Dynamic Air Deposition (DyAir) is a novel coating method designed to protect the tubing of power and black liquor recovery boilers against corrosion attack at elevated temperatures. The method utilizes the energy of combustion of gaseous fiel and air to heat the powder material to a temperature just below its melting point and accelerate it over 600 m/s to form a coating. The Ni-Cr and Ni-Cr-Mo DyAir coatings revealed no gas permeability and extremely low oxygen content. Compared to the electric
arc and HVOF-sprayed coatings, the DyAir coatings exhibited higher hardness and better crack resistance. During aging at 400 and 700°C the bond strength and crack resistance of the DyAir coatings increased dramatically due to intensive difision processes in absence of internal corrosion attack. The DyAir coatings revealed outstanding resistance to corrosion, such as sulfidation attack in presence of hydrochloric acid gas at 400°C, oxidation attack at 700°C and oxidation attack in presence of chlorine at 400°C. Keywords: boiler, coating, gas permeation corrosion resistance, sulfidation, oxidation, chlorine, alloy 625, alloy 671