In order to assess cathodic protection (CP) criteria in the presence of alternate current (AC)
interference, weight loss tests on cathodically protected carbon steel specimens (CP current density in
the range of 0.2 to 10 A/m2) were performed in soil-simulated conditions in the presence of AC densities ranging from 10 to about 500 A/m2. Aim of the research is to define threshold of AC-parameters to assure no risk of corrosion on metallic structures under CP. Tests allow to state that in the presence of AC interference, the risk of corrosion depends on: AC density, protection potential and the ratio between
AC and DC densities. On the basis of obtained results, CP level may be considered effective if
protection potential is in the range –1.0 to –1.15 V CSE, provided iAC/iDC ratio is lower than 200 and no
overprotection conditions were established. In 2008, field test started on thirty carbon steel coupon
subjected to AC interference. Both cathodic protection and free corrosion conditions were considered.
Keywords: AC interference, cathodic protection, true potential, monitoring