Distribution of Steady-State Cathodic Currents Underneath a Disbonded Coating

Pipeline corrosion frequently persists underneath disbonded coatings on pipelines that appear to be well protected cathodically. Application of higher cathodic potentials for improved protection may produce hydrogen gas (H₂) bubbles that block current flow underneath a disbonded coating. A project was undertaken to determine whether an increase in applied potential results in higher polarization levels on the crevice steel underneath a disbonded coating. With a higher applied potential, pH levels in a crevice should increase. Steady-state cathodic protection experiments were performed at three applied potentials in an electrochemical cell simulating the crevice steel under a disbonded coating. The recorded profiles showed that higher levels of protection underneath a disbonded coating could be achieved by applying higher cathodic potentials. Penetration of the cathodic currents underneath a disbonded coating also was more difficult in higher resistivity solutions.