Ī

ᾬ Ņ ᾬLN Ü Ñ Ń

ᾟ Üᾟ ŇÌ

where:

ᾬL = maximum working pressure of the inner pipe

ᾟ = Cp/Cv constant pressure specific heat divided by the constant volume specific heat(1.31 for CH4)

The tangential membrane stress of a straight pipe is not to exceed the tensile strength divided by 1.5 (Rm/1.5) when subjected to the above pressures. The pressure ratings of all other piping components are to reflect the same level of strength as straight pipes.

As an alternative to using the peak pressure from the above formula, the peak pressure found from representative tests can be used. Test reports are then to be submitted.

(4) For low pressure piping, the duct is to be dimensioned for a design pressure not less than the maximum working pressure of the gas pipes. The duct is also to be pressure tested to show that it can withstand the expected maximum pressure at gas pipe rupture.

(5) The arrangement and installation of the high-pressure gas piping are to provide the necessary

flexibility for the gas supply piping to accommodate the oscillating movements of the main en- gine, without running the risk of fatigue problems. The length and configuration of the branch lines are important factors in this regard.

2. Gas supply system for ESD-protected machinery spaces is to comply with the following.

(1) The pressure in the gas supply system is not to exceed 1.0 MPa.

(2) The gas supply lines are to have a design pressure not less than 1.0 MPa.

108.

1.

Gas fuel storage

Liquefied gas storage tanks

(1) The storage tank used for liquefied gas is to be an independent tank designed in accordance with the Rules for Steel Ships Pt. 7 Ch. 5 , Sec. 4.

(2) Pipe connections to the tank are normally to be mounted above the highest liquid level in the

tanks. However, connections below the highest liquid level may be accepted after special consid- eration by the Society.

(3) Pressure relief valves as required in the Rules for Steel Ships Pt. 7 Ch. 5 , Sec. 8. are to be fitted.

(4)

(5)

The outlet from the pressure relief valves is normally to be located at least B/3 or 6 m,

whichever is greater, above the weather deck and 6 m above the working area and gangways, where B is the greatest moulded breadth of the ship in meters. The outlets are normally to be located at least 10 m from the nearest:

(A) Air intake, air outlet or opening to accommodation, service and control spaces, or other gas safe spaces; and

(B) Exhaust outlet from machinery or from furnace

installation.

Storage tanks for liquid gas are not to be filled to more than 98% full at the reference temper- ature, where the reference temperature is as defined in the Rules for Steel Ships Pt. 7 Ch. 5, paragraph 1501.4. A filling limit curve for actual filling temperatures is to be prepared from the formula given in the Rules for Steel Ships Pt. 7 Ch. 5, paragraph 1501.2. However, when the tank insulation and tank location makes the probability very small for the tank contents to be heated up due to external fire, special considerations may be made to allow a higher filling

(6) limit than calculated using the reference temperature, but never above 95%.

Means that are not dependent on the gas machinery system are to be provided whereby liquid

(7) gas in the storage tanks can be emptied.

It is to be possible to empty, purge gas and vent gas fuel tanks with gas piping systems. Procedures are to be prepared for this. Inerting is to be performed with, for instance, nitrogen, CO2 or argon prior to venting to avoid an explosion hazardous atmosphere in tanks and gas

2. Compressed gas storage tanks

(1) The storage tanks to be used for compressed gas are to be certified and approved by the Society.

(2) Tanks for compressed gas are to be fitted with pressure relief valves with a set point below

the design pressure of the tank and with outlet located as required in 1.(4).

3. Storage on open deck

(1) Both gases of the compressed and the liquefied type may be accepted stored on open deck.

(2) The storage tanks or tank batteries are to be located at least B/5 from the ship's side. For ships other than passenger ships a tank location closer than B/5 but not less than 760 mm from the ship's side may be accepted.

(3) The gas storage tanks or tank batteries and equipment are to be located ural ventilation, so as to prevent accumulation of escaped gas.

(4) Tanks for liquid gas with a connection below the highest liquid level

to assure sufficient nat-

(See 1.(2) ) are to be

fitted with drip trays below the tank which are to be of sufficient capacity to contain the vol- ume which could escape in the event of a pipe connection failure. The material of the drip tray is to be stainless steel, and there are to be efficient separation or isolation so that the hull or deck structures are not exposed to unacceptable cooling, in case of leakage of liquid gas.

4. Storage in enclosed space

(1) Gas in a liquid state may be stored in enclosed spaces, with a maximum acceptable working pressure of 1.0 MPa. Storage of compressed gas in enclosed spaces and location of gas tanks with a higher pressure than 1.0 MPa in enclosed spaces is normally not acceptable, but may be permitted after special consideration and approval by the Society provided the following is ful- filled in addition to (3).

(A) Adequate means are to be provided to depressurize the tank in case of a fire which can af- fect the tank; and

(B) All surfaces within the tank room are to be provided with suitable thermal protection

against any lost high pressure gas and resulting condensation unless the bulkheads are de- signed for the lowest temperature that can arise from gas expansion leakage; and

(2) The gas storage tank(s) are to be placed as close as possible to the center line. But, for ships other than passenger ships and multi-hulls, a tank location closer than B/5 from the ship side may be accepted:

(A) Minimum, the lesser of B/5 and 11.5m from the ship side;

(B) Minimum, the lesser of B/15 and 2m from the bottom plating;

(C) Not less than 760 mm from the shell plating.

(3) The storage tank and associated valves and piping are to be located in a space designed to act as a second barrier, in case of liquid or compressed gas leakage. The material of the bulk- heads of this space is to have the same design temperature as the gas tank, and the space is to be designed to withstand the maximum pressure build-up. Alternatively, pressure relief venting to a safe location (mast) can be provided. The space is to be capable of containing leakage, and is to be isolated thermally so that the surrounding hull is not exposed to unacceptable cool- ing, in case of leakage of the liquid or compressed gas. This second barrier space is in other parts of these Guidance called "tank room". When the tank is double walled and the outer tank shell is made of cold resistant material, a tank room could be arranged as a box fully welded to the outer shell of the tank, covering all tank connections and valves, but not necessarily all of the outer tank shell.

(4) The tank room may be accepted as the outer shell of a stainless steel vacuum insulated tank in combination with a stainless steel box welded to the outer shell, containing all tank pipe con- nections, valves, piping, etc. In this case, the requirements for ventilation and gas detection are to be made applicable to the box, but not to the double barrier of the tank.

(5) Bilge suctions from the tank room, if provided, are not to be connected to the bilge system for the rest of the ship.

109. Gas fuel bunkering system and distribution system outside machinery spaces

1. Fuel bunkering station

(1) The bunkering station is to be so located that sufficient natural ventilation is provided. Closed or semi-enclosed bunkering stations are to be subject to special consideration. The bunkering station is to be physically separated or structurally shielded from accommodation, cargo/working deck and control stations. Connections and piping are to be so positioned and arranged that any damage to the gas piping does not cause damage to the vessel’s gas storage tank arrangement leading to uncontrolled gas discharge.

(2) Drip trays are to be fitted below liquid gas bunkering connections and where leakage may occur. The drip trays are to be made of stainless steel, and are to be drained over the ship's side by a pipe that preferably leads down near the sea. This pipe could be temporarily fitted for bunkering operations. The surrounding hull or deck structures are not to be exposed to un- acceptable cooling, in case of leakage of liquid gas. For compressed gas bunkering stations, low temperature steel shielding are to be provided to prevent the possible escape of cold jets im- pinging on surrounding hull structure.

(3)

Control of the bunkering is to be possible from a safe location in regard to bunkering operations. At this location tank pressure and tank level are to be monitored. Overfill alarm and

automatic shutdown are also to be indicated at this location.

2. Bunkering system

(1) The bunkering system is to be so arranged that no gas is discharged to air during storage tanks.

(2) A manually-operated stop valve and a remote operated shutdown valve in series, or a

manually-operated and remote valve are to be fitted in every bunkering line close to

filling of combined

the shore

3.

110.

1.

connecting point. It is to be possible to release the remote-operated valve in the control lo-

cation for bunkering operations and/or another safe location.

(3) If the ventilation in the ducting around the gas bunkering lines stops, an audible and visual alarm is to be provided at bunkering control location.

(4) If gas is detected in the ducting around the bunkering lines, an audible and visual alarm is to be provided at the bunkering control location.

(5) Means are to be provided for draining the liquid from the bunkering pipes at bunkering

completion.

(6) Bunkering lines are to be arranged for inerting and gas freeing. During operation of the vessel, the bunkering pipes are to be gas free.

Distribution outside of machinery spaces

(1) Gas fuel piping is not to be led through accommodation spaces, service spaces or control stations.

(2) Where gas pipes pass through enclosed spaces in the ship, they are to be enclosed in a duct.

This duct is to be mechanically under pressure ventilated with 30 air changes per hour, and gas detection as required in 405. is to be provided.

(3) The duct is to be dimensioned according to 107. 1.(3) and (4).

(4) The ventilation inlet for the duct is to always be located in open air, away from ignition

sources.

(5) Gas pipes located in open air are to be so located that they are not likely to be damaged by accidental mechanical impact.

(6) High-pressure gas lines outside the machinery spaces containing gas-fuelled engines are to be installed and protected so as to minimize the risk of injury to personnel in case of rupture.

Ventilation system

General

(1) Any ducting used for the ventilation of hazardous spaces is to be separated from that used for the ventilation of non-hazardous spaces. The ventilation is to function at all temperature con- ditions the ship will be operating in. Electric fan motors are not to be located in ventilation ducts for hazardous spaces unless the motor is certified for the same hazard zone as the space served.

(2) Design of ventilation fans serving spaces containing gas sources is to fulfil the following:

(A) Electric motors driving fans are to comply with the required explosion protection in the in-

stallation area. Ventilation fans are not to produce a source of vapour ignition in either the ventilated space or the ventilation system associated with the space. Ventilation fans and fan ducts, in way of fans only, are to be of non-sparking construction defined as:

(a) impellers or housings of non-metallic material, due regard being paid to the elimination of static electricity;

(b) impellers and housings of nonferrous metals;

(c) impellers and housing of austenitic stainless steel;

(d) impellers of aluminium alloys or magnesium alloys and a ferrous (including austenitic stainless steel) housing on which a ring of suitable thickness of non-ferrous materials is fitted in way of the impeller, due regard being paid to static electricity and corrosion between ring and housing; or

(e) any combination of ferrous (including austenitic stainless steel) impellers and housings with not less than 13 mm tip design clearance.

(B) In no case is the radial air gap between the impeller and the casing to be less than 0.1 of

the diameter of the impeller shaft in way of the bearing but not less than 2 mm. The gap need not be more than 13 mm.

(C) Any combination of an aluminium or magnesium alloy fixed or rotating component and a

ferrous fixed or rotating component, regardless of tip clearance, is considered a sparking

hazard and should not be used in these places.

(D) The installation on board of the ventilation units is to be such as to ensure the safe bond- ing to the hull of the units themselves.

(3) Any loss of the required ventilating capacity is to give an audible and visual alarm at a perma- nently manned location.

(4)

(5)

Required ventilation systems to avoid any gas accumulation are to consist of independent fans,

each of sufficient capacity, unless otherwise specified in this Guidance.

Air inlets for hazardous enclosed spaces are to be taken from areas which, in the absence of the considered inlet, would be non-hazardous. Air inlets for non-hazardous enclosed spaces are to be taken from non-hazardous areas at least 1.5 m away from the boundaries of any hazard- ous area. Where the inlet duct passes through a more hazardous space, the duct is to have over-pressure relative to this space, unless mechanical integrity and gas-tightness of the duct will ensure that gases will not leak into it.

(6) Air outlets from non-hazardous spaces are to be located outside hazardous areas.

(7) Air outlets from hazardous enclosed spaces are to be located in an open area which, in the ab-

sence of the considered outlet, would be of the same or lesser hazard than the ventilated space.

(8)

The required capacity of the ventilation plant is normally based on the total volume of the room. An increase in required ventilation capacity may be necessary for rooms having a compli-

cated form.

(9) Non-hazardous spaces with opening to a hazardous area are to be arranged with an air-lock and be maintained at overpressure relative to the external hazardous area. The overpressure ven- tilation is to be arranged according to the following requirements:

(A) During initial start-up or after loss of overpressure ventilation, before energizing any elec- trical installations not certified safe for the space in the absence of pressurization, it is to be required to:

(a) proceed with purging (at least 5 air changes) or confirm by measurements that the space

is non-hazardous; and

(b) pressurize the space.

(B) Operation of the overpressure ventilation is to be monitored.

(C) In the event of failure of the overpressure ventilation:

(a) an audible and visual alarm is to be given at a manned location; and

(b) if overpressure cannot be immediately restored, automatic or programmed disconnection of electrical installations according to a recognized standard(Refer to IEC 60092-502 Electrical Installations in Ships Tankers-Special Features, table 5.) is to be conducted.

2. Tank room

(1) The tank room for gas storage is to be provided with an effective mechanical forced ventilation system of the under pressure type, providing a ventilation capacity of at least 30 air changes per hour. The rate of air changes may be reduced if other adequate means of explosion pro- tection are installed. The equivalence of alternative installations is to be demonstrated by a safe- ty analysis.

(2) Approved automatic fail-safe fire dampers are to be fitted in the ventilation trunk for tank room.

3. Machinery spaces containing gas-fuelled engines

(1) The ventilation system for machinery spaces containing gas-fuelled engines is to be independent of all other ventilation systems.

(2) ESD-protected machinery spaces are to have changes per hour. The ventilation system is to

in particular ensure that any formation of gas

ventilation with a capacity of at least 30 air ensure a good air circulation in all spaces, and

pockets in the room are detected. As an alter-

native, arrangements whereby under normal operation the machinery spaces is ventilated with at least 15 air changes an hour is acceptable provided that, if gas is detected in the machinery

space, the number of air changes will automatically be increased to 30 an hour.

(3) The number and power of the ventilation fans are to be such that the capacity is not reduced

by more than 50% of the total ventilation capacity, if a fan with a separate circuit from

main switchboard or emergency switchboard or a group of fans with common circuit from main switchboard or emergency switchboard, is out of action.

4. Pump and compressor rooms

(1) Pump and compressor rooms are to be fitted with effective mechanical ventilation system of under pressure type, providing a ventilation capacity of at least 30 air changes per hour.

the the

the

(2) The number and power of the ventilation fans are to be such that the capacity is not reduced by more than 50%, if a fan with a separate circuit from the main switchboard or emergency switchboard or a group of fans with common circuit from the main switchboard or emergency switchboard, is out of action.

(3) Ventilation systems for pump and compressor rooms are to be in operation when pumps or compressors are working.

(4) When the space is dependent on ventilation for its area classification, the following is to apply:

(A) During initial start-up, and after loss of ventilation, the space is to be purged (at least 5 air

changes), before connecting electrical installations which are not certified for the area classi- fication in absence of ventilation. Warning notices to this effect are to be placed in an easily visible position near the control stand.

(B) Operation of the ventilation is to be monitored.

(C) In the event of failure of ventilation, the following is to apply:

(a) an audible and visual alarm is to be given at a manned location;

(b) immediate action is to be taken to restore ventilation; and

(c) electrical installations are to be disconnected( Intrinsically safe equipment suitable for zone 0

is not required to

be switched off. Certified flameproof lighting may have a separate

switch-off circuit.), if ventilation cannot be restored for an extended period. The dis-

connection is to be

made outside the hazardous areas, and be protected against unauthorized

re-connection, e.g., by lockable switches.