STEADY-STATE MODEL FOR EROSION-CORROSION OF FEEDWATER PIPING

The erosion-corrosion (EC) of carbon steel in water of low dissolved oxygen content occurs due to flow-assisted dissolution of a normally protective magnetite film that forms on the surface. From the overall reaction involved in formation and dissolution of the film, one mole of hydrogen gas is generated for each mole of iron consumed. A fraction, b, of the hydrogen generated will diffuse into the steel From the hydrogen generation and the flux rates, the EC rate was calculated by using a simple model consisting of two stages in series. The first stage is the dissolution of the oxide film, and the second stage is a hydrodynamic diffusion of ferrous ions across the mass transfer boundary layer. The EC rate, calculated by using this model using known thermodynamic, hydrodynamic, and diffusional parameters, is in good agreement with published values. In particular, the evaluation of the steady state EC rate showed a peak in the rate vs temperature in agreement with experimental results.