Corrosion Under Insulation (CUI) Part III – Protective Jacket Design

Wednesday, March 19, 2014 7:30 pm MDT


IIG Editors

In an earlier blog post (“Corrosion Under Insulation” December 18, 2013), we discussed the conditions necessary for corrosion under insulation (CUI) to occur:

  • 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 insulation specifiers direct their efforts in order to control the presence of water:

  • Selection of the insulation material
  • Protective jacketing design
  • Protective coatings
  • Insulation system maintenance

In this post, we will discuss the design of the protective jacket.

Because corrosion cannot happen without the presence of water, the selection and design of the protective jacketing material is a critical issue for engineers and designers.  If water is prevented from entering the assembly and coming into contact with the pipes, corrosion will not occur.  The most effective means of keeping this moisture out of the insulation altogether is with properly designed, properly installed, and well-maintained jacket systems.

The standard protective jacketing used in the North American industrial insulation industry is 0.016-inch-thick (16 mil) aluminum, with a factory-applied moisture barrier.  The jacket specification should also include instructions for properly caulked and sealed joints, penetrations, and transitions.  It is important to understand that at this thickness, aluminum cannot withstand much compressive force (foot traffic, tied-off ladders, etc.) on its own without collapsing or denting.

This damage typically results in a compromise of the joints in the jacket, which then can form a conduit for the entry of water.  By also specifying insulation with high compressive strength like calcium silicate, the system can better withstand the physical abuse that typically occurs in industrial settings.  Where fibrous (low-compressive- strength) insulations are specified for a project, it is advisable to also specify a thicker aluminum jacketing material (0.024 or 0.032 inches thick or 24 to 32 mils) to increase the resistance to foot traffic and other on-site wear.

Another type of jacketing, which has been around for decades, is a fiberglass mesh/cloth coated with an acrylic, weather-resistant mastic.  This system is a useful option for weatherproofing uneven surfaces and other insulated surfaces that would be difficult to protect and seal with aluminum jacket materials.  Properly installed, it is very durable, long-lasting, and waterproof.

Additionally, there is a relatively new weatherproof jacketing option for protecting insulation materials – a flexible composite material formed with several layers of components. The material is supplied with a factory-applied peel-and-stick surface on one side that directly bonds to the surface of the insulation.  This “stick-on” feature, and the material’s flexibility, allows for tightly sealed joints and penetrations.

Future blog posts will discuss additional methods to control the incursion of water in installed industrial insulations.  In addition, there are several articles related to CUI contained in the publication archives of the National Insulation Association.


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