One of the most difficult safety problems associated with gas pipeline to be solved is the control of ductile fracture propagation. To address this issue, the crack tip opening angle (CTOA) criterion is becoming one of the more widely accepted properties for characterizing fully plastic fracture. Our current research has applied the CTOA concept in pipeline characterization. A test technique for direct measurement of CTOA was developed that uses a modified double cantilever beam specimen. In this article, CTOA data on high-strength API X100 pipeline steel are presented. Different optical measurement methods are evaluated, which use the crack edges and the specimen surface grid lines. Crack growth in the base metal and through pipeline girth welds was studied. The effect of specimen thickness on CTOA results was noticeable, with thicker specimens producing a greater resistance to fracture. Finally, the influence of the crack velocity on CTOA material strength was found to be small.
Proceedings Title: Proceedings of the 12th International Conference on Fracture
Conference Dates: July 12-17, 2009
Conference Location: Ottawa, CA
Conference Title: 12th International Conference on Fracture
Pub Type: Conferences
API X100 steel, crack growth, CTOA, fracture, pipelines, steel