"C-276 and C-22 Materials and SCC"

Question:

"We have seen about 6 months of service life from a vessel that sublimes Aluminum Chloride. The liner of this vessel is constructed from Hastelloy C-276. We have repeatedly experienced intergranular stress corrosion cracking in the Heat Affected Zones of the C-276 welds. This is supposedly caused by the C-276 sensitizing (precipitates out chromium) during welding. We are using the correct filler rod materials? The liner sees 525 degress F and the vessel operates under a nitrogen purge to eliminate moisture contacting the AlCl3. There is no corrosion on the C-276 base material. Has anyone experienced a similar situation? The recommended fix thus far is to change to Hastelloy C-22 which is less likely to sensitize during welding. There are a lot of questions whether stress relieving, shot-peening, or passivating techniques should be utilized to improve these HAZ areas?"

Answer:

I am familiar with intergranular corrosion issues with C-276, but not IGSCC, as occurs with the 300 series austenitic stainless steels. Yes, Haynes standard recommendation is to "upgrade" to C-22. I am presuming that someone has accurately disgnosed the problem as IGSCC. In similar discussions with Haynes they have stated that one can use a C-22 or even B-2 filler metal to improve the corrosion resistance of welds; however, that will not improve HAZ resistance. Shot peening should help with IGSCC but not intergranular corrosion.

 

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