CP Design - Anode Temperature/Efficiency

[JLiotta]

I have been tasked with designing a CP system for several marine risers. The client's specification says to use the internal fluid temperature as the anode temperature. Then, the anode electrochemical efficiency is a function of temperature.

We have also been instructed to use the latest revision of the DNV code. The 2005 revision does not provide a curve for anode efficiency vs temperature. However, the 1993 code (previous revision) does provide a curve. By looking at that curve to get some idea, the internal temperatures of our production risers exceeds the curve. In other words, the temperatures yield a negative (or *extremely* low) efficiency!

I don't have anyone in the office with experience in CP design to consult, so I am wondering: What is the norm for designing CP systems (temperature/efficiency)? I see that a base value of 2000-2500 A_h/kg is frequently used. What about for high temperature application? Also, most of the production risers are insulated. It seems that a simple heat Xfer calc could determine an estimated average anode temperature which could be used to determine efficiency. Using internal temp seems overly conservative...(or, rather, non-applicable for these high temps)

Any help is greatly appreciated.

Thanks,
Joe

 

[MASE81]

From the information given, the temperature requirement may be too conservative. You may want to revisit this spec requirement with the client. Particularly where size and weight of the anodes could impact the riser design itself. Are anodes supplemental to coatings? What is the frequency of inspection, and replacement?
Rgds,
RKK

http://www.rkkimmons.com