How to Weld 90/10 and 70/30 Copper-Nickel Alloys with ERCuNi

Copper-nickel alloys are widely used in marine, offshore, desalination, shipbuilding, heat exchanger, and seawater piping applications. Among the most common grades are 90/10 copper-nickel and 70/30 copper-nickel, both valued for their corrosion resistance in seawater and industrial environments. When these alloys need to be welded, one of the most important choices is the filler metal. For many TIG and MIG welding applications, the preferred filler is ERCuNi.

ERCuNi is a copper-nickel filler metal classified under AWS A5.7 and is commonly used for welding 90/10, 70/30, and 80/20 copper-nickel alloys. Copper Development Association guidance identifies 90/10 and 70/30 as the two main copper-nickel grades used in marine service, while AWS A5.7 ERCuNi is listed as a Cu-30% Ni bare wire for TIG and MIG welding.

This guide explains how to weld 90/10 and 70/30 copper-nickel alloys with ERCuNi, including filler metal selection, TIG and MIG welding setup, joint preparation, shielding gas, defect prevention, and best practices for marine-grade welds.

What Is ERCuNi Welding Wire?

ERCuNi is a copper-nickel welding wire or TIG rod designed for joining copper-nickel alloys. It is often described as a Cu-30% Ni filler metal and is used in gas tungsten arc welding, gas metal arc welding, oxy-fuel welding, and other suitable welding processes. Washington Alloy lists ERCuNi as an AWS A5.7 Class ERCuNi / ASME SFA5.7 Class ERCuNi filler metal used for welding wrought or cast 70/30, 80/20, and 90/10 copper-nickel alloys to themselves or to each other.

In practical terms, ERCuNi is used when the weld deposit must offer:

Good seawater corrosion resistance
Compatibility with copper-nickel base metals
Stable weldability in TIG and MIG processes
Good ductility
Reliable performance in marine and industrial service
A weld metal chemistry suitable for both 90/10 and 70/30 CuNi alloys

Because 90/10 and 70/30 copper-nickel alloys are often used in demanding seawater systems, filler metal selection should not be treated as a minor detail. The wrong filler can reduce corrosion resistance, increase galvanic concerns, or produce welds that do not meet the required service conditions.

Understanding 90/10 and 70/30 Copper-Nickel Alloys

The names 90/10 and 70/30 refer to the approximate copper-to-nickel ratio in the alloy.

Alloy	Common UNS Grade	Approximate Composition	Typical Use
90/10 copper-nickel	C70600 / C70620	About 90% copper, 10% nickel	Seawater piping, ship systems, condensers, heat exchangers
70/30 copper-nickel	C71500 / C71520	About 70% copper, 30% nickel	Higher-velocity seawater, more demanding marine service, tubesheets

Copper Development Association guidance notes that 70/30 copper-nickel is stronger and has greater resistance to seawater flow, while 90/10 copper-nickel performs well in many applications and is more widely used because it is less expensive.

Both alloys also contain small but important additions such as iron and manganese. These elements help improve resistance to flowing seawater and contribute to the overall durability of the alloy in marine environments.

Why ERCuNi Is Used for Both 90/10 and 70/30 Copper-Nickel

One of the most important points in copper-nickel welding is that a 70/30 copper-nickel filler material is commonly recommended for welding both 90/10 and 70/30 copper-nickel alloys. This is because the higher nickel content in the weld metal provides better strength and a more noble weld deposit compared with 90/10 base metal.

That is why ERCuNi is often selected for:

90/10 CuNi to 90/10 CuNi
70/30 CuNi to 70/30 CuNi
90/10 CuNi to 70/30 CuNi
Copper-nickel repair welding
Copper-nickel pipe welding
Marine fabrication and maintenance
Offshore and desalination equipment

Using ERCuNi simplifies filler selection because the same filler can often cover multiple copper-nickel base metal combinations. However, welding procedures should still be qualified according to the application, code requirements, wall thickness, service environment, and inspection standard.

Before Welding: Cleanliness Is Critical

Copper-nickel alloys are weldable, but they are sensitive to contamination. Dirt, oil, grease, paint, marking crayons, sulfur-containing materials, and other contaminants can create weld problems. Copper Development Association guidance emphasizes that cleanliness is paramount because contamination can cause cracking, porosity, and reduced corrosion resistance during fabrication and welding.

Before welding with ERCuNi:

Remove oil, grease, dirt, paint, and shop contamination.
Mechanically clean the weld area to bright metal.
Use stainless steel brushes dedicated only to copper-nickel.
Avoid carbon steel contamination from grinding tools or work surfaces.
Keep filler wire dry and clean.
Avoid touching cleaned weld edges with bare hands.
Protect the joint from moisture before welding.

A clean joint is especially important for pipe welding, root passes, and critical seawater service. Even a small amount of contamination can lead to porosity or reduced service life.

Do 90/10 and 70/30 Copper-Nickel Alloys Need Preheat?

Unlike pure copper, copper-nickel alloys generally do not require preheat or post-weld heat treatment under normal welding conditions. Copper Development Association guidance states that copper-nickels can be welded by conventional processes and, because of their simple metallurgical structure, do not require preheat or post-weld heat treatment.

This is one reason CuNi alloys are often considered easier to weld than many other copper alloys. However, “no preheat required” does not mean heat input can be ignored. Welders still need to control:

Arc length
Travel speed
Shielding gas coverage
Interpass temperature
Heat input
Joint fit-up
Root protection

The goal is to produce a sound weld without overheating, oxidation, undercut, or porosity.

TIG Welding 90/10 and 70/30 Copper-Nickel with ERCuNi

TIG welding, also known as GTAW, is commonly used for copper-nickel pipe, thin-wall fabrication, root passes, and applications requiring high control. Copper Development Association guidance describes TIG/GTAW as frequently used for joining copper-nickel pipe sections and attaching fittings and flanges.

Recommended TIG Welding Setup

For TIG welding 90/10 or 70/30 copper-nickel with ERCuNi:

Process: GTAW / TIG
Filler metal: ERCuNi TIG rod
Current: Direct current
Shielding gas: Argon
Backing gas for pipe root: Argon
Arc length: As short as practical
Technique: Add filler metal; avoid autogenous fusion where filler is required

For TIG root passes in pipe welding, argon backing gas is normally used. Argon is also listed as a suitable shielding gas, and the arc should be kept short to ensure the shielding gas protects the weld pool properly.

TIG Welding Best Practices

A good TIG weld on copper-nickel starts with joint cleanliness and a stable arc. Keep the torch angle steady, maintain a tight arc, and feed ERCuNi filler smoothly into the leading edge of the weld pool.

Avoid simply melting the base metal without filler. In copper-nickel welding, filler addition is important for controlling weld metal chemistry and reducing the risk of porosity. For root passes, make sure backing gas flow is stable before welding starts.

Practical TIG tips:

Use a clean, sharp tungsten suitable for DC welding.
Keep the filler rod inside the shielding gas envelope.
Avoid a long arc.
Do not overheat the joint.
Use consistent travel speed.
Clean between passes when multi-pass welding is required.
Inspect the root bead before continuing with fill passes.

MIG Welding 90/10 and 70/30 Copper-Nickel with ERCuNi

MIG welding, also known as GMAW, is useful when higher productivity is required. It is often better suited for longer welds, thicker materials, shop fabrication, or production environments.

Copper Development Association guidance notes that MIG/GMAW can be faster and closely controlled with modern equipment. It also explains that MIG transfer modes may include short-circuiting, pulsed-arc, and spray transfer, with spray transfer generally suitable for thicker material and downhand welding.

Recommended MIG Welding Setup

For MIG welding with ERCuNi wire:

Process: GMAW / MIG
Filler metal: ERCuNi MIG wire
Shielding gas: Argon or argon-helium mixture
Transfer mode: Based on thickness and position
Wire condition: Dry, clean, and free from contamination
Wire feeding: Use suitable liners and feeding equipment

Argon or a helium-containing mixture is preferred for MIG welding copper-nickel, and spooled filler wire must be kept dry and protected from contamination. Because copper-nickel wire is relatively soft, wire feeding performance is also important.

MIG Welding Best Practices

For MIG welding ERCuNi, the key is stable wire feed and controlled heat input. Poor wire feeding can cause arc instability, burnback, stubbing, or inconsistent bead appearance.

Use a clean liner, proper drive rolls, correct contact tip size, and suitable wire feed speed. If the wire is dragging or shaving, correct the feed system before welding production joints.

Practical MIG tips:

Use clean ERCuNi wire.
Keep spools dry.
Avoid excessive torch cable bends.
Use low-friction liners where needed.
Confirm gas flow and shielding coverage.
Use pulsed MIG when heat control is important.
Use spray transfer only when material thickness and position allow it.

Joint Design for Copper-Nickel Welding

Joint design depends on wall thickness, welding process, and inspection requirements. Thin-wall pipe may be welded with a simple butt joint and proper root gap, while thicker plate or pipe may require bevel preparation.

A good joint design should allow:

Complete root fusion
Proper filler metal access
Adequate shielding gas protection
Consistent penetration
Easy cleaning between passes
Minimal crevices that trap contamination

For pipe welding, root quality is critical. A poorly protected root can oxidize, become porous, or fail inspection. That is why backing gas is often used on TIG root passes.

Common Welding Defects and How to Prevent Them

1. Porosity

Porosity is one of the most common problems when welding copper-nickel alloys. Copper Development Association guidance notes that if porosity persists even with the correct filler material, likely causes include inadequate shielding, improper joint cleaning, long arc length, moisture, or insufficiently dry coated electrodes.

How to prevent porosity:

Clean the joint thoroughly.
Use proper shielding gas flow.
Keep the arc short.
Keep filler wire dry.
Avoid drafts near the weld zone.
Use backing gas for pipe roots.
Remove moisture before welding.

2. Lack of Fusion

Lack of fusion usually results from poor joint preparation, incorrect travel speed, insufficient heat input, or poor torch angle.

How to prevent lack of fusion:

Use the correct joint bevel.
Maintain a stable arc.
Avoid excessive travel speed.
Watch the weld pool edges.
Clean between passes.
Use an approved welding procedure.

3. Undercut

Undercut can occur when travel speed is too high, heat input is excessive, or the arc is poorly directed.

How to prevent undercut:

Reduce travel speed slightly.
Keep the arc centered.
Avoid excessive current.
Use controlled bead placement.
Avoid aggressive weaving.

4. Oxidized Root Bead

This is especially important in pipe welding. Poor backing gas protection can produce a dirty or oxidized root surface.

How to prevent root oxidation:

Use argon backing gas.
Purge long enough before welding.
Maintain purge flow during the root pass.
Seal pipe ends properly.
Avoid turbulence from excessive gas flow.

Post-Weld Cleaning and Inspection

Copper-nickel welds usually do not require post-weld heat treatment, but the weld area should be cleaned after welding. Copper Development Association guidance states that spatter and slag should be removed, and the weld area may be cleaned with a flap wheel or stainless steel brush to leave a bright finish. Welds should also be visually inspected for cracks, undercut, lack of fusion, penetration issues, and weld contour.

ERCuNi Applications in Marine and Industrial Welding

ERCuNi is most often associated with copper-nickel welding in environments where corrosion resistance matters. Typical applications include:

Shipbuilding
Seawater piping systems
Offshore platforms
Desalination plants
Condensers
Heat exchangers
Waterboxes
Pump components
Marine repair welding
Copper-nickel clad steel components

Copper Development Association guidance identifies desalination plants as a major application area for copper-nickel alloys, including brine piping, waterboxes, evaporator shells, and tube plates.

This makes ERCuNi highly relevant for companies serving marine engineering, offshore fabrication, seawater systems, and industrial corrosion-resistant equipment.

FAQ About Welding 90/10 and 70/30 Copper-Nickel with ERCuNi

Is ERCuNi suitable for both 90/10 and 70/30 copper-nickel?

Yes. ERCuNi is commonly used for welding 90/10, 70/30, and 80/20 copper-nickel alloys. It is widely used for welding these alloys to themselves or to each other.

Why use ERCuNi instead of matching 90/10 filler for 90/10 copper-nickel?

A 70/30 copper-nickel filler is commonly recommended for both 90/10 and 70/30 copper-nickel alloys because the higher nickel content provides a stronger and more noble weld metal compared with 90/10 base metal.

Does copper-nickel need preheat before welding?

Normally, no. Copper-nickel alloys generally do not require preheat or post-weld heat treatment, but cleanliness and welding procedure control are essential.

What shielding gas is used for TIG welding ERCuNi?

Argon is commonly used for TIG welding copper-nickel. For pipe root welding, argon backing gas is normally used to protect the root side of the weld.

What shielding gas is used for MIG welding ERCuNi?

For MIG welding copper-nickel, argon or an argon-helium mixture is preferred. The exact gas choice depends on equipment, material thickness, transfer mode, and welding procedure.

What causes porosity when welding copper-nickel?

Common causes include poor shielding gas coverage, dirty weld joints, excessive arc length, moisture, and contaminated filler material.

Conclusion

Welding 90/10 and 70/30 copper-nickel alloys with ERCuNi requires the right combination of filler metal, cleanliness, shielding gas, and welding technique. Although copper-nickel alloys are generally easier to weld than many other copper alloys and usually do not require preheat, they still demand careful surface preparation and strict contamination control.

For TIG welding, ERCuNi provides excellent control for pipe roots, thin-wall components, fittings, and high-quality marine fabrication. For MIG welding, ERCuNi offers productivity advantages in longer welds and larger fabrication projects when wire feeding and shielding gas are properly controlled.

When used correctly, ERCuNi produces strong, ductile, corrosion-resistant welds suitable for seawater systems, shipbuilding, offshore equipment, desalination plants, heat exchangers, and other demanding industrial applications. For any critical project, always follow an approved welding procedure specification and verify that the ERCuNi filler metal meets the required AWS A5.7 classification.