Corrosion under insulation (CUI) is one of the most deceptive and damaging forms of corrosion affecting industrial pipelines and process systems. Unlike external corrosion which is typically visible, CUI occurs beneath thermal insulation, making it difficult to detect until significant degradation has occurred.
🔍 What Causes CUI?
CUI typically arises when moisture penetrates the insulation material and comes into contact with the pipe surface. Factors that contribute to this include:
- Damaged or degraded insulation
- Poor sealing around pipe supports or fittings
- Exposure to harsh environments (salt-laden air, rain, condensation)
Steel operating within the temperature range of 25°C to 175°C (77°F to 347°F) is particularly vulnerable, as it promotes the evaporation-condensation cycle conducive to corrosion.
🛠 How to Identify CUI?
Detecting CUI requires a proactive strategy:
- Non-destructive inspection (NDT) techniques such as ultrasonic testing or radiography
- Visual inspection during shutdowns or insulation replacement
- Using CUI assessment tools like our Pipeline Inspection Plan Generator to recommend likely risk zones
🧰 Prevention and Best Practices
CUI prevention starts with design and extends through operations:
- Use moisture-resistant insulation and vapor barriers
- Apply coatings suitable for under-insulation service
- Design piping to avoid water traps
- Implement a corrosion monitoring strategy for insulated systems
📈 Assessing Risk with Engineering Tools
To support engineers and integrity managers, tools like our Corrosion Rate & Remaining Life Calculator and Fitness-for-Service Screening Tool help quantify risks, remaining strength, and inspection needs — all within a structured, standards-aligned framework.
✅ Conclusion
CUI is often overlooked until failures occur, but with the right awareness and tools, it can be effectively managed. If your facility relies on insulated pipelines, consider conducting a full review of your inspection intervals, insulation integrity, and corrosion protection systems.