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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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$20.00
$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.  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 51318-10544-Cathodic Protection, Coatings that Shield Cathodic Protection, Stress Corrosion Cracking and Corrosion Assessment in Aging Coated Pipe Lines and Buried Utility Structures
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51318-10544-Cathodic Protection, Coatings that Shield Cathodic Protection, Stress Corrosion Cracking and Corrosion Assessment in Aging Coated Pipe Lines and Buried Utility Structures

Product Number: 51318-10544-SG
Author: Mehrooz Zamanzadeh / George T. Bayer / Anil Kumar Chikkam
Publication Date: 2018
$20.00

Here we would like to elaborate on corrosion risk associated with coatings that shield cathodic protection.
Testing of Coatings for Shielding of Cathodic Protection Currents
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Testing of Coatings for Shielding of Cathodic Protection Currents

Product Number: 51220-235-SG
Author: Ben Bussard
Publication Date: 2020
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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.
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