The main applications for the engineering grades 90-10 and 70-30 copper-nickel alloys are in seawater piping, heat exchangers and condensers. The main industries are marine-based and cover thermal desalination, offshore oil and gas, power generation and commercial and naval shipping. Copper-nickel alloys are also used for hydraulic tubing, including brake tubing.

Desalination

Copper-nickel alloys are widely used in multi-stage flash (MSF) and multiple effect distillation (MED) desalination plants. In addition to cost considerations, the alloy choice depends on corrosion conditions in the various sections of the plant.

MSF plant

An MSF plant uses a process that essentially consists of a series of tube/plate heat exchangers that can reach temperatures of 120^oC in the brine heater, decreasing as the flashing brine and distillate travels through the plant through to the heat recovery and then the heat rejection sections. The brine heater and heat recovery sections require exposure to hot de-aerated seawater and brine, whereas the heat rejection section uses natural seawater. The tubing exteriors handle water vapour and non-condensable gases.

Typical alloy choices are:

Table: Typical applications for Copper-Nickel Alloys in MSF desalination plant

MED plant

There are two types of MED plants; one uses thermo-compression distillation (TCD), the other mechanical vapour compression (MVD); TCD is the more common. There can be several evaporator stages and a final heat rejection section. Vapour is introduced into the first evaporator at temperatures of around 75°C.
Copper alloys are the primary choice for tubes in the evaporator sections. Here, the top environment is fully aerated with the oxygen level decreasing in the lower sections. Copper-nickel is also sometimes used in the final heat recovery exchanger, which operates fully aerated.

Offshore Oil and Gas

Copper-nickel alloys have found applications on both platforms and FPSOs (Floating Production Storage and Offloading vessels) and are used in seawater, cooling and firewater/deluge systems. They are favoured in warmer climates for their resistance to chloride crevice corrosion and stress corrosion cracking.

The 90-10 copper nickel alloy has also been used for splash zone sheathing on platform legs in Phase 1 of the Morecambe Field, UK.

Power generation

Generating electricity in both nuclear and fossil-fuelled power plants involves important heat transfer processes; steam generators, heat exchangers, coolers, condensers, tanks, pipework, valves and fittings. Copper-nickel alloys are well-suited for these applications, as they can be used successfully in a range of environments, including clean seawater with high-total dissolved solids, brackish water, fresh water and cooling tower water.

Shipbuilding and Repair

The 90-10 and 70-30 copper-nickel alloys were originally developed for naval condensers and seawater piping more than 60 years ago. It is a testament to their resilience in severe conditions that they are still used in many of the world’s navies. They are also used on FPSOs and commercial shipping.

Seawater is used for cooling, tank cleaning and heating, ballast, waste disposal, firefighting and, through distillation, as a source of fresh water for boiler feed water and sanitary hot and cold water. All require piping systems that consist of pumps, valves, pipes and fittings. For cooling systems, heat exchangers are also required.

Applications for copper-nickel alloys can include condensers, coolers and other heat exchangers, onboard seawater desalination plants, systems for compressed air, sanitary systems, bilge, ballast water, brine, fire mains and sprinklers, fuel oil, lube oil, warm water heating, grey and black water, hydraulic lines and tank heating.
A novel application is that of sheathing or plate for boat hulls. 

A few dozen hulls have been fabricated this way, using 90-10 or 70-30 Copper-Nickel.