Corrosion and deposition mechanism at position of defect in circumferential weld of gas pipeline

Metallographic microscope and EDS (energy dispersive spectrometer) were used to investigate the reason which caused the pipe blockage of the gas field in Jingbian. Results showthat there are CO₂ corrosion, H₂S corrosion and crevice corrosion in the natural gas pipeline.The deposits are mainly corrosion products such as iron oxides, iron chlorides and iron sulfides at this stage. As the corrosion continues, the pipe and the fluid inside the pipe are separated by the compact corrosion products. The type of deposits transforms from corrosion products to dust as the corrosion rate drops. When the height of deposits reaches a certain value, the top of the pipe suffers from erosion corrosion because the flow direction of fluid inside the pipe changes. And the corrosion rate accelerates. The thickness of pipe is so thin that it endangers the safety operation of the pipeline.