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Pitting Initiation and Propagation of X70 Pipeline Steel Exposed to Chloride-Containing Environments

Corrosion and Protection Center, Key Laboratory for Environmental Fracture (MOE), University of Science and Technology Beijing, Beijing 100083, China
Department of Mechanical Engineering, University of South Florida, Tampa, FL 33620, USA
Author to whom correspondence should be addressed.
Materials 2017, 10(9), 1076;
Received: 20 July 2017 / Revised: 5 September 2017 / Accepted: 6 September 2017 / Published: 13 September 2017
(This article belongs to the Section Energy Materials)
PDF [6971 KB, uploaded 14 September 2017]


Inclusion-induced pitting initiation mechanisms in X70 steel were investigated by scanning electron microscopy, scanning Kelvin probe force microscopy (SKPFM), immersion and electrochemical polarization tests in chloride-containing ion solutions. There are three inclusion types in the X70 steel. Corrosion test results indicated that pitting corrosion resistance of type A inclusion < type C inclusion < type B inclusion, i.e., (Mn, Ca)S < matrix < (Al, Ca)O. SKPFM test results show that the type A inclusion exhibited both lower and higher potentials than the matrix, while the type B inclusion exhibited higher potential than the matrix. The corrosion test and the SKPFM potential test results are consistent. Potentiodynamic polarization results indicate that the type A and C are active inclusions, while the type B is an inactive inclusion. Three kinds of possible mechanisms of inclusion-induced pitting corrosion are established for the X70 steel. View Full-Text
Keywords: pitting corrosion; inclusions; SKPFM; X70 pipeline steel pitting corrosion; inclusions; SKPFM; X70 pipeline steel

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Yang, Z.; Kan, B.; Li, J.; Su, Y.; Qiao, L.; Volinsky, A.A. Pitting Initiation and Propagation of X70 Pipeline Steel Exposed to Chloride-Containing Environments. Materials 2017, 10, 1076.

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