For carbon steel piping, which operating temperature range is most susceptible to CUI due to moisture condensation?

For carbon steel piping, which operating temperature range is most susceptible to CUI due to moisture condensation?

• A. Between -20°F and 0°F
• B. Between 400°F and 600°F
• C. Between 10°F and 350°F
• D. Above 650°F

Answer: (C)

Moisture under insulation causes CUI when liquid water can condense on the outer surface of the insulation and remain there long enough to attack the steel. For carbon steel, that condensation-friendly window is roughly 10°F up to about 350°F. In this range the surface is cool enough to be at or below the dew point so water can condense, yet warm enough that the water stays liquid and can penetrate micro-gaps in the insulation to reach the metal. If the temperature is much colder (around -20°F to 0°F), moisture tends to freeze as frost, which reduces the rate of corrosion. If the temperature is higher (400–600°F or above 650°F), the surface is too hot for liquid water to condense, so CUI driven by condensation is much less likely. Hence, the 10°F to 350°F range is the most susceptible to CUI from moisture condensation.

Moisture under insulation causes CUI when liquid water can condense on the outer surface of the insulation and remain there long enough to attack the steel. For carbon steel, that condensation-friendly window is roughly 10°F up to about 350°F. In this range the surface is cool enough to be at or below the dew point so water can condense, yet warm enough that the water stays liquid and can penetrate micro-gaps in the insulation to reach the metal. If the temperature is much colder (around -20°F to 0°F), moisture tends to freeze as frost, which reduces the rate of corrosion. If the temperature is higher (400–600°F or above 650°F), the surface is too hot for liquid water to condense, so CUI driven by condensation is much less likely. Hence, the 10°F to 350°F range is the most susceptible to CUI from moisture condensation.