caustic embrittlement

[whaider]

Can some body explain the phenomenon of caustic embrittlement, conditions promoting it and supressing it etc.

[ashfaqanwer]

Caustic embrittlement is a form of stress corrosion cracking which is normally observed in carbon steel and austenitic stainless steel materials (like SS 304, 316 and other 300 series SS) in concentrated hydroxide service with temperature between 100 to 250 deg C (depends upon caustic concentration).
It reduces the ductility of a material and makes it brittle which can eventually fail under stress.

More the concentration of hydroxides and with carbon steel material in service, caustic embrittlement occurs at even lesser temperature. You may consider following factors to mitigate the chances of caustic embrittlement:
1. Reducing stresses after welding or other fabrication operations. PWHT shall be done on the weld joints to reduce the residual stresses.
2. Control hardness of weld joints.
3. Use the appropriate material considering two important factors hydroxide concentration and the service temperature.
4. Service temperature must be maintained within the limits as allowed by the applied material.

[whaider]

thanks ashfaq can you plz share some sort of curve or other data so that i can use it for practical purposes.

[ashfaqanwer]

Attached find a graph which takes temperature and concentration to suggest the right material.