What ASTM B111 C44400 Tubing Is
C44400 is the antimony-inhibited grade of admiralty brass listed in ASTM B111/B111M, the specification for seamless copper and copper alloy condenser tubes and ferrule stock. It is a copper-zinc alloy with copper held between 70.0 % and 73.0 %, tin between 0.9 % and 1.2 %, and a small controlled antimony addition that protects the alloy against dezincification in cooling water. C44400 sits in the same admiralty metal family as the arsenic-inhibited C44300 and the phosphorus-inhibited C44500, and the three grades are selected mainly on the inhibitor that the cooling water chemistry tolerates.
Two points about naming cause most of the confusion. First, C44400 is not a water-service copper tube grade: the type K, type L and type M designations belong to the ASTM B88 specification for copper water tube in the C12200 family and have nothing to do with B111 condenser tubing. Second, the Chinese designation HSn70-1 corresponds to the arsenic-inhibited tin brass of the admiralty family, so it should not be quoted as a direct equivalent of the antimony-inhibited C44400 without checking the inhibitor requirement of the application.
Chemical Composition
| Element | Requirement | Function in the alloy |
|---|---|---|
| Copper | 70.0-73.0 % | Matrix, carries heat along the tube wall |
| Tin | 0.9-1.2 % | Raises strength and resistance to impingement attack |
| Antimony | 0.02-0.10 % | Inhibitor that suppresses selective zinc loss |
| Iron | 0.06 % max | Residual element |
| Lead | 0.07 % max | Residual element |
| Zinc | Remainder | Principal alloying element |
Arsenic, antimony and phosphorus all work the same way in this family: they form a thin, self-healing surface film that stops the zinc-rich phase from dissolving out of the alloy. The choice between the three is driven by availability, by the customer specification and by the sensitivity of the cooling water, not by any large difference in mechanical behaviour. Adding nickel or boron to the alloy, as is sometimes suggested, is not part of the C44400 composition and would in fact move the material into a different grade.
Physical and Mechanical Properties
Values for annealed tube are a density of about 8.53 g/cm³, an electrical conductivity of roughly 28 % IACS, a thermal conductivity near 110 W/(m·K) and an elastic modulus of about 117 GPa. The table below gives typical mechanical figures for the tempers that are actually ordered; the specification minima are lower than the typical values.
| 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 is ordered whenever the finished bundle calls for U-bending or for rolling into a tube sheet, because both operations need elongation. Hard drawn tube is used for straight runs that must resist higher internal pressure or vibration, and it must not be bent after drawing.
Corrosion Behaviour in Cooling Water
Admiralty brass of this type performs best in clean, aerated seawater and in fresh water, and it tolerates moderate chloride levels in once-through and recirculating cooling circuits. Dezincification resistance is demonstrated by the ISO 6509 test for copper alloys containing zinc, which measures the depth of selective attack on a prepared specimen, and the result is normally reported on the mill certificate.
Flowing seawater velocity is usually limited to about 1-2 m/s to keep impingement attack under control.
Service temperature much above 200 °C is not recommended.
Ammonia and ammonium compounds can cause stress corrosion cracking and must be kept out of the water side.
Sulphide-bearing, heavily polluted or sand-laden water, and high free ammonia, call for cupro-nickel grades instead.
Typical Applications
Shell and tube condensers and auxiliary coolers in thermal power plants
Seawater and brackish water heat exchangers, evaporators and distiller bundles
Shipboard cooling systems, oil coolers and fire main heat exchangers
Refrigeration and HVAC condensers working on chlorinated or brackish water
Ferrules, tube-sheet fittings and other components of the same equipment
Fabrication, Installation and Precautions
Tube is cold drawn and annealed to finished size, straightened and cut to length. U-bending is done in the annealed condition on a mandrel, and the bent legs are stress relieved only where the design requires it. Tubes are expanded into tube sheets by rolling; where welded tube-to-tube-sheet joints are needed, inert gas welding or brazing is preferred over oxy-fuel processes because zinc volatilises when the heat input is not controlled.
Cold working leaves residual stress that must be removed by a low-temperature anneal if the tube is to work in an ammonia-bearing environment; this single precaution prevents most early failures. Impurity and grain size control during melting and rolling matter as well, because coarse grains and residual impurities both lower fatigue life in a vibrating bundle.
Mark tubes only with approved, ammonia-free markers; graphite and common ink residues promote cracking.
Clean water-side deposits with inhibited acid or by mechanical means, never with strong mineral acid.
Keep tubes dry and ventilated in storage, away from packaging materials that release ammonia.
Inspection and Quality Control
Incoming inspection normally covers dimensional checks, hardness and temper verification, grain size, hydrostatic or pneumatic tightness, and eddy current examination for wall thinning. Expansion and flattening tests confirm that the tube will survive tube-sheet rolling and handling without cracking. Records of heat number, temper, inhibitor content and test results should be kept with the order so that any problem in service can be traced back to the cast.
Frequently Asked Questions
Q: Is C44400 the same as C44300?
They are close relatives, not the same grade. Both are admiralty brass with 70-73 % copper and about 1 % tin, but C44300 is inhibited with arsenic and C44400 with antimony. The two are selected on the basis of customer specification and water chemistry.
Q: Is C44400 the same as type L copper tubing?
No. Type K, type L and type M are wall-thickness designations in ASTM B88 for water-service copper tube. C44400 is a condenser and heat exchanger tube grade listed in ASTM B111.
Q: How does antimony protect the alloy?
It forms a thin protective film on the water side that blocks the zinc-rich phase from being dissolved out of the metal. That selective loss of zinc, called dezincification, is what destroys uninhibited brasses in chloride-bearing water.
Q: Why is a low-temperature anneal required after cold working?
Bending, rolling and straightening leave residual tensile stresses in the tube. In an environment containing ammonia or ammonium compounds those stresses combine with the chemistry to produce stress corrosion cracking, so a low-temperature stress relief is applied where the duty requires it.
Q: Can C44400 tubing be welded?
It can be welded with inert gas shielding or brazed, but the zinc in the alloy volatilises if the heat input is excessive, which leaves porosity and a lower strength joint. Oxy-fuel welding is therefore avoided on this material.
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 section of tube. The result is reported as a maximum attack depth and should appear on the mill certificate.
