SIST EN ISO 28706-2:2017

SLOVENSKI STANDARD
SIST EN ISO 28706-2:2017
01-maj-2017
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SIST EN ISO 28706-2:2012
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Vitreous and porcelain enamels - Determination of resistance to chemical corrosion -
Part 2: Determination of resistance to chemical corrosion by boiling acids, boiling neutral
liquids, alkaline liquids and/or their vapours (ISO 28706-2:2017)
Emails und Emaillierungen - Bestimmung der Beständigkeit gegen chemische Korrosion
- Teil 2: Bestimmung der Beständigkeit gegen chemische Korrosion durch kochende
Säuren, kochende neutrale Flüssigkeiten, alkalische Flüssigkeiten und/oder deren
Dämpfe (ISO 28706-2:2017)
Émaux vitrifiés - Détermination de la résistance à la corrosion chimique - Partie 2:
Détermination de la résistance à la corrosion chimique par des acides bouillants, ou des
liquides neutres bouillants,ou des liquides alcalins et/ou leurs vapeurs (ISO 28706-
2:2017)
Ta slovenski standard je istoveten z: EN ISO 28706-2:2017
ICS:
25.220.50 Emajlne prevleke Enamels
SIST EN ISO 28706-2:2017 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN ISO 28706-2:2017

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SIST EN ISO 28706-2:2017


EN ISO 28706-2
EUROPEAN STANDARD

NORME EUROPÉENNE

March 2017
EUROPÄISCHE NORM
ICS 25.220.50 Supersedes EN ISO 28706-2:2011
English Version

Vitreous and porcelain enamels - Determination of
resistance to chemical corrosion - Part 2: Determination of
resistance to chemical corrosion by boiling acids, boiling
neutral liquids, alkaline liquids and/or their vapours (ISO
28706-2:2017)
Émaux vitrifiés - Détermination de la résistance à la Emails und Emaillierungen - Bestimmung der
corrosion chimique - Partie 2: Détermination de la Beständigkeit gegen chemische Korrosion - Teil 2:
résistance à la corrosion chimique par des acides Bestimmung der Beständigkeit gegen chemische
bouillants, des liquides neutres bouillants, ou des Korrosion durch kochende Säuren, kochende neutrale
liquides alcalins et/ou leurs vapeurs (ISO 28706- Flüssigkeiten, alkalische Flüssigkeiten und/oder deren
2:2017) Dämpfe (ISO 28706-2:2017)
This European Standard was approved by CEN on 28 February 2017.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, 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: Avenue Marnix 17, B-1000 Brussels
© 2017 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 28706-2:2017 E
worldwide for CEN national Members.

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SIST EN ISO 28706-2:2017
EN ISO 28706-2:2017 (E)
Contents Page
European foreword . 3

2

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SIST EN ISO 28706-2:2017
EN ISO 28706-2:2017 (E)
European foreword
This document (EN ISO 28706-2:2017) has been prepared by Technical Committee ISO/TC 107
"Metallic and other inorganic coatings" in collaboration with Technical Committee CEN/TC 262
“Metallic and other inorganic coatings” 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 September 2017 and conflicting national standards
shall be withdrawn at the latest by September 2017.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
This document supersedes EN ISO 28706-2:2011.
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, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 28706-2:2017 has been approved by CEN as EN ISO 28706-2:2017 without any
modification.
3

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SIST EN ISO 28706-2:2017

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SIST EN ISO 28706-2:2017
INTERNATIONAL ISO
STANDARD 28706-2
Second edition
2017-02
Vitreous and porcelain enamels —
Determination of resistance to
chemical corrosion —
Part 2:
Determination of resistance to
chemical corrosion by boiling acids,
boiling neutral liquids, alkaline
liquids and/or their vapours
Émaux vitrifiés — Détermination de la résistance à la corrosion
chimique —
Partie 2: Détermination de la résistance à la corrosion chimique par
des acides bouillants, des liquides neutres bouillants, ou des liquides
alcalins et/ou leurs vapeurs
Reference number
ISO 28706-2:2017(E)
©
ISO 2017

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SIST EN ISO 28706-2:2017
ISO 28706-2:2017(E)

COPYRIGHT PROTECTED DOCUMENT
© ISO 2017, Published in Switzerland
All rights reserved. Unless otherwise specified, 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
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Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2017 – All rights reserved

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SIST EN ISO 28706-2:2017
ISO 28706-2:2017(E)

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus and materials. 3
6.1 Test apparatus . 3
6.2 Test materials . 8
7 Packing rings . 8
7.1 General . 8
7.2 Packing A . 8
7.3 Packing B . 9
8 Test specimens. 9
9 Procedure. 9
10 Expression of results .10
10.1 Total loss in mass per unit area .10
10.2 Corrosion rate .10
11 Boiling citric acid .11
11.1 General .11
11.2 Test solution .11
11.3 Duration of the test .11
11.4 Test report .11
12 Boiling sulfuric acid .11
12.1 General .11
12.2 Test solution .11
12.3 Duration of the test .12
12.4 Test report .12
13 Boiling hydrochloric acid .12
13.1 General .12
13.2 Test solution .12
13.3 Duration of the test .12
13.4 Test report .13
14 Boiling distilled or demineralized water .13
14.1 General .13
14.2 Test solution .13
14.3 Duration of the test .13
14.4 Test report .14
15 Standard detergent solution .14
15.1 General .14
15.2 Test solution .14
15.3 Test temperature .15
15.4 Duration of the test .15
15.5 Test report .15
16 Other test solutions and/or conditions .15
16.1 General .15
© ISO 2017 – All rights reserved iii

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SIST EN ISO 28706-2:2017
ISO 28706-2:2017(E)

16.2 Test solution .15
16.3 Duration of the test .15
16.4 Test report .16
Bibliography .17
iv © ISO 2017 – All rights reserved

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SIST EN ISO 28706-2:2017
ISO 28706-2:2017(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 on 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 the following
URL: w w w . i s o .org/ iso/ foreword .html.
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.
This second edition cancels and replaces the first edition (ISO 28706-2:2008), which has been
technically revised with changes as follows.
— This document can also be used to determine resistance to chemical corrosion using alkaline
liquids. The title of this document has therefore been amended and a section on standard detergent
solutions has been included.
— Additional reagents can be used for testing purposes and these have been included.
A list of all parts in the ISO 28706 series can be found on the ISO website.
© ISO 2017 – All rights reserved v

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SIST EN ISO 28706-2:2017
ISO 28706-2:2017(E)

Introduction
Corrosion of vitreous and porcelain enamels by aqueous solutions is a dissolution process. The
main component of the enamel, SiO2, forms a three-dimensional silica network. After hydrolysis, it
decomposes and forms silicic acid or silicates. These are released into the attacking medium. Other
components, mainly metal oxides, are hydrolysed as well and form the corresponding hydrated metal
ions or hydroxides. All corrosion products are more or less soluble in the attacking medium. The whole
process results in a loss in mass per unit area.
For some aqueous solutions, the attack on the enamel proceeds linearly during the corrosion time;
for other aqueous solutions, the attack on the enamel proceeds in a logarithmic manner during the
corrosion time. Only for the first series of solutions can a scientifically exact rate of loss in mass per unit
area (g/m2·h) be calculated as well as a corrosion rate (millimetres per year).
The most important parameters influencing aqueous corrosion of the enamel are the enamel quality,
the temperature and the pH value. Inhibition effects resulting from the limited solubility of silica can
also contribute. The following list describes different types of enamel attack for different corrosion
conditions.
a) In aqueous alkali solutions such as 0,1 mol/l NaOH (see ISO 28706-4:2016, Clause 9), the silica
network of the enamel is considerably attacked at 80 °C. Silicates and most of the other hydrolysed
components are soluble in the alkali. Attack proceeds linearly during regular test times. Therefore,
test results are expressed in terms of a rate of loss in mass per unit area (mass loss per unit area
and time) and a corrosion rate (millimetres per year).
b) At room temperature, in weak aqueous acids such as citric acid (see ISO 28706-1:2008, Clause 9) or
also in stronger acids such as sulfuric acid (see ISO 28706-1:2008, Clause 10), there is only minor
attack on the silica network of the enamel. Other constituents are leached to some extent from
the surface. Highly resistant enamels will show no visual change after exposure. On less resistant
enamels, some staining or surface roughening will occur.
c) In boiling aqueous acids (as described in this document), the silica network of the enamel is being
attacked, and silica as well as the other enamel components are released into solution. However,
the solubility of silica in acids is low. Soon, the attacking solutions will become saturated with
dissolved silica and will then only leach the surface. The acid attack is inhibited and the rate of
corrosion drops markedly.
NOTE The glass test equipment also releases silica by acid attack and contributes to the inhibition of
the corrosion.
Inhibition is effectively prevented in vapour phase tests. The condensate formed on the test
specimen is free of any dissolved enamel constituents.
Examples of enamel corrosion proceeding in a logarithmic manner [see 1)] and linearly [see 2)] are
as follows:
1) Boiling citric acid (see Clause 11) and boiling 30 % sulfuric acid (see Clause 12).
Since only minute amounts of these acids are found in their vapours, the test is restricted to
the liquid phase. The attack is influenced by inhibition effects and corrosion depends on the
time of exposure. Therefore, test results are expressed in terms of loss in mass per unit area;
no rate of loss in mass per unit area is calculated.
2) Boiling 20 % hydrochloric acid (see Clause 13).
Since this is an azeotropic boiling acid, its concentration in the liquid and the vapour phase
are identical, and liquid phase testing need not be performed. Vigorous boiling supplies an
uninhibited condensate, and the attack proceeds linearly with time of exposure. Therefore,
vi © ISO 2017 – All rights reserved

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SIST EN ISO 28706-2:2017
ISO 28706-2:2017(E)

test results are only expressed in terms of rate of loss in mass per unit area (mass loss per unit
area and time) and the corrosion rate (millimetres per year).
d) At high temperatures, with tests in the liquid phase under autoclave conditions (see ISO 28706-5),
aqueous acid attack is severe. To avoid inhibition, the test time is restricted to 24 h and the ratio of
attacking acid to attacked enamel surface is chosen so that it is comparatively high (similar to that
in a chemical reaction vessel). In addition, only low-silica water is used for the preparation of test
solutions. Under these conditions, attack will proceed linearly with time of exposure. Therefore,
test results with 20 % hydrochloric acid (see ISO 28706-5:2010, Clause 8), artificial test solutions
(see ISO 28706-5:2010, Clause 10) or process fluids (see ISO 28706-5:2010, Clause 11) are also
expressed in terms of a rate of loss in mass per unit area (loss in mass per unit area and time).
e) In boiling water (see Clause 14), the silica network is fairly stable. The enamel surface is leached
and silica is dissolved only to a small extent. This type of attack is clearly represented by the vapour
phase attack. In the liquid phase, some inhibition can be observed with highly resistant enamels.
However, if the enamel being tested is weak, leached alkali from the enamel can raise pH values to
alkaline levels, thus increasing the attack by the liquid phase. Both liquid and vapour phase testing
can give valuable information.
f) Since the attack may or may not be linear, the results are expressed only in terms of loss in mass
per unit area and the test time should be indicated.
g) For standard detergent solution (see ISO 28706-3:2008, Clause 9), it will not be certain whether the
linear part of the corrosion curve will be reached during testing for 24 h or 168 h. Calculation of the
corrosion rate is therefore not included in the test report.
h) For other acids (see Clause 15) and other alkaline solutions (see ISO 28706-3:2008, Clause 10 and
ISO 28706-4:2016, Clause 10), it will also not be known if a linear corrosion rate will be reached
during the test period. Calculation of the corrosion rate is therefore not included in the test reports
of those parts of this document.
For vitreous enamels fired at temperatures below 700 °C, the test parameters (media, temperatures and
times) of this document are not appropriate. For such enamels, for example aluminium enamels, other
media, temperatures and/or times should be used. This can be done following the procedures described
in the clauses for “Other test solutions” in ISO 28706-1, ISO 28706-2, ISO 28706-3 and ISO 28706-4.
© ISO 2017 – All rights reserved vii

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SIST EN ISO 28706-2:2017

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SIST EN ISO 28706-2:2017
INTERNATIONAL STANDARD ISO 28706-2:2017(E)
Vitreous and porcelain enamels — Determination of
resistance to chemical corrosion —
Part 2:
Determination of resistance to chemical corrosion by
boiling acids, boiling neutral liquids, alkaline liquids and/
or their vapours
WARNING — This document calls for the use of substances and/or procedures that may be
injurious to health if adequate safety measures are not taken. This document does not address any
health hazards, safety or environmental matters associated with its use. Is it the responsibility
of the user of this document to establish appropriate health, safety and environmentally
acceptable practices and take suitable actions for any national and international regulations.
1 Scope
This document specifies a test method for the determination of the resistance of flat surfaces of vitreous
and porcelain enamels to boiling acids, boiling neutral liquids, alkaline liquids and/or their vapours.
This method allows the determination of the resistance of vitreous and porcelain enamels to the liquid
and vapour phases of the corrosive medium simultaneously.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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.
ISO 48, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and
100 IRHD)
ISO 649-1, Laboratory glassware — Density hydrometers for general purposes — Part 1: Specification
ISO 718, Laboratory glassware — Thermal shock and thermal shock endurance — Test methods
ISO 3585, Borosilicate glass 3.3 — Properties
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 4788, Laboratory glassware — Graduated measuring cylinders
ISO 4799, Laboratory glassware — Condensers
ISO 28764, Vitreou
...