Heat Resistant Coatings for Enhanced Protection

Corrosion Under Insulation (CUI)

Corrosion Under Insulation is a severe form of localized external corrosion that occurs in carbon and low alloy steel equipment that has been insulated. This form of corrosion occurs when water is absorbed by or collected in the insulation. The equipment begins to corrode as it is exposed to water and oxygen. 

Examples of CUI damage 

Mitigating or eliminating Corrosion Under Insulation

Coating solutions for the prevention of CUI come in two forms:

1. Mitigation is defined as ‘the action of reducing the severity or painfulness from the occurrence of an undesirable event’. In this case we use the Heat-Flex CUI coatings to provide a last line of defence when used alongside conventional insulation types such as mineral/calcium silicate.

2. Elimination is defined as ‘the process of removing or getting rid of something completely’. To eliminate the risk of CUI, we remove the traditional insulation system and replace it with a Thermal Insulation Coating (TIC) which removes the corrosion zone created by the gap between the insulation and the primed or un-primed surface.

Valves protected with Heat-Flex 750

Corrosion Under Insulation Test Methods

There two common CUI test methods which are being used globally:

Test Method 1: ISO19277: 2018

This is a suite of tests which are carried out to determine the suitability of coating for use under insulation. Tests include:

• Anticorrosive tests before and after heat conditioning at target temperatures.
• Water immersion testing before and after heat conditioning at target temperatures.
• Cryogenic Cycling testing before and after heat conditioning at target temperatures.
• Heat Cycling at target temperatures.
• Simulation CUI testing utilising either the multiphase CUI test method or the vertical pipe test.

Test Method 2: AMPP 21442:2022 

This is a dedicated CUI simulation test for the prequalification of a coating for CUI service. It consists of cycling between wet and dry conditions and low and high temperatures over a six month period. The performance of the coated pipe is assessed using Electrochemical Impedance Spectroscopy (EIS) and followed by a visual inspection at the end of the test for holiday detection.