Simulation And Experiment System Design Of Flow-Accelerated Corrosion In Different Flow Fields Of Power Plants

Flow-accelerated corrosion?FAC?is a phenomenon in which a single-phase flow or a two-phase flow causes protective oxide film on the surface of a carbon steel to accelerate dissolution,which is a common corrosion failure mode of pipeline metals in thermal power plant and nuclear power plant.Although commercial software currently predicts the FAC rate,it still requires a large amount of field data to correct the model,which is not convenient for promotion.This paper will use the numerical calculation method to deeply study the influencing factors of FAC and modify the FAC model.Based on the MIT model,the FAC mathematical model of carbon steel in single-phase flow is established.The solubility of Fe₃O₄ in solution at different temperatures and different pH is calculated.The flow field distribution is simulated by the software of Fluent,and the mass transfer coefficient is calculated and applied in corrosion model.Finally,the FAC of the straight pipe is calculated using the established model.The calculation results show that the temperature and pH affect the concentration of Fe²⁺in the solution.The proper increase of pH can effectively inhibit FAC.The temperature reaches the peak at 150°C approximately.The inlet flow velocity affects the flow field distribution in the straight pipe.Increase the flow velocity makes the shear stress on the inner wall surface of the pipe larger and enhances the mass transfer process to increase the FAC rate.Aiming at the influence of flow field variation on FAC,two kinds of pipes,90°elbow and orifice plate,are selected,and geometric models are established in Fluent respectively.CFD technology is used to simulate the flow field distribution of 90°elbow and orifice.The flow field simulation results of the 90°elbow show that at the entrance of the elbow,along the radial direction of the pipe,from the inner curved side to the outer curved side,the fluid velocity gradually decreases;along the flow direction,the fluid velocity on the inner curved side increases rapidly and then gradually decreases,and the fluid velocity on the outer curved side gradually increases.The maximum speed and minimum speed at the elbow are on the inward bend side.Using the FAC calculation model,the FAC rates of the 90°elbow and the downstream of orifice at different inlet velocity are calculated.The calculation results of the90°elbow show that the FAC maximum and minimum values are located on the inward curved side,corresponding to the flow field distribution.Changing the radius of curvature of the elbow affects the flow field distribution inside the tube.Comparing the simulation results of the orifice plate with the FAC calculation results,it is found that increasing the inlet velocity and increasing the aperture ratio shift the FAC peak region position downstream of the orifice plate.When the inlet velocity is between 0.8m/s and 5m/s and the pore size ratio is0.5,the FAC high-incidence zone is distributed from 2.4d to 3.2d.When the aperture ratio is0.4,the FAC hazardous zone is located between 2.1d and 2.9d.When the ratio is 0.25,the peak area of FAC is distributed from 1.4d to 2.2d.The experiment mainly studies the influence of flow field changes on the FAC at the 90°elbow.According to the purpose of the experiment,a circulation loop test bench with heating device is designed and built.The experimental system consists of a circulating water system,a heating device and temperature control,an experimental pipe section,a measuring system and a safety device.The circulating water tank,the water replenishing system and the variable frequency centrifugal pump are used to ensure the circulating flow of the working fluid in the experimental circuit.The high-temperature variable frequency centrifugal pump with appropriate head is selected to control the flow velocity change inside the pipe to prevent the cavitation phenomenon of the pump.The temperature control system is designed to study the effect of fluid temperature changes on FAC.After the design and construction of the test bench is completed,it can be used for in-depth research of subsequent topics.