Goal
To identify the required properties, testing standards and stability of metallic
and non-metallic materials and fabrication processes used in the construction of
cargo containment and piping systems to ensure they serve the functions for
which they have been selected, as required in chapters 4 and 5.
6.1 Definitions
6.1.1 Where reference is made in this chapter to A, B,
D, E, AH, DH, EH and FH hull structural steels, these steel grades are hull
structural steels according to recognized standards.
6.1.2
A piece is the rolled product from a single slab or billet or from a single
ingot, if this is rolled directly into plates, strips, sections or bars.
6.1.3
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 recognized standards.
6.1.4
Controlled rolling (CR) is a rolling procedure in which the final deformation
is carried out in the normalizing temperature range, resulting in a material
condition generally equivalent to that obtained by normalizing.
6.1.5
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 normalizing 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 TMCP.
6.1.6
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 normalizing or other heat treatment.
6.2
Scope and general requirements
6.2.1 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 6.4 and tables
6.1, to 6.5. The requirements for weldments are given in 6.5, and the guidance for
non-metallic materials is given in appendix 4. A quality assurance/quality control
programme shall be implemented to ensure that the requirements of 6.2 are complied
with.
6.2.2 The manufacture, testing, inspection and
documentation shall be in accordance with recognized standards and the specific
requirements given in the Code.
6.2.3 Where post-weld heat treatment is specified or
required, the properties of the base material shall be determined in the
heat-treated condition, in accordance with the applicable table of this chapter, and
the weld properties shall be determined in the heat treated condition in accordance
with 6.5. In cases where a post-weld heat treatment is applied, the test
requirements may be modified at the discretion of the Administration.
6.3
General test requirements and specifications
6.3.1
Tensile test
6.3.1.1 Tensile testing shall be carried out in
accordance with recognized standards.
6.3.1.2 Tensile strength, yield stress and elongation
shall be to the satisfaction of the Administration. For carbon-manganese steel and
other materials with definitive yield points, consideration shall be given to the
limitation of the yield to tensile ratio.
6.3.2
Toughness test
6.3.2.1 Acceptance tests for metallic materials shall
include Charpy V-notch toughness tests, unless otherwise specified by the
Administration. The specified Charpy V-notch requirements are minimum average energy
values for three full size (10 mm × 10 mm) specimens and minimum single energy
values for individual specimens. Dimensions and tolerances of Charpy V-notch
specimens shall be in accordance with recognized standards. The testing and
requirements for specimens smaller than 5 mm in size shall be in accordance with
recognized standards. Minimum average values for subsized specimens shall be:
| Charpy V-notch
specimen size (mm)
|
Minimum average
energy of three specimens
|
| 10 x 10
|
KV
|
| 10 x 7.5
|
5/6 KV
|
| 10 x 5
|
2/3 KV
|
where:
|
KV |
= |
the energy values (J) specified in tables 6.1 to 6.4. |
Only one individual value may be below the specified average value,
provided it is not less than 70% of that value.
6.3.2.2 For base metal, the largest size Charpy V-notch
specimens possible for the material thickness shall be machined with the specimens
located as near as practicable to a point midway between the surface and the centre
of the thickness and the length of the notch perpendicular to the surface as shown
in figure 6.1.
6.3.2.3 For a weld test specimen, the largest size
Charpy V-notch specimens possible for the material thickness shall be machined, with
the specimens located as near as practicable to a point midway between the surface
and the centre of the thickness. In all cases, the distance from the surface of the
material to the edge of the specimen shall be approximately 1 mm or greater. In
addition, for double-V butt welds, specimens shall be machined closer to the surface
of the second welded section. The specimens shall be taken generally at each of the
following locations, as shown in figure 6.2, on the centreline of the welds, the
fusion line and 1 mm, 3 mm and 5 mm from the fusion line.
Notch locations in figure 6.2:
-
.1 Centreline of the weld.
-
.2 Fusion line.
-
.3 In heat-affected zone (HAZ), 1 mm from the
fusion line.
-
.4 In HAZ, 3 mm from the fusion line.
-
.5 In HAZ, 5 mm from the fusion line.
6.3.2.4 If the average value of the three initial
Charpy V-notch specimens fails to meet the stated requirements, or the value for
more than one specimen is below the required average value, or when the value for
one specimen is below the minimum value permitted for a single specimen, three
additional specimens from the same material may be tested and the results be
combined with those previously obtained to form a new average. If this new average
complies with the requirements and if no more than two individual results are lower
than the required average and no more than one result is lower than the required
value for a single specimen, the piece or batch may be accepted.
6.3.3
Bend test
6.3.3.1 The bend test may be omitted as a material
acceptance test, but is required for weld tests. Where a bend test is performed,
this shall be done in accordance with recognized standards.
6.3.3.2 The bend tests shall be transverse bend tests,
which may be face, root or side bends at the discretion of the Administration.
However, longitudinal bend tests may be required in lieu of transverse bend tests in
cases where the base material and weld metal have different strength levels.
6.3.4
Section observation and other testing
Macrosection, microsection observations and hardness tests may also be
required by the Administration, and they shall be carried out in accordance with
recognized standards, where required.
6.4
Requirements for metallic materials
6.4.1
General requirements for metallic materials
6.4.1.1 The requirements for materials of construction
are shown in the tables as follows:
-
.1 Table 6.1: Plates, pipes (seamless and
welded), sections and forgings for cargo tanks and process pressure vessels
for design temperatures not lower than 0°C.
-
.2 Table 6.2: Plates, sections and forgings for
cargo tanks, secondary barriers and process pressure vessels for design
temperatures below 0°C and down to -55°C.
-
.3 Table 6.3: Plates, sections and forgings for
cargo tanks, secondary barriers and process pressure vessels for design
temperatures below -55°C and down to -165°C.
-
.4 Table 6.4: Pipes (seamless and welded),
forgings and castings for cargo and process piping for design temperatures
below 0°C and down to -165°C.
-
.5 Table 6.5: Plates and sections for hull
structures required by 4.19.1.2 and 4.19.1.3.
Table 6.1
|
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
|
|
CHEMICAL COMPOSITION AND HEAT TREATMENT
|
| ♦
Carbon-manganese steel
|
| ♦
Fully killed fine grain steel
|
| ♦
Small additions of alloying elements by agreement with the
Administration
|
| ♦
Composition limits to be approved by the Administration
|
| ♦
Normalized, or quenched and tempered See note 4
|
|
TENSILE AND TOUGHNESS (IMPACT) TEST REQUIREMENTS
|
|
Sampling frequency
|
| ♦
Plates
|
Each "piece" to be tested
|
| ♦
Sections and forgings
|
Each "batch" to be tested.
|
|
Mechanical properties
|
| ♦
Tensile properties
|
Specified minimum yield stress not to exceed 410 N/mm2
See note 5
|
|
Toughness (Charpy V-notch test)
|
| ♦
Plates
|
Transverse test pieces. Minimum average energy value (KV)
27J
|
| ♦
Sections and forgings
|
Longitudinal test pieces. Minimum average energy (KV) 41J
|
| ♦ Test temperature
|
Thickness t
(mm)
|
Test
temperature (°C)
|
| t≤20
|
0
|
| 20<t≤40
See note 3
|
-20
|
| Notes
|
| 1 For seamless pipes and fittings normal practice
applies. The use of longitudinally and spirally welded pipes shall
be specially approved by the Administration or recognized
organization acting on its behalf.
|
| 2 Charpy V-notch impact tests are not required for
pipes.
|
| 3 This table is generally applicable for material
thicknesses up to 40 mm. Proposals for greater thicknesses shall be
approved by the Administration or recognized organization acting on
its behalf.
|
| 4 A controlled rolling procedure or TMCP may be used
as an alternative.
|
| 5 Materials with specified minimum yield stress
exceeding 410 N/mm2 may be approved by the Administration
or recognized organization acting on its behalf. For these
materials, particular attention shall be given to the hardness of
the welded and heat affected zones.
|
Table 6.2
|
PLATES, SECTIONS AND FORGINGSSee note1 FOR CARGO
TANKS, SECONDARY BARRIERS AND PROCESS PRESSURE VESSELS FOR
DESIGN TEMPERATURES BELOW 0°C AND DOWN TO -55°C Maximum
thickness 25 mmSee note 2
|
|
CHEMICAL COMPOSITION AND HEAT TREATMENT
|
| ♦
Carbon-manganese steel
|
| ♦
Fully killed, aluminium treated fine grain steel
|
| ♦
Chemical composition (ladle analysis)
|
| C
|
Mn
|
Si
|
S
|
P
|
| 0.16%maxSee note 3
|
0.7-1.60%
|
0.1-0.50%
|
0.025%
max
|
0.025%
max
|
| Optional additions: Alloys and grain refining elements may be
generally in accordance with the following:
|
| Ni
|
Cr
|
Mo
|
Cu
|
Nb
|
V
|
| 0.8%
max
|
0.25%
max
|
0.08%
max
|
0.35%
max
|
0.05%
max
|
0.1%
max
|
| Al
content total 0.02% min (Acid soluble 0.015% min)
|
| ♦
Normalized, or quenched and tempered See note 4
|
|
TENSILE AND TOUGHNESS (IMPACT) TEST REQUIREMENTS
|
| Sampling frequency
|
| ♦
Plates
|
Each "piece" to be tested
|
| ♦
Sections and forgings
|
Each "batch" to be tested
|
|
Mechanical properties
|
| ♦
Tensile properties
|
Specified minimum yield stress not to exceed 410 N/mm2
See note 5
|
|
Toughness (Charpy V-notch test)
|
| ♦
Plates
|
Transverse test pieces. Minimum average energy value (KV)
27J
|
| ♦
Sections and forgings
|
Longitudinal test pieces. Minimum average energy (KV) 41J
|
| ♦
Test temperature
|
5°C below the design temperature or -20°C, whichever is
lower
|
Notes
1 The Charpy V-notch and chemistry requirements for forgings may be specially
considered by the Administration.
2 For material thickness of more than 25 mm, Charpy V-notch tests shall be conducted
as follows:
| Material thickness (mm)
|
Test temperature (°C)
|
| 25 < t ≤ 30
|
10°C below design temperature or -20°C, whichever is
lower
|
| 30 < t ≤ 35
|
15°C below design temperature or -20°C, whichever is
lower
|
| 35 < t ≤ 40
|
20°C below design temperature
|
| 40 < t
|
Temperature approved by the Administration or
recognized organization acting on its behalf
|
- 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 the Administration, the carbon content may be
increased to 0.18% maximum, provided the design temperature is not lower than
-40°C.
4 A controlled rolling procedure or TMCP may be used as an
alternative.
5 Materials with specified minimum yield stress exceeding 410
N/mm2 may be approved by the Administration or recognized
organization acting on its behalf. For these materials, particular attention shall
be given to the hardness of the welded and heat affected zones
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 6.3 may be necessary.
Table 6.3
|
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°CSee note
2 Maximum thickness 25 mmSee notes 3 and
4
|
| Minimum design
temperature (°C)
|
Chemical composition See note 5 and heat
treatment
|
Impact test
temperature (°C)
|
| -60
|
1.5% nickel steel – normalized or normalized and tempered or
quenched and tempered or TMCP See note 6
|
-65
|
| -65
|
2.25% nickel steel – normalized or normalized and tempered or
quenched and tempered or TMCP See notes 6 and 7
|
-70
|
| -90
|
3.5% nickel steel – normalized or normalized and tempered or
quenched and tempered or TMCP See notes 6 and 7
|
-95
|
| -105
|
5%
nickel steel – normalized or normalized and tempered or quenched and
tempered See notes 6, 7 and 8
|
-110
|
| -165
|
9% nickel steel – double normalized and tempered or quenched and
tempered See note 6
|
-196
|
| -165
|
Austenitic steels, such as types 304, 304L, 316, 316L, 321 and 347
solution treated See note 9
|
-196
|
| -165
|
Aluminium alloys; such as type 5083 annealed
|
Not
required
|
| -165
|
Austenitic Fe-Ni alloy (36% nickel). Heat treatment as
agreed
|
Not
required
|
| TENSILE AND TOUGHNESS (IMPACT) TEST
REQUIREMENTS
|
| Sampling frequency
|
| ♦ Plates
|
Each "piece" to be tested
|
| ♦ Sections and
forgings
|
Each "batch" to be tested
|
| Toughness (Charpy V-notch test)
|
| ♦ Plates
|
Transverse test pieces. Minimum average energy value (KV)
27J
|
| ♦ Sections and
forgings
|
Longitudinal test pieces. Minimum average energy (KV) 41J
|
Notes
1 The impact test required for forgings used in critical applications
shall be subject to special consideration by the Administration.
2 The requirements for design temperatures below -165°C shall be
specially agreed with the Administration.
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:
| Material thickness (mm)
|
Test temperature (°C)
|
| 25 < t ≤ 30
|
10°C below design temperature
|
| 30 < t ≤ 35
|
15°C below design temperature
|
| 35 < t ≤ 40
|
20°C below design temperature
|
- 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 recognized
standards.
6 TMCP nickel steels will be subject to acceptance by the
Administration.
7 A lower minimum design temperature for quenched and tempered steels may
be specially agreed with the Administration.
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 the
Administration.
Table 6.4
|
PIPES (SEAMLESS AND WELDED)See note 1,
FORGINGSSee note 2 AND CASTINGSSee note
2 FOR CARGO AND PROCESS PIPING FOR DESIGN TEMPERATURES
BELOW 0°C AND DOWN TO -165°CSee note 3 Maximum
thickness 25 mm
|
| Minimum design temperature (°C)
|
Chemical composition See note 5 and heat treatment
|
Impact test
|
| Test temp.
(°C)
|
Minimum average
energy (KV)
|
| -55
|
Carbon-manganese steel. Fully
killed fine grain. Normalized or as agreed See note
6
|
See note
4
|
27
|
| -65
|
2.25% nickel steel.
Normalized, normalized and tempered or quenched and tempered
See notes 6 and 7
|
-70
|
34
|
| -90
|
3.5% nickel steel. Normalized,
normalized and tempered or quenched and temperedSee note
6
|
-95
|
34
|
|
|
9% nickel steelSee note
7. Double normalized and tempered or quenched and tempered
|
-196
|
41
|
| -165
|
Austenitic steels, such as
types 304. 304L, 316, 316L, 321 and 347. Solution treatedSee
note 8
|
-196
|
41
|
|
|
Aluminium alloys; such as type
5083 annealed
|
|
Not
required
|
| TENSILE AND TOUGHNESS (IMPACT) TEST
REQUIREMENTS
|
| Sampling frequency
|
| ♦
Each "batch" to be tested.
|
| Toughness (Charpy V-notch
test)
|
| ♦
Impact test: Longitudinal test pieces
|
| Notes
|
| 1
The use of longitudinally or spirally welded pipes shall be
specially approved by the Administration.
|
| 2
The requirements for forgings and castings may be subject to special
consideration by the Administration.
|
| 3
The requirements for design temperatures below -165°C shall be
specially agreed with the Administration.
|
| 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 recognized
standards.
|
| 6
A lower design temperature may be specially agreed with the
Administration for quenched and tempered materials.
|
| 7
This chemical composition is not suitable for castings.
|
| 8
Impact tests may be omitted, subject to agreement with the
Administration.
|
Table 6.5
|
PLATES AND SECTIONS FOR HULL STRUCTURES REQUIRED BY 4.19.1.2 AND
4.19.1.3
|
| Minimum design temperature of hull structure
(°C)
|
Maximum thickness (mm) for steel
grades
|
| A
|
B
|
D
|
E
|
AH
|
DH
|
EH
|
FH
|
| 0 and
aboveSee note 1
|
Recognized
standards
|
| -5 and aboveSee note 2
|
| down to
-5
|
15
|
25
|
30
|
50
|
25
|
45
|
50
|
50
|
| down to
-10
|
x
|
20
|
25
|
50
|
20
|
40
|
50
|
50
|
| down to
-20
|
x
|
x
|
20
|
50
|
x
|
30
|
50
|
50
|
| down to
-30
|
x
|
x
|
x
|
40
|
x
|
20
|
40
|
50
|
| Below -30
|
In accordance with table 6.2, except that the thickness limitation
given in table 6.2 and in note 2 of that table does not apply.
|
| Notes
|
| "x" means steel grade not to be used.
|
| 1 For the purpose of 4.19.1.3.
|
| 2 For the purpose of 4.19.1.2.
|
6.5
Welding of metallic materials and non-destructive testing
6.5.1
General
6.5.1.1 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 the Administration, impact testing of stainless steel and aluminium
alloy weldments may be omitted and other tests may be specially required for any
material.
6.5.2
Welding consumables
6.5.2.1 Consumables intended for welding of cargo tanks
shall be in accordance with recognized standards. Deposited weld metal tests and
butt weld tests shall be required for all consumables. The results obtained from
tensile and Charpy V-notch impact tests shall be in accordance with recognized
standards. The chemical composition of the deposited weld metal shall be recorded
for information.
6.5.3
Welding procedure tests for cargo tanks and process pressure vessels
6.5.3.1 Welding procedure tests for cargo tanks and
process pressure vessels are required for all butt welds.
6.5.3.2 The test assemblies shall be representative
of:
6.5.3.3 For butt welds in plates, the test assemblies
shall be so prepared that the rolling direction is parallel to the direction of
welding. The range of thickness qualified by each welding procedure test shall be in
accordance with recognized standards. Radiographic or ultrasonic testing may be
performed at the option of the fabricator.
6.5.3.4 The following welding procedure tests for cargo
tanks and process pressure vessels shall be carried out in accordance with 6.3, with
specimens made from each test assembly:
-
.1 cross-weld tensile tests;
-
.2 longitudinal all-weld testing, where
required by the recognized standards;
-
.3 transverse bend tests, which may be face,
root or side bends. However, longitudinal bend tests may be required in lieu
of transverse bend tests in cases where the base material and weld metal
have different strength levels;
-
.4 one set of three Charpy V-notch impacts,
generally at each of the following locations, as shown in figure 6.2:
-
.1 centreline of the weld;
-
.2 fusion line;
-
.3 1 mm from the fusion line;
-
.4 3 mm from the fusion line; and
-
.5 5 mm from the fusion line; and
-
.5 macrosection, microsection and hardness
survey may also be required.
6.5.3.5 Each test shall satisfy the following
requirements:
-
.1 tensile tests: cross-weld tensile strength
shall not be less than the specified minimum tensile strength for the
appropriate parent materials. For aluminium alloys, reference shall be made
to 4.18.1.3 with regard to the requirements for weld metal strength of
under-matched welds (where the weld metal has a lower tensile strength than
the parent metal). In every case, the position of fracture shall be recorded
for information;
-
.2 bend tests: no fracture is acceptable after
a 180° bend over a former of a diameter four times the thickness of the test
pieces; and
-
.3 Charpy V-notch impact tests: Charpy V-notch
tests shall be conducted at the temperature prescribed for the base material
being joined. The results of weld metal impact tests, minimum average energy
(KV), shall be no less than 27 J. The weld metal requirements for subsize
specimens and single energy values shall be in accordance with 6.3.2. The
results of fusion line and heat-affected zone impact tests shall show a
minimum average energy (KV) in accordance with the transverse or
longitudinal requirements of the base material, whichever is applicable, and
for subsize specimens, the minimum average energy (KV) shall be in
accordance with 6.3.2. If the material thickness does not permit machining
either full-size or standard subsize specimens, the testing procedure and
acceptance standards shall be in accordance with recognized standards.
6.5.3.6 Procedure tests for fillet welding shall be in
accordance with recognized standards. In such cases, consumables shall be so
selected that exhibit satisfactory impact properties.
6.5.4
Welding procedure tests for piping
Welding procedure tests for piping shall be carried out and shall be
similar to those detailed for cargo tanks in 6.5.3.
6.5.5
Production weld tests
6.5.5.1 For all cargo tanks and process pressure
vessels, except integral and membrane tanks, production weld tests shall generally
be performed for approximately each 50 m of butt-weld joints and shall be
representative of each welding position. For secondary barriers, the same type
production tests as required for primary tanks shall be performed, except that the
number of tests may be reduced subject to agreement with the Administration. Tests,
other than those specified in 6.5.5.2 to 6.5.5.5 may be required for cargo tanks or
secondary barriers.
6.5.5.2 The production tests for type A and type B
independent tanks and semi-membrane tanks shall include bend tests and, where
required for procedure tests, one set of three Charpy V-notch tests. The tests shall
be made for each 50 m of weld. The Charpy V-notch tests shall be made with specimens
having the notch alternately located in the centre of the weld and in the
heat-affected zone (most critical location based on procedure qualification
results). For austenitic stainless steel, all notches shall be in the centre of the
weld.
6.5.5.3 For type C independent tanks and process
pressure vessels, transverse weld tensile tests are required in addition to the
tests listed in 6.5.5.2. Tensile tests shall meet the requirements of 6.5.3.5.
6.5.5.4 The quality assurance/quality control programme
shall ensure the continued conformity of the production welds as defined in the
material manufacturers quality manual.
6.5.5.5 The test requirements for integral and membrane
tanks are the same as the applicable test requirements listed in 6.5.3.
6.5.6
Non-destructive testing
6.5.6.1 All test procedures and acceptance standards
shall be in accordance with recognized standards, unless the designer specifies a
higher standard in order to meet design assumptions. Radiographic testing shall be
used, in principle, to detect internal defects. However, an approved ultrasonic test
procedure in lieu of radiographic testing may be conducted, but, in addition,
supplementary radiographic testing at selected locations shall be carried out to
verify the results. Radiographic and ultrasonic testing records shall be
retained.
6.5.6.2 For type A independent tanks and semi-membrane
tanks, where the design temperature is below -20°C, and for type B independent
tanks, regardless of temperature, all full penetration butt welds of the shell
plating of cargo tanks shall be subjected to non-destructive testing suitable to
detect internal defects over their full length. Ultrasonic testing in lieu of
radiographic testing may be carried out under the same conditions as described in
6.5.6.1.
6.5.6.3 Where the design temperature is higher than
-20°C, all full penetration butt welds in way of intersections and at least 10% of
the remaining full penetration welds of tank structures shall be subjected to
radiographic testing or ultrasonic testing under the same conditions as described in
6.5.6.1.
6.5.6.4 In each case, the remaining tank structure,
including the welding of stiffeners and other fittings and attachments, shall be
examined by magnetic particle or dye penetrant methods, as considered necessary.
6.5.6.5 For type C independent tanks, the extent of
non-destructive testing shall be total or partial according to recognized standards,
but the controls to be carried out shall not be less than the following:
6.5.6.6 The quality assurance/quality control programme
shall ensure the continued conformity of the non-destructive testing of welds, as
defined in the material manufacturer's quality manual.
6.5.6.7 Inspection of piping shall be carried out in
accordance with the requirements of chapter 5.
6.5.6.8 The secondary barrier shall be non-destructive
tested for internal defects as considered necessary. Where the outer shell of the
hull is part of the secondary barrier, all sheer strake butts and the intersections
of all butts and seams in the side shell shall be tested by radiographic
testing.
6.6
Other requirements for construction in metallic materials
6.6.1
General
6.6.1.1 Inspection and non-destructive testing of welds
shall be in accordance with the requirements of 6.5.5 and 6.5.6. Where higher
standards or tolerances are assumed in the design, they shall also be satisfied.
6.6.2
Independent tank
6.6.2.1 For type C tanks and type B tanks primarily
constructed of bodies of revolution, the tolerances relating to manufacture, such as
out-of-roundness, local deviations from the true form, welded joints alignment and
tapering of plates having different thicknesses, shall comply with recognized
standards. The tolerances shall also be related to the buckling analysis referred to
in 4.22.3.2 and 4.23.3.2.
6.6.2.2 For type C tanks of carbon and carbon-manganese
steel, post-weld heat treatment shall be performed after welding, if the design
temperature is below -10°C. Post-weld heat treatment in all other cases and for
materials other than those mentioned above shall be to recognized standards. The
soaking temperature and holding time shall be to the recognized standards.
6.6.2.3 In the case of type C tanks and large cargo
pressure vessels of carbon or carbon-manganese steel, for which it is difficult to
perform the heat treatment, mechanical stress relieving by pressurizing may be
carried out as an alternative to the heat treatment and subject to the following
conditions:
-
.1 complicated welded pressure vessel parts
such as sumps or domes with nozzles, with adjacent shell plates shall be
heat treated before they are welded to larger parts of the pressure
vessel;
-
.2 the mechanical stress relieving process
shall preferably be carried out during the hydrostatic pressure test
required by 4.23.6, by applying a higher pressure than the test pressure
required by 4.23.6.1. The pressurizing medium shall be water;
-
.3 for the water temperature, 4.23.6.2
applies;
-
.4 stress relieving shall be performed while
the tank is supported by its regular saddles or supporting structure or,
when stress relieving cannot be carried out on board, in a manner which will
give the same stresses and stress distribution as when supported by its
regular saddles or supporting structure;
-
.5 the maximum stress relieving pressure shall
be held for 2 h per 25 mm of thickness, but in no case less than 2 h;
-
.6 the upper limits placed on the calculated
stress levels during stress relieving shall be the following:
-
.1 equivalent general primary membrane
stress: 0.9 Re
;
-
.2 equivalent stress composed of
primary bending stress plus membrane stress: 1.35 Re
, where Re
is the specific lower minimum yield stress or 0.2% proof stress
at test temperature of the steel used for the tank;
-
.7 strain measurements will normally be
required to prove these limits for at least the first tank of a series of
identical tanks built consecutively. The location of strain gauges shall be
included in the mechanical stress relieving procedure to be submitted in
accordance with 6.6.2.3;
-
.8 the test procedure shall demonstrate that a
linear relationship between pressure and strain is achieved at the end of
the stress relieving process when the pressure is raised again up to the
design pressure;
-
.9 high-stress areas in way of geometrical
discontinuities such as nozzles and other openings shall be checked for
cracks by dye penetrant or magnetic particle inspection after mechanical
stress relieving. Particular attention in this respect shall be paid to
plates exceeding 30 mm in thickness;
-
.10 steels which have a ratio of yield stress
to ultimate tensile strength greater than 0.8 shall generally not be
mechanically stress relieved. If, however, the yield stress is raised by a
method giving high ductility of the steel, slightly higher rates may be
accepted upon consideration in each case;
-
.11 mechanical stress relieving cannot be
substituted for heat treatment of cold formed parts of tanks, if the degree
of cold forming exceeds the limit above which heat treatment is
required;
-
.12 the thickness of the shell and heads of the
tank shall not exceed 40 mm. Higher thicknesses may be accepted for parts
which are thermally stress relieved;
-
.13 local buckling shall be guarded against,
particularly when tori-spherical heads are used for tanks and domes; and
-
.14 the procedure for mechanical stress
relieving shall be to a recognized standard.
6.6.3
Secondary barriers
During construction, the requirements for testing and inspection of
secondary barriers shall be approved or accepted by the Administration or recognized
organization acting on its behalf (see 4.6.2.5 and 4.6.2.6).
6.6.4
Semi-membrane tanks
For semi-membrane tanks, the relevant requirements in section 6.6 for
independent tanks or for membrane tanks shall be applied as appropriate.
6.6.5
Membrane tanks
The quality assurance/quality control programme shall ensure the
continued conformity of the weld procedure qualification, design details, materials,
construction, inspection and production testing of components. These standards and
procedures shall be developed during the prototype testing programme.
6.7 Non-metallic materials
6.7.1
General
The information in the attached appendix 4 is given for guidance in the
selection and use of these materials, based on the experience to date.