Cathodic Protection Current Shielding

Thanks for the undefined acronyms!

SNAFU

..."A holiday or discontinuity in a coating is a small defect that is frequently very minute and not readily visible, such as a pinhole, void, crack, thin spot, foreign inclusion, or contaminant in the coating film. When a coating holiday or degradation provides a pathway for corrosive species to reach the metal substrate, Wong notes, the CP system should be capable of providing enough continuous current to polarize the steel surface to a potential that stops the oxidation of the steel. A coating with a holiday may disbond and the metal substrate can experience corrosion issues if the CP current is not adequate.

Wong defines shielding as high-resistance or nonconducting materials preventing CP current from reaching the structure to be protected, or low-resistance material diverting the current away from the structure to be protected. He emphasizes that many times cathodic shielding is not a coating issue, but rather an environmental or a CP system design issue—such as soil that is very resistive or an anode bed that is too far away—that prevents the appropriate amount of CP current from reaching the vulnerable metal surface. The term “nonshielding coating” is very misleading, he adds. “FBE is considered nonshielding in the United States, but the data I presented and the data from FBE suppliers clearly show that it will not allow enough CP current to pass through to achieve the protective level,” he says. “If a coating allows enough CP current to pass through it for protection of the underlying metal, then it defeats the purpose of a barrier coating and is not needed.” For a buried pipeline, shielding of a CP system with remote anode beds can be caused by rocky soils, wet and dry seasons, foreign metallic structures in the path, shorted casings, etc. A well-designed CP system will ensure an uninterrupted current supply to areas on a structure where the coating is damaged so corrosion issues will be minimized. The current requirement to achieve protection, which is generally about 10–5A/cm2, Wong says, depends on the resistivity of the environment as well as the conductivity of the electrolyte and its oxygen content."...

http://www.materialsperformance.com/articles/cathodic-protection/2016/04/using-pipeline-coatings-with-cathodic-protection

..."Fusion bonded epoxy coating, also known as fusion-bond epoxy powder coating and commonly referred to as FBE coating, is an epoxy-based powder coating that is widely used to protect steel pipe used in pipeline construction, concrete reinforcing bars (rebar) and on a wide variety of piping connections, valves etc. from ..."...

https://en.wikipedia.org/wiki/Fusion_bonded_epoxy_coating

Never, ever before, have I tried making a post at 2 AM via my iPhone.

However, I will make the exception here, to ask:

why on earth are you asking THIS question HERE, instead of on the NACE Corrosion Network...?!?!?

if you are not aware of them, navigate your way to www.nace.org, and find their list server networks, of professional corrosion engineers all over the globe, and "participate"...

Hmmmmm...... totally unsure as to why "these" are directed-towards me, since, IF the OP does-in-fact navigate his way to the link I gave www.nace.org, he will find out MOST assuredly what NACE (National Association of Corrosion Engineers, International for those who can't "navigate") is all about.....

I posted here as these are Engineering Forums and it is an Engineering Issue.

I shall appreciate if you can help me to reach NACE Forums as I didn't find any.