Development of a Hydrogen Aging Test Apparatus for the Liner of Vehicle-Mounted Type IV Hydrogen Storage Cylinders

• • After 1000 h at 85 °C and 87.5 MPa, HDPE's hydrogen permeation coefficient (Pe) increased by 4.76% to a value that, while still low, elevates the risk of hydrogen accumulation in the liner; this 4.76% rise directly informs safety margins for 70 MPa cylinder design, as even minor increases in permeation can lead to localized hydrogen pockets and potential blistering. • • The hydrogen diffusion coefficient (D) decreased by 3.08% while the solubility coefficient (S) increased by 8.10%, indicating that aging-induced structural changes (e.g., crosslinking) hinder hydrogen mobility but enhance its uptake; this counterintuitive trade-off necessitates coupled permeation–solubility models for accurate lifetime prediction, as Fickian diffusion alone would underpredict hydrogen inventory. • • Tensile strength increased by 6.51% and nominal elongation at break by 15.33% after aging, suggesting a post-aging embrittlement reversal or annealing effect; industrially, this implies that HDPE liners may retain structural integrity beyond 1000 h, but the simultaneous increase in solubility (8.10%) could offset mechanical gains by promoting plasticization under cyclic loading. • • The apparatus achieved stable operation at 87.5 MPa and 85 °C for 1000 h, exceeding the 1.25× NWP requirement of ISO 11114-5 and GB/T 42610—2023; this validated capability closes a critical gap in domestic Chinese test infrastructure, enabling accelerated qualification of HDPE liners and reducing reliance on foreign test facilities for Type IV cylinder certification.