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Here we would like to elaborate on corrosion risk associated with coatings that shield cathodic protection.
Underground coated structures such as pipelines, transmission towers & poles, galvanized guy anchors, tanks and coated galvanized anchors are aging and are at risk of corrosion failure due to coating shielding cathodic protection, localized corrosion and stress corrosion cracking. Those tasked with maintaining these structures require an in-depth understanding of the locations where these aging pipelines are at risk of localized corrosion due to cathodic protection shielding. Corrosion failures in aging pipelines are either sudden catastrophic ruptures or gradual leaks due to localized corrosion. Corrosion failures in transmission structures or galvanized anchors are also at risk of loss in thickness and catastrophic ruptures. Major factors associated with these corrosion areas are coating dis-bondment, blistering/delamination, the presence of moisture, corrosive soils, inadequate cathodic protection and cathodic protection shielding. These areas have a much higher statistical probability of catastrophic failure and rupture. In pipelines, most of the time initiation of stress corrosion cracking (SCC) and pitting corrosion are detected by coincidence in excavation and digs and is not targeted or predicted by analysis of corrosion performance parameters. Internal or In-line inspection (ILI) tools have limited capability for detecting or identifying stress corrosion cracking and pitting corrosion initiation. Here we would like to elaborate on corrosion risk associated with coatings that shield cathodic protection.
Key words: cathodic protection shielding by coatings, stress corrosion cracking (SCC); pitting corrosion; corrosion risk assessment; soil resistivity; soil corrosivity mapping; coating dis-bondment; cathodic protection.
CP Interference and CP Influence and how the two differ. Both will be demonstrated by case histories and some solutions will be presented.
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Concerns related to stray DC interference. Including safety, testing, documentation and lessons learned. Also addressed are DC powered transit systems and other unordinary sources of DC interference.
This paper reviews the concerns of applying excessive levels of cathodic protection current to pipelines and the need for establishing an upper potential limit. Coating disbondment, hydrogen induced stress cracks, stress corrosion cracking, hard spots and the problems associated with measurement of a true polarized pipe-to-electrolyte potential are addressed.