There is an abundance of information available on the internet on the topic of coil failure and/or formicary corrosion. Please find herein a collection of information we feel offers the most comprehensive answers to the often asked question, “Why does my Coil require replacement after only a few years of service?” References are credited on the last page of this document.
Indoor coil corrosion failures are an issue in the HVAC industry today. Although the occurrence rate of these failures is low nationwide, some geographic areas have experienced higher incidence rates. For instance, some homes experience multiple failures while those around them have none. Failures are typically characterized by leaks that form in the fin pack area of the coil after one to four years of installation and use.
This issue exists industry-wide. A competitive study has shown identical corrosion failure leaks in all coil brands investigated. The progression of the corrosion is from the exterior of the tube inward, eating away at the copper, until penetration occurs and a leak results.
There are many potential causes of coil leaks in indoor coils, ranging from manufacturing or process-related defects to copper corrosion. Additionally, there are several different corrosion mechanisms that can affect copper tubing. The following discussion focuses on pitting corrosion failures of indoor coils. There are two main forms of pitting corrosion found in indoor coils: (1) general pitting; and (2) formicary corrosion, sometimes called “ant’s nest” corrosion. General pitting corrosion is caused by aggressive anion attack on the copper tube. An anion is a negatively charged chemical species. Due to this negative charge, anions aggressively search for positively charged species called cations. Copper is an abundant source of cations. Large pits resembling bite marks characterize the footprint of general pitting. These pits can often be observed with the human eye. Chlorides are the most common source of the aggressive anions known to cause general pitting corrosion. Formicary corrosion, on the other hand, appears as multiple tiny pinhole leaks at the surface of the copper tube that are not visible to the human eye. Upon microscopic examination, the formicary corrosion pits show networks of interconnecting tunnels through the copper wall, hence the association with ants’ nests. The agents of attack involved in this corrosion mechanism are organic acids.
Common household substances that may contain chlorides include:
- Aerosol sprays
- Degreasing and Detergent cleaners
- Dishwasher detergents
- Laundry bleach
- Fabric softeners
- Paint removers
- Tub and tile cleaners
- Vinyl fabrics
- Vinyl flooring
A recent study was conducted to measure the volatile organic compound concentrations and emission rates in new manufactured and site-built houses.8 The E.O. Lawrence Berkeley National Laboratory performed this research with the support of the U.S. Department of Energy. This study shows that many materials used in the construction of new houses emit VOCs, including formaldehyde. Plywood, engineered wood products such as flooring and cabinetry, latex paint, and sheet vinyl flooring all have been identified as major sources for these compounds.
There is increasing evidence showing the home environment to be a primary contributor to coil corrosion.
- Cleaning solvents
- Foam insulation
- Paints (oil based)
- Particle boards
- Silicone caulking
- Building materials
Typical household sources of acetic acid or acetate include:1-7
- Disinfectants and deodorizers
- Tobacco and wood smoke
- Foam insulation
- Paints (latex and oil based)
- Particle boards
- Building materials
There is increasing evidence linking the primary cause of indoor coil leak failures to agents present in the household environment. Significant levels of corrosive agents known to cause these failures have been quantified in indoor condensate sampling during recent studies. The trend toward decreased home ventilation rates likely contributes to the elevated levels of indoor contaminants. In addition, increased environmental awareness to identify and fix refrigerant leaks will continue to focus attention on these indoor coil failures as an industry issue. Carrier is dedicated to continuing field and laboratory testing and research efforts to identify an effective method of preventing coil failures caused by agents in the household environment. To date, no solution has been identified that is functional, cost effective and feasible to manufacture.
- Tetley, M. Heidenreich and K. Smith, “The Basics of Formicary Corrosion,” The Air Conditioning,, Heating & Refrigeration News, March 30, 1998, pp. 5-6.
- Fairley and S. Gislason, M.D., “Handbook of Indoor Environments – Materials and Their Chemicals,” http://www.nutramed.com/environment/ handbook-materials.htm, pp. 1-8.
- Notoya, “Localized Corrosion in Copper Tubes by Volatile Organic Substance,” Journal of University of Science and Technology Beijing, Vol. 6 (1999), No. 2, p. 131.
- S. Lenox and P. A. Hough, “Minimizing Corrosion of Copper Tubing Used in Refrigeration Systems,” ASHRAE Journal, November 1995, pp. 52-56.
- Notoya, “Ant Nest Corrosion in Copper Tubing,” Corrosion Engineering, Volume 39, Number 6, p. 361.
- Elliott and R. Corbett, “Ant Nest Corrosion—Exploring the Labyrinth,” Corrosion 99, Paper No. 342, p. 2.
- T. Hodgson, A. F. Rudd, D. Beal and S. Chandra, “Volatile Organic Compound Concentrations and Emission Rates in New Manufactured and Site-Built Houses,” Indoor Air 2000, in press, ISSN 0905-6947.
- Lange, O. Wilke, D. Broedner, and O. Jann, “Measuring the Emission Behavior of Organic Acids From Wooden Products in Test Chambers,” Indoor Air 99; Volume 5.
This study was taken by Carrier on 12 major manufactures’ of air conditioning equipment in the United States and Worldwide. The information contained in this document is in part or in whole reproduce from the Carrier Corp.