How to weld repair 304H flange that has SCC due to polythionic acid
How to weld repair 304H flange that has SCC due to polythionic acid
(OP)
I have a large diameter SS304H flange that has several cracks in the process exposed face. Flange has been in 1300F service for 17 years. Cracking seems to have developed after shutdown and exposure to atmosphere. Suspect polythionic acid attack. Has anyone developed a recommended cleaning, excavation and weld repair procedure?





RE: How to weld repair 304H flange that has SCC due to polythionic acid
RE: How to weld repair 304H flange that has SCC due to polythionic acid
Thanks for you question and reply
RE: How to weld repair 304H flange that has SCC due to polythionic acid
You can look at polishing spots and looking at the microstructure.
It is probably sensitized (chrome carbides in the grain boundaries. This makes it much more susceptible to SCC (chlorides or pta).
If the micro isn't too bad then maybe clean, re-anneal, inspect, grind out cracks, weld repair, inspect, chase new cracks, and so on.
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Plymouth Tube
RE: How to weld repair 304H flange that has SCC due to polythionic acid
RE: How to weld repair 304H flange that has SCC due to polythionic acid
It is foolish to try a repair.
Replace it with the correct metallurgy.
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Plymouth Tube
RE: How to weld repair 304H flange that has SCC due to polythionic acid
RE: How to weld repair 304H flange that has SCC due to polythionic acid
You can repair, but will still have suspect metallurgy in remaining, uncracked material, as well as a dog's breakfast of different metallurgies and PASCC susceptibilities.
RE: How to weld repair 304H flange that has SCC due to polythionic acid
RE: How to weld repair 304H flange that has SCC due to polythionic acid
As hastelloy or inconcel are exorbitantly expensive, I would chose the refractory line nozzle if your nozzle is >= 12". (and you can probably even go to a carbon steel nozzle)