ISO 14692-3:2002

INTERNATIONAL ISO
STANDARD 14692-3
First edition
2002-12-15
Petroleum and natural gas industries —
Glass-reinforced plastics (GRP) piping —
Part 3:
System design
Industries du pétrole et du gaz naturel — Canalisations en plastique
renforcé de verre (PRV) —
Partie 3: Conception des systèmes

Reference number
©
ISO 2002
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©  ISO 2002
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ii © ISO 2002 — All rights reserved

Contents Page
Introduction . vi
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 Symbols and abbreviated terms. 1
5 Layout requirements. 2
5.1 General. 2
5.2 Space requirements. 2
5.3 System supports . 3
5.4 Isolation and access for cleaning . 5
5.5 Vulnerability. 5
5.6 Joint selection . 6
5.7 Fire and blast. 7
5.8 Control of electrostatic discharge. 8
5.9 Galvanic corrosion. 9
6 Hydraulic design . 9
6.1 General. 9
6.2 Flow characteristics. 9
6.3 General velocity limitations . 9
6.4 Erosion. 10
6.5 Water hammer . 10
6.6 Cyclic conditions . 11
7 Structural design. 11
7.1 General. 11
7.2 Manufacturer's pressure rating . 11
7.3 Qualified pressure. 11
7.4 Factored qualified pressure. 12
7.5 System design pressure. 13
7.6 Loading requirements . 14
7.7 Allowable displacements . 16
7.8 Qualified stress . 16
7.9 Factored stress . 16
7.10 Limits of calculated stresses due to loading . 17
7.11 Determination of failure envelope. 18
8 Stress analysis . 25
8.1 Analysis methods . 25
8.2 Analysis requirements. 25
8.3 External pressure/vacuum . 26
8.4 Thermal loading . 27
8.5 Stresses due to internal pressure . 27
8.6 Stresses due to pipe support . 28
8.7 Axial compressive load (buckling). 29
9 Fire performance. 30
9.1 General. 30
9.2 Fire endurance . 31
9.3 Fire reaction. 32
9.4 Fire-protective coatings . 32
10 Static electricity.33
10.1 General .33
10.2 Classification code for control of electrostatic charge accumulation.33
10.3 Mitigation options.33
10.4 Design and documentation requirements .34
10.5 Pipes that contain a fluid with an electrical conductivity more than 10 000 pS/m.36
10.6 Pipes that contain a fluid with an electrical conductivity less than 10 000 pS/m.36
10.7 Pipes exposed to weak/moderate external electrostatic-generation mechanisms.37
10.8 Pipes exposed to strong external electrostatic generation mechanisms.37
10.9 Continuity of electrical path within piping system .38
10.10 Lightning strike.38
11 Installer and operator documentation.38
Annex A (informative) Guidance for design of GRP piping system layout.40
Annex B (informative) Description and guidance on selection of jointing designs .42
Annex C (informative) Guidance on material properties and stress/strain analysis .47
Annex D (normative) Guidance on flexibility analysis.49
Annex E (normative) Calculation of support stresses for large-diameter liquid-filled pipe .59
Annex F (informative) Guidance on quantifying fire performance properties.63
Annex G (informative) Static electricity.68
Annex H (informative) Inspection strategy.76
Bibliography.79

iv © ISO 2002 — All rights reserved

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 14692-3 was prepared by Technical Committee ISO/TC 67, Materials, equipment and offshore structures
for petroleum, petrochemical and natural gas industries, Subcommittee SC 6, Processing equipment and
systems.
ISO 14692 consists of the following parts, under the general title Petroleum and natural gas industries —
Glass-reinforced plastics (GRP) piping:
 Part 1: Vocabulary, symbols, applications and materials
 Part 2: Qualification and manufacture
 Part 3: System design
 Part 4: Fabrication, installation and operation
Introduction
The objective of this part of ISO 14692 is to ensure that piping systems, when designed using the components
qualified in ISO 14692-2, will meet the specified performance requirements. These piping systems are
designed for use in oil and natural gas industry processing and utility service applications. The main users of
the document will be the principal, design contractors, suppliers contracted to do the design, certifying
authorities and government agencies.
An explanation of the pressure terminology used in this part of ISO 14692 is given in ISO 14692-1.

vi © ISO 2002 — All rights reserved

INTERNATIONAL STANDARD ISO 14692-3:2002(E)

Petroleum and natural gas industries — Glass-reinforced
plastics (GRP) piping —
Part 3:
System design
1 Scope
This part of ISO 14692 gives guidelines for the design of GRP piping systems. The requirements and
recommendations apply to layout dimensions, hydraulic design, structural design, detailing, fire endurance,
spread of fire and emissions and control of electrostatic discharge.
This part of ISO 14692 is intended to be read in conjunction with ISO 14692-1.
2 Normative references
The following referenced documents are indispensable for the application 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 14692-1:2002, Petroleum and natural gas industries — Glass-reinforced plastics (GRP) piping — Part 1:
Vocabulary, symbols, applications and materials
ISO 14692-2:2002, Petroleum and natural gas industries — Glass-reinforced plastics (GRP) piping — Part 2:
Qualification and manufacture
ISO 14692-4:2002, Petroleum and natural gas industries — Glass-reinforced plastics (GRP) piping — Part 4:
Fabrication, installation and operation
BS 7159:1989 Code of practice for design and construction of glass-reinforced plastics (GRP) piping systems
for individual plants or sites
ASTM E1118, Standard practice for acoustic emission examination of reinforced thermosetting resin pipe
(RTRP)
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 14692-1 apply.
4 Symbols and abbreviated terms
For the purposes of this part of ISO 14692, the symbols and abbreviated terms given in ISO 14692-1 apply.
5 Layout requirements
5.1 General
GRP products are proprietary, and the choice of component sizes, fittings and material types may be limited
depending on the supplier. Potential vendors should be identified early in design to determine possible
limitations of component availability. The level of engineering support that can be provided by the supplier
should also be a key consideration during vendor selection.
Where possible, piping systems should maximize the use of prefabricated spoolpieces to minimize the amount
of site work. Overall spool dimensions should be sized taking the following into consideration:
 limitations of site transport and handling equipment;
 installation and erection limitations;
 limitations caused by the necessity to allow a fitting tolerance for installation (“cut to fit” requirements).
The designer shall evaluate system layout requirements in relation to the properties of proprietary pipe
systems available from manufacturers, including but not limited to:
a) axial thermal expansion requirements;
b) ultraviolet radiation and weathering resistance requirements;
c) component dimensions;
d) jointing system requirements;
e) support requirements;
f) provision for isolation for maintenance purposes;
g) connections between modules and decks;
h) flexing during lifting of modules;
i) ease of possible future repair and tie-ins;
j) vulnerability to risk of damage during installation and service;
k) fire performance;
l) control of electrostatic charge.
The hydrotest provides the most reliable means of assessing component quality and system integrity.
Whenever possible, the system should be designed to enable pressure testing to be performed on limited
parts of the system as soon as installation of those parts is complete. This is to avoid a final pressure test late
in the construction work of a large GRP pipe system, when problems discovered at a late stage would have a
negative effect on the overall project schedule.
Further guidance about GRP piping system layout is given in Annex A.
5.2 Space requirements
The designer shall take account of the larger space envelope of some GRP components compared to steel.
Guidance on fitting sizes is given in Clause 7 of ISO 14692-2:2002. GRP fittings generally have longer lay
lengths and are proportionally more bulky than the equivalent metal component and may be difficult to
2 © ISO 2002 — All rights reserved

accommodate within confined spaces. If appropriate, the problem can be reduced by fabricating the pipework
as an integral spoolpiece in the factory rather than assembling it from the individual pipe fittings.
If space is limited, consideration should be given to designing the system to optimize the attributes of both
GRP and metal components.
5.3 System supports
5.3.1 General
GRP piping systems can be supported using the same principles as those for metallic piping systems.
However, due to the proprietary nature of piping systems, standard-size supports will not necessarily match
the pipe outside diameters. The use of saddles and elastomeric pads may allow the use of standard-size
supports.
The following requirements and recommendations apply to the use of system supports.
a) Supports shall be spaced to avoid sag (excessive displacement over time) and/or excessive vibration for
the design life of the piping system.
b) In all cases, support design should be in accordance with the manufacturer’s guidelines.
c) Where there are long runs, it is possible to use the low modulus of the material to accommodate axial
expansion and eliminate the need for expansion joints, provided the system is well anchored and guided.
d) Valves or other heavy attached equipment shall be independently supported.
NOTE Valves are often equipped with heavy control mechanisms located far from the pipe centreline and can cause
large bending and torsional loads.
e) GRP pipe shall not be used to support other piping, unless agreed with the principal.
f) GRP piping should be adequately supported to ensure that the attachment of hoses at locations such as
utility or loading stations does not result in the pipe being pulled in a manner that could overstress the
material.
g) Consideration shall be given to the possible design requirements of the support to provide electrical
earthing in accordance with the requirements of 5.8 and clause 10.
Pipe supports can be categorized into those that permit movement and those that anchor the pipe.
5.3.2 Pipe-support contact surface
5.3.2.1 Guidelines
The following guidelines to GRP piping support should be followed.
a) Supports in all cases should have sufficient width to support the piping without causing damage and
should be lined with an elastomer or other suitable soft material. The minimum saddle width, in
millimetres, should be 30D , where D is the mean diameter of the pipe, in millimetres.
b) Clamping forces, where applied, should be such that crushing of the pipe does not occur. Local crushing
can result from a poor fit and all-round crushing can result from over-tightening.
c) Supports should be preferably located on plain-pipe sections rather than at fittings or joints.
d) Consideration shall be given to the support conditions of fire-protected GRP piping. Supports placed on
the outside of fire protection could result in loads irregularly transmitted through the coating, which could
result in shear/crushing damage and consequent loss of support integrity.
5.3.2.2 Supports permitting pipe movement
Pipe resting in fixed supports that permit pipe movement shall have abrasion protection in the form of saddles,
elastomeric materials or sheet metal.
5.3.2.3 Supports anchoring pipe
The anchor support shall be capable of transferring the required axial loads to the pipe without causing
overstress of the GRP pipe material. Anchor clamps are recommended to be placed between two double 180°
saddles, adhesive-bonded to the outer surface of the pipe. The manufacturer’s standard saddles are
recommended and shall be bonded using standard procedures.
5.3.3 Support and guide spacing
The spanning capability of GRP piping spans is generally less than that for steel pipe, due to the lower
modulus of the material. Supports shall be spaced to avoid sag (excessive displacement over time) and/or
excessive vibration for the design life of the piping system.
GRP pipes, when filled with water, should be capable of spanning at least the distances specified in Table 1
while meeting the deflection criterion of 0,5 % of span or 12,5 mm centre, whichever is smaller. Spans are
assumed to be simply supported. In some cases, bending stresses or support contact stresses may become a
limiting factor (see 8.6), and the support spacing may have to be reduced.
Table 1 — Guidance to span lengths (simply supported)
Pipe nominal diameter Span
mm m
25 2,0
40 2,4
50 2,6
80 2,9
100 3,1
150 3,5
200 3,7
250 4,0
300 4,2
350 4,8
400 4,8
450 4,8
500 5,5
600 W 6,0
Larger spans are possible, and the designer should verify that stresses are within allowable limits according
to 8.6. The designer shall take into consideration the effect of buckling (8.7). The effect of temperature on the
axial modulus of the GRP material shall also be considered.
4 © ISO 2002 — All rights reserved

5.4 Isolation and access for cleaning
The designer should make provision for isolation and easy access for maintenance purposes, for example for
removal of scale and blockages in drains. The joint to be used for isolation or access should be shown at the
design stage and should be located in a position where the flanges can in practice be jacked apart, e.g. it
should not be in a short run of pipe between two anchors.
5.5 Vulnerability
5.5.1 Point loads
Point loads should be minimized and the GRP piping locally reinforced where necessary.
5.5.2 Abuse
The designer should give consideration to the risk of abuse to GRP piping during installation and service and
the need for permanent impact shielding.
Sources of possible abuse include:
a) any area where the piping can be stepped on or used for personnel support;
b) impact from dropped objects;
c) any area where piping can be damaged by adjacent crane activity, e.g. booms, loads, cables, ropes or
chains;
d) weld splatter from nearby or overhead welding activities.
Small pipe branches (e.g. instrument and venting lines), which are susceptible to shear damage, should be
designed with reinforcing gussets to reduce vulnerability. Impact shielding, if required, should be designed to
protect the piping together with any fire-protective coating.
NOTE Further guidance on the design of gussets can be found in BS 4994 [1].
5.5.3 Dynamic excitation and interaction with adjacent equipment and piping
The designer should give consideration to the relative movement of fittings, which could cause the GRP piping
to become overstressed. Where required, consideration shall be given to the use of flexible fittings.
The designer should ensure that vibration due to the different dynamic response of GRP (as compared with
carbon steel piping systems) does not cause wear at supports or overstress in branch lines. The designer
should ensure that the GRP piping is adequately supported to resist shock loads that may be caused by
transient pressure pulses, e.g. operation of pressure safety valves, valve closure etc.
5.5.4 Effect of external environment
5.5.4.1 Exposure to light and ultraviolet radiation (UV)
Where GRP pipe is exposed to the sun, the designer should consider whether additional UV protection is
required to prevent surface degradation of the resin. If the GRP is a translucent material, the designer should
consider the need to paint the outside to prevent possible algae growth in slow-moving water within the pipe.
5.5.4.2 Low temperatures and requirements for insulation
The designer shall consider the effects of low temperatures on the properties of the pipe material, for example
the effect of freeze/thaw. For liquid service, the designer should pay particular attention to the freezing point of
the internal liquid. For completely filled lines, solidification of the internal fluid may cause an expansion of the
liquid volume, which could cause the GRP pipe to crack or fail. For water service, the volumetric expansion
during solidification or freezing is more than sufficient to cause the GRP pipe to fail.
The pipe may require to be insulated and//or fitted with electrical surface heating to prevent freezing in cold
weather or to maintain the flow of viscous fluids. The designer shall give consideration to:
a) additional loading due to mass and increased cross-sectional area of the insulation;
b) ensuring that electrical surface heating does not raise the pipe temperature above its rated temperature.
Heat tracing should be spirally wound onto GRP pipe in order to distribute the heat evenly round the pipe wall.
Heat distribution can be improved if aluminium foil is first wrapped around the pipe.
5.6 Joint selection
5.6.1 General
Various types of bonded and mechanical joints are available. These tend to be proprietary in nature but can
generally be categorized into the following types:
 adhesive-bonded joints;
 laminated joints;
 elastomeric bell-and-spigot sealed joints (with/without locks);
 flanged joints;
 threaded joints;
 metallic/GRP interfaces;
 other mechanical joints.
A description and further guidance about the use of these joint types is given in Annex B. The designer should
take into account the following factors when selecting the jointing method:
a) criticality;
b) reliability;
c) ease of joint assembly;
d) ease of repair, and future modifications and tie-ins.
5.6.2 Criticality and reliability
The designer should give consideration to the requirements for evaluating the performance of the joint during
service.
The selection of the joint shall take into account the environmental conditions likely to be present during
assembly, e.g. temperature and humidity.
The selection of the joint should take into account the presence of significant axial and in-plane axial bending
stresses, which are more likely to expose the weakness of poorly made up joints than pressure alone.
6 © ISO 2002 — All rights reserved

The selection of joint shall take into account possible movement of the pipe caused by flexing of the hull, in
the case of a floating offshore installation or flexing of the module during lifting operations.
5.6.3 Ease of joint assembly
The designer should give consideration to ensure the layout enables a site joint to be assembled to the correct
dimensions and without the need to pull the joint into position such that the material is subject to overstress.
The selection of site joint should take into account the ease of access required by fitters to assemble the
connection correctly. Site joints should be located in accessible locations away from supports and fittings.
The designer should give consideration to the preferred location of the last site joint in a piping loop to ensure
the necessary access is available since this joint is often the most difficult to complete.
5.6.4 Ease of repair and access for future modifications and tie-ins
If bell-and-spigot joints are used in locations where future modifications are likely, the designer should
consider the need for axial displacement of the pipe to enable the joints to be opened without the need to cut
the pipe.
5.6.5 Metallic/GRP interfaces
Interfaces with metallic tanks, vessels, equipment or piping shall be by flanged (i.e. mechanical) connection.
In order to achieve reliable flange sealing, even with relatively low bolt-tensioning, steel-ring-reinforced
elastomer gaskets should be used. Only soft type elastomers should be used, preferably with a hardness
within the range Shore A 55 to A 75. The gasket material shall match the pressure, temperature and chemical
resistance capabilities of the piping system. In general, PTFE envelope-type gaskets are not recommended
and should not be used for pipes of large diameters (> 600 mm) and at high pressures (> 3,2 MPa).
The making of connections by other means, e.g. overwrapping of metallic pipe ends with GRP, is not
acceptable unless qualified in accordance with 6.2.3.2 in ISO 14692-2:2002.
5.7 Fire and blast
5.7.1 General
The effect of a fire event (including blast) on the layout requirements should be considered. The possible
events to be considered in the layout design of a GRP piping system intended to function in a fire include:
a) blast;
b) fire protection of joints and supports;
c) interface with metal fixtures;
d) formation of steam traps;
e) jet fire;
f) heat release and spread of fire;
g) smoke emission, visibility and toxicity.
The methodology for assessing fire performance is given in Clause 9.
5.7.2 Blast
If components may be exposed to explosion hazards, the effect of blast overpressure, drag forces and
projectile impacts should be considered (see 7.6.1), including the possible effect on support spacing.
5.7.3 Steam traps
Consideration should be given to the possibility of steam traps forming in pipe containing stagnant water,
which would reduce the conduction of heat away by water.
5.7.4 Jet fires
Jet fires pose a significant threat to all types of piping systems because of the very high heat flux and erosive
conditions that they produce. Whilst GRP pipe systems can be designed to withstand jet fires for a required
period, the layout should be designed, if possible, to route piping away from areas which could be exposed to
direct impingement by a jet fire.
5.7.5 Heat release and spread of fire
Consideration should be given to the contribution to the fire inventory and the risk of surface spread of flame
to other areas, particularly if the pipes are empty and/or are no longer in service. The designer should
consider the effect of the orientation of the piping and the possibility of thermal feedback from nearby
reflective surfaces on the fire performance of the pipe.
5.7.6 Smoke emission, visibility and toxicity
Performance criteria for smoke and toxic emissions are primarily applied to the use of GRP piping in confined
spaces, escape routes or areas with limited ventilation and where personnel are at risk. Consideration should
be given to the risk of the spread of smoke and toxic emissions to other areas, particularly if the pipes are
empty and/or are no longer in service.
5.7.7 Penetrations
Penetrations (wall, bulkhead, deck) shall not weaken the division that they penetrate. The main requirements
are to prevent passage of smoke and flames, to maintain structural integrity and to limit the temperature rise
on the unexposed side. Penetrations shall therefore comply with the same requirements that apply to the
relevant hazardous divisions. This requires the penetration to have been fire-tested and approved for use with
the specific type of GRP pipework under consideration.
5.8 Control of electrostatic discharge
GRP piping and associated systems may be required to be electrically conductive/electrostatic dissipative and
earthed, depending on service and location.
The location of the pipe determines the magnitude of external electrostatic charge-generation mechanisms to
which the pipe may be exposed, and determines the consequences of an incendive discharge. For example,
the effect of changing atmospheric electrical fields is mitigated by the shielding provided by metal walkways
and decks located above the pipe.
In hazardous areas, the designer should be aware of the proximity of process pipe and other sources of high-
pressure gas effluxes that may provide a strong external electrostatic-generation mechanism. The designer
should also be aware of other potential sources of electrostatic-generation mechanisms, such as tribocharging
and the presence of charged mists and soots produced in tank cleaning operations. In such locations and
where practicable, the designer shall minimize the presence of unearthed metal objects attached to the pipe
and take into account the proximity of nearby earthed metal objects when considering the risk analysis,
see 10.1.
8 © ISO 2002 — All rights reserved

Further guidance for assessing the requirements for control of electrostatic discharge is given in Clause 10
and Annex G.
5.9 Galvanic corrosion
Galvanic corrosion is unlikely to be a concern at the interface of metal and GRP piping components if the GRP
component incorporates small quantities of carbon fibre to provide electrical conductivity. This is because the
exposed area of the carbon fibre (the cathode) is likely to be small compared to the adjacent metal
component. The converse of a high cathode to anode ratio is usually needed to give rise to rapid corrosion.
However, if GRP components incorporate significant quantities of carbon or other cathodic material, e.g. for
additional strengthening purposes, then precautions may be required to electrically isolate the carbon fibre at
the interface with the metal component. Under such circumstances, the use of an impressed current from a
cathodic protection system is not recommended.
6 Hydraulic design
6.1 General
The aim of hydraulic design is to ensure that GRP piping systems are capable of transporting the specified
fluid at the specified rate, pressure and temperature throughout their intended service life. The selection of
nominal pipe diameter depends on the internal diameter required to attain the necessary fluid flow consistent
with the fluid and hydraulic characteristics of the system.
6.2 Flow characteristics
Fluid velocity, density of fluid, interior surface roughness of pipes and fittings, length of pipes, inside diameter
of pipes, as well as resistance from valves and fittings shall be taken into account when estimating pressure
[2]
losses. Guidance for the calculation of pressure losses is given in ISO 13703 . The smooth surface of the
GRP may result in lower pressure losses compared to metal pipe. Conversely the presence of excessive
protruding adhesive beads will increase pressure losses.
6.3 General velocity limitations
Concerns that limit velocities in piping systems include:
a) unacceptable pressure losses;
b) prevention of cavitation at pumps and valves;
c) prevention of transient overloads (water hammer);
d) reduction of erosion;
e) reduction of noise;
f) reduction of wear in components such as valves;
g) pipe diameter and geometry (inertia loading).
The designer shall take into account these concerns when selecting the flow velocity for the GRP piping
system. For typical GRP installations, the mean linear velocity for continuous service of liquids is between
1 m/s and 5 m/s with intermittent excursions up to 10 m/s. For gas, the mean linear velocity for continuous
service is between 1 m/s and 10 m/s with intermittent excursions up to 20 m/s. Higher velocities are
acceptable if factors that limit velocities are eliminated or controlled, e.g. vent systems that discharge into the
atmosphere.
6.4 Erosion
6.4.1 General
The following factors influence the susceptibility of GRP piping to erosion damage:
a) fluid velocity;
b) piping configuration;
c) particle size, density and shape;
d) particulate/fluid ratio;
e) onset of cavitation.
The designer shall refer to the manufacturer and consider reducing the velocity if doubts exist on erosion
performance.
6.4.2 Particulate content
The erosion properties of GRP are sensitive to the particulate content. The designer shall take into account
the likely particulate content in the fluid and reduce the maximum mean velocity accordingly. For GRP, the
maximum erosion damage typically occurs at a hard-particle impingement angle of between 45° and 90°, i.e.
at bends and tees. At low impingement angles (< 15°), i.e. at relatively straight sections, erosion damage is
[3]
minimal. Further information on erosion can be found in DNV RP 0501 .
6.4.3 Piping configuration
The presence of turbulence generators can have a significant influence on the erosion rate of GRP piping,
depending on fluid velocity and particulate content. The designer shall consider the degree of turbulence and
risk of possible erosion when deciding the piping configuration. To minimize potential erosion damage in GRP
pipe systems, the following should be avoided:
a) sudden changes in flow direction;
b) local flow restrictions or initiators of flow turbulence, e.g. excessive adhesive (adhesive beads) on the
inside of bonded connections. Limits for the maximum size of adhesive beads are given in Table 4 of
ISO 14692-4:2002.
6.4.4 Cavitation
GRP piping is susceptible to rapid damage by cavitation. Cavitation conditions are created in piping systems
more easily than is generally realized, and the general tendency for systems to be designed for high velocities
exacerbates the situation further. Potential locations of cavitation include angles at segmented elbows, tees
and reducers, flanges where the gasket has been installed eccentrically and joints where excessive adhesive
has been applied.
The designer shall use standard methods to predict the onset of cavitation at likely sites, such as control
valves, and apply the necessary techniques to ensure that cavitation cannot occur under normal operating
conditions.
6.5 Water hammer
The susceptibility of GRP piping to pressure transients and out-of-balance forces caused by water hammer
depends on the magnitude of pressure and frequency of occurrence. A full hydraulic surge analysis shall be
carried out, if pressure transients are expected to occur, to establish whether the GRP piping is susceptible to
water hammer. The analysis shall cover all anticipated operating conditions including priming, actuated
10 © ISO 2002 — All rights reserved

valves, pump testing, wash-down hoses, etc. Water hammer shall be defined as an occasional load, see
7.6.2.3.
If there is a significant risk of water hammer, the designer shall employ standard techniques to ensure that
pressure transients do not exceed the hydrotest pressure.
NOTE A typical cause of water hammer is the fast closing of valves. The longer the pipeline and the higher the liquid
velocity, the greater the shock load will be. Shock loading generally induces oscillation in the pipe. Since GRP pipe has a
lower axial modulus of elasticity than the equivalent steel pipe, longitudinal oscillations are generally more significant.
6.6 Cyclic conditions
The maximum pressure shall not exceed the design pressure. If the predicted number of pressure or other
loading cycles exceeds 7 000 over the design life, then 7.4.4 shall apply.
7 Structural design
7.1 General
The aim of structural design for GRP piping systems is to ensure that they shall perform satisfactorily and
sustain all stresses and deformations during construction/installation and throughout their service life. This
clause identifies the service design criteria and the loads to which GRP may be subjected. The requirements
for the stress analysis are given in Clause 8.
7.2 Manufacturer's pressure rating
The manufacturer's pressure rating provided in product literature is not the same as the qualified pressure, p ,
q
defined in 7.3 or the system design pressure. The manufacturer's pressure rating is defined as:
p = f ⋅ f ⋅ p (1)
NPR 3,man q
where f is defined as a load factor (see 7.6.2) and f is a factor based on f , chosen by the manufacturer
2 3,man 3
to account for the limited axial load capability of GRP, see 7.10.
f is not a fixed parameter and is strongly dependent on application and p of the component. The value of f
q 3
for a component in a complex piping system, where significant non-pressure stresses can be produced, may
be about 0,5. Conversely f may have a value of 0,9 or more if the component is well supported and part of a
long pipe run.
Use of the manufacturer's rating shall only be used for guidance purposes. Manufacturers should always
provide the value of f used to develop a purchase quotation.
NOTE For GRP pipes with a regression gradient less than 0,03 it may be required to de-rate, p , in Equation (5). The
qf
derating factor is described in 7.6.2.1.
7.3 Qualified pressure
1)
The qualified pressure, p , in megapascals for pipe and fittings shall be determined using the procedure
q
described in 6.2.2 of ISO 14692-2:2002. The qualified pressure is based on a design life of 20 years. The
qualified pressure for service lives other than 20 years shall be determined in accordance with 6.2.7 of
ISO 14692-2:2002. The relationship between the qualified pressure and the design pressure for a component
is defined in 7.5.
1) 1 bar = 0,1 (MPa).
7.4 Factored qualified pressure
7.4.1 General
The factored qualified pressure is defined as the pressure to be used in determining the safe operating
envelope of the GRP pipe or piping system. It takes account of specific service conditions that could not be
considered in the qualification programme.
The factored qualified pressure, p , in megapascals, for pipe and fittings shall be calculated using
qf
Equation (2):
...