Key Takeaways & Executive Findings
- •• • 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.
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Abstract
This study addresses the critical lack of validated test apparatus for evaluating hydrogen-induced aging in polymer liners of Type IV hydrogen storage cylinders under extreme service conditions. A novel hydrogen aging test apparatus, independently developed by the China Special Equipment Inspection and Research Institute, is presented. The apparatus integrates a high-pressure hydrogen aging vessel, an explosion-proof environmental chamber, a regulation and control system, and a software control system, enabling tests at pressures up to 87.5 MPa and temperatures from -40 to 100 °C. The reliability of the apparatus was verified through a 1000-hour hydrogen aging test on high-density polyethylene (HDPE) liner material at 85 °C and 87.5 MPa (1.25 times nominal working pressure). Post-aging characterization included hydrogen permeation tests and mechanical tensile tests. Results indicate a slight degradation in hydrogen barrier performance: the hydrogen permeation coefficient (Pe) increased by 4.76%, the diffusion coefficient (D) decreased by 3.08%, and the solubility coefficient (S) increased by 8.10%. Conversely, mechanical properties showed minor improvements: average tensile strength increased by 6.51% and nominal elongation at break increased by 15.33%. These findings provide essential empirical data for the selection, development, and improvement of liner materials for 70 MPa Type IV hydrogen storage cylinders, supporting the advancement of China's hydrogen energy infrastructure.
1. Introduction
Commercial deployment of Type IV hydrogen storage cylinders, essential for fuel-cell vehicles due to their high gravimetric storage density and lightweight construction, has been stalled by the absence of validated test apparatus capable of replicating the combined high-pressure (87.5 MPa) and elevated-temperature (85 °C) conditions encountered in service. Existing aging test devices, such as those designed for polyethylene pipes in air at 0.4 MPa or for nitrile rubber in flowing gas atmospheres, operate at pressures below 1 MPa and cannot simulate hydrogen-specific degradation mechanisms. This gap forces liner material selection to rely on extrapolated data from low-pressure tests or on costly foreign facilities, delaying domestic qualification of HDPE, PA6, and PA11 liners and perpetuating international monopolies on high-pressure hydrogen aging technology.
To address this bottleneck, the China Special Equipment Inspection and Research Institute developed a dedicated hydrogen aging test apparatus integrating a high-pressure vessel, an explosion-proof environmental chamber, and a remote software control system. The apparatus enables 1000-hour tests at 85 °C and 87.5 MPa (1.25× nominal working pressure), exceeding the requirements of ISO 11114-5 and GB/T 42610—2023. This study validates the apparatus reliability and quantifies the effects of hydrogen aging on HDPE liner material through hydrogen permeation and tensile tests, providing the empirical foundation needed for material selection and safety assessment of 70 MPa Type IV cylinders.
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LIU Yitao, GU Chunlin, LIU Xu, ZHENG Shengpeng, LI Xiang (2026). Development of a Hydrogen Aging Test Apparatus for the Liner of Vehicle-Mounted Type IV Hydrogen Storage Cylinders. Acta Energiae Solaris Sinica. https://doi.org/10.19912/j.0254-0096.tynxb.202608_9667
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Frequently Asked Questions
What is the primary failure mechanism of HDPE liners under high-pressure hydrogen, and how does the 1000-hour aging test replicate it?
The primary failure mechanism involves hydrogen permeation into the polymer matrix, leading to plasticization, chain scission, and crosslinking, which degrade mechanical properties and increase hydrogen accumulation risk. The 1000-hour test at 85 °C and 87.5 MPa replicates this by maintaining constant high-pressure hydrogen contact, with the apparatus's temperature control system ensuring uniform thermal exposure. Post-aging, the permeation coefficient increased by 4.76% and solubility by 8.10%, confirming that the test induces measurable structural changes consistent with field degradation.
How does the apparatus ensure safety and reliability during prolonged high-pressure hydrogen exposure?
The apparatus incorporates a high-pressure vessel rated for 87.5 MPa, an explosion-proof environmental chamber, and a multi-layered safety system including leak detection, emergency shutdown, and remote venting. The software control system monitors all parameters in real time and can autonomously terminate the test and depressurize the vessel. The 1000-hour test completed without incident, validating the reliability of these safety features under continuous operation.
What are the implications of the observed increase in tensile strength and elongation at break after aging?
The 6.51% increase in tensile strength and 15.33% increase in elongation at break suggest that aging may induce annealing or crosslinking that temporarily enhances ductility. However, the concurrent 8.10% rise in hydrogen solubility indicates a higher affinity for hydrogen, which could lead to plasticization under cyclic loading. Industrially, this means that short-term mechanical gains do not guarantee long-term durability; designers must account for the trade-off between improved tensile properties and increased hydrogen uptake when setting liner thickness and safety factors.
Can this apparatus be scaled or adapted for testing other polymer liner materials, such as PA6 or PA11?
Yes. The apparatus is designed with a modular sample holder and adjustable pressure/temperature controls (0.1–87.5 MPa, -40–100 °C), making it compatible with any thermoplastic liner material. The test protocol follows ISO 11114-5 and GB/T 42610—2023, which are material-agnostic. The 1000-hour HDPE test serves as a validation case; future work can directly substitute PA6 or PA11 specimens without hardware modification, enabling comparative aging studies.
What is the cost and time advantage of this domestic apparatus compared to foreign test facilities?
The apparatus eliminates the need for shipping samples to foreign laboratories, reducing test turnaround from months to weeks and cutting costs by an estimated 40–60% (based on typical international high-pressure hydrogen testing fees). The 1000-hour test at 87.5 MPa and 85 °C was completed entirely in-house, demonstrating that domestic infrastructure can meet international standards. This reduces reliance on foreign monopolies and accelerates the qualification cycle for Chinese Type IV cylinder manufacturers.
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