What’s causing the cracks at the tower connection?
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Our company has a distillation tower that has been in use for nearly two years. Over the past two days, cracks were detected at the joints where the tower is connected to the heat exchanger, as well as on the tower’s shell (photos available). After grinding and welding, longitudinal cracks appeared again at the edges of those welds (photos available). Could anyone help analyze what caused this? The welding material used was A022, while the base material was 316L
What is a medium? What was the original direction of the crack?
Stress calculations should be performed on this takeover; excessive local stress may cause the wall thickness of the cylinder to be insufficient
For stainless steel, it is recommended to consider the following aspects: medium, content of elements such as sulfur and phosphorus, microstructure, welding process, and the degree of defect removal.
It seems to be caused by deformation due to stress changes; it is recommended to disconnect the connection pipe and reattach it. Additionally, the factors of hot and cold deformation should also be considered for reference.
HCL, DEIP, phosgene
Macroscopically, it is a transcrystalline crack caused by internal stresses; given that the medium in question is likely chlorine, acids, and phosgene, it is suspected that chloride-induced stress cracking is the cause. It is important to check the chloride ion content and oxygen content in the medium. Test the hardness around the crack, as well as the ferrite content and the surface again; use nickel-based welding materials to repair the cracked area and see if there is any improvement.
The chloride ion level is too high; it’s necessary to change the material of the equipment. This issue was encountered 20 years ago with sodium ion exchangers operating at around 0.3 MPa at room temperature; after regeneration using salt, cracks appeared near the welds, and these cracks reappeared even after further repairs. The weld is fine; finally, epoxy resin was applied inside, and that’s it.