Fatigue Analysis Technique of Deepwater Steel Catenary Risers

With the advances in deepwater offshore industries, Steel Catenary Riser (SCR) offers advantages over others and has been widely deployed worldwide including Gulf of Mexico (GoM), West of Africa (WoA), and Offshore Brazil. SCR concept has been applied to all types of deepwater floaters. Among analyses and design criteria, fatigue is still the number one governing design criterion of the deepwater SCR regardless the floater types (SPAR, TLP, SEMI, and FPSO). Typical SCR fatigue analyses include first order and second order floater motion induced fatigue; vortex induced vibration (VIV), deep draft floater vortex induced motion (VIM) fatigue, floater vertical motion induced VIV, slugging fatigue, start-up and shut-down, installation, and other kinds of dynamic loading imposed to the SCR. This paper presents the state-of-art fatigue analysis requirement and technique of different kinds of fatigue analysis for deepwater SCRs. Detailed discussion is given to different kinds of fatigue damage of SCRs. Focus of fatigue analysis of each type of deepwater floater is pointed out. Detailed discussion is also given to the selection of SN curves, stress concentration factors, influence of sweet and sour service, and post-processing of fatigue sensitive welds. Several examples of SCR fatigue analysis are given to demonstrate the analysis techniques and practices.