Abstract
Water systems with mixed metallurgies require proper low carbon steel and copper alloy metal corrosion control. Improper copper corrosion control can lead to failure of copper alloys, such as admiralty brass metal within the system and cause galvanic corrosion on less noble metal, like carbon steel and cast iron. Azoles, benzotriazole (BZT) and tolyltriazole (TTA), are generally used to control copper corrosion in heat exchangers that are employed in open recirculation cooling tower systems, via a film forming mechanism on the metal surface. Monitoring of corrosion control can be done by using metal coupons or corrosion rate meter (CRM) utilizing linear polarization methods. Often there is a discrepancy between coupon and a CRM probe corrosion rates due to each technique acquiring corrosion rate values by different means: mechanical (weight loss) and electrochemical, respectively. CRM data suggests a steady state in admiralty brass (ADM) corrosion rate is reached anywhere from 2 to 6 hours with an azole inhibitor present in typical cooling water chemistry. Surface analysis revealed coupons to achieve maximum azole coverage in 30-60 min. This report utilizes electrochemical techniques and surface analysis to identify early passivation mechanism differences between TTA treated ADM coupon and CRM probes. Various water matrix conditions will be used to determine drivers for changes in surface chemistry.
