Subjects: Materials Science >> Materials Science (General) submitted time 2023-03-31 Cooperative journals: 《腐蚀科学与防护技术》
Abstract： Incident involving failure occurred for a 40 months old upright type tee of gas filed gathering and transmission pipeline in a west natural gas field. The tee consisted of a main pipe of 16Mn steel and branch pipes of bimetal composite of 316L stainless steel+L416 steel. Examinations were performed to identify the cause of the failure, which include visual physical inspection, pipe thickness measurement and acquiring the galvanic corrosion behavior of 16Mn steel and 316L stainless steel in an oxygen-free medium containing chloride ion concentration 150 g/L with CO2 partial pressure 0.1 MPa at 65 ℃ using electrochemical methods, as well as Computational Fluid Dynamics (CFD) analysis of the tee with assumed angles as 90°, 45°and 30°respectively between the branch pipe and main pipe along the direction of inlet using the FLUENT software. Investigations revealed that for the present tee design, there existed galvanic couple of the metallic materials and the straight cutting structure of the tee caused the fluid changes radically. Gas field water gradually adhered to the inner side of the pipe due to the low velocity that caused by the vortex which was formed nearby the pipe explosion site. Corrosion then ensued as CO2 dissolved in the water. The area around the explosion site suffered from large wall shear stress caused by the fluid scouring action. Because of the synergy of galvanic corrosion and fluid flow erosion the pipe gradually thinned, and then perforated.
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