. The leadership of India in NDT, welding, Sodium Cooled Fast Reactors and Aqueous. Fuel Cycle Technologies is validation of my approaches to make successes and obtain recognition successively. Vibrant, autonomous ecosystem of DAE provided robust platform for me to experiment and deliver.

For Example: It was a time when USSR split into various republics and we had at that time many air crafts and helicopters purchased out of USSR because of the splits.

Maintaining these air crafts and helicopters posed a problem as we were not getting spares. Then the department started looking for people who could address this issue. In spite of being a metallurgist, engaged in reactor and nuclear industry and not an aerospace man, I convinced the authorities that I would take up the challenge. I identied people from IIT’s, HAL, NAL, LISC and formed an excellent team within very short time.

Finally, we were able to provide a suitable solution. So, in the

FACE TO FACE

You need to be a psychologist too to understand people’s needs, capacities, etc. Every single individual is unique, no two humans are alike. Once you understand their needs, aspiration and passion to serve the organization you have a good opportunity to build a task force committed to the challenges we take. Then rest is comfortable. It is one's responsibility to stay to one’s ethics, discipline, not to overstep or hurt anyone. It is not machines, money or materialistic possessions, but people, who make the planet. So, I make sure to take equal interest in working with my people. All successful people have a huge network of people who they can count on & you need to make your network naturally by your goodness.

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All successful people have a huge network of people who they can count on & you need to make your network naturally by your goodness.

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When talking about nurturing you were also passionate about NDT and instrumental in bringing together top names in NDT to ISNT, can you throw some light as why you felt a strong society was required to further the cause of this science.

In early 90’s when there were two societies, a need arose to amalgamate both to form a single society, to project to the international community, that India - in spite of being looked down in those days, was formidable in the area of engineering.

Many pioneering efforts in NDT were being carried out by individual organizations in various industrial sectors. I was fortunate enough to have doyens in the eld like Prof. Rama Rao, Mr. Kondal Rao, Dr. CRL Murthy, Mr. Deenadayalu and many more who shared the same thought. It was easy to bring in like-minded people and you know the rest is history. Today, our society has representation in all the international committees. This denitely will pave way for a robust platform for future.

When Prof. Halmshaw came to India for the rst time. He felt our technical competence in NDT was not up to the international standards and during a private conversation with me he expressed this view. I calmly explained to him why he was not correct in his opinion. I wrote him in my letter, Indians, generally do not argue with their elders and would passively listen without reacting and please do not mistake that for their

Today, our society has representation in all the international committees. This denitely will pave way for a robust platform for future.

You held important positions both in ISNT as well as ICNDT. What would you rate as the single most achievement during your tenure?

We have to be rm in believing what is good for the NDT community and as a president of both ISNT as well as ICNDT, I formed various working groups like PGPC, training and certication committee for certication in BIS, which are very active today to serve the society. Not only at ICNDT, even later on when I became the alternative Chairman of Senior Advisory Group of Nuclear Energy, IAEA, Apex body; we were able to bring about changes without debating bur?? by engaging the wisdom of the entire team. This was again successfully employed in International Institute of Welding, a group of 60 societies, representing 60 Countries. I was President from (2011-2014) for three years.

I am a strong believer in discriminating between issues that are important and ones that are not so important. Prioritizing the importance of issues makes the difference.

What would you rate as single most achievement in our society?

“The condence built in my people that our society can deliver”, is the single most satisfying achievement for me.

At this juncture, when India is striving forward, what role you envisage for our society.

Today for me, skill development is the most important role that the society should aspire for. Society should not shy away from the responsibility to take this single agenda to make world take note of our skill development program to meet the challenging demands of the industry.

We know of your passion for interacting with students and young professionals for mutual inspirations and service to society. What is your advice to them?

Coming from humble background, I believe that best gift you can give back to the nation is to motivate, trigger, a group of students. I may not be able to change a person in an hour’s talk.

Nevertheless, I would not miss a single opportunity to address young minds & inspire them. If I am successful to plant a seed in their thought process, then who knows it may lead to an outstanding performance in their chosen area.

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I may not be able to change a person in an hour’s talk, Nevertheless, I would not miss a single opportunity to address young minds & inspire them.

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Talking about empowering, one trait any successful leader employs is delegation of responsibilities, many of us know you excelled in that area. How did you identify, nurture and monitor and empower those to whom you delegated assignments.

I have been fortunate to have young colleagues and friends in many organisations who have been ever helpful. I base it on emotional banking; hence, you need to give in a great amount of sensitivity & dignity when working with people.

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I respect all women and a strong believer that women in our country should he empowered, for our country to progress.

incompetence. It’s just that, they do not want to prove they are right by arguing. Dr. Halmshaw, later acknowledged and accepted my explanation and corrected his view point on the core competence of our professionals.

As interviewed by Mr. V. Pari - Past President - ISNT, Proprietor & Chief Executive Scaanray Matallurgical Services, Chennai.

FACE TO FACE

beginning nobody knows the answer to a problem but as we take the challenge in a committed manner one can conquer any challenge.

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HIGH ENERGY X-RAY FLAT PANEL IMAGERS AND SYSTEMS William Ross 1, Clifford BUENO 1, Jeffrey SHAW 1, Joshua SALISBURY 1, Edward J NIETERS 1, Carl LESTER 1, Mark OSTERLITZ 1, Doug ALBAGLI 1, Walter GARMS 2 1 GE Global Research Center, Niskayuna, NY, USA 2 Morpho Detection, Inc., Newark, CA, USA Contact e-mail: - rossw@ge.com ABSTRACT Use of large area X-ray thin lm transistor (TFT) at panel imagers (FPIs) is increasing in high energy (~1–16MeV) medical imaging, security scanning, and nondestructive testing applications. Modalities in use include fast radiography, laminography, and computed tomography (CT). In this effort, commercial at panels, initially developed for use in low energy medical and industrial applications, were updated to mitigate radiation damage of electronic components, and to improve x-ray efciency for enhanced detection, speed, and image quality (SNR and CNR). Corrections for various forms of x-ray scatter were implemented to manage the loss of image quality performance. Additionally, the TFTs were further modied to manage scintillator radiation damage. This document will address the physical alterations of a series of 20-cm x 20-cm at panels for use in high energy digital radiography, laminography, and computed tomography.

This work has been supported by the US Department of Homeland Security, Domestic Nuclear Detection Ofce, under competitively awarded contracts HSHQDC-07-C-00036 and HSHQDC-08-C-00138. This support does not constitute an express or implied endorsement on the part of the Government.

1.0

L

INTRODUCTION

arge scale high energy (>1 MeV) non-destructive imaging systems typically used for rocket motor [1] and automotive [2], and other similarly-sized asset inspections are often formed using linear detector arrays (LDAs). These detection devices are optimized for high x-ray absorption (>50%), have discretized scintillator/diode modules, have limited sensitivity to x-ray scatter and have moderate spatial resolution. Due to their linear geometry, signicant time is needed to scan across large objects, be it for radiography, laminography, or computed tomography (CT). In this effort, modied at panel imagers (FPIs) were used in prototype cargo inspection systems to vastly decrease the time to scan pallets and containers while maintaining good image quality. The FPIs increase the vertical height of the detector, transitioning away from standard single (or double)-row multi-line arrays (fan-beam geometry), to an array with many hundreds or thousands of pixel rows (conebeam geometry). Coincident with increasing detector height, multiple FPIs were tiled horizontally to increase the detector width.

These large area (typically 1m x 20 cm) compound detectors then enable improved high speed radiography and, due to their extent, laminography. These same detectors can also be used to complete cone beam CT scans in a fraction of the time compared to fan-beam scanners.

To manage some of the drawbacks of larger area devices when used with high energy x-rays, commercially available amorphous Si (a-Si) thin lm transistor-based (TFT) FPIs, initially developed for lower energy (60keV-450keV) medical and industrial applications by General Electric, were modied to mitigate the radiation damage suffered by the FPI data phy, laminography, and computed tomography.

acquisition electronics and to improve x-ray absorption efciency at high energies. This was achieved by 1) physically removing the tightly bundled electronics from the standard FPI package, and 2) depositing ultra-thick ( 23mm) layers of needle-based CsI:Tl scintillator onto bare TFTs for improved stopping power. Furthermore, corrections were developed to remediate several sources of x-ray scatter that are prevalent in these energy ranges.

This paper will describe the above physical alterations of a series of stock 20-cm x 20-cm at panels for use in high energy digital radiogra 2.0 LARGE AREA SCINTILLATOR DEVELOPMENT

Figure : 1a) 2-mm CsI:Tl needle-based scintillator, 1b) 3-mm pitch NaI, 1c) 1-mm pitch CdWO4, 1d) 2.5-mm CsI:Tl. Needle-based CsI compared to various segmented single crystal scintillators. The structure visible in the segmented scintillators signicantly reduced the visibility of important features in the image. These segmented devices have trouble imaging even a simple Pb letter (B).

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For these limited thickness changes at 9 MeV, output signal is observed to increase almost linearly with scintillator thickness, as expected. SNR values obtained on gain/offset corrected images also demonstrate improvements close to the ideal square root dependence. For example, the 10mm scintillator has a 5X improvement in SNR for a 25X enhancement in During this project, it was discovered that the needle structure thickness over the 0.4mm scintillator.

The modulation transfer functions (MTFs) of the 3 of chemical vapor deposited (CVD) CsI:Tl scintillator can be detectors (0.4-mm, 2-mm, and 10-mm) were also obtained at 9 maintained up through several mm in height as shown in Fig. 2.

MeV. A rolled W edge was placed on each detector face at a 5degree angle from the column direction to measure the response. Note that the 3 scintillator thicknesses have roughly the same resolution performance at this energy, indicating that Compton scatter and pair production dominate any blurring effects. At 20% modulation, the spatial resolution is approximately 0.3-0.4 lp/mm (~1mm spatial resolution).

Selection of Needle-Based CsI:Tl Scintillator Several phosphor and scintillator materials were considered and coupled to bare a-Si TFT arrays for testing. These included segmented ceramic and crystal scintillators, such as those shown in Fig. 1.

3.0 P R O T O T Y P E L A R G E A R E A X- R AY DETECTOR (LAXD) A large area imaging device was assembled by combining several 20 cm x 20 cm FPIs into a 1 x 5 grouping. Each detector consisted of a GE Healthcare TFT array coupled to needle-based CsI:Tl scintillator, as described above. The thick scintillator layer is topped by a reective lm for improved light capture efciency, and hermetically sealed by an aluminium cap. The build steps for this large area assembly are shown in Fig. 4.

Figure : 2 a) Ultra-thick needle-based CsI:Tl layer grown directly on a-Si read structures, b) 10-mm scintillator a-Si at panel detector, with of a tape measure and a level, c) resulting x-ray image acquired using 9MeV x-ray beam. The windings of the tape measure are visible. The ultra-thick needle-based scintillator is maintaining high spatial resolution.

Comparison of Different thicknesses of Needle-based CsI:Tl The performance of various thicknesses of CsI:Tl at 9 MeV is shown in Fig. 3. The 3 thicknesses used are 0.4 mm, 2 mm, and 10 mm. The underlying TFT arrays consisted of a 1024 x 1024 grid, with a pitch of 200 microns.

Figure 4 : Starting from an amorphous Si panel, ultra-thick CsI:Tl (10mm thick) is grown on the panel, control electronics are added, the mother board is removed and shielded from the direct x-ray beam, and multiple detectors are overlapped to provide a 1m long x 20 cm high array. This is assembled in a light tight box, with ports for incoming/outgoing signals.

A 1 mm sheet of copper is placed across all 5 detectors (only 4 shown in Fig. 4). All 5 detectors are read-out simultaneously and are treated as a single detector unit. The native pixel layout is 5120 x 1024 with 200 micron pitch, with a maximum read-out rate of 30 frames/sec. When binned by up to 3 x 3 pixels, the maximum read-out rate increases to 100 frames/sec. This high readout rate is important for detecting features in fast moving objects, such as scanned cargo. Source, a Varian M9 LINATRON accelerator, pulsing (1-16 pulses/frame) is synched to detector read-out to Figure 3 : Upper left: signal response normalized for dose rate of avoid image artefacts. the 3 scintillators as a function of steel lter thickness. Upper right: the Modulation Transfer Function of the same scintillators using a A prototype cargo inspection system built around this detector 2-in lter. Lower left: SNR levels VS lter thickness array is shown in Fig. 5. The compound detector assembly can

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CONCLUSIONS either be oriented horizontally, for static radiography, 4.0 laminography and CT, or vertically, for dynamic scanning across large cargoes. An image acquired with this system is shown in Flat panel imagers originally developed for medical applications Fig. 6. are nding new applications in x-ray inspection of large, dense objects ranging from heavy cargo, to additively manufactured components. Many of the risks associated with these devices for use in high energy megavolt x-ray beams have been addressed by developing ultra-thick high resolution CsI:Tl needle based scintillators, reducing the sensitivity to scatter, and protecting the readout electronics of the array. Tiling of these at panels has been shown to be successful in that assemblies larger than 1 m have recently been manufactured Figure 5 : Different congurations of the LAXD systemwhere vertical and horizontal scanning of surrogate cargo is achieved.

The detector can also be rotated to be in a horizontal or vertical conguration. The system is capable of large scans where the detector can be moved horizontally on a track 6m long. This also enables laminographic and large area radiographic scans. The rotation stage provides a CT capability.

with manageable artefacts.

5.

REFERENCES

[1] Burstein, P; Bjorkholm, PJ; Chase, RC; Seguin, FH; “The largest and smallest X-ray computed tomography systems”, Nuclear Instruments and Methods in Physics Research, Volume 221, Issue 1, 15 March 1984, Pages 207–212.

[2] Salamon, M; Boehnel, M; Reims, N; Ermann, G; Voland, V; Schmitt, M; Uhlmann, N; Hanke, R; “Applications and Methods with High Energy CT Systems”, 5th International Symposium on NDT in Aerospace, 13-15th November 2013, Singapore http://212.8.206.21/article/aero2013/content/papers/36_Sala

Figure 6 : Lateral scan across the 5-detector module in its vertical conguration. Running at 200 mm/sec, the SNR is improved by combining subsequent frames through temporal averaging (TDI mode), or shift and add image processing. This image is obtained in about 5 sec. The system has been demonstrated up to 1.5m/sec.

mon.pdf [3] Droege, RT; Bjngard, BE, “Metal screen-lm detector MTF at megavoltage x-ray energies” Medical Physics; v:6 i:6 p:515-8; 11/1979.

[4] ISO 16371-1:2011, Non-destructive testing -- Industrial computed radiography with storage phosphor imaging plates -Part 1: Classication of system.

Figure 7 : provides an example of a laminographic scan of a pallet laden with two layers of automotive alternators and a box of laptops, with solid cubes and spheres in and among the cargo.

Following the laminographic reconstruction, shown on the right, the constituents of each layer of material are easily separated in depth, resulting in much higher contrast detectability while demonstrating the high spatial resolution of the detector panels.

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AUTOMATIC RECOGNITION OF BURN-THROUGH IN WELDS USING DIGITAL RADIOGRAPHIC IMAGE PROCESSING TECHNIQUES Shilpa .I. C (a), Deepesh. V (b) (a) Sastra University, Tanjore. (b) Bharat Heavy Electricals Limited, Tiruchirappalli.

Email: d2208881@gmail.com ABSTRACT Digital radiographic imaging systems have signicantly enhanced the reliability and productivity in industrial radiography. This has also resulted in the development of automatic evaluation systems for several applications, and thereby addressed the problems such as subjectivity, inconsistency etc. associated with manual evaluation.

However, automatic defect recognition in the case of welds is still considered a challenging area, due to the complex gray level variation in the weld prole. This article presents the studies done for the development of image processing techniques for automatic detection of ‘burn-through’ defect in tubular butt welds. Most of the available ADR algorithms rely on the well-dened patterns of typical defects such as pores, lack of fusion etc.

However, this approach is not effective in the case of burn-through, since it is highly unpredictable and inconsistent in terms of its features. This study proposes, a morphological image processing based approach as well as texture feature based approach for burn through detection and characterization respectively.

1.0

INTRODUCTION

E

xtensive research has taken place on the development of efcient computer programs, inspired by the pattern recognition skills of human beings. As humans, we observe several characteristics of objects, such as colour, shape, size, smell, etc. These characteristics act as inputs to our sensors for grouping the objects in to various categories. The basic idea of pattern recognition in automatic systems is the classication of data, based on regularity or irregularity [1]. Pattern recognition has found its application in several elds such as industrial automation, remote sensing, speech and image recognition, data mining, natural language processing etc. One of the major applications in the industrial automation is the inspection of product quality, using automatic image recognition systems, wherein the digital image processing and pattern recognition techniques are blended together. These systems, used in lieu of manual evaluation, reduce subjectivity, fatigue etc. and results in faster inspection.

Radiographic Testing (RT) is a very powerful and well established Non-Destructive Evaluation (NDE) method for the assessment of the quality of engineering materials, in a wide range of elds such as power, aerospace, energy, transportation etc. Evaluation of radiographic images for the detection of defects in the industrial applications is a challenging task and normally performed by specially trained, certied and experienced RT Level II personnel. It is the pattern recognition skills which help the human operator, detect and characterize the defects in order to arrive at the decision regarding acceptance / rejection of the test object. However, human

interpretation of complex objects such as weld joints on a large scale basis is cumbersome and dependent upon the knowledge and experience of the inspector [2]. Studies show that continues evaluation causes monotony and fatigue to inspectors, affecting the consistency and effectiveness [3]. Researchers have found out that this inconsistency and subjectivity induced uncertainty is sometimes as high as 20 %, which drives expensive redundancy measures to ensure an error free evaluation [4].

2.0 NDE BASED ON DIGITAL RADIOGRAPHY (DR) Despite several advantages, conventional lm radiography is expensive, hazardous and time consuming [5]. Limitations such as long exposure times, delays on account of the chemical processing of lms, handling and disposal of hazardous chemicals, lm archival cost etc. are the strong reasons for the need of a better alternative to lm radiography. Over the time, there have been signicant technological developments, leading to new materials, fabrication processes, advanced electronic systems, etc. which have led to the steady transformation from lm based techniques to digital image based RT. A number of technologies viz., lm digitization, digital detector arrays, photo luminescence exible re-usable phosphor imaging plates, etc. have been developed in the category of Digital radiography.

Digital Detector arrays (DDA) or Digital at panel based imaging devices convert the incident X-ray image to digital image almost instantaneously and thus facilitate real time radiography wherein the irradiation and evaluation of images happen concurrently. Digital radiographic systems provide a safer and faster RT experience by avoiding the chemical processing of

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Moreover, the overall image quality is superior than lms with excellent signal to noise ratio, spatial resolution, dynamic range and linearity [6]. Quantization factor during the analog to digital conversion stage in digital radiography is one aspect which underwent signicant improvement, resulting in the digital images containing much more information than that of the corresponding lm images [7]. Commercially available DDAs provide 14-16 bit digital radiographic images which offer signicant opportunities for image enhancement and thereby improved defect detection capability. These imaging devices have facilitated the development of Automatic Defect Recognition (ADR) in various applications.

concavity etc. Common defects found in RT of fusion weld joints are porosities, gas holes, lack of fusion, incomplete penetration, crack, excess penetration, burn-through, slag, tungsten inclusion, root concavity etc., depending upon the welding process, joint conguration, etc. Image processing of the digital radiographic gray scale images should consider the features of each of these defects to make sure that the operations extract all the defects. If the best suited image processing steps for one type of defect could potentially erase another type of defect in the same weld joint, then unique steps should be used for each defect.

3.0 AUTOMATIC DEFECT RECOGNITION (ADR) In Radiographic Examination, an ADR system scans through the gray scale radiographic image, detects the defects and classies the same as per the pre-determined features, and in many cases takes the decision of acceptance or rejection of the test object.

The basic steps of ADR are image registration, segmentation, detection of the defect, and classication.

Two common approaches followed for defect detection in radiographic images are, detection based on similarity and detection based on variation [5]. The former approach involves matching the features of a region with that of the typical defects stored in the data base, whereas the latter is based on comparison of an image with that of the features of a set of good weld images, for verication of signicant variation. Most of the weld detection algorithms use the former approach [16, 18].

Researchers have suggested a number of image processing techniques for the detection of porosities, incomplete penetration, lack of fusion etc. in welds [16, 19-21]. In all these works, the key idea is the recognition of the common patterns of a particular type of defect appearing in the sample images under study. However, defects such as burn-through, excess penetration etc. are reported to be difcult for automatic recognition, due to the inconsistency in their patterns.

Several approaches have been suggested by researchers for ADR problems. Gayer et al., showed the application of Fast Fourier Transform (FFT) for defect detection in the case of weld radiography [8]. Liao and Li introduced back ground subtraction method which is a popular method in a number of applications such as welding and casting inspection [9]. Similarly, morphological operations such as erosion and dilation have been used for the defect detection [10].

A number of methods have been suggested in the area of defect classication also. These include shape features, linear correlation classiers, texture feature based classication, fuzzy logic etc. [10-13]. Articial Neural Networking (ANN) techniques are used in many ADR systems for training of the systems for enhanced efciency and speed. Some of the ANN learning algorithms used in ADR applications are Multi-Layer Perceptron (MLP), Radial Basis Function (RBF), Support Vector Machine (SVM) etc. [14-17].

5.0 AUTOMATIC RECOGNITION OF BURNTHROUGH Burn-through is a defect, which is normally found in the case of steel tubular butt welding processes using automatic or semiautomatic equipment [16]. It occurs as a result of local explosions within the weld pool during the progress of welding process, as a result of excessive current uctuations.

4.0 DETECTION OF WELD DEFECTS In the context of ADR for industrial inspection, welds are considered amongst the most challenging problems, due to the complex gray level variations in the radiographic images.

Typical welds subjected to RT, have highly irregular surfaces, which result in drastic variations in the digital radiographic images, and sometimes even mask or misguide the detection of defects. In fact this evaluation is considered very challenging even for expert inspectors, when the irregularity of weld surface disturbs the gray level homogeneity of the good (non-defective) regions, since the basic criteria for recognition of the defects is the pattern of variation of gray level with respect to the neighborhood Common defects found in RT of fusion weld joints are porosities, gas holes, lack of fusion, incomplete penetration, crack, excess Figure 1: Schematic diagram of Double Wall Double Image penetration, burn-through, slag, tungsten inclusion, root Technique in RT (22).

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Consequently, a lump of molten weld metal gets thrown out from the weld pool and falls in the neighborhood as spatters.

The extent of this explosion is unpredictable, as the possibility of current uctuations when the weld electrode reaches a weaker region of the tube is quite random. Similarly, the nature of explosion, the potential shape of the voids created by this explosion, as well as the location of spatter deposition is random.

In order to detect burn-through and other defects, RT of tubular butt welds is done using double wall double image technique, wherein, the radiation passes through both source side as well as lm (or imaging devise) sides of the tube weld and forms an elliptical image of the Region of Interest (ROI), showing the entire circumference, as shown in gure 1[22].

5.1

PRE-PROCESSING

Figure 3. Edge detection of the tube butt weld region of interest using Sobel operation.

The geometric features are calculated from the edge detected image and compared with that of a standard set of ROI pruned images, and based on this, the coordinates of cropping are determined in the case of each input image. Figure 4 shows the image where the ROI is extracted. This shows the elliptical weld portion and immediate neighborhood.

The image processing operations in this work were executed using MATLAB R2014a [23]. A number of DR sample images of tubular butt welds were chosen, in which burn-through is the prominent defect. Typical DR image obtained with DWDI technique is shown in gure 2.

Figure 4. ROI after segmentation

Figure 2. Typical DR image of tubular butt weld joint captured by DWDI technique.

Only a small portion of this image is the ROI, which includes the elliptical weld prole, which appears darker than it back ground, and the adjacent tubular portion, which is lighter. The rst step is the extraction of ROI, which is done based on the detection of approximate coordinates of the tube with respect to the dark (black) back ground. Further extraction of ROI from the tubular portion is done by the edge detection, using a 3 x 3 Sobel operator [24]. This operator measures the gradient of gray level in the image and produces an output image where the edge features such as wall of the tube, boundary of the weld etc. which corresponds to high spatial frequency are emphasized. A kernel of size 3x3 and values (1, 2, 1), (0, 0, 0) and (-1, -2, -1) in the rst, second and third rows respectively, was used. The gradient measurement by this operator is performed in horizontal as well as vertical directions. Features such as tube wall thickness, are enhanced in vertical operation and weld edges in horizontal operation. Figure 3 shows the effect of this operation on an image.

5.2.

BURN-THROUGH DETECTION Analysis of the sample shows that, unlike other defects, burnthrough does not have consistency in its shape, size, orientation or location. Moreover, this defect cannot be encompassed in a conned space. As learnt from the manual evaluation practices, commonly seen feature which is used to distinguish burnthrough, is the brighter spots accompanied by sporadic dark gray spots due to spatters. These dark spots may appear anywhere in the region of interest, or even at locations outside ROI. Therefore, it is not reliable to follow the conventional approach of tracking shape or size based patterns in the case of burn-through. The approach followed in this work involves image processing activities which extract the drastic gray level variations, within the ROI, which is unique to the burn-through.

ROI of a burn-through image is shown in gure 5. The contrast of ROI was enhanced with the stretch limit option, as shown in gure 6. This image was used as the input for certain morphological operations to extract burn-through features.

These are non-linear operations related to the shape or morphology of features in an image [25]. This concept deals with the transition in gray level in an image, and these are represented as closed contours. Based on the analysis of outputs of various morphological transforms, top-hat transform was chosen for the extraction of burn-through.

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Figure 5: ROI of a typical input image of weld with burn through

Figure 7: Image of burn through after application of top-hat transformation and contrast enhancement

Figure 6: Edge detection of the tube butt weld region of interest using Sobel operation

This transform looks for the difference between the input image and it’s opening by the structuring element [26]. Based on trial and error approach, a disk element was used as structuring element, in this study. Linear transform based Contrast enhancement was done on this image in order to stretch the relative brightness and darkness of pixels. In this operation the darkest pixel in the image is transformed in to the lowest possible value (=0) and the brightest pixel is assigned the highest possible value as shown in equation 1.

(1) im’ (x, y) = INT {

2K (im (x, y) - Gmin)} Gmax - Gmin

Where im(x, y) and im'(x, y) are the input and out-put gray value of the pixel respectively. Gmax and Gmin are respectively the maximum and minimum gray values within image. ‘k’ is the size of the image in terms of number of bits. Since the out-put gray value may be a fraction, this has to be converted to the closes integer value, which is represented by INT. Results of top-hat transformation and subsequent contrast enhancement are presented in gure 7.

5.3.

BURN-THROUGH FEATURE EXTRACTION Classication of defects in to various categories is a critical activity in ADR, as the decision of disposition depends upon primarily the nature and size of the defect. During the course of image processing operations it is quite possible that many indications emerge out may not fall in the expected category.

Therefore it is important to look for certain features of the defects, to short list and classif y the indications.

Figure 8: Edge enhanced image showing the edges of burn through.

In the case of burn-through, the texture features were considered for classication. These features dene the gray level variation between two pixels separated by a spatial relationship [12]. There are 14 commonly used texture features known as Haralick features [27-28]. The basis for these features is a Mc x Mc sized matrix, known as Gray-Level Co-occurrence Matrix (GLCM), where Mc represents the total number of gray levels in an image. The generation of an element [i, j] of GCLM is done by adding the number of times a pixel of gray-value ‘i’ and ‘j’ occur adjacent to each other and subsequent division of these matrix by the total number of comparisons considered. Hence each entry indicates that i and j come together, which could happen in horizontal, vertical and diagonal directions. Amongst these, the features used for burn-through feature extraction problem are contrast, correlation, energy and homogeneity. These features are dened in equations 2 to 5[12].

(2)

(3)

(4)

23

(5)

Where µx, µy, σx, σy are the means and standard deviations of px, py, the partial probability density functions.

In the case of burn through feature extraction, the out-put is an array of values corresponding to these texture features. The range of values of these features were established based on the review of a set of sample images, containing burn through, other defects, and no defects respectively.

6.0

CONCLUSIONS

This study focuses on the development of an image processing algorithm leading to the detection of burn-through, which is considered a challenging defect to defect using ADR programs, unlike other weld defects such as porosity, lack of fusion etc.

This work shows the use of morphological operators in the detection of burn-through.

Even though the image processing steps here address burnthrough in an exclusive manner, the applicability of this program for screening of weld joints which contain other defects also has been ensured, by trials on sample DR images of tube butt welds containing other type of defects. The results showed that, this algorithm does not give false positives with respect to the images containing other defects.

7.0

REFERENCES

1. Bishop, C.M., 2006, “Pattern Recognition and Machine Learning”, Springer science LLC. 2. Fucsok, F., and Scharmach, M., 2000, “Human factors: The NDE reliability of routine radiographic lm evaluation”, Proc. 15th World Conference on Non-Destructive Testing, Roma.

3. Lim, Y., Ratnam, M.M., and Khalid, M.A., 2007, “Automatic classication of weld defect using simulated data and an MLP neural network”, Insight, 49(3), pp. 154-159.

4. Merry, D., 2005, “Digital Radiography”, Workshop on Digital Radiography, GE Global Research Centre, Bangalore.

5. Pardikar, R.J., 2008, “Digital radiography and computed radiography for enhancing the quality and productivity of weldments in boiler components”, Proc.17th WCNDT, Shanghai, China.

6. Vaidya, P.R., Narayana Rao, A.V.S.S., 2000, “Performance Evaluation of the Imaging Plates for Industrial Radiography Application”, Journal of Non-Destructive Evaluation, 20(3), pp. 53-56.

7. Williams, M.B., Krupinski, E.A., Strauss K.J., Breeden W.K., Applegate, K., Wyatt, M., Bjork, S., Rzeszotarski, M.S., and Seibert J.A., 2007, “Digital Radiography Image Quality: Image Acquisition”, Journal of American College of Radiology, 4(6), pp. 371-388.

8. Gayer, A., Saya, A., and Shiloh, A., 1990, “Automatic recognition of welding defects in real-time radiography”, NDT&E International, 23(4), pp.131-136.

9. Liao, T. W., and Li, Y. M., 1998, “An Automated Radiographic NDT System for Weld Inspection: Part II - Flaw detection”, NDT&E International, 31(3), pp. 183-192.

10. Soa, M., and Redouane, D., 2002, “Shapes recognition system applied to the non- destructive testing”, In Proc. 8th European

Conference on Non-Destructive Testing (ECNDT 2002), Barcelona, Spain.

11. Silva, R. R., Siqueira, M. H. S., Calôba, L. P., da Silva, I. C., De Carvalho, A.A., and Rebello, J. M. A., 2002, “Contribution to the development of a radiographic inspection automated system”, In Proc.

8th European Conference on Non-Destructive Testing (ECNDT 2002), Barcelona, Spain.

12. Merry, D., and Berti, M.A., 2003, “Automatic detection of welding defects using texture features”, Insight, 45(10), pp.676-681.

13. Wang, G., and Liao, W., 2002, “Automatic Identication of different types of welding defects in radiographic images”, NDT&E International, 35, pp. 519-528.

14. Lawson, S.W., and Parker, G.A., 1994, “Intelligent segmentation of industrial radiographic images using neural networks”. In: Machine Vision Applications and Systems Integration III, Proc. of SPIE, 2347, pp.245–255.

15. Liao, T.W., 2003, “Classication of welding aw types with fuzzy expert systems”, Expert Systems with Applications, 25, pp. 101-111.

16. Deepesh, V., Pardikar, R.J., Karthik, K., Sricharan, A., Chakravarthy, S., and Balasubramaniam, K., 2011, “Automatic Defect Recognition (ADR) system for real time radiography(RTR) of straight tube butt (STB) welds”, Proc. National Seminar and Exhibition on Non-Destructive Evaluation, Dec 8-11, Chennai, India., pp.355-359.

17. Wang, X., Wong, B.S., and Tan C.S., 2010, “Recognition of Welding Defects in Radiographic Images by Using Support Vector Machine Classier”, Research Journal of Applied Sciences, Engineering and Technology, 2(3), pp. 295-301.

18. Srikanth, T., Kamala, V., 2012, “An innovative method for defect detection in Digital Radiography Images”, International Journal of Engineering and Innovative Technology (IJEIT), 1(6), pp.194-196.

19. Yahia, N.B., Belhadj, T., Brag, S., Zghal, A., 2011, “Automatic detection of welding defects using radiography with a neural approach”, Procedia Engineering 10, pp.671–679.

20. Hassan, J., Awan, A.M., Jalil, A., 2012, “Welding defect detection and classication using geometric features”, Proc. 10th International Conference on Frontiers of Information Technology, pp.140-144.

21. Mythili, T., Magret, A.S., Sachin, K., 2010, “Welding defect detection and classication using geometric features”, International Journal of Computer Applications, (0975 – 8887)10(2).

22 ASME Boiler and Pressure Vessel Code, 2015, sec. 5, article 2.

23. MATLAB R2014a, “Digital Image Processing”, Prentice Hall, New Jersey. <http://in.mathworks.com> 24. Marr, D., and Hildreth, E., 1980, “Theory of Edge Detection”, Proc.

Royal Society of London, Series B, Biological Sciences, 207(1167), pp.

187-217.

25. Heijmans, H., 1994, “Morphological image operators, Advances in Electronics and Electron Physics”, Academic Press.

26. Raid, A.M., Khedr, W.M., El-dosuky, M.A., and Aoud, M., 2014, “Image restoration based on morphological operations”, International Journal of Computer Science, Engineering and Information Technology (IJCSEIT), 4(3).

27. Haralick, R.M., Shanmugam, K., and Dinstein, I., 1973, “Textural features for Image Classication”, IEEE Trans. Systems, Man and Cybernetics, 3, pp. 610-621.

28. Castleman, K.R, 1996,

24

UNDERSTANDING DEFECT CRITICALITY USING DIGITAL RADIOGRAPHY *Adal Arasu, Adjunct Professer, VIT University, Tamil Nadu Formerly DGM, QIT, QCG, MME, Vikram Sarabhai Space Centre, Trivandrum-695022 Email: arasutvl@gmail.com ABSTRACT Recent advancements in digital imaging technology provide ample opportunities for formulating programs to study the image of a defect, to understand its nature and to envisage the possible harm that can be initiated from these defects. Well-experienced inspectors trained in radiography read and interpret the images in a radiograph and correlate the images to possible defects. The interpreter, based on acquired knowledge and wisdom, denes the defect and decides the disposition as stipulated by the acceptance criteria. It goes without saying that the process of image interpretation is highly heuristics and person dependent. There is no rule-based methodology for interpreting the images and correlating to its characteristics. The inuence of illusions in interpreting x-ray radiograph is ver y high. To overcome this problem, initiatives are on to automate the aw indication interpretation using Articial Neural Network (ANN). The ANN also requires numerous training with efcient features for aw characterization. Though there are many characteristic features that can jointly identif y the nature of defect, the defect prole is a unique feature as it distinguishes planar defect and a volume defect efciently. In this paper attempt is made for proling few defects and how the derived data are useful in decision making are explained. Details of essential image processing techniques, procedures adopted and its deliverables are also explained. This paper highlights the benecial usage of a methodology over the historical way of interpretation. The knowledge-based way of interpretation can be transformed to rule based interpretation by using this approach. The feature that can distinguish a planar and a volume defect is its sur face prole. The defect sur face prole will indicate the nature of the defect and its criticality. Defect prole can also be one of the effective features in an articial neural network that can identif y and differentiate various types of defects.

1.0

INTRODUCTION

X

-ray radiography is one of the well-established and wellreceived nondestructive testing technique for evaluating the quality of weld joint that are directly coming under stress in pressure vessels. The principle of this technique is differential absorption of an electromagnetic wave when it is transmitted through a medium. The absorption is the major subset of attenuation in a material or weld pool. The absorption of electromagnetic energy depends upon of the characteristic nature of the medium [1]. This energy absorption is measured in terms of mass absorption coefcient or linear absorption coefcient. The linear absorption coefcient is same as mass absorption coefcient but expressed per unit length. The mass attenuation coefcient depends upon the effective atomic number and the electron density of the medium. The attenuation coefcients of photons in materials are signicant in determining the image intensity. The governing equation of photon energy transmission in a material is as given below (1)

I = I 0e

- mx

Where I and I0 are respectively the transmitted and incident photon energy intensities, m the linear absorption coefcient and x is the thickness of the medium. On recording the transmitted energy data on to a x-ray lm or a digital screen, makes the image in black and white densities. The density mentioned here refers to the degree of darkness of an image.

The density strip, used to assess the lm density during interpretation of radiographs shows different densities that can

be seen on a radiograph. The density depends mainly on the transmitted energy photon that falls on the recording medium.

The density measurement is a meandering measurement of transmitted photon. The transmitted photon differs from the incident photon due to the absorption of energy by the medium.

For a material, the transmitted energy is proportional to the thickness of the medium as the effective atomic number and the electron density of the medium is constant. Even a small change in thickness of the medium can make a variation in the image contrast. Contrast is the most signicant characteristic of an image recorded on lm. Contrast is the variation in lm density (shades of gray) that actually forms the image. The amount of contrast in an image depends on a number of factors, including the ability of the particular lm to record contrast. But in case of lm radiography the lms have a limited exposure range in which they can produce contrast. If areas of a lm receive exposures either below or above the useful exposure range (the linear range in lm characteristic curve), contrast will be diminished or perhaps absent. A lm also has a reduced ability to transfer contrast in areas that receive relatively high exposures. This condition corresponds to the upper portion of the characteristic curve in which the slope decreases with increasing exposure. This portion of the curve is known as the shoulder. Image contrast can also be reduced when a lm is either underexposed or overexposed. The image on a lm is an analog image; measurement of minute density variation detail will be difcult and inaccurate. The density measurement of the image will not truly represent the transmitted energy that falls on the lm if the exposure is in the shoulder region of the lm [2, 3].

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On the other hand the digital radiographic images obtained with a at panel detector (FPD) have excellent uniformity, repeatability, and linearity as the modulation transfers function (MTF) and detective quantum efciency (DQE) are superior to any other conventional image acquisition device. In case of FPD system, as the dynamic range is large, even a minute changes in image density will not be left unnoticed. But in lm radiography the lm latitude will be linear for a limited range of exposures within which good contrast is possible. The contrast resolution of a FPD is far better than a lm mainly because the images in FPD are of 12 or 14 bit depth. The color depth or bit depth, is a term describing the number of bits used to represent the colour of a single pixel in a bitmapped image. This concept is also known as bits per pixel (bpp), particularly when specied along with the number of bits used. Higher colour depth gives a broader range of distinct colours. Colour depth is only one aspect of colour representation expressing how nely levels of colour can be expressed [4, 5]. The higher the number of colours, the more realistic the image will appear. On the other hand the number of individually addressable points that make up the image determines the resolution of an image. In case of FPD, it is the number of pixels that make up a screen image.

Contrast resolution refers to the ability of the imaging method to distinguish between differences in image intensity. The inherent contrast resolution of a digital image is given by the number of possible pixel values, and is dened as the number of bits per pixel value. Films, on the other hand, can be considered as a contrast converter. One of its functions is to convert differences in exposure (subject contrast) into lm contrast (differences in density). The amount of lm contrast resulting from a specic exposure difference can vary considerably. The spatial resolution refers to the number of pixels utilized in construction of a digital image. Images having higher spatial resolution are composed with a greater number of pixels than those of lower spatial resolution. The spatial resolution is a measure of the accuracy or detail of an image obtained on lm. It is a measure of how ne an image is, and it is usually expressed in lines per mm (lpm). The resolution of the lms is of the order of 10 lpm that of FPD is of the order of 4 lpm [3, 4]. The details of an image, properly harnessed, can yield an insight into the defect. Even the characteristic nature of the defect can be extracted from such images. In this paper one such attempt wherein the prole of a defect is deciphered using the image depth information. FPD is of the order of 4 lpm [3, 4]. The details of an image, properly harnessed, can yield an insight into the defect. Even the characteristic nature of the defect can be extracted from such images. In this paper one such attempt wherein the prole of a defect is deciphered using the image depth information.

2.0 DEFECTS AND ITS PROFILE Defects in any manufacturing process are inevitable. The normally occurring defects in welds are crack, lack of fusion, lack of penetration, porosity, piping, tungsten inclusion and undercuts. The underlying cause for porosity is the entrapment of gas within the solidied weld. Lack of fusion is the poor adhesion of the weld bead to the base metal; incomplete penetration is a weld bead that does not start at the root of the weld groove. Incomplete penetration forms channels and crevices in the root of the weld which can cause serious issues in pipes because corrosive substances can settle in these areas.

Presence of geometric discontinuities in a weld increases the intensity of stress eld. The defects that cause these concentrations are cracks, sharp corners, holes, and changes in the cross-sectional area of the object. High local stresses can result in failure of a structure more quickly. Based on fracture mechanics, the stress concentration due to defect can be calculated as shown below.

The theoretical stress concentration at the edge of a hole is (2) Also the stress concentration factor k is (3) When b approaches zero the stress at the edge becomes very large. The defect size and its orientation with respect to the applied stresses play a major role. Hence it can be inferred that as b tends to lower value the stress concentration will tend towards higher value. In case of a crack, b will be approaching zero and the stress concentration will be high at the crack tip. If root (tip) radius of a defect is with large diameter then it causes a smaller stress concentration than the defect with sharp root radius. In aerospace specications, defects like lack of penetration and undercut can be tolerated if the root radius is more than 1.5mm. Otherwise these defects are not tolerable irrespective of its length. Hence it is imperative to know about the root of a defect. Defects like piping and inclusions sometime may not be with smooth uniform shape [6]. But there are cases wherein the defects like piping and hot cracks are to be distinguished using many more features. In such cases if the defect prole is also taken into consideration, then the defect classication will be precise and unambiguous. The image on a lm or a FPD is the projected image of a defect on a plane. The defect however is of three dimensions, the third dimension of the defect including the surface condition of the defect are embedded within the contrast of the image. In order to establish this fact an experiment using standard surface roughness blocks was conducted. The digital images of the roughness block are analysed using texture analysis tool box in MatLab. Texture analysis refers to the characterization of regions in an image by their texture content. Texture analysis attempts to quantify intuitive qualities described by terms such as rough, smooth, silky, or bumpy as a function of the spatial variation in pixel intensities. In this sense, the roughness or bumpiness refers to variations in the intensity values, or gray levels. The toolbox includes several texture analysis functions that lter an image using standard statistical measures. These statistics can characterize the texture of an image because they provide information about the local variability of the intensity values of pixels in an image. For example, in areas with smooth texture, the range of values in the neighborhood around a pixel will be a

26

small value; in areas of rough texture, the range will be larger.

Similarly, calculating the standard deviation of pixels in a neighborhood can indicate the degree of variability of pixel values in that region. The standard surface roughness block used for assessing the surface roughness of a machined part is as shown in Fig 1. The digital image of the block is shown as Fig 2. Sections 1 to 8 in the block represent areas in decreasing order of surface roughness.

Fig 1: Surface Roughness Block

Fig. 2: Digital Image of the Surface Roughness Block

default is azimuth = 0° and elevation = 90°. For 3-D plots, the default is azimuth = -37.5° and elevation = 30° [9]. The surface prole views of the defects are shown with X &Z axis representing the length in pixels and grey level variation respectively. In isometric view Y axis is also shown.

Fig 4. View point

Each area (1-8) shown in Fig 1 is represented by a roughness number (N classes) as per BS 1134/1972 & ISO/ R 468. The surface roughness is expressed in terms of Ra i.e. Area Radius and its tolerance is +12% to - 17%. The roughness value is as shown in Table. 1 Sr. No. N12 N11 N10 N9 N8 N7 N6 N5

Surface Roughness Ra 50 µm - CLA 2000 µ” Ra 12.5 µm - CLA 500 µ” Ra 12.5 µm - CLA 500 µ” Ra 6.3 µm - CLA 250 µ” Ra 3.2 µm - CLA 125 µ” Ra 1.6 µm - CLA 63 µ” Ra 0.8 µm - CLA 32 µ” 0.4 µm - CLA 16 µ”

Table. 1 Roughness value of the Block

Fig. 5 Porosity at the marked location

(a)

Fig. 6 Crack at the marked location

(b)

The images of each area of the roughness block (shown in Fig 2) are acquired and images are read processed using Matlab image processing tool box. The intensity data is proled using Matlab. The view planes mentioned in this paper are as shown in Fig. 4. The isometric view and xz view of N5 specimen is ( c) shown in Fig. 3. z axis here species the color data, as well as Fig 7: Surface Prole of Porosity (a)Isometric b)XZ Plane c)YZ Plane surface height, so color is proportional to surface height. Image depth which is an average measure of the variation along the vertical axis is computed and correlated with the known surface roughness.

Fig 3: Isometric & XZ plane Views of N5 Roughness Block

Fig 8: Grey level variation vs pixel length along a) longitudinal and b) transverse directions

As the methodology is found to be appropriate, the same method is adopted to obtain the defect prole using image processing tool box. The image of porosity and crack is shown in Fig. 5 and Fig. 6. The image is cropped to 1.5 mm ×1.5 mm analysis portion and that includes the defect completely. It is calibrated & cropped using rhythm review software. Analysis window is taken as 15 ×15 pixels size. MATLAB automatically selects a viewpoint as shown here [Fig. 4]. For 2-D plots, the

The image of lack of fusion and lack of penetration is shown in Fig. 11 and Fig. 12. These images are cropped to 1.5 mm x 1.5 mm (15 x 15 pixels) for analysis that includes the defect completely. The surface proles are shown below in Fig 13 and Fig 15. The grey level variation measured along the longitudinal and transverse direction of the defect is presented in graphs shown in Fig 14 and Fig 16.

27

(a)

(b) ( c) Fig 9: Surface prole of crack (a) Isometric, (b) XZ plane and (c) YZ plane

Fig 10: Grey Level Variation Vs pixel length along (a) long & (b) trans directions of crack

Fig 15: Surface prole of Lack of Penetration a) Isometric b) XZ plane c) YZ planes

Fig 16: Grey level variation vs pixel length along a) longitudinal and b) transverse direction of lack of penetration

3.0 RESULTS AND DISCUSSIONS From the surface proles and the graphs showing grey level variation vs pixel length along longitudinal and transverse direction of the defects it can be seen that the views of the defects and their image depth details along longitudinal and transverse directions are distinctly different. The porosity, being a volume defect, shows a smooth surface prole in isometric, XZ Fig. 11 Image of Lack of Fig. 12 Image of Lack of Fusion Penetration and YZ planes. The graphs representing grey level variation along the longitudinal direction and transverse direction are also smooth curves indicating the absence of alarming stress concentration locations (absence of sharp edge). Hence porosity may not be critical. On the contrary, the crack being a planar defect, shows prole with sharp corners in all the three views.

The image depth detail variations along longitudinal and (a) (b) transverse directions are also with many maxima and minima indicating sharp corners in the defect. As explained earlier, the sharp radii points are the stress concentration points. Since the surface prole of the crack are having sharp radii points, cracks are functionally critical and need to be repaired. Similarly for lack of fusion and lack of penetration, shown in Fig 13 and Fig. 15 and the grey level variations in longitudinal and transverse ( c) direction of the defects in Fig 14 and Fig 16 we can see that the Fig 13: Surface prole of Lack of Fusion a) Isometric b) XZ plane c) proles of lack of fusion in all the three views are showing YZ plane smooth radius except in three locations. The grey level variations in the transverse direction are not indicating sharp stress concentration points. But there are few sharp corners in longitudinal direction. The possible stress concentration due to these sharp corners can be calculated using the equations 2 and 3 shown above. The prole views of lack of penetration are showing acute angle points at few locations and acute radius in Fig 14: Grey level variation vs pixel length along a) long b) trans direction for lack of fusion.

YZ plane. The grey level variation along the longitudinal

28

direction indicates few sharp nodes. However in transverse direction it is smooth. The sharp radius locations, depending upon its orientation with respect to the direction of principal stress may become intolerable. Also, if the radius, as discussed above, is less than 1.5mm then it will be a severe stress concentrator. Instead of doing an ingenious interpretation and deciding disposition, it will be desirable to calculate the effective stress concentration due to the presence of the defects with sharp corners and decides its disposition. This will avoid unnecessary repair or rejection. However to arrive at a reliable conclusion on deciding the criticality of a defect, more analysis window along the defect are to be taken and analyzed.

CONCLUSIONS Before deciding the disposition of a defect it is essential to understand its functional criticality. This trial provides a methodology to understand the criticality of a defect and provides a decision making process based on fracture mechanics. Defects like lack of fusion and lack of penetration of smaller length can be analysed and possible stress concentrations can be estimated using this method. Large numbers of analysis window are to be taken on a defect image to achieve accuracy. The surface nish estimation on inaccessible region can also be attempted by image processing route.

By this methodology the historical way of interpretation using heuristics and human knowledge base can be transformed to rule based interpretation.

ACKNOWLEDGEMENT The author acknowledges the help and support rendered by Director, VSSC, and Dy. Director, MME, VSSC Trivandrum to accomplish this program & the contributions of Shri Vishak Chandran.P, M.Tech Student from NIT, Trichy and staff of NDT, QIT, VSSC in this initiative.

REFERENCES 1.A L Conner, H F Atwater, E H Plassman and J H McCray, “Gamma-Ray Attenuation-Coefcient Measurements”, Physical Review A, vol. 1, Issue 3, 1970, pp. 539-544 2. Perry Sprawls, “Film contrast Characteristics”, Medical Physics Publishing, Sprawls Educational Foundation, Montreal, NC, USA , 1999 3. Lanca Land Silva A, “Digital radiography detectors – a technical overview” 2009, 15, 134-138 4. Markus K ner, MD, Christof H. Weber, MD, Stefan Wirth,MD et al Advances in Digital Radiography: Physical Principles and System Overview Radigraphics, RSNA, Volume 27, Issue 3 May-June 2007 Paul Bourke 5. “A Beginners Guide to Bitmaps” Dmutro Nechuporyk, Ukraine, November 2015.

6. James W. Ramsey, Jr “Stress concentration factors for circular, reinforced penetrations in pressurized Cylindrical shells”, Ph.D. Thesis - Virginia University.., May 1975, springeld, va.

22161. (NASA-TM-X-68733) 7. Kelly Bennett” MATLAB Applications for the Practical Engineer”, InTech Open access book publishers, 2014 8. Rudra Pratap,”Getting Started with MATLAB a Quick Introduction for Scientists and Engineers”, oup USA, September, 2005.

9. Brian Hahn and Daniel T Valentine, “Essential MATLAB for Engineers and Scientists”, III Edition, Elsevier ltd, the Netherlands, 2008.

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DIGITAL RADIOGRAPHY METHODS AND FACTORS GOVERNING THE IMAGING QUALITY *Ayaz Jhanorwala*, Jignesh Dhimar, Satish Tilva L & T MHPS Boilers Pvt Ltd., Hazira, Surat-394 510, India *Email : ayaz.jhanorwala@lntmhps.com ABSTRACT This article describes two methods Computed Radiography (CR) and Digital Radiography (DR) along with its pros and cons with respect to conventional lm radiography. Understanding the effect of the variable operational parameters along with the specication of component of digital radiography system on image quality is important for the careful selection and effective use of digital radiography system.

• A very wide dynamic exposure range/latitude due to the provision of adjustment of contrast and brightness of the image igital radiography offers the potential of improved in digital systems. image quality as well as providing opportunities for • Possibility of assisted defect recognition (ADR). ease of archiving for recording purpose and computeraided diagnosis in industrial radiography. Although the process In this paper, both the methods of CR & DR are described in itself is different from lm radiography, digital radiography terms of working with used technology and suitability of methods resembles traditional radiography to a large extent. applications. Later on, the parameters affecting the imaging The optical impression of the X-Ray image is similar so that RT quality are described. These parameters are governed by the trained personnel can quickly adopt this new technology and properties of detecting medium (Imaging plates, Flat panel or adapt to it without great efforts. Moreover the images can be at bed detectors) as well as characteristics of radiation devise (isotopes & X-Ray tube) and geometric parameters. interpreted in analogy to lm.

1.0

INTRODUCTION

D

Two main methods of real lm less digital imaging can be distinguished: 1. Digital radiography by means of phosphor coated semiexible or rigid imaging plates in combination with computer processing. It is considered as indirect Digital Radiography and called as “Computed Radiography”. Short form CR will be used further in this paper for this method.

2.0 COMPUTED RADIOGRAPHY (CR) CR is the generic term applied to an imaging system comprised of followings: 1. Photostimulable Storage Phosphor to acquire the X- Ray projection image 2. CR Reader to extract the electronic latent image 3. Digital electronics to convert the signals to digital form

In CR, an imaging plate (IP) containing the Photostimulable storage phosphor is positioned in a light-tight enclosure, exposed to the X-Ray image and then read out by raster scanning with a laser in CR scanner to release the PSL. The blue Photo Stimulated Luminescence (PSL) light is collected with a light guide and detected with a Photo Multiplier Tube (PMT).

Each method has differing strengths, advantages and The PMT signal is digitized by digital electronics to form the limitations that should be evaluated in terms of specic image on a point-by-point basis. application, inspection requirements and economics: capital, human investment and productivity (number of exposures in a 2.1 Working of CR: certain time).

The major merits of digital radiography compared to conventional lm are: • Shorter exposure times and thus potentially more radiation safety and • Faster processing: DR image processing simultaneously with exposure and CR scanning process can be done in few minutes after the exposure.

• No chemicals, thus no environmental pollution • No consumables, thus low operational costs because plates, panels and at beds can be used repeatedly.

Figure 1 : Electron movement between energy bands 2. Digital radiography with rigid at panel or at bed detectors and instant computer processing. It is considered as the genuine (true) or direct form of digital radiography method and so called “Digital Radiography”. Short form DR will be used further in this paper for this method.

30

Computed radiography uses a reusable imaging plate (IP) in place of the lm. This plate employs a coating of photostimulable storage phosphors to capture images. The ionizing radiation imparting on the imaging plate interact with its phosphor layer. The radiation interaction with the phosphor crystal causes electrons to be excited. Some of these produce light in the phosphor in the normal manner, but the phosphor is intentionally designed to contain traps which store the charges in metastable stage (gure 1). The quantity of trapped electrons is proportional to the quantum of radiation received at the point of IP. Thus latent image of object can be made by such trapped electrons which are in metastable stage.

After completion of radiation exposure of IP, it is scanned by laser light. Laser light stimulates the crystal by irradiation with red light such that electrons are released from the traps and raised to the conduction band of the crystal. Subsequently these electrons of conduction band triggering the emission of shorterwavelength (blue) light by moving in lower energy band. This process is called Photo Stimulated Luminescence (PSL). The emitted light is collected and detected with a photomultiplier tube (PMT) whose output signal is digitized to form the image (gure 2). This image can be viewed on the display.

CR is a two-step process of exposure and scanning. The image is not formed directly, but through an intermediate phase as is the case with conventional X-Ray lms. The image information is, elsewhere and later, converted into light in the CR scanner by laser stimulation and only then transformed into a digital image.

Instead of storing the latent image in silver-halide crystals and developing it chemically, as happens with lm, the latent image with CR is stored (the intermediate metastable phase) in a radiation sensitive photostimulable phosphor layer. In short, the whole process is comprised of exposure, capturing, reading and detection as shown in gure 1.

be any of the halogens Cl, Br or I (or an arbitrary mixture of them). Many manufacturers have used BaFBr0.85I0.15:Eu2+ not for the marginal increase in X-Ray absorption compared to BaFBr:Eu2+2 but rather for the better optical match of the wavelength of maximum stimulation of the phosphor to diode lasers [4].

3.0 DIGITAL RADIOGRAPHY (DR) Digital radiography with rigid at panel- or at bed detectors enables simultaneous happening of the exposure and image formation which leads to near real-time image capture. Due to this the radiographic image available for review only few seconds after the exposure. This almost instant image formation is the reason that some consider DR the only "genuine" (true) method of digital radiography. This instant availability of results offers immediate feedback to the manufacturing process to quickly correct production errors.

It is also called as "direct" radiography to indicate the difference with CR, which is a two-step. Thus DR is faster compared to CR. Detector used in DR are of liner detectors and 2D detectors having one and two dimensional array of sensors respectively.

Liner detectors are commonly used for airport luggage inspection. In NDT, similar linear arrays with small sensor elements are typically used in high speed testing machines for production inspection applications that incorporate either a manipulator or a conveyor to move parts past a stationary X-Ray tube detector arrangement. They are also used for Computed Tomography (CT) applications.

Figure 2 : Laser scanning of IP

After laser scan also some of the electrons remain in higher energy band that must be moved to lower energy band.

Therefore the IP latent image remained after laser scan must be erased by light before reuse to avert the double image formation.

2.2 Photostimulable phosphors: Photostimulable phosphors, also known as storage phosphors.

These phosphors are commonly in the barium uorohalide family, typically BaFBr:Eu2C where the atomic energy levels of the europium activator determine the characteristics of light emission [3]. The photostimulable phosphor rst used for CR was BaFBr:Eu22+. BaFBr:Eu22+is a good storage phosphor in that it can store a latent image for a long time, e.g. the latent image eight hour after irradiation will still be ~75% of its original size. The family of phosphors BaFX:Eu22+ where X can

Figure 3 : Conversion of ionizing radiation into electrons

2D Flat Panel Detectors have emerged as the next generation digital X-Ray technology. A number of detector technologies have been developed based on amorphous silicon Thin Film Transistor (TFT) arrays. Other type is CMOS detectors. For amorphous materials with every 5°C to 10°C of temperature variation a recalibration is recommended but CMOS has a wider tolerance of up to 40°C. In addition they show no ghost/memory effect, thus no latent images. Also it has lower noise and higher readout speed. In spite of these advantages a major drawback of CMOS technology is the limited radiation hardness and has limited use up to 160 kV. Amorphous silicon is highly resistive to X-ray radiation and can be used up to radiation energy in the range of MV. The working of amorphous silicon TFT Flat Panel Detector (FPD) is explained in next paragraph.

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3.1 Working of Flat Panel Based DR: Ionizing radiation interact with the layer of scintillating material that converts them into visible light photons. These photons then strike an array of photodiodes which converts them into electrons that can activate the pixels in a layer of amorphous silicon (gure 3 and 4). The activated pixels generate electronic data that a computer can receive through output signal to convert it into a high-quality image (gure 4). Since the number of electron produced will vary with the intensity of incoming light photons and number of light photons are proportional to the incident intensity of radiation on FPD, the pixel (or grey) value will be governed by the transmitted radiation from the object of radiography.

photon uctuations, analogue to digital conversion, readout electronic noise and so on. Noise is measured by SNR which is the ratio of signal intensity and the standard deviation [6].

Therefore the SNR can be increased by either increasing the signal or reducing the noise. Increase in SNR leads to better image quality as shown in gure 5.

Figure 4 : Schematic of amorphous silicon TFT FPD

Figure 5 : Images of tube weld butt joint at different SNR

Most commonly used scintillator material are powdered Gadolinium Oxy Sulde (GOS) and needle-crystal Caesium Iodide (CsI). Due to needle type structure of CsI, light spread is less in compared to GOS layer which leads to more spatial resolution that will be discussed in later in paragraph 4.2. The disadvantage of CsI is higher tendency of memory (ghosting) effect i.e. the previous image detail overlap over the next image and so double images are getting produced.

Effect of frame rate i.e time per frame has also effect on SNR. Time per frame is the time duration in which the FPD is receiving X-Ray dose in formation of an image frame. Higher the time FPD receives the X-Ray for an image frame, the subsequent signal will be more strengthened, and so higher grey value of pixel and less noise. The other variable is the frames averaging. The noise in image reduces as the more no. of frames are averaged. Both frame rate and the frame averaging is controlled by selecting the available values in the software. Their effect on SNR is similar to 4.0 FACTORS GOVERNING THE IMAGING curve shown in the gure 6. Also some lters can be used for QUALITY: reducing noise in the image, if available to use with software.

Any DR system comprises of a radiation source and a detector.

The user has options of various radiation energy (kV), radiation intensity (mA), source/focal size etc from the available isotopes and X-Ray tubes. Also from the detector side, user has options for variation in parameters like sensitivity/gain, time per frame, no. of frames etc. Other detector properties like pixel pitch, scintillator material etc are xed once the detector has been purchased. Though the DR has very large dynamic range, the above mentioned both xed and variable parameters have substantial effect on important factors involved in image quality like Signal to Noise Ratio (SNR), specic contrast and spatial resolution. In CR system, the X-Ray tube related parameters and the pixel size of IP has same role in image quality as in DR. Therefore, in the subsequent paragraphs the effects of Figure 6 : Effect of X-Ray intensity on SNR parameters of X-Ray tube and FPD on the image quality governing factors in DR system will be discussed. From the gure 6, a point can be noted that each factor can increase the SNR up to a level and after that the curve become saturate and further increase in the variables cannot increase the 4.1 SNR: Noise is the main factor in decreasing the image quality in such SNR. Therefore optimum setting of all above SNR controlling an extent that an operator may get confused or feel difculties in parameters is required to reduced FPD exposure and reduce the distinguishing the defects. Noise is usually from the X-Ray load of X-Ray generation on X-Ray tube.

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4.2 Spatial Resolution: Resolution is dened as the smallest separation (distance) between two objects that the human eye can distinguish.

Because the human eye is not easily quantiable, an objective method to indicate resolution is needed. Resolution is dependent on contrast (grey levels) and separation (distance).

Resolution is expressed as the number of line pairs that can be distinguished in one mm.

Spatial resolution can be measured in terms of line pair resolution per mm or cm (LP/cm). To determine the spatial resolution, Line Pair (LP) gauge or Duplex IQI EN 462-5 can be imaged on detector and the maximum line pair resolution can be read either by human eye or by evaluating the grey value pattern in line prole drawn over the particular value of line pair.

As the line pair per mm or cm increases, the gap between the lines reduces and the contrast also reduces. After certain value of line pair per cm, the line prole do not shows the clear variation in grey value and that value is the spatial resolution of the digital radiography system for a particular setup.

Modulation transfer function (MTF) describes the relation between relative contrast and spatial frequency [1, 5]. If the relative contrast is measured on each line pair and plotted against the spatial resolution then MTF curve can be generated [2]. So MTF is the graphical representation of the spatial resolution and relative contrast. The right end of the MTF curve in the graph represents the maximum spatial resolution.

Spatial resolution in radiography is determined both by the detector characteristics and by unsharpness arising from geometrical factors. Examples are: 'penumbra' due to the effective size of the X-Ray source, the magnication of object of radiography, relative motion between the X-Ray source, object and detector during the exposure etc. Detector-related factors arise from its effective sensor/pixel size and any lateral signal spreading effects within the detector scintillating layer.

According to the sampling theorem, spatial frequency of signal below Nyquist frequency can be faithfully imaged [7]. If the signal contains higher frequencies, then a phenomenon known as aliasing occurs wherein the frequency of the signal beyond the Nyquist frequency is mirrored or folded about that frequency in accordion fashion [3]. The value of Nyquist frequency is 2p−1, where p is the pixel pitch. Therefore according to above discussion, for the detector of 0.2 mm pixel pitch, it is not possible to resolve the signal having frequency greater than 2.5 cycles / mm (25 cycles / cm) [1]. In short, lower the pixel size of detecting medium (at panel or IP), better the resolution due to higher value of Nyquist frequency.

image presentation without loss of information as contained in the original digital data.

Light is produced due to the interaction of X-Ray photon with scintillator material. The light propagates from the place of XRay interaction to the photodiode element under the scintillating material layer. Spatial resolution is affected due to spreading of light within the thickness of the layer (gure 7). CsI scintillator has needle like crystal structure through which scintillation light propagates as shown in gure 7. Therefore light spread over the adjacent sensing element is less in FPD having CsI scintillator compared to GOS scintillator having unstructured powder form. Therefore the spatial resolution with CsI is comparatively better.

The other effective factor in inuencing the spatial resolution is the focal spot size of X-Ray. It is easy to understand that lower the focus size, lower the unsharpness, and better the spatial resolution.

Figure 8 : MTF graphs for two X-Ray focus size at different magnication

Measured Resolution with Set up magnication 0.4 mm focus no M [LP/cm]

Resolution with 1.0 mm focus [LP/cm]

1

1.07

26

26

2

1.35

33.5

29

3

1.74

43

24

4

2.32

48

20

Table 1: Spatial resolution at different magnication

The other important variable factor contributing to the spatial resolution is the geometric magnication of the object of radiography. Different geometric magnications are obtained by relative position of X-Ray tube, object and the detecting medium. The geometric magnication has both the positive and negative effect on spatial resolution depending upon the focus size of the X-Ray tube and the degree of magnication as The monitor display used for DR system should have pixel size revealed from the MTF curves of gure 8 obtained after a equal to or less than the detector pixel size so that best possible meticulous study on a DR system having X-Ray tube of 0.4 mm and 1 mm focus size and FPD having 0.2 mm pixel size [1].

Figure 7 Light propagation in CsI and GOS

In MTF graph of gure Z, "M" is the geometric magnication.

Spatial resolution continuously increased with increment of M for small focus size of 0.4 mm but for 1 mm focus size, spatial resolution rst increased with increase in value of M from 1.07 to 1.35 and then spatial resolution has reduced with further increment in M as shown in gure 8 and Table 1.

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The bit depth has also effect on the resolution. Higher the bit depth, more no. of grey value are available for mapping an image, and better the resolution. 12, 14 & 16 bit CR/DR system would have 4096 (212), 16384, 65536 grey value levels respectively.

4.3 Other factors Energy of X-Ray has effect on contrast and visibility of detail increase with contrast. So as the kV decreases the contrast sensitivity (CS) increases. To evaluate the CS of DR system, contrast sensitivity blocks and gauges can be used. ASTM E 1647-03 is "Standard Practice for Determining CS in Radiology" in which the gauges comprises a rectangular block with four at-bottom recesses that represent 1%, 2%, 3% and 4% of the gauge total thickness.

The phosphor crystals on a CR plate and scintillator material on DR detector panels react almost linearly to incident radiation, while in a conventional lm the silver-halide crystals react exponentially. As a result the dynamic range in digital radiography methods is much wider than for conventional lm.

Due to provision of adjustment of image contrast & brightness at workstation exposure times are less critical and various material thicknesses can be examined at the same time.

If any image degradation due to scattered radiation is present, then some lters can be used to lter out the low energy radiation. Shielding and masking can be provided on either side of FPD. Proper front masking on FPD will be proved advantageous by protecting the active area of FPD and its electronics from radiation which leads to higher FPD useful life due to less tendency for bad or dead pixel formation and other image artefacts. Also the rear side shielding of detector reduce the detrimental effect of back scattered radiation.

Proper FPD offset calibration disables the effect of any present dark current in image processing chain of electronics. Gain calibration also improves the image quality and it has marginal effect on image contrast. Gain calibration done at lower kV offers better contrast. Dead or bad pixel grey value can be calculated from the adjacent pixels if the bad pixels are properly mapped and linked with imaging software and it helps in eliminating the occurrence of artefacts and bad pixels over the displayed image.

5.0 CONCLUSION: Digital radiography partly replaces conventional lm and also permits new applications. Depending upon the application, the proper method can be selected. There are a number of factors to be considered when evaluating a radiographic imaging system beginning with the size, shape and the exibility of the sensor.

Contrast sensitivity or grey scale range (bit), resolution (pixel size), scan rate and nally the cost.

DR detectors are fragile, bulky and large in volume compared to the thin and exible IP, therefore the application require the radiography at conned places or require the bending of imaging medium, CR is the best choice. On the other hand DR is extremely useful in automated, robotic, production processes due to its instant image processing and display competency and

if used with correct exposure parameters, it offers better image quality than CR. Any digital radiography system has high initial cost for detector for DR, work station comprising of computer and imaging software, scanner and imaging plates in case of CR. Selection of a DR solution requires careful considerations with regard to return of investment because detectors has limited lifetime caused by the accumulated radiation. Flat panel detectors can be used continuously for years in mass production processes and lifetime is determined by a combination of total dose, the dose rate and radiation energy. Therefore averting use of higher radiation energy, restricting the active area of detector from the radiation bombarding, and using optimum exposure parameters [2] superior FPD life can be obtained with reduced memory effect problem called as "ghosting".

Despite of all positive features, the image resolution of even the most optimised digital method is not as high as can be achieved with nest grain lm. During use of digital method, a risk is always pretended for arisen of adverse situation due to the nonfunctionality or manifestation of fault of any hardware parts of digital system like computer, scanner, detector power supply, Flat panel etc. The repair, maintenance and replacement of any part involved in digital systems are costly and takes time that may be associated with huge production loss depending upon the type of industry and dependency over the digital radiography system. Also comparatively more sophisticated and trained humans are required for the operation and handling of digital systems than the lm radiography, but the number of persons required for the same task may be reduced.

At last, in summary, numerous aspects with a great diversity such as: image quality, process speed, productivity, portability, robustness/fragility, exibility of plate or panel, available eld space, logistics, environmental issues, capital investment, human investment, existence of industrial standards etc. play a role in the ultimate choice between conventional lm or CR or DR. 6.0

REFERENCES

1] Ayaz Jhanorwala, Rishikesh Kumar, Satish Tilva, National Seminar & Exhibition on NDE 2014, Pune, December 4-6, 2014 (NDE-India 2014)Vol.20 No.6 (June 2015) - The e-Journal of Non-destructive Testing - ISSN 1435-4934 www.ndt.net/?id=17842, Study of Spatial Resolution in LP/cm for FPD Based Digital Radiography System by Imaging the Converging Line Pair at Different Geometric Magnications.

2] Ayaz Jhanorwala, Satish Tilva, NDE 2015, Hyderabad, November 2628,2015, Determination of Optimum X-Ray Tube Output Parameters kV and mA for Digital Radiography Testing of Welded Tubes.

3] M J Yaffe and J A Rowlands, Phys. Med. Biol. 42 (1997) 1–39. Printed in the UK, X-Ray detectors for digital radiography.

4] J A Rowlands, INSTITUTE OF PHYSICS PUBLISHING PHYSICS IN MEDICINE AND BIOLOGY Phys. Med. Biol. 47 (2002) R123–R166 PII: S0031-9155(02)24746-6, The physics of computed radiography.

5] Industrial Radiography Image forming techniques, GE Inspection Technologies,https://www.gemeasurement.com/sites/gemc.dev/les/i ndustrial_radiography_image_forming_techniques_english_4.pdf 6] Fanqin KONG, 17th World Conference on Non-destructive Testing, 25-28 Oct 2008, Shanghai, China, Quality Evaluation for Digital Radiography Inspection Based on Imaging Parameters.

7] Bruno A. Olshausen, PSC 129 - Sensory Processes, October 10, 2000; Aliasing.

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RESIDUAL STRESS MEASUREMENTS IN CARBON STEEL WELD JOINTS MADE BY SEQUENTIAL WELDING PASSES USING X-RAY DIFFRACTION TECHNIQUE *A. Joseph, S. Mahadevan, S. Arun Kumar and B. Purna Chandra Rao Nondestructive Evaluation Division, Metallurgy and Materials Group Indira Gandhi Centre for Atomic Research, Kalpakkam - 603102 *Email: joseph@igcar.gov.in ABSTRACT Carbon steel is widely used for various applications. Different methods are employed to reduce residual stresses in carbon steel weld joints. Post weld heat treatment (PWHT) is the most commonly used method to relieve/reduce the residual stresses. Use of different sequential weld passes during welding is one of the alternate methods used to get minimum residual stresses in higher thickness double V carbon steel weld joints.

X-ray diffraction (XRD) is one of the widely used nondestructive techniques for estimating residual stresses. A study was undertaken using XRD technique to quantify the residual stresses present in three sets of carbon steel weld joints made using three different weld pass sequences. The surface residual stresses obtained using the XRD technique showed minimum longitudinal tensile residual stresses in the weld joints made by alternate weld pass sequence as compared to the other two weld pass sequences 1.0

R

INTRODUCTION

esidual stresses are the stresses that exist within a material without application of an external load. They are sometimes called as internal stresses or locked-in stresses and their magnitudes are within the elastic limit of the material.

Residual stresses can be tensile as well as compressive in nature. Generally, presence of tensile residual stresses in components is detrimental to the integrity of component/structure [1,2] as they tend to open a crack.

Knowledge of residual stresses allows us to estimate more accurately the safety factor and remaining useful life for any component in fabricated condition and in service, respectively [3,4]. Since, fatigue and stress corrosion cracking failures are surface sensitive phenomena, it is often accepted that evaluation of surface residual stresses should be adequate to assess the resistance to fatigue and stress corrosion cracking [57]. Various nondestructive and destructive techniques are employed to measure the residual stresses and their proď&#x20AC; les in weld joints [8-12]. X-ray diffraction method is one of the widely used techniques for residual stress measurements [13-15]. It is a nondestructive technique and it uses the change in interplanar distance (d-spacing) with angle to estimate the strain. This method can be applied to metallic materials. When the material is in tension, the d-spacing increases and when the material is in compression, the d-spacing decreases. The presence of residual stresses in the material produces a shift in the angular position of X-ray diffraction peak that is directly measured by the detector.

residual stresses in welded structures [16-20]. The most common methods used for residual stress relieving are (i) Post weld heat treatment (PWHT) (annealing) (ii) Vibration and shot peening. However, PWHT can be detrimental for certain steels.

Detrimental effects of PWHT include distortion, temper embrittlement, over-softening, sensitization and reheat cracking, which means that control of heating and cooling rates, holding temperature tolerances and the times at holding temperature are extremely important, and must be carefully controlled in order to realise the full beneď&#x20AC; t of the PWHT process [16,19]. The extent of relaxation of the residual stresses depends on the material type and composition, the temperature of PWHT and the soaking time at that temperature. The other methods (vibration and shot peening) are rarely used for residual stress relieving. Use of different sequential weld passes during welding is an effective method to get minimum residual stresses in higher thickness double V weld joints. Hence, a study using XRD technique was undertaken to quantify the surface residual stresses present in three sets of low carbon steel weld joints made using three different weld pass sequences which would enable optimizing the weld pass sequence.

2.0 FABRICATION OF LOW CARBON STEEL WELD JOINTS USING THREE SEQUENTIAL WELDING PASSES The chemical composition of the low carbon steel plates used for making the weld joints is given in Table 1.

Element C Mn

Si

Cr

Ni

V

P

S

Fe

Low carbon steel is the most commonly used steel for many Wt. % 0.15 1.46 0.34 <0.3 <0.3 <0.00 0.015 0.021 Bal structural applications and it is often used when large quantities of steel are needed. Different methods are employed to reduce Table 1: Chemical composition of the low carbon steel

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For this study, three sets of 20 mm thick low carbon steel double 'V' weld joints were fabricated with three different weld pass sequences using the manual metal arc welding (MMAW) process with 7018 type electrodes. The details of the weld sequences employed during welding of the plates are given in the Fig. 1. Totally eight weld passes were used to fabricate each of the weld joints. In the rst set of double V weld joint (Plate A); the weld passes were alternatively made on both the sides (1,3,5,7 and 2,4,6,8). In the second set of double V weld joint (Plate B), four passes were made on one side (1,2,3,4) and then four passes were made on the other side (5,6,7,8). In the third set (Plate C), root passes were made alternatively on both the sides and then two lling passes were made alternatively on both the sides and then nal lling passes were made alternatively on both sides (1,3,4,7 and 2,5,6,8). The side in which the nal pass is done is identied as top and is marked as A0, B0 and C0 whereas the other side (bottom side) is identied as A1, B1 and C1 in the three plates. During welding, same weld parameters (i.e. voltages, current and welding speed etc.) were used to fabricate the weld joints and only the weld pass sequence was varied. The weld parameters used in the welding are given in Table 2. The photographs of the three carbon steel weld joints fabricated by sequential welding are given in Fig. 2.

Fig. 2 Photographs of the three carbon steel weld joints (Plate A, Plate B and Plate C) fabricated by different sequential welding passes

3.0 RESIDUAL STRESS (RS) MEASUREMENTS USING XRD TECHNIQUE 3 A. Experimental The residual stresses present in the low carbon steel weld joints were measured using the XRD technique. In the XRD technique, strain in the surface layers of a material is estimated by measuring the shift in the diffraction peak position of a set of planes. These strains are then converted into stresses analytically using various assumptions. In this study, a X-ray stress analyser (Rigaku Strain Flex Model: MSF-2M) was used for the measurements. Figure 3 shows the XRD equipment used for residual stress measurements. XRD technique measures only surface residual stresses (within about top 20μm thick layer).

The experimental parameters used for carrying out XRD based residual stress measurements are given in Table 3.

Base material

Low carbon steel

Base material plate size (mm)

200×150×20

Voltage & Current

30 kV, 7 mA

Weld geometry

Double ‘V’ butt joint

X-ray radiation

Chromium Kα

Electrode used and size

E-7018, 3.15 mm dia.

Wavelength

2.2896 Å

Polarity and weld position

Reverse and 1G

ψ range

0˚ to 57°

Type of welding process

MMAW

2q range

148°-163°

Open circuit voltage

96.8 V

Step Width

0.2°

Welding current and Voltage

90 – 95 A and 22 - 25V

Aperture

2×4 mm2

Welding speed

95 – 98 mm/min

Kβ Filter

2 Nos. (Vanadium)

Dwell Time

3s

Plane considered

(211)

Table 2: Details of the weld parameters used

Table 3. Experimental parameters used in XRD based residual stress measurements

Fig. 1: (a-c) Details of different weld pass sequences employed during the welding of carbon steel plates are shown for three Fig. 3 XRD equipment used for RS measurement different weld joints (Plate A, Plate B and Plate C) respectively

36

This XRD instrument has a back reection type goniometer with 2θ scan range from 140 to 170 degrees. Multiple ψ method was used for the estimating the stress. The ψ angles used were in the range of 0 to 57 degrees. The radiation used for the measurements was CrKα and the set of planes considered was (211) and the scan range of 2θ was 148 -163 deg. XRD data was corrected for background and absorption before locating the peak. The peak location was determined by suitable tting algorithms. Using the XRD technique, longitudinal residual stresses (stresses parallel to weld direction) and transverse residual stresses (stresses perpendicular to weld direction) were measured both on the top and bottom surfaces of the welded joints.

In plate A, the stresses at 15 mm distances are close to zero as compared to a tensile stress of 50 MPa present in plates B and C. 4 B. Residual stress in the transverse direction At the WC, comparing the residual stresses in the top and bottom surfaces, Plate A showed a difference of 60 MPa whereas large variations of stresses were observed in the Plates B and C.

The maximum transverse tensile residual stress on the top surface 'A0, B0, C0' of the weld joints were present at a distance of about 10 mm from the weld centre. The maximum transverse tensile residual stress on the bottom surface 'A1, B1, C1' of the weld joints were present at a distance of about 20 mm from the weld centre. Along the transverse direction, in all the joints, 3 B. Locations of Residual stress measurements on the three higher stress gradient was observed between the WC and at 10 low carbon steel weld joints mm distances from the weld centre.

To measure the residual stress on the low carbon steel weld joints, straight line were marked at the centre of each weld DISCUSSION joints on both the sides and then measurement points were 5. marked with regular intervals of 5, 10, 15, 25 and 35 mm on the The maximum value of tensile RS present along the longitudinal top surface and 5, 10, 20 and 30 mm on the bottom side. The direction in each of the sides of weld joints is shown in Fig. 6 carbon steel weld joints were used in as welded condition and along with location which marked as legend. It is observed that weld crowns were not ushed out. Before the residual stress the minimum (close to zero) longitudinal tensile residual measurements, the scales/oxides on the selected locations on stresses are present in the rst set of weld joint (Plate A) made by the top surface of the weld joints were removed using electro- alternate weld pass sequence (1-3-5-7 and 2-4-6-8) as chemical polishing. At each location, measurements were compared to the other two weld pass sequences in the carried out two times and the average of two measurements is longitudinal direction. In Plate C, the range of tensile stresses reported here. Thus, residual stresses at similar locations were was higher compared to the other weld joints. measured in all the weld joints. In this study, changes in the The maximum values of compressive RS present on both the residual stresses values due to changes in the sequence of weld sides along longitudinal and transverse directions in weld centre of all the 3 joints are shown in Fig.7. The dash line boxes passes were determined. in Fig. 7 show the range of maximum compressive stress between the top and bottom surfaces of the weld joints. The 4.0 RESULTS The residual stress proles obtained in the top (nal pass) and maximum compressive stress in the plate A ranged between bottom surfaces of the three carbon steel weld joints in the 200 to 300 MPa and is lesser as compared to the other joints. In longitudinal and transverse directions are shown in gures 4 the alternate weld pass sequence, the heat from the subsequent and 5 respectively. The legends 'A0, B0, C0' and 'A1, B1, C1' in weld passes has effectively annealed the previous weld passes the RS prole plots correspond to the top & bottom surfaces of and hence the residual stresses got relieved and also the three weld joints A, B and C. The residual stress distribution redistributed which lead to minimum difference between both proles of joints were similar in trend when compared with each the sides. The nal pass induced shrinkage and transformation other. The residual stress values ranged from compressive to effects have created compressive stresses at the weld centre tensile stress. At the weld centre of the joints, compressive [21]. residual stresses were observed on top and bottom surface of CONCLUSION the joints, which is attributed to the phase transformation 6.

The surface residual stress values obtained using the XRD induced changes [21]. technique showed that minimum longitudinal tensile residual stresses are present in the rst set of weld double V joint (Plate 4 A. Residual stress in the longitudinal direction Along the longitudinal direction, the stresses beyond 15 mm A) made by alternate weld pass sequence (1-3-5-7 and 2-4-6-8) from the WC were almost uniform in all plates. At the WC as compared to the other two weld pass sequences in the comparing the residual stresses in the top and bottom surfaces, longitudinal direction.

Plate A & B showed a difference of 60 MPa whereas large When comparing the stresses (at the location of measurement) variation of stresses were observed in the Plate C. The stresses between the top and bottom surfaces in Plate A, the differences at the weld centre of all the three weld joints A, B and C were in residual stress were ranging between zero to 60 MPa. At the weld centre of all joints, higher compressive residual compressive and maximum in magnitude.

The maximum longitudinal tensile residual stress on the top stresses were present on the top surface (nal pass side) as surface 'A0, B0, C0' and on the bottom surface 'A1, B1, C1' of the compared to the bottom side. It is recommended to use weld joints are present at a distance of 15 mm from the weld alternate weld pass sequence during the welding of thick carbon steel to get minimum residual stress values. centre.

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Similar studies are planned for austenitic stainless steel welding which would be useful to minimize residual stresses and to prevent stress corrosion cracking.

Fig. 6 Maximum Tensile Residual stress in the weld joints

Fig. 4 Residual stress proles along longitudinal direction in carbon steel weld joints made by sequential weld passes. (A0, B0, C0 and A1, B1, C1 correspond to the two sides of the three weld joints A, B and C respectively)

Fig. 7 Maximum Compressive Residual stress in the weld joints 7.0

Fig. 5 Residual stress proles along transverse direction in carbon steel weld joints made by sequential weld passes. (A0, B0, C0 and A1, B1, C1 correspond to the two sides of the three weld joints A, B and C respectively)

ACKNOWLEDGEMENTS

The authors wish to thank Dr. A. K. Bhaduri, Director, Metallurgy and Materials Group (MMG) and also Director, IGCAR, Kalpakkam and Dr. T. Jayakumar, former Director, MMG, IGCAR for their support and encouragements towards this study.

References [1]. Koichi Masubuchi, 'Residual Stress and Distortion' ASM Hand Book, Vol.6, Welding Brazing and Soldering, ASM International, USA, 1993, pp. 1094-1102.

[2]. 'Residual Stress for Designers and Metallurgists', Proc. of a Conference. Ed. Larry J. Vande Walle, American Society for Metals, Metals Park. Ohio, USA, 1981, pp. 189-221.

[3]. Koichi Masubuchi, 'The Need for Analytical/Experimental Orchestrated Approaches to Solve Residual Stress Problems in Real Structures', Nondestructive methods for materials properties determination, Eds. C. O. Ruud and R. E. Green Jr., Plenum press London, UK., 1984, pp. 123-124.

[4]. S. K. Bate, D. Green and D. Buttle, 'Review of Residual Stress Distribution in Welded Joints for the Defect Assessment of Offshore Structures' AEA Technology Plc., Health and Safety Executive (HSE) Book, Offshore Technology Report, Shefeld, U. K. (ISBN 0-7176-2411-0), 1997.

[5]. T. R. Gurney, 'Some Recent Works Relating to Inuence of Residual Stresses on Fatigue Strength', Residual Stress Effects in Fatigue, ASTM STP-776, pp.151-157, 1981.

[6]. J. C. Denko, 'Effects of Residual Stresses on Stress Corrosion Cracking of Austenitic Stainless Steel Pipe Weldments', Practical Applications of Residual Stress Technology, Proc. of Inter. Conf., Ed. C. O. Ruud, ASM International, Metals Park, Ohio, USA., 1991, PP. 27-37.

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[7]. P. S. Lam, C. Cheng, Y. J. Chao, R. L. Sindelar, T. M. Stefek, J. B. Elder, 'Stress Corrosion Cracking of Carbon Steel Weldments'. In: Proceedings of 2005 ASME Pressure Vessels and Piping Division Conference, PVP2005:71327, 2005, pp. 1–9.

[8]. C. O. Ruud, 'A Review of Selected Non-destructive Methods for Residual Stress Measurement', NDT International, Vol.15 (1), 1982, pp.15-23.

[9]. 'Handbook of Measurement of Residual Stresses', Society for Experimental Mechanics, Edited by Jian Lu, Fairmont Press, USA, 1996.

[10]. Don E. Bray and W. Tang, 'Evaluation of Stress Gradient in Steel Plates Bars with the Lcr Ultrasonic Wave', Nuclear Engineering and Design, Vol. 207, 2001, pp. 231-240.

[11]. A. Joseph, P. Palanichamy, S. K. Rai, T. Jayakumar, and B. Raj: 'Non-destructive Measurement of Residual Stresses in Carbon Steel Weld Joints', Science and Technology of welding and Joining, Vol.6 (3), 1998, pp. 267-271.

[12]. P. Palanichamy, A. Joseph, D. K. Bhattachraya and Baldev Raj, 'Residual Stresses and Their Evaluation in Welds', Welding Engineering Hand Book, Ed. S. Soundararajan, Radiant Publications Pvt. Ltd., Secundrabad, India, Vol.1, 1992. pp. 26929 [13]. I. C. Noyan and J. B. Cohen, 'Residual Stress: Measurement

by Diffraction and Interpretation', Springer Verlag, New York, USA., 1997.

[14]. A. M. Jones, 'Residual Stresses: A review of their Measurements and Interpretation using X-ray Diffraction, Report AERE-R-13005, United Kingdom Atomic Energy Authority, Harwell, 1989.

[15]. P. S. Prevey, 'X-ray Diffraction Residual Stress Techniques', Metals Hand Book, Metals Park, Ohio, ASM, Vol. 10, 1986.

[16]. J. H. Root, C.E. Coleman, J.W. Bowden, M. Hayashi, 'Residual Stress reduction in Steel and Zirconium Weldments by Heat Treatments', Trans. Am. Soc. Mech. Eng., J. Pressure Vessel Technol., 119 (2) (1997), pp. 137–141.

[17]. 'Residual Stress Reduction by Shot Peening', American Society of Metals, 1983. Metals Handbook, pp. 856–895.

[18]. G. Gnirss, 'Vibration and Vibratory stress relief. Historical Development, Theory and Practical Application', Welding in the World, 26 (11/12), 1988, pp. 4–8 [19]. B. L. Josephson, 'Stress redistribution during annealing of a multi-pass butt-welded pipe', ASME, J Pressure Vessel Technol, 105 (2) (1983), pp. 165–170.

[20]. A. K. Bhaduri, S. Venkadesan, P. Rodriguez and P. G. Mukunda, 'Combined effects of post-weld heat treatment and aging on alloy 800/2·25Cr–1Mo steel joint', Materials Science and Technology, 7 (11), 1991, pp. 1051-1056.

[21]. M. Zubairuddin, S. K. Albert, V. Chaudhri and V. K. Suri, "Inuence of phase transformation on thermo-mechanical analysis of modied 9Cr-1Mo steel", Procedia Materials Science, 5, 2014 pp. 832 – 840

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A Review of Industrial Computed Tomography Standards Clifford BUENO GE Global Research Center, Niskayuna, NY, USA E-mail: bueno@GE.com ABSTRACT This paper provides a summary of the widely used computed tomography (CT) standards published by the American Society of Testing and Materials (ASTM International standards), European Committee for Standardization (CEN - European EN standards) and the VDI/VDE Society for Metrology and Automation (GMA). In each of these organizations, a series of standards has been developed that include background information on the physics, technology, and the use of CT by the intended audience. Following a review of these standards from each organization, some suggested next steps in the evolution of these standards will be discussed.

1.0

INTRODUCTION

I

ndustry standards for computed tomography and digital radiography have taken on greater importance as this technology transitions from the lab to the factory oor.

Recent mass production manufacturing of large area digital detector arrays (DDAs) for radiography in the healthcare industry has led to ready availability for industrial imaging, namely for nondestructive testing and for 3D metrology applications.

In particular, these devices are now being used for (1) high speed real-time (live imaging) digital radiography for shop oor, in-line manufacturing quality control operations, (2) high delity “radiation bunker based” radiography covering a wide range of x-ray energies, and resolving power, and thus a wide range of inspection applications, (3) fully automated systems either with multi-axis manipulators or robotics, again inside xray enclosures, (4) eld service inspection on assets already deployed or nearing deployment and (5) various applications of computed tomography, including small eld and large elds, low and moderate energies (10kV to 750kV), as well as high energies (1-20 MeV). CT applications range from locating small indications in an aircraft engine fuel nozzle to larger discontinuities in solid rocket motors. Each of these applications have their own imaging requirements, and therefore it is very challenging to develop standards that cross these different capabilities and technologies.

Over the past 10 years, new standards covering the use of these area DDAs have been released by several standards committees for radiographic purposes [1, 2, 3, 4, 5, 6, 7]. This has helped to gain acceptance in the industry to use this technology in production and manufacturing applications, for example to help direct changes needed from the day-to-day use of x-ray lm.

With standards in hand, the development of the systems mentioned above ourished, and many of these systems have now become commoditized and are used in many different industries from aerospace, to automotive, to power generation.

This paper describes the state of the current industrial CT

standards. It is to be noted that the ASTM standards discussed were originally written with the then more widely available linear detector arrays that employ a fan beam. With the assimilation of DDAs into these systems, and the increasing use of cone beam imaging systems to improve throughput, for example on factory oors, the existing standards must be updated to support the larger eld practices and the nuances that arise in the move to cone beam CT.

2.0 EXISTING CT STANDARDS A list of some of the current CT standards are listed below. This includes standards from ASTM International (ASTM), The European Committee for Standardization (CEN), Association of German Engineers (VDI), Association of Electrical Engineering, Electronics and Information Technology (VDE), Society for Metrology and Automation (GMA - VDI/VDE), and ISO (International Organization for Standardization). This is not an exhaustive list, but demonstrates where the technology is for these standards in the industry. By treating each organization’s standards together, one can determine the overall message that the respective committees have been relaying in these standards, and thus decisions on new standards can then be devised. These standards may be purchased through their parent organizations,, or through Thomson Reuters TechStreet (as an example) that services the Standards industry.

A summary of each Standards organization’s documents will be discussed in turn. Other relevant standards developed under ISO/TC 135/SC 5 Radiographic testing are: ISO 15708-1:2002 Non-destructive testing - Radiation methods - Computed tomography - Part 1: Principles; and ISO 15708-2:2002 Nondestructive testing - Radiation methods - Computed tomography - Part 2: Examination practices. These are not discussed herein since they have similar content to such standards as ASTM E1441, and E1570, and the ISO subcommittee is replacing these by the CEN documents discussed below. For example, ISO 15708-4:2017 Nondestructive testing — Radiation methods for computed tomography — Part 4: Qualication has been recently published based on EN 16016-4 discussed below.

40

N ote that ISO/TC 213/WG10 - Dimensional and geometrical product specications and verication committee/Coordinate Measuring Machines work group that works on Metrology standards is developing a CT Metrology standard based on VDI/VDE series of standards discussed below. The ASME B89 committee on Dimensional Metrology is also developing standards around CT for metrology purposes. Coordination around these standards organization with respect to CT standards is growing. Two good summary articles on this topic may be found here [8, 9].

3.0

ASTM STANDARDS

ASTM International currently provides 6 standards devoted to CT under the Radiography Subcommittee, E07.01. Within this subcommittee is the non-lm section (E07.01.02) that supports the management of these standards as well as any new standards deemed necessary by an active industry wide, global working group. The ASTM set of documents listed above, when taken together provide a developer or user of CT technology with:

ASTM E1441-11 - Standard Guide for Computed Tomography • Background information, physics of CT, dened terminology, some information on available systems (CT) Imaging • A guide to selecting a CT system _______________________________________________ • Test methods for measurement of CT system performance ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, US or www.ASTM.org •A means for specication of certain performance criteria based European Committee for Standardization, Management Centre: Avenue Marnix 17, Brussels, Belgium on detection needs as well as guidance for setting an evaluation International Organization for Standardization, ISO copyright ofce, Ch. de Blandonnet 8, CP 401, and scoring system.

CH-1214 Vernier, Geneva, Switzerland 1

2

3

4 5

WWW.Techstreet.com, all standards in this article are available for purchase from this site ASME B89.4.23 – CT Measuring Machines (SC4/B89), www.asme.org

ASTM E1570-11- Standard Practice for Computed Tomographic (CT) Examination ASTM E1672-12 - Standard Guide for Computed Tomography (CT) System Selection ASTM E1695-95(2013) - Standard Test Method for Measurement of Computed Tomography (CT) System Performance ASTM E1814-14 - Standard Practice for Computed Tomographic (CT) Examination of Castings ASTM E1935-97(2013) - Standard Test Method for Calibrating and Measuring CT Density EN 16016-1:2011- Non destructive testing. Radiation methods. Computed tomography. Terminology EN 16016-2:2011- Non destructive testing. Radiation methods. Computed tomography. Principle, equipment and samples EN 16016-3:2011 - Non destructive testing. Radiation methods. Computed Tomography. Operation and interpretation EN 16016-4:2011 - Non destructive testing. Radiation methods. Computed tomography. Qualication VDI/VDE 2630 Sheet 1.1 - Computed tomography in dimensional measurement - Fundamentals and denitions VDI/VDE 2630 Sheet 1.2 - Computed tomography in dimensional measurement - Inuencing variables on measurement results and recommendations for computed tomography dimensional measurements VDI/VDE 2630 Sheet 1.3 - Computed tomography in dimensional measurement – Guideline for the application of DIN EN ISO 10360 for coordinate measuring machines with CT sensors VDI/VDE 2630 Sheet 1.4 - Computed tomography in dimensional metrology - Measurement procedure and comparability VDI/VDE 2630 Sheet 2.1 - Computed tomography in dimensional measurement – Determination of the uncertainty of measurement and the test process suitability of coordinate measurement systems with CT sensors.

One common theme across the rst 4 standards listed above (E1441, E1570, E1672, and E1695) is a means to evaluate a CT system of its intrinsic properties to determine if such a system would be useful for the application at hand. The plot of the contrast required for 50% discrimination of pairs of features as a function of their diameters in pixels is known as the contrastdetail-dose (CDD) curve ([see Figure 1. A Contrast-Detail-Dose Curve (CDD) for a six-inch and 8-inch disk of Aluminum]. The CDD combines the metrics of spatial resolution (modulation transfer function - MTF) and contrast sensitivity (contrast discrimination function - CDF) into a single metric to estimate detection as a function of pixel size. If the size of the discontinuity that needs to be detected lies on the right side of the CDD curve, then it will be detected more than 50% of the time. To the left side of the curve, the detection will have a probability of less than 50%. That said, there are certain limitations with CT due to image artifacts that can inuence this detection capability, such as beam hardening artifacts and this determination needs to be used with caution. In moving to cone beam CT systems, additional artifacts due to scatter and large angle artifacts “Feldkamp artifacts” (>5 degrees) may further weaken this determination.

Figure 1. A Contrast-Detail-Dose Curve (CDD) for a six-inch and 8inch disk of Aluminum. “Reprinted, with permission, from ASTM E1570-13 Standard Practice for Computed Tomographic (CT) Examination, copyright ASTM International, 100 Barr Harbor Drive, West Conshohocken, PA 19428. A copy of the complete standard may be obtained from ASTM, www.astm.org."

41

The Standard Guide for CT System Selection (E1672) provides additional guidance on detectability as follows: “The prospective purchaser can make a preliminary determination as to whether a given CT system has the necessary spatial resolution for a given application using the following guidelines. First, if dimensioning is important, sharp highcontrast edges free of artifacts typically can be located to about one tenth of the effective beam width associated with a given system. Effective beam width is the x-ray beam size at the detector and could be dened by a fan-beam collimator, detector aperture, or by the pixel height. As long as the estimated accuracy is within a factor of close to two of the dimensional accuracy requirement set by the application, the particular system being considered should be deemed a potential candidate for use.”

acquisition, reconstruction, visualization and analysis. Like E1441, it discusses artifacts that can arise such as beam hardening and cone beam artifacts. It provides a descriptive narrative of equipment and apparatus. Given that the origin of this standard was started at a much later time than E1441, the technology in this document is more up to date, including various radiation sources, and a variety of detectors. An Annex also provides greater details into these technologies, including description of the now abundant CT systems based on areal digital detector arrays (DDAs) and microfocus x-ray tubes.

A nice addition to this standard is a recommended listing of the accelerating voltage, a corresponding scintillator type and thickness, and an associated beam lter thickness to achieve a 10% transmission level for several different thicknesses of materials ranging from water to tungsten. The standard recommends that a 10% transmission level provides an optimal Next, E1672 goes on to discuss visibility of indications: “if small- SNR in the CT image. area high-contrast (that is, inclusions) discrimination is important, small (approximately 4 pixels) regions typically can Part 3: Operation and Interpretation – This document provides be discriminated against a uniform background when the a good introduction to operational choices to achieve effective relative contrast between feature and host is greater than 5 to 6 CT performance. For 3D-CT (cone beam CT) the standard times the single-pixel image noise in the vicinity. For example, if recommends “the (in general vertical) total cone beam angle the image noise in the region of interest is about 2 %, a small measured parallel to the rotation axis should typically be less feature will need to have a contrast of at least 10 % to be visible. than 15o, … in order to minimize reconstruction-determined As long as the expected or estimated image noise associated (Feldkamp) distortions of the 3D model.” Additional guidance with a given system is within a factor of two or so of the noise includes “the rotation of the object must take place at, at least requirement set by the application, the particular system being 180o plus the beam angle of the x-ray beam, whereby an considered should be deemed a potential candidate for use.” improved data quality is the result of an increasing number of Note that this convention with the factor of 5-6, considering angular increments. For this reason, the object is typically CNR and object diameter to pixel width (see also E1441), turned through 360o. Ideally, the number of angular enables an indication to be visible. If a higher factor is achieved, increments should be at least π/2 x matrix size where the matrix this would certainly improve the probability of detection of an size is the number of voxels across the sample diameter or the indication. largest dimension.” Other options for data collection, for example range extension is mentioned to achieve CT of large These are key statements for whether any CT system will be components that exceed the beam cone. appropriate for the application at hand if the detailed requirements are known for that inspection.

ASTM also provides a standard for measurement of the CT The standard also mentions region of interest scans, where data system performance (E1695) that again uses the quantitative is collected only of a given segment of the object. The standard data of MTF and noise (CDF) to test the CT system. This can be states that truncation artifacts will result from this approach. A used as a baseline of the system as it is introduced into useful article on truncations, and management thereof may be production, and then periodically to test ongoing performance found here [10]. In this standard, there is guidance for the beam spectrum for successful imaging, detector corrections, as the system is placed into service. reconstruction and visualization parameters. Under analysis Finally, there is a practice for CT examination (E1570) that and interpretation of CT images, the standard suggests that “For focuses specically on how to collect CT imagery, including the detectability of singular pores, cavities and cracks, their acquisition, post processing, reconstruction, display, analysis, minimum extent should typically be 2 to 3 times the demagnied pixel size ...” archive, and documentation.

4.0 CEN STANDARDS As with the ASTM CT standards, the EN standards start with an introductory standard, part 1 of EN 16016. In this case, it simply provides a glossary of terms. This glossary of terms is somewhat different than the glossary found in ASTM E1441, with some minor overlap of critical terms.

The standard devotes a good amount of discussion to dimensional testing, including the necessary precise measurement of the voxel size, and an accurate determination of the surface threshold. Means for obtaining these are discussed leading to the generation of geometric data from the volume. A further discussion on CT (actual) comparison to CAD (nominal) geometries is provided.

Part 2 then provides the principles of CT including its Much like E1441, EN 16016-3 provides a discussion on advantages, limitations, and main process steps: from requirements for acceptable results and image quality

42

parameters, including contrast, signal to noise ratio, contrast to noise ratio, and spatial resolution. The Annex presents a new disc phantom to obtain the CT response to a series of holes in the disc to result in the percentage of contrast as a function of resolution in line pairs per centimeter. This measurement may be used to compare several CT systems.

One effective presentation in the EN standard is a description of many of the artifacts that can arise in a CT scan, including example imagery of each artifact discussed. Some guidelines are provided to manage these artifacts.

Part 4: Qualication. This document provides a narrative on checks to make to qualify a CT system. It lists the critical factors to consider, including imaging parameters, reference samples to use, consistency checks, and system components to be checked.

Detailed tests for these are not provided in this document. It goes on to state that the performance of a CT system depends on the various parameters such as (1) spatial resolution, (2) density resolution and (3) acquisition time. Since these are interdependent, changing one, will likely change another. The standard recommends the spatial resolution test dened in Part 3, and then denes a density resolution test at the end of the Part 4 document. This test is important for differentiating multimaterial components of an object.

In general, the EN standards tend to be written more as guides rather than as test methods or practices. Given that there are a very large number of CT system types, the guidance is valued in trying to devise specications, and qualication tests for the application at hand.

5.0 VDI / VDE STANDARDS Experts involved in the technical committee Computed Tomography in Dimensional Metrology within the VDI/VDE society for Metrology and Automation Engineering (GMA) produced the 5 standards listed above. Part 1.1 provides fundamentals and denitions, and like the two organizations discussed above provides a glossary of CT terms. The denitions are broken down into the following categories: (1) General terms and denitions, (2) Radiation sources, (3) Radiation detectors, (4) Scan Parameters, (5) Image reconstruction, (6) Artifacts, and (7) Dimensional measuring.

This list and those of the two other standards organizations discussed above provides a comprehensive list of terms needed for this eld.

form. This can be related back to factors that inuence the detection of discontinuities, and similar discussion is found in the ASTM and CEN standards. The annex includes recommendations for quality assurance in dimensional measurements using CT. Part 1.3 – Computed tomography in dimensional measurement provides guidelines to dene specications and procedures for testing coordinate measurement machines (CMMs) with sensors relying on the principle of X-ray computed tomography.

This standard is written from the viewpoint of CMM metrology and treating the CT sensor as an extension of CMM. It describes the possible errors one might encounter with this technology, from form errors to distance errors. The document provides details in how to measure these errors and how to then limit them. A test specimen for determining geometry dependent errors is presented. Like the other standards listed above, there is an annex on structural resolution for dimensional measurements. In summary, this document provides the acceptance and reverication tests for CMMs with CT sensors.

In Part 1.4 - Computed tomography in dimensional metrology, Measurement procedure and comparability; this guide provides a discussion on the various metrological tools, and how CT may compare against these.

Part 2.1 – Determination of the uncertainty of measurement and the test process suitability of coordinate measurement systems with CT sensors describes a procedure for determining the taskspecic uncertainty of a measurement using CT. This standard provides a means to determine the system uncertainty and knowing the tolerance to be fullled, a test process suitability can be obtained. This document delves into not only the uncertainty of the CT measurement, but uncertainty in the calibrated workpiece and a full uncertainty budget is delineated. A step-by-step process for tracking all sources of error is provided, including sample worksheets to ll out.

6.0 SUMMARY OF THE EXISTING STANDARDS AND POSSIBLE FUTURE DIRECTIONS The ASTM standards provide a good basis of knowledge for fan beam CT, but have not yet been fully updated to accommodate cone beam CT, and possible issues associated with this approach. ASTM provides details into procedures and test methods, but some of the phantoms will need to be extended to test area digital detector arrays, and corresponding cone beam CT system performance tests. Here some of the ASTM standards Part 1.2 provides a comprehensive narrative of typical variables on DDAs [1, 2, 3, 4] may be employed to test the components of inuencing the results of dimensional measurements that are the cone beam systems. performed using industrial computed tomography. Here the standard classies typical measurement tasks into 4 categories: The EN standards are descriptive in nature, as only a few (1) nominal/actual comparison based on nominal geometry procedures are presented to check system or component (CAD), (2) nominal/actual comparison based on reference performance. Since detailed procedures are common inASTM measurement, (3) analysis of size, shape, and position standards, a merging of the narrative of the descriptive tests tolerances and determination of compensating elements of described in the EN standards including reference to cone beam ruled geometries and free shaped surfaces, and (4) wall methods with new ASTM test methods and procedures will thickness measurements. A comprehensive list of inuencing accelerate the further acceptance of this technology in the variables based on the system properties is provided in tabular industry.

43

A simplied set of phantoms and tests are needed to test key elements of any system: x-ray source, detector, and manipulator (rotation stage) performance. These should be used by both the manufacturing community and the user community, with similar tests performed by both parties. This will support the industry in the selection, purchase, and qualication of now widely available cone beam systems, assist with baselining performance and long term stability testing, and provide methodology and procedures for using this equipment in production imaging. Where possible, detailed examples of the tests should be provided, with very specic information on the purpose of the test. This has been demonstrated with the ASTM DDA tests. Specic recommendations for the frequency of the testing should also be included that makes sense for the component or system under test.

Simple changes to the phantoms presented in the EN and ASTM standards may be warranted. For example, is a solid rod a better phantom for a cone beam system that employs an area DDA, instead of the disc used for the fan beam system that employs a linear DDA (LDA)? Will this identify variations in performance as a function of the projected position onto the detector, for example Feldkamp artifacts, or other large area artifacts? Is the cupping artifact consistent across the detector eld of view? How well does a beam hardening correction perform to manage that cupping? Are there other variations along this rod, for example SNR or MTF variations? Can the rod be used to test the performance of range extension discontinuities? These are but a few of the questions that arise in differences between fan beam and cone beam CT. The VDI/VDE standards have both descriptive and procedural guidelines and practices to test CT hardware for use in metrology. That said, the standards have been written from the Coordinate Measurement Machine (CMM) perspective. These standards need to be simplied for the industrial CT nondestructive testing audience that normally use said machines for discontinuity detection purposes, but want to extend their capability to metrological applications. Clear guidance on process suitability should be very obviously addressed throughout documents associated with CT for metrology.

In summary, a new set of test methods and practices for cone beam standards are needed. The global standards committees will need to review these pre-existing standards to determine what can be leveraged to address these new methods for nondestructive testing and metrological applications. The design and options for the phantoms need to accommodate different types of systems and energy ranges. For example, a large diameter Inconel rod is not appropriate to evaluate a low energy CT system, while a plastic rod is not an effective test for a high-energy system.. Similarly, for microfocus systems, the phantom selection should be exible to accommodate high magnication inspections, and the phantom should have the desired accuracy for these tests. A common set of the underlying test algorithms to analyze results from the tests developed should be co-developed by the standards teams and disseminated across the industry to facilitate comparison of CT

systems, and for consistent tracking of long term stability testing of these systems.

7.0

REFERENCES

[1] ASTM, "E2597/E2597M-14, Standard Practice for Manufacturing Characterization of Digital Detector Arrays," ASTM International, West Conshohocken, PA, 2014.[2] ASTM, "E2698-10, Standard Practice for Radiological Examination Using Digital Detector Arrays," ASTM International, West Conshohocken, PA, 2010.[3] ASTM, "E2736-10, Standard Guide for Digital Detector Array Radiology," ASTM International, West Conshohocken, PA, 2010.[4] ASTM, "E2737-10, Standard Practice for Digital Detector Array Performance Evaluation and Long-Term Stability," ASTM International, West Conshohocken, PA, 2010.[5] ISO10893-7, "Non-destructive testing of steel tubes - Part 7: Digital radiographic testing of the weld seam of welded steel tubes for the detection of imperfections," 2011. [6] ISO17636-2, "Non-destructive testing of welds - Radiographic testing - Part 2: X- and gamma-ray techniques with digital detectors," 2013.[7] EN16407-2, "Non-destructive testing.

Radiographic inspection of corrosion and deposits in pipes by Xand gamma rays. Double wall radiographic inspection," 2014.[8] M. Bartscher, O. Sato and F. Hartig, "Current state of standardization in the eld of dimensional computed tomography," Measurement Science and Technology, vol. 25, no. 064013, 2014. [9] M. Bartscher, J. Illemann and U. Neuschaefer-Rube, "ISO test survey on material inuence in dimensional computed tomography," Case Studies in Nondestructive Testing and Evaluation, vol. 6, p. 79–92, 2016.

[10] R. Chityala, K. R. Hoffmann, S. Rudin and D. R. Bednarek, "Artifact reduction in truncated CT using Sinogram completion," Proceedings of SPIE--the International Society for Optical Engineering, vol. 5747, no. 3, pp. 2110-2117, 2005.

ACKNOWLEDGMENTS The author would like to thank Dr. Uwe Ewert and Dr. Uwe Zscherpel both from Bundesanstalt für Materialforschung und prüfung (BAM), Dr. Claudia Kropas-Hughes from the US Air Force-Wright Patterson Air Force Base, Dr. Thomas Wenzel from YXLON International GmbH , and Dr. Holger Roth from GE Inspection Technologies for helpful discussions. The author would also like to thank the non-lm section task group members of the Radiology subcommittee of ASTM for fruitful discussions on this topic.

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Slots allotted on first cum first serve basis after receipt of duly filled Order Form & 50% advance payment. Service Tax extra as applicable, presently 15%.

10% Discount on Ads Booked for 4 Issues together with full advance payment.

Book your space by mailing the completed form to Rachna Jhaveri - JNDE Executive at isnt.jnde@gmail.com (subject to availability) at least 2 months prior each issue along with 50% advance payment & remaining 30 days before publishing of journal.

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Mr. Rajul Parikh, Managing Editor - JNDE 8, 2nd Floor, Jyoti Wire House, Near Kolsite, Off Veera Desai Road, Andheri (W), Mumbai – 400 053. INDIA. Tel : 022 – 61503800 / 61503839

45

Back to Basics: Image Quality Parameters and Standards in Digital Radiography *V Manoharan & Megha Navalgund GE India Technology Center Pvt. Ltd. 122, EPIP, Hoodi Village, Whiteeld Road, Bangalore - 560067 *Email : Manoharan.V@ge.com

F

ilm radiography has been in practice over 100 years by industries for NDT applications. Factors which inuence image quality are well understood, image quality metrics and international standards are well established for lm radiography. Required image quality can be achieved by selecting appropriate type of lm and radiation energy, achieving required lm density and meeting geometrical unsharpness requirements. Use of Digital Radiography technologies such as Computed Radiography (CR) and Digital Detector Arrays(DDA) by industries has increased in last 15 years and new digital radiography standards towards these technologies are being developed by international standards organizations. The image quality in digital radiography depends on the exposure conditions and the properties of the digital detectors. This article discusses basic parameters which inuence image quality in digital radiography. It will be useful for operators towards understanding key parameters that inuence image quality and their optimization to achieve optimum image quality. This back-to-basics article also list some of the readily available digital radiography standards.

These standards should help the end user to select the optimum setup, identify qualication methods of new inspection equipment for their application and tracking long term stability of the setup.

ESSENTIAL IMAGE QUALITY PARAMETERS IN DIGITAL RADIOGRAPHY Image quality indicators (IQIs) are used to ensure that an optimum radiography technique is applied to meet the required image quality. There are different types of image quality indicators such as plaque type and wire type as recommended by international standards. The visibility of boundary of plaque and holes in plaque type IQI or wire of required diameter in wire type IQI decides acceptance of radiograph for further evaluation. It is proved that visibility of hole or wire in a digital radiograph is a function of three essential parameters – Signal to Noise Ratio(SNR), Basic Spatial Resolution(BSR) and specic contrast. The visibility of the smallest hole in plaque type IQI or smallest wire element in wire type IQI can be numerically predicted, if the essential parameters of the digital image are known.

SIGNAL TO NOISE RATIO (SNR) Signal to noise ratio (SNR) is dened as the ratio of mean and standard deviation of pixel values of a region of interest in a digital radiograph. The gray value (intensity) of pixels in a radiograph of an object even with uniform thickness will not be

same and there will be deviation from pixel to pixel. This deviation from the expected is noise and is measured by computing standard deviation of pixel values in a region of interest. The measurement of SNR in a digital radiograph is illustrated in Fig.1.

Fig 1: Illustration of SNR measurement in a digital radiograph

Noise in a radiography process is Poison distributed which means that standard deviation (of photons) is directly proportional to square root of mean (average number of photons). This noise is called quantum noise. Hence, noise in radiography is directly proportional to square root of intensity.

So, if the mean intensity is 25 then noise equals 5 which is 20% of the intensity. Similarly, if the mean intensity is 100 then noise is 10 which is 10%. This quantum noise can be reduced by increasing radiation intensity (dose) or acquisition time. It can also be reduced by averaging multiple frames of radiographs.

The total noise in a radiographic image is due to quantum noise and electronic/ structural or xed pattern noise (from the detecting/ image formation technology).

The effect of SNR is illustrated in g.2. The region of interest -1 is acquired using low intensity of radiation and region of interest 2 is acquired with higher intensity of radiation. The visibility of white circle is poor in region 1 due to high noise as compared region-2.

Fig 2: Illustration of SNR on image quality.

46

SNR can be improved by calibration procedure of Digital Detector Arrays(DDA). There is always inherent pixel to pixel variation, called structural noise, because of non-uniform gain of a-Si diodes and thickness variation in phosphor layer. This variation can be corrected by offset and gain correction procedure. The manufacturer will specify type of calibration procedure and frequency of calibration to be followed.

BASIC SPATIAL RESOLUTION Spatial resolution is associated with the ability to distinguish between two closely spaced features in a radiograph. It is quantitatively measured by basic spatial resolution (SRb) and is dened as the smallest visible detail within a digital image and is considered as effective pixel size (square root of pixel area). If two closely spaced features of individual size "a" are minimally separately seen in a radiograph, then size of single feature "a" is basic spatial resolution or effective pixel size. Poor spatial resolution of imaging system will produce blurriness in image and this is illustrated in Fig. 3. Fig. 4 is a radiograph of Duplex wire gauge which consists of many pairs of wires separated by different spacing. In the gure.3, The wires are seen separately for rst 3 pairs. The wires in rest of pairs are blurred and merged together. This is due to poor spatial resolution of the system.

Fig. 4 is a radiograph acquired using a system with good spatial resolution and the wires are seen separately till 5th pair.

interest here is the white (lighter color) circle over a dark background. The visibility of a region (in this case the white circle) is good when contrast is high and poor when contrast is low. The contrast observed in a radiograph is mainly attributed by subject contrast or specic contrast. Subject contrast is dened as difference in transmitted radiation intensity ΔI of an object of thickness difference ΔT for a given radiation energy.

The difference in radiation intensity (ΔI) will be decreased if radiation energy is increased and hence subject contrast will be reduced. Subject contrast is a function of object thickness variation, radiation energy and scattered radiation. Poor subject contrast leads to poor radiographic contrast. Hence, it is very important to choose optimum radiation energy and control scattered radiation during radiography. The measure of contrast in a radiograph is contrast sensitivity and it is dened as minimum % change in thickness of an object which produces a measurable gray level change in a radiograph.

Fig 5: Illustration of contrast in a radiography image

Fig 3: Illustration of poor spatial resolution

CONTRAST TO NOISE RATIO While contrast enables visualization of different regions as being different, Contrast to Noise Ratio (CNR) enables clear denition of where the boundaries of these regions are. In other words, the sharpness and the perceived image quality of an image is improved when the image has high CNR. It is measured as the ratio between contrast and noise. Thus when contrast increases and noise decreases the, CNR improves. As seen in Fig. 6, for the same contrast as noise decreases the image quality improves.

Fig 3: Illustration of good spatial resolution

Spatial resolution of computed radiography system is a function of laser spot diameter, translational speed of IP, thickness of phosphor layer, particle size, decay lag of PSL, speed of laser beam sweep and the frequency sampling of PMT signal.

For digital detectors, it is inuenced by pixel size, scintillator thickness and internal scattered radiation.

SPECIFIC CONTRAST Contrast in a digital radiograph is dened as difference in gray levels of area of interest and adjacent area in a radiograph. Fig 5. illustrates different levels of contrast in an image. The area of

Fig. 6: Illustration of CNR in a digital radiograph

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NON-PERFORMING PIXELS (BAD PIXEL) ASTM document E2597 presents a very well dened set of rules to dene a pixel as bad. Bad pixels can be "dead" pixels or pixels which do not behave in a predictable way like, there can be some pixels which are bad since they may have more lag or noise or can have different response. Sometimes, these kind of pixels may appear to be good visually but due to their nonlinear behavior will present error during tomographic reconstruction or quantitative analysis of the image.

Bad pixels are mainly classied as relevant clusters and irrelevant clusters. A cluster is a case where two or more bad pixels are connected. A relevant cluster is a cluster with a Kernel pixel. A Kernel pixel is dened as a bad pixel with less than ve good pixels in its immediate neighborhood. For most applications, there should be no relevant clusters in the imaging area of the DDA. But any irrelevant cluster and isolated bad pixels can be corrected using some form of mathematical interpolation.

CODES & STANDARDS FOR D I G I TA L R A D I O G R A P H Y 1

ISO-16371-1

Non-destructive testing -- Industrial computed radiography with storage phosphor imaging plates -- Part 1: Classication of systems.

Non-destructive testing -- Industrial computed radiography with storage 2 ISO - 16371-2 phosphor imaging plates -- Part 2: General principles for testing of metallic materials sing X-rays and gamma rays.

Non-destructive testing of welds -3 ISO - 17636-2 Radiographic testing -- Part 2: X- and gamma-ray techniques with digital detectors.

4

ASTM E2597 / E2597M - 14

Standard Practice for Manufacturing Characterization of Digital Detector Arrays.

5

ASTM E2736 - 10

Standard Guide for Digital Detector Array Radiology.

6

ASTM E2737 - 10

Standard Practice for Digital Detector Array Performance Evaluation and Long-Term Stability.

7

ASME – SECTION V

Non-destructive examination.

COMPENSATION PRINCIPLE Compensation principle allows the user to compensate for some effect by adjusting another parameter during the radiography process. There are three compensation principles proposed in ISO 16371-2 for optimization of radiography techniques to achieve requires CNR. Principle-I: Compensation for reduced contrast by increased SNR. It means you can use higher energy of radiation if required, the loss in contrast can be compensated by increasing SNR. Principle-2: Compensation of insufcient detector unsharpness by increased SNR. It means if we don't have a detector of required basic spatial resolution as per standards, we can still use the detector provided, we compensate for loss of resolution using higher SNR. Principle-3 : Compensation of increased local un-sharpness due to bad pixel correction by increased SNR. The loss of CNR in the region of bad pixel correction can be compensated by increasing SNR.

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PROBES (TRANSDUCERS) EECI offers wide range of transducers for various applications such as Flaw Detection, Thickness Gauging & Material Research. Our Probe Range includes: Ÿ Ÿ Ÿ Ÿ Ÿ Ÿ

Contact normal beam transducers (N / NM / NF Type) Dual element transducers (TR / TRM / TRF Type) Angle beam transducers (A/ AMB/ AMK /AM / AF Type) Immersion transducers (Focused / Non-focused) Transducers with replaceable delay line / angle wedges Special customized probes

Transducers are manufactured in subminiature, miniature, normal & large Crystal size, to suit the component shape & test requirements. A wide range of frequency & size of crystal is available. Ÿ

Special custom designed transducers are also manufactured to suit specific test requirements, with modified case designs, connectors, special wedges, etc.

Ÿ

EECI’s standard range of probes are equipped with Ultrasonic Transducer Test Report as well as Probe Data Sheet Certicate.

ELECTRONIC & ENGINEERING CO (I) PVT. LTD. www.eecindia.com

UVA ASSEMBLY - UMC NUMBER: 708002 FEATURES

Ÿ UVA Light Assembly, which is a source of UVA light of wavelength 365nm, is used by all operators for MPI (Magnetic Particle inspection) Testing. Ÿ The testing quantities are generally very high and the operator has to conduct inspection in darkened conditions.

The assembly is handled frequently and repeatedly by the operator for inspection purpose. Ÿ The above working conditions demand that the UVA Assembly used for inspection should be Strong, Sturdy, having Long life and Convenient for use. The assembly should necessarily be light weight and not very costly. Ÿ FerroChem have developed a lamp holder i.e. UVA Assembly (UMC No.708002) which meets all the aforesaid requirements.

The UVA assembly comprises of two parts: 1) Power Pack and 2) UVA Lamp Holder Assembly

FERROCHEM NDT SYSTEMS PVT. LTD. www.ferrochemndtsystems.com

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RADIATION SURVEY METER DIGIRAD The DIGIRAD is a light portable battery operated instrument which provides a fast and accurate measure of GAMMA & XRAY radiation leaks at X-Rayinstallation, industrial facilities, etc.

It also fulls the requirement for industrial radiography. Digirad makes use of a miniature halogen quenched GM counter as the GAMMA ray detector. This detector is mounted in the front portion of the DIGIRAD and has a small dead time and works reliably even in adverse conditions.

FEATURES Ÿ Digital, Compact and Rugged radiation survey meter. Ÿ Available in Low, Standard & High Ranges and we ‘MAKE IN INDIA’. Ÿ Incorporates advance techniques of auto ranging and auto/manual response time. Ÿ The response is energy independent in the energy range 100KeV to 1.27MeV within +/- 20% by using suitable lters. Ÿ Over range indication and a switch-off timer.

Ÿ

The state-of-the art circuitry is fully solid state using CMOS ICs and works on four penlite batteries giving more than 60 operating hours.

PULSECHO SYSTEMS www.pulsecho.com

IPLEX NX Olympus introduces the videoscope which combines the high quality images, intuitive user interface , ergonomic design, durabe in harsh environment and with powerful measurement features. The IPLEX NX - Olympus Most Advanced Videoscope for Critical Inspection Tasks.

FEATURES Ÿ High Quality Images for Clear Visualization Ÿ Expanded Measurement Capabilities for Fast and User friendly defect measurement Ÿ 8.4 Inch Screen Display for better visualization Ÿ Multi Spot Ranging for Accurate and Repetitive Defect Measurement Readings Ÿ Multi Position Design which avoids special Arrangement to position Instrument at any type of Remote area.

OLYMPUS MEDICAL SYSTEMS INDIA PVT. LTD. www.olympus-ims.com

ARJUN 10 Modsonic has added one more unique product to its family of Ultrasonic Flaw Detectors, Arjun 10 which is India’s rst ultralight palmtop ultrasonic aw detector, which offers state of the art technology in package that is compact and light weight (800 grams along with the battery). It provides high performance conventional aw detection and can be easily operated with one hand due to simple key structure and menu navigation settings. It has a wide variety of standard as well as specialized features to meet your inspection needs.

FEATURES: Ÿ One Handed operation Ÿ Auto plotting Dynamic DAC Ÿ Only few keys for user friendly menu navigation.

Ÿ

The state-of-the art circuitry is fully solid state using CMOS ICs and works on four penlite batteries giving more than 60 operating hours.

MODSONIC INSTRUMENTS MFG.CO.(P) LTD www.modsonic.com

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FLIR X6570sc High Speed Longwave Infrared (LWIR) Camera for most demanding R & D professionals. The FLIR X6570sc Thermal Imaging Cameras are designed to provide the best thermal measurement performance together with the most advanced connectivity. To analyze high-speed processes with microsecond precision or monitor fast temperature spikes, the X6570sc has the integration time and frame speed needed to collect the most accurate data.

FEATURES Ÿ The X6570sc is equipped with a cooled mercury cadmium telluride (MCT) detector that’s sensitive enough to distinguish temperature differences less than 25 mK (20 mK typical). Ÿ The camera produces temperature measurements with an accuracy of +/-1% and a wide temperature range up to 350°C that automatically adjusts to best t the thermal scene. Ÿ Design with 640 x 512 pixels IR Resolution to capture crisp and detailed thermal image for R & D application and measure accurately in high-speed processes. Ÿ View live, analysis and record thermal imagery on the detachable LCD touchscreen monitor. This camera works with FLIR Research IR Max software for both viewing and processing thermal data. Ÿ Connect over Camera Link Medium for full-bandwidth data acquisition, Gigabit Ethernet for simple connectivity or standard BNC for frequently used features such as detector sync, acquisition trigger and analog locking input.

Ÿ

The camera’s state-of- the-art connectivity and intuitive user experience allow researchers to focus on their experiments instead of the camera controls.

FLIR SYSTEMS INDIA PVT. LTD. www.ir.in

GE’S UTILITY VIDEO BORESCOPE The XL Lv VideoProbe from GE’s Measurement is a recently launched Video Boroscope, equipped to handle a wide variety of remote visual inspection needs. It provides one of the best equipment values in the industry. XL Lv VideoProbe system provides inspectors with unparalleled access without a bulky base unit, weighing as little as 1.77 kg. The system is supplied in a convenient light-weight shipping/storage case which protects the system when not in use and keeps it organized when in use. It can be provided in standard diameters of 3.9,6.1 & 8.4mm with various tips.

FEATURES Ÿ 360 Degrees Servo motor All-Way* Probe articulation. Ÿ White LED mounted inside the unit with light transmission using ber optics. Ÿ 1 GB internal ash memory. Ÿ 1 USB 2.0 port, along with 8 GB pen drive Ÿ Full-tip optic interchangeability with secure double threads Ÿ Two hours battery with on board charging. Ÿ Works upto 100 Deg C with two level of temperature warning. Ÿ Still image and live video capture with audio recording. Ÿ Certied to IP55

KRONIX XRAY & ALLIED PRODUCTS www.kronix.in

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NDE 2016 - A Report 15TH TO 17TH DECEMBER 2017 ORGANISED BY INDIAN SOCIETY FOR NON DESTRUCTIVE TESTING THIRUVANANTHAPURAM CHAPTER Compiled by : A.SHUNMUGAVEL, SECRETARY - NDE 2016

N

DE 2016, 26th National Seminar & International exhibition was conducted by ISNT Thiruvananthapuram chapter during 1517 December, 2016 at Al Saj Convention Centre, Thiruvananthapuram.

PRE-CONFERENCE TUTORIAL As a prelude to the main event, pre conference tutorial was arranged on 13th & 14th December, 2016 at HRDD seminar halls of Vikram Sarabhai Space Centre (VSSC). It was inaugurated by Shri S. Pandian, Associate Director, VSSC. Around 50 delegates participated in the pre conference tutorials conducted on topics; Digital NDE - Principles & Practices, Corrosion- Detection, Measurement & Evaluation & Advanced NDE for Propellants & Composites.

SPONSORS OF THE EVENT Principal Sponsor :GE Oil & Gas Digital Solutions, India Platinum Sponsor :Olympus Silver Sponsor :Blue Star E & E Ltd, Chennai & VJ Imaging Technologies Pvt. Ltd. Bronze Sponsor :LPS Industrial Technologies Pvt. Ltd. & Varian An exclusive presentation by the sponsors was arranged on 1st day and all the sponsors were given opportunity to brief about their products and services. All leading international & domestic players in NDE eld participated in the exhibition and was well attended by all participants on all three days of the seminar.

TECHNICAL LECTURES

All the lectures were handled by experienced faculty from ISRO & other leading private and Government organizations like BARC, IGCAR, DRDO, GE, Olympus etc. The program was concluded on 14th December 2017 with valedictory function attended by Shri B.Jayakumar, Project Director, PSLV, VSSC. Participation certicates were distributed to all the participants.

INAUGURATION OF NDE 2016 The seminar was inaugurated in a grand function held at Al SAJ Convention center on 15th December 2016. The function was presided over by Shri D.J Varde, President ISNT. Shri G Levin, Chairman, Organising Committee welcomed the gathering and Sri S. Saratchandran, Co-Chairman, Organising Committee introduced the theme of the seminar. Shri A.S Kiran Kumar, Chairman, ISRO/Secretary, Department of Space inaugurated the seminar through live video address from NRSC, Hyderabad.

Keynote address was delivered by Dr. K. Sivan, Director, VSSC. Shri. M.C. Dathan, Scientic Advisor to Chief Minister of Kerala & Former Director, VSSC released the souvenir & proceedings and offered felicitations. Shri Rajul R Parikh, Honorary Secretary offered felicitations. The NDT national awards 2016 were distributed at the function. Shri Mohan Ananthanarayanan, Convener, NDE 2016 proposed vote of thanks.

INTERNATIONAL EXHIBITION The exhibition was inaugurated by Dr. K. Sivan, Director, VSSC. A total of 46 leading players in the eld of NDT equipments and services showcased their products & services.

Ÿ Memorial & Plenary lectures (First day) A.K Rao memorial lecture by Dr. P. Kalyanasundaram, Former Director (FRTG), IGCAR & VS Jain memorial lecture by Prof.

Krishnan Balasubramanian, IIT Madras were arranged in the forenoon session.

Three plenary lectures by Dr. B. Venkatraman, Director HESG, IGCAR; Shri R.S. Sundar, Site Director & Dr. Suresh Babu, Chief Engineer (QA), Koodankulam Nuclear Power Plant; Dr. Prabhat Munshi, IIT Kanpur were arranged in the afternoon session. Ÿ Parallel technical sessions (2nd and 3rd days) Parallel sessions as below covering all techniques of NDT, advancements, various applications, training and safety were arranged. Each session began with a lecture from eminent experts in the relevant topic of the session.

Total 24 sessions were held. In Oral presentation, 22 lecturers were invited & 132 contributory papers presented.

SOUVENIR & PROCEEDINGS A souvenir of the event containing all abstracts of invited & contributory papers including posters, complimentary advertisements of sponsors & exhibitions, along with delegate kit was released at the inaugural function and distributed to all delegates.

DELEGATE REGISTRATION 420 paid delegates & 115 Sponsored delegates attended the event.

55

CULTURAL PROGRAM On ď&#x20AC; rst day, a fascinating fusion dance program was performed by artists from Kerala Kalamandapam, Thrissur. They all performed classical dance forms of India viz. Bharat natyam, Kuchipudi, Mohiniattam, Kathakali etc. along with classical music. On second day, an exciting music program was performed by Digital voice group with popular singers from various music contests. This was arranged at KTDC Hotel Samudra, Kovalam, a popular international tourist destination.

All guests enjoyed the evening near the beautiful beach of Kovalam.

AGM OF ISNT AGM was conducted on 2nd day evening at main hall of Al Saj convention centre.

More than 100 members participated and made it a grand success with lively interactions.

VALEDICTORY FUNCTION (17.12.16) Prof. Dr. Kuncheria P. Isaac, Vice Chancellor, APJ Abdul Kalam Technological University, Kerala was the chief guest of the function. He distributed best oral presentation, best poster presentation & best exhibitor awards at the function to the winners. Both President & Hon. Secretary, ISNT spoke on the occasion.

Delegates also gave feedback on the occasion. The event concluded with a photography session of all members of Team NDE 2016.

56

TEAM NDE

58

59

60

61

63

MONTH

MEETING

DAY / DATE OF MEETING

February, 2017

Chairman Meet

Saturday, 25th February

June, 2017 September, 2017 December, 2017

NCB Meeting

Saturday, 25th February

NGC Meeting

Sunday, 26th February

NCB Meeting

Saturday, 10th June

NGC Meeting

Sunday, 11th June

NCB Meeting

Saturday, 23rd Sep.

NGC Meeting

Sunday, 24th Sep.

NCB Meeting

Wednesday, 13th Dec.

NGC Meeting

Wednesday, 13th Dec.

AGM

Thursday, 15th Dec

VENUE

Chennai

Mumbai Bangalore

Chennai

65

NDT Level III Refresher Courses in 2017 COURSE SCHEDULE Method

Course

Dates

Course

Tax

Total

Magnetic Particle Testing-MT

3 days

2nd to 4th April 20 17

9,000

1,350

10,350

Radiographic Testing -RT

5 days

5th to 9th April 2017

15,000

2,250

17,250

Basic

5 days

10th to 14th April 2017

15,000

2,250

17,250

Ultrasonic Testing -UT

5 days

16th to 20th April 2017

15,000

2,250

17,250

Liquid Penetrant Testing-PT

3 days

21st to 23rd April 2017

9,000

1,350

10,350

Visual testing - VT*

4days

24th to 27th April 2017

16,000

2,400

18,400

Eddy current - ET *

4 days

28th April to 1st May 2017

16,000

2,400

18,400

NOTE : *VT & ET will be conducted if sufcient no. of candidates are indicated by 15th March 2017 and registered by 10th April 2017.

Please indicate your interest in enrolling for the course in advance for us to conrm the course.

For Further Information Contact : Indian Society for Non-Destructive Testing- Mumbai Chapter Shri Niranjan Sthalekar. Ph:+91 22 28327521 Mob:+919869642505 (Monday to Saturday- From IST 09:00 hrs to 17:00 hrs) E Mail: isntmumbai@gmail.com; offc@isnt.org

Course Calendar for year 2017- 18 by S.N Month

Certication Scheme

Course Code ASUT-171

Examination Date

**Course Last Fees date to submit Rs.

28.04.17 & 29.04.17

9,600/- 15.04.17

Training Period Courses From

To

1.

April

IS: 13805 / SNT-TC-1A

2.

May

SNT-TC-1A

3.

May

IS: 13805 / SNT-TC-1A

ASRT-173

Radiographic Testing

17.05.17 24.05.17

26.05.17 & 27.05.17

9,600/- 11.05.17

4.

June

IS: 13805 / SNT-TC-1A

ASVT -174

Visual Testing Level-II

05.06.17 08.06.17

10.06.17

5,000/- 31.05.17

5.

June

IS: 13805 / SNT-TC-1A

ASST-175

Surface NDT Level-II

22.06.17 28.06.17

30.06.17 & 01.07.17

8,400/- 17.06.17

6.

July

SNT-TC-1A

ASIR-176

Infra Red Level - II

03.07.17 09.07.17

11.07.17 & 12.07.16

20,000/- 26.06.17

7.

July

IS: 13805 / SNT-TC-1A

ASUT-177

Ultrasonic Testing Level 19.07.17 26.07.17

28.07.17 & 29.07.17

9,600/- 13.07.17

8.

August

ASET-172 Eddy Current Testing L-II 02.05.17 09.05.17 11.05.17 & 12.05.2017 12,000/- 25.04.17

IS: 13805 / SNT-TC-1A ASRT – 178

9. September IS: 13805 / SNT-TC-1A

Ultrasonic Testing Level 19.04.17 26.04.17

Radiographic Testing

08.08.17 16.08.17

18.08.17 & 19.08.17

9,600/- 01.08.17

ASST -179

Surface NDT Level-II

14.09.17 20.09.17

22.09.17 & 23.09.17

8,400/- 08.08.17

10.

October

IS: 13805 / SNT-TC-1A

ASRT-180

Radiographic Testing

04.10.17 11.10.17

13.10.17 & 14.10.17

9,600/- 29.09.17

11.

October

SNT-TC-1A

AAUT-181

Advance UT (TOFD +

23.10.17 06.11.17

08.11.17 & 09.11.17

60,000/- 17.10.17

12. November IS: 13805 / SNT-TC-1A

ASUT -182 Ultrasonic Testing Level 08.11.17 15.11.17

17.11.17 & 18.11.17

9,600/- 02.11.17

13.

January

IS: 13805 / SNT-TC-1A

ASVT-183

Visual Testing Level II

08.01.18 11.01.18

13.01.18

5,000/- 02.01.18

14. February

IS: 13805 / SNT-TC-1A

ASST-184

Surface NDT Level-II

07.02.18 14.02.18

16.02.18 & 17.02.18

8,400/- 01.02.18

15.

IS: 13805 / SNT-TC-1A

10.03.18

6,000/- 28.02.18

March

ASRI – 185 RT Film Interpretation II 05.03.18 08.03.18

For Further Information Contact : Indian Society for Non-Destructive Testing - Chennai Chapter Shri R. Vivek (Hon. Secretary) M: Ph : 0 9840023015 Phone: 044-6538 6075, 45532115 Email:isntchennaichapter@gmail.com

67

Compiled by Dr. Shyamsunder Mandayam Chairman, National Certication Board - ISNT United States Patent 9,057,680 Portable industrial limited angle gamma-ray tomography scanning system Inventors: Jung Sung-Hee, Kim Jong-bum, Moon Jinho Assignee: Korea Atomic Energy Research Institute-Daejeon, KR Korea Hydro and Nuclear Power Co., Ltd. (Seoul, KR) Provided is a diagnostic method and system capable of applying tomography to industrial long cylindrical process systems, such as a pipe line, which are difcult to diagnose using existing medical or industrial computed tomography (CT) scanners. Existing industrial Xray CT scanners cannot be used for such a pipe that is attached to the process system and thus cannot be placed on the turntable, and existing image diagnostic apparatuses of a fan beam type, a collimated beam type, etc. having a stereotyped structure are next to impossible to move and use for undetachable process systems and their peripheral devices. To solve these problems, there is provided a gamma-ray tomography scanning system that is capable of being directly attached to a pipe in operation and measuring a cross section of the pipe.

United States Patent 9,058,658 Methods and devices for locating object in CT imaging Inventors: Li Liang, Zhang Li, Chen Zhiqiang, Zhao Ziran, Xing Yuxiang, Xiao Yongshun, Wang Qingli Assignee: Tsinghua University (Beijing, CN) & Nuctech Company Limited (Beijing, CN) The present disclosure provides methods and devices for locating a plurality of interested objects in CT imaging. Location of the interested objects in the three-dimensional space can be determined by using three projection images that are substantially perpendicular to each other. The method can rapidly locate interested objects in a CT image without pre-reconstruction of the CT image even if there are a plurality of interested objects in the eld of view. The algorithm does not involve interactive steps. The method is rapid and effective, and thus applicable to industrial applications United States Patent 9,538,968 Apparatus and method for digital radiography Inventors: Rotondo Giuseppe, Lissandrello Fabio, Giani Claudio Assignee: DE GOTZEN S.R.L. (Olgiate Olona (Varese), IT) An X-ray apparatus for digital radiography has a rotating arm where the X-ray source and X-ray sensor cassette are oppositely mounted.

The source has a primary collimator to adjust the X-ray beam size according to the selected imaging modality. The sensor cassette encloses a rst X-ray detector for a rst imaging mode, while a second X-ray detector usable for a second imaging mode is detachably mounted on the external side of the sensor cassette. The sensor cassette accommodates a second collimator to create a fan shaped Xray beam for a third imaging modality. The sensor cassette has a linear motorized movement which is used for: aligning the X-ray beam with respect to the rst and second detector; positioning the rst detector in the rst imaging mode to achieve an extended view; and scanning movement during the third imaging modality synchronized with the horizontal movement of a third X-ray detector.

United States Patent 9,418,405 Method and system for reducing motion blurring in digital radiography

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Inventors: Venkatesan Varun Akur, Issani Siraj, Methani Chhaya, Prabhu Vishal Assignee: Siemens Aktiengesellschaft (Munich, DE) A method of reducing motion blurring in digital radiography includes capturing at least one temporally coded blurred image of an object generated by using a coded pattern, and generating a de-blurred image from the at least one temporally coded blurred image by using the coded pattern and an estimate of a motion vector of the object. The at least one temporally coded blurred image is captured by using a total amount of generated light corresponding to at least a portion of radiation transmitted by the object. A digital radiography system is also provided.

United States Patent 9,105,087 System for uncollimated digital radiography Inventors: Wang Han, Hall James M, McCarrick James F, Tang Vincent Assignee: Lawrence Livermore National Security, LLC (Livermore, CA) The inversion algorithm based on the maximum entropy method (MEM) removes unwanted effects in high energy imaging resulting from an uncollimated source interacting with a nitely thick scintillator.

The algorithm takes as input the image from the thick scintillator (TS) and the radiography setup geometry. The algorithm then outputs a restored image which appears as if taken with an innitesimally thin scintillator (ITS). Inversion is accomplished by numerically generating a probabilistic model relating the ITS image to the TS image and then inverting this model on the TS image through MEM. This reconstruction technique can reduce the exposure time or the required source intensity without undesirable object blurring on the image by allowing the use of both thicker scintillators with higher efciencies and closer source-to-detector distances to maximize incident radiation ux. The technique is applicable in radiographic applications including fast neutron, high-energy gamma and x-ray radiography using thick scintillators.

United States Patent 9,002,088 Method and apparatus for creating nondestructive inspection porosity standards Inventors: Ferguson Kathy L. Assignee: The Boeing Company (Chicago, IL) A method and apparatus for establishing nondestructive inspection porosity standards. In one illustrative embodiment, a plurality of samples is formed using a different technique for each sample in the plurality of samples such that each sample in the plurality of samples has a different porosity from other samples in the plurality of samples.

Each sample in the plurality of samples has a same set of selected properties as a selected part type. A porosity level is identied for each sample using volumetric data extracted from a three-dimensional image for each sample generated using a computed tomography system. A group of standards is established for a group of selected porosity levels from the plurality of samples based on the porosity level identied for each sample in the plurality of samples. The group of standards is congured for use in performing nondestructive inspection of a part of the selected part type.

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