Fracture toughness measurements from circumferentially-notched pipes tests

Fracture toughness for full scale steel pipe of API 5L grade X65 PSL1 (ASTM A694) medium strength grade pipeline steel has been measured by a new test specimen utilizing the same procedures of the standard test methods ASTM E399-90 and ASTM E1820-01. Full scale pipe sections with circumferentially machined notches were pulled axially by tensile loads until fracture. An external circumferential sharp notch was machined in the wall of the pipe to simulate the crack. In addition to testing a plain pipe, a well lubricated and axially free loaded plug was mounted inside the pipe to provide plane strain condition for notch failure. Ductile dimple fracture was observed on fractured surfaces of plain pipes, while evidences of cleavage fractures have been observed when the internal plug was used. The measured value of the fracture toughness has been found to be in good agreement with the values measured according to the standard tests for steel plates of similar grade and with the with those measured using in situ Automated Ball Indentation (ABI) tests conducted on the same pipe section. The new testing method for full scale pipe can be used regardless of pipe dimensions since it appears to provide plane strain conditions around the crack.