ASTM B111 C70600 Copper Nickel Tube：Dimensions, Wall Thickness, and Tolerances Explained

When you are ready to order ASTM B111 C70600 copper nickel tube, one question always comes first： what size do I need? But B111 uses BWG (Birmingham Wire Gauge) for wall thickness, not the Schedule numbers you see on pipe. If you do not understand BWG, you may order the wrong wall thickness and your tubes will fail pressure testing or be too heavy to roll into a tube sheet.

Below is a complete guide to dimensions, wall thickness, tolerances, and how to read a C70600 tube specification.

ASTM B111 C70600 tube is available from 6.35mm (0.25 inch) up to 76.2mm (3 inches) outside diameter. Larger ODs are possible but less common and may require special mill agreement. Most heat exchanger and condenser tubes fall between 12.7mm (0.5 inch) and 25.4mm (1 inch).

Common OD sizes for ASTM B111 C70600 tube：

BWG (Birmingham Wire Gauge) numbers run backward： the larger the BWG number, the thinner the wall. BWG 22 is thin (0.711mm). BWG 10 is thick (3.404mm). Do not assume a higher number means thicker wall.

Complete BWG to mm conversion for ASTM B111 C70600 tube：

BWG 18 (1.24mm) and BWG 16 (1.65mm) are the two most common wall thicknesses for ASTM B111 C70600 tube. Start there unless your engineer specifies otherwise.

ASTM B111 has strict tolerances because C70600 tubes are rolled into tube sheets. Loose tubes will leak. Oversize tubes will not fit. Below are the standard tolerances you should expect from a qualified mill.

OD tolerance for ASTM B111 C70600 tube：

Wall thickness tolerance for ASTM B111 C70600 tube：

Length tolerance for ASTM B111 C70600 tube：

OD tolerance is critical for tube sheet fit. Always confirm your supplier can meet the ±0.004" standard for 1" and smaller tubes.

Standard random length is 5 to 7 meters (16 to 23 feet). Cut lengths from 1 meter to 15 meters are available. For heat exchangers, tubes are often ordered to exact bundle length plus 50-100mm for rolling.

Common length options：

Use a tubing micrometer or ultrasonic thickness gauge. Do not use a standard caliper for thin walls. Standard calipers can give false readings because the tube surface is curved.

Correct measuring steps：

Clean the tube end to remove oil and debris

Use a tubing micrometer with a curved anvil

Take readings at 3 or 4 points around the circumference

Average the readings

For ultrasonic testing, calibrate on a sample of known thickness

Common mistakes to avoid：

Measuring with standard flat anvil calipers (adds error)

Measuring only one spot (tube may be oval)

Measuring painted or coated surface (coating adds thickness)

Q1： What OD range does ASTM B111 C70600 cover?

ASTM B111 covers C70600 tube from 1/4 inch (6.35mm) to 3 inches (76.2mm) outside diameter. Larger ODs up to 4 inches may be available by special agreement, but most mills do not stock them. For ODs above 3 inches, check if ASTM B466 (pipe) is acceptable for your application.

Q2： What does BWG 18 mean in mm?

BWG 18 is 0.049 inches, which is 1.24mm wall thickness. This is the most common wall thickness for marine C70600 tubes. BWG numbers decrease as wall thickness increases, so BWG 16 (1.65mm) is thicker than BWG 18 (1.24mm).

Q3： Is a thicker wall always better for C70600 tube?

No, thicker wall reduces heat transfer and increases cost. In a heat exchanger, you want the thinnest wall that still provides enough corrosion allowance and pressure containment. Too thick a wall means lower efficiency and higher material cost. Follow the engineer's specified BWG number.

Q4： What is the standard tolerance for C70600 tube OD?

±0.004 inch (0.10mm) for OD up to 1 inch. For 1 to 1.5 inch OD, tolerance is ±0.005 inch (0.13mm). These tight tolerances are necessary because C70600 tubes are rolled into tube sheets. Loose OD will cause leaks. Oversize OD will not enter the tube hole.

Q5： Can I get C70600 tube in custom lengths?

Yes, most mills cut to exact lengths from 1 meter to 15 meters. For heat exchanger bundles, tubes are cut to the tube sheet length plus 50-100mm for rolling out the other side. Length tolerance is typically +6mm / -0mm for lengths under 6 meters.

Q6： What does "hard temper" and "annealed" mean for C70600 tube?

Annealed (O60) is soft and easy to bend or roll into tube sheets. Hard drawn (H80) is strong but brittle and cannot be flared. Almost all ASTM B111 C70600 tube is supplied annealed. Hard temper is rarely used because rolling thin hard tube into a tube sheet will crack it.

Q7： How do I specify C70600 tube for a heat exchanger?

Write： ASTM B111 C70600 – [OD] x [BWG] – Annealed – [length]. Example： ASTM B111 C70600 – 3/4" OD x BWG 18 – Annealed – 6.0m. Also specify quantity (number of tubes) and any special requirements like eddy current testing certification.

Q8： What is the difference between BWG and SWG?

BWG (Birmingham Wire Gauge) and SWG (Standard Wire Gauge) are different scales. A BWG 18 tube is 1.24mm wall. An SWG 18 tube is 1.22mm wall – very close but not identical. ASTM B111 specifically calls for BWG, not SWG. Always confirm your supplier uses BWG.

Q9： Can I get C70600 tube with epoxy coating inside?

Not under ASTM B111. The standard does not cover internal coatings. If you need coated tube, it must be specified as a supplementary requirement. However, C70600 generally does not need internal coating because it resists corrosion naturally. Coating is more common on carbon steel or stainless steel tubes.

Q10： What is the maximum straightness deviation for C70600 tube?

ASTM B111 does not specify a numerical straightness tolerance. However, industry practice is 1.5mm per 3 meters of length (0.05" per 10 feet). Tubes that are visibly bent should be rejected. For critical bundles, specify a straightness requirement on your purchase order.

Q11： Does ASTM B111 allow welded tube or only seamless?

ASTM B111 covers both seamless and welded tubes. However, for C70600 copper nickel, seamless is the standard choice. Welded C70600 tube is rare and usually requires agreement between buyer and mill. If you receive welded tube without asking for it, reject it.

Q12： How to check if C70600 tube meets ASTM B111 tolerance?

Request the mill test report (MTR). The MTR will show measured OD, wall thickness, and whether eddy current testing passed. You can also measure sample tubes yourself with a tubing micrometer and compare to the tolerances listed above.

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