ABSTRACT
Brass is a commonly used material in water and steam systems for tubing, fittings, fasteners, and various cast components. Brass is a generic term that refers to several different copper and zinc containing alloys. One particular brass alloy that is commonly used in water and steam systems, which has excellent corrosion resistance in a wide variety of different water chemistries, is inhibited admiralty brass. This alloy has been used with great success in water cooled industrial heat exchangers and power plant surface condensers for many years. Other brass alloys have been used to construct components in water and steam systems that do not have the same composition and microstructure as admiralty brass. Of particular concern is the use of brass alloys containing high concentrations of zinc. These alloys tend to experience premature failures in large part due to their composition and microstructure. This paper will describe how various alloying elements and microstructures of brass alloys influence corrosion. Case histories will illustrate failures that occurred in components that were made of different brass alloys in water and steam systems. Recommendations will be made to mitigate the damage that occurred in each case.
INTRODUCTION
Brass is defined as “an alloy consisting mainly of copper (>50%) and zinc, to which smaller amounts of other elements may be added”1. Brass is an important industrial alloy valued for its thermal and electrical conductivity, corrosion resistance, strength, and ductility. Brasses also offer excellent machinability, are easily cast, and certain alloys exhibit good cold forming or hot forging properties2. Brasses are commonly used in water and steam systems in heat exchangers, condensers, and other domestic and industrial water piping and processes. Relative to commercially pure copper, brasses are often used in water systems when higher strength and/or erosion resistance is required. In addition to water environments, brass is used for decorative purposes and for mechanical applications in which its near net shape and machining properties are valued3.
