Annex - Guidelines for the Acceptance of Alternative Metallic Materials for Cryogenic Service in Ships Carrying Liquefied Gases in Bulk and Ships Using Gases or Other Low-Flashpoint Fuels
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Statutory Documents - IMO Publications and Documents - Circulars - Maritime Safety Committee - MSC.1/Circular.1622 - Guidelines for the Acceptance of Alternative Metallic Materials for Cryogenic Service in Ships Carrying Liquefied Gases in Bulk and Ships Using Gases or Other Low-Flashpoint Fuels - (2 December 2020) - Annex - Guidelines for the Acceptance of Alternative Metallic Materials for Cryogenic Service in Ships Carrying Liquefied Gases in Bulk and Ships Using Gases or Other Low-Flashpoint Fuels

Annex - Guidelines for the Acceptance of Alternative Metallic Materials for Cryogenic Service in Ships Carrying Liquefied Gases in Bulk and Ships Using Gases or Other Low-Flashpoint Fuels

Part 1 General

1 Introduction

1.1 Ships carrying liquefied gases in bulk should comply with the requirements of the IGC Code adopted by resolution MSC.370(93), as amended. Ships using gases or other low-flashpoint fuels should comply with the requirements of the IGF Code, adopted by resolution MSC.391(95), as amended.

1.2 The requirements for metallic materials used in low temperature applications on board ships constructed in accordance with the IGC and IGF Codes are contained in tables 6.2, 6.3 and 6.4 of the IGC Code and tables 7.2, 7.3 and 7.4 of the IGF Code, respectively. The requirements are identical in both Codes and specify the minimum design temperatures for specific materials based upon chemical composition, mechanical properties and heat treatment. These approved materials have been incorporated in the Codes since their inception and have provided over 40 years of satisfactory service experience.

1.3 There is recent interest in adding new metallic materials to the list of those already covered by the Codes. Interim guidelines on the application of high manganese austenitic steel for cryogenic service were adopted and disseminated as MSC.1/Circ.1599. In the process of developing the Interim guidelines, significant experience in the evaluation of this alternative material was acquired. The recommendations contained in MSC.1/Circ.1599 are used as the basis for these Guidelines.

2 Application

2.1 These Guidelines apply to metallic materials not listed in tables 6.2, 6.3 and 6.4 of the IGC Code and tables 7.2, 7.3 and 7.4 of the IGF Code respectively. The testing requirements set out herein provide guidance for the acceptance of alternative metallic materials based upon the equivalency provisions contained in section 1.3 of the IGC Code or alternative design requirements contained in section 2.3 of the IGF Code. The Guidelines apply only to materials used for products listed in chapter 19 of the IGC Code or MSC circulars approved by the Organization, or fuels addressed by the IGF Code.

2.2 The Guidelines also apply to alternative metallic materials having a minimum design temperature between 0oC and -165oC or lower if authorized by the Administration in the range of minimum and maximum thicknesses tested during the approval process, up to a maximum thickness of 40 mm. Thicknesses in excess of 40 mm should be approved by the Administration or recognized organization acting on its behalf. In addition to approval for a minimum design temperature of -165oC, alternative metallic materials may be approved for intermediate minimum design temperatures of -55oC, -60oC, -65oC, -90oC and -105oC. Alternative metallic materials qualified at a lower temperature are suitable for use at the intermediate minimum design temperature.

2.3 The Guidelines only apply to alternative metallic materials formed or manufactured by rolling, extrusion, casting or forging.

2.4 Alternative metallic materials approved in accordance with the Guidelines may be used in the construction of cargo containment and piping system under chapter 4 of the IGC Code or similar parts of fuel tanks, under chapter 6 of the IGF Code or piping systems under section 5.12 of the IGC Code and section 7.4.1.2 of the IGF Code. They should be approved for specific cargoes or fuels listed in the IGC or IGF Codes based upon their design temperature and their compatibility with the cargo or fuel. This Guideline does not address material forming part of the hull structure.

3 Definitions

3.1 Alternative metallic materials: Homogeneous ferrous and non-ferrous alloys having uniform composition in any direction formed by hot rolling, cold rolling, extrusion, casting or forging, whose compositions or heat treatments are not listed in tables 6.2, 6.3 and 6.4 of the IGC Code and tables 7.2, 7.3 and 7.4 of the IGF Code, respectively.

3.2 Established metallic materials: Metallic materials listed in tables 6.2, 6.3 and 6.4 of the IGC Code and tables 7.2, 7.3 and 7.4 of the IGF Code, respectively, or by an IMO MSC circular.

3.3 Equivalent alternative metallic materials: Alternative metallic materials having chemical and mechanical properties that are equivalent or superior to those listed in tables 6.2, 6.3 and 6.4 of the IGC Code and tables 7.2, 7.3 and 7.4 of the IGF Code, respectively, that have been approved under these Guidelines.

3.4 Other alternative metallic materials: Alternative metallic materials having mechanical properties that do not meet those listed in tables 6.2, 6.3 and 6.4 of the IGC Code and tables 7.2, 7.3 and 7.4 of the IGF Code, respectively.

3.5 Recognized standards: Applicable international or national standards acceptable to the Administration, or standards laid down and maintained by the recognized organization.

3.6 Administration: Government of the State whose flag the ship is entitled to fly.

Part II Material Specifications and Testing Requirements

4 Material specification

4.1 All alternative metallic materials should have a recognized standard for cryogenic service for consideration under these Guidelines. The standard should cover specific forms of the material being approved, including plates, sections, castings, forgings or pipes, and should specify heat treatment and grain structure. The standard should meet the scope and general requirements of section 6.2 of the IGC Code. Micro-alloying elements not identified in the recognized standards may be considered subject to approval by the Administration.

4.2 Alternative metallic material, including plates, castings and forgings, should be joined using an approved method specified by a recognized standard. When applied, conventional welding procedures qualified in accordance with a recognized standard and complying with procedures contained in chapter 6.5 of the IGC Code and part B-1, section 16.3 of the IGF Code should be specified for the welding of alternative metallic materials. The welding procedures should specify heat input and pre- and post-weld heat treatment.

4.3 Welding procedures and non-destructive testing (NDT) should be specified for all alternative metallic materials. These procedures should conform to a recognized standard and comply with testing requirements specified in chapter 6.5 of the IGC Code and part B-1, section 16.3 of the IGF Code.

5 Testing

5.1 Test requirements are provided in the appendix to the Guidelines and are based upon section 6.3 of the IGC Code and part B-1, section 16.2 of the IGF Code.

5.2 Depending on the design temperature, Charpy V-notch tests should be conducted in accordance with the footnotes in the applicable tables given in chapter 6 of the IGC Code and section 7 of the IGF Code.

5.3 Subject to the approval of the Administration, consideration can be given to alternative test methods that provide an equivalent level of safety. Test requirements should not be waived unless there is a valid technical justification, or the material properties can be confirmed by another test method. Test requirements may be waived if not required for specific tank types within chapter 4 of the IGC Code, section 6 of the IGF Code or if not required for similar established metallic materials.

5.4 The testing of alternative metallic material should be conducted on at least one of the following forms: plates, castings, forgings or pipes. The testing of any form should meet the sampling and specimen position requirements of section 6.4 of the IGC Code and section 7.4 of the IGF Code. Initial testing should be conducted on the form reflecting the application of an alternative metallic material. Approval is limited to forms for which test results are provided; however, all forms do not have to be considered for approval of the alternative metallic material.

5.5 Corrosion sensitization can occur in stainless and other austenitic steels. In such cases, the Administration may require additional corrosion testing such as an Intergranular Corrosion Test such as ASTM A262 and a Stress Corrosion Cracking Test such as ASTM G36 or ASTM G123.

6 Acceptance criteria

6.1 Test acceptance criteria are provided in the appendix to this Guideline and are based upon section 6.3 of the IGC Code and part B-1, section 16.2 of the IGF Code.

6.2 The application of an alternative metallic material in a specific design should be based upon the adequacy of the material for the design loads and the suitability of the material properties for their intended use in accordance with the design conditions specified in section 4.18 of the IGC Code and section 6.4.12 of the IGF Code.

6.3 Approval of alternative metallic materials should be for each form of the material for which there are satisfactory test results.

 7 Novel design and equivalent arrangements

Alternative metallic materials may be used in the design of novel containment systems under section 4.27 of the IGC Code and section 6.4.16 of the IGF Code. Section 2.1 in appendix 5 of the IGC Code and part A-1 annex, section 2.1 of the IGF Code require the use of established metallic materials. The use of other alternative metallic materials should not be considered in a design.

Part III Application

8 Approval procedures

8.1 Upon satisfactory completion of testing of the appropriate forms and acceptance of the results, an alternative metallic material is considered to be an accepted equivalent alternative metallic material for the purpose of the Guidelines.

8.2 The approval should specify any limitations that have been identified in the inherent properties of the approved alternative metallic material that may need to be considered in its use. These properties may include, but are not limited to:

  • .1 under-matching/over-matching of welds;

  • .2 pre- and post-weld heat treatment;

  • .3 corrosion;

  • .4 specific NDT requirements or limitations; and

  • .5 toxicity of welding fumes.

8.3 Tables 6.2, 6.3 and 6.4 of the IGC Code and tables 7.2, 7.3 and 7.4 of the IGF Code may be modified to incorporate new alternative metallic materials subject to the following:

  • .1 material should be qualified using these Guidelines;

  • .2 material compatibility for all intended cargoes should be demonstrated;

  • .3 relevant fabrication experience on any tank type on a ship should be documented;

  • .4 material should have minimum of 5 years of service experience on board a ship or equivalent to one special survey cycle;

  • .5 service experience should be on a ship in service, relevant to the material's future use; and

  • .6 if simulation is used, credit may be given to a reduced service period upon completion of the first intermediate survey. The scope of this survey should be in accordance with the requirements of the first special survey, including NDT, of the tank.

9 Application

The Administration should assign approved safety factors based upon those for nickel steels, carbon manganese steels, austenitic steels or aluminium alloys in the IGC and IGF Codes.

10 References

MSC.1/Circ.1599 Interim guidelines on the application of high manganese austenitic steel for cryogenic service.

Parent topic: MSC.1/Circular.1622 - Guidelines for the Acceptance of Alternative Metallic Materials for Cryogenic Service in Ships Carrying Liquefied Gases in Bulk and Ships Using Gases or Other Low-Flashpoint Fuels - (2 December 2020)
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