SIST EN 12923-1:2007
(Main)Advanced technical ceramics - Monolithic ceramics - Part 1: General practice for undertaking corrosion tests
Advanced technical ceramics - Monolithic ceramics - Part 1: General practice for undertaking corrosion tests
This part of EN 12923 specifies guidelines to be employed when undertaking corrosion tests on advanced technical ceramics. The mechanisms of chemical attack on advanced ceramics are widely varied and depend on the chemical and phase composition and the phase morphology of the material, as well as the corrosive conditions imposed. For any particular engineering application it is usually necessary to model expected conditions of use in order to obtain quantitative data on the ability to withstand the proposed end-use conditions.
This European Standard is not restricted to specific material types, nor does it prescribe particular test conditions or a test duration. The actual testing requirements might be very specific, for example, in order to investigate the suitability of a range of materials for a given application in which certain specified conditions occur. This European Standard provides recommended methods for undertaking the assessment of the effect of corrosion and provides guidance on practical issues related to undertaking the tests.
Hochleistungskeramik - Monolithische Keramik - Teil 1: Allgemeines zur Durchführung von Korrosionsprüfungen
Céramiques techniques avancées - Céramiques monolithiques - Partie 1: Pratique générale destinée aux essais de corrosion
La présente partie de l’EN 12923 spécifie des lignes directrices à employer lors de la réalisation d’essais de corrosion sur les céramiques techniques avancées. Les mécanismes d’attaque chimique des céramiques avancées sont extrêmement variés et dépendent de la composition chimique et de la composition de la phase, de la morphologie de la phase du matériau, ainsi que des conditions de corrosion imposées. Dans le cas d’une application d’ingénierie particulière, il est généralement nécessaire de modéliser les conditions d’utilisation escomptées, afin d’obtenir des données quantitatives sur l’aptitude à résister aux conditions prévues lors de l’utilisation finale.
La présente Norme européenne ne se limite pas à des types de matériaux spécifiques et ne prescrit ni conditions d’essai particulières, ni durée d’essai. Les exigences relatives aux essais réels peuvent être très spécifiques, afin de rechercher, par exemple, l’adéquation d’une gamme de matériaux à une application donnée pour laquelle certaines conditions sont spécifiées. La présente Norme européenne indique les méthodes recommandées pour évaluer les effets de la corrosion et constitue un guide des opérations pratiques liées à la réalisation des essais.
Sodobna tehnična keramika - Monolitna keramika – 1. del: Splošni postopki za izvajanje korozijskih preskusov
General Information
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Advanced technical ceramics - Monolithic ceramics - Part 1: General practice for undertaking corrosion testsCéramiques techniques avancées - Céramiques monolithiques - Partie 1: Pratique générale destinée aux essais de corrosionHochleistungskeramik - Monolithische Keramik - Teil 1: Allgemeines zur Durchführung von KorrosionsprüfungenTa slovenski standard je istoveten z:EN 12923-1:2006SIST EN 12923-1:2007en81.060.30Sodobna keramikaAdvanced ceramicsICS:SIST ENV 12923-1:20001DGRPHãþDSLOVENSKI
STANDARDSIST EN 12923-1:200701-maj-2007
EUROPEAN STANDARDNORME EUROPÉENNEEUROPÄISCHE NORMEN 12923-1December 2006ICS 81.060.99Supersedes ENV 12923-1:1997
English VersionAdvanced technical ceramics - Monolithic ceramics - Part 1:General practice for undertaking corrosion testsCéramiques techniques avancées - Céramiquesmonolithiques - Partie 1: Pratique générale destinée auxessais de corrosionHochleistungskeramik - Monolithische Keramik - Teil 1:Allgemeines zur Durchführung von KorrosionsprüfungenThis European Standard was approved by CEN on 25 November 2006.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this EuropeanStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the Central Secretariat or to any CEN member.This European Standard exists in three official versions (English, French, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the officialversions.CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania,Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMITÉ EUROPÉEN DE NORMALISATIONEUROPÄISCHES KOMITEE FÜR NORMUNGManagement Centre: rue de Stassart, 36
B-1050 Brussels© 2006 CENAll rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN 12923-1:2006: E
EN 12923-1:2006 (E) 2 Contents Page Foreword.4 1 Scope.5 2 Normative references.5 3 Terms and definitions.6 4 Significance and use.6 5 Assessment of corrosive attack.7 5.1 Introduction.7 5.2 Method A: Depth of penetration.7 5.3 Method B: Mass change.8 5.4 Method C: Change of test piece size.9 5.5 Method D: Strength change.9 5.6 Method E: Change in surface roughness.9 5.7 Method F: Change in hardness.9 6 Apparatus for laboratory corrosion testing.10 6.1 Container for corroding medium.10 6.2 Heating device.10 6.3 Thermocouple.10 6.4 Chemical balance.10 6.5 Oven.10 6.6 Dye penetrant equipment.10 6.7 Travelling microscope or optical microscope.11 6.8 Micrometer.11 6.9 Vernier callipers.11 6.10 Surface roughness measuring equipment.11 6.11 Flexural strength test facility.11 6.12 Hardness measurement equipment.11 7 Test pieces.11 7.1 General requirements.11 7.2 Specific requirements.11 7.3 Number of test pieces.12 8 Test procedure.12 8.1 Safety considerations.12 8.2 Corrosion test.12 8.3 Procedure.12 9 Expression of results.14 9.1 Calculation of mass change (Method B).14 9.2 Change of component or test piece size (Method C).14 9.3 Calculation of flexural strength (Method D).15 10 Test report.15 Annex A (informative)
Appropriate container and specimen holder materials for corrosion testing.17 A.1 Mineral acids, excluding hydrofluoric acid.17 A.2 Hydrofluoric acid (HF).17 A.3 Aqueous-based alkaline solutions.17 A.4 Molten metal alloys.17 A.5 Molten slags.18
EN 12923-1:2006 (E) 3 A.6 Corrosive gases.18 Bibliography.19
EN 12923-1:2006 (E) 4 Foreword This document (EN 12923-1:2006) has been prepared by Technical Committee CEN/TC 184 “Advanced technical ceramics”, 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 June 2007, and conflicting national standards shall be withdrawn at the latest by June 2007. This document supersedes ENV 12923-1:1997. EN 12923 Advanced technical ceramics — Monolithic ceramics consists of two parts:
Part 1: General practice for undertaking corrosion tests
Part 2: Oxidation test At the time of publication of this edition of Part 1, Part 2 was a European Prestandard. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.
EN 12923-1:2006 (E) 5 1 Scope This part of EN 12923 specifies guidelines to be employed when undertaking corrosion tests on advanced technical ceramics. The mechanisms of chemical attack on advanced ceramics are widely varied and depend on the chemical and phase composition and the phase morphology of the material, as well as the corrosive conditions imposed. For any particular engineering application it is usually necessary to model expected conditions of use in order to obtain quantitative data on the ability to withstand the proposed end-use conditions. This European Standard is not restricted to specific material types, nor does it prescribe particular test conditions or a test duration. The actual testing requirements might be very specific, for example, in order to investigate the suitability of a range of materials for a given application in which certain specified conditions occur. This European Standard provides recommended methods for undertaking the assessment of the effect of corrosion and provides guidance on practical issues related to undertaking the tests. 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. EN 623-1, Advanced technical ceramics — Monolithic ceramics — General and textural properties — Part 1: Determination of the presence of defects by dye penetration EN 623-4, Advanced technical ceramics — Monolithic ceramics — General and textural properties — Part 4: Determination of surface roughness EN 843-1, Advanced technical ceramics — Mechanical properties of monolithic ceramics at room temperature — Part 1: Determination of flexural strength EN 843-4, Advanced technical ceramics — Mechanical properties monolithic ceramics at room temperature — Part 4: Vickers, Knoop and Rockwell superficial hardness ENV 1006, Advanced technical ceramics — Monolithic ceramics — Guidance on the selection of test pieces for the evaluation of properties EN 60584-1, Thermocouples — Part 1: Reference tables EN 60584-2, Thermocouples — Part 2: Tolerances EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories (ISO/IEC 17025:2005) ISO 3611, Micrometer callipers for external measurement ISO 6906, Vernier callipers reading to 0,02 mm
EN 12923-1:2006 (E) 6 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 corrosion process of degradation induced by chemical attack by a surrounding medium on a ceramic body 3.2 oxidation process of reaction of a ceramic material with oxygen in the surrounding atmosphere, including any internal reactions as a result of the presence of open porosity or of diffusion of ions to or from the ceramic surface 4 Significance and use Advanced technical ceramic materials are widely regarded as being generally resistant to corrosion, and many types find applications in highly corrosive conditions where other materials are not viable. However, this is not always the case, and the selection of the most appropriate material requires some form of assessment to provide assurance that it has adequate resistance to the conditions to which it is to be exposed. The rate of chemical attack is determined by: i) the chemical nature, phase composition, phase distribution and degree of continuous porosity in the material; ii) the temperature, pressure, composition, concentration and flow rate of the corroding medium and whether these are constant or vary with time; iii) the mechanical forces applied to the material in terms of internal stress condition and the degree of surface abrasion or wear due to contact with other surfaces, the presence of abrasive particles or the dissolving effect of the corroding medium itself; iv) the period for which the test is performed, because it cannot be assumed that the rate of attack is constant with time. Adjusting test conditions to accelerate the corrosion process and extrapolating corrosion rates to times longer than that of the test should not be done. These factors need to be carefully selected, clearly specified and reported in any corrosion test. The undertaking of corrosion tests is normally for two principal purposes: a. to simulate performance in an application, which will require careful consideration of all factors pertaining to the conditions under which corrosion is occurring, and which will require these to be modelled in the test environment; b. to provide a comparative measure of performance of a range of materials under defined corrosion conditions. This European Standard provides a basis for undertaking corrosion tests and details the criteria which might be considered for determining whether attack has taken place and has significant consequences for subsequent use of a material. Since corrosion is dependent on a wide range of parameters, this European Standard does not prescribe particular environments or durations of attack, but provides guidance on the key factors that need to be considered or specified in undertaking tests and gives a general framework for conducting tests in a meaningful manner.
EN 12923-1:2006 (E) 7 5 Assessment of corrosive attack 5.1 Introduction Chemical attack is manifest in a number of ways: a. change of dry mass; b. change of section thickness; c. change of colour; d. penetration of corrodent into the material rendering the surface open porous; e. development of surface skins of altered composition; f. development of a surface skin of reaction product; g. change of surface finish; h. change in strength; i. change of hardness or wear resistance. Furthermore, attack might not be linear with time, notably if the diffusion path for corroding species increases with increasing corrosion. Table 1 summarizes the areas of validity of using these criteria for various types of corrosive attack. These criteria apply to passive conditions of corrosion, i.e. not when the component is under an externally applied stress. NOTE 1 Other situations might exist in which it is desirable to record changes in other properties, for example, thermal conductivity and thermal shock resistance, either whilst immersed in the corroding medium, or after extraction from it. Such methods are not specifically included in this European Standard and might require special equipment not covered by this European Standard. Change of colour might be subjective. NOTE 2 This European Standard does not lay down any recommended methods for determining the quantity of test piece species dissolved in a corrodent (Method G). Reference should be made to standard analytical practices. Care should be taken in selection of the container material, corrosion of which may influence the results of such an analysis. 5.2 Method A: Depth of penetration 5.2.1 For materials subjected to corrodents which result in grain boundary attack and penetration of the corrodent, the depth of penetration might be strongly influenced by the microstructural nature of the original test piece surface. Some as-fired surfaces might have better resistance to penetration than bulk microstructures exposed by machining test pieces. When possible, testing should avoid as-fired surfaces unless the testing is specifically to evaluate the performance of such surfaces. 5.2.2 The depth of penetration might be variable if the microstructure is inhomogeneous. The greatest depth of penetration is to be recorded. 5.2.3 In materials with substantial pre-existing closed porosity, it might be difficult to determine the true depth of penetration if there is no major change in the appearance of the microstructure. Reliance should be placed on the use of penetrant dyes in accordance with EN 623-1.
EN 12923-1:2006 (E) 8 Table 1 — Appropriateness of methods of assessing corrosive attack Assessment method Aqueous based corrosion Corrosion by melts Corrosion by gases and vapours A. Penetration Appropriate Might be
Appropriate in some
appropriate cases
B. Change of mass Appropriate, but Inappropriate Appropriate if non-
sometimes inadequate
slagging
C. Change of cross- Not always appropriate Appropriate Appropriate section when change is small
D. Change of strength Appropriate Might be
Appropriate if non-
appropriate if adherent
slagging; might be
material is removed appropriate if adherent
material is removed
E. Change of surface Appropriate for slight Usually inappropriate Usually inappropriate roughness corrosion
F. Change of hardness Appropriate Usually inappropriate Might be
appropriate if
non-slagging G. Change of Appropriate Usually inappropriate Appropriate corrodent composition
5.3 Method B: Mass change 5.3.1 Accurate determination of change in dry mass might not properly reflect the extent of attack as a result of either the adherence of solid surface deposits or the retention of corrosion products within porosity generated by corrodent penetration. A change in mass therefore indicates that some attack might have occurred, but other criteria need to be employed to quantify its overall effect on performance. 5.3.2 Assuming that the process of mass gain or mass loss is attributable to the test piece behaviour, accurate determination of change in dry mass relies on being able to minimize contact between the test piece and the apparatus in which it is housed for the duration of the corrosion test. If strong reaction occurs between the test piece surface and its support, a significant error in registered mass change might result. NOTE 1 It might be necessary to perform some preliminary tests to ensure that the supporting material is sufficiently non-reactive with the test material before conducting the required tests. In some atmospheres, for example in low oxygen content atmospheres at high temperatures, the evolution of volatile species from one test piece can interact with or contaminate adjacent test pieces. Cases of this type necessitate separately exposing each test piece to the corroding medium. NOTE 2 For the particular case of high temperature oxidation tests, further information is given in
ENV 12923-2 [1]. 5.3.3 Free circulation of corrodent around the test piece is required. If this is for any reason significantly reduced by the geometrical arrangement of test pieces and supporting apparatus, rates of corrosion might be reduced as the corroding species become consumed. A very high velocity of
EN 12923-1:2006 (E) 9 corrodent can change the mechanism of corrosion from that expected under low flow rate and therefore should be avoided unless the high flow rate is a specific requirement of the test. 5.3.4
...
SLOVENSKI oSIST prEN 12923-1:2005
PREDSTANDARD
februar 2005
Sodobna tehnična keramika - Monolitna keramika – 1. del: Splošni postopki za
izvajanje korozijskih preskusov
Advanced technical ceramics - Monolithic ceramics - Part 1: General practice for
undertaking corrosion tests
ICS 81.060.30 Referenčna številka
oSIST prEN 12923-1:2005(en)
© Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno
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EUROPEAN STANDARD
DRAFT
prEN 12923-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2004
ICS Will supersede ENV 12923-1:1997
English version
Advanced technical ceramics - Monolithic ceramics - Part 1:
General practice for undertaking corrosion tests
Céramiques techniques avancées - Céramiques Hochleistungskeramik - Monolithische Keramik - Teil 1:
monolithiques - Partie 1 : Pratique générale destinée aux Allgemeines zur Durchführung von Korrosionsprüfungen
essais de corrosion
This draft European Standard is submitted to CEN members for enquiry. It has been drawn up by the Technical Committee CEN/TC 184.
If this draft becomes a European Standard, 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.
This draft European Standard was established by CEN 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 Management Centre has the same
status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia,
Slovenia, Spain, Sweden, Switzerland and United Kingdom.
Warning : This document is not a European Standard. It is distributed for review and comments. It is subject to change without notice and
shall not be referred to as a European Standard.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36 B-1050 Brussels
© 2004 CEN All rights of exploitation in any form and by any means reserved Ref. No. prEN 12923-1:2004: E
worldwide for CEN national Members.
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prEN 12923-1:2004 (E)
Contents Page
Foreword. 3
1 Scope. 4
2 Normative references . 4
3 Definitions. 4
4 Significance and use . 5
5 Criteria for determining corrosive attack . 5
6 Interferences. 7
7 Apparatus for laboratory corrosion testing . 9
8 Test pieces. 11
9 Test procedure . 11
10 Expression of results. 13
11 Report. 14
Annex A (informative) Appropriate container and specimen holder materials for
corrosion testing. 16
Bibliography . 18
2
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prEN 12923-1:2004 (E)
Foreword
This document (prEN 12923-1:2004) has been prepared by Technical Committee CEN/TC 184
“Advanced technical ceramics”, the secretariat of which is held by BSI.
This document is currently submitted to the CEN Enquiry.
This document will supersede ENV 12923-1: 1997.
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prEN 12923-1:2004 (E)
1 Scope
This Part of EN 12923 describes general procedures to be employed when undertaking corrosion tests
on advanced technical ceramics. The mechanisms of chemical attack on advanced ceramics are widely
varied, and depend on the chemical and phase composition and the phase morphology of the material,
as well as the corrosive conditions imposed. For any particular engineering application it is usually
necessary to model expected conditions of use in order to obtain quantitative data on ability to withstand
the proposed end-use conditions.
This standard is not restricted to specific material types, nor does it prescribe particular test conditions or
test period. The actual testing requirements may be very specific, in order to investigate for example the
suitability of a range of materials for a given application in which certain specified conditions occur. This
standard provides methods for undertaking the assessment of the effect of corrosion, and provides
guidance on practical issues related to undertaking the tests.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
EN 623-1, Advanced technical ceramics — Monolithic ceramics. General and textural properties —
Part 1: Determination of the presence of defects by dye penetration tests
EN 623-4, Advanced technical ceramics — Monolithic ceramics. General and textural properties —
Part 4: Determination of surface roughness
EN 843-1, Advanced technical ceramics — Monolithic ceramics. Mechanical properties at room
temperature — Part 1: Determination of flexural strength
EN 843-4, Advanced technical ceramics — Monolithic ceramics. Mechanical properties at room
temperature — Part 4: Determination of hardness
ENV 1006, Advanced technical ceramics — Methods of testing monolithic ceramics — Guidance on
the sampling and selection of test pieces
ENV 12923-2, Advanced technical ceramics — Monolithic ceramics — Part 2: General oxidation test
EN ISO/IEC 17025, General requirements for the competence of testing and calibration laboratories
EN IEC 60584-1, Thermocouples — Part 1: Reference tables
EN IEC 60584-2, Thermocouples — Part 2: Tolerances
ISO 3611, Micrometer callipers for external measurement
ISO 6906, Vernier callipers for external measurement
3 Definitions
For the purposes of this standard the following definitions apply:
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prEN 12923-1:2004 (E)
3.1
corrosion
process of degradation induced by chemical attack by a surrounding medium on a ceramic body
3.2
oxidation
process of reaction of a ceramic material with oxygen in the surrounding atmosphere, including any
internal reactions as a result of the presence of open porosity or of diffusion of ions to or from the ceramic
surface
4 Significance and use
Advanced technical ceramic materials are widely regarded as being generally resistant to corrosion, and
many types find applications in highly corrosive conditions where other materials are not viable. However,
this is not always the case, and the selection of the most appropriate material requires some form of
assessment to provide assurance that it has adequate resistance to the conditions to which it is to be
exposed.
The rate of chemical attack is determined by:
1. The chemical nature, phase composition, phase distribution and degree of continuous porosity in
the material;
2. The temperature, pressure, composition, concentration and flow rate of the corroding medium,
and whether these are constant or vary with time;
3. The mechanical forces applied to the material in terms of internal stress condition and the degree
of surface abrasion or wear due to contact with other surfaces, the presence of abrasive particles
or the dissolutioning effect of the corroding medium itself.
4. The period for which the test is performed, because it cannot be assumed that the rate of attack
is constant with time. Adjusting test conditions to accelerate the corrosion process and
extrapolating corrosion rates to times longer than that of the test should not be done.
These factors need to be carefully selected, clearly specified and reported in any corrosion test.
The undertaking of corrosion tests is normally for two principal purposes:
1. To simulate performance in an application, which will require careful consideration of all factors
pertaining to the conditions under which corrosion is occurring, and which will require these to be
modelling in the testing environment
2. To provide a comparative measure of performance of a range of materials under defined corrosion
conditions
This standard provides a basis for undertaking corrosion tests and details the criteria which might be
considered for determining whether attack has taken place and has significant consequences for
subsequent use of a material. Since corrosion is dependent on a wide range of parameters, this standard
does not prescribe particular environments or durations of attack, but provides guidance on the key
factors that need to be considered or specified in undertaking tests and gives a general framework for
conducting tests in a meaningful manner.
5 Criteria for determining corrosive attack
Chemical attack is manifest in a number of ways:
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prEN 12923-1:2004 (E)
1. change of dry mass;
2. change of section thickness;
3. change of colour;
4. penetration of corrodent into the material rendering the surface open porous;
5. development of surface skins of altered composition;
6. development of a surface skin of reaction product;
7. change of surface finish;
8. change in strength;
9. change of hardness or wear resistance.
Furthermore, attack may not be linear with time, notably if the diffusion path for corroding species
increases with increasing corrosion.
The extent of chemical attack may be ascertained using a number of simple criteria, the most important
being:
A depth of penetration of corrodent;
B. change of mass;
C. change of cross-section;
D. change of strength;
E. change of surface roughness;
F. change of hardness;
G. changes in the chemical composition of the corroding medium.
NOTE Other situations may exist in which it is desirable to record changes in other properties, for example,
thermal conductivity and thermal shock resistance, either whilst immersed in the corroding medium, or after
extraction from it. Such methods are not specifically included in this standard, and may require special equipment
not covered by this standard. Change of colour may be subjective.
Table 1 summarises the areas of validity of using these criteria for various types of corrosive attack.
These criteria apply to passive conditions of corrosion, i.e. not when the component is under an externally
applied stress.
6
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prEN 12923-1:2004 (E)
Table 1 — Appropriateness of methods of assessing corrosive attack
Test type Aqueous based Corrosion by melts Corrosion by gases
corrosion and vapours
A. Penetration Appropriate May be appropriate Appropriate in some
cases
B. Change of mass Appropriate, but Inappropriate Appropriate if non-
sometimes inadequate slagging
C. Change of cross- Not always appropriate Appropriate Appropriate
section when change is small
D. Change of strength Appropriate May be appropriate if Appropriate if non-
adherent material is slagging; may be
removed appropriate if adherent
material is removed.
E. Change of surface Appropriate for slight Usually inappropriate Usually inappropriate
roughness corrosion
F. Change of hardness Appropriate Usually inappropriate May be appropriate if
non-slagging.
G. Change of Appropriate Usually inappropriate Appropriate
corrodent composition
6 Interferences
6.1 Test type A: Depth of penetration
6.1.1 For materials subjected to corrodents which result in grain boundary attack and penetration of
the corrodent, the depth of penetration may be strongly influenced by the microstructural nature of the
original test piece surface. Some as-fired surfaces may have better resistance to penetration than
bulk microstructures exposed by machining test-pieces. When possible, testing should avoid as-fired
surfaces unless the testing is specifically to evaluate the performance of such surfaces.
6.1.2 The depth of penetration may be variable if the microstructure is inhomogeneous. The
greatest depth of penetration is to be recorded.
6.1.3 In materials with substantial pre-existing closed porosity, it may be difficult to determine the
true depth of penetration if there is no major change in the appearance of the microstructure. Reliance
must be placed on the use of penetrant dyes (see EN 623-1).
6.2 Test type B: Mass change
6.2.1 Accurate determination of change in dry mass may not properly reflect the extent of attack as
a result of either the adherence of solid surface deposits or the retention of corrosion products within
porosity generated by corrodent penetration. A change in mass therefore indicates that some attack
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prEN 12923-1:2004 (E)
may have occurred, but other criteria need to be employed to quantify its overall effect on
performance.
6.2.2 Assuming that the process of mass gain or mass loss is attributable to the test-piece
behaviour, e.g. in an oxidation test (see ENV 12923-2), accurate determination of change in dry mass
relies on being able to minimise contact between the test piece and the apparatus in which it is
housed for the duration of the corrosion test. If strong reaction occurs between the test piece surface
and its support, a significant error in registered mass change may result.
NOTE It may be necessarily to perform some preliminary tests to ensure that the supporting material is
sufficiently non-reactive with the test material before conducting the required tests. In some atmospheres, for
example in low oxygen content atmospheres at high temperatures, the evolution of volatile species from one test-
piece can interact with or contaminate adjacent test-pieces. Cases of this type necessitate separately exposing
each test-piece to the corroding medium.
6.2.3 Free circulation of corrodent around the test-piece is required. If this is for any reason
significantly reduced by the geometrical arrangement of test-pieces and supporting apparatus, rates
of corrosion may be reduced as the corroding species become consumed. A very high velocity of
corrodent can change the mechanism of corrosion from that expected under low flow rate, and
therefore should be avoided unless the high flow rate is a specific requirement of the test.
6.2.4 For very low levels of mass change, the potential error of measurement is large. It may be
more appropriate to monitor changes in chemical concentration of dissolved materials in the corrodent
medium. In this case an alternative method of assessment should be considered, for example,
measurement of change in strength.
6.2.5 In cases where material is lost due to spallation, it may be useful to incorporate a plate or tray
under the test material to catch debris for later analysis. Caution must be exercised such that the tray
does not increase the contact area with the test-piece or restrict the flow of the corroding medium.
6.3 Test type C: Change of test-piece size
Measurement of true test-piece dimensions after corrosion may become uncertain due to the formation of
rough layers, pitting, loose scale or loss of scale. The measurement can be approached in two ways:
1. Measurement of overall external dimensions with any adherent surface layer. The uncertainties
associated with this method can be large if the corrosion product has non-uniform thickness or
partial loss of scale. This method is suited primarily to cases where no scale develops, or where
the corrosion product layers are compact, uniform in thickness and adherent to the test material.
2. Measurement of section thickness unaffected by corrosive attack. This method involves
sectioning and polishing which may change the morphologies of corrosion products and
introduce artifacts. Considerable care should be exercised in test-piece preparation. Provided
that sufficient measurements are made, typically at least 10, using a travelling microscope for
example, it should be possible to provide a sound statistical assessment of change in cross-
section. This method is appropriate to situations where corrosion has caused a loss of material
from one surface exceeding 5 µm.
6.4 Test type D: Strength change
The close specification in EN 843-1 for flexural strength testing designed to achieve results with minimal
errors may not be achievable on test-pieces after corrosion if surfaces become rough or uneven, or if
corrosion deposits cannot be
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