EN 13941-1:2019

SLOVENSKI STANDARD
01-julij-2019
Nadomešča:
SIST EN 13941:2009+A1:2010
Cevi za daljinsko ogrevanje - Projektiranje in vgradnja toplotno izoliranih spojenih
eno- in dvocevnih sistemov za neposredno zakopana vročevodna omrežja - 1. del:
Projektiranje
District heating pipes - Design and installation of thermal insulated bonded single and
twin pipe systems for directly buried hot water networks - Part 1: Design
Auslegung und Installation von werkmäßig gedämmten Verbundmantelrohren für die
Fernwärme
Tuyaux de chauffage urbain - Conception et installation des systèmes bloqués de
monotubes ou bitubes isolés thermiquement pour les réseaux d'eau chaude enterrés
directement - Partie 1 : Conception
Ta slovenski standard je istoveten z: EN 13941-1:2019
ICS:
23.040.07 Cevovodi za daljinsko Pipeline and its parts for
ogrevanje in njihovi deli district heat
91.140.10 Sistemi centralnega Central heating systems
ogrevanja
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 13941-1
EUROPEAN STANDARD
NORME EUROPÉENNE
April 2019
EUROPÄISCHE NORM
ICS 23.040.10; 91.140.10 Supersedes EN 13941:2009+A1:2010
English Version
District heating pipes - Design and installation of thermal
insulated bonded single and twin pipe systems for directly
buried hot water networks - Part 1: Design
Tuyaux de chauffage urbain - Conception et installation Auslegung und Installation von werkmäßig
des systèmes bloqués de monotubes ou bitubes isolés gedämmten Verbundmantelrohren für die Fernwärme
thermiquement pour les réseaux d'eau chaude enterrés
directement - Partie 1 : Conception
This European Standard was approved by CEN on 14 December 2018.

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, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION

EUROPÄISCHES KOMITEE FÜR NORMUNG

CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 13941-1:2019 E
worldwide for CEN national Members.

Contents Page
European foreword . 8
Introduction .10
1 Scope .11
2 Normative references .11
3 Terms and definitions, units and symbols .12
3.1 Terms and definitions .12
3.1.1 Symbols .13
3.1.2 Abbreviations .19
4 General requirements .19
4.1 Functional requirements.19
4.2 Service life .19
4.3 Preliminary investigations .20
4.4 Determination of project class .21
4.4.1 Risk assessment .21
4.4.2 Project classes .21
4.5 Design documentation .23
4.5.1 General .23
4.5.2 Operational data .24
4.5.3 Data related to the pipe system .24
4.6 Route selection and positioning of the pipes .26
4.6.1 Minimum distances between parallel pipes .26
4.6.2 Parallel excavations and works of third parties .27
4.6.3 Minimum distance between district heating pipes and underground structures .27
4.7 Venting and draining .27
4.8 Valves.27
4.9 Procurement of materials .28
4.9.1 Manufacturer of pipeline components .28
4.10 Quality control .28
4.10.1 General .28
4.10.2 Design phase .28
4.10.3 Installation phase .28
5 Requirements for components and materials .29
5.1 Basic requirements .29
5.2 Steel service pipe components .29
5.2.1 General .29
5.2.2 Specification .30
5.2.3 Characteristic values for steel .30
5.2.4 Specific requirements for bends and T-pieces .31
5.2.5 Specific requirements for small angular deviations .32
5.2.6 Specific requirements for reducers .33
5.3 Polyurethane foam thermal insulation .33
5.4 Casing .33
5.5 Materials for casing and thermal insulation of field joints .33
5.6 Expansion cushions .33
5.6.1 General .33
5.6.2 Materials .34
5.6.3 Stiffness properties . 34
5.6.4 Selecting required thickness of expansion cushions . 35
5.6.5 Marking . 35
5.7 Valves and accessories . 35
5.7.1 General requirements . 35
5.7.2 Marking and documentation . 36
6 Design and calculation . 36
6.1 General procedure . 36
6.2 Pipeline components, areas, conditions and interfaces to be included in the
analyses . 37
6.2.1 Components . 37
6.2.2 Areas requiring specific analyses . 38
6.2.3 Special conditions . 38
6.2.4 Interfaces . 38
6.3 Simplified analysis procedure . 39
6.4 Actions . 39
6.4.1 General . 39
6.4.2 Classification of actions and load combinations . 39
6.4.3 Temperature variations . 41
6.4.4 Top load from soil. 42
6.4.5 Traffic loads . 42
6.5 Global analysis and pipe-soil interaction . 44
6.5.1 General . 44
6.5.2 Modelling pipe-soil interaction . 44
6.5.3 Pipe to soil friction (axial) . 46
6.5.4 Horizontal soil reaction (lateral) . 48
6.5.5 Combined lateral stiffness of steel service pipe, PUR, expansion cushions and soil . 53
6.5.6 Soil properties . 55
6.5.7 Thermal expansion of buried pipe sections: . 55
6.5.8 Pipe systems with single use compensators (SUC’s) . 58
6.5.9 Specific requirements for vertical and horizontal stability . 60
6.5.10 Parallel excavations . 63
6.5.11 Requirements for soft soils and settlement areas . 64
6.5.12 Specific design requirements for above-ground pipelines with factory made pipe
and fitting assemblies . 64
6.5.13 Insertion into protection pipe. 64
6.6 Determination of stresses and strains . 65
6.6.1 General . 65
6.6.2 Cross section analyses, steel . 65
6.6.3 Assessment on the basis of a resultant (equivalent) stress . 66
6.6.4 Stresses and ovalization from top load . 67
6.6.5 Deflection . 69
6.6.6 Bends . 69
6.6.7 T-pieces . 70
6.6.8 Single Use Compensators (SUC’s) . 73
6.6.9 PUR and casing . 74
6.7 Fatigue analyses . 75
6.7.1 General . 75
6.7.2 Action cycles . 75
6.8 Further actions . 77
7 Limit states . 77
7.1 General . 77
7.2 Limit states for service pipes of steel . 78
7.2.1 General .78
7.2.2 Limit state A: Failure caused by plastic deformation .78
7.2.3 Limit state B: Failure caused by fatigue .81
7.2.4 Limit state C: Failure caused by instability of the system or part of it .84
7.2.5 Limit state D: Serviceability limit state .86
7.2.6 Survey of limit states for steel .86
7.3 Limit states for PUR and PE .89
7.3.1 Compressive stress .89
7.3.2 Limit state for shear stress .89
7.3.3 Limit state for PE .89
7.4 Limit states for valves .89
Annex A (normative) Design of piping components under internal pressure .91
A.1 General .91
A.2 Straight pipe and bends .91
A.2.1 Straight pipes .91
A.2.2 Bends .91
A.3 T-pieces and branch connections .92
A.3.1 General aspects and limitations .92
A.3.2 Reinforcement .92
A.3.2.1 General .92
A.3.2.2 Dissimilar material of shell and reinforcement .92
A.3.2.3 Thickness ratio .93
A.3.2.4 Calculation method for reinforcement area .93
A.3.2.5 Reinforcement by increased wall thickness .93
A.3.2.6 Reinforcement by compensating plates.94
A.4 Reducers and extensions .95
A.5 Dished ends .95
A.5.1 General .95
A.5.2 Ellipsoidal Dished Head Minimum required wall thickness for internal pressure .96
A.5.3 Straight cylindrical shells .96
Annex B (informative) Soil properties and geotechnical parameters for pipe/soil
interaction analyses .97
B.1 General requirements .97
B.2 Geotechnical parameters for global analysis (pipe-soil interaction) .97
B.3 Geotechnical Study .98
B.3.1 Field study .98
B.3.2 Typical values, referred to mean value .98
B.3.3 Investigation of interface friction .98
B.4 Characteristic values for soil properties .98
B.4.1 Typical values, referred to mean value .98
B.4.2 Spatial variation of soil properties .99
B.5 Model uncertainty when determining geotechnical parameters. 100
Annex C (informative) Flexibility and stress concentration of pipe components . 102
C.1 General . 102
C.2 Flexibility factors for pipe components. 102
C.2.1 Bends . 102
C.2.2 T-pieces . 102
C.2.3 Other components . 103
C.3 Stress concentration in pipe elements . 103
C.3.1 Butt welds . 103
C.3.2 Bends . 103
C.3.2.1 Stress concentration factors for bends: Simplified method . 103
C.3.2.2 Stress concentration factors for bends: exact calculation . 104
C.3.3 T-pieces . 105
C.3.3.1 General . 105
C.3.4 Small angular deviations . 107
C.3.5 Reducers . 108
Annex D (informative) Calculation of heat losses . 110
D.1 General . 110
D.2 Heat losses of thermal insulated pipes . 110
D.2.1 Pair of single pipes — calculation of specific heat loss . 110
D.2.2 symmetrical and (a) antisymmetrical heat loss factors according to zero-order
multipole formulae: . 111
D.2.3 Using Zero-order approximation for (s) symmetrical and (a) antisymmetrical
problem the heat resistance can be calculated: . 111
D.2.4 specific heat loss of pipes . 112
D.2.5 Twin Pipes — calculation of specific heat loss . 112
D.2.6 temperatures of pipes . 113
D.2.7 (s) symmetrical and (a) antisymmetrical heat loss factors according to first-order
multipole formula: . 114
D.2.8 specific heat loss of pipes . 115
Annex E (informative) Specific requirements for twin pipe systems . 116
E.1 General . 116
E.2 Component and materials . 116
E.2.1 Twin Pipe assembly . 116
E.2.2 Fixing bars . 117
E.3 Max. allowable stresses for specific twin pipe system elements: . 118
E.3.1 Project classes . 118
E.3.2 Soil friction, twin pipe friction length and pipe expansion . 118
E.3.3 Axial stress in the flow and return steel service pipes . 120
E.3.4 Dimensions of the fixing bars . 122
E.3.4.1 General . 122
E.3.4.2 loads on the fixing bars type A . 123
E.3.4.3 loads on the fixing bar type B . 124
E.3.5 Stress proof of the fixing bar . 126
E.3.6 Proof of the welds . 127
E.3.7 Vertical and horizontal stability of the twin pipe assembly in the soil . 129
E.3.8 Stress concentration factors for bends, T-pieces. 129
E.3.9 Fatigue . 129
E.4 Installation requirements . 130
E.4.1 Installation methods: . 130
E.4.2 Straight pipe section terminations: . 130
E.4.3 Use of insulated twin pipe valves: . 130
E.4.4 Use of transition assembly (twin pipe — single pipe): . 130
E.4.5 requirements for welding and testing of steel service pipe joints: . 130
Annex F (normative) Compressive testing of expansion cushions . 131
Annex G (informative) Principles for determination of bending moments and axial forces
for testing of district heating valves . 133
G.1 Introduction . 133
G.2 General considerations for determination of test values for bending moments . 133
G.3 Determination of bending moments from soil settlements . 134
G.4 Calculation results and evaluation . 134
G.5 Resistance to axial forces . 137
Annex H (informative) Scope of EN 13941 in relation to Pressure Equipment Directive
(PED), 2014/68/EU, May 15th, 2014 . 138
H.1 General . 138
H.2 Guidelines . 139
Annex I (informative) Quality control program and documentation . 142
Annex J (informative) Casing: Formulas for Miner Rule . 145
Annex K (informative) Strength calculation of horizontal directional drillings . 147
K.1 Introduction . 147
K.2 Determination of pulling forces . 148
K.2.1 Pulling force, resulting from the roller system . 148
K.2.2 Pulling force, resulting from a straight section of borehole . 148
K.2.3 Pulling force, resulting from curved sections of the borehole . 150
K.2.3.1 General friction force . 150
K.2.3.2 Friction resulting from elastic soil reaction in curved borehole sections . 150
K.2.3.3 Friction due to the axial pulling force in curved borehole sections . 151
K.2.3.4 Total force in a curved section . 152
K.2.4 Total pulling force . 152
K.3 Determination of the longitudinal bending moment . 153
K.4 Determination of the circumferential bending moment from top load. 153
K.5 Determination of stress . 153
K.6 Assessment of possible collapse of the pipeline due to external drilling fluid
pressure or external ground water pressure (risk of buckling) . 153
K.7 Assessment of maximum soil pressure on PUR and casing . 153
K.8 Determination of maximum allowable pressure in the bore hole . 154
K.9 Vertical soil load after completion of horizontal directional drilling (HDD) . 154
K.9.1 Introduction . 154
K.9.2 Arching . 154
K.9.3 Calculation method for vertical soil load (homogeneous soil mass) . 154
K.9.4 Calculation method for horizontal support pressure (with reduced vertical load) 155
Bibliography . 156

European foreword
This document (EN 13941-1:2019) has been prepared by Technical Committee CEN/TC 107
“Prefabricated district heating and district cooling pipe system”, the secretariat of which is held by DS.
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 October 2019, and conflicting national standards shall
be withdrawn at the latest by October 2019.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes EN 13941:2009+A1:2010.
EN 13941, District heating pipes — Design and installation of thermal insulated bonded single and twin
pipe systems for directly buried hot water networks consists of the following parts:
— Part 1: Design;
— Part 2: Installation.
In comparison to EN 13941:2009+A1:2010, the following changes have been made:
a) EN 13941 is considered to be the “system standard”, including all requirements for materials and
components and where necessary referring to the related product standards
b) chapters related to installation are moved to EN 13941-2;
c) terms and definitions are moved to EN 17248
d) the document structure is improved, giving a better balance between standard text and annexes;
e) twin pipes are included in a new Annex E;
f) Annex H: “Scope of EN 13941 in relation to Pressure Equipment Directive (PED)” was added;
g) requirements for horizontal and vertical stability and for parallel excavations are made more explicit;
h) minimum free distances between parallel pipes are introduced as well as a warning to be aware of
works of third parties that might endanger the integrity or the required design conditions of the
district heating pipes;
i) requirements for horizontal directional drillings are included (also in EN 13941-2);
j) required properties and testing methods for expansion cushions are included;
k) a design fatigue curve for fillet welds (e. g in single use compensators) is included;
l) the use of stress concentration factors for butt welds in district heating pipes is, in line with present
international pipeline codes, not considered necessary anymore;
m) a great number of smaller adjustments and editorial improvements.
According to the CEN-CENELEC Internal Regulations, the national standards organisations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Croatia,
Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France,
Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands,
Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
the United Kingdom.
Introduction
This document has been prepared by CEN/TC 107/WG 13 “Prefabricated district heating and district
cooling pipe system”.
According to the scope of CEN/TC 107:
— the task of CEN/TC 107/WG 13 is to specify rules for design, calculation and installation for factory
made thermal insulated bonded single and twin pipe systems for directly buried hot water networks;
— CEN/TC 107/WG 13 also contributes to rules for functional tests for thermal-insulated bonded pipe
systems for underground hot water networks;
When use is made of the standard, the different sections of which it is made up is to be interpreted as
being interdependent and, because of this, cannot be dissociated.
The revision of EN 13941:2009+A1:2010 involves the subdivision of the document in two separate
documents:
— EN 13941-1, District heating pipes — Design and installation of thermal insulated bonded single and
twin pipe systems for directly buried hot water networks — Part 1: Design;
— EN 13941-2, District heating pipes — Design and installation of thermal insulated bonded single and
twin pipe systems for directly buried hot water networks — Part 2: Installation.
This volume (Part 1) consists of a main part and eight annexes.
Annexes A, and F are normative. Annexes B, C, D, E, G, H, I, J and K are informative.
This document contains a number of requirements aimed at ensuring the sound execution of distribution
networks and transportation pipelines for district heating.
The requirements and regulations contained in this document should be assessed and applied in
compliance with the intentions of the standard and in due consideration of the development taking place
in the field it concerns. It is therefore assumed that the user of the standard has the requisite technical
insight and that the user of the standard has adequate knowledge of legal and other external regulations
that are of consequence to the practical application of the standard.
Some paragraphs of this standard are possibly covered by national regulations in some countries which
NOTE
naturally apply instead of this standard.

1 Scope
This document specifies requirements for design, calculation and installation of factory made thermal
insulated bonded single and twin pipe systems for buried hot water networks for continuous operation
with treated water at various temperatures up to 120 °C and occasionally peak temperatures up to 140 °C
for maximum 300 h/a, and maximum internal pressure 2,5 MPa.
Flexible pipe systems according to the EN 15632 series are not under the scope of this standard.
The standard EN 13941, Design and installation of thermal insulated bonded single and twin pipe systems
for directly buried hot water networks consists of two parts:
a) EN 13941-1: Design;
b) EN 13941-2: Installation.
The requirements in this part, EN 13941-1, form a unity with those of EN 13941-2.
The principles of the standard may be applied to thermal insulated pipe systems with pressures higher
than 2,5 MPa, provided that special attention is paid to the effects of pressure.
Adjacent pipes, not buried, but belonging to the network (e.g. pipes in ducts, valve chambers, road
crossings above ground etc.) may be designed and installed according to this standard.
This document presupposes the use of treated water, which by softening, demineralization, de-aeration,
adding of chemicals, or otherwise has been treated to effectively prevent internal corrosion and deposits
in the pipes.
NOTE For further information on water qualities to be used in district heating pipe systems see also
bibliographic entry [2].
This standard is not applicable for such units as:
a) pumps;
b) heat exchangers;
c) boilers, tanks;
d) systems behind domestic substations.
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 253, District heating pipes — Bonded single pipe systems for directly buried hot water networks —
Factory made pipe assembly of steel service pipe, polyurethane thermal insulation and outer casing of
polyethylene
EN 448, District heating pipes - Preinsulated bonded pipe systems for directly buried hot water networks -
Fitting assemblies of steel service pipes, polyurethane thermal insulation and outer casing of polyethylene
EN 488, District heating pipes - Preinsulated bonded pipe systems for directly buried hot water networks -
Steel valve assembly for steel service pipes, polyurethane thermal insulation and outer casing of polyethylene
EN 489-1, District heating pipes — Bonded single and twin pipe systems for directly buried hot water
networks — Casing joint assemblies and thermal insulation for hot water networks in accordance with
EN 13941-1
SIST EN 13941
...