Abstract
Buried gas pipeline is subjected to axial load due to liquefaction-induced ground flow during large earthquake. The deformability of pipeline depends on the strength of girth weld joint. The heat affected zone (HAZ) in girth weld joint may be locally softened, because the grain size of tempered steel becomes coarsened and softened due to the heat input of girth welding. When weld joint with local softened zone is subjected to tensile load in perpendicular direction to welding line, the tensile strength of the weld joint is higher than the tensile strength of HAZ itself by plastic constraint effect. As for girth weld joint of gas pipeline, in addition to tensile load in pipe axial direction, internal pressure also affects the stress and strain state of girth weld joint. As a results, it is assumed that the tensile strength of girth weld joint varies depending on internal pressure. Therefore, this paper investigates the effect of internal pressure on the tensile strength and deformability of girth weld joint with softened HAZ. The tensile strength of girth weld joint with softened HAZ under internal pressure is formulated by modifying the existing tensile strength evaluation formula of welded wide plate specimen with softened HAZ. In this modification, the effects of internal pressure on the apparent tensile strength of pipe material and shrinkage behavior of pipe material are focused on using FEM results. Furthermore, by using the proposed formula, the effect of internal pressure on the tensile strength and deformability of girth weld joint with softened HAZ is evaluated.
