Experimental Methods for Assessing Mechanical Properties and Fracture Resistance of Steels from LNG to Liquid-Hydrogen Temperatures: A Critical Review

Qualification of metallic structures for liquefied natural gas (LNG), liquid nitrogen, liquid hydrogen, and other low-temperature services requires a mechanical-property database that is consistent with the relevant failure mode. Tensile strength, Charpy energy, drop-weight tear-test (DWTT) shear area, J-R resistance, CTOD, KJc/T0, fatigue- crack-growth rate, and crack-arrest toughness are not interchangeable measures, because each interrogates a different stage of failure under a different constraint and loading condition. This review critically examines experimental methods for characterizing mechanical properties and fracture resistance of steels and welded joints from LNG service near -163 °C down to liquid-hydrogen temperature (20 K). A total of 105 peer-reviewed studies, standards, and technical reports covering X70 line-pipe steel, 9%Ni steel, EH36/EH47 and offshore steels, high-Mn steels, weld heat-affected zones (HAZs), hydrogen-assisted fracture, small-scale testing, and crack-arrest evaluation are assessed against the requirements of quantitative flaw assessment. Particular attention is given to temperature control, fatigue precracking, notch acuity, specimen size and constraint, HAZ notch placement, crack-growth measurement, hydrogen charging history, and the distinction between crack initiation and arrest. Literature figures and selected source-based schematics illustrate the reviewed methods; their sources and presentation types are identified in the captions. Evidence obtained above 20 K is treated as methodological or screening evidence, not as direct qualification for liquid-hydrogen service. A test-selection framework is proposed that links the intended structural question to the corresponding specimen geometry, fracture parameter, and validity criteria. The principal conclusion is that a defensible cryogenic property cannot be defined only by a low test temperature: validity requires equivalence among service condition, specimen constraint, crack geometry, loading rate, environmental history, and the selected fracture parameter.