17.20.1 Products transported
under the provisions of this section should be acetylene-free.
17.20.2.1 Unless cargo
tanks are properly cleaned, these products should not be carried in
tanks which have contained as one of the three previous cargoes any
product known to catalyse polymerization, such as:
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.1 anhydrous ammonia and ammonia solutions;
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.2 amines and amine solutions;
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.3 oxidizing substances (e.g. chlorine).
17.20.2.2 Before loading,
tanks should be thoroughly and effectively cleaned to remove all traces
of previous cargoes from tanks and associated pipework, except where
the immediate prior cargo has been propylene oxide or ethylene oxide-propylene
oxide mixtures. Particular care should be taken in the case of ammonia
in tanks made of steel other than stainless steel.
17.20.2.3 In all cases,
the effectiveness of cleaning procedures for tanks and associated
pipework should be checked by suitable testing or inspection to ascertain
that no traces of acidic or alkaline materials remain that might create
a hazardous situation in the presence of these products.
17.20.2.4 Tanks should
be entered and inspected prior to each initial loading of these products
to ensure freedom from contamination, heavy rust deposits and any
visible structural defects. When cargo tanks are in continuous service
for these products, such inspections should be performed at intervals
of not more than two years.
17.20.2.5 Tanks for the
carriage of these products should be of steel or stainless steel construction.
17.20.2.6 Tanks which
have contained these products may be used for other cargoes after
thorough cleaning of tanks and associated pipework systems by washing
or purging.
17.20.3.1 All valves,
flanges, fittings and accessory equipment should be of a type suitable
for use with these products and should be constructed of steel or
stainless steel in accordance with recognized standards. The chemical
composition of all material used should be submitted to the Administration
for approval prior to fabrication. Discs or disc faces, seats and
other wearing parts of valves should be made of stainless steel containing
not less than 11% chromium.
17.20.3.2 Gaskets should
be constructed of materials which do not react with, dissolve in,
or lower the autoignition temperature of these products and which
are fire-resistant and possess adequate mechanical behaviour. The
surface presented to the cargo should be polytetrafluoroethylene (PTFE)
or materials giving a similar degree of safety by their inertness.
Spirally-wound stainless steel with a filler of PTFE or similar fluorinated
polymer may be accepted by the Administration.
17.20.3.3 Insulation and
packing if used should be of a material which does not react with,
dissolve in, or lower the autoignition temperature of these products.
17.20.3.4 The following
materials are generally found unsatisfactory for gaskets, packing
and similar uses in containment systems for these products and would
require testing before being approved by the Administration:
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.1 Neoprene or natural rubber if it comes into
contact with the products;
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.2 Asbestos or binders used with asbestos;
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.3 Materials containing oxides of magnesium, such as
mineral wools.
17.20.4 Filling and discharge
piping should extend to within 100 mm of the bottom of the tank or
any sump.
17.20.5.1 The products
should be loaded and discharged in such a manner that venting of the
tanks to atmosphere does not occur. If vapour return to shore is used
during tank loading, the vapour return system connected to a containment
system for the product should be independent of all other containment
systems.
17.20.5.2 During discharging
operations, the pressure in the cargo tank should be maintained above
0.07 bar gauge.
17.20.5.3 The cargo should
be discharged only by deepwell pumps, hydraulically operated submerged
pumps, or inert gas displacement. Each cargo pump should be arranged
to ensure that the product does not heat significantly if the discharge
line from the pump is shut off or otherwise blocked.
17.20.6 Tanks carrying these
products should be vented independently of tanks carrying other products.
Facilities should be provided for sampling the tank contents without
opening the tank to atmosphere.
17.20.7 Cargo hoses used
for transfer of these products should be marked “FOR ALKYLENE
OXIDE TRANSFER ONLY”.
17.20.8 Hold spaces should
be monitored for these products. Hold spaces surrounding type A and
B independent tanks should also be inerted and monitored for oxygen.
The oxygen content of these spaces should be maintained below 2%.
Portable sampling equipment is satisfactory.
17.20.9 Prior to disconnecting
shore-lines, the pressure in liquid and vapour lines should be relieved
through suitable valves installed at the loading header. Liquid and
vapour from these lines should not be discharged to atmosphere.
17.20.10 Tanks should be
designed for the maximum pressure expected to be encountered during
loading, carriage or unloading of cargo.
17.20.11 Tanks for the carriage of propylene oxide with a
design vapour pressure of less than 0.6 bar and tanks for the carriage of ethylene
oxide-propylene oxide mixtures with a design vapour pressure of less than 1.2 bar should
have a cooling system to maintain the cargo below the reference temperature. For
reference temperature see 15.1.4.1.
17.20.12 Pressure relief
valve settings should not be less than 0.2 bar gauge and for type
C independent cargo tanks not greater than 7.0 bar gauge for the carriage
of propylene oxide and not greater than 5.3 bar gauge for the carriage
of ethylene oxide-propylene oxide mixtures.
17.20.13.1 The piping
system for tanks to be loaded with these products should be completely
separate from piping systems for all other tanks, including empty
tanks, and from all cargo compressors. If the piping system for the
tanks to be loaded with these products is not independent as defined
in 1.3.20 the required piping separation
should be accomplished by the removal of spool pieces, valves, or
other pipe sections and the installation of blank flanges at these
locations. The required separation applies to all liquid and vapour
piping, liquid and vapour vent lines and any other possible connections
such as common inert gas supply lines.
17.20.13.2 The products
should be transported only in accordance with cargo handling plans
that have been approved by the Administration. Each intended loading
arrangement should be shown on a separate cargo handling plan. Cargo
handling plans should show the entire cargo piping system and the
locations for installation of blank flanges needed to meet the above
piping separation requirements. A copy of each approved cargo handling
plan should be kept on board the ship. The International Certificate
of Fitness for the Carriage of Liquefied Gases in Bulk should be endorsed
to include reference to the approved cargo handling plans.
17.20.13.3 Before each
initial loading of these products and before every subsequent return
to such service, certification verifying that the required piping
separation has been achieved should be obtained from a responsible
person acceptable to the port Administration and carried on board
the ship. Each connection between a blank flange and pipeline flange
should be fitted with a wire and seal by the responsible person to
ensure that inadvertent removal of the blank flange is impossible.
17.20.14 The maximum allowable
tank loading limits for each cargo tank should be indicated for each
loading temperature which may be applied and for the applicable maximum
reference temperature, on a list to be approved by the Administration.
A copy of the list should be permanently kept on board by the master.
17.20.15 The cargo should
be carried under a suitable protective padding of nitrogen gas. An
automatic nitrogen make-up system should be installed to prevent the
tank pressure falling below 0.07 bar gauge in the event of product
temperature fall due to ambient conditions or malfunctioning of refrigeration
system. Sufficient nitrogen should be available on board to satisfy
the demand of the automatic pressure control. Nitrogen of commercially
pure quality (99.9% by volume) should be used for padding. A battery
of nitrogen bottles connected to the cargo tanks through a pressure
reduction valve satisfies the intention of the expression "automatic"
in this context.
17.20.16 The cargo tank
vapour space should be tested prior to and after loading to ensure
that the oxygen content is 2% by volume or less.
17.20.17 A water spray
system of sufficient capacity should be provided to blanket effectively
the area surrounding the loading manifold, the exposed deck piping
associated with product handling and the tank domes. The arrangement
of piping and nozzles should be such as to give a uniform distribution
rate of 10 l/m2 per minute. The water spray
system should be capable of both local and remote manual operation
and the arrangement should ensure that any spilled cargo is washed
away. Remote manual operation should be arranged such that remote
starting of pumps supplying the water-spray system and remote operation
of any normally closed valves in the system can be carried out from
a suitable location outside the cargo area, adjacent to the accommodation
spaces and readily accessible and operable in the event of fire in
the areas protected. Additionally, a water hose with pressure to the
nozzle, when ambient temperatures permit, should be connected ready
for immediate use during loading and unloading operations.