Section 4 Linked emergency shutdown (ESD) system

4.1.1 An emergency shutdown (ESD) system shall be fitted to all ship units to stop cargo flow in the event of an emergency, either internally within the ship unit, or during cargo transfer with shuttle tankers. The design of the ESD system shall avoid the potential generation of surge pressures within cargo transfer pipe work, see Pt 11, Ch 18, 4.2 ESD valve requirements 4.2.1.(d). For linked ESD systems the requirements in Pt 7, Ch 1, 7.4 Linked ESD systems are to be satisfied.

4.1.2 Auxiliary systems for conditioning the cargo that use toxic or flammable liquids or vapours shall be treated as cargo systems for the purposes of ESD. Indirect refrigeration systems using an inert medium, such as nitrogen, need not be included in the ESD function.

4.2.1  General

1. The term ESD valve means any valve operated by the ESD system.
2. ESD valves shall be remotely operated, be of the fail closed type (closed on loss of actuating power), shall be capable of local manual closure and have positive indication of the actual valve position. As an alternative to the local manual closing of the ESD valve, a manually operated shut-off valve in series with the ESD valve shall be permitted. The manual valve shall be located adjacent to the ESD valve. Provisions shall be made to handle trapped liquid should the ESD valve close while the manual valve is also closed.
   A manually operated vent valve in the pneumatic/hydraulic logic is preferable to an additional in-line valve.

   Table 18.4.1 ESD Functional Arrangements

   		Pumps		Compressor Systems				Valves	Link
   Shut-down action →		Cargo pumps/cargo booster pumps	Spray/ stripping pumps	Vapour return compressors	Fuel gas compressors and system	Reliquefaction plant****, including condensate return pumps, if fitted	Gas combustion unit	ESD valves	Signal to ship unit-shuttle tanker link *****
   Initiation ↓
   Emergency push buttons (see Pt 11, Ch 18, 4.1 General 4.1.2)					Note 2
   Fire detection on deck or in compressor house*					Note 2
   High level in cargo tank***					Note 1 Note 2	Note 1	Note 1	Note 4
   Signal from ship unit-shuttle tanker link					Note 2	Note 3	n/a		n/a
   Loss of motive power to ESD valves**					Note 2	n/a	n/a
   Main electric power failure (‘blackout’)		Note 5	Note 5	Note 5	Note 5	Note 5	Note 5
   NOTES 1. These items of equipment can be omitted from these specific automatic shut-down initiators provided the compressor inlets are protected against cargo liquid ingress. 2. If the fuel gas compressor is used to return cargo vapour to the ship unit, it shall be included in the ESD system only when operating in this mode. 3. If the reliquefaction plant compressors are used for vapour return/ship unit line clearing, they shall be included in the ESD system only when operating in that mode. 4. Alternatively, a stage 1 high level in an individual cargo tank may initiate the closure of the shut-off valve referred to in Pt 11, Ch 13, 1.3 Overflow control 1.3.2, and not the ESD valve referred to in Pt 11, Ch 18, 4.2 ESD valve requirements 4.2.1.(c). The sensor indicated in Pt 11, Ch 13, 1.3 Overflow control 1.3.2 shall also ensure that when all tank valves referred to in Pt 11, Ch 13, 1.3 Overflow control 1.3.2 are shut that the ESD in Pt 11, Ch 18, 4.1 General 4.1.2 is operated. 5. These items of equipment shall not be started automatically upon recovery of main electric power and without confirmation of safe conditions.
   Remarks *      Fusible plugs, electronic point temperature monitoring or area fire detection may be used for this purpose on deck. **     Failure of hydraulic, electric or pneumatic power for remotely operated ESD valve actuators. ***   See Pt 11, Ch 13, 1.3 Overflow control 1.3.2 and Pt 11, Ch 13, 1.3 Overflow control 1.3.3. ****  Indirect refrigeration systems using an inert medium, such as nitrogen, need not be included in the ESD function. ***** Signal need not indicate the event initiating ESD.     Functional requirement. n/a   Not applicable.

3. ESD valves in liquid piping systems shall close fully and smoothly within 30 seconds of actuation. Information about the closure time of the valves and their operating characteristics shall be available on board, and the closing time shall be verifiable and repeatable.
4. The closing time of the valve referred to in Pt 11, Ch 13, 1.3 Overflow control 1.3.1 to Pt 11, Ch 13, 1.3 Overflow control 1.3.1 (i.e. time from shut-down signal initiation to complete valve closure) shall not be greater than:
   

   where

   U

   =

   ullage volume at operating signal level (m3)

   LR

   =

   maximum loading rate agreed between ship unit and shuttle tanker (m3/h).

   The loading rate shall be adjusted to limit surge pressure on valve closure to an acceptable level, taking into account the loading hose or arm and the piping systems of the ship unit and shuttle tanker where relevant.

4.2.5  Additional shut-downs

1. The requirements of Pt 11, Ch 8, 1.3 Vacuum protection systems 1.3.1.(a) to protect the cargo tank from external differential pressure may be fulfilled by using an independent low pressure trip to activate the ESD system, or as a minimum to stop any cargo pumps or compressors.
2. An input to the ESD system from the overflow control system required by Pt 11, Ch 13, 1.3 Overflow control may be provided to stop any cargo pumps or compressors running at the time a high level is detected, as this alarm may be due to inadvertent internal transfer of cargo from tank to tank.