Abstract: During the regular inspection of a certain gasifier, it was found that there were a large number of dendritic cracks in the welding layer of the quenching chamber wall of the gasifier, and penetrating cracks appeared at the inlet connection of the quenching water. The causes of cracking in the gasifier were analyzed using methods such as macroscopic observation, water quality analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that the black water at the bottom of the gasifier contained a large amount of chloride ions, and the nickel element content in the stainless steel cladding layer of the quenching chamber was relatively low. Moreover, the gasifier had been in service under high temperature and stress conditions for a long time, ultimately led to stress corrosion cracking of the cladding layer.