A series of single-edge notched tension (SENT or SE(T)) and single-edge notched bend (SENB or SE(B)) testing was carried out at −15°C using BxB specimens machined from two API X70 large diameter pipeline girth welds. An initial notch was placed either on the heat-affected zone (HAZ) or the weld metal center from the outer diameter side of pipe to simulate a circumferential surface flaw. SE(T) and SE(B) tests were performed according to the CANMET procedure and ASTM E1820, respectively. For all HAZ SE(B) specimens machined from one pipe, ductile cracks initially propagated away from the fusion line and toward the base metal side due to asymmetric deformation, and then pop-in (i.e., the initiation and arrest of a brittle crack) occurred after ductile crack growth of approximately 1 mm where the crack reached around the inter-critical heat-affected zone. HAZ SE(T) specimens also showed that the ductile crack propagation deviated toward the base metal side, but an unstable brittle crack extension was not observed from any SE(T) specimens as opposed to SE(B) specimens. None of the weld metal SE(T) and SE(B) specimens showed pop-in or brittle fracture at −15°C or room temperature. The difference in test results, for the same material, is likely due to the different constraint levels in the two loading modes. While pop-ins were triggered in high-constraint SE(B) tests, it was not the case for the low-constraint SE(T) tests. This paper presents these observations and discussion.
Effects of Loading Mode on Brittle Fracture of X70 Pipe Girth Welds
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Park, D, & Gravel, J. "Effects of Loading Mode on Brittle Fracture of X70 Pipe Girth Welds." Proceedings of the ASME 2016 Pressure Vessels and Piping Conference. Volume 6B: Materials and Fabrication. Vancouver, British Columbia, Canada. July 17–21, 2016. V06BT06A045. ASME. https://doi.org/10.1115/PVP2016-63079
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