Strength of trunk pipelines with critical damages

Abstract

High internal pressure combined with external loading (bending/tension) and aggressive environment, along with the potential presence of local damages makes the assessment of strength and structural integrity of long-distance pipelines a formidable challenge. The paper considers the influence of local buckling (hereafter referred to as crimp) on the reduction of the static strength of pipelines. The reduction of plasticity and the increase of yield limit due to aging; decrease of the operation temperature; residual tensile stresses acting in the inner part of the pipe at the crimp top during plastic crimp formation; and residual tensile stresses caused by welding are assessed. The account of the influence of these damaging factors allows one to evaluate the reduction of the load carrying capacity of damaged pipelines. Threat of occurrence of damages in the form of crimps is either ignored or only partially taken into account by the existing procedures for pipeline strength analysis. The paper is aimed at filling this gap by analyzing strength of pipelines with crimps. Changes of the pipeline geometry, mechanical properties of the material, and stress concentration due to crimp formation are considered; results of calculations and tests are presented.