To ensure that the cargo containment system, primary
and secondary barriers, the thermal insulation, adjacent ship structure
and other materials in the cargo containment system are constructed
from materials of suitable properties for the conditions they will
experience, both in normal service and in the event of failure of
the primary barrier, where applicable.
4.19.1
Materials forming ship structure
4.19.1.1 To determine the grade of plate and sections
used in the hull structure, a temperature calculation shall be performed
for all tank types when the cargo temperature is below -10°C.
The following assumptions shall be made in this calculation:
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.1 the primary barrier of all tanks shall be assumed
to be at the cargo temperature;
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.2 in addition to .1, where a complete or partial
secondary barrier is required, it shall be assumed to be at the cargo
temperature at atmospheric pressure for any one tank only;
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.3 for worldwide service, ambient temperatures
shall be taken as 5°C for air and 0ºC for seawater. Higher
values may be accepted for ships operating in restricted areas and,
conversely, lower values may be fixed by the Administration for ships
trading to areas where lower temperatures are expected during the
winter months;
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.4 still air and seawater conditions shall be
assumed, i.e. no adjustment for forced convection;
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.5 degradation of the thermal insulation properties
over the life of the ship due to factors such as thermal and mechanical
ageing, compaction, ship motions and tank vibrations, as defined in
4.19.3.6 and 4.19.3.7, shall be assumed;
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.6 the cooling effect of the rising boil-off vapour
from the leaked cargo shall be taken into account, where applicable;
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.7 credit for hull heating may be taken in accordance
with 4.19.1.5, provided the heating arrangements are in compliance
with 4.19.1.6;
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.8 no credit shall be given for any means of heating,
except as described in 4.19.1.5; and
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.9 for members connecting inner and outer hulls,
the mean temperature may be taken for determining the steel grade.
The ambient temperatures used in the design, described in this
paragraph, shall be shown on the International Certificate of Fitness
for the Carriage of Liquefied Gases in Bulk required in 1.4.4.
4.19.1.2 The shell and deck plating of the ship
and all stiffeners attached thereto shall be in accordance with recognized
standards. If the calculated temperature of the material in the design
condition is below -5°C due to the influence of the cargo temperature,
the material shall be in accordance with table 6.5.
4.19.1.3 The materials of all other hull structures
for which the calculated temperature in the design condition is below
0°C, due to the influence of cargo temperature and that do not
form the secondary barrier, shall also be in accordance with table
6.5. This includes hull structure supporting the cargo tanks, inner
bottom plating, longitudinal bulkhead plating, transverse bulkhead
plating, floors, webs, stringers and all attached stiffening members.
4.19.1.4 The hull material forming the secondary
barrier shall be in accordance with table 6.2. Where the secondary
barrier is formed by the deck or side shell plating, the material
grade required by table 6.2 shall be carried into the adjacent deck
or side shell plating, where applicable, to a suitable extent.
4.19.1.5 Means of heating structural materials
may be used to ensure that the material temperature does not fall
below the minimum allowed for the grade of material specified in table
6.5. In the calculations required in 4.19.1.1, credit for such heating
may be taken in accordance with the following:
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.1 for any transverse hull structure;
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.2 for longitudinal hull structure referred to
in 4.19.1.2 and 4.19.1.3 where colder ambient temperatures are specified,
provided the material remains suitable for the ambient temperature
conditions of +5°C for air and 0°C for seawater with no credit
taken in the calculations for heating; and
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.3 as an alternative to .2, for longitudinal bulkhead
between cargo tanks, credit may be taken for heating, provided the
material remain suitable for a minimum design temperature of -30°C,
or a temperature 30°C lower than that determined by 4.19.1.1 with
the heating considered, whichever is less. In this case, the ship's
longitudinal strength shall comply with SOLAS regulation II-1/3-1 for both when those bulkhead(s)
are considered effective and not.
4.19.1.6 The means of heating referred to in 4.19.1.5
shall comply with the following requirements:
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.1 the heating system shall be arranged so that,
in the event of failure in any part of the system, standby heating
can be maintained equal to not less than 100% of the theoretical heat
requirement;
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.2 the heating system shall be considered as an
essential auxiliary. All electrical components of at least one of
the systems provided in accordance with 4.19.1.5.1 shall be supplied
from the emergency source of electrical power; and
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.3 the design and construction of the heating
system shall be included in the approval of the containment system
by the Administration or recognized organization acting on its behalf.
4.19.2
Materials of primary and secondary
barriers
4.19.2.1 Metallic materials used in the construction
of primary and secondary barriers not forming the hull, shall be suitable
for the design loads that they may be subjected to, and be in accordance
with, table 6.1, 6.2 or 6.3.
4.19.2.2 Materials, either non-metallic or metallic
but not covered by tables 6.1, 6.2 and 6.3, used in the primary and
secondary barriers may be approved by the Administration or recognized
organization acting on its behalf, considering the design loads that
they may be subjected to, their properties and their intended use.
4.19.2.3 Where non-metallic materials, including
composites, are used for, or incorporated in the primary or secondary
barriers, they shall be tested for the following properties, as applicable,
to ensure that they are adequate for the intended service:
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.1 compatibility with the cargoes;
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.2 ageing;
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.3 mechanical properties;
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.4 thermal expansion and contraction;
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.5 abrasion;
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.6 cohesion;
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.7 resistance to vibrations;
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.8 resistance to fire and flame spread; and
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.9 resistance to fatigue failure and crack propagation.
4.19.2.4 The above properties, where applicable,
shall be tested for the range between the expected maximum temperature
in service and +5°C below the minimum design temperature, but
not lower than -196°C.
4.19.2.5.1 Where non-metallic materials, including
composites, are used for the primary and secondary barriers, the joining
processes shall also be tested as described above.
4.19.2.5.2 Guidance on the use of non-metallic
materials in the construction of primary and secondary barriers is
provided in appendix 4.
4.19.2.6 Consideration may be given to the use
of materials in the primary and secondary barrier, which are not resistant
to fire and flame spread, provided they are protected by a suitable
system such as a permanent inert gas environment, or are provided
with a fire-retardant barrier.
4.19.3
Thermal insulation and other
materials used in cargo containment systems
4.19.3.1 Load-bearing thermal insulation and other
materials used in cargo containment systems shall be suitable for
the design loads.
4.19.3.2 Thermal insulation and other materials
used in cargo containment systems shall have the following properties,
as applicable, to ensure that they are adequate for the intended service:
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.1 compatibility with the cargoes;
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.2 solubility in the cargo;
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.3 absorption of the cargo;
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.4 shrinkage;
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.5 ageing;
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.6 closed cell content;
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.7 density;
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.8 mechanical properties, to the extent that they
are subjected to cargo and other loading effects, thermal expansion
and contraction;
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.9 abrasion;
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.10 cohesion;
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.11 thermal conductivity;
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.12 resistance to vibrations;
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.13 resistance to fire and flame spread; and
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.14 resistance to fatigue failure and crack propagation.
4.19.3.3 The above properties, where applicable,
shall be tested for the range between the expected maximum temperature
in service and 5°C below the minimum design temperature, but not
lower than -196°C.
4.19.3.4 Due to location or environmental conditions,
thermal insulation materials shall have suitable properties of resistance
to fire and flame spread and shall be adequately protected against
penetration of water vapour and mechanical damage. Where the thermal
insulation is located on or above the exposed deck, and in way of
tank cover penetrations, it shall have suitable fire resistance properties
in accordance with recognized standards or be covered with a material
having low flame-spread characteristics and forming an efficient approved
vapour seal.
4.19.3.5 Thermal insulation that does not meet
recognized standards for fire resistance may be used in hold spaces
that are not kept permanently inerted, provided its surfaces are covered
with material with low flame-spread characteristics and that forms
an efficient approved vapour seal.
4.19.3.6 Testing for thermal conductivity of thermal
insulation shall be carried out on suitably aged samples.
4.19.3.7 Where powder or granulated thermal insulation
is used, measures shall be taken to reduce compaction in service and
to maintain the required thermal conductivity and also prevent any
undue increase of pressure on the cargo containment system.