Cathodic Protection for subsea pipeline

[abhishekp]

Hi, I am new to the Pipeline Industry and interested in CP system topic. I wanted to know that, Usually one anode provide cp for certain length of the pipeline, after that we need to provide another anode for furthur protection, what if two anodes are provided 100 mm apart from each other, would that give same effect as previous arrangement or would that be uselful.i am inexperienced in this field and i appreciate you`lls experienced opinion.

 

[SJones]

First gather the standards: ISO 15589-2 and DNV-RP-F103, then look at "attenuation" in Annex A of the former. The latter offers a simplified approach in subclause 5.6:

https://exchange.dnv.com/Publishing/Codes/download.asp?url=2010-10/rp-f103.pdf

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[LittleInch]

You can find basic guides to how CP works which should give you more of a background, but at it's most basic, CP is an electric circuit. You have a voltage difference in this case generated by the anode ( a few volts only), part of the circuit is the pipe (good conductor) and part the seawater (not as good a conductor) via a hole in the coating. The anode needs to provide both voltage and current. If you do what you say, all you are doing is doubling the current capacity or doubling the life (there are other limits). Hence two anodes very close together simply act like one big anode.

The actual length of protection from one anode is determined by many factors, not just mass of the anode (though that is one input).

This is a very very simple explanation and there are lots of other issues about anode life, current density, coating insulation, number of defects etc which need to go into the calculation in the codes S Jones has mentioned above.

I assume you are talking about offshore lines here, but whilst the theory onshore is simialr, there the current is normally supplied by a transformer which has a much higher driving voltage and can cover much longer distances between inpuit points.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[abhishekp]

Thank you Mr Steve and Little inch for the knowledge, you guys rock..!!