Basic Corrosion Technology for Scientists and Engineers

178 Pages·1996·11.267 MB·178\178

by  Mattsson, Einar

Basic Corrosion
Technology
for Scientists and Engineers
Second Edition
Einar Mattsson
THE INSTITUTE OF MATERIALS
Book753
This paperback edition first published in2001 by
10M Communications Ltd
1Carlton House Terrace
London SWIY 5DB
First English language edition published in 1989by
Ellis Horwood Ltd
Second edition ©The Institute ofMaterials 1996
Illustrations ©Einar Mattsson
10M Communications isawholly-owned subsidiary of
The Institute ofMaterials
ISBN 1861251386
All Rights Reserved. No part of this publication may be reproduced, stored in aretrieval
system, ortransmitted, in any form orby any means, electronic, mechanical, photocopy-
ing, recording orotherwise, without thepermission ofThe Institute ofMaterials, 1Carlton
House Terrace, London SWIY 5DB, UK.
Neither thepublishers, nor theEditors and theauthors and their employing organisations,
not anyperson acting onbehalf ofany ofthem (a)makes any warranty, express orimplied,
with respect to the use ofany information, apparatus, method orprocess disclosed inthis
book orthat such use may not infringe privately owned right or(b)assumes any liabilities
with respect to the use of, orfor damages resulting from the use of, any information,
apparatus, method or process disclosed in this book, and the use of any materials or
methods issolely at the risk ofthe user.
Printed and bound inthe UK by
The Chameleon Press Ltd, Wandsworth
Preface
The first edition of this book was published in 1989 by Ellis Horwood Ltd,
Chichester, UK. When this edition had been sold out in 1994, there was still an
interest in the book. For that reason The Institute of Materials, London has decided to
publish asecond edition, updated with respect torecent developments.
When preparing the manuscript for the second edition, I have received assistance
from Kaija Eistrat, Louise Hult, Bror Sederholm and Bengt Sundvall, Swedish
Corrosion Institute, from Christofer Leygraf, Royal Institute of Technology,
Stockholm, and from Christer Ornby, MMS, Stockholm. Many thanks for this
valuable support.
Ihope the book will be ofcontinued interest and value tothe readers.
Stocksund Einar Mattsson
15December 1995
Table of Contents
Preface 9
1. CORROSION ANDITS IMPORTANCE TO THE COMMUNITY 11
2. BASIC ELECTROCHEMICAL CONCEPTS 15
2.1 Electrochemical reactions 15
2.2 Faraday's law 16
2.3 The concept ofelectrode potential 16
2.4 The galvanic cell 18
2.5 Reference electrodes 20
2.6 The electrochemical series 22
2.7 The phenomenon ofpolarisation 23
2.8 Electrolytic conductance 27
3. BASIC CORROSION CONCEPTS 29
3.1 The driving force ofcorrosion 30
3.2 Electrochemical and chemical corrosion 32
3.3 The rate ofcorrosion 33
4. TYPES OF CORROSION 37
4.1 Uniform corrosion 37
4.2 Pitting 37
4.3 Crevice corrosion 38
4.4 Deposit corrosion 41
4.5 Selective corrosion 41
4.6 Intergranular corrosion 41
4.7 Layer corrosion 46
4.8 Erosion corrosion 46
4.9 Cavitation corrosion 48
4.10 Fretting corrosion 49
4.11 Environment-induced cracking 50
4.12 Bimetallic corrosion orgalvanic corrosion 59
4.13 Stray current corrosion 61
6 Basic Corrosion Technology for Scientists and Engineers
5 CORROSION ENVIRONMENTS 65
5.1 Water 65
5.2 Soil 73
5.3 Atmosphere 79
5.4 Dry gases 86
5.5 The human body 92
6 CORROSION PROTECTION 95
6.1 Cathodic protection 95
6.2 Anodic protection and passivation 103
6.3 Corrosion inhibitors 103
6.4 Metal coatings 107
6.5 Chemical conversion coatings 114
6.6 Corrosion-preventing painting 115
6.7 Coatings ofplastics orrubber 120
6.8 Temporary corrosion prevention 123
7 CORROSION PREVENTION BYDESIGN 127
7.1 The thickness ofthe material 127
7.2 'Pockets' with accumulated water ordirt 127
7.3 Water in crevices 130
7.4 Metallic contact between dissimilar metals inmoist environments 130
7.5 'Streamline shape' ofconstructions which are exposed to
flowing liquids 132
7.6 'Thermal bridges' 132
7.7 Design for surface treatment 133
8 THE CORROSION CHARACTERISTICS OF THE MOST COMMON
METALS INUSE 135
8.1 Steel and cast iron 135
8.2 Stainless steel 144
8.3 Aluminium and its alloys 157
8.4 Copper and its alloys 166
8.5 Titanium and its alloys 179
9 THE METHODOLOGY OF CORROSION INVESTIGATIONS 181
9.1 Corrosion testing 184
9.2 Corrosion monitoring 184
9.3 Electrochemical investigations ~ 185
9.4 Physical methods 187
10 CORROSION INFORMATION 189
10.1 Corrosion data collections, handbooks and standards 189
10.2 Journal articles and patents 189
10.3 Conferences 190
10.4 Data banks, expert systems and computerised corrosion libraries 190
Table of Contents 7
REFERENCES 191
APPENDICES 193
1. Risk ofbimetallic corrosion (BC) in different types of atmosphere 193
2. Hoover's alignment chart for determination ofthe saturation pH (pHs)
acccording tothe Langelier equation 194
3. Some physical methods used in corrosion investigation 195
4. A Selection ofHandbooks on Corrosion 196
5. ASelection ofjournals and abstract periodicals for corrosion information 198
6. Some regular international corrosion events 199
Index 201
1
Corrosion and its importance to
the community
The word corrosion comes from theLatin word 'corrodere', which means 'gnaw away'.
The rusting of iron and steel is the most well-known form of corrosion.
Similar processes occur in other metals and also in non-metallic materials, such as
plastics, concrete and ceramics. According tothe definition, theterm 'corrosion' stands
for a process. This takes place via a physicochemical reaction between the material
and itsenvironment and leads tochanges inthe properties ofthe material. The result is
acorrosion effect which isgenerally detrimental but can sometimes beuseful. Examples
of detrimental corrosion effects are corrosion attack on the actual material,
contamination of the environment with corrosion products and functional impairment
ofthe system, e.g. asteam power plant, inwhich both the material and the environment
form parts. The disintegration of scrap metal such as empty cans and abandoned cars
are examples of useful corrosion effects (Fig. 1), as is the deliberate use of corrosion
processes in, for example, the reaction between steel and phosphoric acid toproduce a
phosphated surface suitable forpainting. Generally, however, corrosion isadeleterious
process and causes agreat deal of destruction and inconvenience in our communities.
Some examples are as follows:
The operational reliability of structures can bejeopardised. This is the case in,
forexample, underground water mains, which can beput out ofaction by corrosion
(Fig. 2). Other examples occur in electronic equipment where important control
functions can be affected by corrosion, on offshore oil platforms which operate
under extremely corrosive conditions andinnuclear power stations where corrosion
damage can give rise to costly production breakdowns which in certain cases are
completely unacceptable from the safety viewpoint.
Natural resources arelost.Eventually corrosion leads toenergy losses, since energy
is consumed during the production of metals from their ores, and the corrosion
process returns the metal to the ore. Furthermore, corrosion products, which may
be widely distributed by water and wind cannot be used to reclaim metal.
The environment can be damaged. Underground oil tanks, which become
perforated as a result of corrosion, are an example where a threat is posed to
ground water (Fig. 3).
12 Basic Corrosion Technologyfor Scientists and Engineers
Fig. 1: Ascrapcarlefttobe'destroyed' bytheenvironment.
Corrosion and its importance tothe community 13
Fig.2: Corrosiondamagetomainswaterpipewhichcausedabout 10,000householdstobe
withoutwater.
Many attempts havebeen made toestimate thecoststothecommunity caused by
corrosion. These include the costswhich canariseintheform ofcorrosion protection
measures, throughreplacement ofcorrosion-damaged partsorthrough differenteffects
deriving from corrosion, such asshut-down ofproduction oraccidents which lead to
injuries ordamage toproperty. Several estimations have arrived attheconclusion that
the total annual corrosion costs inthe industrialised countries amount to about 4% of
the gross national product. Parts ofthese costs areunavoidable since itwould notbe
economically viable to carry out the necessary precautions to eliminate completely
corrosion damage. It is, however, certain that one could reduce losses considerably
solelybybetterexploitingtheknowledge wehavetodayand,accordingtooneestimate,
about 15% ofcorrosion costs areofthis type [1].
14 Basic Corrosion Technologyfor Scientists and Engineers
Fig.3: Pittinginanoiltankafter6yearsunderground (Bergsoe& Son).
Withregard totheimportance tothe community ofcorrosion itisvital thatevery
engineerduringhiseducationismadeawareoftheeffectsandimplications ofcorrosion
and that the knowledge available is stored in such away that it is easily retrievable
andready tobeused.
Technical advances continuously bring in their train, however, new corrosion
problems. Thus, onthe one hand, the corrosion behaviour ofnew materials needs to
beevaluated, while, ontheother,well-known materials maybeusedinnew situations
sothat new corrosion environments are created. For this reason, the current level of
knowledge isnot sufficient andfurther research anddevelopment arerequired inthe
area ofcorrosion, tocomplement technical developments atlarge.