Laboratory and field investigation of the effect of the chemical environment on AC corrosion

AC corrosion is dependent on both AC and DC current densities, but only little is known about the effect of the chemical environment. In this paper, laboratory soil-box experiments are made for a better understanding of the effect of specific chemical constituents in soil on corrosion in relation to the AC and DC current densities.

A field investigation of AC corrosion on an operational pipeline where AC interference and CP levels could be controlled, is presented. Soil analysis from the field study is discussed in relation to the laboratory experiments. Distinction between AC corrosion caused by anodic depolarization of the steel or by excessive cathodic protection and alkalization is made and discussed in relation to the current density criteria in industry standards.