STRESS-STRAIN STATE SIMULATION OF AN UNDERGROUND LIQUEFIED NATURAL GAS PIPELINE

In recent years, there has been a steady development of systems for the production of small-scale liquefied natural gas for gas supply to remote consumers in cases where the possibilities of pipeline construction are limited. In addition, there is a tendency to use liquefied gas to replace liquid hydrocarbon fuels (gasoline, kerosene, gasoil, fuel oil). Due to the growth and emergence of new industries for liquefied natural gas consumption, the infrastructure necessary for its production, transportation and storage is being developed.  The article presents an analysis of the use of the most common polymers for the pipeline construction in the oil and gas industry. The possibility of using ultra-high molecular weight polyethylene for the construction of process lines for pumping cryogenic liquids was considered. The results of experimental studies on tensile strength test and Charpy impact strength test after exposure to liquid nitrogen are presented. As a result of tensile strength tests, an increase in the strength properties of the material was observed while maintaining its plasticity. The breaking stress was 37.7 MPa, the yield strength was 27.1 MPa at liquid nitrogen temperature, while at ambient temperature, the specimen failed at 26.9 MPa, the yield strength was 20.2 MPa. The specimens, tested for impact strength by the Charpy method, after exposure for 2 h in liquid nitrogen, a certain margin of plastic properties was also showed. The stress-strain state of a liquefied natural gas pipeline made of ultra-high molecular weight polyethylene in an insulating coating was simulated using the ANSYS Mechanical software package, taking into account its thermal interaction with the soil. The maximum equivalent stress in the model was 14.4 MPa, with calculated value of 12.7 MPa, which does not exceed the yield point of the material. Thus, ultra-high molecular weight polyethylene can be considered as a promising material for use at cryogenic temperatures.