As facilities engineers and operators know, a Corrosion Under Insulation (CUI) mitigation plan is critical to combating the problems that arise from wet insulation and CUI, such as process instability, reduced outputs, loss of containment, and personnel safety incidents.
But, it's the designer of industrial insulation systems that creates a system that stands the test of time in CUI defense. That being said, the designer has three main weapons in the fight against CUI. The first and primary defense against CUI is a high quality, immersion-grade coating. The second is a properly designed and installed weather barrier jacketing and, if operating below the atmospheric dew point, vapor barrier. The third and, arguably, least understood element is the choice of insulation material. Historically, hot insulation products have been divided into categories of wetting and non-wetting, or “hydrophobic” materials. The distinction is important because, as pointed out in NACE Standard RP0198-98:
“Because CUI is a product of wet metal exposure duration, the insulation system that holds the least amount of water and dries most quickly should result in the least amount of corrosion damage to equipment.”
A more recent European monograph states flatly:
“Insulation that minimizes water ingress and does not retain water can effectively act as a barrier to CUI.”