ISO/FDIS 25780

Plastics piping systems for pressure and non-pressure water supply, drainage or sewerage — Glass-reinforced thermosetting plastics (GRP) systems based on unsaturated polyester (UP) resin — Pipes with flexible joints intended to be installed using jacking techniques

ISO 25780:2011 specifies the properties of the piping system and its components made from glass-reinforced thermosetting plastics (GRP) based on unsaturated polyester resin (UP) for water supply, irrigation, drainage or sewerage systems with or without pressure. ISO 25780:2011 is applicable to GRP-UP piping systems, with flexible joints, intended to be installed using jacking techniques. It specifies the characteristics of pipes made from GRP-UP, with or without aggregates or fillers and also specifies the test parameters for the test methods referred to in ISO 25780:2011. ISO 25780:2011 is applicable to pipes and joints with a size range from DN100 to DN4000 which are intended to be used for the conveyance of water or sewage at temperatures up to 50ºC, with or without pressure. ISO 25780:2011 covers requirements to improve the design of the joint and specifies type test performance requirements for the joints as a function of the declared nominal pressure rating of the pipeline system and the required joint deflection capability of the system.

Titre manque

General Information

• Status: Not Published
• ICS: 23.040.20 - Plastics pipes
• ICS: 91.140.60 - Water supply systems
• ICS: 91.140.80 - Drainage systems
• ICS: 93.030 - External sewage systems
• Technical Committee: ISO/TC 138/SC 6 - Reinforced plastics pipes and fittings for all applications
• Drafting Committee: ISO/TC 138/SC 6 - Reinforced plastics pipes and fittings for all applications
• Current Stage: 5000 - FDIS registered for formal approval
• Start Date: 16-Dec-2025
• Completion Date: 06-Jan-2026

Relations

• Revises: ISO 25780:2011 - Plastics piping systems for pressure and non-pressure water supply, irrigation, drainage or sewerage — Glass-reinforced thermosetting plastics (GRP) systems based on unsaturated polyester (UP) resin — Pipes with flexible joints intended to be installed using jacking techniques
• Effective Date: 16-Jul-2022

Overview

ISO/PRF 25780 sets out requirements and test methods for plastics piping systems constructed from glass-reinforced thermosetting plastics (GRP) based on unsaturated polyester (UP) resin. The standard specifically addresses pipes fitted with flexible joints designed for installation using jacking techniques. This standard applies to systems used for water supply, irrigation, drainage, and sewerage, for both pressure and non-pressure applications, accommodating pipe sizes from DN 100 to DN 4000 and service temperatures up to 50°C.

ISO/PRF 25780 is aimed at ensuring system reliability and performance in underground pipeline installations, emphasizing joint integrity and resistance to the unique stresses of trenchless construction methods. It includes design, material, and construction criteria to support safe and efficient implementation of GRP-UP piping systems under varied operating conditions.

Key Topics

• Material Specifications
  • Requirements for glass-reinforced thermosetting plastics and unsaturated polyester resin
  • Rules for the use of aggregates, fillers, elastomers, thermoplastic liners, and metals
• Pipe and Joint Design
  • Geometrical characteristics (diameter, wall thickness, length, straightness)
  • Joint flexibility, sealing systems, and deflection capability
  • Design rating in terms of nominal pressure and stiffness for both pipes and joints
• Mechanical and Performance Testing
  • Resistance to internal pressure and external loads
  • Long-term creep stiffness and ring stiffness assessments
  • Performance of flexible joints under load and deflection
  • Assessment of conformity for manufacturers
• Installation Considerations
  • Suitability for jacking (trenchless) installation methods, such as microtunneling and pipe jacking
  • Design of joints to ensure function under installation and service conditions
  • Requirements for marking and traceability

Applications

ISO/PRF 25780 is highly relevant for the following sectors and scenarios:

• Municipal Infrastructure: Installation of new or replacement water supply, stormwater, and sewer pipelines, especially in urban areas where open trenching is disruptive or impractical.
• Industrial Facilities: Conveyance of process water, cooling water, or other fluids where resistance to internal pressure and chemical compatibility are necessary.
• Irrigation Systems: Underground pressurized and non-pressurized pipelines for agriculture and landscape irrigation, using trenchless technologies to minimize environmental impact.
• Marine and Saline Environments: Suitable for pipelines transporting saltwater or brackish water due to superior corrosion resistance of GRP-UP materials.
• Trenchless Rehabilitation: Projects involving the replacement or augmentation of aging infrastructure without surface excavation, leveraging the jacking capability and flexibility of the joint systems.

Related Standards

For optimal system design and compliance, ISO/PRF 25780 should be used in conjunction with other international standards for plastics piping systems and components, including:

• ISO 23856: Plastics piping systems for water supply, drainage, or sewerage - GRP systems based on UP resin
• ISO 7685: Determination of initial ring stiffness in GRP pipes
• ISO 8521: Test methods for circumferential tensile strength of GRP pipes
• ISO 8639: Methods for testing leaktightness and structural performance of flexible joints
• ISO 10468: Determination of ring creep properties under wet or dry conditions for GRP pipes
• ISO 2394 / EN 1990: General principles for structural design and reliability
• CEN/TS 14632: Guidance for assessment of conformity for plastics piping systems

Adherence to these standards supports quality assurance in the design, manufacture, and installation of safe, durable, and high-performance pressure and non-pressure piping systems for water and wastewater applications.

---

Keywords: ISO 25780, GRP pipes, UP resin, plastics piping systems, jacking techniques, flexible joints, trenchless installation, water supply, drainage, sewerage, pressure pipe standards, non-pressure pipe, pipe performance testing.

Standards Content (Sample)

DRAFT
International
Standard
ISO/DIS 25780
ISO/TC 138/SC 6
Plastics piping systems for
Secretariat: ASI
pressure and non-pressure water
Voting begins on:
supply, drainage or sewerage —
2025-06-24
Glass-reinforced thermosetting
Voting terminates on:
plastics (GRP) systems based on
2025-09-16
unsaturated polyester (UP) resin —
Pipes with flexible joints intended
to be installed using jacking
techniques
ICS: 91.140.60; 91.140.80; 93.030; 23.040.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
This document is circulated as received from the committee secretariat.
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Reference number
ISO/DIS 25780:2025(en)
DRAFT
ISO/DIS 25780:2025(en)
International
Standard
ISO/DIS 25780
ISO/TC 138/SC 6
Plastics piping systems for
Secretariat: ASI
pressure and non-pressure water
Voting begins on:
supply, drainage or sewerage —
Glass-reinforced thermosetting
Voting terminates on:
plastics (GRP) systems based on
unsaturated polyester (UP) resin —
Pipes with flexible joints intended
to be installed using jacking
techniques
ICS: 91.140.60; 91.140.80; 93.030; 23.040.20
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2025
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
This document is circulated as received from the committee secretariat. BE CONSIDERED IN THE LIGHT OF THEIR
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
PROVIDE SUPPORTING DOCUMENTATION.
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/DIS 25780:2025(en)
ii
ISO/DIS 25780:2025(en)
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 2
3.1 Design values declared by the manufacturer .2
3.2 Measured values .4
4 Requirements .13
4.1 Pipe properties . 13
4.1.1 Manufacturer's declared diameters . 13
4.1.2 Design jacking load for closed joint . 13
4.1.3 Nominal stiffness . 13
4.1.4 Nominal pressure . 13
4.1.5 Appearance .14
4.2 Materials .14
4.2.1 General .14
4.2.2 Reinforcement .14
4.2.3 Resin .14
4.2.4 Aggregates and fillers . 15
4.2.5 Thermoplastics liners . 15
4.2.6 Elastomers . 15
4.2.7 Metals . 15
4.3 Pipe wall construction . 15
4.3.1 Inner layer . 15
4.3.2 Structural layer . 15
4.3.3 Outer layer . 15
4.4 Reference conditions for testing . 15
4.4.1 Temperature . 15
4.4.2 Properties of water for testing .16
4.4.3 Loading conditions .16
4.4.4 Preconditioning .16
4.4.5 Measurement of dimensions .16
4.5 Elapsed time ,x, for determination of long-term properties .16
4.6 Joint properties .16
4.6.1 Types of joint .16
4.6.2 Flexibility of the jointing system .17
4.6.3 Sealing ring . . .18
4.6.4 Effect on water quality .18
4.7 Assessment of conformity .18
5 Pipes . 19
5.1 Geometrical characteristics .19
5.1.1 Wall thickness .19
5.1.2 Nominal length L .19
5.1.3 Straightness .19
5.1.4 Squareness of end faces.19
5.2 Mechanical characteristics .21
5.2.1 Initial ring stiffness .21
5.2.2 Long-term creep stiffness .21
5.2.3 Initial resistance to failure in a deflected condition .21
5.3 Resistance to strain corrosion .21
5.4 Longitudinal compressive strength .21
5.4.1 General .21
5.4.2 Initial longitudinal compressive stress at break (prism test pieces) . 22
5.4.3 Initial longitudinal compressive stress at break (spool test pieces) . 22
5.4.4 Test piece de-rating factor, f . 22
s
iii
ISO/DIS 25780:2025(en)
5.4.5 Requirements . 22
5.5 Design loads . 22
5.5.1 Design longitudinal load . . 22
5.5.2 Design jacking load . . 23
5.6 Longitudinal compressive modulus . 23
5.6.1 Initial longitudinal compressive modulus (prism test pieces). 23
5.6.2 Initial longitudinal compressive modulus (spool test pieces) . 23
5.6.3 Declared value . 23
5.7 Resistance of pressure pipes to internal pressure . 23
5.8 Marking . 23
6 Joints .24
6.1 General requirements .24
6.2 Performance requirements .24
6.3 Geometrical characteristics . 25
6.4 Interchangeability . 25
6.5 Marking . 25
Annex A (normative) Determination of the longitudinal compressive properties of a pipe, using
a sample of prism test pieces cut from a ring from the pipe .27
Annex B (normative) Determination of the longitudinal compressive properties of pipes, using
spool test pieces .33
Annex C (normative) Procedure for the calculation of the design jacking load on a GRP (UP)
pipe, F .39
j,d
Bibliography .44

iv
ISO/DIS 25780:2025(en)
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 documents 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 ISO/TC 138, Plastics pipes, fittings and valves for the transport of fluids,
Subcommittee SC 6, Reinforced plastics pipes and fittings for all applications.
This second edition cancels and replaces the first edition (ISO 25780:2011), which has been technically
revised.
The main changes are as follows:
The document was thoroughly revised, and many inconsistencies and errors corrected in all chapters.
Several parameters which were not considered useful were deleted. Some new parameters, such as partial
factors, were added.
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.

v
DRAFT International Standard ISO/DIS 25780:2025(en)
Plastics piping systems for pressure and non-pressure
water supply, drainage or sewerage — Glass-reinforced
thermosetting plastics (GRP) systems based on unsaturated
polyester (UP) resin — Pipes with flexible joints intended to
be installed using jacking techniques
1 Scope
This document specifies the properties of the piping system and its components made from glass-reinforced
thermosetting plastics (GRP) based on unsaturated polyester resin (UP). It is suited for all types of water
supply, drainage and sewerage with or without pressure. Types of water supply include, but are not limited
to, raw water, irrigation, cooling water, potable water, salt water, sea water, penstocks in power plants,
processing plants and other water-based applications.
This document is applicable to GRP-UP piping systems, with flexible joints, intended to be installed using
jacking techniques. It specifies the characteristics of pipes made from GRP-UP, with or without aggregates
or fillers and also specifies the test parameters for the test methods referred to in this document.
The requirements for the hydrostatic pressure design of pipes referring to this document meet the
requirements of ISO/TS 20656-1 and the general principle for the reliability of structures detailed in
ISO 2394 and in EN 1990. These documents provide procedures for the harmonization of design practices
and address the probability of failure, as well as possible consequences of failures. The design practices are
based on a partial safety factor concept, as well as on risk management engineering.
This document is applicable to circular pipes and joints with a size range from DN 100 to DN 4000 at normal
service conditions.
It covers requirements to prove the design of the joint and specifies type test performance requirements for
the joints as a function of the declared nominal pressure rating of the pipeline system and the required joint
deflection capability of the system.
GRP-fittings, used between pipe systems covered by this document, shall be in accordance with ISO 23856.
In a pipe-work system, pipes of different nominal pressure and stiffness ratings may be used together.
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 75-2, Plastics — Determination of temperature of deflection under load — Part 2: Plastics and ebonite
ISO 604, Plastics — Determination of compressive properties
ISO 2078, Textile glass — Yarns — Designation
ISO 3126, Plastics piping systems — Plastics components — Determination of dimensions
ISO 4633, Rubber seals — Joint rings for water supply, drainage and sewerage pipelines — Specification for
materials
ISO 7685, Glass-reinforced thermosetting plastics (GRP) pipes — Determination of initial ring stiffness

ISO/DIS 25780:2025(en)
ISO 8521, Glass-reinforced thermosetting plastic (GRP) pipes — Test methods for the determination of the initial
circumferential tensile wall strength
ISO 8639, Glass-reinforced thermosetting plastics (GRP) pipes and fittings — Test methods for leaktightness and
proof of structural design of flexible joints
ISO 10466, Glass-reinforced thermosetting plastics (GRP) pipes — Test method to prove the resistance to initial
ring deflection
ISO 10468, Glass-reinforced thermosetting plastics (GRP) pipes — Determination of the ring creep properties
under wet or dry conditions
ISO 10471, Glass-reinforced thermosetting plastics (GRP) pipes — Determination of the long-term ultimate
bending strain and the long-term ultimate relative ring deflection under wet conditions
ISO 10928, Plastics piping systems — Glass-reinforced thermosetting plastics (GRP) pipes and fittings —
Methods for regression analysis and their use
ISO 10952, Glass-reinforced thermosetting plastics (GRP) pipes and fittings — Determination of the resistance
to chemical attack for the inside of a section in a deflected condition
ISO 23856, Plastics piping systems for pressure and non-pressure water supply, drainage or sewerage — Glass-
reinforced thermosetting plastics (GRP) systems based on unsaturated polyester (UP) resin
CEN/TS 14632, Plastics piping systems for drainage, sewerage and water supply, pressure and non-pressure —
Glass-reinforced thermosetting plastics (GRP) based on unsaturated polyester resin (UP) — Guidance for the
assessment of conformity
3 Terms, definitions, symbols and abbreviated terms
For the purposes of this document, the following terms, definitions, symbols and abbreviated terms 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 Design values declared by the manufacturer
a) Section through a rebated un-grooved spigot b) Section through a rebated grooved spigot
Key
d pipe outside diameter, in mm e minimum wall thickness of pipe, in mm
OD min
d maximum spigot inside diameter, in mm
i,max
d minimum spigot or groove diameter, in mm
g,min
Figure 1 — Diameters declared by the manufacturer

ISO/DIS 25780:2025(en)
3.1.1
pipe outside diameter
jacking diameter
d
OD
maximum external diameter of the pipe barrel declared by the manufacturer
Note 1 to entry: The pipe outside diameter is expressed in millimetres (mm).
Note 2 to entry: See Figure 1.
3.1.2
maximum spigot inside diameter
d
i,max
maximum internal diameter of the pipe spigot, at the groove location where applicable, as declared by the
manufacturer
Note 1 to entry: Note to entry: See Figure 1.
3.1.3
minimum spigot or groove diameter
d
g,min
minimum external diameter of the spigot [see Figure 1 a) diameter], or in the groove of the spigot [see
Figure 1 b) diameter, if applicable], declared by the manufacturer
Note 1 to entry: Spigot or groove diameter is expressed in millimetres (mm).
Note 2 to entry: See Figure 1.
3.1.4
minimum wall thickness
e
min
minimum wall thickness of the pipe barrel declared by the manufacturer
Note 1 to entry: The minimum wall thickness is expressed in millimetres (mm).
Note 2 to entry: See Figure 1.
3.1.5
minimum cross-sectional area at the spigot
A
s
minimum area of the cross-section of the pipe at the spigot, or in the groove of the spigot, if applicable
Note 1 to entry: Minimum cross-sectional area at the spigot is derived using the following formula and is expressed in
square millimetres (mm )
 
Ad=π 05,,− 05d
()
()
sg,,mini max
 
 
Note 2 to entry: See Figure 1.
3.1.6
cross-sectional area at the barrel
A
b
area of the cross-section of the pipe barrel
Note 1 to entry: The cross-sectional area at the pipe barrel is derived using the following formula and is expressed in
square millimetres (mm )
 
Ad=π 05,,− 05d
() ()
bODi,max
 
 
Note 2 to entry: See Figure 1.

ISO/DIS 25780:2025(en)
3.1.7
minimum initial longitudinal compressive stress at break
σ
b
manufacturer's declared minimum value, derived from tests, for the initial longitudinal compressive stress
at break of the pipe
Note 1 to entry: When tested in accordance with Annex A or Annex B, the minimum initial longitudinal compressive
stress at break is expressed in megapascals (MPa).
3.1.8
declared initial longitudinal compressive modulus
E
c
manufacturer's declared value, derived from tests, for the initial longitudinal compressive modulus E
c,m
Note 1 to entry: When tested in accordance with Annex A or Annex B, the declared initial longitudinal compressive
modulus is expressed in megapascals (MPa).
3.2 Measured values
a) Section through a rebated un-grooved spigot b) Section through a rebated grooved spigot
Key
d measured external diameter, in mm
e
d measured spigot inside diameter, in mm
i
d measured spigot or groove diameter, in mm
g
d mean diameter, in mm
m
e measured wall thickness of pipe, in mm
Figure 2 — Measured diameters
3.2.1
mean diameter
d
m
diameter of the circle corresponding to the middle of the pipe wall cross-section and given by the following
formula:
dd=−e
me
where
d is the measured external diameter, in mm;
e
e is the measured wall thickness of the pipe, in mm.
Note 1 to entry: It is expressed in millimetres (mm).

ISO/DIS 25780:2025(en)
[SOURCE: ISO 23856:2021, amended by “measured”]
Note 2 to entry: If measured values are not available (e.g. for design purposes) declared values may be used.
Note 3 to entry: See Figure 2.
3.3
jacking
trenchless construction method which installs a pipeline by inserting pipes one by one under the ground by
pressing with one or more hydraulic jacks, while the excavated ground is simultaneously evacuated from
the cutting head
3.4
nominal length
pipe length without tolerance
Note 1 to entry: It is expressed in metres (m).
3.5
de-rating factor
f
s
factor correcting for the relationship between compression test results obtained on spool test pieces and
results obtained using prism test pieces with the unrebated spigot geometry
Note 1 to entry: de-rating factor is determined using the following formula and is a dimensionless number
f = σ / σ
sb,,sb pI, TT
where
σ is the initial longitudinal compressive stress at break (spool test pieces) according to 5.4.2, in
b,s
in MPa;
σ is the initial longitudinal compressive stress at break (prism test pieces) for initial type tests,
b.p,ITT
according to 5.4.3, in MPa.
3.6
initial longitudinal compressive modulus
E
c,p
ratio of the applied stress to the resulting strain below the elastic limit, both measured concurrently during
a short-term compression test with prism
3.7
E
c,s
ratio of the applied stress to the resulting strain below the elastic limit, both measured concurrently during
a short-term compression test with spool
Note 1 to entry: When tested in accordance with Annex A or Annex B, the initial longitudinal compressive modulus is
expressed in megapascals (MPa).
3.8
design longitudinal load
F
d
design value of the concentric longitudinal load that the pipe withstands taking into account the material
partial factor
Note 1 to entry: The ultimate longitudinal load is determined using the following formula and is expressed in
kilonewtons (kN)
1 1
FA=⋅ σ ⋅⋅
db s
1 000 γ
M
ISO/DIS 25780:2025(en)
where
σ is the declared minimum initial compressive stress at break, in MPa;
b
A is the minimum pipe cross-sectional area at the spigot, in mm ;
s
γ material partial factor, γ = 1,37; see also Table C.1.
M M
3.9
design jacking load
F
j,d
longitudinal compressive load that a pipe can withstand during a jacking operation, taking into account
installation partial factor and the stress eccentricity dependence factor
Note 1 to entry: Design jacking load is determined using the following formula and is expressed in kilonewtons (kN)
F
d
F =
jd,
S ⋅γ
σ i
where
F is the design longitudinal load, in kN;
d
S is the stress eccentricity dependence factor, with S ≥ 2;
σ σ
γ is the installation partial factor, see Table C.1.
i
Note 2 to entry: For the design jacking load for closed joint (considering full contact between the spigots) the stress
eccentricity dependence factor S = 2.
σ
Note 3 to entry: For the design jacking load for open joint (considering incomplete contact between the spigots) the
stress eccentricity dependence factor S > 2. For the determination of S see C.2.5.
σ σ
3.10
nominal stiffness
SN
alphanumerical designation for stiffness classification purposes, which has the same numerical value as the
minimum initial value required, when expressed in newtons per square metre (N/m )
Note 1 to entry: The designation for reference or marking purposes consists of the letters SN plus a number.
[SOURCE: ISO 23856:2022, 3.8]
3.11
ring stiffness
S
physical characteristic of the pipe which is a measure of the resistance to ring deflection per metre length
under external load
Note 1 to entry: ring stiffness is determined using the following formula and is expressed in newtons per square
metre (N/m )
EI⋅
S =
d
m
where
ISO/DIS 25780:2025(en)
E is the apparent modulus of elasticity, which can be derived from the result of the ring stiffness test,
i.e. ISO 7685, in N/m ;
d is the mean diameter, in m;
m
I is the second moment of area in the longitudinal direction per metre length, in m4/m;
e
I= (6)
where e is the measured wall thickness of pipe, in m.
3.12
initial ring stiffness
S
value of ring stiffness, S, obtained when tested in accordance with ISO 7685
The initial stiffness shall be computed by:
  y 
−5
1 860+ 2500 ⋅10
 
 
d
  
m
S =
Ly⋅ kd⋅
R m
−⋅0,392 7
F Ge⋅
R
where
y is the measured deflection, in m;
d is the mean diameter, in m;
m
L is the length of the specimen, in m;
R
F is the measured load, in N;
R
k is a shape factor for the wall cross section, can be assumed to be equal to 1.2, dimensionless;
G is the shear modulus, in N/m .
Note 1 to entry: The shear modulus to be used in the calculation can be determined through calibration between
measured and computed values on various products, or other suitable means.
Note 2 to entry: Initial ring stiffness is expressed in newtons per square metre (N/m ).
Note 3 to entry: The test shall be performed at relative deflection, y/d calculated by:
m
y
()% =
d 3
m
SN
3.13
calculated long-term ring creep stiffness
S
x
calculated value of ring creep stiffness, S, at x years
Note 1 to entry: Long-term ring creep stiffness is obtained using the following formula
SS=⋅α
xx01,,creep
where
ISO/DIS 25780:2025(en)
x is the elapsed time in years specified in this document (see 4.6);
α is the creep factor at x years, determined according to ISO 10468 under wet conditions;
x,creep
S is the ring stiffness at position 1 at 0,1 hour.
0,1
3.14
pressure pipe
pipe having a nominal pressure (PN) classification greater than 1 bar and which is intended to be used with
the internal pressure equal to or less than its nominal pressure when expressed in bars
3.15
non-pressure pipe
pipe subjected to an internal pressure not greater than 1 bar
3.16
nominal pressure
PN
alphanumeric designation for pressure classification purposes, which has a numerical value equal to the
resistance of a component of a piping system to internal pressure
Note 1 to entry: Nominal pressure is a designation for reference or marking purposes that consists of the letters PN
plus a number which is related to a component's pressure rating in bars.
3.17
normal service conditions
conveyance of water or sewage, in the temperature range 2 °C to 50 °C, with or without pressure, for 50 years
3.18
service temperature
maximum sustained temperature, at which the system is expected to operate continuously
Note 1 to entry: Service temperature is expressed in degrees Celsius (°C).
3.19
rerating factor
R
RF
multiplication factor that quantifies the relation between a mechanical, physical or chemical property at the
service condition compared to the respective value at 23 °C and 50 % relative humidity (RH)
3.20
relative ring deflection
y/d
m
ratio of the change in diameter of a pipe, y, in metres, to its mean diameter, d , in metres
m
Note 1 to entry: Relative ring deflection is derived as a percentage, %, i.e.:
 y 
⋅100
 
d
 
m
3.21
type test
tests carried out in order to assess the fitness for purpose of a product or assembly of components to fulfil
its or their function(s) in accordance with this document
3.22
flexible joint
joint which allows relative movement between components being joined

ISO/DIS 25780:2025(en)
3.23
flush coupling
joint component with either an external diameter equal to the pipe's outside diameter or an inside diameter
equal to the pipe's inside diameter
3.24
closed joint
joint condition where the pipe ends, with or without a transfer ring, are in full contact around the whole
circumference
3.25
open joint
joint condition where the pipe ends, with or without a transfer ring, are in incomplete contact with each
other thereby forming a gap
3.26
angular deflection
δ
angle between the axes of two adjacent pipes
Note 1 to entry: Angular deflection (see Figure 3) is expressed in degrees (°).
3.27
draw
D
longitudinal movement of a joint
Note 1 to entry: Draw (see Figure 3) is expressed in millimetres (mm).
3.28
total draw
T
sum of the draw, D, and the additional longitudinal movement, J, due to the presence of angular deflection
Note 1 to entry: Total draw (see Figure 3) is expressed in millimetres (mm).
3.29
misalignment
M
amount by which the centrelines of adjacent pipes fail to coincide
Note 1 to entry: Misalignment (see Figure 3) is expressed in millimetres (mm).
a) Draw
ISO/DIS 25780:2025(en)
b) Angular deflection
c) Total draw
d) Deformation
Key
D draw
J longitudinal movement arising from angular deflection of the joint
δ angular deflection of the joint
T total draw
M misalignment
NOTE The joint in this figure is an example of a typical joint but is not intended to fix design. Other joints are
available.
Figure 3 — Joint movements
ISO/DIS 25780:2025(en)
3.30
break
condition where the test piece can no longer carry the load to which it is being subjected
3.31
thickness to diameter ratio
e /d
min OD
the thickness to diameter ratio is the ratio between the minimum wall thickness of pipe, e , and the pipe
min
outside diameter, d , expressed in promille
OD
3.32
controlled installation process
installation process during which the steering and jacking forces are continuously monitored and recorded
to ensure that design limits on angular deflection and jacking load are not exceeded
3.33
uncontrolled installation process
installation process during which the steering and jacking forces are not continuously monitored and
recorded
A initial mean cross-sectional area
A cross-sectional area at the barrel
b
A minimum cross-sectional area at the spigot
s
A calculated minimum area of the cross-section of the pipe at the spigot, or in the groove of the
spool
spigot
D draw
E apparent modulus of elasticity
E declared initial longitudinal compressive modulus
C
E initial longitudinal compressive modulus (prism test piece)
c,p
E initial longitudinal compressive modulus (spool test piece)
c,s
F compressive load
F measured load
R
F maximum compressive force at failure
c
F design longitudinal load
d
F design jacking load
j,d
F load at fracture
fr
G shear modulus
I second moment of area in the longitudinal direction
J longitudinal movement arising from angular deflection of the joint
L nominal length
L actual length of the pipe
p
L length of the specimen
R
L length of the test spool
S
L measured length of coupling
c
M misalignment
R rerating factor
RF
R slenderness ratio
SL
S ring stiffness
S initial ring stiffness
S ring stiffness at position 1 at 0,1 hour.
0,1
ISO/DIS 25780:2025(en)
S calculated long term ring creep stiffness
x
S minimum long-term creep stiffness
x, creep, min
S stress eccentricity dependence factor
σ
T total draw
T measured spigot thickness
g
T minimum spigot thickness
g,min
X coefficient
Z diametrical extent of compression in the joint segments
a deflection offset
d measured external diameter
e
d measured spigot or groove diameter
g
d minimum spigot or groove diameter
g,min
d measured spigot inside diameter
i
d maximum spigot inside diameter
i,max
d mean diameter
m
d pipe outside diameter
OD
d deviation from squareness across a joint's external diameter
sq,d
d deviation from squareness across a joint's wall thickness
sq,e
e measured wall thickness of pipe
e/d thickness to diameter ratio
OD
e minimum wall thickness of pipe
min
f test piece de-rating factor
s
h measured height of test piece
k shape factor for the wall cross section
p probability of failure
f
r radius of gyration for a rectangle
G
w measured width of test piece
x elapsed time
x measured rebated length
x measured distance from the groove to spigot end
y measured deflection
y/d relative ring deflection
m
(y /d ) initial relative ring deflection at 2 min
2, bore m min
α creep factor at x years
x,creep
δ angular deflection
ε strain
ε strain at failure
b
γ total safety factor
γ installation partial factor
i
γ material partial factor
M
η coefficient
λ coefficient
φ angular deflection, in accordance with the design jacking load
v number equal to the component's nominal pressure

ISO/DIS 25780:2025(en)
σ minimum initial longitudinal compressive stress at break
b
σ initial longitudinal compressive stress at break (spool test piece)
b,s
σ initial longitudinal compressive stress at break (prism test piece) for initial type tests
b.p,ITT
σ initial longitudinal compressive stress at break (prism test piece) for quality control tests
b,p;QC
σ stress at the value of the strain ε = 0,000 5
1 1
σ stress at the value of the strain ε = 0,002 5
2 2
ξ coefficient
i subscript, which refers to individual test piece
j subscript, which refers to individual gauge
BRT batch release test
CC consequence class
GRP glass reinforced thermosetting plastics
DN nominal size
PN nominal pressure
PVT process verification tests
TT type test
SN nominal stiffness
UP unsaturated polyester
4 Requirements
4.1 Pipe properties
4.1.1 Manufacturer's declared diameters
The outside diameter of GRP pipes conforming with this document shall conform to the requirements given
in Table 4 and be designated by the pipe outside diameter, d . The manufacturer shall also declare the
OD
maximum spigot inside diameter, d .
i,max
4.1.2 Design jacking load for closed joint
The manufacturer shall declare the design jacking load for closed joint that can be applied to the pipe during
the jacking operation, in kilonewtons.
4.1.3 Nominal stiffness
For jacking applications, the pipe shall have a nominal stiffness of at least SN 20 000. The nominal stiffness
shall be at least SN 30 000 for the following conditions: curved installations, uncontrolled installations, or
installation lengths of more than 50 m.
NOTE This requirement for SN 30000 as a minimum is necessary to prevent failures of the spigot due to lateral
forces resulting from the curvature and/or steering of the tunnel boring machine
4.1.4 Nominal pressure
The nominal pressure (PN) shall conform to one of those given in Table 1.
Where pressure ratings other than the nominal values in Table 1 are to be supplied, by agreement between
the manufact
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