CharCoat CTI stopping Corrosion Under Insulation (CUI)

Corrosion under insulation (CUI) is the corrosion of piping and vessels that occurs beneath insulation as a result of water penetration. The water can come from rain water, leakage, deluge system water, wash water, or sweating from temperature cycling or low temperature operation such as refrigeration units.

Unfortunately, because the corrosion is hidden under the insulation, CUI tends to remain undetected until the insulation is removed for inspection or when leaks occur. CUI is a common problem across many industries, including refining, petrochemical, power, industrial, onshore and offshore industries.

CUI can take place under any insulation. For corrosion to occur, the carbon steel must be directly contacted by aerated water and may be accelerated by other factors such as temperature or other contaminants. Water enters an insulated system primarily through breaks in the weatherproofing from sources such as:

• • Rainfall
  • Drift from cooling towers
  • Condensation on cold surface after vapor barrier damage (when the temperature of the steel surface is lower than the atmospheric dew point).

Contaminants can increase the rate of corrosion by increasing the conductivity and/or the corrosiveness of the water environment and reducing the protection offered by corrosion scale product.

Chlorides and sulphides are the principal contaminants of concern and can arise from sources external to the insulation or leached from the insulation itself. Testing and plant experience shows that chlorides most frequently come from external sources such as coastal atmospheres, nearby chemical process units, fire protection deluge systems etc rather than from the actual insulation.

Elevated temperatures typically result in increased corrosion rates in proportion to the temperature rise up to temperatures around 150C where the rate of corrosion starts to decrease.