ISO/PRF 28706-4

• Abstract:

  ISO 28706-4:2016 describes a test method for the determination of the resistance of vitreous and porcelain enamelled articles to attack by alkaline liquids at temperatures between 25 °C and 95 °C. The apparatus used is a cylindrical vessel in which only one enamelled specimen is tested. NOTE 1 The test method was initially set up for determination of the resistance of vitreous and porcelain enamels to a hot sodium hydroxide solution. Within the scope of this part of ISO 28706, the resistance of other alkaline liquids can be tested. NOTE 2 This part of ISO 28706, which uses a cylindrical vessel, is generally used for tests carried out on vitreous and porcelain enamel coatings for the chemical industry.

• Status: Not Published
• ICS: 25.220.50 - Enamels
• Technical Committee: ISO/TC 107 - Metallic and other inorganic coatings
• Drafting Committee: ISO/TC 107/WG 2 - Vitreous and porcelain enamel coatings
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 22-Oct-2026
• Completion Date: 24-Oct-2026

• Consolidates: prEN ISO 28706-4 - 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)
• Effective Date: 12-Feb-2026
• Revises: ISO 28706-4:2016 - 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
• Effective Date: 15-Jun-2024

International
Standard
ISO 28706-4
Fourth edition
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
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
PROOF/ÉPREUVE
Reference number
ISO 28706-4:2026(en) © ISO 2026

ISO 28706-4:2026(en)
© ISO 2026
All rights reserved.
This ISO publication is protected by copyright and is owned by ISO and/or its licensors.
The content of this ISO publication is provided under licence, not sold. Use is subject to the applicable licence terms issued by ISO,
an ISO member body, or an authorized third-party distributor.
Except as required for implementation or expressly permitted by a separate licence, no part of this ISO publication may be
reproduced, distributed, modified, used, or made available in any form or by any means – electronic or mechanical, including
photocopying, scanning, recording, or posting on internal or external digital platforms.
Any use beyond the scope of the granted rights is prohibited and may result in legal action.
ISO copyright office
CP 401 • CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
PROOF/ÉPREUVE
ii
ISO 28706-4:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Reagents . 2
6 Apparatus and material . 2
6.1 Test apparatus.2
6.1.1 General .2
6.1.2 Apparatus .5
7 Test specimens . 7
8 Procedure for test with an apparatus with a volume surface ratio 20:1 cm . 7
9 Expression of results . 8
9.1 Total loss in mass per unit area .8
9.2 Corrosion rate .8
10 Hot 0,1 mol/l sodium hydroxide test . 9
10.1 General .9
10.2 Test solution, c(NaOH) = 0,1 mol/l .9
10.3 Test temperature .9
10.4 Duration of the test .9
10.5 Test report .9
11 Other test solutions . . 9
11.1 General .9
11.2 Test solution .10
11.3 Test temperature .10
11.4 Duration of the test .10
11.5 Test report .10
Bibliography .11
PROOF/ÉPREUVE
iii
ISO 28706-4:2026(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 document 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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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 www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings,
in collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC
262, Metallic and other inorganic coatings, including for corrosion protection and corrosion testing of metals
and alloys, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This fourth edition cancels and replaces the third edition (ISO 28706-4:2016), which has been technically
revised.
The main changes are as follows:
— Terms and definitions have been included.
— References to the volume surface ratio of 20:1 of the apparatus has been included.
— The hot 1,0 mol/l sodium hydroxide test has been removed.
— Additional information has been included relating to the material and type of protective envelope that
can be used.
A list of all parts in the ISO 28706 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
PROOF/ÉPREUVE
iv
ISO 28706-4:2026(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 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 root-t 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 document), 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) and 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 show no visual change after exposure. On less resistant enamels, some staining or
surface roughening occurs.
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 become saturated with dissolved silica and 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:—, Clause 10) and boiling 30 % sulfuric acid (see
ISO 28706-2:—, 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:—, Clause 12)
Since this is an azeotropic boiling acid, its concentration in the liquid and the vapour phase are
identical and liquid phase testing is not required. The corrosion mechanism is non-linear but follows
a root-t law. 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
PROOF/ÉPREUVE
v
ISO 28706-4:2026(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 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 ISO 28706-2:—, Clause 13), 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 it is possible that the attack is not 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 ISO 28706-2:2008, Clause 14) and other alkaline solutions (see ISO 28706-3:2008,
Clause 10 and Clause 11 of this document), 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 docu
...

Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
ISO/TC 107
Style Definition
...
Style Definition
...
Secretariat: KATS
Style Definition
...
Date: 13 August 2026-10-22
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Vitreous and porcelain enamels — Determination of resistance to
Style Definition
...
chemical corrosion —
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Part 4: Style Definition
...
Determination of resistance to chemical corrosion by alkaline Style Definition
...
Style Definition
liquids using a cylindrical vessel
...
Style Definition
...
Émaux vitrifiés — Détermination de la résistance à la corrosion chimique —
Style Definition
...
Partie 4: Détermination de la résistance à la corrosion chimique par des liquides alcalins dans un récipient Style Definition
...
cylindrique
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
...
Style Definition
© PROOF
Formatted: Font: Bold
Formatted: HeaderCentered, Left
Formatted: Default Paragraph Font
Formatted: Adjust space between Latin and Asian text,
All rights reserved. Unless otherwise specified,
Adjust space between Asian text and numbers
This ISO publication is protected by copyright and is owned by ISO and/or its licensors.
The content of this ISO publication is provided under licence, not sold. Use is subject to the applicable licence terms issued
Formatted: Right: 1.5 cm, Gutter: 0 cm, Header
by ISO, an ISO member body, or an authorized third-party distributor.
distance from edge: 1.27 cm, Footer distance from
Except as required in the context of its for implementation or expressly permitted by a separate licence, no part of this
edge: 0.5 cm
ISO publication may be reproduced or utilized otherwise, distributed, modified, used, or made available in any form or
by any means, – electronic or mechanical, including photocopying, scanning, recording, or posting on internal or external
digital platforms.
Any use beyond the internet or an intranet, without prior written permission. Permission can be requested from either
Formatted: Adjust space between Latin and Asian text,
ISO at the address below or ISO’s member body in the countryscope of the requestergranted rights is prohibited and may
Adjust space between Asian text and numbers
result in legal action.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Formatted: zzCopyright address, Adjust space between
Phone: + 41 22 749 01 11
Latin and Asian text, Adjust space between Asian text
Email: [e-mail]
and numbers
Website: www.iso.orgwww.iso.org
Published in Switzerland
Formatted: Font: 10 pt, Not Bold
Formatted: Font: 10 pt, Not Bold
ii
Formatted: Font: 11 pt, Bold, Font color: Auto
Formatted: Font: 11 pt, Bold, Font color: Auto
Formatted: Font: Bold
Contents
Formatted: HeaderCentered, Left
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 2
4 Principle . 2
5 Reagents . 2
6 Apparatus and material . 2
6.1 Test apparatus . 2
7 Test specimens . 11
8 Procedure for test with an apparatus with a volume surface ratio 20:1 cm . 11
9 Expression of results . 12
9.1 Total loss in mass per unit area . 12
9.2 Corrosion rate . 12
10 Hot 0,1 mol/l sodium hydroxide test . 13
10.1 General . 13
10.2 Test solution, c(NaOH) = 0,1 mol/l . 13
10.3 Test temperature . 13
10.4 Duration of the test . 13
10.5 Test report . 13
11 Other test solutions . 13
11.1 General . 13
11.2 Test solution . 14
11.3 Test temperature . 14
11.4 Duration of the test . 14
11.5 Test report . 14
Bibliography . 15

Formatted: Font: 10 pt
Formatted: Font: 10 pt
Formatted: Font: 10 pt
Formatted: FooterCentered, Left, Space Before: 0 pt,
Tab stops: Not at 17.2 cm
Formatted: Font: 11 pt
© ISO 2026 – All rights reserved
iii
Formatted: Font: Bold
Formatted: HeaderCentered, Left
Foreword Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
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 document 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).
Formatted: English (United Kingdom)
Formatted: Default Paragraph Font, English (United
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
Kingdom)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents.www.iso.org/patents. ISO shall not be held responsible for identifying any or all such
patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of 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
Formatted: English (United Kingdom)
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
Formatted: Font: Not Italic
This document was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings, in
Formatted: Font: Not Italic
collaboration with the European Committee for Standardization (CEN) Technical Committee CEN/TC 262,
Formatted: Default Paragraph Font
Metallic and other inorganic coatings, including for corrosion protection and corrosion testing of metals and
alloys, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna Agreement).
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
This thirdfourth edition cancels and replaces the third edition (ISO 28706--4:2016), which has been
technically revised. Formatted: Default Paragraph Font
Formatted: Adjust space between Latin and Asian text,
The main changes are as follows:
Adjust space between Asian text and numbers
Formatted: Adjust space between Latin and Asian text,
— — Terms and Definitionsdefinitions have been included.
Adjust space between Asian text and numbers, Tab
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
— — References to the volume surface ratio of 20:1 of the apparatus has been included.
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
— — The hot 1,0 mol/l sodium hydroxide test has been removed.
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
— — Additional information has been included relating to the material and type of protective envelope that
Formatted: Default Paragraph Font
can be used.
Formatted: Adjust space between Latin and Asian text,
A list of all parts in the ISO 28706 series can be found on the ISO website.
Adjust space between Asian text and numbers
Formatted: English (United Kingdom)
Any feedback or questions on this document should be directed to the user’s national standards body. A
Formatted: English (United Kingdom)
complete listing of these bodies can be found at www.iso.org/members.htmlwww.iso.org/members.html.
Formatted: Font: 10 pt, Not Bold
Formatted: Font: 10 pt, Not Bold
iv
Formatted: Font: 11 pt, Bold, Font color: Auto
Formatted: Font: 11 pt, Bold, Font color: Auto
Formatted: Font: Bold
Introduction
Formatted: HeaderCentered, Left
Formatted: Adjust space between Latin and Asian text,
Corrosion of vitreous and porcelain enamels by aqueous solutions is a dissolution process. The main
Adjust space between Asian text and numbers
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.
Formatted: Default Paragraph Font
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 root-t law during the corrosion time. Only
Formatted: Default Paragraph Font
for the first series of solutions can a scientifically exact rate of loss in mass per unit area (g/m ⋅h) be calculated
Formatted: Default Paragraph Font
as well as a corrosion rate (mm/year).
Formatted: Default Paragraph Font
The most important parameters influencing aqueous corrosion of the enamel are the enamel quality, the
Formatted: Default Paragraph Font
temperature and the pH-value. Inhibition effects resulting from the limited solubility of silica can also
Formatted: Default Paragraph Font
contribute. The following list describes different types of enamel attack for different corrosion conditions:
Formatted: Default Paragraph Font
a) a) In aqueous alkali solutions like 0,1 mol/l NaOH (see Clause 9Clause 9 of this document), the
Formatted: Default Paragraph Font
silica network of the enamel is considerably attacked at 80 °C. Silicates and most of the other hydrolysed
Formatted: Default Paragraph Font
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
Formatted: Default Paragraph Font
(mass loss per unit area and time) and a corrosion rate (millimetres per year).
Formatted: Default Paragraph Font
b) b) At room temperature, in weak aqueous acids like citric acid (see ISO 28706--1:2008, Clause 9) Formatted: Default Paragraph Font
and in stronger acids like sulfuric acid (see ISO 28706--1:2008, Clause 10), there is only minor attack on
Formatted: Default Paragraph Font
the silica network of the enamel. Other constituents are leached to some extent from the surface. Highly
Formatted: Default Paragraph Font
resistant enamels show no visual change after exposure. On less resistant enamels, some staining or
surface roughening occurs. Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
c) c) In boiling aqueous acids (see ISO 28706--2), the silica network of the enamel is being attacked
Formatted: Default Paragraph Font
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 become saturated with dissolved silica and then only
Formatted
...
leach the surface. The acid attack is inhibited, and the rate of corrosion drops markedly.
Formatted: Default Paragraph Font
NOTE The glass test equipment also releases silica by acid attack and contributes to the inhibition of the Formatted: Default Paragraph Font
corrosion.
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
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.
Formatted: Body Text Indent 2
Examples of enamel corrosion proceeding in a logarithmic manner [see 1)]1)] and linearly [see 2)]2)] are:
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
1) 1) Boiling citric acid (see of ISO 28706--2:—, Clause 10) and boiling 30 % sulfuric acid (see
ISO 28706--2:—, Clause 11)
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
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. Formatted
...
Therefore, test results are expressed in terms of loss in mass per unit area; no rate of loss in mass per
Formatted: Body Text Indent 2
unit area is calculated.
Formatted: Font: 10 pt
2) 2) Boiling 20 % hydrochloric acid (see ISO 28706--2:—, Clause 12)
Formatted: Font: 10 pt
Formatted: Font: 10 pt
Since this is an azeotropic boiling acid, its concentration in the liquid and the vapour phase are
Formatted
identical and liquid phase testing is not required. The corrosion mechanism is non-linear but follows
...
a root-t law. In order toTo obtain results which can be compared, a fixed test time is necessary.
Formatted: Font: 11 pt
© ISO 2026 – All rights reserved
v
Formatted: Font: Bold
Formatted: HeaderCentered, Left
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) d) At high temperatures, with tests in the liquid phase under autoclave conditions (see
Formatted: Numbered + Level: 1 + Numbering Style: a,
ISO 28706--5), aqueous acid attack is severe. To avoid inhibition, the test time is restricted to 24 h and
b, c, … + Start at: 4 + Alignment: Left + Aligned at: 0
the ratio of attacking acid to attacked enamel surface is chosen so that it is comparatively high (similar to cm + Indent at: 0 cm
that in a chemical reaction vessel). In addition, only low-silica water is used for the preparation of test
Formatted: Default Paragraph Font
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) e) In boiling water (see ISO 28706--2:—, Clause 13), the silica network is fairly stable. The enamel
Formatted: Default Paragraph Font
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) f) Since it is possible that the attack is not linear, the results are expressed only in terms of loss
in mass per unit area, and the test time should be indicated.
g) g) For standard detergent solution (see ISO 28706--3:2008, Clause 9), it will not be certain
Formatted: Default Paragraph Font
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) h) For other acids (see ISO 28706--2:2008, Clause 14) and other alkaline solutions (see
Formatted: Default Paragraph Font
ISO 28706--3:2008, Clause 10 and Clause 11 of this document), 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
Formatted: Adjust space between Latin and Asian text,
times) of this document are not appropriate. For such enamels, for example aluminium enamels, other media, Adjust space between Asian text and numbers
temperatures, or times should be used. This can be done following the procedures described in ISO 28706--1,
Formatted: Default Paragraph Font
ISO 28706-2, ISO 28706--3 and this document. .
Formatted: Font: 10 pt, Not Bold
vi
International Standard ISO 28706-4:2026(en)

Formatted: Font: Not Bold
Formatted: Header, Centered, Space After: 0 pt, Line
spacing: single
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
Formatted: Right: 1.5 cm, Gutter: 0 cm, Header
Vitreous and porcelain enamels — Determination of resistance to distance from edge: 1.27 cm, Footer distance from
edge: 0.5 cm
chemical corrosion —
Part 4:
Determination of resistance to chemical corrosion by alkaline liquids
using a cylindrical vessel
WARNING — This document calls for the use of substances and/or procedures that can be injurious to
Formatted: Adjust space between Latin and Asian text,
health if adequate safety measures are not taken. This document does not address any health hazards,
Adjust space between Asian text and numbers
safety or environmental matters associated with its use. It is the responsibility of the user of this
document to establish appropriate health, safety and environmentally acceptable practices and take
Formatted: Body Text, Adjust space between Latin and
suitable actions for any national and international regulations. Conformance with this document does
Asian text, Adjust space between Asian text and
not of itself confer immunity from legal obligations.
numbers, Tab stops: Not at 0.7 cm + 1.4 cm + 2.1 cm
+ 2.8 cm + 3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3
1 Scope
cm + 7 cm
Formatted: Adjust space between Latin and Asian text,
This document describes a test method for the determination of the resistance of vitreous and porcelain
Adjust space between Asian text and numbers
enamelled articles to attack by alkaline liquids at temperatures between 25 °C and 95 °C. The apparatus used
is a cylindrical vessel with a volume-surface ratio 20:1 cm in which only one enamelled specimen is tested.
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
This document, which uses a cylindrical vessel, is generally used for tests carried out on vitreous and porcelain
Formatted: Default Paragraph Font
enamel coatings for the chemical industry.
Formatted: Default Paragraph Font
2 Normative references
Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers, Tab
The following documents, in whole or in part, are normatively referenced in this document and are
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
indispensable for its application. For dated references, only the edition cited applies. For undated references,
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
the latest edition of the referenced document (including any amendments) applies.
Formatted: Default Paragraph Font
ISO 48, Rubber, vulcanized or thermoplastic — Determination of hardness (hardness between 10 IRHD and
Formatted: Default Paragraph Font
100 IRHD)
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font
ISO 1042, Laboratory glassware — One-mark volumetric flasks
Formatted: Default Paragraph Font
ISO 3696, Water for analytical laboratory use — Specification and test methods
Formatted: Default Paragraph Font
ISO 28764, Vitreous and porcelain enamels — Production of specimens for testing enamels on sheet steel, Formatted: Default Paragraph Font
sheet aluminium and cast iron
Formatted: Default Paragraph Font
Formatted: Default Paragraph Font

Formatted: Default Paragraph Font
Formatted: Font: Bold
Formatted: HeaderCentered, Left
3 Terms and definitions
Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers
No terms and definitions are listed in this document.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
Formatted: English (United Kingdom)
Formatted: Font: Cambria, 11 pt, English (United
— — ISO Online browsing platform: available at https://www.iso.org/obphttps://www.iso.org/obp
Kingdom)
Formatted: English (United Kingdom)
— — IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
Formatted: Default Paragraph Font, Font color: Auto,
4 Principle
English (United Kingdom)
Formatted: English (United Kingdom)
An enamelled specimen is exposed to attack by an alkaline liquid under specified conditions of temperature
Formatted: Default Paragraph Font, Font color: Auto,
and time. The solution is not stirred during the test.
English (United Kingdom)
The loss in mass is determined and used to calculate the rate of loss in mass per unit area and, if necessary,
Formatted: Adjust space between Latin and Asian text,
the corrosion rate.
Adjust space between Asian text and numbers
5 Reagents
During the determination, use only reagents of recognized analytical grade, unless otherwise specified.
5.1 5.1 Water, in accordance with grade 3 of ISO 3696, i.e. distilled water or water of equivalent
Formatted: Font: 11 pt, Not Bold
purity.
Formatted: Adjust space between Latin and Asian text,
Adjust space between Asian text and numbers, Tab
5.2 5.2 Acetic acid solution, 50 ml/l, for cleaning the test specimens.
stops: Not at 0.7 cm + 1.4 cm + 2.1 cm + 2.8 cm +
3.5 cm + 4.2 cm + 4.9 cm + 5.6 cm + 6.3 cm + 7 cm
5.3 5.3 Degreasing solvent, e.g. ethanol (C H OH) or water containing a few drops of liquid
2 5
Formatted: Font: Not Bold
detergent, suitable for cleaning and degreasing the test specimens.
Formatted: Font: 11 pt, Not Bold
5.4 5.4 Sodium hydroxide (NaOH).
Formatted: Font: Not Bold
6 Apparatus and material Formatted: Font: 11 pt, Not Bold
Formatted: Font: Not Bold
6.1 Test apparatus
Formatted: Font: 11 pt, Not Bold
Cylindrical vessel with a volume-surface ratio 20:1 cm.
Formatted: Font
...