How to Simplify Corrosion Control in Cooling Towers
By Eric C. Ward, Emily M. Crane, and Gregory J. Koniges
It is well known that phosphorous-based corrosion inhibitors cause fouling with calcium if they are not adequately treated with a stabilizing product to prevent foulant precipitation. This shortcoming makes this stabilizing product an essential component of any phosphorous-based inhibitor program. In this article, a new corrosion inhibitor will be presented that provides a single-component replacement for the aforementioned dual-component system.
This new inhibitor can not only replace phosphorous-based inhibitors used for mild steel corrosion control; laboratory testing has shown the product has corrosion inhibition properties for zinc and galvanized metal and can also reduce white rust formation in high-pH, high-alkalinity water chemistry. This new inhibitor performs well across a wide range of hardness conditions and pH values, it allows for the reduction of the product used to stabilize phosphorous-based inhibitors, and is an environmentally friendly alternative for corrosion control. It has also shown excellent compatibility with other commonly used corrosion inhibitive chemistries. To demonstrate this new corrosion inhibitors performance benefits, both laboratory and pilot testing performance data will be presented in the article
Since the ban on chromates more than 30 years ago, the cooling water industry has predominantly relied on phosphorous-based corrosion inhibitors. Initially, these treatment programs were stabilized phosphate programs that used sulfuric acid to control pH and limit calcium phosphate saturation. Over time, these programs transitioned into alkaline phosphate and all-organic phosphonate programs; largely in response to industry trends to reduce the use of sulfuric acid and operate at higher cycles of concentration.
Both of these trends drove the pH and hardness values for typical cooling water systems to a higher range, which in turn increased the drive for calcium phosphate or calcium phosphonate precipitation. This precipitation, if not controlled, can result in system fouling, loss of corrosion inhibitor, and thus loss of corrosion protection. To combat these problems, the water treatment professional must increase the dosage of calcium phosphate inhibitor to control system fouling. As more stringent water conservation efforts continue to loom, the challenge posed with using phosphate-based inhibitors in high-hardness, high-pH water will likely become more and more challenging.
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