Thermal insulation coatings

Corrosion under insulation (CUI) is often seen in the coatings protective area. CUI typically occurs when 1) moisture (water vapour), originating from rain, washes down in the process plant, 2) steam discharge or process liquid spills, penetrates the outer membrane and insulation material and condenses on the steel pipe surface. An electrolyte solution, a requirement for low temperature corrosion, is formed when contaminants (mainly chlorides and sulphates), present in the insulation material, dissolve in the water. For example, if the rain frequency is high, the insulation material may not have sufficient time to dry and regain thermal efficiency.

Insulation coatings may, in some cases, be an alternative. Such coatings cannot provide the same degree of insulation as traditional methods but are much better than having no insulation, and inspection and maintenance costs are typically lower. The most common use of insulation coatings is for personal protection. Industrial workers can be protected against burns from contact with hot surfaces (safe-touch properties). Here thermal insulation coatings can help reducing the surface temperature and the rate of thermal energy transfer from equipment and piping. 

The two dominant technologies for insulation coatings are based on hollow spheres and silica aerogel particles. They each have both advantages but also some potential disadvantages. The thermal conductivity of an aerogel is very low, but polymer (binder) intrusion into the open cell pore structure may take place during coating formulation and application and displace some of the air. Likewise, high shear forces during mixing and spraying of a coating may break hollow glass spheres. In both cases, the thermal efficiency of the coating will be reduced.

Disciplines involved in understanding the working mechanisms of insulating coatings are paint formulation, heat transport phenomena and mathematical modelling.