Which of the following insulated vessels is most likely to experience corrosion under insulation (CUI)?

Which of the following insulated vessels is most likely to experience corrosion under insulation (CUI)?

• A. CS vessel that operates continuously at 375°F
• B. CS vessel that operates at cyclic temperatures ranging from 400-600°F
• C. Austenitic SS vessel that operates continuously at 100°F
• D. CS vessel that operates at 600°F but is in an intermittent service

Answer: (A)

The selection of the carbon steel (CS) vessel that operates continuously at 375°F as the most likely to experience corrosion under insulation (CUI) is grounded in the understanding of the conditions that promote CUI. CUI typically occurs when moisture is present on the surface of the insulated vessel, often due to condensation, and is most prevalent within specific temperature ranges. For carbon steel vessels, temperatures between 140°F and 350°F are particularly susceptible to corrosion, especially when thermal cycling leads to frequent condensation. The vessel operating at 375°F, while slightly above this critical range, indicates a continuous operating condition where insulation could trap moisture, thereby creating an environment conducive for CUI to occur due to the thermal stability that allows for moisture retention and potential for localized corrosion. The other choices present conditions that either reduce the risk of CUI or operate outside the more critical susceptibility range. The CS vessel with cyclic temperatures of 400-600°F may avoid CUI due to increased operating temperatures that limit moisture retention and generally do not fall within the susceptible range for CUI concerns in carbon steel. The austenitic stainless steel vessel operating continuously at 100°F is less susceptible to CUI because stainless steel has better corrosion resistance, particularly in lower temperature

The selection of the carbon steel (CS) vessel that operates continuously at 375°F as the most likely to experience corrosion under insulation (CUI) is grounded in the understanding of the conditions that promote CUI.

CUI typically occurs when moisture is present on the surface of the insulated vessel, often due to condensation, and is most prevalent within specific temperature ranges. For carbon steel vessels, temperatures between 140°F and 350°F are particularly susceptible to corrosion, especially when thermal cycling leads to frequent condensation. The vessel operating at 375°F, while slightly above this critical range, indicates a continuous operating condition where insulation could trap moisture, thereby creating an environment conducive for CUI to occur due to the thermal stability that allows for moisture retention and potential for localized corrosion.

The other choices present conditions that either reduce the risk of CUI or operate outside the more critical susceptibility range. The CS vessel with cyclic temperatures of 400-600°F may avoid CUI due to increased operating temperatures that limit moisture retention and generally do not fall within the susceptible range for CUI concerns in carbon steel. The austenitic stainless steel vessel operating continuously at 100°F is less susceptible to CUI because stainless steel has better corrosion resistance, particularly in lower temperature