Cylinders and Tubes Used as Buffers in Filling Stations

Buffers are key components for hydrogen filling stations that are currently being developed. Type 1 or composite cylinders are used for this application. The type used depends on many parameters including pressure level, cost and space available for the filling station. No international standards exist for such high pressure vessels whereas many standards exist, covering Types 1,2,3 and 4 used for transport of gas or on-board fuel tanks. It is suggested to use the cylinders approved for transport or on-board applications as buffers. This solution appears to be safe if, at least, one issue is solved. The main difference is that transport or on-board cylinders are cycled from a low pressure to a high pressure during service whereas buffers are cycled from a relatively high pressure (corresponding to the vehicle’s filling pressure) to the MAWP. Another difference is that buffers are cycled many times per day. For standards developers, requesting to systematically verify that buffers pass millions of cycles at low pressure amplitude would be impractical. Several standards and codes give formulae to estimate the number of shallow cycles when number of deep cycles are known. In this paper, we describe tests performed on all types of composite cylinders to verify or determine the appropriate formulae.