Compressed hydrogen storage tanks are critical components in hydrogen energy systems, particularly for automotive applications. Ensuring their safety and reliability requires adherence to stringent international standards and testing protocols. Key standards governing these tanks include ISO 15869, UN Global Technical Regulation No. 13 (GTR 13), and NFPA 2. These frameworks establish rigorous testing procedures for burst pressure, cyclic endurance, permeation limits, and crashworthiness, while certification bodies such as TÜV and the U.S. Department of Energy (DOE) oversee compliance.
ISO 15869 outlines general requirements for the design, manufacturing, and testing of compressed hydrogen storage systems. It specifies performance criteria for tanks intended for vehicular use, including type approval tests and in-service inspections. Burst testing is a fundamental requirement, where tanks must withstand pressures significantly higher than their working pressure without failure. For example, a tank with a nominal working pressure of 70 MPa must demonstrate a burst pressure ratio of at least 2.25, meaning it should not fail below 157.5 MPa. This ensures a substantial safety margin under extreme conditions.
Cyclic pressure endurance testing is another critical evaluation under ISO 15869. Tanks undergo repeated pressurization and depressurization cycles to simulate long-term usage. The standard typically requires a minimum of 5,500 cycles for Type III (metal-lined, composite-wrapped) and Type IV (non-metallic liner, composite-wrapped) tanks. These tests validate the structural integrity of the tank over its operational lifespan, detecting potential fatigue-related failures.
Permeation limits are also addressed to minimize hydrogen leakage through tank materials. ISO 15869 sets a maximum allowable permeation rate, usually measured in normal cubic centimeters per liter of tank volume per minute (Ncc/L/min). For instance, the permeation rate must not exceed 0.25 Ncc/L/min at 85% of the nominal working pressure and 15°C. This ensures that hydrogen losses remain within safe and economically viable limits.
UN GTR 13 complements ISO 15869 by providing a globally harmonized regulatory framework for hydrogen and fuel cell vehicles. It includes additional safety provisions, such as bonfire testing to assess tank behavior under high-temperature exposure. Tanks must withstand direct flame impingement for a specified duration without catastrophic failure, ensuring they can endure post-crash fire scenarios.
Crashworthiness is a pivotal aspect of UN GTR 13, requiring tanks to maintain integrity during vehicular collisions. Tests include pendulum impacts, drop tests, and projectile penetration assessments. For example, a pendulum impact test involves striking the tank with a 15 kg mass at 7.5 m/s to simulate crash forces. The tank must not rupture or exhibit excessive deformation. Similarly, projectile tests evaluate resistance to sharp object penetration, which could occur during accidents.
NFPA 2, the Hydrogen Technologies Code, provides comprehensive safety guidelines for hydrogen systems, including storage tanks. It references ISO 15869 and UN GTR 13 but also incorporates regional requirements, such as those from the U.S. Department of Transportation (DOT). NFPA 2 emphasizes material compatibility, mandating that tank materials resist hydrogen embrittlement and chemical degradation over time.
Certification bodies play a vital role in enforcing these standards. TÜV, a globally recognized testing organization, conducts independent assessments to verify compliance with ISO, UN, and regional regulations. The U.S. DOE collaborates with industry stakeholders to advance tank technologies while ensuring safety through programs like the Hydrogen Fuel Cell Technologies Office. These entities perform audits, witness tests, and issue certifications to validate tank designs.
Burst testing procedures involve gradually increasing internal pressure until failure occurs. The test measures the ultimate strength of the tank and identifies weak points in design or manufacturing. Data from burst tests inform safety margins and material selection for future iterations.
Cyclic pressure testing replicates real-world conditions by subjecting tanks to repeated filling and emptying. Advanced monitoring systems track microstructural changes, such as crack initiation or delamination in composite layers. Tanks that pass cyclic testing demonstrate resilience to operational stresses, reducing the risk of in-service failures.
Permeation testing quantifies hydrogen leakage through tank walls using mass spectrometry or pressure decay methods. Low permeation rates are essential for maintaining system efficiency and preventing hazardous accumulations in enclosed spaces.
Crashworthiness evaluations combine mechanical testing with computational simulations to predict tank behavior under impact. Finite element analysis (FEA) models help optimize tank designs before physical prototypes are tested. This reduces development costs while ensuring compliance with safety standards.
In summary, international standards like ISO 15869, UN GTR 13, and NFPA 2 establish a robust framework for compressed hydrogen storage tank safety. Burst testing, cyclic endurance, permeation limits, and crashworthiness assessments are integral to these protocols. Certification bodies such as TÜV and the DOE enforce compliance, ensuring tanks meet global safety requirements. These measures collectively support the safe integration of hydrogen storage systems into automotive and energy applications.
The continuous evolution of materials science and testing methodologies will further enhance tank performance and reliability. As hydrogen adoption grows, adherence to these standards will remain paramount in mitigating risks and fostering public confidence in hydrogen technologies.