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Overview Of Latest Advances In Understanding The Limited Ability Of Fusion Bonded Epoxy To Stop Corrosion Within Disbondments

Picture for Overview Of Latest Advances In Understanding The Limited Ability Of Fusion Bonded Epoxy To Stop Corrosion Within Disbondments
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Product Number: 51321-16808-SG
Author: Facundo Varela; Mauricio Latino; Yongjun Tan; Maria Forsyth
Publication Date: 2021
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It has been hypothesized that fusion bonded epoxy (FBE) could be partially permeable to cathodic protection (CP, producing an imbalance between cathodic and anodic reactions and inducing a high pH environment within disbonded areas that would impede corrosion. However, this hypothesis arose from incorrectly inversing causes and effects by assuming that the only reason for the presence of a high pH environment under disbonded FBE coatings is their partial permeability to CP current. This work presents experimental measurements of the CP permeability of FBE coatings and its effects on mitigating corrosion using a recently developed electrochemical self-validating technique. Some degree of CP permeability has been found for FBE only after considerable hydrothermal aging. However, steel corrosion products had been found to significantly hinder the chances of generating a pH capable of inducing passivation, even for the most CP permeable coating tested.

It has been hypothesized that fusion bonded epoxy (FBE) could be partially permeable to cathodic protection (CP, producing an imbalance between cathodic and anodic reactions and inducing a high pH environment within disbonded areas that would impede corrosion. However, this hypothesis arose from incorrectly inversing causes and effects by assuming that the only reason for the presence of a high pH environment under disbonded FBE coatings is their partial permeability to CP current. This work presents experimental measurements of the CP permeability of FBE coatings and its effects on mitigating corrosion using a recently developed electrochemical self-validating technique. Some degree of CP permeability has been found for FBE only after considerable hydrothermal aging. However, steel corrosion products had been found to significantly hinder the chances of generating a pH capable of inducing passivation, even for the most CP permeable coating tested.

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Fusion Bonded Epoxy Coatings (FBE) and Disbondment

Product Number: 51316-7246-SG
ISBN: 7246 2016 CP
Author: Mehrooz Zamanzadeh
Publication Date: 2016
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In this paper, failure analysis methodology will be applied to the principal mechanisms by which FBE coatings fail during long term service; with specific application to case studies involving blistering. The case studies apply standard failure analysis techniques to determine the primary causes and modes of failures.
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Overview of latest advances in measuring and understanding cathodic protection current permeability by organic coatings

Product Number: 51320-14685-SG
Author: Facundo Varela, Mauricio Latino, Yongjun Tan, Maria Forsyth
Publication Date: 2020
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Shielding of cathodic protection (CP) by disbonded coatings is considered a “worst case scenario” for external corrosion in the pipeline industry. It has been hypothesized that if coatings were partially permeable to CP, the imbalance between cathodic and anodic reactions would induce a high pH environment under disbonded coatings and that would impede corrosion. However, direct experimental evidence of this process has been limited. Moreover, this line of reasoning is often inversed incorrectly assuming that the only reason for the presence of a high pH environment under disbonded coatings is their partial permeability to CP current. 

The recent development of an electrochemical self-validating technique to measure the relatively small ionic currents that could permeate through defect free coatings has shed a new light on the topic. It has been found that most of the commercial pipeline coatings tested in unaged conditions present a CP shielding behavior. Accelerated hydrothermal ageing of fusion-bonded epoxy (FBE) coatings was performed to study the effect of water absorption. Ageing resulted in major plasticization, which increased the conduction of CP current through FBE coatings. However, FBE seems to be partially permeable to H+ and/or OH-, which reduces its ability to form and retain a high pH environment under disbonded coatings. In conjunction, these results thus indicate the extremely limited capability of commercial pipeline coatings to prevent corrosion in case of disbondment. 
Picture for CORROSION 2021 Virtual Conference Digital Conference Proceedings
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51321-All-CORROSION 2021 Virtual Conference Digital Proceedings

Product Number: 51321-ALL-SG
Publication Date: 2021
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Conference Proceedings for papers presented at the CORROSION 2021 Virtual conference & Expo. Included in the download is a table of contents of the papers. 
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