CORROSION RESISTANCE

Of all the commonly available casting metals, the alloys ~f copw per offer the best general corrosion resistance. This unique and important characteristic is onc of the chief reasons why these aUoys are used so extensively in industry_
Virtually al1 aUoys of copper bave good resistance to corro­sion. When this characteristic is combined with such other val­uable properties as strength, electrical conductivity and machin­ability, the engineer and designer have a highly useful group of marerials with which to work.
Pure copper is highly resistant to the atmosphere; to natural hot, fresh and salt water; and to all alkaline solutions except those distinctly anunoniacal. In general, the copper alloys retain these inherent resistances.
For exposure to weather, the entire group of alloys behaves excellently. For underground water or gas service all of the tin bronzes, leaded tin bronzes and silicon bronzes are acceptable. In ma~y instances, they are the only alloys specified for water or gas systems, since tin bronze and silicon bronze valves and fit. tings retain good operating characteristics indefinitely in service. Tin bronze has long been a standard alloy for use in sea water. The United States Navy specifies these alloys for equip­ment such as heat exchangers, condensers, and marine bard­ware for which sea water corrosion is an important considera­tion. Manganese or aluminum bronze is used extensively for pro­peller wheels of an sizes from those for small outboard engines to large wheels weighing over 75,000 pounds.
Copper alloys offer resistance to many chemicals, acid, alka­line or organic. They are widely used in equipment for industrial and chemical plants involving exposure to many types of COrTO­sive agents.
Numerous tabulations are avajIable to indicate the materials with which the various groups of copper alloys can be success­fully used. However, since corrosion of any metal depends on a variety of conditions, including concentration of the liquid, temperature., agitation, etc., it is difficult and unsafe to gen­eralize.