Probabilistic fracture assessment of snake laid pipelines under high pressure/high temperature conditions by engineering critical assessment

Abstract

Offshore pipelines are the most effective way to transport of oil and gas. High Pressure/ High Temperature fluid in the pipeline can cause axial expansion, which this expansion is limited by pipe-soil interactions or end connections of pipes that keep them in position. Due to that, axial stresses are created, that can cause pipeline buckling. According to DNV-RP-F110, global buckling is not a failure mode, but it may indicate ultimate failure modes like local buckling, fracture, and fatigue. The purpose of the present study is to investigate the second mode (fracture) by using Engineering Critical Assessment. In order to perform Engineering Critical Assessment, a snake laid pipeline under High Pressure/High Temperature conditions is simulated, and pipe-soil interaction is considered using spring elements. The fracture response of pipelines with semi-elliptical cracks, the influence of loading (pressure and temperature), and crack geometry are investigated. Using Response Surface Method, a polynomial model for Crack Tip Opening Displacement is introduced. Results showed that temperature is the most influential parameter. To consider the uncertainties in geometry, loading, and material and present more accurate results, probabilistic methods such as First Order Reliability Method and Second Order Reliability Method are used. It is concluded that Second Order Reliability Method can give more conservative results.