EN 448:2025

SLOVENSKI STANDARD
01-junij-2025
Cevi za daljinsko ogrevanje - Poviti enocevni sistemi za neposredno vkopana
vročevodna omrežja - Tovarniško izdelana armatura iz jeklenih delovnih cevi,
obdanih s poliuretansko toplotno izolacijo in zaščitnim plaščem iz polietilena
District heating pipes - Bonded single pipe systems for directly buried hot water networks
- Factory made fitting assemblies of steel service pipes, polyurethane thermal insulation
and a casing of polyethylene
Fernwärmerohre - Einrohr-Verbundsysteme für direkt erdverlegte Fernwärmenetze -
Werkmäßig gefertigte Formstückbaueinheiten, bestehend aus Stahl-Mediumrohren,
einer Wärmedämmung aus Polyurethan und einer Ummantelung aus Polyethylen
Tuyaux de chauffage urbain - Systèmes bloqués monotube pour les réseaux enterrés
d'eau chaude pour des réseaux d'eau chaude enterrés directement - Assemblages de
raccords manufacturés pour tubes de service en acier, isolation thermique en
polyuréthane et tube de protection en polyéthylène
Ta slovenski standard je istoveten z: EN 448:2025
ICS:
23.040.07 Cevovodi za daljinsko Pipeline and its parts for
ogrevanje in njihovi deli district heat
23.040.40 Kovinski fitingi Metal fittings
91.140.65 Oprema za ogrevanje vode Water heating equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EN 448
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2025
EUROPÄISCHE NORM
ICS 23.040.07; 23.040.45 Supersedes EN 448:2019
English Version
District heating pipes - Bonded single pipe systems for
directly buried hot water networks - Factory made fitting
assemblies of steel service pipes, polyurethane thermal
insulation and a casing of polyethylene
Tuyaux de chauffage urbain - Systèmes bloqués Fernwärmerohre - Einrohr-Verbundsysteme für direkt
monotubes pour les réseaux d'eau chaude enterrés erdverlegte Fernwärmenetze - Werkmäßig gefertigte
directement - Assemblages de raccords manufacturés Formstückbaueinheiten, bestehend aus Stahl-
pour tubes de service en acier, isolation thermique en Mediumrohren, einer Wärmedämmung aus
polyuréthane et tube de protection en polyéthylène Polyurethan und einer Ummantelung aus Polyethylen
This European Standard was approved by CEN on 27 January 2025.

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, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye 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
© 2025 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN 448:2025 E
worldwide for CEN national Members.

Contents Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 8
4 Requirements . 8
4.1 Steel parts . 8
4.1.1 Specification . 8
4.1.2 Wall thickness and diameter . 9
4.1.3 Bends . 9
4.1.4 T-pieces .10
4.1.5 Reducers .10
4.1.6 Welding of steel parts .10
4.1.7 Surface condition .15
4.2 Casing .15
4.3 Polyurethane foam thermal insulation .15
4.4 Fitting assembly .15
4.4.1 General .15
4.4.2 Thermal insulation series .15
4.4.3 Fitting ends .15
4.4.4 Angle between casing segments of bend and minimum length .16
4.4.5 Polyethylene welding .16
4.4.6 Diameter and wall thickness of the casing .17
4.4.7 Minimum thickness of the thermal insulation in fitting assembly .18
4.4.8 Tolerances of the main fitting dimensions .18
4.4.9 Expected thermal life and long term temperature resistance .18
4.4.10 Thermal conductivity .18
4.4.11 Surface conditions at delivery .19
4.4.12 Measuring wires for surveillance system .19
5 Test methods .19
5.1 General .19
5.2 Test specimens .19
5.3 Steel parts .19
5.3.1 Leak-tightness test with water .19
5.3.2 Visual leak-tightness test by air with over pressure .20
5.3.3 Visual leak-tightness test by air with below atmospheric pressure.20
5.4 Casing .20
5.4.1 Visual testing of weld seams on casing .20
5.4.2 Bending test of weld seams on casing .23
5.5 Fitting assembly .24
5.5.1 Centre line deviation and angular deviation .24
5.5.2 Minimum thickness of the polyurethane foam thermal insulation .24
5.5.3 Thermal conductivity in unaged condition .24
6 Marking .24
6.1 General . 24
6.2 Steel service pipe . 25
6.3 Steel fittings . 25
6.4 Casing . 25
6.5 Fitting assembly . 25
Annex A (informative) Guidelines for inspection and testing . 26
Annex B (informative) Procedures for casing welding . 29
Annex C (informative) Waste treatment and recycling . 32
Bibliography . 33

European foreword
This document (EN 448:2025) has been prepared by Technical Committee CEN/TC 107 “District heating
and cooling systems”, 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 September 2025, and conflicting national standards shall
be withdrawn at the latest by September 2025.
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 448:2019.
— two more ultrasonic testing methods for testing of welds are added to Table 4;
— alignment with the structure of EN 253;
— according to 4.1.3.3, the requirements for hot-formed bends are to be agreed between purchaser and
supplier;
— anchors are no longer included;
— single use compensators and caps are no longer included; they are covered by EN 13941-1;
— for steel welding, requirements for the welding contractor and welding consumables are specified in
4.1.6.1 and 4.1.6.3;
— requirements for steel weld preparation are omitted;
— requirements for distance between parallel weld seams are specified in 4.1.6.5.2;
— preparation of set-on branch with steel plate for reinforcement has been added in 4.1.6.5.3;
— requirement for imperfections of weld seams in 4.1.6.6.1 has been adapted to EN 13941-2;
— non-destructive testing (NDT) of weld seams in 4.1.6.6.2 is adapted to EN 13941-2;
— test methods for leak testing of steel weld seams have been clarified in 5.3;
— requirements for visual inspection of PE weld seams in 5.4.1 have been revised and explanatory
figures have been added;
— requirements for marking of fitting assemblies have been added in 6.5;
— recommendations for qualifications of PE welders have been added to B.1.
Any feedback and questions on this document should be directed to the users’ national standards body.
A complete listing of these bodies can be found on the CEN website.
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, France, Germany, Greece, Hungary, Iceland, Ireland,
Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of North
Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the United
Kingdom.
Introduction
Other standards from CEN/TC 107 are:
— 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 a casing of
polyethylene
— EN 488-1, District heating pipes — Bonded single pipe systems for directly buried hot water networks
— Part 1: Factory made steel shut-off valve assembly for steel service pipes, polyurethane thermal
insulation and a casing of polyethylene;
— EN 488-2, District heating and district cooling pipes — Bonded pipe systems for directly buried hot and
cold water networks — Part 2: Factory made steel valve assembly for steel service pipes, polyurethane
thermal insulation and a casing of polyethylene
— EN 489-1, District heating pipes — Bonded single and twin pipe systems for buried hot water networks
— Part 1: Joint casing assemblies and thermal insulation for hot water networks in accordance with
EN 13941-1
— 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
— EN 14419, District heating pipes — Bonded single and twin pipe systems for buried hot water networks
— Surveillance systems
— EN 15632 (all parts), District heating pipes — Factory made flexible pipe systems
— EN 15698-1, District heating pipes — Bonded twin pipe systems for directly buried hot water networks
— Part 1: Factory made twin pipe assembly of steel service pipes, polyurethane thermal insulation and
one casing of polyethylene
— EN 15698-2, District heating pipes — Bonded twin pipe systems for directly buried hot water networks
— Part 2: Factory made fitting and valve assemblies of steel service pipes, polyurethane thermal
insulation and one casing of polyethylene
— EN 17248, District heating and district cooling pipe systems — Terms and definitions
— EN 17414 (all parts), District cooling pipes — Factory made flexible pipe systems
— EN 17415 (all parts), District cooling pipes — Bonded single pipe systems for directly buried cold water
networks
— EN 17878 (all parts), District heating pipes — Factory made flexible pipe systems with a lower
temperature profile
Waste management and recycling of materials is dealt with in Annex C.
1 Scope
This document specifies requirements and test methods for factory made thermally insulated bonded
fitting assemblies for hot water networks in accordance with EN 13941-1, comprising a steel service pipe,
in most cases a steel fitting, polyurethane (PUR) foam thermal insulation and a casing of polyethylene.
The fitting assembly can also include the following additional elements: measuring wires, spacers and
diffusion barriers.
This document specifies the characteristics of the following fitting assemblies:
— bends, T-pieces, and reducers.
This document applies to fitting assemblies with a design pressure of at least 1,6 MPa.
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 a casing of
polyethylene
EN 1708-1, Welding — Basic welded joint details in steel — Part 1: Pressurized components
EN 10204, Metallic products — Types of inspection documents
EN 10216-2, Seamless steel tubes for pressure purposes — Technical delivery conditions — Part 2: Non-
alloy and alloy steel tubes with specified elevated temperature properties
EN 10217-2, Welded steel tubes for pressure purposes — Technical delivery conditions — Part 2: Electric
welded non-alloy and alloy steel tubes with specified elevated temperature properties
EN 10217-5, Welded steel tubes for pressure purposes — Technical delivery conditions — Part 5:
Submerged arc welded non-alloy and alloy steel tubes with specified elevated temperature properties
EN 10253-2, Butt-welding pipe fittings — Part 2: Non alloy and ferritic alloy steels with specific inspection
requirements
EN 12814-1, Testing of welded joints of thermoplastics semi-finished products — Part 1: Bend test
EN 13018, Non-destructive testing — Visual testing — General principles
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
EN 14419, District heating pipes — Bonded single and twin pipe systems for buried hot water networks —
Surveillance systems
EN 17248, District heating and district cooling pipe systems — Terms and definitions
EN ISO 3452-1, Non-destructive testing — Penetrant testing — Part 1: General principles (ISO 3452-1)
EN ISO 3834-3, Quality requirements for fusion welding of metallic materials — Part 3: Standard quality
requirements (ISO 3834-3)
EN ISO 4761, Non-destructive testing of welds — Phased array ultrasonic testing (UT-PA) for thin-walled
steel components — Acceptance levels (ISO 4761)
EN ISO 5579, Non-destructive testing — Radiographic testing of metallic materials using film and X- or
gamma rays — Basic rules (ISO 5579)
EN ISO 5817, Welding — Fusion-welded joints in steel, nickel, titanium and their alloys (beam welding
excluded) — Quality levels for imperfections (ISO 5817)
EN ISO 9606-1, Qualification testing of welders — Fusion welding — Part 1: Steels (ISO 9606-1)
EN ISO 9934-1, Non-destructive testing — Magnetic particle testing — Part 1: General principles (ISO 9934-
1)
EN ISO 10675-1, Non-destructive testing of welds — Acceptance levels for radiographic testing — Part 1:
Steel, nickel, titanium and their alloys (ISO 10675-1)
EN ISO 10863, Non-destructive testing of welds — Ultrasonic testing — Use of time-of-flight diffraction
technique (TOFD) (ISO 10863)
EN ISO 11666, Non-destructive testing of welds — Ultrasonic testing — Acceptance levels (ISO 11666)
EN ISO 13588, Non-destructive testing of welds — Ultrasonic testing — Use of automated phased array
technology (ISO 13588)
EN ISO 14732, Welding personnel — Qualification testing of welding operators and weld setters for
mechanized and automatic welding of metallic materials (ISO 14732)
EN ISO 15607, Specification and qualification of welding procedures for metallic materials — General rules
(ISO 15607)
EN ISO 15609-1, Specification and qualification of welding procedures for metallic materials — Welding
procedure specification — Part 1: Arc welding (ISO 15609-1)
EN ISO 15609-2, Specification and qualification of welding procedures for metallic materials — Welding
procedure specification — Part 2: Gas welding (ISO 15609-2)
EN ISO 15610, Specification and qualification of welding procedures for metallic materials — Qualification
based on tested welding consumables (ISO 15610)
EN ISO 15613, Specification and qualification of welding procedures for metallic materials — Qualification
based on pre-production welding test (ISO 15613)
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 15626, Non-destructive testing of welds — Time-of-flight diffraction technique (TOFD) —
Acceptance levels (ISO 15626)
EN ISO 16810, Non-destructive testing — Ultrasonic testing — General principles (ISO 16810)
EN ISO 17636-1, Non-destructive testing of welds — Radiographic testing — Part 1: X- and gamma-ray
techniques with film (ISO 17636-1)
EN ISO 17636-2, Non-destructive testing of welds — Radiographic testing — Part 2: X- and gamma-ray
techniques with digital detectors (ISO 17636-2)
EN ISO 17637, Non-destructive testing of welds — Visual testing of fusion-welded joints (ISO 17637)
EN ISO 17638, Non-destructive testing of welds — Magnetic particle testing (ISO 17638)
EN ISO 17640, Non-destructive testing of welds — Ultrasonic testing — Techniques, testing levels, and
assessment (ISO 17640)
EN ISO 19285, Non-destructive testing of welds — Phased array ultrasonic testing (PAUT) — Acceptance
levels (ISO 19285)
EN ISO 23277, Non-destructive testing of welds — Penetrant testing — Acceptance levels (ISO 23277)
EN ISO 23278, Non-destructive testing of welds — Magnetic particle testing — Acceptance levels
(ISO 23278)
3 Terms and definitions
For the purpose of this document, the terms and definitions given in EN 17248 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— IEC Electropedia: available at https://www.electropedia.org/
— ISO Online browsing platform: available at https://www.iso.org/obp
4 Requirements
4.1 Steel parts
4.1.1 Specification
Steel grades are specified in EN 13941-1.
All steel service pipes, and steel fittings used for manufacturing of fitting assemblies under the scope of
this document shall as a minimum be delivered to the manufacturer with an inspection certificate 3.1
according to EN 10204. The inspection certificate shall on request be passed on to the customer.
In case a material related inspection certificate 3.1 according to EN 10204 is required by the customer
who orders the fitting assemblies, this request shall be given whilst placing the order with the
manufacturer of the fitting assemblies.
NOTE 1 Any later request for provision of such documentation could be too late and possibly can't be met by the
manufacturer, since the manufacturer organizes the assignment of inspection certificates 3.1 to the steel service
pipes before starting the production.
NOTE 2 For cold-formed bends, the material inspection certificate 3.1 according to EN 10204 apply to the values
of the chemical composition, but not to the values of the mechanical properties.
4.1.2 Wall thickness and diameter
According to the scope of this document, all steel components shall be designed for a pressure of at least
1,6 MPa.
If the fitting assemblies shall be used in situations with design pressures higher than 1,6 MPa, extra
calculations will be necessary.
The nominal diameter and the minimum nominal wall thickness of all steel components shall prior to
processing be at least the same as for the service pipes regarding EN 253.
At the end of the fitting assembly, the outside diameter, the tolerances on the diameter of the pipe ends
and the wall thickness shall be the same as for the service pipes in accordance with EN 253.
Subject to design considerations other wall thicknesses than those given in EN 253 may be used, but in
no case shall these be less than the minima indicated in EN 253.
All components shall be designed in accordance with EN 13941-1, for the actions and stresses that
normally occur during the service life of the fitting assembly (or of the component).
4.1.3 Bends
4.1.3.1 Heated tool butt welding bends
The manufacturing process and dimensions shall be in accordance with EN 10253-2 with the exception
that the bend radius shall be ≥ 1,5 times the outer diameter.
4.1.3.2 Cold formed bends
Cold formed bends shall be produced from seamless pipe or longitudinal welded pipes.
After bending, the minimum wall thickness of the bent pipe shall be not less than 85 % of the wall
thickness of the straight service pipe, see EN 253.
The maximum ovality in the bent area shall not exceed 6 %.
The formula for the calculation of the ovality is:
DD−
s,,max s min
O ⋅ 100 (1)
D
s
where
O is the ovality, in %;
is the maximum outside diameter;
D
s,max
is the minimum outside diameter in the same cross section in the bended area;
D
s,min
is the specified outside diameter.
D
s
There shall be no folding in the bent area. Waves may be accepted, when the maximum height between
trough and crest of the wave does not exceed 25 % of the nominal wall thickness of the bent pipe.
4.1.3.3 Hot-formed bends
Hot-formed bends shall be delivered by agreement between purchaser and supplier. If nothing else is
agreed, the same requirements apply as in 4.1.3.2.
=
4.1.3.4 Tolerances of bending angles
The deviation from the nominal bending angle shall not exceed the tolerances given in Table 1.
Table 1 — Deviations from nominal bending angle
Nominal diameter of Deviation
service pipe
≤ DN 200 ±2,0°
> DN 200 ±1,0°
4.1.4 T-pieces
4.1.4.1 T-piece produced in a hot deformation process
T-pieces shall be produced in a hot deformation process according to EN 10253-2.
The wall thickness t and t , see EN 10253-2, shall be at least the same as those for the straight pipes, see
EN 253. All other dimensions shall be in accordance with EN 10253-2.
4.1.4.2 T-piece using a set-on branch
T-pieces using a set-on branch shall be manufactured by welding the branch pipe directly to the main
pipe, without or with compensating (reinforcement) plates according to EN 13941-1 requirements, see
Figure 2 and Figure 3. The branch pipes shall be perpendicular to the main pipes within a tolerance
of ± 2,0°.
4.1.4.3 T-piece using a drawn collar
T-pieces using a drawn collar shall be manufactured by hot drawing a collar on which the branch pipe is
welded. The wall thickness of the collar shall be at least the same as that for the branch pipe, see EN 253.
The collar shall be drawn opposite the welding seam in the main pipe.
T-pieces manufactured by drawing a collar shall be free from external and internal surface defects that
can be detected by visual testing.
The internal and external surface finish of the fittings shall be typical of the manufacturing process and,
where applicable, the heat treatment employed. Normally the finish and surface condition shall be such,
that any surface imperfections requiring dressing shall be identified.
4.1.5 Reducers
Reducers shall be in accordance with EN 10253-2, except for the wall thicknesses T and T see EN 10253-
1,
2, which shall be at least the same as for the straight pipes, see EN 253, to be welded to the fittings.
4.1.6 Welding of steel parts
4.1.6.1 Qualification of the manufacturer
The manufacturer shall fulfil the quality requirements according to EN ISO 3834-3.
4.1.6.2 Qualification of the welder
Welders for manual welding shall be qualified in accordance with EN ISO 9606-1.
Welding operators and weld setters for mechanized and automatic welding shall be qualified in
accordance with EN ISO 14732.
4.1.6.3 Welding process and welding procedure
Any type of welding process is permitted as long as it is demonstrated that the welded joint has
comparable mechanical and technological properties to the base material.
The welding procedure shall be specified and approved in accordance with EN ISO 15607. The method of
approval may be chosen by the manufacturer.
Welding procedure specification (WPS) shall fulfil the requirements given in EN ISO 15609-1 or
EN ISO 15609-2.
The welding procedure should be qualified in accordance with EN ISO 15610, EN ISO 15613 or
EN ISO 15614-1.
All weld seams shall be completely welded through.
4.1.6.4 Welding consumables
Welding consumables shall be of such a quality that the weld seams have mechanical characteristics at
least equivalent with the parent metal and shall fit with the welding procedure and welding conditions.
4.1.6.5 Performance of welding work
4.1.6.5.1 Transition with different wall thicknesses
For joints between steel parts of different wall thickness Figure 1 shall apply.
For the different values of the possible misalignment and difference in wall thicknesses Table 2 shall
apply.
Table 2 — Adaptation of misalignment and transition with different wall thicknesses following
EN 13941-2
Adaptation Required action
Misalignment
Misalignment h ≤ 0,3 t, max. 1 mm Figure 1 detail A
Misalignment 1 mm < h ≤ 10 mm  Adaptation of pipe ends
Misalignment h > 10 mm Extra fitting Extra prepared steel fitting minimum
length.
Difference in wall thickness
Differences in wall thickness: t' ≤ 1,5 t Figure 1 detail B Adaptation of thicker wall t' according
n
to EN 1708-1
Differences in wall thickness: t' > 1,5 t Figure 1 detail C Adaptation of the thicker wall t'
n
according to EN 1708-1
Key
h misalignment
t smallest wall thickness
n
t’ largest wall thickness
Figure 1 — Misalignment, transition with different wall thicknesses following EN 13941-2
4.1.6.5.2 Distance between parallel seams
The minimum distance between two parallel seams shall be such that the heat-affected zones do not
overlap or interact, the minimum distance is 50 mm, in particular cases the minimum distance may be
reduced to 7 times the wall thickness.
A distance of 100 mm or more is recommended.
4.1.6.5.3 Welding of set-on branches
When manufacturing T-pieces with the branch pipe welded directly to the main pipe, the preparations
shall comply with Figure 2.
Key
a section X at crotch of right-angle branch d section W at flank of equal branch
b section Y at flank of unequal branch. Ratios of
diameters ≤ 2/3
c section Y at flank of unequal branch. Ratios o
...