8 ROD, BAR, AND MECHANICAL WIRE 185
is available in the annealed state (generally in coils) and in drawn tempers
(straight lengths).
7.2 Commercial Tube and Fittings
Commercial tube is primarily used in air-conditioning and refrigeration systems.
The tube is chemically similar to plumbing tube; however, dimensions are based
on outside diameters, and some tubes are produced with enhanced inside and
outside profiles for better heat transfer.
Other applications for copper tube include condenser, evaporator, and heat
exchanger tubes; gas, heater, and oil burner lines; fire sprinkler systems; plumb-
ing pipe and steam tubes; brewery and distillery tubes; gasoline, hydraulic, and
oil lines, and rotating bands. A new designation, type G, refers to tube for fuel
gas [both natural and liquid propane (LP) gas] distribution systems, a relatively
new but rapidly growing application.
7.3 Alloy Tube
Copper–iron (UNS C19200), and in recent years, copper–nickel (UNS C70600)
is specified for automotive hydraulic brake lines. The copper–nickel is especially
resistant to stress–corrosion cracking and to attack by road salts.
Selection of alloys for condenser and heat exchanger tube is based on heat
transfer rate (conductivity), corrosion resistance, and resistance to cavitation and
biofouling. In general, conductivity is highest in pure copper and high-copper
alloys, whereas mechanical and chemical properties are highest in more highly
alloyed grades. Corrosion resistance of alloys cannot be ranked quantitatively
since performance depends strongly on specific exposure conditions; however,
resistance also generally increases with the degree of alloying.
Thus, the designer’s choice ranges from simple brasses such as UNS C23000,
tin brasses such as UNS C43500, UNS C44300, and UNS C68700 (arsenical
aluminum brass), through silicon bronzes C65100 and C65500, aluminum
bronzes such as UNS C60800, and finally copper–nickels UNS C70600 and
C71500. Alloy C70600 is widely used for seacoast power plant condensers and
critical piping systems on offshore platforms. The alloy’s high biofouling resis-
tance keeps piping systems free from marine growth. Alloy C71500, with 30%
nickel, is used in severe-duty marine condensers and saltwater systems, as well
as desalination equipment. Further information on copper tube, pipe and fit-
tings, and on the selection of copper alloys and other commercial tube prod-
ucts can be found at http://piping.copper.org/ and http://www.copper.org/
mechanical/homepage.htm, respectively.
8 ROD, BAR, AND MECHANICAL WIRE
Copper metals used in products manufactured by machining, hot forging, and
cold heading are supplied as extruded and/or drawn rods, bars, and mechanical
wire. When referring to copper products, rod means round, hexagonal, or oc-
tagonal forms supplied in straight lengths, i.e., not coiled. Bar products have
square or rectangular cross sections and are also sold in straight lengths. Shapes
are straight lengths with oval, half-round, geometric, or custom-ordered cross
sections, and wire can have any cross section and is supplied in coils or on
spools.