Corrosion of metals and alloys - Vocabulary (ISO 8044:2020)

EN-ISO 8044 defines terms relating to corrosion that are widely used in modern science and technology. In addition, some definitions are supplemented with short explanations.

Korrosion von Metallen und Legierungen - Grundbegriffe (ISO 8044:2020)

Dieses Dokument definiert Korrosionsbegriffe, die in der modernen Wissenschaft und Technologie weit verbreitet benutzt werden. In Ergänzung dazu sind einige Definitionen mit kurzen Erklärungen versehen.
ANMERKUNG 1 In diesem Dokument werden die IUPAC-Empfehlungen für das Vorzeichen des Elektrodenpotentials beachtet. Der Begriff „Metall“ wird so verwendet, dass er Legierungen und andere metallene Werkstoffe einschließt.
ANMERKUNG 2 Für Begriffe und Definitionen im Zusammenhang mit der anorganischen Oberflächenbehandlung von Metallen gilt ISO 2080.

Corrosion des métaux et alliages - Vocabulaire (ISO 8044:2020)

Le présent document définit les termes relatifs à la corrosion qui sont largement employés dans les sciences et techniques modernes. Certaines définitions sont complétées par de brèves explications.
NOTE 1 Dans tout le document, on applique les conventions de l'IUPAC concernant le signe des potentiels d'électrode. Le terme «métal» est utilisé aussi pour désigner les alliages et autres matériaux métalliques.
NOTE 2 Les termes et définitions relatifs au traitement de surface des métaux avec des revêtements inorganiques sont donnés dans l'ISO 2080.

Korozija kovin in zlitin - Slovar (ISO 8044:2020)

General Information

Status
Published
Public Enquiry End Date
14-Apr-2019
Publication Date
06-Apr-2020
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
05-Mar-2020
Due Date
10-May-2020
Completion Date
07-Apr-2020

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SLOVENSKI STANDARD
SIST EN ISO 8044:2020
01-maj-2020
Nadomešča:
SIST EN ISO 8044:2015
Korozija kovin in zlitin - Slovar (ISO 8044:2020)
Corrosion of metals and alloys - Vocabulary (ISO 8044:2020)
Korrosion von Metallen und Legierungen - Grundbegriffe (ISO 8044:2020)
Corrosion des métaux et alliages - Vocabulaire (ISO 8044:2020)
Ta slovenski standard je istoveten z: EN ISO 8044:2020
ICS:
01.040.77 Metalurgija (Slovarji) Metallurgy (Vocabularies)
77.060 Korozija kovin Corrosion of metals
SIST EN ISO 8044:2020 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 8044:2020
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SIST EN ISO 8044:2020
EN ISO 8044
EUROPEAN STANDARD
NORME EUROPÉENNE
February 2020
EUROPÄISCHE NORM
ICS 01.040.77; 77.060 Supersedes EN ISO 8044:2015
English Version
Corrosion of metals and alloys - Vocabulary (ISO
8044:2020)

Corrosion des métaux et alliages - Vocabulaire (ISO Korrosion von Metallen und Legierungen -

8044:2020) Grundbegriffe (ISO 8044:2020)
This European Standard was approved by CEN on 27 January 2020.

CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this

European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references

concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN

member.

This European Standard exists in three official versions (English, French, German). A version in any other language made by

translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management

Centre has the same status as the official versions.

CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,

Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,

Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and

United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2020 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 8044:2020 E

worldwide for CEN national Members.
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SIST EN ISO 8044:2020
EN ISO 8044:2020 (E)
Contents Page

European foreword ....................................................................................................................................................... 3

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SIST EN ISO 8044:2020
EN ISO 8044:2020 (E)
European foreword

This document (EN ISO 8044:2020) has been prepared by Technical Committee ISO/TC 156 "Corrosion

of metals and alloys" in collaboration with Technical Committee CEN/TC 262 “Metallic and other

inorganic coatings, including for corrosion protection and corrosion testing of metals and alloys” the

secretariat of which is held by BSI.

This European Standard shall be given the status of a national standard, either by publication of an

identical text or by endorsement, at the latest by August 2020, and conflicting national standards shall

be withdrawn at the latest by August 2020.

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CEN shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN ISO 8044:2015.

According to the CEN-CENELEC Internal Regulations, the national standards organizations of the

following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,

Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,

Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of

North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the

United Kingdom.
Endorsement notice

The text of ISO 8044:2020 has been approved by CEN as EN ISO 8044:2020 without any modification.

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SIST EN ISO 8044:2020
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SIST EN ISO 8044:2020
INTERNATIONAL ISO
STANDARD 8044
Fifth edition
2020-02
Corrosion of metals and alloys —
Vocabulary
Corrosion des métaux et alliages — Vocabulaire
Reference number
ISO 8044:2020(E)
ISO 2020
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2020

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting

on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Fax: +41 22 749 09 47
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2020 – All rights reserved
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

Introduction ..................................................................................................................................................................................................................................v

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms related to corrosion in general ........................................................................................................................................... 1

4 Terms related to types of corrosion ................................................................................................................................................. 4

5 Terms related to corrosion protection .......................................................................................................................................... 9

6 Terms related to corrosion testing .................................................................................................................................................11

7 Terms related to electrochemical matters .............................................................................................................................12

7.1 The electrochemical cell ..............................................................................................................................................................12

7.2 Reaction rates .......................................................................................................................................................................................16

7.3 Passivation ...............................................................................................................................................................................................17

7.4 Electrochemical protection .......................................................................................................................................................19

7.5 Electrochemical corrosion tests ............................................................................................................................................20

Annex A (informative) Graphical representations of certain terms .................................................................................22

Bibliography .............................................................................................................................................................................................................................24

Index .................................................................................................................................................................................................................................................25

© ISO 2020 – All rights reserved iii
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/ directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www .iso .org/ patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO’s adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see www .iso .org/

iso/ foreword .html.

This document was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys, in

collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/

TC 262, Metallic and other inorganic coatings, including for corrosion protection and corrosion testing of

metals and alloys, in accordance with the Agreement on technical cooperation between ISO and CEN

(Vienna Agreement).

This fifth edition cancels and replaces the fourth edition (ISO 8044:2015), which has been technically

revised to include additional terms and definitions.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www .iso .org/ members .html.
iv © ISO 2020 – All rights reserved
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
Introduction

The definitions in this document have been drawn up with the objective of achieving a proper balance

between precision and simplicity. The main objective of this document is to provide definitions that

can be understood to have the same meaning by all concerned. Some corrosion terms in present use

have developed through common usage and are not always logical. It has not, therefore, been possible

to define certain terms in the form they are used in some countries. Because of the occasional conflicts

between tradition and logic, some definitions inevitably represent a compromise.

An example of this kind of conflict is the term “corrosion”. This has been used to mean the process,

results of the process and damage caused by the process. In this document, corrosion is understood

to mean the process. Any detectable result of corrosion in any part of a corrosion system is termed

“corrosion effect”. The term “corrosion damage” covers any impairment of the function of the technical

system of which the metal and the environment form a part. Consequently, the term “corrosion

protection” implies that the important thing is to avoid corrosion damage rather than to prevent

corrosion, which in many cases is impossible and sometimes not necessary.
© ISO 2020 – All rights reserved v
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SIST EN ISO 8044:2020
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SIST EN ISO 8044:2020
INTERNATIONAL STANDARD ISO 8044:2020(E)
Corrosion of metals and alloys — Vocabulary
1 Scope

This document defines terms relating to corrosion that are widely used in modern science and

technology. In addition, some definitions are supplemented with short explanations.

NOTE 1 Throughout the document, IUPAC rules for electrode potential signs are applied. The term “metal” is

also used to include alloys and other metallic materials.

NOTE 2 Terms and definitions related to the inorganic surface treatment of metals are given in ISO 2080.

2 Normative references
There are no normative references in this document.
3 Terms related to corrosion in general

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
3.1
corrosion

physicochemical interaction between a metallic material and its environment that results in changes in

the properties of the metal, and that may lead to significant impairment of the function of the metal, the

environment or the technical system, of which these form a part
Note 1 to entry: This interaction is often of an electrochemical nature.
3.2
corrosive agent

substance that will initiate or promote corrosion (3.1) when in contact with a given metal

3.3
corrosive environment
environment that contains one or more corrosive agents (3.2)
3.4
corrosion system

system consisting of one or more metals and those parts of the environment that influence corrosion (3.1)

Note 1 to entry: Parts of the environment may be, for example, coatings, surface layers or additional electrodes

(7.1.2).
3.5
corrosion effect
change in any part of the corrosion system (3.4) caused by corrosion (3.1)
3.6
corrosion damage

corrosion effect (3.5) that causes impairment of the function of the metal, the environment or the

technical system, of which these form a part
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
3.7
corrosion failure

corrosion damage (3.6) characterized by the total loss of function of the technical system

3.8
corrosion product
substance formed as a result of corrosion (3.1)
3.9
scale
solid layer of corrosion products (3.8) formed on a metal at high temperature

Note 1 to entry: The term “scale” is also used in some countries for deposits from supersaturated water.

3.10
rust
visible corrosion products (3.8) consisting mainly of hydrated iron oxides
3.11
corrosion depth

distance between a point on the surface of a metal affected by corrosion (3.1) and the original surface

of the metal
3.12
corrosion rate
corrosion effect (3.5) on a metal per unit time

Note 1 to entry: The unit used to express the corrosion rate depends on the technical system and on the type of

corrosion effect. Thus, corrosion rate is typically expressed as an increase in corrosion depth (3.11) per unit time,

or the mass of metal turned into corrosion products (3.8) per area of surface and per unit time, etc. The corrosion

effect may vary with time and may not be the same at all points of the corroding surface. Therefore, reports

of corrosion rates are typically accompanied by information on the type, time dependency and location of the

corrosion effect.
3.13
corrosion resistance

ability of a metal to maintain serviceability (3.16) in a given corrosion system (3.4)

3.14
corrosivity

ability of an environment to cause corrosion (3.1) of a metal in a given corrosion system (3.4)

3.15
corrosion likelihood

qualitative and/or quantitative expression of the expected corrosion effects (3.5) in a defined corrosion

system (3.4)
3.16
serviceability

ability of a corrosion system (3.4) to perform its specified functions without impairment

due to corrosion (3.1)
3.17
durability

ability of a corrosion system (3.4) to maintain serviceability (3.16) over a specified time

when the specified requirements for use and maintenance have been fulfilled
3.18
service life

time during which a corrosion system (3.4) meets the requirements for serviceability (3.16)

2 © ISO 2020 – All rights reserved
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
3.19
critical humidity

value of the relative humidity of an atmosphere above which there is a sharp increase in the corrosion

rate (3.12) of a given metal
3.20
corrosion attack

corrosion effect (3.5) that is detrimental but has not progressed to the point of impairment of the

function of the metal, the environment or the technical system, of which these form a part

3.21
pickling

removal of oxides or other compounds from a metal surface by chemical or electrochemical action

3.22
pitting resistance equivalent number
PREN

indication of the resistance of stainless steels and nickel-based alloys to pitting in the presence of

chloride-containing water
Note 1 to entry: An example formula for PREN is given by
PREN=+%,Cr 33[]()%,Mo ++05()%%WN16()

Note 2 to entry: In general, the higher the PREN the higher the resistance to pitting corrosion (4.15).

3.23
trap

micro structural site at which the residence time for a hydrogen atom is long compared to the residence

time in an interstitial lattice site
3.24
time of wetness

period when a metallic surface is covered by adsorptive and/or liquid films of electrolyte (7.1.1) to be

capable of causing atmospheric corrosion (4.4)
3.25
threshold stress

tensile stress above which stress corrosion cracks initiate and grow for

specified test conditions
3.26
threshold stress intensity factor for stress corrosion cracking
ISCC

stress intensity factor above which stress corrosion crack propagation is sustained

Note 1 to entry: The threshold stress intensity factor is a concept of linear elastic fracture mechanics (LEFM)

and is applicable when the plastic zone size is large compared with the microstructure, the crack is sufficiently

long, and a high constraint to plastic deformation prevails, i.e. under plane strain predominant conditions. For

growing stress corrosion cracks, LEFM is not necessarily applicable in all detail but is adopted as a pragmatic

tool that is commonly used.

Note 2 to entry: Stress corrosion cracks may initiate at a surface or a surface defect and grow in the “small crack”

regime at stress intensity factor levels below the apparent threshold stress intensity factor. Therefore, LEFM is

not applicable in the “small crack” regime.
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
4 Terms related to types of corrosion
4.1
electrochemical corrosion

corrosion (3.1) involving at least one anodic reaction (7.1.9) and one cathodic reaction (7.1.6)

4.2
chemical corrosion
corrosion (3.1) not involving an electrochemical reaction
4.3
gaseous corrosion

corrosion (3.1) with dry gas as the corrosive environment (3.3) and without any liquid phase on the

surface of the metal
4.4
atmospheric corrosion

corrosion (3.1) with the earth’s atmosphere at ambient temperature as the corrosive environment (3.3)

4.5
marine corrosion

corrosion (3.1) with sea water as the main agent of the corrosive environment (3.3)

Note 1 to entry: This definition includes both immersed and splash zone conditions.

4.6
underground corrosion
corrosion (3.1) of buried metals, soil being the corrosive environment (3.3)

Note 1 to entry: The term soil includes not only the naturally occurring material but also any other material, such

as ballast and backfill, used to cover a structure.
4.7
bacterial corrosion
microbiologically influenced corrosion (4.37) due to the action of bacteria
4.8
general corrosion

corrosion (3.1) proceeding over the whole surface of the metal exposed to the corrosive environment (3.3)

4.9
uniform corrosion

general corrosion (4.8) proceeding at almost the same rate over the whole surface

4.10
localized corrosion

corrosion (3.1) preferentially concentrated on discrete sites of the metal surface exposed to the corrosive

environment (3.3)

Note 1 to entry: Localized corrosion can result in, for example, pits, cracks or grooves.

4.11
galvanic corrosion
corrosion (3.1) due to the action of a corrosion cell (7.1.13)

Note 1 to entry: The term has often been restricted to the action of bimetallic corrosion cells, i.e. to bimetallic

corrosion (4.12).
4.12
bimetallic corrosion
DEPRECATED: contact corrosion

galvanic corrosion (4.11) where the electrodes (7.1.2) are formed by dissimilar metals

4 © ISO 2020 – All rights reserved
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
4.13
impressed current corrosion

electrochemical corrosion (4.1) due to the action of an external source of electric current

4.14
stray-current corrosion

impressed current corrosion (4.13) caused by current flowing through paths other than the intended

circuits
4.15
pitting corrosion

localized corrosion (4.10) resulting in pits, i.e. cavities extending from the surface into the metal

4.16
crevice corrosion

localized corrosion (4.10) associated with, and taking place in or immediately around, a narrow aperture

or clearance formed between the metal surface and another surface (metallic or non-metallic)

4.17
deposit corrosion

localized corrosion (4.10) associated with, and taking place under or immediately around, a deposit of

corrosion products (3.8) or other substance
4.18
water-line corrosion

corrosion (3.1) along, and as a consequence of the presence of, a gas/liquid boundary

4.19
selective corrosion
dealloying

corrosion (3.1) of an alloy whereby the components react in proportions that differ from their

proportions in the alloy
4.20
dezincification of brass

selective corrosion (4.19) of brass resulting in the preferential removal of zinc

4.21
graphitic corrosion

selective corrosion (4.19) of grey cast iron resulting in the partial removal of metallic constituents and

leaving graphite
4.22
intergranular corrosion
corrosion (3.1) in or adjacent to the grain boundaries of a metal
4.23
weld corrosion

corrosion (3.1) associated with the presence of a welded joint and taking place in the weld or its vicinity

4.24
knife-line corrosion

corrosion (3.1) resulting in a narrow slit in or adjacent to the filler/parent boundary of a welded or

brazed joint
4.25
erosion corrosion
process involving conjoint corrosion (3.1) and erosion

Note 1 to entry: Erosion corrosion can occur in, for example, pipes with high fluid flow velocity and pumps and

pipe lines carrying fluid containing abrasive particles in suspension or entrained in a gas flow.

© ISO 2020 – All rights reserved 5
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
4.26
cavitation corrosion
process involving conjoint corrosion (3.1) and cavitation

Note 1 to entry: Cavitation corrosion can occur, for example, in rotary pumps and on ships’ propellers.

4.27
fretting corrosion

process involving conjoint corrosion (3.1) and oscillatory slip between two vibrating surfaces in contact

Note 1 to entry: Fretting corrosion can occur, for example, at mechanical joints in vibrating structures.

4.28
wear corrosion

process involving conjoint corrosion (3.1) and friction between two sliding surfaces in contact

4.29
corrosion fatigue

process involving conjoint corrosion (3.1) and alternating straining of the metal, often leading to

cracking

Note 1 to entry: Corrosion fatigue can occur when a metal is subjected to cyclic straining in a corrosive

environment (3.3).
4.30
stress corrosion

process involving conjoint corrosion (3.1) and straining of the metal due to applied or residual stress

4.31
stress corrosion cracking
cracking due to stress corrosion (4.30)
4.32
hydrogen embrittlement

process resulting in a decrease of the toughness or ductility of a metal due to absorption of hydrogen

Note 1 to entry: Hydrogen embrittlement often accompanies hydrogen formation, for example, by corrosion (3.1)

or electrolysis, and can lead to cracking.
4.33
blistering

process resulting in a dome-shaped defect visible on the surface of an object and arising from localized

loss of cohesion below the surface

Note 1 to entry: For example, blistering can occur on coated metal due to loss of adhesion between coating and

substrate, caused by accumulation of products from localized corrosion (4.10). On uncoated metal, blistering can

occur due to excessive internal hydrogen pressure.
4.34
spalling
fragmentation and detachment of portions of the surface layer or scale (3.9)
4.35
tarnishing

dulling, staining or discoloration of a metal surface, due to the formation of a thin layer of corrosion

products (3.8)
4.36
aqueous corrosion

corrosion (3.1) with water or a water-based solution as the corrosive environment (3.3)

6 © ISO 2020 – All rights reserved
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
4.37
microbiologically influenced corrosion
MIC
corrosion (3.1) influenced by the action of microorganisms
Note 1 to entry: Compare with bacterial corrosion (4.7).
4.38
environmentally assisted cracking

cracking of a susceptible metal or alloy due to the conjoint action of an environment and mechanical stress

4.39
hydrogen-induced cracking
HIC

planar cracking that occurs in metals due to induced stresses when atomic hydrogen diffuses into the

metal and then combines to form molecular hydrogen at trap (3.23) sites
4.40
hydrogen stress cracking
HSC

cracking that results from the presence of hydrogen in a metal and tensile stress (residual or applied

or both)

Note 1 to entry: HSC describes cracking in metals that are not sensitive to sulfide stress corrosion cracking (SSCC)

(4.43) but which may be embrittled by hydrogen when galvanically coupled, as the cathode (7.1.3), to another

metal that is corroding actively as an anode (7.1.4). The term “galvanically induced HSC” has been used for this

mechanism of cracking.
4.41
irradiation-assisted stress corrosion cracking

intergranular cracking of austenitic stainless steels resulting from a reduction in the chromium

concentration in a very narrow band at the grain boundaries following exposure to high neutron

irradiation doses exceeding one displacement per atom, which causes the migration of point defects to

the grain boundaries
4.42
stepwise cracking
SWC

cracking that connects hydrogen-induced cracking (HIC) (4.39) on adjacent planes in a metal

Note 1 to entry: This term describes the crack appearance. The linking of hydrogen-induced cracks to produce

stepwise cracking is dependent upon local strain between the cracks and embrittlement of the surrounding steel

by dissolved hydrogen. HIC/SWC is usually associated with low-strength plate steels used in the production of

pipes and vessels.
4.43
sulfide stress corrosion cracking
SSCC

cracking of metal involving corrosion (3.1) and tensile stress, residual and/or applied, in the presence of

water and hydrogen sulfide

Note 1 to entry: SSCC is a form of hydrogen stress cracking (HSC) (4.40) and involves the embrittlement of

the metal by the atomic hydrogen that is produced by acid corrosion on the metal surface. Hydrogen uptake

is promoted in the presence of sulfides. The atomic hydrogen can diffuse into the metal, reduce ductility and

increase susceptibility to cracking. High strength metallic materials and hard weld zones are prone to SSCC.

© ISO 2020 – All rights reserved 7
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SIST EN ISO 8044:2020
ISO 8044:2020(E)
4.44
stress-oriented hydrogen-induced cracking
SOHIC

staggered small cracks formed approximately perpendicular to the principal stress (residual or applied)

resulting in a “ladder-like” crack array linking (sometimes small) pre-existing HIC (4.39) cracks

Note 1 to entry: The mode of cracking can be categorised as sulfide stress corrosion cracking (SSCC) (4.43) caused

by a combination of external stress and the local strain around hydrogen-induced cracks. SOHIC is related to SSCC

and HIC/stepwise cracking (SWC) (4.42). It has been observed in parent material of longitudinally welded pipe

and in the heat-affected zone (HAZ) of welds in pressure vessels. SOHIC is a relatively uncommon pheno

...

SLOVENSKI STANDARD
oSIST prEN ISO 8044:2019
01-april-2019
Korozija kovin in zlitin - Osnovni pojmi in definicije (ISO/DIS 8044:2019)
Corrosion of metals and alloys - Basic terms and definitions (ISO/DIS 8044:2019)
Korrosion von Metallen und Legierungen - Grundbegriffe (ISO/DIS 8044:2019)

Corrosion des métaux et alliages - Termes principaux et définitions (ISO/DIS 8044:2019)

Ta slovenski standard je istoveten z: prEN ISO 8044
ICS:
01.040.77 Metalurgija (Slovarji) Metallurgy (Vocabularies)
77.060 Korozija kovin Corrosion of metals
oSIST prEN ISO 8044:2019 en,fr,de

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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oSIST prEN ISO 8044:2019
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oSIST prEN ISO 8044:2019
DRAFT INTERNATIONAL STANDARD
ISO/DIS 8044
ISO/TC 156 Secretariat: SAC
Voting begins on: Voting terminates on:
2019-01-30 2019-04-24
Corrosion of metals and alloys — Basic terms and
definitions
Corrosion des métaux et alliages — Termes principaux et définitions
ICS: 77.060; 01.040.77
THIS DOCUMENT IS A DRAFT CIRCULATED
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Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national

standards bodies (ISO member bodies). The work of preparing International Standards is normally

carried out through ISO technical committees. Each member body interested in a subject for which a

technical committee has been established has the right to be represented on that committee.

International organizations, governmental and non-governmental, in liaison with ISO, also take part in

the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all

matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation on the meaning of ISO specific terms and expressions related to conformity

assessment, as well as information about ISO's adherence to the WTO principles in the Technical

Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information

The committee responsible for this document is ISO/TC 156, Corrosion of metals and alloys.

This fourth edition cancels and replaces the third edition (ISO 8044:1999), which has been revised to

include additional terms and definitions.
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Contents
Foreword 1
Introduction 3
1 Scope 4
2 General terms 4
3 Types of corrosion 7
4 Corrosion protection 14
5 Corrosion testing 16
6 Electrochemical terms 17
6.1 The electrochemical cell 17
6.2 Reaction rates 22
6.3 Passivation 24
6.4 Electrochemical protection 26
6.5 Electrochemical corrosion tests 27
Figure 1 — Current/Potential curves for a corroding electrode 29

Figure 2 — Anodic current density/potential curve showing active, passive and transpassive states 30

Bibliography 31
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Introduction

The definitions in this International Standard have been drawn up with the objective of achieving a

proper balance between precision and simplicity. The main objective of this International Standard is to

provide definitions that can be understood to have the same meaning by all concerned. Some corrosion

terms in present use have developed through common usage and are not always logical. It has not,

therefore, been possible to define certain terms in the form they are used in some countries. Because of

the occasional conflicts between tradition and logic some definitions inevitably represent a compromise.

An example of this kind of conflict is the term “corrosion”. This has been used to mean the process,

results of the process and damage caused by the process. In this International Standard corrosion is

understood to mean the process. Any detectable result of corrosion in any part of a corrosion system is

termed “corrosion effect”. The term “corrosion damage” covers any impairment of the function of the

technical system of which the metal and the environment form a part. Consequently the term “corrosion

protection” implies that the important thing is to avoid corrosion damage rather than to prevent

corrosion, which in many cases is impossible and sometimes not necessary.
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Corrosion of metals and alloys — Basic terms and definitions
1 Scope

This International Standard defines terms relating to corrosion that are widely used in modern

science and technology. In addition, some definitions are supplemented with short explanations.

NOTE 1 Throughout the document IUPAC rules for electrode potential signs are applied. The term “metal”

is also used to include alloys and other metallic materials.

NOTE 2 Terms and definitions related to inorganic surface treatment of metals are given in ISO 2080.

NOTE 3 See also the ISO online browsing platform (OBP): www.iso.org/obp/ui/
2 General terms
2.1
corrosion

physicochemical interaction between a metalic material and its environment that results in changes

in the properties of the metal, and which may lead to significant impairment of the function of the

metal, the environment, or the technical system, of which these form a part
Note 1 to entry: This interaction is often of an electrochemical nature.
2.2
corrosive agent

substance which will initiate or promote corrosion when in contact with a given metal”

2.3
corrosive environment
environment that contains one or more corrosive agents (2.2)
2.4
corrosion system

system consisting of one or more metals and those parts of the environment that influence corrosion

(2.1)

Note 1 to entry: Parts of the environment may be, for example, coatings, surface layers or additional electrodes

(6.1.2).
2.5
corrosion effect
change in any part of the corrosion system (2.4) caused by corrosion (2.1)
2.6
corrosion damage
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corrosion effect (2.5) that causes impairment of the function of the metal, the environment or the

technical system, of which these form a part
2.7
corrosion failure

corrosion damage (2.6) characterized by the total loss of function of the technical system

2.8
corrosion product
substance formed as a result of corrosion (2.1)
2.9
scale
solid layer of corrosion products (2.8)formed on a metal at high temperature

Note 1 to entry: The term “scale” is also used in some countries for deposits from supersaturated water.

2.10
rust
visible corrosion products (2.8) consisting mainly of hydrated iron oxides
2.11
corrosion depth

distance between a point on the surface of a metal affected by corrosion (2.1) and the original

surface of the metal
2.12
corrosion rate
corrosion effect (2.5) on a metal per time

Note 1 to entry: The unit used to express the corrosion rate depends on the technical system and on the type

of corrosion effect. Thus corrosion rate may be expressed as an increase in corrosion depth (2.11) per time, or

the mass of metal turned into corrosion products (2.8) per area of surface and per time, etc. The corrosion

effect may vary with time and may not be the same at all points of the corroding surface. Therefore, reports of

corrosion rates should be accompanied by information on the type, time dependency and location of the

corrosion effect.
2.13
corrosion resistance

ability of a metal to maintain serviceability (2.16) in a given corrosion system (2.4)

2.14
corrosivity

ability of an environment to cause corrosion (2.1) of a metal in a given corrosion system (2.4)

2.15
corrosion likelihood

qualitative and/or quantitative expression of the expected corrosion effects (2.5) in a defined

corrosion system (2.4)
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2.16
serviceability (with respect to corrosion)

ability of a corrosion system (2.4) to perform its specified functions without impairment due to

corrosion (2.1)
2.17
durability (with respect to corrosion)

ability of a corrosion system (2.4) to maintain serviceability (2.16) over a specified time when the

specified requirements for use and maintenance have been fulfilled
2.18
service life (with respect to corrosion)

time during which a corrosion system (2.4) meets the requirements for serviceability (2.16)

2.19
critical humidity

value of the relative humidity of an atmosphere above which there is a sharp increase in the

corrosion rate (2.12) of a given metal
2.20
corrosion attack

corrosion effect (2.5) that is detrimental but has not progressed to the point of impairment of the

function of the metal, the environment, or the technical system of which they form a part

2.21
pickling

removal of oxides or other compounds from a metal surface by chemical or electrochemical action

2.22
pitting resistance equivalent number
PREN

indication of the resistance of stainless steels and nickel-based alloys to pitting in the presence of

chloride-containing water
Note 1 to entry: An example formula for PREN is given by
PREN %Cr3,3%Mo 0,5 % W 16 %N .
     

Note 2 to entry: The higher the PREN, the higher is the resistance to pitting corrosion.

2.23
trap

micro structural site at which the residence time for a hydrogen atom is long compared to the

residence time in an interstitial lattice site
2.24
time of wetness
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period when a metallic surface is covered by adsorptive and/or liquid films of electrolyte to be

capable of causing atmospheric corrosion
2.25
threshold stress (for stress corrosion cracking)

tensile stress above which stress corrosion cracks initiate and grow, for the specified test conditions

2.26
threshold stress intensity factor for stress corrosion cracking
ISCC

stress intensity factor above which stress corrosion crack propagation is sustained

Note 1 to entry: The threshold stress intensity factor is a concept of linear elastic fracture mechanics (LEFM)

and is applicable when the plastic zone size is large compared with the microstructure, the crack is sufficiently

long, and a high constraint to plastic deformation prevails, i.e. under plane strain predominant conditions. For

growing stress corrosion cracks, LEFM is not necessarily applicable in all detail but is adopted as a pragmatic

tool that is commonly used.

Note 2 to entry: Stress corrosion cracks may initiate at a surface or a surface defect and grow in the “short

crack” regime at stress intensity factor levels below the apparent threshold stress intensity factor. Therefore,

LEFM is not applicable in the “short crack” regime.
3 Types of corrosion
3.1
electrochemical corrosion

corrosion (2.1) involving at least one anodic reaction (6.1.9) and one cathodic reaction (6.1.6)

3.2
chemical corrosion
corrosion (2.1) not involving electrochemical reaction
3.3
gaseous corrosion

corrosion (2.1) with dry gas as the only corrosive environment (2.3) and without any liquid phase on

the surface of the metal
3.4
atmospheric corrosion

corrosion (2.1) with the earth's atmosphere at ambient temperature as the corrosive environment

(2.3)
3.5
marine corrosion

corrosion (2.1) with sea water as the main agent of the corrosive environment (2.3)

Note 1 to entry: This definition includes both immersed and splash zone conditions.

3.6
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underground corrosion
corrosion (2.1) of buried metals, soil being the corrosive environment (2.3)

Note 1 to entry: The term soil includes not only the naturally occurring material but also any other material,

such as ballast and backfill, used to cover a structure.
3.7
bacterial corrosion
microbial corrosion (3.7) due to the action of bacteria
3.8
general corrosion

corrosion (2.1) proceeding over the whole surface of the metal exposed to the corrosive environment

(2.3)
3.9
uniform corrosion

general corrosion (3.9) proceeding at almost the same rate over the whole surface

3.10
localized corrosion

corrosion (2.1) preferentially concentrated on discrete sites of the metal surface exposed to the

corrosive environment (2.3)

Note 1 to entry: Localized corrosion can result in, for example, pits, cracks, or grooves.

3.11
galvanic corrosion
corrosion (2.1) due to the action of a corrosion cell (6.1.13)

Note 1 to entry: The term has often been restricted to the action of bimetallic corrosion cells, i.e. to bimetallic

corrosion (3.13).
3.12
bimetallic corrosion
DEPRECATED: contact corrosion

galvanic corrosion (3.12), where the electrodes (6.1.2) are formed by dissimilar metals

3.13
impressed current corrosion

electrochemical corrosion (3.1) due to the action of an external source of electric current

3.14
stray-current corrosion

impressed current corrosion (3.14) caused by current flowing through paths other than the intended

circuits
3.15
pitting corrosion
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localized corrosion (3.10) resulting in pits, i.e. cavities extending from the surface into the metal

3.16
crevice corrosion

localized corrosion (3.10) associated with, and taking place in, or immediately around, a narrow

aperture or clearance formed between the metal surface and another surface (metallic or non-

metallic)
3.17
deposit corrosion

localized corrosion (3.10) associated with, and taking place under, or immediately around, a deposit

of corrosion products (2.8) or other substance
3.18
water-line corrosion

corrosion (2.1) along, and as a consequence of the presence of, a gas/liquid boundary

3.19
selective corrosion

corrosion (2.1) of an alloy whereby the components react in proportions that differ from their

proportions in the alloy
3.20
dezincification of brass
selective corrosion (3.20) of brass resulting in preferential removal of zinc
3.21
graphitic corrosion

selective corrosion (3.20) of grey cast iron, resulting in partial removal of metallic constituents,

leaving graphite
3.22
intergranular corrosion
corrosion (2.1) in or adjacent to the grain boundaries of a metal
3.23
weld corrosion

corrosion (2.1) associated with the presence of a welded joint and taking place in the weld or its

vicinity
3.24
knife-line corrosion

corrosion (2.1) resulting in a narrow slit in or adjacent to the filler/parent boundary of a welded or

brazed joint
3.25
erosion corrosion
process involving conjoint corrosion (2.1) and erosion
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Note 1 to entry: Erosion corrosion can occur in, for example, pipes with high fluid flow velocity and pumps

and pipe lines carrying fluid containing abrasive particles in suspension or entrained in a gas flow.

3.26
cavitation corrosion
process involving conjoint corrosion (2.1) and cavitation

Note 1 to entry: Cavitation corrosion can occur, for example, in rotary pumps and on ships' propellers.

3.27
fretting corrosion

process involving conjoint corrosion (2.1) and oscillatory slip between two vibrating surfaces in

contact

Note 1 to entry: Fretting corrosion can occur, for example, at mechanical joints in vibrating structures.

3.28
wear corrosion

process involving conjoint corrosion (2.1) and friction between two sliding surfaces in contact

3.29
corrosion fatigue

process involving conjoint corrosion (2.1) and alternating straining of the metal, often leading to

cracking

Note 1 to entry: Corrosion fatigue can occur when a metal is subjected to cyclic straining in a corrosive

environment (2.3).
3.30
stress corrosion

process involving conjoint corrosion (2.1) and straining of the metal due to applied or residual

stress
3.31
stress corrosion cracking
cracking due to stress corrosion (3.32)
3.32
hydrogen embrittlement

process resulting in a decrease of the toughness or ductility of a metal due to absorption of

hydrogen

Note 1 to entry: Hydrogen embrittlement often accompanies hydrogen formation, for example by corrosion

(2.1) or electrolysis, and can lead to cracking.
3.33
blistering

process resulting in dome-shaped defect visible on the surface of an object and arising from

localized loss of cohesion below the surface
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Note 1 to entry: For example, blistering can occur on coated metal due to loss of adhesion between coating

and substrate, caused by accumulation of products from localized corrosion (3.10). On uncoated metal,

blistering can occur due to excessive internal hydrogen pressure.
3.34
spalling
fragmentation and detachment of portions of the surface layer or scale
3.35
tarnishing

dulling, staining or discoloration of a metal surface, due to the formation of a thin layer of corrosion

products (2.8)
3.36
aqueous corrosion
corrosion with water or a water-based solution as the corrosive environment
3.37
microbiologically influenced corrosion
MIC
corrosion influenced by the action of microorganisms
Note 1 to entry: Compare with microbial corrosion (3.7).
3.38
dealloying
see selective corrosion (3.20)
3.39
environmentally assisted cracking

cracking of a susceptible metal or alloy due to the conjoint action of an environment and mechanical

stress
3.40
hydrogen induced cracking
HIC

planar cracking that occurs in metals due to induced stresses when atomic hydrogen diffuses into

the metal and then combines to form molecular hydrogen at trap sites
3.41
hydrogen stress cracking
HSC

cracking that results from the presence of hydrogen in a metal and tensile stress (residual or

applied or both)

Note 1 to entry: HSC describes cracking in metals that are not sensitive to sulphide stress corrosion cracking

(SSCC) (3.46) but which may be embrittled by hydrogen when galvanically coupled, as the cathode, to another

metal that is corroding actively as an anode. The term “galvanically induced HSC” has been used for this

mechanism of cracking.
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3.42
irradiation assisted stress corrosion cracking

intergranular cracking of austenitic stainless steels resulting from a reduction in the chromium

concentration in a very narrow band at the grain boundaries following exposure to high neutron

irradiation doses exceeding one displacement per atom (which causes the migration of point defects

to the grain boundaries)
3.43
stepwise cracking
SWC

cracking that connects hydrogen induced cracks (HICs) on adjacent planes in a metal

Note 1 to entry: This term describes the crack appearance. The linking of hydrogen induced cracks to produce

stepwise cracking is dependent upon local strain between the cracks and embrittlement of the surrounding

steel by dissolved hydrogen. HIC/SWC is usually associated with low-strength plate steels used in the

production of pipes and vessels.
3.44
sulfide stress corrosion cracking
SSCC

cracking of metal involving corrosion and tensile stress (residual and/or applied) in the presence of

water and hydrogen sulfide

Note 1 to entry: SSCC is a form of hydrogen stress cracking (HSC) and involves embrittlement of the metal by

atomic hydrogen that is produced by acid corrosion on the metal surface. Hydrogen uptake is promoted in the

presence of sulfides. The atomic hydrogen can diffuse into the metal, reduce ductility and increase

susceptibility to cracking. High strength metallic materials and hard weld zones are prone to SSCC.

3.45
stress oriented hydrogen induced cracking
SOHIC

staggered small cracks formed approximately perpendicular to the principal stress (residual or

applied) resulting in a “ladder-like” crack array linking (sometimes small) pre-existing HIC cracks

Note 1 to entry: The mode of cracking can be categorised as SSCC caused by a combination of external stress

and the local strain around hydrogen induced cracks. SOHIC is related to SSCC and HIC/SWC. It has been

observed in parent material of longitudinally welded pipe and in the heat affected zone of welds in pressure

vessels. SOHIC is a relatively uncommon phenomenon usually associated with low-strength ferritic pipe and

pressure vessel steels.
Note 2 to entry: cf. hydrogen embrittlement (3.34).

[SOURCE: ISO 15156-1:2009, 3.22; modified — In Note 1, SSC has been replaced with SSCC and

Note 2 has been added]
3.46
exfoliation corrosion

stratified form of subsurface stress corrosion of susceptible primary wrought alloy mill products

materials having a highly directional grain structure, accompanied by detachment of separate layers

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from the body of the material, formation of cracks and finally usually complete layer-by-layer

disintegration of metal

Note 1 to entry: Exfoliation generally proceeds along grain boundaries, but with certain alloys and tempering

it may develop along transgranular paths or a mixed intergranular/transgranular path.

Note 2 to entry: Layer corrosion (3.26) can be developed on the first stage.
3.47
filiform corrosion

type of corrosion proceeding under coating materials on metals in the form of threads, generally

starting from bare edges or from local damage to the coating

Note 1 to entry: Usually the threads are irregular in length and direction of growth, but they may also be

nearly parallel and of approximately equal length. It should be noted that filiform corrosion can occur under

different protective coatings.
3.48
tribo-corrosion

any form of corrosion that involves constant removal of the passive layer due to fluid or particles

impact on the corroding surface or the friction between the corroding surface and another surface

Note 1 to entry: Tribo-corrosion includes but is not restricted to: wear corrosion (3.30), fretting corrosion

(3.29) and erosion corrosion (3.27).

Note 2 to entry: This process may result in an increase in friction of bearing surfaces in addition to causing

material loss.
3.49
impingement attack

form of erosion corrosion in aqueous liquids under high velocity or turbulent flow conditions

associated on the metal surface causing repetitive disruption of protective films leading to

accelerated localised corrosion
3.50
high temperature corrosion

corrosion by gases or deposits or both gases and deposits occurring at elevated temperatures under

conditions where aqueous electrolytes no longer exist

Note 1 to entry: High temperature corrosion can become significant at temperatures above 170 °C depending

on material and environment.
3.51
hot corrosion

corrosion by gases or deposits or both gases and deposits forming a liquid phase during a high

temperature corrosion (3.52) reaction

Note 1 to entry: Hot corrosion is a sub-term of high temperature corrosion (3.52).

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Note 2 to entry: The most common liquid phases in which hot corrosion occurs are metal sulfates, metal

vanadates and metal chlorides.
3.52
sulfidation

reaction of a metal or alloy with a sulfur-containing species to produce metal sulfides on or beneath

the surface of the metal or alloy
3.53
metal dusting

carburization of metallic materials in process gases containing carbon oxides and hydrocarbons and

with extremely low oxygen partial pressures leading to disintegration of the metal into dust of

graphite, metal or carbides, or combinations

Note 1 to entry: The temperature range for metal dusting lies between 400 °C and 900 °C. For the mechanism

to happen, a carbon activity higher than 1 in the process gas is required.
3.54
rebar corrosion
corrosion of reinforcement bars in concrete
4 Corrosion protection
4.1
corrosion protection

modification of a corrosion system (2.4) so that corrosion damage (2.6) is reduced

4.2
degree of protection

(percentage) reduction in corrosion damage (2.6) achieved by corrosion protection (4.1)

Note 1 to entry: All types of corrosion (2.1) present have to be considered.
4.3
temporary protection
corrosion protection (4.1) intended to last for a limited time only

Note 1 to entry: Temporary protection is used, for example, during storage and transportation of metal

products or during shut-down of equipment.
4.4
protective layer
layer of a substance on a metal surface that decreases the corrosion rate (2.12)

Note 1 to entry: Such layers may be applied or arise spontaneously, for example by corrosion (2.1).

4.5
protective coating

layer(s) of material applied to a metal surface to provide corrosion protection (4.1)

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4.6
corrosion inhibitor

chemical substance that when present in the corrosion system (2.4) at a suitable concentration

decreases the corrosion rate (2.12), without significantly changing the concentration of any

corrosive agent (2.2)

Note 1 to entry: A corrosion inhibitor is generally effective in a small concentration.

4.7
volatile corrosion inhibitor
corrosion inhibitor (4.6) that can reach the metal surface in the form of vapour
4.8
de-aeration
removal of air from environment

Note 1 to entry: If only oxygen is removed the term “de-oxygenation” is more appropriate.

4.9
protective atmosphere

artificial atmosphere the corrosivity (2.14) of which has been reduced by the removal or exclusion of

corrosive agents (2.2) or by the addition of corrosion inhibitors (4.6)
4.10
critical potential
...

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