What SB111 C44300 Actually Designates
ASME SB111 is the ASME Boiler and Pressure Vessel Code identifier for the specification that is technically identical to ASTM B111, the standard covering seamless copper and copper-alloy condenser tubes and ferrule stock. Within that specification, UNS C44300 is arsenical admiralty brass: an alpha-phase copper-zinc alloy containing roughly 71 % copper, 28 % zinc and 1 % tin, together with a deliberate arsenic addition that inhibits dezincification.
C44300 is often described loosely as naval brass, but the two belong to different families. Naval brass such as UNS C46400 is a tin-bearing 60/40 alloy supplied mainly as bar and rod, whereas admiralty brass keeps a much higher copper content and is produced almost exclusively as tube for heat-transfer service. That higher copper level is what gives C44300 its combination of thermal conductivity, resistance to sea water and reasonable cost, and it is the reason the grade has remained in continuous use in condensers and coolers for well over half a century.
Chemical Composition and Physical Properties
ASTM B111 and ASME SB111 control the composition of C44300 within narrow limits, because the tin and arsenic contents directly govern corrosion performance.
| Element | Requirement, % | Function |
|---|---|---|
| Copper (Cu) | 70.0-73.0 | Base of the alpha solid solution; carries heat and current |
| Tin (Sn) | 0.9-1.2 | Strengthens the alloy and stabilises the protective film |
| Arsenic (As) | 0.02-0.06 | Dezincification inhibitor for aggressive and polluted waters |
| Lead (Pb) | 0.07 max | Impurity limit |
| Iron (Fe) | 0.06 max | Impurity limit |
| Zinc (Zn) | Remainder | Balances the composition |
The physical properties used in heat-transfer calculations are listed below.
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.53 g/cm³ | 0.308 lb/in³ |
| Melting range | 899-938 °C | 1650-1720 °F |
| Thermal conductivity at 20 °C | 109 W/(m·K) | 64 Btu·ft/(ft²·h·°F) |
| Specific heat capacity | 0.09 cal/(g·°C) at 20 °C | 0.09 Btu/(lb·°F) at 70 °F |
| Mean coefficient of thermal expansion | 20.2 × 10-6 per °C, 20-300 °C | 11.2 × 10-6 per °F, 70-570 °F |
Mechanical Requirements and Available Tempers
In the O61 annealed temper, which is the normal delivery condition for condenser and heat-exchanger tube, C44300 is specified with a minimum tensile strength of 310 MPa (45 ksi) and a minimum yield strength of 105 MPa (15 ksi). Drawn tempers are also produced when higher strength and better resistance to water-side erosion are required. The specification lists each temper code together with its minimum tensile and yield values and the corresponding grain-size band, so that the strength level and the forming behaviour of the tube stay predictable from one order to the next.
Tubes are supplied in straight lengths or as U-bends, are eddy-current tested over their full length, and pass a hydrostatic or pneumatic pressure test before despatch. Because the alloy is single phase, it cold works readily and can be expanded into tubesheets without difficulty.
Where Admiralty Brass Tube Is Used
Steam surface condensers and feedwater heaters in thermal power stations
Sea water and brackish water shell-and-tube heat exchangers, oil coolers and intercoolers
Desalination and water-treatment heat-transfer trains
Marine engine cooling circuits, evaporators and distilling plant
Ferrule stock and condenser-tube fittings
Process coolers in the oil and gas sector where a copper alloy is acceptable to the process stream
The grade is chosen where water-side heat transfer and material cost carry more weight than tolerance of the highest flow velocities or of ammonia-bearing condensates, conditions for which copper-nickel alloys are normally preferred.
Selection, Installation and Service Points
Admiralty brass performs best in clean, aerated waters, where it forms a thin protective oxide film that the arsenic addition keeps stable. Dezincification resistance therefore depends on the alloy remaining within the specified composition range, and tube of uncertain origin should not be substituted for compliant material.
The alloy is sensitive to ammonia and ammonium compounds, which can produce stress-corrosion cracking in the expanded region of the tube. Condensate chemistry should be monitored whenever C44300 is used in steam service. Wall thickness, baffle spacing and support arrangement must be selected so that both water-side and steam-side erosion remain acceptable: raising flow velocity improves heat transfer but also accelerates impingement attack, especially at the tube inlet. Where sea water is chlorinated or polluted, a planned cleaning routine and suitable inhibitor programme help to preserve the protective film.
Tube-to-tubesheet joints are normally made by rolling to a controlled degree of wall reduction. A light anneal of the tube ends reduces residual stress and improves rolling behaviour, and the sequence of rolling, seal welding where used, and retubing should follow the exchanger manufacturer's written procedure.
FAQ
Q: Is C44300 the same as naval brass?
No. C44300 is arsenical admiralty brass with 70-73 % copper, 0.9-1.2 % tin and a small arsenic addition, while naval brass such as UNS C46400 is a 60/40 tin-bearing alloy supplied mainly as bar and rod. The two are often confused because both are used in marine service.
Q: Why is arsenic added to admiralty brass?
Arsenic at 0.02-0.06 % acts as a dezincification inhibitor. It keeps the protective surface film intact in aggressive, polluted or low-velocity waters where plain copper-zinc alloys would lose zinc selectively.
Q: What is the difference between ASTM B111 and ASME SB111?
The two are technically identical in requirements. ASTM B111 is the ASTM specification, and SB111 is the designation used when the same material is ordered for ASME code construction.
Q: Can C44300 tube be welded?
The alloy can be joined by brazing and soldering without difficulty, and welding is possible with care, but the preferred methods in exchanger construction are rolling, brazing or welding of tube ends to the tubesheet. Suitable filler metals and procedures are required because zinc volatilises at welding temperatures.
Q: Which temper should be ordered for a condenser?
The O61 annealed temper is the standard choice, giving 310 MPa minimum tensile strength, 105 MPa minimum yield strength and the ductility needed for rolling and U-bending. Drawn tempers are ordered only where erosion resistance justifies the loss of formability.
Q: When should copper-nickel be chosen instead of C44300?
Copper-nickel alloys such as UNS C70600 are preferred where water velocities are high, where the water is heavily polluted or contains ammonia and sulphides, and where longer intervals between retubing are required. C44300 remains the economical choice for clean water, moderate velocities and normal condenser duty.
