Investigation the Influence of Post-Weld Heat Treatment Parameters on the Impact Toughness of ASTM A106 Grade B Thick-Walled Pipes

Abstract

The paper investigates the effects of post-weld heat treatment (PWHT) parameters on impact toughness of ASTM A106 Grade B steel with wall thickness of 21.44 mm, in which PWHT is mandatory. Welding had a considerable effect on the toughness of the material, dropping to 54.73 J after welding as compared to 107.36 J in the as-received state, mainly because of the residual stresses and microstructural heterogeneity due to welding. The Taguchi Design of experiments was used to design the PWHT process to restore and enhance toughness. The parameters of the process chosen were the temperature of PWHT, the holding time and cooling medium. Analysis of Variance (ANOVA) was conducted to evaluate the significance and percentage contribution of each factor to reach a statistical evaluation. The findings showed that PWHT was very effective in restoring welding-induced toughness loss; reported impact energy values were between 64.82 J and 115.32 J. In optimized PWHT conditions, the impact toughness was higher than that of the as-received material. ANOVA showed that the temperature was the most significant factor that accounted 63.44% of the toughness variation, followed by the cooling medium (18.40%), and holding time (17.72%). All the parameters were considered statistically significant (p < 0.05).