Abstract

The change of protective current density, the formation and growth of calcareous deposits, and the evolution of passive film on 304 stainless steel (SS) were investigated at different potentials of cathodic polarization in sea water. Potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and surface analysis techniques of scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis and X-ray diffraction (XRD) were used to characterize the surface conditions. It was found that the protective current density was smaller for keeping polarization at −0.80 V (vs. saturated calomel electrode (SCE), same as below) than that at −0.65 V. The calcareous deposits could not be formed on 304 SS with polarization at −0.50 V while it was well protected. The formation rate, the morphology, and the constituent of the calcareous deposits depended on the applied potential. The resistance of passive film on 304 SS decreased at the first stage and then increased when polarized at −0.80 V and −0.65 V, which was related to the reduction and the repair of passive film. For the stainless steel polarized at −0.50 V, the film resistance increased with polarization time, indicating that the growth of oxide film was promoted.

Highlights

  • Type 304 stainless steel (SS) is often used for facilities and structures exposed in sea water, and is prone to suffering from localized corrosion like pitting and crevice corrosion due to chloride ion attack [1,2,3]

  • The suitable potential range for cathodic protection of the stainless steel can be determined from the potentiodynamic polarization curve

  • Type 304 SS was polarized in sea water at −0.80 V vs. SCE, −0.65 V vs. SCE and −0.50 V vs. SCE

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Summary

Introduction

Type 304 stainless steel (SS) is often used for facilities and structures exposed in sea water, and is prone to suffering from localized corrosion like pitting and crevice corrosion due to chloride ion attack [1,2,3]. For moving parts in sea water such as rotating shaft in contact with bearings or hydraulic piston rods, smooth and clean surfaces are needed In these cases, proper cathodic potential shall be applied to protect the parts of stainless steel from corrosion and to avoid the formation of calcareous deposits on the surfaces. The formation of calcareous deposits is influenced by many factors, such as temperature, hydrostatic pressure (depth), velocity, chemistry of sea water; current density, potential and period of cathodic polarization; biofilms; substrate materials and surface preparation; and so on [26,28,29,30,31,32]. Obtaining a better understanding of the evolution of passive film and calcareous deposits on stainless steel with potential and time of polarization is of great significance to ascertain the effective protection and improve the corrosion resistance of stainless steels in sea water. The evolution of calcareous deposits and passive film on the surface of 304 SS was discussed

Electrode Preparation
Test Solution
Electrochemical Tests
SEM and XRD Analysis
Polarization Tests
Variation of of current density of 304
EIS Measurement
Fitting parameters spectra of 304
EIS evolution of 304 under polarization
SEM Analysis
The were composed fine andon covered sample surface as shown in
EDX Analysis
10. EDX of 304
Discussion
Conclusions
Full Text
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