Evaluation of Cathodic Protection Under Disbonded Coating on Buried Steel Structures by Laboratory and Field Tests

Purpose This paper aims to research the corrosion behavior of the metal under the disbonded coatings interfered with AC through electrochemical method. Design/methodology/approach The corrosion behavior of the metal under disbond coating interfered with alternate stray current (AC) was studied by electrochemical methods using the rectangular coating disbonded simulator. The obtained data from electrode potential test, electrochemical impedance spectroscopy (EIS) and polarization curves in simulated soil solution indicated that under the natural corrosion condition, the self-corrosion potential and the corrosion current density of the metal at different depths under disbond coating had obviously changed if there was AC interference. Findings The self-corrosion potential of the metal at the same depths under disbond coating shifted negatively with the rising of the AC voltage. Under the condition of cathode polarization, there was still obvious potential gradient with the extension of the deep peeling of the coating gap, and the corrosion current density of the test points was minimum, and the protection effect was best when the cathode protection potential was −1.0 V. When the metal was applied with over-protection, the corrosion rate of the metal increased as AC stray current flowing through it increased. Originality/value This paper used the rectangular aperture device to study the corrosion behavior of X80 steel under the disbonded coatings through electrochemical methods when the AC stray current interference voltage was 0V, 1V, 5V or 10V and the protection potential was 0V, −0.9V, −1.0V, −1.2V or −1.3V, respectively. There is great significance to the safe operation and long-term service of pipeline steel in soil environment.

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Strain-Aging-Assisted Localized Corrosion of a Mill-Scaled X-65 Pipeline Steel

Wang

Lamborn²,

Chevil

et al. 2021

Corrosion

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This investigation was designed to study whether strain aging could assist localized corrosion of pipeline steels under realistic conditions, which is an unsolved problem in the evaluation of strain-aging-induced stress corrosion cracking of pipeline steels in the field. It was found that the corrosion severity was significantly aggravated after strain aging because of the increase in yield strength and the transformation of oxide scales on the steel surface. These variations caused by strain aging lead to lesser exfoliation and longer life of the oxide scales under cyclic loading in air and during subsequent corrosion exposure, which enhances the galvanic corrosion between oxide scales and the steel substrate. The composition of oxide scales, mechanical properties of steels, and magnitude of the stress cycles, which could all impact localized corrosion, were studied. The findings of this investigation suggest that the severe localized corrosion leading to crack initiation is a vital factor for the higher SCC susceptibility of pipeline steels associated with strain aging, in addition to the enhanced hydrogen embrittlement as usually believed.

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Evaluation of Cathodic Protection Under Disbonded Coating on Buried Steel Structures by Laboratory and Field Tests

Cited by 3 publications

References 15 publications

Corrosion Control

Corrosion Control

Corrosion behavior of X80 steel under disbond coating interfered with AC

Strain-Aging-Assisted Localized Corrosion of a Mill-Scaled X-65 Pipeline Steel

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