ASTM B111 C70600 Copper Nickel Tube – Welding, Bending and Installation Guide

GTAW (TIG) with ERCuNi filler metal is the standard method.

Three rules for C70600 welding:

Never use pure copper filler (ERCu) – causes galvanic corrosion at the weld

Never weld without argon purge inside the tube – root side will oxidize

Never overheat – C70600 becomes brittle if interpass temperature exceeds 200°C

Use a mandrel bender with minimum bend radius of 1.5 x tube OD.

For U-bend heat exchanger tubes:

Use stress-relieved tubes, not annealed (O60)

Bend slowly at 10–15 mm per second

Check for ovality – max 8% reduction in OD

Inspect outer wall for thinning – max 15% reduction

Do not:

Bend without mandrel for thin wall tubes (20 BWG or thinner)

Bend annealed tubes into tight U-bends – they will spring back or kink

Use heat bending – C70600 does not require heat and overheating causes grain growth

Use tube cutter or bandsaw. Never use abrasive wheel on thin wall tubes.

After cutting:

Remove all burrs inside and outside

Clean 25mm from each end to bright metal

Do not use steel brush – use stainless or nylon brush

Roller expansion is the standard method for heat exchangers.

Expansion parameters for 19.05mm OD x 1.24mm wall tube:

Check after expansion:

No visible gap between tube and tube sheet

No cracking at tube end

No ovality of tube beyond the expanded zone

Do not:

Weld C70600 tube to steel tube sheet without a transition joint

Use seal welding alone without mechanical expansion

Over-expand – causes tube thinning and cracking

Use a dielectric union or a lined spool piece.

If direct connection is unavoidable:

Keep wet length of steel pipe as short as possible

Install sacrificial anodes on the steel side

Inspect annually for galvanic corrosion

Essential tools:

Tube cutter or bandsaw

Deburring tool (inside and outside)

Mandrel bender (for tube bending)

Tube roller expansion tool (for tube sheet)

Argon purge kit (for welding)

PMI gun (for material verification before installation)

Do not use:

Steel wire brushes – use stainless or nylon

Carbon steel clamps – use copper alloy or plastic lined

Abrasive cutting wheels on thin wall – leaves embedded grit

Can C70600 tube be welded to stainless steel pipe?

Yes, but use ERNiCr-3 (Inconel 82) filler metal. Direct C70600 to 316L welding with ERCuNi causes brittle intermetallic layers. For critical service, use a transition spool piece.

What shielding gas is best for C70600 welding?

100% Argon only. Do not use Argon-CO₂ mixes. CO₂ causes oxidation and poor weld quality. Do not use Argon-Helium mixes unless welding thick wall above 5mm.

Does C70600 require preheating before welding?

No. Preheating is not required and can actually cause problems. C70600 welds cold very well. Keep interpass temperature below 150°C.

How to repair a cracked weld on C70600 tube?

Grind out the crack completely until clean metal is exposed. Re-weld using ERCuNi filler. If crack extends into tube base metal, cut out the damaged section and add a new piece.

What is the maximum ovality allowed after bending C70600 tube?

8% reduction in outside diameter is the maximum allowed per ASTM B111. For example, a 19.05mm tube can have minimum OD of 17.53mm at the bend.

Can C70600 tube be used for threaded connections?

Yes, but only for thick wall tubes (minimum 2.5mm wall). Use PTFE tape or anaerobic thread sealant. Do not use pipe dope containing graphite – it causes galvanic corrosion.

How to mark C70600 tube without damaging it?

Use low stress permanent marker or vinyl tape. Do not use steel stamping – it creates stress risers and potential crack initiation points. Do not use electric engraver – it removes the protective oxide layer.

What is the minimum wall thickness for field bending C70600 tube?

1.24mm (18 BWG) is recommended for field bending. Thinner walls (0.89mm or 20 BWG) require mandrel bending with careful control. For thin wall field bends, use pre-bent elbows instead.

Is soldering or brazing acceptable for C70600 tube?

Soldering is acceptable for low temperature, low pressure applications (below 100°C, below 1.0 MPa). Use 95/5 tin-antimony solder. Brazing with silver braze is also acceptable. For high temperature or high pressure, weld instead.

How to pressure test C70600 tube after installation?

Hydrostatic test at 1.5 x design pressure, minimum 10 minutes hold time. Use clean fresh water with corrosion inhibitor. Do not use seawater for hydrotest – chlorides may remain and cause pitting later. Drain and dry immediately after test.

Eddy current test (ECT) to ASTM E243

Hydrostatic test up to 20 MPa

PMI (XRF) for alloy verification on every heat

Mechanical property test (tensile, hardness, flattening, expansion)

Microscopic examination for grain structure

Flattening test per ASTM B111

Reverse flattening test for welded tubes (where applicable)

Plastic end caps on both ends to prevent contamination

Individual polybag wrapping for each tube

Wooden crates or steel spools for export

Moisture-proof paper and desiccant for sea shipment

Label with heat number, size, and quantity on each package

Color-coded bands for alloy identification

Extrusion press (1500T and 2500T)

Cold drawing machines (10 lines, OD range 4mm to 90mm)

Annealing furnaces (controlled atmosphere, 650–750°C)

Straightening and cutting lines

U-bending machine for heat exchanger tubes

Eddy current testing machines (3 units)

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