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Effect of Chemical Environment and pH on AC Corrosion of Cathodically Protected Structures

AC corrosion of structures under cathodic protection (CP) is a major concern for pipelines. This work investigates the effect of soil constituents - earth alkali elements Ca and Mg - believed to have a large influence on the precipitation of hydroxides and carbonates in front of a coating damage.

Product Number: 51317--9352-SG
ISBN: 9352 2017 CP
Author: Andreas Junker-Holst
Publication Date: 2017
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AC corrosion of cathodically protected structures is a major concern for pipelines in case of even minor AC perturbations. There are indications that the specific chemical environment has a large influence on the AC mitigation current density criteria outlined in EN 15280:2013. This work investigates the effect of soil constituents the earth alkali elements Ca and Mg traditionally believed to have a large influence on the formation of hydroxides and carbonates and the so-called ‘stone hard soil’-phase in front of a coating damage. Recent findings from excavations imply that the alkalization from cathode reactions can affect the stability of quartz sand SiO2 and induce the formation of iron containing neso-silicates hence also the influence of Si and Fe is investigated. Corrosion rate measurements in different environments and at different cathodic overpotentials is measured using ER-coupons and the chemistry and phase analysis is made using SEM/EDS ICP-OES and XRD.

Key words: AC corrosion, SEM, EDS, XRD, Cathodic protection, Calcareous deposits

 

AC corrosion of cathodically protected structures is a major concern for pipelines in case of even minor AC perturbations. There are indications that the specific chemical environment has a large influence on the AC mitigation current density criteria outlined in EN 15280:2013. This work investigates the effect of soil constituents the earth alkali elements Ca and Mg traditionally believed to have a large influence on the formation of hydroxides and carbonates and the so-called ‘stone hard soil’-phase in front of a coating damage. Recent findings from excavations imply that the alkalization from cathode reactions can affect the stability of quartz sand SiO2 and induce the formation of iron containing neso-silicates hence also the influence of Si and Fe is investigated. Corrosion rate measurements in different environments and at different cathodic overpotentials is measured using ER-coupons and the chemistry and phase analysis is made using SEM/EDS ICP-OES and XRD.

Key words: AC corrosion, SEM, EDS, XRD, Cathodic protection, Calcareous deposits

 

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