I have chosen SS316 as the tubing material for my application, wherein high temperature corrosive fluid is to be passed the tube. Can anybody suggest me a better alternative for SS316? The temperature of the fluid is about 700-800 °C.
What kind of corrosive liquid? Melted salt or salt mixture? Which composition? Without an answer to this question, one can not suggest suitable material. There are several nickel-base alloys that are sure to show better durability in your conditions than SS316, but different alloys exist for different corrosive media.
Hi Hakeem,
If your salt is an alkali metal salt, such as NaNO3, Na2B4O7, NaCl, KCl, Na2CO3, NaVO3, and so forth, then the selected corrosion resistant nickel base alloy should contain as little chromium as possible. In the presence of oxygen, chromium from the alloy reacts with alkaline melt with the formation of chromates: Na2CrO4 and K2CrO4. These reactions destroy chromium-containing alloys as low as 600°C. For such corrosion media, the alloys of the NiCrBSi series with approximately 11% chromium would be better than oxidation-resistant alloys based on Ni80Cr20.
However, if your molten salt is not an alkali salt or react acidic, for example, CaCl2, MgCl2, Na2O.6(V2O5), K2O.6(WO3), Li2MoO4 and others, then chromium is, conversely, the most corrosion resistant component of the alloy. In this case, chromium content in the nickel-based alloy should be as high as possible. All alloys with 20% and 30% chrome are recommended, but also Ni50Cr50 casting alloy can be very good.
Regards
Vadim
@ Vadim - Thank you very much for the detailed response. The information provided is really very useful to me.
You can go for SS 310S, a specialized material for molten salts operating at high temperatures. The only problem is the cost. It might cost you double than SS 316L depending upon sizes and availability.
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