Relationship Between the Structure of Disturbed Flow and Erosion–Corrosion

Flow-dependent erosion–corrosion often occurs under disturbed flow conditions at geometrical irregularities such as fittings, valves, and weld beads. Flow separation and reattachment produces high turbulence intensity and particle–wall interactions that can lead to high erosion–corrosion rates. This paper presents the predictions of 2-D turbulent, single and two-phase liquid/particle flow with recirculation, after a sudden constriction and expansion. The model is based on a two-phase flow version of a standard k–ϵ model of turbulence and a stochastic simulation of particle–fluid turbulence interactions. It is capable of successfully predicting local values of time-averaged fluid velocities and turbulence intensities, as well as predicting particle dispersion, and particle–wall interaction. The numerical predictions of the flow structure are used to explain the results of an experimental erosion–corrosion study of water and water/sand mixture flowing in a pipe with a sudden constriction and expansion. It is shown that in case of disturbed single-phase flow, it is appropriate to correlate local near-wall parameters of flow with the metal loss rates. The simulations have shown that local near-wall intensity of turbulence is the important factor affecting mass transfer-controlled corrosion in disturbed flow, rather than the wall shear stress. In case of single-phase flow, comparisons revealed a significant effect of local turbulence intensity on corrosion rate of the base metal. In case of two-phase flow, maximum metal loss coincided with local maximums of particle–wall mean impact frequency.