DESIGN OF CATHODIC PROTECTION USING BEM FOR COMPONENTS

OF THE PILOT OCEAN ENERGY SYSTEM

by

Nicolas Gantiva

A Thesis Submitted to the Faculty of

The College of Engineering and Computer Science

In Partial Fulfillment of the Requirements for the Degree of

Master of Science

Florida Atlantic University

Boca Raton, Florida

August 2010

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ACKNOWLEDGEMENTS

The author wishes to express his most heartfelt thanks to his family for their constant

support and encouragement in the pursuit of this year-and-a-half-long enterprise. It played a key

role in enduring this experience being far from home. The author is also immensely grateful to

both the US and UK technical support staff from the BEASY Software company for all their help

and patience. To the Center for Ocean Energy Technology thanks for having established the

project and providing the funds for this thesis to materialize. To the advisory committee for being

part of this endeavor and for their words of advice, many thanks. Finally, a special thanks to

thesis advisor Dr. Francisco Presuel-Moreno, without whom none of this could have been

possible.

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ABSTRACT

Author: Nicolas Gantiva

Title: Design of Cathodic Protection Using BEM for Components of the Pilot Ocean Energy System.

Institution: Florida Atlantic University

Thesis Advisor: Dr. Francisco Presuel-Moreno

Degree: Master of Science

Year: 2010

The Center for Ocean Energy Technology at Florida Atlantic University is developing an

ocean energy turbine system to investigate the feasibility of harnessing Floridas Gulf Stream

current kinetic energy and transforming it into a usable form. The turbine system has components

which are prone to marine corrosion given the materials they are made of and to the harsh

environment they will be exposed to. This study assumes a two-part system composed of a

coating system acting as a barrier and sacrificial anode cathodic protection which polarizes the

metal structures to a potential value where corrosion is significantly reduced. Several

configurations (varying in anode quantity, size and location) were considered in order to

cathodically protect the structures with various coating qualities (poor, good and excellent). These

cases were modeled and simulated via Boundary Element Method software and analyzed so as

to assess the most appropriate design.

DEDICATION

This manuscript and all the work associated to it are entirely dedicated to my family,

particularly to my father, Diego, my constant role model in integrity and exceptional

professionalism. I only wish I can follow in your footsteps. To the love of my life, this work and

the effort I poured into it represents my commitment of returning by your side as I had promised.

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DESIGN OF CATHODIC PROTECTION USING BEM FOR COMPONENTS OF THE PILOT OCEAN ENERGY SYSTEM

List of Tables ............................................................................................................................. ix

List of Figures ............................................................................................................................. x

Nomenclature ........................................................................................................................... xiii

1. Introduction ......................................................................................................................... 1

1.1. Ocean Energy Project...................................................................................................... 2

1.2. Purpose Statement.......................................................................................................... 3

1.3. Structure Characteristics.................................................................................................. 4

1.3.1. Base Material............................................................................................................... 5

1.3.2. Coatings ...................................................................................................................... 5

1.4. Concept of Operation....................................................................................................... 8

1.4.1. Environment and Location ........................................................................................... 8

1.5. Preliminary Suggestions ................................................................................................ .. 9

2. Background....................................................................................................................... 10

2.1. Corrosion ...................................................................................................................... 10

2.1.1. Corrosion Theory ....................................................................................................... 12

2.1.1.1. Polarization............................................................................................................ 13

2.2. Cathodic Protection ....................................................................................................... 18

2.2.1. Graphical Representation of Cathodic Protection ....................................................... 20

2.2.2. Impressed Current ..................................................................................................... 22

2.2.3. Sacrificial Anode (Galvanic) ....................................................................................... 22

2.3. Coated vs. Uncoated Structures .................................................................................... 25

2.4. Stationary vs. Moving Structures.................................................................................... 27

2.5. Location Corrosion by Seawater ................................................................................. 28

2.6. BEM to Model CP.......................................................................................................... 30

2.6.1. BEM Mathematics...................................................................................................... 31

2.6.2. Beasy Software ......................................................................................................... 36

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3. Previous Work................................................................................................................... 38

3.1. The Structures and Their Simpler Models ...................................................................... 38

3.2. General Boundary Conditions ........................................................................................ 44

4. Exact Geometry Creation ................................................................................................ .. 45

4.1. Monitoring and Telemetry Buoy ..................................................................................... 45

4.2. A-Frame........................................................................................................................ 48

4.3. Anodes.......................................................................................................................... 51

4.3.1. Sacrificial Anode: 0.6lb .............................................................................................. 52

4.3.2. Sacrificial Anode: 1lb ................................................................................................ . 52

4.3.3. Sacrificial Anode: 2lb ................................................................................................ . 53

5. Polarization Data............................................................................................................... 55

5.1. Carbon Steel ................................................................................................................. 55

5.2. Stainless Steel............................................................................................................... 56

5.3. Zinc............................................................................................................................... 57

6. Simulation Results............................................................................................................. 59

6.1. MTB Lead Hull Buoy................................................................................................ ... 60

6.1.1. Two-Anode Configuration .......................................................................................... 61

6.1.1.1. Bare Steel.............................................................................................................. 61

6.1.1.2. Coating Efficiency: 80% ......................................................................................... 65

6.1.1.3. Coating Efficiency: 90% ......................................................................................... 68

6.1.1.4. Coating Efficiency: 98% ......................................................................................... 70

6.1.2. Four-Anode Configutation.......................................................................................... 73

6.1.2.1. Bare............................................................................