Most industrial cooling systems have copper and brass in them, in heat-exchanger tubing, fittings, and fasteners. In recirculating water, those yellow metals corrode. The damage shows up two ways: the copper components themselves pit and thin, and the copper that dissolves into the water travels downstream and attacks the steel. Benzotriazole and tolyltriazole are the inhibitors that shut both problems down. Here is how they work.
Copper corrosion in a recirculating loop
Copper is a relatively noble metal, but it still corrodes in water that carries dissolved oxygen, chloride, sulfate, or ammonia. As copper corrodes, it releases copper ions into the water. Those ions do not just represent lost metal. When they reach mild steel elsewhere in the system, they plate out onto it, and the copper deposit and the steel form a galvanic couple. The steel then corrodes fast at that spot. So a copper problem in the cooling tower becomes a steel problem in the chiller.
Controlling copper corrosion is the way to stop both failures at the source.
The copper-azole film
Benzotriazole and tolyltriazole are azole molecules that bond to copper. When they meet a copper surface, they react with the surface copper ions and form an insoluble copper-azole complex. That complex lays down as a thin film, close to a single molecular layer, across the metal.
The film is what does the work. It is a hydrophobic barrier that keeps the corrosive species in the water, chloride, sulfate, and oxygen, from reaching the copper underneath. It is held in place by the bond between the azole and the copper, so it is durable and self-repairing as long as inhibitor stays in the water. And it forms and holds at very low concentrations, which is why a small inhibitor dose protects a large metal surface.
The result is a passivated copper surface. It stops pitting, and it stops dissolving copper into the water. With less copper in the water, there is less copper plating onto steel, so the inhibitor protects the steel in the loop as a second-order effect of protecting the copper.
Why the choice of azole matters in cooling water
Cooling water is rarely gentle. Open recirculating towers concentrate dissolved solids, and most carry chlorine or another oxidizing biocide to control microbial growth. Those conditions are hard on a corrosion inhibitor.
This is where benzotriazole and tolyltriazole separate. Benzotriazole works well in mild, stable, closed-loop water. In hot or chlorinated service it degrades faster. Tolyltriazole, which carries a methyl group on its ring, is more thermally stable and more resistant to chlorine and other halogen biocides. In an open tower under active chlorination, tolyltriazole keeps the copper-azole film intact longer. For cooling water that needs both biocide and steady metal protection, tolyltriazole is the usual choice.
Dosing form follows the program
The inhibitor goes in whichever way the treatment program is built. Benzotriazole and tolyltriazole both come as a solid 99% granular and as a water-soluble sodium-salt liquid. Programs built around liquid feed meter the sodium benzotriazole or sodium tolyltriazole liquid, supplied ready to dose. Programs that make up their own concentrate often take the solid granular and dissolve it. The chemistry on the metal is the same either way.
Documentation and supply
P.A.T. Products stocks benzotriazole and tolyltriazole in North American warehouses, in both forms, and ships across the United States, Canada, and Mexico. TDS, SDS, and a Certificate of Analysis per lot are available, with REACH statements on request, and samples typically go out the same business day. Tell us your water chemistry and your feed method, and we will recommend a product and a form and send a sample.
See cooling-water corrosion control