Scope of ASTM B111 for C70600 Tube
ASTM B111/B111M specifies seamless copper and copper alloy tube for surface condensers, evaporators and heat exchangers, and UNS C70600 is the 90/10 copper-nickel grade within its range. Tube is supplied in annealed O61 or light drawn H55 temper, ready for rolling into a tubesheet. The specification controls the alloy composition, the temper, the mechanical properties, the dimensions and tolerances, and the acceptance tests, so that every length can be traced to a test certificate.
C70600 is chosen because it combines good strength with strong resistance to seawater and to erosion at moderate flow velocity. In flowing seawater the alloy forms a protective surface film that also limits marine fouling, which keeps heat transfer close to the design value over long campaigns.
Chemical Composition and Mechanical Properties
| Element | Composition, % |
|---|---|
| Copper | Balance, 86.5 min |
| Nickel including cobalt | 9.0 to 11.0 |
| Iron | 1.0 to 1.8 |
| Manganese | 1.0 max |
| Zinc | 1.0 max |
| Lead | 0.05 max |
| Temper | Tensile strength, min | Yield strength, min, 0.5% extension | Elongation, min |
|---|---|---|---|
| O61 annealed | 275 MPa / 40 ksi | 105 MPa / 15 ksi | 30% |
| H55 light drawn | Higher than annealed, tabulated in ASTM B111 | Higher than annealed, tabulated in ASTM B111 | Lower than annealed, tabulated in ASTM B111 |
Annealed tube is normally ordered for exchangers because it can be rolled and bent without cracking. Light drawn tube is used where additional strength is needed and the tube will not be formed after delivery.
Standard Sizes and Tolerances
Condenser and heat exchanger tube is supplied in outside diameters that match the tubesheet layout, with wall thickness chosen from the pressure, the allowable corrosion allowance and the mechanical cleaning method used on site.
| Outside diameter | Common wall, BWG | Wall, mm | Typical service |
|---|---|---|---|
| 15.88 mm, 5/8 in | 20, 18 | 0.889, 1.245 | Small condensers and coolers |
| 19.05 mm, 3/4 in | 18, 16 | 1.245, 1.651 | Power station and process condensers |
| 25.4 mm, 1 in | 16, 14 | 1.651, 2.108 | Large condensers and seawater duty |
Straight lengths are cut to the length requested by the customer, and U-bend tube is produced for two-pass and multi-pass exchangers. Diameter and wall tolerances follow the tables of ASTM B111, and the wall is measured at several points around the circumference so that the minimum wall governing the pressure rating is confirmed.
Testing and Inspection
Chemical analysis of each lot, checked against the composition limits of the grade.
Tension test to confirm tensile strength, yield strength at 0.5% extension and elongation.
Expansion test, or flaring test, to prove that the tube is ductile enough for roller expansion into the tubesheet.
Flattening test and, where specified, a reverse bend test to reveal seam or wall defects.
Eddy current test to ASTM E243 for full length examination, with drilled reference holes and notches setting the sensitivity, or a hydrostatic test at the pressure stated in the purchase order.
Dimensional and visual inspection: diameter, wall, length, ovality, straightness and surface condition.
Test certificates are issued with the bundle, and the marking on each bundle allows the tube to be traced back to the heat and to the test report during erection, which is important when an exchanger is retubed several years after the original order.
Condenser and Heat Exchanger Applications
Steam surface condensers in power stations and cogeneration plants.
Seawater cooled heat exchangers, oil coolers and intercoolers.
Desalination evaporators and multi-stage flash units.
Marine and shipboard heat exchangers, including central cooling systems.
Refinery and chemical plant condensers where cooling water is brackish or saline.
Installation and Maintenance Notes
Tubes are rolled into the tubesheet with a controlled expansion, because over rolling thins the wall and reduces the tube life. A seal weld is applied for critical services, and the tube ends are deburred and cleaned before expansion. Baffles and supports should be positioned so that flow induced vibration does not damage the tube, and the water velocity is kept inside the limit agreed for the alloy and water chemistry. During service, eddy current inspection of a sample of tubes at each shutdown detects wall loss before it becomes a leak, and the tubesheet and water boxes are kept free from debris and from chloride bearing materials. Where tubes are replaced, the replacement tube should match the grade, temper and wall of the original so that the thermal and corrosion performance of the bundle is unchanged.
FAQ
Q: What grade of copper-nickel does ASTM B111 C70600 represent?
C70600 is the 90/10 copper-nickel grade, containing about 10% nickel with iron and manganese additions in a copper base, and it is the most widely used copper alloy condenser tube for seawater duty.
Q: Which temper should be ordered?
Annealed O61 is standard for condensers because it can be rolled into the tubesheet and bent without cracking. Choose light drawn H55 only where higher strength is required and no forming follows.
Q: Why is iron added to the alloy?
Iron at about 1.0% to 1.8% strengthens the protective surface film that forms in seawater, which improves resistance to erosion and helps the tube tolerate flowing water.
Q: What tests come with the tube?
Chemical analysis, tensile testing at 0.5% extension, expansion and flattening tests, dimensional inspection and either an eddy current test to ASTM E243 or a hydrostatic test, depending on the order.
Q: Can the tube be supplied as U-bends?
Yes. U-bend tube for multi-pass exchangers is formed from the same stock, stress relieved when the bend radius requires it, and supplied with the leg lengths stated in the order.
Q: How is wall thickness verified?
The wall is measured at several points around the circumference of sample lengths, and the minimum value is compared with the nominal wall and tolerance tabulated in ASTM B111 for the size ordered.
