Increasing Acid Dew POINT Corrosion Resistance with Thin Coating Layer on STEEL

Abstract

Acid dew point corrosion is a common phenomenon for industrial equipments such as duct, stack, gas gas heater (GGH) in plants using fossil fuels. During the burning process, sulfur in fossil fuel is oxidized to produce sulfuric dioxide (SO2) and further oxidized to sulfuric trioxide (SO3). Under the dew point temperature, water drops form on the surface of equipments along with sulfuric trioxide to develop sulfuric acid (H2O+SO3àH2SO4). Sulfuric acid causes severe damages to equipments and special steel products that are strong against acid dew point corrosion are on the market in the form of cold rolled (CR) or hot rolled (HR) steel. Although these products have stronger corrosion resistance than normal steel to sulfuric acid, life span is still short and further increase of corrosion resistance is required. In this research, we applied thin coating layer to steel and studied how corrosion resistance is changed. Concentration of sulfuric acid on steel equipments is varied according to temperature. A couple of test coupons with 38 mm diameter were immersed in controlled sulfuric acid solutions and weight differences were measured before and after corrosion test. Different types of coatings were applied and tested. Inorganic type coating seems to provide efficient protection against sulfuric acid corrosion but localized corrosion occurrs. We propose a possible solution for localized corrosion as well. Bar coating was used to prepare coating steels and spark erosion was used to make coin type test coupons. Coating layers were observed by various analytical tools including FT-IR, SEM, EPMA, GDS etc.