Analysis of leakage causes of stainless steel condenser, when using stainless steel condenser, it is inevitable that leakage will occur. Then what are the reasons for leakage of stainless steel condenser? Next, we will analyze the leakage reasons of stainless steel condenser, hoping to be helpful to users'friends. 1. Appearance inspection. After water leak test, it is found that there are leak points at the joint of nozzle and shell. After careful observation, there are obvious tiny cracks in the weld. 二、断口宏观检查
2. Macroscopic examination of fracture surface
It is found that the cracks in the shell are located near the welding seam of the nozzle, showing a zigzag morphology.
III. Check of Chemical Constituents
The chemical composition of the shell and nozzle samples were analyzed. The chemical composition of the shell met the GB/T4237-2007 standard, the chemical composition of the nozzle met the GB/T14976-2012 standard, and the data met the standard requirements.
IV. Metallographic Detection
Metallographic specimens were prepared by intercepting specimens from cracked parts of the shell. Microstructure of the specimens was observed without corrosion. The grade of non-metallic inclusions in the shell specimens was evaluated as C1.5 and D1.5 according to GB/T10561-2005 standard, and the grade of inclusions was relatively low. Further observation shows that the crack propagates from the shell surface to the interior in a transgranular manner, and the crack appears as a net shape as a whole. Combined with the crack appearing near the weld zone, it should belong to the welding heat affected zone, so the crack is the crystalline crack in the welding hot crack.
After erosion by aqua regia, it was found that the structure of shell matrix was austenite + a small amount of carbide. Further observation showed that the crack originated in the heat-affected zone of the weld, and the black part was where the crystals fell off, and black carbides precipitated near the grain shedding and at the grain boundary.
The hardness test pieces were intercepted at the crack position of the shell. Four points were detected, and three points were greater than the standard value of 210HV.
According to the above analysis, in the process of shell and nozzle welding, the heat affected zone adjacent to the shell, the temperature is 500-850 C, forming a welding sensitization zone. At the same time, the hardness value of shell steel plate exceeds the standard, the effect of solution treatment is not good, the carbon in austenite and not all solid solution also increase the tendency of welding sensitization. The joint action of the two causes intergranular corrosion cracking of the shell, which results in cracking and leakage. 。
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