In-Service Welding Simulation of 28” Pipeline Using Finite Element Method

Abstract

To maintain the integrity of the gas pipeline, the repairing of pipeline system with common method such as cut and replaces method by conducting hot tap and bypass or clamp method is conducted. Both methods require in-service welding in the process. During in-service welding, the process affects the structure strength. The structure then needs to be analysed during the welding process. There are two common problems associated with in-service welding. Firstly, the high gas flow in pipe causes the weld rapidly to cool due to the convective transfer of heat. The other problem is burn-through during in-service welding. Pressurized natural gas imposes a significant stress on the pipe wall, and since the pipe strength is decreased during welding, this cause failure in pipe wall. Burn-through occurs when the region around the weld pool has insufficient strength to withstand the internal gas pressure. This paper shows the finite element analysis procedure of In-Service Welding Analysis to avoid burn-through failure. A thermal-mechanical based Finite Element model had been conducted to assess the risk. The model is simulated using three-dimension (3D) mechanical, thermos-elastic-plastic-metallurgical finite element computational procedure. The temperature, stress and strain parameters of inner surface were used to assess the model. The temperature and strain check are below the allowable value while the stress check with some applicable method which are based on either stress or strain based.