Marine

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:

Copper
Copper-nickels
Bronzes
Brasses
Copper-beryllium

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
  • Seawater piping
  • Heat exchangers
  • Fuel lines
  • Nails
• 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)
  • Seawater cooling and firewater systems
  • Heat exchangers
  • Condensers and piping
  • Offshore platform leg and riser sheathing
  • MSF desalination units
  • Aquaculture cages
  • Boat hulls
  • 0.2% proof strength 100-450 N/mm2
  • Tensile strength 290-520 N/mm2
  • High corrosion resistance. Piping typically used up to 100oC
  • Good thermal conductivity
  • Ductile
  • Weldable
  • Low susceptibility to the attachment of marine grasses and shellfish
Copper-nickel-chromium
  • Wrought condenser tubing
  • Cast seawater pump and valve components
High-strength copper-nickels Cu-Ni-Al
  • Shafts and bearing bushes
  • Bolting, pump and valve trim
  • Gears
  • Fasteners
  • 0.2% proof strength 400-630 N/mm2
  • Tensile strength 710-850 N/mm2
  • Can be precipitation hardened
  • Good corrosion resistance
  • High strength
  • Bearing and anti-galling properties
  • Low susceptibility to the attachment of marine grasses and shellfish
Cu-Ni-Sn
  • Bearings
  • Drill components
  • Subsea connectors
  • Valve actuator stems and lifting nuts
  • Subsea manifold and ROV lock-on devices
  • Seawater pump components
  • 0.2% proof strength 620-1030 N/mm2
  • Tensile strength 825-1100 N/mm2
  • Good corrosion resistance
  • High strength
  • Bearing and anti-galling properties
  • Low susceptibility to the attachment of marine grasses and shellfish

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)
  • Springs
  • Bearings
  • Gears
  • Fasteners
  • Rods
  • Slides
  • 0.2% proof strength 170-1000 N/mm2
  • Tensile strength 390-1100 N/mm2
  • Good corrosion resistance with little tendency to pit
Silicon bronze
  • Fasteners – screws, nuts, bolts, washers, pins, lag bolts and staples
  • 0.2% proof strength 200-890 N/mm2
  • Tensile strength 380-900 N/mm2
  • Very good resistance to corrosion and stress corrosion
Aluminium bronze
  • Sea cocks
  • Pumps
  • Valves
  • Bushes
  • 0.2% proof strength 280-680 N/mm2
  • Tensile strength 600-850 N/mm2
  • Excellent resistance to cavitation
  • Complex metallurgical structure requiring careful processing
Nickel aluminium bronze, NAB (cast and wrought)

 

  • Propellers and shafts
  • Pumps
  • Valves
  • Bushing and bearings
  • Fasteners
  • Tube plate for titanium tubing in condensers
  • 0.2% proof strength 280-680 N/mm2
  • Tensile strength 600-850 N/mm2
  • Excellent resistance to cavitation
  • Complex metallurgical structure requiring careful processing
Aluminium silicon bronze
  • Minesweeper components
  • As above plus low magnetic permeability
Gunmetal (castings)
  • Pumps
  • Valves
  • Stern tubes
  • Deck fittings
  • Gears and bearings
  • Bollards
  • Fairleads
  • Lead can ensure pressure tightness in valves and pumps
  • Not prone to dezincification, ammonia stress corrosion or pitting

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
  • Seawater tube and pipe
  • 0.2% proof strength 120-380 N/mm2
  • tensile strength 280-580 N/mm2
  • Tough, more ductile than copper
  • Can be subject to dezincification. This can be controlled by alloying or cathodic protection (CP)
  • Susceptible to ammonia stress corrosion cracking, particularly in marine atmospheres. Can be prevented by stress relieving and, when submerged, by use of cathodic protection
  • Aluminium brass (an alpha brass used for tube and pipe) contains As to prevent dezincification. Tin is used in naval brass (alpha beta brass) and will slow down dezincification e.g. in heat exchanger tube plates
  • Tungum® (commonly used for marine hydraulic control and instrument lines) contains Al, Ni and Si. High resistance to dezincification
  • High tensile brass (can be called manganese bronze) needs cathodic protection to avoid dezincification
Naval brass
  • Tubesheet
Aluminium-nickel-silicon brass
  • Hydraulic, pneumatic and instrument lines
Dezincification-resistant brass (DZR)
  • Through hull fittings
Manganese bronze (cast and wrought)
  • Propellers
  • Shafts
  • Deck fittings
  • Yacht winches
UR 30TM (proprietary alloy)
  • Aquaculture

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
  • Springs
  • Drill components
  • Subsea connectors
  • Actuators
  • Locking rings
  • Lifting nuts
  • Valve gates
  • 0.2% proof strength 200-1300 N/mm2
  • Tensile strength 410-1400 N/mm2
  • In age hardened condition can achieve highest strength of any copper alloy
  • Low corrosion rates
  • High galling resistance.
  • Low susceptibility to the attachment of marine grasses and shellfish

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.

Copper Alloys for Marine Environments

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.

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.

Click here to view the publication page, with individual sections available for download.

Click here to download it in full.

View the Series of 5 Training Videos on Welding of Copper-nickel

  1. Cleaning and preparation for welding of copper-nickel alloy
  2. TIG welding copper-nickel alloy
  3. Pipe welding copper-nickel alloy
  4. Shielded metal arc welding copper-nickel alloy
  5. Pulsed MIG welding copper-nickel alloy

FAQs

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.

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.

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.

I am designing a hinge in a lock gate which is under water and, since access is difficult, I am looking for a maintenance free bearing for a hinge. What do you suggest?

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.

I have a number of machined aluminium bronze components which are to be packed in wooden boxes and shipped to Australia. How do I avoid corrosion/staining?

The key is to clean thoroughly, remove water, protect and keep dry:

  1. After cleaning dry thoroughly using a de watering fluid such as WD40.
  2. Remove displaced water with forced warm air.
  3. Coat with protective coating such as benzotriazole inhibitor or a block copolymer.
  4. Pack into benzotriazole treated paper lined wooden boxes. Moisture absorbent granules may also be used to keep the air inside the boxes dry.
  5. Remove the coatings with a phosphoric based solution.
  6. Dry thoroughly.
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.

We have supplied copper nickel tubes to the UK from overseas. The wooden boxes containing the tubes became saturated with rain water at the port of exit and on arrival in the UK were heavily tarnished (green). Is there any way of cleaning the tubes?

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.

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.

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.

I am a manufacturer of hose end couplings in brass used in an oil refinery. They are subject to salt spray. What brass should I use?

Use a corrosion resistant leaded naval brass, CW 712R (CZ112).

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.

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.