Glycerin Antifreeze May Only Last a Few Years

What’s That Awful Smell?

TIM O’LEARY | Huguenot Laboratories
Published in Sprinkler Age MAgazine | March/April 2018

Antifreeze-based fire protection systems need to be monitored and tested on a routine basis to ensure there is an adequate level of freeze protection. What isn’t required is any testing to determine product stability. This isn’t likely to change anytime time soon due to the inability to do anything about the degradation (due not only to the ambiguity about the ability to add compounds to a product that is required to be premixed but more critically the lack of listed stabilizers). The point of this article though, is that antifreeze (especially glycerin) can have a life span as short as two years instead of the commonly identified (by the manufacturers) expectation of 6 years. I’ve personally seen systems that have lasted 8 years.
 
Needless to say, it’s an unpleasant discussion when trying to explain to a customer why you’re having to replace the antifreeze after just a couple of years.  All glycerin-based antifreeze products oxidize when exposed to air and heat.  When this occurs, organic acids are formed. Some key indicators to be aware of are:
 
• For glycerin, a reddish-brown discoloration;
• A pH between 6.0 and 4.0;
• Foaming of the solution;
• The presence of a foul (vomit-like) odor;
• Sprinkler leaks where green patina corrosion debris is witnessed around the seat or thread area; and Glycerin
• Pinhole leaks appearing in for the
steel pipes.
 
If you have witnessed any or all of the above conditions, then you are likely experiencing the breakdown of the glycerin antifreeze by way of the Krebs cycle. This breakdown of glycol is a normal course of bacterial digestion. When a fire sprinkler system is filled with antifreeze, the bacteria leave their spore form to become live bacteria cells.  The different strains of bacteria are facultative anaerobe, which means they live with and without oxygen being present.  The Krebs cycle is often described as the citric acid cycle. The waste byproducts of these bacteria are highly acidic and are composed of acid aldehydes, formaldehyde, and butyric acid. The byproducts produced
by bacteria oxidize the glycerin which rapidly reduces the pH of the antifreeze solution. Factory premixed glycerin
antifreeze solutions are chemically buffered to a pH of 7.5. The reduction in pH causes iron to oxidize and solubilize into solution, which promotes additional bacterial growth. This increases the rate of degradation
of the antifreeze (as well as degradation of the steel piping). Oh, did I forget to mention the horrible odor?
 
An additional mechanism that contributes to the degradation of the antifreeze is the commonly occurring dilution of the antifreeze solution at the connection to the water supply. Antifreeze solutions have a higher expansion and contraction rate than water, meaning the pressure will be higher on the antifreeze side of the interface with the water supply. System design considerations are critical to avoid over-pressurization and possible failure of the piping system. Expansion tanks are engineered and sized based on the overall volume of the antifreeze system. Alternate methods of compensating for the expansion and contraction of antifreeze involve an antifreeze loop configuration or drilling a hole in the check valve that isolates the supply water from the antifreeze system.
This drilled check valve allows the antifreeze and water to mix as temperature rises and falls. Also on smaller systems a pressure relief device is allowed to be used. This influx of water naturally causes some reduction in the level of freeze protection but a more critical aspect is that it accelerates the degradation process.

Glycerin-based antifreeze products are manufactured from food-grade raw materials which is a highly desirable food source for bacteria. The antifreeze solution is formulated with buffering agents as well as inhibitors to protect the solution and system components. Even with these additives, the antifreeze can gradually decompose producing acids that can cause corrosion in a system. There are things that can be done to greatly improve the life span of glycerin. It is important to be aware of the potential for degradation as well as the destruction caused by oxidized antifreeze.  Biological fouling contamination can occur in as little as 1 year and is a common cause of failure in fire sprinkler systems that contain glycerin based antifreeze solutions.

Monitoring of the glycerin antifreeze freeze protection level is a primary test method to document the  degradation of the antifreeze solution. It is critical that the system pH of the solution be maintained.  The pH measurements are normally tested with a hand held calibrated pH meter or Litmus paper. pH electrodes can be
adversely affected by contamination, so Litmus paper is the preferred method for reliable ease of measurement. Litmus is water-soluble, and is extracted from certain lichens which are then absorbed onto the filter paper. The resulting piece of paper becomes a pH indicator and is commonly used to test materials for acidity. The litmus paper, when wetted will turn a specific color depending on the pH of the solution being tested. A color chart is then referenced to determine the actual pH of the solution being tested. Litmus paper can be found in any pool supply store. It is inexpensive and if used correctly, is a good ball park indicator for pH monitoring. There are more accurate techniques for measuring pH, but none are less expensive then litmus paper.

Unfortunately, we can’t really fix this problem once it has started but it should initiate a discussion with the owner regarding the degradation and possible solutions.  
 
One needed course of action is to eliminate the equipment that allows fresh water to dilute the concentration. In other words, replace the allowed check valve and associated hole with a backflow preventer and an expansion chamber. This would also include replacing the allowed relief valve (on small systems with a backflow preventer)
with an expansion chamber.

At some point in time, all systems will need to be refilled with a new glycerin solution.  In order to avoid having the new glycerin antifreeze becoming contaminated by the residual oxidized antifreeze located in the sprinkler piping network and sprinkler head drops, the system should be cleaned. This requires flushing valves to be installed at all
end points of the system. Drain hoses are connected to end point drains and routed to sanitary sewer for disposal. The systems are thoroughly flushed and cleaned with a CPVC friendly alkaline cleaner. The use of CPVC friendly corrosion inhibitors can provide added corrosion protection to steel piping networks that supply water to the
antifreeze system. Once the system has been cleaned, it is then refilled with a new glycerin-based antifreeze solution.

In summary, antifreeze systems provide fire protection in areas where freezing is probable. Assuring that the water and glycerin remain isolated from each other via a check valve and an expansion tank is vital to the longevity of the antifreeze solution.  Mixing water and antifreeze quickly diminishes the level of freeze protection to protect the piping and also promotes the oxidation of the glycerin via the Krebs cycle.  The isolation of water from the antifreeze portion of the system is fundamental in assuring reliable operation of your antifreeze fire sprinkler system.