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, Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and
process, Table 6.1.3 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and
process, Table 6.1.4 Pipes (seamless and
welded, see Note 1), forgings and castings (see Note 2) for cargo
and and Table 6.1.5 Plates and sections for hull
structures. The
requirements for weldments are given in Table 6.1. and the guidance
for non metallic materials is given in Pt 11, Ch 21 Appendix 1 Non-Metallic Materials. A quality
assurance/quality control (QA/QC) program shall be implemented to ensure the
requirements of Pt 11, Ch 6, 1.2 Scope and general requirement 1.2.1 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:
Pt 11, Ch 6, 1.4 Requirements for metallic materials 1.4.1:
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Plates, pipes
(seamless and welded), sections and forgings for
cargo tanks and process pressure vessels for 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:
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Plates,
sections and forgings for cargo tanks, secondary
barriers and process pressure vessels for design
temperatures below 0°C and down to –55°C.
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Table 6.1.3 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and
process:
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Plates,
sections and forgings for cargo tanks, secondary
barriers and process pressure vessels for design
temperatures below –55°C and down to –165°C.
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Table 6.1.4 Pipes (seamless and
welded, see Note 1), forgings and castings (see Note 2) for cargo
and:
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Pipes (seamless
and welded), forgings and castings for cargo and
process piping for design temperatures below 0°C and
down to –165°C.
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Table 6.1.5 Plates and sections for hull
structures:
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Plates and
sections for hull structures required by Pt 11, Ch 4, 5.1 Materials
and Pt 11, Ch 4, 5.1 Materials.
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Plates, pipes (seamless and welded, see Notes 1 and 2), sections and
forgings for cargo tanks and process pressure vessels for design
temperatures not lower than 0°C
Table 6.1.1 Plates, pipes
(seamless and welded, see Notes 1 and 2), sections and forgings for
cargo tanks and
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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Plates, sections and forgings (see Note 1) for cargo tanks, secondary
barriers and process pressure vessels for design temperatures below 0°C and
down to –55°C, maximum thickness 25 mm (see Note 2)
Table 6.1.2 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and
process
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 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 design
temperature or –20°C, whichever is lower
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30 < t ≤ 35
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15°C below design temperature or
–20°C, whichever is lower
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35 < t ≤ 40
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20°C below 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 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
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 Pt 11, Ch 6, 1.4 Requirements for metallic materials 1.4.1
may be necessary.
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Plates, sections and forgings (see Note 1) for cargo tanks, secondary
barriers and process pressure vessels for design temperatures below –55°C
and down to –165°C (see Note 2), maximum thickness 25 mm (see
Notes 3 and 4)
Table 6.1.3 Plates, sections and
forgings (see Note 1) for cargo tanks, secondary barriers and
process
Minimum 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 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 design temperature
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30 < t ≤ 35
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15°C
below design temperature
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35 < t ≤ 40
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20°C below
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 Pt 11, Ch 3, 1.6 Airlocks of
the Rules for Materials.
6. TMCP nickel steels will be subject to
acceptance by LR.
7. A lower minimum 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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Pipes (seamless and welded, see Note 1), forgings and castings
(see Note 2) for cargo and process piping for design temperatures
below 0°C and down to –165°C (see Note 3), maximum thickness 25 mm
Table 6.1.4 Pipes (seamless and
welded, see Note 1), forgings and castings (see Note 2) for cargo
and
Minimum 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 design temperature or –20°C whichever is lower.
5. The composition limits shall be in
accordance with Pt 11, Ch 6, 1.4 Requirements for metallic materials of
the Rules for Materials.
6. A lower 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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Plates and sections for hull structures required by Pt 11, Ch 4, 5.1 Materials and Pt 11, Ch 4, 5.1 Materials
Table 6.1.5 Plates and sections for hull
structures
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
|
50
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down to –20
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x
|
x
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20
|
50
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x
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30
|
50
|
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, 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 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.
2. For the purpose of Pt 11, Ch 4, 5.1 Materials.
Required by Pt 11, Ch 4, 5.1 Materials
and Pt 11, Ch 4, 5.1 Materials
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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 4 and 5 of the Rules for Materials
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
Materials. 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 design temperature is less than or equal to –20°C, the
extent and type of testing shall be as for Type B tanks in Pt 11, Ch 6, 1.6 Specific welding requirements for liquefied petroleum gas and liquefied natural gas systems.
- where the
minimum 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 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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