86-19: A Chrome/Zinc-Based Cooling Water Treatment for Systems Operating

Where the use of hexavalent chrome is permissible, chrome-zinc based cooling water programs are perhaps the most cost-effective means of treatment.  Chromate and zinc, however, offer only limited protection against the pitting type corrosion associated with iron deposition on cooling system surfaces.  Under reducing conditions the effectiveness of chrome-zinc based programs for corrosion control is severely limited.  Reducing conditions generally require the implementation of a non-chrome contingency program.  In this paper a chromate/zinc-phosphonate organic program is evaluated as a means of controlling general etch and pitting type corrosion in systems frequently operated under reducing conditions where iron deposition has been a problem.  Our evaluation of this novel approach was based on laboratory data and on data generated in operating systems where reducing contaminants and iron deposition have limited the effectiveness of conventional chrome-zinc programs.