Stable crack growth emanated from circumferential through-wall crack in X65 steel pipe under pure bending was evaluated. Seamless carbon steel pipes grade X65 PL5 with an inner diameter of 42.9 mm and an outer diameter of 60.3 mm were used in the present experimental work. This type of pipes is of common use in piping systems of gas and oil industry. Pipes of different circumferential crack depths were tested. J-R curve was used to characterize the nonlinear fracture behavior of the through-wall crack pipe. Variation of J with crack growth, crack surface area and deflection of the pipe were obtained. J-integral-crack growth curve was used in the calculation of critical crack size based on the Jc value measured in our previous experimental work by testing full scale pipe made from the same material. The length of crack at unstable crack growth is also determined. Both critical and instability crack sizes can be used for fracture assessment of X65 steel pipes.