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

Andreas Junker-Holst, Lars Vendelbo Nielsen, Per Møller

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review


AC corrosion of structures under cathodic protection (CP) 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 [1]. This work investigates the effect of soil constituents, the 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. The formation of different polymorphous calcium carbonates, depending on the cathodic potential are observed as well as calcium hydroxides at high cathodic protection levels. This indicates a highly alkaline (pH > 11) environment locally. Corrosion rates at different cathodic potentials are measured using electrical resistance (ER) probes and a chemical and phase analysis of the calcareous deposits and corrosion products is made using scanning electron microscopy and energy dispersive x-ray spectroscopy (SEM/EDS) and x-ray diffraction (XRD). The findings suggest an AC corrosion mechanism highly dependent on the build-up and break-down of calcareous deposits at high CP, which is clearly reflected in variations in the spread resistance.
Original languageEnglish
Title of host publicationCorrosion Conference and Expo 2017
Number of pages14
PublisherNACE International
Publication date2017
Article number9352
ISBN (Electronic)9781510840348
Publication statusPublished - 2017
EventNACE Corrosion 2017: Conference & Expo - New Orleans, United States
Duration: 26 Mar 201730 Mar 2017


ConferenceNACE Corrosion 2017: Conference & Expo
CountryUnited States
CityNew Orleans


  • AC corrosion
  • SEM
  • EDS
  • XRD
  • Cathodic protection
  • Calcareous deposits


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