Insulation Materials’ Influence On Corrosion Under Insulation (CUI)

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By John Williams

March 20, 2019

As facilities engineers and operators know, a Corrosion Under Insulation (CUI) mitigation plan is critical to combating the problems that arise from wet insulation and CUI, such as process instability, reduced outputs, loss of containment, and personnel safety incidents.

But, it’s the designer of industrial insulation systems that creates a system that stands the test of time in CUI defense. That being said, the designer has three main weapons in the fight against CUI.

  • The first and primary defense against CUI is a high quality, immersion-grade coating.
  • The second is a properly designed and installed weather barrier jacketing and, if operating below the atmospheric dew point, vapor barrier.
  • The third and, arguably, least understood element is the choice of insulation material.

Historically, hot insulation products have been divided into categories of wetting and non-wetting, or “hydrophobic” materials. The distinction is important because, as pointed out in NACE Standard RP0198-98:

“Because CUI is a product of wet metal exposure duration, the insulation system that holds the least amount of water and dries most quickly should result in the least amount of corrosion damage to equipment.”

A more recent European monograph states flatly:

“Insulation that minimizes water ingress and does not retain water can effectively act as a barrier to CUI.”

Nevertheless, though many engineers do prescribe the use of water-repellent materials on equipment operating in the CUI range (-4 to 175°C, or 25-347°F), the practice is far from universal. Some of the reluctance undoubtedly stems from cost sensitivity, since water-repellent insulation materials are generally more expensive than their water-absorbent cousins. Such sensitivity is often misplaced, as the cost, hazard, and disruption of even one corrosion event can far outweigh any savings – real or perceived – on insulation materials.

Another barrier to the effective use of water-repellent materials is simply the general lack of comparative material data for different insulation products. Although previous authors have addressed the pros and cons of various insulation materials, the approach has typically been one of cataloging corrosion under insulation outcomes within operating facilities. While those insights are invaluable, they don’t allow the isolation of specific variables or mechanisms – of which there are many – because they are basically uncontrolled experiments.

Download our white paper “The Influence of Insulation Materials on Corrosion Under Insulation” to discover how important your choice of insulation really is in combating CUI, and how Aspen’s hydrophobic, breathable insulation can help defend against CUI in your facility.