Experimental investigation of CTOA in linepipe steels

The crack-tip-opening angle (CTOA) criterion has been introduced to the natural gas transmission industry for pipeline applications but has not yet achieved widespread use. There have been ongoing efforts funded by TransCanada PipeLines Limited to establish a fundamentally based test procedure to extract a true measure of the dynamic, ductile, and steady-state fracture toughness of linepipe steels, i.e., the critical CTOA. This paper summarizes experimental results being used in establishing a test procedure that will produce a measure of the steady-state ductile fracture toughness for linepipe steels. Several drop-weight-tear-test type specimens were tested and the CTOA was measured using high-speed video equipment. Comparisons of the measured CTOA values are made for different crack speeds and between standard critical CTOA calculations. The anticipated goal of this research is a test method that is suitable for use at the pipe mills.