Simulation on venting and pressure-relieving rules of long-distance subsea natural gas pipelines

Venting and pressure relieving are important operations on high-pressure natural gas pipelines. In the process of venting, the gas is unsteady flow. Venting process has great influence on pipeline parameters and venting process factors. In this paper, the practical pressure-relieving process of one 98 km pipeline in China was taken as the example to conduct mathematic simulation on venting of natural gas pipeline and analyze the dynamic simulation of venting process using the software SPS. The parametric variation rules (e.g. vented gas amount, vent temperature, and pressure and temperature of the pipeline) in the process of venting were analyzed and different pressure relieving processes were compared to choose the most economical and effective operation program. It can be used as the reference for the actual operation of pipelines so as to guide the venting operation of natural gas pipelines. Several problems are encountered in the process of actual venting and pressure relieving. For example, the temperature of venting pipeline and flare separation tank is too low, liquid production is excessive and lock of vented gas occurs at the nozzle of the pipe. However, the actual venting rules are basically consistent with the simulation results.