Offshore Pipeline C.P. design

[Hariharan]

I am looking for the basis for determining the coating breakdown factor
for a submarine pipeline coated with about 500 microns of Fusion
bonded epoxy and having a concrete weight coating of 1-3 inches.
This type of system, I understand, is common in GOM. The coating
breakdown factor is required for design of the Cathodic Protection System.

DNV RP B401 is not explicit for this combination. Any other standard,
or interpretation and GOM Practice or references would be useful.

Thanks

Hariharan