Calculation of Fatigue Threshold and Crack Expansion Rate of Natural Gas Pressure Vessel Steels and Yield Strength Dependence Analysis

In this paper, the strain law of natural gas pressure vessel steel fatigue is firstly analyzed through the stress-strain curve and steel fatigue life curve, and the finite element model of natural gas pressure vessel is constructed by combining ABAQUS simulation software, and the fatigue performance of natural gas pressure vessel steel is analyzed from the cyclic softening behavior of the material and S-N curve.Then the stress intensity factor theory combined with Paris formula is introduced to calculate the crack expansion rate, and ABAQUS and FTANC3D are jointly simulated to study the crack expansion law.Finally, the fatigue yield strength of the natural gas pressure vessel was analyzed based on the elastic-viscoplastic constitutive model combined with the finite element model.It is found that the stress intensity factor along the path under hydrostatic loading is larger than that under stresscontaining loading, but the difference in stress intensity factor is only about 1.42%.When the cracks of the natural gas pressure vessel extended to the vicinity of 20 mm, its crack extension rate showed a sharp downward trend.When the temperature comes to 900C, the yield strength value of the steel of natural gas pressure vessel is only 280.42 MPa.Exploring the steel fatigue performance and crack extension rate of natural gas pressure vessel can help to better ensure the stable and safe operation of natural gas pressure vessel.