Riser systems are subjected to complex loading spectra induced by sea states. The complex loading spectrum differs sensibly from the constant amplitude loading commonly adopted for qualification of the product (riser pipe and its girth welds).
The present work deals with numerical calculations of the actual loading spectrum experienced by a Steel Catenary Riser when adopted in different scenarios, Gulf of Mexico (GoM) and West of Africa (WoA). Sensitivity analyses have been performed to evaluate the influence on applied fatigue loading of different parameters, like: water depth, seabed stiffness, hang-off angle.
The variable amplitude loading, derived from in-service conditions, has been applied to laboratory scale, full thickness specimens from X65 SCR girth welds. The fatigue performance of these samples has been compared to analogous samples subjected to constant amplitude loading. The samples subjected to in-service loading conditions exhibited a lower fatigue performance than in constant amplitude.
To allow a comparison with common qualification procedure under constant amplitude, full scale testing of SCR girth welds have been performed on resonance machine by in-service loading spectra rearranged in constant amplitude blocks. Laboratory full thickness specimens have been adopted to compare the girth weld fatigue performance when subjected to the original cycle-by-cycle sequence and the in-blocks rearranged sequence.
