Leak-before-break (LBB) behavior was evaluated for two series of conventional line pipes (X65) and three series of high-grade line pipes (X80) with various fracture toughness value. Full-scale hydrostatic burst tests were conducted for the line pipes with an axial through-wall flaw to determine hoop stress for LBB. The experimental results were then compared to the estimation using a Charpy V-notched impact energy (CVN)–based equation by Battelle. The present study clarified that the CVN-based equation was applicable to the pipes with CVN energy less than 130 J. On the contrary, the equation was not applicable to the pipes with CVN energy grater than 130 J. The results of instrumented Charpy tests showed that the load versus load-point displacement response for the high CVN energy pipes was different from that for the low CVN energy pipes. Therefore, the applicability of the CVN-based equation was dependent on the load versus load-point displacement response. This result suggested that the CVN-based equation should be modified to evaluate the LBB criterion for the pipes with relatively high toughness.

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