Elucidating the Differences Between Weight Loss and Instantaneous Corrosion Rates for Azole Films on Copper Metallurgy

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Product Number: 51315-5924-SG

ISBN: 5924 2015 CP

Author: Paul Frail

Publication Date: 2015

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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 metals 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). 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 corrosion rate is reached anywhere from 4 to 24 hours with an azole inhibitor present in typical cooling water chemistry. This report utilizes electrochemical techniques and surface analysis to identify what is happening on the surface of the coupon versus the CRM probe during the early passivation period with TTA and admiralty brass to determine if the passivation mechanism is different for the two monitoring techniques. Various water matrix conditions will be used to determine drivers for changes in surface chemistry using either lab-based cooling water systems or field cases.