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Join Date: Aug 2009
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Cathodic Protection Current Shielding

08/10/2017 10:04 AM

I am trying to workout Cathodic Protection Current Shielding mitigation strategy.

The CP system is in-tact as per PSP, DCVG & CIPS Surveys but leakages occurring. Which tests on coating (3LPE) or elsewhere in the system should be conducted to avoid leakages?

Thanks

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Pathfinder Tags: CP System Mitigation shielding
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#1

Re: Cathodic Protection Current Shielding

08/10/2017 11:24 AM

Thanks for the undefined acronyms!

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#5
In reply to #1

Re: Cathodic Protection Current Shielding

08/11/2017 3:03 AM

SNAFU

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#8
In reply to #5

Re: Cathodic Protection Current Shielding

08/11/2017 5:25 AM
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#2

Re: Cathodic Protection Current Shielding

08/10/2017 1:36 PM

..."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

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#4
In reply to #2

Re: Cathodic Protection Current Shielding

08/11/2017 3:02 AM
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#12
In reply to #4

Re: Cathodic Protection Current Shielding

08/11/2017 1:34 PM

..."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

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#9
In reply to #3

Re: Cathodic Protection Current Shielding

08/11/2017 8:39 AM

I'm going with Play Station Portable...

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#6

Re: Cathodic Protection Current Shielding

08/11/2017 3:28 AM

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"...

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#7
In reply to #6

Re: Cathodic Protection Current Shielding

08/11/2017 5:24 AM
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#10
In reply to #7

Re: Cathodic Protection Current Shielding

08/11/2017 9:15 AM

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.....

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Participant

Join Date: Aug 2009
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#11
In reply to #10

Re: Cathodic Protection Current Shielding

08/11/2017 12:50 PM

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.

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#13
In reply to #11

Re: Cathodic Protection Current Shielding

08/11/2017 1:58 PM

At https://www.nace.org, click on [RESOURCES] (5th "brown" menu item from left):

then,

select ONLINE CORROSION COMMUNITY SERVERS {bottom-most item}

At That Page, click on:

http://www.nacecorrosionnetwork.com/read/all_forums/

WHEN you get there, you will see :

Select Cathodic Protection forum, Coatings forum, perhaps even Materials, and/or MR0175 Maintenance Panel (if so interested). When you click "Subscribe" in the right hand column, you'll be prompted to enter your email address (etc).

DO *read* a number of threads, first, to get a feel for the BEST way to word your inquiries. Specificity/Clarity/Conciseness/(some)Detail is necessary for best results.

You might need to ask a couple different ways, on a couple different forums, over a couple weeks-time, too... in order to "Capture-the-Attention" of the BEST expert , who will yield the BEST / most thorough response for your particular issue/problem.

But it WILL come.....

{BTW} in the same context as W.E.Deming's aphorism that "You cannot INSPECT Quality into a product..."

I see you have performed Voltage Gradient / Close Interval surveys ... and .... ("still, leakages are occurring"). Obviously, the TESTS do not perform any "fixing". As I read into it (your post), you are apparently experiencing a parasitic drain from the structure being protected. You had BETTER be prepared to explain (in the NACE forum), exactly WHAT the structure is (pipeline, storage tank / facility, etc), WHERE it is, and what other industries "surround" it, among other things......

Wishing you "SUCCESS"...!

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