Date of Award

12-2023

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Ocean Engineering and Marine Sciences

First Advisor

Geoffrey Swain, Ph.D.

Second Advisor

Nakin Suksawang, Ph.D., P.E.

Third Advisor

Kenyon C. Lindeman, Ph.D.

Fourth Advisor

Chungkuk Jin, Ph.D.

Abstract

Steel monopile support structures for offshore wind turbines require protection from corrosion on their external and internal surfaces. Cathodic protection (CP) works effectively to protect the external surfaces of monopiles, but internally, byproducts from aluminum sacrificial anode CP (SACP) and impressed current CP (ICCP) induce acidification that accelerates steel corrosion. This project investigated the effects of perforations on the performance of aluminum SACP and ICCP when used inside of steel pipes. Additionally, marine growth on the external and internal surfaces of the pipes was assessed to determine if CP byproducts affect marine organism development.

Two sealed and two perforated steel pipes utilizing SACP or ICCP systems were deployed in seawater in Cape Canaveral, FL for eight weeks. The final internal current density of the perforated pipes using SACP and ICCP systems was 56 and 31 mA/m2, respectively. Both densities were nearly equivalent to their respective external protection systems on the sealed pipes and significantly lower than the sealed pipes’ internal current densities. The sealed pipes experienced internal water acidity or a buildup of chlorine products which caused the high CP current demand. A visual assessment of the marine communities that developed on the external and internal cathodically protected surfaces found similar coverages of species between the two CP methods.

The results of this deployment suggest that Al SACP and ICCP can be used to protect the internal surface of perforated offshore monopiles. Additionally, marine organisms should be able to grow within and around these structures to form healthy marine ecosystems.

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