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Development of flaw acceptance criteria for welded joints in PE pipes

 

Papers # 2016 Berlin

 the inspection of butt fusion and electrofusion joints in polyethylene (PE) pipes. Depending on the technique and inspection procedure, various types of flaw, including discrete planar lack of fusion, particulate contamination, voids, cold fusions and pipe under-penetration can be detected. However, the usefulness of these techniques is limited due to the fact that there are currently no acceptance criteria available for the size or concentration of any detected flaws. Some work is being carried out in ASME in the US to use the same fracture mechanics approach that is used for metals to predict the critical sizes of lack of fusion flaws and voids. However, since polyethylene is very ductile, this methodology is not suitable for this material and the results will be very conservative. In addition, this approach is not applicable to either particulate contamination or cold fusions.

This paper presents a methodology for determining flaw acceptance criteria in PE pipe joints using experimental data from mechanical testing, by comparing the results on joints containing flaws of known size or concentration with results on unflawed joints. With this approach it is important that the mechanical tests used are sufficiently discriminating to be able to distinguish between flawed and unflawed joints. For this reason, this paper also describes work that has been carried out to compare different mechanical tests on both butt fusion and electrofusion joints in PE pipes in order to determine which tests are the most suitable for determining flaw acceptance criteria. 

Related keywords : PE, NDT, flaws, acceptance criteria, mechanical testing.
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