Hydrogen is expected to play a central role in achieving net-zero emission targets, particularly in hard-to-electrify sectors such as high-temperature industry, seasonal energy storage, and long-distance heavy transport [1]. In this context, many countries are planning to repurpose existing natural gas pipelines for hydrogen service, alongside the construction of new hydrogen-dedicated infrastructure. However, the safe and reliable operation of hydrogen pipelines presents significant material and structural integrity challenges. As the smallest atom, hydrogen readily enters and diffuses into engineering materials, including pipeline steels. This interaction degrades the mechanical response of the material, leading to reduced fracture toughness and accelerated fatigue crack growth. From an engineering perspective, these effects necessitate rigorous fracture-mechanics assessments to define safe operating conditions for hydrogen pipelines [2]. Two key material inputs for such assessments are fracture toughness and fatigue crack growth behaviour. Unfortunately, these properties are expensive and difficult to measure experimentally under hydrogen environments. As a result, many existing assessments rely on so-called master curves that are assumed to be conservative [2]. However, the degree of conservatism is often unknown and may be excessively restrictive, leading to inefficient or overly pessimistic design and lifetime predictions. In this study, a comprehensive database of fracture-mechanics properties of pipeline steels under hydrogen exposure, compiled from the literature, is systematically analysed. Based on this dataset, probabilistic surrogate models are developed for fracture toughness and fatigue crack growth rate. These models describe the fracture-mechanics behaviour of pipeline steels as functions of steel grade, hydrogen pressure, stress intensity factor range, loading ratio, loading frequency, and the desired level of conservatism. The developed probabilistic framework is then integrated into the fracture assessment procedures of ASME B31.12 to predict the allowable lifetime of an exemplary hydrogen pipeline for any specified level of conservatism. The resulting predictions are compared with and discussed alongside those obtained using conventional master-curve approach. REFERENCES [1] European Commission, A Hydrogen Strategy for a Climate-Neutral Europe, 2020. [2] ASME, B31.12 – Hydrogen Piping and Pipelines, American Society of Mechanical Eng