Section 3 System arrangements

Storage capacities are to take into account both average and peak loadings, the latter of which may be typically three times the normal usage rate. The personal daily allowance is not to be taken as less than that required by National Authority Regulations, where such a requirement exists.

3.1.2 At least two storage tanks are to be fitted, each with separate means of supplying on-specification fresh water to the distribution main. The tanks are to be sited and be of such dimensions that they are readily accessible to facilitate inspection, cleaning and coating.

3.1.3 The internal structure of fresh water tanks is to be designed to ensure efficient drainage to the suction point. Transfer pump suctions for potable water tanks are to be placed higher than drain connections in order to avoid tank sediment from entering the piping system. Fresh water tanks are not to have a common boundary with another tank that can contain oil or any other liquid except fresh water ballast. Access arrangements to storage tanks are to be arranged and sited clear of sources of possible contamination. Storage tanks and manholes are to be designed to facilitate inspection and cleaning of the tanks while the offshore unit is in operation.

3.1.4 Pipes other than piping containing fresh water of the same quality as the tank contents are not to pass through or be located within a fresh water tank. Pipes carrying fresh water are not to pass through tanks other than fresh water tanks.

3.1.5 The storage facilities for potable water are to be independent of fresh water systems for other uses e.g. boiler feed services. The storage and piping arrangements are to comply with Pt 5, Ch 14, 6 Boiler feed water, condensate and thermal fluid circulation systems of the Rules and Regulations for the Classification of Ships, July 2022.

3.1.6 Water storage tanks are to be provided with means of indicating the water level. The means of routine level inspection is to be by means other than those that require breach of the tank containment such as sounding rods or similar.

3.1.7 Air and filling arrangements for fresh water storage tanks are to be located and arranged to prevent ingress of a contaminant/foreign matter. The arrangements for filling are to include a deck connection to facilitate external loading.

3.1.8 The local strength of fresh water tanks is to comply with Pt 10, Ch 3 Scantling Requirements for ship units and Pt 4, Ch 1, 6 Inspection, workmanship and testing for other units.

3.2.1 Installed sea water desalination plants are to be capable of producing fresh water. A more stringent quality of water production may be necessary in the case of water for use in, for example, boiler feed systems. In these cases, an alternative means of fresh water production is to be provided or a further stage of desalination included in the production arrangements.

3.2.2 The capacity of the plant and tank storage is to be specified by the Owner in the Fresh Water System Design Description.

3.2.3 Two or more plants for desalinating water are to be provided, of sufficient combined capacity to produce sufficient water under defined levels of requirements stated in the Fresh Water System Design Description. Provision of single plant will be considered in conjunction with the operational requirements of the offshore unit and any assigned service restriction.

3.2.4 The design of sea water desalination plants is to be such to permit cleaning, maintenance and repair of any plant whilst the other is in service.

3.2.5 Adequate cleaning arrangements are to be fitted to sea water desalination plants. A suitable safe area is to be designated for system cleaning agents.

3.2.6 In the case of distilling type plants, adequate safeguards are to be incorporated to prevent excess steam pressure. Steam piping arrangements are to comply with Pt 5, Ch 14, 5 Steam piping systems of the Rules and Regulations for the Classification of Ships, July 2022.

3.2.7 Where there are low pressure evaporators using diesel engine jacket water as the heating medium, any corrosion inhibitors in the jacket water are specifically approved for that application.

3.2.8 Means are to be provided to automatically prevent off-specification fresh water from entering systems and storage. The arrangements are to minimise the risk of contamination.

3.3.1 Piping system arrangements are to be such that the supply of fresh water to systems such as chilled water, machinery cooling water and boiler feed water can be made in the event of a single failure or damage of a system or item of equipment. As far as possible, permanent connections to such systems are to be avoided to prevent contamination of the fresh water by additives such as corrosion inhibitors that may be present in the systems. Where it is essential to fit permanent connections, means are to be provided to isolate the systems from the fresh water supplies to ensure that cross-contamination cannot take place when the systems are operating normally.

3.3.2 The design of piping systems is to be consistent with the operational philosophy for the offshore unit and is to be declared in the Fresh Water System Design Description.

3.3.3 All equipment fitted in piping systems is to be readily accessible to facilitate maintenance and survey. For this purpose, valves or cocks are to be fitted between items of equipment and the inlet and outlet pipes in order that any item of equipment may be shut off for opening up and overhauling.

3.3.4 Any filter elements fitted in equipment or piping systems are to be capable of being cleaned and/or changed.

3.3.5 Pressure relief devices, if required, are to be mounted in such a way that it is not possible to isolate them from the part of the system which they are protecting except that, where duplicated, a changeover valve may be fitted that will enable either device to be isolated for maintenance purposes without it being possible to shut off the other device at the same time.

3.3.6 Shipside valves and fittings are to comply with Pt 5, Ch 13, 2.5 Ship-side valves and fittings (other than those on scuppers and sanitary discharges) of the Rules and Regulations for the Classification of Ships, July 2022.

3.3.7 Sea water inlets for desalination plants should be located in order to minimise the potential for ingress of polluted water e.g. from bilge and sanitary discharges from the offshore unit and cooling water inlets and outlets. In order to assess the pollution threat, the discharge dispersal area is to be determined. Sea water inlets should be located as far away from the discharge points as practicable and preferably upstream of the discharge point, considering the most common current direction.

3.3.8 Not less than two sea inlets, as far apart as practicable, are to be provided for pumps supplying sea water to the sea water desalination plant. Where these inlets are shared with other systems, e.g. ballast and sea water cooling, sea water desalination plants are to have dedicated connections with non-return valves at manifold pipes or crossover pipes.

3.3.9 Where a high pressure sea water system is installed (see Pt 5, Ch 13 Ship Piping Systems of the Rules and Regulations for the Classification of Ships, July 2022), provision is to be made for emergency supply to the sea water desalination plant.

3.3.10 Provision is to be made for all sea water to pass through suitable filters before being introduced to the sea water desalination plant. The filters are to be in accordance with the equipment manufacturer's recommendations.

3.3.11 Piping system arrangements and associated equipment are to be capable of operating satisfactorily under the conditions shown in Pt 5, Ch 1, 2 Operating conditions.

3.3.12 The system is to be capable of being cleaned, with arrangements for safely flushing out any cleaning chemical agents after use and for storing or disposing of them safely.

3.3.13 Gaskets and sealing materials in contact with fresh water are to be suitable for the containment of fresh water in accordance with a recognised National or International Standard e.g. NSF/ANSI 61 - Drinking Water System Components - Health Effects

3.4.1 Two or more water pumps are to be provided of sufficient capacity to supply the fresh water distribution system with any one pump out of action.

3.4.2 The fresh water distribution system is to be capable of providing a steady flow of water at any point in the system in accordance with the Fresh Water System Design Description. Where a pneumatically pressurised tank arrangement is used, the tank is to be provided with water level indication and a means of indicating the pressure. The compressed air connection to the pressurised tank is to incorporate a non-return valve arrangement at the tank to prevent the possibility of water entering the compressed air system and it is recommended that the connection be made via a portable hose connection.

3.4.3 Each user or group of users of fresh water are to be provided with means of isolation such that the distribution system can continue to function when a user or group of users has been isolated.

3.4.4 Air vent and drain points are to be provided throughout the system at all high and low points.

3.4.5 Provision is to be made to connect an alternative source of fresh water supply in emergency conditions. Where the fresh water main is unavailable, stand-by arrangements are to be provided for fresh water supplies, which meet the required water quality, to medical spaces and galleys. The supply arrangements in emergency conditions are to be included in the Fresh Water System Design Description and agreed by the Owner.

3.4.6 There are to be no permanent connections between fresh water and sea water systems. Where emergency connections have been designed for the supply of fresh water to fresh and sea water cooled equipment, the fresh water is to be supplied by means of a portable hose with screw down non-return valve isolation or equivalent arrangements at the connection to the equipment.

3.4.7 Calorifiers are to be provided with drainage arrangements and adequate access to enable cleaning.

3.4.8 Provision is to be made to sterilise all water supplies (including fresh water taken from shore, water barge or supply ship) for potable water by chlorination or by an equivalent sterilisation method. The residual quantities of chlorine and chlorodioxide are to be in accordance with ISO 15748-1.

3.4.9 The water supply arrangements for potable water are to be independent of other services wherever possible. Where there are no alternative supply arrangements to other services requiring fresh water (e.g. machinery cooling water, purifiers or a fresh water WC flushing system), a clear air break is to be provided in the fresh water supply pipe to such a system or tank. If it is impracticable to provide a clear air break, the supply pipe to each system is to be provided with an efficient non-return valve and a vacuum breaker or back-flow preventer.

3.4.10 Physical measures are to be in place to prevent incorrect connection between parts of the system which use different chemicals during all normal and reasonably foreseeable abnormal conditions.

3.5.1 Gas detection for hazardous gases resulting from water purification processes (e.g. chlorine, sulphur dioxide, ammonia, ozone and chlorine dioxide) is to comply with Pt 7, Ch 2, 17 Gas detection of the Rules and Regulations for the Classification of Ships, July 2022.