Modelling of mechano-electrochemical interaction at overlapped corrosion defects and the implication on pipeline failure prediction

Defect assessment is essential at determination of fitness-for-service of pipelines. While various codes and methods have been developed, none of them focuses on overlapped corrosion defects, especially the investigation of local mechanical-chemical interaction at the overlapped defects. In this work, a finite element-based mull-physics one-way coupling model was developed to simulate and determine the mechano-electrochemical (M-E) interaction at overlapped corrosion defects on an X46 steel pipeline. It is found that the presence of overlapped corrosion defects results in a local stress concentration and enhanced M-E interaction effect on corrosion defect growth. The maximum stress always generates at the corner of the bottom defect. The enhanced M-E interaction causes an accelerated corrosion at the bottom defect, resulting in the rapid defect growth to cause pipeline leaking. The geometry of corrosion defects, especially the defect depth and length, affects local stress concentration and the M-E interaction. With the increasing length and depth of either top or bottom corrosion defects, the overall stress level increases, but the effect is more apparent at the bottom defect. Similarly, the increased M-E interaction due to the increasing length and depth of the corrosion defects results in a more accelerated corrosion at the bottom defect than the top one.