The document compares three common standards for specifying the quality of glass fused-to-steel coatings on bolted steel liquid storage tanks: ISO 28765, EEA, and AWWA D103. ISO has the most stringent requirements with 19 tests, while EEA has 15 tests and is less stringent. AWWA only requires thickness and a wet sponge holiday test. Each standard has different quality levels for applications. ISO has four levels covering municipal and industrial uses, while EEA has three levels for agriculture and industry. The standards differ significantly in their testing protocols and quality criteria.

1. A Comparison of Commonly Specified
Quality Standards
a) Background
b) The Question
c) Research
d) Conclusions
e) Specifier – Buyer - Provider Recommendations

2. Glass Fused-to-
Steel Bolted Tank
Coatings
• Bolted Steel Tanks are unique in their
ability to utilize high-grade Glass Fused-
to-Steel (gf2s™) factory applied coatings
• The gf2s coatings are applied to both
the interior and exterior surfaces
• In many liquid storage applications,
gf2s coatings provide the best available
and longest lasting service with the
lowest life-cycle cost of ownership
• HOWEVER – NOT ALL GLASS COATINGS
ARE CREATED EQUAL!

3. Comparing
Commonly
Referenced
gf2s Bolted
Steel Tank
Standards
Coating
Quality
Three (3) standards are commonly used for specifying the quality of gf2s coatings on
bolted steel liquid storage tanks. The ISO and EEA requirements are both based on a
regimen of specific tests, while the AWWA standard incorporates a less structured
approach.
The goals of this presentation are to…
• provide a comparison of the 3 standards relative to gf2s quality requirements, to…
• determine if a gf2s quality hierarchy exists across the 3 standards, to…
• provide simple comparative tools to better allow buyers and specifiers to designate
the gf2s coating quality requirements for their specific projects, and to…
• provide suppliers with a structured approach to communicating their quality offerings
to the market.
The Standards Referenced
• ISO 28765:2016 (International Standards Organization) – Vitreous and porcelain
enamels – Design of bolted steel tanks for the storage or treatment of water or
municipal or industrial effluents and sludges
• EEA 7.20, 7.24, 7.25 (European Enamel Authority e.V.) - Quality Requirements 4th
Edition
• ANSI/AWWA D103-19 (American National Standards Institute/ American Water Works
Association) - Factory-Coated Bolted Carbon Steel Tanks for Water Storage

4. gf2s Quality
Levels and
Applications
• Each Standard has specific quality
level applications
• AWWA has only one application –
municipal potable water storage
• EEA has three quality levels – 2 for
agriculture and 1 for industrial
• ISO has 4 quality levels covering a
wide range of municipal and
industrial water and wastewater
applications
Standard
Quality
Level Applications
AWWA D103-19 Municipal potable water
European
Enamel
Authority –
4th Edition
7.25 Dung silos
7.24 Animal feed silos
7.20 Industrial tanks
ISO
28765:2016
QL-1* Biogas digester for agricultural waste - cylinders
QL-2*
Municipal mesophilic digester – cylinders
Municipal sludge treatment – cylinders
Municipal sludge/sludge cake storage
Filter tanks
Storm/firewater
Potable water - DWI listed Reg 31 and ANSI/NSF 61 listed
QL-3*
Industrial effluent process/treatment
Biogas digester for agricultural waste – roof and rings exposed to gaseous zone
Thermophilic/pasteurization digester – cylinders
Municipal mesophilic digester – roof and rings exposed to gaseous zone
Liquid leachate
Municipal sludge treatment – roof and rings exposed to gaseous zone
Borehole/brackish/seawater
QL-4* Thermophilic/pasteurization digester – roof and rings exposed to gaseous zone
* For the purposes of this presentation we
have arbitrarily assigned each of the ISO
28765 quality levels an individual quality
name – i.e. QL-1, QL-2, QL-3 and QL-4.

5. So… What’s the difference?
It’s All About the Glass!
• The 3 Standards each have unique testing protocols and
quality criteria
• EEA and ISO have similar structures with specific testing and
result requirements
• ISO has the most stringent requirements with 19
listed tests
• EEA is similar but with 15 listed tests and less
stringent test result requirements
• AWWA has only…
• A thickness requirement, and…
• An interior surface low-voltage wet sponge “holiday”
test with any holidays found to be repaired
Property, Test, Inspection Method (From ISO 28765) Inspection Frequency
1 Resistance to chemical corrosion by citric acid at room termparature: ISO 28706-1:2008 Clause 9 Monthly or with each batch
2 Resistance to chemical corrosion by sulphuric acid at room termparature: ISO 28706-1:2008 Clause 10 Monthly or with each batch
3 Resistance to chemical corrosion by hydrochloric acid at room termparature: ISO 28706-1:2008 Clause 11
(10% solution for 15 minutes)
Monthly or with each batch
4 Resistance to chemical corrosion by boiling citric acid at room termparature: ISO 28706-1:2008 Clause 10
- Max mass loss after 2.5 hours
Annually
5 Resistance to chemical corrosion by hydrochloric acid at room termparature; ISO 28706-2:2008 Clause 12
- Vapour phase - Max mass loss after 7 days
Annually
6a Resistance to chemical corrosion by boiling distilled or demineralized water; ISO 28706-2:2008 Clause 13
- Liquid phase - Max mass loss after 48 hours
Annually
ISO 28765
QL-4
Class AA
Class AA
Class AA
0.75 gm/m2
7.0 gm/m2
2.5 gm/m2
EEA
7.20
Class A
Class A
Class A
5.0 gm/m2
Not required
5.0 gm/m2
6b Resistance to chemical corrosion by boiling distilled or demineralized water; ISO 28706-2:2008 Clause 13
- Vapour phase - Max mass loss after 48 hours
Annually 5.0 gm/m2 10.0 gm/m2
7 Resistance to chemical corrosion by standard detergent solutions; ISO 28706-3:2008 Clause 9 - Max mass
loss after 24 hours
Annually 2.5 gm/m2 5.0 gm/m2
8 Resistance to chemical corrosion by hot sodium hydroxide; ISO 28706-4:2008 Clause 9 - Max mass loss
after 24 hours
Annually 6.0 gm/m2 8.0 gm/m2
9 Resistance to thermal shock; ISO 28763:2008, Annex A - Damage at 350 ℃ Annually No damage Not required
10 Resistance to impact: Pistol test; ISO 4532 - Max damage < 2 mm in diameter after 24 hours Monthly or with each batch 40 N force 20 N force
11 Determination of the resistance to abrasion; ISO 6370-2 - Max mass loss Annually 45 gm/m2 Not required
12 Scratch hardness of surface according to Mohs; EN 15771 Monthly or with each batch Mohs 5 Mohs 5
13 Adherence level; EN 10209:2013, Annex C Monthly or with each batch Class 2 Class 2
14 Enamel Thickness - Inside Surface; ISO 2178 Per ISO 2859-1:1999 300 - 500 µm 180 - 500 µm
15 Enamel Thickness - Outside Surface; ISO 2178 Per ISO 2859-1:1999 160 - 500 µm 180 - 500 µm
16 Defects - Inside Surface - No Discontinuities — Classes AA, A, B - ISO 2746:2015 Test A High Voltage
Test. Class C - ISO 8289:2000 Method A Low Voltage Wet Sponge Test
Every panel 1500 v - No
Discontinuities
High Voltage per
agreement - No
Discontinuities
18 Colour - Outside Surface, Colour and colour tolerances shall be agreed between interested parties Per ISO 2859-1:1999 Not required
ISO 28765
QL-1
Class A
Not required
Not required
5.0 gm/m2
Not required
5.0 gm/m2
Not required
Not required
7.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
160 - 360 µm
160 - 500 µm
9 v - No
Discontinuities
Inspection using a colour comparator approved prior to produciton by the
vitreous enameller
ISO 28765
QL-2
Class A+
Not required
Not required
3.0 gm/m2
Not required
5.0 gm/m2
Not required
Not required
7.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
200 - 400 µm
160 - 500 µm
700 v - No
Discontinuities
ISO 28765
QL-3
Class AA
Class A+
Class A+
1.5 gm/m2
8.0 gm/m2
2.5 gm/m2
7.5 gm/m2
5.0 gm/m2
6.0 gm/m2
No damage
40 N force
45 gm/m2
Mohs 5
Class 2
260 - 460 µm
160 - 500 µm
1100 v - No
Discontinuities
EEA
7.24
Class A
Not required
Not required
7.0 gm/m2
Not required
7.0 gm/m2
Not required
Not required
8.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
9 v Wet Sponge -
Max 5 defects/m2
EEA
7.25
Class A
Not required
Not required
7.0 gm/m2
Not required
7.0 gm/m2
Not required
Not required
8.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
AWWA
D103
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
150 - 480 µm
150 - 480 µm
Max 67.5 v
Wet Sponge, # of
defects not limited
Not required
ISO 28765:2016 - Vitreous and porcelain enamels - Design of bolted steel tanks for the storage or treatment of water or municipal or industrial effluents and sludges
European Enameling Authority e.V. - Quality Requirements - 4th Edition
American Water Works Association/American National Standards Institute D103-19 Factory-Coated Bolted Carbon Steel Tanks for Water Storage
17 Defects - Outside Surface, mximum visible defects Every panel Max defect size 1mm, max 5 defects/m2
Max defect size 1 mm, max 3 defects per m2 No limit
The next slide shows the details of the testing
requirements and the results.

6. Property, Test, Inspection Method (From ISO 28765) Inspection Frequency
1 Resistance to chemical corrosion by citric acid at room termparature: ISO 28706-1:2008 Clause 9 Monthly or with each batch
2 Resistance to chemical corrosion by sulphuric acid at room termparature: ISO 28706-1:2008 Clause 10 Monthly or with each batch
3 Resistance to chemical corrosion by hydrochloric acid at room termparature: ISO 28706-1:2008 Clause 11
(10% solution for 15 minutes)
Monthly or with each batch
4 Resistance to chemical corrosion by boiling citric acid at room termparature: ISO 28706-1:2008 Clause 10
- Max mass loss after 2.5 hours
Annually
5 Resistance to chemical corrosion by hydrochloric acid at room termparature; ISO 28706-2:2008 Clause 12
- Vapour phase - Max mass loss after 7 days
Annually
6a Resistance to chemical corrosion by boiling distilled or demineralized water; ISO 28706-2:2008 Clause 13
- Liquid phase - Max mass loss after 48 hours
Annually
ISO 28765
QL-4
Class AA
Class AA
Class AA
0.75 gm/m2
7.0 gm/m2
2.5 gm/m2
EEA
7.20
Class A
Class A
Class A
5.0 gm/m2
Not required
5.0 gm/m2
6b Resistance to chemical corrosion by boiling distilled or demineralized water; ISO 28706-2:2008 Clause 13
- Vapour phase - Max mass loss after 48 hours
Annually 5.0 gm/m2 10.0 gm/m2
7 Resistance to chemical corrosion by standard detergent solutions; ISO 28706-3:2008 Clause 9 - Max mass
loss after 24 hours
Annually 2.5 gm/m2 5.0 gm/m2
8 Resistance to chemical corrosion by hot sodium hydroxide; ISO 28706-4:2008 Clause 9 - Max mass loss
after 24 hours
Annually 6.0 gm/m2 8.0 gm/m2
9 Resistance to thermal shock; ISO 28763:2008, Annex A - Damage at 350 ℃ Annually No damage Not required
10 Resistance to impact: Pistol test; ISO 4532 - Max damage < 2 mm in diameter after 24 hours Monthly or with each batch 40 N force 20 N force
11 Determination of the resistance to abrasion; ISO 6370-2 - Max mass loss Annually 45 gm/m2 Not required
12 Scratch hardness of surface according to Mohs; EN 15771 Monthly or with each batch Mohs 5 Mohs 5
13 Adherence level; EN 10209:2013, Annex C Monthly or with each batch Class 2 Class 2
14 Enamel Thickness - Inside Surface; ISO 2178 Per ISO 2859-1:1999 300 - 500 µm 180 - 500 µm
15 Enamel Thickness - Outside Surface; ISO 2178 Per ISO 2859-1:1999 160 - 500 µm 180 - 500 µm
16 Defects - Inside Surface - No Discontinuities — Classes AA, A, B - ISO 2746:2015 Test A High Voltage
Test. Class C - ISO 8289:2000 Method A Low Voltage Wet Sponge Test
Every panel 1500 v - No
Discontinuities
High Voltage per
agreement - No
Discontinuities
18 Colour - Outside Surface, Colour and colour tolerances shall be agreed between interested parties Per ISO 2859-1:1999 Not required
ISO 28765
QL-1
Class A
Not required
Not required
5.0 gm/m2
Not required
5.0 gm/m2
Not required
Not required
7.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
160 - 360 µm
160 - 500 µm
9 v - No
Discontinuities
Inspection using a colour comparator approved prior to produciton by the
vitreous enameller
ISO 28765
QL-2
Class A+
Not required
Not required
3.0 gm/m2
Not required
5.0 gm/m2
Not required
Not required
7.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
200 - 400 µm
160 - 500 µm
700 v - No
Discontinuities
ISO 28765
QL-3
Class AA
Class A+
Class A+
1.5 gm/m2
8.0 gm/m2
2.5 gm/m2
7.5 gm/m2
5.0 gm/m2
6.0 gm/m2
No damage
40 N force
45 gm/m2
Mohs 5
Class 2
260 - 460 µm
160 - 500 µm
1100 v - No
Discontinuities
EEA
7.24
Class A
Not required
Not required
7.0 gm/m2
Not required
7.0 gm/m2
Not required
Not required
8.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
9 v Wet Sponge -
Max 5 defects/m2
EEA
7.25
Class A
Not required
Not required
7.0 gm/m2
Not required
7.0 gm/m2
Not required
Not required
8.0 gm/m2
Not required
20 N force
Not required
Mohs 5
Class 2
AWWA
D103
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
Not required
150 - 480 µm
150 - 480 µm
Max 67.5 v
Wet Sponge, # of
defects not limited
Not required
ISO 28765:2016 - Vitreous and porcelain enamels - Design of bolted steel tanks for the storage or treatment of water or municipal or industrial effluents and sludges
European Enameling Authority e.V. - Quality Requirements - 4th Edition
American Water Works Association/American National Standards Institute D103-19 Factory-Coated Bolted Carbon Steel Tanks for Water Storage
17 Defects - Outside Surface, mximum visible defects Every panel Max defect size 1mm, max 5 defects/m2
Max defect size 1 mm, max 3 defects per m2 No limit

7. Initial Comparison
Between Standards
• Each Standard has its own quality level
hierarchy, for example…
• EEA – 7.20 is better than 7.24 which is
better than 7.25
• ISO – QL-4 is better than QL-3 which is
better than QL-2 which is better than QL-1
• AWWA – there is only one quality level
• Is it possible to create a quality hierarchy
comparing all three Standards?
• For the most part yes, but there is some
ambiguity when comparing ISO QL-1 and QL-2 to
EEA 7.20. Comparing the general testing sections,
we observe that…
• Acid resistance: QL-2 is notably better while 7.20
and QL-1 are essentially the same
• Pure water resistance: No significant difference
• Alkali resistance: No significant difference
• Physical properties: No difference
• Thickness & defects: QL-2 and 7.20 are notably
better than QL-1 as they require the more
demanding high voltage discontinuity testing
• Based on this comparison, we suggest that
ISO QL-2 is somewhat better than EEA 7.20,
which is somewhat better than ISO QL-1
Test ISO QL - 1 EEA 7.20 ISO QL - 2
Citric Acid Resistance Class A Class A Class A+
Sulphuric Acid Resistance Not Req’d Class A Not Req’d
Hydrochloric Acid Resistance Not Req’d Class A Not Req’d
Boiling Citric Acid Resistance (max mass loss) 5.0 gm/m2 5.0 gm/m2 3.0 gm/m2
Hydrochloric Acid Vapor Resistance (max mass loss) Not Req’d Not Req’d Not Req’d
Boiling DI/Demin Water Resistance (max mass loss) 5.0 gm/m2 5.0 gm/m2 5.0 gm/m2
Boiling DI/Demin Vapor Resistance (max mass loss) Not Req’d 10.0 gm/m2 Not Req’d
Detergent Resistance (max mass loss) Not Req’d 5.0 gm/m2 Not Req’d
Sodium Hydroxide Resistance (max mass loss) 7.0 gm/m2 8.0 gm/m2 7.0 gm/m2
Thermal Shock Resistance Not Req’d Not Req’d Not Req’d
Impact Resistance (force) 20 N 20 N 20 N
Abrasion Resistance (mass loss) Not Req’d Not Req’d Not Req’d
Hardness (Mohs) 5 5 5
Adhesion Class 2 Class 2 Class 2
Inside Enamel Thickness (µm) 160 - 360 180 - 500 200 - 400
Outside Enamel Thickness (µm) 160 - 500 180 - 500 160 - 500
Defects - Inside Zero at 9 v
low voltage
wet sponge
Zero at high
voltage per
agreement
Zero at 700 v
high voltage
Defects – Outside (max size/max # per m2) 1 mm / 3 1mm / 5 1mm / 3
Outside Color (color comparator) yes Not Req’d yes

8. gf2s Quality Protocol
Levels
Using the information from the
ISO QL-2, QL-2 and EEA 7.20
comparison, we can now
compare these with the other
categories and establish the
quality hierarchy shown in this
table.
Standard Glass Quality
Category
Quality
Protocol Level
QL - 4 Highest
QL - 3 High
QL - 2 Medium High
7.20 Medium +
QL - 1 Medium
7.24 Medium Low
7.25 Low
AWWA D103 Lowest
ISO
EEA
ISO
ISO
ISO
EEA
EEA

9. gf2s Bolted Tank Coating
Quality Comparative Hierarchy
This table makes it easy to
compare individual glass fused-
to-steel bolted tank coatings
from the three Standards using
a simple “meets or exceeds”
structure
Relative Comparison of the Glass Quality Requirements of the Three Standards Reviewed
AWWA D103-19 EEA - 4th Edition ISO 28765:2016
AWWA D103 EEA 7.25
Does AWWA D103 meet or exceed the
glass quality requiremenets of:
No
Does EEA 7.25 meet or exceed the glass
quality requiremenets of:
Yes
Does EEA 7.24 meet or exceed the glass
quality requiremenets of:
Yes Yes
Does EEA 7.20 meet or exceed the glass
quality requiremenets of:
Yes Yes
Does ISO Class “QL-1” meet or exceed
the glass quality requiremenets of:
Yes Yes
Does ISO Class “QL-2” meet or exceed
the glass quality requiremenets of:
Yes Yes
Does ISO Class “QL-3” meet or exceed
the glass quality requiremenets of:
Yes Yes
Does ISO Class “QL-4” meet or exceed
the glass quality requiremenets of:
Yes Yes
EEA 7.24
No
No
Yes
Yes
Yes
Yes
Yes
EEA 7.20
No
No
No
No
Yes
Yes
Yes
ISO
“QL-1”
No
No
No
Yes
Yes
Yes
Yes
ISO
“QL-2”
No
No
No
No
No
Yes
Yes
ISO
“QL-3”
No
No
No
No
No
No
Yes
ISO
“QL-4”
No
No
No
No
No
No
No

10. …so… Are All Glass
Fused-to-Steel Coatings
Created Equal?
While one of the Standards (AWWA) implies that
“glass is glass,” the other Standards provide a
discrete differentiation between glass quality
levels. Should one decide to use the AWWA
Standard in bolted glass fused-to-steel tank
specifications it is fully appropriate, and perhaps
wise, to supplement the AWWA Standard with gf2s
quality requirements from either the ISO or EEA
Standard. For instance, if specifying AWWA D103
for potable water storage we would suggest
including a requirement that the gf2s coating
comply with the potable water quality
requirements of ISO 28765 (i.e. QL-2).

11. Buyers –
The key for Buyers is to simply make sure you know what you are
getting, and that you are getting what you want. A core intent of this
presentation is to simplify the gf2s information to allow the Buyer to
easily understand the different quality levels, to determine which quality
level is wanted, and to determine what quality levels different suppliers
may be offering.
Suppliers –
Using the information herein, Suppliers have a simple and transparent
method to communicate their gf2s product offerings to Specifiers and
Buyers. We encourage suppliers to download and use this presentation
as an education tool for their clients, their quotations and their
supporting documentation. We also encourage suppliers to openly and
publicly indicate their gf2s product quality levels.
Specifiers - Buyers
- Suppliers
Recommendations
Specifiers –
Specifiers should be aware of the differences between the Standards and
how glass fused-to-steel coating quality is addressed. If a particular
service level is desired but not fully addressed by the design standard
being considered, it is fully acceptable to use a different standard for
specifying the gf2s quality. For instance, if using AWWA D103 for the
design standard, it is certainly appropriate to include that the gf2s
coating shall comply with ISO 28765:2016 quality regime for potable
water (i.e. QL-2).

12. Notes: The Author
Thomas Renich
Thomas Renich is the owner of JATO Services LLC, a private consulting and services
business focused on bolted tanks, international sales and international marketing.
Mr. Renich has more than forty-five years’ experience in concrete and steel tank
construction with an emphasis on international marketing, operations, and project
management. Mr. Renich can be reached at:
JATO Services LLC – 27018 W 73rd St. – Shawnee, KS 66227 USA
Email – trenich@me.com
The author wishes to thank, and acknowledge the support of, Mr. James Mansour, the
founder and President of United Industries Group, Inc. for his assistance in gathering the
information contained herein. Mr. Mansour has over fifty years’ experience in the design,
supply, and installation of cylindrical above ground bolted steel storage tanks and can be
reached at: United Industries Group, Inc. – 11 Rancho Circle – Lake Forest, CA 92630 USA;
Email – info@unitedind.com; Website – www.unitedind.com
Images are courtesy of JATO Services LLC and United
Industries Group, Inc.
© 2021 - JATO Services LLC
The information herein is deemed accurate as of the date of
publication.
The information provided in this document is provided “as is”
without warranty of any kind. The authors disclaim all
warranties, either express or implied, including warranties of
merchantability and fitness for a particular purpose. In no
even shall the authors be liable for any damages whatsoever
including direct, indirect, incidental, consequential, loss of
business profits or special damages, even if the authors have
been advised of the possibility of such damages.
gf2s™ is a trademark of JATO Services LLC