A comparative study on the effect of GMAW welding current on the performance of API 5 L GrB pipeline steel welds for oil and gas industrial applications

Abstract

The reliability of oil and gas transportation depends heavily on weld quality during pipeline construction. This study investigates the effect of gas metal arc welding (GMAW) current on API 5 L GrB pipeline weld joint. Welding experiments were conducted using currents from 140 A to 170 A, at constant voltage of 22 V and welding speed of 6 m/min. Finite Element Modelling (FEM) simulations were performed using Simufact Welding 6.0 software to compare with experimental data. Results showed that an increase in welding current improved penetration depth (91.35% to 124.95%) and weld width (15.17 mm to 16.12 mm), before declining to 12.32 mm at 170 A. 170 A caused undercutting and sagging, while 140 A resulted in incomplete penetration. Microstructural analysis revealed grain coarsening at higher currents, with acicular ferrite dominating the fusion zone and mixed ferrite morphologies in the HAZ. The fusion zone at 170 A exhibited a micro-hardness of 260 HV_0.3, exceeding the 248 HV_0.3 limit for API 5 L GrB, increasing susceptibility to hydrogen-induced cracking (HIC) and stress-corrosion cracking (SCC). Residual stress shifted from −228 ± 7.5 MPa in the base metal to −268.73 ± 8.5 MPa at 150 A, then decreased to −182.7 ± 13.4 MPa at 160 A and −118.3 ± 13 MPa at 170 A. Simulation results closely matched the experiment, with deviations of 6.72%, 4.08%, and 12% for weld width, depth, and residual stress, respectively. The study supports the combined utilisation of physical and computational tools to optimise pipeline welding performance.