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Seawater

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Copper-Nickel Alloys used in Shipbuilding and Repair

Ship Systems Hulls

   SHIP SYSTEMS

Sea water is used for cooling, tank cleaning and heating, ballasting, waste disposal, firefighting and by distillation as a source of fresh water for boiler feed water and sanitary hot and cold water. All require piping systems which essentially consist of pumps valves, pipes and fittings. In cooling systems, heat exchangers are also required.

Applications for Cu-Ni alloys include the following: -

Condensers, coolers and other heat exchangers, seawater desalination plant and systems for compressed air, sanitary cold and hot water, bilge, ballast water, brine, fire mains and sprinklers, fuel oil, lube oil, warm water heating, grey and black water, hydraulic lines and tank heating.

   Sea water Cooling Systems

Conventional sea water systems consist of shell and tube heat exchangers supplied with seawater through a piping system; the power being supplied by electrically driven centrifugal pumps. Flow is controlled by valves. The cooling system for the main engine is normally separate from that used for auxiliary units. The main engine systems in diesel-powered ships consist of heat exchangers, water jacket, lubricating oil and charge air coolers. Cu-Ni can be used for these applications.

Centralised cooling systems involve one large seawater cooled titanium plate heat exchanger to cool fresh water which circulates through various heat exchangers in the engine room. Inhibitors can be used to control corrosion on the fresh water side and therefore Cu-Nis for their good resistance to seawater are confined to the primary side and inlet pipes.

For steam ships, such as nuclear powered ships or LNG tankers, Cu-Ni is of potential for the condensers and sea water systems. The use of scoop intake systems on steam turbine powered ships normally require 70-30 or 66-30-2-2 Cu-Ni alloys with high resistance to impingement corrosion.

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   Bilge and Ballast Systems

These are used to empty bilges and to fill or empty cargo and ballast spaces within the ship with sea water. The systems operate intermittently, often once per week. The pipes are not exposed to flowing sea water for lengthy times but could spend most of their life holding stagnant sea water. In oil tankers, the cargo pipes and pumps are often used for ballast purposes as the quantities of sea water are large and require massive pipes and pumps to handle the volume efficiently.

Cu-Ni's can be used in these systems in areas not exposed to polluted, stagnant water for prolonged times. Cu-Ni's are particularly suitable for pressure and return lines of hydraulically operated components such as cargo and ballast pumps and control valves.

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   Sanitary Systems

Discharges from sanitary systems, cabin and galley drains are collected and passed through a sewage treatment plant before being discharged overboard. Cu-Ni piping can be used to supply water to these systems.

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   Fire Fighting Systems

Sea water is used for firefighting on ships and is distributed throughout the ship by a fire main served by its own pump. This system is often used for other purposes such as deck washing being used frequently but for only comparatively short periods.

90-10 Cu-Ni is used for this application.

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   Inert Gas Systems

These are used on tankers to blanket cargo tanks with seawater scrubbed flue gas. Sea water supply uses 90-10 Cu-Ni pipes. However, the effluent is acidic and is normally handled by other materials.

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   Deck Steam Pipes

These are not part of the sea water system but are important on steam-powered tankers. These lines are used to carry steam-to-steam powered auxiliary equipment, such as windlasses, and pass along the deck of the tanker where they are exposed to the marine atmosphere. 90-10 and 70-30 Cu-Ni's are used for this piping and also condensate return lines.

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   Cargo Tank Heating Coils

Where cargoes are too viscous to be pumped at ambient temperatures, tank heating systems are required. This is achieved by passing steam through a system of tank heating coils. 90- 10 Cu-Ni can be used for this task with appropriate cargoes including asphalt and bitumen.

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   Feed lines to desalination plant

Fresh water is normally produced by distillation in compact desalinators. These are often constructed in 90-10 Cu-Ni, the system pipe work being the same alloy. Hot fresh water is passed through the tubes of a heat exchanger in the desalinator causing the sea water to boil. The resulting vapour is condensed and collected after passing through demister and deflector plates. Brine is discharged or re-circulated through the system in 90-10 Cu-Ni piping.

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   Hydraulic and Pneumatic Systems

Most ships have remote controlled equipment such as valves, which are operated by hydraulic or pneumatic pressure. These can be used for cargo handling systems, hatch covers and engine controls. For high-pressure systems, 90-10 Cu-Ni is a normal choice whereas for very high pressures, the 70-30 alloy may be used.

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   Chiller Systems

Chiller systems are required to meet the demands for top-quality fish and the post-catch refrigeration requirements in the fishing industry. They are also required to control temperature in the cargo holds, to provide both heating, ventilating and air conditioning (HVAC) and provision plants for cruise vessels and other passenger ships, and other marine type refrigeration needs. Water-cooled condensing units are designed and manufactured using cleanable, shell-and-tube condensers with tubes in Cu-Ni for seawater and Cu for freshwater application.

To improve condenser and condensing unit efficiencies, internally and externally enhanced tubes have been developed and are extensively being used to increase the heat transfer capabilities of the tubes in the condenser while minimizing the fouling impact.

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   HULLS

Ship And Boat Hulls

Cu-Ni possesses the ideal requirements for a boat hull. With both good resistance to corrosion and macrofouling, coatings are unnecessary, providing both savings in fuel and hull maintenance time and cost. Over the last 30 years, experience has been gained in constructing hulls using different product forms of Cu-Ni.

  • Construction of the hull from Cu-Ni alloy plate onto steel or Cu-Ni frames
  • Construction of the hull from Cu-Ni roll-bonded onto steel plate
  • Cladding a fibreglass, wood or steel hull with Cu-Ni alloy sheet or foil.
With tight restrictions on the use of organo-tin copolymer coatings and the quest for alternative antifoulants underway, Cu-Ni as a boat hull material can offer many practical benefits.

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