On the design table, many insulation materials can work for a variety of piping and tank applications; design considerations often include insulating value, fire safety, resistance to corrosion, and other factors. However, planning must also take into account real-world conditions that may be likely to occur, such as freeze/thaw cycles, system movement, potentially crushing loads with direct burial, wash downs, or simply damage by workers.

Once an insulation system becomes damaged or absorbs moisture, the insulation enables accelerated heat gain or loss, increased energy consumption, and loss of process control; in cryogenic systems and high-temperature systems, solidification is also a concern. Damage or moisture can also lead to corrosion and be a potential danger to personnel. Selecting the right insulation for a project can make the difference between long-term performance and the need for replacement or retrofitting. It can also determine whether a system has constant thermal efficiency or expensive stoppage of production because gases turn to liquid or liquids turn to solids.

Moisture Is a Problem

Regardless of the application or temperature range, the most likely cause of damage to insulation is moisture. The vast majority of insulation system problems are caused by moisture, which typically enters through the jacketing and can be retained within in the insulation.

In the theoretical design stage, a permeable insulation will not absorb moisture if protected with the proper jacketing. However, in a critical application like chilled water—where there is a strong vapor drive from the air to the cold piping—even a small tear, crack, or pinhole can develop, allowing an entryway for damaging moisture in either liquid or vapor form. In high-temperature applications, this can become a personnel safety issue. The severity of moisture issues will depend partially on the temperature range of the system.

Cold/Cryogenic

While moisture can enter the system directly as absorbed water, an even more significant source of moisture penetration is diffusion of water vapor, which can condense as a liquid or ice. As the temperature gradient increases between the exterior insulation surface and the surface of the insulated equipment itself, so does the potential rate of water-vapor penetration. Thus, it is more important that the insulation has a low vapor-transmission rate than an initially low thermal conductivity.

High Temperature

Potential issues can arise in high-temperature systems when using a permeable insulation or relying on water-repellant treatments on the material. At these temperatures, an insulation can become completely saturated in less than a few hours. Also, most water-repellant treatments deteriorate and become ineffective at temperatures as low at 265°F. While process heat can drive water back to a certain point, some will always remain in the insulation layers that are below 212°F, resulting in substantial heat loss and a compromise in process control.

The best way to prevent damage to the system is to specify an impermeable insulation system that does not rely on vapor retarders and jacketing to keep moisture out of the system.

Accessories Are Important

While much emphasis is placed on the details of the physical and performance characteristics of the insulation material itself, the importance of accessory products is often overlooked.

Some view accessory products as commodities that can be mixed and matched. However, history and performance have proven that if high-quality, compatible accessories are not used, the performance and dependability of the entire insulation system can be compromised.

Taking a “total-system” approach to design can be the best way to ensure optimal operations. A total-system approach is simply using accessory components that have been tested and recommended as compatible for the specific insulation being used. This approach can best achieve the desired results of a high-quality, long-lasting insulation system.

Any coatings planned for use in a system should be tested for chemical resistance, weathering, and appearance. Adhesives and sealants need to be tested to perform with a specific insulation material to prevent water vapor entry, especially on below-ambient and cyclic systems, or systems subject to wash down. Again, the best way to reduce the threat of insulation failure due to moisture is to use an impermeable insulation product.

If the insulation material is impermeable, a jacketing is needed to provide mechanical protection on above-ground and below-ground installations. Metal jacketing provides mechanical protection on above-ground applications, while bituminous jackets prevent water and water-vapor intrusions in below-ground applications.

Preventing Corrosion under Insulation

One of the most critical problems caused by moisture is metallic corrosion under insulation (CUI). When water comes into contact with either carbon steel or stainless steel, corrosion or stress cracking can occur. This can remain undetected for years, hidden by the insulation and outer jacketing.

Unfortunately, CUI is often detected only after the equipment and insulation system have been damaged and need to be replaced. This can be a costly proposition as it is associated with downtime, lost productivity, and even total facility shutdown. In a worst-case scenario, sudden, dangerous leaks are possible, which can result in the release of hazardous material, depending on the type of system.

To protect your system from CUI, specifying a vapor retarder is a start. However, these may not provide complete protection from CUI. Other accessories that can assist in isolating water from the insulation are flexible cauls, which are either moisture resistant or serve as vapor retarders.

Physically providing a barrier directly on the surface of the steel, such as corrosion-resistant coating, may protect steel from the effects of water. However, regardless of accessories such as jacketing and sealants (which are all subject to potential failure due to movement in the system or external physical abuse), the selection of an insulation material that will not absorb moisture and not contribute chemically to corrosion is the best course of action.

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