Section 7 Cargo Pressure/Temperature Control

701.

General

1. Unless the entire cargo system is designed to withstand the full pressure gauge of the cargo under conditions of the upper ambient design temperatures, maintenance of the cargo tank pressure below the MARVS are to be provided by one or more of the following means, except as otherwise pro- vided in 701.

(1) a system which regulates the pressure in the cargo tanks by the use of mechanical refrigeration;

(2) a system allowing the product to warm up and increase in pressure. The insulation or cargo tank design pressure or both is to be adequate to provide for a suitable margin for the oper ating time and temperatures involved. The system is to be acceptable to this Society in each case.

(3) other systems acceptable to the Society;

2. The systems required by Par 1 are to be constructed, fitted and tested to the satisfaction of the Society. Materials used in their construction are to be suitable for use with the cargoes to be carried. For normal service, the upper ambient design temperatures are to be:

- sea : 32°C

- air : 45°C.

For service in especially hot or cold zones these design temperatures are to be increased or re- duced, as appropriate, by the Society.

702.

1.

Refrigeration systems

A refrigeration system is to consist of one or more units capable of maintaining the required cargo pressure/temperature under conditions of the upper ambient design temperatures. Unless an alter- native means of controlling the cargo pressure/temperature is provided to the satisfaction of the Society, a stand-by unit (or units) affording spare capacity at least equal to the largest required sin- gle unit are to be provided. A stand-by unit is to consist of a compressor with its driving motor, control system and any necessary fittings to permit operation independently of the normal service units. A stand-by heat exchanger is to be provided unless the normal heat exchanger for the unit has an excess capacity of at least 25 % of the largest required capacity. Separate piping systems are not required.

2. Where cooling water is required in refrigeration systems, an adequate supply are to be provided by a pump or pumps used exclusively for this purpose. This pump or these pumps are to have at least two sea suction lines, where practicable leading from sea-chests, one port and one starboard. A spare pump of adequate capacity are to be provided, which may be a pump used for other serv- ices so long as its use for cooling would not interfere with any other essential service.

3. All primary and secondary refrigerants must be compatible with each other and with the cargo with which they come into contact. The heat exchange may take place either remotely from the cargo tank or by cooling coils fitted inside or outside the cargo tank.

4. Refrigerating plants are also to comply with the provisions of Pt 5 Ch 6, Sec 12 of the Rules.