Under what circumstances is CUI considered an inspection concern for insulated vessels operating at 500°F?

Corrosion Under Insulation (CUI) can be a significant concern for insulated vessels, especially when they operate at elevated temperatures like 500°F. Intermittent service creates conditions that are particularly conducive to CUI. This is primarily because such service may lead to fluctuations in temperature that can cause condensation to form between the insulation and the vessel surface. When these vessels heat up, moisture trapped within the insulation can evaporate, but during cool down periods, particularly in environments with varying temperatures, the moisture can condense back, leading to the risk of corrosion.

With intermittent service, the insulation may remain wet for extended periods, especially if it is not well-ventilated or waterproofed. As insulation retains moisture in these instances, it heightens the likelihood of corrosion forming on the vessel surface. Therefore, under these specific circumstances, CUI becomes a primary inspection concern, as it may compromise the integrity and reliability of the vessel over time.

Continuous operation might help reduce the risk of CUI, as a consistently high temperature can minimize the condensation effect. Low ambient temperatures and high humidity can also contribute to corrosion problems, but they are generally less critical factors for vessels operating at elevated temperatures if the insulation remains intact and dry.