Corrosion Under Insulation (CUI)

Corrosion Under Insulation (CUI) is a major issue in industrial maintenance, yet it often doesn’t get the attention it deserves. The problem isn’t just the corrosion itself—it’s the fact that many people don’t realise it’s happening until it’s too late. While insulation specialists understand the risks, day-to-day maintenance teams are focused on keeping plants running. Insulation can seem like an afterthought, but ignoring it comes at a cost.

Why Does CUI Happen?

CUI occurs when water seeps into insulation, creating the perfect conditions for corrosion to develop underneath. It’s particularly common in industries like oil & gas, chemical processing, and power generation, where extreme temperatures and weather exposure accelerate deterioration. By the time corrosion is visible, the damage is often severe, leading to expensive repairs, safety hazards, and unplanned shutdowns.

Preventing CUI: What the Experts Say

Industry bodies such as CINI (Committee of Insulation Experts), ICorr (The Institute of Corrosion), and FROSIO stress that proper insulation, protective coatings, and regular maintenance are essential to preventing CUI. Despite this, many facilities still rely on outdated insulation systems, poor weatherproofing, or neglect inspections altogether.

The Hidden Cost of CUI

One of the biggest challenges with CUI is that it doesn’t always present immediate issues. Unlike a leaking pipe or a failed pump, corrosion under insulation happens out of sight and out of mind—until a failure occurs. Studies have shown that CUI accounts for 40-60% of piping maintenance costs in industrial plants, with some companies spending millions on emergency repairs. In many cases, these costs could have been avoided with proactive prevention strategies.

Real-World Example: Pembrokeshire, Wales

At an energy facility in Pembrokeshire, Wales, Fenix was called in after corrosion was discovered beneath insulation that had been in place for years. The issue had been missed because insulation wasn’t seen as a priority. By upgrading to vapour-tight insulation systems, applying hydrophobic coatings, and improving weatherproofing, we eliminated water ingress and extended the lifespan of critical pipework. The site avoided costly shutdowns, and future maintenance requirements were significantly reduced.

Common CUI Risk Areas

Certain areas of a plant are more prone to CUI than others. Some of the most common problem areas include:

• Pipe supports and hangers – These points create pressure on insulation, increasing the risk of moisture ingress.
• Valves and flanges – Regular maintenance can lead to compromised insulation and exposed metal surfaces.
• Horizontal pipe runs – Water can collect and pool within insulation if not properly drained.
• Cold service systems – Chilled pipes and vessels are particularly vulnerable due to condensation and temperature fluctuations.

The Future of CUI Prevention

New technologies are emerging to combat CUI more effectively. Smart coatings with moisture detection capabilities, drone-assisted thermal imaging inspections, and improved non-metallic insulation systems are all changing the way we approach asset protection. However, no technology can replace proper planning, installation, and ongoing maintenance.

What Happens If CUI Is Ignored?

It’s easy to assume insulation is just about keeping heat in or cold out, but when it’s not specified or maintained correctly, it can cause significant long-term problems. Corrosion under insulation has led to major failures, shutdowns, and even safety incidents across multiple industries. Taking the right preventative steps now can avoid unexpected failures and unnecessary costs later.
If you’re unsure about the condition of your insulation or want to improve long-term asset protection, we’re here to help. Get in touch today to discuss how we can support your site.