Finite Element Simulation of Ultimate Internal Pressure of Pipes Containing Crack with Different Size and Its Calculation Equation Modification

Model for X80 welded pipeline containing heat affected zone crack was estabilished, and residual stress distribution was simulated and verified. Ultimate internal pressures of welded pipeline with and without welding residual stress and with different crack size were simulated by finite element method, and compared with those calculated by ASME B31G, DNV RP-F101 and PCORRC methods, respectively. The ultimate internal pressure equations were modified on basis of the results by PCORRC method and finite element simulation. The results show that whether the welding residual stress existed or not, the ultimate internal pressures of the welded pipeline all decreased with increasing depth or length of the crack. The effect of welding residual stress on ultimate internal pressure decreased with increasing crack length. The ultimate internal pressures by three methods decreased with increasing crack depth. The higher the crack depth, the larger the error between calculation and simulation. The relative errors between the calculation by matified equations and the simulation of the ultimate internal pressures of pipeline with surface crack and welded pipeline with heat affected zone crack were below 8% and 7%, respectively, indicating that the modified equations for ultimate internal pressure can be used for practical engineering.