51313-02121-CP of Offshore Jacket by Remote Anode Sleds and Discussion About Current Drain to Buried Structures

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Product Number: 51313-02121-SG

ISBN: 02121 2013 CP

Author: Svenn Magne Wigen

Publication Date: 2013

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“Current drain to mud exposed (buried) structure such as piles is in reality dependent on the soil resistivity. The prevailing CP design standards varies in the recommended current drain to structures in mud. I.e NACE RP0176 recommends a range of 15 to 5 Amps per pile while DNV RP B 401 recommends 20 mA/m2 for the total surface areas below mud line. A recent design case for an offshore jacket i fairly shallow waters around 37 meters water depth with eight piles piled 135 metes in the mud where the intention was to cathodically protect the entire structure with remote sacrificial anode sleds show that the influence of current drain to mud exposed structures may be critical for dimensioning the CP system. For this actual case where the CP requirements were to fulfill CP criteria as per DNV RP B 401 with additional 10% current density on the seawater exposed surface areas the current drain to the mud exposed sections of the piles represented around 30% of the total current demand for the jacket.

The paper will show how the CP design carried out by engineering company was verified by Boundary Element Modelling (BEM) and further discuss current drain to mud exposed structures and the different recommendations in the prevailing CP design standards”