What ASTM B111 C44300 Tin Brass Is
C44300 is the UNS designation for tin brass, the alloy the heat transfer industry calls admiralty brass. It is a copper-zinc alloy in which copper is held between 70.0 % and 73.0 %, about one percent of tin is added, and a small controlled addition of arsenic suppresses dezincification. The grade is listed in ASTM B111/B111M, the specification for seamless copper and copper alloy condenser tubes and ferrule stock, in the same admiralty metal family as the antimony-inhibited C44400 and the phosphorus-inhibited C44500. The matching Chinese designation under GB/T 5231 is HSn70-1.
Compared with plain 70/30 brass, the tin addition raises strength and improves resistance to impingement attack and to the selective loss of zinc that destroys ordinary brass tubes in seawater. Because the alloy stays single phase alpha brass across its normal processing range it cold draws and bends well, which is why it is supplied as straight or U-bent tube rather than as castings.
Chemical Composition and Physical Properties
The table below summarises the controlled ranges for C44300, expressed in mass percent, and the role each element plays in service.
| Element | Requirement | Function in the alloy |
|---|---|---|
| Copper | 70.0-73.0 % | Matrix that carries thermal and electrical conduction |
| Tin | 0.9-1.2 % | Raises strength, retards dezincification and impingement attack |
| Arsenic | 0.02-0.06 % | Inhibitor that blocks selective zinc loss at the water side |
| Iron | 0.06 % max | Residual element, kept low to protect conductivity |
| Lead | 0.07 % max | Residual element |
| Zinc | Remainder | Principal alloying element |
Typical physical values for annealed tube are a density of about 8.53 g/cm³, an electrical conductivity of the order of 28 % IACS, a thermal conductivity near 110 W/(m·K) at room temperature and an elastic modulus of about 117 GPa. These figures place C44300 close to the other admiralty and aluminium brasses and well behind pure copper in conductivity, which is the accepted trade-off for durability in cooling water.
Mechanical Properties and Temper Selection
ASTM B111 fixes minimum tensile and yield strengths for each UNS number and temper, and requires expansion and flattening tests as well as an eddy current examination when these are called up in the order. Tube is normally ordered annealed in the O61 temper so that it can be rolled into U-bends; light drawn and hard drawn tempers are used where straight tubes must carry higher internal pressure or resist vibration. The values below are typical of commercial tube, and the specification minima are lower.
| Condition | Tensile strength | Yield strength | Elongation |
|---|---|---|---|
| Annealed O61 | 330-380 MPa | 105-150 MPa | 40 % minimum |
| Light drawn H55 | 400-470 MPa | 250-350 MPa | 15-25 % |
| Hard drawn H80 | 500-600 MPa | 400-480 MPa | 8-15 % |
Annealed tube must retain enough elongation to accept U-bending and tube-sheet rolling without cracking, while hard drawn tube trades ductility for strength. Grain size in the annealed condition is controlled as well, because coarse grains reduce fatigue life in a vibrating condenser and roughen the surface during bending.
Corrosion Behaviour in Seawater and Fresh Water
The arsenic addition is what separates C44300 from ordinary brass. In cooling water the alloy forms a protective film, and the inhibitor stops the zinc-rich phase from being attacked preferentially. Dezincification resistance is normally demonstrated by the standard test for copper alloys containing zinc, ISO 6509, rather than by room-temperature exposure of finished tube.
Admiralty brass performs best in clean, aerated seawater and in fresh water, and tolerates moderate chloride levels in cooling circuits. Its practical limits are well known. Flowing seawater velocities are usually kept between 1 and 2 m/s to avoid impingement attack, the alloy is not recommended for service much above 200 °C, and it is sensitive to ammonia and ammonium compounds, which can cause stress corrosion cracking. Waters carrying sulphides, high free ammonia or suspended sand call for cupro-nickel grades instead.
Typical Service Applications
Surface condensers and auxiliary heat exchangers in power generation
Seawater and brackish water coolers, evaporators and distiller tube bundles
Shipboard condensers, oil coolers and desalination plant tubing
Refrigeration and HVAC condensers working on chlorinated or brackish water
Ferrules and tube-sheet fittings for the equipment listed above
Fabrication, Installation and Inspection Points
Tubes are cold drawn and annealed to finished size, then straightened and cut to length. U-bending is carried out in the annealed condition with a mandrel, and the bent legs are stress relieved only where the design requires it. Tubes are expanded into tube sheets by rolling; welded tube-to-tube-sheet joints are used for special duties, and inert gas welding or brazing is preferred over oxy-fuel processes because the zinc in the alloy volatilises when the heat input is not controlled.
Three practical rules prevent most field failures. First, never mark tin brass tube with ordinary graphite or ammonia-containing markers, since the residue promotes stress corrosion cracking. Second, clean water-side deposits with inhibited acids or by mechanical means, because strong mineral acids attack the alloy. Third, keep tubes dry and ventilated in storage so that condensate and ammonia from packaging materials do not build up.
Incoming inspection normally covers dimensional checks, hardness and temper verification, grain size, hydrostatic or pneumatic tightness, and eddy current examination for wall thinning. Records of heat number, temper and test results should be kept with the tube so that a failed bundle can be traced back to its cast.
Frequently Asked Questions
Q: Is C44300 the same as admiralty brass?
Yes. C44300 is the UNS number for the arsenic-inhibited admiralty metal that the heat transfer trade calls admiralty brass. The antimony-inhibited C44400 and the phosphorus-inhibited C44500 sit in the same family with different inhibitor additions.
Q: Why is arsenic added to a copper alloy?
It is not present for strength. The arsenic forms a stable surface film that prevents the zinc-rich phase from being dissolved out of the alloy, which is the mechanism that destroys uninhibited brasses in cooling water containing chlorides.
Q: What flow velocity is safe in a seawater condenser?
Clean seawater service is normally limited to about 1-2 m/s. Higher velocity raises impingement attack at tube inlets, and sandy or aerated water lowers the practical limit further.
Q: Can C44300 be used in ammonia-bearing cooling water?
No. The alloy is sensitive to ammonia and ammonium compounds, which can cause stress corrosion cracking. Cupro-nickel grades are the usual substitute where ammonia is expected.
Q: Which temper should be ordered for U-bent tubes?
Annealed O61 is the normal choice because it has the elongation needed for mandrel bending and tube-sheet rolling. Hard drawn tempers are reserved for straight tubes that must resist pressure or vibration.
Q: How is dezincification resistance verified?
By the ISO 6509 test for copper alloys containing zinc, which measures the depth of selective attack on a prepared specimen. The test result is a material property and should be recorded on the mill certificate.
