High And Low Cycle Fatigue Testing Of Reeled Steel Catenary Risers

摘要

A critical aspect to address in the design of SCRs is the in-service fatigue endurance. In recentrntimes, installation of complete SCRs by reelship has been discussed but not yet performed duernto concern over the plastic deformation of the welded pipe and it’s effect on fatigue performance.rnCoflexip Stena Offshore (CSO) therefore embarked upon a development programme torninvestigate the issue and to relieve these concerns held by the industry. The two and a half yearrndevelopment programme has been completed successfully, and has qualified the CSO ReeledrnSteel Catenary Riser (RSCR). This paper presents a summary of the fatigue testing results.rnThe fatigue testing was performed at The Welding Institute (TWI) near Cambridge, England. Thernprogramme included full-scale high cycle fatigue tests using a rig that is both cost effective andrnunique in its ability to apply a high mean axial stress, in conjunction with cyclic bending stresses.rnAnother highlight of the programme was an investigation of the low cycle high strain fatiguernperformance of CSO welds.rnAnalysis and evaluation of the fatigue data resulted in the following conclusions:rn· No noticeable difference exists between the high cycle fatigue performance of girthrnwelds that have undergone simulated reeling and those that have not.rn· The CSO girth welded SCR test specimens that have undergone simulated reelingrnachieve excellent fatigue performance in excess of currently proposed fatigue designrncurves I.e. API X’ and the UK E Classificationrn· Low cycle, high strain fatigue testing was performed to provide additional confidence inrnthe quality of CSO welds. In all cases, a significant number of cycles were appliedrnbefore failure occurred.rn· Reeled girth welded pipe, fabricated and installed as per methods and procedures of thernCSO development programme, are qualified for use in dynamic SCRs.