Pipelines are the most efficient and safest gas transportation systems. Due to the increased use of high strength steels, the fracture mechanics assessments complementing the classical stress and strain-based design computations have gained remarkable importance. The mechanical properties and microstructure of API 5L X100M steel and weldments were investigated. The mechanical properties were characterized by tensile tests, Charpy-V impact test and quasi-static fracture mechanics tests. Numerical calculations of a pipe, compact tension (CT), single edge notched bend (SENB) and single edge notched tension (SENT) specimens from the base material were performed with the finite element package Abaqus to compare the stress and strain distributions in front of a crack. The difference in the stress state was evaluated by means of a constraint parameter such as the Q-value. Using this constraint parameter it is possible to correct the crack growth resistance curve (J-R-curve) determined on laboratory specimens in order to obtain the J-R-curve of the pipe. With these results a crack driving force diagram was calculated and used for assessing the pipe integrity.