Monitoring dynamic corrosion and coating failure on buried steel using an multi-electrode arrayM. YJ Tan* F. Varela Y. Huo F. Mahdavi M. Forsyth and B. HintonInstitute for Frontier Materials and School of EngineeringDeakin University Victoria 3220 Australia*Presenting author mike.tan@deakin.edu.auDynamic events that may cause the breakdown of passivity and the initiation of localized corrosion remain the subject of much debate and are probably the least understood aspects of corrosion science. It is well known that passivity and localized corrosion are affected by various critical factors such as a changing electrode potential and surface pH [1]; however the effects of dynamically fluctuating electrode potential and environmental conditions on passivity and localised corrosion of critical infrastructure such as buried energy pipelines are not well understood. A reason is probably that current techniques have limited temporal and spatial resolutions required for studying dynamically changing passivity and localized corrosion processes occurring on buried pipelines. Conventional corrosion testing methods such as weight-loss coupons and electrochemical polarisation measurements are generally considered unsuitable for studying these dynamic processes because they provide only averaged corrosion information over a period of time and are unable to provide data of high temporal resolution. In this work we take advantage of the high temporal and spatial resolution of an electrochemically integrated multi-electrode array for probing localised electrode processes which evolve dynamically and propagate freely on pipeline steel surfaces under the effect of cathodic protection and anodic transients. We present three cases to illustrate the study of dynamically changing passivity and localized corrosion processes on simulated steel pipelines: (i) monitoring localized corrosion under the dynamically changing electrochemical environment beneath a simulated pipeline coating [23] (ii) visualising passivityits breakdown and localized pipeline corrosion under the effect of dynamic anodic transients [4] and (iii) visualising coating disbondment under excessive cathodic protection conditions [5].REFERENCES1. G.S. Frankel Pitting corrosion of metals. A review of the critical factors J. Electrochem. Soc. 145 (1998) 2186-21982. F. Varela M. Y.J. Tan and M. Forsyth Electrochemical method for studying localized corrosion beneath disbonded coatings under cathodic protection Journal of the Electrochemical Society 162(10):C515-C527 01 Jan 20153. F. Varela M. Y.J. Tan and M. Forsyth An electrochemical method for measuring localized corrosion under cathodic protection. ECS Electrochemistry Letters 4(1):C1-C4 014. Y Huo M. YJ Tan and M Forsyth Visualising dynamic passivation and localised corrosion processes occurring on buried steel surfaces under the effect of anodic transients Electrochemistry Communications (Available online 24 February 2016)

Key words: Corrosion monitoring, corrosion sensor, multi-electrode array, pipeline corrosion; protective coating, cathodic protection, localized corrosion, stray current corrosion