Section
1 Materials of Construction and Quality Control
1.1 Definitions
1.1.1 Where reference is made in this Chapter to Grades A, B, D, E, AH, DH, EH
and FH hull structural steels, these steel grades are hull structural steels
according to the Rules for the Manufacture, Testing and Certification of
Materials (hereinafter referred to as the Rules for Materials).
1.1.2
A piece is the rolled product from a single slab or billet or from a single
ingot if this is rolled directly into plates, strip, sections or bars.
1.1.3
A batch is the number of items or pieces to be accepted or rejected together,
on the basis of the tests to be carried out on a sampling basis. The size of a batch
is given in the recognised Standards.
1.1.4
Accelerated Cooling (AcC) is a process that aims to improve mechanical
properties by controlled cooling with rates higher than air cooling, immediately
after the final TMCP operation. Direct quenching is excluded from accelerated
cooling. The material properties conferred by TMCP and AcC cannot be reproduced by
subsequent normalising or other heat treatment.
1.1.5
Controlled Rolling (CR), also known as Normalising Rolling (NR), is a
rolling procedure in which the final deformation is carried out in the normalising
temperature range, resulting in a material condition generally equivalent to that
obtained by normalising.
1.1.6
Normalising (N) refers to an additional heating cycle of rolled steel above
the critical temperature, Ac3, and in the lower end of the austenite
recrystallisation region followed by air cooling. The process improves the
mechanical properties of as-rolled steel by refining the grain size.
1.1.7
Quenching and Tempering (QT) is a heat treatment process in which steel is
heated to an appropriate temperature above the Ac3 and then cooled with
an appropriate coolant for the purpose of hardening the microstructure, followed by
tempering, a process in which the steel is re-heated to an appropriate temperature,
not higher than the Ac1 to restore the toughness properties by improving
the microstructure.
1.1.8
Thermo-Mechanical Controlled Processing (TMCP) is a procedure that involves
strict control of both the steel temperature and the rolling reduction. Unlike CR,
the properties conferred by TMCP cannot be reproduced by subsequent normalising or
other heat treatment. The use of accelerated cooling on completion of TMCP may also
be accepted subject to approval by the Administration. The same applies for the use
of tempering after completion of the TMCP
1.2 Scope and general requirement
1.2.1 This Chapter gives the requirements for metallic and non-metallic
materials used in the construction of the cargo system. This includes requirements
for joining processes, production process, personnel qualification, NDT and
inspection and testing including production testing. The requirements for rolled
materials, forgings and castings are given in Pt 11, Ch 6, 1.4 Requirements for metallic materials and Table 6.1.1 Plates, pipes (seamless
and welded, see Notes 1 and 2), sections and forgings for cargo tanks
and process pressure vessels for cargo design temperatures not lower than
0°C, Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below 0°C and down to –55°C,
maximum thickness 25 mm (see Note 2), Table 6.1.3 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below –55°C and down to
–165°C (see Note 2), maximum thickness 25 mm (see Notes 3 and
4), Table 6.1.4 Pipes (seamless and
welded, see Note 1), forgings and castings (see Note 2) for
cargo and process piping for cargo design temperatures below 0°C and down to
–165°C (see Note 3), maximum thickness 25 mm and Table 6.1.5 Plates and sections for
hull structures required by . The requirements for weldments are given in Pt 11, Ch 6, 1.5 Welding of metallic materials and non-destructive testing and the guidance for non metallic materials is given in Pt 11, Ch 21 Non-Metallic Materials. A quality assurance/quality control (QA/QC) program shall be
implemented to ensure these requirements are complied with.
1.2.2 The manufacture, testing, inspection and documentation shall be in
accordance with the requirements of this Chapter and the Rules for Materials.
Testing and inspection to other recognised Standards will be subject to special
agreement.
1.2.3 Where post-weld heat treatment is specified or required, the properties
of the base materials, weld and heat affected zone shall be determined in the heat
treated condition, in accordance with the requirements specified in this Chapter.
Alternative arrangements for Charpy V-notch impact test temperature following
post-weld heat treatment will be subject to special consideration.
1.3 General test requirements and
specifications
1.3.1 All mechanical tests required by this Chapter shall be carried out in
accordance with the Rules for Materials.
1.3.2 Acceptance tests for metallic materials shall include Charpy V-notch
impact tests unless specified otherwise; the largest specimen possible for the
material thickness should be machined. Requirements for testing specimens smaller
than 5,0 mm in size shall be in accordance with recognised Standards.
1.3.3 The bend test may be omitted as a material acceptance test, but is
required for weld tests.
1.4 Requirements for metallic
materials
1.4.1
General requirements for metallic materials
- The requirements for
materials of construction are shown in the Tables as follows:
Table 6.1.1 Plates, pipes (seamless
and welded, see Notes 1 and 2), sections and forgings for cargo tanks
and process pressure vessels for cargo design temperatures not lower than
0°C:
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Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below 0°C and down to –55°C,
maximum thickness 25 mm (see Note 2):
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Table 6.1.3 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below –55°C and down to
–165°C (see Note 2), maximum thickness 25 mm (see Notes 3 and
4):
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Table 6.1.4 Pipes (seamless and
welded, see Note 1), forgings and castings (see Note 2) for
cargo and process piping for cargo design temperatures below 0°C and down to
–165°C (see Note 3), maximum thickness 25 mm:
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Table 6.1.5 Plates and sections for
hull structures required by :
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Table 6.1.1 Plates, pipes (seamless
and welded, see Notes 1 and 2), sections and forgings for cargo tanks
and process pressure vessels for cargo design temperatures not lower than
0°C
Chemical composition and heat treatment
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- Carbon-manganese steel
- Fully killed fine grain steel
- Small additions of alloying elements by agreement with
LR
- Composition limits to be approved by LR
- Normalised, quenched and tempered, see Note 4
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Tensile and toughness (impact) test
requirements
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Sampling frequency
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Each ‘piece’ to be tested
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Each ‘batch’ to be tested
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Mechanical properties
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Specified minimum yield stress not to exceed 410
N/mm2, see Note 5
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Toughness (Charpy V-notch test)
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Transverse test pieces. Minimum average value
(KV) 27J
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Longitudinal test pieces. Minimum average energy
(KV) 41J
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Thickness t (mm)
t ≤ 20
20 < t ≤ 40, see Note 3
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Test temperature (°C)
0
–20
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NOTES
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1. For seamless pipes and fittings,
normal practice applies. The use of longitudinally and spirally
welded pipes shall be specially approved by LR.
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2. Charpy V-notch impact tests are not
required for pipes where the thickness is less than 15 mm.
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3. This Table is generally applicable for
material thicknesses up to 40 mm. Proposals for greater
thicknesses shall be approved by LR.
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4. A controlled rolling (normalising
rolling) procedure may be used as an alternative. In addition,
TCMP steel may be used as an alternative in applications where
post-weld heat treatment is not required.
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5. Materials with specified minimum yield
stress exceeding 410 N/mm2 may be approved by LR. For
these materials, particular attention shall be given to the
hardness of the welded and heat affected zones.
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Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below 0°C and down to –55°C,
maximum thickness 25 mm (see Note 2)
Chemical composition and heat treatment
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- Carbon-manganese steel
- Fully killed, aluminium treated fine grain steel
- Chemical composition (ladle analysis)
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C
0,16% max.
see Note 3
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Mn
0,70-1,60%
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Si
0,10-0,50%
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S
0,025% max.
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P
0,025% max.
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Optional additions: Alloys and grain refining
elements may be generally in accordance with the following:
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Ni
0,80% max.
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Cr
0,25% max.
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Mo
0,08% max.
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Cu
0,35% max.
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Nb
0,05% max.
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V
0,10% max.
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Al content total 0,020% min. (acid soluble
0,015% min.)
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- Normalised, or quenched and tempered, see Note 4
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Tensile and toughness (impact) test
requirements
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Sampling frequency
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Each ‘piece’ to be tested
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Each ‘batch’ to be tested
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Mechanical properties
|
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Specified minimum yield stress not to exceed 410
N/mm2, see Note 5
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Toughness (Charpy V-notch test)
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Transverse test pieces. Minimum average energy
value (KV) 27J
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Longitudinal test pieces. Minimum average energy
(KV) 41J
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5°C below the cargo design temperature or –20°C,
whichever is lower
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NOTES
1. The Charpy
V-notch and chemistry requirements for forgings may be
specially considered by LR.
2. For
material thickness of more than 25 mm, Charpy V-notch tests
shall be conducted as follows:
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Material thickness (mm)
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Test temperature (°C)
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25 < t ≤ 30
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10°C below cargo design
temperature or –20°C, whichever is lower
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30 < t ≤ 35
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15°C below cargo design temperature or
–20°C, whichever is lower
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35 < t ≤ 40
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20°C below cargo design temperature
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40 < t
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Temperature approved by LR
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- The impact energy value shall be in
accordance with the Table for the applicable type of
test specimen.
- Materials for tanks and parts of tanks
which are completely thermally stress relieved after
welding may be tested at a temperature 5°C below
cargo design temperature or –20°C, whichever is
lower.
- For thermally stress relieved
reinforcements and other fittings, the test
temperature shall be the same as that required for
the adjacent tank shell thickness.
3. By special agreement with LR, the carbon
content may be increased to 0,18% maximum provided the cargo
design temperature is not lower than –40°C.
4. A controlled rolling (normalising rolling)
procedure may be used as an alternative. In addition, TMCP
steel may be used as an alternative in applications where
post-weld heat treatment is not required.
5. Materials with specified minimum yield stress
exceeding 410 N/mm2 may be approved by LR. For
these materials, particular attention shall be given to the
hardness of the welded and heat affected zones.
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Guidance
For materials exceeding 25 mm in thickness for
which the test temperature is –60°C or lower, the
application of specially treated steels or steels in
accordance with Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below 0°C and down to –55°C,
maximum thickness 25 mm (see Note 2) may be necessary.
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Table 6.1.3 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below –55°C and down to
–165°C (see Note 2), maximum thickness 25 mm (see Notes 3 and
4)
Minimum cargo design temperature
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Chemical composition,
see Note 5, and heat treatment
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Impact test temperature (°C)
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–60
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1,5% nickel steel – normalised or normalised and
tempered or quenched and tempered or TMCP, see Note 6
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–65
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–65
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2,25% nickel steel – normalised or normalised and
tempered or quenched and tempered or TMCP, see Notes 6
and 7
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–70
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–90
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3,5% nickel steel – normalised or normalised and
tempered or quenched and tempered or TMCP, see Notes 6
and 7
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–95
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–105
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5% nickel steel – normalised or normalised and
tempered or quenched and tempered, see Notes 6, 7 and 8
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–110
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–165
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9% nickel steel – double normalised and tempered or
quenched and tempered, see Note 6
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–196
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–165
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Austenitic steels, such as types 304, 304L, 316,
316L, 321 and 347 solution treated, see Note 9
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–196
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–165
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Aluminium alloys; such as type 5083 annealed
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Not required
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–165
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Austenitic Fe-Ni alloy (36% nickel) heat
treatment as agreed
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Not required
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Tensile and toughness (impact) test
requirements
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Sampling frequency
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Each ‘piece’ to be tested
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Each ‘batch’ to be tested
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Toughness (Charpy V-notch test)
|
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Transverse test pieces. Minimum average energy
value (KV) 27J
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Longitudinal test pieces. Minimum average energy
(KV) 41J
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NOTES
1. The impact test required for
forgings used in critical applications shall be subject to
special consideration by LR.
2. The
requirements for cargo design temperatures below –165°C
shall be specially agreed with LR.
3. For
materials 1,5% Ni, 2,25% Ni, 3,5% Ni and 5% Ni, with
thicknesses greater than 25 mm, the impact tests shall be
conducted as follows:
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Material thickness (mm)
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Test temperature (°C)
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25 < t ≤ 30
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10°C below
cargo design temperature
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30 < t ≤ 35
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15°C below
cargo design temperature
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35 < t ≤ 40
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20°C below
cargo design temperature
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- The energy value shall be in
accordance with the Table for the applicable type of
test specimen. For material thickness of more than
40 mm, the Charpy V-notch values shall be specially
considered.
4. For 9% Ni steels, austenitic stainless steels
and aluminium alloys, thickness greater than 25 mm may be
used.
5. The chemical composition limits shall be in
accordance with Ch 3, 6 Carbon–manganese and nickel alloy steels for low temperature service of the
Rules for Materials.
6. TMCP nickel steels will be subject to
acceptance by LR.
7. A lower minimum cargo design temperature for
quenched and tempered steels may be specially agreed with
LR.
8. A specially heat treated 5% nickel steel, for
example, triple heat treated 5% nickel steel, may be used
down to –165°C, provided that the impact tests are carried
out at –196°C.
9. The impact test may be omitted subject to
agreement with LR.
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Table 6.1.4 Pipes (seamless and
welded, see Note 1), forgings and castings (see Note 2) for
cargo and process piping for cargo design temperatures below 0°C and down to
–165°C (see Note 3), maximum thickness 25 mm
Minimum cargo design temperature
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Chemical
composition, see Note 5, and heat treatment
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Impact test
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Test temp. (°C)
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Minimum average energy (KV)
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–55
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Carbon-manganese steel. Fully killed fine grain.
Normalised or as agreed, see Note 6
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See Note 4
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27
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–65
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2.25% nickel steel. Normalised, normalised and
tempered or quenched and tempered, see Note 6
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–70
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34
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–90
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3.5% nickel steel. Normalised, normalised and
tempered or quenched and tempered, see Note 6
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–95
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34
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–165
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9% nickel steel, see Note 7. Double normalised
and tempered or quenched and tempered
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–196
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41
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–165
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Austenitic steels, such as types 304. 304L, 316,
316L, 321 and 347. Solution treated, see Note 8
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–196
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41
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–165
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Aluminium alloys, such as type 5083 annealed
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Not
required
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Tensile and toughness (impact) test
requirements
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Sampling frequency
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- Each ‘batch’ to be tested.
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Toughness (Charpy V-notch test)
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- Impact test: longitudinal test pieces
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NOTES
1. The use of longitudinally or spirally welded
pipes shall be specially approved by LR.
2. The requirements for forgings and castings may
be subject to special consideration by LR.
3. The requirements for design temperatures
below –165°C shall be specially agreed with LR.
4. The test temperature shall be 5°C below the
cargo design temperature or –20°C whichever is lower.
5. The composition limits shall be in accordance
with Ch 6, 4 Ferritic steel pressure pipes for low temperature service of the
Rules for Materials.
6. A lower cargo design temperature may be
specially agreed with LR for quenched and tempered
materials.
7. This chemical composition is not suitable for
castings.
8. Impact tests may be omitted subject to
agreement with LR.
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Minimum
design temperature of hull structure (°C)
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Maximum thickness (mm)
for steel grades
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A
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B
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D
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E
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AH
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DH
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EH
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FH
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0 and above, see Note 1
–5 and above, see Note 2
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To comply with Pt 10, Ch 1, 3 Materials
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down to –5
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15
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25
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30
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50
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25
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45
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50
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50
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down to –10
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x
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20
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25
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50
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20
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40
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50
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50
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down to –20
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x
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x
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20
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50
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x
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30
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50
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50
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down to –30
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x
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x
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x
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40
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x
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20
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40
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50
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Below –30
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In accordance with Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below 0°C and down to –55°C,
maximum thickness 25 mm (see Note 2), except that the thickness
limitation given in Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and process
pressure vessels for cargo design temperatures below 0°C and down to –55°C,
maximum thickness 25 mm (see Note 2) and in Note 2 of that Table
does not apply
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NOTES
‘x’ means steel grade not to be used.
1. For the purpose of Pt 11, Ch 4, 5.1 Materials 5.1.2.(c).
2. For the purpose of Pt 11, Ch 4, 5.1 Materials 5.1.2.(b).
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1.4.3 The sheerstrake is to be of Grade E/EH steel for ship units storing and
offloading liquefied gases in bulk.
1.5 Welding of metallic materials and
non-destructive testing
1.5.1
General
- This Section shall
apply to primary and secondary barriers only, including the inner hull where
this forms the secondary barrier. Acceptance testing is specified for
carbon, carbon-manganese, nickel alloy and stainless steels, but these tests
may be adapted for other materials. At the discretion of LR, impact testing
of stainless steel and aluminium alloy weldments may be omitted and other
tests may be specially required for any material.
1.5.3
Welding procedure tests for cargo tanks and process pressure vessels
- Welding procedure tests
for cargo tanks, secondary barriers, process pressure vessels and pressure
pipework are to be qualified in accordance with Ch 12 Welding Qualifications of the Rules for
Materials.
1.6 Specific welding requirements for
liquefied petroleum gas and liquefied natural gas systems
1.6.1
Scope
- The requirements of
this Section apply to welding of cargo tanks, storage tanks, containment
systems, process pressure vessels and pressure piping for liquefied natural
gas systems.
- The requirements of
this Section include the welding of carbon, carbon-manganese, nickel alloy,
austenitic stainless steels and aluminium alloys specified in the Rules for
Materials, as suitable for use in low temperature service.
- The requirements of
this Section are in addition to those requirements specified in Chapter 13, Sections 1, 4 and 5 of the Rules for Materials.
1.6.2
Welding qualifications
All welding procedures used during construction are to be qualified in
accordance with the requirements specified in Ch 12 Welding Qualifications of the Rules for Materials for liquid gas
applications.
1.6.3
Production weld test frequency
- For cargo tanks and
process pressure vessels, except integral and membrane tanks, production
weld tests shall be performed for each 50 m of butt weld joint and should be
representative of each welding procedure and position used in construction.
- Production tests are
required for secondary barriers but the number of tests required may be
reduced to 1 in every 100 m of butt weld.
- Requirements for
production testing of integral and membrane tanks are to be agreed with LR
prior to manufacture.
1.6.4
Production weld testing requirements
- The type and number
of specimens to be removed from each test plate for mechanical testing shall
be as specified for the original welding procedure qualification test,
except that:
- the all weld
tensile test may be omitted; and
- the number of
impact tests from the heat affected zone may be reduced to sampling
the location that demonstrated the lowest impact energy during
procedure qualification.
- For independent
tanks, Types A and B, the transverse tensile tests may also be omitted.
- The results of the
mechanical tests are to meet the minimum requirements specified for the
original welding procedure qualification test as specified in Ch 12 Welding Qualifications of the Rules for
Materials.
- Should any impact
test fail to meet requirements, consideration will be given to acceptance
based on satisfactory results from two drop weight tests from the failed
location. The test temperature for these shall be no higher that that
specified for the impact tests and the acceptance criteria for both tests
shall be no break.
1.6.5
Non-destructive examination
- All welds are to be
subject to non-destructive examination in accordance with requirements
specified in Ch 4 Steel Castings and Ch 5 Steel Forgings of the Rules for the Manufacture, Testing and Certification of Materials, July 2022 unless more stringent
requirements are specified below.
- Radiographic
examination may be substituted by ultrasonic examination, see
Ch 13, 4.15 NDE Method of the Rules for the Manufacture, Testing and Certification of Materials, July 2022. In addition, ultrasonic
examination may be used to augment radiographic testing for complex or
critical welds.
-
Type A independent and semi-membrane tanks:
- where the
minimum cargo design temperature is less than or equal to –20°C, the
extent and type of testing shall be as for Type B tanks in (d).
- where the
minimum cargo design temperature is greater than –20°C, the extent
and type of testing shall include 100 per cent volumetric
examination of butt weld intersections, plus 10 per cent of other
butt welds.
- the remaining
tank structure shall be subject to crack detection examination in
accordance with recognised standards and the extent of examination
is to be agreed with LR.
- Type B independent
tanks:
Irrespective of cargo design temperature, all full
penetration butt welds will be subject to 100 per cent volumetric
examination. Other welds shall be subject to crack detection examination
in accordance with recognised Standards and the extent of examination is
to be agreed with LR.
- Type C independent
tanks and process pressure vessels:
The extent of examination is dependent on the design
conditions. Where the design incorporates a joint factor greater than
0,85, all butt welds will be subject to 100 per cent volumetric
examination plus 10 per cent surface crack detection. Where the weld
joint factor is less than or equal to 0,85, partial inspection may be
considered. However, this should not be less than 10 per cent volumetric
examination of full penetration butt welds, and 100 per cent surface
crack detection of nozzle reinforcing rings and other vessel openings.
-
Integral and membrane tanks:
Inspection is to be in accordance with recognised Standards
and the extent and type of inspection is to be agreed with LR.
- Secondary barrier:
Where the outer shell of the hull is part of the secondary
barrier, all sheerstrake butt welds and the intersections of all butt
and seam welds in the side shell shall be examined volumetrically. The
extent of inspections is to be agreed with LR.
- Inner hull and
independent tank structures supporting internal insulation tanks:
Inspection requirements are to be in accordance with
recognised Standards and are to be agreed with LR.
- Piping:
- for piping
systems with design temperatures lower than –10°C and with inside
diameters of more than 75 mm or wall thicknesses greater than 10 mm,
piping shall be subject to 100 per cent radiographic inspection of
butt-welded joints;
- for butt-welded
joints made using fully automatic welding procedures during pipe
shop fabrication, the extent of radiographic inspection may be
progressively reduced by special agreement with LR. In no case will
this be reduced below 10 per cent of joints. If defects are revealed
the extent of examination shall be increased to 100 per cent and
will include inspection of previously accepted welds. This special
approval will only be granted where the fabricator has a
well-documented quality assurance system that is working effectively
and will be subject to audit by LR;
- for other
butt-welded joints, spot radiography or other non-destructive tests
shall be carried out depending on the service, position and
materials. In general, at least 10 per cent of butt-welded joints of
pipes should be radiographed. The extent of examination is to be
agreed with LR.
1.7 Non-metallic materials
1.7.1
General
The information in the attached Appendix 1 is given for guidance in the
selection and use of these materials, based on the experience to date.
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