The addition of nickel to copper improves strength and corrosion resistance without reducing the good ductility. Copper-nickel alloys have excellent resistance to marine corrosion, strength and durability.
The two main alloys are 90/10 (90% copper, 10% nickel) and 70/30 (70% copper, 30% nickel). The 70/30 is the stronger and has greater resistance to seawater flow, but the 90/10 will provide good service for most applications and, being less expensive, tends to be more widely used. Both alloys contain small but important additions of iron and manganese which have been chosen to provide the best combination of resistance to flowing seawater and to overall corrosion.
Copper-nickel alloys are widely used for marine applications due to their excellent resistance to seawater corrosion, their ease of fabrication and their high inherent low susceptibility to the attachment of marine organisms. They have provided reliable service for several decades whilst offering effective solutions to today’s technological challenges.
- Seawater pipework
- Offshore fire water systems
- Heat exchangers and condensers
- Sheathing of legs and risers on offshore platforms and boat hulls
- Hydraulic lines
- Fish cages for aquaculture
- Desalination units.
Copper-nickel Fabrication Guide
This publication provides an understanding of the two primary copper-nickel alloys to allow good fabrication and operational practices. Topics covered include general engineering properties of 90/10 and 70/30 copper-nickels, welding and fabrication practices and a basic overview of corrosion and other properties beneficial for marine environments.
Download the Copper-nickel Fabrication Guide
View the Series of 5 Training Videos on Welding of Copper-nickel
- Cleaning and preparation for welding of copper-nickel alloy
- TIG welding copper-nickel alloy
- Pipe welding copper-nickel alloy
- Shielded metal arc welding copper-nickel alloy
- Pulsed MIG welding copper-nickel alloy
They are available but 70-30 copper-nickel consumables are preferred for welding both the 90-10 and 70-30 alloys due to superior deposition characteristics.
Yes they can be brazed by all processes. Appropriate silver brazing alloys should be used as phosphorus bearing brazing alloys cause a reaction with nickel to form a brittle phosphide phase.
Yes they can using appropriate 65% nickel-copper consumables to avoid iron dilution effects.
Post weld heat treatment is normally unnecessary.
Copper-nickel alloys can harbour slimes, but the attachment of macro-organisms—such as marine grasses and shellfish—is impaired. If these do become attached under quiet conditions, adherence is poor and they can be easily removed mechanically.
If the oxide is tenacious, grit blasting may be required. This should be followed by pickling in a hot 5-10% sulphuric acid solution containing 0.35 g/litre potassium dichromate. The pickled tubes should be rinsed thoroughly in hot fresh water and finally dried in hot air.
It is important that maximum velocity guidelines are adhered to for piping and heat exchanger/condenser service, as high velocities can cause impingement attack. Exposure to sulphides and ammonia in polluted seawater can lead to pitting or high corrosion rates and it is important to avoid these conditions, particularly during commissioning, start up and standby.
Copper and copper-nickel tubes are used for vehicle brake pipes due to their good fatigue and corrosion resistance (especially against salt on the roads), where fluid loss could be disastrous. Because of their ductility, they are easy to fit; they are standard equipment for many cars, fire engines, military vehicles, JCBs and other heavy vehicles.