CTOAC of typical X70, X80 and X90 pipeline steels plates were evaluated by using energy based regression method upon their single specimen. Clear difference in the material resistance to ductile cracking could be distinguished by the values of CTOAC and their characteristic fracture surface. The region of stable cracking on the fracture surface could be identified from the dynamic crack extension curve, with the help of key-curve method. In the meanwhile, the crucial material based parameter required by many other CTOAC algorithm, (A∗σf) of present X70, X80 and X90 plates were experimentally determined, also proving the validity of theoretical geometric factor A∗ to be 0.30–0.34, close to the commonly cited constant of 1/3.
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