Understanding Corrosion Under Insulation
Corrosion Under Insulation (CUI) remains one of the most persistent and costly challenges facing the process industries today. Despite being hidden from view, its impact on asset integrity, safety, and operational efficiency is anything but invisible.
Drawing on insights from David Hunter of Hempel, published in Protective Coating Expert Magazine, CUI is described as an accelerated form of corrosion that occurs when moisture penetrates insulation systems and comes into contact with carbon or low-alloy steel. Because it develops beneath insulation, it often goes undetected until significant damage has already occurred, leading to unplanned downtime, costly repairs, and potential safety risks.
Why CUI Is So Problematic
As highlighted by Hunter, one of the biggest challenges with CUI is that it is not visible during normal operation. Inspection typically requires removal of insulation, making the process both time-consuming and costly.
Additional contributing factors include:
- Temperature fluctuations and thermal cycling
- Moisture ingress and trapped water
- Contaminants such as chlorides
- Complex equipment geometries (valves, joints, penetrations)
This combination makes CUI a difficult issue to monitor and manage effectively.
The Role of Protective Coatings
Hunter emphasises that while protective coatings are a key part of any CUI mitigation strategy, they must be carefully selected and correctly applied. Coatings need to perform under demanding conditions, including:
- Wide temperature ranges
- Wet and dry cycling
- Mechanical stress from insulation systems
- Chemical exposure
Critically, even high-performance coatings can fail if surface preparation and application standards are not properly followed.
ISO 19277: A Step Forward
A major development discussed in the article is the introduction of ISO 19277, which provides a framework for testing coatings used in CUI environments.
The standard includes testing methods designed to simulate real-world conditions such as:
- Thermal cycling
- Immersion and moisture exposure
- Salt spray
- Long-term durability
As Hunter explains, this helps ensure coatings are “fit for purpose” and suitable for the environments in which they will operate.
From Testing to Real-World Performance
While laboratory testing is essential, Hunter notes that real-world performance remains the ultimate benchmark. Coatings must be able to withstand the full lifecycle of operating conditions—from installation through to long-term service.
Case examples show how advanced coating systems can be applied efficiently, sometimes even while assets remain operational, helping to minimise downtime and improve long-term protection.
Building Expertise in CUI
As this insight highlights, understanding and managing CUI requires a combination of technical knowledge, practical experience, and informed decision-making.
At Corrodere Academy, our Corrosion Under Insulation (CUI) course is designed to equip professionals with the skills needed to identify, assess, and mitigate CUI in real-world environments.
Whether you’re working in inspection, coatings, or asset integrity, developing expertise in CUI can significantly improve reliability and reduce lifecycle costs.
👉 Read the original article at Protective Coatings Expert Magazine
