Traditional copper coil showing formicary corrosion. Field failure occurring just two months from manufacture date.
Formicary corrosion is a type of corrosion also referred to by HVAC contractors as "ant's nest" corrosion.
This is because of the distinct ant tunnel pattern that this type of corrosion makes in copper and copper alloys (the metals that it exclusively attacks). Detecting formicary corrosion is tricky because it cannot be seen with the naked eye. This makes it difficult to be detected before the problem is too severe and causes a coil leak. If you can see corrosion occurring, the corrosion is probably not formicary corrosion.
In order for formicary corrosion to occur, a couple things need to be present. There are four components for formicary corrosion: water, oxygen, copper and an organic acid. Formicary corrosion is more likely to occur in southern areas with high levels of humidity because there is more water to react with the other components in the air.
Organic acids are hard to avoid. They are found in anything from Chinese manufactured drywall to make-up. Although it is possible to lower the amount of organic acids found in a home, it is near impossible to eliminate them completely. If there is one specific source that is causing the corrosion it is possible to weed it out, but it is still difficult.
It is because of the absence of copper in the new Micro-Channel coils that makes the problem of formicary corrosion a smaller issue. If you eliminate a component in this formicary corrosion equation, it can't occur.
Where can you find organic acids?
Adhesives, cabinets, countertops, foam insulation, laminates, oil based paints, paneling, plywood, silicone caulking, latex paints, cosmetics, disinfectants, deodorizers, wallboard, even some make-up the list goes on and on.
Eliminate one of the components in the formicary corrosion equation and reduce the likelihood of formicary corrosion occurring in a coil.