Thick-walled round tube in C28000 is the heavy-duty member of the brass tube family. Where a condenser or heat exchanger tube must survive abrasive cooling water, mechanical cleaning and the vibration of tube bundles, and where U-bends must be formed without collapsing the bore, the 60/40 brass grade supplies the strength that thin-wall tube cannot.
What the Product Is
C28000 is the 60/40 copper-zinc alloy known as Muntz metal. Its microstructure is predominantly beta grains, which makes the alloy stronger, harder and stiffer than the lower-zinc brasses, and gives it the warm gold colour that resembles architectural bronze. The trade-off is rapid work hardening, so the alloy is not intended for severe cold forming; it nevertheless bends and shapes well when the operation is planned, which is why bent thick-walled tube is a standard supply form.
Thick-walled round tube in this grade is produced as seamless tube by extrusion and drawing, or as welded and drawn tube where the application permits, then finished to the ordered temper and, in most condenser work, delivered with formed bends as a U-tube or hairpin section.
Tube Specifications and Dimensions
| Item | Specification |
|---|---|
| Seamless brass tube | ASTM B135 |
| Condenser and heat exchanger tube | ASTM B111 |
| Japanese seamless tube designation | JIS H3300, grade C2800 |
| Eddy-current examination | ASTM E243 |
| Copper (Cu) | 59.0 – 63.0 % |
| Density | 8.39 g/cm³ (0.303 lb/in³) |
| Thermal conductivity | about 120 W/(m·K) |
Tubes are ordered by outside diameter, wall thickness, length or developed length, temper, and the required test regime. Wall thickness is selected from the design pressure, the corrosion allowance and the mechanical cleaning method; heavy walls are specified where the tube will be rod-cleaned, where abrasive silt is present or where the bundle is subject to vibration. Tolerances on wall thickness, ovality and straightness are agreed at order stage, because they determine how the tube rolls into the tubesheet.
Bending Practice for Thick-Walled Tube
Bending is the operation that separates a good thick-wall tube from a rejected one. The outside of the bend stretches while the inside compresses, so the wall thins at the extrados and thickens at the intrados; the thicker the wall, the more forgiving the geometry becomes.
Bend radius: a generous centreline radius relative to outside diameter keeps wall thinning inside the acceptance limit; heavy walls allow tighter radii than thin walls.
Method: mandrel or plug bending supports the bore and prevents flattening; draw bending with a wiper die is common for tight U-bends.
Condition: bending is easier in a softer temper, and where the bend region is heavily worked a local stress-relief anneal of that region is performed, without softening the straight length that must roll into the tubesheet.
Post-bend checks: ovality, wall thickness at the extrados, bend angle, leg length and surface condition are measured on a sample from each batch.
Stress relief: residual stress from bending is relieved at low temperature, which also removes the risk of stress corrosion cracking in ammonia-bearing condensate.
Condenser and Heat Exchanger Service
In a shell-and-tube exchanger the tube carries cooling water on one side and process fluid on the other. C28000 performs well in fresh water, brackish water and marine atmospheres, resists salt spray and tolerates the slight acidity of many cooling circuits. Three service limits belong in the specification:
Velocity: keep water velocity inside the range recommended for the tube system, since excessive velocity causes impingement attack at the inlet end.
Chloride aggressiveness: brass is assessed for dezincification resistance, tested under ISO 6509, before it is approved for continuously aggressive sea water.
Ammonia and sulphide: where these species are present at significant levels, stress corrosion cracking becomes the governing risk and the alloy choice is revisited.
Inspection, Handling and Installation
Eddy-current examination of the full length to ASTM E243 reveals wall defects that visual inspection cannot.
Hydrostatic or pneumatic testing as required by the governing tube standard.
Dimensional verification of diameter, wall, bend geometry and tube-end roundness.
Clean, dry packing with capped ends to protect the bore from moisture and contamination in transit.
Tube rolling practice matched to tube hardness, since a work-hardened alloy needs a different expansion setting from soft copper tube.
FAQ
Q: What is Muntz metal tube made of?
It is the 60/40 copper-zinc alloy, UNS C28000, with copper specified at 59.0 – 63.0 % and zinc as the balance.
Q: Why use thick-walled tube instead of thin-wall tube?
Heavy walls add stiffness against vibration, provide a corrosion allowance and allow mechanical cleaning and tighter bends without collapsing the bore.
Q: Can C28000 tube be bent after delivery?
Yes, using mandrel or plug bending in a suitable temper; heavy walls tolerate tighter radii but the bend region is usually stress relieved afterwards.
Q: Is C28000 suitable for sea water condensers?
It is used widely in marine and condenser service; continuous aggressive sea water is assessed for dezincification resistance under ISO 6509 before approval.
Q: What tests are supplied with the tube?
Certified chemical and mechanical results, dimensional records, hydrostatic or pneumatic test data and eddy-current examination to ASTM E243 when specified.
Q: How is tube hardness controlled for rolling into the tubesheet?
By specifying a consistent temper, because the expansion setting and achieved joint tightness depend on the hardness of the tube end.
