Section
21 Natural Gas Fuel Installations
21.1 General
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 1.5.16 (natural gas is hereinafter referred to as fuel).
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 and 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:
- Relevant instruction and information such as loading limit curve
information, bunkering procedures, cooling down procedures and fuel installation
test and inspection procedures.
- Condition-Monitoring or Condition-Based Maintenance documentation as
applicable.
- Test records for bunkering ESD systems.
- Records of crew tests/inspections of the fuel installation.
21.2 Survey Following Repair
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 Annual Surveys − General Requirements for
Fuel Systems
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:
- 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:
- Comparison of read-outs from local and remote
indicators.
- Consideration of read-outs with regard to the actual
conditions.
- Examination of maintenance records with reference to the
approved maintenance management system.
- Verification of calibration status of the measuring
instruments.
- 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:
- fuel storage tank and processing system high and low
pressure
- fuel storage tank high and high-high level
- fuel storage tank overfill level
- fuel storage tank high temperature.
- 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.
- 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.
- 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:
- Portable and/or fixed drip trays, or insulation providing protection
in the event of fuel leakage, are to be examined.
- Components of the fuel installation fitted with insulation to
provide protection against ice formation on are to be examined for satisfactory
condition.
- 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.
21.3.6 Ventilation systems are to be surveyed as follows:
- Ventilation systems and air-locks including their alarm system
are to be generally examined.
- Ventilation fans in hazardous areas are to be visually
examined.
- For ventilated double-walled piping or ducting containing fuel
piping within machinery spaces, exhaust fans and/or supply fans are to be
examined to ensure that the air-flow is not impeded.
- Fuel piping and components associated with the fuel processing
equipment are to be visually examined.
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 Annual Surveys – Fuel Processing
Equipment
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:
- Heat exchangers and pressure vessels.
- Natural gas fuel heaters, vaporisers, masthead heaters.
- 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.
- 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:
- Containment to prevent fuel leakage from any valve arrangements
installed within the machinery space.
- Connections to the inerting and venting arrangements.
- 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 Annual Surveys – Fuel Storage
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 Annual Survey - Fuel Bunkering
System
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 Intermediate Surveys
21.7.1 In addition to the requirements below, the requirements of Pt 1, Ch 3, 21.9 Complete Surveys − Natural gas fuelled consumers and other equipment to Pt 1, Ch 3, 21.6 Annual Survey - Fuel Bunkering System are to be complied with.
- 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:
- 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.
- 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.
- 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).
- Fuel installation shutdown as a result of gas
detection.
- Safety interlocks on fuel-processing equipment are to be
examined and tested as necessary to confirm satisfactory condition.
- 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.
- 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 Complete Surveys − General
requirements
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 21.8.6.(d).(i)).
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:
- 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.
- 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.
- 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.
- 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:
- 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:
- 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:
- 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 21.8.9.(b), 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.
- 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.
- 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.
- 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.
21.8.16 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 Complete Surveys − Natural gas fuelled
consumers and other equipment
21.9.1 Heat exchangers associated with the fuel installation are to be opened
out and examined as follows:
- The water end covers of evaporators are to be removed for
examination of the tubes, tube plates and covers.
- Heating medium pumps, including standby pump(s) which may be
used on other services, are to be opened out for examination.
- Where a pressure vessel is insulated, sufficient insulation is
to be removed, especially in way of connections and supports, to enable the
vessel’s condition to be ascertained.
Note this refers to external insulation, not additional
insulation that may be installed in the annular space of a vacuum
insulated tank.
- Insulated piping is to have sufficient insulation removed to
enable its condition to be ascertained. Vapour seals are to be specially
examined for their condition. Vacuum-insulated piping is to be visually
examined and records of maintenance and vacuum monitoring are to be
reviewed.
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.
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