Abstract
Determination of fracture toughness for weld has always been a difficult problem because of the existence of defects and material discontinuity in weld. In this paper, the fracture toughness distribution and ductile-brittle transition characteristic of X70 pipeline steel girth weld were investigated by means of fracture toughness curves based on RTNDT, master curve method, instrument indentation method and convention fracture toughness test, applicability of these methods is studied by comparing with actual-measured fracture toughness values and charpy impact test results. The results show that fracture toughness curves based on RTNDT are sufficiently conservative in the whole ductile-brittle transition zone and lower bound. The lower envelop curve is more conservative when it is higher than DBTT, while revised fracture toughness curve is more conservative when it is lower than DBTT. The reference temperature of Master Curve for X70 pipeline steel girth weld by 0.5T SE(B) specimens equals −98 °C, 1% and 95% cumulative failure probability curves can well envelop the fracture toughness distribution of X70 girth weld, which shows great flexibility in the estimation of fracture toughness of X70 pipeline steel girth weld. Fracture toughness values of ductile mode by instrumented indentation can be used to estimate the DBTT of X70 girth weld.
