Any piping that operates at a temperature lower than ambient air must be

• A. Insulated with moisture barrier
• B. Painted
• C. Not required
• D. Vapor sealed

Answer: (D)

When a pipe carries fluid colder than the surrounding air, moisture in the air can diffuse into the insulation and condense on the cold surface. This condensation can cause corrosion, insulation deterioration, and reduced thermal performance. Sealing the insulation with a vapor barrier (vapor sealing) blocks water vapor from moving into the insulation, keeping it dry and effective. Painting or relying on insulation alone won’t prevent this moisture migration, and some piping should not be left unsealed. So, vapor sealing is required to control moisture and protect both the insulation system and the pipe.