prEN ISO 28706-2

SLOVENSKI STANDARD
01-februar-2026
Steklasti in porcelanski emajli - Ugotavljanje odpornosti proti kemični koroziji - 2.
del: Ugotavljanje odpornosti proti kemični koroziji s kislinami in nevtralnimi
tekočinami, ki vrejo, bazami in/ali njihovimi parami (ISO/DIS 28706-2:2025)
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/DIS 28706-2:2025)
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/DIS 28706-2:2025)
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 (ISO/DIS 28706-
2:2025)
Ta slovenski standard je istoveten z: prEN ISO 28706-2
ICS:
25.220.50 Emajlne prevleke Enamels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 28706-2
ISO/TC 107
Vitreous and porcelain enamels —
Secretariat: KATS
Determination of resistance to
Voting begins on:
chemical corrosion —
2025-12-08
Part 2:
Voting terminates on:
2026-03-02
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
ICS: 25.220.50
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 28706-2:2025(en)
DRAFT
ISO/DIS 28706-2:2025(en)
International
Standard
ISO/DIS 28706-2
ISO/TC 107
Vitreous and porcelain enamels —
Secretariat: KATS
Determination of resistance to
Voting begins on:
chemical corrosion —
Part 2:
Voting terminates on:
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
ICS: 25.220.50
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: +41 22 749 01 11
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 28706-2:2025(en)
ii
ISO/DIS 28706-2:2025(en)
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 . 2
6.1 Test apparatus.2
6.2 Test materials .7
7 Packing rings . 7
7.1 General .7
7.2 Packing A .7
7.3 Packing B .7
8 Test specimens . 8
9 Procedure . 8
10 Expression of results . 9
10.1 Total loss in mass per unit area .9
10.2 Corrosion rate .9
11 Boiling citric acid . 9
11.1 General .9
11.2 Test solution .10
11.3 Duration of the test .10
11.4 Test report .10
12 Boiling sulfuric acid . 10
12.1 General .10
12.2 Test solution .10
12.3 Duration of the test .10
12.4 Test report .11
13 Boiling hydrochloric acid .11
13.1 General .11
13.2 Test solution .11
13.3 Duration of the test .11
13.4 Test report .11
14 Boiling distilled or demineralized water .12
14.1 General . 12
14.2 Test solution . 12
14.3 Duration of the test . 12
14.4 Test report . 12
15 Standard detergent solution .13
15.1 General . 13
15.2 Test solution . 13
15.3 Test temperature . 13
15.4 Duration of the test . 13
15.5 Test report .14
16 Other test solutions and/or conditions . 14
16.1 General .14
16.2 Test solution .14

iii
ISO/DIS 28706-2:2025(en)
16.3 Duration of the test .14
16.4 Test report .14
Bibliography .16

iv
ISO/DIS 28706-2:2025(en)
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:
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings.
This third edition cancels and replaces the second edition (ISO 28706-2:2017), which has been technically
revised with changes as follows.
— The simmering aid part of the test apparatus has been removed as it is not required for this test.
— The testing procedure has been updated to include the requirement for tests to be carried out in a
temperature controlled environment and to define a time for emptying the test cycliner.
A list of all parts in the ISO 28706 series can be found on the ISO website.

v
ISO/DIS 28706-2:2025(en)
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, 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).

vi
ISO/DIS 28706-2:2025(en)
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.

vii
DRAFT International Standard ISO/DIS 28706-2:2025(en)
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 da
...