Corrosion Under Insulation (CUI) Part IV: Insulation System Maintenance

In Part I of our blog series on CUI, published on December 18, 2013, we discussed the simultaneous conditions necessary for CUI to occur:

  • Liquid water
  • Oxygen
  • Corrosive chemicals
  • Operating temperatures in the range of 100°F – 300°F (38°C – 149°C)

The article also noted four general areas in which the insulation industry and specifiers direct their efforts in order to control the presence of water:

  • Selecting the proper insulation material
  • Protective jacketing design and installation
  • Protective coatings
  • Insulation system maintenance

In this post, we will continue to elaborate on CUI, and discuss the importance of proper insulation system maintenance.

Because corrosion cannot happen without the presence of water, the selection and design of the protective jacket material is a critical issue for engineers and designers. If water is not permitted to penetrate the assembly and come in contact with the pipes, corrosion will not occur. Properly designed, installed, and maintained jacket systems are the most effective means of protecting pipe systems from CUI.

When an insulation system is not properly maintained, water will eventually find its way past the weather protection. Additionally, rain water entering the system will most likely contain impurities, such as dissolved salts and chlorides that can lead to corrosion of the pipes.

Even if the entire system was properly designed and installed, regular inspection and maintenance is absolutely necessary to keep the system functioning throughout the life of the equipment. Physical abuse over time, such as foot traffic or anchoring scaffolding to insulated pipes, can cause dents and even punctures in metal jackets, providing access points for rainwater. One way to help prevent such compromises to the jacket systems is to specify and install high-compression-strength insulation materials, such as calcium silicate or expanded perlite.

Another key element to ensuring the longevity of all insulation systems is the integrity of the caulking system. All joints, transitions and penetrations are specified to be caulked with a product designed for this application. However, caulks are affected by weather and UV rays and can stiffen and become brittle over time. One of the most important steps to safeguard the long-term performance of an insulation system is caulk maintenance. The caulk that seals every penetration and joint needs to be inspected, maintained and replaced periodically.

The bottom line for preventing corrosion under insulation is properly designing and installing the entire insulation system, developing a maintenance program that keeps water out of the insulation for the life of the equipment and specifying an insulation material with corrosion inhibitors in case the weatherproofing system fails.

There are several articles related to CUI contained in the publication archives of the National Insulation Association