Section 1 Materials of Construction and Quality Control
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Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 11 Production, Storage and Offloading of Liquefied Gases in Bulk - Chapter 6 Materials of Construction and Quality Control - Section 1 Materials of Construction and Quality Control

Section 1 Materials of Construction and Quality Control

Parent topic: Chapter 6 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
  1. 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:
    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:
    Table 6.1.5 Plates and sections for hull structures required by :

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
  • 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
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 value (KV) 27J
  • Sections and forgings
Longitudinal test pieces. Minimum average energy (KV) 41J
  • Test temperature

Thickness t (mm)

t ≤ 20

20 < t ≤ 40, see Note 3

Test temperature (°C)

0

–20

NOTES
1. For seamless pipes and fittings, normal practice applies. The use of longitudinally and spirally welded pipes shall be specially approved by LR.
2. Charpy V-notch impact tests are not required for pipes where the thickness is less than 15 mm.
3. This Table is generally applicable for material thicknesses up to 40 mm. Proposals for greater thicknesses shall be approved by LR.
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.
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.

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
 
  • Carbon-manganese steel
  • Fully killed, aluminium treated fine grain steel
  • Chemical composition (ladle analysis)
   
 

C

0,16% max.

see Note 3

Mn

0,70-1,60%

Si

0,10-0,50%

S

0,025% max.

P

0,025% max.

 
  Optional additions: Alloys and grain refining elements may be generally in accordance with the following:  
 

Ni

0,80% max.

Cr

0,25% max.

Mo

0,08% max.

Cu

0,35% max.

Nb

0,05% max.

V

0,10% max.

 
  Al content total 0,020% min. (acid soluble 0,015% min.)
  • Normalised, 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 cargo design temperature or –20°C, whichever is lower
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:

  Material thickness (mm) Test temperature (°C)
  25 < t ≤ 30 10°C below cargo design temperature or –20°C, whichever is lower  
  30 < t ≤ 35 15°C below cargo design temperature or –20°C, whichever is lower  
  35 < t ≤ 40 20°C below cargo design temperature  
  40 < t Temperature approved by LR  
  • 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.

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.

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 Chemical composition, see Note 5, and heat treatment Impact test temperature (°C)
–60 1,5% nickel steel – normalised or normalised and tempered or quenched and tempered or TMCP, see Note 6 –65
–65 2,25% nickel steel – normalised or normalised and tempered or quenched and tempered or TMCP, see Notes 6 and 7 –70
–90 3,5% nickel steel – normalised or normalised and tempered or quenched and tempered or TMCP, see Notes 6 and 7 –95
–105 5% nickel steel – normalised or normalised and tempered or quenched and tempered, see Notes 6, 7 and 8 –110
–165 9% nickel steel – double normalised 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 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:

  Material thickness (mm) Test temperature (°C)  
  25 < t ≤ 30 10°C below cargo design temperature  
  30 < t ≤ 35 15°C below cargo design temperature  
  35 < t ≤ 40 20°C below cargo 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 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.

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 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. Normalised or as agreed, see Note 6 See Note 4 27
–65 2.25% nickel steel. Normalised, normalised and tempered or quenched and tempered, see Note 6 –70 34
–90 3.5% nickel steel. Normalised, normalised and tempered or quenched and tempered, see Note 6 –95 34
–165 9% nickel steel, see Note 7. Double normalised and tempered or quenched and tempered –196 41
–165 Austenitic steels, such as types 304. 304L, 316, 316L, 321 and 347. Solution treated, see Note 8 –196 41
–165 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 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.

Table 6.1.5 Plates and sections for hull structures required by Pt 11, Ch 4, 5.1 Materials 5.1.2.(b)

Minimum design temperature of hull structure (°C) Maximum thickness (mm) for steel grades
A B D E AH DH EH FH

0 and above, see Note 1

–5 and above, see Note 2

To comply with Pt 10, Ch 1, 3 Materials
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 6.1.2 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

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).

1.4.2  The material grades for the construction of the hull structure are to comply with the requirements of Table 2.4.1 Thickness limitations for structural steels for various application categories and design temperatures for use in welded construction including plates, bars, sections forgings, and castings in Pt 4, Ch 2 Materials unless the minimum metal temperature is the result of heat conduction from the cargo, in which case hull materials shall be in accordance with Table 6.1.5 Plates and sections for hull structures required by .

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
  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 LR, impact testing of stainless steel and aluminium alloy weldments may be omitted and other tests may be specially required for any material.
1.5.2  Welding consumables
  1. Consumables for welding of cargo tanks shall be in accordance with Ch 11 Approval of Welding Consumables of the Rules for Materials and recognised Standards.
1.5.3  Welding procedure tests for cargo tanks and process pressure vessels
  1. 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
  1. 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.
  2. 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.
  3. 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
  1. 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.
  2. 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.
  3. 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
  1. 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:
    1. the all weld tensile test may be omitted; and
    2. 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.
  2. For independent tanks, Types A and B, the transverse tensile tests may also be omitted.
  3. 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.
  4. 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
  1. 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.
  2. 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.
  3. Type A independent and semi-membrane tanks:
    1. 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).
    2. 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.
    3. 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.
  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. Piping:
    1. 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;
    2. 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;
    3. 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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