How to Check for Leakage in Stainless Steel Storage Tanks

Stainless steel storage tanks have strong corrosion resistance and are not affected by external air and water. And it has good sealing performance. It is also a widely used storage tank in various industries. Stainless steel storage tanks may experience leakage after being used for a long time. How should we check if this situation occurs

1. Conduct appearance inspection: Through a water filled test for leakage, it was found that there were leakage points at the connection between the connecting pipe and the shell. Carefully observe the welding part for small cracks.

2. Macroscopic examination of fracture surface: Observe the crack location of the shell, and the shell crack is located in the welding area close to the nozzle, showing a serrated shape feature.

3. Chemical composition inspection: Conduct chemical composition analysis on the shell and nozzle samples. The shell chemical composition meets the GB/T4237-2007 standard, the nozzle chemical composition meets the GB/T14976-2012 standard, and the data meets the standard requirements.

4. Metallographic inspection: Cut off the test block at the ruptured part of the stainless steel storage tank to make a metallographic test sample. The test sample is first observed under a microscope without corrosion, and the material is relatively low. Further observation reveals that the crack extends inward along the crystal from the surface of the shell, forming a network like structure. The combined crack appears near the welding zone and should belong to the welding heat affected zone. Therefore, the crack is a crystal crack in the welding heat affected zone.

After water erosion, it was found that the matrix structure of the shell was austenite+a small amount of carbides. Continuing observation, the crack begins in the welding heat affected area, and the black part is the site of crystal detachment. Black carbides can be seen near the grain detachment and at the grain boundaries.

5. Hardness inspection: Cut off the hardness test piece at the cracked part of the shell, and inspect 4 points, with 3 points exceeding the standard value of 210HV.

Based on the above analysis, during the welding process of the shell and connecting pipe, it is adjacent to the heat affected zone of the shell, with a temperature of 500-850 ℃, forming a welding sensitive zone. At the same time, the hardness value of the shell steel plate exceeds the standard, and the solid solution treatment effect is poor. The carbon in the non solid solution and austenite also increases the inclination of the welding sensitive zone. The combined effect of the two causes intergranular corrosion cracks in the stainless steel storage tank, causing crack leakage.