Prevention and Performance

Corrosion under insulation (CUI) is a common concern in chilled water or refrigeration systems because the equipment operates below the ambient temperature making condensation a huge source for moisture. Designing the system to include insulation and specifying the right type and thickness of insulation is a preventative best practice. CUI can considerably reduce the service life of mechanical systems and causes more frequent shutdowns and overhauls. There are a wide range of products available to insulate cold surfaces; however, selecting the wrong insulation can also lead to disastrous consequences from CUI.

Best Practices

  • Multiple design factors, advice, installation, and maintenance recommendations to consider when insulating chilled-water, refrigeration, and below-ambient piping systems. 
  • Installation of insulation and accessory products should follow recommended procedures in the Armacell North American Application Manual
  • Use correct thickness of insulation for design parameters. To determine correct thickness, please contact our Technical Manager, Kartik Patel at
  • All openings, protrusions, gaps, etc. need to be properly sealed with an Armacell recommended adhesive.
  • Utilizing pipe hangers like Armacell Insuguard supports material longevity and reduces compression points by accommodating movement of the pipes generated by thermal expansion and vibration.
  • Cooling and refrigeration systems must be turned off and be at room temperature during install to prevent trapping of moisture inside insulation.
  • Moisture can form and become trapped between the insulation and pipe surfaces and if the pipes are iron or steel, there is the possibility that rust will form. Continued exposure to rust has been known to cause thinning of the insulation.
  • In constant high humidity areas with above 80% relative humidity, where vapor pressure drive is constant on the insulation, it may be necessary to install zero perm jacketing to prevent formation of condensation.
  • A rust inhibitor coating is recommended for the piping to protect the metal surface prior to insulating or reinsulating the repaired pipe section(s). Refer to the pipe manufacturer or engineer for recommended coating.
  • Performing an annual inspection of the system, piping, and insulation is recommended, noting seals and joints.
  • If moisture does occur under insulation, identify all areas between the insulation and piping that need to be repaired being careful to note that moisture travels the path of least resistance within the system.
  • If rust or corrosion is found on pipes, seeking advice from the pipe manufacturer or an engineer to determine the correct course of action that is recommended.
  • Insulation materials can be reinstalled if there is damage, with proper care to make sure that the insulation is installed at proper thickness and sealed correctly. 

The fact that closed-cell structures are inherently durable and virtually impermeable to water means better lifetime efficiency. This is recognized in ASHRAE Fundamentals 2017 which suggests that cold pipe systems be protected through the use of very low permeance insulating material with a water vapor transmission rate (WVT) of 0.10 per inches or less. Closed-cell elastomeric foam, specifically ArmaFlex, has a very low permeability rating of 0.05 and resists condensation which causes corrosion. Therefore selecting closed-cell elastomeric foams is one sure way to prevent moisture on piping systems.