Flow-Accelerated Corrosion (FAC) is a phenomenon that induces carbon steel to degrade, which usually occurs in secondary loop pipes of nuclear power plant. Many accidents have happened because of FAC in many countries in the world. FAC rate and the sensitive positions which were prone to FAC for carbon steel in single liquid phase flow were studied by means of numerical simulation with reasonable assumptions.
Wall function and turbulence model were used in this study. The numerical hydrodynamics models and mass transfer model were defined in accordance with the basic theory of hydrodynamics and conservation principle of mass, momentum and energy. The FAC model for carbon steel in single liquid phase flow was proposed according to basic processes of FAC.
FAC rate for straight pipe was firstly calculated with the model. It was found that FAC rate was influenced greatly by temperature, pH value and flow velocity. With the increasing of temperature, the variation of FAC rate was presented as a bell-shaped curve with a maximum around 150℃. The solubility of Fe3O4 reduced with increasing pH value, which caused reduction of FAC rate. FAC rate changed greatly as the flow velocity increased due to that the thickness of fluid boundary layer reduced with the increasing of flow velocity. The numerical FAC rate was in accordance with that measured by experiments, which proved that the FAC model was correct and accurate and the hypothesis was reasonable. These results were very significant and helpful in preventing FAC-induced accidents from happening.
The positions which tended to FAC were studied for sudden pipe expansion and adapter bonnet. Vortexes were formed for sudden pipe expansion which resulted in the increase of shear stress and FAC rate. FAC rate changed with gradient changing for adapter bonnet. When gradient was less than 30o, fluctuation of FAC rate was slightly.
The positions which were prone to FAC were finally studied for three-dimensional elbow. It was found that FAC rate was greater at intrados of upstream position and extrados of downstream position than other positions.
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