Fatigue crack growth rate of API X70 steel pipelines under spectrum loading

Pipelines offer the most efficient way to transport bulk quantities of gas and oil, either from points of production to storage locations or from storage locations to distributed points of end use. As one of the main materials of west–east gas transmission pipes, X70 pipelines usually serve under variable amplitude loading (VAL). Base on the importance of in-service API X70 pipelines, it is important for the safe operation of this system to know its behaviour under VAL. This paper focuses on the ability of using the NASGRO model to predict the fatigue crack growth (FCG), based on investigation with the modified Wheeler model and experimental data. The results show that the NASGRO model give a fatigue life near by to that published in literatures and also showed the FCG rate response of X70 pipeline steels when exposed to VAL with different overload values. Extra modification to the NASGRO model may lead to better representing of FCG rate.

► The assessment of fatigue crack propagation under different load histories are proposed and presented in this paper.
► Due to lack of knowledge in the related area, as yet no universal model exists.
► The output was based on both simulation and experiments. The simulation part was carried out based on the NASGRO model.
► This work focus on fatigue crack growth (FCG) and fatigue life based on the comparison with the previous work.