Chrome-molybdenum steels are in common use in pressure vessels for high temperature and high pressure hydrogen applications. The proper alloy is usually determined from the Nelson Curves.The 2 ¼ Cr-1 Mo steel has found particular favor in services such as hydrodesulfurization. For 2 ¼ Cr-1 Mo, the mode of damage expected is surface decarburization-not the more far-reaching hydrogen attack.A more detailed confirmation of all the effects of temperature and hydrogen pressure was thought useful.