Initial Corrosion Behaviour of E690 Steel in Different Seawater Corrosion Zones in Qingdao Sea Area

6-month outdror exposure experiment was carried out on E690 steel in four zones (atmospheric zone, splash zone, tidal differential zone and total immersion zone) in Qingdao seawater environment. The corrosion behaviour of E690 steel was studied by corrosion rate test, surface and cross-sectional morphology observation and corrosion product composition analysis. The results show that the corrosion mass loss rate and corrosion rate of the steel were the highest in the tidal differential zone and the lowest in the atmospheric zone after 6 months exposure test. The corrosion products of the steel in the four zones were mainly composed of α-FeOOH, γ-FeOOH and Fe₃O₄. The difference in zones had a significant effect on the formation of corrosion products. The sufficient presence of oxygen in the splash zone was conducive to the formation of Fe₃O₄, and the periodic submergence of seawater in the tidal zone made the electrolyte layer persistent and promoted the formation of γ-FeOOH. Localized corrosion existed in all zones. The corrosion pits on the surface of the steel in the atmospheric zone and the full immersion zone were small and densely distributed, while the corrosion pits on the surface of the steel in the tidal zone were connected to each other, and the size and depth were significantly larger than those in other zones.