Development of a silicate-nitrite-borate corrosion inhibitor

A corrosion inhibitor consisting of 1000 mg/L nitrite (NO2-), 500 mg/L silicate (SiO2), 300 mg/L boron as a pH buffer, 50 mg/L of a biocide, and 5 mg/L tolyltriazole in deionized water was developed for use in the machine-cooling water system of the Department of Energy's Gas Centrifuge Enrichment Plant (GCEP) at Portsmouth, Ohio. Corrosion tests in this solution using six different types of metals, including 6061 aluminum, have failed to show any corrosion at the 0.05-μ/y (0.002-mil/y) detection limit. The use of deionized water for this inhibitor solution is strongly recommended for any system containing aluminum because the presence of 30 mg/L of chloride ions is known to cause pitting in 6061 aluminum. The purity of the corrosion inhibitor can be maintained by using a small mixed-bed demineralizer in the water system. The demineralizer originally loads up with sodium and silicate ions, which then exchange for any contaminating ions-such as calcium, magnesium, or chromate-that might enter the corrosion-inhibitor solution