Cupronickels are a group of copper-nickel alloys known for their superior resistance to corrosion, especially in seawater and challenging environments. These alloys combine the best properties of copper and nickel in varying compositions. Two of the most commonly used cupronickel alloys are 70/30 and 90/10. At Columbia Metals, we stock both, and here’s what you need to know.

Why use cupronickels?

Cupronickel alloys offer exceptional resistance to:

• Atmospheric and freshwater corrosion
• Biofouling (marine growth)
• Stress corrosion cracking
• Corrosion fatigue

These properties make cupronickel alloys the material of choice for shipbuilding, heat exchangers and even automotive brake tubing. However, the right alloy depends on the specific needs of the application.

The higher nickel content in 70/30 makes it stronger and more resistant to corrosion, particularly in aggressive seawater environments. However, this also increases the cost. Choosing between the two depends on balancing performance needs with budget constraints.

Alloying Additions and Workability

Both 90/10 and 70/30 are single-phase alloys. Alongside nickel, two other key alloying elements improve performance:

• Manganese acts as a deoxidizer and desulphurizer, enhancing welding properties and improving corrosion resistance in seawater.
• Iron increases resistance to impingement attack from fast-flowing seawater, making it particularly useful in marine applications.

Both grades are suitable for hot and cold working, with cold working typically preferred. 70/30 allows for higher hot-working temperatures. Cold working of up to 50% reduction can be achieved before annealing is required. The full annealing temperature ranges from:

• 700-800°C for 90/10
• 750-850°C for 70/30

Both grades can be stress-relieved between 300-400°C. Before annealing, oily residues should be removed to prevent carbonaceous films that could exacerbate pitting corrosion.

Welding of cupronickel alloys is satisfactory with conventional techniques. They can also be joined to dissimilar metals using appropriate filler materials. Proper fluxing or gas shielding is essential to prevent oxygen and hydrogen contamination, which can cause weld porosity. Titanium can be used in filler metals as a deoxidant.

Applications of Cupronickel Alloys

In the marine and shipbuilding sector, copper was historically used to protect wooden ships from the dreaded Teredo worm, which bored into hulls. Today, cupronickel alloys provide modern vessels with:

• Superior biofouling resistance
• Protection against corrosion from seawater
• Long-term cost savings through reduced maintenance

Used as cladding or foils on steel hulls, cupronickels ensure ships remain efficient and require less frequent cleaning.

In the automotive industry, cupronickels are used as brake tubing. Braking systems are particularly safety critical and mild steel tubing, even when coated, is vulnerable to corrosion, especially in winter road conditions with salt exposure. 90/10 cupronickel tubing, used in original equipment (OE) manufacturing, ensures:

• An extended lifespan
• Corrosion resistance inside and out
• Enhanced reliability and safety

In heat exchangers, tubes carry seawater to cool industrial processes. Cupronickel alloys are the preferred materials because they offer:

• Resistance to erosion in flowing seawater
• Prevention of pitting corrosion
• Stress corrosion resistance
• Good strength and durability

Interestingly, 90/10 is often favoured over 70/30 in heat exchangers due to its better resistance to pitting corrosion under deposits.

Our Stock Range

At Columbia Metals, we have decades of experience in the supply of both 90/10 and 70/30. Both alloys are available from stock between 10mm and 8” diameter in round bar and up to 50mm A/F in hexagon.

Our stock of 70/30 is released to CN107, CW354H, C71500, Def Stan 02-879 Annex B, C71520 and MIL-C-15726F.

90/10 is available as CN102, CW352H, C70600 and Def Stan 02-879 Annex C.