Development of Girth Weld Flaw Assessment Procedures for Pipelines Subjected to Plastic Straining

摘要

Numerical finite element analyses (FE) have been undertaken of circumferential flaws in the girth weld of a pipeline subjected to plastic straining simulating installation by reeling, and the J driving force curves derived. These were then compared with J driving force curves derived using the guidelines described in DNV-RP-F108 intended for installation methods involving repeated plastic straining. The assessment procedure is based on BS 7910 FAD methods. Strains up to 2% were considered. Analyses were undertaken for surface breaking weld root flaws located at the weld fusion boundary. The pipe was nominally to API 5L Grade X65 strength, with a 323.9-mm diameter (12 3/4-in) and 20.6-mm wall thickness. Conclusions are drawn concerning the conservatism in flaw assessment procedures conducted to DNV-RP-F108 and the treatment of welding residual stress.