EN ISO 28765:2011

SLOVENSKI STANDARD
01-januar-2012
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SIST EN 15282:2007
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MHNOHQLKUH]HUYRDUMHY]DVNODGLãþHQMHDOLSULSUDYRYRGHDOLNRPXQDOQLKDOL
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Vitreous and porcelain enamels - Design of bolted steel tanks for the storage or
treatment of water or municipal or industrial effluents and sludges (ISO 28765:2008)
Emails und Emaillierungen - Gestaltung von verschraubten Stahlbehältern für die
Speicherung oder Behandlung von Wasser oder kommunalen und industriellen
Abwässern und Abwasserschlamm (ISO 28765:2008)
Émaux vitrifiés - Conception de réservoirs en acier boulonnés pour le stockage ou le
traitement des eaux ou des effluents d'eaux usées urbains ou industriels (ISO
28765:2008)
Ta slovenski standard je istoveten z: EN ISO 28765:2011
ICS:
23.020.10 1HSUHPLþQHSRVRGHLQ Stationary containers and
UH]HUYRDUML tanks
25.220.50 Emajlne prevleke Enamels
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 28765
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2011
ICS 25.220.50 Supersedes EN 15282:2007
English Version
Vitreous and porcelain enamels - Design of bolted steel tanks
for the storage or treatment of water or municipal or industrial
effluents and sludges (ISO 28765:2008)
Émaux vitrifiés - Conception de réservoirs en acier Emails und Emaillierungen - Gestaltung von verschraubten
boulonnés pour le stockage ou le traitement des eaux ou Stahlbehältern für die Speicherung oder Behandlung von
des effluents d'eaux usées urbains ou industriels (ISO Wasser oder kommunalen und industriellen Abwässern und
28765:2008) Abwasserschlamm (ISO 28765:2008)
This European Standard was approved by CEN on 3 March 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 28765:2011: E
worldwide for CEN national Members.

Contents Page
Foreword .3

Foreword
The text of ISO 28765:2008 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
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 September 2011, and conflicting national standards shall be
withdrawn at the latest by September 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 15282:2007.
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 28765:2008 has been approved by CEN as a EN ISO 28765:2011 without any modification.

INTERNATIONAL ISO
STANDARD 28765
First edition
2008-10-01
Vitreous and porcelain enamels —
Design of bolted steel tanks for the
storage or treatment of water or
municipal or industrial effluents and
sludges
Émaux vitrifiés — Conception de réservoirs en acier boulonnés pour le
stockage ou le traitement des eaux ou des effluents d'eaux usées
urbains ou industriels
Reference number
ISO 28765:2008(E)
©
ISO 2008
ISO 28765:2008(E)
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ii © ISO 2008 – All rights reserved

ISO 28765:2008(E)
Contents Page
Foreword. iv
1 Scope . 1
2 Normative references . 2
3 Terms and definitions. 3
4 Symbols and abbreviated terms . 5
5 Units . 6
6 Information and requirements to be agreed and documented . 6
6.1 General. 6
6.2 Information to be provided by the purchaser . 6
6.3 Information to be provided by the designer .7
7 Applicable standards. 7
8 Loads. 8
8.1 General. 8
8.2 Contents . 8
8.3 Tank structure . 9
8.4 Roof. 9
8.5 Equipment loads . 10
8.6 Access . 10
8.7 Environmental . 10
8.8 Ancillary items . 11
9 Design . 11
9.1 General. 11
9.2 Steel. 11
9.3 Tank. 12
9.4 Openings . 17
9.5 Effects of accidents. 18
10 Vitreous-enamel coating . 19
10.1 Vitreous enamel . 19
10.2 Coating. 19
10.3 Vitreous-enamel quality . 19
10.4 Protection during shipping. 25
10.5 Maintenance . 25
11 Installation . 25
11.1 General guidance. 25
11.2 Foundations . 25
11.3 Inspection of the vitreous-enamel coating at the construction site. 25
12 Disinfection . 25
Bibliography . 26

ISO 28765:2008(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 28765 was prepared by the European Committee for Standardization (CEN) (as EN 15282) 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.

iv © ISO 2008 – All rights reserved

INTERNATIONAL STANDARD ISO 28765:2008(E)

Vitreous and porcelain enamels — Design of bolted steel tanks
for the storage or treatment of water or municipal or industrial
effluents and sludges
1 Scope
This International Standard establishes the requirements for the design and use of vitreous-enamel-coated
bolted cylindrical steel tanks for the storage or treatment of water or municipal or industrial effluents and
sludges.
It applies to the design of the tank and any associated roof and gives guidance on the requirements for the
design of the foundation.
It applies where
a) the tank is cylindrical and is mounted on a load-bearing base substantially at or above ground level;
b) the product of the tank diameter in metres and the wall height in metres lies within the range 5 to 500;
c) the tank diameter does not exceed 100 m and the total wall height does not exceed 50 m;
d) the stored material has the characteristics of a liquid, exerting a negligible frictional force on the tank wall;
the stored material may be undergoing treatment as part of a municipal or industrial effluent treatment
process;
e) the internal pressure in the headspace above the liquid does not exceed 50 kPa and the internal partial
vacuum above the liquid does not exceed 10 kPa;
f) the walls of the tank are vertical;
g) the floor of the tank is substantially flat at its intersection with the wall; the floor of the tank may have a
rise or fall built in to allow complete emptying of the tank contents, the slope of which does not exceed
1:100;
h) there is negligible inertial and impact load due to tank filling;
i) the minimum thickness of the tank shell is 1,5 mm;
j) the material used for the manufacture of the steel sheets is carbon steel (tanks constructed of sheets
made from aluminium or stainless steel are outside the scope of this International Standard);
k) the temperature of the tank wall during operation is within the range −50 °C to +100 °C under all
operating conditions.
This International Standard also gives details of procedures to be followed during installation on site and for
inspection and maintenance of the installed tank.
It does not apply to chemical-reaction vessels.
It does not apply to tanks fitted with floating roofs.
It does not cover resistance to fire.
ISO 28765:2008(E)
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 2178, Non-magnetic coatings on magnetic substrates — Measurement of coating thickness — Magnetic
method
ISO 2747, Vitreous and porcelain enamels — Enamelled cooking utensils — Determination of resistance to
thermal shock
ISO 2859-1, Sampling procedures for inspection by attributes — Part 1: Sampling schemes indexed by
acceptance quality limit (AQL) for lot-by-lot inspection
ISO 4532, Vitreous and porcelain enamels — Determination of the resistance of enamelled articles to
impact — Pistol test
ISO 6370-2, Vitreous and porcelain enamels — Determination of the resistance to abrasion — Part 2: Loss in
mass after sub-surface abrasion
ISO 8289:2000, Vitreous and porcelain enamels — Low voltage test for detecting and locating defects
ISO 15686-1, Buildings and constructed assets — Service life planning — Part 1: General principles
ISO 28706-1:2008, Vitreous and porcelain enamels — Determination of resistance to chemical corrosion —
Part 1: Determination of resistance to chemical corrosion by acids at room temperature
ISO 28706-2:2008, 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 28706-3:2008, Vitreous and porcelain enamels — Determination of resistance to chemical corrosion —
Part 3: Determination of resistance to chemical corrosion by alkaline liquids using a hexagonal vessel
ISO 28706-4:2008, 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
EN 101, Ceramic tiles — Determination of scratch hardness of surface according to Mohs
EN 1993-1-6, Eurocode 3 — Design of steel structures — Part 1-6: Strength and Stability of Shell Structures
EN 1993-4-1, Eurocode 3 — Design of steel structures — Part 4-1: Silos
EN 1993-4-2, Eurocode 3 — Design of steel structures — Part 4-2: Tanks
EN 1998-4, Eurocode 8 — Design of structures for earthquake resistance — Part 4: Silos, tanks and pipelines
EN 10209:1996, Cold rolled low carbon steel flat products for vitreous enamelling — Technical delivery
conditions
EN 14430:2004, Vitreous and porcelain enamels — High voltage test
ANSI/AWWA D 103-97, Factory-Coated Bolted Steel Tanks for Water Storage
2 © ISO 2008 – All rights reserved

ISO 28765:2008(E)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
brief
working document which specifies at any point in time the relevant needs and aims of the project, the
resources to be provided by the client, the details of the project and any applicable design requirements within
which all subsequent briefing (when needed) and designing can take place
3.2
client
person or organization that requires a tank to be provided, altered or extended and is responsible for initiating
and approving the brief
3.3
defect
break in the surface of the vitreous enamel
3.4
designer
person or organization responsible for stating the shape and specification of the component to be designed
3.5
design life
service life intended by the designer
3.6
discontinuity
defect area or spot that allows an electric current to pass when tested with low-voltage or high-voltage test
apparatus
3.7
enamel supplier
person or organization supplying materials for use by the vitreous enameller in the enamelling process
3.8
freeboard
distance between the top of the cylindrical-tank vertical shell wall and the surface of the contained liquid at the
specified operating level
3.9
headspace pressure
pressure within a roofed tank above the stored liquid
3.10
inspection area
area inside a boundary 25 mm from any panel edge or hole and outside a boundary 25 mm from any opening
or hole within the body of a panel
3.11
liquid
bulk substance that exerts substantially the same vertical and horizontal pressures and has no fixed shape
ISO 28765:2008(E)
3.12
maintenance
combination of all technical and associated administrative actions during the service life to retain a tank or its
parts in a state in which it can perform its required function
3.13
manufacturer
person or organization that manufactures the tank or parts of the tank
3.14
purchaser
person or organization purchasing the tank from the supplier
NOTE The purchaser can also be the client.
3.15
rectification
return of a tank or its parts to an acceptable condition by the renewal, replacement or repair of worn, damaged
or degraded parts
3.16
supplier
person or organization that supplies the tank or parts of the tank
3.17
service life
period of time after installation during which the tank or its parts meets or exceeds the performance
requirements
3.18
tank
cylindrical, vertical shell for containing liquid, with or without a roof, which is constructed from vitreous-
enamelled curved steel panels bolted together on the construction site and mounted on a base which may
also form the floor of the container
3.19
vitreous enameller
person undertaking and controlling the process of preparing the steel sheets and applying the vitreous-enamel
coating to the surfaces of the steel sheets
NOTE The vitreous enameller will normally be the manufacturer.
3.20
vitreous enamel
substantially vitreous, or glassy, inorganic silica coating bonded to steel by fusion at a temperature above
750 °C
NOTE 1 This coating is applied for protective purposes to the internal liquid contact surface of the steel and for
functional and decorative purposes to the external surface of the steel.
NOTE 2 The coating is produced by a proprietary formulation of silica glass, minerals and clays to produce a medium,
dry or suspended in water, which can be sprayed on to the surface of curved steel sheets and subsequently fusion bonded.
4 © ISO 2008 – All rights reserved

ISO 28765:2008(E)
4 Symbols and abbreviated terms
For the purposes of this document, the following symbols and abbreviations apply.
D tank diameter
E Young's modulus of elasticity
F static hoop force
H
g acceleration due to gravity
H depth of liquid at point under consideration, measured from the liquid surface at the maximum
possible filling level
H total vertical wall height
l length of shell between intermediate stiffeners
I second moment of area of a stiffener
z
p static liquid pressure at a specified depth
n
p headspace pressure
h
r tank radius
q critical external buckling pressure

r,cr
q maximum stagnation pressure due to wind
w
max
w proportion of dissolved solids in sludge
t shell plate thickness
ν Poisson's ratio
γ partial load factor
ρ relative density of a liquid
σ stress
σ critical axial buckling resistance

z,cr
(subscript) critical
cr
(subscript) dissolved solids
ds
(subscript) headspace
h
(subscript) maximum value
max
(subscript) normal to the tank wall
n
(subscript) sludge
s
(subscript) wind
w
(subscript) coincident with the central axis of a shell of revolution
z
(subscript) coincident with the radial axis of a shell of revolution
ϕ
ISO 28765:2008(E)
5 Units
The use of one of the following sets of consistent units is recommended:
⎯ dimensions: m, mm
3 3
⎯ unit weight: kN/m , N/mm
⎯ forces and loads: kN, N
⎯ line forces and line loads: kN/m, N/mm
⎯ pressures and area-distributed actions: kPa, MPa
3 3
⎯ unit mass: kg/m , kg/mm
2 2
⎯ acceleration: km/s , m/s
⎯ membrane-stress resultants: kN/m, N/mm
⎯ bending-stress resultants: kNm/m, Nmm/mm
⎯ stresses and elastic moduli: kPa, MPa (1 MPa = 1 N/mm )
6 Information and requirements to be agreed and documented
6.1 General
For the safe design and manufacture of the tank and associated parts, the specification shall be agreed
between the contracting parties.
6.2 Information to be provided by the purchaser
The purchaser shall provide the supplier with a specification that shall include, but not be limited to, the
following:
a) The specification of the stored liquid, that shall include, but not be limited to, the following:
1) the name and/or a description of the liquid;
2) the relative density;
3) any relevant properties or characteristics particular to the liquid to be stored;
4) the operating-temperature range.
b) The environmental conditions, that shall include, but not be limited to, the following:
1) wind;
2) seismic action;
3) snow;
4) ice;
5) temperature ranges.
6 © ISO 2008 – All rights reserved

ISO 28765:2008(E)
c) The use and planned dimensions of the tank, that shall include, but not be limited to, the following:
1) the rates of fill and discharge;
2) a summary describing the purpose of the tank and its method of operation;
3) the net effects of the process on the tank or any of its components;
4) the tank dimensions.
d) The planned location of all openings in the tank shell and roof.
e) Attached equipment:
1) method of attachment;
2) dead and live loads;
3) connections.
f) The proximity of other tanks and buildings.
6.3 Information to be provided by the designer
The designer shall provide essential data concerning the design limitations of the tank, that shall include, but
not be limited to, the following:
a) the name and a description of the stored liquid or liquids;
b) the range of the relative densities of the stored liquid or liquids;
c) the limits of the environmental criteria used in the design, including, where relevant, the design wind
speed, the design operating-temperature range, the design snow load and the seismic zone and seismic
coefficients;
d) the maximum access and superimposed loads used in the design;
e) a maintenance plan conforming to the requirements of ISO 15686-1;
f) guidance concerning change of use;
g) all relevant data assumed by the designer in the design process.
7 Applicable standards
All activities specified in this International Standard shall be carried out under an appropriate quality
[1]
management system. A quality management system conforming to ISO 9001 will be deemed to satisfy this
requirement.
The designer and client shall agree, through consultation, upon the applicable standards to be used for design
purposes. Where provision is not made within this International Standard, other international or national
standards may be specified.
The applicable standards agreed upon shall include, but not be limited to, standards providing details of
parameters for the following design procedures:
a) hydrostatic loads;
b) wind loads;
ISO 28765:2008(E)
c) seismic loads;
d) access loads;
e) snow loads;
f) rain loads;
g) load factors;
h) sheet strength calculations;
i) bolt strength calculations;
j) stability calculations;
k) foundation design.
8 Loads
8.1 General
All tanks and supporting structures shall be designed on a “limit state design” basis.
8.2 Contents
8.2.1 General
Loads due to the liquid shall be calculated considering:
a) the relative density of the specified range of liquids to be stored in the tank;
b) the geometry of the tank;
c) the maximum possible depth of the liquid in the tank.
If the liquid to be stored is sludge, and unless reliable or measured data are provided, the value of the relative
density of the sludge, ρ , may be estimated by simple proportion using the following equation:
s
ρρ=+11w − (1)
()
sds
where ρ is taken as 1,9 in the case of municipal sewage sludge.
ds
8.2.2 Freeboard
The freeboard used for design purposes shall be as agreed between the client and the designer.
Where the tank is designed for seismic conditions, sufficient freeboard shall be provided to contain the
sloshing wave determined in accordance with EN 1998-4. This shall take account of any equipment and
structural members in the top of the tank.
8 © ISO 2008 – All rights reserved

ISO 28765:2008(E)
8.2.3 Hydrostatic pressure
Determine the hydrostatic pressure, p , in kPa, acting on the tank shell at depth H using the following
n
equation:
p=×Hgρ×+p (2)
nh
8.2.4 Axial wall forces
The axial wall forces per unit shell width shall be determined taking account of the following:
a) the tank dead weight;
b) the imposed load;
c) the axial tension and compression due to the wind overturning moment;
d) the axial tension and compression due to seismic actions.
8.2.5 Filling and discharging
The method of filling and discharging the liquid can affect the load and shall be considered by the designer.
These influences include, but are not limited to, the following:
a) the filling position — the inlet stream impinging on the tank wall;
b) completion of discharge — the risk of a hydrodynamic “water hammer” effect if the outlet is closed rapidly;
c) fatigue — the effect of the frequency of the filling and discharge cycles;
d) pressure and/or partial vacuum;
e) venting;
f) rapid changes in temperature.
8.3 Tank structure
The dead load shall be determined as the total weight of all structural components and permanent fittings.
8.4 Roof
The tank designer shall take account of all forces on the tank shell from the roof. These forces may include,
but are not necessarily limited to, the following:
a) distributed in-plane and radial forces transmitted by structural roof members;
b) concentrated in-plane and radial forces resulting from structural features of the roof;
c) asymmetrical forces due to uneven distribution of imposed roof loads;
d) forces induced in the roof by differential settlement of the foundation.
ISO 28765:2008(E)
8.5 Equipment loads
8.5.1 General
In the calculation of the total load on the tank, the designer shall take into account the effect of the attached
equipment for both static and dynamic loads.
8.5.2 Static load
The static load of any equipment attached to the tank shall be determined as the weight of the equipment,
including associated mounting fixtures and any liquid within the equipment, as advised by the purchaser.
8.5.3 Dynamic load
The dynamic forces caused by any equipment shall be determined, where applicable. They may include, but
are not necessarily limited to, the following:
a) starting and operating forces from any rotating or moving piece of equipment mounted on or in the tank;
b) forces imposed on the tank or its attachments from installed process equipment (e.g. forces from
restraining cables of floating aerators);
c) forces imposed on the tank or its attachments due to the operation of installed process equipment
(e.g. forces on attached baffle plates due to forced movement of the tank contents).
8.6 Access
Loads due to access equipment such as walkways and platforms shall be determined taking account of the
type of access required.
a) Where access is for cleaning and repair only, the superimposed load shall be taken as not less than
0,75 kN/m .
b) Where access is required for operational procedures, the superimposed load shall be taken as not less
than 3,0 kN/m .
Where a roof is fitted with a hand-railing, the area within the hand-railing shall be considered as accessible.
8.7 Environmental
8.7.1 General
Environmental loads shall be determined taking into account the design life of the tank.
8.7.2 Seismic action
Where relevant, seismic action shall be determined from the applicable standard.
The designer shall consider the following as a minimum requirement:
a) horizontal acceleration;
b) vertical acceleration;
c) sloshing of the contents;
10 © ISO 2008 – All rights reserved

ISO 28765:2008(E)
d) the anchorage method;
e) dynamic ground response.
Guidance on the determination of seismic action can be found in the International Building Code, in
ANSI/AWWA D 103-97 and in EN 1998-1 and EN 1998-4. When applying ANSI/AWWA D 103-97 in locations
outside North America, zones determined from the 1997 Uniform Building Code may be taken as equivalent.
For the purposes of this International Standard, the loads determined in accordance with
ANSI/AWWA D 103-97 may be considered as characteristic loads.
8.7.3 Wind
The wind speed and pressure to be used for design purposes shall be determined from the applicable
standard for the site location.
8.7.4 Snow
Where applicable, the load induced by snow shall be determined from the applicable standard for the site
location.
8.7.5 Ice
Where applicable, the load induced by ice on the roof shall be determined from the applicable standard for the
site location.
8.8 Ancillary items
The designer shall take account of the forces from ancillary items such as ladders, platforms, valves and
machinery.
9 Design
9.1 General
The design of the tank shall be carried out using a “limit state design” approach. Design life assessment shall
be based on ISO 15686-1.
9.2 Steel
9.2.1 Specification
The steel used shall have a specification, as agreed between the manufacturer, the designer and the steel
supplier, having due regard to the requirements of the enamelling process.
[2] [3]
NOTE Steels conforming to the requirements of EN 10111 and EN 10149-1 (including grades DD 11, S235, S420
[4]
and S460), ASTM A 1011 and other standards can be used successfully for vitreous enamelling with appropriate pre-
treatments.
9.2.2 Effects of the enamelling process
The designer shall take account of the effects of the vitreous-enamelling process on the strength properties of
the steel and shall make details of such effects available to the client on request.
The effect of the enamelling process shall be assessed and monitored over a period of time, using a regular
and documented test regime from which steel strength properties can be predicted with a 95 % confidence
level.
ISO 28765:2008(E)
Where regular and documented testing is not carried out, the yield and tensile strengths of the enamelled
steel used for design purposes shall be reduced by 30 % from the guaranteed minimum strengths confirmed
by the steel manufacturer.
9.3 Tank
9.3.1 Load factors
The load factors used in the design process shall be taken from Table 1.
Table 1 — Load factors
Maximum load factor
Basic load case
γ
Dead load 1,4
Liquid load 1,4
Imposed load 1,6
Wind load 1,4
a
Seismic load 1,4
Wind load acting with seismic load and 1,2
liquid load combined
1,2
Seismic load acting with wind load and
a
liquid load combined
Stability 1,7
Any load when the action is beneficial to 1,0
the load case being considered
a
Seismic actions need not be considered to act under test conditions.
9.3.2 Tank walls
9.3.2.1 General design
The walls of the tank shall be designed to resist the most demanding load combination.
The tank walls shall be designed to resist the forces and moments due to the connection to the foundation,
including any non-linear and stability effects.
For the purposes of this International Standard, wall friction forces due to the stored liquid are small and may
safely be ignored.
9.3.2.2 Hoop force
The hoop force used in the determination of the shell plate thickness and vertical bolted-joint configuration
shall take into account hydrostatic pressure and hydrodynamic pressure due to seismic action.
12 © ISO 2008 – All rights reserved

ISO 28765:2008(E)
9.3.2.3 Static
−1
Determine the hydrostatic hoop force per unit height, F , in kN⋅m , at any level using the equation:
H
D
Fp=× (3)
Hn
9.3.2.4 Seismic
The design method employed by the designer shall take account of the following as a minimum requirement:
a) hydrodynamic hoop forces;
b) axial shell-compression forces;
c) lateral and vertical anchorage forces;
d) the dynamic ground response profile.
The design of tanks for seismic resistance shall be in accordance with EN 1998-4 or Section 12 of
ANSI/AWWA D 103-97.
Where the design is in accordance with ANSI/AWWA D 103-97, the loads determined shall be considered as
characteristic loads, factored using load factors from Table 1 and compared to limit state capacities and
buckling resistances determined in accordance with this International Standard.
9.3.2.5 Bolted joints
Bolts subject to shear forces shall be designed such that they are able to transmit forces between the shell
plates which they connect. The bolt shall be proportioned such that the joint shear plane does not pass
through any part of the thread or the thread run-out.
The vertical bolted joints between shell plates shall be designed to transfer the design hoop force between
adjacent shell plates.
The vertical bolted joints shall be designed taking account of, as a minimum, the following:
a) the tensile stress on any net section through any structurally continuous sequence of bolts;
b) the bearing stress on the steel plates connected by the bolts;
c) the bearing stress on the bolts;
d) the shear stress in the bolts.
The hole bearing strength of the steel may be determined by testing or may be taken from the applicable
standard for the steel being used. Where the bearing strength is determined by testing, details of the test
method shall be made available to the client on request.
The bearing strength and shear strength of the bolts shall be taken from the applicable standard for the bolts
being used.
ISO 28765:2008(E)
9.3.2.6 Axial wall forces
The designer shall consider the effects of axial wall forces on the axial buckling resistance of the tank shell.
The effects of axial load combined with external wind pressure, roof live loads and any internal partial vacuum
due to operational procedures or to the effects of wind-induced suction at roof vents shall also be considered.
The critical axial buckling resistance shall be determined by rigorous analysis. Critical buckling strengths
determined in accordance with EN 1993-4-2 may be considered to satisfy this requirement.
Alternatively, the critical axial buckling resistance, σ , in MPa, may be determined using the following
z,cr
equation:
t
σ =×0,3 E× (4)
z,cr
r
Second-order effects can be present due to irregularities in the shell, particularly with large-diameter tanks,
and the designer should preferably take account of these effects, where relevant.
9.3.2.7 External wind pressure
The designer shall consider the effects of external wind pressure on the following, with the tank in the empty
condition:
a) external pressure buckling;
b) circumferential bending of the tank shell caused by wind pressure variation;
c) axial shell tension and compression;
d) the overturning resistance of the tank hold-down system.
The designer shall take account of the proximity of other tanks and buildings.
The resistance to external wind pressure buckling may be determined by rigorous analysis. Resistance to
external wind pressure buckling determined in accordance with EN 1993-4-1 or EN 1993-1-6 may be taken to
satisfy this requirement.
Alternatively, the critical external buckling pressure, q , in MPa, may be determined using the equation:
r,cr
Et⎛⎞1 t
q =×0,8 (5)
r,cr ⎜⎟
lr
1−υ r
⎝⎠
This equation shall be applied to the shell between the top shell stiffener and the first intermediate shell
stiffener (or the base of the tank where no intermediate shell stiffeners are fitted), and to each successive
portion between any subsequent intermediate shell stiffeners. Where the portion of shell under consideration
is of non-uniform thickness, the mean thickness shall be used.
When comparing this resistance to the wind pressure acting on the tank, the wind pressure shall be taken as
equal to the maximum wind pressure in the radial direction acting equally around the full 360° circumference
of the tank.
The designer may consider a reduced wind speed when designing for test conditions.
The effect of the vitreous-enamel coating may be included in the calculation of shell stiffness in radial-buckling
design.
14 © ISO 2008 – All rights reserved

ISO 28765:2008(E)
9.3.2.8 Top shell stiffener
For open-top tanks, the top shell stiffener shall be proportioned such as to provide sufficient support to prevent
radial buckling of the tank shell. The top shell stiffener may be proportioned by rigorous analysis taking
account of both ring buckling and bending effects. A top shell stiffener proportioned in accordance with
EN 1993-4-1 may be deemed to satisfy this requirement.
Alternatively, the second moment of area of the top shell stiffener, I , in m , may be proportioned using the
z
equation:
qHr
w0
max
I = (6)
z
6E
Additionally, for tanks fitted with a roof, the size of the top shell stiffener shall take account of the magnitude
and distribution of the forces imposed by the roof structure and any fittings.
9.3.2.9 Intermediate shell stiffeners
Any intermediate shell stiffeners may be proportioned by rigorous analysis such as to provide sufficient
support to prevent radial buckling of the ring or group of rings of the tank shell over which it can be shown to
be effective. Intermediate shell stiffeners proportioned in accordance with EN 1993-4-1 may be deemed to
satisfy this provision.
Alternatively, the second moment of area of the intermediate shell stiffeners, I , in m , may be proportioned
z
using the equation:
qlr
w
max
I = (7)
z
3E
where l is the distance between intermediate stiffener rings or between the lowest intermediate stiffener ring
and the bottom of the tank.
9.3.2.10 Thermal
The design of the tank structure shall consider the consequences of thermal effects (displacement, strain,
curvatures, stresses, forces and moments) due to the temperature difference between the stored liquid and
the tank structure and/or between the external environment and the tank structure. The designer shall also
consid
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