Stress intensity factors analyses for external semi-elliptical crack for repaired gas-pipeline by composite overwrap under pressure

Abstract

The purpose of this article is to present the stress intensity factors (SIF) solutions for semi-elliptic crack in pipelines under internal pressures, the stress intensity factors are calculated by the three-dimensional finite element method (FEM) for cracked pipelines and repaired pipe by composite patch. The distribution of normalized stress intensity factors (KI, KII and KIII) along the crack front for different crack lengths, crack depth, crack geometry, lap length and composite thickness was obtained by nodal calculations. Our results show the presence of three failure modes along the semi elliptical crack front and has three zones in which the stress intensity factor in mixed mode (KII) the higher-values comparing to KI and KIII. It can also be noted that the composite repair reduces the SIF KI by 46% and the KII by 55% and the KIIIby 72% near the outside diameter of the pipe in each zone. However, the reduction of the SIF KI is more significant for the rectangular crack than for the semi-elliptic crack, from which it is concluded that the composite repair is very effective for a rectangular crack with respect to the semi-elliptic crack. Thereby, the fracture behavior of the semi-elliptic crack is governed by the three modes of failure and not only by mode I.