JNDE by ram jnde

from the Chief Editor

The second issue in 2011 continues on the previous issue with the several recently introduced features such as IQ Forum, Probe, NDT Puzzle, etc. In this issue, the HORIZONS features new applications in the field of NDT of a rather well known technique of photoacoustics. The BASICS covers some of the fundamental learnings and issues in the field of Digital Radiography. The 4 Technical papers in this issue of JNDTE includes an experimental report on the use of high frequency C-scans for the characterization of the grain structure of as-cast steel billets and using this information for the optimization of the magnetic stirring. The second paper discusses the use of Radiometry measurements for the characterization of Nuclear Fuel Elements from BARC authors. The paper on the Health Assessment of Structure reviews the comprehensive approach by the nuclear industry towards assurance of safety of the various components in the reactor. The final paper from IISc presents a new approach for the computed tomography reconstruction using a fan-beam approach for radiographical imaging of the internals of components. During March 2011, an international workshop on Electromagnetic

Journal of Non Destructive Testing & Evaluation

Nondestructive Evaluation ENDE2011 was held in Chennai, co-organized by IGCAR and IITM. The ENDE series is and international event and held every year. The NDE2011 edition boasted of the highest attendance of more than 150 participants to this workshop series with participation from USA, UK, France, Germany, Japan, Korea, China among other countries. The technical presentations and posters were of very high quality. The next ENDE2012 will be held in Brazil. The NDE2011 will be held between 6-10 Dec 2011 in the Chennai Trade Center and augers to be a very grand conference, which will be augmented by a large technical exhibition. It is hoped that all authors will submit their technical abstracts to the conference well in advance in order to avoid any disappointments. It is anticipated that there will be approximately 200 technical papers (both oral and posters) presented in the conference. In addition, 4 pre-conference workshops are also planned. For more information, visit www.nde2011.com.

Dr. Krishnan B alasubramaniam Balasubramaniam Professor Centre for Non Destructive Evaluation IITMadras, Chennai balas@iitm.ac.in jndte.isnt@gmail.com

URL: http://www.cnde-iitm.net/balas

vol 10 issue 1 June 2011

I S N T - National Governing Council Chapter - Chairman & Secretary President Shri K. Thambithurai President-Elect Shri P. Kalyanasundaram Vice-Presidents Shri V. Pari Swapan Chakraborty Shri D.J.Varde Hon.General Secretary Shri R.J.Pardikar Hon. Treasurer Shri T.V.K.Kidao Hon. Joint Secretaries Shri Rajul R. Parikh

Ahmedabad

Kota

Shri D.S. Kushwah, Chairman, NDT Services, 1st Floor, Motilal Estate, Bhairavnath Road, Maninagar, Ahmedabad 380 028. dskushwah@icenet.net 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 modsonic@modsonic.com

Shri R.C. Sharma, Chairman Associate Director (QA), Rawatbhata 323 307 rcsharma@npcil.co.in Shri S.V. Lele, Hon. Secretary, T/IV – 5/F, Anu Kiran Colony, PO Bhabha Nagar, Rawatbhata 323 307. svlele@npcil.co.in

Mumbai Bangalore Dr. M.T. Shyamsunder, Chairman, NDE Modelling & Imaging Lab., Cassini Building, GE Global Research, John F. Welch Technology Center EPIP Phase 2, Whitefield Road, Bangalore-560066. Mt.shyamsunder@ge.com

Nagpur Chennai

Immediate Past President Shri Dilip P. Takbhate Past President Shri S.I.Sanklecha Members Shri Anil V. Jain Shri Dara E. Rupa Shri D.K.Gautam Shri Diwakar D. Joshi Dr. Krishnan Balasubramaniam Shri Mandar A. Vinze Shri B.B.Mate Shri G.V.Prabhugaunkar Shri B.K.Pangare Shri M.V.Rajamani Shri P.V. Sai Suryanarayana Shri Samir K. Choksi Shri B.K.Shah Shri S.V.Subba Rao Shri Sudipta Dasgupta Shri N.V.Wagle Shri R.K.Singh Shri A.K.Singh (Kota) Shri S. Subramanian Shri C. Awasthi Brig. P. Ganesham Shri Prabhat Kumar Shri P. Mohan Shri R. Sampath Ex-officio Members Managing Editor, JNDT&E Shri V. Pari Chairman, NCB & Secretary, QUNEST Dr. Baldev Raj Controller of Examination, NCB Dr. B. Venkatraman President, QUNEST Prof. Arcot Ramachandran All Chapter Chairmen/Secretaries Permanent Invitees Shri V.A.Chandramouli Prof. S. Rajagopal Shri G. Ramachandran & All Past Presidents of ISNT

vol 10 issue 1 June 2011

Shri R.S. Vaghasiya, Chairman, B 4/7, Sri Punit Nagar, Plot 3, SV Road, Borivile West, Mumbai 400 092. ravji.vaghasiya@gmail.com Shri Samir K. Choksi, Hon. Secretary, Director, Choksi Brothers Pvt. Ltd., 4 & 5, Western India House, Sir P.M.Road, Fort, Mumbai 400 001. Choksiindia@yahoo.co.in

Shri T.V.K. Kidao, Chairman Madras Metallurgical Services Pvt. Ltd. 14, Lalithapuram Street, Royapettah Chennai – 600 014 mmspl@vsnl.net Shri R. Balakrishnan, Hon. Secretary, No.13, 4th Cross Street, Indira Nagar, Adyar, Chennai 600 020. rbalkrishin@yahoo.co.in

Shri Pradeep Choudhari, Chairman Parikshak & Nirikshak, Plot M-9, Laxminagar Nagpur - 440 022 Mr. Jeevan Ghime, Hon. Secretary, Applies NDT & Tech Services, 33, Ingole Nagar, B/s Hotel Pride, Wardha Road, Nagpur 440 005. antstg_ngp@sancharnet.in

Pune Delhi Shri Ashok Singhi, Chairman, MD, IRC Engg Services India Pvt. Ltd 612, Chiranjiv Tower 43, New Delhi irc_engg@hotmail.com Shri Dinesh Gupta, Hon.Secretary, Director, Satya Kiran Engg. Pvt. Ltd BU 3 SFS Pitampura, New Delhi 110034 sathyakiran@bal.net.in

Hyderabad Shri G. Narayanrao, Chairman, Chairman & Managing Director, MIDHANI, Kanchanbagh, Hyderabad 500 058. cmd.midhani@ap.nic.in Shri J.R. Doshi, Hon.Secretary, Scientist, Project LRSAM DRDL, Hyderabad 500 058. joshidrdl@gmail.com

Jamshedpur Dr N Parida, Chairman, Senior Deputy Director Head, MSTD, NML, Jamshedpur - 831 007 nparida@nmlindia.org Mr. GVS Murthy, Hon. Secretary, MSTD, NML, Jamshedpur gvs@mnlindia.org / gvsmurthy_mnl@yahoo.com

Kalpakkam Shri YC Manjunatha, Chairman Director ESG, IGCAR, Kalpakkam – 603 102 ycm@igcar.gov.in Shri BK Nashine, Hon.Secretary Head, ED &SS, C&IDD, FRTG IGCAR, Kalpakkam – 603 102 bknash@igcar.gov.in

Kochi Shri CK Soman, Chairman, Dy. General Manager (P & U), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal 682 302. Kochi soman@bharatpetroleum.in Shri V. Sathyan, Hon. Secretary, SM (Project), Bharat Petroleum Corporation Ltd. (Kochi Refinery), PO Ambalamugal-682 302. Kochi sithyan@bharatpetroleum.in

Kolkata Shri Swapan Chakraborty, Chairman Perfect Metal Testing & Inspection Agency, 46, Incinerator Road, Dum Dum Cantonment, Kolkata 700 028. permeta@hotmail.com Shri Dipankar Gautam, Hon. Secretary, 4D, Eddis Place, Kolkata-700 019. eib1956@gmail.com

Shri PV Dhole, Chairman NDT House, 45 Dr Ambedkar Road, Sangam Bridge, Pune- 411 001 info@technofour.com Shri VB Kavishwar, Hon Secretary, NDT House, 45 Dr Ambedkar Road, Sangam Bridge, Pune- 411 001 eddysonic@gmail.com

Sriharikota Shri S.V. Subba Rao, Chairman, General Manager, Range Operations SDSL, SHAR Centre Sriharikota 524124. svsrao@shar.gov.in Shri G. Suryanarayana, Hon. Secretary, Dy. Manager, VAB, VAST, Satish Dhawan Space Centre, Sriharikota-524 124. isnt@shar.gov.in

Tarapur Shri PG Behere, Vice Chairman, AFFF, BARC, Tarapur-401 502. pgbehere1@rediffmail.com Shri Jamal Akftar, Hon.Secretary, TAPS 1 & 2, NPCIL, Tarapur. jakftar@npcil.com

Tiruchirapalli R.J. Pardikar AGM, (NDTL) BHEL Tiruchirapalli 620 014. rjp@bheltry.co.in Shri A.K.Janardhanan, Hon. Secretary, C/o NDTL Building 1, H.P.B.P., BHEL, Tiruchirapalli 620 014. akjn@bheltry.co.in

Vadodara Shri P M Shah, Chairman, Head-(QA) Nuclear Power Corporation Ltd. npcil.bar@gmail.com M S Hemal Mehta, Hon.Secretary, NBCC Plaza, Opp.Utkarsh petrol pump, Kareli Baug, Vadodara-390018. pmetco@gmail.com

Thiruvananthapuram Dr. S. Annamala, Chairman Group Director, Structural Design & Engg Group, VSSC, Thiruvananthapuram 695022 sannamala@vssc.gov.in Shri. Imtiaz Ali Khan Hon.Secretary, Engineer, Rocket Propellant Plant, VSSC, Thiruvananthapuram 695 022 imtiaz_ali@vssc.gov.in

Visakhapatnam Shri Om Prakash, Chairman, MD, Bharat Heavy Plate & Vessels Ltd. Visakhapatnam 530 012. Shri Appa Rao, Hon. Secretary, DGM (Quality), BHPV Ltd., Visakhapatnam 530 012

Journal of Non Destructive Testing & Evaluation

Journal of Non Destructive3 Testing & Evaluation About the cover page:

Volume 10 issue 1 June 2011

Contents 5

Finite element (FE) simulation of multiple scattering of bulk ultrasonic shear waves from a horizontal crack

Basics - Digital Industrial Radiography

Horizon - Photoacoustics - Can we hear Photosynthesis?

Chapter News

IQ forum

NDE events

NDE patents

NDT puzzle Technical papers

Image shows two snapshots of the contour of displacement magnitude obtained from Finite Element (FE) simulation of the scattering of bulk ultrasonic shear (SV) waves from a horizontal crack. In the first snapshot, we see waves reflected from the crack front, diffracted at the crack tips and transmitted across the crack. However, the scattering is a complicated process, involving multiple passes of waves that can travel along the crack also, causing interference patterns in the scattered signals. The second snapshot taken from a simulation with a much larger crack illustrates the power of modern numerical simulation; we are able to observe the cylindrical â&#x20AC;&#x2DC;primaryâ&#x20AC;&#x2122; diffraction, as well as Rayleigh-like waves that are introduced along the crack faces and make multiple trips across the crack. These images were obtained using ABAQUS commercial package.

Quality control of Nuclear Fuel Elements by Gamma Radiometry Assay M.S.Rana, Benny Sebastian, Sanjoy Das, D. Mukherjee, B.K. Shah

Health Assessment of Structures, Systems and Components (SSCs) beyond initial design life: Role of NDE during License Renewal of Tarapur Atomic Power Station-1&2; Nuclear Power Corporation of India Limited A.Ramu, C.S.Mali, J.Akhtar, V.S.Daniel, Ravindranath, B.K.Shah, S.Bhattacharjee, R.K.Gargye

Courtesy: this picture comes from research carried out by Dr Prabhu Rajagopal, Assistant Professor, Centre for NDE, IIT-Madras during his PhD at the NDT Laboratory, Imperial College London.

Analysis and computer simulations of fan-beam algorithms with no backprojection weight for equi-space linear array detector A.V. Narasihmadhan and Kasi Rajgopal

Probe

Chief Editor Prof. Krishnan Balasubramaniam e-mail: balas@iitm.ac.in The Journal is for private circulation to members only. All rights reserved throughout the world. Reproduction in any manner is prohibited. Views expressed in the Journal are those of the authors' alone. Published by Shri RJ Pardikar, General Secretary on behalf of Indian Society for Non Destructive Testing (ISNT)

Co-Editor Dr. BPC Rao bpcrao@igcar.gov.in

Managing Editor Sri V Pari e-mail: scaanray@vsnl.com

Topical Editors Dr D K Bhattacharya

Modules 60 & 61, Readymade Garment Complex, Guindy, Chennai 600032 Phone: (044) 2250 0412 Email: isntheadoffice@gmail.com and Printed at VRK Printing House 3, Potters Street, Saidapet, Chennai 600 015 vrkonline@gmail.com Ph: 09381004771

Electromagnetic Methods

Dr T Jayakumar, Ultrasonic & Acoustic Emission Methods

Sri P Kalyanasundaram Advanced NDE Methods

Sri K Viswanathan Radiation Methods

Journal of Non Destructive Testing & Evaluation

Editorial Board Dr N N Kishore, Sri Ramesh B Parikh, Dr M V M S Rao, Dr J Lahri, Dr K R Y Simha, Sri K Sreenivasa Rao, Sri S Vaidyanathan, Dr K Rajagopal, Sri G Ramachandran, Sri B Ram Prakash

Advisory Panel Prof P Rama Rao, Dr Baldev Raj, Dr K N Raju, Sri K Balaramamoorthy, Sri V R Deenadayalu, Prof S Ramaseshan, Sri A Sreenivasulu, Lt Gen Dr V J Sundaram, Prof N Venkatraman

Objectives The Journal of Non-Destructive Testing & Evaluation is published quarterly by the Indian Society for Non-Destructive Testing for promoting NDT Science and Technology. The objective of the Journal is to provide a forum for dissemination of knowledge in NDE and related fields. Papers will be accepted on the basis of their contribution to the growth of NDE Science and Technology.

vol 10 issue 1 June 2011

Classifieds Scaanray Metallurgical Services

Transatlantic Systems

(An ISO 9001-2000 Certified Company)

NDE Service Provider Process and Power Industry, Engineering and Fabrication Industries, Concrete Structures, Nuclear Industries, Stress Relieving Call M. Nakkeeran, Chief Operations, Lab: C-12, Industrial Estate, Mogappair (West), Chennai 600037 Phone 044-2625 0651 Email: scaanray@vsnl.com ; www.scaanray.com

Electro-Magfield Controls & Services & LG Inspection Services We manafucture : Magnetic Crack Detectors, Demagnetizers, Magnetic Particles & Accessories, Dye Penetrant Systems etc Super Stockist & Distributors: M/s Spectonics Corporation, USA for their complete NDT range of productrs, Black Lights, Intensity Meters, etc. Plot 165, SIDCO Industrial Estate, (Kattur) Thirumullaivoil, Vellanur Village, Ambattur Taluk Chennai 600062 Phone 044-6515 4664 Email: emcs@vsnl.net

Madras Metallurgical Services (P) Ltd Metallurgists & Engineers

Metallography Strength of Materials Non Destructive Testing Foundry Lab

Serving Industries & Educational Institutes for the past 35 years

24, Lalithapuram street, Royapettah, Chennai 600014 Ph: 044-28133093 / 28133903 Email: mmspl@vsnl.com

OP TECH ASNT Level III Intensive Taining Educational CDs PT, UT, RT, MT, ET, Basic Metallurgy and Mechanical Testing Call 93828 12624 Land 044 - 2446 1159

B Ram Prakash A 114, Deccan Enclave, 72, T M Maistry Street, Thiruvanmiyur, Chennai 600 041

Southern Inspection Services NDT Training & Level III Services in all the following ten NDT Methods

Shri. K. Ravindran, Level III RT, VT, MT, PT, NR, LT, UT, ET, IR, AE

vol 10 issue 1 June 2011

Support for NDT Services NDT Equipments, Chemicals and Accessories Call DN Shankar, Manager 14, Kanniah Street, Anna Colony, Saligramam, Chennai 600093 Phone 044-26250651 Email: scaanray@vsnl.com

Betz Engineering & Technology Zone An ISO 9001 : 2008 Company 49, Vellalar Street, near Mount Rail Station, Chennai 600088 Mobile 98401 75179, Phone 044 65364123 Email: betzzone@vsnl.net / rg_ganesan@yahoo.com

International Training Division 21, Dharakeswari Nagar, Tambaram to Velachery Main Road, Sembakkam, Chennai 600073 www.betzinternational.com / www.welding-certification.com

KIDAO Laboratories NABL Accredited Laboratory carrying out Ultrasonic test, MPL and DP tests, Coating Thickness and Roughness test. We also do Chemical and Mechnical tests

A-3, Mogappair Indl. Area (East) JJ Nagar, Chennai 600037 Phone 044-26564255, 26563370 Email: kidaolab@giasmd01.vsnl.net.in; kidaolabs@vsnl.net www.kidaolabs.com

Dhvani R&D Solutions Pvt. Ltd 01J, First Floor, IITM Research Park, Kanagam Road, Taramani, Chennai 600113 India Phone : +91 44 6646 9880

• Inspection Solutions • Software Products • Training • Services & Consultancy

CUPS, TAPS, CRISP, TASS SIMUT, SIMDR Guided Waves, PAUT, TOFD Advanced NDE, Signal Processing C-scans, On-line Monitoring

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No.2, 2nd Floor, Govindappa Naicker Complex, Janaki Nagar, Arcot Road, Valasaravakkam, Chennai-600 087 Tamil Nadu, India Phone : 044-2486 8785, 2486 4481 E-mail: sisins@gmail.com and sisins@hotmail.com Website: www.sisndt.com

Journal of Non Destructive Testing & Evaluation

Basics

digital image which are discussed below.

Digital IIndustrial ndustrial Radiography Dr. H elmut Wolf Helmut Anna University Chennai

Dr.Theobald F uchs Fuchs Fraunhofer Development Center X-ray Technology, Fuerth, Germany

1. Introduction In the previous issues, the physical principals of industrial radiography (RT) and high resolution radiography were discussed. Digital radiography (DIR) is the topic of this article. DIR is based on the same principles of imaging as RT, i.e. the recording of spatially resolved radiation intensities. The only difference is that the method of recording and visualization follows a digital route. We always have to keep in mind that we deal with X-ray absorption images and not optically focused photographs. Digital images are nowadays found in many applications. In photography they almost completely replaced film imaging. In RT, the process of transition to digital methods is slower, mainly for economic considerations.

2. Fundamentals – 2.1

Analog and digital

When discussing images, often times the distinction between analog and digital is made. Analog means proportional or continuous. Digital means discrete, or stepwise.

Computers require discrete numerical values for processing and storing. The conversion of an analog signal or intensity to a number means that a fixed step value is assigned to a small continuous range. The process is called A/D conversion or digitization. The quality of digital conversion depends on the number of steps we assign to a continuous range of values. In the case of radiographs, a film is often considered analog. This is it not quite correct. The darkening of the film after exposure and development is due to very tiny silver crystals, also called the film grain. It is only because the eye cannot normally resolve the individual grains that a radiograph is considered continuous. Actually these grains are randomly arranged, separate particles, a few micrometers in size. When viewing a film the grains can normally not be seen individually, but are perceived as a continuous variation in density.

2.2

Digital images

Digital images are made up of a fixed rectangular arrangement of square dots. The requirement of storage of a digital image can be very large depending on the parameters of a

Spatial resolution. The dots that make up a digital image are called “picture elements” or pixels. A pixel has a definite size. In high resolution images a pixel may have a size of 50 μm x 50 μm. Actually, this size is about the best resolution the human eye can achieve and again, when we view such an image, we would think it is continuous in space and not broken down to individual elements. If we take a standard 5 cm by 20 cm radiograph at 50 μm pixel size (i.e. 200 Pixel per cm), this image requires 5 x 200 x 20 x 200 or 44 million pixels. Depth resolution. One more property of a digital image is important. We can assign intensities or shades of grey to each pixel. If only black and white is required, we can represent this in terms of 0 or 1. We would describe it as every pixel having a depth of one bit (2**1). More shades can be represented with a larger pixel depth. If we take an 8 bit pixel depth, we have 2**8 = 256 shades. Mostly, instead of bit, the unit byte is used, 8 bit = 1 byte. In this case one pixel has the storage requirement of one byte. Again it is interesting to take the human vision as a reference. We can distinguish two shades of grey, if their difference is at least 2%. This is also called visual contrast resolution. For the whole range of greys from black to white, at best we can recognize only 50 separate shades, each 2% apart. This means that a digital image that is based on 8 bit resolution appears as a continuous image to the human eye. However, a digital system is capable to meaningfully resolve and record as many as 12 bit (4096 shades) or 16 bit (65536 shades). This also increases the storage requirement. If we take the radiograph of the above example and assign 12 bit (= 1.5 byte) for every pixel, 44 million pixels require 66 million bytes or roughly 63 MB of storage for a single 5 cm x 20 cm radiograph. Temporal resolution. For completeness, we look at the resolution in time, which could be important for real time radiography. Movies take advantage of the fact that we cannot resolve individual images, if we see more than about 25 frames per second. A movie appears to be continuous, though objectively, we are presented with a sequence of still photographs.

Converting an analog range to digital values. Each signal is assigned to the closest discrete value out of a finite number of values at typically equidistantly sampled positions. Journal of Non Destructive Testing & Evaluation

Considering these fundamentals of digital imaging, we can understand vol 10 issue 1 June 2011

Basics

how digital radiographs can contain more information than what can be seen with the naked eye. They can be superior with respect to all resolutions - space, depth or time. All we need is sufficient memory space and accurate conversion devices. In this way we can obtain more information that is immediately visible. Digital images can be numerically evaluated or visualised by digital processing. The image can be magnified (spatial, also called pixel mapping), a limited tone range can be converted to a larger range of shades (depth mapping, contrast adjustment) or the time intervals of display can be increased (time mapping, slow motion). Digital images are also required for automated systems where features are automatically detected and evaluated. In Computed Tomography (CT) images are superimposed for reconstruction of the inspected volume. Without digital technology CT would not be possible.

3. Creation of digital radiographs There are different procedures to arrive at a digital radiograph. Conventional film can be a starting point. Real time systems often use conversion by scintilization (light flashes) combined with photomultipliers. Computed radiography uses storage phosphors that are read out after exposure. Only recently directly converting flat panel detectors have become available.

3.1

Conversion of conventional radiographic film

on the opposite. The principle is the same as in a film densitometer, except that the density is recorded electronically and within smaller areas. To read an entire film, the film is moved point by point by a mechanical X-Y scanner and the pixels with the density values are assembled to form a digital image. Line scanners became available, where an image is read line by line. The scanner consists of many sensors along one line. The sensor is moved by an index value and the pixels covering a complete film area are assembled into a digital image. This procedure is very much like in an office scanner, except that office scanners work in reflection. X-ray film scanners work in transmission mode and need the ability to process larger density ranges, as much as 1 to 10000, corresponding to densities of 4. 2-D scanners. The film can be read in a whole area. The pixels are defined by the resolution of the optical sensor. These are often CCD cameras. Since CCD sensors have a limited dynamic range, X- ray images are often processed with multiple exposures, each exposure in a different dynamic range, to preserve the maximum density nuances of a film image.

3.2 Computed Radiography Computed radiography (CR) is a method that uses imaging phosphor plates. The radiation received is stored in the phosphor and read out by thermoluminescence effect. The work flow is very similar to conventional radiography. The plates can be handled like film, even bent around a

weld. In principle, the plates can be reused more than 1000 times, but in practical applications this is hardly reached, because any mechanical damage or finger print shows up on subsequent images. CR is ideal for laboratory environments where the plates are not handled, but placed in cassettes and automatically processed in reader scanners. A laser beam is stimulating visible light emission proportional to the radiation exposure of the plate. In a special read out scanner, the laser beam is focused on one spot. The laser stimulates the emission of light at one spot. The spot is shifted by a rotating prism and covering the entire area of a film. This readout process can only be performed once. By reading the plate, the latent image is removed. The process cannot be repeated. The parameters of the digital image, especially the pixel size is dependent on the focal spot of the laser. Each spots becomes one pixel of the digital image.

3.3

Digital Flatpanel Detector Arrays - What is a flat panel detector array?

A Flat-panels detector array (FDA) is subdivided into pixels already. Each channel of the flat panel matrix can be considered a separate X-ray detector, comprising -

a photo-diode/capacitor

a TFT switch for read-out,

followed by an amplifier, a multiplexer and an analogue-todigital converter (ADC).

Conventional radiographic film is converted into digital images for a number of reasons. An important reason is that radiographic film contains more information than can be seen, as discussed earlier. We can detect more details in an image. When ISNT held a first DIR workshop in India in 1999, the cost of storage media (DVDs, Hard Disks etc) was so high, that it was not economical to keep scanned image files for storage purposes. However, the advantages of processing and evaluation were sufficient reason to digitize films. A number of digitization procedures were developed: Point scanners. The digitization process reads the film density and converts it to a numerical value. The first digitizers worked with a single light source one side and a light sensor vol 10 issue 1 June 2011

Projection imaging geometry Journal of Non Destructive Testing & Evaluation

Basics There is a strong similarity to an instrument in nuclear physics: A large number of individual detector channels (105 up to 107) are assembled within the same electronic device – the detector matrix.

Signal characteristics of realworld flat panel detector devices FDAs have to be understood as a complex electronic instrument for signal acquisition and processing: the signals contain thermal electrical noise; often there are bad channels (black or white pixels); there might occur some coupling with electromagnetic fields in the cables and the electronics; there is a finite digitization depth (number of bits of ADC); there is a read-out time (dead time) and a cycle time (given as frames per sec); the signal from each pixel of the matrix (“intensity” in grey values) is a measure of the number of photons absorbed by that particular pixel during integration time. A FDA is usually not one single piece of amorphous silicon of 200 mm or 400 mm lateral size, but the detector

matrix is made up of several tiles with a read-out chip assigned to each. Thus, the “raw” images reflect the internal structure of the device. The there can be overlaying patterns that are characteristic for a particular detector arrangements of detectors. Since quality of semi-conductor material and processing of the microelectronics may be inhomogeneous, the sensitivity of the channels may vary from chip to chip, from line to line, and in large irregularly shaped areas (clouds). If we want to obtain a uniform image output, for a uniform input, we have to calibrate every pixel electronically to compensate differences in linearity and sensitivity.

Gain-offset-correction Each pixel has to be treated as an independent measurement channel. The electrical signal from an individual detector pixel can be written in a linear approximation: V(I) - Vdark + I.g Thereby, I denotes the X-ray intensity reaching a single pixel. Each individual channel is characterized by its dark

Arrangement and Internal structure of a typical FDA

current v dark and gain g. These parameters are generally unknown and have to be determined by calibration measurements. The dark current (offset) is measured with zero X- ray dose: I = 0. The bright image is measured with the primary intensity I0 applied during measurement. Its calibrated value can be chosen arbitrarily, e.g. vcalibrated (I0) = 40.000 grey value level. Usually, the intensity (e.g. dose or photon flux) is not measured directly by an additional instrument. Thus, for reasons of practicability, the gain is not measured directly. The variation in gain between different channels is corrected by applying a scaling factor.

Commercially available FDAs There are various types of flat panel detectors commercially available today. The devices offered by several manufacturers vary in pixel size, pixel format, the type of X-ray conversion, read out frequency and – last but not least – price.

pixel size: 50 μm up to 400 μm

area: 50 mm x 50 mm up to 400 mm x 400 mm

read out cycle between 5 and 30 frames per second

indirect conversion (scintillator CsI, Gd2O2S:Tb)

amorphous silicon (Perkin-Elmer, Varian, Trixell, GE)

CMOS (Hamamatsu, Rad Icon)

direct conversion

Cadmium-Telluride (Ajat, MediPix)

Gallium-Arsenide (MediPix)

Uncorrected dark image. The thermal noise caused by the read out electronics can be seen clearly (left hand side: full panel, right: zoom). Journal of Non Destructive Testing & Evaluation

vol 10 issue 1 June 2011

Basics in Computed Tomography. A detailed treatment of the latter techniques is far beyond of the scope of this publication, but of course they and all other image processing methods require digital images as input data.

5. Automatic Defect Recognition (ADR) in industrial production

Digital output signal as a function of the X-ray intensity measured for every detector pixel. Each of the three lines stands for a particular detector pixel.

Â&#x192;

CCD-based

Â&#x192;

Selenium

The costs for a FDA range between 10.000 and 100.000 Euro today, but prices are decreasing as the numbers of sold systems increase. The life-time of a FDA is limited due to the inevitable radiation damages to the microelectronics. According to the experience of the authors the life-time of a device which operated in a 24/7mode is between 12 and 36 months.

4. Digital image processing Exactly the same way as in digital photography, nowadays, there are countless methods for digital image processing, which can be applied to the X-ray images. One of the most simple options is the enhancement of the images by use of local or global filters. A very common example is the median filter which

helps to smoothen regions of the image where the dectability of details suffers from high image noise. As well median filters serve in removing irregular pixels while preserving edgelike structures. Another example of common tools for the enhancement of images are look-up tables which serve to adapt the grey scale range for visualization purposes. The same, contrast and brightness of digital Xray images can be modified easily and repeatedly. Moreover, the digital technology allows for a computer aided analysis of any kind of X-ray images. Algorithms for pattern recognition and feature extraction can be applied, for instance in order to detect automatically voids, cracks or inclusions in various kinds of materials and components. Data fusion with other NDT methods is possible as well as more complex operations like the reconstruction of 3D volume data sets from projections

As an example for a fully automatic inspection system, the Fraunhofer ISAR system is capable of acquiring a single digital radioscopy image within 200 milliseconds. Typically, for each part 3 to 14 different images are acquired, and evaluated, thereby keeping up with a production cycle of about 10 seconds per part or less. Subsequently, the software makes a decision, if the current part can be accepted as defect-free, according to the limits which are prescribed to the component manufacturer by the OEM.

6. Digital images, issues of archival, durability and integrity 6.1 Archival and durability Films deteriorate over time. Films that have not been washed well or are stored in humid places develop spots and patches soon, but there are well processed and stored films that have survived more than 100 years. As for digital images, it is true that there is no deterioration of images. The data can be copied any number of times and there is no loss of quality. However, if a set of data becomes unreadable, the loss is total. This can be due to mechanical damage of medium such as a hard disk or CD. If long term archiving is required, it is more likely that data become unavailable because the reading devices become technically outdated. Just consider diskettes or data tapes.

Commercially available FDAs â&#x20AC;&#x201C; PerkinElmer (left), Hamamatsu (center), Vidisco (right). vol 10 issue 1 June 2011

Journal of Non Destructive Testing & Evaluation

Basics National Certification Board Indian Society for Non Destructive Testing

Announcement ASNT NDT Lev el III E xamination Level Examination Mumbai 28, 29 & 30 November 2011 ASNT NDT Level III Examination will be conducted in the following methods:

Fully automatic X-ray inspection system of aluminium castings. Casting and three digital radiographs processed for defect detection.

Today you really have to search for readers to recover old data. 20 years from now CD and DVD drives may be hard to find.Experts consider this to be the more important issue. Accidental loss of data can be taken care of by multiple copies, stored at different locations, but the loss of data due to obsolescence also has to be addressed.

6.2

Data compression

It is obious that the availability of digital X-ray images leads to a previously unknown amount of data. In particular, 3-D volume data afford a large amount of storage, a challenge that is to be addressed in medical imaging but as well as in industrial inspection. On the other hand a manifold of algorithms for data compression is available today. In general, these algorithms can be devided into two classes: lossy and lossless compression techniques. The decision on which type of compression is to used has to be made case by case. Although the efficiency of lossy compression algorithms in terms of storage saving is higher than with lossless methods, there may be legal requirements or safety issues which prohibit any reduction of information within the digital X-ray images.

6.3

Data integrity

X-rays are often required for legal purposes and digital images have the reputation is that they can be altered or manipulated easily. Common software allows to add or remove image details. This is also possible in digital X-rays. Today there is no universal standard or a fool proof system that can guarantee that there has not been an alteration of an image. In principle authentification systems are possible, but have not been standardized.

7. Summary This paper discusses the basic principles of digital X-ray imaging, further techniques like film digitization and computed radiography (CT). The latest development of flat panel arrays (FPA) is explained in detail with respect to possibilities and challenges. A number of applications of digital X-ray images are pointed out, as well as the issues of image processing, compression and archiving. Overall, the rapid progress in digital imaging has also affected the full spectrum of industrial X- ray inspection. A large variety of new methods and inspection possibilities are emerging with these new devices.

Journal of Non Destructive Testing & Evaluation

1. Basic 2. Radiographic Testing 3. Magnetic Particle Testing 4. Ultrasonic Testing 5. Liquid Penetrant Testing 6. Eddy Current Testing 7. Neutron Radiographic Testing 8. Leak Testing 9. Visual Testing 10. Acoustic Emission Testing 11. Thermal / Infrared Testing It may please be noted that the basic examination by itself is not considered as a method. Basic and method examination(s) must be taken to become eligible to receive a certificate for that method(s). The maximum number of examinations that can be taken is six during the three days of the Examination. Dr. B. Venkatraman ASNT Level III Examination Coordinator, Modules 60 & 61, Readymade Garment Complex, SIDCO Industrial Estate, Guindy, Chennai 600 032, India Ph:91 44 22500412 & 91 44 42038175 91 44 27480500 Ext.22306 E Mail: isntheadoffice@gmail.com Alternate E Mail: ncbisnt@gmail.com Venue and R efr esher courses Refr efresher date will be intimated later later.. Please visit www .isnt.org.in www.isnt.org.in for application and other details vol 10 issue 1 June 2011

Horizon

Photoacoustics

equation for temperature in the surrounding medium as a function of both position and time

Can w hotosynthesis? wee hear P Photosynthesis? Dr. CVK Krishnamurthy

where the complex temperature

Centre for NDE and Department of Physics, IIT Madras

amplitude θ1+iθ2, and thermal diffusion coefficient The photoacoustic effect was first discovered by Alexander Graham Bell around 1880. He was surprised to discover that a sound wave could be produced directly from a solid sample if the incident light was rapidly interrupted—typically on the order of kHz. Bell used a spinning slotted wheel to mechanically “chop” the incident sunlight at this frequency. He observed that the resulting acoustic signal is dependent on the composition of the sample and correctly conjectured that the effect was caused by absorption of the incident light. Bell’s initial experiments focused on the solid phase of matter, but John Tyndall and Wilhelm Roentgen performed subsequent experiments demonstrating the same effect in liquids and gases. Tyndall was the first to discover that the intensity of the produced sound was directly proportional to the amount of heat absorbed, or equivalently, the intensity of the applied light. The most commonly employed model for describing the photoacoustic effect in condensed samples was developed in the 1970s by Rosencwaig and Gersho (see Figure 1). Pulsed light that is incident on a sample is absorbed

and the constituent molecules become thermally excited. Periodic heat flow from the sample to the surrounding gas causes pressure waves that are in turn detected by an acoustic sensor. The pressure waves are characteristic of the sample and are used to determine composition, concentration, and other thermophysical properties. Suppose the incident radiation is modulated with frequency ω. Then the incident intensity, taking into account Beer’s Law with optical absorption coefficient β, is given by:

The sample and the gas must each satisfy the heat-diffusion equation, which for the case of the sample is given by:

where σrt is the probability of radiationless transition, and thermal diffusivity where k is thermal conductivity of the sample, ρ is the density, and Cp is the specific heat. Rosencwaig and Gersho determined the following

Figure 1: Comparison of photoacoustic signal generation in the right-angle (left) and frontface (right) geometries. In the right-angle geometry, the pump beam (green) is shaped with a slit to obtain a planar acoustic wavefront (taken from T.Gensch and C.Viappiani, Photochem. Photobiol. Sci., 2, (2003) 699–721) vol 10 issue 1 June 2011

The equation describes a periodic wave of temperature that propagates through the medium surrounding the sample. The temperature fluctuation described by this equation is the cause of the pressure waves that are detected. Since the e-ax term causes the wave to decay away from the sample, the sensor should be located within the thermal diffusion length

order to maximize the strength of the acoustic signal. Surprisingly, modern photoacoustic analysis has not deviated far from Bell’s original “chopped light” setup, apart from the introduction of lasers and generation. Typically, laser pulses on the order of 10 nsec are used for generation of ultrasound in the order of 10-MHz freqency range. For even higher frequencies, pulse widths on the order of 100 psec (resulting in ultrasound in the order of 100-MHz frequency range) or even femtosecond (for GHz range) laser systems may be necessary. They can be nondestructive if the optical power is kept sufficiently small. In cases where a strong ultrasonic signal is needed but ablation is unacceptable, a sacrificial layer (typically a coating or a fluid) is used. Laser ultrasonic measurement systems are particularly attractive to nondestructive structural and materials characterization of solids because (a) they are noncontact and in situ leading to increased speed of inspection, (b) they do not require any couplant, (c) they have a very small footprint and can be operated on curved complex surfaces, and (d) they are broadband systems providing information from the kHz to the GHz range, enabling the probing of macrostructures to very thin films.

Journal of Non Destructive Testing & Evaluation

HORIZON On a free surface, a laser pulse generates bulk waves (longitudinal and shear) as well as surface waves. Optimized generation of waves is possible with optical manipulation of the laser beam, as shown in Figure 2.

modulation frequency by a fixed amount, serving as the local oscillator for superheterodyne detection. Figure 3 shows the results obtained through superheterodyne detection.

Using optical methods to detect ultrasound greatly extends the scope of photoacoustic technique and makes it completely remote. An example is a laser ultrasonic system that incorporates cw laser generation and superheterodyne detection of acoustic waves. An amplitude modulated laser source is used to excite high frequency, narrow bandwidth acoustic waves. The resulting surface displacement is detected using a stabilized Michelson interferometer. The detection laser used in the interferometer is modulated at a frequency that is offset from the generation laser

Photoacoustic (PA) and photothermal (PT) methods are attractive for modern diagnostics and imaging of the near surface structure where defects may result in excessively high operational and residual stresses. Recently, a technique for nonlinear photoacoustic imaging of cracks has been reported that is based on laser excitation with intensity modulation at two fundamental frequencies combined with detection at mixed frequencies. By exploiting the strong dependence of the photoacoustic emission efficiency on the state— open or closed—of the contacts between the crack faces, remarkably

Figure 2: (a) Crossed beam interference for narrowband generation of high frequency surface acoustic waves. (b) Time-domain signal of a narrowband surface acoustic wave on a thin film. (c) Spectrum of the narrowband surface acoustic wave showing high frequency generation.(taken from Nelson et al, J. Appl. Phys., 53, (1982) 1144–1149)

Figure 3: (left) Time domain signal on a 90 μm Al plate with a source-to-receiver distance of 60 μm obtained through a discrete inverse Fourier transform of frequency domain data measured from 100 MHz to 1.0 GHz. Key: SSL, surfaceskimming-longitudinal wave; SAW, surface acoustic wave; L, longitudinal wave; SL, mode-converted SL wave; and S, shear wave. (right) Experimental and theoretical dispersion curves for two Al films of thickness (h) on Si substrates. The best-fit Young’s modulus (Efit) is also shown. (from Bramhavar et al., Appl. Phys. Lett. 94, (2009) 114102)

Journal of Non Destructive Testing & Evaluation

enhanced image contrast is observed, about 20 times higher than in linear photoacoustic images at the highest of the fundamental frequencies. Photoacoustic Imaging In the last decade, work on photoacoustic imaging in biomedical applications has come a long way. The motivation for photoacoustic imaging is to combine ultrasonic resolution with high contrast due to light, or radiofrequency (rf), absorption. Unlike ionizing x-ray radiation, nonionizing waves pose no health hazard. Unfortunately, however, in the pure optical imaging methodologies, optical scattering in soft tissues degrades spatial resolution significantly with depth. Since ultrasound scattering is two to three orders of magnitude weaker than optical scattering in biological tissues, ultrasound can provide a better resolution than optical imaging in depths greater than ∼1 mm. However, pure ultrasound imaging is based on the detection of the mechanical properties in biological tissues, so its weak contrasts are not capable of revealing early stage tumors. Moreover, ultrasound cannot image either oxygen saturation or the concentration of hemoglobin, to both of which optical absorption is very sensitive. These physiological parameters can provide functional imaging. Likewise, pure rf imaging cannot provide good spatial resolution because of its long wavelength. Utilizing operating frequencies in the range of 500–900 MHz, pure rf imaging can only provide a spatial resolution of ∼1 cm. The significance of PA imaging is that it overcomes the above problems and yields images of high EM contrast at high ultrasonic resolution in relatively large volumes of biological tissues. It is interesting to note that no other EM spectrum seems practical for PA generation in deep tissues. For example, terahertz rays that lie between the above two EM spectra do not penetrate biological tissue well due to water-dominated absorption. In the short-wavelength spectrum below the visible region, such as ultraviolet rays, radiation has high photon energy and, therefore, is harmful to human subjects. vol 10 issue 1 June 2011

HORIZON

The spatial resolution of PA imaging, as well as the maximum imaging depth, is scaleable with the detected ultrasonic bandwidth. For example, PA signals with a 1 MHz bandwidth can provide approximately 1 mm spatial resolution since the velocity of sound in soft tissues is ∼1.5 mm/ s. If the bandwidth is increased to 10 MHz, approximately 0.1 mm resolution can be achieved at the expense of ultrasonic penetration. In a simple case where a wide beam of light pulse heats a layered medium, the detected PA signal replicates the light energy deposition profile throughout the depth. Then, the depth-dependent information of the sample, such as the depth structure and properties (e.g., the absorption coefficient in a nonscattering medium) can be determined directly from the temporal PA signal. As shown in Figure 4, it is possible to have a combined photoacoustic and ultrasonic imaging configuration. In this hybrid method, the signals of 64 transducer elements are simultaneously recorded with an ultrasound system and passed onto a computer. The computer reconstructs an absorption distribution image and displays it on a screen with a repetition rate of 7.5 Hz. One single laser pulse is enough to get a complete image on the screen in less than 100 ms reconstruction time. Classical echo ultrasound images can also be acquired for side by side comparison or for mixed mode imaging. However, to image more complicated structures, a more complex imaging method referred to as PA tomography (PAT) is preferred. PAT makes use of PA signals measured at various locations around the subject under study as shown in Figure 5. PAT is also called optoacoustic tomography (OAT) or thermoacoustic tomography (TAT), with the term “thermoacoustic” emphasizing the thermal expansion mechanism in the PA generation. OAT refers particularly to lightinduced PAT, while TAT is used to refer to rf-induced PAT. Depth profiling can be regarded as onedimensional (1D) PAT. PA imaging with a laser can be scaled down for microscopic imaging. A laser system can easily vol 10 issue 1 June 2011

PA microscopy imaging does not rely on ballistic or quasiballistic photons and can, therefore, penetrate deeper. To generate PA signals efficiently, two conditions, referred to as thermal and stress confinements, must be met. The time scale for the heat dissipation of absorbed EM energy by thermal conduction can be approximated by τth ∼ Lp 2/4DT,

Figure 4: Combined optoacoustic and ultrasound real-time imaging setup. This system can image several millimeters below the skin with 0.4 mm and 0.3 mm lateral and axial resolutions, respectively (taken from C.Li and L.V. Wang, Phys. Med. Biol. 54 (2009) R59–R97)

generate laser pulses with a pulse energy of 100 mJ and a pulse duration of 10 ns or shorter, which can sufficiently excite PA signals at high frequencies up to 100 MHz in large-area soft tissues with a good SNR. Therefore, laser-based PA scanning tomography can perform microscopic imaging with an axial resolution of 30 μm or less. PA microscopy has critical advantages over other opticalcontrast imaging methods, including current high-resolution optical imaging techniques such as confocal microscopy and optical coherence tomography (OCT). These optical imaging techniques can image only approximately one transport mean free path (∼ 1 mm) into tissue because they depend on ballistic or quasiballistic photons.

where Lp is the characteristic linear dimension of the tissue volume being heated (i.e., the penetration depth of the EM wave or the size of the absorbing structure). Actually, heat diffusion depends on the geometry of the heated volume, and the estimation of τth may vary. Upon the absorption of a pulse with a temporal duration of τp, the thermal diffusion length during the pulse period can be estimated by, δT = 2(DTτp)½, where DT is the thermal diffusivity of the sample, and a typical value for most soft tissues is DT ∼ 1.4×10"3 cm2/s. The pulse width τp should be shorter than τth to generate PA waves efficiently, a condition that is commonly referred to as thermal confinement where heat diffusion is negligible during the excitation pulse. For example, for a rf pulse of τp = 0.5 μs, δT ≈ 0.5 μm, which is much less than the spatial resolution that most PA imaging systems can achieve. Therefore, the thermal confinement condition is typically met. Similarly, the time for the stress to transit the heated region can be estimated by

Figure 5: (left) Schematic for Photoacoustic Tomography (from http:// en.wikipedia.org/ wiki/ Photoacoustic_imaging_in_biomedicine). (right) A cross-sectional photoacoustic image of a rat brain. RH, right cerebral hemisphere; LH, left cerebral hemisphere; L, lesion; MCA, middle cerebral artery (from X. Wang et al., Nat. Biotechnol. 21, (2003) 803. Journal of Non Destructive Testing & Evaluation

HORIZON τs = Lp /c, where c is the speed of sound. The pulse width τp should be shorter than τs, a condition that is commonly referred to as stress confinement. Under the stress confinement condition, high thermoelastic pressure in the sample can build up rapidly. For example, to achieve a spatial resolution at Lp=150 μm, if c =1.5 mm/μs and DT ∼ 1.4×10-3 cm2/ s, then τth∼ 40 ms and τs ∼100 ns. Hence, τp must be less than 100 ns to guarantee the more stringent stress confinement. When both thermal and stress confinements are satisfied, thermal expansion causes a pressure rise p0 that can be estimated by

Figure 6: In vivo photoacoustic image of the vasculature in the palm using an excitation wavelength of 670 nm. Left: photograph of the imaged region, Middle: volume rendered image. Right: lateral slices at different depths. The arrow ‘A’ indicates the deepest visible vessel, which is located 4 mm beneath the surface of the skin. (taken from E Z Zhang et al., Phys. Med. Biol. 54 (2009) 1035–1046)

p0 = (βc2/Cp)μaF = ΓA, where β is the isobaric volume expansion coefficient in K-1, Cp is the specific heat in J/(K kg), μa is the absorption coefficient in cm-1, F is the local light (or rf) fluence in J / cm2, A is the local energy deposition density in J /cm3: A=μaF, and Γis referred to as the Grüneisen coefficient expressed as βc2/Cp. Figure 6 shows a recent effort to provide high-resolution 3D images of vascular structures to depths of up to 5 mm based upon a Fabry–Perot polymer film ultrasound sensor. Can we hear Photosynthesis? We all know that energy taken up by absorption of light by the leaf pigments is mainly used up for photosynthesis. What is less well known is that a smaller part of this absorbed energy is transformed into chlorophyll (Chl) fluorescence and thermal dissipation (i. e. heat). The thermal dissipation leads to the heating of the gas surrounding the sample. Heating the gas leads to an increased pressure inside the tightly closed measuring chamber (the “photo-acoustic cell”). If the modulation frequency of the illuminating light is chosen within the audible range, pressure changes can be measured by a microphone. This photoacoustic (PA) signal is stored or recorded after specifically amplifying by means of a lock-in amplifier only those microphone signals which were detected with the frequency of the modulated light.

Figure 7: (left) Scheme of the Open Photoacoustic Cell (OPC) (from P. R. Barja, Revista Physicae, (2000), 1) . (right) Photoacoustic (PA) signal of a tobacco leaf in the millisecond time domain after a 0.72 ms light pulse (light-emitting-diode: peak wavelength 650 nm) applied at time = 0. The photothermal component (thin continuous line) was deduced from a separate measurement with continuous, non-modulated light saturating photosynthesis and normalized to fit the overall PA signal (thick continuous line). The photobaric component (thin dotted line) was calculated by subtracting the deduced photothermal signal from the overall PA signal (from Kolbowski et al., Photosynth. Res., 25, (1990) 309–316). Figure 7 shows the schematic of the open photoacoustic cell that facilitates working with live specimens and a typical photoacoustic response of a leaf involved in photosynthesis. Photoacoustic imaging offers unique advantages over existing imaging modalities. The imaging field is broad with many exciting applications in biology, chemistry, and material science. References A. Rosencwaig and Gersho, Theory of the Photoacoustic effect with solids, J. Appl. Phys. 47 (1976) 64 A.C.Tam, Applications of Photoacoustic sensing techniques, Rev. Mod. Phys. 58 (1986) 381

Journal of Non Destructive Testing & Evaluation

K. L. Muratikov and A. L. Glazov, Photoacoustic effect in stressed elastic solids, J. Appl. Phys. 88, (2000) 2948 J. P. Monchalin, Laser-Ultrasonics: From The Laboratory To Industry, CP700, Rev. of Quan. Nondest. Eval. 23, (2004) ed. by D. O. Thompson and D. E. Chimenti, 3 Minghua Xu, and Lihong V. Wang, Photoacoustic imaging in biomedicine, Rev. Sci. Instrum. 77 (2006) 041101 N. Chigarev, J. Zakrzewski, V. Tournat, and V. Gusev, Nonlinear frequency-mixing photoacoustic imaging of a crack, J. Appl. Phys. 106, (2009) 036101

vol 10 issue 1 June 2011

CHAPTER NEWS Chennai Chapter UT Level-II (ASNT) course was conducted from 22.04.11to 30.04.11. No. of participants were 1. R.Balakrishnan was the course director and Mr.E Sathya Srinivasan was the examiner. In – house training MT – Level II(ASNT),M.M.Forgings Ltd course was conducted from 24th Apr ,08th ,15th ,22nd May 2011 No. of participants were 9. Mr.M S Ramachandran was the course Director and Mr.E Sathya Srinivasan was the examiner. Surface NDT ( MT & PT) Level - II (ASNT) course was conducted from 20.05.2011 to 26.05.2011. No. of participants were 20 for course and 18 for examination. Mr. G Jothinathan was the course Director and Mr.P.N.Udayasankar was the examiner. ISNT DAY had been celebrated on 21st April 2010 at Hotel Radha Regent. About 190 members along with their families attended the function. Mr.S. Swaminathan, was the Convener of the meeting. Mr.M.V. Rajamani Chairman presided over the meeting and the Chief Guest of the day was Mr.N. Balakrishnan, Vice President, M/s.Sundram Fasteners Limited, Chennai. The faculty, the examiners and the dignitaries who were associating with Chapter were honored

and presented mementos by the Chief Guest. Gifts were distributed to spouse and children. Three awards, the Best Member Award, Thambithurai Award & Best Achievement Award which was promoted by Shri.M.V.Rajamani and Shri.S.Swaminathan were presented to Mr.B.Ram Prakash the recipient of The Best Member award and to Dr.Krishnan Balasubramaniam, I.I.T., Chennai the recipient of Thambithurai award and Mr.Suresh Kaushal, Caterpillar India Limited, Tiruvallur the recipient of Best Achievement Award. Magic Show and Tattos to children were conducted by Mr.S. Swaminathan for the children. It was well received EC Meeting 01.05.2011 EC Meeting 11.06.2011 UT L- II (ASNT) course was conducted from 30.05.2011 to 05.06.2011. No. of participants were 14 for course and 18 for examination. Mr.R.Subburathinam was the course Director and Mr.P.N.Udayasankar was the examiner. RT L- II (ASNT) course was conducted from 10.06.2011 to 16.06.2011. No. of participants were 17 for course and 18 for examination. Mr. M S Ramachandran was the course Director.

Bangalore Chapter A Technical Talk NADCAP NDT & Training by Mr. James Bennett, Performance Review Institute, USA was held on May 10, 2011 in ASI Building of Aeronautical Society of India

Chief Guest Mr. N. Balakrishnan along with Council Members during ISNT Day

vol 10 issue 1 June 2011

Congr atula ti ons ongra tulati tions

Dr. Amitava Mitra, Life Fellow of ISNT and Sr. Deputy Director (Scientist –G) and group Leader of NDE and Magnetic Materials of National Metallurgical Laboratory, Jamshedpur received the prestigious Materials Research Society of India Medal (MRSI Medal) for his outstanding work on nanostructured magnetic materials and use of magnetic NDE for materials characterization. He received the award at the Annual General Meeting of MRSI held * Dr. Narayan Parida, Life Member of ISNT and Sr. Deputy Director (Scientist –G) has takenover as the Head of Materials Science and Technology Division at National Metallurgical LaboratoryJamshedpur

Journal of Non Destructive Testing & Evaluation

i q forum Problem: 06-2011-Detection of inclusions and cracks before machining. Posted by : AQUASUE ENGINEERING, Tudiyalur post, Coimbatore - 641 034 Problem: Steel rods are machined as stepped bar specimens. What is the bet method to detect cracks and inclusions to satisfy the acceptance criteria given? Material: Steel EN 8 Raw Material: The bar stock used for machining is shown in Figure 1.

15 The finished machined specimen should satisfy the acceptance criteria given below. ACCEPTANCE STANDARD FOR INCLUSION & CRACK CONTENT: 1. THREE - STEP STEP - TURN DOWN METHOD: 1 a. For diameter below 60mm, minimum 5 bars shall be drawn from each lot for estimating the indusion content. Only one test specimen shall be cut as per drawing from each bar for step turning. 1 b. For diameter above 60mm, minimum 3 bars shall be drawn from each lot for estimating the, inclusion content. Only one test specimen sample shall be machined as per drawing from each bar. 2. ACCEPTANCE STANDARD: Under Visual inspection, 2.1 a: For the diameter below 60mm, 4 out of 5 specimens shall be free from any steak/ inclusion. If present, indications less than or equal to 3mm in length is taken to be acceptable. 2.1 b: For the diameter above 60mm, 2 out of 3 specimens shall be free from any steak / inclusion. If present, indications less than or equal to 3mm in length length is taken to be acceptable. 2.2 Remaining specimens can have maximum two indications.

Machining:

2.3 The maximum length of an indication shall not exceed 10 mm. 2.4 The total length of two indications, when added, shall not exceed 15mm. 2.5 In case of any doubt in 2.2,2.3,2.4 retest may be considered. 3. RETEST: 3.1 Two more specimens are taken for retest. If both the retest results conform to the specification the lot is accepted otherwise rejected. The Query:

Figure 1 : Steel rods used for machining

The steel rods are machined into a stepped bar whose drawing is given in Figure 2. Note: Tolerance on all diameters: ±0.30

Which is or are the suitable NDT techniques to test the bar stock before machining so that after machining the acceptance criteria will be satisfied? Reader’s are encouraged to send replies to the query to jndte.isnt@gmail.com “To establish a connect between the Researchers and Practitioners in NDE, this new forum INDUSTRIAL QUERY (IQ) FORUM is being created in our journal. We wish to bring together the underlying scientific principles, engineering and technological aspects and the most probable solutions for a NDT problem posed by our readers and members.”

Figure 2: Machined steel specimen NDT Required:

If you are in the industry and have a IQ, send an MSWord document with associated drawings to jndte.isnt@gmail.com with subject title “IQ Problem” for consideration for publication in a future issue. Also include any attempts at solving this problem. If you have a suggestion or solution for this, issue of IQ, please send it to jndte.isnt@gmail.com with subject title “IQ Solution- 03-2011” along with your contact information. Selected responses will be published in the June 2011 issue. All responses will be forwarded to the person posing the IQ. “Readers are welcome to contribute their own experiences in this kind of problems. ISNT would select the best answer for a possible reward.” -Prof. O. Prabhakar and -Prof. Krishnan Balasubramaniam

Figure 3: Dimensions of the stepped bar Journal of Non Destructive Testing & Evaluation

vol 10 issue 1 June 2011

NDE events

Materials Testing 2011 Materials Testing show to host ‘NDT hall of fame’ Which person or event has made the single biggest contribution to non-destructive testing and condition monitoring? That’s the question which the British Institute of Non-Destructive Testing (BINDT) is asking practitioners in the run-up to its 50th anniversary celebrations later this year.

We hope that this new feature added to the journal since the last issue was found useful by the readers to plan their activities in terms of paper submissions, registering for seminars, etc. Please send your feedback, comments and suggestions on this section to mandayam.shyamsunder@gmail.com

July 2011

5th ECCOMAS Thematic Conference on “Smart Structures and Materials” (SMART’11) July 6 to 8, 2011 ; Saabruecken, Germany http://www.izfp.fraunhofer.de/smart11/ EPRI Buried Pipe Integrity Group Open Door Meeting and Vendor Expo July 11 to 12, 2011 ; St. Louis, Missouri, USA http://www.cvent.com/events/buriedpipe-integrity-group-open-doormeeting-and-vendor-expo/eventsummary 05da397431e246c0a6453b2da9972dd1.aspx

NC, USA h t t p : / / w w w . a i r l i n e s . o r g / S a f e t y O p s / E M / P a g e s / 2011NDTForum.aspx October 2011 V Pan American Conference on NDT October 2 to 6, 2011 ; Cancun, Mexico http://www.copaend5.com/en/ index.php VIth International Workshop NDT in Progress, October 10 to 12, 2011 : Prague, Czech Republic h t t p : / / cndt.cz/ndt_in_progress2011/

Digital Imaging XIV July 18 to 20, 2011 ; Foxwoods Resort, CT, USA http://www.asnt.org/events/ conferences/digital/digital.htm

2011 IEEE International Ultrasonics Symposium (IUS) October 18 – October 21 ; Orlando, FL, USA http://ewh.ieee.org/conf/ius_2011/

38th Annual Review of progress in Quantitative NDE July 17 to 22, 2011 ; Burlington, VT, USA http://www.qndeprograms.org/2011/ Conference2011.html

2011 ASNT Fall Conference & Quality Testing SHow October 24 to 28, 2011 ; Palm Springs, CA, USA http://www.asnt.org/events/ conferences/fc11/fc11.htm

August 2011

November 2011

World Conference on Acoustic Emission August 24 to 26, 2011 ; Beijing, China http://www.wcae2011.org/

International Workshop on Smart Materials & Structures and NDT in Aerospace, November 2 to 4, 2011 ; Montreal, Quebec, Canada http://www.cansmart.com/

September 2011 International Congress on Ultrasonics (ICU 2011) September 5 to 8, 2011 ; Gdansk, Poland http://icu2011.ug.edu.pl/ocs233-1/ index.php/icu/icu2011 8th International Workshop on Structural Health Monitoring (IWSHM 2011) September 13 to 15, 2011 ; Stanford, CA, USA http://structure.stanford.edu/ workshop/ Materials Testing 2011 September 13 to 15, 2011 ; Telford, UK h t t p : / / w w w. b i n d t . o r g / E v e n t s / Exhibitions/MT_2011 5th Conference in Emerging Technologies in NDT (ETNDT) September 19 to 21, 2011 ; Ioannina, Greece http://www.etech-ndt5.uoi.gr/ 2011 ATA NDT Forum September 26 to 29, 2011 ; Charlotte,

vol 10 issue 1 June 2011

Singapore International NDT Conference & Exhibition (SINCE 2011) November 3 to 4, 2011 ; Singapore http://www.ndtss.org.sg/ 41st International Conference and NDT Exhibition; NDE for Safety 2011 / Defektoskopie 2011, November 9 to 11, 2011, Ostrava, Czech Republic http://cndt.cz/nde_for_safety2011/ Malaysia International NDT Conference & Exhibition 2011 (MINDTCE ‘11) November 21 to 22, 2011 ; Malaysia http://www.aindt.com.au/images/ stories/page_images/conferences/ i n t e r n a t i o n a l / mindtce_11_brochure_revision_1.pdf 2011 Aircraft Structural Integrity program Conference November 29 to December 1, 2011 ; San Antonio, Texas http://www.asipcon.com/

The institute is inviting NDT professionals from around the world to nominate the characters and the events that have had the greatest influence on the industry’s development. They will be commemorated in a ‘hall of fame’ at Materials Testing 2011, the bi- annual exhibition, which takes place this year on 13-15 September in Telford, UK. To enter, you should name a person (living or dead), an event, or both, along with a brief explanation as to what you believe they contributed to the industry and why it was so important. BINDT is also keen to receive memoirs and photos relating to the industry to be part of a display telling the story of NDT through the years. Send your contributions to joy@lavender-ndt.com all comments will be collated and the institute will set up a panel to discuss the contributions. A special award will also be made by the BINDT presidentelect Steve Lavender at the 50th annual dinner which is part of the annual conference running alongside the exhibition. John Hansen, chairman of the Materials Testing organising committee, said: “Although it plays such a critical role in industry, NDT remains a relatively new industry with many of the key developments having taken place within living memory. We’d like practitioners’ views on what they believe have been the key influences which have shaped the industry - both people and events so we can commemorate these and capture them for posterity.” Materials Testing 2011 is free of charge for visitors and will feature over 50 exhibitors from around the world along with a programme of talks and seminars. The show, which takes place once every two years, is recognised as one of the most comprehensive international exhibitions in NDT and related disciplines. The venue - the International Centre in Telford, in the West Midlands - is less than one-anda-half hours from three international airports and only five minutes from rail and motorway networks. For further information, www.materialstesting.org

see

<http:www.materialstesting.org> <http://www.materialstesting.org>

Journal of Non Destructive Testing & Evaluation

Malaysian International NDT Confer ence and E xhibition 2011 Conference Exhibition (MINDT CE 11) (MINDTCE November 21-22, 2011, Thistle Port Dickson Resort www.msnt.org.my The Malaysian Society for NDT (MSNT) cordially invites you and your staffs to participate and present your paper in the 2011 Malaysian International NDT Conference and Exhibition 2011 (MINDTCE 11). We expect there will be a lot of participation from NDT professionals and with your participation we look forward to sharing knowledge and experience in the field of NDT. MINDTCE 11 is jointly organized with the Malaysian Welding and Joining Society (MWJS) and strongly supported by PETRONAS, International Committee for NDT (ICNDT), Malaysian Nuclera Agency and SIRIM. The organizers invite scientists, engineers, educators, researchers and managers to submit paper to this wonderful conference. Revised Final date for full paper submission 5th September 2011 Notification of acceptance : 15th July 2011 Final date for full paper submission : 5th September 2011

“WCAE-2011” World Conference on Acoustic Emission–2011 Beijing (WCAE-2011) is organized by the Chinese Society for NonDestructive Testing (ChSNDT) and undertaken by Technical Committee on Acoustic Emission of ChSNDT (TCAE). Confer ence D ate: A ugust 24 to 26, 2011 Conference Date: August Venue: Beijing International Convention Center and Beijing Continental Grand Hotel, No.8 Beichen Dong Road, Chaoyang District, Beijing 100101, P.R. China RoomReservations: Tel: ++86-10-84980105 ; Fax: ++86-10-84970106 E-mail: bcgh@bcghotel.com Website: www.bcghotel.com www.bicc.com.cn Contact Conference-secretariat and Mailing Address en Wu, WCAE-2011 Secretariat Mr.. Zhanw Zhanwen Mr China Special Equipment Inspection and Research Institute Building 2, Xiyuan, Hepingjie, Chaoyang District, Beijing 100013, China Email:wcae2011@vip.csei.org.cn Phone: +86-10-59068313 ; Fax: +86-10-59068666

National NDT Awards

No.

Award Name

Sponsored by

ISNT - EEC National NDT Award (R&D)

M/s. Electronic & Engineering Co., Mumbai

ISNT - Modsonic National NDT Award (Industry)

M/s. Modsonic Instruments Mfg. Co. (P) Ltd., Ahmedabad

ISNT - Sievert National NDT Award (NDT Systems)

M/s. Sievert India Pvt. Ltd., Navi Mumbai

ISNT - IXAR Best Paper Award in JNDE (R & D)

M/s. Industrial X-Ray & Allied Radiographers Mumbai

ISNT - Eastwest Best Paper Award in JNDE (Industry)

M/s. Eastwest Engineering & Electronics Co., Mumbai

ISNT - Pulsecho Best Chapter Award for the Best Chapter of ISNT

M/s. Pulsecho Systems (Bombay) Pvt. Ltd. Mumbai

ISNT - Ferroflux National NDT Award

M/s. Ferroflux Products Pune

(International recognition)

ISNT - TECHNOFOUR National NDT Award for Young NDT Scientist / Engineer

ISNT - Lifetime Achievement Award

M/s. Technofour Pune

Note-1: The above National awards by ISNT are as a part of its efforts to recognise and motivate excellence in NDT professional enterpreneurs. Nomination form for the above awards can be obtained from ISNT head office at Chennai, or from the chapters. The filled application are to be sent to Chairman, Awards Committee, Indian Society for Non-destructive Testing, Module No. 60 & 61, Readymade Garment Complex, SIDCO Ind. Estate, Guindy, Chennai-600 032. Telefax : 044-2250 0412 Email: isntheadoffice@gmail.com

Journal of Non Destructive Testing & Evaluation

vol 10 issue 1 June 2011

NDE patents

Compiled by Dr. M.T.Shyamsunder, GE Global Research, Bangalore, India

We hope that the section on NDE Patents, which featured in the March 2011 issue of this journal, has continued to trigger your curiosity on this very important topic of Intellectual property. We continue this section with a few more facts on patents and a listing of a few selected NDE patents. Please send your feedback, comments and suggestions on this section to mandayam.shyamsunder@gmail.com Here are some interesting snippets from the world of patents : -

The Indian Institute of Technology, Madras has recently won the award for securing the highest number of patents in the last five years amongst the educational institution or university It is reported that the premier institute has filed 78 patent applications in the last five years. The award was instituted by the Confederation of Indian Industries in collaboration with the central department of industrial policy and promotion and the Indian Intellectual Property Office. In addition, Lalit Mahajan, an alumnus of IIT Madras, won the award for an individual securing the highest number of patents in the last five years. (Source : Times of India. April 30, 2011) Filing of an application for a patent should be completed at the earliest possible date and should not be delayed until the invention is fully developed for commercial working. A provisional application can be filed with a brief synopsis disclosing the essence or the nature of the invention.

Publication or disclosure of the invention anywhere by the inventor before filing of a patent application would disqualify the invention to be patentable. Hence inventors should not disclose their inventions before filling of the patent application. When disclosing, the number and the date of the patent application should be given by way of information to public. The date of patent is the priority date, which is the date on which first application (provisional / Complete / PCT) filed disclosing the invention . However, the date of publication is also important because it is from this date that the legal protection of an invention disclosed in the patent takes effect. The term of the patent is counted from this date of application. A patent can expire in the following ways ; The patent has lived its full term i.e. the term specified by the patent act of the country ; The vol 10 issue 1 June 2011

patentee fails to pay the renewal fee. A patent once granted b y the Government has to be maintained by paying annual renewal fee ; The validity of the patent has been successfully challenged by an opponent by filing an opposition ; The patent is revoked. (Source : http:// www.rkdewan.com ) Listed below are a few selected patents in the area of Liquid / Dye Penetrant testing, which were issued by USPTO since 1976. If any of the patents are of interest to you, a complete copy of the patent including claims and drawings may be accessed at http:// ep.espacenet.com/

UNITED STATES PATENT 7,215,807 NONDESTRUCTIVE INSPECTION METHOD AND APPARATUS Inventors: Nomoto; Mineo, Katsuta; Daiske, Asano; Toshio, Sakai; Kaoru , Taguchi; Tetsuo , Tanaka; Isao Assignee: Hitachi Ltd. (Tokyo, JP) The present invention relates to a method for inspecting a crack in a metal surface or the like, and, particularly, to an inspection method and apparatus for nondestructive inspection such as liquid penetrant inspection and magnetic particle testing. The present invention provides a flaw inspection method that essentially comprises the steps of illuminating a surface of a sample to be inspected, obtaining an image of the surface, characterizing a potential flaw on the inspected surface by processing the obtained image, displaying an image of the potential flaw, verifying that the potential flaw is a true flaw, and storing an image of the verified flaw in memory.

UNITED STATES PATENT 6,087,179 METHOD FOR NONDESTRUCTIVE TESTING OF MATERIALS AND WARES

Inventors: Beriozkina; Nadejda G, Leipunsky; Ilia O, Maklashevsky; Victor J Assignee: Marvic Ltd. (Moscow, RU), Marotta Scientific Controls, Inc. (Montville, NJ) A non-destructive testing method for revealing surface and through defects in materials and articles. The method comprises filling up defects with a volatile penetrant, applying indicator material to a surface to be tested, removing the indicator material from the surface and registrating defects according to the presence color spots, shapes and dimensions which are functions of shapes and dimensions of real defects. The indicator material comprises a gas-permeable base with applied sulfonephthalein indicator in the range of 0.0001 to 0.001 grams per 1 cubic centimeter of the base.

UNITED STATES PATENT 4,392,982 EXTENDED BIODEGRADABLE DYE PENETRANT COMPOSITION Inventors: Molina; Orlando G. Assignee: Rockwell International Corporation (El Segundo, CA) A liquid dye penetrant composition for use in non-destructive testing of objects to locate cracks and other defects or flaws therein, said composition comprising (1) a nonionic surfactant, such as an oxyalkylated aliphatic alcohol, (2) a small amount of a dye soluble in the surfactant and (3) a substantial and preferably a major proportion, of an N-alkyl-2pyrrolidone, preferably N-methyl-2p yrrolidone, as extender. Such composition is applied to the surface of an object containing cracks and other defects, water is applied to the surface of the object to remove excess liquid dye penetrant composition from the surface without removing such penetrant from such cracks and other defects, and with or without a developer, the surface of the object is

Journal of Non Destructive Testing & Evaluation

19 viewed under suitable lighting conditions, e.g. ultraviolet or black light when the dye in the penetrant is a fluorescent dye to locate any cracks or other defects in the surface of the body as indicated by colored traces from the dye penetrant remaining in such cracks and other defects.

UNITED STATES PATENT 4,351,185 HIGH TEMPERATURE PENETRANT SYSTEM Inventors: Garcia; Vilma A. Assignee: Magnaflux Corporation (Chicago, IL) A method and composition for nondestructive testing using the dye penetrant technique, and adapting the use of this technique at high temperatures. The invention is involved with using a marking crayon which includes a carrier composed of a solid which melts at a temperature below the temperature at which the work piece is to be inspected and a visible or fluorescent dye. Upon application of the crayon to a hot work piece, the solid penetrant composition becomes molten and the visible or fluorescent dye penetrates into any flaws in the surface in the usual manner. A remover, also consisting of a crayon composition, is used to remove excess penetrant, leaving only penetrant entrapped in the flaws. Upon removal of the excess penetrant and remover, the entrapped penetrant deposits are drawn to surface by the application of a finely divided developer either in dry form or as an aerosol. Inspection of the piece is then carried out under visible or ultraviolet light, depending upon the nature of the penetrant.

UNITED STATES PATENT 4,302,678

specimen provides a means for confirming instrumentation stability despite changes in temperature.

UNITED STATES PATENT 4,281,033 FLUORESCENT PENETRANT SYSTEM Inventors: Mlot-Fijalkowski; Adolf Assignee: Magnaflux Corporation (Chicago, IL) A method for non-destructive testing for flaws on the surface of a workpiece which includes the step of applying a penetrant composition including a fluorescent dye in a liquid vehicle onto the surface to permit the penetrant to become trapped in the flaws and then removing excess penetrant from the surface while leaving penetrant entrapped in such flaws. A remover is then applied to the surface, the remover composition including a solvent, at least one surface active agent which serves as an emulsifier for the liquid vehicle of entrapped penetrant, and a fluorescent material which is more readily soluble in the liquid vehicle of the penetrant than it is in the solvent. Upon contact of the entrapped penetrant with the remover, the fluorescent material from the remover is preferentially absorbed in the penetrant vehicle entrapped in the flaws thereby enhancing the fluorescent indication provided by the entrapped penetrant. The indications are developed in the usual way by applying a developer to the surface to draw the entrapped penetrant to the surface of the workpiece where it is contrastingly visible to the surface and is observable by viewing the surface under ultraviolet light.

UNITED STATES PATENT 4,191,048

FLUORESCENT STANDARD FOR SCANNING DEVICES

RED-VISIBLE DYE PENETRANT COMPOSITION AND METHOD EMPLOYING SAME

Inventors: Schiffert; Phillip W.

Inventors: Molina; Orlando G.

Assignee: Magnaflux Corporation (Chicago, IL)

Assignee: Rockwell International Corporation (El Segundo, CA)

A standard specimen for calibrating an ultraviolet scanning system of the type used to detect surface flaws in work pieces by penetrant testing including a piece of glass which has the characteristic of emitting fluorescent radiation upon excitation by ultraviolet light, and a heat conductive carrier element rigidly supporting the piece of glass therein. The standard

A liquid dye penetrant composition for use in non-destructive testing of objects to locate cracks and other defects or flaws therein, said composition comprising a liquid vehicle, preferably a nonionic surfactant such as an oxyalkylated aliphatic alcohol, and a single phase liquid red azo dye composition consisting essentially of C5-C12 alkyl

Journal of Non Destructive Testing & Evaluation

beta naphthols, particularly C7-H15 beta naphthols, and containing a liquid organic viscosity depressant compatible with the azo dyes, such as xylene, as represented by the dye composition marketed as Automate Red â&#x20AC;&#x153;Bâ&#x20AC;?, and which is substantially free of insolubles. The dye penetrant composition may include an extender, preferably an isoparaffinic solvent consisting essentially of a mixture of isoparaffins having a chain length of about 10 to about 17 carbon atoms, and an average chain length of about 13 to about 14 carbon atoms. Such dye penetrant composition is applied to the surface of an object containing cracks and other defects, water is applied to the surface of the object to remove excess liquid dye penetrant composition from the surface without removing such penetrant from the cracks and other defects, and with or without a developer, the surface of the object is viewed under visible light to locate any cracks or other defects in the surface of the body as indicated by brilliant red traces from the dye penetrant remaining in such cracks and other defects.

UNITED STATES PATENT 4,152,592 WATER WASHABLE DYE PENETRANT COMPOSITION AND METHOD FOR UTILIZING SAME Inventors: Molina; Orlando G. Assignee: Rockwell International Corporation (El Segundo, CA) A water washable substantially biodegradable dye penetrant composition having excellent sensitivity and high stability, for use in non-destructive testing of objects to locate voids and defects therein, said composition consisting essentially of an organic dye, preferably a fluorescent dye, and a carrier or solvent for said dye, in the form of certain ethoxylated linear alcohols, particularly the biodegradable nonionic surfactants comprised of ethoxylates of a mixture of secondary alcohols having linear alkyl chains of from 10 to 17 carbon atoms. In the method of application of the dye penetrant compositions, such composition is applied to the surface of an object containing cracks and flaws, water is applied to the surface of the object to remove excess liquid dye penetrant composition from the surface without removing such penetrant from the cracks and defects, and with or without a developer, the surface of the object is viewed under suitable lighting vol 10 issue 1 June 2011

20 conditions, e.g., ultraviolet or black light when the dye in the penetrant is a fluorescent dye, to locate any cracks or defects in the surface of the body as indicated by colored traces from the dye penetrant remaining in the cracks and flaws.

UNITED STATES PATENT 4,002,905 PENETRANT FLAW INSPECTION METHOD Inventors: Molina; Orlando G. Assignee: Rockwell International Corporation (El Segundo, CA) A water washable substantially biodegradable dye penetrant composition having excellent sensitivity and high stability, for use in non-destructive testing of objects to locate voids and defects therein, said composition consisting essentially of an organic dye, preferably a fluorescent dye, and a carrier or solvent for said dye, in the form of a

mixture of certain ethoxylated linear alcohols, particularly a combination of biodegradable nonionic surfactants each comprised of ethoxylates of a mixture of secondary alcohols having linear alkyl chains of from 11 to 15 carbon atoms, one of which contains an average of 5 moles of ethylene oxide, and another of which contains an average of 9 moles of ethylene oxide. In the method of application of the dye penetrant compositions, such composition is applied to the surface of an object containing cracks and flaws, water is applied to the surface of the object to remove excess liquid dye penetrant composition from the surface without removing such penetrant from the cracks and defects, and with or without a developer, the surface of the object is viewed under suitable lighting conditions, e.g. ultraviolet or black light when the dye in the penetrant is a fluorescent dye, to locate any cracks or defects in the surface of the body as indicated by colored traces from the dye penetrant remaining in the cracks and flaws.

UNITED STATES PATENT 4,000,422 METHOD OF LUMINESCENCE DETECTION OF SURFACE DISCONTINUITIES Inventors: Kuzmina; Nadezhda Vasilievna, Vanina; Ljudmila Ivanovna, Vdovenko; Nadezhda Vasilievna, Melikadze; Leonid Davidovich, Malkes; Leonid Yakovlevich, Vasiliev; Nikolai Grigorievich, Borovikov; Alexandr Sergeevich A method for detection of surface discontinuities by luminescence which consists in the successive treatment of the surfaces of materials subject to testing and inspection with the following compositions of a penetrant, cleaning fluid and a developer, whereupon they are inspected under an ultraviolet light at wavelength of 340-420 nm. Liquid constituents are in volume percent. The invention enables the revealing of surface discontinuities with a minimum width of 1-4 micrometers and provides adequate contrast and reliability in flaw detection.

Answ ers for P d SSear ear ch Q uiz 1 Answers Prrevious issue - NDT Wor ord earch Quiz Discountinuities Reference Defects Porosities Thermography Ferromagnetic Amplitude Contrast Penetrant Sensor Probes Reliability Iridium Cobalt maxwell Krautkramer ultraviolet Gauss borescope welds frequency longitudinal beam transverse volumetric

vol 10 issue 1 June 2011

Acoustic Calibration Delamination Cracks Ultrasonic Radigraphy Threshold Phase Flourescent Transducer Impedance Gamma Selenium Oersted Roentgen Faraday Electromagnetic Castings indications rayleigh angle wave surface prod yoke

Journal of Non Destructive Testing & Evaluation

vol 10 issue 1 June 2011

Contact Mr. D. Simon Amallaraja |

0 9866343309,9848043309|amallraja@fourvector.com

Ms.Gomathi Ramasamy |

0 7702733309 | gomathi@fourvector.com

Mr. Frank Edwin Vedam |

0 8978517118 | frankedwinz@fourvector.com

ndt puzzle Conceptualized & Created by Dr. M.T. Shyamsunder, GE Global Research, Bangalore

We hope you enjoyed solving the “NDT Word Search Puzzle” which was published in the last issue. We received many entries from the readers and based on the maximum number of correct words identified, the following are the WINNERS -

NDT WORDSEARCH - 2

TK Abhilasha, CNDE, IIT, Madras

P Selvaraj, ISRO-SHAR, Shriharikota

Sunita Thomas, BARC, Mumbai

TK Manoj Kumar, Brahmos Aerospace Ltd, Thiruvananthapuram

Congratulations to all the Winners. They will receive their prizes from the Chief Editor of the journal shortly. The correct answers to the Puzzle are published in page 20 of this issue. In this issue, we have another puzzle to continue stimulating your brain cells! We hope you will find this section interesting, educative and fun filled. In the next issue, we will be featuring a crossword puzzle. Please send your feedback, comments and suggestions on this section to mandayam.shyamsunder@gmail.com Introduction The “Word Search Puzzle”, contains forty (40) words related to “Liquid / Dye Penetrant Testing”. These include terminologies commonly associated with the technique. These words are hidden in the puzzle and may be present horizontally, vertically, diagonally in a forward or reverse manner but always in a straight line. Instructions All you have to do is identify these words and mark them on the puzzle with a black pen. Preferably you may take a photocopy of the Puzzle sheet and mark your answers on that. Once completed please scan your answered puzzle sheet as a PDF file and email the scanned sheet to jndte.isnt@gmail.com along with your name, organization, contact number and email address Rules & Regulations - Only one submission per person is allowed -

The marked answers should be legible and clear without any scratching or overwriting

The decision of the Editor-in-Chief, Journal of NDT &E is final and binding in all matters

NAME

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The correct answers and the names of the prize winners will be published in the next issue of the journal. vol 10 issue 1 June 2011

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vol 10 issue 1 June 2011

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Payments should be made by Demand Draft, drawn favoring “JNDE – ISNT”, payable at Chennai. Mr. V. Pari Managing Editor Journal of Non Destructive Testing & Evaluation Modules 60 & 61, Readymade Garment Complex, SIDCO Industrial Estate, Guindy, Chennai 600032 Phone: (044) 2250 0412 Email: isntheadoffice@gmail.com ; jnde.scaanray@gmail.com

Journal of Non Destructive Testing & Evaluation

Local Conference Secretariat The Conference Company South Africa Tel: 27 31 303 9852 Fax: 27 31 303 9529 Nina Freysen-Pretorius - nina@confco.co.za Deidre Hancke-Haysom - deidre@confco.co.za www.wcndt2012.org.za vol 10 issue 1 June 2011

vol 10 issue 1 June 2011

Journal of Non Destructive Testing & Evaluation

vol 10 issue 1 June 2011

Technical Paper

Development of an Immersion-based Ultrasonic C-Scan Technique to Evaluate the Performance of the Electro-Magnetic Stirrer for Improving Internal Quality of Continuously Cast High Carbon Steel Billets Manish Raj*, E Z Chacko*, Sanjay Chandra*, Issac Anto #, Krishnan Balasubramaniam$ * Tata Steel Ltd., Jamshedpur, India # M/s Dhvani R & D Solutions Pvt. Ltd., IITM Research Park, Chennai, India $ Centre for Nondestructive Evaluation, Indian Institute of Technology, Madras, Chennai

ABSTARCT Effect of electro-magnetic stirring on soundness of continuously cast billets and slabs can be assessed by many methods like visual inspection of macro-etch & sulphur print evaluation. But ultrasonic assessment provides through thickness information of the test samples, whereas, macro-etching and sulphur print methods provide information in one plane only. An attempt has been made to evaluate the effect of electro-magnetic stirring on soundness (inhomogeneities / flaws as well as effect of columnar / equiaxed grains) of continuously cast low carbon and high carbon continuously cast steel billets by ultrasonic attenuation as well as high gain pulse-echo technique in transverse cut slices. With increasing demand for steels for drawing at higher speeds, the quality, in terms of internal defects and macro structural features (central porosity, equiaxed zone, etc.), of billets has become of paramount importance. By optimizing the Electro Magnetic Stirrer (EMS) parameters viz., EMS current and frequency the severity of defects, area of columnar zone as well as central porosity, in continuously cast billet can be effectively minimized. The result would be an increase in equiaxed zone area and improved internal soundness. In the present work attempts have been made to determine the best combination of EMS current as well as frequency to ensure good internal soundness of billets. The EMS current and frequency were changed to different values in the range of 300A to 350 A and 4Hz to 6Hz respectively. Corresponding billet samples were collected for macro structural evaluation. The samples were scanned using an immersion ultrasonic C-scanner to get images of samples. Macro structural features revealed by ultrasonic C-Scan were analysed for determining the best combination of EMS parameters. It was observed that in the range under trial, % equiaxed zone and % central void area were not affected significantly by varying the EMS parameters. Keywords: Billet Casting, EMS Current, EMS Frequency, Ultrasonic C-scan, Columnar Zone, Equiaxed Zone, Central Porosity

1. INTRODUCTION With improvements in wire drawing processes, wire drawing plants are taking continuous steps to increase drawing speeds. Wire drawers are thus demanding better quality steels with lower inclusion ratings and lower fraction of hard phases (cementite and martensite). Apart from going for closed casting to reduce inclusion content, billet casters are under pressure to reduce segregation in their products.

is induced in it. The induced current (j) and magnetic field (B) further induce an electromagnetic force (F) which puts the liquid metal into rotation. By controlling the EMS current and frequency, the force of rotation can be varied. The primary benefits obtained with EMS have been thoroughly treated in literature (1). Simply put, the purpose of EMS is to homogenize the steel melt in order to obtain a favourable solid structure after solidification. The benefits are :

The Steel Plant located in South East Asia has a three strand billet caster producing low carbon, high carbon and cold heading quality grades equipped with a Mould EMS. The high carbon billets produced are rolled at the plants rolling mill and sold to wire drawing customers. For the purpose of the study billets of a high carbon PC (pre-stressed concrete) grade steel were selected. 1.1 Electro Magnetic Stirring

The principle of the EMS is similar to that of an AC motor. The rotating magnetic field (B) produced by the stirrer penetrates across the solidified shell into the liquid steel (Fig 1). The liquid steel is thus rotating at a speed ‘u’ relative to the magnetic field and an electric current ‘j’ Journal of Non destructive Testing & Evaluation

Fig. 1 : Schematic diagram of an EMS showing the direction of j, B, u, F inside the mould Vol. 10, Issue 1 June 2011

Technical Paper

1. Improvement in cast structure through increased volume of equiaxed grains. 2. Reduced degree of macro-inclusions, especially in the central portion of cross sections. 3. Improved surface quality and 4. Reduced shrinkage porosity. Effect of EMS frequency and current on stirring force :

The following relationship describe the effect of EMS frequency and current on stirring force, F f α B2M(f)f

the length of the mold tube was measured by suspending the measuring probe at various heights along the length of the empty mold tube in a mold fitted on the caster. The primary cooling water was running at its standard flow rate of 2000 lpm. The intensity at a particular height was obtained by positioning the tip of the probe at the required height manually, in the centre of the mold. These measurements were carried out at six different currents and three different frequencies in strand 1 of the caster as shown in Table 2. Table 2 : Setting for magnetic flux density measurement inside the mould

(1) 200 Amps

250 Amps

300 Amps

320 Amps

350 Amps

380 Amps

Where, BM = magnetic flux intensity in the considered point inside the mould (in Gauss)

4Hz

f = Frequency of rotation of the magnetic field

5Hz

6Hz

The magnetic flux intensity (BM) decreases with increasing frequency due to “skin effect” according to which eddy currents are more concentrated on the outer part of the conductor as the frequency increases. At frequency zero the force is zero and at higher frequency the force 2 (f) becomes approaches to zero again because the term BM very small. In between, there is a specific frequency, at which the stirring force is maximum. The current of the EMS coil has a more direct effect on the rotational force as the magnetic flux (BM) is proportional to the current.

The magnetic flux density measured is illustrated in Figures 2 (a) and 2 (b) for varying frequencies and currents respectively. The intensity of magnetic field decreases with increasing frequency and increases with increasing current.

3. EXPERIMENTAL SET-UP Two sets of trials were conducted for the purpose of the study. In order to ensure comparability of readings, each

During any metallurgical improvement obtained by EMS, a low rotational force gives insufficient improvements while a too high rotational force may give practically no further improvement. Moreover, too high rotational force may give rise to negative effects. Consequently, the optimum current and frequency settings are desired to be found out.

MATERIAL AND METHOD

2.1 Chemical Composition of Material Used

The chemical composition of steel grade considered in the present work is shown in Table 1. Table 1 : Chemical composition of HC Grade selected for study Grade

Chemical Composition (Wt %) C

0.79- 0.63- 0.030 0.030 0.20- 0.050 0.18- 0.0640.82 0.68 Max. Max. 0.25 Max. 0.22 0.068

2.2 Measurement of Magnetic Flux in the Mould

A ‘Link-Magnetic Magnetic Fieldmeter MPU-ST’, was used to measure the strength of the magnetic field produced by the EMS. The design range for the current of the EMS coil was from 0 to 400 A and the design range of the frequency was from 4 Hz to 12 Hz. The intensity along Vol. 10, Issue 1 June 2011

Fig. 2 : Variation in magnetic flux density at (a) 320 A current with varying frequency, and (b) 4 Hz frequency with varying current Journal of Non destructive Testing & Evaluation

Technical Paper

trial was conducted across the same heat and in the two strands i.e., strand 1 and strand 2, simultaneously. The normal casting duration of a heat is around 56 minutes. EMS settings were changed at an interval of 10 minutes. At each setting, one sample of six inches length was cut for the study. In the first trial, the EMS current was kept constant at 320 amps and the frequency was varied. In the second trial the EMS frequency was kept constant at 4 Hz and the current was varied. The details of the trials conducted are given in Table 3. The settings for these trials were chosen considering that higher currents and lower frequencies gave higher magnetic flux values as depicted in Figs. 2 (a) and 2 (b). Prior to this work, the billet caster used a setting of 320 A EMS current and 4 Hz EMS frequency for all the close casting grades. Table 3 : Setting for samples collection Trial No. 1

Heat No.

Trial

Sample Sample Sample 1 2 3

001069 Constant current 320Amps and varying frequency 001070 Constant frequency 4Hz and varying current

4Hz

5Hz

6Hz

300 Amps

320 Amps

350 Amps

Each six inch long billet sample was further machine cut into two one inch samples as shown in Figure 3. Each sample was then surface ground and scanned using a computer-controlled immersion ultrasonic C-scan equipment. The samples were then rated with respect to central porosity and percentage equiaxed zone by both the methods using the methodology given in Table 4. Central porosity was rated based on the area fraction of the central void. Percentage equiaxed zone was rated based on the area fraction of the equiaxed zone.

EQUIPMENT USED

The samples were tested in a water tank using a 2 inches diameter 5 MHz ultrasonic focused beam probe. The Cscan images were obtained with the help of a computer controlled immersion ultrasonic C-scan system. 4.1 Ultrasonic Immersion C-scan Imaging Technique

During the continuous casting process, due to the differential cooling from the outside surface to the inside, the grain structure is expected to take the distribution as represented by the classic schematic shown in Fig. 4 (a). Here, the chill zone (A) is found on the outer most layer that is in contact with the mould. The anisotropic columnar grain structure (B) is found below the chill zone. The inside regions are found to be equiaxed (C). At the centre, owing to the metal shrinkage, central void (D) is found. The relative areas of these zones will depend on various casting process parameters. Ultrasonic technique was applied to evaluate the above mentioned zones of the billet samples. This method revealed the four different regions in the samples, chilled zone, columnar zone, equiaxed zone and central void, in different gray / colour scale Fig. 4 (b). Ultrasonic C-scan can image five different intermediate layers of billet samples and plot the results in two dimensions. Therefore, all the internal defects appear as well giving an advantage over normal macro-etching where

Fig. 3 : Schematic diagram of CC billet sample collected for ultrasonic evaluation.

Table 4 : Quality evaluation methodology Parameters Unit of measure

Measurement system

Central porosity

Area of central void/ total transverse area x 100

% Equiaxed zone

Area of equiaxed zone/total transverse area Ă&#x2014; 100

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Fig. 4 : Macro-structure of a continuous cast billet sample (a) Schematic diagram, and (b) Image revealed by Ultrasonic C-Scan Vol. 10, Issue 1 June 2011

Technical Paper

only the top etched layer of the sample can be inspected. One major advantage of ultrasonic C-scan over A-scan is that classification of different kinds of defects is possible by imaging of the defects by this method. A series of C-scan tests (24 nos.) were carried out with varying parameter settings. The instrument variables for these tests were as follows :

PRF

: 100 Hz

Gain

: 40 dB

Energy

: 50 uj

Damping

: 100 ohms

Voltage output (amplitude)

: + 3 to - 3 and

Resolution

: 0.2 mm x 0.2 mm

Grey scale was used to evaluate and analyze the results obtained from the gated area. Referring to ultrasonic C-scan images, and based on a grey scale that depicts attenuated signals darker, one may see clear identification of different macro structures by the darker areas. Although not very sharp, each and every one of the areas is reproduced with a certain degree of dimensional accuracy. However, the boundary of each defect is not well defined. Top and bottom surfaces as well as three intermediate layers of each billet sample were scanned at an interval of around 7 mm in the ultrasonic C-scanner. The two dimensional image obtained from the C-scanner distinguished different macro structural regions such as equiaxed, columnar and chilled zones, and casting defects, if any.

RESULTS AND DISCUSSION

5.1 Optimization of EMS frequency

Figures 5 (a), (b) and (c) show the ultrasonic C-Scan images of transverse section of CC billet sample of HC Grade cast at strand 1 at EMS current 320 A and EMS frequency 4 Hz, 5 Hz and 6 Hz respectively whereas the C-scan images of transverse section of CC billet sample of HC Grade cast at strand 2 at EMS current 320 A and EMS frequency 4 Hz, 5 Hz and 6 Hz respectively have been illustrated in Figs. 6 (a), (b) and (c). Fig. 7 (a) and (b) show the effect of EMS current on the % equiaxed zone and % area of central void of total area of billet samples cast at strand 1 respectively whereas 8 (a) and (b) show the effect of EMS frequency on the % equiaxed zone and % area of central void of total area of billet samples cast at strand 2 respectively. The results have been tabulated in Table 5.

Fig. 5 : Ultrasonic C-Scan image of transverse section of CC billet sample cast in strand 1 at EMS current 320 A and (a) Frequency 4 Hz, (b) Frequency 5 Hz, and (c) Frequency 6 Hz

billet section, also does not change considerably with increase in EMS frequency. Therefore, EMS frequency was not raised further and considered optimum as 4 Hz. Table 5 : % Equiaxed zone and % central void measured in CC billets samples cast in strand 1 and strand 2 at EMS current 320 A at EMS frequency 4, 5 and 6 Hz EMS EMS % Equiaxed zone Current Freq. Strand 1 Strand 2 * S1

It is found, from the above mentioned figures and table, that the % equiaxed zone is quite significant and consistent at EMS frequency 4 Hz and it do not increases significantly with the increase in EMS frequency. The % area of central void in the billet samples, with respect to the total area of Vol. 10, Issue 1 June 2011

% Central void Strand 1 Strand 2 S1

320A 4Hz

50.78 51.36 45.01 50.35 0.5

0.6

0.1 0.12

320A 5Hz

49.88 49.12 49.09 47.38 0.6

0.4 3.03 0.21

320A 6Hz

50.42 54.31 47.35 46.03 0.68 0.61 0.12 0.32

* S = sample no.

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Fig. 7 : Effect of EMS frequencies (at current 320 A) on (a) % equiaxed zone, and (b) % area of central void of total area of billet samples cast at strand 1.

Fig. 6 : Ultrasonic C-Scan image of transverse section of CC billet sample cast in strand 2 at EMS current 320 A and (a) Frequency 4 Hz, (b) Frequency 5 Hz, and (c) Frequency 6 Hz

5.2 Optimization of EMS Current

Figures 9 (a) and (b) show the ultrasonic C-Scan images of transverse section of CC billet sample of HC Grade cast at strand 1 at EMS frequency 4 Hz and EMS current 300 and 350 A respectively whereas the C-scan images of transverse section of CC billet sample of same grade cast at strand 2 at EMS frequency 4 Hz and EMS current 300 and 350 A respectively have been illustrated in Figs. 10 (a) and (b). Fig. 11 (a) and (b) show the effect of EMS current on the % equiaxed zone and % area of central void of total area of billet samples cast at strand 1 respectively whereas Fig. 12 (a) and (b) show the effect of EMS current on the % equiaxed zone and % area of central void of total area of billet samples cast at strand 2 respectively. The results have been tabulated in Table 5. Journal of Non destructive Testing & Evaluation

Fig. 8 : Effect of EMS frequencies (at current 320 A) on (a) % equiaxed zone, and (b) % area of central void of total area of billet samples cast at strand 2. Vol. 10, Issue 1 June 2011

Technical Paper

Fig. 9 : Ultrasonic C-Scan image of transverse section of CC billet sample cast in strand 1 at EMS frequency 4 Hz and (a) Current 300 A, and (b) Current 350 A

Fig. 10 : Ultrasonic C-Scan image of transverse section of CC billet sample cast in strand 2 at EMS frequency 4 Hz and (a) Current 300 A, and (b) Current 350 A Vol. 10, Issue 1 June 2011

Fig. 11 : Effect of EMS Current (at frequency 4 Hz) on (a) % equiaxed zone, and (b) % area of central void of total area of billet samples cast at strand 1.

Fig. 12 : Effect of EMS Current (at frequency 4 Hz) on (a) % equiaxed zone, and (b) % area of central void of total area of billet samples cast at strand 2. Journal of Non destructive Testing & Evaluation

Technical Paper

Table 6 : % Equiaxed zone and % central void measured in CC billets samples cast in strand 1 and strand 2 at EMS frequency 4 Hz at EMS current 300, 320 and 350 A. EMS EMS % Equiaxed zone Current Freq. Strand 1 Strand 2 * S1

% Central void Strand 1 Strand 2 S1

300A 4Hz

49.59 51.08 45.77 48.27 0.91 0.42 0.32 0.47

350A 4Hz

51.72 50.76 46.53 50.03 1.59 0.64 0.05 0.14

It can be observed, from the above mentioned figures and table, that the % of equiaxed zone is significant as well as consistent at EMS current 320 A (existing practice) and it does not increases significantly with the further increase in EMS current. The % area of central void in the billet samples, with respect to the total area of billet section, also does not change considerably with further increase in EMS current. Therefore, EMS current was not increased further and considered optimum as 320 A.

6. CONCLUSIONS It is important to control the EMS motion within the meniscus and bulk regions of the casting to achieve the desired product quality and operating flexibility. The stirring of molten steel by EMS is effective to improve the homogeneity of the cast, which solidifies with enough amounts of equiaxed crystals. Based on the experiments and analysis it was concluded that z

Magnetic flux density (Gauss) inside the mould increased with increasing EMS current and decreasing frequency.

The change in EMS frequency from 4 Hz to 6 Hz, with varying EMS current 300 A to 350 A did not resulted in further improvement in billet quality.

The current setting of EMS i.e. 4 Hz frequency and 320 A current is the optimum setting to get good quality of CC billets.

The qualitative as well as quantitative evaluation of central void and columnar/equiaxed zone in the

Journal of Non destructive Testing & Evaluation

continuously cast billets was possible using ultrasonic immersion C-Scan imaging technique.

ACKNOWLEDGEMENTS

The authors are thankful to the management of Tata Steel for giving permission to publish this paper. The authors also acknowledge the assistance of Mr. Thepthemrong Wongwiriyakul, Mr. Krittawit Sajawirote and Mr. Dhanupol Uaapisitwong of Tata Steel Thailand during the course of the study.

REFERENCES 1. A. Badidi Buda, S. Liable, A. Enchilada, 2003, Grain size influence on ultrasonic velocities and attenuation, NDT & E International 36, 1-5. 2. J.C. Pandey and Manish Raj, 2007, Evaluation of internal and subsurface quality of continuously cast billets & slabs by ultrasonic techniques, Ironmaking and Steelmaking, Vol. 34, No. 6, 482-490. 3. J.C. Pandey, Manish Raj, T.K. Roy and T. Venugopalan, June 2008, A Novel Method to Measure Cleanliness in Steel Using Ultrasonic C-scan Image Analysis, Metallurgical and Materials Transactions B, Vol. 39B, 439-446. 4. M. Yoshimura, S. Suzuki, S. Takagawa and H. Ueno, Oct. 1980, On the Quality Improvements of Continuously Cast Products through Electromagnetic Stirring at Mold and secondary Cooling Zone, 100th th ISIJ Meeting, Lecture No. S802. 5. Manish Raj and J.C Pandey, March 2007, An ultrasonic technique to evaluate the performance of the electro-magnetic stirrer for improving internal quality of continuously cast billets, Material Evaluation, Vol. 65, No. 3, 329-334. 6. Manish Raj and J.C. Pandey, 2008, Optimization of Electro Magnetic Stirring in Continuously Cast steel billet using Ultrasonic C-Scan Imaging Technique, Ironmaking & Steelmaking, Vol. 35, No. 4, 289-296. 7. Preeti Prakash Sahoo, Ankur Kumar, Jayanta Halder and Manish Raj, 2009, Optimisation of Electromagnetic Stirring in Steel Billet Caster by Using Image Processing Technique for Improvement in Billet Quality, ISIJ International Vol. 49, No. 4, 521-528.

Vol. 10, Issue 1 June 2011

Technical Paper

Quality control of Nuclear Fuel Elements by Gamma Radiometry Assay M.S.Rana, Benny Sebastian, Sanjoy Das, D. Mukherjee and B.K. Shah Quality Assurance Division Bhabha Atomic Research Centre Mumbai 400085

ABSTRACT Determination of fissile material concentration and its variation along length of fuel element is a critical requirement for qualification of nuclear fuel. All the fuel elements are evaluated by non-destructive method to ensure uniform distribution of fissile material for reliable performance in reactor. Although several NDT methods such as micro radiographic testing for smaller diameter fuel pin and conventional radiographic testing for the large diameter fuel pin have been tried, but these methods do not provide adequate quantitative information. An alternative method to mitigate these problems is being tried by observing the attenuation characteristics of gamma photon beam from a radioactive isotope by the fuel. One such technique is radiometric gamma scanning of nuclear fuel element. Radiometry is a procedure in which, gamma rays produced by the radioactive source gets attenuated by the material under test and the transmitted beam of gamma rays are detected by the scintillation detector. The detector - photo multiplier tube coverts the radiation beam into weak voltage pulses through a series of opto-electrical phenomena. These pulses are subsequently amplified by the use of amplifier and are processed in Single Channel Analyzer (SCA). The final output for a fuel element is in the form of series counts across the length of fuel element, which are analyzed by application software to produce quantitative information about it. The operational procedure of radiometric technique developed for qualification of fuel has been described in this paper. Effect of different parameter on the scanning and their interdependency are also discussed.

INTRODUCTION

Dispersion type fuel elements are fabricated through powder metallurgical route where fissile material in form of intermetallic compound (eg. UAl3) is dispersed in the matrix of aluminium alloy. This method of fabrication involves different process such as vibro compaction of intermetallic compound in the clad tube and infiltration of the matrix into it. Different NDT methods are used for monitoring the fabrication process. Eddy current testing is done to check the continuity of the matrix through out the length of the fuel element. Helium leak testing ensures the leak tightness of the element. The linear power rating of a fuel pin in the reactor depends upon the fuel density as well as its axial distribution. Axial uniformity of fuel density is essential to avoid the formation of hot spots in the fuel pins and form an important quality control requirement during fabrication. Non destructive technique using radiometry has been developed for determination of uniformity of axial distribution of fissile material density along the fuel element. Passive gamma scanning is not sensitive to linear density change because of severe self absorption of low energy, low intensity gamma rays from fuel material and can reveal only surface characteristic of the sample. Radiometry technique using active gamma scanning has been used for such application in which an appropriate external radioactive isotope is used as source and scintillation detector for detecting and counting of transmitted beam of photon. This attenuated beam will be analyzed to find out distribution of heavy material along the fuel column. Vol. 10, Issue 1 June 2011

2. PRINCIPLE Radiometry is a technique where gamma rays from a radiation source pass through material and the attenuated beam is detected by a radiation detector. The result is available in the form of counts, i.e. number of pulses recorded in the gamma counting device. The attenuation of gamma rays in a solid medium follows the modified Beer-Lambert law. I= I0 exp(-μg ρx)

Where I0 and I are intensities of incident and transmitted radiation respectively, μg and x are mass attenuation coefficient and distance traversed respectively, ρ is density of the material. Taking natural logarithms both sides of Beer-Lambert equation yields. ln (I) = ln (I0) - μg ρx

Since photon flux recorded in a detector is proportional to the intensity of radiation, the above expression can be written as, ln (counts) = ln (counts)0 - μg ρx

In the above equation, the counting of incident beam is fixed for given setup and mass attenuation co-efficient is also constant for a given material and is independent of it’s physical form. The diameter of fuel pin is also fixed for a given type of fuel. Therefore ln (counts) is a direct linear function of density of fuel pin. Journal of Non destructive Testing & Evaluation

Technical Paper

Radiometry Scanning Unit (Plan view)

Fig. (1)

Fig (2)

3. RADIOMETRY SETUP A schematic of the radiometry mechanical setup is shown in Fig. (1). The radiometry setup consists of the followings a) Mechanical Scanning unit and its control electronics b) Nuclear data acquisition system. c) PC Hardware and Application software.

of mechanical movements in proper sequence as required by the system. It provides start signal and linear motion signal to data acquisition electronics for synchronization. This synchronization of data acquisition by scintillation detector and linear motion start is vital because it correlate between the coordinates of fuel element and radiation absorption data.

3.1 Scanning unit

3.2 Nuclear data acquisition electronics

Scanning unit consist of lead shielded source and detector assembly and mechanism for translational (linear) and rotational motion of the fuel element. The collimating aperture would always be smaller than the diameter of the fuel element. Thus some material on periphery will lie outside the radiation beam. Rotation is necessary to bring this into the field of testing. The mechanical scanner should satisfy the following criteria for precision in results:

It consists of detector front end electronics, single channel analyzer (SCA) with programmable dwell time, lower level discriminator (LLD) and upper level discriminator (ULD) and scalar. The front end electronics consists of voltage sensitive preamplifier, amplifier and high voltage bias to the detector. The output form detector assembly is low amplitude â&#x20AC;&#x201C; short duration current pulse. Preamplifier converts this current pulse into voltage pulse whose amplitude is proportional to energy deposited in detector medium during gamma ray interaction. The signal from preamplifier is not suitable for processing in SCA. For this, shaping of output signal from preamplifier is required. The amplified pulses are fed into SCA in order to discriminate pulses of different heights, which in-turn shows different energies. The analyzer consists of two discriminators with independent voltage thresholds. Unless the pulse height is greater than the setting of LLD, it is disregarded. If the pulse larger enough to exceed the LLD,

Uniform speed, i.e. equal linear or angular movement should occur in equal time interval.

ii) No slippage, i.e. it should not happen that during some small time interval, the fuel element remains stationary at a place with only rotation and no linear motion. iii) Vibrations should be minimum. The control electronics consists of motor drives and control, sensors logic. The control electronics takes care Journal of Non destructive Testing & Evaluation

Vol. 10, Issue 1 June 2011

Technical Paper

but not too large to exceed the ULD, SCA produces an output. SCA is connected to scalar and the scalar will count all gamma rays in a selected energy interval. 3.3 Computer Hardware and Application software:

Computer is connected to nuclear data acquisition unit by a USB cable or through RS232 cable. Integrated application software is designed and developed to analyze the counts obtained from the counter electronics. The application software not only supports the acquisition but also controls the system mechanical operation.

6.1 Collimator slit dimensions

The collimator slit is present on both side i.e. source and detector. The dimension of the slit is very important, since it significantly affect the sensitivity of the result. Length of the slit should be such that it can detect the smallest local variation in the linear density as per the acceptance standard. On the other hand many factors are to be considered in the selection of the width of the slit. It can not be too wide, or else so called ‘direct shine’ will occur, which means that the external radiation will by-pass the fuel and directly enter the detector. This can greatly reduce the counting accuracy.

RADIATION DETECTOR 6.2 Linear and Rotational Speeds

Detector used for the application mentioned above is 1" dia. x 1" length NaI(TI) scintillation detector. Selection of detector material is governed by the following requirements. i)

Detector should possess good resolution. Resolution is the ability of detector to distinguish between two closest energy levels. High resolution gives more accurate assay. The resolution of germanium detector is 0.5 to 2.0 Kev where as resolution of NaI(TI) detector is 20 to 60 Kev.

ii)

Efficiency means probability with which detector can detect in-coming photons. Efficiency can be achieved at the cost of resolution. A given efficiency is less expensive to obtain in low resolution NaI (TI) crystal than in high resolution germanium detector.

iii) Other parameters such as space and cooling requirement and portability must be considered and may be prime criteria in detector selection.

RADIATION SOURCE

The selection of proper radiation source for the application is necessity for good quantitative resolution. In other words, a minute change in heavy material density should result in as large count rate variation as possible. Other factors such as diameter of the fuel element, packing density and source properties such as half life, availability and cost have to be considered. In case of uranium bearing fuel, an isotope of Cobalt is generally used as source. The energy of the source selected is close to K-edge absorption energy of the uranium atom. This ensures that the absorption is high in the fuel and sensitivity in quantitative assessment is high.

INTERDEPENDENCE OF OPERATION PARAMETERS

The operation parameters such as linear and rotary speeds, collimator slit length and width, source strength, acquisition time etc need to be properly selected and fixed for the application. These selections are done to obtain best possible result. The interdependence of the operation parameters are discussed bellow Vol. 10, Issue 1 June 2011

At the outer periphery, radiation path lengths vary greatly with distance from the centre of the fuel and hence some of this portion will be left out of the slit. To test this portion of the fuel element rotation motion is very important parameter. Linear and rotational speeds for scanning are synchronized to ensure that no portion of fuel, particularly from the periphery, escapes coming in line with the source and detector. Higher linear speed and low rotational speed will result in this situation. Pitch can be defined as the axial length moved per rotation. If l mm/sec is linear speed and r revolution/sec is rotational speed. Pitch p = l / r 6.3 Acquisition time

Acquisition time is nothing but the counting time per channel. It also plays part in coverage of the volume inspected. If counting time is t then fuel length travelled in one acquisition is l x t. To ensure that counts are collected at least for every mm of the fuel length, it is to be ensured that magnitude of l x t i.e. | l x t| ≤ r 6.4 Source strength

Source type and strength is very important parameter, which dictates all the parameters discussed above. As discuss earlier source type is selected by ensuring that the absorption is high in the fuel and sensitivity in quantitative assessment is high. It is well known that the counting statistics improves with the count rate and hence proper selection of source strength is required. The linear speed l and the acquisition time t are to be selected in such a way that the count rate is high enough to satisfy the requirement of precision laid down in the specifications.

7. RADIOMETRY SCANNING PROCEDURE In order to use the radiometry system for quality evaluation, the equipment has to be calibrated with standard fuel pin. After the standardization of the system, the machine is ready for inspection. Journal of Non destructive Testing & Evaluation

Technical Paper

7.1 Calibration

Radiometry testing discussed here is an indirect method for determination of heavy material linear density and hence calibration of the counting system is necessity for this application. Calibration of the gamma ray spectroscopy system is done to establish relationship between counts and linear density of the material under examination. To calibrate the system, a set of standard elements are scanned first. The standard elements are made up of same fissile material as that of actual fuel but with slight variation in its linear density. The variations in linear density of the standard elements are required so that the equation between counts and the linear density can be established. The variation of the linear density must be such that it covers the entire range of inspection values set by the designer. The standard must contain minimum three elements of variable density for calibration but for better accuracy one should always use more numbers of standards. One of the standard elements must have linear density very close or equal to the nominal value. After all the standard elements are scanned, the counts are stored for calibration. The calibration is performed by plotting graph of linear density versus natural logarithm of counts {ln (counts)} as shown in Fig. (3). The by using least square method the relationship between linear density and count can achieved.

understood. These variables are selected to obtain the best possible result. The data obtained in terms of counts are fed to the calibration equation and the distribution of linear density of that element can be obtained by using analyzing software as shown in Fig. (4). The various measurement parameters are derived after data processing and analysis through special algorithms. These measurement parameters are then compared and based on the specification accept or reject decision is taken.

CONCLUSION

Though passive gamma scanning is much simpler in operation, but it is a surface or sub-surface technique.

Linear Density = - m {ln (count)} + C Where, m = Slope of the curve C = Constant. Fig. (4)

Negative (-m) slope indicate that the linear density is inversely proportional to the counts. 7.2 Inspection

Radiometry inspection of nuclear fuel elements is done by scanning the elements one after the other. The purpose of the inspection is to check the distribution of fissile material throughout the active length of the element. There are large number of variables whose value needs to be fixed either at design stage or during operation. These are linear and rotary speeds, collimator slit length and width, source strength, acquisition time etc. As they influence the overall accuracy of the result, their interdependence should be

The information obtained in passive scanning is qualitative. Active gamma scanning has an added advantage of full cross sectional examination and information obtained is precise and quantitative. The variables in active scanning are more than the passive gamma scanning. Hence process parameter needs to be standardized before operation. Radiometry using active gamma scanning is currently adopted for quality control of dispersion fuel element.

ACKNOWLEDGMENT

The authors acknowledge the support and constant encouragement from Shri H.S. Kamath, Director, Nuclear Fuels Group and Shri. R.P. Singh, Associate Director, Nuclear Fuels Group for carrying out the work. The effort of our colleges in Quality Control Section is duly acknowledge.

REFERENCES 1. Hastings Smith Jr. and Phyllis Russo in Chap 9 of “Passive nondestructive assay of nuclear materials”, NUREG/CR-5550 Ed: Dong Reilly et al (1991). 2. Sanjoy Das, P.R.Vaidya & B.K.Shah “Assessment of pipe wall thickness radiation technique”, Inspectioneering Journal July/ August 2007.

Fig. (3) Journal of Non destructive Testing & Evaluation

3. Robert C. Mc Master, Non-destructive Testing Hand book, Volume-3, 2nd edition, The American Society for Non-destructive Testing, (ASNT), Ohio, USA. Vol. 10, Issue 1 June 2011

Technical Paper

Health Assessment of Structures, Systems and Components (SSCs) beyond initial design life: Role of NDE during License Renewal of Tarapur Atomic Power Station-1&2; Nuclear Power Corporation of India Limited A.Ramu, C.S.Mali1, J.Akhtar1, V.S.Daniel1, Ravindranath1, B.K.Shah2, S.Bhattacharjee1 and R.K.Gargye1 1

Tarapur Atomic Power Station, Tarapur Maharashtra Site; Nuclear Power Corporation of India Limited PO: TAPP; Dist: Thane; Maharashtra: State; Pin: 401 504 2 Head, Quality Assurance Division, Bhabha Atomic Research Centre, Mumbai, India. E-mail : akkalaramu@gmail.com; aramu@npcil.co.in

ABSTRACT Tarapur Atomic Power Station-1&2 (TAPS) is one of the Boiling Water Reactors (BWRs) operating in the world and belongs to earlier generation of BWRs. These units were commissioned in late 60’s and have successfully completed 40 years of commercial, reliable and safe operation. Ageing of plant Structures, Systems and Components (SSCs) important to safety need to be effectively identified using various Non-Destructive Testing (NDT) methods to ensure their integrity and functional capability throughout their service life. The process of license renewal of Tarapur – BWR units was initiated well in advance with the Indian regulatory authority, the Atomic Energy Regulatory Board (AERB) before the license expires. A systematic approach has been devised and followed in identifying & addressing the critical areas/components important to nuclear safety. Comprehensive assessment of SSCs and material condition of the station has been identified as key factors to determine fitness of Systems, Structures and Components (SSCs) for continued operation beyond its initial designed life of 40-years. The expertise gained from the operation and maintenance of both the units for the past four decades has strengthened the capabilities of the station personnel to develop various inspection methodologies & their application in the field. The inspection programmes has been revised based on the feedback obtained from In-Service Inspection results and ageing management related comprehensive inspection & testing programmes. In addition to this, TAPS has developed and established many of the inspection techniques/ procedures to assess the component’s integrity using various non-destructive testing methods. In some of the critical areas, independent review from various governmental research agencies has also been sought. TAPS had also taken up corrective steps in this regard and a comprehensive study was conducted in association with the expertise from NPCIL Directorates and various R&D agencies such as Bhabha Atomic Research Centre (BARC) and Indira Gandhi Centre for Atomic Research (IGCAR). This paper gives a brief of various Non-Destructive Evaluation (NDE) methodologies followed during Condition Assessment of various critical nuclear components during license renewal of TAPS for Long Term Operation (LTO) beyond its initial design life. Keywords: AMP, SSCs, PSI, ISI, Integrity, NDE, BWRs, License Renewal, LTO.

INTRODUCTION-TARAPUR BWRS

Tarapur Atomic Power Station-1&2 is one of the Light Water Reactors – BWR type design constructed and commissioned in late ‘60s with an installed capacity of 220MWe. Tarapur-BWRs is one of the vintage reactors (BWR-1/Mark I)which were built on turnkey basis by General Electric, USA. These units were designed to operate with load following characteristics with the help of secondary steam generators. As per the design 70% of the power output was from the Reactor (Boiler) core thermal power and the balance 30% power was from the Secondary Steam Generators (SSGs). Due to the frequent tube leaks of SSGs, these were isolated from the system in the year 1985 and units were re-rated to 160MWe and operating since then at this re-rated capacity. Both the units have completed 40 years of commercial operation till Vol. 10, Issue 1 June 2011

date and still giving excellent performance with a station capacity factor close to 90%. The performance of both units improved over the years. Tarapur reactors were designed in early 60’s with the technology and standards available at that time giving considering more safety margins while designing plant layout, selection of material of construction, following best engineering practices during fabrication and maintaining the appropriate quality standards. Three more reactors are in operation in the world which belongs to similar age of Tarapur-BWRs and these are Tsuruga of Japan and Oyster Creek & Nine Mile Point of USA which belongs to BWR-2 design and also operating since 1969. The design life of most of the components is 40 years and hence a detailed review was carried out to ascertain the balance life of Structures, Systems and Components Journal of Non destructive Testing & Evaluation

Fig. 1 : Tarapur Atomic Power Station 1&2 (2001)

(SSCs). Most of the components in conventional systems are replaceable including piping, equipments and various structurals. Therefore, as part of plant ageing management programme, a comprehensive study & review of all the safety systems was carried out and modifications implemented to improve the plant safety and reliability. Various degradation mechanisms were identified using appropriate NDE methods and replacements with suitable material/design modifications were implemented. However, the non-replaceable components such as Reactor Pressure Vessels (RPVs) and Civil Structures - Containment metallic vessels were subjected to both comprehensive inspections and analytical evaluation. In this regard, various inspection methodologies were developed and examination techniques were established on full-scale mock-up facilities with the help of the expertise from NPCIL-HQ and various units of Department of Atomic Energy (DAE) such as BARC (Bhabha Atomic Research Centre), IGCAR (Indira Gandhi Centre for Atomic Research) and in addition regulatory authorities, the Atomic Energy Regulatory Board (AERB). The following paragraphs would give insight to the various methodologies followed during the process of license renewal of SSCs using various NDE techniques.

2. LICENSE RENEWAL – A CHALLENGING TASK [1] In late 90’s several nuclear power plants all over the world had completed their initial authorized periods of operation. Review of safety performance, operating experience and material condition of majority of these reactors had established that these NPPs could be safely operated for several more years. The international nuclear community got convinced that these early generation NPPs could be operated for significant periods beyond their original authorized period. In this regard, IAEA has laid down broad guidelines i.e. Safety Series No. 50-SG-O12 on “Periodic Safety Review of Operational Nuclear Power Plants”, for assessing the condition of NPPs with the aim to operate them beyond the initial permitted operating period. Meanwhile, Probabilistic Safety Assessment (PSA) has been developed as a tool for risk assessment and Journal of Non destructive Testing & Evaluation

Technical Paper

resultant risk-informed safe operation and maintenance of NPPs. For Critical components inspection methodologies have been enhanced based on the Operating Experience (OE) feedback received from time to time from overseas BWRS including various agencies such as BWROG (BWR Owners Group) and GE in the form of SIL (Service Information Letters) & other technical correspondences. A comprehensive review of SSCs for renewal of authorization involves in-depth analysis & review covering (a) Operational Performance of the station till date (b) Ageing Management (c) Design Basis (d) Safety Analysis & (e) Seismic Re-evaluation. Out of these, ageing management is one of the critical issues where-in application of NDE is associated with for detection and evaluation of component’s fitness for service.

AGEING MANAGEMENT PROGRAMME (AMP) OF SSCS[2]

3.1 Managing ageing for nuclear power plants means ensuring the availability of required safety functions throughout the service life of the plant, with account taken of changes that occur with time and use. This requires addressing both physical ageing of structures, systems and components (SSCs), resulting in degradation of their performance characteristics, and obsolescence of SSCs, i.e. their becoming out of date in comparison with current knowledge, standards and regulations, and technology. Effective management of ageing of SSCs is a key element of the safe and reliable operation of nuclear power plants. Effective ageing management is in practice accomplished by coordinating existing programmes, including maintenance, in-service inspection and surveillance, as well as operations, technical support programmes (including analysis of any ageing mechanisms) and external programmes such as research and development. 3.2 The purpose of Ageing Management Programme (AMP) is to assess the condition at the component level and put the same in service meeting functional as well as design intent. Ageing effects is one of the concerns of older generation plants and methodologies are being adopted to identify various degradation mechanisms and are eliminated either by design modification or by replacements with better resistant materials. This process is required to enhance the life of components for continued service. 3.3 In order to address the ageing of SSCs, a comprehensive study was carried out by the station with the help of expertise from NPCIL-HQ and identified the list of the SSCs important to safe operation that needs to be addressed and evaluated for its integrity either by analysis or by using various inspections & testing methods. The total plant components were categorized into two, i.e., (a) Components that are replaceable either with new design or by reverse engineering methodology and (b) Vol. 10, Issue 1 June 2011

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Components that are not replaceable. Components are further divided based on its safety significance on nuclear safety/reliability and plant availability. The critical components that can not be replaced are (a) Reactor Pressure Vessels (RPV) (b) Containment Pressure Vessels (drywell) (c) Containment civil structures (CC). The components and systems that can be replaced are Equipments in conventional systems including both mechanical & electrical components, pressure vessels & heat exchangers, Piping-fitting components, Pumps & Valves and Supporting structures of these.

DEGRADATION MECHANISMS IDENTIFICATION

4.1 TAPS has engineered many inspection methodologies to detect various degradation mechanisms such as IGSCC (Inter Granular Stress Corrosion Cracking), TGSCC (Trans Granular Stress Corrosion Cracking), Erosion-Corrosion (EC), Stress Corrosion Cracking (SCC), Mechanical Fatigue and Flow Accelerated Corrosion (FAC). These degradation mechanisms were timely detected using various inspection methodologies/ techniques developed from time to time. TAPS has developed a data base with regard to surveillance, inspection and testing of primary system components including RPVs [5] & its associated components, Primary system piping/components, Recirculation Coolant Pumps (RCPs), Containment Vessels etc.,. The requirements enlisted while formulating the inspection & testing programmes are based on the generic issues [5] . The test results from these inspections have been utilized for enhancing the inspection scope of SSCs, in few cases with advanced NDE techniques. 4.2 Examples of degradation mechanisms that have occurred in LWR components are (a) Intergranular stress corrosion cracking (IGSCC) in boiling water reactor (BWR) piping (b) Stress corrosion cracking (SCC), pitting, wastage, and other degradation in steam generator tubes (c) Thermal fatigue cracking in reactor piping components (d) Flow-accelerated corrosion (e) Irradiation-assisted SCC of reactor internal components (f) Boric acid corrosion of low alloy and carbon steels and (g) SCC in Alloy 600 and weld Alloy 182/82 dissimilar metal welds. 4.3 The cause of components degradation has been identified and mitigated either by replacements with suitable technical advancements in material selection or by strengthening the surveillance. Some of the generic issues pertaining to BWRs primary piping have also been addressed as part of Plant ageing management programme and feedback from overseas reactors experience coupled with in-house practical experience on various inspection observations/results, a systematic methodology-cum-guidelines were established for developing surveillance programme of monitoring. Vol. 10, Issue 1 June 2011

4.4 The inspection programmes has been revised based on the feedback obtained from In-Service Inspection results and ageing management related comprehensive inspection & testing. In addition to this, TAPS has developed and established many of the inspection techniques/procedures to assess the componentâ&#x20AC;&#x2122;s integrity using various non-destructive testing methods.

5. INSPECTION METHODOLOGIES SURVEILLANCE, INSPECTION & TESTING CRITERIA 5.1 Managing the effects of Systems Structures Components (SSCs) ageing requires effective implementation of ageing management programme. This includes timely detection and mitigation of degradation mechanisms of SSCs so that their integrity and capability is ensured throughout the plant life. The aim of ageing management programme of SSCs is to identify the components affected by various degradation mechanisms and assess their condition vis-Ă -vis its integrity for continued service life. Therefore surveillance programmes of critical system components were devised based on OE and implemented effectively to identify the degradation mechanisms. 5.2 Methodology for assessing ISI effectiveness including (a)Determination of inspection effectiveness (b)Type of NDE being implemented in the ISI program and its associated Probability Of Detection (POD) for reliably detecting the expected degradation mechanism (c) determining degradation that may remain undetected after inspection and (d) Frequency of inspections coupled to growth rates for the targeted degradation mechanism(s). 5.3 Over the years, TAPS has accumulated four decades of experience in identifying various degradation mechanisms with various non-destructive testing methods; mitigation of the degradation by either repair or replacement with suitable material; monitoring the condition of SSCs with appropriate NDE techniques for continued service. A systematic methodology has been evolved for timely identification of degradation mechanisms, making appropriate modifications materials, procedures and environmental conditions vulnerable to degradation. TAPS has referred many of the documents with respect to inspection requirements including IAEA-TECDOCs [2,3,4] and AERB Safety Guides etc., 5.4 A comprehensive inspection programme has been prepared and followed while assessing the integrity & condition of critical components such as primary system piping, reactor pressure vessels, Vessels other than reactor pressure vessels etc., Even though most of the components are being inspected as per the plant in-service inspection programme in a specified inspection interval as indicated above, additional examinations have been planned covering the effects of ageing also. The components were examined using Journal of Non destructive Testing & Evaluation

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various non-destructive testing techniques; special examination techniques were also developed in some cases based on the operating experience feed back received from time to time from overseas BWRs. 5.5 In addition to the feedback from overseas BWRs on inspection & testing requirements, TAPS followed ASME Boiler & Pressure Vessels Code, Section-XI, 1998 edition in formulating the surveillance programme of class-1,2&3 system components. As per this code, a comprehensive inspection & testing programme was prepared and followed scrupulously for the 3rd & 4th inspection interval. Some of the generic issues were also identified and addressed along with the routine inspection requirements.

6. EXAMINATION OF CRITICAL COMPONENTS- HEALTH ASSESSMENT USING NDE TECHNIQUES: Following paragraphs indicates some of the critical components which were assessed for their integrity using various NDE methods for license renewal of TAPS units in the year 2006. A comprehensive inspection and independent assessment was done by various agencies of DAE and confirming the codal requirements based on the examination &test results. 6.1 Reactor Pressure Vessels (RPVs) & its associated components

One of the degradation mechanism associated with RPV is Irradiation/neutron Embitterment of vessel material including weld/HAZ. Tarapur reactor pressure vessels are designed for integrated neutron (energy > 1 Mev) exposure over Lifetime is 2.3x1018nvt. The specified designed life of vessels is 40 Effective Full Power Years (EFPY) and so far both the reactors have completed nearly 24 EFPYs. The health assessment of RPV includes Nozzles & its welds, safe end welds, RPV head welds, RPV welds and internal core support structures. In-Service Inspection enhances confidence in component performance. Periodic in-service inspection provides vital information in the form of flaw characterization for assessment of structural integrity of reactor pressure vessels. The intent of ISI is to detect any discontinuities or flaws in the areas of interest, which affects the functional requirement of the components for continued service. Calibration blocks were developed as per ASME Section XI. RPV is having corrosion resistant internal clad in as-deposited condition and hence, calibration blocks have been developed simulating the actual field condition. RPV head consists of 3 nozzles and entire head surface is accessible for both surface & volumetric examination. Based on the generic issue, high cycle thermal fatigue [6] with regard to Primary Feed water Nozzles, a detailed examination was carried out and subsequently monitored for its condition. The condition is found to be healthy and no degradation was noticed in any of the feed water nozzles. Similarly, some of the safe ends connected with the nozzles of Reactor core spray and reactor cleanJournal of Non destructive Testing & Evaluation

Fig. 2 : Reactor Pressure Vessel (RPV)

up system were found to have IGSCC type of indications. Hence, these safe ends were subsequently replaced with corrosion resistant nuclear grade material with modified welding procedures. Thus cause of SCC has been eliminated. The examinations as indicated above were completed during the four 10-year inspection interval have been completed and the condition of the Pressure vessel welds and associated components is satisfactory. Examination did not show any relevant indications either in LPT as well as in Ultrasonic testing. In order to assess the condition of internal clad of RPV head, a representative clad surface area has been identified â&#x20AC;&#x153;Surveillance areaâ&#x20AC;? which was also subjected to surface examination, did not show any abnormality. 6.2 RPV-Internal Core Support Structure

The core support structures & its welded attachments which provide lateral support to the fuel is vulnerable to IGSCC as well as IASCC type of degradation mechanisms. Some of the overseas BWRs detected these mechanisms during their in-service inspection programmes. Based on the OE, TAPS also had also conducted a comprehensive inspection using IVVI (In-Vessel Visual Inspection) systems especially developed using radiation resistant under water camera system coupled with remote handling manipulators. These manipulators were designed and developed jointly by NPCIL-HQ, DRHR/BARC and TAPS-site personnel. Vol. 10, Issue 1 June 2011

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Fig. 3 : Visual Inspection, Grappler Operated (GOM) Manipulator, Weld cleaning manipulator, Weld/HAZ UT manipulator for fillet welds and butt welds

The examinations were independently verified by QAD & IGCAR inspection personnel. Special VT qualifications were conducted for inspection personnel to meet the codal requirements. All the required examinations (VT-3) as per ASME SectionXI did not show any deficiency; hence the condition of reactor core support structures is healthy. 6.3 RPV closure studs

The closure studs of RPV at the main closure flange are susceptible to fatigue and Stress Corrosion Cracking (SCC) as well. The reactor pressure vessel closure studs are subject to high tensile stress during bolt-up, hydrostatic test and normal operation. The bolt-up is the most severe condition because the temperature and, therefore the fracture toughness are lower and the applied tensile loads are higher. The lower potion of the closure studs may be exposed to oxygenated BWR coolant water during bolt up. Also the threaded holes in the RPV shell flanges without bushings are subjected to wear because the flange material is considerably softer than the studs. These studs are subjected to volumetric examination with enhanced UT technique. 6.4 BWR pressure vessel nozzle and attachment welds

These welds are susceptible to IGSCC. High residual and applied stress, use of Alloy 182 weld material, and BWR coolant with high electrochemical potential can cause IGSCC. In addition to this, stainless steel cladding with very low ferrite can also cause Inter-Dendritic Stress Corrosion Cracking (IDSCC). GE-BWR reactor pressure vessel safe ends are fabricated from low alloy steel, carbon steel, stainless steel, or Ni-Cr-Fe alloy. IGSCC has been observed in many stainless steel and Alloy-600 safe ends [7] . IGSCC in stainless steel safe ends was caused by sensitization from welding or furnace post weld heat treatment. In view of this all the nozzle-safe ends were being examined by both surface (LPT) and Volumetric examination. In addition to this integrity of these components is checked during each system leakage tests Vol. 10, Issue 1 June 2011

as well as system hydrostatic tests as per the ASME section-XI requirements. 6.5 Class-1, 2&3 system pressure boundary components

The primary system pressure piping of Tarapur BWRs is mainly austenitic stainless steel either TP-304/TP-316 grade and is susceptible for IGSCC, which is identified as generic phenomenon of BWRs piping welds. Therefore, a comprehensive review was carried out and the vulnerable piping has been replaced with corrosion resistant/ nuclear grade piping (TP-316LN/L) and welding procedures were modified to eliminate IGSCC. Based on the experience TAPS had developed various interim repair methodologies and effectively implemented for limited period of operation. Subsequently all the temporary repairs were removed and re-installed with corrosion resistant material. 6.6 Metallic Containment pressure vessels & Concrete containment (CC) structures

As part of plant ageing management programme a comprehensive inspection programme was prepared which includes visual inspection of all piping components for any signs of corrosion, ultrasonic thickness gauging of pressure vessels and containment penetrations sealing areas pneumatic testing as integrity checks were also carried out. By adopting these systematic inspection methodologies

Fig. 4 : Tarapur Atomic Power Station (2006) Journal of Non destructive Testing & Evaluation

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Fig. 5 : Rehabilitation of feed water heaters with design Modifications

health assessment and integrity of the metallic containment structures and CC structures were ensured. In addition all the CC structures were assessed by using ultrasonic testing techniques (Velocity measurement) to ascertain the condition of civil structures. 6.7 Heat Exchangers, Pumps, Valves and other equipments (Nuclear & Conventional)

Special procedures were developed to assess the condition of all the critical heat exchangers, including main condensers, shut down cooling water Hx., reactor cleanup system Hx, plant cooling water system Hxs. In case of conventional systems, all the feed water heaters were replaced with modified designs to mitigate degradations mechanisms associated with heaters. These are (a) Inletend erosion, (b) Fretting (c) Shell erosion due to FAC (d) Nozzle erosion due to impingement attack. Vibration analysis of the rotating equipments is one of the NDE technique implemented effectively and high vibration related deficiencies were diagnosed and corrective actions were implemented to eliminate fatigue related degradation mechanism. As per the plant ISI document all the safety related motor Operated valves (MOVs) were subjected to internal examination to ascertain the condition of trim material for integrity. In addition to this MOV-signature analysis of critical safety related systems was also conducted to check the integrity and base line data was documented for reference after maintenance. All the equipment supports and piping supports were verified for its set points and hydraulic snubbers were examined (VT) in detail during the maintenance. 6.8 Piping components vulnerable to Flow Accelerated Corrosion (FAC) (Nuclear & Conventional systems):

Of late it has been identified that Flow Accelerated Corrosion/Flow Assisted Corrosion (FAC) is one of the degradation mechanisms with High Energy system piping components. Wall thinning in steel piping due to flowaccelerated corrosion FAC has resulted in pipe ruptures in high-energy (Enthalpy) systems, resulting in forced unit outages and posing great concern for personnel and equipment safety. The recent pipe rupture incidents in Journal of Non destructive Testing & Evaluation

Fig. 6 : Performance Demonstration Assessment (PDA) on FullScale mock-up at NDE facility.

overseas nuclear power plants in secondary cycle piping have alarmed Indian NPPs. In order to effectively implement the detection methodologies a full-scale mockup blocks were engineered and examination procedure for ultrasonic thickness measurement (UTG) were established. Other than UTG, various alternate NDE methods were also developed and engineered to detect FAC related degradation mechanisms more effectively.

CONCLUSION

The examination and test results observed so far did not reveal any abnormality in any of Class-1, 2&3 system components as well as the critical components as explained above. The present inspection methodology & examination techniques are sufficient to identify the component degradations very effectively. During the plant ageing management programme (AMP) all the safety related Vol. 10, Issue 1 June 2011

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structures, systems and components (SSCs) were assessed with respect to their condition and integrity. Measures were also taken to protect the structures and components against their degradation mechanisms. The availability of safety related/critical equipments has been improved to a greater extent. With the various design related modifications, the performance of station has been improved in terms of plant safety reliability as well as availability. Unit no.2 of Tarapur Atomic Power Station is running successfully and continuously for the past 478 days. This is an indication of systematic efforts that were put-in during the plant re-licensing programme and the methodologies followed meticulously by the plant management. It can be further concluded that the degradation mechanisms could be effectively detected & identified in time using various NDE techniques. These techniques were developed and implemented with in-house NDE facility and corrective measures were taken has enhanced plant safety, reliability and availability with which the units can run continuously for Long Term Operation (LTO) beyond its initial design life.

ACKNOWLEDGEMENTS The author is thankful to TAPS-1&2/NPCIL management in giving me the opportunity to publish the study carried out on the above issue. Various NDE techniques were developed with in-house NDE facilities of QA section at TAPS-1&2/NPCIL is possible with the management support. Also we are also thankful to Technical Committee of NDE -2010 in accepting the above technical paper in “National seminar & Exhibition on Non-Destructive Evaluation-NDE 2010”.

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REFERENCES 1. License renewal of boiling water reactors - experience at Tarapur Atomic Power Station -1&2 Published in “Nu-Power” Magazine; Volume 20 (2006) & Volume 21(2007), N.N.Pisharody, A.Ramu and B.L.Sharma. 2. IAEA safety Standards, safety Guide. NS-G-2.12 “Ageing management for Nuclear Power Plants”, (2009). 3. Assessment and management of ageing of major power plant components important to safety: BWR pressure vessels, IAEATECDOC-1430. 4. Assessment and management of ageing of major power plant components important to safety: BWR pressure vessel internals, IAEA-TECDOC-1431. 5. Assessment and management of ageing of major power plant components important to safety: Metal components of BWR containment systems, IAEA-TECDOC-1181. 6. Generic Ageing Lessons Learned (GALL) Report, NUREG-1801, Volume 1, USNRC. 7. IAEA-TECDOC-1470 “Assessment and management of ageing of major nuclear power plant components important to safety: BWR pressure vessels”, (2005). 8. Instruction manual Tarapur Reactor Vessel, Combustion Engineering, Inc. GE, C.E.Book No. 5363, September 1966. 9. ASME Boiler & Pressure Vessel code, Section-XI, In-service Inspection of Nuclear Plant Components. 10. AERB Safety Code. AERB/NPP/SC/QA (Rev.01), “Quality Assurance in Nuclear Power Plants” January 2009 11. AERB Safety guide no.AERB/NPP/SG/O-2" In-Service Inspection of Nuclear Power plants”March 2004.

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PROBE

Probe The world was recently a mute witness to an unforeseen natural calamity in Japan. Earthquake resulting in Tsunami of horrendous magnitude resulting in unprecedented devastation as well as ravaging a Nuclear power plant culminating evacuation of thousands of people from their land, creating a big question mark on their future. Several TV Channels relayed again and again the agony of the people and the waves progressing at great speed sweeping (moving) cars and houses as if they were just toys. The safety of Nuclear Power Plants have become a question mark. Several arguments are put forth for and against Nuclear energy as safety has become a main concern. What is the guarantee that an earthquake greater than 9 on Reichter Scale cannot occur (Circle of influence)? Earthquake happens due to movement of the tectonic plates of the earth. Tsunami is energy. Movement causes not only devastation. It is the basis of generating energy. The difference between useful energy and devastation is the magnitude. Move : To go or cause to go from one place to another. (Dictionary meaning). The molten core of the earth is constantly moving, Earth exhibits magnetism producing magnetic flux lines. The electron flows and hence electricity is generated. Change : To alter. When a movement takes place things are altered. So we can construe that change represents movement. The earth is moving. The universe is expanding. If the movements are stopped abruptly everything will collapse. Hence the oft repeated phrase “Change is permanent”. Hence we can deduce that change is the basis of life (energy flow). Life is built upon the fundamental principle of change and so we cannot resist it but adapt to it. Meditation helps the adaptation to the change. Meditation is the art of going into silence and observing the change (become a witness). By going into meditative silence we develop the “Art of Allowing it to Happen”. The Art of Allowing it to Happen can be divide into 7 areas. They are 1. Patience, 2. Possibility thinking, 3. Perception, 4. Peace with self, 5.Process, 6.Pondering over the past success, and 7. perseverance. Each area plays an important role in the Art of Allowing it to Happen. As more and more areas merge with each other the holistic picture develops. This state can be attained only through Practice, Patience and Perseverance and a wantonness to arouse the our souls and arise higher in the echelons of evolution. Please allow me to express each one in the coming issues.. Ram.