Strategy and Results of an Impressed Current Cathodic Protection Retrofit in the North Sea

by Edgar Rodrigues, Alex Delwiche, Tim Queen

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An oil drilling and producing jacket was installed in the North Sea in 1980, 100 miles off the coast of Scotland in 160 m depth seawater. The jacket has 8 legs and was installed with traditional standoff galvanic anodes. Surveys from 2010 to 2013 indicated a reduction in corrosion protection from the cathodic protection system, and plans were implemented to upgrade the cathodic protection (CP) system.

A remote anode sled impressed current cathodic protection (ICCP) system was selected, installed and commissioned in early 2016. This paper discusses the design process and challenges in choosing what was at the time, the largest ever cathodic protection retrofit in terms of delivered current capacity offshore, and the actual current the structure required to maintain protection.

Figure 1 - Typical Offshore Oil and Gas Structure

Figure 2 - Example of CP Potential “Dropping Off” in 2013 and 2015

Figure 3 - Average Potentials Vs Over Time for Varying Depths (from COABIS inspection data)

Figure 4 - Example of Depleted Anode at EL158

Figure 5 - DropCell Potentials for Varying Depths

Figure 6 - Average Potentials Vs Over Time for Varying Depths Updated

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