A Study on the Prediction of Welding Distortion of 9 Ni Steel for the Offshore LNG Storage Tank

摘要

The purpose of this study is to establish the predictive equations for welding distortion and residual stress in the weldment of 9% Ni steel in consideration of the solid-state transformation. In order to do it, high speed quenching dilatometer is used to evaluate the coefficient of thermal expansion (CTE) of 9% Ni steel with the fraction of martensite. With CTE obtained, an uncoupled thermal-mechanical finite element (FE) model was developed to evaluate the effect of solid-state phase transformation on welding distortion and residual stress of the weldment and verified by comparing with the results of experiment. The variations of welding distortion in the weldment of 9% Ni steel with welding process, welding heat input and plate thickness were investigated. Based on the results, the predictive equations for welding distortion and residual stress in the weldment of 9% Ni steel were formulated as a function of welding heat input and plate thickness. The distributions of welding distortion of the actual welded structure obtained by STEM (Simplified Thermo-Elastic Method, Shin and Lee, 2002) with the predictive equations have a good agreement with the measured results.