Hydrogen: a fuel for the future
Hydrogen is a promising alternative to fossil fuels whose benefits include abundance, efficiency, a low carbon footprint and absence of other harmful emissions. However, there are safety issues surrounding its use, especially when stored at the high pressures required for it to be economical. Higher pressure means increased risk of tank rupture during storage or transportation.
Hydrogen can easily pass through interstices between atoms of many structural materials. In metals, this can cause degradation by a process called hydrogen embrittlement. Tanks also experience continuous cyclic loading between ambient and storage pressure, which stresses the tank material. Additional, residual stresses may also remain from manufacture, and this mix of stresses can result in the development of fatigue cracks. The combination of fatigue cracks and the process of hydrogen embrittlement become significant over time, resulting in accelerated crack growth rates. Several accidents and injuries have been caused by this going undetected in the past.
Storage tanks made from a composite material lined internally with a polymer (Type IV) or metals such steel or aluminium (Type III) are generally used in vehicles, whereas tanks for stationary storage and transport applications are more commonly made from steel (Type I).
SafeHPower project activities
1. Miniature AE sensor system for continuous monitoring in composite tanks (Type IV)
The SafeHPower project developed a miniature AE sensor prototype for continuous monitoring and detection of fatigue cracks in Type IV fuel tanks for vehicles. The prototype comprises an AE sensor, control box and embedded software. The system was designed and developed with several features to enhance its suitability for installation in a vehicle:
- All power needs are satisfied by the vehicle’s battery.
- The control box can act as a Faraday cage to provide protection against electromagnetic interference produced by the external electronic components, as well as being resistant to water and dust particles.
- The embedded software can permanently monitor all AE events and makes a yes/no decision to activate a vehicle dashboard warning.
Successful laboratory and field trials have been conducted on composite Type IV and Type III tanks respectively. During the field trials, the AE sensor prototype experienced conditions representative of real-world operation in terms of temperature and exposure to water, dust particles, humidity and vibrations. The results of these field trials showed that the fuelling cycle generates little AE activity (because the tank on the vehicle did not have any defects) compared to the laboratory tests which showed significantly higher activity (because flaws were manually introduced in these tanks).