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Coatings Used in Conjunction with Cathodic Protection - Shielding vs NonShielding Pipeline Coatings

Picture for Coatings Used in Conjunction with Cathodic Protection - Shielding vs NonShielding Pipeline Coatings
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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.  

Product Number: 41212-693-SG
Author: Richard Norsworthy
Publication Date: 2012
Industries: Coatings , Corrosion Monitoring and Control
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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.  Cathodic protection (CP) current is very effective when it actually has a path to the pipe metal.  Most external corrosion on pipelines is caused by disbonded coatings that shield CP, not lack of CP. When disbondment or blistering occurs, most coating types divert current from its intended path, therefore, CP current cannot adequately protect the external surfaces of a pipe.  These are called “shielding” pipeline coatings. There are certain types of pipeline coatings that will allow the CP current to effectively protect the pipe if disbondment occurs and water penetrates between the coating and the pipe.  These are called “nonshielding” pipeline coatings.  This paper will discuss the differences in the two types of coating systems and how CP works with these coatings.

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.  Cathodic protection (CP) current is very effective when it actually has a path to the pipe metal.  Most external corrosion on pipelines is caused by disbonded coatings that shield CP, not lack of CP. When disbondment or blistering occurs, most coating types divert current from its intended path, therefore, CP current cannot adequately protect the external surfaces of a pipe.  These are called “shielding” pipeline coatings. There are certain types of pipeline coatings that will allow the CP current to effectively protect the pipe if disbondment occurs and water penetrates between the coating and the pipe.  These are called “nonshielding” pipeline coatings.  This paper will discuss the differences in the two types of coating systems and how CP works with these coatings.

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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 Penetration of Cathodic Protection into Pipeline Coating Disbondment
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Penetration of Cathodic Protection into Pipeline Coating Disbondment

Product Number: 51317--9146-SG
ISBN: 9146 2017 CP
Author: Li Yan
Publication Date: 2017
$20.00

An experimental setup was designed to investigate the cathodic protection (CP) penetration into coating disbondment. Embedded detection probes underneath the disbondment enabled pH and steel potential measurements without disturbing the environment inside the disbondment.
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