Simulation And Experimental Research On Flow Accelerated Corrosion Of Single-phase Flow Carbon Steel Pipes In Power Station

The water and vapor transmission pipelines of nuclear and thermal power plants are made of carbon steel,and the flow of the mass will accelerate the decomposition and destruction of the protective oxide film on the inner wall of the pipeline,resulting in the continuous oxidative consumption of the pipe wall.This process is known as flow accelerated corrosion(Flow accelerated corrosion,FAC).Since it was first reported,the pipeline rupture accidents caused by FAC have never ceased worldwide,which not only caused huge economic losses,but also resulted in tragedy of human casualties.This paper uses a combination of numerical simulation and experimental methods to investigate the mechanism of FAC in single-phase flow carbon steel pipelines,establishes a corrosion rate prediction model,and proposes methods to mitigate FAC on this basis.The main contents are as follows.(1)A high-temperature recirculation loop experimental bench was built and temperature,pressure,flow rate,p H and other key operating parameters were regulated to conduct singlephase flow carbon steel pipeline FAC tests reflecting actual operating conditions.A 90° eblow was used as the test section,and an array of electrodes was embedded at different locations on the pipe wall.The polarization curves measured at each electrode were analyzed to obtain corrosion currents,and the local FAC rate at each electrode location was calculated.Based on this method,the effect of different inlet flow rates on the FAC of different carbon steel materials(10#,45# and Q235 carbon steel)eblow under high temperature conditions was investigated.The experiments show that the maximum FAC rate in the test section all appear downstream of the outward curve side,which is the most prone location of FAC accidents;the FAC rate increases with the increase of the inlet flow rate;the corrosion process becomes slower with the increase of the Cr content of carbon steel.(2)A FAC prediction model with the introduction of geometric influence factor was established,the FAC rate distribution law of the inner wall of the eblow was analyzed,and the mechanism of the local flow field affecting the FAC of the eblow was investigated.Simulating the distribution of fluid dynamics parameters in the eblow of the test section,the local flow parameters were substituted into the Sanchez-Caldera prediction model,and the calculated FAC rate results were not consistent with the test results.The local geometric influence factor in the eblow was introduced to modify the prediction model,and the calculated results of the modified model were in good agreement with the experimental results.The calculation results show that the maximum value of FAC in the eblow section is located at the downstream position of the outward curve side,which is consistent with the experimental results;the FAC rate on the upstream inward curve side of the eblow is larger than that on the outward curve side,and the maximum value on the inward curve side is located upstream of the eblow;the magnitude of the absolute flow velocity on the inwed curve side of the eblow can reflect the magnitude of the FAC rate;the FAC rate in the eblow increases with the increase of the inlet flow velocity.(3)The established FAC prediction model was used to analyze the characteristics of the FAC distribution in the pipe downstream of the throttling orifice,and the effects of chamfering angles and inlet flow rates on the FAC distribution downstream of the orifice was studied,and methods to mitigate FAC were proposed.The distribution of flow parameters in the downstream pipe of the orifice plate was simulated and substituted into the prediction model to calculate the distribution of mass transfer coefficient and FAC rate in the downstream of the orifice.The simulation results are in good agreement with the experimental results in literature.The results show that when the chamfer angle is certain,the mass transfer coefficient and flow-accelerated corrosion rate increase with the increase of the inlet flow rate,and the peak corrosion position is slightly shifted downstream;when the inlet flow rate is certain,the mass transfer coefficient and corrosion rate decrease and then increase with the increase of the chamfer angle,and the peak corrosion position moves downstream from the orifice.The mass transfer coefficient and FAC rate are maximum at 90° and minimum at 45°.Therefore,setting the chamfer angle to 45°when designing the throttle orifice can slow down the FAC rate downstream of the throttle orifice.The use of carbon steels with higher Cr content at locations with high incidence of FAC can also slow down the FAC rate.The research results of this paper are important for nuclear and thermal power plants to mitigate single-phase flow accelerated corrosion and improve the safety of unit operation.