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Corrosion under insulation (CUI) has long been a silent menace affecting refineries, petrochemical plants, and natural gas/LNG plants—anywhere hot or cold equipment is insulated for thermal protection, energy conservation, or process stabilization. Nevertheless, despite increasing interest in the issue since the 1980s, CUI remains a costly challenge (NACE International, 2017).
These costs extend beyond the annual maintenance dollars spent on detecting, repairing, and preventing CUI. CUI-related leaks and ruptures can cause process stoppages and even entire plant shutdowns, detrimentally impacting production and profitability. CUI events can also lead to health, safety, and environmental damage, potentially resulting in regulatory and legal action, as well as reputational harm.
Unfortunately, there is no simple solution to CUI. Every plant offers slightly different process complexities, making each CUI situation unique. That said, every instance of CUI shares four main ingredients: unprotected metal, water, elevated process temperature, and oxygen. These ingredients provide the foundation for a recipe designed to target CUI, beginning with the protection of metal surfaces.
Various coating types, such as epoxy and TSA, can mitigate CUI; however, applying and maintaining a perfect coating over the equipment’s lifetime is almost impossible. And then there are the hundreds of thousands of kilometers of unprotected pipelines already installed globally. It would be prudent to add another line of defense.
As nitrogen purging is an unrealistic solution, there is little we can do about the presence of oxygen. Meanwhile, elevated pipe and equipment operating temperatures are often necessary to meet given process criteria. This leaves us with water. Water is the essential medium for corrosion; without water, corrosion does not occur. Unfortunately, water is adept at finding its way into places we would rather it not be. It is particularly destructive in environments where condensation and temperature cycling occur, and that is without mentioning process leaks or spills, washdown water, and natural precipitation. In the words of the Ancient Mariner, there is “water, water, everywhere.”
Tackling corrosion with stone wool insulation
ROCKWOOL Technical Insulation’s ProRox® stone wool insulation products have long-proven thermal and acoustic insulating properties. However, ROCKWOOL’s new and innovative ProRox® PS 965 pipe sections now deliver significant corrosion mitigation benefits, as proven in an extensive and expanding array of industry-standard testing.
Since 2017, ProRox® pipe sections have been treated with a water-repellent additive (WR-Tech™) to help shed water from insulation. Testing has shown that WR-Tech-treated pipe sections are five times more water-repellent than standard stone wool at 482°F, even after heating and aging (Zwaag & Rasmussen, 2018). In parallel and importantly, stone wool insulation has an open-cell structure that allows water to escape through evaporation. Combining WR-Tech with this open structure significantly reduces the time for insulation to become wet, directly lowering corrosion rates.
However, water-repellent insulation is not fail-safe. There will always be weak spots, joints, or gaps (typically caused by poor installation practices or unexpected damage to the jacketing) through which water can penetrate and migrate to the metal surface. This is where a multi-layered CUI defense comes into play.
Launched in 2023, CR-Tech™ corrosion-resistant technology comprises a proprietary corrosion inhibitor applied to the inner surface of the stone wool during manufacturing in conjunction with the WR-Tech™ additive, which is applied throughout the material. The inhibitor activates on contact with leachate water as it migrates through the insulation, neutralizing acidity and forming a low-solubility protective film that shields the pipe from corrosive attack. Extensive industry-standard testing demonstrates that ProRox® PS 965 pipe sections featuring CR-Tech™ and WR-Tech™ protect pipes from CUI (Blundell, 2024).
ProRox® PS 965 pipe sections with CR-Tech™ won the 2025 Corrosion Innovation of the Year Award at the Association for Materials Protection and Performance's annual conference, following in the footsteps of the WR-Tech additive, which received the award in 2019. The award highlights progressive technological developments in all aspects of corrosion prevention and mitigation, recognizing the innovators who have developed groundbreaking solutions to combat corrosion and protect vital assets from its damaging effects. Selected by a panel of corrosion experts, winning technologies have to demonstrate (via third-party testing) “the potential for a significant positive impact in controlling corrosion”. Nominations are rated by a panel of leading corrosion experts using a numerical scoring system, with the highest-rated innovations receiving the award.
Testing CR-Tech™ to the limits
ROCKWOOL
Not one to settle on its success, additional recent testing has pushed ProRox® PS 965 pipe sections with CR-Tech™ to the limits, demonstrating the technology’s ability to control corrosion in even the most extreme process environments.
The ASTM G189-21 standard tests an insulation’s corrosion-mitigating properties when water is exposed directly to the pipe surface. Standard testing measures CUI in laboratory conditions that mimic 10-year rainfall levels. In previous testing, ProRox® PS 965 pipe sections with CR-Tech™ proved five times better at mitigating CUI under these conditions than other insulation materials (Blundell, 2004). In other words, at least five times less uniform corrosion was measured on the pipe surface at the end of the test.
In new testing, ROCKWOOL wanted to push these limits further and study the effects of water exposure similar to those of a severe rain event. To achieve this, the amount of water exposure was increased to reflect the average rainfall in Houston, Texas (selected for its proximity to industrial facilities that experience high CUI) over a 15-year period. ProRox® PS 965 pipe sections with CR-Tech™ exhibited significantly lower corrosion rates compared to other insulation products, demonstrating its effectiveness in mitigating CUI, even in extreme weather conditions (Seto, 2025).
Continuing to push the performance limits, ROCKWOOL commissioned third-party testing on ProRox® PS 965 with CR-Tech™ under high chloride concentrations and heat conditions using modified ASTM C1617-19 tests. These measure the corrosion tendency of metals in the presence of a solution leached from the insulation.
Chlorides are commonly present in process plants and are known to exacerbate CUI. The impact of increasing chloride concentrations was tested by dosing the insulation solution with varying chloride concentrations up to 600 ppm. The results showed that CR-Tech™ actively protects the metal even at high chloride concentrations, which was not the case with all insulation types tested (Seto, 2024).
ProRox® PS 965 pipe sections with CR-Tech™ were also tested at temperatures ranging from 600°F to 1200°F, the maximum service temperature. This used a modified ASTM C1617 test in which the insulation solution was made using heat-aged samples. Corrosion rates remained relatively unchanged up to 1200°F, highlighting the inhibitor's durability and reliability in high-temperature conditions (Seto, 2025).
Taken together, these results provide fact-driven proof that CR-Tech™ provides beneficial protection against CUI.
Build in confidence with CR-Tech™
ProRox® PS 965 pipe sections with CR-Tech are revolutionizing corrosion mitigation on insulated pipework. Process plants can now build confidently with ROCKWOOL stone wool insulation, relying on it to deliver high insulation performance while providing lasting, durable, and resilient protection against corrosion, even in extreme process environments, including high temperatures, high chloride levels, and high rainfall. The bottom line is improved economics, energy efficiency, and lower maintenance costs.
Now is the time to incorporate ROCKWOOL ProRox® PS 965 pipe sections with CR-Tech™ at your process plant. Made in North America and supported by ROCKWOOL’s global network of insulation experts, ProRox PS 965 pipe sections with CR-Tech™are ready to help you stay competitive and compliant.
Check out more on the ROCKWOOL website.
References
Blundell, J. (2024). ‘Protecting plant piping from CUI with water repellency, BIC, March/April 2024, p. 38.
NACE International (2017). NACE SP0198-2017 Control of corrosion under thermal insulation and fireproofing materials—a systems approach.
Seto, R. (2024). ‘Mineral wool CUI mitigation improvements’, paper no. 20798, presented at AMPP Annual Conference + Expo, 3-7 March 2024, New Orleans, Louisiana.
Seto, R. (2025). ‘Mineral wool with durable corrosion inhibitor for effective CUI mitigation in LNG applications’, LNG Industry, 01 April 2025.
Zwaag, C. and Rasmussen, S.N. (2018). ‘Mineral wool and water repellency’, paper no. 10929, presented at CORROSION 2018, 15-19 April, Phoenix, Arizona.
