Physical-chemical significance of the IRfree potential and methods for assessing the effectiveness of cathodic protection

The effectiveness of the cathodic protection according to EN 12954 is demonstrated by measuring the IR-free potential of the steel. Various investigations of the a.c. corrosion of pipelines have resulted in an improved understanding of the processes taking place at the steel surface. Additionally, the requirements of EN 15280 result in many cases in a shift of the on-potential in positive direction to mitigate the risk of a.c. corrosion. As a consequence, meeting the requirements of EN 12954 becomes more difficult. The present paper discusses the physical-chemical significance of the parameter with respect to the corrosion protection by means of theoretical considerations and numerical simulation. The resulting consequences for cathodic protection are discussed and an alternative method for assessing the effectiveness of cathodic protection based on a pH-measurement is presented.