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Shimadzu Review 82[3・4] (2026)
Abstract
Offshore steel structures, such as wind farms, are protected from corrosion using cathodic protection methods. The cathodic protection offered by these methods is expressed in terms of a design current density, which is the current density anticipated to provide protection. This varies substantially depending on water temperature, flowrate, and other local environmental factors. Cathodic protection also generates a surface scale on structures due to electrodeposition over time. After this layer reaches a steady state, the current density required for cathodic protection can be less than half the initial current density. Nevertheless, no instrument can currently measure cathodic protection current density, and cathodic protection is instead verified and maintained by measuring protection potential. Shimadzu Corporation has developed an underwater electric potential (UEP) sensor for the non-contact measurement of electric potential in water, and is using this instrument to develop methods of diagnosing the deterioration of underwater structures. We have used this UEP sensor to develop a method of measuring current density in water. This involved devising a method of calculating current density from underwater electric potential measurement by the UEP sensor and correcting for offset caused by the underwater environment and the UEP sensor itself. We also created a prototype current density sensor, and verified its ability to measure current density by collecting protection current density measurements for harbor infrastructure in situ. Next, we are planning to verify the validity of these measurements and develop a current density meter that can be mounted on an underwater robot.
1Geoscience Department, Machinery Division, Shimadzu Corporation, Kyoto, Japan
2Department of Civil Engineering, Faculty of Science and Technology, Tokyo University of Science, Chiba, Japan
3Materials Group, Structural Engineering Department, Port and Airport Research Institute, National Institute of Maritime, Port and Aviation Technology, Kanagawa, Japan
4Industrial System Research Group, Structural and Industrial System Engineering Department, National Maritime Research Institute, National Institute of Maritime, Port and Aviation Technology, Tokyo, Japan
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