How Cathodic Protection Works

This video depicts the conventional current flow for an impressed current cathodic protection system on a pipeline with a protective coating. Current flows from the positive terminal of the rectifier through the anodes and down into the earth and is then picked up on the pipeline at coating faults where bare metal makes electrical connection with the earth. The current then flows along the pipeline back to the negative terminal of the rectifier. Current flow on the pipeline is greatest near the rectifier, and much lower further away where fewer coating faults have picked up current from the earth. To measure the effectiveness, the cathodic protection current is interrupted and a pipe to soil potential (PSP) is measured between the and a copper-copper sulfate reference electrode (half cell) placed on the earth as near as possible to the buried pipeline.  The "On" and "Instant Off" PSP are recorded, and protection is assumed if the instant off PSP is more negative than -850mV as measured through the half cell.