High-voltage switchgear and controlgear - Gas-filled wrought steel enclosures

This European Standard applies to welded wrought steel enclosures pressurised with dry air, inert gases, for example sulphur hexafluoride or nitrogen or a mixture of such gases, used in indoor and outdoor installations of high-voltage switchgear and controlgear with rated voltages above 1kV, where the gas is used principally for its dielectric and/or arc-quenching properties with rated voltages.
-   above 1 kV and up to and including 52 kV and with gas-filled compartments with design pressure higher than 300 kPa relative pressure (gauge);
-   and with rated voltage above 52 kV.
The enclosures comprise parts of electrical equipment not necessarily limited to the following examples:
-   circuit-breakers;
-   switch-disconnectors;
-   disconnectors;
-   earthing switches;
-   current transformers;
-   voltage transformers;
-   surge arrestors;
-   busbars and connections;
-   etc.
The scope also covers enclosures of pressurized components such as the centre chamber of live tank switchgear, gas-insulated current transformers, etc.

Hochspannungs-Schaltgeräte und Schaltanlagen - Gasgefüllte Kapselungen aus Schmiedestahl

Appareillage électrique haute tension - Enveloppes sous pression en acier corroyé et en alliage d´acier

La présente Norme européenne s'applique aux enveloppes en acier corroyé soudé sous pression d'air sec et de gaz inertes, par exemple l'hexafluorure de soufre ou l'azote ou un mélange de tels gaz, utilisées dans les installations intérieures et extérieures d'appareillage à haute tension sous des tensions assignées supérieures à 1 kV. Le gaz est utilisé principalement pour ses propriétés diélectriques et/ou d'extinction de l'arc avec des tensions assignées:
-   supérieures à 1 kV et inférieures ou égales à 52 kV, et avec des compartiments à remplissage de gaz dont la pression de calcul est supérieure à une pression relative (manométrique) de 300 kPa;
-   et avec une tension assignée supérieure à 52 kV.
Les enveloppes contiennent des parties d'équipements électriques qui ne se limitent pas nécessairement aux exemples suivants:
-   disjoncteurs;
-   interrupteurs-sectionneurs;
-   sectionneurs;
-   sectionneurs de terre;
-   transformateurs de courant;
-   transformateurs de tension;
-   parafoudres;
-   jeux de barres et barres de raccordement;
-   etc.
Le domaine d'application couvre également les enveloppes de composants sous pression tels que le carter d'appareillage à mécanisme sous tension, les transformateurs de courant à isolation gazeuse, etc.

Visokonapetostne stikalne in krmilne naprave - S plinom polnjena ohišja iz gnetljivega jekla

General Information

Status
Published
Public Enquiry End Date
31-Jan-2018
Publication Date
09-Dec-2018
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
05-Dec-2018
Due Date
09-Feb-2019
Completion Date
10-Dec-2018

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SLOVENSKI STANDARD
SIST EN 50068:2019
01-februar-2018
1DGRPHãþD
SIST EN 50068:1995
SIST EN 50068:2015
Visokonapetostne stikalne in krmilne naprave - S plinom polnjena ohišja iz
gnetljivega jekla
High-voltage switchgear and controlgear - Gas-filled wrought steel enclosures
Hochspannungs-Schaltgeräte und Schaltanlagen - Gasgefüllte Kapselungen aus
Schmiedestahl

Appareillage électrique haute tension - Enveloppes sous pression en acier corroyé et en

alliage d´acier
Ta slovenski standard je istoveten z: EN 50068:2018
ICS:
29.130.10 Visokonapetostne stikalne in High voltage switchgear and
krmilne naprave controlgear
77.080.20 Jekla Steels
SIST EN 50068:2019 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 50068:2019
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SIST EN 50068:2019
EUROPEAN STANDARD EN 50068
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2018
ICS 29.130.10 Supersedes EN 50068:1991
English Version
High-Voltage Switchgear and Controlgear - Gas-filled wrought
steel enclosures

Appareillage électrique haute tension - Enveloppes sous Hochspannungs-Schaltgeräte und Schaltanlagen -

pression en acier corroyé et en alliage d'acier Gasgefüllte Kapselungen aus Schmiedestahl

This European Standard was approved by CENELEC on 2018-08-27. CENELEC 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 CENELEC 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 CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the

same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,

Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,

Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,

Switzerland, Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels

© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.

Ref. No. EN 50068:2018 E
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SIST EN 50068:2019
EN 50068:2018 (E)
Contents Page

European foreword .............................................................................................................................................4

Introduction .........................................................................................................................................................5

1 Scope ......................................................................................................................................................6

2 Normative references ............................................................................................................................6

3 Terms and definitions ...........................................................................................................................7

4 Quality assurance ..................................................................................................................................9

5 Normal and special service conditions ...............................................................................................9

6 Materials .............................................................................................................................................. 10

7 Design .................................................................................................................................................. 10

7.1 General ................................................................................................................................................ 10

7.2 Calculation methods .......................................................................................................................... 10

7.2.1 General ................................................................................................................................................ 10

7.2.2 Evaluation of mechanical strength using “Design by Formula” ................................................... 11

7.2.3 Evaluation of mechanical strength using “Design by Analysis” .................................................. 11

7.2.4 Evaluation of mechanical strength using “Design by Burst test” ................................................ 12

7.2.5 Flanges ................................................................................................................................................ 14

7.2.6 Bolted connections ............................................................................................................................ 14

7.3 Inspection and access openings ...................................................................................................... 15

8 Manufacture and workmanship ......................................................................................................... 15

8.1 Material identification ......................................................................................................................... 15

8.2 Order of completion of weld seams .................................................................................................. 15

8.3 Cutting of materials ............................................................................................................................ 15

8.4 Forming of shell sections and end plates ........................................................................................ 15

8.5 Assembly tolerances .......................................................................................................................... 15

8.6 Welded joints ...................................................................................................................................... 15

8.7 Assembly for welding......................................................................................................................... 16

8.8 General welding requirements .......................................................................................................... 16

8.9 Preheating ........................................................................................................................................... 16

8.10 Surface finish ...................................................................................................................................... 16

9 Repair of welding defects .................................................................................................................. 16

10 Inspection, testing and certification ................................................................................................. 17

10.1 Type tests ............................................................................................................................................ 17

10.1.1 General ................................................................................................................................................ 17

10.1.2 Burst test procedure .......................................................................................................................... 17

10.1.3 Strain measurement test .................................................................................................................... 17

10.2 Inspection and routine tests .............................................................................................................. 17

10.2.1 General ................................................................................................................................................ 17

10.2.2 Routine pressure tests ....................................................................................................................... 18

10.3 Welding procedure specifications .................................................................................................... 18

10.4 Welder performance tests ................................................................................................................. 18

10.5 Non-destructive testing ..................................................................................................................... 18

10.5.1 Amount of testing of welded joints ................................................................................................... 18

10.5.2 Test methods for weld seams ........................................................................................................... 19

10.5.3 Surface conditions and preparations for testing ............................................................................ 19

10.5.4 Marking of the enclosure welds ........................................................................................................ 20

10.5.5 Reporting ............................................................................................................................................. 20

10.5.6 Minimum acceptance levels .............................................................................................................. 20

10.5.7 Assessment of imperfections ........................................................................................................... 20

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SIST EN 50068:2019
EN 50068:2018 (E)

10.6 Design specification, drawings and data sheets ............................................................................ 22

10.7 Certificate ............................................................................................................................................ 22

10.8 Stamping ............................................................................................................................................. 22

10.9 Final inspection .................................................................................................................................. 22

11 Pressure relief devices ...................................................................................................................... 23

11.1 General ................................................................................................................................................ 23

11.2 Bursting discs ..................................................................................................................................... 23

11.3 Self-closing pressure relief valves ................................................................................................... 23

11.4 Non-self-closing pressure relief devices ......................................................................................... 23

Annex A (informative) A-deviations .............................................................................................................. 25

Bibliography ..................................................................................................................................................... 26

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SIST EN 50068:2019
EN 50068:2018 (E)
European foreword

This document (EN 50068:2018) has been prepared by CLC/TC 17AC, “High-voltage switchgear and

controlgear”.
The following dates are fixed:
• latest date by which this document has (dop) 2019-08-27
to be implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2021-08-27
standards conflicting with this document
have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent

rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

This document supersedes EN 50068:1991, EN 50068:1991/corrigendum Aug. 2007 and
EN 50068:1991/A1:1993.

This document has been revised by CENELEC Technical Committee 17AC “High-voltage switchgear and

controlgear”. It supplements the relevant product standards on gas-insulated switchgear and controlgear in

that it provides specific requirements for pressurized high-voltage switchgear and controlgear.

The present document has been written to get a European specification for the design, construction, testing,

inspection and certification of pressurized enclosures used in high-voltage switchgear and controlgear.

In this respect, this document constitutes the exclusion of HV switchgear from the scope of the Directive

2014/68/EU (superseding 97/23/EC) concerning pressure equipment. Article 1, 2. (l) excludes “enclosures

for high-voltage electrical equipment such as switchgear, controlgear, transformers, and rotating machines”

from the scope of the Directive.

This document deals with gas-insulated switchgear enclosures of wrought steel and their welding. For

different enclosure materials, other European Standards are available.
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SIST EN 50068:2019
EN 50068:2018 (E)
Introduction

This document covers the requirements for the design, construction, testing, inspection and certification of

gas-filled enclosures for use specifically in high-voltage switchgear and controlgear, or for associated gas-

filled equipment.
Special consideration is given to these enclosures for the following reasons.

(a) The enclosures usually form the containment of electrical equipment, thus their shape is determined by

electrical rather than mechanical requirements.

(b) The enclosures are installed in restricted access areas and the equipment is operated by instructed,

authorized persons only.

(c) As the thorough drying of the inert, non-corrosive gas-filling medium is fundamental to the satisfactory

operation of the electrical equipment, the gas is periodically checked. For this reason, no internal corrosion

allowance is required on the wall thickness of these enclosures.

(d) The enclosures are subjected to only small fluctuations of pressure as the gas-filling density will be

maintained within close limits to ensure satisfactory insulating and arc-quenching properties. Therefore, the

enclosures are not liable to fatigue due to pressure cycling.
(e) The operating pressure is relatively low.

Due to the foregoing reasons and to ensure maximum service continuity as well as to reduce the risk of

moisture and dust entering the enclosures which could endanger safe electrical operation of the switchgear,

no pressure tests should be carried out after installation and before placing in service and no periodic

inspection of the enclosure interiors or pressure tests should be carried out after the equipment is placed in

service.
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SIST EN 50068:2019
EN 50068:2018 (E)
1 Scope

This document applies to wrought steel enclosures and their welding. These enclosures are pressurized with

dry air, inert gases, for example sulphur hexafluoride or nitrogen or a mixture of such gases, used in indoor

and outdoor installations of high-voltage switchgear and controlgear with rated voltages above 1kV, where

the gas is used principally for its dielectric and/or arc-quenching properties with rated voltages:

— above 1 kV and up to and including 52 kV concerning gas-filled compartments with design pressure

higher than 300 kPa relative pressure (gauge);
— above 52 kV concerning all gas-filled compartments.

The enclosures comprise parts of electrical equipment not necessarily limited to the following examples:

— circuit-breakers;
— switch-disconnectors;
— disconnectors;
— earthing switches;
— current transformers;
— voltage transformers;
— surge arrestors;
— busbars and connections;
— etc.

The scope also covers enclosures of pressurized components such as the centre chamber of live tank

switchgear, gas-insulated current transformers, etc.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content constitutes

requirements 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.

EN 13445-2:2014, Unfired pressure vessels — Part 2: Materials
EN 13445-3, Unfired pressure vessels — Part 3: Design

EN ISO 15614-1, Specification and qualification of welding procedures for metallic materials — Welding

procedure test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys (ISO

15614-1)

EN ISO 17636 (all parts), Non-destructive testing of welds — Radiographic testing (ISO 17636)

EN ISO 17640, Non-destructive testing of welds — Ultrasonic testing — Techniques, testing levels, and

assessment (ISO 17640)

EN 62271-1:2017, High-voltage switchgear and controlgear — Part 1: Common specifications for alternating

current switchgear and controlgear (IEC 62271-1:2017)

EN ISO 898-1:2013, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts,

screws and studs with specified property classes — Coarse thread and fine pitch thread (ISO 898-1:2013)

EN ISO 898-2:2012, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 2: Nuts

with specified property classes — Coarse thread and fine pitch thread (ISO 898-2:2012)

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SIST EN 50068:2019
EN 50068:2018 (E)
EN ISO 3452 (all parts), Non-destructive testing — Penetrant testing (ISO 3452)

EN ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels (ISO 9606-1)

EN ISO 9712, Non-destructive testing — Qualification and certification of NDT personnel (ISO 9712)

3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following addresses:

• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
enclosure

part of gas-insulated metal-enclosed switchgear retaining the insulating gas under the prescribed conditions

necessary to maintain safely the rated insulation level, protecting the equipment against external influences

and providing a high degree of protection to personnel
3.2
manufacturer

organization that is responsible for the design of the enclosure and the production of the gas-insulated

switchgear. In this standard this is the switchgear manufacturer
3.3
design pressure

pressure, expressed in relative terms (gauge), used to determine the thickness of the enclosure

Note 1 to entry: It is at least equal to the maximum pressure in the enclosure at the highest temperature that the gas

used for insulation can reach under specified maximum service conditions.
3.4
design temperature
design temperature of an enclosure

maximum temperature that the enclosures can reach under specified maximum service conditions

Note 1 to entry: This is generally the upper limit of ambient air temperature increased by the temperature rise due to

the flow of rated normal current.

Note 2 to entry: Solar radiation should be taken into account when it has a significant effect on the temperature of the

gas and on the mechanical properties of materials. Similarly, the effects of low temperatures on the properties of some

materials should be considered.

[SOURCE: EN 62271-203:2012, 3.112, modified – Note 1 to entry and Note 2 to entry have been added]

3.5
design stress

maximum permissible stress on the enclosure imposed by conditions of operation, environment or test that

determine the (material) characteristics of an enclosure
3.6
normal load
load whose occurrence and level can be planned or predicted
3.7
exceptional load

load whose probability of occurrence during the lifetime of product is very small or accidental

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SIST EN 50068:2019
EN 50068:2018 (E)
3.8
alloy

substance having metallic properties and composed of two or more elements so combined that they cannot

readily be separated by physical means
[SOURCE: EN 12258-1:2012, 2.2.1]
3.9
weld defect
imperfections in metallic fusion welds
3.9.1
lack of fusion

lack of union between the weld metal and the parent material or between the successive layers of weld metal

[SOURCE: EN ISO 6520-1:2007, Reference No. 401]
3.9.2
overlap
excessive weld metal covering the parent material surface but not fused to it
[SOURCE: EN ISO 6520-1:2007, Reference No. 506]
3.9.3
undercut

irregular groove at a toe of a run in the parent material or in previously deposited weld metal

[SOURCE: EN ISO 6520-1:2007, Reference No. 5011]
3.9.4
hot crack
hot tear

crack formed in a cast metal or in a welding because of internal stress developed upon cooling at the solidus

temperature or slightly above
[SOURCE: EN 12258-1:2012, 5.2.8]
3.9.5
inclusion

extraneous material accidentally entrapped into the liquid metal during melting or melt treatment or

entrapped into the metal surface during hot or cold working
[SOURCE: EN 12258-1:2012, 5.5.7]
3.9.6
blister

raised spot whose inside is hollow, that forms on the surface of products and is caused by the penetration of

a gas into a subsurface zone typically during thermal treatment
[SOURCE: EN 12258-1:2012, 5.5.10]

Note 1 to entry: A void resulting from a blister that has ruptured is often termed “blow hole”.

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EN 50068:2018 (E)
3.10
thermal treatment

heating, holding at elevated temperature and cooling of the solid metal in such a way as to obtain desired

metallurgical structure or properties
[SOURCE: EN 12258-1:2012, 3.6.1]

Note 1 to entry: The term “heat treatment” is used for the same concept as a synonym.

3.11
ductility
ability of a material to deform plastically before fracturing
[SOURCE: EN 12258-1:2012, 4.3.15]
3.12
fatigue

tendency for a metal to break under conditions of repeated cyclic stressing considerably below the tensile

strength
[SOURCE: EN 12258-1:2012, 4.3.23, modified – Note 1 to entry has been removed]
3.13
tensile strength

ratio of maximum load before rupture in a tensile test to original cross-sectional area

[SOURCE: EN 12258-1:2012, 4.3.3, modified – Note 1 to entry has been removed]
3.14
yield stress

stress necessary to produce a defined small plastic deformation in a material under uniaxial tensile or

compressive load
[SOURCE: EN 12258-1:2012, 4.3.4, modified]
3.15
test piece

two or more parts of material welded together in accordance with a specified weld procedure, in order to

make one or more test specimens
3.16
test specimen

portion detached from a test piece, in specified dimensions, finally prepared as required for testing

4 Quality assurance

It is the intention of this document that the switchgear manufacturer shall be responsible for achieving and

maintaining a consistent and adequate quality of the product.

Sufficient examinations shall be made by the enclosure manufacturer to ensure that the materials,

production and testing comply in all respects with the requirements of this document.

Inspection by the user`s inspectors shall not absolve the switchgear manufacturer from his responsibility to

exercise such quality assurance procedures as to ensure that the requirements and the intent of this

document are satisfied.
5 Normal and special service conditions
Clause 2 of EN 62271-1:2017 is applicable.
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SIST EN 50068:2019
EN 50068:2018 (E)
6 Materials

Any suitable steel is permissible. A list of recommended materials is given in EN 13445-2:2014.

General requirements are defined in EN 13445-2:2014, 4.1.
NOTE Contact with more noble metals can lead to heavy galvanic corrosion.
7 Design
7.1 General

The rules for the design of enclosures of gas-insulated switchgear and controlgear prescribed in this clause

take into account that these enclosures are subjected to particular operating conditions (refer to Introduction)

which distinguish them from compressed air receivers and similar storage vessels. Examples of such

enclosures are listed in Clause 1.

As part of the validation process of the enclosure the mechanical strength of an enclosure shall be proven by

a type test according to subclause 10.1.
An enclosure can be designed by two alternative methods:
— Design by Formula (DbF)
— Design by Analysis (DbA)

The geometry of an enclosure is determined by electrical rather than mechanical considerations. Moreover,

constraints in shape can be enforced by the casting process used. These constraints can result in an

enclosure geometry which cannot be calculated by DbF. In such cases DbA shall be applied.

When designing an enclosure, account shall be taken of the following, if applicable:

a) the evacuation of the enclosure as part of the filling process;
b) the full differential pressure across the enclosure wall or partition;

c) superimposed loads and vibrations by external effects, e.g. as they are caused by thermal or seismic

effects.

The enclosures are filled in service with a non-corrosive thoroughly dried gas. Therefore no internal

corrosion allowance is necessary.
7.2 Calculation methods
7.2.1 General

This part provides calculation rules, design stresses and boundary conditions for the design of enclosures. In

7.2.5 and 7.2.6 boundary conditions for the design of flanges and bolts are given. For the design of the

enclosure itself three methods may be used to proof appropriate design stress (Table 1): the preferred

method, Design by Formula is given in 7.2.2. The alternative methods, Design by Analysis or Design by

Burst test are given in 7.2.3 and 7.2.4.
Table 1 — List of design methods
1 Design by Formula preferred
7.2.2
2 Design by Analysis
7.2.3
3 Design by Burst test
7.2.4
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EN 50068:2018 (E)
7.2.2 Evaluation of mechanical strength using “Design by Formula”

When the wall and flange thicknesses of the enclosure are calculated, the formulas from established

specifications such as the following codes shall be taken, using the design pressure, the design temperature

as defined in 3.3 and 3.4 and the safety factor as defined in this subclause:
EN 13445-3
AD 2000 Regelwerk [2]
ASME Code [3]
CODAP [4]
Raccolta VSR [5]
SVTI [6]

The formulas in the specifications are equivalent to each other; the choice is left to the manufacturer.

The design stress (fd) at the design pressure including the safety factor of the appropriate formulae is given

by:
f ⋅ν
1,5
where

Re is yield stress of the material at the design temperature taken from the material standard for the

chosen alloy;
1,5 is safety factor;
ν is welding factor to be taken as 0,75 or 1 depending of the situation.
Selection of the welding factor according to 10.5.1.
7.2.3 Evaluation of mechanical strength using “Design by Analysis”
7.2.3.1 Normal loads
dn_
The design stress ( ) for normal loads is given by:
f ⋅ν
dn_
where
is maximum permissible design stress for normal loads
dn_

Re is yield stress of the material at the design temperature taken from the material standard for the

chosen alloy
Sn is safety factor for normal loads Sn = 1,05
ν is welding factor to be taken as 0,75 or 1 depending of the situation
Selection of the welding factor according to 10.5.1.
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SIST EN 50068:2019
EN 50068:2018 (E)
Examples for normal loads includes:
— gas pressure;
— temperature (ambient, current);
— dead load;
— erection load (transportation and handling on site);
— ice and/or wind;
— tension loads (cable, overhead lines).

Combinations of different loads shall reflect the operating conditions on site. Load combinations do not

change the overall safety factor.
7.2.3.2 Exceptional loads
d _e
The design stress ( ) for exceptional loads is given by:
f ⋅ν
d _e
where
is maximum permissible design stress for exeptional loads
d _e

R is minimum tensile strength of the material at the design temperature taken from the

material standard for the chosen alloy
S is safety factor for exceptional loads S = 1,05
e e
ν is welding factor to be taken as 1
Examples for exceptional loads include:
— earthquakes;
— extreme wind and/or ice;
— short-circuit tensile loads (overhead lines, cable).

Combinations of different loads shall reflect the operating conditions on site. Load combinations do not

change the overall safety factor.
7.2.4 Evaluation of mechanical strength using “Design by Burst test”
7.2.4.1 General

When the thickness of the pressure parts are not calculated or where doubt exists regarding the accuracy of

the ca
...

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