Corrosion Under Insulation (CUI) Q&A: Solutions for Long-Term Equipment Protection

October 15, 2024 by

Introduction: The Urgent Need to Combat Corrosion Under Insulation (CUI)

Corrosion Under Insulation (CUI) is a significant challenge for industries that rely on insulated piping and equipment, such as the oil, gas, and chemical processing sectors. CUI accounts for up to 10% of all corrosion-related costs in these industries and is responsible for 60% of piping failures in refineries. Globally, corrosion is estimated to cost an astonishing $2.5 trillion annually.

The hidden nature of CUI beneath layers of insulation makes it difficult to detect until substantial damage has already occurred. The result? Increased maintenance costs, unexpected downtime, and compromised safety. With these issues in mind, adopting effective CUI prevention and maintenance strategies is critical for companies seeking long-term operational integrity and cost efficiency.

Factors Leading to Coating Failure in Corrosion Under Insulation (CUI) Prevention

Coating failure in systems designed to prevent CUI can occur due to several interrelated factors. Below are the key factors that can contribute to the breakdown of a coating system:

1. Improper Surface Preparation

Why it matters: Surface preparation is critical for ensuring a strong bond between the coating and the substrate. If the surface is not cleaned properly, contaminants like dust, oil, or rust can prevent the coating from adhering correctly.

Common issues: Inadequate cleaning, incomplete removal of rust or old coatings, and insufficient roughening (profiling) of the surface before applying the new coating.

2. Poor Application Practices

Why it matters: Even a high-quality coating will fail if it’s applied incorrectly. Factors such as improper mixing, incorrect application thickness, or failure to follow manufacturer guidelines can all cause premature coating failure.

Common issues: Coatings applied too thinly may not offer adequate protection, while coatings that are too thick may crack. Insufficient drying or curing times can also lead to issues like blistering or poor adhesion.

3. Thermal Cycling

Why it matters: Coatings are often subjected to constant heating and cooling cycles in industrial environments. If the coating lacks the flexibility to expand and contract with the substrate, it may crack, peel, or delaminate over time.

Common issues: Coatings with a high coefficient of thermal expansion that do not match the substrate can be prone to failure during repeated thermal cycling (Courtesy – University of Stavanger).

4. Chemical Exposure

Why it matters: Exposure to harsh chemicals, such as acids, alkalis, hydrocarbons, or salt, can degrade the coating over time. If a coating is not specifically designed to resist the chemicals present in the environment, it will break down more quickly.

Common issues: Incompatibility with aggressive chemicals, particularly in petrochemical or coastal environments (Courtesy –Corrosionpedia).

5. Moisture Ingress and Trapped Water

Why it matters: One of the main causes of CUI is water penetrating the insulation and reaching the substrate. If the coating becomes permeable over time or if there are small breaches, water can become trapped between the coating and the substrate, leading to corrosion.

Common issues: Blistering, underfilm corrosion, and loss of adhesion due to prolonged moisture exposure(Courtesy – Armacell).

6. Mechanical Damage

Why it matters: Physical damage to the coating can occur during installation, maintenance, or regular operation. Once the coating is compromised, the underlying metal is exposed to the environment, increasing the risk of CUI.

Common issues: Scratches, impacts, or abrasion during handling, insulation installation, or due to equipment vibration.

7. Inappropriate Coating Selection

Why it matters: Not all coatings are suitable for all environments. Factors such as temperature, humidity, and exposure to chemicals should all influence the choice of coating. Using a coating not rated for the operating environment can lead to rapid failure.

Common issues: Coatings not designed to handle high temperatures or aggressive chemical exposure breaking down prematurely(Johns Manville).

8. Insufficient Inspection and Maintenance

Why it matters: Coatings require periodic inspection and maintenance to ensure long-term performance. Neglecting regular inspections can allow small defects, like cracks or blisters, to grow into larger issues.

Common issues: Failing to detect and repair early signs of coating failure, allowing corrosion to take hold unnoticed(Corrosionpedia).

To avoid these failure modes, it’s critical to select the right coating for the environment, follow proper surface preparation and application procedures, and perform regular inspections to catch any early signs of degradation.

In this Q&A guide, we’ll explore the key aspects of CUI, the importance of protective coatings, and the factors to consider when selecting and applying coatings to ensure long-term equipment protection.

Q&A: Choosing the Right Coating for Corrosion Under Insulation (CUI)

Q: Why is Corrosion Under Insulation (CUI) such a significant problem in industrial environments?

CUI is a challenging form of corrosion because it often goes undetected until serious damage has occurred. When water gets trapped beneath insulation, it remains in contact with the equipment's surface, accelerating corrosion. The problem is compounded in industries that operate with insulated piping, vessels, or equipment, where fluctuating temperatures cause thermal expansion and contraction, drawing in moisture. Over time, this moisture leads to localized corrosion, which weakens the material and can result in equipment failure, costly repairs, or even hazardous situations.

Q: How do coatings help prevent CUI?

 Coatings play a vital role in preventing CUI by acting as a barrier between the steel surface and any moisture that penetrates the insulation. A high-quality CUI coating provides protection from both external environmental factors and the corrosive reactions that occur when moisture is present. The key is to select coatings that can endure the thermal, chemical, and physical conditions in which the equipment operates. For example, the best CUI coatings resist cracking, handle thermal cycling, and maintain strong adhesion to the substrate, even under challenging conditions like fluctuating temperatures or chemical exposure.

Q: What are the key characteristics to look for in a good CUI coating?

When selecting a CUI coating, the following characteristics are essential:

Thermal Resistance: The coating should be capable of withstanding the operating temperatures of the equipment without degrading. Coatings that can handle both high temperatures and the thermal cycling that occurs during shutdowns or changes in process conditions are crucial.
Moisture Resistance: A good CUI coating should be impermeable to water and vapor. This helps prevent moisture from penetrating to the steel surface, where it could cause corrosion.

Adhesion and Flexibility: High adhesion ensures that the coating remains firmly attached to the steel, even when subjected to thermal expansion or contraction. Flexibility is also important to prevent cracking, which could allow moisture to reach the underlying metal.
Chemical Resistance: The coating should resist the various chemicals commonly found in industrial environments, including acids, alkalis, hydrocarbons, and oils. This ensures the coating continues to protect the surface, even in the presence of harsh substances.
Ease of Application: In real-world conditions, perfect surface preparation isn’t always possible. Look for coatings that can be applied to surfaces with minimal preparation, such as directly over hot surfaces or onto lightly corroded steel, to save time and reduce downtime during maintenance.

Q: Are there coatings that work better in different temperature ranges?

Yes. Different CUI coatings are designed to handle specific temperature ranges, which is crucial for selecting the right solution for your equipment. For instance, in environments where the equipment operates at medium temperatures (30°C to 80°C or 86°F to 176°F), a robust, solvent-free coating can provide excellent protection. These coatings often excel in bonding to grit-blasted or prepared steel surfaces, maintaining strong adhesion while resisting thermal cycling. On the other hand, for high-temperature applications (up to 150°C or 302°F), a heat-activated coating may be more appropriate. These coatings are designed to be applied directly to hot surfaces, curing as they are exposed to heat, and forming a highly durable and corrosion-resistant layer.

Q: How can I ensure the coating will withstand physical stresses, such as impacts or temperature fluctuations?

It's important to choose a coating that has been tested for impact resistance and thermal cycling durability. For example, some coatings can withstand hundreds of thermal cycles without cracking, which is critical for equipment that experiences repeated heating and cooling. Additionally, coatings that demonstrate high impact resistance ensure they remain intact even if the equipment is subject to physical knocks or vibration during operation.

Q: What should I look for in terms of chemical resistance for a CUI coating?

Many industrial environments expose equipment to chemicals such as acids, alkalis, hydrocarbons, and oils. The coating you choose should have strong resistance to these chemicals to prevent degradation.

Q: What testing should a good CUI coating pass to ensure long-term durability?

 Industry standards, such as ASTM B117 for salt spray resistance and ASTM D1002 for adhesion, are commonly used to assess a coating’s performance. A good CUI coating should demonstrate excellent salt spray resistance, with no visible corrosion after prolonged exposure, and strong adhesion, even to less-than-ideal surfaces. Coatings that pass these rigorous tests provide reliable, long-term protection against CUI.

Q: What makes Belzona products particularly effective for CUI prevention?

Belzona coatings, such as those designed for CUI, exemplify many of the desirable characteristics mentioned earlier. These products have been rigorously tested for thermal cycling, impact resistance, and chemical durability, making them well-suited for industrial environments. For example, Belzona’s heat-activated coatings perform exceptionally well in high-temperature applications, with strong adhesion even on surfaces with minimal preparation. Additionally, their solvent-free, two-component coatings provide excellent protection in medium-temperature environments, offering robust chemical and corrosion resistance.
While every facility's needs will differ, choosing a coating with these superior parameters ensures long-lasting protection against CUI, minimizing downtime and extending equipment life.

Q: How do I know if a coating is suitable for insulated equipment?

Check if the coating has been designed for use under insulation and if it withstands moisture and heat retention. Ensure it meets key performance indicators like salt spray resistance, adhesion to steel, and impact strength.

Q: How important is salt spray resistance for a CUI coating?

Salt spray testing simulates corrosive environments to see how well the coating resists corrosion. Coatings that show no signs of corrosion after 1,000 hours of salt spray testing are highly reliable for long-lasting protection.

Q: Can I apply a coating to hot equipment, or does it need to be shut down?

Some coatings are designed for direct application onto hot surfaces, making it unnecessary to shut down equipment. These coatings begin to cure when they reach the required temperature.

Q: What about coatings for high-temperature equipment?

For high-temperature systems, use coatings that remain stable up to 150°C (302°F) and have high dry heat resistance to avoid degradation over time.

Q: Can these coatings be applied to rusty or partially corroded steel?

Yes, some coatings bond well even when the surface is not perfectly clean, such as rusted steel. While ideal surface preparation is recommended, these coatings can still deliver strong adhesion and corrosion protection.

Q: How do I ensure the coating will last long-term?

Regular maintenance and proper application are key. Choose a coating that’s been tested for chemical resistance, thermal stability, and impact strength. Perform routine inspections to ensure the coating remains intact.

Q: How does thermal cycling affect the performance of coatings?

Thermal cycling can cause expansion and contraction of the equipment, stressing the coating. A good CUI coating should be tested for thermal cycles and maintain its protective properties without cracking or peeling.

Q: What other factors should I consider when selecting a CUI coating?

In addition to the product's performance characteristics, consider the ease of application, the required cure time, and the specific environmental conditions of your facility. Coatings that can be applied during normal operations (for example, directly to hot surfaces) can save significant time and reduce the need for equipment shutdowns. Likewise, coatings with a fast cure time can allow you to return equipment to service more quickly.

Some Examples of Belzona Application on CUI

Overall, selecting the right CUI protection requires understanding your facility’s specific challenges and choosing a coating that combines durability, flexibility, and chemical resistance with ease of use. For more tailored recommendations, consult with a supplier who understands both the demands of your environment and the capabilities of modern CUI protection technologies.

References

https://www.jm.com/en/blog/2017/march/nace-study-estimates-global-cost-of-corrosion-at-25-trillion-annually/

https://www.corrosionpedia.com/understanding-the-causes-and-cures-for-corrosion-under-insulation/2/7297

https://www.uis.no/en/faculty-of-science-and-technology/corrosion-under-insulation-one-of-the-largest-integrity

NICCO is the sole distributor in India, Bangladesh, Nepal and Bhutan for Belzona® range of Cold Repair Polymeric Compounds, produced at the advanced facilities of Belzona® Polymerics Ltd., U. K., an ISO 9001:2008 & ISO 14001:2004 certified company.
The company has ready access to the latest technological breakthrough that helps to meet the increasingly stringent demands of modern industry.

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