ISO 8044:2015
(Main)Corrosion of metals and alloys — Basic terms and definitions
Corrosion of metals and alloys — Basic terms and definitions
ISO 8044:2015 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/
Corrosion des métaux et alliages — Termes principaux et définitions
ISO 8044:2015 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. NOTE 3 Voir aussi la plateforme de consultation en ligne (OBP): www.iso.org/obp/ui/
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 8044
NORME
Fourth edition
Quatrième édition
INTERNATIONALE 2015-09-01
Corrosion of metals and alloys — Basic
terms and definitions
Corrosion des métaux et alliages —
Termes principaux et définitions
Korrosion von Metallen und
Legierungen — Grundbegriffe
Reference number
Numéro de référence
ISO 8044:2015(E/F)
©
ISO 2015
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ISO 8044:2015(E/F)
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ISO 8044:2015(E/F)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 General terms . 1
3 Types of corrosion . 3
4 Corrosion protection . 9
5 Corrosion testing .11
6 Electrochemical terms .12
6.1 The electrochemical cell .12
6.2 Reaction rates .16
6.3 Passivation .18
6.4 Electrochemical protection .19
6.5 Electrochemical corrosion tests .20
Bibliography .23
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ISO 8044:2015(E/F)
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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ISO 8044:2015(E/F)
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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INTERNATIONAL STANDARD ISO 8044:2015(E/F)
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 metal 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
corrodent
substance which when in contact with a given metal will cause corrosion (2.1)
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
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
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ISO 8044:2015(E/F)
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)
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
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ISO 8044:2015(E/F)
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: A widely accepted formula for PREN is given by
PREN =+%,Cr 33 %,Mo +05 %%WN+16 .
() () ()
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
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
K
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
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ISO 8044:2015(E/F)
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
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
microbial corrosion
corrosion (2.1) associated with the action of micro-organisms present in the corrosion system (2.4)
3.8
bacterial corrosion
microbial corrosion (3.7) due to the action of bacteria
3.9
general corrosion
corrosion (2.1) proceeding over the whole surface of the metal exposed to the corrosive environment
(2.3)
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
uniform corrosion
general corrosion (3.9) proceeding at almost the same rate over the whole surface
3.12
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).
3.13
bimetallic corrosion
DEPRECATED: contact corrosion
galvanic corrosion (3.12), where the electrodes (6.1.2) are formed by dissimilar metals
3.14
impressed current corrosion
electrochemical corrosion (3.1) due to the action of an external source of electric current
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ISO 8044:2015(E/F)
3.15
stray-current corrosion
impressed current corrosion (3.14) caused by current flowing through paths other than the intended
circuits
3.16
pitting corrosion
localized corrosion (3.10) resulting in pits, i.e. cavities extending from the surface into the metal
3.17
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)
3.18
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
3.19
water-line corrosion
corrosion (2.1) along, and as a consequence of the presence of, a gas/liquid boundary
3.20
selective corrosion
corrosion (2.1) of an alloy whereby the components react in proportions that differ from their proportions
in the alloy
3.21
dezincification of brass
selective corrosion (3.20) of brass resulting in preferential removal of zinc
3.22
graphitic corrosion
selective corrosion (3.20) of grey cast iron, resulting in partial removal of metallic constituents, leaving
graphite
3.23
intergranular corrosion
corrosion (2.1) in or adjacent to the grain boundaries of a metal
3.24
weld corrosion
corrosion (2.1) associated with the presence of a welded joint and taking place in the weld or its vicinity
3.25
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
3.26
layer corrosion
corrosion (2.1) of internal layers of wrought metal, occasionally resulting in exfoliation, i.e. detachment
of unattacked layers
Note 1 to entry: Exfoliation is generally oriented in the direction of rolling, extrusion or principal deformation.
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ISO 8044:2015(E/F)
3.27
erosion corrosion
process involving conjoint corrosion (2.1) 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.
3.28
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.
3.29
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.
3.30
wear corrosion
process involving conjoint corrosion (2.1) and friction between two sliding surfaces in contact
3.31
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).
3.32
stress corrosion
process involving conjoint corrosion (2.1) and straining of the metal due to applied or residual stress
3.33
stress corrosion cracking
cracking due to stress corrosion (3.32)
3.34
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.
3.35
blistering
process resulting in 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 (3.10). On uncoated metal, blistering can
occur due to excessive internal hydrogen pressure.
3.36
spalling
fragmentation and detachment of portions of the surface layer or scale
3.37
tarnishing
dulling, staining or discoloration of a metal surface, due to the formation of a thin layer of corrosionproducts
(2.8)
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ISO 8044:2015(E/F)
3.38
aqueous corrosion
corrosion with water or a water-based solution as the corrosive environment
3.39
microbiologically influenced corrosion
MIC
corrosion influenced by the action of microorganisms
Note 1 to entry: Compare with microbial corrosion (3.7).
3.40
dealloying
see selective corrosion (3.20)
3.41
environmentally assisted cracking
cracking of a susceptible metal or alloy due to the conjoint action of an environment and mechanical
stress
3.42
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
3.43
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.
3.44
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)
3.45
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.
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ISO 8044:2015(E/F)
3.46
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.
3.47
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]
3.48
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 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.
3.49
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.
3.50
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.
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ISO 8044:2015(E/F)
3.51
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
3.52
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.
3.53
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).
Note 2 to entry: The most common liquid phases in which hot corrosion occurs are metal sulfates, metal vanadates
and metal chlorides.
3.54
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
3.55
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.
3.56
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.
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ISO 8044:2015(E/F)
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)
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-oxygenatio
...
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