Dissolution kinetics of the sulfide-oxide complex inclusion and resulting localized corrosion mechanism of X70 steel in deaerated acidic environment

[Display omitted] •A new corrosion form around sulfide-oxide complex inclusion is reported.•Chemical dissolution of CaS generates H2S and deposits, providing the condition for the formation of galvanic couple.•CaS and appropriate electrolyte chemistry are prerequisites for the formation of galvanic...

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Bibliographic Details
Published in:Corrosion science 2020-09, Vol.174, p.108815, Article 108815
Main Authors: Li, Gengxin, Wang, Liwei, Wu, Huiliang, Liu, Chao, Wang, Xin, Cui, Zhongyu
Format: Article
Language:English
Subjects:
Acidic oxides
Anodes
Cathodes
Corrosion
Corrosion mechanisms
Dissolution
Galvanic corrosion
High strength low alloy steels
Hydrogen sulfide
Inclusion
Kinetics
Localized corrosion
Low-alloy steel
Pitting corrosion
SEM
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Summary:[Display omitted] •A new corrosion form around sulfide-oxide complex inclusion is reported.•Chemical dissolution of CaS generates H2S and deposits, providing the condition for the formation of galvanic couple.•CaS and appropriate electrolyte chemistry are prerequisites for the formation of galvanic couples.•Cathode/anode area ratio is calculated to be around 50 based on the statistic data.•Galvanic corrosion disappears as CaS is completely dissolved. Dissolution kinetics of the sulfide-oxide complex inclusion and its surrounding matrix of X70 steel in deaerated acidic environment was investigated. The dissolution process can be divided into three stages including the initiation stage, galvanic corrosion stage, and the corrosion propagation stage. Chemical dissolution of CaS generates H2S and deposits, providing the condition for the formation of the galvanic couple in which the occluded micro-pits serve as anode and the surrounding matrix serves as cathode. The presence of CaS and appropriate electrolyte chemistry are indispensable for the formation of galvanic couple, of which the cathode/anode area ratio is about 50.
ISSN:0010-938X
1879-0496
DOI:10.1016/j.corsci.2020.108815