基于有限元法的深水钻井隔水管压溃评估

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

压溃是深水钻井隔水管主要的失效模式之一,现有的理论算法无法考虑缺陷对隔水管压溃的影响。因此,考虑磨损和腐蚀对隔水管压溃性能的影响,建立了深水钻井隔水管非线性压溃有限元评估方法,并与深水钻井隔水管压溃理论评估方法进行了对比。结果表明:有限元压溃分析方法与API RP 2RD、DNV OS F101推荐算法的分析结果基本一致,验证了隔水管压溃有限元分析方法的准确性;压溃过程的初始阶段隔水管发生弹性变形,当内外压差达到临界压力时,隔水管开始发生塑性变形,弹性阶段向塑性阶段的突变点即为隔水管压溃临界点;完好隔水管压溃后截面呈扁平状,缺损隔水管压溃后截面呈锥形;随着隔水管缺陷尺寸增大,隔水管临界压溃压力逐渐降低。

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.