In your closed heating and cooling systems, proper water treatment is required to prevent corrosion. Years ago, alkaline chromate inhibitors provided excellent protection for these systems. However, chromate was identified as a highly toxic and carcinogenic chemical and this led to the development of non-chromate inhibitors. These newer treatments have been equally effective in controlling corrosion while, at the same time, overcoming many of the problems associated with the use of chromate.
Most non-chromate inhibitors are formulated with sodium nitrite, in combination with silicates, molybdates, and borates. For the most common nitrite based programs, complete protection is only assured if the level of nitrite is maintained within prescribed limits, depending upon system temperature and other factors. Loss of treatment can result from water leakage in the system. Occasionally, reduction of the nitrite level occurs without a corresponding reduction in other treatment components. This is due to biological denitrification.