Applications of materials in marine water

Cupronickel alloys

Copper-Nickel alloys such as 90/10 and 70/30 are used for heat exchanger tubings for several years. The demand for high consistency in major modern plants has preferred the service of cupronickels instead the conventional brass.

In the major significance has been the development of desalination market. Around 75% of this capacity includes distillation procedures, multistage flash distillation is very popular.

The plants include heavy duty heat exchangers and they demand tubing in the large scale. For every meter cube per day of output needs around 25 kg of tubing, the installed capacity is around 200,000 tonnes.

Besides of tubing applications, a vast growth in various applications where weldability and fabricability are needed in addition of resistance to attack. Cupronickel 90/10 offers good weldability  and is producible in complex shapes like water boxes and ship hulls. Major increase has been observed in recent times in the applications where making is included such as seawater pipes. Large tones of cupronickel 90/10 alloy pipes are installed in the various plants in the coastal oil industry.

Initially in the Gulf of Mexico practice, galvanized steel marine units were utilized. They couldn’t offer consistent performance and in the vigorous service conditions their maintenance expenses were very intolerable. The cupronickel alloy 90/10 has offered economical and consistent service. The application of cupronickel has now increased surpassing North Sea to the areas like Arabian Gulf and Brazil.

Cupronickel 90/10 alloy is also made as clad plate that carbon steel is cladded with a cupronickel alloy’s layer. It is used in large magnitudes in the desalination plants for water boxes and pipes of big diameters and also prevented the corrosion issues that occurred with coated steel water boxes and pipes.

In the latest times in Italy, an array of fireboats with hulls made from cupronickel 90/10 alloy steel has been built. These vessels prevent attack of fouling and corrosion because of copper alloy hull. The attractive characteristics of cupronickel alloy 90/10, combining with its fabricability and weldability, confirms that this versatile material is used widely in marine applications.

Stainless Steel

Issues of pitting and crevice attack have forced designers to use stainless steel grades in marine water. The benefits of other characteristics can be received, although the resistance to rapidly flowing marine water for outstanding service in few applications. The common use is for pump impellers and shafts. Several pumps use Super Duplex Stainless steel 2507 for these components and offered the pump is not left standing for prolong periods, issues with crevice corrosion are nominal.

Where static conditions are assumed, benefit is usually taken of the cathodic security offered to
austenitic steel grades by Nickel Resist cast irons. The alloys containing high nickel content offer supreme corrosion resistance in marine conditions and are usually used for pump casing components like inlet bell mouths, column pipes and discharge heads in big vertical pumps like are used for flowing marine water in MSF and power production units. Various factors apply to valve stems and valve trim offer good resistance to turbulent marine water makes stainless steels captivating.

The rapid use of steel grades in heat exchanger tubes is noticed. The steel grades are perfect for power plant condenser tubing and to control pollution of marine water specifically where it contains hydrogen sulfide- rules the use of cupronickel alloys.

In the desalination plants, large magnitudes of steel grades are used in applications like vent piping, distillate trays and transfer troughs, evaporator vessel linings and demisters.

In the latest plants, the whole distillate system is usually in stainless steel 316 as test has described that this highly pure water can be attacking to carbon steel. The low oxygen levels in these plants allow stainless steels are used to handle boiling sea water and brine. These grades also avoid stress corrosion cracking in the hot conditions.

The advanced use for stainless steels is in reverse osmosis, a membrane process allows fresh water to be developed from marine water by pressure. In the RO process, natural aerated marine water is utilized that means stainless steel 316 experiences crevice attack at the various joints related with the numerous modules used to fabricate these plants.

The piping material in the plants is being enhanced to high alloy steels as in the piping system. The major marine markets include the development of ship tanks for handling chemicals, solvents and wine, fittings for craft and fasteners.

This method of weld overlaying of crucial areas with a very resistant material like alloy 625 is commonly used for marine and offshore applications.

Conclusions

Nickel based alloys like cupronickels, stainless steels and nickel based alloys have characteristics featured for marine applications. Advanced needs for high reliability and small life cycle costs are preferable to result in enhanced used of these alloys in the marine fields.

Nickel alloys are used in pollution control, nuclear power, solar energy, coal gas plants, gas turbines and in various phases of industrial production features high temperature service is allowing the designers to further test the high temperature properties of construction materials. The latest processes are commercialized and as production capacities are improved, temperature normally becomes necessary factor in the selection of materials.

The stainless steels are normally selected initially, depending on the corrosion resistance and on the base of their mechanical properties. With improvement in the service temperature, high temperature characteristics quickly become the major concern. The stainless steels are highly versatile in its potential to meet the requirements of high temperature applications.