ISO 16486-6:2023

INTERNATIONAL ISO
STANDARD 16486-6
Second edition
2023-10
Plastics piping systems for the supply
of gaseous fuels - Unplasticized
polyamide (PA-U) piping systems
with fusion jointing and mechanical
jointing —
Part 6:
Code of practice for design, handling
and installation
Systèmes de canalisations en matières plastiques pour la distribution
de combustibles gazeux — Systèmes de canalisations en polyamide
non plastifié (PA-U) avec assemblages par soudage et assemblages
mécaniques —
Partie 6: Code de pratique pour la conception, la manutention et
l'installation
Reference number
© ISO 2023
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ii
Contents Page
Foreword .v
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms, definitions and abbreviated terms . 2
3.1 Terms and definitions . 2
3.2 Symbols and abbreviated terms . 3
4 Design . 4
4.1 General and regional requirements . 4
4.1.1 General . 4
4.1.2 Regional requirements . 4
4.2 Materials, components and jointing equipment . 5
4.3 Maximum operating pressure . 5
4.3.1 General . 5
4.3.2 Maximum operation pressure based on long-term hydrostatic strength . 5
4.3.3 Maximum operation pressure based on rapid crack propagation . 5
4.4 Assembly techniques. 6
4.5 Squeeze-off properties . 6
5 Construction . 7
5.1 Competence . 7
5.2 Storage, handling and transport . . 7
5.2.1 General . 7
5.2.2 Storage . 7
5.2.3 Handling . 8
5.2.4 Transport . 9
5.3 Jointing. 9
5.4 Laying . 9
5.4.1 General . 9
5.4.2 Trench . 10
5.4.3 Drag forces . 10
5.4.4 Valves . 11
5.4.5 Connection to existing systems . 11
5.4.6 Backfilling . 11
5.4.7 Non-conventional installation .12
5.5 Pressure testing and commissioning .12
6 Quality control .12
6.1 General .12
6.2 Inspection prior to laying .12
6.3 Inspection during laying . .13
6.3.1 Laying .13
6.3.2 Joint integrity . 13
Annex A (normative) Butt fusion jointing procedure .20
Annex B (normative) Electrofusion jointing .25
Annex C (normative) Mechanical jointing .31
Annex D (informative) Squeeze-off and re-rounding .32
Annex E (normative) Derating coefficients for various operating temperatures .35
Annex F (informative) Regional requirements for CEN member countries .36
Annex G (informative) Additional information for demonstrating the fitness of PA-U piping
systems for non-conventional installation techniques .37
iii
Bibliography .39
iv
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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 138, Plastics pipes, fittings and valves for
the transport of fluids, Subcommittee SC 4, Plastics pipes and fittings for the supply of gaseous fuels.
This second edition cancels and replaces the first edition (ISO 16486-6:2012), which has been
technically revised.
The main changes are as follows:
— the structure of the document has been modified in order to generally align with the structure of
ISO/TS 10839:2022;
— the normative references have been updated;
— a new subclause 4.1.2 has been added, concerning regional requirements and with reference to a
new Annex F, also about regional requirements for CEN member countries;
— subclause 4.3 has been subdivided into three further subclauses: general, MOP(LTHS) and MOP(p );
c
— a more detailed definition of MOP(p ) has been included in subclause 4.3.3 for temperatures below
c
zero;
— a reference to Annex G has been added to subclause 4.5;
— information from subclause 5.3 for jointing procedures has been moved to the new Annexes B, C and
D;
— in subclause 5.4.1, the former drag force formula for PE with fixed limiting stress (F = 14 N) has been
opened for PA-U;
— a new subclause 5.4.7 for non-conventional installation has been added;
v
— for visual inspection of butt fusion joints, subclause 6.3.2.2.1 shows figures with the typical single
bead shape, which replaces the previous double bead;
— a new informative Annex G has been added concerning the fitness of PA-U piping systems for non-
conventional installation techniques;
— the Bibliography has been updated.
A list of all parts in the ISO 16486 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
vi
Introduction
This document specifies the requirements for a piping system and its components made from
unplasticized polyamide (PA-U), and which is intended to be used for the supply of gaseous fuels.
Requirements and test methods for material and components of the piping system are specified in
ISO 16486-1, ISO 16486-2, ISO 16486-3 and ISO 16486-4.
Characteristics for fitness for purpose of the system and generic fusion parameters are covered in
ISO 16486-5.
Recommended practice for installation is given in this document, which will not be implemented as a
European Standard under the Vienna Agreement.
Assessment of conformity of the system is to form the subject of ISO/TS 16486-7.
Training and assessment of fusion operators is covered by ISO/TS 16486-8.
[3]
NOTE 1 For CEN member countries, the recommended practice for installation is given in CEN/TS 12007-6
[4]
and the qualification of welders is given by EN 13067 .
NOTE 2 A list of imperial ASTM or PPI standards related to polyamide pipes and fittings for the supply of gas
is given in References [5], [6], [7], [8], [9], [10] and [11].
NOTE 3 ISO 16486-1, ISO 16486-2, ISO 16486-3, ISO 16486-5 and ISO 16486-6 (this document) as well as
ISO/TS 16486-7 and ISO/TS 16486-8 have been prepared by ISO/TC 138, SC 4. ISO 16486-4 has been prepared by
ISO/TC 138, SC 7.
vii
INTERNATIONAL STANDARD ISO 16486-6:2023(E)
Plastics piping systems for the supply of gaseous fuels -
Unplasticized polyamide (PA-U) piping systems with fusion
jointing and mechanical jointing —
Part 6:
Code of practice for design, handling and installation
1 Scope
This document specifies a code of practice dealing with unplasticized polyamide (PA-U) pipes and
fittings for buried pipeline systems outside buildings and designed to transport gaseous fuels (as
defined in ISO 16486-1, e.g. methane, LPG, manufactured gas and hydrogen) within the temperature
range –20 °C to +40 °C. This document also gives appropriate temperature-related requirements.
The code of practice covers mains and service lines whose components are prepared for fusion or
mechanical jointing and gives instructions for the design, storage, handling, transportation, laying
conditions and fusion quality control of PA-U pipes and fittings as well as subsequent joint testing,
backfilling, pipe system testing and commissioning.

NOTE Principal information for rehabilitation can be found in ISO 11295 for classification, ISO 11299-1 and
ISO 11299-2 for renovation, and ISO 21225-1 and ISO 21225-2 for trenchless replacement.
More detailed national standards or codes of practice can exist. This document is intended to be applied
in association with such national standards or codes of practice related to the above-mentioned basic
principles.
The jointing methods covered by this document are:
— butt fusion jointing (see Annex A);
— electrofusion jointing (see Annex B) and
— mechanical jointing (see Annex C).
In the case of ground movement or shaking (e.g. earthquakes, etc.) precautions mentioned in this
[17]
document can need to be implemented following guidelines provided by authorities (e.g. EN 1998-4 ,
[18]
EN 12007-1:2012, Annex A etc.).
Workers' health and safety issues are outside the scope of this document
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.
ISO 12176-1, Plastics pipes and fittings — Equipment for fusion jointing polyethylene systems — Part 1:
Butt fusion
ISO 12176-2, Plastics pipes and fittings — Equipment for fusion jointing polyethylene systems — Part 2:
Electrofusion
ISO 12176-3, Plastics pipes and fittings — Equipment for fusion jointing polyethylene systems — Part 3:
Operator's badge
ISO 12176-4, Plastics pipes and fittings — Equipment for fusion jointing polyethylene systems — Part 4:
Traceability coding
ISO 12176-5, Plastics pipes and fittings — Equipment for fusion jointing polyethylene systems — Part 5:
Two-dimensional data coding of components and data exchange format for PE piping systems
ISO 13477, Thermoplastics pipes for the conveyance of fluids — Determination of resistance to rapid crack
propagation (RCP) — Small-scale steady-state test (S4 test)
ISO 13478, Thermoplastics pipes for the conveyance of fluids — Determination of resistance to rapid crack
propagation (RCP) — Full-scale test (FST)
ISO 13950, Plastics pipes and fittings — Automatic recognition systems for electrofusion joints
ISO 16486-1, Plastics piping systems for the supply of gaseous fuels — Unplasticized polyamide (PA-U)
piping systems with fusion jointing and mechanical jointing — Part 1: General
ISO 16486-2:2020, Plastics piping systems for the supply of gaseous fuels — Unplasticized polyamide (PA-
U) piping systems with fusion jointing and mechanical jointing — Part 2: Pipes
ISO 16486-3, Plastics piping systems for the supply of gaseous fuels — Unplasticized polyamide (PA-U)
piping systems with fusion jointing and mechanical jointing — Part 3: Fittings
ISO 16486-4, Plastics piping systems for the supply of gaseous fuels — Unplasticized polyamide (PA-U)
piping systems with fusion jointing and mechanical jointing — Part 4: Valves
ISO 16486-5, Plastics piping systems for the supply of gaseous fuels — Unplasticized polyamide (PA-U)
piping systems with fusion jointing and mechanical jointing — Part 5: Fitness for purpose of the system
ISO 17885:2021, Plastics piping systems — Mechanical fittings for pressure piping systems — Specifications
EN 12327, Gas supply systems — Pressure testing, commissioning and decommissioning procedures —
Functional requirements
3 Terms, definitions and abbreviated terms
For the purposes of this document, the terms and definitions given in ISO 16486-1, ISO 16486-5 and the
following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 Terms and definitions
3.1.1
butt fusion machine pressure
pressure indicated on the gauge or on a pressure display on a butt fusion machine, giving an indication
of the interface force applied to the pipe and/or fitting ends
3.1.2
clearance
shortest distance between the outer limits of two objects
3.1.3
drag resistance
frictional resistance due to the weight of the length of pipe fixed in the moveable clamp at the point
at which movement of the moveable clamp is initiated (peak drag), or the friction occurring during
movement (dynamic drag)
3.1.4
electrofusion control unit
equipment implementing the output fusion parameters of voltage or current and time or energy to
execute the fusion cycle as specified by the electrofusion fitting manufacturer
3.1.5
frictional losses in the butt fusion machine
force necessary to overcome friction in the whole mechanism of a butt fusion machine
3.1.6
fusion operator
person trained to carry out fusion jointing between unplasticized polyamide (PA-U) pipes and/or
fittings
Note 1 to entry: Fusion jointing is based on a written procedure agreed by the pipeline operator.
Note 2 to entry: The fusion operator is trained for one or more fusion–jointing procedures.
3.1.7
interface force
force between the fusion surfaces of the pipe(s) and/or fitting(s) during the fusion cycle, as specified in
the fusion diagram
3.1.8
operator
person authorized to build PA-U systems from pipes and/or fittings, based on a written procedure
agreed by the pipeline operator
3.1.9
overall service (design) coefficient
C
overall coefficient, with a value greater than 1, which takes into consideration service conditions as
well as properties of the components of a piping system
3.1.10
pipeline operator
private or public organization authorized to design, construct or operate and maintain a gas supply
system
3.1.11
soil cover
vertical distance between the top of a buried pipe and the normal surface after finishing work (e.g.
including pavement)
3.2 Symbols and abbreviated terms
B bead width
B mean bead width
m
B maximum bead width
max
B minimum bead width
min
C overall service (design) coefficient
d external diameter of pipe or spigot fitting at any point
e
D temperature derating coefficient
F
e nominal wall thickness of pipe or fitting
n
F maximum drag force, in newtons
f is the safety factor
s
MOP maximum operating pressure
MRS minimum required strength
p full-scale critical pressure determined in accordance with ISO 13478 at zero degrees Celsius
C
p small scale critical pressure determined in accordance with ISO 13477 at zero degrees Celsius
C,S4
p reference value of p to be referred to in the requirement of the S4 test specified in
C,S4,REF C,S4
ISO 16486-2:2020, Table 4, footnote c.
RCP rapid crack propagation
SDR standard dimension ratio
T temperature below zero degrees Celsius
bz
V misalignment
σ maximum tensile stress in MPa
σ tensile stress at yield in MPa
y
4 Design
4.1 General and regional requirements
4.1.1 General
A written laying procedure, authorized by the pipeline operator, shall be made available prior to the
construction of a pipeline. The laying procedure shall include specification of the jointing procedure
(butt or electrofusion or mechanical), the pipe and fitting materials to be used, the trenching and
backfilling requirements, the pressure testing and commissioning requirements, and the data to be
collected for the traceability system.
The selection of materials, standard dimension ratio (SDR) series, dimensions and assembling
techniques shall be the responsibility of the pipeline operator.
There are two SDR series in common use for gas supply systems: SDR 13.6 and SDR 11. Other SDR series
can also be used, such as SDR 26 for renovation.
The training and the level of skill of the operator(s) shall be in accordance with the requirements of the
jointing procedures.
General guidelines for supervision and quality control are given in Clause 6.
4.1.2 Regional requirements
[3]
For CEN member countries, this document is substituted by CEN/TS 12007-6 ,where the MOP is
1)
limited to up and to including 16 bar for the whole piping system with all components. CEN/TS 12007-
[3]
6 references several functional standards prepared by CEN/TC 234. More detailed information about
regional requirements for CEN member countries is given in Annex F.
5 2
1) 1 bar = 0,1 MPa = 10 Pa; 1 MPa = 1 N/mm .
In addition to CEN member countries, there are also other regions for which this document is not
suitable. These other regions follow individual solutions.
EXAMPLE India, Egypt, Indonesia and some other countries besides the US and Canada follow North
[19]
American ASME B 31.8 while using the ISO 16486 series as the product standard.
4.2 Materials, components and jointing equipment
The PA-U materials and components used shall conform to the relevant ISO International Standards: the
ISO 16486 series and ISO 17885. Other components not covered by the ISO 16486 series or ISO 17885
shall conform to relevant standards or in the absence of such documents, the components shall meet
the performance requirements of the system as demonstrated by the manufacturer.
As specified by ISO 16486-5, the fusion equipment used for the construction of the pipeline shall
conform to the requirements of ISO 12176-1 or ISO 12176-2. If the operation of the fusion equipment
requires an operator's badge, the badge shall conform to ISO 12176-3. Traceability of PA-U materials
should refer to ISO 12176-4 and/or ISO 12176-5.
4.3 Maximum operating pressure
4.3.1 General
The maximum operating pressure (MOP) of the system shall be selected by the pipeline operator on
the basis of the gas supply system operating requirements and the materials used. The MOP of a PA-U
system depends upon the type of resin used (the MRS), the pipe SDR series and the service conditions.
It is limited by the overall service (design) coefficient, C, and the rapid crack propagation (RCP) criteria.
The MOP is the lower value when calculated using Formula (1) and Formula (2) with the critical
pressure calculated from Formula (4).
4.3.2 Maximum operation pressure based on long-term hydrostatic strength
The overall service (design) coefficient C for thermoplastics materials is specified in ISO 12162. This
coefficient is used to calculate the MOP of the pipeline. C shall be ≥ 2 for PA-U pipeline systems for natural
gas. For other gases, a higher overall service (design) coefficient C according to ISO 16486-5:2021,
Clause 6, can be defined.
The MOP shall be calculated using Formula (1):
20 * MRS
MOP = (1)
CS **()DR−1 D
F
where D is the temperature derating coefficient.
F
The temperature derating coefficient D for various operating temperatures shall be in accordance
F
with Annex E.
4.3.3 Maximum operation pressure based on rapid crack propagation
The critical RCP pressure, p , is dependent upon the temperature, pipe diameter, SDR and type of PA-U
c
material used.
For design temperatures ≥ 0 °C, the rules for the MOP pressure are given by ISO 16486-1 and
ISO 16486-2.
In case of design temperatures < 0 °C, the MOP pressure shall be determined by following equivalent
Formula (2):
p
cb,(T z)
MOP= (2)
15,
The full-scale critical pressure for temperatures < 0 °C, p shall be determined in accordance with
c,T(bz)
ISO 16486-1 and ISO 16486-2. The lab-scale critical pressure for temperatures shall be defined by
RCP-S4 testing according to ISO 13477 at the < 0 °C design temperature.
Where p ≥ 0,9 * p , the critical reference pressure from full-scale testing, p , shall be used
c,S4,T(bz) c,S4,REF c
as the critical full-scale pressure for < 0 °C as shown by Formula (3):
p = p (3)
c,T(bz) c
where p < 0,9 * p .
c,S4,T(bz) c,S4,REF
The MOP shall be determined by Formula (4):
p +1
p +1
c,T(bz)
c
==const (4)
p +1 p +1
c,S4,REF c,S4,(T bz)
This RCP Formula (4) converts to Formula (5), where the result shall be used for calculating Formula (2).
p + 1
c,REF
p = ∗ (p +−11) (5)
c,TT(bz) c,S4,(bz)
p + 1
c,S4,REF
4.4 Assembly techniques
Jointing procedures may vary depending upon the pipe size used. Butt fusion and electrofusion are the
preferred jointing methods. Butt fusion jointing shall be in accordance with Annex A and electrofusion
in accordance with Annex B.
For electro-fusion processing, including the operation of fusion control units, reference is made to the
manufacturers.
For fusion joints, evidence of the fusion compatibility between the jointing materials should be given.
Components made from PA-U 11 shall be fusion jointed only to components made from PA-U 11.
Components made from PA-U 12 shall be fusion jointed only to components made from PA-U 12.
Components made from PA-U are not fusion-compatible with components made from other polymers.
A written jointing procedure, authorized by the pipeline operator, shall be available prior to the
construction of a pipeline. The jointing procedure shall include specification of the jointing method, the
fusion parameters, the fusion equipment, the jointing conditions, the level of skill of the fusion operator,
and the quality control methods to be used.
4.5 Squeeze-off properties
When squeeze-off techniques are considered, the suitability of the pipe for squeeze-off shall be
confirmed in accordance with ISO 16486-2:2020, Annex A.
Further information can be taken from Annex D.
5 Construction
5.1 Competence
Operators shall be competent in the field of the assigned job. Operators shall possess the necessary skill
and required knowledge and the ability to operate with awareness.
NOTE 1 Specific courses provide competency training that can be certified by a third party organization
operating, for example, in accordance with ISO/IEC 17020.
NOTE 2 Examples of specific training courses for fusion operators can be found in ISO/TS 16486-8.
NOTE 3 Operators and supervisors can receive formal training under the supervision of a qualified instructor.
The gas company can require a certificate indicating that the operator has reached an adequate standard in
accordance with national regulations.
5.2 Storage, handling and transport
5.2.1 General
Polyamide pipes are available in coils, drums or straight lengths. Fittings are normally individually
packed.
Mishandling of the pipes and fittings shall be avoided to protect them against gouges, scratches, cuts or
holes, kinks or flattening.
5.2.2 Storage
PA-U pipes can be stored outside and under UV radiation provided that requirements for the resin stated
in ISO 16486-1 are met. Coloured pipes (e.g. yellow) can be subject to degradation if solar UV radiation
exceeds the values given in ISO 16486-1. The user of this document should consider the information
provided by the pipe manufacturer regarding the allowable UV radiation dose with determined regional
UV radiation level during storage.
NOTE 1 Information on regional levels of UV radiation can be found on webpages of national authorities, e.g.
meteorological institutes.
NOTE 2 According to ISO 16486-1, resistance to weathering is based on a cumulative exposure of 7,0 GJ/m UV
radiation level.
Non-black pipes which have been stored outdoor for longer than the period recommended by the
manufacturers shall only be used if tested prior to installation for conformity with the relevant part of
the ISO 16486 series. The minimum tests that shall be performed are listed in Table 1.
Table 1 — Minimum tests to evaluate coloured pipes when over-exposed to the UV radiation
Test Source and method
Elongation at break (all wall thicknesses) ISO 16486-2:2020, Table 4
Hydrostatic strength (80 °C, 1 000 h) ISO 16486-2:2020, Table 4
Cohesive resistance ISO 16486-5:2020, Table 5
PA-U fittings and valves should be stored following the manufacturer’s recommendation.
Straight pipes should be stacked on a suitable surface, preferably flat and free from stones or other
projections or sharp objects likely to deform or damage the pipes. Pipes and fittings shall be stored in
such a way as to minimize the possibility of the material being damaged by crushing or piercing.
The distances, “x” (see Figure 1), between support frames holding packs of pipes together should be
equal in order to allow the frames to be stacked.
The support frame should not be nailed together and should be constructed in such a way that the load
is directly supported by the frame and not by the pipes.
Key
x distance between supports
1 support frame
Figure 1 — Support frame
The exact height to which straight pipes can be stacked depends on many factors, such as material, size,
wall thickness and ambient temperature. During storage, stacking shall avoid the distortion of pipes in
storage over the limits as given by the manufacturer. The manufacturer’s stacking recommendations
shall be followed.
Polyamide pipes may be coiled or wound on drums. Coils of large-diameter pipes with d ≥110 mm
e
shall be stored vertically in purpose-built racks or cradles. Where loose straight pipes are stacked in
pyramidal fashion, it shall not exceed a height of 1 m. Fittings shall be stored in their original packaging
until being prepared-for use. Contact with aggressive reagents or solvents shall be avoided.
The pipes with the earliest extrusion date should be used first for installation. It is recommended that
fittings with the earliest manufacturing date should be used first for installation. Guidance from the
product manufacturer should be considered.
Fittings and valves shall be packed and transported in cartons and/or on pallets.
5.2.3 Handling
Initial handling of straight pipes shall be made with the pipes as delivered by the manufacturer (e.g.
in their own packaging) in packaged form, thus minimizing damage during this phase. When loading,
unloading or handling, it is preferable to use mechanical equipment to move or stack the packages.
The pipes shall not be dragged or thrown along the ground. If handling equipment is not used, choose
techniques which are not likely to damage the pipes and/or fittings.
Coils of pipe stacked on pallets are easily handled using a forklift truck. Individual coils shall not be
rolled off the edge of a vehicle load platform. Coils shall be slung individually when off-loading with a
crane. Before laying a pipe, ensure that the drum is positioned correctly and that its axle will remain
stable during the unrolling operation. While unrolling, ensure that the pipe is not damaged.
Fittings and valves shall be handled in accordance with manufacturer instructions and left in original
packaging until use.
5.2.4 Transport
When transporting straight pipes, flatbed vehicles shall be used. The bed shall be free from nails and
other protuberances. The pipes shall rest uniformly on the vehicle over their whole length and shall be
securely held in place during transport.
Coiled pipes shall be transported stacked on a pallet or as individual coils and be firmly secured to the
vehicle. For safety reasons, the height of the top of a drum when loaded on a vehicle shall not be larger
than the maximum height and any limitations expected on the route. Drums shall be firmly secured to
the vehicle.
Fittings and valves shall be transported in accordance with manufacturer instructions.
5.3 Jointing
The jointing operation, either mechanical or fusion, shall be performed in accordance with the
pipeline operator’s written procedure. The fusion procedure specification shall take into account the
relevant fusion standards, if existing, and any recommendation from the pipe, fitting and accessory
manufacturers. The relevant standard for the butt-fusion jointing procedure is ISO 16486-5.
NOTE 1 In some countries “fusion procedure specification” is also defined as “welding procedure specification
(WPS)”.
Polyamide pipes, fittings and accessories may be jointed either by heated-tool fusion jointing,
electrofusion jointing or mechanical jointing. The jointing and quality control methods used for the
construction of the gas supply system shall be appropriate to the design of the network.
Fusion operators shall possess the necessary skill and knowledge and ability to produce joints of
consistently high quality. Therefore, they shall receive formal training under the supervision of a
qualified instructor.
The jointing methods covered by this document are:
— butt fusion jointing (which shall conform to Annex A);
— electrofusion jointing (which shall conform to Annex B); and
— mechanical jointing (which shall conform to Annex C).
The gas company can require evidence of training or qualification for fusion. Examples of training and
assessment can be found in ISO/TS 16486-8.
[4]
NOTE 2 For qualification purposes, ISO/TS 16486-8 is replaced by EN 13067 for example.
The same level of skill, knowledge and ability is required for mechanical jointing. The gas company may
require evidence of training or qualification. When tightening or untightening a mechanical joint, it is
essential that torsional stress is not transmitted to the pipe.
5.4 Laying
5.4.1 General
Care shall be taken to prevent damage to the pipes and fittings during the whole of the laying process.
Changes in direction of a polyamide pipeline when laying can be made using pre-formed bends or elbow
fittings or by making use, within limits, of the natural flexibility of the pipe. Natural flexibility may be
used for bend radii ≥ 25 × d , and also for smaller radii for certain SDR values and materials provided
e
this is consistent with operational experience and good engineering practice.
NOTE 1 In general, the flexibility is a factor of SDR, environmental temperature and material. Consult the pipe
manufacturer for additional guidance or instructions.
NOTE 2 Information on the bend radii for mechanical joints are given in Annex C.
The flexibility of polyamide pipes is reduced in cold weather. If the temperature falls below 0 °C, special
handling instructions, issued by the manufacturers, shall be followed for straight or coiled pipes and
for fittings.
Machine-bending of pipes or bending after the application of heat in the field shall not be used.
Where PA-U pipes, fittings and valves are allowed to be installed above ground they shall be protected
against mechanical damage and, in case of non-black pipes, UV degradation.
If the gas pipeline is not protected by the surrounding soil, special consideration should be taken to
reduce any kind of risk, e.g. ignition sources, high temperatures, etc.
The minimum clearance between the pipe and obstacles (e.g. utilities, structures or immovable rocks)
shall be 200 mm from the pipe surface. If this minimum clearance cannot be observed, a protection
barrier shall be installed. Special precautions shall be taken if the gas pipeline crosses or is laid
alongside other buried services, e.g. a hot water or steam pipeline, a petrol-carrying pipe, a petrol
station or a high-voltage cable, etc.
Stresses caused by differences in temperature between laying and operation shall be taken into
consideration. The position of the pipeline shall be recorded before backfilling.
To minimize the possibility of damage to the pipeline by external influences, at least one of the following
measures shall be considered:
a) place a warning device, for example a protection tile, hazard tape, etc. along the top of the pipe;
b) place a tracer wire to enable the pipe to be located again in future;
c) install permanently visible above-ground markings, especially at road, railway and water crossings,
at blow-off devices, on private land, at boundaries between plots of land, and at points where the
pipeline changes direction.
5.4.2 Trench
Excavating and backfilling of the trench shall be in accordance with the written procedure authorized
by the pipeline operator. The width of the trench bottom shall be large enough to allow correct
installation and backfilling.
If it should be necessary to perform any fusion jointing in the trench, the width of the trench may need
to be larger, depending on the type of fusion jointing and the type of equipment used.
Pipes may be laid in the trench without preparation of the bottom if it consists of uniform, relatively
soft, fine-grained soils free of large flints, stones and other hard objects, and where the bottom of the
trench can readily be brought to an even finish providing uniform support for the pipes over their whole
length.
5.4.3 Drag forces
Pipes shall not be overstressed by tensile forces during laying. If the pipe is laid by drag, care shall be
taken to ensure that the drag force is not greater than the values given by Formulae (6) and (7):
σ **π d
e
F = (6)
fS* DR
s
σ
y
σ = (7)
12, 5
where
F is the maximum drag force, in Newtons;
σ is the maximum tensile stress in MPa;
σ is the tensile stress at yield in MPa;
y
f is the safety factor
s
SDR is the standard dimension ratio;
d is the external diameter of the pipe, in millimetres;
e
NOTE 1 As the safety factor, f , a value of 2,0 is normally used.
s
NOTE 2 The tensile stress at yield, σ , as provided by the pipe manufacturer.
y
The drag force, F, obtained by Formula (1) relates to an environmental temperature of 20 °C and it can
be applied to the pipe for during the drag. For higher temperatures, derating factors from Table E.1
should be applied in the denominator of Formula (6).
5.4.4 Valves
Valves shall be installed so that they do not expose the PA-U pipe to unnecessary stress during opening
or closing. PA-U valves shall conform to ISO 16486-4.
Valves are available with either a steel/iron or a plastics body. With steel/iron-body valves, special
precautions shall be taken against corrosion and to avoid stresses to the PA-U pipe induced by their
weight.
5.4.5 Connection to existing systems
Where there can be a release of gas in the working area, static-charge accumulation shall be avoided.
In order to avoid static charges, the pipeline system shall be connected to earth during manipulations,
for example by draping water-soaked cloths, made of natural fibre, over all pipes and fittings likely to
be handled so that the cloths touch both the pipe and the ground.
5.4.6 Backfilling
Unless otherwise specified, buried pipelines and casings
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