51313-02443-Cathodic Protection Design of Submarine Pipelines with Direct Electric Heating

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Product Number: 51313-02443-SG

ISBN: 02443 2013 CP

Author: Sven Hesjevik

Publication Date: 2013

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In some cases submarine pipelines are installed with a direct electric heating system to avoid formation of wax and hydrates. The principle is that an alternating current is applied between each end of the pipeline and heat is generated in the pipe material. The pipe is fully electrically grounded to the sea trough sacrificial anodes but still some current can be transferred from the pipe to sea through coating holidays and that may lead to AC corrosion.

As presented in earlier papers at CORROSION conferences installation of additional sacrificial anodes is used as a mean to avoid AC corrosion. However when the direct electric heating system is in operation it will influence known design parameters for cathodic protection such as sacrificial anode capacity protection potential and design current densities. This may have large consequences for design of the CP system in terms of number anodes and required anode mass. Testing has been carried out to identify these relationships and this paper discusses how to design cathodic protection for submarine pipelines with a direct electric heating system.

Test results showing the relationship between applied AC and protection potential protection current density and anode capacity will be presented. One finding is that the protection current density increases with increased AC and this need to be considered in the CP design.