Ammonia (NH 3 ) is a promising hydrogen carrier, yet the corrosion mechanisms of pipeline steels in impurity-contaminated NH 3 environments remain unclear. This study elucidates the effects of chloride ions (Cl − ) and dissolved oxygen (O 2 ) on the corrosion behaviour of X80 pipeline steel in aqueous NH 3 . Electrochemical measurements, potentiodynamic polarisation, and surface characterisation reveal a mechanistic transition from Cl − -dominated localised pitting to NH 3 -driven mild corrosion as NH 3 concentration increases. Cl − exacerbates passive film breakdown and pitting, whereas NH 3 suppresses Cl − aggressiveness via cation complexation. O 2 contributes to partial passivation by facilitating the formation of Fe(OH) 3 and Fe 2 O 3 , although the resulting films are discontinuous and microcracked. A mechanistic framework is proposed, highlighting the competitive and sequential interplay among NH 3 , Cl − , and O 2 , which provides guidance for corrosion control in NH 3 storage and transport pipelines.
Li et al. (Sun,) studied this question.