RP3.4-07: Supplementary tests on the effect of bi-directional potential excursions on cathodic protection

Executive Summary

Cathodic protection (CP) in combination with a high quality coating system is the primary method used to protect buried pipelines from corrosion. In the field it is often difficult to continuously maintain the minimum accepted CP level owing to stray currents from anthropogenic or telluric effects. These so-called transient events are problematic when the pipeline potential deviates in the anodic and cathodic direction (i.e. to more positive or negative values of potential than the CP potential) – which promotes anodic metal dissolution or extent of cathodic disbondment of coatings.

Over the past several years extensive experiments have been conducted through Energy Pipelines CRC (EPCRC) on the effects of anodic transients on pipeline cathodic protection (CP).  The work was focused on anodic transients because these have historically been of most concern. Critical factors affecting the occurrence of corrosion were found to include the amplitude and duration of anodic transients and the water saturation levels of soil.

Some tests that were carried out in the closing phases of the last test program indicated that cathodic transients occurring in conjunction with anodic ones could affect corrosion significantly. These results were not expected and could be highly significant in terms of determining the changes that might be made to existing stray current corrosion protection criteria.  However, the observations were from only limited data collected under a few selected test conditions and there is a need to conduct a short supplementary test program.

This project conducted a series of tests to confirm and quantify the degree of the effect of cathodic transients under different conditions. Some major results and findings include:

  • Compared to anodic transients alone, cyclic bi-directional potential fluctuations caused more corrosion on steel coupons.
  • More localised and general corrosion occur when longer duration and larger amplitude bi-directional transients were applied on steel coupons.

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Commencement / End Date August 2020 to January 2021
Outcomes / Impact

The conditions tested in this project are realistic replication of actual stray current activity, especially from traction systems. These new data can provide more evidences for revising criteria in AS 2832.1 for corrosion protection of pipelines in areas affected by stray current. The outcome is believed to be extremely valuable in the preparation of the next revision to AS 2832.1 in its stray current criteria section.

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Research Contact

Douglas Proud

Research & Utilisation Program Coordinator