Appendix - Material Testing Requirements and Acceptance Criteria
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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) - Appendix - Material Testing Requirements and Acceptance Criteria

Appendix - Material Testing Requirements and Acceptance Criteria

1 Test of base material

1.1 Material specifications: Chemical composition and mechanical properties meeting a recognized standard for the alternative metallic material intended for cryogenic service.

Acceptance criteria: in accordance with the recognized standard.

1.2 Micrographic examination: The test should be carried out in accordance with section 6.3.4 of the IGC Code using recognized standards such as ASTM E112.

Acceptance criteria: Microstructure including grain size. The absence of precipitations, segregation and cracking should be reported. Acceptance should be to the satisfaction of the Administration.

1.3 Tensile test: The test should be carried out in accordance with section 6.3.1 of the IGC Code. Samples should be taken from three heats of different compositions, both at room and cryogenic temperatures equal to the minimum design temperature of the alternative metallic material. The number of samples should be sufficient to provide statistically valid results.

Acceptance criteria: The yield strength, tensile strength and elongation should be in accordance with the recognized standard for the chemical composition given in 1.1 of this appendix.

1.4 Charpy impact test: The test should be carried out in accordance with section 6.3.2 of the IGC Code. Samples should be taken from three heats of different compositions, both at room and cryogenic temperatures equal to the required test temperature. Impact tests should not be omitted for austenitic steels due to lack of experience. Test temperatures should be as follows:

Material thickness (mm) Test temperature (oC)
t < 25 5oC below design temperature

(ferritic steel only)

25 < t ≤ 30 10oC below design temperature
30 < t ≤ 35 15oC below design temperature
35 < t ≤ 40 20oC below design temperature

Acceptance criteria: unless higher values are required by the material specification.

Material Test piece Minimum average energy

(KV)
Ferrous alloy plates Transverse 27 J
Ferrous alloy sections and forgings Longitudinal 41 J
Non-Ferrous alloy   Not required, subject to the approval of the Administration

1.5 Charpy impact test on strain aged specimens: The test should be carried out in accordance with a recognized standard such as ASTM E23. Strain ageing consists of 5% deformation for 1 hour at 250oC in accordance with IACS UR W11. Samples should be taken from three heats of different compositions, both at room and cryogenic temperatures equal to the minimum test temperature. Impact tests should not be omitted for austenitic steels due to lack of experience. Test temperatures should be as follows:

Material thickness (mm) Test temperature (oC)
t < 25 5oC below design temperature

(ferritic steel only)

25 < t ≤ 30 10oC below design temperature
30 < t ≤ 35 15oC below design temperature
35 < t ≤ 40 20oC below design temperature

Acceptance criteria: unless higher values are required by the material specification.

Material Test piece Minimum average energy

(KV)
Ferrous alloy plates Transverse 27 J
Ferrous alloy sections and forgings Longitudinal 41 J
Non-Ferrous alloy - Not required, subject to the approval of the Administration

1.6 Drop weight test: Applicable only for ferritic steels including ferritic-austenitic (duplex) grade. The aim of the test is to establish the nil ductility transition temperature (NDTT). Samples should be taken from three heats of different compositions, both at room and cryogenic temperatures equal to the minimum test temperature. The test should be carried out in accordance with a recognized standard such as ASTM E208 for ferritic steels.

Acceptance criteria: No break at 10oC below the design temperature.

1.7 Fatigue test: The basis for documenting adequate fatigue performance (S-N curves) should be in accordance with paragraph 4.18.2.4.2 of the IGC Code. The extent of fatigue testing is based on comparison with recognized S-N curves for metallic materials (such as IIW or DNVGL-RP-C203 or BS 7608).

The fatigue tests should be based on a minimum of five test samples at each stress level. For a "one slope S-N curve" a minimum of three stress levels should be tested. Additional stress levels are to be tested for "two slope S-N curves". As guidance, stress levels should be selected to achieve in the range of 105 to 108 cycles.

Acceptance criteria: The fatigue test results should be at least equal to or better than the reference S-N curve.

1.8 CTOD (Crack Tip Opening Displacement) test: The test should be carried out in accordance with a recognized standard such as ASTM E1820, BS 7448 or ISO 12135.

Acceptance criteria: CTOD minimum value should be in accordance with the design specification for testing at room and cryogenic temperatures equal to the minimum design temperature of the material. A minimum of three successful tests should be performed at room and cryogenic temperatures. As guidance a minimum CTOD value of 0.2 mm is often required.

1.9 Corrosion test: The type of corrosion tests to be applied will depend on the material to be qualified. The tests should include tests for general corrosion, intergranular corrosion and stress corrosion. The tests should be carried out in accordance with relevant standards.

Acceptance criteria: In accordance with the relevant recognized standard approved by the Administration for the material's intended service.

2 Test of welded condition (including HAZ)

2.1 Micrographic examination: The test should be carried out in accordance with section 6.3.4 of the IGC Code using recognized standards such as ASTM E112.

Acceptance criteria: Microstructure including grain size, absence of precipitations, segregation, and cracking should be reported. Acceptance should be to the satisfaction of the Administration.

2.2 Hardness test: The test should be carried out in accordance with section 6.3.4 and paragraph 6.5.3.4.5 of the IGC Code in accordance with recognized standards such as ISO 6507-1.

Acceptance criteria: The hardness value should be to the satisfaction of the Administration.

2.3 Cross-weld tensile test: This test should be carried out in accordance with paragraph 6.5.3.4.1 of the IGC Code. Recognized standards such as ASTM E8/E8M may be applied.

Acceptance criteria: In accordance with paragraph 6.5.3.5.1 of the IGC Code. The presence of under-matched welds should be considered for the intended application in accordance with paragraph 4.18.1.3.1.2 of the IGC Code.

2.4 Charpy impact test: This test should be carried out in accordance with section 6.3.2 and paragraph 6.5.3.4.4 of the IGC Code.

Acceptance criteria: In accordance with paragraph 6.5.3.5.3 of the IGC Code.

2.5 CTOD (Crack Tip Opening Displacement) test: The test should be carried out in accordance with a recognized standard such as ASTM E1820 or ISO 15653. The notch introduced in the test should be positioned in the microstructure with the lowest fracture toughness.

Acceptance criteria: CTOD minimum value should be in accordance with the design specification for testing at room and cryogenic temperatures equal to the minimum design temperature of the material. A minimum of three successful tests should be performed at room and cryogenic temperatures. As guidance a minimum CTOD value of 0.2 mm is often required.

2.6 Ductile fracture toughness test (JIc): The test should be carried out in accordance with a recognized standard such as ASTM E1820, ASTM E2818, ISO 15653 or ISO 12135. The notch introduced in the test should be positioned in the microstructure with the lowest fracture toughness. The ductile fracture toughness test may be carried out as an alternative to the CTOD test in 2.5 at the discretion of the Administration.

Acceptance criteria: In accordance with the recognized standard. A minimum of three successful tests should be performed at room and cryogenic temperatures.

2.7 Bending test: The test should be carried out in accordance with section 6.3.3 of the IGC Code.

Acceptance criteria: No fracture should be acceptable after a 180o bend as required for welded material in accordance with paragraph 6.5.3.4.3 and 6.5.3.5.2 of the IGC Code.

2.8 Fatigue test: The basis for documenting adequate fatigue performance (S-N curves) should be in accordance with paragraph 4.18.2.4.2 of the IGC Code. The extent of fatigue testing is based on comparison with recognized S-N curves for metallic materials (such as IIW or DNVGL-RP-C203). The fatigue tests should be based on a minimum of five test samples at each stress level. For a "one slope S-N curve" a minimum of three stress levels should be tested. Additional stress levels to be tested for "two slope S-N curves". As guidance, stress levels should be selected to achieve in the range of 105 to 108 cycles.

Acceptance criteria: The fatigue test results should be at least equal to, or better than, the reference SN curve.

2.9 Corrosion test: The type of corrosion tests to be applied will depend on the material and type of weld to be qualified. The tests should include tests for general corrosion, intergranular corrosion and stress corrosion. The tests should be carried out in accordance with relevant standards.

Acceptance criteria: In accordance with the relevant standard approved by the Administration for the material's intended 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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