Effects from Alternating Current on Cathodic Protection of Submarine Pipelines

EFFECTS FROM ALTERNATING CURRENT ON CATHODIC

PROTECTION OF SUBMARINE PIPELINES

 

L. Sund Lilleby¹, S. M. Hesjevik¹, K. Nisancioglu², S. Olsen¹

 

1. STATOIL, Trondheim, Norway
2. Norwegian University of Science and Technology, Trondheim, Norway

 

 

 

 

         Submarine pipelines are sometimes installed with a direct electric heating system to avoid formation of wax and hydrates.  In short an alternating current is applied between each end of the pipeline. Sacrificial anodes are used for cathodic protection, hence the system must be considered fully grounded to sea. With a fully grounded system, electric current will be transferred from sacrificial anodes and any potential coating holydays to sea.

In this work interactions between cathodic protection and alternating current have been studied. The effects of superimposed AC voltage on specimen made from typical pipeline, steels polarized to a common cathodic protection level have been investigated. Special focus has been put on development of calcareous deposits under influence from AC voltage. Furthermore, effects from AC voltage on cathodic protection current density and protection potential have been studied.

Key words: Alternating current, cathodic protection, calcareous deposit