Experimental research on fracture toughness of high grade line pipe

Crack tip opening displacement(CTOD) tests were carried out on different positions of X70, X80 and X100 pipe by three-point bend testing method. The results show that the crack propagation resistance and the tear modulus of base metal, heat affected zone(HAZ), and weld of X70 and X80 pipe are larger than that of X100 pipe. At the same time,The initial CTOD values and the CTOD values withmaximum load of X70 and X80 pipe are larger than that of X100 pipe.The test results suggest that the fracture toughness, crack initiation and propagation resistance of theX70 and X80 pipe are greater than that of X100 pipe, and the mechanismis analyzed finally. Nowadays X70 pipe has been used widely, and X80 pipe has been put into service already. As to the higher grade linepipe, X100 pipe has been used for trial segment successfully, while X120 pipe has been conducted small scale trial production([1-6]). This article is based on CTOD tests on the base metal, the weld and HAZ of X70, X80 and X100 pipe by three-point bend testing method. Then the fracture toughness is compared among different positions of different grade line pipe to facilitate the engineering application and the research on the high grade linepipe.