A Study of Deformation Behavior of Double Jointing Girth Welds

Abstract

Demand for double jointing technology is increasing to improve pipeline construction productivity. Submerged arc welding (SAW) utilized for double jointing is likely to cause a much wider heat affected zone (HAZ) than those of typical field welding by gas metal arc welding (GMAW), and it should be taken into account for strain-based design of high strength line-pipes. However, guidelines for SAW welds properties to ensure strain capacity of high strength line-pipes such as X80 have not been established yet. In this study, a submerged arc weld joint was produced using tensile strength (TS) over-matching welding consumable. API standard type transverse weld tension test was conducted to measure local elongation at weld metal, HAZ, and base material. Elongation at weld metal increases prior to base material, but soon after that elongation at the HAZ softening region and base material adjacent to the HAZ catch up with the elongation in the weld metal, and finally, deformation concentrates at the HAZ softening region before final fracture. Deformation behavior of the joint was analyzed to verify applicability to double jointing girth welds for strain-based design. From finite element (FE) analysis of notched wide plate test which characterizes tensile strain capacity of a pipeline, it is suggested that ductile crack would not initiate before base material start necking in this particular TS over-matching weld joint in which the defect size is 1mm of notch depth and 25mm of notch length. Thus, the weld joint would be applicable for double jointing girth welds based on strain-based design.