In this study, the time-dependent behavior and stress relaxation of API-X42 seamless steel pipes reinforced with glass fiber composites were investigated to assess the effects of time on system stability and load-bearing capacity. A composite layer of E-glass fibers embedded in epoxy resin was applied to the pipe joint regions. Tensile tests were conducted in single-step and multi-step modes, with a 10minute hold at each stage, and the stress–time data were recorded in normalized form. The results indicated that lower loading rates promoted gradual stress relaxation and extended system stability, whereas higher rates led to faster stress release and attainment of a stable state in the early stages. Moreover, increasing the number of loading steps resulted in cumulative stress reduction and brought the system behavior closer to a quasi-stable state. At loading rates of 50, 100, and 200 mm/min, the final stress relaxation values were recorded as 8.9%, 7.7%, and 9.4%, respectively. These findings highlight the key role of resin viscoelasticity and stress distribution between fibers and steel in the mechanical stability of the system and underscore the importance of evaluating time-dependent behavior in the design and long-term performance prediction of reinforced steel pipes. The results of this study provide clear guidance for future research aimed at comprehensively investigating the effects of multi-step loading and ultimate failure mechanisms in steel–composite hybrid systems.