Corrosion Under Insulation (CUI) is one of the (petro) chemical processing industries worst problems and the costs associated to mitigating it are astronomical. CUI is any type of corrosion that occurs due to a moisture buildup on the external surface of insulated equipment. If undetected, the results of CUI can lead to the shutdown of a process unit or an entire facility, and in rare cases it may lead to a process safety incident. While carbon and low-alloy steels operating between –4°C and 149°C are most at risk from CUI, the intermittent boiling and flashing that occurs above a metal temperature of 100°C (212°F) produces a fairly aggressive CUI environment. CUI is one of the most difficult processes to prevent. The reason for that is, by and large, no matter the precautions taken, water invariably seeps into the insulation and begins its dirty work—sometimes unseen until process leakage occurs.