Which type of insulated vessel has the highest likelihood of experiencing CUI?

The type of insulated vessel that has the highest likelihood of experiencing Corrosion Under Insulation (CUI) is typically the one that operates under conditions most conducive to moisture accumulation and retention. In this scenario, a carbon steel (CS) vessel operating at 600°F but in intermittent service presents a significant risk for CUI.

At elevated temperatures, such as 600°F, carbon steel is susceptible to CUI because moisture can infiltrate the insulation. When operating intermittently, the vessel can experience significant thermal cycling, which can lead to condensation forming within the insulation during cool-down periods. This condensation can lead to moisture retention, creating an ideal environment for corrosion to occur under the insulation, especially since carbon steel is highly prone to rust when exposed to water.

In contrast, while options involving a CS vessel at 450°F and a low alloy steel vessel at 350°F are also vulnerable to CUI, the higher temperature and the intermittent operating nature of the 600°F scenario escalate the risk considerably. The austenitic stainless steel vessel at 300°F generally has a much lower likelihood of CUI due to its improved corrosion resistance compared to carbon steel varieties. Thus, the specific conditions of Option B contribute to its classification as having the highest likelihood of