Scope of the Specification
ASTM B111 is the specification for seamless copper and copper-alloy condenser tubes and ferrule stock. For UNS C23000 it fixes the chemical composition range, the permissible impurities, the temper designations, the mechanical property minima and the non-destructive tests that must be applied to every tube. A purchase to this standard is therefore a purchase of a defined quality system as well as of a material.
C23000 is a low-zinc brass, also known as red brass, containing about 84 to 86 per cent copper. Its relatively high copper content places it between commercially pure copper and the higher-zinc brasses in both appearance and behaviour.
Chemical Composition of C23000
| Element | Composition (% by weight) | Note |
|---|---|---|
| Copper (Cu) | 84.0 - 86.0 | Copper plus silver by difference |
| Zinc (Zn) | Remainder | Principal balance element |
| Lead (Pb) | 0.05 max | Restricted for ductility and lead control |
| Iron (Fe) | 0.05 max | Residual |
| Other impurities | 0.15 max each | Individual limit |
| Total impurities | 0.50 max | Sum of all other elements |
The limits are narrow on purpose. The copper content must be kept within a two-point band to preserve the single-phase structure that gives the alloy its ductility, while iron, lead and the other residuals are capped because excesses promote hard particles, reduce formability and, in the case of some residuals, undermine the corrosion behaviour.
What Each Element Does
Copper. Forms the matrix and provides the corrosion resistance, ductility, thermal conductivity and reddish colour. At 84 to 86 per cent the alloy is closer to copper than to brass in character.
Zinc. Dissolves in the copper and raises strength and hardness while reducing cost. Because it is present at only 14 to 16 per cent, the alloy is far less susceptible to dezincification than the 70/30 and 60/40 brasses.
Lead. Kept at 0.05 per cent maximum. Lead improves machinability but reduces hot ductility and is restricted in drinking water and food contact applications, so its low level is a deliberate feature of the grade rather than an incidental result.
Iron. Held at 0.05 per cent maximum because coarse iron-rich particles act as stress raisers during drawing and can reduce the finish of the tube surface.
Other impurities. Controlled individually at 0.15 per cent and collectively at 0.50 per cent, which keeps the electrical conductivity and the corrosion behaviour predictable from batch to batch.
Tempers and Mechanical Requirements
| Temper | Tensile strength | Hardness | Elongation |
|---|---|---|---|
| Annealed, O60 | About 260 - 300 MPa | About 50 HRB | 40 per cent or more |
| Light drawn, H55 | About 300 - 350 MPa | About 55 - 60 HRB | 20 - 30 per cent |
| Half hard, H04 | About 400 - 450 MPa | About 70 HRB | 10 - 15 per cent |
The mechanical minima for each temper are defined in the standard and are verified on finished tube. Because the temper changes both the strength and the forming behaviour, the required condition must be stated on the order and matched to the way the tube will be bent, flared, coiled or expanded in service. Harder tempers give higher pressure capability but leave less elongation for installation work.
Analytical and Non-Destructive Verification
Compliance with the composition limits is demonstrated by chemical analysis of a sample taken from each lot or heat, commonly by optical emission spectrometry, with the result expressed against the table above. Mechanical requirements are verified by tensile testing to establish the tensile strength, yield strength and elongation for the ordered temper.
Because condenser tube failure usually begins at an internal defect, the standard also requires non-destructive testing. Eddy-current examination is applied to the finished tube to detect cracks, inclusions, laps and other discontinuities along the length, and supplementary mechanical checks such as flattening and expansion tests are used to confirm that the tube can be installed without splitting. Dimensional verification covers outside diameter, wall thickness and length, together with a visual inspection of the bore and surface finish.
Applications of C23000 Tube
Heat exchanger and condenser tubing in fresh water and low-chloride cooling circuits
Condensate, water and low-pressure process lines where a lead-free or low-lead material is preferred
Plumbing and sanitary tube, valve bodies and fittings
Architectural and decorative tube, mouldings and rail fittings
Low-current electrical and instrument tubing
Musical instrument components and general tube assemblies
The grade should not be used for continuous seawater immersion or for service in contact with ammonia, ammonium compounds or strongly acidic media. In fresh water circuits, pH and dissolved oxygen should be kept within the ranges accepted for copper alloys to avoid localised attack, and the tube should not be left standing wet in stagnant conditions before commissioning.
FAQ
Q: What is the copper content of ASTM B111 C23000 brass pipe?
The copper content is specified between 84.0 and 86.0 per cent by weight, including silver, with zinc making up the remainder. This places the alloy in the low-zinc, red brass family.
Q: Why is the lead limit set at 0.05 per cent?
Lead improves machinability but harms hot ductility and is restricted in drinking water and food-contact service. Keeping it at 0.05 per cent maximum preserves formability and keeps the tube suitable for low-lead applications.
Q: What does the total impurity limit mean?
Individual residual elements are capped at 0.15 per cent and their sum at 0.50 per cent. This keeps conductivity, ductility and corrosion behaviour consistent from lot to lot.
Q: How is the composition verified?
By chemical analysis of a sample from each lot, normally using optical emission spectrometry and reported against the limits in the specification.
Q: What non-destructive testing does the standard require?
Finished tube is examined by the eddy-current method to find internal and external discontinuities, supplemented by mechanical tests such as flattening and expansion and by dimensional and visual inspection.
Q: Which temper should be ordered for a heat exchanger?
Annealed tube is used where the tube must be bent, coiled or rolled into tube sheets, while a light-drawn or half-hard temper is chosen when higher strength and stiffness are needed and forming is limited.
