Cathodic Protection vs. Wrapping and Coating

What is this in application to? This sounds suspiciously like a homework question.

If this is a homework question, give some details about what you know about the benefits of each method and we can explain both further.

Drew

See this post.

information on small flywheel enrgy storage

Your "request" seems arrogant to me.

I want the answers with value w.r.t. to some physical parameter regards

Go here and read: http://en.wikipedia.org/wiki/Cathodic_protection

Cathodic or anodic protection (- or +) is beneficial when different materials (see galvanic tabel) can act as galvanic provider -one to another- within a carrier, liquid or damp. Oxidation is a different matter.

Ok, my turn.

Cathodic protection is useful when you can use it. It is limited by the conductive ability of the soil your metal structure is in. If your soil is conductive, you will have cathodic and anodic action no matter how perfect you think wrapping and coating is (there are always small voids) where stray currents in the ground will use your metal as a conductor. It will not be a problem where the current jumps onto your structure, but when it jumps back off it will become a anode and begin degrading.

The advantage of wrapping and coating is that it reduces the amount of current required to protect it with impressed current.

When you do not need impressed current you can use a passive system by installing an anode bed of a more reactive metal that will degrade more readily and protect your structure.

If you are in a very dry area that does not support current flow you only need wrapping and coating due to the limited anodic action.

Sorry, I am uncertain what you mean by W.R.T.

Drew

I don't see the image. Where is the sacrificial pole in your theory? I think you are on the road of galvanizing or anodizing or phosphate threatment, which is IMHO electrolytic coating.

You are correct, I did not explain that with an impressed current method the current is impressed into the soil through the sacrificial anode. It is a DC current that flows from the anode to the cathode ensuring the cathode will be protected.

This must be monitored to make sure there are not any positive sections of pipe or other protected underground metal structure.

Here is a website created for the purpose of educating people about cathodic protection.

A quick search here should discover the thread where the author of the training website speaks about it.

Drew

Re: w.r.t. ~

I, too, am bereaved that all-too-many texting addicts are bringing their worthless jargonal-abbreviations here to the forums.

With Respect To ain't all that hard to type-out...

• Sand/Shot blasting, priming, wrapping and cathodic protection are required for underground carbon steel piping and equipment.

• Sand/Shot blasting, priming, and coating are required for aboveground carbon steel piping and equipment.

I am not aware of the laws or restrictions on piping. Your comments are consistent with all of the fuel pipeline carbon steel equipment I have encountered.

The original post only asked about comparing the two methods listed.

Drew

From that ol' For-What-Its-Worth department, I believe Abdel's comments were consistent with what should be expected, in reply to such an original post as this one.

While impressed current C.P. can, in fact, protect VAST amounts of uncoated steel, it could possibly be prohibitively expensive (energy-wise, depending on the extent of the project), and there would be the case of possibly severe corrosion anytime that power went down for whatever reason.

The O.P's request for : "with value w.r.t. to some physical parameter regards" is FAR too ambiguous. We could create a virtual Wiki-environment here, piling "answer-on-top-of-answer", reaching into all of the far-flung possibilities out there......

But, to what avail...?

The poster should give all the design 'basics' that he can, including the type of environment (desert, bayou, mountains?), and at least a smidge of specificity about the materials in question. NOTE that he does not even begin to address these issues!

Abdel is 100% correct ... having specified his response *with respect to* carbon steel products ...

Above ground CS requires a good coating system, properly prepared and applied ; below ground, likewise, requires proper coating in order to insure longevity and performance of the C.P. system.

"Wrapping and coating" (CS) alone is never sufficient for below ground protection. That old statement that : "oftentimes, NO coating at all would be better that a poor coating (exhibiting holidays)" should be enough to justify that ... even without the various accompanying "horror-stories" (failures).

Cheers to all ~

have a look at this MIL-STD

MIL-HDBK-1004/10, MILITARY HANDBOOK, ELECTRICAL ENGINEERING CATHODIC PROTECTION (31 JAN 1990)., This manual is intended for use in the design and construction of cathodic protection systems for the mitigation of corrosion of buried or submerged metallic structures. Design of cathodic protection systems is somewhat different than design of other electrical or mechanical systems because it must be based on local environmental conditions such as soil resistivity. This manual presents criteria for cathodic protection, methodologies for design of cathodic protection systems, examples of typical systems, and design calculations, installation, and construction practices, recommended initial system checkout procedures, and system maintenance requirements.

http://www.everyspec.com/MIL-HDBK/MIL-HDBK+(1000+-+1299)/MIL-HDBK-1004-10_7893/

hope this help

S

corrosion & rust prevention