Which statement best describes the risk of CUI under insulation?

Which statement best describes the risk of CUI under insulation?

• A. CUI risk is unrelated to moisture and is dictated only by metal type
• B. Moisture ingress into insulation is the primary driver of CUI risk
• C. CUI cannot occur in stainless steels under insulation
• D. CUI risk is eliminated when insulation is dry

Answer: (B)

Moisture in insulation is the main driver of CUI risk. When insulation holds water or allows moisture to diffuse to the metal surface, an electrolyte forms at the metal–insulation interface. Heat from the service, temperature cycling, and the presence of salts or chemicals can drive condensation and transport corrosive species to the surface, accelerating under-insulation corrosion even on materials like stainless steel. Dry insulation reduces but does not eliminate the risk, because moisture can be introduced later or remain trapped inside and become active under operating conditions. Relying on metal type alone ignores the crucial role of moisture, and saying CUI cannot occur in stainless steels or that risk is eliminated when insulation is dry both misstate how CUI develops and persists in real service.

Moisture in insulation is the main driver of CUI risk. When insulation holds water or allows moisture to diffuse to the metal surface, an electrolyte forms at the metal–insulation interface. Heat from the service, temperature cycling, and the presence of salts or chemicals can drive condensation and transport corrosive species to the surface, accelerating under-insulation corrosion even on materials like stainless steel. Dry insulation reduces but does not eliminate the risk, because moisture can be introduced later or remain trapped inside and become active under operating conditions. Relying on metal type alone ignores the crucial role of moisture, and saying CUI cannot occur in stainless steels or that risk is eliminated when insulation is dry both misstate how CUI develops and persists in real service.