Causes of large area corrosion of ND steel for low temperature economizer

A large area of corrosion occurred in ND steel of low temperature economizer in a power plant. The causes of corrosion were studied by means of macroscopic observation, chemical composition analysis, metallographic examination, hardness test, scanning electron microscope analysis, X-ray diffraction analysis and ion chromatography analysis. The results show that the chemical composition, microstructure and microhardness of the samples all met the requirements of the standard. The leaked water dissolved the sulfide in the flue gas to form an acidic solution, which was adsorbed to the outer surface of the pipe. The dissolved F^-, Cl^-and SO^2-₄ destroyed the protective film on the surface of the ND steel pipe wall, resulting in large-scale corrosion of the low-temperature economizer. Finally, suggestions for improvement were put forward to avoid large-scale corrosion of ND steel in low-temperature economizer.