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Corrosion Under Insulation

Corrosion under insulation (CUI) is one of the biggest problems associated with high temperature insulated steel. The highly aggressive environment created beneath insulation materials, in conjunction with the lack of visible evidence of corrosion, means that if not correctly managed, CUI can lead to catastrophic and expensive failures.

CUI Coatings

The use of protective coatings on insulated steelwork is recognized as one of the most effective methods of combating CUI. However it is essential that the coating has been specifically approved for use beneath insulation and is suitable for the expected service temperature.

Why insulate?

Insulation is used to minimize heat loss, reduce costs and improve efficiency. It may also be employed to minimize heat gain or to protect personnel from the risk of injury from hot or cold surfaces.

Traditional insulation systems typically consist of an insulating material such as mineral wool or calcium silicate, which is then protected by an outer layer of cladding. Thin metal sheet or composite wraps are the most common cladding materials.

Risk of Water Ingress

To help combat the risk of CUI, insulation systems are designed and installed with great care given to sealing joints, terminations and protrusions. Despite these efforts, water ingress over time is inevitable. Mechanical damage, degradation of sealants, rainwater, deluge systems and atmospheric moisture will all contribute to water ingress through the insulation system, resulting in a warm, damp corrosive environment against the steelwork. It is therefore essential that an appropriate protective coating is in place to offer long term protection.

Increased Corrosion Rates


Once water penetrates an insulation material, a highly corrosive environment can be created at the interface between insulation and steel substrate. Moisture is often unable to escape, leading to prolonged periods of moisture contact and further build-up of corrosive contaminants. This raises the boiling point of the water, extending the risk of corrosion to higher temperatures and vastly increasing the corrosion rates of inadequately protected steelwork.

CUI Coatings from the Intertherm Range


The following products have been specifically developed to protect against CUI:

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