Residual Stress Study of High Manganese Steel Riser Pipe Manufactured by Longitudinal Butt Welding (2) : Equation for Predicting Welding Induced Residual Stresses Established through Parametric Study

Abstract

In recent years, the deep and ultra-deep seas are recognized as the last remaining regions on the planet where oil and natural gas resources are discovered and produced. In order to develop such natural resources in an environmentally safe and cost-effective method, various engineering systems and technologies are being developed. In keeping with this direction of development, there is significant worldwide interest among major offshore structural and system operators in examining the possibility of using high-strength steel for long-distance gas transmission pipelines and risers. In particular, riser pipes using high manganese steel are often made by longitudinal butt welding, but studies related to the prediction of residual stresses for this are insufficient.In general, it is known that in a cylindrical structure such as steel catenary risers (Hereafter, ‘SCRs’), residual stress in the through-thickness direction can be decomposed into a membrane component and a bending component. In this paper, a parametric study through nonlinear finite element analysis was performed to predict the residual stress for each direction of a longitudinal butt-welded riser by considering the main parameters (r/t) of the pipe that can affect the actual residual stress. A new predicting equation for estimating the residual stress profile was proposed using the results of a number of parametric precision numerical analysis derived through this process. Key words: Riser, High manganese steel, Longitudinal butt welding, Residual stress, FEA, Parametric study, Through-thickness, Membrane stress, Bending stress, Self-equilibrium stress, Empirical formulae