Applications of cupronickel alloys in seawater

Cupronickel clad steel

The applications that require economic or engineering considerations solid cupronickel alloy is not perfect hence using the cupronickel clad steel is suggested. Mining, MIG spot welded linings and adhesive bonding are used successfully however for few applications clad steel is bonded.

The clad plate is developed by hot roll bonding, bursting bonding or weld overlaying. The economical breakpoint for specific thickness in three ways is a part of some assumption and thumb rule, cupronickel alloy is roll bonded about 35 mm thickness. Bursting bonding is usually covered above 35mm and weld overlay is the recommended method for thickness above 100mm. Normally the cladding thickness is above 1.5mm and 2 – 3mm is usually considered, wide accumulations are hardly discovered excluding the explosively bonded tube plates or weld overlayerd components.

Besides of lucrative factors, the  application of clad plate, take the advantage of higher strength of the steel bases, are a significant factor in design, if the developed components need to withstand large loads or high pressures.

Cupronickel clad plate is easily welded based on the availability from steel or clad side, welding processes are adequately made. Normally, to avoid the embrittlement because of copper entrance in the steel, root runs are made with cupronickel alloy with high tolerance to iron dilution. If cupronickel alloys are selected for their anti-fouling characteristics, their capping layer on the weld must be made from cupronickel alloy 90/10 to prevent biofouling.

Cupronickel clad plate is a new material and its main application is in water boxes and flash chambers in multistage flash desalination plant in the middle east also used large magnitude of cupronickel clad plate. The major applications for this material are noticed in marine industry.

Cupronickel alloy Welding

While considering the welding of cupronickel alloy, it is important to avoid local changes in chemical composition of weld metal. Specific control on the welding is important. Larger content of nickel creates nominal iron corrosion problems, and it is significant to improve the composition of filler metal slightly through continuous cycles to use the maximum nickel concentration as filler metal for the initial stack and to end with normal cupronickel chemical chemistry.

The choice of filler metals is also influenced by taking the corrosion strength into account with cupronickel alloy 70/30 and 90/10. These are easily solderable. This technique is not normally followed due to insignificant weld strength in the application media in which the use of these materials is recommended and problems of bimetallic corrosion may occur in vigorous conditions.

For the conventional brazing methods, the filler alloys comprising high silver concentration are recommended to decrease the specific corrosion issues.

The alloys of copper-phosphorus, copper-silver-phosphorus brazing alloys must not be used due to their sensitivity to intergranular attack and embrittlement. The extremely cold processed material must be annealed before brazing to avoid extensive penetration and cracking of base metal by brazing of alloy.

Cupronickel alloy for seawater plants

The  cupronickel alloy super metals are widely used for their outstanding resistance to biofouling, corrosion on the running and static marine water. The ships and many offshore plants use marine water cooling applications and various industrial configurations cooling applications. The marine pipes are also configured for conveying ballast, tank cleaning water and steam for emergency fire extinguishing applications.

Seawater is a severe mixture of salts, abrasive solids, gases dissolved and bubbles and organic matter and organisms and its chemistry may change in composition as per the tide and weather. The types of problems noticed in pipeline materials are general corrosion in the fresh marine water, impingement attack by turbulent flow round bends or objects, pitting attack by the interaction with neighbor materials , crevice attack in area of insufficient oxygen and erosion by the mounted solids. Therefore, the piping units are designed to be suitable and affordable during the service life of the configuration rather the economical price.

Normally considered as the very economical material for pipes, carbon steel offers a costlier service as compare to cupronickel alloys, it requires to be replaced one or two times in its service. Comparing the installation costs, it may be more expensive due to the corrosion wastage, it needs to be thicker and heavier than cupronickel alloy. The welding costs for thin gauge cupronickel alloy can be smaller for the same weight of steel. As the water flow resistance of cupronickel alloy is smaller than steel, it is feasible for designs to use the smaller internal diameter without the need to allow for increase in hardness of the surface while in use.

Using noble materials for pipes or organic lines inside the  pipes may result into troubles besides the system. Although fouling may be limited at service speeds, quiescent conditions may result into connection among germs that will then continue to grow while service in seawater units.