Fatigue Crack Growth Assessment of Pipeline Steels and Girth Welds

Fatigue test specimens were prepared and tested with an API 5L X70 spiral welded pipe steel and girth weld. For a few selected specimens, two unloading compliance techniques (elastic compliance and back-face strain compliance) were applied simultaneously to a single specimen for direct comparisons of in-situ crack size estimation. This paper also includes fatigue crack growth rate (FCGR) data of other pipe steels and welds available in the literature. It was observed that most FCGR curves of pipeline steels (X65∼X100) remained within the BS 7910 mean and upper bound design curves in the Paris region. On the contrary, the fatigue crack growth rate of the X42 pipeline steel from a reference was high — a very steep slope of the FCGR curve, crossing over the BS 7910 design criteria. It was noted that the FCGR of austenitic stainless pipe steel and girth weld obtained from Arora et al. (2014) showed a very excellent fatigue property.