Fuel cell driven vehicles operated with compressed hydrogen are typically using composite cylinders in order to store the gas at pressures of up to 700 bar. The supply of hydrogen in the required volume and pressure is the logistical challenge of every filling station since the gas has to be transferred and compressed with minimal use of energy. However, the technical challenges are sometimes not noticed and should be looked at in this paper. The compression technology we are looking at is the reciprocating air driven booster. They are an economical alternative to electrical driven compressors and comply with the explosion proof directive 94/9/EC in the category 2G/2D, group IIC. Boosters used for filling station pressures of up to 700 bar are typically operated in different stages up to 1000 bar in order to enable an adequate differential pressure. At these pressures materials with high yield strengths (Rp0,2) are required. Austenitic stainless steel of the 316L series as referred to in the IGC document 121/04/E has become a standard for many high pressure hydrogen applications since it shows good resistance against hydrogen embrittlement. The corresponding material code for 1.4404 lists yield strengths of up to 320 MPa [1] which can be improved by cold working to values of about 750 MPa [2]. Since one of the limiting factors for the cold working process is the dimension, different solutions have to be found when the available mechanical properties are not sufficient. For the final compression stage of a typical booster station the standard material comes to its limits according to the FEM analysis and the use of cold worked material is not possible because of the diameter and the limitation of cold working. An alternative material suitable for hydrogen with yield strengths of greater 500 MPa is required and found with the creep resistant steel 1.4980. The material has a yield strength (Rp0,2) of 600 MPa [3] and a high nickel content of 25.3% [3] which meets the mechanical requirements plus those of the Japanese KHK regulation which opens a new geographical target market.
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