Effect of Strength Matching on Ductile Fracture Behavior of X80 Linepipe Girth Welds Subjected to Tensile Loading

Abstract

This paper describes the effects of yield stress matching on the ductile fracture behavior of X80 linepipe girth welds. Three girth welded joints were made on an X80 linepipe using several consumables to obtain about a 20% yield stress overmatched, evenmatched and about a 20% undermatched weld metal. For these three welded joints, curved wide plate tensile tests were then conducted with a surface notch in the weld metal and the heat affected zone. The yield stress matching significantly affected fracture behavior and the ductile crack initiation, that is, the overmatched welded joint had a higher resistance to ductile fracture than that of the undermatched welded joint for both the weld metal and HAZ notch. The ductile crack initiation was successfully detected using a direct-current electric potential method. The allowable strength matching level could be determined using the relationship between the strength matching and the gauge length strain from the viewpoint of preventing the ductile crack initiation.