Effect of Thermal Insulation and Welding Parameters on Residual Stresses of Welded Joints

Abstract

Welding is widely used in manufacturing for its ability to produce high-strength joints. However, the process inherently introduces residual stresses as a result of localised heating and non-uniform cooling. In pipelines, surface tensile stresses con tribute to failures such as fatigue failure and stress corrosion cracking. Therefore, minimizing residual stresses is essential to ensuring the reliability and longevity of welded components. The aim of this study is to evaluate methods for minimizing residual stresses in welded structures using Manual Metal Arc Welding (MMAW). Two approaches were employed. The first approach involved the application of ther mal insulation (lagging) to reduce the cooling rate of welded API 5L X65M pipe coupons, the resulting residual stresses were calculated using ABAQUS software. The second approach studied the effect of varying of welding parameters (welding current, number of weld passes, and bevel angle) on 8 mm mild steel plates. The resulting residual stresses were measured using the crack compliance method. Com parative analyses were conducted using graphs to assess the effect of each method. The findings indicated that applying a 25 mm thick insulation (lagging) to welded pipe sections decreased the tensile residual stresses on the pipes inner surface by 31.4%. Additionally, when the insulation thickness was increased to 37.5 mm, the compressive residual stresses on the pipes outer surface rose by 176.9%. Increasing the number of weld passes raised tensile residual stresses, with five passes resulting in 676 Pa and three passes in 441 Pa. Higher welding currents also increased ten sile residual stresses, with 115 Amperes yielding 1091 Pa and 90 Amperes giving a stress of 473 Pa. A larger bevel angle led to higher tensile residual stresses, with a 45◦ bevel recording 1824 Pa and a 15◦ bevel recording 749 Pa. The study demon strates that thermal insulation effectively reduces tensile residual stresses on the inner surface of pipes, which is critical for preventing failures. It also highlights the importance of optimizing welding parameters to control residual stress formation. A key challenge was measuring residual stresses, which was addressed through coupled thermal-structural analysis in Abaqus. Additionally, the crack compliance method was investigated for its potential use in residual stress measurement. The findings are valuable for welding engineers, pipeline designers, manufacturers, researchers, and quality control professionals working to improve weld integrity and manage residual stresses. x