Glycol based systems, using Propylene Glycol or Ethylene Glycol, without any corrosion inhibitors or additives, are more corrosive and aggressive than water alone. Reactions with dissolved oxygen can lead to the formation of organic acids that attack unprotected metal surfaces. Since the surface tension of a glycol & water mixture is lower than with water, layers of rust can be dissolved easily, uncovering fresh metal surfaces that can be oxidized again, and the corrosion process will cause significant damage to the HVAC piping system.

To prevent corrosion, maintain the closed loop chemistry within prescribed limits through the addition of corrosion inhibitors and other supplemental additives.
Closed loop inhibitor formulations are available from the three basic categories:  Nitrite based formulations, low-solids Molybdate blends, and the All Organic or Food Grade corrosion inhibitors. Supplemental additives to restore solution pH levels or provide enhanced copper and copper alloy corrosion control are also available for severely stress systems. 

Nitrite Based Inhibitors These products utilize Nitrite to provide the mechanism for corrosion control for mixed metallurgy systems. All the components necessary for complete system protection make these products an economical choice for use in both hot water and chilled water applications.
Molybdate Based Inhibitors  Molybdate is the main component that provides primary corrosion control. These products provide improved corrosion control under static conditions, are less abrasive to pump seals because of the lower solids contribution to the treated solution, and offer reduced potential for microbiological activity.
All-Organic Inhibitors These blended inhibitors can replace typical nitrite and molybdate based treatment programs. For applications where there is no potential for food or beverage contact, our formulations will include azoles for yellow metal protection and dispersants for improved deposit control. Food Grade organic inhibitors are recommended for use with Food Grade Propylene Glycol when there is a potential for beverage or food contact. All-Organic inhibitors provide additional environmental benefits and are an effective replacement for nitrite or molybdate based programs.
Yellow Metal Protectors These supplements are used to control copper and copper alloy corrosion. Yellow metal inhibitors are built into many of our formulations, however, some severe service systems will require additional corrosion control specifically directed at copper and copper alloys. Especially useful in all copper or copper alloy systems where a low solids treatment is required.  
Buffers Water-Glycol systems become acidic over time, leading to glycol degradation and corrosion. pH Buffers are used to help counteract this pH change, and inhibit glycol oxidation reactions.