Functional and General Requirements for LNG Bunkering Operation

LNG bunkering requirements operations must comply with stringent safety standards to mitigate risks associated with handling liquefied natural gas. These requirements encompass proper training for personnel, adherence to strict operational procedures, and the implementation of robust emergency response plans.

Additionally, facilities and equipment used for LNG bunkering must meet specific safety certifications to ensure the safe transfer of LNG to vessels.

Pre-bunkering phase

The pre-bunkering phase starts from the first communication between receiving ship and bunkering facility for ordering a bunker of LNG, and ends with the physical connection of the bunker line to the bunker station.

Definition

Goal. The goal of the pre-bunkering phase is the preparation and the completion of a safe connection between the transfer systems of the bunkering facility and the receiving ship.

Functional requirements

The following functional requirements should be considered during the pre-bunkering phase:

• the risk assessment has been conducted and the findings have been implemented;
• an LNG Bunker Management Plan has been established and is applicable to the ship;
• a compatibility check demonstrates that the safety and bunkering systems of the bunkering facility and the ship to be bunkered match;
• the necessary authorities have been informed regarding the LNG bunkering operation;
• the permission for the transfer operation is available from the relevant authority;
• the boundary conditions such as transfer rate, boil-off handling and loading limit have been agreed between the supplier and the ship to be bunkered;
• initial checks of the bunkering and safety system are conducted to ensure a safe transfer of LNG during the bunkering phase.

General requirements

Personnel on duty

During the transfer operation, personnel in the safety zone should be limited to essential staff only. All staff engaged in duties or working in the vicinity of the operations should wear appropriate personal protective equipment (PPE) and an individual portable gas detector as required by the LNG Bunker Management Plan.

Compatibility assessment (prior to confirming the bunkering operation)

A compatibility assessment of the bunkering facility and receiving ship should be undertaken prior to confirming the bunkering operation to identify any aspects that require particular management.

The compatibility assessment should be undertaken with the assistance of an appropriate Checklist to be completed and agreed by Master(s) and PIC prior to engaging in the bunkering operation.

As a minimum, compatibility of the following equipment and installation should be checked prior to engaging further in any LNG bunkering operation:

• communication system (hardware, software if any and language) between the PIC, ship’s crew and BFO personnel;
• ESD system;
• bunker connection;
• emergency release system (ERS) or coupling (ERC);
• vapour return line when appropriate;
• nitrogen lines availability and connection;
• mooring equipment;
• bunker Station location;
• transfer system sizing and loading on manifold;
• location of ERS;
• closure speed of valves;
• HAZOP results as applicable.

Preparation for bunker transfer

Environmental conditions

The environmental conditions (weather (especially lightening), sea state, temperature, and visibility limitation such as fog or mist) should be acceptable in terms of safety for all the parties involved.

Mooring

Mooring condition of receiving ship. The ship should be securely moored to the bunker supplier to prevent excessive relative movement during the Ship to Ship Bunkering Operations of the Liquefied Natural Gasbunkering operation.

Mooring condition of bunker ship. For ship-to-ship bunkering the bunker ship should be securely moored according to the result of the compatibility check, so that excessive movements and overstressing of the bunkering connections can be avoided. Refer below. For the mooring of the bunker ship the limiting conditions should be considered such as weather, tide, strong wind and waves.

Parking condition of truck LNG tanker(s). The truck LNG tanker(s) should be securely parked, to prevent unintended movements. All ignition sources linked to the truck are to be managed in accordance with the bunkering management plan/procedure taking into account Hazardous areas and Safety Zones. Any situation whereby this requirement cannot be met, special consideration must be provided (i. e. non-standard) to ensure the risk of ignition is managed to ALARP.

In any case, the truck engine should not be running during connection and disconnection of the transfer system.

Communication

Communication should be satisfactorily established between the bunkering facility and the receiving ship prior to any transfer operation. If they are to be used, visible signals should be agreed by and clear to all the personnel involved in the LNG bunkering operation.

In case of communication failure, bunkering operations should be stopped and not resumed until communication is re-established.

Agreement of the transfer conditions

The following should be agreed before commencing the bunker transfer:

• transfer time, temperature and pressure of the delivered LNG, pressure inside the receiving ship tank, delivery line measurement, vapour return line measurement (if any) should be agreed and checked prior to engaging in any LNG Bunkering Operation;
• the maximum LNG temperature that the receiving ship can handle should be stated by the receiving ship in order to avoid excessive boil-off generation;
• liquid levels, temperature and pressure for the LNG bunker tanks of the receiving ship should be checked and noted on the bunkering checklist;
• the maximum loading level and transfer rate, including cool down and topping up should be agreed upon. This includes the pressure capacity of pumps and relieving devices in the connected transfer system. The filling limit of the receiving tank depends on MARVS (as per IGC / IGF codes) and accounts for the possible expansion of cold LNG.

The agreed transfer conditions should be included in the LNG Bunker Management Plan.

Individual safety equipment in place (PPE). All personnel involved in the LNG bunkering operation should properly wear adequate Personal Protective Equipment (PPE). It should be ensured that all the PPEs have been checked for compliance and are ready and suitable for use.

Protection of the hull plate, shell side and ship structure

Protection from cryogenic brittle fracture of the receiving ship deck and structure caused by leakage of LNG should be fitted as per IGF code requirements.

When appropriate one or more of the following protective measures may be utilised:

• a water curtain may be installed to protect the ship’s hull;
• a cover of suitable material grade to withstand LNG temperatures may be installed underneath the transfer hose to protect deck plating;
• a drip tray of suitable material grade to withstand LNG temperatures may be fitted below the pipe coupling to collect LNG spill.

It is recommended that spill protection is also provided for the BFO equipment, this may be governed by local regulations for truck-to-ship bunkering and shore based facilities.

Safety zone requirements and mark out

• the boundaries of the safety zone associated with bunker station and BFO connection should be clearly marked out;
• any non-EX equipment installed in hazardous areas and/or in safety zone, such as the bunker station, should be electrically isolated before the bunkering operation commences and throughout the bunkering process until such time as the area is free of any gas leak hazard. Any such arrangement where there is non-Ex rated equipment installed in a hazardous zone should be subject to special consideration by the classification society;
• radio communications equipment not needed during bunkering and cell phones should be switched off as appropriate.

Electric isolation

A single isolation flange should be provided, in each arm or hose of the transfer system, between the receiving ship manifold and the bunker pipeline. The installation should not permit shorting out of this insulation for example by, leaving the flange resting in stainless steel drip tray. This flange prevents galvanic current flow between the receiving ship and the bunkering facility. Steel to steel contact between receiving ship and bunkering facility e. g. via mooring lines, ladders, gangways, chains for fender support etc. should be avoided through the use of insulation. Bunker hoses/pipes should be supported and isolated to prevent electrical contact with the receiving ship.

When bunkering from trucks, the truck should be grounded to an earthing point at the quay to prevent static electricity build up. Where approval has been given for the bunkering truck to be parked on the deck of the ship then the truck should be grounded to the receiving ship.

Ship-shore bonding cables/straps should not be used unless required by national or local regulations.

ERS

Simulated testing of all types of coupling having the function of ERC within the ERS should be performed according to a recognised standard. Testing records should be retained with the bunkering operator or organisation responsible for such equipment ready for immediate inspection by authorities. Any transfer/support system should be proved operational (if necessary by inspection of marine loading arm or supported hose) and be confirmed as part of the pre-transfer checklist.

Testing of the system prior to each bunkering operation should prove all components are satisfactory, with the exception of actually releasing the ERC. The system used to link the ERS system with the ships’ ESD1 trip circuit should be tested and proved operational.

Emergency Release Coupling (Break away coupling). The disconnection can be triggered manually or automatically. In either case, activation of the ERS system should trigger activation of the ESD (ESD1) before release of the ERC (ESD2).

Where applicable, step-by-step operating instructions should be permanently affixed to the ERC equipment and all personnel involved in its operations should be trained and made familiar with its correct use. Additionally, clear procedures should be in place identifying the process for authorisation to remotely activate the ERC.

In the event of ESD2 activation, i. e. breakaway coupling sudden release triggered due to emergency event or overstress on the transfer line induced by ship movement, the backlashing hoses can damage hull structure and injure personnel in the absence of an appropriate supporting arrangement. This supporting arrangement, if fitted, should not prevent the correct operation of the breakaway coupling, any relative motion between the receiving ship and the bunkering facility should act directly on the ERC to ensure its correct operation if the event of vessel drift or unexpected truck movement.

Routine inspection and testing of the release equipment is required, responsibility for this testing will depend on agreements between the BFO and RSO.

ESD testing. The Technical requirements for LNG bunkering systems on shipsbunkering facility and receiving ship should both test their emergency shutdown systems not more than 24 hours before bunkering operations commence. The PIC should then be advised of the successful completion of these tests. These tests should be documented in accordance with the bunkering procedure.

Visual inspection of bunker hose or arm before physical connection. Bunker hoses and connecting systems should be visually examined for wear and tear, physical damage and cleanliness. If any defects are found during this inspection, the bunkering operation is cancelled until the transfer hose is replaced.

Liquid and gas leakage detection systems activated. The gas detection system as described in Chapter 1, 5.4 should be activated. Temperature sensor(s) should be installed in the bunker station below the drip tray and their temperature calibration(s) should be checked. Their function should also be tested.

Preparation of the transfer system. The piping at the bunkering facility should be inerted and cooled down (as far as practicable) prior to the connection with the ship to be bunkered. If this operation may cause any specific hazards when connecting to the transfer line it should be carried out after the connection has been carried out. The specific cooling down procedure for the transfer system in terms of cooling down rate should be observed with special care regarding the potential for induced thermal stresses and damage and leaks that may occur. Connections to the bunkering facility and the receiving ship should be visually checked and if necessary retightened. During this operation there should be no release of any LNG or natural gas.

Pre-bunkering checklist

The LNG Bunker Management Plan should include a checklist to be used during LNG bunkering operation by all involved personnel. This checklist should be elaborated once the full agreement on:

• procedures to apply;
• equipment to be used;
• quantity and quality of LNG to bunker;
• and training is obtained by all involved parties.

At the time of writing this guideline a LNG bunkering operation checklist is under development within ISO and IMO. In the meantime the LNG bunkering operation specific checklist should be therefore adapted from the examples checklists for truck-to-ship, shore-to-ship and ship-to-ship LNG bunkering that have been elaborated by WPCI and IAPH.

Connection of the transfer system

Connecting

Equipment utilised with the transfer system such as couplings and hoses should be approved and tested both before and after installation. For emergency release coupling requirements (ERC), see Technical requirements for LNG bunkering systems on ships“Emergency Release Coupling (ERC)”.

The transfer system should be connected such that all the forces acting during the transfer operation are within the operating range.

Condition of flange and sealing surfaces prior to connection

During connecting of the transfer system, humidity at the flange mating surfaces should be avoided and it should be ensured that all mating surfaces are clean. When necessary, compressed air should be used for cleaning the contact surface of flanges and seals before physical connection and clamping of the couplings. Heating of the connections to dry them prior to connecting may be considered in some circumstances.

Minimum bending radius of the hose

Hoses should be suitably supported in a manner that the minimum acceptable bending radius according to the qualification standard of the hose is not exceeded. Equipment utilised with the transfer system such as hose rests, saddles, and guidance systems (as applicable) should be approved and tested.

A LNG transfer hose should normally not lie directly on the deck plate and should be isolated thermally from the deck. As a minimum, suitable protection such as wooden boards should also be provided to avoid damage from friction on the quay.

The hose arrangement should be so designed with enough slack to allow for all possible movements between the receiving ship and the bunkering facility.

Transfer line purging

After connection of the transfer system it should be purged to ensure that no oxygen or humidity remains in the transfer system. Nitrogen should be used for purging of any parts of the system that will be cooled to cryogenic temperatures during the bunkering operation.

Attention is drawn to quantity of the inert gas used for purging/inerting, which may result in high inert gas content in the LNG tank of the receiving ship, which may affect the proper operation of engines. A typical purging sequence of the transfer line involves the injection of five (5) times the volume of the bunker line. The volume of inert gas required may be minimised by the design of the transfer system (i. e. using shorter lengths of hose).

Transfer line pressure testing

During inerting of the transfer system the leak test according to the bunkering procedure should be carried out. As a minimum, a leak test of the connection points and flanges in the system from the bunkering facility up to the ESD valve on the receiving ship should be performed prior to any transfer operation.

Bunkering phase

Definition

The bunkering phase begins after the physical connection between the bunkering facility and the receiving ship’s bunker station has been safely completed with the opening of the LNG transfer valve from the bunker ship, the truck tanker or the onshore bunkering facility.

It continues with the cooling down of the transfer line followed by the LNG bunker transfer and ends at the end of the topping up phase and the closure of the LNG valve from the bunkering facility.

Goal. Transfer of the required quantity of LNG without release of LNG and/or natural gas to the surrounding environment in a safe and efficient operation.

Functional requirements

• during the whole transfer process a suitable ESD and ERS system should be provided for the transfer system;
• after connection of the transfer system a suitable cooling down procedure should be carried out in accordance with the specification of the transfer system and the receiving tank supplier requirements;
• flash gas or boil-off gas will not be released to atmosphere during normal transfer operations;
• bunker lines, transfer system and tank condition should be continuously monitored for the duration of the transfer operation.

General requirements

ERS

The ERS control signals and actuators should be checked and tested and should be ready for use.

The mechanical release mechanism of the ERS system should be proven operational and ready for use before fuel bunkering operation commences.

ESD connection testing

It should be ensured that a linked ESD system connected, tested and ready for use is available. There are two phases of testing Warm ESD testing and Cold ESD testing.

Warm ESD Testing. The ESD Equipment and cargo system of LNG onshore terminalssystem should be tested following completion of manifold connection & ESD link. The testing should take place between the receiving ship and the bunkering facility prior to commencement of operation (warm ESD1) to confirm that the systems are compatible and correctly connected. The initiation of the warm ESD1 signal should be done from either one of the receiving ship or the bunkering facility.

Cool down of transfer system

As far as practicable, cooling down of the transfer lines should be carried out according to the requirements of the transfer system and according to the bunkering procedure with special care regarding the potential leaks that may occur as components shrink as they are cooled. Connections to the bunkering facility and the receiving ship should be monitored and, if necessary, tightened.

If a pump is used to deliver the required pressure for the tank to be filled, it is necessary to cool it to operating temperature before starting. This is done by filling the pump circuit with liquid from the tank.

Cold ESD Testing. Following the successful completion of cool down operation the cold test should be carried out as far as practicable to ensure that the ESD valves operate correctly in cold conditions before initiating the main LNG bunker transfer.

Main bunker transfer

After proper cooling down of the transfer system and a stable condition of the system the transfer rate can be increased to the agreed amount according to the bunkering procedure. The transfer process should be continuously monitored with regard to the operating limits of the system.

If there are any deviations from the operation limits of the system the transfer of LNG should be immediately stopped.

Monitoring pressure and temperature. Receiving tank pressure and temperature should be monitored and controlled during the bunkering process to prevent over pressurisation and subsequent release of natural gas or liquid natural gas through the tank pressure relief valve and the vent mast.

Vapour management

The vapour management methodology will vary depending on tank type, system type and system condition, but should be agreed on during the compatibility check. For atmospheric tanks a vapour return line may be used but also other systems like reliquefaction units or pressurised auxiliary systems can also be used to regulate the pressure of the return vapour.

If the receiving tank is a Type C tank, the above remains valid. An alternative practise of LNG bunkering widely used, especially in a truck-to-ship bunkering situation or when no vapour return line is available, is to spray LNG into the top of the receiving tank through diffusers in order to cool the vapour space. As a result the tank pressure will be reduced and therefore the pressure increase due to flash gas can be contained and managed for the duration of the LNG bunkering.

Topping up of the tank. The topping up of the tank should be carefully surveyed by the Person in Charge and/or the Chief Engineer surveying the filling up of the LNG tank(s). The LNG fuel transfer flow rate should be slowed with an appropriate declining value when the receiving tank LNG level approaches the agreed loading limit. The loading limit of the tank and the tank pressure should be paid special attention by the PIC during this operational step. The opening of the tank’s Pressure Relief Valve (PRV) due to overpressure in tank, for example following overfilling, should be avoided.

Selection of measurement equipment. The impact on the safety of the transfer system by any equipment used for the measurement of LNG quantity during the bunkering operation should be considered. The measurement method selected, and the equipment used (flow meters, etc.), should minimise disruption to the flow of LNG to prevent pressure surge, excess flash gas generation, or pressure losses in the transfer system.

Bunkering completion phase

Definition

The post bunkering phase begins once the bunker transfer (final topping up phase) has been completed and the bunkering facility LNG delivering valve has been closed. It ends once the receiving ship and bunkering facility have safely separated and all required documentation has been completed.

Goal. This phase should secure a safe separation of the transfer systems of the receiving ship and bunkering facility without release of LNG or excess vapour to the surrounding environment.

Functional requirements

The following functional requirements should be considered during the Post Bunkering Phase:

• the draining, purging and inerting sequences as described below for the different bunkering cases are fulfilled without release of excess natural gas to the atmosphere;
• the securing and safe storage of transfer system equipment is ensured;
• the unmooring operation and separation of ship(s) is completed safely.

Draining, purging and inerting sequence

This part of the process is intended to ensure that the transfer system is in a safe condition before separation, the couplings should not be separated unless there is an inert atmosphere on both sides of the coupling.

Read also: Examples of the Emergency Situations with Liquefied Gas Carriers

The details of this process will be design dependent but should include the following steps:

• shut down of the supply;
• safe isolation of the supply;
• draining of any remaining LNG out of the transfer system;
• purging of natural gas from the transfer system;
• safe separation of the transfer system coupling(s);
• safe storage of the transfer system equipment in a manner that the introduction of moisture or oxygen into the system.

LNG Bunkering from Truck LNG Tank. The process of purging and inerting will follow the general outline described above, all purged gasses are generally returned to the receiving ship tank.

LNG Bunkering from Bunker ship. The process of purging and inerting will follow the general outline described above, all purged gasses are generally returned to the bunker ship tank.

LNG Bunkering from shore based terminal. The process of purging and inerting will follow the general outline described above, all purged gasses are generally returned to the shore facility.

LNG Bunkering using portable tanks

The method for safe disconnection of portable tanks will vary depending on the specific design of the system. The general principles remain the same:

• all pipe connections to be isolated at the delivery and receiving ends;
• the connecting hose(s) should be purged and inerted to below the lower flammable limit to prevent risk of ignition and minimise release of natural gas during disconnection;
• Hoses and connections should be securely blanked or otherwise protected to avoid introduction of moisture and oxygen into the system.

Post-bunkering documentation

Upon completion of bunkering operations the checklist in the LNG bunkering management plan (as described in the pre-bunkering section above) should be completed to document that the operation has been concluded in accordance with the agreed safe procedure. The vessel PIC should receive and sign a Bunker Delivery Note for the fuel delivered, the details of the bunker delivery note are specified in the annex to part C-1 of IGF Code.