Should the pressure inside a pipeline decrease or increase as a fluid flows through it? The usual answer would be that it should decrease. However, this was not what we found during the flow assurance study of a Liquid Natural Gas (LNG) project.
During the setup phase, LNG was shipped in and vaporised back into gas state. The gas was then pumped to a power plant and into the national gas grid system. Surprisingly, the flow assurance analysis revealed that, as the gas moved through the pipeline towards the plant and the grid, its pressure gradually increased, despite the significant elevation rise to the plant. Initially, this puzzled everyone, as it is highly unusual to see pressure increase as fluid travels along a pipeline. Typically, friction along the pipeline walls and the energy required to transport the fluid cause the pressure to gradually decrease.
After extensive investigation, it was discovered that the pressure increased because the gas temperature rose as it travelled along the pipeline. The vaporised gas was initially much colder than the ambient temperature. As the cold gas moved through the pipeline, the warmer surrounding environment heated it up. This heating caused the gas volume to expand, which in turn led to a corresponding increase in pressure.
This was a perplexing and unusual scenario but proved to be a fascinating challenge for the engineers involved. Therefore, when asked, “Should the pressure inside a pipeline decrease or increase as a fluid flows through it?” you now know that a decrease in pressure is not always the only answer.
To find out more about Jee's flow assurance capability, visit https://www.jee.co.uk/flow-assurance.