Cracks appeared 20 mm at the front end of the weld in stainless steel S30408
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Our unit has a jacketed low-pressure pressure vessel (0.5 MPa). After being in use for half a year, oil leakage occurred at the welds of the tubes inside the vessel, which are made of S30408 material. We had the manufacturer carry out repair welding, using A102 welding rods and a DC welder with a current of 110 A. Cracks appeared 20 mm ahead of the weld area; after repairing those cracks, new cracks formed in other places. We then tried TIG welding with a current of 60–80 A, but the same problem occurred. We seek advice from experts regarding the causes and solutions
What material is it? What is the operating temperature?
It may be due to the influence of the medium or temperature; the solution is to replace the new pipe fittings for both sides of the weld as well as the heat-affected zone.
Was the oil cleaned off completely during the patch welding? If this happens after cleaning, it means the carbon content in the material has increased, and it’s difficult to fix it. Wherever you try to repair it, cracks will appear; it’s better to replace it
The material is desulfurization gypsum, which has weak acidity. The operating temperature inside the container is 150 degrees, and the operating pressure is 0.4 MPa. Heat transfer oil is used in the jacket, with a temperature of 180 degrees
The cracks within the existing welds were not thoroughly removed, resulting in delayed cracking
This situation is still rare; did it crack right after welding? Or does it crack after being welded and used for some time? The former mainly focuses on welding process control, while the latter focuses on the influence of the medium! These are just my personal opinions!
If such problems occur during welding, it is mainly likely to be a problem with the S304 stainless steel material. A batch of flanges from our company also encountered similar problems; a material analysis revealed that it was due to issues with trace elements in the stainless steel!