Thermal Analysis of In-Service Welding Process for Pipeline

Abstract

A numerical model had been developed using three dimensional finite element method to predict temperature history of pipe wall thickness by using a FORTRAN computer program. The developed numerical model concerned with the effect of power and velocity of moving heat source, temperature dependent material properties, and transient heat transfer and phase change transformation. Also the effect of heat flux and flow rate on cooling time was investigated numerically.

An experimental setup had been designed, manufactured and instrumented to investigate the thermal history of an in-service welding process considering air as the flowing fluid inside test pipe. The burn-through was investigated experimentally under the influence of gas flow rate, heat flux and the depth of defect presented in pipeline wall. It has been concluded that the burn-through do not occur for the studied parameter range. The results showed that as the flow rate increases from (24 - 30 lpm) the cooling time decrease by a rate of (11.7 %) and when the flow rate increase from (24-60 lpm) the cooling time decrease by a rate of (41.1 %) without affecting peak temperature with pipe wall thickness of (6mm). Also it has been concluded that as the heat flux increases from (1110- 1370 kJ/mm) the peak temperature increases with a rate of (22.11 %) and cooling time increase with (25.4 %) when the heat flux increases from (1110- 1659 kJ/mm) the peak temperature increases with a rate of (46.86%) and cooling time increase with (50.7 %) with pipe thickness of (6mm).