Strain-based reliability analysis of dented pipelines using a response surface method

Abstract

Dent defects can decrease the life span of oil and gas pipelines. Therefore, they need constant monitoring and maintenance to ensure the pipeline’s safety and integrity. Subsequently, this paper performs a strain-based reliability analysis on pipe dent defects using a response surface method (RSM) with a quadratic response surface (RS), including the interaction terms between the RS variables. The analyses are performed to determine the factors controlling the dent defects’ probability of failure (POF). Different pipe configurations, pipe lengths, indenter sizes, and dent depths are considered in this study. A suitable finite element (FE) model for the reliability analysis was developed for this study using the FE analysis software ABAQUS. The uncertainties in the pipe wall thickness, the dent depth, the yield strength of the pipe material, and the strain capacity are considered for the reliability analysis. The first-order reliability method (FORM) is used in the RSM as the reliability method to calculate the POF and the most probable point (MPP). The POFs of several dent defects were calculated. It has been found that the POF, which is highly related to the nominal value of the maximum equivalent plastic strains generated in the dent defect, is not only related to the indentation depth or the size of the indenter. Thus, the dent depth criterion used in the engineering practice can lead to inconsistent reliability levels in dented pipes.

Keywords

• Pipeline reliability
• Probability of failure
• Defected pipes
• Dent defects
• Response surface method
• Interaction terms