How to repair cracks that occur due to hydrogen infiltration in stainless steel equipment

Hydrogen infiltration causes the steel to reach its allowable stress limit and crack; it is estimated that it shouldn’t be just in one place. . . It is best to first determine whether the material chosen is appropriate, and then decide whether to repair it or use it for another purpose. . . During repair, use appropriate testing methods for spot checks. . . Generally, electric heating is used to preheat the steel in order to remove the dissolved hydrogen within it before welding. . . . The hydrogen embrittlement problem is very serious. . .

Then, could you explain to me the mechanism by which hydrogen penetration occurs? Isn’t stainless steel resistant to hydrogen?

This is already the stage of hydrogen corrosion; hydrocarbon reactions occur, producing methane which leads to decarburization of the steel, as well as the formation of numerous grain boundary cracks. The strength and ductility of the steel change significantly, resulting in permanent brittleness. At this point, even dehydrogenation treatment cannot restore the properties of the steel. Hydrogen corrosion occurs mainly due to excessively high temperatures; moreover, choosing materials resistant to hydrogen corrosion is an option – one can refer to the Nelson curve for this purpose, though I find it a bit difficult to understand. Please give me some advice.

Hydrogen corrosion generally comes in low-temperature and high-temperature types. The low-temperature type is generally considered to be electrochemical corrosion, which occurs in the presence of an aqueous solution. The hydrogen generated by metal electrochemical reactions penetrates into the steel; where cracks, inclusions, and other defects are present in the steel, hydrogen atoms combine to form hydrogen molecules, resulting in the formation of bubbles. The high-temperature type occurs when hydrogen penetrates into steel in an anhydrous solution, primarily causing hydrogen embrittlement, surface decarburization, and hydrogen erosion. Currently, chromium-molybdenum steel is commonly used for hydrogen-resistant steel. It can basically meet the requirements. During welding, special attention should be paid to the quality of the weld; appropriate welding techniques as well as necessary pre- and post-weld heat treatment methods must be employed.

Perform patch welding, then conduct non-destructive testing to check for any remaining defects

If there are few cracks, it can be repaired by welding after heat treatment; if there are many cracks, it is basically beyond repair.