Development of Finite Element-based Models for Defect Assessment on Pipelines

Abstract

Pipelines have been the most effective and efficient method for transportation of oil and gas from production sites to their markets and end users. Assessment of corrosion defects and their effect on pipeline integrity are critical to the safe operation of pipeline systems. Although numerous efforts have been made on defect assessment, there are still significant rooms for research and development in assessment of the interaction of multiple features on pipelines. In this work, finite element (FE) based models were developed to assess API X46, X60 and X80 steel pipelines containing multiple corrosion defects, which were either longitudinally aligned, circumferentially aligned or overlapped with each other. The defect size and the grade of pipeline steels were considered to evaluate the interaction between adjacent defects. The critical spacing between the defects with various orientations was determined, enabling assessment whether an interaction existed to affect the failure pressure of the pipeline. FE models enabling predictions of the failure pressure of pipelines containing a dent associated with a corrosion defect were also developed. In addition, a failure pressure-based criterion to properly assess the interaction of the dent and its adjacent corrosion feature was established. The mutual interaction between the adjacent corrosion defects affects not only the local stress and distribution, but also the electrochemical corrosion rate, due to the so-called mechano-electrochemical (M-E) effect. Due to the existence of the M-E effect, a new criterion is proposed to determine whether the mutual interaction exists between the adjacent corrosion defects, i.e., on the ratio of the anodic current density at the defect adjacency to that of the non-corrosion region on the pipe body.