Numerical Analysis of Residual Stresses in V-Butt Welded Joint of Two Dissimilar Pipes

In this paper a three-dimensional welding simulation was carried out by commercially available finite element software to predict temperature and the residual stress distributions in V-butt welded joint of two dissimilar pipes. Low carbon steel and stainless steel pipe welding is widely used in a variety of engineering applications such as oil and gas industries, nuclear and thermal power plants and chemical plants. Inelastic deformations during heat treatment are the major cause of residual stress. Heat during welding causes localized expansion as some areas cool and contract more than others. The stress variation in the weldment can be very complex and can vary between compressive and tensile stresses. The mismatching (in the weld in general) occurs due to joint geometry and plate thickness. Welding procedures and degree of restraints also influences the residual stress distributions. To understand the behavior of residual stress, two dissimilar pipes one of stainless steel and another of low carbon steel with outer diameter of 356 mm and internal diameter 240 mm were butt welded. The welding was completed in three passes. The first pass was performed by Manual TIG Welding using ER 309L as a filler metal. The remaining weld passes were welded by Manual Metal Arc Welding (MMAW) and ER 309L-16 was used as a filler metal. During each pass, attained peak temperature and variation of residual stresses and magnitude of axial stress and hoop stress in pipes has been calculated. The results obtained by finite element method agree well with those from Ultrasonic technique (UT) and Hole Drilling Strain-Gauge (HDSG) as published by Akhshik and Moharrami (2009) for the improvement in accuracy of the measurements of residual stresses.