With respect to CUI, how well do thermal insulating coatings retard the spread of corrosion?

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Thermal insulation coatings (also known as thermal barrier coatings) provide both a resistance to heat flow and a protective finish to the objects (such as pipelines and process vessels) to which they are applied.

Together with a corrosion protective primer, the system does very well to minimize or prevent corrosion under insulation (CUI).

First, there is no gap between the thermal insulation coating and the primer where water can ingress and quickly degrade the corrosion protective primer. (For more information on this topic, read The Detrimental Effects of Wet Insulation in the CUI Range.)

Second, with the temperature gradient in the insulation coating, moisture from the environment will be kept away from the metal substrate. Think of it as the opposite of the cold-wall effect, where moisture is drawn into the coating if the substrate metal is at cooler temperatures relative to the external temperature. For coating defects, like delamination and blistering, the temperature gradient should also keep moisture from migrating into the blister or delaminated area.

Third, if the insulation coating and primer are damaged and the metal substrate is exposed, resulting in rust formation at the defect, the rust will stain the area around the defect, making it highly visible so that it can be repaired well before significant metal or wall loss occurs.