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.

Cathodic Shielding Explained - Pipeline Corrosion - Polyguard

Polyguard's Pipeline Division has been active in the Pipeline Protective Coating industry for more than 50 years. In addition to standard types of Corrosion Coatings, we designed, manufactured, and introduced a number of innovative Underground Pipeline Coatings and Girth Weld Coatings, which have become commercially accepted as standards for the industry. Polyguard’s Pipeline Division was the first coating manufacturer to highlight the cathodic shielding problem, and the first to develop a coating to address the shielding problem. Our products include both Non-Shielding Coatings and Soil Stress Tolerant, such as NHT-5600 2-Part Epoxy, Reactive Gel, in addition to our popular RD-6 Coating System. Our 2-part epoxy coating has a 30% – 50% longer pot life than the competition. RD-6® pipeline corrosion coating is a non-shielding system that allows cathodic protection currents to reach any disbonded area which occurs on the pipeline. RD-6 has been used on thousands of projects for over 25 years. Yet, to our knowledge, neither external corrosion nor SCC (stress corrosion cracking) has been a problem under RD-6. In addition, RD-6 is not a tape. North American pipeline operators have virtually banished solid film backed tapes and shrink sleeves. RD-6 is quite different.