2.1.4 Effect on Materials
Hydrogen is the smallest of all molecules, and it can diffuse through materials that other gases cannot. Seals and connections in high-pressure hydrogen storage systems must, therefore, be designed very carefully, with attention to both the materials used and the geometry of the mating surfaces of joints.
Over time, constant exposure to hydrogen can cause many materials to loose strength and develop small cracks. This phenomenon is called hydrogen embrittlement, and it can cause leakage or catastrophic failure in hydrogen tanks and lines. The mechanisms of hydrogen embrittlement are not well-understood, but certain factors are known to effect the rate of embrittlement, including hydrogen concentration, pressure, and temperature.
Stain less steel is more resistant to hydrogen embrittlement than ordinary steels, and both pure aluminum and many aluminum alloys are even more resistant than stainless steel if the gas is dry (Ringland, 1994). All components of hydrogen fuel systems must be constructed of materials known to be compatible with hydrogen.
During maintenance and overhaul, only manufacturer-approved replacement parts specifically designed for use in hydrogen systems must be used. Parts that “look the same,” even if they fit properly, could result in failures over time if they are made from incompatible materials.
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