Strategies of using Cathodic Protection for Buried Metal Culverts

The primary concern in managing steel culverts is corrosion. While corrosion on the exposed inside face of the culvert is identified during inspections, the corrosion on the outside face (backfill) is not visible. Current inspections involve use of thickness gauges to measure the remaining thickness of the steel, but it is only measured at a few points. Controlling the backfill corrosion of culverts is paramount to extending the steel culvert service life by mitigating the hidden deterioration and prevent sudden failures. Cathodic protection (CP) has been used in many applications as an effective technology to control corrosion of metal structures and was used in this work in a pilot application to prolong the service life of steel culverts. This paper discusses the learnings and describes the implementation of a CP system in a steel culvert.  The galvanic CP system was initially chosen for its compatibility with culverts, soil resistivity, and corrosion levels. Monitoring over four months showed partial success in meeting protection criteria due to inadequate soil resistivity testing before CP installation. Preliminary impressed current testing indicated accurate soil resistivity could have achieved protection criteria, suggesting impressed current cathodic protection (ICCP) with accurate data would be preferable. Converting the CP system to ICCP through battery and solar setups was proposed for consistent protection and prolonged anode life. The pilot installation identified a need to consider the suitability of CP systems on a site-by-site basis and the importance of the site appraisal stage. This paper discusses the insights of the pilot installation and system conversion process, outlining future steps for monitoring pilot system efficiency.