Hydrophobicity is Only Part of the Solution to Prevent CUI

By David Shong
Published: April 5, 2018 | Last updated: January 31, 2022
Key Takeaways

The secret to expanded perlite’s success is that it has a two-pronged defense to help combat CUI: it is hydrophobic and it has an inherent chemical makeup that actively inhibits corrosion.

Expanded perlite has been a popular insulation in the humid climate of the Gulf Coast. For decades, it has been used extensively in the oil and gas processing industries because it has become well known for its excellent capacity to inhibit corrosion under insulation (CUI). This begs the question: why is it so successful?


Many industrial experts may jump to the conclusion that expanded perlite is hydrophobic. Yet, so are many other insulation options out there. So what makes expanded perlite any different when it comes to CUI protection performance?

The secret to expanded perlite’s success is that it has a two-pronged defense to help combat CUI. (For more on this topic, see Combat CUI: Major Advancements in Material Standards, Insulation Features and Metal Jacketing.)


Expanded perlite is hydrophobic, and it has an inherent chemical makeup that actively inhibits corrosion. The dual nature of perlite allows it to work to prevent CUI even after elevated temperatures (greater than 450°F or 232°C) have oxidized the organic ingredients that make the insulation hydrophobic. Once the hydrophobic nature of the insulation has ceased to function, water will eventually infiltrate the system. For most hydrophobic insulations, this would create a flaw in the system, significantly reducing its ability to prevent CUI; however, when this happens to perlite, it activates the chemistry of the insulation, causing corrosion inhibitors to migrate to the pipe surface, creating a protective coating between the pipe and the insulation.

This is the same concept as installing a coating between the insulation and the pipe; however, it occurs naturally as a result of the formulaic makeup of perlite. The passive layer of protection prevents the electrolytes contained in the water from reacting with the pipe, thus inhibiting corrosion. Additionally, perlite’s unique chemistry ensures that the pH levels of the water remain around 10, well above acidic levels of 7 and below.

These active corrosion inhibitors are only present in the expanded perlite and calcium silicate currently produced by Johns Manville’s Industrial Insulation Group. They account for 95% of the makeup of both insulations, and remain present and active for the life of the installation.


Expanded perlite has a long history of excellent corrosion-inhibiting performance in hot and humid environments, like the Gulf Coast. Since it is both hydrophobic and inherently resistant to CUI, it has proven itself to be an exceptional ally in the battle against corrosion under insulation. Additionally, its compressive strength and service life make it an ideal product for application in tough environments where weather makes CUI a very real risk.

To learn more, view notes from the Understanding Insulation Chemistry Proven to Inhibit CUI webinar.


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Written by David Shong

David Shong

David Shong has spent his entire career in the construction materials industry and developed an early passion for insulation. He has worked in the industrial insulation field since 2014.

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