INFLUENCE OF SLUG FLOW ON LOCAL CORROSION OF PIPELINES

Abstract

The influence of slug flow on local corrosion of pipeline was studied, and the protection measures for slug flow corrosion were well done to improve the safety of oil-gas-water-humidity mixed pipeline. An indoor loop test was designed to simulate the slug flow in real undulating pipelines. The surface microstructures of X70 hanging pieces were studied by scanning electron microscopy (SEM) under slug flow conditions at different test stages. At the beginning of the test, there was much pitting corrosion on the surface of the hanging pieces, but at the end of the test, only some pitting or pitting spots developed into serious local corrosion. The flow corrosion of slug in pipe had obvious characteristics of cavitation corrosion. Its occurrence was the result of synergistic action of various mechanisms. The strong impact force, high impact velocity and mechanical action of multi-frequency micro-jet produced by cavitation annihilation significantly affected the development process and characteristics of electrochemical corrosion, which resulted in that the cavitation corrosion was mostly pitting corrosion. The damage of corrosion product film caused by high-speed micro-jet impact caused by cavitation cracking was local, and the pitting tendency increased at the local damage of corrosion product film. However, with the formation of electrochemical corrosion products, the destroyed corrosion product film was repaired continuously, but did not develop into local corrosion. Local corrosion occurred only when the high-speed micro-jet with cavitation breakdown repeatedly impacted a point of pitting tendency, but this probability was smaller than that of pitting tendency.