NABL 108
NABL
NATIONAL ACCREDITATION BOARD FOR TESTING AND CALIBRATION LABORATORIES
SPECIFIC CRITERIA for NON-DESTRUCTIVE TESTING LABORATORIES
ISSUE NO : 02 ISSUE DATE: 28.03.2008
AMENDMENT NO : 00 AMENDMENT DATE: --
AMENDMENT SHEET Sl
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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
Specific Criteria for Non-Destructive Testing Laboratories Issue Date: 28.03.2008 Amend No: 00 Amend Date: --
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Contents S.NO.
SECTION
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Amendment Sheet
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Contents
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1.
Introduction
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2.
Classes of tests
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3.
Criteria for Accreditation
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4.
Specific Criteria
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National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
Specific Criteria for Non-Destructive Testing Laboratories Issue Date: 28.03.2008 Amend No: 00 Amend Date: --
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1
Introduction
Laboratories Accreditation activities are administered under the direction of the National Accreditation Board for Testing and Calibration Laboratories (NABL) and involving Technical Committees and Accreditation Committees as recommending bodies. NABL assessment system is based on ISO/ IEC 17011: 2004 and APLAC/ ILAC recommendations. This document on “Specific Criteria for Non-Destructive Testing Laboratories” is one of a series of supplementary booklets of the document ISO/ IEC 17025:2005 “General Requirements for the Competence of Testing and Calibration Laboratories”. Non-Destructive is one of the following fields of testing in which NABL currently gives accreditation. Fields of Testing •
Biological
•
Chemical
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Electrical
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Electronics
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Fluid Flow
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Mechanical
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Non-Destructive
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Optical and Photometry
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Radiological
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Thermal
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Forensic
The field of NDT covers examination of materials, components and assemblies by means of non-destructive testing techniques at field sites, in workshops and in laboratories. It is basically applied to examine the material quality and to determine internal construction and dimensions. The information contained in this document must be read alongwith the document ISO/ IEC 17025:2005.
National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
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2
Classes of Tests
The field of NDT is divided into two groups ‘metals and alloys’ and ‘building materials’. Each group is further classified into subgroups (classes). The classes of test are given hereunder. Applications for accreditation may be made for one more classes of tests. 2.1
Metals and Alloys
2.1.1
Eddy Current Testing Conductivity variation measurement Detection of surface and sub-surface defects Dimensional variations Irregularities in microstructures Variation in chemical composition
2.1.2
Emerging Areas Testing Acoustic emission Holography Infra – red applications Leakage flux techniques Microwave applications Neutron radiography Real time radiography
2.1.3
Leak Testing Argon leak test Detection of leak by pressure rise or pressure drop Halogen leak test Helium leak test Radio-isotope tracer leak test Ultrasonic leak test
National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
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2.1.4
Magnetic Particle Testing Detection of sub surface flaws Detection of surface flaws
2.1.5
Penetrant Testing Detection of surface flaws of materials with visible dye Detection of surface flaws of materials with fluorescent dye
2.1.6
Radiography Testing Detection of flaws with radio isotopes Detection of flaws with X-rays
2.1.7
Ultrasonic Testing Corrosion survey Detection of internal flaws Detection of surface and sub surface flaws Thickness measurements Measurement of variation in material properties
2.1.8
Under Water Testing Corrosion survey Detection of internal flaws Detection of surface and sub surface flaws Thickness measurements
2.2
Building Materials – Reinforced Concrete Structures
2.2.1
Ultrasonic Pulse Velocity Tests
2.2.2
Rebound Hammer Test
2.2.3
Cover Meter Test
2.2.4
Half Cell Potential difference test
2.2.5
Carbonation test
2.2.6
Deflection measurement data (Load Test)
2.2.7
Crack width measurement in reinforcement concrete structures
National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
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3
Criteria for Accreditation
This section provides interpretations of some of the clauses of ISO/ IEC 17025: 2005. 3.1
Staff The Board needs to satisfy that testing services have at least one person who has the competence, time and authority to achieve adequate technical control of its operations. A large testing service may need more than one such person.
3.2
Staff Structure The Board classifies non-destructive testing staff into three tiers (categories): i.
Officers exercising technical control – those who are responsible for control of non-destructive tests, including the drafting of specifications for meeting requirements of standards and codes.
ii.
Officers who, under direction, can take responsibility for performance of specific procedures; and
iii.
Assistants who perform routine technical an non-technical duties, under close supervision.
3.2.1
Officers Exercising Technical Control The officers must have authority and time for effective control of the nondestructive testing operations that they superintend. They should have: i.
Sound knowledge of, and expertise in use of, applicable non-destructive testing techniques;
ii.
Knowledge of relevant materials, manufacturing processes and service conditions;
iii.
Experience and ability in interpretation of data from relevant service conditions;
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iv.
Experience in use of relevant codes and standards, and ability to prescribe suitable procedures in the absence of appropriate codes and standards;
v.
Ability to prepare routine and critical reports; and
vi.
Ability to control quality of performance of non-destructive tests.
Persons controlling a significant range of non-destructive tests should have tertiary qualifications in science or engineering, adequate training and have the level of knowledge that would enable them to gain the relevant ISNT/ ASNT/ equivalent Level III qualification. A person who does not possess formal tertiary qualifications may be considered acceptable to exercise technical control if he has all the attributes as detailed above, together with compensating practical experience. 3.2.2
Officers Responsible for Carrying out Tests as per Specific Procedures Persons who, under direction, take responsibility for performance of specific tests as per procedure should have at least: i.
Experience in performance of applicable non-destructive tests;
ii.
Experience in use of relevant codes and standards, and ability to apply appropriate codes and standards to the requirements of specific projects;
iii.
Experience and ability in interpretation of data from non-destructive tests;
iv.
Ability to maintain job records and to prepare routine reports.
In addition, they must have a background of knowledge and experience which enables them to understand the response for the purposes of the operations for which they are responsible. They should have a level of knowledge that would enable them to obtain the relevant ISNT/ ASNT/ Level II qualification. 3.2.3
Assistants Assistants must have knowledge and experience commensurate with the duties that they are required to perform.
National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
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3.2.4
Approved Signatory The role of NABL signatory is to ensure the reliability and adequacy of the test document. Any officer of a registered testing service who is competent to make a critical evaluation of test results, and occupies a position in his organization’s staff structure which makes him responsible for the adequacy of test results related, is eligible for approval as a signatory for test documents. An approval may be limited to specific tests, or may be granted for all tests for which the testing service is registered. The criterion of “competence in critical evaluation of test results” may extend signatory approval well down the staff scale. When non-destructive testing is performed away from the base and prompt on-the-spot reports are required, it is obviously necessary for the officer Incharge on site to be an approved signatory.
3.2.5
Qualifications NABL recognizes the qualifications granted by ISNT/ ASNT or equivalent through its Qualifying Board as evidence of the possession of adequate general knowledge of a particular NDT method.
3.3
Equipment and Housing A testing service must be fully equipped for performance of all tests for which accreditation is sought. If tests are performed confirming to codes or standards which define particular items or types of equipment becomes mandatory. All equipment must be maintained in good condition. The mobile laboratories must provide facilities comparable to fixed laboratories. Adequate storage facilities must be available for equipment and records. 3.3.1
Magnetic Particle and Penetrant Testing. The performance of equipment and materials used for magnetic particle testing and penetrant testing must be checked periodically.
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3.3.2
Eddy Current Testing. Eddy current testing instrument of adequate sensitivity over wide range of frequency must be available. The equipment should have stable electronic characteristics & should be checked for performance with standard calibrators as per specific codes. The derive for tubular product testing system should have stable response without creating undue vibrations during testing. Proper recording media like strip chart, oscilloscope trace, tape recording or PC base data acquisition systems should be available. Adequate numbers of variety of test coils (encircling, bobbin, probe or flat coils) should be available.
3.3.3
Radiographic Testing. X-ray equipment and radioactive sources must be suitable for the materials to be examined. They should cover the expected thickness range and the shape, nature and location of items likely to be submitted for examination. Required accessories such as image quality indicators and intensifying screens must be provided. Reference density standards or a densitomater must be available for measurement of film density. Facilities for processing films consistently at a high level of quality must be available. They must be adequate for the number of films to be processed. Procedures must be followed which ensure that the processing remains satisfactory. Facilities must be available for viewing radiographs under optimum conditions of illumination. Viewing facilities should be located where operators are free from disturbance.
3.3.4
Ultrasonic Testing. Ultrasonic equipment of appropriate sensitivity and resolution for each application must be available. Equipment must be checked for performance in accordance with relevant standards. Records of checks must be kept. A separate work area for calibration and development work is desirable.
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3.3.5
Leak Testing Leak testing instruments like helium leak detector, halogen leak detector, ultrasonic leak detector, pressurise or drop test set up, bubble emission test set up etc. of adequate sensitivity must be available. In case of helium leak detector, standard leak calibrator, sniffer probes, spray probes, capillary leak calibrator etc., adequate spares like maintenance tool kit containing set of ‘0’ rings, filaments, discharge gauge liner tubes, mechanical & diffusion pump oil etc., must be available. Helium gas cylinders, liquid nitrogen etc. should be available. The detector must have a stable & fast electronic meter response when calibrated with a calibrator & tested over many hours of testing. Calibrated pressure gauges, tube- fittings etc. should be available for sniffer test. Adequate test space area should be available for testing long jobs like tubes, heat exchangers, vessels etc.
3.4
Operating a Testing Service Sound management is essential if a testing service is to operate at a satisfactory standard. Particular attention should be given to the following aspects of management. There must be clearly defined and recognisable lines of authority and responsibility within the organisation, each officer being aware of both the extent and limitations of his own responsibility. Job records must include instructions for each job. Records of field jobs must include evidence of checking of records and reports of senior staff during supervisory visits. All field work must be under effective technical control. 3.4.1
Test Procedure When the code or standard for a project specifies a test procedure, that procedure must be followed exactly. When the test procedure is not specified the officer incharge of the job must select an appropriate documented/ written test procedure. A copy of the written/ documented test procedure must be available to the staff performing the test.
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Any variation from a standard test procedure must be noted and reported in test documents. Each testing service must have a routine arrangement for keeping codes and standards upto date. Its reference library should include recommended particles, codes for identification of indications and a selection of reference books. 3.4.2
Records System An adequate records system is essential. It must contain sufficient information on each test to permit a repeat performance. Identification of each test article, the client’s instructions, the test procedure, all test data and the test results must be recorded. All records, including radiographs, must be traceable to the article under test. When record such as worksheets and viewing sheets are checked, they must be signed or initialed by the checking officer as an indication that this has been carried out. Signed copies of test documents and all related records must be retained for not less than five years after completion of the work involved. All the test records must be kept confidential and they may be accessible to the competent authority; and client only if needed. Radiographs must remain the property of the testing service. If required radiographs may be taken by the client and there should be record/ signature to that effect and if the client is not taking them, these should be kept for 5 years.
3.4.3
Interim and Final Reports There are many circumstances in which clients must have an immediate report of results of non- destructive testing examinations. Irrevocable decisions are frequently made on the basis of these immediate reports. This has led to the practice of issuing, in some circumstances, “interim” and “final” reports.
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When a testing service is required to issue interim and final reports, the NABL endorsement must not be applied to the final report unless the corresponding interim reports have also been endorsed. 3.4.4
Vision It is the responsibility of the testing authority to ensure adequacy of the natural or corrected vision of the staff responsible for viewing non- destructive indications.
3.5
Interpretation of Test Data Thorough training of all staff engaged in interpretation of test data is essential. Each interpreter must have all available information on the article under examination. 3.5.1
Magnetic Particle and Penetrant Testing Operators using surface methods must be fully competent to interpret indications for the specific work on which they are engaged. Regular checking of the competence of each operator is essential.
3.5.2
Eddy Current Testing Operators using Eddy Current test instrumentation must be well trained & preferably certified by ISNT/ ASNT. The signals due to spurious reasons like – noise, vibration, lift- off, baffles/ support plates etc. must not be taken as defect indications. On the other hand, genuine defect signals should not be missed. The controlling officer shall have the authority to give final interpretation.
3.5.3
Radiographical Testing Check Viewing Systematic check- viewing of interpretation of radiographs on each assignment is essential. The percentage to be check- viewed will depend on the nature of the work and the experience of the interpreter. The signatory must participate personally in the viewing.
National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
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Separate accreditation can be given for either the taking and processing of radiographs or the interpretation of radiographs on the following conditions:
i)
An endorsed reports covering the taking and processing of the radiographs shall be available.
ii)
The interpreter shall be provided with a copy of the job record covering the taking and processing, and shall have the ability to assess the quality of the radiographs.
iii)
Standards shall be available which specify the radio- graphic technique and the product quality requirements. The radio- graphic technique used and the quality of the radiographs produced shall comply with the requirements of the standards.
iv)
Both laboratories shall have adequate radiographic viewing equipment and film density standards.
v)
The interpretation report shall identify the laboratory which produced the radiographs, and shall note the serial numbers of the endorsed reports covering the taking and processing of the radiographs.
vi)
Radiographs shall remain the property of the laboratory responsible for taking and processing. Sensitivity Compliance or otherwise each of radiograph exposure with sensitivity requirements must be recorded. The sensitivity achieved in each exposure outside the specified range, must be recorded and reported, but if all exposures are within the specified range, it is sufficient to note this in the report.
3.5.4
Ultrasonic Testing The quality of an ultrasonic examination depends largely on the knowledge and experience of the person performing the work. Complex one- off ultrasonic examinations may be conducted only by people with ISNT/ ASNT ultrasonic qualification or equivalent qualifications, together with appropriate experience.
National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
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The expression “complex or one- off� covers most ultrasonic examinations. The only exceptions are ultrasonic thickness measurements and routine ultrasonic flaws detections made in circumstances in which it is possible for the controlling officer to define the test procedure in detail and to specify the circumstances in which the operator must seek assistance or advice. 3.5.5
Leak Testing Only experienced operator well versed in operating the leak detectors like helium leak detector, halogen leak detector, ultrasonic leak detector will be employed. The interpretation of test result data will be carried out by experienced and preferably certified officer.
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4
Specific Criteria
This section gives the specific details applicable for the tests to be conducted by the laboratories seeking accreditation. 4.1
Control of Non Destructive Test Systems Assuring confidence in the results of non- destructive testing necessitates various controls on the measurements or examination process, as listed below:
i)
Specifying the physical characteristic to be determined or examined, and any acceptance/ rejection criteria.
ii)
Setting a level of discrimination and measurement uncertainty that is adequate to give confidence in the examinations and acceptances/ rejections concerned.
iii)
Ensuring, through traceable calibrations (or by other methods of measurement correlation, where the concept of traceability is not directly applicable) that equipment is maintained so as to provide the appropriate discrimination and measurement uncertainty.
iv)
Taking any other necessary steps to ensure that test results are reproducible, within the level of discrimination and measurement uncertainty claimed.
v)
Meeting the calibration and traceability requirement of any standard or other relevant specification.
4.2
Eddy Current Testing 4.2.1
An ongoing record of the performance of eddy current test sets must be maintained.
4.2.2
For portable equipment, a reference ‘sensitivity block’ dimensionally certified by the manufacturer will normally be used for checking the response of the equipment to known flaws. For specilalised applications, such as tube testing, reference standards shall be prepared from material of the same alloy, temper and nominal dimensions as the product to be tested. The dimensions of holes or notches and the thickness of the calibration piece must be certified by the manufacturer or established in-house by means, which are traceable to National Standards.
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4.2.3
Where eddy current examination is used for sorting of materials or products, reference test standards shall be prepared from materials of the same alloy(s), heat treatment conditions and nominal dimensions as the materials or products to be tested.
4.2.4
Reference test standards shall be carefully maintained and properly identified.
4.2.5
The calibration of reference measuring equipment used for in- house dimensional verification shall be recorded.
4.3
Emerging Areas Testing The guidelines for accreditation of tests under this category will be provided on case by case basis as applications are received.
4.4
Leak Testing 4.4.1
The equipment used for leak testing shall have adequate sensitivity to detect the leaks as specified in the work order or the specification. Depending on the leak tightness required in the job, a suitable leak testing method (from amongst many) will be selected.
4.4.2
Leak testing should preferably be carried out in two ranges- gross leak testing & fine leak testing. Examples of gross leak test are, pressure change test/ bubble emission test and for fine leak test are- helium leak test, halogen leak test etc.
4.4.3
Any leak test must be carried out as per some standard code like BIS, ASTM, and ASME etc. The personnel carrying out the test must preferably be certified.
4.4.4
The acceptance criteria giving the minimum acceptable leak rate in the job with the particular technique of leak test should be clearly spelt out in the specification.
4.4.5
Accessories of helium leak detection, like- sniffer, spray probe, pressure gauges, liquid- nitrogen should be available.
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4.5
Magnetic Particle Testing 4.5.1
The solids content of magnetic inks must be checked as specified in National/ International standards. In case of aerosols, a representative sample from each batch shall be tested.
4.5.2
When using fluorescent inks/ powders, the intensity of black light at the test surface should be checked as frequently as necessary to monitor possible deterioration of the illumination. Where grimy, dusty or other contaminating environments are involved, checking should be carried out each time the equipment is used. This will require the use of black light meter complying with national standards.
4.5.3
Black light meters and ammeter shall be calibrated at twelve monthly intervals by a manufacturer or appropriate services organisation.
4.5.4
The ambient white light level should be checked at least once every three months where illumination is controlled on a long term basis and should be checked from time from which the equipment is used in situations where illumination may be variable from test to test (e.g. in day light conditions). These checks will require the use of a white light meter.
4.6
Liquid Penetrant Testing 4.6.1
The liquid penetrant shall be suitable for the application for which it is intended. A specific statement by the manufacturer is required, but this may be in the form of a letter, certificate or technical leaflet or may be included in the labelling of the product. The relevant national/ international standard, provisions of which are applicable should be mentioned.
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4.6.2
In fluorescent penetrant examination areas, the intensity of black light illumination at the inspection surface should be checked as frequently as necessary to monitor possible deterioration of the illumination.. Where grimy, dusty or other contaminating environments are involved, checking should be carried out each time the equipment is used.
4.6.3
In non-fluorescent i.e. colour contrast penetrant examination areas, the intensity of illumination at the inspection surface should be checked at least once every three months where illumination is controlled on long term basis. It should be checked each time the equipment is used, in situations where illumination may be variable from test to test (e.g. in daylight conditions). The checks will require the use of a white light meter.
4.6.4
White light meters shall be calibrated at twelve monthly or shorter intervals if appropriate by a manufacturer or appropriate service organisation.
4.6.5
For both types of meter, the calibrations must be evidenced by certificates from the appropriate service organisation.
4.6.6
Where the temperature of a bath or a test is of extreme values, quoted in procedures, or other relevant specifications, the temperature shall be monitored using a national standard stamped thermometer.
4.6.7
4.7
The laboratory should preferably have standard calibration blocks.
Radiographic Testing 4.7.1
The sensitivity of a radiograph shall be established by means of an IQI or penetrameter, appropriate to the material and thickness.
4.7.2
Where the radiography is being performed in accordance with an agreed Standard or Code, the requirements of the Standard or Code with respect to the type and location of the IQI or penetrameter shall be strictly observed. IQIs will be manufactured to meet the requirements of national standards.
4.7.3
The density of radiographs shall be ascertained using densitometers or film density strips.
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4.7.4
Densitometer shall be checked and linearity should be calibrated against a reference density strip. Hand-held densitometers must be checked each time they are used as part of the setting up procedure against the level of background illumination on which they will be used. Linear calibration shall be checked every twelve months and recorded.
4.7.5
Reference film density strips shall be uniquely identified and traceable by certificate to a National Standard of Measurement.
4.7.6
Reference film density strips shall carry a manufacture’s certificate less than five years old.
4.7.7
Film density strips used, as comparators will have the density of each step ascertained using a calibrated and certified densitometer and recorded either directly onto the film or onto a card strip permanently attached to the film. The date of first calibration shall be recorded on the strip. All film density strips which are more than five year old, or which have been subject to undue wear, shall be taken out of use and destroyed.
4.7.8
Film density strips are subject to discolouring or fading and must be carefully maintained and stored.
4.7.9
Where appropriate, thermometers must be used to check chemical process or air dryer temperatures. The accuracy of working thermometers shall be checked.
4.7.10 The overall effectiveness of radiographic processing carried out by the laboratory shall be monitored every three months, or more frequently according to the throughout of work, by comparison of results of tests on standard test pieces. 4.7.11 The focal characteristics of an X-ray set are critical to the definition and sensitivity of radiographs. The laboratory shall monitor any significant changes in these focal characteristics, by comparison of results of tests on standard test pieces, carried out over an appropriate period of time (e.g. once per year, for the lifetime of the set). 4.7.12 A formal procedure for determining and monitoring the focal characteristics of an X-ray set is provided by the pin- hole method (ASTM specifications). National Accreditation Board for Testing and Calibration Laboratories Doc. No: NABL 108 Issue No: 02
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4.7.13 Each isotope used shall be accompanied by a decay chart for that isotope together with an official record of dimensions, which must be certified by the manufacturers of the isotope. 4.7.14 Safety aspects are to be adhered to as required by the stipulation of NABL Specific Criteria for Radiological Testing. 4.8 Ultrasonic Testing 4.8.1
Ultrasonic calibration blocks should be used to set up the assembly of probe and sensory electronics, each time the equipment is used. The blocks shall be manufactured
in
accordance
with
the
appropriate
specification
and
conformance with the requirements shall be evidenced by a manufacturer’s certificate. 4.8.2
One set of calibration blocks shall be designated as master blocks and shall be dimensionally calibrated with traceability established to National Standards at intervals not exceeding five years.
4.8.3
Dimensional calibration shall be evidenced by a certificate. The calibration of reference measuring equipment used for in- house dimensional calibration shall be evidenced by a certificate.
4.8.4
Working standard calibration blocks shall be verified at intervals not exceeding two years as follows: Visual Examination for deterioration such as corrosion or mechanical damage. By comparison with corresponding Master Calibration Block, using a calibrated ultrasonic test set Attenuation check Radio and other dimensional checks.
4.8.5
Ultrasonic equipment sets shall be verified in accordance with National Standards daily, or each time the equipment is used including: Visual checks for damage Linearity of time base Calibration of time base Linearity of equipment gain
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4.8.6
The performance characteristics of ultrasonic probes shall be checked in accordance with national standards as appropriate: Probe index Probe beam angle Probe beam alignment Frequency of checking may depend on volume of work.
4.8.7
Ultrasonic flaw detectors shall be calibrated at intervals not exceeding twelve months in accordance with national standards and as appropriate, including: Linearity of time base Linearity of amplifier Accuracy of calibrated attenuator
4.8.8
Calibrated must be evidenced by a certificate provided by the manufacturer of the equipment or an established service agency. The calibration of reference measuring equipment used for in- house calibration shall be traceable to national standards and, where practical, must be evidenced by an official certificate.
4.9
Underwater Non-Destructive Testing The following specific requirements apply: i)
In general, for underwater ultrasonic examination, ultrasonic thickness measurement and magnetic particle testing, the operator/ diver must have signatory approval for these tests if he is responsible, below surface, for the operation of these tests.
ii)
In cases where these examinations are controlled and monitored on the surface by another NDT operator holding signatory approval for the relevant tests, the above requirements may be waived off provided the diver conducting the tests holds an appropriate underwater NDT qualification.
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iii)
It is the responsibility of the NDT testing service to ensure that all divers supplied to them by diving companies satisfy the criteria set out in (i) or (ii) above.
iv)
The operators nominated as exercising technical control must satisfy the criteria detailed in section 3.1 of this document. Additionally, the officers exercising technical control over ultrasonic flaw examinations must be experienced in this area and have underwater NDT experience.
v)
Where conditions (i) to (iv) above do not apply, then registration will be considered only if the laboratory can demonstrate both adequate technical control over testing and expertise in the areas of test requested.
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National Accreditation Board for Testing and Calibration Laboratories 3rd Floor, NISCAIR 14, Satsang Vihar Marg New Mehrauli Road New Delhi – 110 067 Tel.: 91-11 26529718 – 20, 26526864 Fax: 91-11 26529716 Website: www.nabl-india.org