Section 7 Cargo heating arrangements

7.1.1 In addition to the requirements detailed in this Section, the requirements of Pt 5, Ch 12, 11 Thermal oil systems for thermal oil systems to be installed on Type C and N tankers are to be complied with as far as they are applicable.

7.1.2 Outlets of exhaust gas lines from thermal oil heaters are to be provided with spark arrestors or equivalent and are not to be led through the cargo zone. The distance between the outlet and the cargo zone is to be not less than 2 m.

7.1.3 The air intakes from the thermal oil heater are to be so arranged that their openings are not less than 2 m outside the cargo zone and not less than 6 m from openings of cargo or slop tanks, cargo pumps on deck, openings of high velocity vents or over pressure devices and shore connections of the cargo lines. Furthermore, the air intakes are to be arranged not less than 2 m above deck.

7.1.4 Thermal oil heaters are to be situated in the engine room or, alternatively, in a special space outside the cargo zone accessible from deck or from within the engine room.

7.1.5 Where heating systems are provided for the cargo tanks, the arrangements are to comply with the requirements of Pt 5, Ch 13, 7.2 Blanking arrangements to Pt 5, Ch 13, 7.5 Temperature indication.

7.2.1 Spectacle flanges or spool pieces are to be provided in the heating medium supply and return pipes to the cargo heating system, at a suitable position within the cargo area, so that the lines can be blanked off in circumstances where the cargo does not require to be heated or where the heating coils have been removed from the cargo tanks. Alternatively, blanking arrangements may be provided for each tank heating circuit.

7.3.1 The heating medium is to be compatible with the cargoes to be heated. Where a cargo is highly water reactive, water or steam is not to be used as the medium. For lists of chemicals containing information on water reactivity, see ADN, Table C, see also Pt 5, Ch 13, 1.3 Materials 1.3.9 for reference.

7.3.2 Where a combustible liquid is used as the heating medium, it is to have a flash point of 55°C or above (closed cup test).

7.3.3 In general, the temperature of the heating medium is not to exceed 220°C.

7.4.1 The heating medium supply and return lines are not to penetrate the cargo tank plating, other than at the top of the tank, and the main supply lines are to be run above the deck.

7.4.2 Isolating shut-off valves or cocks are to be provided at the inlet and outlet connections to the heating circuit(s) of each tank, and means are to be provided for regulating the flow.

7.4.3 In case of direct heating arrangements valves for the individual heating coils are to be provided with locking arrangements to ensure that the coils are under static pressure at all times.

7.4.4 For direct heating systems, isolation valves are to be provided in the cargo heating supply and return line in a readily accessible position in the cargo zone.

7.4.5 Where steam or water is employed in the heating circuits of Type N-open ships, the returns are to be led to an observation tank, which is to be in a well ventilated and well lighted part of the machinery space remote from highly heated surfaces or possible sources of ignition.

7.4.6 Where a thermal oil is employed in the heating circuits, the arrangements are to be such that contamination of the thermal oil with cargo liquid cannot take place under normal operating conditions.

7.4.7 A heat exchanger, situated in the cargo zone, is to be incorporated in the heating systems of tankers carrying toxic cargoes Class 6.1. In these cases the tank heating circuits are also to lie entirely within the cargo zone.

7.4.8 In any heating system a positive pressure in the coils of at least 30 kPa above the static liquid pressure of the cargo, increased with the relevant set pressure of the high velocity valve as far as applicable, shall be maintained under all conditions of service when the circulation pump is not in operation.

7.4.9 Alternatively, the heating system may be drained and blanked when the circuit is not in use, provided the heating system is to be verified on the presence of previous cargo at the commencement of heating another product.

7.4.10 Arrangements are to be provided to monitor the pressure in the heating coils.

7.4.11 In view of the dangerous situation which may arise in the event of contamination of the thermal fluid with low flash cargo oil, for oil and chemical tankers intended for the carriage of products having a flash point below 55°C, permanent notice boards should be displayed in prominent positions in the engine room and on deck, stating that the thermal oil system should remain under pressure, see also Pt 5, Ch 13, 7.4 Heating circuits 7.4.8, except when the ship is either carrying cargoes having a flash point above 55°C, or the cargo tanks are empty and gas free and will be pressurised again before low flash oil is loaded.

7.5.1 Means are to be provided for measuring the cargo temperature. Where overheating could result in a dangerous condition, an alarm system which monitors the cargo temperature is to be provided.