An investigation of flow parameters near material surface to predict unusual corrosion in piping system

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The purpose of this study is to predict unusual corrosion occurring in piping systems in chemical plants. The relationship between corrosion of metallic materials and the flow parameters they were exposed to at their surface was investigated. The measurement of fluid pressure and flow simulation in the testing apparatus were carried out, and the flowing results were obtained.(1) An apparatus for measuring fluid pressure near the specimen surface in a jet-in-slit corrosion testing apparatus was developed, and it was recognized that pressure fluctuation was related to large damage occurring on the specimen. The flow parameters were selected as average differential pressure, fluctuation of differential pressure and wall pressure on the specimen surface. The equation to predict the erosion-corrosion damage was proposed. The damage of copper alloys calculated by this equation was consistent with the experimental data.(2) Calculation by flow simulation was carried out to apply the proposed equation to piping systems in plants. The flow simulation in a jet-in-slit corrosion testing apparatus was carried out to confirm whether or not the fluctuation of flow velocity near the material surface could be calculated. The 2D axisymmetric model was applied for flow simulation. The flow velocities near the surface of the specimen and wall pressure were calculated as an unsteady-state laminar flow. As a result, the flow velocity fluctuation could be calculated by flow simulation through application of a fine mesh to the model.(3) The damage of brass by erosion-corrosion was calculated by a proposed equation with hydrodynamic and material parameters, and thus the damage depth could be predicted. The flow condition of an orifice was calculated, and the flow velocity fluctuation could be confirmed downstream of the orifice. The flow parameter was calculated by flow simulation and applied to the proposed equation, which yielded the damage estimate.