Systematically Making Insulation Part of the CUI Solution

FIGURE 2 CUI development can pose multiple challenges for a facility.

Globally speaking, destruction wrought by corrosion is estimated to bear an annual price tag upwards of $2.5 trillion, according to a NACE International study from 2016.1 To put that figure in context, consider that it is close to the cost of the first U.S. economic stimulus package in 2020.

NACE’s findings on the cost of corrosion highlight that 15 to 35%, or US $375 to $875 billion, could be saved annually by developing and implementing a multi-step corrosion control plan.1

By documenting a multi-step plan to prevent corrosion under insulation (CUI) and implementing steps to protect and preserve equipment, facilities can save on repair costs, reduce unexpected downtime, and improve the safety culture (Figure 1). However, fully realizing the long-term cost savings of insulation may call for a shift in thinking about the economics at play. Rather than viewing insulation as an area to cut short-term costs, stakeholders need to understand how a systematic approach to insulation utilization and maintenance can save time and money in the longer term. Approaching insulation from a systems perspective means taking steps to ensure it functions for a longer period, rather than anticipating it will fail and value engineering a cheaper insulation for short-term cost cutting.

FIGURE 1 Facilities can save on repair costs, reduce unexpected downtime, and improve safety with a multi-step plan to prevent CUI.

Planning for insulation to function as intended across its lifetime necessitates that the insulation be water repellent, used with the correct jacketing, and that both are properly installed. Pipe temperatures also should be considered as it can influence the potential for corrosion to develop—most corrosion occurs when pipes are 0 to 149 °C.2 Additionally, routine inspection outlined in a facility-specific maintenance plan may help ensure the longevity of the system.

The CUI Challenge

Corrosion can appear in many locations, such as coastal, offshore, or humid regions. Conditions for corrosion to develop are also influenced by pipe temperatures. Pipes ranging from 0 to 149 °C can see a higher rate of corrosion than pipes below freezing or above 149 °C. An area of particular interest for industry is corrosion that develops on piping or containment units covered by insulation. More than $10 billion is spent annually to remediate petrochemical and petroleum refinery equipment and electrical utilities following problems from corrosion.3

CUI development can pose multiple challenges for a facility: unexpected failure of a process system, costly repairs, unexpected downtime, and damage to expensive equipment (Figure 2). Corrosion can increase the risk of leaks, pipe failures, fire, explosions, and employee injury or death. It also reduces the lifetime of piping and equipment.

There are relatively few factors that contribute to corrosion, including the presence of moisture (in both liquid and vapor form), the pipe or unit temperature—the danger zone is 0 to 149 °C—temperature cycling of pipes, environmental contaminants, and facility location.

Moisture can be introduced into a system in several ways, including through condensation, mist or precipitation, leaks, and even routine facility cleaning. Increasing the acidity or basicity of the moisture or raising its temperature will hasten the development of corrosion. Certain environments, like marine areas, provide sustained exposure to corrosion risk.

Additionally, intruding moisture often carries chlorides that can interact with any contaminants present in insulation and improve conditions for corrosion to form on covered pipes.

Water retention in insulation causes additional unwanted effects. Moisture in insulation can increase its thermal conductivity, meaning additional heat is lost as energy is used to remove water from insulation. Moisture adds weight to a system and may not have been accounted for when an insulated system was designed and supported.

Potential ways to prevent or reduce the development of corrosion include sealing a system to keep water out, giving moisture a path out of the system, or neutralizing the pH of the moisture present.

A major factor to consider when planning CUI mitigation is that corrosion is not just an insulation problem—it is indicative of a system problem. Improving how insulation is selected, installed, and maintained supports the evolution of industry thinking regarding insulation’s role in protecting piping and equipment from corrosion. While insulation used in industrial facilities tends to be selected for several factors, including thermal performance, linear shrinkage, and fire resistance, considering how insulation responds to or manages moisture also should be examined.

Five Steps to Limit Chances for CUI

When properly designed and installed, an insulation system can provide years of performance while minimizing or preventing the development of corrosion and improving the materials-based sustainability of a facility. According to a NACE report of a Battelle-NBS study, about $10 billion spent on repairing corrosion could be saved annually in the United States using available anticorrosion technology.1

A five-step plan developed to reduce the occurrence of CUI and improve the selection, installation, and maintenance of insulation includes:

1) Select an insulation that is water repellent.

Mineral wool insulation provides several physical properties that suggest it for use in industrial applications. The fibrous structure of the mineral wool restricts air movement to provide better insulation while allowing moisture vapor to pass out of the system. Any water that enters the insulation is not trapped against the covered pipe.

In high-temperature industrial situations, most often the insulation used is vapor open. Using a water-repellent mineral wool as insulation in these situations prevents water from being trapped in the insulating material. Water-repellent mineral wool allows for moisture to dissipate quickly. Reducing the amount of moisture present limits the potential for corrosion to develop.

2) Select a jacketing that is of sufficient thickness and material for the application.

For jacketing to be most effective in protecting insulation and piping from damage and moisture, the correct type and thickness needs to be selected and used with the right accessories (Figure 3). Industry jacketing standards ASTM C1729 (aluminum)4 and C1767 (stainless steel)5 can be used to aid selection. Pipe coatings also may be considered to provide an additional layer of protection. However, attention needs to be paid to whether pipe coatings and specific insulation types can be used together.

In a high-traffic area, or in a situation where pipes may be walked over or be at risk of physical damage, thicker jacketing could improve the longevity of the insulation.

FIGURE 3 Insulation and jacketing should be installed to direct water flow.

Periodically updating the design specifications used to select the best insulation for a project could streamline the selection process. The National Insulation Association’s (NIA) National Insulation Training Program uses Process Industry Practices as a basis for establishing effective industrial specifications.6 While specifications used for a project don’t have to be long and complicated, they should be able to logically relate to what is needed.

3) Require proper installation of the system by qualified and experienced installers.

For an insulation system to be most effective, the selected system also needs to be correctly installed and maintained.

Some factors to consider when insulation is installed include that all longitudinal and circumferential joints need to be closed and sealed, and that insulation should be cut to fit snugly against penetrations, which also should be sealed.

For horizontally installed pipe, the downward-facing longitudinal edge of the jacketing needs to be in either the 4- or 8-o’clock position and lapped over the bottom edge to manage water flow and direct it away from the pipe.

The NIA Thermal Insulation Inspector Certification™ trains future inspectors to have knowledge of mechanical insulation, verifies that the insulation is being installed to the specification, and identifies potential areas of concern during initial installation and/or in ongoing operations.7

4) Create a long-term inspection and maintenance plan specific to the facility.

Developing recurring inspection and maintenance plans could improve the longevity of installed insulation systems. Locations of particular interest to check would be at joints, where there are protrusions in piping, and where pipes may be subjected to physical damage.

AIChE, the chemical engineering organization, suggests understanding which equipment in a facility is most at risk for CUI.8

5) Routinely check the insulation system for signs of physical damage.

To function optimally, insulation and its related accessories need to remain in good condition. A common reason for jacketed insulation to fail is the repeated impact of people stepping on the pipe.8

FIGURE 4 Water-repellent mineral wool allows for moisture to dissipate quickly, limiting the potential for corrosion to develop.Making periodic checks of piping could be one way to prevent water or moisture from entering insulation at a site of external damage (Figure 4).

Work Smarter, Not Harder, by Choosing Better Insulation

As the focus on insulation shifts from short-term cost savings to the development of an insulation system intended for long-term use and prevention of CUI, select pipe insulation that is intended to help facilities mitigate CUI, conserve energy and reduce noise, and can be used in fire-resistant applications. The mineral wool should not pose the same weight-related challenge as wet calcium silicate, which increases in weight and can put unanticipated strain on pipe hangers.

Ensure that the material can manage high-temperature situations when tested according to ASTM C4119 and ASTM C447.10 Establish a limit for insulation water adsorption that is tested in accordance with EN 13472 (Figure 5).11

To minimize the risk of corrosion, the mineral wool pipe insulation sections, while dry, are chemically inert to steelwork. The content of water-leachable ions such as chlorides, sodium, silicates, and fluorides in the pipe insulation should not exceed 10 ppm and meet the standards of ASTM C795.12

If the pipe insulation is used in coating facilities and during painting operations, make sure the insulation is certified according to the requirements of the coating compatibility standard VDMA 24364.13 Owens Corning has developed Thermafiber® Pro Section WR Pipe Insulation† that meets the above tests. It has a maximum use temperature of 649 °C, maintains water repellency up to 300 °C, and absorbs <0.1 kg/m2 when tested in accordance with EN 13472, meaning it takes in 10 times less water than the requirements of that tough standard.

FIGURE 5 Materials that meet EN 13472 are generally considered to be “water resistant.”


The long-term benefits yielded from approaching the use of insulation as a system rather than value engineered for shortterm cost cutting includes a sustained lifespan for equipment and facilities, time savings, reduced need for surprise repairs, and an improved safety profile for the facility and company.

Selecting an insulation that is water repellent and able to shed moisture quickly and effectively reduces the chance for corrosion to form. Adding jacketing of the necessary thickness—and installing the insulation correctly—supports the long-term functionality of the insulation. Creating and instituting a policy of periodic review and maintenance for the insulation fosters the understanding that insulation is meant to function over time and helps ensure it does so.

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