Modelling of the kinetics of pitting corrosion by metal dusting

Commercial 800HT alloy was exposed to 49.1%H2-12.8%CO-3.1%CO2-1.6CH4-33.4%H2O gas at 21 bars and 570 °C up to 5000 h. Metal dusting attack by pitting was observed. The kinetics parameters were identified to be the incubation time, pit density and individual pit growth rate. These parameters were introduced in a nucleation-growth model to simulate the pitted surface area kinetics. This model was then extended to the volume considering several geometrical hypotheses. Considering only surface coalescence of the pits without their volume coalescence allowed to correctly reproduce the experimental mass loss kinetics. An even simpler conservative model was proposed for an easy lifetime modelling.