The failure process of localized hydrogen-induced damage (HID) in longdistance oil and gas pipelines involves the coupled effects of material mechanical behavior, magnetic response, and hydrogen diffusion, which makes early detection challenging with conventional non-destructive testing (NDT) techniques, posing a significant threat to the safety of energy transport systems. Weak magnetic inline inspection (WMII) technology, due to its intrinsic sensitivity to early-stage damage in ferromagnetic materials and its capability for online monitoring, exhibits great application potential in the detection and evaluation of HID. Based on this technology and combined with first principles, a multiscale cross-analysis method is proposed to explore the relationship between localized HID and magnetic signal response in pipelines. Furthermore, a Qaverage multi-component magnetic feature fusion parameter is introduced to effectively characterize the failure behavior and hazard level of HID under multi-physical field conditions. The results reveal that under magnetic flux leakage (MFL) testing, the saturation magnetization aligns the magnetic domains in a highly ordered state, rendering it difficult for hydrogeninduced high-pressure stress concentration zones to cause significant perturbations in the overall leakage flux. Consequently, no distinct magnetic response features are observed. In contrast, the characteristic components of the weak magnetic signal exhibit an average increase of approximately doubling compared with the metal magnetic memory method, demonstrating superior applicability and effectiveness for the detection of early-stage HID. In addition, with increasing internal pipeline pressure and external excitation intensity, the stress concentration and magnetic domain reconstruction behavior in hydrogen-enriched zones intensify. Specifically, the Qaverage response curve shows a nonlinear increase with rising internal pressure, with average response growth rates of 137 and 195 A·m-1/MPa for Q235 and Q345 steels, respectively. With increasing excitation intensity, the response increases approximately linearly, and the corresponding rates are 61.24 A·m-1/A for Q235 and 69.06 A·m-1/A for Q345 steels.