Abstract
High temperature corrosion of the water-wall tubes for the low grades oil firing boilers was investigated during operation under low-oxygen combustion condition. Adjacent to the corroded area near the burner, combution gas contained 0.3-0.6% of oxygen, 0.4-1.0% of hydrogen, hydrogen sulfide and other reducing compounds. The scale deposited on the corroded surface of the water-wall tubes was mainly composed of the metal oxide at outer layer and the metal sulfide at inner layer. Corrosion in these cases was caused by sulfidation reaction of the metal surface with sulfate compounds such as sodium sulfate and unburned carbon in the low oxygen concentration combustion gas. The sulfidation of water-wall tubes in actual boilers can be prevented by Plasma spray coating of 50%Ni-50% Cr alloy.
