LOCALIZED AND GENERAL CORROSION OF COPPER IN AZOLES AND SILICA INHIBITED ZERO BLOWDOWN COOLING WATER IN AN AUTOMOTIVE PLANT

摘要

In the spring of 2007, the cooling water chemistry at a large automotive plant in Los Angeles, California, was changed from traditional chemical treatment of potable water to recycled water treated with a new zero blowdown chemistry. To establish the localized copper corrosion baseline during this transition, coupled multielectrode array sensors (CMAS) were installed in the sampling station of the cooling water system and corrosion monitoring was performed on real time basis in the plant. The CMAS corrosion monitoring was implemented as a means to rapidly confirm the effectiveness of the new corrosion control technology in protecting copper exchanger tubes in a potential highly corrosive environment. The need for rapid real time confirmation of effective copper corrosion inhibition with CMAS was based on presence of critical copper exchange surfaces in the customer system that would be exposed to the presence of 30 to 40 mg/L of ammonia in the recycled municipal waste water used as tower makeup. Prior experience using linear polarization resistance (LPR) and weight loss methods to determine corrosion rates indicated they were not effective in reliably detecting changes in corrosion in high dissolved solids water with this treatment method, primarily due to the extraordinarily low corrosion rates with this chemistry for steel, copper and other metals. Further, there was no prior monitoring experience with copper exposed to ammonia in high TDS chemistry to indicate that previous low corrosion rates could be maintained with this new chemistry.