How must be the anode distribution for a CP in pipelines?

Question

How must be the anode distribution for a CP in pipelines?

alfyner (Electrical)

(OP)

5 Aug 03 16:38

Hi,

I am designing a CP for a gas pipeline. I will use impressed current to do this. My questions are:

Where is the best location for the bed of anodes? What is the best distance between de pipeline and the anodes?

Could somebody suggest me any reference?

I will appreciate a lot your help

flames (Materials) · Answer 1 · 2003-08-06 22:23:23

In your case you would be likely placing your bed at "remote earth" to provide the current distribution to a long pipeline.

You will need to understand the soil resistivities to properly size the anode bed as well as a current test to determine the required current to achieve protection.

The new Peabody book that came out in 2001 is the best starting point.

I am assuming you have never designed a system before. Could I suggest using a cathodic protection company and working closely with them to see how they design the system to gain the experience. As well the NACE CP are excellent, but design isn't really covered until the third course.

srisomashekar (Industrial) · Answer 2 · 2003-08-07 08:02:53

The first and foremost for designing a Cathodic Protection System for gas pipeline would be to collect various data like Soil Resistivity, the type of protective coating on the pipeline, number of crossings like railway, high tension corssings, rivers, canal etc. Apart from the above the C.P. design life has to be determined. Regarding your query for the best location of anode bed ideally the anode bed should be minimum 50 to 70 metres upto the maximum of 100 mtrs away from the pipeline.

NACE Standards can be referred.

Srisomashekar

alfyner (Electrical) · Answer 3 · 2003-08-07 08:56:45

Thanks for your prior answers, but I need to be clear respect to the following:

Which criteria is applicable to place one or more anode beds and where they must be located?

pik199 (Materials) · Answer 4 · 2003-08-07 19:21:31

Hi,

You must setup anodes to obtain the most possible uniform current distribution, or at least big enougth protection current on the most resistive part of your system.

Good luck in protection!

Aleksandr

sngpl (Electrical) · Answer 5 · 2003-08-07 19:21:43

I think normally one anode bed is laid at a distance of not less than 500 feet and perpendicular to the pipeline.

alfyner (Electrical) · Answer 6 · 2003-08-08 14:07:18

Yes my friends, I am agree with your suggestions, but I have calculated the quantity of anodes that the system requires and it seems to me that they are few for the length of the pipeline.

The pipeline is 12 km length, (12").
# of anodes: 8 (Ti MMO)
Coating efficiency=90%

sngpl (Electrical) · Answer 7 · 2003-08-08 17:34:46

For curiosity's sake, how did you calculate the number of anodes?

flames (Materials) · Answer 8 · 2003-08-10 01:58:33

Your coating efficiency seems a bit low. Is this an older pipeline, designing for a degraded coating, portions not coated, company design standard? We find that most of our coatings (three layer system with corrosion barrier, insulation, outer protective layer) have efficiency >99%, but this is abnormally high.

jerba (Materials) · Answer 9 · 2003-08-14 12:30:33

Hi there
i thing it will be dangerous to give a solution like that about the design of the CP. one pipe is different to the next and one site is different to the next. I do no think that you can design based on rules of thumb. this is a gas pipe not water and one have to be careful. i will refere you as it was said before to the book by peabody or to nace design document.

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How must be the anode distribution for a CP in pipelines?