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Corrossion Under Insulation (CUI)

Corrosion is a process of electro-chemistry which involves an electrolyte that reacts with a metal and water forming a depositing salt layer on the surface of the metal which we know as Rust. Corrosion can affect pipes, vessels,tanks and other equipment usually with a metallic surface which oxidizes it when it comes in-contact with the electrolyte. This electrolyte is usually water in the form of free or condensed liquid. Some good immersion grade coatings and proper weather barrier jacketing and insulation materials can help minimize the corrosion on the equipment. Other methods for corrosion inhibition include cathodic protection which involves using an easily corroded metal in contact with the metal you are trying to protect to act as a sacrificial metal. There is no permanent solution for corrosion, so the best solutions are the ones that lasts the longest whilst minimizing the corrosion rate.

Corrosion Under Insulation (CUI) is a more problematic form of corrosion which plagues most industries as the accumulation of water or humid air under the layer of insulation allows the electrolyte to maintain longer contact with the metal surface and remains largely undetected until which time the insulation is removed for inspection. Often times, the corrosion occurring under insulation systems are quite severe and can lead to accelerated and unexpected failures.

When does CUI happen?

Ineffective weather barrier on the insulation system allows water from rain and storms to ingress into the insulation system and often times soaks it.


When the coating surface of the metal is not effective, the water absorbed or retained by the insulation layer comes into direct contact with the bare metal allowing corrosion to develop and propagate.


Material with high absorption and high porosity to allow water and oxygen ingress, such as foam rubbers, polyurethane and Rockwool severely accelerates corrosion.

Corrosion Under Insulation Inspection

How to Prevent CUI?

By understanding the basics of corrosion, it can be concluded that the best solution is by preventing moisture and other electrolytes from contacting the metal surface. Selecting the ideal insulation material includes considering its thermal performance as well as its ability or inherent property to minimize corrosion under insulation. The proper selection of insulation material is important as it will reduce future costs as properly protected assets will last longer and require less maintenance.

One of the best solutions used in the industry are Aerogel based insulation materials which. It is one of the best because of the Nano pores within it that makes it a poor conductor thus a great insulator material and its hydrophobic properties which repels liquid water while still breathable, allowswater vapors to pass outwards keeping the system dry. Systems, Pyrogel® XT-E is a great insulator widely used in the industry and marine environments.

It is made up of lightweight silica solid derived from gel material in which the liquid component of the gel is replaced with gas, so the remaining is the puffed-up sand having a 99% porosity. 

Aerogel Insulation Sheets
High Temperature Aerogel Insulation
Flexible Aerogel Insulation

How Aerogel Can Help Mitigate CUI

  • Hydrophobic - Aerogels innate hydrophobicity repels water from seeping through the insulation layer.
  • Breathability - Even if moisture finds its way through the insulation layers, Aerogel’s open-cell construction allow a quick exit for trapped moisture.
  • Chemical Corrosion Mitigation - Aerogel is designed with corrosion inhibitors such that water entering the system will be buffered to a pH > 7.
  • Robust Resilience - Aerogel is a flexible yet durable material with excellent spring back. Hence, allowing it to last longer compared to other insulation materials ensuring long term asset integrity.
  • Faster, Less Costly CUI Inspections - Sections of aerogel can be easily removed and reused making inspection and maintenance more cost effective.

Where Can You Apply?

Thermal Insulation Efficiency Condensation Insulation
Observations Day 1 Day 85 Day 85, Insulation removed
Pyrogel XTE No corrosion observed except for a thin area directly benath the two clamp bands Clamp Bands Corrossion Clamp Bands Corrosion Free Bands
Cryogel Z No Corrosion Clamp Bands Aerogel Aerogel Inspection