Technical requirements for LNG bunkering systems on ships

Key technical requirements for bunkering systems on ships include high-capacity pumps, filtration systems, flow meters, safety features like emergency shutdown valves, fuel compatibility, and monitoring/control systems.

Bunkering systems on LNG/vapour ships are responsible for transferring fuel (such as diesel or heavy fuel oil) from storage tanks to the ship’s engines. They ensure a continuous and safe supply of fuel to power the vessel during its voyage.

General

The LNG/vapour transfer system should be designed and the bunkering procedure carried out so as to avoid the release of LNG or natural gas. The transfer system should be designed such that leakage from the system cannot cause danger to personnel, the receiving ship, the bunkering facility or the environment when the system is well maintained and properly used. Where any spillage of LNG can occur provisions should be taken protect personnel, ship’s structure and equipment from cryogenic hazards. The consequences of other Flammability, Explosion and other Hazards of Liquefied Gasnatural gas fuel related hazards (such as flammability) should be limited to a minimum through the arrangement of the transfer system and the corresponding equipment.

Specific means should be provided to purge the lines efficiently without release of natural gas with all purged gasses either retained by the receiving ship or returned to the bunkering facility.

Accidental leakage from the LNG/vapour transfer systems including the connections with the receiving ship bunkering manifold and with the bunkering facility should be detected by appropriate means.

Loading arms and hoses arrangements

Transfer installation

Arrangements should be made for:

• purging and inerting the bunkering lines (or between designated ESD valves for systems with long LNG transfer lines) prior to the LNG transfer;
• draining, purging and inerting the transfer system after completion of the LNG transfer.

LNG and vapour transfer systems (loading arm and/or flexible hose) should be fit for marine LNG bunkering operations. Design should be according to Tables 1 and 2 in ISO/TS 18683. The hoses and loading arms should be specially designed and constructed for the transfer products (LNG and Nitrogen) with a minimum temperature of -196 °C.

Pressure relief devices should be provided so that the hose or loading arm is not over-pressurised in the event that liquid is trapped between its isolating valves (for example if the ERS is activated).

Hoses, loading arms and parts of the ship manifold should be designed for loads which may be experienced during operation such as self-weight (including fully loaded), loads due to relative motion between receiving ship and bunker supplier, and loads due to any lifting equipment used to handle the hose. The loading arms and parts of the ships manifold may also need to be designed to support the weight of an emergency release coupling.

Care should be taken when choosing the transfer system particularly with regards to:

• potential movements between the receiving ship and the bunkering facility;
• operating envelope of transfer system;
• minimum bending radius allowed for hoses;
• ERS system functionality;
• means of purging and draining the transfer lines;
• material selection and structural support;
• type of connectors;
• electrical insulation;
• continuity of earthing system;
• system design to address potential surge pressures developed during an ESD;
• flash gas handling system;
• and arrangements for pressure relief.

Hoses

Hoses should comply with appropriate recognized standards such as EN 1474-2, EN 12434 or BS 4089. Transfer hose manufacturer’s instructions, regarding testing and number of temperature and pressure operating cycles before removal from service, should be strictly followed.

Depending on which party owns the bunkering hose, a document should be included in the LNG Crew Responsibilities for LNG BunkeringBunker management plan and a copy kept by the receiving ship containing the following information as applicable:

• hose identification number;
• date of initial entry into service;
• initial test certificate and all subsequent test reports and certificates.

The cryogenic hose should be subjected to hydrostatic testing once a year, if any defects appears during this inspection, the hose should be replaced. In addition the manufacturer of these hoses may lay down requirements relating to service life, inspection and maintenance. The manufacturer’s instructions should be followed.

Lifting and supporting devices

The lifting devices, where fitted, should be of suitable capacity to handle the LNG transfer hoses and associated equipment. Hoses should be suitably supported in such a way that the allowable bending radius is satisfied. They should normally not lie directly on the ground and should be arranged with enough slack to allow for all possible movements between the receiving ship and the bunkering facility.

Lifting and supporting devices should be suitably electrically insulated and should not impair the operation of any emergency release coupling or other safety devices.

Coupling and connecting flanges

General. The use of dry disconnect couplings is recommended for day-to-day bunkering operations using small hose diameters that will require several connections and disconnections.

Standard. An ISO standard for LNG bunkering connections is currently under development within TC8 WG8. In the meantime, couplings used for LNG Bunkering operation should be designed according to the requirements in ISO EN 16904:2016 and 1474-3 or any other applicable standards.

Spool piece. When spool pieces are used to connect to different sizes and geometries of connectors, they should be installed and tested as part of the preparation for bunkering. The leak testing would be applicable to ensure that the arrangement including spool piece is fully inerted and gas tight before transfer.

Leakage detection

As a minimum, in an enclosed or semi enclosed bunker station (on the receiving ship) or discharging station (of the bunker facility), the following safety devices should be in place:

• Gas detector(s), in suitable location(s) taking into consideration the rate of dispersion of cold vapour in the space, or temperature detection sensor(s), installed in the drip trays, or any combination to immediately detect leakage.
• CCTV is recommended to observe the bunkering operation from the bridge or operation control room. The CCTV should provide images of the bunker connection and also if possible the bunker hose such that movement of transfer system during bunkering are visible. CCTV is particularly recommended for enclosed bunker stations. Where CCTV is not provided, a permanent watch should be maintained from a safe location.

Gas detectors should be connected to the ESD system for monitoring leakage detection on the receiving ship.

Consideration may be given to the use of thermal imaging equipment or other suitable technology for leakage detection, especially in semi-enclosed bunkering stations.

A gas dispersion analysis will aid in identifying the critical locations and the extent of the LEL range where gas detectors should be fitted to enable early detection of any leakage.

ESD systems

The bunkering facility and receiving ship should be fitted with a linked ESD system such that any activation of the ESD systems should be implemented simultaneously on Risk Assessment in the Liquefied Natural Gas Bunkering Operations, Hazard Identificationboth bunkering facility and receiving ship. Any pumps and vapour return compressors should be designed with consideration to surge pressure in the event of ESD activation. The bunkering line should be designed and arranged to withstand the surge pressure that may result from the activation of the emergency release coupling and quick closing of ESD valves.

On ESD activation, manifold valves on the receiving ship and bunkering facility and any pump or compressor associated with the bunkering operation are to be shut down except where this would result in a more hazardous situation (see table).

An ESD activation should not lead to LNG being trapped in a pipe between closed valves. An automatic pressure relief system is to be provided that is designed to release the natural gas to a safe location without release to the environment.

If not demonstrated to be required at a higher value due to pressure surge considerations, a suitably selected closing time up to 5 seconds should be selected, depending on the pipe size and bunkering rate from the trigger of the alarm to full closure of the ESD valves, in accordance with the IGF Code.

Read also: Ship to Ship Bunkering Operations of the Liquefied Natural Gas

The emergency shutdown system ESD should be suitable for the capacity of the installation. The minimum alarms and safety actions required for the transfer system are given in table below:

The manual activation position for the ESD system should be outside the bunker station and should have a clear view of the manifold area (the “clear view” may be provided via CCTV).

LNG bunker transfer should not be resumed until the transfer system and associated safety systems (fire detection, etc.) are returned to normal operation condition. All electrical components of the emergency release coupling actuator and of the ESD systems that are considered as provided by the ship side should be type approved/certified by the classification society. When the ESD hardware and components are part of the onshore facility they should be designed and tested according to the industry standards.

Emergency Release Coupling (ERC)

General

Transfer arms and hoses should be fitted with an emergency release coupling (ERC) designed to minimize the release of LNG on emergency disconnection. The emergency release coupling may be designed for:

• manual or automatic activation;
• and activation as a result of excessive forces i. e. automatic disconnection in case the safe working envelope of the transfer system is exceeded.

The breakaway coupling (BRC) should be subjected to a type test to confirm the values of axial and shear forces at which it automatically separates. For an emergency release coupling (ERC), the tightness of the self-closing shut-off valves after separation should be checked.

The ERC coupling should be designed and installed so that, in the worst allowable conditions for current, waves and wind declared in the bunkering conditions, it will not be subjected to excessive axial and shear forces likely to result in the loss of tightness or opening of the coupling. When the Safe working envelope of the transfer system is exceeded, the ERC system should be triggered.

Means should be provided in order to avoid a pressure surge in the bunker hose after release of the ERC when the connecting end of the hose is fitted with a dry disconnect coupling type. Full operating instructions, testing and inspection schedules, necessary records and any limitations of all emergency release systems should be detailed in the ship’s operating manuals.

ERC Activation. Where manual activation type ERC is fitted, the means of remotely operating the ERC should be positioned in a suitability protected area both on bunkering facility and receiving ship allowing visual monitoring of the bunkering system operation. A physical ESD link should bond the two parties. This does not apply to a dry breakaway coupling as this is a passive component which cannot be remotely activated.

Hose Handling after ERC Release

An integrated hose/support handling system should be in place, capable of handling and controlling the bunker transfer hoses after release of the ERC. In addition, it should be capable of absorbing all shock loadings imposed by the release of ERC during maximum capacity transfer conditions.

The system should ensure that, as far as practicable, upon release the hoses, couplings and supports do not contact the metal structure of the ship and bunkering facility, thereby reducing the risk of sparking at the contact point, injury to personnel or mechanical damage.

Communication systems. A communication system with back-up should be provided between the bunkering facility and the receiving ship. The components of the communication system located in hazardous and safety zones should be type approved according to IEC 60079.

Bunkering transfer rate

The maximum LNG transfer rate from the BFO should be adjusted, taking into consideration:

• maximum allowable flow rate of the bunker station manifold;
• maximum allowable cooling down rate acceptable regarding induced thermal stresses in the LNG receiving ship piping and tank;
• management of the flash gas generated during bunkering;
• temperature of the LNG supplied from the bunkering facility;
• temperature of the LNG remaining in the receiving ship tank;
• and pressure in both bunkering facility tank and receiving ship tank.

Adequate provisions should be made for the management of the flash gas generated during the bunkering operation, without release to the atmosphere. This may be done by:

• considering the capacity of the available vapour spaces and allowable pressure build-up of both ships;
• or burning additional volumes in boilers, gas combustion units or gas engines;
• or cooling the vapour space to control the pressure by using LNG spray in the receiving tank;
• or reliquefaction.

The LNG velocity in the piping system should not exceed 12,0 m/sec under the rated equipment capacity in order to avoid the generation of static electricity, additional heat, and consecutive boil off gas due to nonlinear flow.

Vapour return line

Vapour return line(s) may be used in order to control the pressure in the receiving tank or to reduce the time required for bunkering (refer to 2.4.6 of Chapter 3). This is particularly applicable to atmospheric pressure fuel storage tanks (type A, prismatic type B or membrane tanks). The most relevant factors that will affect the amount of flash gas generation in a typical bunkering operation are as follows:

• cool down of the transfer system;
• difference in the conditions prevailing between the bunkering facility tanks and the receiving tanks (particularly the temperature of the receiving tank);
• transfer rates (ramp up, full flow, ramp down/topping up);
• heat gain in pipe line between bunkering facility tank and receiving ship tank;
• pumping energy.

Lighting

Lighting should illuminate the bunker station area, and if installed in a hazardous area should be compliant with applicable hazardous area equipment requirements. Lighting should adequately illuminate the bunkering operation work area especially:

• LNG bunker hose(s);
• connection and couplings on both receiving ship and bunkering facility;
• ESD system call points;
• communication systems;
• fire-fighting equipment;
• passage ways/gangways intended to be used by the personnel in charge of the bunkering operation;
• and vent mast(s).