EN ISO 28706-2:2011

SLOVENSKI STANDARD
01-januar-2012
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SIST EN 14483-2:2004
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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 and/or their vapours (ISO 28706-2:2008)
Emails und Emaillierungen - Bestimmung der Beständigkeit gegen chemische Korrosion
- Teil 2: Bestimmung der Beständigkeit gegen chemische Korrosion durch kochende
Säuren, kochende neutrale Flüssigkeiten und/oder deren Dämpfe (ISO 28706-2:2008)
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, et/ou leurs vapeurs (ISO 28706-2:2008)
Ta slovenski standard je istoveten z: EN ISO 28706-2:2011
ICS:
25.220.50 Emajlne prevleke Enamels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 28706-2
NORME EUROPÉENNE
EUROPÄISCHE NORM
May 2011
ICS 25.220.50 Supersedes EN 14483-2:2004
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 and/or
their vapours (ISO 28706-2:2008)
Émaux vitrifiés - Détermination de la résistance à la Emails und Emaillierungen - Bestimmung der Beständigkeit
corrosion chimique - Partie 2: Détermination de la gegen chemische Korrosion - Teil 2: Bestimmung der
résistance à la corrosion chimique par des acides bouillants Beständigkeit gegen chemische Korrosion durch kochende
ou des liquides neutres bouillants, et/ou leurs vapeurs (ISO Säuren, kochende neutrale Flüssigkeiten und/oder deren
28706-2:2008) Dämpfe (ISO 28706-2:2008)
This European Standard was approved by CEN on 15 April 2011.

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, 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 STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2011 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 28706-2:2011: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
The text of ISO 28706-2:2008 has been prepared by Technical Committee ISO/TC 107 “Metallic and other
inorganic coatings” of the International Organization for Standardization (ISO) and has been taken over as EN
ISO 28706-2:2011 by 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 November 2011, and conflicting national standards shall be withdrawn
at the latest by November 2011.
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 14483-2:2004.
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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 28706-2:2008 has been approved by CEN as a EN ISO 28706-2:2011 without any
modification.
INTERNATIONAL ISO
STANDARD 28706-2
First edition
2008-12-01
Vitreous and porcelain enamels —
Determination of resistance to chemical
corrosion —
Part 2:
Determination of resistance to chemical
corrosion by boiling acids, boiling neutral
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 ou des liquides neutres bouillants, et/ou leurs vapeurs

Reference number
ISO 28706-2:2008(E)
©
ISO 2008
ISO 28706-2:2008(E)
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ii © ISO 2008 – All rights reserved

ISO 28706-2:2008(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references. 1
3 Principle. 1
4 Reagents. 2
5 Apparatus and materials. 2
6 Packing rings. 7
6.1 General. 7
6.2 Packing A. 7
6.3 Packing B. 8
7 Test specimens. 8
8 Procedure. 8
9 Expression of results. 9
9.1 Total loss in mass per unit area . 9
9.2 Corrosion rate . 9
10 Boiling citric acid. 9
10.1 General. 9
10.2 Citric acid test solution . 10
10.3 Duration of the test. 10
10.4 Test report. 10
11 Boiling sulfuric acid. 10
11.1 General. 10
11.2 Test solution. 10
11.3 Duration of the test. 10
11.4 Test report. 11
12 Boiling hydrochloric acid. 11
12.1 General. 11
12.2 Test solution. 11
12.3 Duration of the test. 11
12.4 Test report. 12
13 Boiling distilled or demineralized water. 12
13.1 General. 12
13.2 Test solution. 12
13.3 Duration of the test. 12
13.4 Test report. 13
14 Other test solutions and/or conditions. 13
14.1 General. 13
14.2 Test solution. 13
14.3 Duration of the test. 13
14.4 Test report. 14
Bibliography . 15

ISO 28706-2:2008(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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 28706-2 was prepared by the European Committee for Standardization (CEN) (as EN 14483-2) and was
adopted, under a special “fast-track procedure”, by Technical Committee ISO/TC 107, Metallic and other
inorganic coatings, in parallel with its approval by the ISO member bodies.
It cancels and replaces ISO 2733:1983, ISO 2742:1998, ISO 2743:1986 and ISO 2744:1998, which have
been technically revised.
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 2008 – All rights reserved

ISO 28706-2:2008(E)
Introduction
Corrosion of vitreous and porcelain enamels by aqueous solutions is a dissolution process. The main
component of the enamel, 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 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/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 ISO 28706-4:2008), 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 like citric acid (see Clause 9 of ISO 28706-1:2008) or also in
stronger acids like sulfuric acid (see Clause 10 of ISO 28706-1:2008), 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 28706-2:2008), 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:
1) Boiling citric acid (see Clause 10 of ISO 28706-2:2008) and boiling 30 % sulfuric acid (see
Clause 11 of ISO 28706-2:2008)
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 12 of ISO 28706-2:2008)
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
ISO 28706-2:2008(E)
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 Clause 8 of ISO 28706-5:2008), artificial test solutions (see Clause 10 of
ISO 28706-5:2008) or process fluids (see Clause 11 of ISO 28706-5:2008) 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 13 of ISO 28706-2:2008), 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 Clause 9 of ISO 28706-3:2008), 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 14 of ISO 28706-2:2008) and other alkaline solutions (see Clause 10 of
ISO 28706-3:2008 and Clause 10 of ISO 28706-4:2008), 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 International Standard.
For vitreous enamels fired at temperatures below 700 °C, the test parameters (media, temperatures and
times) of this International Standard 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” of Parts 1, 2, 3 and 4 of this International Standard.

vi © ISO 2008 – All rights reserved

INTERNATIONAL STANDARD ISO 28706-2:2008(E)

Vitreous and porcelain enamels — Determination of resistance
to chemical corrosion —
Part 2:
Determination of resistance to chemical corrosion by boiling
ac
...