ISO/TS 10986:2021

TECHNICAL ISO/TS
SPECIFICATION 10986
First edition
2021-07
Plastics piping systems — Glass-
reinforced thermosetting plastics
(GRP) pipes — System design of above
ground pipe and joint installations
without end thrust
Systèmes de canalisations en plastiques — Tubes en plastiques
thermodurcissables renforcés de verre (PRV) — Conception de
système d'installations de tubes et d'assemblages en aérien sans
poussée d'extrémité
Reference number
©
ISO 2021
© ISO 2021
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ii © ISO 2021 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Angular deflection of joints . 1
4.1 General . 1
4.2 Effects of loads on joint angular deflection . 3
4.3 Measuring deflections . 3
4.4 Checking the installed joint . 4
4.4.1 General. 4
4.4.2 Coupling-to-pipe position . 4
4.4.3 Joint misalignment . 5
4.4.4 Gap between pipe ends . 5
4.4.5 Adjusting joints . 6
5 Installation of above ground pipes . 6
5.1 General . 6
5.2 Supporting of pipes . 7
5.2.1 General. 7
5.2.2 Support design . 9
5.2.3 Loads on supports .10
5.3 Anchor design .11
5.4 Guide design .11
5.5 Maximum support spacing .14
5.5.1 General.14
5.5.2 Perpendicular forces .15
5.5.3 Forces due to angular deviation .15
5.5.4 Axial forces .15
5.5.5 Maximum total axial force .17
5.5.6 Deformations and bending moments for pipes resting on two supports .18
5.5.7 Deformations and bending moments for pipes resting on multiple supports .21
5.5.8 Load cases and combinations of long- and short-term loads.23
5.5.9 Checking of stresses and deformations .24
Annex A (informative) Pipeline pressure testing and inspection .27
Annex B (informative) Recording above ground joint deflection data .34
Bibliography .37
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
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electrotechnical standardization.
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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).
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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 6, Reinforced plastics pipes and fittings for all applications.
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.
iv © ISO 2021 – All rights reserved

Introduction
While pipes manufactured according to ISO 23856 are typically utilized in buried installations, there
are circumstances where installing above ground is the preferred practice. These can include terrain
not suitable for burial (e.g. rock), road or river crossings, unsuitable soils and installation on steep
slopes.
For information on subjects such as shipping, handling, inspecting, rigid connections, thrust restraint
and joining pipes, refer to ISO/TS 10465-1 which addresses the buried installation of GRP pipes. The
guidelines and information on these subjects are also applicable to pipes used above ground. The
information in this document is intended to supplement ISO/TS 10465-1 with practices and guidelines
specific to above ground installation.
TECHNICAL SPECIFICATION ISO/TS 10986:2021(E)
Plastics piping systems — Glass-reinforced thermosetting
plastics (GRP) pipes — System design of above ground pipe
and joint installations without end thrust
1 Scope
This document addresses the system design of pipe and joints of above ground installations without
end-thrust as specified in systems standard ISO 23856. It is directed to pipelines with a minimum
stiffness of SN 5000 laid in a straight line between thrust blocks. It is based on the safety concepts
described in ISO TS 20656-1, with consequence class 2 (CC2) as default. For other consequence classes,
certain details specified in this document can need to be modified. This document is directed to double
bell coupling. However, much of the information can be adapted and utilized for other flexible joints
systems.
This document does not cover fittings nor detailled engineering work like thrust blocks, support and
anchor designs.
As installation is not included in the scope of this document and to assist system design, Annex A
provides a pressure testing and inspection procedure. However, to ensure the use of clearly defined
field test data in system design, Annex A can be used normatively by agreement between purchaser and
supplier. An example of recording above ground joint deflection data is given in Annex B.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at http:// www .electropedia .org/
4 Angular deflection of joints
4.1 General
The angular deflection at flexible joints shall be controlled to avoid excessive loads on the pipeline
and its supporting structures. Above ground installations do not benefit from the stabilizing support
that is given by the soil in buried installations, and they are therefore more susceptible to problems
of joint misalignment. For this reason, control and measurement of joint angular deflection is of
great importantance. It is necessary to limit angular deflections to lower values than those normally
permitted for buried applications.
There are two types of deflection to consider: pipe-to-pipe angular deflection and coupling-to-pipe
deflection, as shown in Figure 1. Both need to be considered as coupling-to-pipe angular deflection can
be larger than the pipe-to-pipe angular deflection.
Key
1 coupling-to-pipe angular deflection
2 pipe-to-pipe angular deflection
Figure 1 — "Pipe-to-pipe" and "coupling-to-pipe" deflection, example 1
For some designs of double socket joint the pipe can only move on one side of the coupling. In that case,
the pipe-to-pipe angular deflection is equal to the coupling-to-pipe angular deflection on one side (see
Figure 2). The manufacturer should advise which case will occur with their design of joint.
Key
1 pipe-to-pipe = pipe-to-coupling angular deflection
Figure 2 — "Pipe-to-pipe" and "coupling-to-pipe" deflection, example 2
2 © ISO 2021 – All rights reserved

4.2 Effects of loads on joint angular deflection
The angular deflection is influenced by several factors in addition to the initial pipe installation, such as
load-induced pipe deflections and support settlement.
Pipe deflections after inital installation are caused by forces produced by the weight of fluid in the pipe,
external loads and pressure within the pipeline. These forces can produce significant pipe-to-coupling
deflections which, if acting in a similar plane to the initial installation deflection, can result in the total
deflection at the coupling exceeding the allowable limit. An example of this effect is shown in Figure A.3.
The initial pipe angular deflection therefore should be limited to allow for this effect to ensure that the
total deflection does not exceed the maximum coupling deflection specification.
4.3 Measuring deflections
The coupling-to-pipe angular deflection is measured as an angular offset, see Figure 3.
Key
L coupling offset (left L
off,l off,l,min
minimum coupling offset (left pipe)
pipe) = L − L
off,l,max off,l,min
L coupling offset (right L
off,r off,l,max
maximum coupling offset (left pipe)
pipe) = L − L
off,r,max off,r,min
L minimum coupling offset (right pipe)
off,r,min
L maximum coupling offset (right pipe)
off,r,max
Figure 3 — Measurements for determining the angular offset
Coupling offsets L and L should be measured as follows:
off,l off,r
Find the maximum and the minimum distance between the homeline and the face of the coupling along
the circumference of the pipe. Subtract the minimum found value from the maximum found value.
The total pipe-to-pipe offset, L , is calculated by additioning L and L , see Formula (1):
off,tot off,l off,r
LL=+L (1)
offt, ot off,loff,r
The total pipe-to.pipe offset, L , shall be smaller or equal to the maximum allowable coupling offset
off,tot
L , see Formula (2):
off,max
LL≤ (2)
offt,,ot offmax
with Formula (3):
α π
max
L =DN∙ (3)
offm, ax
NOTE Formula (1) and Formula (2) are only valid for conditions given in Figure 3, but not for conditions
seen in Figure 9, where the coupling-to-pipe angular deflection is larger than the pipe-to-pipe angular deflection.
However, the same logic applies.
The maximum pipe-to-pipe offset for empty pipes installed in straight alignment is shown in Table 1.
Table 1 — Maximum pipe-to-pipe offset for pressure pipes installed in straight alignment
Pipe nominal size Declared allowable joint Maximum allowable Example
(pipe-to-pipe) installed angular deflection,
DN Maximum value
DN
angular deflection, α , α, in degrees
max
(L +L ) in
off,l off,r
in degrees (not filled, no pressure)
mm
≤ 500 3 1 500 9
500 < DN ≤ 900 2 2/3 900 10
900 < DN ≤ 1 800 1 1/3 1 800 10
> 1 800 0,5 1/6 3 600 10
In service, the following factors cause an increase in the angle, α, and as a result, L :
off,tot
— weight of water
— pressurizing
— creep in the pipe material.
See 5.5.9.3 for further details.
4.4 Checking the installed joint
4.4.1 General
The quality of the joint installation should be checked as soon as possible after assembly as correction
can be difficult when the coupling gaskets have settled. Information regarding forms that can be used
for recording the joint quality control is given in Annex B.
The installed joint should be checked at normal ambient temperatures. High or uneven pipe
temperatures as can be caused by direct sunlight, for example, affect the results of the checks.
4.4.2 Coupling-to-pipe position
It is important for the coupling to be located as centrally as possible between the two pipe ends in order
to avoid interference of the pipe end with the gasket or the pipe ends touching during operation.
4 © ISO 2021 – All rights reserved

4.4.3 Joint misalignment
Maximum misalignment of pipe ends should not exceed the lesser of 0,5 % of pipe diameter or 3 mm.
The misalignment can be measured with two identical notched rulers pressed against the pipe at both
sides of the coupling, see Figure 4. If the depth of the machined spigot surface is different for the two
pipes, the measured misalignment should be corrected accordingly. For pipes 700 mm and larger the
misalignment can be measured with a ruler from the inside of the pipe, see Figure 4.
Key
1 rulers
2 joint misalignment
3 machined spigot surfaces (measure gaps between rulers and spigot surface)
NOTE On some pipes there is no machined spigot surface, either because it is not designed to have one or
because it is negligible because the pipe barrel OD is the correct spigot diameter.
Figure 4 — Misalignment
4.4.4 Gap between pipe ends
The gap between pipe ends is checked by measuring the distance between the homelines (see Figure 5).
The gap, d , is then calculated using Formulae (4) and (5):
g
dd=−2d (4)
g,minmin 1
dd=−2d (5)
g,maxmax 1
where
d is the minimum measured gap between pipe ends;
g,min
d is the maximum measured gap between pipe ends;
g,max
d is the minimum measured distance between homelines;
min
d is the maximum measured distance between homelines;
max
d is the distance from the pipe end to the homeline
The engineer should decide what the value of the gap should be, based on maximum and minimum
allowable draw and installation and service conditions. These include at least increased rotation due to
weight of water and effects of pressure and creep, Poisson’s effect and temperature change.
The distance from the pipe end to the homeline, d , can be found in the pipe specifications or measured
prior to installation, see Figure 5.
Key
1 homeline d distance of homeline from end of pipe
d minimum measured distance between homelinesd minimum measured gap between pipe ends
min g,min
d maximum measured distance between d
max g,max
maximum measured gap between pipe ends
homelines
Figure 5 — Gap between pipe ends
For pipes 700 mm and larger the gap can be measured directly from the inside of the pipe.
4.4.5 Adjusting joints
The joint should be adjusted if any of the checks described in the preceding clauses fall outside the
specified limits. The necessary adjustments of coupling or pipe position should be made carefully,
avoiding concentrated loads or impact loads that can damage the pipe or the coupling.
5 Installation of above ground pipes
5.1 General
The designer of an above ground pipe installation should be aware of the forces that act on the pipe
system, particularly where high system pressures exist.
When a component in a pressurized pipeline has a change in cross-sectional area or alignment
direction, a resultant force is induced. All components such as bends, reducers, tees, wyes or valves
shall be anchored or restrained to withstand these loads. This is the case for above ground as well as
buried pipes.
In buried pipelines, adequate resistance to movements at joints in undeflected installations is generally
provided by the pipe embedment. Such resistance shall be provided at the supports of an above ground
6 © ISO 2021 – All rights reserved

pipeline. Care shall be exercised to minimize misalignments and all components shall be properly
supported to ensure the stability of the pipeline.
5.2 Supporting of pipes
5.2.1 General
A range of joint designs are manufactured for which a variety of support configurations are
recommended. Generally, pipes are supported on either side of the joint, but some systems allow direct
support under the joint.
To minimize the loads induced in pipes and supports, the supports should not restrain longitudinal
expansion of the pipes. However, it is essential that the pipe movements be guided and controlled in
such a way that all pipe sections are stable and that acceptable longitudinal movement of the pipe in the
couplings is not exceeded.
As non-restrained couplings are flexible, it is very important for the stability of every pipe component
to be ensured by the supports. Each pipe should therefore be supported by at least two cradles and
anchored by a pipe anchor at one of these cradles, while the remaining cradles should be designed as
guides, allowing longitudinal expansion of the pipe but restraining lateral movements. With direct
support under the joints, the coupling clamp can act as anchor, see Figure 6 (1) and Figure 8.
For pipes supported in more than two cradles, the cradle closest to the middle of the pipe should be
used as an anchor.
The anchors should be located with regular spacing to ensure even distribution of longitudinal pipe
expansion on the joints. However, the maximum distance between two anchors shall not result in
exceeding the draw limits specified for the joint given in ISO 23856.
Figure 6 shows typical support arrangements for pipes.
Key
1 one cradle A coupling with anchor, which acts as pipe anchor
2 two cradles B guide
3 multiple cradles C pipe anchor
a maximum distance from the centreline of the D coupling anchor, if necessary, see 5.4
joint to centreline of a support, see Table 2
b maximum distance between two pipe anchors,
depending on the limits specified for the joint
given in ISO 23856
Figure 6 — Typical support arrangements
Table 2 — Maximum distance from the centreline of the joint to centreline of a support, a
DN a
DN ≤ 500 max. 250 mm
600 ≤ DN ≤ 1 000 max. 0,5 × DN
DN > 1 000 max. 500 mm
When a pipe is supported on more than two supports, the pipe supports should be in straight alignment.
The maximum deviation from the straight alignment should not exceed 0,1 % of the span length, L .
s
This applies to all load conditions of the system.
It is important that support displacement does not exceed the maximum misalignment of pipe ends in
joints as specified in 4.4.3.
8 © ISO 2021 – All rights reserved

The pipes shall be supported adjacent to the joints, or directly under the joints, to ensure the stability
of the couplings.
5.2.2 Support design
Any excessive point or line loading should be avoided when pipes are installed above ground. Above
ground pipes should therefore be supported in cradles. Typically, the cradles are made from concrete
or steel, with a supporting angle of 150°. A smaller angle (but never smaller than 120°) or a larger angle
(but never larger than 180°) may be used, if it can be demonstrated that it will not cause excessive local
stresses.
The diameter of the finished cradle, with cradle liners, should be 0,5 % larger than the outer diameter
of the non-pressurized pipe. The cradles should have a minimum width of:
— 150 mm for all pipes with DN ≤ 1 000 mm,
— 200 mm for pipes with 1 000 mm < DN ≤ 2 000 mm, and
— 250 mm for pipes with DN > 2 000 mm.
See Figure 7.
Cover the inside of the cradles with a 5 mm thick cradle liner to avoid direct contact between pipe and
cradle. Liners should be made from materials that are resistant to the actual environment. High friction
liners should be applied at anchors while low friction liners should be applied at guides. See 5.3 and 5.4.
Figure 7 shows the cradle design for support under the pipe barrel.
Key
1 cradle liner, minimum thickness 5 mm 2 cradle width
Figure 7 — Typical cradle design for support under the pipe barrel
Figure 8 shows the cradle design for support under the coupling.
Key
1 anchor strap also lined 3 anchor strap width, equal to 30 % of L
c
2 cradle liner 25 mm larger than cradle 4 cradle width, equal to 90 % of L
c
L coupling length
c
Figure 8 — Typical cradle design for support under the coupling
5.2.3 Loads on supports
The supports should be rigid and designed to withstand the loads caused by:
— external and environmental loads,
— weight of pipe and fluid,
— reaction forces caused by internal pressure,
— friction induced in couplings and against guides in case of temperature and/or pressure variations.
— head loss in pipe.
It is the responsibility of the owner's engineer to determine the actual design loads for the supports.
NOTE The reaction forces, caused by the weight of water, act perpendicular to the pipe. For pipe installations
on steep slopes this results in a significant horizontal load component acting on the pipe foundations. A common
error is to regard the reaction from water as vertical since it is a gravitational force.
Table 3 provides approximate axial forces that should be considered in the design of support cradles.
These loads result from contraction and elongation of pipes during operation and frictional resistance
in the gasketed joint.
Table 3 assumes simultaneous expansions and contractions of the neighbouring pipes. If non-
simultaneous expansions and contractions can be expected, contact the pipe supplier for adequate
axial forces.
Frictional force between pipe and guide should be determined based on total compression between
pipe and cradle and the frictional coefficient between the pipe material and the cradle liner.
For the cradle liners suggested in 5.4, the frictional coefficient can be assumed to be 0,3.
10 © ISO 2021 – All rights reserved

Table 3 — SN 5 000 pipes — Typical axial loads due to pipe expansion/contraction and friction
at joints in kN
DN PN 6 PN 10 PN 16
≤ 300 5 6 7
350 6 6 8
400 6 7 8
450 6 7 9
500 7 8 10
600 8 9 11
700 8 10 12
800 9 11 14
900 10 12 15
1 000 11 13 16
1 200 12 15 19
1 400 14 17 21
1 600 15 19 24
1 800 17 21 27
2 000 18 23 29
2 200 20 25 32
2 400 22 27 35
2 600 23 29 37
2 800 25 31 40
3 000 26 33 43
3 200 28 35 45
3 400 30 37 48
3 600 31 39 51
3 800 33 41 53
4 000 34 43 56
NOTE  These typical values result from experience and depend on sealing type used. For
exact figures, consult the manufacturer.
5.3 Anchor design
The function of the anchor support is to prevent the pipe from moving in the longitudinal and vertical
direction. It also needs to be able to transfer the longitudial loads (see 5.2.3) acting on the pipe to the
fixed supports.
There are several ways to design the anchor, such as clamping or using bonded saddles.
When clamping is used, the designer needs to be aware that GRP pipes have higher design strain and
can have higher coefficient of thermal expansion than steel. The anchor shall therefore be designed
to compensate for these differences. It shall be designed to give sufficient strap tension at low
temperatures without overloading the strap or the pipe in situations involving high temperatures and
high pressure which cause diametral expansion of the pipe. As an example, spring loaded bolts could be
considered.
5.4 Guide design
Guides should be designed as cradles with low-friction cradle liners. This requirement is fulfilled by
using liners such as Ultrahigh-molecular Polyethylene and Polytetrafluorethylene. It shall be ensured
that the liner material will not deteriorate in the anticipated environment.
The cradle liner should be permanently attached to the guide cradle to ensure its stability.
In many situations, the weight of pipe and fluid is sufficient to ensure the lateral stability of a pipe in
a guide. The ends of short high-pressure pipes may lift up from guides as a result of an unfavourable
combination of high-compression forces in the fluid and pipe-to-coupling angular deflection. The need
for securing of pipe ends depends on the combination of internal pressure, pipe diameter, pipe-to-
coupling angular deflection and the supporting conditions.
Pipe-to-coupling vertical convex offset and internal pressure results in a force that tends to lift the pipe
end, as illustrated in Figure 9.
Key
1 Pipe-to-coupling vertical convex offset OD outer diameter of the pipe
2 lift
Figure 9 — Instability of pipe ends on guides
If this lifting force under unfavourable conditions is large enough to lift the pipe end, the end shall
be secured. The securing of pipe ends is best achieved by anchoring the coupling to the foundation
supporting the pipe ends. For supports made in-situ from concrete, the lower half of the coupling can be
embedded, and the coupling anchored to the support with steel strap, see Figure 10.
12 © ISO 2021 – All rights reserved

Key
1 cradle liner: high friction for anchors; low friction for guides
2 sealing compound
3 high friction cradle liner
4 sectional detail
Figure 10 — Anchoring of couplings to concrete supports
A typical clamp design for anchoring couplings to concrete supports is shown in Figure 10.
NOTE When couplings are embedded it is necessary to ensure that the gap between coupling and pipe is
kept free from concrete, e.g. by applying sealing compound “B”, see Figure 10.
The weight of pipe and fluid is sufficient to stabilize the pipe ends if the buckling length, L (see
b
Figures 12, 13, 15 and 16), exceeds the amounts calculated by the following Formulae (6) and (7).
For a pipe on two supports:
fp⋅⋅AL⋅ OD
()
somaxx ff,c,max
L = (6)
b,min,2S
cos,φ⋅+ww ⋅05
()
pf
For pipe on three or more supports:
fp⋅⋅AL⋅ OD
()
somaxx ff,c,max
L = (7)
b,min,3S
cos,φ⋅+ww ⋅0 375
()
pf
where
L is the minimum buckling length;
b,min
f is the factor of safety;
s
p is the maximum pressure occurring in the pipe (including field hydrotest, surge pressure etc.);
max
A is the cross-sectional area of the pipe, π × OD /4;
x
L is the pipe-to-coupling vertical convex offset (A in Figure 9);
off,c,max
OD is the outer diameter of the pipe;
ϕ is the slope angle of the pipe;
w is the dead weight of the pipe;
p
w is the dead weight of fluid in the pipe.
f
5.5 Maximum support spacing
5.5.1 General
This subclause provides guidance on computation of pipe stresses and deflections as well as
requirements for pipe buckling stability for pressure pipes installed above ground on supports at
intervals to determine maximum support spacing.
A pressurized water column by itself is unstable. The stability of the pressurized water column is
provided by the axial stiffness of the pipe.
The water column within a pressure pipe carries an axial pressure thrust. In a flexible, non-restraint
joint piping system, this axial pressure thrust is restrained by external anchoring but not by the pipe
itself. The axial thrust does, however, typically affect the stresses and deflections of an above ground
pipe to a significant extent. The thrust affects the bending moments and deflections of the pipe. Pipe
bending moments and deflections shall therefore be computed using beam-column formulation.
Ultimately, an above ground pipe with flexible, non-restrained joints can buckle as a column if not
properly supported.
To determine the maximum support spacing for a pipe the following forces, stresses and deformations
shall be computed and checked against allowable limits:
— maximum total axial compressive force acting in the pipe and the water column to be checked
against global buckling of pipe as a column;
— maximum axial tensile stress acting in the pipe wall to be checked against allowable stress;
— maximum pipe deflection (sagging) to be checked against allowable deflection;
— maximum pipe end rotation to be checked against joint capacity for angular deflection accounting
for installation tolerances.
Both long- and short-term loading conditions need to be analysed.
As the critical force for a long-term load is lower than the critical force for short-term, both long- and
short-term loading conditions need to be analysed.
The dead weight of fluids and some environmental loads result in loading perpendicular to the pipe
whilst loads from the dead weight of the pipe and external loads such as snow act vertically (see 5.2.2).
A combination of vertical and perpendicular loads give the largest sum for a horizontal pipe therefore
the horizontal case should be assumed for general evaluation of a project.
14 © ISO 2021 – All rights reserved

In order to limit the complexity of calculations, loads are classified as being either short-term or long-
term. Long-term loads cause creep and the apparent axial long-term modulus shall be used to calculate
long-term deflections. It is assumed that short-term loads do not cause creep and a short-term modulus
with an aging factor (and where appropriate an environmental factor) is used to estimate deflections.
The apparent axial long-term modulus shall be determined according to the procedures in ISO 4152.
Loads can be classified as longitudinal or perpendicular to the pipe direction. Angular deviation at the
coupling produces a perdendicular component from the longitudinal force acting on the end of the pipe.
5.5.2 Perpendicular forces
The typical perpendicular loads acting on the pipe are the dead weights of the pipe and the fluid in the
pipe, environmental loads (e.g. snow, wind), and live loads (e.g. people, traffic, construction), as well as
seismic loads.
5.5.3 Forces due to angular deviation
Angular deviation, α, between the pipe and coupling creates a lateral force, V , on the end of the pipe.
p
When evaluating this force, maximum angular deviation should be assumed in the most unfavourable
direction, considering rotation of the pipe end due to deflection. This lateral force can be calculated
using Formula (8).
VF=⋅tanα (8)
p A
where
F is the total axial force;
A
α is the angular deviation.
5.5.4 Axial forces
5.5.4.1 General
The typical axial loads are those created by the fluid static pressure, the dynamic pressure (resulting
from head loss or surge) and friction forces induced in the pipe at the coupling or pipe support by axial
movement of the pipe resulting from temperature or pressure changes.
5.5.4.2 Axial forces due to pressure
Internal pressure results in force acting in both the fluid and the pipe. The working pressure, p , can
w
be considered as creating a long-term load whereas the surge pressure, p , and the field hydro-test
s
pressure will create a short-term loading condition.
The long-term axial pressure force, F acting in the fluid, is described in Formula (9):
pwfl,
Fp= ∙A (9)
pwfl w b
The long-term axial pressure force, F , acting in the pipe, is described in Formula (10):
pwp
Fp= ∙A (10)
pwppw
The short-term axial pressure force, F acting in the fluid, is described in Formula (11):
psfl,
Fp= ∙A (11)
psfl sb
The short-term axial pressure force, F , acting in the pipe, is described in Formula (12):
psp
Fp= ∙A (12)
psps p
where
p is the long-term working pressure;
w
p is the short-term pressure, e.g. surge pressure or field hydro-test pressure;
s
A is the cross-sectional area of pipe wall;
p
A is the cross-sectional area of pipe bore
b
Unless defined otherwise by client's engineer, the surge pressure and the field hydro-test pressure used
in general evaluation of a pipe installation is limited to 1,4 PN and 1,5 PN respectively.
Where surge- and/or field hydro-test pressure exceeds these values, the use of a sufficiently higher
rated PN product should be considered.
5.5.4.3 Axial forces due to friction
Friction forces between the pipe and coupling, F and between the pipe and the support, F are the
c, s,
result of axial movement in the pipe caused by temperature and/or pressure changes. These can cause
either tensile or compressive axial forces to act on the pipe. These forces are considered to be short
term loads.
Friction forces between the pipe spigot and the sealing ring, which is constrained within the coupling,
are a function of gasket width, gasket compression, pipe diameter and fluid pressure. Friction forces
will vary according to the coupling/gasket design and will vary from one product to another. Empirical
values related to pressure activated seals are given in Table 3.
The friction between the support and the pipe is a function of the reaction force, the saddle geometry
and the coefficient of friction for the saddle lining material. The force due to this friction, F is estimated
s,
using Formula (13):
μβ∙∙R π∙
F = (13)
s
β
 
2∙∙360 sin
 
 
where
μ is the coefficient of friction between pipe and saddle lining material;
R is the reaction force at support, see calculation in 5.5.6 and 5.5.7;
β is the cradle support angle.
16 © ISO 2021 – All rights reserved

5.5.4.4 Axial forces due to head loss
Head loss which occurs due to the flow of liquid within the pipe creates an axial force on the pipe, due
to friction between the liquid and the pipe. This can be calculated as the head loss over the pipe times
the cross-sectional area of the pipe wall and the pipe bore. This force is small when compared to other
forces and can be neglected when calculating pipe stresses and deflections, but in extreme cases can
affect the design of pipe anchors.
The magnitude of the axial head loss force, F can be calculated using Formula (14):
hl,
Fh=⋅Δγ ⋅⋅gA +A (14)
()
hl fl pb
where
Δh is the head loss in pipe (fluid column);
γ is the unit weight of fluid in pipe;
fl
g is gravity;
A is the cross-sectional area of pipe wall;
p
A is the cross-sectional area of pipe bore.
b
5.5.4.5 Axial force of vertical loads
When pipes are installed on slopes, ϕ, the vertical loads resulting from items such as pipe weight and
environmental loads will have axial components. These components will not cause increased stresses
in the pipe, but it is necessary to consider them when designing the pipe anchors. This force, F , can be
q
calculated using Formula (15):
Fq= ∙∙L sinφ (15)
qvert p
where
q is the sum of vertical loads on pipe;
vert
L is the pipe length;
p
ϕ is the slope angle of the pipe.
5.5.5 Maximum total axial force
The maximum long- and short-term compressive forces, F and F , shall be calculated as the most
Alt Ast
unfavorable combination of axial forces due to pressure thrust and axial forces due to friction. The
compressive forces consist of at least the following components, see Formulae (16) and (17):
FF=+ FF++F (16)
Altpwflpwp hl q
FF=+ FF++F (17)
Astpsflpsp hl q
where
F is the long-term axial pressure force, acting in the fluid, see Formula (9);
pwfl
F is the long-term axial pressure force, acting in the pipe, see Formula (10);
pwp
F is the axial head loss force, see Formula (13);
hl
F is the axial component of vertical load, see Formula (14);
q
F is the short-term axial pressure force, acting in the fluid, see Formula (11);
psfl
F is the short-term axial pressure force, acting in the pipe, see Formula (12).
psp
5.5.6 Deformations and bending moments for pipes resting on two supports
This subclause is valid for pipes resting on two supports as shown in Figure 11.
Key
1 guide
2 anchor
L pipe length
p
a maximum distance from the centreline of the joint to centreline of a support, calculation see Table 2
Figure 11 — Pipes supported on two cradles
The calculation of maximum flexural deflection, y , pipe end rotation, θ, and maximum bending
max
moment, M , is provided:
max
a) for pipes supported at the ends, see Figure 12; or
b) close to the ends, see Figure 13.
NOTE An example for case a) is shown in Figure 6 (1) and for case b) in Figure 6 (2).
18 © ISO 2021 – All rights reserved

Pipes supported on two supports at pipe ends
Key
F axial force A, B support
q load L span length
s
L buckling length
b
Figure 12 — Pipes supported at ends (static model)
The pipe maximum flexural deflection, y , at the centre of the pipe span is calculated using
max
Formula (18):
5qL
s
y =⋅a (18)
max 1
384EI
A
The rotation of the pipe end, θ, is calculated using Formula (19):
qL
s
θ =⋅a (19)
24EI
A
The maximum bending moment, M , at the centre of the pipe span is calculated using Formula (20):
max
qL
s
M =⋅a (20)
max 1
with the magnification factor, a , calculated using Formula (21):
a = (21)
F
1−
F
crit
where
E is the apparent axial modulus of elasticity, short-term E or long-term E , as applicable;
A Ast Alt
I
is the moment of inertia for the pipe cross section: ID=−π OID /64 with DO as pipe outer
()
diameter and ID as pipe inner diameter;
F is the critical beam column buckling force, see Formula (49) and (50).
crit
The reaction forces, R, at support A and B are calculated using Formula (22):
qL
b
RR== (22)
AB
Pipes supported on two supports close to pipe ends
Key
F axial force L overhang length
o
q L span length (length between the centre of the
s
load
supports)
L buckling length A, B support
b
Figure 13 — Pipes supported close to ends (static model)
The exact beam column solution of a pipe with overhanging ends is complicated. The bending
deflections, rotations and bending moments can, however, be calculated with sufficient accuracy using
the following formulae, provided that the overhang length, L , is 10 % or less of the buckling length, L /
o o
L ≤ 0,10.
b
The pipe maximum flexural deflection, y , at the centre of the pipe span is calculated using
max
Formula (23):
...