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

本研究的目的是预测发生在化工厂管道系统中的异常腐蚀。研究了金属材料腐蚀与其表面流动参数之间的关系。在试验装置上进行了流体压力测量和流动模拟，得到了流动结果。(1)研制了一种用于测量狭缝喷射腐蚀试验装置中试样表面附近流体压力的装置，并认识到压力波动与试样上发生的大损伤有关。流动参数选择为平均压差、压差波动和试样表面壁面压力。提出了预测冲刷腐蚀损伤的方程。用该方程计算的铜合金损伤与实验数据吻合较好。(2)通过流动模拟计算，将所提出的方程应用于工厂管道系统。对狭缝射流腐蚀试验装置中的流动进行了模拟，以验证是否可以计算材料表面附近的流速波动。流动模拟采用二维轴对称模型。试样表面附近的流速和壁面压力被计算为非稳态层流。因此，通过对模型应用细网格，可以通过流动模拟来计算流速波动。(3)根据流体力学参数和材料参数建立了黄铜冲刷腐蚀损伤计算公式，从而预测了黄铜的冲刷腐蚀损伤深度。计算了节流孔的流动状况，确定了节流孔下游的流速脉动。通过流场模拟计算了流场参数，并将其应用于所提出的方程，得到了损伤估计。

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.