The purpose of this work was to evaluate the fracture toughness for different plastic constraint levels of a grade X63 line pipe representative of in-service line pipes in France. This study was carried out for high constraint levels using Compact Tensile (CT) specimens and low constraint levels using Single Edge Notched Tensile (SENT) specimens. Moreover, in order to reduce the amount of tested samples, silicone replicas of crack advance were made all along the test. The results show that the loss of plastic constraint induces J–values about 70% higher compared to high constraint tests. A strong crack growth resistance anisotropy was observed at high constraint. This anisotropy is significantly reduced at low constraint.

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