Collapse Assessment for Deepwater Drilling Risers on the Basis of Finite Element Method

Collapse is one of the major failure modes in deepwater drilling risers. In the existing theoretical algorithm, the effects of defects on riser collapse cannot be considered. This paper describes the effects of wear and corrosion on the potential for riser collapse, sets up a method of finite element evaluation for nonlinear collapse of deepwater drilling risers, and details how the verification and analysis for the method were carried out. It showed that the analysis results of finite element stress analysis coincided well with that recommended by API RP 2RD and DNV OS F101, the accuracy of finite element analysis method for riser collapse was verified. At the initial stage of riser collapse, risers were elastically deformed. After the difference between internal and external pressures reaches a critical value, risers were plastically deformed. The point of abrupt change from elastic to plastic deformation is the critical point of riser collapse. After collapsing, the original intact risers became flat and some risers that had defects initially became cone-shaped. In addition, the critical collapse pressure of risers decreased gradually with the increase of the defect sizes of risers.