Save 20% on select titles with code HIDDEN24 - Shop The Sale Now
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.
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.
We are unable to complete this action. Please try again at a later time.
If this error continues to occur, please contact AMPP Customer Support for assistance.
Error Message:
Please login to use Standards Credits*
* AMPP Members receive Standards Credits in order to redeem eligible Standards and Reports in the Store
You are not a Member.
AMPP Members enjoy many benefits, including Standards Credits which can be used to redeem eligible Standards and Reports in the Store.
You can visit the Membership Page to learn about the benefits of membership.
You have previously purchased this item.
Go to Downloadable Products in your AMPP Store profile to find this item.
You do not have sufficient Standards Credits to claim this item.
Click on 'ADD TO CART' to purchase this item.
Your Standards Credit(s)
1
Remaining Credits
0
Please review your transaction.
Click on 'REDEEM' to use your Standards Credits to claim this item.
You have successfully redeemed:
Go to Downloadable Products in your AMPP Store Profile to find and download this item.
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.