Tuesday, 12 June 2012

ships freshwater systems

ships freshwater systems
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Freshwater loading and supply arrangements

Fresh water loaded from shore mains or water barge- should be done so via dedicated hoses. Every effort should be made to avoid possible contamination of the loading line and manifold Treatment of freshwater- All fresh water loaded from shore or barge should be tested and treated to ensure a residual chloride reading of 0.2ppm

Fresh water from low pressure evaporator or reverse osmosis- Should only be made when outside 25 miles from shore or 50 miles from an estuary. The suctions should be separate to other suctions and forward of effluent outlets. Antifouling equipment used should be of an approved type suitable for use with potable water production.

New ships fitted with an ultra-violet steriliser must in addition be fitted with an automatic chlorinator system. As an alternative full flow silver ion systems may be used

Alternative means for sterilisation may be submitted to the classification society for approval.

Storage tank arrangements

Storage tanks and delivery systems intended for drinking or washing water-It is preferable that systems used for drinking and washing are kept isolated from the system supplying such circuits as jacket water and oil purifier seal water. Where this is impractical then effort must be made, say by the fitting of efficient non-return valves or an air break in the pipe work to prevent back contamination. Sitting of tanks-Tanks designed for drinking water should be sited to allow easy inspection and maintenance. Fore peaks which are susceptible to damage should not be used or aft peaks which are too difficult to clean. No freshwater tank should be sited to an oil tank.
Construction-The internal structure should allow easy drainage and cleaning. The tank should be pressure tested every 10 years to ensure no seepage in or out, particularly where the tank is adjacent to the ships side. Manholes should be of an adequate size and raised above deck level. Only pipework containing the same quality of water in the tanks should be allowed to pass through the tank. Goose necks should be suitably designed to prevent the ingress of sea water
Coatings-Coatings should be applied and allowed to cure strictly with adherence of the manufacturers instructions.
Distribution systems

Water treatment, filters, mineralises, softeners etc.-Water supplied to evaporators and reverse osmosis plant should pass through a suitable filtration system. A form of sterilisation must be applied to fresh water. Neutralisers and mineralises may be optionally fitted to make the water more palatable. Pumps-must be dedicated for freshwater only with no cross connections.
Calorifiers, hydrophore tanks etc.-Should be designed to allow proper cleaning and prevent sludge and scale build up
Design of fw systems-Dead legs are to be avoided, with temperatures between 15-50oC these can promote bacterial growth. Hot water line should be suitably insulated especially where they run adjacent to the cold water line. Special attention to the toxicity of material used in jointing and mechanical of the pump should be made at the design stage.
Maintenance

Freshwater storage tanks-These to be inspected every 12mths an refilled with sterilised water following cleaning with a 50ppm chlorine solution Distribution system-Including sterilisation plant, should come under the planned maintenance system and regularly inspected. Chlorinators should be raised to 70oC before opening for inspection to kill of any bacteria colonies.
Opportunity should be taken at refits to flush the system with 50ppm chlorine solution.
Shower heads and taps should be cleaned in a similar solution every 3 months.
Where water production systems utilise treated water for cooling (Condensate cooled evap on steam ship) or heating (jacket water evap on motor ship) only approved treatment chemicals should be used.

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