Copper alloys have a long history of proven performance as durable marine materials for applications in contact with seawater
Copper alloys have been widely used in seawater for many years for applications such as piping, propellers, valves, pumps and heat exchanger tubing, due to their combination of properties: corrosion resistance, durability, thermal conductivity, ease of forming and low susceptibility to attachment of marine macro-organisms.
Copper alloys offer a range of materials to suit different designs, manufacturing techniques, applications and operating environments and can be grouped by alloy families:
Coppers
In addition to high thermal and electrical conductivity, coppers have good corrosion resistance in the marine atmosphere and seawater, showing very little pitting or crevice corrosion.
Alloy | Applications | Properties |
Engineering copper |
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• 0.2% proof strength 50-340 N/mm2 • Tensile strength 200-400 N/mm2 • High thermal and electrical conductivity • Good corrosion resistance in the marine atmosphere and seawater • Low susceptibility to the attachment of marine grasses and shellfish |
Copper-nickels
The addition of nickel (30% in 70/30, 10% in 90/10) enhances strength, durability and corrosion resistance as well as 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 in seawater.
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.
Alloys with higher nickel content, and those which are more highly alloyed with chromium, aluminium and tin, are used where greater resistance to flow conditions, sand abrasion, wear and galling are required, as well as higher mechanical properties or castability.
Alloy | Applications | Properties | |
Copper-nickels (70/30, 90/10) |
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Copper-nickel-chromium |
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High-strength copper-nickels | Cu-Ni-Al |
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Cu-Ni-Sn |
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Bronzes
Traditionally, copper-tin alloys are associated with the word ‘bronze’. However, today, the term refers to copper-tin alloys with further alloy additions to give improved strength such as copper-tin-zinc alloys (gunmetals) and copper-tin-phosphorus alloys (phosphor bronzes). Importantly, it also now covers copper alloys which do not have a tin addition but are considered to provide the high qualities associated with the word bronze including copper-silicon (silicon bronzes) and copper-aluminium (aluminium bronzes). Bronzes have superior resistance to ammonia stress corrosion cracking compared with brasses.
Alloy | Applications | Properties |
Phosphor bronze (cast and wrought) |
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Silicon bronze |
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Aluminium bronze |
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Nickel aluminium bronze, NAB (cast and wrought)
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Aluminium silicon bronze |
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Gunmetal (castings) |
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Brasses
Copper-zinc alloys are commonly known as brasses and often have small additions of other elements to enhance their properties, such as tin or aluminium to improve corrosion resistance, or arsenic for inhibition of dezincification or lead to aid pressure tightness or machining. Their strength increases with zinc content and also with additional alloying elements.
Alloy | Applications | Properties |
Aluminium brass |
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Naval brass |
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Aluminium-nickel-silicon brass |
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Dezincification-resistant brass (DZR) |
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Manganese bronze (cast and wrought) |
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UR 30TM (proprietary alloy) |
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Copper-beryllium
Copper-beryllium has high strength, corrosion resistance and galling resistance, and is immune to hydrogen embrittlement and chloride-induced stress corrosion cracking.
Alloy | Applications | Properties |
Copper-beryllium |
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Copper Alloys for Marine Environments
Copper Alloys for Marine Environments 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.
Copper Alloys in Seawater: Avoidance of Corrosion
Copper Alloys in Seawater: Avoidance of Corrosion gives practical guidance for engineers on the avoidance of corrosion in copper alloys for seawater applications.
For many years, copper alloys have been widely used in seawater and related brines, such as in thermal desalination plants, generally with excellent results.
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.
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
FAQs
Q1 Which copper alloy has the best corrosion resistance in seawater?
Various copper alloys have particular strengths under specific sea water conditions but on balance 90-10 copper-nickel has excellent corrosion resistance in many applications and is perhaps the most versatile. There is a detailed description of the properties and applications of this and other popular copper nickel alloys on the www.coppernickel.org website. Of course, aluminium bronze alloys, particularly nickel aluminium bronze, are also recognised for their corrosion resistance in severe seawater conditions and for that reason also have established applications as propellers and pumps and valves.
Q2 Are 90-10 and 70-30 copper-nickels susceptible to stress corrosion cracking?
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.
Q3 Are copper-nickel alloys susceptible to the attachment of marine organisms in seawater?
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.
Q4 Is Naval Brass CZ112 (1-1.4% tin) still available?
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.
Q5 What are the critical pitting and crevice corrosion temperatures for copper-nickels in chloride environments?
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.
Q6 What does the term DEF STAN (DStan) mean?
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.
Q7 What types of corrosion are copper-nickels sensitive to?
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.org
Visit the dedicated web section on copper-nickels for a broad technical overview of copper-nickel alloys and a wealth of information/data useful for good practices in design, fabrication and application.
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