Guidance for Fatigue Design and Assessment of Pipeline Girth Welds

Risers and sections of pipeline in free-span can be subjected to cyclic loading from flow-induced vibrations and other fluctuating forces leading to fatigue loading of the structure. Single-sided welds are of particular interest, however current design codes take a pessimistic view of their fatigue performance. Improvements in the quality of the finished weld produced by modern pipeline welding technology, and indeed advances made in knowledge about fatigue of such welds, mean that revision of the design guidance is now warranted. This paper reviews the fundamental basis of the existing S-N curves used for North Sea applications and considers their applicability in the light of research on fatigue of girth welds. Based on the review, proposals are made for revised fatigue design rules for girth welds in pipelines.