During the operation of multiphase and single-phase pipelines, gas/liquid phase transitions can significantly influence the efficiency of the pipeline. Gas/liquid phase changes occur when pipes are exposed to particularly high or low temperatures. The energy absorbed or released during the phase change will impact the temperature and pressure of the fluid. Failing to account for that impact can result in inaccurate predictions for temperatures and pressures.

The formation of a 2nd phase in single-phase pipelines can also introduce slugging, interfere with the operation of the compressors/pumps, and damage the equipment that runs the pipeline. Incorporating gas/liquid equilibrium into the modeling of single-phase pipelines allows users to identify conditions that produce significant amounts of condensation/evaporation.

This paper describes a procedure that was developed to simulate the impact that evaporation and condensation have on the behavior of pipelines. It also discusses the results of two case studies that were performed to test the accuracy and efficiency of the new method.

In one of the case studies, the new method was used to simulate the behavior of a commercial pipeline. The data obtained from that simulation was compared to field data that was collected for the pipeline under the same operating conditions.

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