What does a blue-green stain on the brass valve indicate?

• A. Exposure to water.
• B. Anhydrous ammonia.
• C. Propane.
• D. Oxygen.

Answer: (B)

Blue-green staining on brass indicates contact with anhydrous ammonia. Brass contains copper, and when ammonia is present (often with a bit of moisture), it reacts with the copper to form copper-ammonia complexes that leave a distinctive blue-green discoloration on the surface. This staining is a practical clue that ammonia has touched the valve, rather than just simple oxidation from air or exposure to water or propane. If you see this color, treat it as indicating ammonia presence and follow appropriate safety and leak-check procedures to address potential contamination or leaks.