The global push for green hydrogen as a sustainable energy carrier requires the selection of structural materials that provide sufficient mechanical properties and are resistant to hydrogen degradation. This study investigates the compatibility of two low-alloy structural steels, P355NL1 and S500MLO, and their corresponding weld metals under high-purity pressurised gaseous hydrogen using the slow strain rate testing (SSRT) method coupled with the hollow specimen technique (HST). Tests were conducted at room temperature under 60 bar of 99.999% pure hydrogen at strain rates ranging from \({10}^{-4}\) to \({10}^{-7} {s}^{-1}\) . Results show that hydrogen exposure significantly reduces ductility, while having a minimal effect on yield strength and ultimate tensile strength (UTS). P355NL1 exhibited greater resistance to hydrogen degradation compared to S500MLO. Weld metal specimens demonstrated lower ductility than base metals, and a more pronounced reduction in elongation was observed with decreasing strain rate due to longer exposure to the hydrogen environment. Fractographic analyses confirmed a transition from ductile to brittle fracture in hydrogen-exposed specimens. The findings underscore the critical role of weld microstructure in hydrogen compatibility and support the application of HST as a reliable tool for in-situ hydrogen performance evaluation of structural steels in hydrogen infrastructure.