Copper-nickel Alloys are used for Seawater Systems, Desalination Units and to Protect Offshore Structures
Copper, the most noble of the metals in common use, has excellent resistance to corrosion in the atmosphere and in fresh water. In seawater, the copper-nickel alloys have superior resistance to corrosion, coupled with excellent anti-fouling properties.
Copper cladding of wooden-hulled warships, introduced by the Royal Navy in the 18th century to prevent damage by wood-boring insects and worms such as the teredo, was discovered to prevent biofouling by weed and molluscs. This meant that ships could stay at sea for long periods without cleaning. Nelson’s successful blockade tactics, and subsequent victory at Trafalgar, was partly due to the superior speed of his clean-hulled ships.
The addition of nickel to copper improves its strength and durability, and also the resistance to corrosion and erosion in natural waters, including seawater, brackish and treated water. The alloys also show excellent resistance to stress-corrosion cracking and corrosion fatigue.
The added advantage of high resistance to macro-fouling provides a material ideal for use in marine and saltwater environments for commercial and naval shipping, desalination plants, heat exchange equipment, seawater and hydraulic pipelines, oil rigs and platforms, fish farming cages, seawater intake screens, offshore renewables, ship and boat hulls and more.
Copper Alloys for Marine Environments
Copper Alloys for Marine Environments is a CDA publication that provides engineers with an appreciation of copper alloys commonly used in marine applications. It gives an overview of the range of alloys and their properties, with references and sources for further information.
Click here to download the publication
Copper Alloys in Seawater: Avoidance of Corrosion
Copper Alloys in Seawater: Avoidance of Corrosion is a CDA publication that gives practical guidance for engineers on the avoidance of corrosion in copper alloys for seawater applications.
Copper alloys have been widely used in seawater and related brines, such as in thermal desalination plants, for many years, generally with excellent results. They are commonly used for piping, valves, pumps and heat exchanger tubing, but have found many other applications.
Occasionally there are failures due to corrosion, and in many cases these could be avoided by following some simple design recommendations, by selecting an alternative copper alloy, or by using a simple preventative strategy. This publication covers the most common types of corrosion and shows simple methods to avoid them. If these are implemented at the design stage, it can save a large expenditure after a corrosion failure.
The guide has been written principally for marine, mechanical and other engineers who have to select materials of construction but do not have a corrosion background.
Click here to view the publication page, with individual sections available for download.
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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 do not experience chloride or sulphide stress corrosion. They have a high resistance to ammonia stress corrosion compared to other copper alloys and do not require a stress relief anneal for seawater service.
As for copper, copper-nickels have a high inherent resistance to macrofouling. However, there will be normally be colonisation of microfouling (slimes).
Cast tin bronze bearing which will have the required corrosion resistance. These are available with carefully machined holes which are filled with a solid lubricant consisting of graphite plus oil. During service a thin film of lubricant is produced as the bearing slowly wears.
The key is to clean thoroughly, remove water, protect and keep dry:
- After cleaning dry thoroughly using a de watering fluid such as WD40.
- Remove displaced water with forced warm air.
- Coat with protective coating such as benzotriazole inhibitor or a block copolymer.
- Pack into benzotriazole treated paper lined wooden boxes. Moisture absorbent granules may also be used to keep the air inside the boxes dry.
- Remove the coatings with a phosphoric based solution.
- Dry thoroughly.
No, the nearest alloy to Naval Brass is a leaded brass CW712R, available in rod, bar and wire. For sheet and plate the UNS Alloy C46400 (0.5 to 1.0% tin ) is used.
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.
Copper-nickels do not behave in the same way as stainless steels do towards corrosion by chlorides and these parameters are not appropriate to them. They do not have a critical temperature limit.
These are the engineering standards prepared for material for use by the Ministry of Defence. They have replaced NES (Naval Engineering Standards), which in their turn replaced DGS (Directorate General Ships) standards.
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.
The copper-nickel needs to be freely exposed and not galvanically connected to less noble alloys to get the best overall resistance to biofouling. Prolonged exposure to quiet waters might lead to some colonisation of macrofouling but is normally loosely attached and can often be removed very easily by a light scraping action.
www.coppernickel.org provides a detailed overview of copper-nickel with data to allow good practices in design, fabrication and application.
Find out more information on our CPD workshop ‘Alloys in the Marine Environment’
The aim of this publication is to provide engineers with an appreciation of copper alloys commonly used in marine applications. It will provide an overview of the range of alloys and their properties, and give references and
sources for further information.
This publication focuses on the properties and corrosion resistance of a wide range of copper alloys used for seawater service – ranging from commercial grades of copper through copper-nickels, bronze, brass and copper beryllium. It allows the reader to understand potential types of corrosion mechanisms for the different alloy types and how to avoid them.