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ABSTRACT
This paper will outline the development of a new Yellow Metal corrosion inhibitor with improved corrosion control capabilities when compared to traditional triazole technology. A four-year R&D effort has led to a new patent pending molecule that develops a thicker, more robust film, greatly reducing the impact of high levels of halogen on the corrosion of copper and copper alloy heat transfer surfaces. This paper will outline laboratory corrosion testing and film formation and finally field applications.
Keywords: Copper, Copper Alloy, Admiralty Brass, Corrosion Inhibitor
INTRODUCTION
Copper and its alloys called yellow metals and include a variety of copper-based alloys including bronze's, brasses and other alloy types. Copper metallurgies are commonly used in cooling water treatment systems for heat exchanger tubing, pump impellers and various other applications owing to its natural corrosion resistance and high thermal conductivity. However, copper and its alloys are not immune to corrosion in cooling water applications especially in the presence of halogen based oxidizing biocides such as (Hypochlorous Acid) HOCI and Hypobromous Acid) HOBr, which results in corrosion and possibly failure of heat exchangers.
Most existing corrosion inhibitors for copper and its alloys are triazole based chemistries, such as Tolyltriazole· (TT), Benzotriazole· (BZT), and Chlorinated Tolyltriazole (CI-TT).1'2 The molecular structures are shown below.
The triazoles work as yellow metal corrosion inhibitors by forming an inhibitor film on the surface of yellow metals through bonding with copper.2'3 The film formed by triazoles can be disrupted by halogen-based biocides (e.g. HOCI). Additionally, In the bulk water, the triazole inhibitor can react and be degraded by halogen-containing biocide and its corrosion inhibition capacity reduced.4 The mechanism for poor halogen stability results from halogen-containing biocide (e.g.HOCI) reacting with the N-H bond on the triazole ring forming an N-Chloro derivative (a highly unstable intermediate).5 The corrosion inhibition efficacy of triazoles are reduced due to this reaction. The film formed by triazoles on the metal surface is also affected by the high free chlorine and it requires additional triazole to re-passivate the film for corrosion protection.3-5
High consumption rates of triazole by halogenation often result in increased feed rates to maintain acceptable residuals and corrosion rates. This increases the cost of the treatment. In addition, halogenated triazole derivatives form as reaction products and are...