For cathodic protection to work, the anode must have a lower potential (i.e. more negative) than the potential of the cathode (the structure to be protected) with respect to a Cu/CuSO4 electrode. The following table shows which metals can be combined.[6]​.

Cathodic shielding

The effectiveness of cathodic protection systems on metal pipes can be negated by the use of solid film dielectric coatings such as polyethylene tapes, heat shrinkable blankets, and single or multiple factory-applied solid film coatings. This phenomenon occurs due to the high electrical resistivity of these coatings.[7]​ The protective electrical current of the cathodic protection system is blocked or shielded, unable to reach the metal that is below the coating due to the high resistivity of the solid film. Cathodic shielding was first defined as a problem in the 1980s, and technical sheets on the subject have been published regularly since then.

In 1999, a report[8]​ on a 20,600 barrel (3,280 m³) oil line spill in Saskatchewan, Canada, was published and contained an excellent definition of the cathodic shielding problem.

Cathodic shielding is referenced in a number of the standards listed below. The new USDOT regulation title 49 CFR 119.112, states in the section for Requirements for additional designs for steel pipe using the maximum allowable operating pressure alternative requires that “the pipe must be protected against external corrosion by a non-shielding coating.” 4.2.3, warns against the use of exterior coatings that create an electrical blockage in section 5.1.2.3, and instructs readers to take “appropriate action” when the electrical shielding effects of cathodic protection current are detected in an operating pipeline, section 10.9.

Techniques * NACE TM 0497 - Measurement related to the criteria for cathodic protection in underground or submerged metal piping systems.

For cathodic protection to work, the anode must have a lower potential (i.e. more negative) than the potential of the cathode (the structure to be protected) with respect to a Cu/CuSO4 electrode. The following table shows which metals can be combined.[6]​.

Cathodic shielding

The effectiveness of cathodic protection systems on metal pipes can be negated by the use of solid film dielectric coatings such as polyethylene tapes, heat shrinkable blankets, and single or multiple factory-applied solid film coatings. This phenomenon occurs due to the high electrical resistivity of these coatings.[7]​ The protective electrical current of the cathodic protection system is blocked or shielded, unable to reach the metal that is below the coating due to the high resistivity of the solid film. Cathodic shielding was first defined as a problem in the 1980s, and technical sheets on the subject have been published regularly since then.

In 1999, a report[8]​ on a 20,600 barrel (3,280 m³) oil line spill in Saskatchewan, Canada, was published and contained an excellent definition of the cathodic shielding problem.

Cathodic shielding is referenced in a number of the standards listed below. The new USDOT regulation title 49 CFR 119.112, states in the section for Requirements for additional designs for steel pipe using the maximum allowable operating pressure alternative requires that “the pipe must be protected against external corrosion by a non-shielding coating.” 4.2.3, warns against the use of exterior coatings that create an electrical blockage in section 5.1.2.3, and instructs readers to take “appropriate action” when the electrical shielding effects of cathodic protection current are detected in an operating pipeline, section 10.9.

Techniques * NACE TM 0497 - Measurement related to the criteria for cathodic protection in underground or submerged metal piping systems.