API 617 Standard (Axial and Centrifugal Compressors), paragraph 2.2.1.9, specified that "Materials that have a yield strength in excess of 120,000 psi or hardness in excess of Rockwell C 34 are prohibited for use in hydrogen gas service where the partial pressure of hdrogen exceeds 100 psi gauge or the hydrogen concentration exceeds 90 molar percent at any pressure. I need to select a material and manufacture a centrifugal compressor wheel (18" OD, 9500 RPM) for the following service: H2 gas, 85.7% by volume Temperature: 170%C2°F Pressure: 460 psi absolute Are there any more requirements that I need to be aware of before making my material selection for hydrogen service? Does NACE MR 0175 cover pure hydrogen service or is there another specification that covers rotating equipment for this type of service? Thank you for your help, Regards, Henry Gonzalez