Effects of intermittent DC stray current on carbon steel under cathodic protection

摘要

Stray currents originating from DC electrical systems may cause severe corrosion damage of buried metal structures, as carbon steel pipes, tanks or vessels. Nowadays, international standards establish the general principles to control DC interference, mainly based on potential and voltage gradients measurements over a 24 h period. As regards carbon steel under cathodic protection condition, anodic DC interference is considered unacceptable if the IR-free potential is more positive than the protection potential provided by standard (-0.850 V CSE in aerobic condition). But, duration and magnitude of the anodic peak should be considered to evaluate the actual corrosion effects of the interference on protected steel. In fact, the -0.850 V CSE criterion appears to be too restrictive if short periods of anodic interference are alternated with the re-establishment of the protection condition. This paper deals with the study of the effects of anodic interference on buried carbon steel structures in cathodic protection: weight loss tests were carried out on cathodically protected steel specimens in soil-simulating environment in the presence of DC interference varying anodic current density (from 0.1 to 10 A/m2) and duration of the interference peaks (from 1 minute up to 1 hour).