CFD Analysis of Gas Pipeline Internal Coating Degradation on Flow Efficiency

Abstract Flow efficiency coating (FEC) is a thin-film, solvent-based epoxy coating that is commonly applied to dry natural gas pipelines. There are a number of benefits in using FEC on the pipe internal surface. The primary benefit is the reduction of pressure drop in the pipeline, which enables an increase in the gas flow rate through the pipeline for a given pressure drop between compressor stations. Therefore, for a given flow capacity, the application of FEC reduces the power consumption of compression and the greenhouse gas emissions for the transportation of natural gas. Secondary benefits include corrosion mitigation, easier and faster drying after hydrostatic testing, improved mobility of ILI tools, and the inhibition of black powder formation within the gas pipeline. It has been postulated that the FEC degradation over time has contributed to the observed loss of flow efficiency. Degradation of the coating film can be in the form of patches of varying area sizes peeling off, or scattered blisters like spots forming on the coated surface. Inspecting the coating quality for operating pipelines is very challenging. The objective of this work is to simulate using computational fluid dynamics (CFD) the effects of “peeling” or “blistering” on the pressure drop along a NPS 16 pipe segment. The CFD results show that only 1% of the surface area covered by small-sized blisters (1.5mm in height) could result in a 22% increase in pressure drop per pipe length as compared to that of a perfectly coated pipe. As for the case where 10% of FEC has been peeled off, this could result in over 30% increase in pressure drop, which is comparable to that of an uncoated pipe. While these quantified losses are specific to the simulated geometries, this information can help with the operation team to decide whether such degradation mechanisms are plausible in explaining the observed flow efficiency losses in their system.