Abstract: To prevent the increasingly serious problems of high temperature corrosion of water walls in boilers, the research on the distribution of the near wall atmosphere is carried out in a 300MW boiler. With the test data of high temperature corrosion kinetics of the water wall materials 12Cr1MoV, the corrosion rate under different temperature, atmosphere and cracking period of corrosion layer is forecasted such that the corrosion tendency standard of water walls in boilers at different running time is put forward. The relationship between the corrosion rate and the H₂S concentration, the corrosion time and the cracking period of the corrosion film is established, and the limiting concentration of atmosphere near walls is obtained with the cracking period of 24 h and 48 h as examples. The results show that the concentration of H₂S near walls is proportional to the concentration of CO, but inversely proportional with the concentration of O₂. The high temperature corrosion rate change with time follows the parabolic law, while the change with temperature complies with the Arrhenius law. and the change with H₂S concentration follows the exponential law. As long as the atmosphere near walls is controlled within the limiting concentration range, the serious high temperature corrosion could be prevented.

Key words: coal fired boiler, water walls, high temperature corrosion, H₂S, corrosion judging standard, cracking of corrosion film