What ASTM B111 C44500 Admiralty Brass Is
UNS C44500 is the phosphorus-inhibited grade of admiralty brass, the alloy family that ASTM B111 lists as admiralty metals B, C and D. The three inhibited versions are chemically almost identical in their copper, tin and zinc balance and differ only in the element used to stop dezincification: arsenic in C44300, antimony in C44400 and phosphorus in C44500. C44500 is therefore usually described as phosphorized admiralty brass.
The alloy is supplied as seamless condenser tube and ferrule stock to ASTM B111/B111M and is also available in other product forms under the applicable copper alloy specifications. Its combination of moderate strength, high thermal conductivity and good resistance to cooling water makes it a standard choice for condensers and heat exchangers where pressures, velocities and temperatures are moderate.
Chemical Composition and Physical Properties
ASTM B111 specifies the following limits for C44500, in mass percent.
| Element | Requirement | Function in the alloy |
|---|---|---|
| Copper (Cu) | 70.0-73.0 % | Matrix; thermal and electrical conduction |
| Tin (Sn) | 0.9-1.2 % | Strength; resistance to impingement attack |
| Phosphorus (P) | Controlled addition, typically 0.02-0.10 % | Dezincification inhibitor; deoxidation during melting |
| Iron (Fe) | 0.06 % max | Residual element |
| Lead (Pb) | 0.07 % max | Residual element |
| Zinc (Zn) | Remainder | Principal alloying element |
| Physical property | Typical value | Condition |
|---|---|---|
| Density | 8.53 g/cm³ | 20 C |
| Elastic modulus | 117 GPa | Room temperature |
| Shear modulus | 40 GPa | Room temperature |
| Poisson ratio | 0.34 | Room temperature |
| Thermal conductivity | About 110 W/(m K) | 20 C |
Mechanical Properties and Fatigue Behaviour
Annealed C44500 tube is a relatively soft, highly ductile material, which is exactly what is needed for U-bending and for rolling into tube sheets. Typical values measured on commercial annealed tube sit in the following bands; ASTM B111 sets lower minimum values and adds expansion and flattening test requirements.
| Property | Typical value (annealed tube) |
|---|---|
| Tensile strength | 331-379 MPa |
| Yield strength, 0.5 % extension | 124-152 MPa |
| Elongation at break | About 65 % |
| Fatigue strength at 10 million cycles | 115-125 MPa |
| Machinability, free-cutting brass taken as 100 | About 30 |
Two numbers govern design more often than the tensile strength. The first is fatigue strength, because condensers vibrate and tubes that touch one another in a bundle wear through at the contact points. The second is the loss of strength that follows even modest cold work, which is why hard drawn tube is not interchangeable with annealed tube in a U-bend application. Service temperature is the third limit: admiralty brass is a low temperature alloy and continuous exposure well above 200 C is outside normal practice, so high temperature creep data have no relevance to condenser design.
Corrosion Resistance in Cooling Water
Phosphorus plays the same role as arsenic in the other admiralty grades. It promotes a protective surface film and blocks the selective dissolution of zinc, so C44500 resists dezincification in fresh water, brackish water and clean seawater. Dezincification resistance of copper-zinc alloys is normally assessed by the ISO 6509 test, and the inhibited admiralty grades are selected precisely because they pass it while uninhibited 70/30 brass does not.
The alloy is nevertheless sensitive to a small number of specific conditions. It is susceptible to stress corrosion cracking in ammonia-bearing environments, so tubes must not be marked with ammonia-containing inks, stored in contact with certain rubbers or cleaned with ammoniacal solutions. It resists general corrosion well at moderate flow rates but suffers impingement attack when seawater velocities are high or when sand and air bubbles are entrained. Chlorinated cooling water is handled comfortably at normal residual levels, while waters with sulphides or large amounts of suspended solids favour cupro-nickel instead.
Applications and Processing Notes
Condenser and heat exchanger tube bundles in power stations and process plants
Seawater and brackish water coolers, evaporators and distiller tubes
Shipboard heat transfer equipment and feedwater heating circuits
Ferrules, tube sheet inserts and small diameter heat transfer tubing
Processing is straightforward. Tube is cold drawn and annealed to size, then bent with a mandrel in the annealed temper. Rolling into the tube sheet is the preferred joining method; welding and brazing are possible but call for controlled heat input because phosphorus-bearing copper alloys can form brittle phases if heated in a reducing atmosphere, and because zinc volatilises at welding temperature. Water-side cleaning should use inhibited acids, brushes or water jets, never strong mineral acids. Before dispatch, tube is verified by chemical analysis, tensile and hardness tests, grain size measurement, dimensional inspection and, where specified, hydrostatic pressure testing and eddy current examination.
FAQ
Q: How does C44500 differ from C44300 and C44400?
All three are admiralty brass grades with essentially the same copper, tin and zinc balance; C44300 uses arsenic, C44400 uses antimony and C44500 uses phosphorus as the dezincification inhibitor.
Q: Is C44500 tube suitable for seawater?
Yes, for clean seawater at moderate velocity and temperature, which is the classic condenser duty; aggressive, sandy or sulphide-bearing waters are better served by a copper-nickel grade.
Q: Why does the specification limit the phosphorus content?
The phosphorus addition has to be high enough to inhibit dezincification but low enough to preserve ductility and thermal conductivity, so it is controlled within a narrow band.
Q: Can admiralty brass tube be used above 200 C?
Long-term service above about 200 C is outside normal practice for this alloy family, and raised temperature creep values quoted in some data sheets are not design data for condenser service.
Q: What causes premature failure of admiralty brass tubes?
The usual causes are excessive water velocity or entrained solids causing impingement attack, ammonia-induced stress corrosion cracking, and vibration damage where tubes touch inside the bundle.
Q: Which temper should be ordered for U-bend condensers?
Annealed tube in the O61 temper is the normal choice, because it has the elongation needed for bending and subsequent tube sheet rolling.
