Influence of inclusion and grain boundary on corrosion behaviour of low alloy steel in cargo oil tank bottom plate environment

Abstract

Corrosion behaviours of low alloy steels with various alloying element contents were studied in simulated corrosion environment (pH50?85, 10% NaCl solution) of cargo oil tank (COT) bottom plate corrosion environment. Corrosion rate was measured, and the surface morphology of test steels was characterised using scanning electron microscope (SEM). The electrochemical results were investigated using polarisation curves and electrochemical impedance spectroscopy (EIS). The corrosion behaviour of inclusion was investigated using in situ SEM images and energy disperse spectroscopy (EDS) analysis. The effect of misorientation distribution on corrosion resistance of steel was evaluated using electron backscattered diffraction microscopy. The results showed that MnS dissolved into the simulated COT corrosion solution before steel matrix, whereas TiO 2 would not be dissolved. A 10-20 mm area was formed as a circular cathode around inclusion centre. The corrosion was inclined to occur in the place where curvature radius of inclusion is small. An increase in the proportion of low energy grain boundaries was conducive to the improvement of corrosion resistance especially in the early stages of corrosion.

Homogenisation effect on mechanical and pitting behaviour of 2205 Duplex Stainless Steel

“…This is consistent with the findings of Paula et al [2] in a lean DSS. Liang et al [28] also reported an improved pitting corrosion resistance, especially in the early corrosion stage with an increase in the low-energy grain boundaries in low-alloy steel. In addition, Li et al [29] reported that the grain size and twin-induced low-CSL boundaries improved the intergranular corrosion resistance of 316L SS processed by a diffusion bonded joint.…”

Corrosion of sedimentary liquids on internal bottom plate of tanks among coal liquefaction process

“…For the sedimentary liquids containing the same additional NaCl, the corresponding sedimentary liquid from hydro‐stabilizing feed oil possesses the most powerful causticity, while that from diesel get the weakest corrosivity. In general, Cl − is provided with high ionic activity and penetrability, which could damage the metal oxide film formed on the steel . Due to the long‐term bathing of internal bottom plates in the sedimentary liquid, the surface of metal plates always stays in the balance between precipitating and dissolving, while the dissolving surface part easily leads to the local spot corrosion in the presence of Cl − .…”