Abstract
The effects of extreme stray current on the anodic dissolution and passivation of X80 steel in NaHCO3 solution were investigated using measurements of polarization curves and EIS, AFM and SEM techniques. Under the interference of anodic current (i = 0~200 A/m2), main constituents of corrosion products of X80 steel were FeO(OH) and Fe3O4. A double-layer film formed at i = 100 A/m2, in which FeOOH was in outer and Fe3O4 lied in inner. The formation mechanism of Fe3O4 was confirmed and described by the electrochemical reaction in various regions on anodic potentiodynamic polarization curve.
Highlights
In recent years, considerable attention has been paid to metal corrosion (Li et al 2015)
Considering the larger corrosion rate caused by anodic current density (i-ACD), the open-circuit potential (EOCP) of X80 steel was tested after immersion in different anodic current densities for 10 mins
As i-ACD continued to increase, the EOCP generally moved to be more positive, indicating that the corrosion tendency of X80 steel increased with the increase in the anodic current density
Summary
Considerable attention has been paid to metal corrosion (Li et al 2015). Buried pipelines have been spotlighted to be protected by combination of coatings (Cui et al 2017; Prasai et al 2012) and cathodic protection (Refait et al 2015) Even though this method is widely considered to be sufficiently effective, stray current makes it impossible to pipeline away from corrosion, especially in which there are some defects on coatings. There are two challenges in elucidating the metal’s corrosion behavior interference by lager anodic current: (1) a deeper insight needs to be put forward for corrosion behavior and process due to DC stray current, and (2) related parameters of anodic passivation should be determined. The polarization curves and electrochemical impedance spectrum were conducted to determine corrosion kinetic parameters under the interference of anodic current, and combining with characterization of corrosion products, anodic passivation process was illustrated. The results can provide a clear explanation for anodic dissolution and corrosion process caused by a larger direct current in near-neutral solution
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