IIW White Paper

TOFD

Phased array

Quality levels ISO 5817

Testing levels ISO 10863

Acceptance levels ISO 15626

Acceptance levels ISO (not available)

Testing levels

B C D

C

1 2 3

B A A

/ / /

B as a minimum A as a minimum

Figure 5.17 Example of levels to apply for TOFD or phased array in agreement with ISO 17635

When the replacement of a NDT technique by another one is not defined within a standard or a construction code, the approach suggested in the IIW V-1502-11 document can be applied. For a specific weld on a given welded construction, the proposed actions are to carry out a systematic analysis called OPC consisting in assessing: The Occurrence of flaws liable to appear while welding (in the conventional risk assessing analysis, this represents the probability of the feared event). The detection Performance of such flaws for each of the used NDT technique/method. The Consequence(s) liable to result from the non detection of these flaws by the NDT technique applied and the alternative one when using construction weld or welded equipment. After this analysis, risks are assessed combining parameters by means of a set of rules allowing comparison of, at least qualitatively, the NDT techniques. This approach is advantageous since it is global and allows a better assessment of the criticality resulting from a undetected flaw and thus to compare the risk induced by changing the NDT method. IIW Sub Commission VC has prepared a Handbook published in 2012 by DVS media GmBh (Handbook on the examination of austenitic and dissimilar welds – ISBN 978-3-87155-969-3). This handbook covers the ultrasonic inspection of austenitic butt welds. The objective of the handbook is to provide all those involved in the volumetric examination of austenitic welds with the background knowledge necessary to perform effective ultrasonic inspections of austenitic welds and to inform them of the limitations caused by the acoustic properties of the material. The handbook is particularly addressed to technicians, engineers and scientists involved in austenitic weld inspection. It should be of particular value to those responsible for preparing inspection procedures, but it does not provide a detailed inspection procedure for any particular weld. The handbook deals mainly with butt welds but the theory and practice presented can be applied to welds with more complex geometries providing the additional difficulties of the geometry are taken into account. The handbook also covers dissimilar-metal welds, which are generally more difficult to examine than a straight butt weld due to the buttering layer. The scope of the handbook includes fabrication and in-service inspections. ISO 22825 was recently revised and issued in May 2012 and specifies the approach for the development of procedures for ultrasonic inspection of welds: stainless and austenitic steel - nickel-based alloys - duplex - dissimilar metals. The objectives of the tests may differ, for example: assessing the level of quality ( manufacturing) or detection of specific indications produced during the service. 5.3.2.2 Ultrasonic testing of austenitic welds The need to test austenitic welds by means of ultrasonic testing is growing in various industry sectors such as nuclear, LNG tank storage and oil and chemical industries.

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