A Master S-N Curve Representation of Subsea Umbilical Tube Weld Fatigue Data

摘要

In this paper, some of the available duplex and super-duplex stainless steel umbilical tube fatigue data are analyzed using an equivalent nominal stress range parameter, which shares a great deal of similarity to the one used in the 2007 ASME Div 2 Code. The proposed fatigue parameter consists of nominal stress range, a size correction term Jr^with RT being the tube radius and tbeing tube wall thickness, and a stress ratio term (I - R)with R being applied stress ratio. With it, the available girth weld fatigue test data are shown to collapse into a narrow band. The equivalent nominal stress range parameter is also shown to be effective in correlating seam weld data collected from seam-welded umbilicals, but with a different slope in log-log based S-N plot. Coiling/uncoiling low-cycle effects can be addressed by introducing a pseudo elastic nominal stress definition. Miner's rule can be used to combine both coiling/uncoiling effects with subsequent high-cycle fatigue loading.