Goal
To set out the additional requirements in respect of specific
cargoes.
17.1 General
The requirements of this chapter are applicable where reference thereto
is made in column "i" in the table of chapter 19. These requirements are
additional to the general requirements of the Code.
17.2 Materials of construction
Materials that may be exposed to cargo during normal operations shall be
resistant to the corrosive action of the gases. In addition, the following materials
of construction for cargo tanks and associated pipelines, valves, fittings and other
items of equipment normally in direct contact with the cargo liquid or vapour shall
not be used for certain products as specified in column "i" in the table of
chapter 19:
-
.1 mercury, copper and copper-bearing alloys,
and zinc;
-
.2 copper, silver, mercury, magnesium and other
acetylide-forming metals;
-
.3 aluminium and aluminium-bearing alloys;
-
.4 copper, copper alloys, zinc and galvanized
steel;
-
.5 aluminium, copper and alloys of either;
and
-
.6 copper and copper-bearing alloys with
greater than 1% copper.
17.3 Independent tanks
17.3.1 Products shall be carried in independent tanks
only.
17.3.2 Products shall be carried in type C independent
tanks, and the requirements of 7.1.2 shall apply. The design pressure of the cargo
tank shall take into account any padding pressure or vapour discharge unloading
pressure.
17.4 Refrigeration systems
17.4.1 Only the indirect system described in 7.3.1.2
shall be used.
17.4.2 For a ship engaged in the carriage of products
that readily form dangerous peroxides, recondensed cargo shall not be allowed to
form stagnant pockets of uninhibited liquid. This may be achieved either by:
-
.1 using the indirect system described in
7.3.1.2, with the condenser inside the cargo tank; or
-
.2 using the direct system or combined system
described in 7.3.1.1 and .3 respectively, or the indirect system described
in 7.3.1.2 with the condenser outside the cargo tank, and designing the
condensate system to avoid any places in which liquid could collect and be
retained. Where this is impossible, inhibited liquid shall be added upstream
of such a place.
17.4.3 If the ship is to consecutively carry products
as specified in 17.4.2 with a ballast passage between, all uninhibited liquid shall
be removed prior to the ballast voyage. If a second cargo is to be carried between
such consecutive cargoes, the reliquefaction system shall be thoroughly drained and
purged before loading the second cargo. Purging shall be carried out using either
inert gas or vapour from the second cargo, if compatible. Practical steps shall be
taken to ensure that polymers or peroxides do not accumulate in the cargo
system.
17.5 Cargoes requiring type 1G ship
17.5.1 All butt-welded joints in cargo piping exceeding
75 mm in diameter shall be subject to 100% radiography.
17.5.2 Gas sampling lines shall not be led into or
through non-hazardous areas. Alarms referred to in 13.6.2 shall be activated when
the vapour concentration reaches the threshold limiting value.
17.5.3 The alternative of using portable gas detection
equipment in accordance with 13.6.5 shall not be permitted.
17.5.4 Cargo control rooms shall be located in a
non-hazardous area and, additionally, all instrumentation shall be of the indirect
type.
17.5.5 Personnel shall be protected against the effects
of a major cargo release by the provision of a space within the accommodation area
that is designed and equipped to the satisfaction of the Administration.
17.5.6 Notwithstanding the requirements in 3.2.4.3,
access to forecastle spaces shall not be permitted through a door facing the cargo
area, unless airlock in accordance with 3.6 is provided.
17.5.7 Notwithstanding the requirements in 3.2.7,
access to control rooms and machinery spaces of turret systems shall not be
permitted through doors facing the cargo area.
17.6 Exclusion of air from vapour spaces
Air shall be removed from cargo tanks and associated piping before
loading and, then, subsequently excluded by:
-
.1 introducing inert gas to maintain a positive
pressure. Storage or production capacity of the inert gas shall be
sufficient to meet normal operating requirements and relief valve leakage.
The oxygen content of inert gas shall, at no time, be greater than 0.2% by
volume; or
-
.2 control of cargo temperatures such that a
positive pressure is maintained at all times.
17.7 Moisture control
For gases that are non-flammable and may become corrosive or react
dangerously with water, moisture control shall be provided to ensure that cargo
tanks are dry before loading and that, during discharge, dry air or cargo vapour is
introduced to prevent negative pressures. For the purposes of this paragraph, dry
air is air that has a dew point of -45°C or below at atmospheric pressure.
17.8 Inhibition
Care shall be taken to ensure that the cargo is sufficiently inhibited
to prevent self-reaction (e.g. polymerization or dimerization) at all times during
the voyage. Ships shall be provided with a certificate from the manufacturer
stating:
-
.1 name and amount of inhibitor added;
-
.2 date inhibitor was added and the normally
expected duration of its effectiveness;
-
.3 any temperature limitations affecting the
inhibitor; and
-
.4 the action to be taken should the length of
the voyage exceed the effective lifetime of the inhibitors.
17.9 Flame screens on vent outlets
When carrying a cargo referenced to this section, cargo tank vent outlets
shall be provided with readily renewable and effective flame screens or safety heads
of an approved type. Due attention shall be paid in the design of flame screens and
vent heads, to the possibility of the blockage of these devices by the freezing of
cargo vapour or by icing up in adverse weather conditions. Flame screens shall be
removed and replaced by protection screens, in accordance with 8.2.15, when carrying
cargoes not referenced to this section.
17.10 Maximum allowable quantity of cargo per
tank
When carrying a cargo referenced to this section, the quantity of the
cargo shall not exceed 3,000 m3 in any one tank.
17.11 Cargo pumps and discharge arrangements
17.11.1 The vapour space of cargo tanks equipped with
submerged electric motor pumps shall be inerted to a positive pressure prior to
loading, during carriage and during unloading of flammable liquids.
17.11.2 The cargo shall be discharged only by deepwell
pumps or by hydraulically operated submerged pumps. These pumps shall be of a type
designed to avoid liquid pressure against the shaft gland.
17.11.3 Inert gas displacement may be used for
discharging cargo from type C independent tanks, provided the cargo system is
designed for the expected pressure.
17.12 Ammonia
17.12.1 Anhydrous ammonia may cause stress corrosion
cracking in containment and process systems made of carbon-manganese steel or nickel
steel. To minimize the risk of this occurring, measures detailed in 17.12.2 to
17.12.8 shall be taken, as appropriate.
17.12.2 Where carbon-manganese steel is used, cargo
tanks, process pressure vessels and cargo piping shall be made of fine-grained steel
with a specified minimum yield strength not exceeding 355 N/mm2, and with
an actual yield strength not exceeding 440 N/mm2. One of the following
constructional or operational measures shall also be taken:
-
.1 lower strength material with a specified
minimum tensile strength not exceeding 410 N/mm2 shall be used;
or
-
.2 cargo tanks, etc., shall be post-weld stress
relief heat treated; or
-
.3 carriage temperature shall be maintained,
preferably at a temperature close to the product's boiling point of -33°C,
but in no case at a temperature above -20°C; or
-
.4 the ammonia shall contain not less than 0.1%
w/w water, and the master shall be provided with documentation confirming
this.
17.12.3 If carbon-manganese steels with higher yield
properties are used other than those specified in 17.12.2, the completed cargo
tanks, piping, etc., shall be given a post-weld stress relief heat treatment.
17.12.4 Process pressure vessels and piping of the
condensate part of the refrigeration system shall be given a post-weld stress relief
heat treatment when made of materials mentioned in 17.12.1.
17.12.5 The tensile and yield properties of the welding
consumables shall exceed those of the tank or piping material by the smallest
practical amount.
17.12.6 Nickel steel containing more than 5% nickel and
carbon-manganese steel, not complying with the requirements of 17.12.2 and 17.12.3,
are particularly susceptible to ammonia stress corrosion cracking and shall not be
used in containment and piping systems for the carriage of this product.
17.12.7 Nickel steel containing not more than 5% nickel
may be used, provided the carriage temperature complies with the requirements
specified in 17.12.2.3.
17.12.8 To minimize the risk of ammonia stress
corrosion cracking, it is advisable to keep the dissolved oxygen content below 2.5
ppm w/w. This can best be achieved by reducing the average oxygen content in the
tanks prior to the introduction of liquid ammonia to less than the values given as a
function of the carriage temperature T in the table below:
T (°C)
|
O2 (% v/v)
|
-30 and below
|
0.9
|
-20
|
0.5
|
–10
|
0.28
|
0
|
0.16
|
10
|
0.1
|
20
|
0.05
|
30
|
0.03
|
Oxygen percentages for intermediate temperatures may be obtained by
direct interpolation.
17.13 Chlorine
17.13.1
Cargo containment system
17.13.1.1 The capacity of each tank shall not exceed
600 m3 and the total capacity of all cargo tanks shall not exceed 1,200
m3.
17.13.1.2 The tank design vapour pressure shall not be
less than 1.35 MPa (see 7.1.2 and 17.3.2).
17.13.1.3 Parts of tanks protruding above the upper
deck shall be provided with protection against thermal radiation, taking into
account total engulfment by fire.
17.13.1.4 Each tank shall be provided with two PRVs. A
bursting disc of appropriate material shall be installed between the tank and the
PRVs. The rupture pressure of the bursting disc shall be 0.1 MPa lower than the
opening pressure of the pressure relief valve, which shall be set at the design
vapour pressure of the tank but not less than 1.35 MPa gauge. The space between the
bursting disc and the relief valve shall be connected through an excess flow valve
to a pressure gauge and a gas detection system. Provisions shall be made to keep
this space at or near the atmospheric pressure during normal operation.
17.13.1.5 Outlets from PRVs shall be arranged in such a
way as to minimize the hazards on board the ship as well as to the environment.
Leakage from the relief valves shall be led through the absorption plant to reduce
the gas concentration as far as possible. The relief valve exhaust line shall be
arranged at the forward end of the ship to discharge outboard at deck level with an
arrangement to select either port or starboard side, with a mechanical interlock to
ensure that one line is always open.
17.13.1.6 The Administration and the port
Administration may require that chlorine is carried in a refrigerated state at a
specified maximum pressure.
17.13.2
Cargo piping systems
17.13.2.1 Cargo discharge shall be performed by means
of compressed chlorine vapour from shore, dry air or another acceptable gas, or
fully submerged pumps. Cargo discharge compressors on board ships shall not be used
for this. The pressure in the vapour space of the tank during discharging shall not
exceed 1.05 MPa gauge.
17.13.2.2 The design pressure of the cargo piping
system shall be not less than 2.1 MPa gauge. The internal diameter of the cargo
pipes shall not exceed 100 mm. Only pipe bends shall be accepted for compensation of
pipeline thermal movement. The use of flanged joints shall be restricted to a
minimum and, when used, the flanges shall be of the welding neck type with tongue
and groove.
17.13.2.3 Relief valves of the cargo piping system
shall discharge to the absorption plant, and the flow restriction created by this
unit shall be taken into account when designing the relief valve system (see 8.4.3
and 8.4.4).
17.13.3
Materials
17.13.3.1 The cargo tanks and cargo piping systems
shall be made of steel suitable for the cargo and for a temperature of -40°C, even
if a higher transport temperature is intended to be used.
17.13.3.2 The tanks shall be thermally stress relieved.
Mechanical stress relief shall not be accepted as an equivalent.
17.13.4
Instrumentation: safety devices
17.13.4.1 The ship shall be provided with a chlorine
absorbing plant with a connection to the cargo piping system and the cargo tanks.
The absorbing plant shall be capable of neutralizing at least 2% of the total cargo
capacity at a reasonable absorption rate.
17.13.4.2 During the gas-freeing of cargo tanks,
vapours shall not be discharged to the atmosphere.
17.13.4.3 A gas detecting system shall be provided that
is capable of monitoring chlorine concentrations of at least 1 ppm by volume. Sample
points shall be located:
-
.1 near the bottom of the hold spaces;
-
.2 in the pipes from the safety relief
valves;
-
.3 at the outlet from the gas absorbing
plant;
-
.4 at the inlet to the ventilation systems for
the accommodation, service and machinery spaces and control stations;
and
-
.5 on deck – at the forward end, midships and
the after end of the cargo area. This is only required to be used during
cargo handling and gas-freeing operations.
The gas detection system shall be provided with an audible and visual
alarm with a set point of 5 ppm.
17.13.4.4 Each cargo tank shall be fitted with a
high-pressure alarm giving an audible alarm at a pressure equal to 1.05 MPa
gauge.
17.13.5
Personnel protection
The enclosed space required by 17.5.5 shall meet the following
requirements:
-
.1 the space shall be easily and quickly
accessible from the weather decks and from accommodation spaces by means of
air locks, and shall be capable of being rapidly closed gastight;
-
.2 one of the decontamination showers required
by 14.4.3 shall be located near the weather deck airlock to the space;
-
.3 the space shall be designed to accommodate
the entire crew of the ship and be provided with a source of uncontaminated
air for a period of not less than 4 h; and
-
.4 one set of oxygen therapy equipment shall be
carried in the space.
17.13.6
Filling limits for cargo tanks
17.13.6.1 The requirements of 15.1.3.2 do not apply
when it is intended to carry chlorine.
17.13.6.2 The chlorine content of the gas in the vapour
space of the cargo tank after loading shall be greater than 80% by volume.
17.14 Ethylene oxide
17.14.1 For the carriage of ethylene oxide, the
requirements of 17.18 shall apply, with the additions and modifications as given in
this section.
17.14.2 Deck tanks shall not be used for the carriage
of ethylene oxide.
17.14.3 Stainless steels types 416 and 442, as well as
cast iron, shall not be used in ethylene oxide cargo containment and piping
systems.
17.14.4 Before loading, tanks shall 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 ethylene oxide,
propylene oxide or mixtures of these products. Particular care shall be taken in the
case of ammonia in tanks made of steel other than stainless steel.
17.14.5 Ethylene oxide shall be discharged only by
deepwell pumps or inert gas displacement. The arrangement of pumps shall comply with
17.18.15.
17.14.6 Ethylene oxide shall be carried refrigerated
only and maintained at temperatures of less than 30°C.
17.14.7 PRVs shall be set at a pressure of not less
than 0.55 MPa gauge. The maximum set pressure shall be specially approved by the
Administration.
17.14.8 The protective padding of nitrogen gas, as
required by 17.18.27, shall be such that the nitrogen concentration in the vapour
space of the cargo tank will, at no time, be less than 45% by volume.
17.14.9 Before loading, and at all times when the cargo
tank contains ethylene oxide liquid or vapour, the cargo tank shall be inerted with
nitrogen.
17.14.10 The water-spray system required by 17.18.29
and that required by 11.3 shall operate automatically in a fire involving the cargo
containment system.
17.14.11 A jettisoning arrangement shall be provided to
allow the emergency discharge of ethylene oxide in the event of uncontrollable
self-reaction.
17.15 Separate piping systems
Separate piping systems, as defined in 1.2.47, shall be provided.
17.16 Methyl acetylene-propadiene mixtures
17.16.1 Methyl acetylene-propadiene mixtures shall be
suitably stabilized for transport. Additionally, upper limits of temperatures and
pressure during the refrigeration shall be specified for the mixtures.
17.16.2 Examples of acceptable stabilized compositions
are:
-
.1 Composition 1:
-
.1 maximum methyl acetylene to
propadiene molar ratio of 3 to 1;
-
.2 maximum combined concentration of
methyl acetylene and propadiene of 65 mol%;
-
.3 minimum combined concentration of
propane, butane, and isobutane of 24 mol%, of which at least one
third (on a molar basis) shall be butanes and one third propane;
-
.4 maximum combined concentration of
propylene and butadiene of 10 mol%;
-
.2 Composition 2:
-
.1 maximum methyl acetylene and
propadiene combined concentration of 30 mol%;
-
.2 maximum methyl acetylene
concentration of 20 mol%;
-
.3 maximum propadiene concentration of
20 mol%;
-
.4 maximum propylene concentration of
45 mol%;
-
.5 maximum butadiene and butylenes
combined concentration of 2 mol%;
-
.6 minimum saturated C4 hydrocarbon
concentration of 4 mol%; and
-
.7 minimum propane concentration of 25
mol%.
17.16.3 Other compositions may be accepted, provided
the stability of the mixture is demonstrated to the satisfaction of the
Administration.
17.16.4 If a ship has a direct vapour compression
refrigeration system, this shall comply with the following requirements, subject to
pressure and temperature limitations depending on the composition. For the example
compositions given in 17.16.2, the following features shall be provided:
-
.1 a vapour compressor that does not raise the
temperature and pressure of the vapour above 60°C and 1.75 MPa gauge during
its operation, and that does not allow vapour to stagnate in the compressor
while it continues to run;
-
.2 discharge piping from each compressor stage
or each cylinder in the same stage of a reciprocating compressor shall
have:
-
.1 two temperature-actuated shutdown
switches set to operate at 60°C or less;
-
.2 a pressure-actuated shutdown switch
set to operate at 1.75 MPa gauge or less; and
-
.3 a safety relief valve set to relieve
at 1.8 MPa gauge or less;
-
.3 the relief valve required by .2.3 shall vent
to a mast meeting the requirements of 8.2.10, 8.2.11 and 8.2.15 and shall
not relieve into the compressor suction line; and
-
.4 an alarm that sounds in the cargo control
position and in the navigation bridge when a high-pressure switch, or a
high-temperature switch, operates.
17.16.5 The piping system, including the cargo
refrigeration system, for tanks to be loaded with methyl acetylene-propadiene
mixtures shall be either independent (as defined in 1.2.28) or separate (as defined
in 1.2.47) from piping and refrigeration systems for other tanks. This segregation
shall apply to all liquid and vapour vent lines and any other possible connections,
such as common inert gas supply lines.
17.17 Nitrogen
Materials of construction and ancillary equipment such as insulation
shall be resistant to the effects of high oxygen concentrations caused by
condensation and enrichment at the low temperatures attained in parts of the cargo
system. Due consideration shall be given to ventilation in areas where condensation
might occur, to avoid the stratification of oxygen-enriched atmosphere.
17.18 Propylene oxide and mixtures of ethylene
oxide-propylene oxide with ethylene oxide content of not more than 30% by
weight
17.18.1 Products transported under the provisions of
this section shall be acetylene-free.
17.18.2 Unless cargo tanks are properly cleaned, these
products shall not be carried in tanks that have contained as one of the three
previous cargoes any product known to catalyse polymerization, such as:
-
.1 anhydrous ammonia and ammonia solutions;
-
.2 amines and amine solutions; and
-
.3 oxidizing substances (e.g. chlorine).
17.18.3 Before loading, tanks shall 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 shall be taken in the
case of ammonia in tanks made of steel other than stainless steel.
17.18.4 In all cases, the effectiveness of cleaning
procedures for tanks and associated pipework shall 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.
17.18.5 Tanks shall 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 shall be performed at intervals of not
more than two years.
17.18.6 Tanks for the carriage of these products shall
be of steel or stainless steel construction.
17.18.7 Tanks that have contained these products may be
used for other cargoes after thorough cleaning of tanks and associated pipework
systems by washing or purging.
17.18.8 All valves, flanges, fittings and accessory
equipment shall be of a type suitable for use with these products and shall be
constructed of steel or stainless steel in accordance with recognized standards.
Disc or disc faces, seats and other wearing parts of valves shall be made of
stainless steel containing not less than 11% chromium.
17.18.9 Gaskets shall be constructed of materials which
do not react with, dissolve in, or lower the auto-ignition temperature of, these
products and which are fire-resistant and possess adequate mechanical behaviour. The
surface presented to the cargo shall 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, if approved by
the Administration or recognized organization acting on its behalf.
17.18.10 Insulation and packing, if used, shall be of a
material which does not react with, dissolve in, or lower the auto-ignition
temperature of, these products.
17.18.11 The following materials are generally found
unsatisfactory for use in gaskets, packing and similar uses in containment systems
for these products and would require testing before being approved:
-
.1 neoprene or natural rubber, if it comes into
contact with the products;
-
.2 asbestos or binders used with asbestos;
and
-
.3 materials containing oxides of magnesium,
such as mineral wools.
17.18.12 Filling and discharge piping shall extend to
within 100 mm of the bottom of the tank or any sump.
17.18.13 The products shall 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 shall be independent of all other containment
systems.
17.18.14 During discharging operations, the pressure in
the cargo tank shall be maintained above 0.007 MPa gauge.
17.18.15 The cargo shall be discharged only by deepwell
pumps, hydraulically operated submerged pumps or inert gas displacement. Each cargo
pump shall be arranged to ensure that the product does not heat significantly if the
discharge line from the pump is shut off or otherwise blocked.
17.18.16 Tanks carrying these products shall be vented
independently of tanks carrying other products. Facilities shall be provided for
sampling the tank contents without opening the tank to atmosphere.
17.18.17 Cargo hoses used for transfer of these
products shall be marked "FOR ALKYLENE OXIDE TRANSFER ONLY".
17.18.18 Hold spaces shall be monitored for these
products. Hold spaces surrounding type A and type B independent tanks shall also be
inerted and monitored for oxygen. The oxygen content of these spaces shall be
maintained below 2% by volume. Portable sampling equipment is satisfactory.
17.18.19 Prior to disconnecting shore lines, the
pressure in liquid and vapour lines shall be relieved through suitable valves
installed at the loading header. Liquid and vapour from these lines shall not be
discharged to atmosphere.
17.18.20 Tanks shall be designed for the maximum
pressure expected to be encountered during loading, carriage or unloading of
cargo.
17.18.21 Tanks for the carriage of propylene oxide with
a design vapour pressure of less than 0.06 MPa, and tanks for the carriage of
ethylene oxide-propylene oxide mixtures with a design vapour pressure of less than
0.12 MPa, shall have a cooling system to maintain the cargo below the reference
temperature. The reference temperatures are referred to in 15.1.3.
17.18.22 Pressure relief valve settings shall not be
less than 0.02 MPa gauge; and for type C independent tanks not greater than 0.7 MPa
gauge for the carriage of propylene oxide and not greater than 0.53 MPa gauge for
the carriage of ethylene oxide-propylene oxide mixtures.
17.18.23 The piping system for tanks to be loaded with
these products shall 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 1.2.28, the
required piping separation shall 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.
17.18.24 The products shall be transported only in
accordance with cargo handling plans approved by the Administration. Each intended
loading arrangement shall be shown on a separate cargo handling plan. Cargo handling
plans shall show the entire cargo piping system and the locations for installation
of the blank flanges needed to meet the above piping separation requirements. A copy
of each approved cargo handling plan shall be kept on board the ship. The
International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk
shall be endorsed to include references to the approved cargo handling plans.
17.18.25 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 shall 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 shall be fitted with a wire
and seal by the responsible person to ensure that inadvertent removal of the blank
flange is impossible.
17.18.26 The maximum allowable loading limits for each
tank shall be indicated for each loading temperature that may be applied, in
accordance with 15.5.
17.18.27 The cargo shall be carried under a suitable
protective padding of nitrogen gas. An automatic nitrogen make-up system shall be
installed to prevent the tank pressure falling below 0.007 MPa gauge in the event of
product temperature fall due to ambient conditions or malfunctioning of
refrigeration system. Sufficient nitrogen shall be available on board to satisfy the
demand of the automatic pressure control. Nitrogen of commercially pure quality
(99.9% by volume) shall 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.
17.18.28 The cargo tank vapour space shall be tested
prior to and after loading to ensure that the oxygen content is 2% by volume or
less.
17.18.29 A water-spray system of sufficient capacity
shall 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 shall be such as to give a uniform distribution
rate of 10l/m2/min. The arrangement shall ensure that any spilled
cargo is washed away.
17.18.30 The water-spray system shall be capable of
local and remote manual operation in case of a fire involving the cargo containment
system. Remote manual operation shall be arranged such that the 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.
17.18.31 When ambient temperatures permit, a
pressurized water hose ready for immediate use shall be available during loading and
unloading operations, in addition to the above water-spray requirements.
17.19 Vinyl chloride
In cases where polymerization of vinyl chloride is prevented by addition
of an inhibitor, 17.8 is applicable. In cases where no inhibitor has been added, or
the inhibitor concentration is insufficient, any inert gas used for the purposes of
17.6 shall contain no more oxygen than 0.1% by volume. Before loading is started,
inert gas samples from the tanks and piping shall be analysed. When vinyl chloride
is carried, a positive pressure shall always be maintained in the tanks and during
ballast voyages between successive carriages.
17.20 Mixed C4 cargoes
17.20.1 Cargoes that may be carried individually under
the requirements of this Code, notably butane, butylenes and butadiene, may be
carried as mixtures subject to the provisions of this section. These cargoes may
variously be referred to as "Crude C4", "Crude butadiene", "Crude steam-cracked C4",
"Spent steam-cracked C4", "C4 stream", "C4 raffinate", or may be shipped under a
different description. In all cases, the material safety data sheets (MSDS) shall be
consulted as the butadiene content of the mixture is of prime concern as it is
potentially toxic and reactive. While it is recognized that butadiene has a
relatively low vapour pressure, if such mixtures contain butadiene they shall be
regarded as toxic and the appropriate precautions applied.
17.20.2 If the mixed C4 cargo shipped under the terms
of this section contains more than 50% (mole) of butadiene, the inhibitor
precautions in 17.8 shall apply.
17.20.3 Unless specific data on liquid expansion
coefficients is given for the specific mixture loaded, the filling limit
restrictions of chapter 15 shall be calculated as if the cargo contained 100%
concentration of the component with the highest expansion ratio.
17.21 Carbon dioxide: high purity
17.21.1 Uncontrolled pressure loss from the cargo can
cause "sublimation" and the cargo will change from the liquid to the solid state.
The precise "triple point" temperature of a particular carbon dioxide cargo shall be
supplied before loading the cargo, and will depend on the purity of that cargo, and
this shall be taken into account when cargo instrumentation is adjusted. The set
pressure for the alarms and automatic actions described in this section shall be set
to at least 0.05 MPa above the triple point for the specific cargo being carried.
The "triple point" for pure carbon dioxide occurs at 0.5 MPa gauge and -54.4°C.
17.21.2 There is a potential for the cargo to solidify
in the event that a cargo tank relief valve, fitted in accordance with 8.2, fails in
the open position. To avoid this, a means of isolating the cargo tank safety valves
shall be provided and the requirements of 8.2.9.2 do not apply when carrying this
carbon dioxide. Discharge piping from safety relief valves shall be designed so they
remain free from obstructions that could cause clogging. Protective screens shall
not be fitted to the outlets of relief valve discharge piping, so the requirements
of 8.2.15 do not apply.
17.21.3 Discharge piping from safety relief valves are
not required to comply with 8.2.10, but shall be designed so they remain free from
obstructions that could cause clogging. Protective screens shall not be fitted to
the outlets of relief valve discharge piping, so the requirements of 8.2.15 do not
apply.
17.21.4 Cargo tanks shall be continuously monitored for
low pressure when a carbon dioxide cargo is carried. An audible and visual alarm
shall be given at the cargo control position and on the bridge. If the cargo tank
pressure continues to fall to within 0.05 MPa of the "triple point" for the
particular cargo, the monitoring system shall automatically close all cargo manifold
liquid and vapour valves and stop all cargo compressors and cargo pumps. The
emergency shutdown system required by 18.10 may be used for this purpose.
17.21.5 All materials used in cargo tanks and cargo
piping system shall be suitable for the lowest temperature that may occur in
service, which is defined as the saturation temperature of the carbon dioxide cargo
at the set pressure of the automatic safety system described in 17.21.1.
17.21.6 Cargo hold spaces, cargo compressor rooms and
other enclosed spaces where carbon dioxide could accumulate shall be fitted with
continuous monitoring for carbon dioxide build-up. This fixed gas detection system
replaces the requirements of 13.6, and hold spaces shall be monitored permanently
even if the ship has type C cargo containment.
17.22 Carbon dioxide: reclaimed quality
17.22.1 The requirements of 17.21 also apply to this
cargo. In addition, the materials of construction used in the cargo system shall
also take account of the possibility of corrosion, in case the reclaimed quality
carbon dioxide cargo contains impurities such as water, sulphur dioxide, etc., which
can cause acidic corrosion or other problems.