Temporal evolution of sweet oilfield corrosion scale: Phases, morphologies, habits, and protection

[Display omitted] •Scale is initially comprised of two components, siderite and chukanovite.•Crystallite habits are explicitly identified.•Final, highly protective, scale is a single layer of siderite crystallites.•At longer immersion times, siderite crystals shrink in size.•Siderite crystal habit exhibits high energy {hk0} facets. Electrochemical measurements and substrate analysis have been employed to study the corrosion of iron in sweet solution (pH = 6.8, T = 80 °C) over a period of 288 h. Correlated with decreasing corrosion rate, diffraction, microscopy, and spectroscopy data reveal the evolution of adhered sweet corrosion scale. Initially, it is comprised of two phases, siderite and chukanovite, with the latter affording little substrate protection. Subsequently, as the scale becomes highly protective, siderite is the sole component. Notably, siderite crystals are concluded to display a somewhat unexpected habit, which may be a trigger for local breakdown of protective sweet scales.