Why Does Corrosion Under Insulation (CUI) Happen? An Annoying Industrial Problem Explained
Published 6th December 2024
Corrosion Under Insulation (CUI) is a pervasive issue in industries like oil and gas, petrochemical, and marine. In these industries, equipment is frequently insulated to maintain temperature and operational efficiency. CUI refers to the corrosion that occurs beneath insulation materials, often remaining hidden until it leads to significant structural damage or even equipment failure. Understanding CUI, its causes, and how to effectively mitigate it is essential for protecting critical infrastructure, reducing maintenance costs, and ensuring operational reliability.
What is CUI, and How Does it Happen?
CUI develops when moisture infiltrates the insulation surrounding the equipment, creating an environment where water and oxygen are trapped against metal surfaces. This constant exposure to moisture leads to the breakdown of protective coatings, exposing the underlying metal to corrosion. CUI can occur on any equipment that has a metal surface which includes pipes, steam drums and vessels.
A primary contributor to CUI is the type of insulation material used. Materials like rockwool, foam glass, and similar products are commonly used due to their thermal insulation properties. However, these materials are highly absorbent, soaking up and retaining water when they come into direct contact with wet surfaces. This moisture retention creates an ideal environment for corrosion to initiate and propagate.
Another key factor is the design of traditional cladding systems. In events where the cladding is not installed properly or damaged, creating an opening, water from rain can seep through. Cladding is non-removable, meaning that once water penetrates beneath the surface, it becomes trapped. Since this water cannot escape, the metal remains in a constantly wet state, accelerating the corrosion process. This situation is exacerbated by the difficulty of inspecting equipment without removing the insulation, often leading to delayed detection of corrosion until severe damage has already occurred.
This CUI issue is also not restricted to insulation, but also applicable to Passive Fire Protection (PFP) applications where rigid metal cladding is applied over the PFP material.
Risks and Consequences of CUI
If left unchecked, CUI can cause extensive damage, posing both safety and financial risks to the personnel on site and the owners.
The risks involved include:
- Operational Failure: Weakening of metal surfaces can lead to pipe ruptures, leaks and catastrophic failures.
- Lost Production Time: Unexpected repairs or replacements can cause operational delays. The cladding material is also difficult to remove, adding on to the maintenance and time needed to resolve the CUI issues
- Increased Maintenance Costs: Addressing severe corrosion requires more extensive and costly repairs.
- Safety Hazards: Corroded equipment pose significant risks to personnel and the environment.
Mitigating CUI is therefore not just a matter of maintenance and cost saving, but also a critical safety measure.
Mitigating Corrosion Under Insulation (CUI): Practical Approaches
Mitigating CUI requires a comprehensive strategy that combines proactive material selection, protective barriers, regular maintenance, and innovative insulation solutions. Here's a look at various mitigation techniques:
1. Material Selection
Choosing the right materials for both insulation and equipment can significantly reduce CUI risks. Corrosion-resistant alloys like stainless steel or duplex steels are often preferred in environments prone to moisture exposure due to their higher resistance to pitting and crevice corrosion. For insulation, materials with low water absorption rates, such as hydrophobic-coated fabrics, offer superior protection.
2. Protective Coatings
Applying anti-corrosion coatings to equipment surfaces forms a primary defense against CUI. Common coatings include thermal spray aluminum (TSA), epoxies, or polymer-based systems that act as a barrier between the metal surface and any water that might infiltrate the insulation layer.
3. Drainage and Ventilation Systems
Ensuring proper drainage and ventilation within insulation systems prevents water accumulation, a key factor in CUI development. Adding drain holes or vents at strategic points allows moisture to escape, reducing prolonged exposure to water
4. Regular Inspection and Maintenance
Routine inspections using non-destructive testing (NDT) methods like radiography or ultrasonic testing allow early detection of corrosion before it becomes severe. Removable insulation solutions enhance this process by allowing easy access to equipment surfaces for inspection, promoting a proactive maintenance culture
5. Use of Removable Insulation Blankets
Removable insulation blankets, particularly those with hydrophobic silicone-coated inner layers, represent a modern solution to CUI. These removable insulation blankets prevent water absorption into the insulation material as the inner material in contact with the surface is non absorbent, significantly lowering the risk of water-induced corrosion. They also simplify maintenance by enabling quick removal for inspections or repairs, making them a cost-effective and efficient alternative to traditional fixed insulation systems
Why Removable Insulation Blankets Stand Out
Traditional insulation methods, such as rock wool or foam glass, often absorb and trap moisture when exposed to water. This leads to a higher risk of Corrosion Under Insulation (CUI) as the trapped water remains in direct contact with the equipment surface. Additionally, non-removable cladding makes regular inspection and maintenance more challenging, leaving potential issues undetected.
In contrast, removable insulation blankets offer a modern, practical alternative. Designed with a hydrophobic silicone-coated inner layer, these blankets prevent moisture from seeping into the insulation material, reducing the likelihood of water retention and subsequent corrosion. Their removable nature also simplifies routine maintenance and inspections, allowing for early detection of any issues and easy drainage of any accumulated water.
This innovative approach helps extend equipment life, lowers maintenance costs, and enhances operational safety. With Ancloz Engineering, we offer these removable insulation solutions (Ancloz Androflex) tailored to meet the demands of challenging environments. Whether you're dealing with extreme temperatures, offshore conditions, or critical equipment, this solution provides both protection and peace of mind.
Addressing the PFP situation is similar, as we have also developed removable PFP jackets (Ancloz Armourflex) that helps address these issues. Removable PFP insulation jackets are applied with the same principles to prevent CUI, where the items can be removed for easy and regular maintenance and the PFP insulation material does not absorb and trap the moisture.
While it is impossible to eliminate all conditions leading to CUI, such as environmental exposure and condensation, removable thermal insulation blankets offer a practical and cost-effective mitigation strategy. By preventing water from becoming trapped in direct contact with equipment surfaces and allowing easy access for inspection and maintenance, our blankets provide a robust defense against CUI. This not only extends the lifespan of your equipment but also reduces overall maintenance costs, enhances safety, and improves operational efficiency.
Conclusion: A Comprehensive Strategy for Tackling CUI
Corrosion Under Insulation (CUI) presents significant risks to industrial equipment, impacting both operational efficiency and maintenance costs. However, through a combination of informed material selection, effective protective coatings, proper drainage and ventilation systems, regular inspection, and innovative insulation solutions, these risks can be minimized.
Selecting materials like corrosion-resistant alloys and hydrophobic insulation fabrics reduces the likelihood of water-induced corrosion from the outset. Protective coatings further enhance this defense by creating a barrier between equipment surfaces and moisture. Meanwhile, well-designed drainage and ventilation systems ensure that any infiltrated water is effectively managed, preventing prolonged exposure.
Regular inspections play a crucial role in early detection and mitigation. Non-destructive testing (NDT) techniques, coupled with easy-access solutions like removable insulation blankets, simplify this process and encourage a proactive maintenance culture. These removable blankets not only prevent water absorption but also allow for quicker and more efficient inspections, offering a practical alternative to traditional fixed insulation systems.
By integrating these preventive measures, industries can extend the lifespan of their critical infrastructure, reduce downtime, and significantly lower long-term maintenance costs. While no solution can completely eliminate the risk of CUI, taking a comprehensive, multi-faceted approach ensures the best protection against this persistent issue.
Ancloz Engineering offers one such solution through removable insulation blankets designed with hydrophobic silicone-coated inner layers, helping industries tackle CUI more effectively. However, the broader strategy involves a collaborative effort between design, material selection, and maintenance practices, ensuring long-term asset protection and operational resilience.
If you are looking for such removable thermal insulation blankets to help address CUI issues or otherwise, do email us at besttech@besttech.com.sg or call us at +6567475688.