Does anyone know where I can find data to confirm/refute the possibility of accelerated sulfidation of 300-series stainless steel when it is sensitized?
High Temperature Corrosion of Engineering Alloys, by George Lai, ASM International, ISBN 0-87170-411-0
This book has the best high temp info. Mechanisms, corrosion rates, mitigation, it is very complete.
Any reduction in Cr will hurt, since the Cr Oxide is your primary protection.
What is your environment, temperature and resulting failure?
Often 321 holds up much better than 304, and people presume that it is related to sensitization. There is another factor, in the 321 a lot of the Ti ends up in the oxide layer and makes it more stable.
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Rust never sleeps
Neither should your protection
Application is a hot feed gas valve in a hydrocracker. Thanks, Ed
Piping upstream is 321 stainless steel. The valve body is 316 stainless steel as is the stem. Environment consists of >985F hot sour gas (approx 2wt%H2S, 78% H2, methane 15%) from a Hydrocracker reactor bypass. The current valve has had to be rebuilt every year because so much corrosion product builds up and the valve body and stem (also 316) are corroding that it needs to be serviced every year. Corrosion product consists primarily of Fe, Cr, Mo, and S. Some minor Ni.
Type 321 or 347 stainless steel seem appropriate for the stem and body.
You mentioned that sensitization is only one factor in lowered sulfidation resistance, but is it the primary reason for lower sulfidation resistance of the 316 vs. 321 at these temperatures? Are there any problems with using 347 in place of 321 or 316 in this service?
316 does not sound like the right choice. Mo will not help in sulfidation. Are you sure that it is sulfidation? Do micros show sulfide nodules in the structure? Or is this surface attack?
If you only need a bit of improvement look at 310 as an option. The higher Cr and Ni help. If you want great resistance we can go to hihger alloy grades.
= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
