Is post-weld heat treatment required for stainless steel composite steel pressure vessels in stress-corrosion environments?
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Is post-weld heat treatment necessary for stainless steel composite steel pressure vessels in stress-corrosion environments? Our facility has a pressure vessel made of 321+Q345R composite steel plates, with a design pressure of 4.0 MPa; the medium used is semi-water gas, which contains high levels of hydrogen sulfide. The device was not originally designed to require post-weld heat treatment. After one year of use, stress corrosion cracks of varying degrees were found in various welds and surfacing areas inside it. Now a new unit needs to be manufactured; in this case, is it necessary to include post-weld heat treatment?
Performing post-weld heat treatment can eliminate the residual thermal stress in the welds; although this affects the stainless steel’s resistance to intergranular corrosion, its resistance to stress corrosion is significantly enhanced
Since the problem has been identified and the cause found, let’s go ahead and do it.
3# csme \ OP, it depends on the thickness of the Q345 plate. Since there was a problem with the previous one, the material can be changed; using duplex steel is also an option
Hydrogen sulfide has no effect on the stress corrosion of stainless steel. Are there chloride ions in the water? That is what causes stress corrosion in stainless steel. I don’t know what the components of semi-water gas are.
Under normal conditions, stainless steel is not sensitive to stress corrosion; however, it is still necessary to conduct a thorough analysis of the causes of the problem in order to find an effective solution. It is recommended to inspect the welding process and perform PT testing on the surfacing surface and the inner surface of the weld joint.
In my personal opinion, post-weld stress relief heat treatment should be carried out
If the drawings do not specify any special requirements, in order to ensure the corrosion resistance of the composite layer, pressure vessels made from stainless steel composite plates are not subjected to post-weld stress-relief heat treatment. As per the issue you mentioned, the problem may lie in the welding process; it is recommended to adjust this process and to follow it strictly during welding. (Your assumption is that the base material is fine.)
Stainless steel cannot be subjected to post-weld heat treatment, as it undergoes sensitization when exposed to certain temperatures for an extended period of time. Stainless steel that has been sensitized is prone to intergranular corrosion in corrosive environments. Therefore, welds of stainless steel are usually not subjected to post-weld heat treatment.
Was any post-weld heat treatment performed in the end?