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Testing of Coatings for Shielding of Cathodic Protection Currents

When a coating disbonds from a structure and prevents cathodic protection (CP) from reaching the metal surface, this is known as “shielding” behavior by the coating. Shielding is a serious issue that has been a contributing cause for several pipeline failures, and expensive replacement programs. There are many factors (Soil resistance, holidays, coating resistance, etc.) that determine whether the coating will behave this way. Federal regulations for transmission gas pipelines require the use of a non-shielding coating.

Product Number: 51220-235-SG
Author: Ben Bussard
Publication Date: 2020
Industry: Coatings
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When a coating disbonds from a structure and prevents cathodic protection (CP) from reaching the metal surface, this is known as “shielding” behavior by the coating. Shielding is a serious issue that has been a contributing cause for several pipeline failures, and expensive replacement programs. There are many factors (Soil resistance, holidays, coating resistance, etc.) that determine whether the coating will behave this way. Federal regulations for transmission gas pipelines require the use of a non-shielding coating. Unfortunately, there is not an accepted test to show if a coating is shielding, and therefore it is difficult to quantify how to meet this regulation. This test shows situations where a coating does not shield, even after disbondment.  The test method in this document was performed to verify if metallic substrates covered by a disbonded test coating could be cathodically protected to a level that meets NACE criteria2 and be shown to be non-shielding in the test environment set up.  

When a coating disbonds from a structure and prevents cathodic protection (CP) from reaching the metal surface, this is known as “shielding” behavior by the coating. Shielding is a serious issue that has been a contributing cause for several pipeline failures, and expensive replacement programs. There are many factors (Soil resistance, holidays, coating resistance, etc.) that determine whether the coating will behave this way. Federal regulations for transmission gas pipelines require the use of a non-shielding coating. Unfortunately, there is not an accepted test to show if a coating is shielding, and therefore it is difficult to quantify how to meet this regulation. This test shows situations where a coating does not shield, even after disbondment.  The test method in this document was performed to verify if metallic substrates covered by a disbonded test coating could be cathodically protected to a level that meets NACE criteria2 and be shown to be non-shielding in the test environment set up.  

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