90/10 vs 70/30 Copper Nickel (Cu-Ni) Fittings: When to Go Custom and Why It Matters

Published on 6 August, 2025

In marine, offshore, and desalination industries, Copper Nickel (Cu-Ni) fittings have built a reputation for unmatched corrosion resistance, biofouling prevention, and durability under seawater exposure. But not all Cu-Ni fittings are the same.

 

The two most widely used alloys are 90/10 (C70600) and 70/30 (C71500). Both are excellent performers, yet they differ in composition, strength, and application suitability. Understanding these differences and knowing when a custom fitting is worth the investment can save your project time, money, and costly rework.

 

The Basics: What Do 90/10 and 70/30 Mean?

 

The numbers refer to the ratio of copper to nickel in the alloy:

1. 90/10 = ~90% copper, ~10% nickel (plus small amounts of iron and manganese)
2. 70/30 = ~70% copper, ~30% nickel (plus similar trace elements)

Both grades conform to standards like ASTM B466 (pipes and tubes) and ASTM B122/B122M (plate, sheet, strip) for marine service.

 

Chemical Composition Table

 

Element	Cu-Ni 90/10 (C70600)	Cu-Ni 70/30 (C71500)
Copper (Cu)	88.6 – 90.0%	69.0 – 71.0%
Nickel (Ni)	9.0 – 11.0%	29.0 – 32.0%
Iron (Fe)	1.0 – 1.8%	0.4 – 1.0%
Manganese (Mn)	1.0% max	1.0% max

 

Performance Comparison Table

 

Where Each Alloy Excels

 

90/10 Copper Nickel

 

1. Best for: Systems where forming, bending, and complex shapes are required.

2. Typical Uses:
a. Heat exchanger and condenser tubing
b. Desalination plant equipment
c. Ballast water and cooling water systems

3. Advantages:
a. Easier to fabricate
b. Cost-effective for large projects
c. Adequate corrosion resistance for most seawater environments

70/30 Copper Nickel

 

1. Best for: High-pressure, high-velocity seawater systems with severe corrosion challenges.

2. Typical Uses:
a. Offshore platform seawater risers
b. Submarine pipelines
c. Fire main systems on naval and commercial ships

3. Advantages:
a. Superior strength and erosion resistance
b. Extended service life in extreme marine environments
c. Better resistance to impingement attack

When to Go Custom?

 

While off-the-shelf Cu-Ni fittings work for many installations, certain project conditions demand custom fabrication:

 

1. Non-Standard Sizes or Wall Thickness
For legacy systems or retrofits where the pipe schedule doesn’t match standard ASME dimensions.

2. Special End Configurations
Bevelled ends for butt welding, grooved ends for mechanical couplings, or dissimilar metal transition joints.

 

3. Complex Geometries
Elbows with non-standard radius, reducers with specific concentricity requirements, or multi-branch tees.

 

4. Material Blends
Hybrid fittings with a Cu-Ni core and stainless steel ends for specific thermal or galvanic requirements.

 

5. Compliance with Naval or Offshore Standards
Projects requiring adherence to DEF STAN, ASTM F467, or DNV-GL certifications.

Custom Fabrication Benefits

 

1. Perfect Fit: No on-site modification needed, reducing installation time.
2. Extended Service Life: Precision machining reduces turbulence and wear.
3. Certified Quality: Every batch can be supplied with Mill Test Certificates (MTCs), pressure test results, and NDT reports.
4. Global Supply: Custom orders can be produced and shipped to meet tight deadlines.

Summing up

 

Both 90/10 and 70/30 copper-nickel fittings are proven performers in seawater applications.

 

Choose 90/10 for most general marine and cooling water systems — especially when cost and ease of fabrication matter most.
Choose 70/30 for high-pressure, high-velocity, or mission-critical applications where superior erosion resistance and mechanical strength justify the higher cost.

And when your project involves non-standard specs, complex designs, or critical performance needs, going custom ensures you get the exact fit your system demands.

 

Ready to source precision Cu-Ni fittings?

At OnlineFittings.com, we manufacture and supply 90/10 and 70/30 Copper Nickel fittings online that fit your exact specifications, certified, tested, and delivered worldwide.

 

From shipyards to offshore platforms, we’ve got you covered.