Email LinkCHLORAMINE RESISTANCE
More aggressive water disinfectants may precipitate sealing changes.
Breaking in: Chloramines can break the
chemical cross-links (shown in
yellow)
that bind the molecular chains of some
materials. Broken linkages
(shown in red)
cause the materials’ physical properties to suffer.
The increasing use of chloramines — in addition to, or in lieu of, chlorine — to disinfect potable water has some seal designers worried. Tests show that chloramines are more detrimental than chlorine to some elastomers, so material choices may need to be re-evaluated to prevent seal failures. Here’s a quick look at chloramine usage and the options available for seal designers:
SWITCHING TO CHLORAMINES
For the past 100 years, water treatment facilities have used disinfectants (typically chlorine) to kill bacteria prior to distribution. Though it is effective against waterborne microbes, chlorine generates DBPs, or disinfection by-products, when it reacts with natural organic matter (like sedimentation) in the water. Having determined that long-term exposure to excessive levels of DBPs may cause cancer, the Environmental Protection Agency (EPA) has set DBP limits.
As a result, many facilities have switched from free chlorine to chloramine (a chlorine-ammonia mixture). This is typically monochloramine (NH2Cl), a colorless liquid, but it may also be dichloramine (NHCl2) or trichloramine (NCl3). Chloramines offer some distinct advantages over free chlorine. Primarily, chloramines generate fewer DBPs. Though they are not quite as good at killing bacteria as chlorine, chloramines last much longer because they don’t evaporate out of water as fast as chlorine does. Chloramines also have less effect on the taste and odor of water.
Chloramines do have drawbacks. Though they are safe for consumption in drinking water (digestion neutralizes them before they enter the bloodstream), other forms of intake can be dangerous. Chloramines interfere with oxygen absorption if taken directly into the bloodstream and thus cannot be present in water used for kidney dialysis. Similarly, chloramines are toxic to fish (freshwater and saltwater), reptiles, and amphibians.
CHARTING THE EFFECTS
So how do chloramines affect the seals and other elastomeric parts within the water distribution chain? With anecdotal evidence suggesting that chloramines hasten elastomer failure in devices ranging from toilets to faucets to fire sprinklers, the American Water Works Association Research Foundation (AWWARF) conducted a study. The results indicate that chloramines do indeed pose a significant threat to many of the most widely used elastomeric materials, including natural and synthetic isoprenes, styrene butadiene (SBR), chloroprene (CR), and nitrile (NBR).
In side-by-side tests with chlorine, chloramines caused more material swell, deeper and denser cracking, faster loss of elasticity, and greater loss of tensile strength. In a susceptible material, chloramines appear to attack the polymer’s cross-links, the connections that give the material a resilient, three-dimensional structure. Cracks develop and water flows in, swelling the material and resulting in a marked loss of other physical properties. Degradation becomes more pronounced as temperatures increase.
CALLING ON US
There are options, however. The AWWARF study showed that fluorocarbon (FKM) and silicone (VMQ) resist the degrading effects of chloramines. To a lesser degree, so does ethylene propylene (EPDM). Many compound manufacturers are currently conducting research to refine formulations that will be both chloramine-resistant and cost-effective. If your application requires it, we at RL Hudson can help you find compounds that will withstand chloramines. Call us at 1-800-722-6766 if we can be of assistance.
