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 damages and that may lead to AC corrosion.

As presented in earlier papers at CORROSION, installation of additional sacrificial anodes is used as a means to avoid AC corrosion. However, the direct electric heating system can influence 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.

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

Subject
Electric current, Test methods, Materials, Galvanic anodes, Anodic protection, Cathodic protection, Corrosion rate, Pipelines, Density, Current densities, Alternating current corrosion, Protection potential, Anodes
Keywords:
CP design, AC corrosion
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2013
Association for Materials Protection and Performance (AMPP)
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