What steps can be taken to avoid stress corrosion cracking (SCC) in steel vessels used for storing anhydrous ammonia?

What steps can be taken to avoid stress corrosion cracking (SCC) in steel vessels used for storing  anhydrous ammonia?
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1 Answer

Answer :

The U.S. National Board of Pressure Vessel Inspectors recommends the following in one of their classic  articles:
1. Pressure vessels should be fully stress relieved or fabricated with heads that are hot-formed or stress  relieved.
2. Extreme care should be used to eliminate air from the ammonia systems; new vessels must be  thoroughly purged to eliminate air contamination.
3. Ammonia should contain at least 0.2 percent water to inhibit SCC. Source: National Board of Pressure  Vessel Inspectors
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