Which chemical is associated with a blue-green stain on the brass valve?

• A. Propane
• B. Anhydrous Ammonia
• C. Water
• D. Oxygen

Answer: (B)

A blue-green staining on brass valves signals ammonia contamination, specifically from anhydrous ammonia. When ammonia comes into contact with copper-containing metals like brass, it forms copper-ammonia complexes and related corrosion products that leave a distinctive blue-green residue. That color acts as a clear diagnostic clue for technicians to investigate cross-contamination with ammonia and take appropriate safety steps.

Propane itself is a colorless hydrocarbon and doesn’t produce that blue-green stain on brass. Water can cause tarnish or corrosion over time, but not the characteristic blue-green ammonia sign. Oxygen can oxidize brass, leading to a general patina, but not the specific blue-green staining associated with ammonia contamination.