63. What Steps Can Be Taken To Avoid Stress Corrosion Cracking (scc) In Steel Vessels Used For Storing Anhydrous Ammonia?
The U.S. National Board of Pressure Vessel Inspectors recommends the following in one of their classic articles: Pressure vessels should be fully stress relieved or fabricated with heads that are hot-formed or stress relieved. Extreme care should be used to eliminate air from the ammonia systems; new vessels must be thoroughly purged to eliminate air contamination. Ammonia should contain at least 0.2 percent water to inhibit SCC. Source: National Board of Pressure Vessel Inspectors
