A review of control methods for impressed current cathodic protection systems

Impressed current cathodic protection (ICCP) systems operate by forcing a current between a permanent anode and the protected structure, using an external electrical power source. ICCP systems have been applied successfully for protecting a wide range of metallic structures in various environments, in particular steel water or fuel pipelines and steel storage tanks in soil. However, their current control methods have limitations to automatically adjust the CP current output or protection potential based on changes in environmental conditions. Structures protected by ICCP systems are typically subjected to a variety of changing conditions that make the use of fixed output currents inadequate. For instance, underground pipelines can be affected by stray currents and changes in the environment that would render, otherwise adequate settings, insufficient to stop corrosion. Thus, since the beginnings of ICCP for corrosion prevention, several methods have been proposed to adjust the current output as a function of electrochemical and physical characteristics of the system. This work reviews previously published literature and patented devices to control the current output of ICCP systems. The review follows a chronological order highlighting how the evolution of electronics had enabled more complex and convenient systems. Due to the limitations of traditional closed-loop ICCP control systems, special attention is placed on methods that aim to reduce the effects of IR drops and eliminate the need for unreliable permanent reference electrodes. In addition, the work covers methods for measuring corrosion rates under CP and their possible use as feedback for the control of ICCP systems.