Mechanical Behavior of Steel Pipes With Local Wall Distortions Under Cyclic Loading

Abstract

Evaluating the severity of pipe wall distortions is a crucial step towards safeguarding the structural integrity of aging hydrocarbon pipeline infrastructure. The present research refers to the remaining life of oil and gas transmission steel pipelines with local wall distortions (i.e. dents and buckles) under repeated loading. The research described in this paper constitutes the first part of a large numerical/experimental research project, aimed at developing methodologies and relevant design guidelines towards assessing and repairing structural pipeline damages in the form of local wall distortions. The paper describes numerical research aimed at investigating the residual structural integrity of smooth dented and buckled steel pipes, with respect to repeated loading that causes fatigue, with the purpose of designing large-scale experiments. Finite element models are developed to simulate the formation of dents and buckles on the pipe wall at various sizes (depths). The deformed steel pipes are further subjected to cyclic pressure or cyclic bending loading in order to estimate the remaining fatigue life of the deformed pipe. The local stress and strain variations due to cyclic loading application are calculated numerically at the deformed area of the pipe wall. In addition, the local strain variations are expressed in terms of strain concentration factors (SNCF) at the critical region of the pipe.