Hygrothermal Aging and Decoupled Axial‐Radial Compressive Failure Mechanisms in Glass Fiber Reinforced Epoxy Filament‐Wound Composite Tubes

ABSTRACT This study examines the hygrothermal degradation of filament‐wound glass fiber‐reinforced epoxy composite tubes designed for application as liners in oil and gas systems, focusing on their response under axial or radial compression. Glass fiber‐reinforced epoxy tubes were conditioned in freshwater at 65°C, 80°C, and 95°C for exposure periods up to 28 days. Moisture uptake was monitored using gravimetric measurements, while mechanical performance was evaluated through axial and radial compression testing followed by post‐mortem damage analysis. Equilibrium moisture contents of ca. 1.75–1.80 wt.% were observed for all temperatures, with similar diffusion times (~676 h), suggesting limited temperature influence on saturation within the studied range. Axial compressive strength remained largely unaffected, with reductions below 7.4% and failure was dominated by local buckling mechanisms. In contrast, radial compression showed pronounced stiffness degradation, reaching up to 79% reduction following prolonged conditioning at 95°C. Arrhenius‐based life prediction using a 50% radial stiffness reduction criterion demonstrated a strong temperature dependence of durability, with a pronounced reduction in service life at elevated temperatures, reaching approximately 17 days at 95°C. These findings highlight distinct degradation behavior and identify radial stiffness as a key durability parameter after hygrothermal aging.