Corrosion Resistances of Steel Pipe Coated with Two Types of Enamel by Two Coating Processes

Abstract

The corrosion behaviors of uncoated, enamel-coated, and epoxy-coated steel samples were evaluated in 3.5 wt.% NaCl solution with open-circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization tests. Two types of enamel (powder and slurry) were coated on steel samples in electrostatic and wet spraying processes, respectively. Twelve 25 mm x 25 mm steel samples were cut from an API 5L X65 pipe of 323.850 mm in outer diameter and 9.525 mm in wall thickness. They were divided into four groups of three identical samples. Each group represents one of the four conditions: uncoated, powder enamel-coated, slurry enamel-coated and epoxy-coated. Scanning electron microscopy images revealed that the powder and slurry enamel coatings were approximately 180 and 235 µm thick, respectively. The powder enamel coating has fewer but larger isolated pores than the slurry enamel coating. Electrochemical tests consistently indicated that the powder and slurry enamel coatings provided slightly better and worse corrosion protection to the coated steel samples, respectively, than the epoxy coating. The charge transfer resistances of all the coated samples are approximately 108 times larger than that of the uncoated samples. All the coated samples were unlikely corroded within 2 h of immersion.

Department(s)

Civil, Architectural and Environmental Engineering

Second Department

Materials Science and Engineering

Comments

The authors gratefully acknowledge the financial support provided by the US Department of Transportation under Award No. DTPH5615HCAP10.

Keywords and Phrases

Charge transfer; Corrosion; Corrosion resistance; Corrosive effects; Electrochemical corrosion; Electrochemical impedance spectroscopy; Enamels; Epoxy resins; Pipeline corrosion; Powder coatings; Scanning electron microscopy; Sodium chloride; Steel corrosion; Steel pipe; Steel testing; Charge transfer resistance; Electrochemical test; Enamel coatings; Epoxy-coated steels; Open circuit potential; Pipeline steel; Potentiodynamic polarization tests; Scanning electron microscopy image; Corrosion resistant coatings

International Standard Serial Number (ISSN)

1059-9495; 1544-1024

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2018 Springer Verlag, All rights reserved.

Publication Date

01 Sep 2018

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