Electrochemical studies of heat‐treated NiCrMoFeCoAl and NiCrMoFeCoAl‐30%Cr₃C₂ HVOF coatings on T22 boiler steel

Abstract

Corrosion is one of the main detrimental aspects that cause major economic losses in various industrial applications. [1][2] The degradation of materials employed in high-temperature boilers by electrochemical corrosive mechanism results in rapid and total process failure and even the loss of life. The failure of the machinery is attributed to metal/alloy corrosion in boilers at elevated temperature and pressure conditions. Annually, multimillion-dollar losses are caused by the corrosion of the metals and alloys in the high-temperature industrial applications. 3 The electrochemical corrosion of metal and alloys is a progressive process that is enhanced by high temperatures and under boiler operating conditions. Generally, the material degradation proceeds both on internal and external surfaces of the boiler steel under extreme thermal, pressure, and electrochemical conditions. The SAE213-T22 steel alloy is widely used in petrochemical and power generation plants. However, the critical issues are the corrosion at high temperatures in the boiler and electrochemical degradation at neutral pH electrolytic conditions. 4 In earlier research reports, the corrosion rates were evaluated for the coated and uncoated alloy exposed to corrosive conditions in a molten salts environment. [5][6][7][8][9][10][11][12] The corrosion rates of bare alloy are higher than the coated samples as the coating act as a protective barrier coating and prevents the easy interfacial charge transfer. 13 Furthermore, these protective layers are formed on metallic surfaces in an impedance model, which acts as a thermal barrier coating and decreases the corrosion rate. At high temperatures, molten salt corrosion is observed in the petrochemical and