The Extended Finite Element Method in Analysis of Fatigue Cracks Propagation in High-Frequency Welded Pipes

摘要

This paper presents an application of the extended finite element method (XFEM) in the modeling and analysis of simultaneous cracks propagations in a seam casing pipe made of API J55 steel by high-frequency (HF) contact welding. The experimental tests are conducted on specimens made from new and from the material made of the pipes after 70 000 hours of service in an oil drilling rig. Fracture behavior by testing the modified compact tension (CT) specimen with a pre-crack in the base material, welded metal and heat affected zone (HAZ) was examined. The geometry used in XFEM simulations is pipe with axial crack subjected to constant amplitude cyclic loads. Short theoretical background information is provided on the XFEM, as well as the demonstration of the method used for verification of computed stress intensity factors (SIFs). The obtained numerical results prove the efficiency of XFEM in the simulation of the axial cracks propagations in tube geometry. Some guidelines for improving the XFEM use in fatigue life predictions are also given.