Abstract: A certain reaction kettle was found to have obvious leakage after 3 months of use. The cracking cause of the reaction kettle was analyzed using macroscopic observation, scanning electron microscopy, energy spectrum analysis, metallographic examination. The results show that the middle of the weld seam of the additional nickel plate inside the reaction vessel cracked, and the toe of the weld seam of the external stainless steel plate cracked, causing leakage in the reaction vessel. The nature of the internal weld crack was welding hot cracking, and the nature of the external weld crack was stress corrosion cracking.