Section 21 Natural Gas Fuel Installations

21.1.1 The requirements of Pt 1, Ch 3, 6 Machinery Surveys – General requirements Machinery surveys – General requirements are to be complied with, as applicable.

21.1.2 In addition to the survey requirements below, further survey requirements may be imposed; as identified during the risk assessment process, see Pt 1, Ch 2, 3.6 Surveys for novel/complex systems.

21.1.3 This Section provides requirements for the survey of natural gas fuel installations as defined in Pt 1, Ch 3, 1.5 Definitions (natural gas is hereinafter referred to as fuel).

21.1.4 The fuel installation is to be surveyed in working condition except at Special Survey where internal examination of some components will be required. See Pt 1, Ch 3, 21.8 Complete Surveys − General requirements and Pt 1, Ch 3, 21.9 Complete Surveys − Natural gas fuelled consumers and other equipment.

21.1.5 Annual Survey should be scheduled, if possible, to coincide with a bunkering operation to allow for verification of fuel storage tank level alarms and bunkering control, alert and safety systems under operational conditions. At annual survey physical testing of alarms and shutdowns is not required unless it is considered necessary by the attending surveyor. In any case records of the alarms are to be retained for the verification of the attending Surveyor.

21.1.6 The Intermediate Survey supplements the Annual Survey by testing the fuel bunkering system including automatic control, alert and safety systems to confirm satisfactory operation. The extent of the testing required for the Intermediate Survey may briefly interrupt the fuel installation and therefore unit operations and the survey are to be scheduled accordingly.

21.1.7 The extent of the testing required for Complete Surveys will normally be such that the full survey cannot be carried out with the fuel installation operating or loaded with fuel. Consequently, aspects of the survey should be coordinated to correspond with drydocking or another period when the system will be gas free. Completion of the survey requires verification of satisfactory condition of the installation at the normal operating temperatures and pressures so will normally be completed once the unit has been bunkered following reactivation of the system.

21.1.8 Prior to any internal inspection of fuel storage tanks, associated piping, fittings and equipment, etc., the respective items are to be made safe for access by means of isolating relevant valves, purging and gas-freeing the space.

21.1.9 Where an approved condition-monitoring system is employed for the fuel system and its constituent components, and the applicable Descriptive Note is assigned, the requirements of these regulations for opening up and internal examination may be waived where the condition of the equipment can be shown to be within agreed acceptable limits as detailed in Pt 5, Ch 21 Requirements for Condition Monitoring Systems and Machinery Condition-Based Maintenance Systems of the Rules and Regulations for the Classification of Ships.

21.1.10 The following documentation, as applicable, is to be available on board the unit:

1. Relevant instruction and information such as loading limit curve information, bunkering procedures, cooling down procedures and fuel installation test and inspection procedures.
2. Condition-Monitoring or Condition-Based Maintenance documentation as applicable.
3. Test records for bunkering ESD systems.
4. Records of crew tests/inspections of the fuel installation.

21.1.11 For Special Survey requirements for electrical equipment see Pt 1, Ch 3, 9 Electrical equipment.

21.2.1 Following repair, independent fuel storage tanks of Type C are to be hydrostatically tested in accordance with the manufacturer’s test and inspection instructions (normally at 1,25 times the approved maximum vapour pressure). Other types of fuel storage tank, such as membrane tanks, are to be tested in accordance with approved procedures provided by the fuel storage tank designers. After testing, suitable drying and consequent air-purging procedures are to be followed to return the tank to operational condition.

21.3.1 The Annual Survey is to be carried out with the fuel installation operational. Gas-freeing will not generally be necessary.

21.3.2 The unit’s log and operational records for the fuel installation, covering the period from the previous survey, are to be examined. Any malfunction of the installation recorded in the log is to be investigated. It is to be verified that any repairs have been carried out to an acceptable standard and in accordance with the applicable Rules and Regulations.

21.3.3 Control, alert and safety systems are to be surveyed as follows:

1. The control, alert and safety systems for the fuel storage tanks and processing system are to be verified in satisfactory condition by one or more of the following methods:
   1. Comparison of read-outs from local and remote indicators.
   2. Consideration of read-outs with regard to the actual conditions.
   3. Examination of maintenance records with reference to the approved maintenance management system.
   4. Verification of calibration status of the measuring instruments.
2. All control, alerts and safety systems are to be tested, where testing is not possible due to operational reasons simulated testing may be accepted by the attending Surveyor. Which are to include but are not limited to:
   1. fuel storage tank and processing system high and low pressure
   2. fuel storage tank high and high-high level
   3. fuel storage tank overfill level
   4. fuel storage tank high temperature.
3. Fuel leakage detection systems (temperature sensors and gas detection as applicable) are to be examined and tested in accordance with the manufacturer’s instructions and calibrated using sample gas.
4. The electrical installation, equipment and cables in areas which may contain flammable gas are to be examined in order to verify that they are in good condition and have been properly maintained. Bonding straps that are installed to control static electricity are to be visually examined.
5. Alerts and safety systems associated with pressurised installations and any safety device associated with non-safe type electrical equipment that is protected by air-locks or pressurisation, are to be verified.

21.3.4 Fuel installations are to be surveyed as follows:

1. Portable and/or fixed drip trays, or insulation providing protection in the event of fuel leakage, are to be examined.
2. Components of the fuel installation fitted with insulation to provide protection against ice formation on are to be examined for satisfactory condition.
3. Fuel piping, valves and fittings are to be generally examined, with particular attention to double-wall or ventilated ducting arrangements, expansion bellows, supports and vapour seals on insulated piping.

21.3.5 Inerting arrangements and associated alarms are to be verified as being in satisfactory condition, including the means for prevention of backflow of fuel vapour to the inert gas system.

21.3.7 The closing devices for all air-intakes and openings into accommodation spaces, service spaces, machinery spaces, control stations and approved openings in superstructures and deckhouses less than 10m from deck-mounted fuel storage tanks, are to be examined.

21.3.8 Venting arrangements, including protection screens if provided, for fuel storage tanks, inter-barrier spaces and tank hold spaces as applicable, are to be visually examined externally. The external condition of the fuel storage tank relief valves is to be verified and records of the last test of the opening/closing pressures are to be reviewed.

21.3.9 Means for draining the vent arrangements from fuel storage tank pressure relief valves and other system relief valves are to be examined to ensure that there is no liquid build-up that would impede effective operation, drain valves are to be checked as applicable.

21.3.10 Heating arrangements, if fitted, for steel structures in cofferdams and other spaces are to be verified in satisfactory condition.

21.3.11 All gas-tight bulkhead penetrations, including any gas-tight shaft seals, are to be visually examined.

21.4.1 The following fuel processing equipment is to be generally examined in working condition and operational parameters verified. Insulation, where fitted, need not be removed but any deterioration of insulation, or evidence of dampness which could lead to external corrosion of the vessels or their connections, is to be investigated:

1. Heat exchangers and pressure vessels.
2. Natural gas fuel heaters, vaporisers, masthead heaters.
3. Heating arrangements, including provision for continuous heating and circulation of heating medium to prevent freezing during start up and when the fuel installation is not in use.
4. Fuel piping and components associated with the fuel processing equipment.

21.4.2 Where the double wall or duct containing fuel piping is protected using a pressurised inert gas atmosphere the monitoring and maintenance of the inert atmosphere is to be confirmed in satisfactory condition.

21.4.3 The condition of the fuel isolation valve and double block and bleed arrangements for each consumer is to be examined with respect to:

1. Containment to prevent fuel leakage from any valve arrangements installed within the machinery space.
2. Connections to the inerting and venting arrangements.
3. General examination to confirm that the valve arrangement and all associated fuel monitoring and control equipment are in satisfactory condition. The external examination is to be supplemented by a review of relevant operational, maintenance and service reports.

21.4.4 Where fuel processing equipment is located within an independent space that functions as containment in the event of a fuel spill (e.g. a tank connection space), the space is to be examined internally and externally to verify that the structure remains in a satisfactory condition to contain any potential leakage of fuel including any thermal isolation to protect surrounding structure from damage due to cryogenic leakage.

21.5.1 Areas in which fuel storage tanks are located (on and below deck) are to be examined for any changes to the arrangements within those areas that may affect the hazardous area rating.

21.5.2 For Type C pressurised fuel storage tanks the external surface of the fuel storage tank insulation is to be visually examined for cold spots to verify the condition of the insulation arrangements. This examination is to be carried out with the fuel storage tanks loaded. Ideally fuel storage tanks should be loaded to the maximum loading limit; examination of partially-filled fuel storage tanks may be accepted alongside a review of records of periodic cold spot examinations carried out by suitably trained and qualified crew.

21.5.3 The supporting structure is to be examined to confirm that the saddle arrangement remains in satisfactory condition in accordance with the approved design.

21.5.4 For vacuum-insulated fuel storage tanks, monitoring records are to be reviewed to confirm satisfactory maintenance of the vacuum. Any trends identifying a breakdown or loss of vacuum containment are to be investigated.

21.5.5 For Type B fuel storage tanks where the insulation arrangements are such that the insulation cannot be examined, the surrounding structures of wing tanks, double bottom tanks and cofferdams are to be visually examined for cold spots. This examination is to be carried out with the fuel storage tanks loaded. Ideally fuel storage tanks should be loaded to the maximum loading limit; examination of partially-filled fuel storage tanks may be accepted alongside a review of records of periodic cold spot examinations carried out by suitable trained and qualified crew.

21.5.6 For membrane fuel storage tanks the performance of the insulation arrangements is to be confirmed in accordance with approved procedures submitted by the containment designers.

21.6.1 The fuel-bunkering system, including manifold connections, isolation valves, bunker piping and linked Emergency Shut Down (ESD) system connection equipment (including cabling and connectors), are to be visually examined.

21.6.2 Bunkering operations are to be observed as far as possible; satisfactory condition of the bunkering control alert and safety system is to be verified. During annual survey it is not expected that ESD1 (stoppage of bunker transfer) or ESD2 (disconnection of bunker piping) will be operationally tested but records of maintenance and testing are to be reviewed. However, prior to starting the bunkering operation, it is expected that an ESD1 is tested with no LNG in the system (i.e. a dry test). Records of the testing are to be available during survey.

21.7.1 In addition to the requirements below, the requirements of Pt 1, Ch 3, 21.1 General to Pt 1, Ch 3, 21.6 Annual Survey - Fuel Bunkering System are to be complied with.

1. Control, alert and safety systems for the bunkering system, fuel-containment systems and processing equipment, together with any associated shutdown and/or interlock, are to be tested under working conditions and, if necessary, recalibrated. Shutdown sequence and extent are to be verified against documented procedures where applicable. Such safety systems include but are not limited to:
   1. Bunkering ESD system is to be tested, without fuel in the piping, to verify that ESD system operation will result in a closure of the isolation valves and a shutdown of machinery associated with bunkering operations. All ESD activations and outputs are to be tested including fuel storage tank overfill protection, bunkering isolation valve closure and automatic shutdown of machinery associated with bunkering operations.
   2. Fuel-processing equipment shutdown and closure of isolation valves resulting from:
      • loss of the valve-actuating medium;
      • loss of ventilation in fuel piping double wall /ventilated duct; or
      • loss of pressure of inert gas in pressurised double-walled pipe arrangement.
   3. Fuel processing equipment shutdown and closure of isolation valves as a result of deviation in the fuel supply to engineroom from the normal operating conditions (temperature and pressure).
   4. Fuel installation shutdown as a result of gas detection.
   5. Safety interlocks on fuel-processing equipment are to be examined and tested as necessary to confirm satisfactory condition.
2. A General Examination within the areas deemed as hazardous, such as bunker stations, vent mast area, tank connection space and spaces adjacent to vent arrangements from the tank connection space (if applicable), to verify the electrical arrangements have been maintained satisfactorily for operation in a hazardous environment.
3. Verification that piping and independent fuel storage tanks are electrically bonded to the hull.

21.7.2 Consideration will be given to simulated testing, provided that it is considered representative. Comprehensive maintenance records, including details of tests carried out in accordance with the fuel plant and instrumentation maintenance manuals may be presented for review. Acceptance of either simulated testing or maintenance records including reports of testing as described above is subject to the satisfaction of the attending Surveyor.

21.8.1 The requirements of Pt 1, Ch 3, 21.1 General to Pt 1, Ch 3, 21.7 Intermediate Surveys are to be complied with.

21.8.2 The items covered by Pt 1, Ch 3, 21.8 Complete Surveys − General requirements to Pt 1, Ch 3, 21.9 Complete Surveys − Natural gas fuelled consumers and other equipment 21.9.5 may, at the request of the Owner, be examined on a Continuous Survey basis provided the interval between examinations of each item does not exceed five years. Exceptions may be made to this requirement if Condition Based Maintenance arrangements have been agreed and maintained satisfactorily (see Pt 1, Ch 3, 21.1 General 21.1.9 ).

21.8.3 Except where alternative provisions are given below, all fuel storage tanks are to be examined externally and internally, particular attention being paid to the plating in way of supports of securing arrangements for independent tanks, pipe connections, also to sealing arrangements in way of the deck penetrations. Insulation is to be removed as required.

21.8.4 Provided that the structural examination is satisfactory, that the gas detection systems have been found to be in satisfactory condition, routine on board checks and maintenance records are satisfactory and that the voyage records have not shown any abnormal operation, fuel storage tanks will not require hydrostatic testing (except as required by Pt 1, Ch 3, 21.8 Complete Surveys − General requirements.

21.8.5 The non-destructive testing (NDT) of independent fuel storage tanks is to supplement visual inspection with particular attention to be given to the integrity of the main structural members, tank shell and highly-stressed parts, including welded connections as deemed necessary by the Surveyor. The following items are considered as highly-stressed parts:

• structure in way of tank supports and anti-rolling/anti-pitching devices,
• web frames or stiffening rings,
• swash bulkhead boundaries,
• dome and stump connections to tank shell,
• foundations for pumps, towers, ladders, etc.,
• pipe connections.

21.8.6 The NDT testing requirements for different types of independent fuel storage tanks are detailed below:

1. For independent fuel storage tanks of Type B, the extent of non-destructive testing is to be given in the test schedule specially prepared for the tank design. The Owner is to submit proposals for the extent of non-destructive testing of the fuel storage tanks in advance of the survey.
2. For vacuum-insulated independent fuel storage tanks of Type C vacuum monitoring is accepted as a demonstration of the internal integrity of the tank. This is subject to verification that the monitoring equipment is being maintained, operated and calibrated in a satisfactory condition. There is no further requirement for internal examination and testing of these tanks. The tank support arrangements are to be visually examined; non-destructive testing may be required if the condition raises doubt as to the structural integrity.
3. For non-vacuum insulated independent fuel storage tanks of Type C non-destructive testing is required on the plating in way of supports and also over selected lengths of welds. Where such testing raises doubt as to the structural integrity, further testing is to be carried out in accordance with the requirements of the manufacturer’s test and inspection instructions for hydraulic testing (normally at 1,25 times the approved maximum vapour pressure). Alternatively, consideration will be given to pneumatic testing under special circumstances, provided full details are submitted for approval.
4. At each alternate Complete Survey (i.e. at 10 year intervals); non-vacuum insulated independent fuel storage tanks of Type C are to be either:
   1. Hydrostatically or hydro-pneumatically tested to not less than 1,25 times MARVS in accordance with the requirements of the manufacturer’s test and inspection instructions. The requirements for non-destructive testing in 21.8.5 are to be carried out following this test as required by the Surveyor.

      Or:

   2. Subject to a thorough, planned, non-destructive testing. This testing is to be carried out in accordance with a test schedule specially prepared for the tank design. If a special programme does not exist, the following should be tested:
      • structure in way of tank supports and anti-rolling/anti-pitching devices;
      • stiffening rings;
      • Y-connections between tank shell and a longitudinal bulkhead of bi-lobe tanks;
      • swash bulkhead boundaries if applicable;
      • dome and sump connections to the tank shell if applicable;
      • pipe connections.

At least 10 per cent of the length of the welded connections in each of the above-mentioned areas is to be tested. This testing is to be carried out internally and externally as applicable. Insulation is to be removed as necessary for the required non-destructive testing.

21.8.7 Membrane fuel storage tank surveys are to be carried out in accordance with approved testing procedures provided by the containment designers.

21.8.8 Fuel storage tank pipe connections and fittings are to be examined, and all valves and cocks in direct communication with the interiors of the tanks are to be opened out for inspection and the connection pipes are to be examined internally, so far as practicable. Special attention is to be paid to the fuel storage tank master isolation valve(s); the valve seat is to be visually examined and the valve tested at the maximum working pressure of the fuel storage tank prior to re-commissioning the fuel system.

21.8.9 Relief valves are to be surveyed as follows:

1. The pressure relief valves for the fuel storage tanks are to be opened for examination, adjusted to the correct operating pressure as indicated in Pt 1, Ch 3, 21.8 Complete Surveys − General requirements, function-tested, and sealed. If the tanks are equipped with relief valves with non-metallic membranes in the main or pilot valves, such non-metallic membranes are to be replaced. Valves may be removed from the tank for the purpose of making this adjustment under pressure of air or other suitable gas. If valves are removed, the tank and fuel piping downstream of the tank isolation valves are to be gas-freed and inerted.
2. Valves are to lift at a pressure not more than the percentage given below, above the maximum vapour pressure for which the tanks have been approved:
   • For 0 to 1,5 bar, 10 per cent.
   • For 1,5 to 3,0 bar, 6 per cent.
   • For pressures exceeding 3,0 bar, 3 per cent.
3. Where a detailed record of continuous overhaul and retesting of individually-identifiable relief valves is maintained, consideration will be given to acceptance on the basis of opening, internal examination, and testing of a representative sampling of valves, including each size and type of relief valve in use, provided there is logbook evidence that the remaining valves have been overhauled and tested since the previous Complete Survey.
4. Relief valves on fuel piping are to have their pressure settings checked. The valves may be removed from the piping for this purpose. At the Surveyor’s discretion a sample of each size and type of valve may be opened for examination and testing.

21.8.10 All fuel pumps, booster pumps and vapour pumps are to be opened out for examination. Where applicable, pumping systems for inter-barrier spaces are to be checked and verified to be in satisfactory condition.

21.8.11 Piping for the fuel processing system including valves, actuators and compensators is to be opened for examination. Insulation may need to be removed, as deemed necessary, to ascertain the condition of the piping. If any doubt exists regarding the integrity of the piping based upon visual examination then, where deemed necessary by the Surveyor, a pressure test at 1,25 times MARVS of the piping is to be carried out. The complete piping systems are to be tested for leaks after re-assembly.

21.8.12 Equipment for the production of inert gas is to be examined and shown to be in satisfactory condition, operating within the gas specification limits. Piping, valves, etc., for the distribution of the inert gas are to be generally examined. Pressure vessels for the storage of inert gas are to be examined internally and externally and the securing arrangements are to be specially examined. Pressure relief valves are to be demonstrated to be in satisfactory condition. Liquid nitrogen storage vessels are to be examined, so far as practicable, and all control equipment, alarms and safety devices are to be verified as operational.

21.8.13 Gastight bulkhead shaft seals are to be opened out so that the sealing arrangements may be checked.

21.8.14 Any sea connections associated with the fuel handling equipment are to be opened out when the unit is in dry dock.

21.8.15 Where an approved condition-monitoring system or condition-based maintenance system is in place, the requirements for opening up of equipment may be reduced accordingly where the condition of the equipment can be shown to be within agreed acceptable limits as detailed inPt 5, Ch 21 Requirements for Condition Monitoring Systems and Machinery Condition-Based Maintenance Systems of the Rules and Regulations for the Classification of Ships.

21.8.16 Testing of the tank connection space and cofferdam leakage-detection arrangement (temperature sensors and gas detectors) is to be carried out.

21.8.17 An electrical insulation resistance test of the circuits terminating in, or passing through, hazardous areas, is to be carried out. If the unit is not in a gas-free condition, the results of previously recorded test readings may be accepted together with a review of the on-board monitoring of the earth loop impedance of relevant circuits.

21.9.2 The steam side of steam heaters is to be hydraulically tested to 1,5 times the design pressure.

21.9.3 Fuel pipe ducts or casings are to be generally examined and the exhaust or inerting arrangements are to be verified.

21.9.4 All alarms associated with the natural gas burning systems are to be verified; including, but not limited to, main and auxiliary engines, boilers, incinerators and gas combustion units.

21.9.5 The satisfactory condition of all pressure relief valves and/or safety discs throughout the installation is to be verified.