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 . 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.
|Title of host publication||Corrosion Conference and Expo 2017|
|Number of pages||14|
|Publication status||Published - 2017|
|Event||NACE Corrosion 2017: Conference & Expo - New Orleans, United States|
Duration: 26 Mar 2017 → 30 Mar 2017
|Conference||NACE Corrosion 2017: Conference & Expo|
|Period||26/03/2017 → 30/03/2017|
- AC corrosion
- Cathodic protection
- Calcareous deposits
Junker-Holst, A., Vendelbo Nielsen, L., & Møller, P. (2017). Effect of Chemical Environment and pH on AC Corrosion of Cathodically Protected Structures. In Corrosion Conference and Expo 2017  NACE International.