Cui-wei Du

Effects of solution environments under disbonded coatings on the corrosion behaviors of X70 pipeline steel in acidic soils

Abstract A rectangle crevice assembly was used to study the effects of cathodic protection (CP) potential, crevice thickness, holiday size, bubbling CO2, and surface condition on the chemical and electrochemical environment of the local solution under disbonded coatings. It is found that the cathodic protection removes dissolved oxygen from the crevice and thus shifts the solution to a more alkaline state. Furthermore, the potential of the steel reaches the protected potential range. The available protection distance increases with the negative applying potential. The steady potential and pH distribution are easily achieved, but the polarization degree is not satisfied within the thinner crevice. The difference in the solution environment is found to correlate to the holiday size. The smaller the holiday, the smaller the difference is. The presence of CO2 inhibits the formation of an alkaline environment. It is also found that the rust layer dramatically decreases the polarization rate in the crevice.

Corrosion behavior and mechanism of the automotive hot-dip galvanized steel with alkaline mud adhesion

The corrosion behavior and mechanism of hot-dip galvanized steel and interstitial-free (IF) substrate with alkaline mud adhesion were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and linear polarization. The results show that non-uniform corrosion occurs on the galvanized steel and IF substrate during 250 h with the mud adhesion. The corrosion products on the galvanized steel are very loose and porous, which are mainly ZnO, Zn5(OH)8Cl2•H2O and Zn(OH)2, and Fe-Zn alloy layer with a lower corrosion rate is exposed on the galvanized steel surface; however, the corrosion products on IF substrate are considerably harder and denser, whose compositions of rust are mainly FeOOH and Fe3O4, and several pits appear on their surface. The results of continuous EIS and linear polarization measurements exhibit a corrosion mechanism, that is, under activation control, the charge transfer resistances present different tendencies between the galvanized steel and IF substrate; in addition, the evolution of linear polarization resistances is similar to that of charge transfer resistances. The higher contents of dissolved oxygen and Cl(superscript -) ions in the mud play an important role in accelerating the corrosion.

Sensing application in the precursor region of localized corrosion by scanning electrochemical microscopy

Scanning electrochemical microscopy (SECM) has been established as an indispensible tool in the analysis of corrosion. The aim of this article is to review the recent advances of this technique and its applications in measuring, characterizing and evaluating the precursor region of localized corrosion. The topography and redox activities of the metal/electrolyte solution interface at a local scale during the corrosion processes can thus be described in real time with high spatial resolution. In addition, relevant references from the advent of SECM integrated with other techniques to improve its resolution in investigating the precursor region during local corrosion are also presented with a special discussion on high resolution images.