FINITE ELEMENT ANALYSIS OF THE EFFECT OF WELD DESIGN ON STRESS DISTRIBUTION IN PIPE WELDS

Abstract

Welding is a reliable joining method having high joint efficiency, water and air tightness and low fabrication cost. Butt welded pipes have been widely employed in a vast variety of practical applications, such as boiling water reactor piping• systems, oil pipe transport systems and steam piping systems. Owing to localized heating by the welding process and subsequent rapid cooling, residual stresses develop in the joint. The presences of residual stresses, especially at the inner surfaces of the welded stainless steel pipes promote intergranular stress corrosion cracking which is a matter of significant concern in proper weld fabrication of thick wall stainless steel pipes. Prior to welding, a proper evaluation of the development of residual stresses in a piping system is very essential. Finite element analysis of the thermo-mechanical behavior of weld joint can provide necessary knowledge to design an appropriate welding procedure specification to ensure better safety to the joint of thick wall stainless steel pipe. In this work residual stresses during multipass Gas Metal Arc welding of austenitic stainless steel pipes using finite element method are predicted. For validating the model two pass butt weld is considered. By considering 2 D model (plane strain condition) residual stress results are calculated and are compared with experimental values obtained from literature. It is found that they are in good agreement with each other. The simplified method for residual stress determination, through uncoupling of the thermal and residual stress analyses, is found to work reasonably well. A considerably high tensile residual stress is observed at weld toe which may promote intergranular stress corrosion cracking. In order to model a pipe joint, axisymmetric model with axisymmetric elements are used. The results of axial stress are compared with that from literature and they are found to be in good agreement.