Galvanic Current Density Measurements Of Anodes For Subsea Vibration Data Logger (SVDL) System

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Product Number: 51321-16717-SG

Author: Suresh Divi; Melissa Gould; and Dan Efird

Publication Date: 2021

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In deep-water applications in the Gulf of Mexico, vibration-induced fatigue issues often arise due to wave induced motion, vessel induced motion, vortex induced vibration, and/or flow induced vibration. A purpose-built vibration monitoring system, Subsea Vibration Data Logger (SVDL), can be installed directly on subsea equipment to monitor these and other forms of vibration and to assess fatigue. The SVDL body is constructed
from stainless steel (SS) and nickel-aluminum bronze (NAB) materials.

Because the SVDL system can be installed at locations ranging from the surface to deepwater, it is subject to a range of temperatures 4–27°C. To protect the SVDL from corrosion in seawater, the system is electrically isolated from the main structure and aluminum anodes are connected to the SVDL body. Based on exposure time and seawater temperature, the size of the anode and its exposed area are very important for protecting the SVDL materials.

This study presents results from laboratory electrochemical corrosion testing involving galvanic current density measurements for various anode/cathode area ratios.1000 series aluminum anodes and three cathode materials, super duplex SS (UNS S32550), 316L SS (UNS 31603) and NAB (UNS C63000), were studied. The laboratory tests were performed at two seawater temperatures, 4°C and 24°C, and three anode:cathode area
ratios.
Galvanic current densities and corrosion rates from the testing indicated that aluminum
anodes provide effective corrosion protection to super duplex SS and 316L SS. An equalarea
aluminum anode was found to be sufficient to protect the NAB material at both
temperatures. Test results also indicated that there is no significant galvanic effect
between the NAB and super duplex SS in the SVDL system.