Effect of strength matching and strain hardening capacity on fracture performance of X80 line pipe girth welded joint subjected to uniaxial tensile loading

By conducting curved wide plate tensile tests for girth welded joints of X80 line pipe containing a surface notch in the weld metal, the effects of strength matching on fracture performance were evaluated. Parametric studies were also conducted using a finite element method simulating the experiments to clarify the effects of strain hardening capacity of the base metal, softening in the heat affected zone, and groove configuration on fracture performance. A strain at failure significantly decreased with the decreasing strength matching. This was expected to be due to a difference in local straining behavior at the notch tip caused by the shielding effect. The analytical studies revealed that the strain hardening capacity of the base metal, the softening in the heat affected zone, and the groove configuration affected the allowable strain for a given toughness level in the case of overmatching. However these factors hardly affected the allowable strain in the case of undermatching.