1. Appearance inspection: water leakage test, it was found that there is a leakage point at the connection between the receiving and the shell. After careful observation, there are obvious small cracks in the welding seam of the Horizontal WFI tank.

2. Macroscopic inspection of the fracture: the shell crack is located adjacent to the connection and welding seam, and it is serrated.

3. Chemical composition detection: carry out chemical composition analysis on the shell and receiving samples. The chemical composition of the shell conforms to the GB/t4237-2007 standard, the receiving chemical composition conforms to the GB/t14976-2012 standard, and the data conforms to the standard requirements.

4. Metallographic inspection: Cut the test block at the crack of the Horizontal WFI tank to prepare the metallographic sample. The samples were visually inspected under a microscope to be free of corrosion. The non-metallic inclusion content in the shell test block is evaluated as c1.5 and d1.5 according to the GB/t10561-2005 standard, and the inclusion content is low. Through further indecent inspection, it was found that the cracks expanded from the shell surface to the interior in the form of crystals, and the entire cracks were in the form of a network. The composite crack is adjacent to the welding seam and belongs to the welding heat affected zone, which is a crystalline crack in the welding hot crack.

5. Hardness test: cut the hardness test block at the crack of the shell, and test 4 points. 3 points higher than the standard value of 210hv.

6. Reason analysis: According to the above analysis, during the welding process of the Horizontal WFI tank and the receiving, in the temperature range of 500-850 ℃, a heat-affected zone close to the tank shell is formed. At the same time, the hardness of the shell plate exceeds the standard, the effect of solution treatment is not good, and the carbon in the solid solution and austenite also increases the tendency of welding sensitization. The mutual cooperation of the two causes the shell to produce intergranular corrosion cracking, resulting in cracking and leakage.