Aluminum brass corrosion potentials

Deminerahzed water also may be used sometimes as makeup. Characteristics of makeup water are important with respect to corrosion in high-temperature hot-water systems. If the circulating water pH is properly adjusted, much of the corrosion potential can be minimized. In all-steel systems, the pH can be adjusted to 11.0 to minimize corrosion. However, in bimetallic systems, pH values should not be allowed to reach this level because of possible alkaline reaction with brass, bronze, copper, and/or aluminum. 

If the buried metal structure involves contact between different metals (such as mild steel, copper, bronze, brass, aluminum, zinc, lead, stainless steel, cast iron, etc.), it is possible that local galvanic cells can form in the contact areas (Figs. 8-9). Each mettd has its own tendency to corrode. An alternative way to express the metal reactivity is to look at the excess of its free energy (standard electrochemical metal potential) and predict the electromotive force emf) between metals in contact, as a general indication for the corrosion process (Table 2). The metal that has a more positive potential is nobler in the galvanic cell, and it is a cathode. The metal with a more negative potential is more active and acts as an anode in the corrosion cell, e.g., it suffers corrosion. 

Piping made of brass, copper, or aluminum is sometimes used for special purposes. These metals have low melting points and thus have a high potential for failure if exposed to fire. Alloy materials are sometimes chosen for severe temperature or corrosion services. 

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