Prediction of H2S corrosion depth for water-cooled wall in lower furnace of utility boiler

The presence of H2S near the water-cooled wall of utility boiler can lead to accelerated corrosion wastage on the furnace wall. While the existing evaluation of annual corrosion wastage caused by H2S is not suitable for the boiler that operated in a wide load range. In this study, a novel H2S corrosion model is developed to predict the metal wastage of water-cooled walls in the lower furnace. Three key independent variables including metal temperature, H2S concentration and corrosion time are considered simultaneously. Based on the experimental corrosion data of pure Fe and boiler steel SA213-T2, the prediction model is represented by a mathematical equation derived from the regression analysis. The validation of this equation is conducted by comparing the predicted and lab-scale corrosion depths, and a reasonable agreement is obtained. The single-factor analyses indicate that the corrosion depth of SA213-T2 almost increases linearly with the increase of H2S concentration, and the growth rate of corrosion depth could raise as the metal temperature increases. Under the extreme condition that temperature as 773 K and H2S as 800 ppm, the predicted annual corrosion depth of SA213-T2 is 1129 mu m. In practical terms, the annual corrosion wastage should be calculated by summing the sub-wastages formed during different periods of a year. The predictive model proposed in this study could play an indispensable role in the sub-wastage calculation and benefit the estimation of the annual corrosion wastage.