Finite element analysis of cyclically-loaded steel pipes during deep water reeling installation

Thick-walled steel pipes during their installation in deep water are subjected to combined loading of external pressure and bending, which may trigger structural instability due to excessive pipe ovalization. In the case of reeling installation method, prior to deep-water installation the pipe is subjected to cold forming associated with strong cyclic bending on the reel, resulting in the development of initial ovalitization and residual stresses, which may affect the pipe structural performance. Using advanced material models and finite element tools, the present study examines the effect of cyclic loading due to reeling on the mechanical behavior of thick-walled seamless steel pipes. In particular, it examines the effects of reeling on cross-sectional ovalization and the corresponding material anisotropy and, most importantly, on pipe resistance against external pressure and pressurized bending. The results show that cyclic bending due to the reeling process induces significant anisotropy and ovalization on the pipe. It is also shown that the mechanical resistance of reeled pipes is lower than the resistance of non-reeled pipes, mainly because of the resulting cross-sectional ovalization at the end of reeling process.