Marine Corrosion and Cathodic Protection

561 Pages·2022·19.182 MB·English

by  Chris Googan

Marine Corrosion and
Cathodic Protection

Marine Corrosion and
Cathodic Protection
Chris Googan
First edition published 2022
by CRC Press
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and by CRC Press
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© 2022 Chris Googan
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British Library Cataloguing-in-Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloging-in-Publication Data
Names: Googan, C. G. (Christopher George), 1952- author.
Title: Marine corrosion and cathodic protection / Chris Googan.
Description: First edition. | Abingdon, Oxon ; Boca Raton : CRC Press, 2022. |
Includes bibliographical references and index.
Identifers: LCCN 2021040846 (print) | LCCN 2021040847 (ebook) |
ISBN 9781032105819 (hbk) | ISBN 9781032105826 (pbk) | ISBN 9781003216070 (ebk)
Subjects: LCSH: Ofshore structures—Protection. | Corrosion and
anti-corrosives. | Cathodic protection. | Seawater corrosion.
Classifcation: LCC TC1670 .G66 2022 (print) | LCC TC1670 (ebook) |
DDC 627/.98—dc23/eng/20211117
LC record available at https://lccn.loc.gov/2021040846
LC ebook record available at https://lccn.loc.gov/2021040847
ISBN: 978-1-032-10581-9 (hbk)
ISBN: 978-1-032-10582-6 (pbk)
ISBN: 978-1-003-21607-0 (ebk)
DOI: 10.1201/9781003216070
Typeset in Sabon
by codeMantra
To my wife Sue

Contents
Preface xxvii
Acknowledgements xxxi
Author xxxiii
Units, abbreviations and symbols xxxv
Cathodic protection codes xxxix
1 The marine corrosion of steel 1
1.1 The corrosion of steel in seawater 1
1.1.1 How much do we know? 1
1.1.2 Why does steel corrode? 1
1.1.3 How does corrosion happen? 2
1.1.3.1 A defnition 2
1.1.3.2 A school corrosion experiment 3
1.1.3.3 Some electrochemistry 3
1.1.3.4 Aerated seawater 8
1.1.3.5 Deaerated seawater 8
1.1.4 What doesn’t the basic science tell us? 10
1.2 Corrosion rates 11
1.2.1 Laboratory tests 11
1.2.1.1 Weight loss tests 11
1.2.1.2 The importance of the “Blank” weight loss measurements 11
1.2.1.3 Limitations of laboratory testing 11
1.2.2 Seawater immersion tests 12
1.2.2.1 Effect of temperature 14
1.2.2.2 Effect of water depth 15
1.2.3 Information from existing structures 16
1.2.3.1 Shipwrecks 16
1.2.3.2 Harbour piling 19
1.2.3.3 Seabed burial 19
1.2.3.4 Intertidal and splash zones 20
1.2.4 How do we use corrosion rate information? 20
1.3 The microbiological dimension 20
1.3.1 Clean seawater 21
1.3.2 Slightly polluted seawater 22
1.3.3 Heavily polluted seawater and sediments 23
vii
viii Contents
1.3.3.1 Sulfate reducing micro-organisms 24
1.3.3.2 MIC mechanisms 24
1.3.3.3 MIC morphology and rates 24
1.4 The forms of corrosion 26
1.4.1 General corrosion 26
1.4.2 Galvanic corrosion 26
1.4.2.1 Classic example 26
1.4.2.2 Why does it happen? 26
1.4.2.3 What are the risk factors? 27
1.4.3 Pitting 28
1.4.4 Crevice corrosion 29
1.4.5 Fatigue and corrosion fatigue 29
1.4.6 Other forms of corrosion 30
References 30
2 Cathodic protection basics 33
2.1 A theoretical experiment 34
2.1.1 Removing electrons 34
2.1.2 Adding electrons 35
2.2 A simple model 35
2.2.1 How does cathodic protection work? 35
2.2.2 Implementation 37
2.3 The two views of current fow 38
2.4 Potential 38
2.4.1 What do we mean by “Potential”? 39
2.4.2 How do we measure the potential? 40
2.4.2.1 The problem 40
2.4.2.2 The solution 41
2.4.3 Potential measurement 42
2.4.4 What is the potential needed for protection? 44
2.5 Current 44
2.5.1 Bare steel 44
2.5.2 Coated steel 45
2.6 Power sources for CP 46
2.6.1 Davy’s work 46
2.6.2 Sacrifcial anodes 46
2.6.3 Impressed current 48
2.6.4 Sacrifcial anodes versus impressed current 50
2.6.4.1 Sacrifcial anodes: advantages 50
2.6.4.2 Sacrifcial anodes: disadvantages 51
2.6.4.3 Impressed current: advantages 52
2.6.4.4 Impressed current: disadvantages 53
2.6.4.5 Selecting between sacrifcial anodes and ICCP 55
2.6.5 Hybrid systems 55
Contents ix
2.7 What does CP achieve? 55
2.8 Where do we go from here? 56
References 57
3 Designing according to the codes 59
3.1 Do we need CP? 59
3.2 Who does the CP design? 60
3.2.1 In the land of the blind 60
3.2.2 Who is the “Expert”? 60
3.2.3 Certifcation of competence 61
3.2.3.1 Is it needed? 61
3.2.3.2 NACE 61
3.2.3.3 ISO 15257 61
3.3 The basis of design 62
3.3.1 System life 62
3.3.2 Environmental parameters 63
3.3.3 Coating 63
3.3.4 Sacrifcial versus impressed current? 64
3.3.5 Which codes? 64
3.3.6 Cathode parameters 64
3.3.6.1 Protection potential 64
3.3.6.2 The protection current density 65
3.3.7 Anode parameters 67
3.3.7.1 General 67
3.3.7.2 Operating potential 67
3.3.7.3 Charge availability 68
3.3.7.4 Utilisation factor 68
3.4 The design process 69
3.4.1 Overview 69
3.4.2 Calculating the cathodic current demand 69
3.4.2.1 Interfaces 69
3.4.2.2 Uncoated zones 70
3.4.2.3 Coated zones 71
3.4.2.4 Additional current demands 71
3.4.3 Minimum anode mass 71
3.4.4 Anode output 72
3.4.4.1 General 72
3.4.4.2 Estimating anode resistance 73
3.4.5 Anode optimisation 74
3.5 Example calculations 74
3.5.1 Case 1 – uncoated structure 74
3.5.1.1 Life 74
3.5.1.2 Structure and area 75
3.5.1.3 Current densities 75