Steel Catenary Riser Fatigue Assessment: Fracture Mechanics Approach Versus S–N Curve Method

In this paper, the fatigue resistance of a full-scale Steel Catenary Riser (SCR) girth weld is investigated using the Strength-Number of cycles (<i>S</i>-<i>N</i>) curve method based on weld formation quality and fracture mechanics approaches. The test results, presented in the form of <i>S</i>-<i>N</i> curves, are superior to the design curve E in BS 7608. Compared with the <i>S</i>-<i>N</i> curve determined by a resonant bending rig, the analytical fracture mechanics, i.e., engineering critical assessment (ECA) based on BS 7910, can provide a rational estimation of full-scale girth welds. For the numerical methods, the short crack growth phase is crucial to improving the accuracy and reliability of the assessment. For the girth weld with a concave root, the geometries of the weld cap are the predominant factors for fatigue life. Although the crack initiation site is always located at the outer surface regardless of the flushed or welded caps, the weld grinding treatment is still effective in promoting fatigue life.