Effect of Doping Trace Rare Earth Elements on Corrosion Behavior of EH36 Offshore Platform Steel

Abstract

EH36 offshore platform steel, La (0.0031%) steel, Ce (0.0027%) steel, and Pr (0.0001%) steel were selected as the research objects. The corrosion of four groups of steel was simulated by immersion experiments. In the presence of Cl− the effect of rare earth elements (La, Ce, Pr) on corrosion was investigated by the weight loss method. The morphology of the corrosion products and the apparent morphology after the removal of the corrosion products were observed by scanning electron microscopy (SEM); the main components of four steel corrosion products were analyzed by X-ray diffraction (XRD). The electrochemical behavior and the influence of temperature and Cl− concentration on the corrosion of the four kinds of steel were analyzed by an electrochemical polarization curve and Nyquist diagram. The results showed that the addition of trace rare earth elements, La, Ce, and Pr, to EH36 offshore platform steel can reduce the corrosion rate and the corrosion current density (Icorr), and increase the charge transfer resistance during the corrosion process. The Icorr of La steel, Ce steel, and Pr steel is 6.59 × 10−5 A·cm−2, 7.57 × 10−5 A·cm−2, and 9.53 × 10−5 A·cm−2, respectively, which is lower than that of EH36 steel (Icorr = 1.82 × 10−4 A·cm−2). The influence of Cl− concentration and temperature on the four steels showed the same trend; that is, with the increase in Cl− concentration, the corrosion rate first rises and then slows down, and with the increase in temperature, the corrosion rate gradually accelerates. Rare earth elements promote the production of more α-FeOOH in the rust layer, and the compactness of this product plays a certain role in protecting the steel matrix. The addition of trace rare earth elements, La, Ce, and Pr (less than 0.004%), improves the corrosion resistance of EH36 steel.