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The corrosion of alloy steels with different amounts of Cr was studied using electrochemical tests, wet–dry cycle corrosion, X-ray diffraction, and Kelvin probe force microscopy. The results show that the content of Cr is positively correlated with the corrosion resistance of bare steel, but the corrosion resistance of atmospheric corrosion does not show the same pattern. The atmospheric corrosion resistance of Cr-containing steel exhibits three different stages with the change of Cr element content. When the Cr content is in the range of 1–4%, the corrosion rate is high and does not change within the Cr content. As the Cr content was further increased from 4 to 7%, the corrosion rate exhibited a linear decrease and then drops rapidly when the Cr content reaches 8%. These three different corrosion rate stages are related to the influence of Cr content on Fe3O4 content in the rust layer.

Purpose To study the corrosion behavior of pipeline steel in coastal areas, a tidal seawater macro-cell corrosion device was built using a cycle soaking tank and a macro-cell corrosion facility to simulate the corrosion behavior of pipeline steel in a simulated coastal environment (dry and wet alternations during seawater-soil corrosion macro-cell processes). Design/methodology/approach The corrosion behaviors were studied via the weight loss method, electrochemical methods and morphological observations on corrosion. Findings The results show that during the initial stage of tidal seawater/soil macro-cell corrosion process of the X65 steel, the working electrode on the seawater side is the anode of the macro-battery. As corrosion progresses, the anode and the cathode of the macro-battery become inverted. As the area ratio and the dry – wet ratio increase, the time of anode and cathode inversion shortens. Galvanic current density decreases as the dry – wet ratio increases and increases as the area ratio increases. The corrosion process of macro-cell is affected by the reversal of anode and cathode. After the reversal of anode and cathode, the corrosion rate is mainly controlled by dry – wet alternating corrosion. Originality/value The corrosion behavior of a pipeline steel in a coastal environment was studied using a tidal seawater macro-cell corrosion device. The synergism effect between the tidal seawater and seawater-soil macro-cell on corrosion behavior was clarified.

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