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Testing of Coatings for Shielding of Cathodic Protection Currents

Testing of Coatings for Shielding of Cathodic Protection Currents
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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.

Product Number: 51220-235-SG
Author: Ben Bussard
Publication Date: 2020
Industry: Coatings
$0.00
$20.00
$20.00

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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CP Shielding and Pipeline Coatings
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CP Shielding and Pipeline Coatings

Product Number: 41206-285-SG
Author: Greg Ruschau
Publication Date: 2006
$20.00

Shielding of cathodic protection (CP) by pipeline coatings poses a serious threat to pipeline integrity.  The difficulty in pipeline coating selection to avoid shielding is that the same properties that make a pipeline coating a good corrosion mitigation material can also lead to CP shielding. The key to proper coating selection is to select a coating that has the necessary properties to provide good corrosion protection but also one that, when disbondment and failure occurs, fails in such a way to allow effective cathodic protection.
Picture for 06043 DETERMINING THE CP SHIELDING BEHAVIOR
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06043 DETERMINING THE CP SHIELDING BEHAVIOR OF PIPELINE COATINGS IN THE LABORATORY

Product Number: 51300-06043-SG
ISBN: 06043 2006 CP
Author: G.R. Ruschau, Y.Chen
Publication Date: 2006
$20.00

The tendency of pipeline girth weld coatings to shield cathodic protection (CP) current was studied in the laboratory. Epoxy, epoxypolyurethane, polyurethane, and wax were investigated.  Results showed that the liquid coatings, when applied extra thin to accelerate the kinetics of absorption and current transmission, all disbonded by blistering, and all allowed CP current to be transmitted.
Picture for Coatings Used in Conjunction with Cathodic Protection - Shielding vs NonShielding Pipeline Coatings
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Coatings Used in Conjunction with Cathodic Protection - Shielding vs NonShielding Pipeline Coatings

Product Number: 41212-693-SG
Author: Richard Norsworthy
Publication Date: 2012
$20.00

When using cathodic protection on coated pipelines, end users must consider the problems that exist if the coating disbonds (loses adhesion).  Many in the pipeline industry assume cathodic protection will solve their external corrosion problems without truly understanding the relationship between the coating and cathodic protection.  
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