Copper Group Explores Formicary Corrosion and Odor
May 9, 2011
It is the time of year when, in many parts of the country, cooling system problems involving coils tend to become more pronounced. Foul odors are especially problematic, but still more insidious are coil failures caused by formicary corrosion.
The NEWS has interviewed members of the Copper Development Association (CDA) for their takes on how these problems are being addressed.
THE OTHER F WORDJim Michel, manager of technical services for the Copper Development Association (CDA), informed us that formicary corrosion (aka “ant’s nest” corrosion due to its pattern seen under magnification) mainly occurs in tubes made from copper alloy 122 C1220. “It happens to be the material of choice for heat exchangers because of its good thermal conductivity,” he said. The industry is looking at both the alloys and the organic materials they come into contact with for solutions.
The corrosion itself looks bluish-black in the affected area. “Until you brush away the surface corrosion, you don’t know about the pitting,” Michel said.
A lot of recent research has been looking at reactions between those alloys and organic materials left on the surface during manufacturing, installation, or service - lubricating materials and fluxes - that are not completely cleaned off, or neutralized. “Petroleum or water-based materials, water, and solvents, end up creating formic acid, or carboxylic acid,” Michel explained.
“Fluxes and lubricants are supposed to be cleaned off with a solvent, like trichloroethylene; that also needs to be cleaned off,” he said. “The development of corrosion is aided by not fully cleaning the parts with water- and nonwater-based fluids,” both in the plant and in the field. Alternative fluids are being tried, Michel said, in an effort on the part of the industry to work through this problem.
The problem with looking for a different copper alloy to use, he said, rests in their varying heat transfer characteristics. “This alloy (122 C1220) has excellent thermal conductivity,” he said. “Other alloys would show a reduction as much as 70 percent. You would need to upsize the equipment and nobody’s gonna do that.”
How many systems does it affect? He called it a “relatively small” number. “We don’t see all of it,” he added. “We’re the trade association for the copper industry. It’s usually a one off.”
His advice to contractors: “Make sure copper materials are thoroughly rinsed of any materials left on or in there. This includes all kinds of regular and/or water-based fluids that are supposed to be rinsed off.” Moisture, he said, causes these particular organic compounds to change their nature.
“Cleanliness is very important in manufacturing and installation.
“It’s an ongoing education process,” he added. “When you’re putting things in, take a little extra care. But you need the knowledge before you go there.” The elimination of lubricating fluids is most important, he said, but so is cleaning off all the flux from soldering and joining.
ODOR CONTROLEarlier this year, the CDA announced that copper HVAC components are now EPA registered for use in protecting heating and air conditioning surfaces from bacteria, mold, and mildew. “HVAC components made from copper and copper alloys suppress the growth of organisms that can cause odors and reduce system efficiency,” stated a press release from the association.
Research conducted in the military barracks at Fort Jackson in Columbia, S.C., showed that copper coil fins and drip pans suppressed the growth of bacteria, mold, and mildew, keeping the units free from buildup. “Cleaner units allow for increased heat transfer, decreased airflow resistance, and overall increased system efficiency, as well as a diminished potential for odor,” the association said.
“The biggest surprise was that the efficiency was so much better,” said Michel. “It was substantial, and affected it much faster than we anticipated.” The minimization of mold on surfaces doesn’t allow the biofilm to grow, and biofilm is insulative. Moreover, “The odor problem is the biofilm that grows on the surface.”
Harold Michels, Ph.D., CDA’s senior vice president of technology and technical services, said that while it does help prevent odors such as those in the so-called Dirty Sock Syndrome, the EPA registration doesn’t allow the mention of specific microbes. “We’re trying to verify it,” he said. “Odor is hard to quantify.”
The real benefit is in an overall reduction in microbes, he said. “So far the results show that reduction.” It is expected to benefit not only the HVACR industry, but the automotive a/c industry as well, which also has had to deal with consumer complaints of odors related to cooling system operation.
Microbe reductions were apparent in both heating and cooling seasons, said Michels. “The reduction in the heating season is greater than the cooling season,” he said; there was a 65 percent reduction in microbes in the heating season, vs. a 40 percent reduction in the cooling season. Additional components could also be made of copper, such as drain pans and the drain line, for additional microbial growth prevention.
For more information, visit www. copper.org.
Publication date: 05/09/2011