Copper, Brass, Bronze, and other copper alloys, collectively known as the “Red Metals,” share a reddish hue but differ significantly in composition, properties, and applications. This overview explores their unique characteristics, focusing on their use in pipes and other applications, with specific alloy grades for clarity.
Copper
Copper is renowned for its excellent electrical and thermal conductivity, good strength, formability, and corrosion resistance. It is widely used in pipes, wiring, and other products due to its durability and versatility. Copper can be soldered, brazed, and welded using various methods, and it can be polished to achieve a desired texture or luster.
One of copper’s standout properties is its antimicrobial effectiveness. After testing by the Environmental Protection Agency, 355 copper alloys were found to kill over 99.9% of bacteria within two hours of contact, even with normal tarnishing.
Corrosion in Pipes
While copper is corrosion-resistant, it is not immune to corrosion, especially in environments with low levels of salt or oxidizing acids. For example, in water containing minute amounts of salt and glucose, copper (e.g., C12200) can corrode at a rate over three times higher than mild steel. For superior corrosion resistance in harsh environments like seawater, copper-nickel alloys (e.g., C70600) are preferred.
Grades and Applications
Unalloyed copper grades vary by impurity content. Oxygen-free grades like C10100 (Cu≥99.99%) and C10200 (Cu≥99.95%) are used where high conductivity and ductility are critical, such as in electrical wiring. C11000 (electrolytic tough-pitch copper, Cu≥99.90%) is common for electrical panels, while C12200 (high-phosphorus deoxidized copper) is widely used for water and gas pipes due to its corrosion resistance and weldability.
Historically, copper was used by Greeks and Romans for tools, adornments, and sterilizing wounds. Today, it is prevalent in electrical wiring (C11000), plumbing pipes (C12200), and heat exchangers.
Brass
Brass is a copper-zinc alloy, with zinc content influencing its color, strength, and ductility. The color ranges from reddish (low zinc) to yellowish (high zinc), resembling gold at certain compositions. Brass is valued for its workability, durability, and corrosion resistance.
Zinc content affects processing:
- 32%-39% zinc (e.g., C26000, ~30% Zn): Enhanced hot-working but limited cold-working capabilities.
- >39% zinc (e.g., C28000, ~40% Zn): Higher strength but lower ductility at room temperature.
Applications
Brass is often used for decorative purposes due to its gold-like appearance (e.g., C26000 for panels). Its high workability makes it ideal for musical instruments (e.g., C44300 for trumpets). Other applications include fasteners and connectors.
Brass Alloys
Tin Brass: Alloys like C44300 (Cu~70%, Zn~29%, Sn~1%) and C46400 (Cu~60%, Zn~39%, Sn~1%), known as admiralty and naval brass, include tin to inhibit dezincification in marine environments. They offer moderate strength, high corrosion resistance, and good formability, used in marine hardware and heat exchanger tubes.
Leaded Brass: Alloys like C36000 (Cu~61.5%, Zn~35.5%, Pb~3%) are free-machining brasses, optimized for automated machining due to lead content. They are used for screws, valves, and fittings.
Bronze
Bronze is a copper alloy, typically with tin, though arsenic, phosphorus, or aluminum may be added. It is harder than pure copper, with a dull-gold color and faint surface rings distinguishing it from brass. Bronze is prized for its strength, wear resistance, and corrosion resistance.
Applications
Bronze is used in sculptures, medals, and musical instruments (e.g., C51900 for cymbals). Its low friction makes it ideal for bushings and bearings (e.g., C54400). In marine applications, bronze (e.g., C52100) resists corrosion, used in propellers and hydraulic pipes.
Phosphor Bronze: Contains 3.5%-11% tin and 0.03%-0.35% phosphorus (e.g., C51000, C51900). It offers toughness, high fatigue resistance, and corrosion resistance, used in springs, electrical connectors, and corrosion-resistant equipment.
Aluminum Bronze: Contains 6%-12% aluminum (e.g., not explicitly listed in the table but similar to C61400). It provides high strength and excellent corrosion resistance, used in marine hardware, pumps, and valves handling corrosive fluids.
Other Copper Alloys
Copper-Nickel (Cupronickel)
Copper-nickel alloys, like C70600 (Cu~90%, Ni~10%) and C71500 (Cu~70%, Ni~30%), contain 2%-30% nickel. They exhibit exceptional corrosion resistance in seawater, thermal stability, and resistance to stress corrosion cracking. Applications include ship hulls, marine pipelines, and valves.
Nickel Silver
Nickel silver alloys, such as C77000 (Cu~55%, Ni~18%, Zn~27%), contain copper, nickel, and zinc, resembling silver in appearance. They offer moderate strength, good corrosion resistance, and are used in musical instruments, optical equipment, and decorative items.
Silicon Bronze
Silicon bronze (e.g., C65500, Cu~96%, Si~3%) is a copper-silicon alloy with high strength and corrosion resistance, used in valve stems and marine components. Silicon brass (e.g., C69400, Cu~81%, Zn~16%, Si~3%) includes zinc and is used for similar applications but is distinct due to its zinc content.
Summary of Key Alloys
| Alloy Type | ASTM Grade | Composition | Key Applications |
|---|---|---|---|
| Pure Copper | C11000 | Cu≥99.90%, O~0.02%-0.04% | Electrical wiring, panels |
| Pure Copper | C12200 | Cu≥99.90%, P~0.015%-0.040% | Water/gas pipes, heat exchangers |
| Brass | C26000 | Cu~70%, Zn~30% | Decorative panels, connectors |
| Brass | C36000 | Cu~61.5%, Zn~35.5%, Pb~3% | Screws, valves, fittings |
| Bronze | C51900 | Cu Rem., Sn 5.5%-7.0%, P 0.03%-0.35% | Springs, marine pipelines |
| Copper-Nickel | C70600 | Cu Rem., Ni 9%-11%, Fe 1%-1.8% | Marine pipelines, ship hulls |
| Nickel Silver | C77000 | Cu~55%, Ni~18%, Zn~27% | Musical instruments, optical equipment |
Conclusion
The Red Metals—Copper, Brass, Bronze, Copper-Nickel, and Nickel Silver—offer a versatile range of properties tailored to specific applications. From copper’s conductivity in wiring (C11000) and pipes (C12200) to brass’s decorative appeal (C26000), bronze’s durability (C51900), and copper-nickel’s seawater resistance (C70600), these alloys meet diverse industrial and aesthetic needs. Understanding their compositions and corrosion behaviors ensures optimal material selection, particularly for critical applications like plumbing and marine environments.
