In the refinery industry, there is continuous dialogue over the cause and effects of molecular
and ionized hydrogen on the corrosion of metals. This paper focuses on the role of nascent
hydrogen, a short-lived, non-ionized, monatomic species at equilibrium with other atomic
hydrogen species within various alloys. Nascent hydrogen, a major corrosion contributor, is
not well understood and not addressed adequately in many refinery standards. The corrosion
mechanisms and mechanical properties of different hydrogen species are discussed including
their formation, interaction, and transportation within various steels. Material composition,
welding techniques, and operating process design conditions to mitigate harmful effects as
well as case histories are also included.