An existing impressed CP system of steel tanks was found to be interfering with newly installed zinc
anodes of an adjacent Pre-stressed Concrete Cylinder Pipeline. The interference prevented the zinc anodes
from providing protection current. The two protected structures are electrically bonded. Field measurements
showed that some zinc anodes were providing current. Other anodes acted as if receiving current from the
pipes. The latter was thought to be a cause of accelerated pipe corrosion (reversed circuit). The tank bottom
plates were also found to have lost protection. In this paper, analysis of field data revealed that all of the zinc
anodes in the vicinity of the tanks were picking up stray current. A mitigation measure was proposed to
remove the existing resistive bond between the two structures and install a few zinc anodes at the discharge
area. An experimental approach was undertaken to determine the effectiveness of this method by simulating
the problem on a lab scale. Experimental measurements showed that installing zinc anodes at the discharge
area successfully prevented the current discharge from the pipe. It might therefore be possible to operate the
two CP systems separately.
Keywords: Cathodic protection, Stray current, Impressed CP system, Interference, Sacrificial anode, Prestressed
concrete cylinder pipes