CP for Insulated Pipeline

[abhishekp]

Hi guys,
here`s a thing for y`ll senior guys, i have a 12 inch subsea pipeline of about 8 km carrying well fluid, the line is insulated with PUF (dry insulation) and then jacket. my problem is that i need to provide cathodic protection to the pipeline field joints, how can i do that without breaking the coating, at what position i can place the anodes, how can i make the connection between anode and the pipeline, is there any code or standard which shows the way, i can do it. has anyone faced similar situation in thr professional carrer, i am a Grad. engineer trainee, please enlighten me.

 

[LittleInch]

As you say PUF is a "dry" insualtion in that it is not 100% closed cell and therefore needs to be kept away from the sea water.

It is not clear how you intend to construct, but normally there are two options - fill in the field joints with foam and then seal the outer casing (usually PE or some sort of plastic) or have individually sealed pipes and the just do a "normal" field joint coating and fill in the gap with some sort of foam and accept the oss of insualtion at the field joint area.

If it is the first one, then normally there is no CP required as the insulation acts as too big a barrier to the current to be effective.

If the latter then just attach an anode in the normal way, but your current drain is limited to the field joint coated area.

Insualted pipelines need very good anti corrosion coating under the insualtion, including the field joint, as CP is at best reduced and at worst completely ineffective and this needs to be reflected in the installation methods used.

Off shore this causes issues as it can reduce laying rates unless you've got a reeled line.

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[RandomAxe]

I would suggest you have a read of DNV RP F103, which is a DNV recommended practice for CP of subsea pipelines. DNV codes and standards can be downloaded for free from here:

http://exchange.dnv.com/publishing/Codes/ToC_edition.asp

You could also read ISO 15589-2.

You haven't mentioned the material the pipeline is made of, if it is a duplex line you will not be able to put anodes directly on the pipeline due to risks of HISC (see DNV RP F112). But could protect it through the use of anode skids or anodes on adjacent structures the pipeline ties into. You will need attentuation calcs for this approach.