Numerical evaluation of the coupled/uncoupled effectiveness of a fluid-solid-thermal multi-field model for a long-distance energy transmission pipeline

As the main component of energy transmission, long-distance energy transmission pipeline (LETP), whose safety problem is becoming more and more prominent with the development of the oil and gas transportation industry, is susceptible to the traffic loading, temperature loading, pressure loading and other loadings. In this paper, the mechanical characteristics of LETP under the interaction of temperature loading and pressure loading are investigated. Based on the theory of multi-field coupling, the mathematical model of fluid-solid-thermal coupling of fluid-filled pipelines under the combined effect of temperature and pressure loadings is established and verified. Meanwhile, an equivalent model is proposed to accurately calculate the stress of any pipeline segment in LETP. The results show that the coupling of temperature loading and the pressure loading is significantly affected by the end-side constraints of the pipelines. For strong end-side constraint, the coupling effect of temperature and pressure loadings has a significant effect on the calculated equivalent stress. The difference between the stress solution under coupling effect and decoupling effect is above 30 MPa. However, for weak end-side constraints, the error is within 10 MPa. The equivalent stress can be approximated by the decoupling solution instead of the coupling solution.