Cathodic Protection for pipelines with Deep well groundbed

[zimou888]

CLient requires us to design the CP system with deepwell groundbed for one 24'' underground pipeline with 39km long and 3PE coating. The project location is in African desert with very high gound level soil resistivity of aroud 500 ohm(7.5m deep).

As my understanding, we have to drill a test hole for the soil investigation first for the deep well anode detail engineering in later stage. Probably, the test hole has to be 100m deep.

My question is what the criteria is to determine the depth of this test hole when we are drilling? Do we have to continue to drill until 1 ohm resistivity is reached or we could stop by water table level, or certain range is ok (for example 50 to 100 ohm)? We have to give specific information to the soil investigation subcontractor. But I have no idea.

It would be appreciated if someone could help me out.

 

[SJones]

This is the job of a specialist CP contractor not a lash up between a pipeline contractor and a survey company. Firstly, consult NACE SP0572 and ISO 15589-1 (which is what the client should have specified). Secondly, a review of the attached paper may be of assistance even though the nature of the soil is probably vastly different.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdoweb/

 

[brimmer]

You can determine soil resistivity to some depths from above ground techniques before drilling. You can also get an idea of soil stratigraphy, (do you have layers in the soil of different resistivities) this will also affect where you put the anodes and depth you might drill to. Can't the soil subcontractor do this? I can only provide the rough guidline at this point to select a lower resistive more uniform area. What soil resistivity is acceptable for the design will depend on the number and size of anodes, backfill etc. If operator(s) have groundbeds on other pipelines in this area you can use this data to assist you. I would take the advice of SJones, definitely a job for CP specialists.