Engineers: Insulation Selection is Critical for Corrosion Resistance
In a recent article, I stated that insulation materials do not cause corrosion under insulation (CUI). They can however significantly impact the rate at which corrosion occurs. It’s extremely important to assess CUI risks and carefully select insulation materials to minimize them.
By accounting for a system’s operating temperatures and your thermal efficiency goals, you can get a starting point for possible insulation materials on a project. Then, you can consider the following technologies in your efforts to minimize the rate of corrosion.
The first line of defense to keep water and moisture from reaching the pipe is a protective jacket. Environmental elements and the extent of vapor drive will be things to consider in the selection process. Will the insulation system be exposed to precipitation? Foot traffic or other abuse? How different is the operating temperature from the surrounding environment?
Weather barrier or cladding solutions are available from a number of companies including: 3M (Venture), Aeroflex, Armacell, Dragon Jacket, Ideal Tape, K-Flex, MFM, Polyguard, and Rockwool. PVC jacketing is not as common for high-risk CUI applications, but it may be able to protect from puncture or abuse when conditions don’t demand a metal jacket. Johns Manville, PIC Plastics, Proto Corporation and Speedline Corporation all offer PVC jacketing solutions.
Stainless steel or aluminum jacketing is especially protective in harsh or outdoor conditions. Manufacturers include: Ideal Products, ITW, RPR Products, Shield Metal Manufacturing, Shur-Fit, Standard Metal Industries, and Volunteer Metal Systems.
I’d recommend viewing NACE International’s website to learn about anti-corrosion coatings. For operating temperatures up to 350°F, Polyguard offers a product called RG2400. It’s a gel-like coating applied directly to the pipe and designed to protect piping and equipment from corrosion in a high-risk environment. This is the only coating of its kind widely available from mechanical insulation distributors and fabricators.
Mastics are another type of coating which are applied with a trowel or brush to the outside of insulation or its vapor retarder jacket. They have long been used to protect insulation from moisture and the elements of weather. This traditional product solution leaves a seamless finish which can be especially useful on tanks, vessels or around turns and obstructions in a piping system. Mastics are produced by: Design Polymerics, Foster Products (Childers), Mon-Eco Industries and Vimasco Corporation.
This type of insulation is characterized by its cellular structure where individual cells share walls with their neighboring cells. Basically, the structure doesn’t allow a path for water or moisture to travel between cells. This technology is commonly used for cold systems, but can be used on hot applications as well. Aeroflex, Armacell and K-Flex offer closed cell elastomeric insulations. Owens Corning recently acquired Pittsburgh Corning, the makers of Foamglas® cellular glass. Other closed-cell foam insulation products are available from: DowDupont, Duna USA, Dyplast Products, ITW, Polyguard and Thermal Pipe Shields.
The demands and external factors of a system sometimes won’t allow for closed-cell products. Fortunately, some insulation materials feature hydrophobic characteristics. This means that they’re highly resistant to liquid water penetration. Aspen Aerogels has made a name for themselves in the world of CUI primarily with their Pyrogel® and Cryogel® insulations. Hydrophobic aerogel insulation materials have gained enough acceptance over the last 10-15 years that Armacell and Lewco recently introduced competive aerogel products. Expanded perlite insulation from Johns Manville Industrial and Howred Corporation also feature hydrophobic properties.
Hydrophobic insulation resists water even if it’s submerged. In contrast, manufacturers may promote their product as water resistant if they can shed bulk water or withstand exposure to rain for a short period of time. Examples of water resistant insulation would be Rockwool International’s new WR-Tech water repellent technology in their mandrel wound mineral wool pipe insulation or calcium silicate offerings from Johns Manville Industrial and Thermal Pipe Shields.
The CUI rate is also effected by the acidity of water when it reacts with oxygen and a metal surface. Although calcium silicate is cement-like and hygroscopic, Johns Manville Industrial promotes their XOX Corrosion Inhibitor as a means to combat corrosion. They state that their proprietary formula reacts with water at the metal surface to create a physical barrier and raise the pH level, thereby decreasing the rate of corrosion. They use the same technology in their expanded perlite insulation.
Thermal Pipe Shields‘ competitive calcium silicate product is described as having an integral inorganic silicate chemistry that performs similar to JM’s XOX Corrosion Inhibitor. Corrosion inhibitors can also be found in other insulations and protective coatings.
The popularity of these products has grown along with CUI awareness in the last decade or so. Inspection plugs usage is a proactive approach to avoiding future problems with CUI issues. They are essentially ports designed to allow fast, non-destructive access to an insulation system. The plugs are placed strategically in places where water is expected to pool if it becomes trapped in the system. Located on the bottom of tanks, vessels or low points in the piping system, CUI mitigation teams can quickly gain confidence or identify areas of concern by inspecting the water concentration. The insulation and jacketing remain intact as the plug is released and re-plugged. Manufacturers of this type of product include: Access Plug Flange, Inspection Point Seals, Integrity Products and NDT Seals.
Insulation does not cause CUI. It can however, drastically increase the rate at which it occurs by holding or trapping water against pipe or tank’s surface. Your understanding of these anti-corrosion technologies can significantly extend the life of your system.
I recommend asking about your client’s CUI mitigation program or maintenance schedule. It may help you better estimate the risks of CUI going unnoticed and effect your insulation specification. One product or combination of products is not the right choice for every application facing CUI. I encourage you to reach out to the sales people representing these manufacturers. Ask them what their system offers, and make informed decisions to offer your client the best all around value in their insulation system.
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