Hi Top 10 HVAC! HVAC Coil Corrosion, Should You Be Concerned!

Hi Top 10 HVAC! HVAC Coil Corrosion, Should You Be Concerned!

Coil corrosion is an expensive problem in the HVAC industry, leading to coil replacement or entire system replacement. 

Corrosion results in failure, and is responsible for about 40% of equipment failures in industrial applications, according to CED Engineering.

As the authors of an article in Reliable Plant explain, coil corrosion comes in the form of either pitting or Formica deterioration. Corrosion may occur as quickly as a few weeks after an installation or it may take up to four years to present itself.

Pitting corrosion is most often caused by exposure to fluoride or chloride. Fluoride is present in municipal water supplies, while chloride is found in a variety of products including snow melt, detergents, cleaners, carpeting and fabrics. 

Pitting occurs when chloride or fluoride ions are transported to the metal via condensate. 

The ions attack the metal, forming pits that form pinholes, causing the coils to leak REFRIGERANT.

Formica corrosion is typically caused by exposure to acetic or formic acids. 

These acids are present in a host of household products including cleaning solvents, insulation, adhesives, paints, plywood and many other materials. 

This type of corrosion is not always immediately visible and sometimes presents itself as black or blue-Gray DEPOSITS.

Formica corrosion creates tunnels within the tubing that result in pinholes forming in the coils, again often leading to a refrigerant leak.

Facilities located in more corrosive environments including near salt water or in industrial sites are particularly prone to experiencing coil corrosion. 

Other environments that may contribute to a higher amount of corrosive materials being expelled include areas around pools, laundry facilities, WATER TREATMENT plants, sewers and high traffic areas.

In such highly corrosive areas, coils have been known to fail in less than one year, according to CED Engineering.

A potential cause of coil corrosion is Chinese drywall, also known as odorous wall-board. 

Chinese drywall is also hazardous to your health. According to an article in G3 Environmental & Industrial Hygiene, an environmental and industrial hygiene service company, the drywall was imported from China from 2004 to 2007 and installed in both residential and COMMERCIAL BUILDINGS. 

The drywall emits sulphur compounds, which corrode metal, including air conditioning coils.

The Centers for Disease Control and Prevention confirms that exposure to Chinese drywall can cause certain health problems such as irritated eyes and skin, respiratory problems and headaches. Exposure to this type of drywall can also exacerbate ASTHMA SYMPTOMS.

You can identify the drywall by looking at the back. It should contain a label with the words: 

“Made in China,” “China,” or “Knauf.” Some Chinese drywall is not marked.

In that case, metal corrosion including in plumbing, electrical, and NATURAL GAS lines, combined with a rotten egg odor may signify a Chinese drywall installation

To combat the problem of coil corrosion, coil manufacturers are applying coatings prior to production. In addition, there are companies offering after market coatings. 

In a BROCHURE, Aeris Technologies Ltd., a manufacturer of after market coil-protection coatings, explains that the consequences of coil corrosion can include reduced efficiency, unattractive surface deterioration and equipment failure.

Additionally, reduced HEAT rejection may occur, resulting in an increasing compressor temperature and lower cooling capacity, which in turn increases the power usage. 

Lower cooling capacity means the compressor doesn’t cycle as intended, which means increased power consumption.

As systems work harder they become more stressed, experience more breakdowns and have higher maintenance costs. 

A lower cooling capacity may also mean occupants aren't very comfortable, resulting in loss of business or productivity. Preventing coil corrosion is much more effective and cheaper than replacing coils or the entire system.

There are basically four types of coil coating materials: polyurethanes, epoxies, fluoropolymers and silanes, according to Reliable Plant. Choose carefully as the wrong coating, especially with after market products, can reduce heat transfer and result in more expensive operating costs. 

An after market application may affect the manufacturer’s specifications.

Thinner coatings have better heat transfer while thicker coatings restrict heat transfer. 

Hydrophobic, or how effectively water DRAINS from the coil, can affect heat transfer. Water build up may also cause mould or mildew growth. 

The advantages of the four types of coatings differ as to how they resist scratching and corrosion; their weights/thickness's; hydrophobic; and heat transfer abilities.

Polyurethane is INEXPENSIVE, flexible and thin, but it’s not as long-lasting as other coating options.

Epoxy is cheap, but it’s usually a thicker coating and can’t be applied in the field; the coils must usually be shipped to a factory for professional application. 

Fluoropolymers are highly resistant to acids and solvents, and are inexpensive, but the sprays generally adhere poorly and their effectiveness wanes quickly.

Silanes form a thin coating that affects HEAT transfer very little and they typically last longer than other coatings, but they’re more expensive and proper application is best done by a professional and usually off-site. Each coating type has varying toxicity levels. 

Technicians applying the coating should wear equipment as specified by OSHA and an appropriate breathing apparatus.

Whether coated or not, continuing maintenance of coils is the primary way to combat the effects of corrosion. 

Twice annual cleaning with an alkaline coil cleaner or pH balanced coil cleaner will clear away any accumulated DEPOSITS, keeping coils safe from corrosion but also positively impacting the efficiency of your system.

Have you experienced coil corrosion? How did you combat the problem? Or did you choose a COOLING SYSTEM with coil coating protection included? And have you been happy with the product?