Copper-Nickel 70/30: Complete Properties & Application Guide

← Back to Knowledge Center

Overview

Copper-Nickel 70/30 (UNS C71500) is a cupronickel alloy with excellent resistance to seawater corrosion and biofouling. The 30% nickel content provides higher strength and corrosion resistance compared to 90/10 Cu-Ni, making it ideal for demanding marine applications.

Chemical Composition

The chemical composition of Copper-Nickel 70/30 is carefully controlled to achieve its unique combination of properties and performance characteristics.

Element	Min %	Max %
Copper (Cu)	Balance	Balance
Nickel (Ni)	29.0	33.0
Iron (Fe)	0.40	1.00
Manganese (Mn)	—	1.0
Zinc (Zn)	—	1.0
Carbon (C)	—	0.05
Lead (Pb)	—	0.05

Mechanical Properties at Room Temperature

The mechanical properties of Copper-Nickel 70/30 vary depending on product form and heat treatment condition. The data below represents typical values for solution-annealed material.

Property	Value
Tensile Strength	380 MPa
Yield Strength (0.2% offset)	125 MPa
Elongation in 2 inches	45%
Density	8.94 g/cm3
Melting Point	1240 °C
Max Service Temperature	300 °C

Corrosion Resistance

Outstanding resistance to seawater corrosion, including pitting, crevice corrosion, and stress corrosion cracking. Excellent resistance to biofouling due to the natural formation of a protective copper oxide film. Good resistance to ammonia stress corrosion cracking and dezincification.

Applications

The unique combination of properties makes Copper-Nickel 70/30 suitable for a wide range of demanding applications:

• Marine Engineering: Seawater piping, heat exchanger tubing, and condenser tubes.
• Offshore Platforms: Riser systems, ballast water systems, and firewater piping.
• Power Generation: Condenser tubing in coastal power plants.
• Shipbuilding: Seawater cooling systems, heat exchangers, and piping.
• Desalination: Heat rejection and recovery tubing in desalination plants.

Available Product Forms

Hangbo Alloy Group manufactures and supplies Copper-Nickel 70/30 in the following product forms, conforming to ASTM, AMS, and ASME specifications:

• Round Bars: Diameters from 6 mm to 300 mm, hot-finished or cold-drawn, solution annealed.
• Seamless Tubes & Pipes: Sizes from 6 mm OD to 219 mm OD, various wall thicknesses.
• Plates & Sheets: Thicknesses from 0.5 mm to 50 mm, hot-rolled or cold-rolled.
• Forgings: Custom flanges, rings, discs, and complex shapes per customer drawing.
• Welding Wire: Diameters 0.8 mm to 5.0 mm, precision-wound coils and spools.

Related Standards

Standard	Description
ASTM B111	Condenser Tube
ASTM B466	Seamless Pipe
ASTM B467	Welded Pipe
ASTM B122	Plate, Sheet, and Strip
ASTM B151	Bar and Rod
ASTM B171	Plate

Seawater Performance and Erosion Limits

With 30 % nickel, this grade carries roughly 50 % more strength than 90/10 and tolerates significantly higher water velocities — the reason it is specified for seawater piping, pump bodies and high-duty condenser tubes.

Parameter	Typical value
Tensile strength (annealed)	≈ 480 MPa
0.2 % yield strength	≈ 200 MPa
Corrosion rate, flowing seawater	< 0.02 mm/yr
Max continuous velocity	3.5–4.5 m/s
Impingement / erosion threshold	Higher than 90/10

The alloy also has strong inherent resistance to macrofouling, which reduces cleaning frequency and preserves heat-transfer performance. As with 90/10, avoid galvanic coupling to stainless steel without insulation.

Fabrication and Welding Guidance

• Weld with ERCuNi filler (AWS A5.7 / CuNi30) — never with a copper filler, which gives a weak, corrosion-prone deposit.
• GTAW for root passes and tube work; GMAW or SAW for thicker plate with matching flux.
• Preheat heavy sections to 150–200 °C; keep the joint absolutely free of oil, paint and sulphur.
• Back-purge tube bores with argon; oxidised roots crack during expansion.
• Stress-relieve at 500–550 °C only where service conditions demand it — most marine fabrications are used as-welded.

Frequently Asked Questions

When should I choose 70/30 instead of 90/10?

When flow velocities exceed roughly 3 m/s, when the system sees suspended solids or turbulence, or where higher mechanical strength is needed. The premium is modest against the cost of a premature tube failure.

Is 70/30 resistant to ammonia?

No. Ammonia and ammonium compounds attack copper alloys rapidly — this is the principal reason copper-nickel is excluded from some chemical processes despite excellent seawater behaviour.

What forms does Hangbo supply?

Seamless tube and pipe to ASTM B111 / B466, plate and sheet to B171, plus bar, fittings and flanges with EN 10204 3.1 certification.

What is the chemical composition of Cu-Ni 70/30?

UNS C71500 / W.Nr. 2.0882: copper balance, 29-33% nickel and 0.4-1.0% iron, with manganese and zinc each limited to about 1.0%.

Why is 70/30 used in marine service?

Its higher nickel content gives greater strength and corrosion resistance than 90/10, and the copper-rich oxide film resists biofouling, pitting and crevice corrosion in seawater.

What are its mechanical properties?

Tensile about 380 MPa, yield about 125 MPa and 45% elongation in the annealed condition.

What standards cover Cu-Ni 70/30?

UNS C71500 / W.Nr. 2.0882, with ASTM B111/B466 for condenser and heat-exchanger tube.

What are typical applications?

Seawater piping, condensers, heat exchangers, offshore platform piping and desalination equipment.

How is 70/30 supplied?

Tube, pipe, plate, bar and fittings, with seamless and welded tube as the common service forms.

Contact Us for Copper-Nickel 70/30

Hangbo Alloy Group maintains extensive inventory of Copper-Nickel 70/30 in all standard product forms. We can provide mill test certificates, third-party inspection reports (SGS, TUV), and custom processing services.

For quotations, material certifications, or technical consultation, contact our sales team or call +86 166 2109 2936. We typically respond within 10 minutes.