Cathodic protection of subsea pipelines

[danodco]

I have a few questions and I would appreciate it if someone tried to answer them. I am doing an anode remanant life assessment and current attenuation test for subsea flowlines. Here are my questions

1. What are typical current attenuation lenghts for bracelet anodes(cosidering it is not buried and has about 20 cm lenght and 15 cm thickness)?

2. Consider a standoff anode. Does the anode resistance equation depend on the dimensions (ie. lenght, breadth & hieght of the block anode) or could I just equate the exposed surface area of the block anode to the exposed surface area of a solid cylinder and use the dimensions of the cylinder in the equation?

3. I need a way (or an equation) to proportionally decrese the remaining utilization of an anode as its depletion percentage increases. Can someone help me with this?

If you have not understood these clearly, please do get back to me.

Thanks in advance

Cheers

 

[SJones]

1.
Current attenuation calculations can be found in ISO 15589-2 or NACE SP0607. The default maximum spacing without attenuation calculations is 300 metres, so that should tell you something.

2.
Anode resistance equations are given in the major CP design standards such as DNV-RP-B401. You don't use standoff anodes on a pipeline though!

3.
Utilisation is the depletion! You will typically have a design depletion (utilisation)of around 0.8 at end of design life. So, calculate your anode consumption and assume that the consumption occurs uniformly around the complete anode.

So, if this is not homework, best get a qualified CP engineer to help you out.

Steve Jones
Materials & Corrosion Engineer

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

 

[Walterke]

It kind of troubles me that the people who are in charge of constructing our sub-sea pipelines need this forum for these kind of questions.

No offense.

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