Scope of ASTM B88 and the C11000 Grade
ASTM B88 is the specification for seamless copper water tube used in plumbing, heating and general water services. It defines the three wall thickness families known as Type K, L and M, the three tempers normally supplied, the dimensional tolerances and the mechanical and tightness tests that finished tube must satisfy. The matching ASME SB88 document is applied to pressure equipment and building services work.
C11000 electrolytic tough pitch copper is the 99.90 % minimum purity grade with roughly 100 % IACS electrical conductivity and a thermal conductivity of about 394 W/(m·K). Tube made from this grade is ordered for heat exchangers, condensers, radiators, cooling coils and water services where high thermal transfer and stable corrosion behaviour are required. The deoxidised grade C12200, which contains 0.015 - 0.040 % phosphorus, is specified instead when joints are to be brazed or welded.
Composition and Physical Properties
| Item | Value |
|---|---|
| Copper plus silver | 99.90 % min |
| Oxygen | 0.02 - 0.04 % typical, controlled |
| Phosphorus | Not specified in the ETP grade |
| Density | 8.94 g/cm³ |
| Melting point | 1,083 °C |
| Thermal conductivity | 394 W/(m·K) |
| Electrical conductivity | 100 % IACS nominal |
| Modulus of elasticity | about 117 GPa |
Small traces of phosphorus shift the grade towards C12000 or C12200, and those deoxidised materials are the correct selection whenever a joint will see a flame. Quoting a phosphorus range on an order for C11000 is a sign that the grade has been confused with the phosphorised family.
Tempers and Dimensional Families
| Temper | Designation | Condition | Typical use |
|---|---|---|---|
| Soft annealed | O60 | Fully annealed | Coils, buried lines, tight bends |
| Light drawn | H55 | Partially hardened | General plumbing and heating |
| Hard drawn | H58 | Drawn, unannealed | Straight runs, exposed pipework, heat exchanger shells |
| Nominal size, in | Outside diameter, mm | Type K wall, mm | Type L wall, mm | Type M wall, mm |
|---|---|---|---|---|
| 3/8 | 12.70 | 1.24 | 0.89 | 0.64 |
| 1/2 | 15.88 | 1.24 | 1.02 | 0.71 |
| 3/4 | 22.23 | 1.65 | 1.14 | 0.81 |
| 1 | 28.58 | 1.65 | 1.27 | 0.89 |
| 1 1/4 | 34.93 | 1.65 | 1.40 | 1.07 |
| 1 1/2 | 41.28 | 1.83 | 1.52 | 1.24 |
| 2 | 53.98 | 2.11 | 1.78 | 1.47 |
Type K is the heavy wall used for underground and buried services, Type L is the standard wall for domestic and commercial plumbing and for most heat transfer work, and Type M is the thin wall used for low pressure drains and vents. Nominal sizes refer to the trade designation rather than to the actual bore, so tube is always selected by outside diameter and type.
Heat Exchanger and Cooling System Performance
The thermal conductivity of copper is roughly twenty-five times that of stainless steel, so a copper bundle transfers heat with a much smaller surface area and a much smaller temperature difference between the two fluids. That efficiency explains the continuing use of copper in chillers, condensers, fan coil units, radiators and process coolers. Additional advantages include a low pressure drop thanks to the smooth bore, freedom from the pitting that affects some stainless grades in chlorinated water, and the anti-microbial behaviour of copper surfaces in potable and process water systems.
Water-side conditions decide service life more than the tube itself. Design velocities in clean cooling water are commonly held between about 1.5 m/s and 2.5 m/s to keep the bore clean without provoking erosion. Suspended sand, entrained air, deposits and ammonia-bearing condensate all cause accelerated attack, and the water treatment programme must be reviewed before the material is fixed.
Corrosion Resistance and Service Limits
Excellent resistance to atmospheric corrosion, soil corrosion and most natural waters.
Immune to chloride stress-corrosion cracking and to the season cracking seen in brasses.
Not suitable for ammonia, amines, acetylene, mercury or strongly oxidising acids.
Sensitive to hydrogen embrittlement when heated above roughly 370 °C in a reducing atmosphere.
Noble in the galvanic series, so contact with steel should be broken by a dielectric fitting.
Fabrication, Joining and Testing
Tube is cut with a rotary cutter or fine toothed saw, reamed and deburred, then bent on a bender matched to the temper. Soft annealed tube bends by hand for small sizes; hard drawn tube needs a mandrel and a generous radius. Joining is by capillary soldering, press fittings, flaring, silver brazing or, less commonly, welding with deoxidised filler metal. Flux residues are flushed out after soldering because they attack the metal in the presence of moisture. Systems are pressure tested with water or dry nitrogen, and heat exchanger bundles are additionally checked for tube-to-tubesheet joint tightness.
Inspection and Documentation
Acceptance testing covers dimensions, wall thickness, straightness, temper, surface finish and internal soundness, with eddy current examination used to detect wall defects and hydrostatic testing to prove pressure tightness. Grain size is verified on annealed tube that will be expanded into a tubesheet. A mill test certificate to EN 10204 3.1 accompanies each heat, and third party inspection can be arranged where a project requires it.
FAQ
Q: Can I use B88 tube in a heat exchanger?
Yes. The dimensional and temper requirements are directly applicable to water-cooled heat transfer equipment, and C11000 tube in the C12200 wall family is regularly used for condensers, coolers and chillers.
Q: Which type should be used underground?
Type K is the correct choice for buried services because its heavier wall gives a larger corrosion allowance. Type L is used for above-ground distribution and Type M for drains and low pressure vents.
Q: Is brazing possible on C11000 tube?
Brazing is possible but the oxygen in the grade makes it more sensitive to hydrogen at high temperature. Joints on C11000 should be made with soft solder or mechanical fittings, or the specification should be changed to a deoxidised grade.
Q: What causes copper tube to fail in a cooling system?
The usual causes are erosion from excessive velocity, impingement from entrained air or sand, under-deposit corrosion from fouling, and attack by ammonia or aggressive water treatment chemicals. Mechanical damage during installation is another common root cause.
Q: Does copper tube need a protective coating?
No coating is needed for normal water and atmospheric service. A coating or wrapping is used where tube is buried in aggressive soil or installed in a highly polluted industrial atmosphere.
Q: What wall thickness should be specified?
Wall is selected from the design pressure, the temperature, and the corrosion allowance required by the service. The Type L wall is the normal starting point for heat transfer work, with the Type K wall where erosion or corrosion allowances are larger.
