Long term performance of reference electrodes for cathodic protection of steel in concrete

Abstract

This paper will report on long term behaviour of potential sensors used in cathodic protection of steel reinforcement in concrete. Cathodic protection (CP) systems, both impressed current CP (ICCP) and galvanic CP (GCP), need regular testing to establish the quality of protection. In addition, ICCP may require adjustment of output voltage or current. Various types of potential sensors have been used in relatively large numbers, comprised of true reference electrodes (RE) based on silver/silver chloride or Mn/MnO2 and decay probes (DP) based on a.o. activated titanium. Failures may occur due to loss of contact, drying out or cable defects. Test methods for potential sensors are discussed. Monitoring of about one hundred CP systems with several thousands of potential sensors over more than ten years allows to analyse their performance and failures. It appears that limited numbers of potential sensors fail over time, but in some cases an insufficient number of working potential sensors are left to properly monitor a CP system or zone. It is recommended to install more potential sensors than strictly needed in order to allow for failures and to maintain testability and save the high cost of installing new potential sensors later.