Copper nickel tubes
A copper nickel tube is made from an alloy of copper that contains a high percentage of nickel. Apart from copper and nickel, there are other elements added to the alloy, such as iron or manganese. These serve the purpose of making the alloy stronger.
Applications/uses of copper nickel tubes
In the past few years, copper nickel tubes have started to be used in more and more industries, give their high resistance to corrosion (especially in seawater). Copper nickel tubes are used in the following domains:
- For the making of complex piping systems (high-pressure water heaters, sea water piping – ships)
- As essential elements in heat exchangers (naval vessels)
- For condensers
- Seawater systems
- Marine hardware
- In the making of boats
- In desalination plants (evaporators)
- For power stations or thermal power plants
- Offshore structures
- For the building of air cooling zones.
Often times, copper nickel tubes are used in heat exchangers on naval vessels. Heat exchangers are actually represented by a set of tubes. These are mounted between tube plates. The whole ensemble is arranged so that it will fit under a protective coverage. The heat exchanger has special holes through which the gas/liquid can enter or exit. The main purpose is for the gas or liquid to be either cooled down or heated. Sometimes, the copper nickel tubes are cooled through internal processes (water-based). In such situations, each tube plate has a water box outside, for the cooling process.
Copper nickel tubes are used in heat exchangers that function through seawater cooling. There are several reasons why copper nickel tubes are chosen, including the high resistance to corrosion (especially since the cooling is done with seawater), the guaranteed strength and flexibility and the life-time resistance. Plus, copper nickel tubes are well known to be resistant against marine deposits, without their integrity being affected.
Titanium – material for heat exchangers tubes
The copper nickel alloy is not the only material used for tubes in heat exchangers. As a matter of fact, titanium is often considered an alternative material to the copper nickel alloy. Titanium is chosen as material for the making of heat exchanger tubes that are going to be used in desalination plants. Just like copper nickel, it delivers an exceptional resistance to corrosion (even in highly corrosive environment, such as seawater).
Any plant that uses a cooling system based on seawater can benefit from the excellent performance titanium delivers. This is the reason why titanium tubes are often found in heat exchangers from desalination plants. Moreover, given its high resistance to corrosion and its existent mechanical properties, using titanium for the making of tubes has allowed for the thickness of the tube walls to be considerably reduced.
As a material chosen for the making of heat exchangers tubes, titanium can guarantee a better rate for the heat transfer, being light and strong. However, it should be mentioned that the heat transfer is not as good as the one delivered by the copper nickel alloy. Also, its specific gravity is half of the copper nickel alloy. Other differences are represented by the coefficient of thermal expansion (almost twice than the one of copper nickel) and the specific heat (bigger than the one of copper nickel).
Returning to the main subject, it should be mentioned that there are two types of copper nickel tubes. The first is C70600 (90/10) and the second is C71500 (70/30). Both of these two types have different mechanical and chemical properties. The first one to have been developed is the 70/30 (1920), being used in condensers for naval vessels. The second is the 90/10 (1950), being used for seawater piping.
Mechanical and chemical properties of copper nickel alloys
|Mechanical and chemical properties||70/30 Copper Nickel||90/10 Copper Nickel|
|Density||8.94 g/cm3||8.94 g/cm3|
|Elastic modulus||150 GPa||140 GPa|
|Electrical conductivity||5% IACS||9% IACS|
|Elongation at break||3-36%||3-35%|
|Melting onset||1170 °C||1100 °C|
|Shear modulus||57 GPa||52 GPa|
|Specific heat capacity||380 J/kg-K||380 J/kg-K|
|Strength to weight ratio||43-65 kN-m/kg||39-63 kN-m/kg|
|Tensile strength (ultimate)||380-580 MPa||350-565 MPa|
|Tensile strength (yield)||125-545 MPa||63-90 MPa|
|Thermal conductivity||29 W/m-K||40 W/m-K|
|Thermal expansion||16.2 µm/m-K||17.1 µm/m-K|
Table source: Make it From
ASTM B111 applicable production standards
The applicable production standards are included within the ASTM B111. This includes the standard specifications for copper alloys, used in general for the making of seamless condenser tubes and Ferrule stock. The specifications related to the copper nickel tubes that are found in naval condensers, evaporators and heat exchangers.
The standard specifications include the chemical requirements for different types of copper nickel alloys, including C70600 and C71500. The first one should have, besides copper, nickel between 9 and 11 and the following as strengthening elements (lead, iron, zinc and manganese). As for C71500, this has copper as primary element, nickel between 29 and 33 and similar strengthening elements as the other one.
Related to tensile requirements, C70600 should exhibit a tensile strength of 45 and yield strength of 35. As for C71500, this should deliver a tensile strength of 52 and a value for 18 for the yield strength. According to the ASTM B111 standard specifications, C70600 can be supplied in two different types of temper, meaning light drawn or annealed. The expansion requirements are as follows: 30 for C70600 and 20 for C71500.
The standard specifications also include the tests that can be made in order to assess the quality standards of the copper nickel tubes. Among these tests, there are: expansion test, flattening test, mercurous nitrate test and non-destructive testing. ASTM B111 also presents the dimensions and permissible variations, delivering useful information about the following aspects: diameter tolerance, wall thickness tolerance and tube length tolerance. Details regarding the density of copper alloys are also presented.
In conclusion, copper nickel tubes are 100% recommended for seawater cooling systems, given their high resistance to corrosion. They also prevent algae and creatures of the marine life (such as mollusks) from destroying their quality. The one thing to keep in mind is that they are not that resistant when the seawater is polluted or stagnant. In order to maintain the quality standards for the copper nickel tubes, it is for the best to avoid such conditions.