ABSTRACT
Selection of a material for a specific kind of hydrogen service requires an understanding of the ways in which hydrogen embrittlement is manifested. There are two rather different regimes of hydrogen behavior for most materials, the "elevated" temperature regime, typically above 500 K (440°F), and the ambient temperature regime. Hydrogen testing at ambient temperature is usually designed to investigate one of two behavior types. One is the short-time or "instantaneous" behavior, where little or no entry of hydrogen into the metal has occurred by diffusion. The second type is the behavior of the material when hydrogen has been introduced into the lattice, as would occur by accumulation during prolonged exposure to hydrogen in service. There are a number of materials variables which can be used as guidelines for satisfactory service in hydrogen environments. Most of these are metallurgical in nature, such as composition, microstructure, strength level, and weldability.
