prEN ISO 28706-4

SLOVENSKI STANDARD
01-februar-2026
Steklasti in keramični emajli - Ugotavljanje odpornosti proti kemični koroziji - 4.
del: Ugotavljanje odpornosti proti kemični koroziji z alkalnimi tekočinami in
valjasto posodo (ISO/DIS 28706-4:2025)
Vitreous and porcelain enamels - Determination of resistance to chemical corrosion -
Part 4: Determination of resistance to chemical corrosion by alkaline liquids using a
cylindrical vessel (ISO/DIS 28706-4:2025)
Emails und Emaillierungen - Bestimmung der Beständigkeit gegen chemische Korrosion
- Teil 4: Bestimmung der Beständigkeit gegen chemische Korrosion durch alkalische
Flüssigkeiten unter Verwendung eines Gerätes mit zylindrischem Gefäß (ISO/DIS 28706
-4:2025)
Émaux vitrifiés - Détermination de la résistance à la corrosion chimique - Partie 4:
Détermination de la résistance à la corrosion chimique par des liquides alcalins dans un
récipient cylindrique (ISO/DIS 28706-4:2025)
Ta slovenski standard je istoveten z: prEN ISO 28706-4
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 28706-4
ISO/TC 107
Vitreous and porcelain enamels —
Secretariat: KATS
Determination of resistance to
Voting begins on:
chemical corrosion —
2025-12-08
Part 4:
Voting terminates on:
2026-03-02
Determination of resistance to
chemical corrosion by alkaline
liquids using a cylindrical vessel
Émaux vitrifiés — Détermination de la résistance à la corrosion
chimique —
Partie 4: Détermination de la résistance à la corrosion chimique
par des liquides alcalins dans un récipient cylindrique
ICS: 25.220.50
THIS DOCUMENT IS A DRAFT CIRCULATED
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IS THEREFORE SUBJECT TO CHANGE
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Reference number
ISO/DIS 28706-4:2025(en)
DRAFT
ISO/DIS 28706-4:2025(en)
International
Standard
ISO/DIS 28706-4
ISO/TC 107
Vitreous and porcelain enamels —
Secretariat: KATS
Determination of resistance to
Voting begins on:
chemical corrosion —
Part 4:
Voting terminates on:
Determination of resistance to
chemical corrosion by alkaline
liquids using a cylindrical vessel
Émaux vitrifiés — Détermination de la résistance à la corrosion
chimique —
Partie 4: Détermination de la résistance à la corrosion chimique
par des liquides alcalins dans un récipient cylindrique
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
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NATIONAL REGULATIONS.
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Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 28706-4:2025(en)
ii
ISO/DIS 28706-4:2025(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Principle . 1
4 Reagents . 2
5 Apparatus and material . 2
6 Test specimens . 7
7 Procedure – Test with an apparatus with a volume surface ratio 20:1 cm . 7
8 Expression of results . 8
8.1 Total loss in mass per unit area .8
8.2 Corrosion rate .8
9 Hot 0,1 mol/l sodium hydroxide test . 9
9.1 General .9
9.2 Test solution, c(NaOH) = 0,1 mol/l .9
9.3 Test temperature .9
9.4 Duration of the test .9
9.5 Test report .9
10 Other test solutions . . 9
10.1 General .9
10.2 Test solution .10
10.3 Test temperature .10
10.4 Duration of the test .10
10.5 Test report .10
Bibliography .11

iii
ISO/DIS 28706-4:2025(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 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 107, Metallic and other inorganic coatings.
This third edition cancels and replaces the third edition (ISO 28706-4:2016).
The main changes are as following:
— The Introduction has been updated;
— emphasised the volume surface ratio 20:1 of the apparatus;
— Delete chapter 10;
— 5.1.3 Protective envelope has been clarified.
ISO 28706 consists of the following parts, under the general title Vitreous and porcelain enamels —
Determination of resistance to chemical corrosion:
— Part 1: Determination of resistance to chemical corrosion by acids at room temperature
— Part 2: Determination of resistance to chemical corrosion by boiling acids, boiling neutral liquids and/or
their vapours
— Part 3: Determination of resistance to chemical corrosion by alkaline liquids using a hexagonal vessel
— Part 4: Determination of resistance to chemical corrosion by alkaline liquids using a cylindrical vessel
— Part 5: Determination of resistance to chemical corrosion in closed systems

iv
ISO/DIS 28706-4:2025(en)
Introduction
Corrosion of vitreous and porcelain enamels by aqueous solutions is a dissolution process. The main
component of the enamel, silica (SiO ), 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 concerning a t-root law during the corrosion time.
Only for the first series of solutions can a scientifically exact rate of loss in mass per unit area (g/m ⋅h) be
calculated as well as a corrosion rate (mm/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 like 0,1 mol/l NaOH (see Clause 9 of this part of ISO 28706), 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. Depending on the test conditions the attack proceeds linearly or follows a root-
t-law. 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 like citric acid (see ISO 28706-1:2008, Clause 9) or also
in stronger acids like 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 (see ISO 28706-2), 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.
The inhibition is only partly prevented in vapour phase. The condensate formed on the test specimen
is nearly free of any dissolved enamel constituents. However the corrosion rate follows a root-t-law.
Examples of enamel corrosion proceeding in a logarithmic manner [see 1)] and linearly [see 2)] are:
1) Boiling citric acid (see of ISO 28706-2:2008, Clause 10) and boiling 30 % sulfuric acid (see
ISO 28706-2:2008, Clause 11)
Since only minor 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 ISO 28706-2:2008, Clause 12)
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. The corrosion mechanism is non-linear
but follows a root-t law. In order to obtain results which can be compared a fixed test time is
necessary. 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).
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

v
ISO/DIS 28706-4:2025(en)
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
...