Chapter 8

Above-Ground Applications for PE Pipe

305
Chapter 8
Above-Ground Applications for PE Pipe
Introduction
In above ground applications PE piping may be suspended or cradled
in support structures or, it may simply be placed directly on the ground
surface. These types of installations may be warranted by any one of
several factors. One is the economic considerations of a temporary
piping system. Another is the ease of inspection and maintenance.
Still another is simply that prevailing local conditions and even the
nature of the application itself may require that the pipe be installed
above ground.
PE pipe provides unique joint integrity, toughness, flexibility, and low
weight. These factors combine to make its use practical for many
above-ground applications. This resilient material has been used
for temporary water lines, various types of bypass lines, dredge lines,
mine tailings, and fines-disposal piping. PE pipe is used for slurry
transport in many industries such as those that work with kaolins
and phosphates. The ease of installation and exceptional toughness
of PE pipe often make it practical for oil and gas collection. The
economics and continued successful performance of this unique
piping material is evident despite the extreme climatic conditions that
may sometimes exist in some of these diverse applications.
This chapter presents design criteria and prevailing engineering
methods that are used for above-ground installation of PE pipe. The
effects of temperature extremes, chemical exposure, ultraviolet
radiation, and mechanical impact are discussed in detail. Engineering
design methodology for both on-grade and suspended
or cradled PE pipe installations are presented and illustrated
with typical sample calculations. All equations in the design
methodology were obtained from published design references. These
references are listed so the designer can verify the applicability of
the methodology to his particular project. Additional installation
considerations are also discussed.
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Design Criteria
Conditions and effects which can infuence the behavior and thus, the design of
above ground PE piping systems include:
Temperature
Chemical exposure
Ultraviolet radiation
Potential mechanical impact or loading
- Internal Pressure
Figure 1 Above-Ground Installation of PE Pipe in a Wyoming Mining Operation
Temperature
The diversity of applications for which PE pipes are used in above-ground
applications refects the usable temperature range for this material. Above-grade
installations are usually exposed to demanding fuctuations in temperature extremes
as contrasted to a buried installation where system temperatures can be relatively
stable. Irradiation by sunlight, seasonal changes, and day-to-night transitions can
impose a signifcant effect on any piping material installed above the ground.
As a general rule, PE pipe for pressure applications can be safely used at
temperatures as low as -40F (-40C) and as high as 140F (60C). For non-pressure
service, the allowable temperature range widens up to 180F (82C). There are a few
PE piping materials that have qualifed for a pressure rating at 180F. The interested
reader is advised to consult with the PPI for more information on these materials.
However, PE is a thermoplastic material and, as such, these extremes impact the
engineering properties of the piping. Additional information in this regard is
available within the engineering properties chapter of this handbook.
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307
Pressure Capability
Because above ground installations of PE piping can be subject to exposures to
wider temperature and pressure fuctuations and, sometimes also to effects of
different environments, careful attention should be paid in the selection of PE
piping which has an appropriate pressure rating for the anticipated temperature
and environmental exposure. A detailed discussion of these issues is included in
Chapters 6.
Low Temperature Extremes
Generally speaking, the limitation for extremely low environmental service
temperature is the potential for embrittlement of the material. Note, however, that
most PE piping materials tested at extremely low temperatures have shown no
indication of embrittlement.
The effect of low temperature on PE pipe is unique. As discussed in Chapter 3 and
as shown in tables in the Appendix of Chapter 3, the apparent modulus of elasticity
increases as temperatures are lowered. In effect, the pipe becomes stiffer but retains
its ductile qualities. The actual low temperature embrittlement of most PE is below
-180F (-118C). In actual practice, PE pipe has been used in temperatures as low
as -75F (-60 C).
(4.5)
Obviously, service conditions at these extremes may warrant
insulation to prevent heat loss and freezing of the material being conveyed.
It should be noted that in extreme service applications operating at high pressure
and increasingly lower temperature that the ability of some PE piping materials to
absorb and dissipate energy such as that associated with sudden impact may be
compromised. In these situations, it is possible that, with the addition of a sustaining
or driving force, a through-wall crack can form which is capable of traveling for
signifcant distances along the longitudinal axis of the pipe. This phenomenon
is generally referred to as rapid crack propagation or RCP, and can occur in any
pressure piping or pressure vessel design regardless of the material of manufacture.
This type of phenomenon is generally not experienced in PE in liquid transport
applications as the energy dissipation associated with the sudden release of fuid
from the pipe mediates the driving force required to sustain the crack. Gas or
compressed air handling applications do not provide for the dissipation of energy
and, as such, a driving or sustaining force is a potential possibility. For these reasons,
the operation of PE pipe above ground in extremely cold environments (<32F)
should be carefully researched in light of the potential application and prevailing
service conditions. The reader is referred to the pipe manufacturer for additional
information regarding RCP and specifc design measurers for above ground, cold
weather installations.
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Expansion and Contraction
The coeffcient of linear expansion for unrestrained PE pipe is approximately ten
times that of metal or concrete. The end result is that large changes in the length
of unrestrained PE piping may occur due to temperature fuctuations. While the
potential for expansion (or contraction) is large when compared with that of metal,
concrete, or vitrifed clay pipe, note that the apparent modulus of elasticity for PE is
substantially lower than that of these alternative piping materials. This implies that
the degree of potential movement associated with a specifc temperature change
may be higher for the PE, but the stress associated with restraint of this movement
is signifcantly less. The end result is that the means of restraint required to control
this movement potential is often less elaborate or expensive. The stresses imposed by
contraction or expansion of a PE piping system are usually on an order of 5% to 10%
of those encountered with rigid piping materials.
Chemical Exposure
Standard pressure ratings for PE pipe are for water at 73F (23C). Also, as is well
established, in common installations either below or above ground, PE pipe will
not rust, rot, corrode or be subject to galvanic corrosion. However, if the pipe is
intended for the conveyance of a fuid other than water or, if it is intended to be
installed in a chemically aggressive environment, consideration should be given to
the appropriateness of the assigned standard pressure rating. Continuous exposure
to certain substances can result in a reduction in the long-term strength of the PE
material due to chemical attack or adsorption.
In some cases, such as with strong oxidizing or other agents that chemically attack
PE, a gradual and irreversible reduction in strength may seriously compromise
performance properties. In these cases the useful service life depends on the chemical
aggressiveness of the agent, its concentration, total time of exposure and temperature.
There are many cases where even though there is gradual chemical attack, PE pipe
still offers suffciently long life and is the most economical alternative.
In cases where PE piping is exposed to liquid hydrocarbons, a small adsorption of
these materials into the pipe wall can occur which may result in a decrease in long-
term strength. The effect is limited by the maximum amount of hydrocarbon that can
be adsorbed which depends on the nature of the hydrocarbon and the temperature
of the service. This effect on long-term strength is generally limited because
hydrocarbon adsorption does not attack PEs chemical structure. Further, it should
be noted that adsorption may slowly reverse when exposure to the hydrocarbon
is decreased or removed. For lighter weight hydrocarbons such as condensates of
gaseous hydrocarbons, adsorption reversal may occur within weeks or months
after removal from exposure. However, the reverse adsorption of heavier liquid
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309
hydrocarbons may be so slow that the effect may be considered permanent. Exposure
to most gaseous hydrocarbons is not known to reduce the long term strength of PE.
Finally, heat fusion joining between pipes after adsorption of liquid hydrocarbons can
be affected. The presence of adsorbed liquid hydrocarbons in the pipe wall can result
in low-strength heat fusion joining because the adsorbed hydrocarbons will liquefy
and then vaporize when heated and reduce or prevent melt fusion. Hydrocarbon
contamination is usually identifed by a bubbly or pockmarked melt appearance
upon heater plate removal. Because the strength and reliability of hydrocarbon
contaminated joints is suspect, mechanical joining methods are used in these
situations. The strength and reliability of heat fusion joints made before hydrocarbon
adsorption is not affected
Ultraviolet Exposure
When PE pipe is utilized outdoors in above-ground applications, it will be subjected
to extended periods of direct sunlight. The ultraviolet component in sunlight can
produce a deleterious effect on the PE unless the material is suffciently protected.
Weathering studies have shown that pipe produced with a minimum 2.0%
concentration of fnely divided and evenly dispersed carbon black is protected
from the harmful effects of UV radiation for indefnite periods of time.
(18)
PE pipe
that is protected in this manner is the principal material selected for above-ground
installations. Black pipe (containing 2.0% minimum carbon black) is normally
recommended for above-ground use. Consult the manufacturers recommendations
for any non-black pipe that is either used or stored above ground.
Mechanical Impact or Loading
Any piping material that is installed in an exposed location is subject to the rigors
of the surrounding environment. It can be damaged by the movement of vehicles
or other equipment, and such damage generally results in gouging, defecting or
fattening of the pipe surfaces. If an above-ground installation must be located in a
region of high traffc or excessive mechanical abuse (along a roadway, etc.), the pipe
requires extra protection. It may be protected by building a berm or by encasing the
pipe where damage is most likely. Other devices may be used, as appropriate to the
situation. Design criteria for the installation of buried fexible thermoplastic pipe
should be used for those areas where the above-ground PE system must pass under
a roadway or other access, and where an underground installation of a portion of the
system is necessary.
(7,8)
In general, in a pressurized installation in which any section
of PE pipe has been gouged in excess of 10% of the minimum wall thickness, the
gouged portion should be removed and replaced. This has long been an established
procedure in the use of smaller diameter (up to 16-inch) PE pipe in natural gas
applications. However, it is noted that this rule only applies to smaller size pipe.
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Therefore, for any gouges or damage to larger pipe sizes with thicker walls, the user
is advised to consult the manufacturer for assistance. When the PE pipe has been
excessively or repeatedly defected or fattened, it may exhibit stress-whitening,
crazing, cracking, or other visible damage, and any such regions should be removed
and replaced with new pipe material.
Design Methodology
As previously discussed, above-ground piping systems can be subjected to
variations in temperature. These temperature fuctuations can impact the pressure
capability of the exposed piping to some degree. The possible effects resulting from
expansion and contraction characteristics of PE pipe must also be addressed in light
of the anticipated variations in temperature. Further, the installation characteristics
of the proposed above-ground system must be analyzed in some detail. Each of these
concerns will be briefy discussed in the sections which follow. This discussion will
be supplemented and facilitated with a few example calculations.
Pressure Capability
As mentioned earlier, the design of PE piping for internal pressure service is covered
in signifcant detail in Chapter 6 of this Handbook. In addition, the Appendix to
Chapter 3 contains a table of re-rating factors that can be applied to arrive at the
appropriate pressure rating for the application under consideration.
Likewise, where the apparent modulus of elasticity of the pipe material is a
consideration, the reader is referred to the modulus tables and associated
temperature re-rating factors also found in Appendix, Chapter 3.
The following four example calculations are being presented to illustrate the effect
of temperature on various design considerations for hypothetical above- ground
PE pipe installations.
ExaMPlE 1
What is the pressure capability of an SDR 11 series of PE 4710 PE pipe used to
transport water at 73F (23C)?
From Chapter 5,
P = 2 ( HDS ) ( F
T
) / ( SDR -1 )
whErE
HDS = Hydrostatic Design Stress for PE Material at 73F (23C). For PE4710 = 1000 psig
F
T
= Temperature Re-rating Design Factor; at 73F, F
T
= 1.0 per Appendix, Chapter 3.
P = 2(1000)(1.0) / (11-1) = 200psig at 73F
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311
What is this pipes pressure capability at 100F (38C)?
From Appendix, Chapter 3, F
T
at 100F = 0.78
P = 2 ( 1000 ) ( 0.78 )/( 11 -1 ) = 156 psig at 100F
Example 1 assumes that exposure of the pipe to sunlight, combined with the
thermal properties of the material fowing within the pipe, has resulted in a normal
average operating temperature for the system at 100F (38C). Exposure of the pipe
to direct sunlight can result in high, up to about 150F outside surface temperatures,
particularly if the pipe is black.
(9)
In the majority of cases, the material fowing
within the pipe is substantially cooler than the exterior of the exposed above-ground
pipe. The cooler nature of the material fowing through the pipe tends to moderate
the outside surface temperature of the exposed pipe. This results in a pipe wall
temperature that is intermediate between that of the outside surface of the pipe and
that of the fow stream. Obviously, the longer the period of irradiation of the pipe by
sunlight, the greater the potential will be to raise the temperature of the fow stream.
Several texts related to temperature design criteria and fow are included in the
literature references of this chapter.
(10,11)

In addition, the reader is referred to Chapters 3 and 6 for more detailed information
on the topic of the pressure ratings of the different PE materials designation codes
and applicable temperature re-rating factors.
Expansion and Contraction
As noted in the Design Criteria section of this chapter, temperature changes
can produce a substantial change in the physical dimensions of PE pipe. This is
evidenced by a coeffcient of expansion or contraction that is notably higher than
that of many other piping materials. The design methodology for above-ground
installation must take this potential for expansion or contraction into consideration.
The expansion or contraction for an unrestrained PE pipe can be calculated by using
the following Equation.
Pipe Length vs. Temperature Change
(3) L= (T
2
T
1
) L
WhErE
L = Theoretical length change (in.)
L>0 is expansion
L<0 is contraction
= Coeffcient of linear expansion, see Appendix, Chapter 3
T
1
= Initial temperature (F)
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312 312
T
2
= Final temperature (F)
L = Length of pipe (in.) at initial temperature, T
1
ExaMPlE 2
A 100 foot section of 10-inch (10.75-inch OD) SDR 11 (PE 4710 pipe) is left unrestrained
overnight. If the initial temperature is 70F (21C), determine the change in length
of the pipe section at dawn the next morning if the pipe stabilizes at a nighttime
temperature of 30F (-1C).
Using Equation 3,
L= ( 8.0 x 10
- 5
) ( 30- 70 ) ( 100 ft ) ( 12 in/ft ) = - 3.84 Inches
The negative sign indicates a contraction, so the fnal length is 99 ft., 8.16 in.
As shown in Example 2, the contraction or expansion due to temperature change
can be quite signifcant. However, this calculated change in length assumes both
an unrestrained movement of the pipe and an instantaneous drop in temperature.
Actually, no temperature drop is instantaneous, and obviously, the ground on which
the pipe is resting creates a retarding effect on the theoretical movement due to
friction. Practical feld experience for PE pipe has shown that the actual contraction
or expansion that occurs as a result of temperature change is approximately one-half
that of the theoretical amount.
Field experience has also shown that changes in physical length are often further
mitigated by the thermal properties or heat-sink nature of the fow stream within the
pipe. However, conservative engineering design warrants that consideration be given
to the effects of temperature variation when the fow stream is static or even when
there is no fow stream.
In cases where PE pipe will be exposed to temperature changes, it is common practice
to control the pipe movement by judiciously placing restraining devices. Typical
devices include tie-down straps, concrete anchors, thrust blocks, etc. The anchor
selection must consider the stresses developed in the pipe wall and the resultant
loads that are generated as a result of the anticipated temperature changes. While
Equations 4 and 5 provide examples of how to calculate generated loads and stress,
the Equations are not all inclusive.
(4) Longitudinal Stress vs. Temperature Change

T
= ( T
2
T
1
) E
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313
Where

T
= Theoretical longitudinal stress (psi)(Negative for contraction; positive for expansion)
= Coeffcient of expansion or contraction (see Eq. 3)
T
1
= Initial temperature (F)
T
2
= Final temperature (F)
E = Apparent short-term modulus of elasticity (see Appendix, Chapter 3) at average temperature (T
m
)
T
m
= (T
2
+ T
1
)/2
(5) Longitudinal Force vs. Temperature Change
F
T
=
T
(A)
Where
F
T
= Theoretical longitudinal force (Ibs)

T
= Theoretical longitudinal stress (psi) from Eq. 4
A = Pipe wall cross-sectional area (in
2
)
example 3
Assuming the same conditions as Example 2, what would be the potential maximum
theoretical force developed on the unrestrained end of the 100 foot section if the
other end is restrained effectively? Assume that the cross-sectional area of the pipe
wall is approximately 30 in
2
, the temperature change is instantaneous, and the
frictional resistance against the soil is zero.

T
= ( T
2
T
1
) E
Note: This E (apparent modulus) value is the average of the materials value at each of the two temperatures
used in this example calculation.
= (

8.0 x 10
-5
)

(

30-70) (130,000 x [

1.65 + 1.00

] /2

)
= -

551 psi
F
T
= (
T
) ( A )
= - 551 psi x 30 in
2
=-

16,530 Ibs
As previously mentioned, for these conditions where the temperature change is
gradual, the actual stress level is approximately half that of the theoretical value.
This would account for an actual force at the free end of about -8,265 Ibs. To illustrate
the differences between the expansion and contraction characteristics of
PE pipe versus those of steel, consider the following example:
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314 314
ExaMPlE 4
Assume the same conditions as Example 2 for 10-inch Schedule 40 steel pipe. The
pipe wall has a cross-sectional area of 11.90 in
2
, the value of for steel is 6.5 x 10
-6
in/in/F, and the value of E for this material is 30,000,000.
(14)

T
=
steel
( T
2
- T
1
) E
= (6.5 x 10
-6
) (30 - 70) (3 x 10
7
)
=-7,800 psi
F
T
= (

T
) ( A )
= -7,800 psi x 11.90 in
2
=-92,820 Ibs
Thus, as shown by Examples 3 and 4, even though the coeffcient of thermal
expansion is high in comparison to other materials, the comparatively low modulus
of elasticity results in correspondingly reduced thermal stresses and generated
loads.
These design considerations provide a general introduction to the understanding
of temperature effects on PE pipe in above-ground applications. They do not
include other factors such as the weight of the installed pipe, frictional resistance
of pipe lying on-grade, or grade irregularities. All of these factors affect the overall
expansion or contraction characteristics, and individual pipe manufacturers should
be consulted for further detail.
Installation Characteristics
There are two basic types of above-ground installations. One of these involves
stringing-out the pipe over the naturally-occurring grade or terrain. The second
involves suspending the pipe from various support structures available along the
pipeline right-of-way. Figure 2 illustrates some typical installations for both types.
Each type of installation involves different design methodologies, so the installation
types are discussed separately.
On-Grade Installations
As indicated previously, pipe subjected to temperature variation will expand
and contract in response to temperature variations. The designer has two options
available to counteract this phenomenon. Basically the pipe may be installed in
an unrestrained manner, thus allowing the pipe to move freely in response to
temperature change. Or the pipe may be anchored by some means that will
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315
control any change of physical dimensions; anchoring can take advantage of PEs
unique stress relaxation properties to control movement and defection
mechanically.
(12)
Free Movement
An unrestrained pipe installation requires that the pipe be placed on a bed or right-
of-way that is free of material that may abrade or otherwise damage the exterior pipe
surface. The object is to let the pipe wander freely without restriction or potential
for point damage. This installation method usually entails snaking the PE pipe
along the right-of-way. The excess pipe then allows some slack that will be taken up
when the temperature drops and the pipe contracts.
Figure 2 Typical Above-Ground Installations with PE Pipe
Figure 2a On-grade Installation of PE Pipe in an Industrial Application.
Note snaking along right of way.
Figure 2b Continuous Support of PE Pipe at Ravine Crossing
14



Figure 2b Continuous Support of Polyethylene
Pipe at Ravine Crossing






Figure 2c Intermittent Support of Polyethylene Pipe
Suspended from Rigid Structure


Figure 2 - Typical Above Ground Installations with Plastic pipe


In all likelihood, a free-moving polyethylene pipe must eventually terminate at or
connect to a rigid structure of some sort. It is highly recommended that
transitions from free-moving polyethylene pipe to a rigid pipe appurtenance be
fully stabilized so as to prevent stress concentration within the transition
connection.

Figure 3 illustrates some common methods used to restrain the pipe at a
distance of one to three pipe diameters away from the rigid termination. This
circumvents the stress-concentrating effect of lateral pipe movement at
termination points by relieving the stresses associated with thermal expansion or
contraction within the pipe wall itself.


Figure 2c Intermittent Support of PE Pipe Suspended from Rigid Structure
14



Figure 2b Continuous Support of Polyethylene
Pipe at Ravine Crossing






Figure 2c Intermittent Support of Polyethylene Pipe
Suspended from Rigid Structure


Figure 2 - Typical Above Ground Installations with Plastic pipe


In all likelihood, a free-moving polyethylene pipe must eventually terminate at or
connect to a rigid structure of some sort. It is highly recommended that
transitions from free-moving polyethylene pipe to a rigid pipe appurtenance be
fully stabilized so as to prevent stress concentration within the transition
connection.

Figure 3 illustrates some common methods used to restrain the pipe at a
distance of one to three pipe diameters away from the rigid termination. This
circumvents the stress-concentrating effect of lateral pipe movement at
termination points by relieving the stresses associated with thermal expansion or
contraction within the pipe wall itself.


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316 316
Figure 3b Connection to Rigid Structure Using Consolidated Earthen Berm
Restrained Pipelines
The design for an above-ground installation that includes restraint must consider the
means by which the movement will be controlled and the anchoring or restraining
force needed to compensate for, or control, the anticipated expansion and contraction
15



Figure 3a - Connection to Concrete Vault Using Grade Beam





Figure 3b - Connection to Rigid Structure Using
Consolidated Earthen Berm



Figure 3 - Typical Anchoring Methods at Rigid
Terminations of Free-Moving Polyethylene Pipe Sections

Restrained Pipelines

The design for an above-ground installation that includes restraint must consider
the means by which the movement will be controlled and the anchoring or
restraining force needed to compensate for or control the anticipated expansion
and contraction stresses. Common restraint methods include earthen berms,
pylons, augered anchors, and concrete cradles or thrust blocks.

In all likelihood, a free-moving PE pipe must eventually terminate at or connect to a
rigid structure of some sort. It is highly recommended that transitions from free-
moving PE pipe to a rigid pipe appurtenance be fully stabilized so as to prevent
stress concentration within the transition connection.
Figure 3 illustrates some common methods used to restrain the pipe at a distance
of one to three pipe diameters away from the rigid termination. This circumvents the
stress-concentrating effect of lateral pipe movement at termination points by
relieving the stresses associated with thermal expansion or contraction within the
pipe wall itself.
Figure 3 Typical Anchoring Methods at Rigid Terminations of Free-Moving
PE Pipe Sections
Figure 3a Connection to Concrete Vault Using Grade Beam
15



Figure 3a - Connection to Concrete Vault Using Grade Beam





Figure 3b - Connection to Rigid Structure Using
Consolidated Earthen Berm



Figure 3 - Typical Anchoring Methods at Rigid
Terminations of Free-Moving Polyethylene Pipe Sections

Restrained Pipelines

The design for an above-ground installation that includes restraint must consider
the means by which the movement will be controlled and the anchoring or
restraining force needed to compensate for or control the anticipated expansion
and contraction stresses. Common restraint methods include earthen berms,
pylons, augered anchors, and concrete cradles or thrust blocks.

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317
stresses. Common restraint methods include earthen berms, pylons, augered
anchors, and concrete cradles or thrust blocks.
The earthen berm technique may be either continuous or intermittent. The pipeline
may be completely covered with a shallow layer of native earth over its entire length,
or it may be stabilized at specifc intervals with the earthen berms between the
anchor locations. Typical earthen berm confgurations are presented in Figure 4.
Figure 4 Earthern Berm Configurations
The continuous earthen berm serves not only to stabilize the pipe and restrain its
movement but also to moderate temperature fuctuations. With less temperature
fuctuation the tendency for pipe movement is reduced.
An intermittent earthen berm installation entails stabilization of the pipe at fxed
intervals along the length of the pipeline. At each point of stabilization the above-
ground pipe is encased with earthen fll for a distance of one to three pipe diameters.
The economy of this method of pipeline restraint is fairly obvious.
Other means of intermittent stabilization are available which provide equally
effective restraint of the pipeline with a greater degree of ease of operation and
maintenance. These methods include pylons, augered anchors
(13)
, or concrete cradles.
These restraint techniques are depicted schematically in Figures 5 through 7.
16
The earthen berm technique may be either continuous or intermittent. The
pipeline may be completely covered with a shallow layer of native earth over its
entire length, or it may be stabilized at specific intervals with the earthen berms
between the anchor locations. Typical earthen berm configurations are presented
in Figure 4.








Figure 4 - Earthern Berm Configurations


The continuous earthen berm serves not only to stabilize the pipe and restrain its
movement but also to moderate temperature fluctuations. With less temperature
fluctuation the tendency for pipe movement is reduced.

An intermittent earthen berm installation entails stabilization of the pipe at fixed
intervals along the length of the pipeline. At each point of stabilization the above-
ground pipe is encased with earthen fill for a distance of one to three pipe
diameters. The economy of this method of pipeline restraint is fairly obvious.

Other means of intermittent stabilization are available, which provide equally
effective restraint of the pipeline with a greater degree of ease of operation and
maintenance. These methods include pylons, augered anchors
[13]
,or concrete
cradles. These restraint techniques are depicted schematically in Fiqures 5
through 7.

16
The earthen berm technique may be either continuous or intermittent. The
pipeline may be completely covered with a shallow layer of native earth over its
entire length, or it may be stabilized at specific intervals with the earthen berms
between the anchor locations. Typical earthen berm configurations are presented
in Figure 4.








Figure 4 - Earthern Berm Configurations


The continuous earthen berm serves not only to stabilize the pipe and restrain its
movement but also to moderate temperature fluctuations. With less temperature
fluctuation the tendency for pipe movement is reduced.

An intermittent earthen berm installation entails stabilization of the pipe at fixed
intervals along the length of the pipeline. At each point of stabilization the above-
ground pipe is encased with earthen fill for a distance of one to three pipe
diameters. The economy of this method of pipeline restraint is fairly obvious.

Other means of intermittent stabilization are available, which provide equally
effective restraint of the pipeline with a greater degree of ease of operation and
maintenance. These methods include pylons, augered anchors
[13]
,or concrete
cradles. These restraint techniques are depicted schematically in Fiqures 5
through 7.

17



Figure 5 - Pylon Type Stabilization






Figure 6 - Augered Anchor Stabilization




Figure 7 - Concrete Cradle or Thrust Block Stabilization



A pipeline that is anchored intermittently will deflect laterally in response to
temperature variations, and this lateral displacement creates stress within the
pipe wall. The relationships between these variables are determined as follows:

Figure 5 Pylon Type Stabilization
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318 318
Figure 6 Augered Anchor Stabilization
Figure 7 Concrete Cradle or Thrust Block Stabilization
A pipeline that is anchored intermittently will defect laterally in response to
temperature variations, and this lateral displacement creates stress within the pipe
wall. The relationships between these variables are determined as follows:
Lateral Defection (Approximate from Catenary Eq.)
17



Figure 5 - Pylon Type Stabilization






Figure 6 - Augered Anchor Stabilization




Figure 7 - Concrete Cradle or Thrust Block Stabilization



A pipeline that is anchored intermittently will deflect laterally in response to
temperature variations, and this lateral displacement creates stress within the
pipe wall. The relationships between these variables are determined as follows:

17



Figure 5 - Pylon Type Stabilization






Figure 6 - Augered Anchor Stabilization




Figure 7 - Concrete Cradle or Thrust Block Stabilization



A pipeline that is anchored intermittently will deflect laterally in response to
temperature variations, and this lateral displacement creates stress within the
pipe wall. The relationships between these variables are determined as follows:

= D 96 (T)
L
(6) y = L 0.5 ( T )
whErE

y
= Lateral defection (in.)
L = Distance between anchor points (in.)
= Coeffcient of expansion/contraction; see Appendix, Chapter 3
T = Temperature change (T
2
- T
1
) in F
(7) Bending Strain Development
whErE
= Strain in pipe wall (%)
D = Outside diameter of pipe (in)
= Coeffcient of expansion/contraction; see Appendix, Chapter 3
T = (T
2
- T
1
) in F
L = Length between anchor points (in)
304-326.indd 318 1/16/09 10:00:39 AM
Chapter 8
Above-Ground Applications for PE Pipe
319
As a general rule, the frequency of stabilization points is an economic decision. For
example, if lateral defection must be severely limited, the frequency of stabilization
points increases signifcantly. On the other hand, if substantial lateral defection
is permissible, fewer anchor points will be required, and the associated costs are
decreased.
Allowable lateral defection of PE is not without a limit. The upper limit is
determined by the maximum permissible strain in the pipe wall itself. This limit is
a conservative 5% for the majority of above-ground applications. It is determined
by use of Equation 7 based on the assumption that the pipe is anchored between
two posts at a distance L from each other. Equations 6 and 7 are used to determine
the theoretical lateral defection or strain in overland pipelines. Actual defections
and strain characteristics may be signifcantly less due to the friction imposed by
the prevailing terrain, the weight of the pipe and fow stream, and given that most
temperature variations are not normally instantaneous. These factors allow for stress
relaxation during the process of temperature fuctuation.
ExaMPlE 5
Assume that a 10-inch ( OD = 10.75 ) SDR 11 (PE 4710 ) pipe is strung out to grade and
anchored at 100-foot intervals. What is the maximum theoretical lateral defection
possible, given a 50F ( 27.8C ) temperature increase? What strain is developed in the
pipe wall by this temperature change? What if the pipe is anchored at
50-foot intervals?
Calculations for 100-foot intervals:
y = L 0.5 ( T )

= 100 x 12 [ 0.5 ( 8 x 10
-5
) (50 ) ]
1/2
= 53.7 inches lateral displacement
= D 96 ( T )
L
= 10.75 ( 96 ) ( 8 x 10
-5
) ( 50 )

100 ( 12 )
= 0.56% strain
Calculations for 50-foot intervals:
y = L0.5(T)
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Chapter 8
Above-Ground Applications for PE Pipe
320 320
= 50 x 12 [ 0.5(8 x 10
-5
)(50) ]
1/2
= 26.8 inches lateral displacement
= D96(T)


L
= 10.75 96 (0.0001 ) (50)

50 ( 12 )
= 1.11% strain
From the calculations in Example 5, it is apparent that lateral defections which
appear signifcant may account for relatively small strains in the pipe wall. The
relationship between lateral defection and strain rate is highly dependent on the
selected spacing interval.
Supported or Suspended Pipelines
When PE pipeline installations are supported or suspended, the temperature
and corresponding defection characteristics are similar to those discussed above
for unsupported pipelines with intermittent anchors. There are two additional
parameters to be considered as well: beam defection and support or anchor
confguration.
Support or Suspension Spacing
Allowable spans for horizontal lines are principally infuenced by the need to comply
with these objectives:
Keep the pipe bending stresses within suitable limits
Limit defections (sagging), if necessary for
- Appearance
- Avoiding pockets (to allow complete drainage)
- Avoid interferences with other pipes or, items
In most cases, the limiting pipe spans which allow the above objectives to be met can
readily be obtained from the equations which are presented below. These equations
are based on the simple beam relationship.
(8) Support Spacing Requirements
3 (OD
4
- ID
4
)
m

8qOD
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Chapter 8
Above-Ground Applications for PE Pipe
321
where
L = Center-to-center span (in)
OD = Outside diameter (in)
ID = Inside diameter (in)

m
= Maximum allowable bending stress (psi); see Note below
= 100 psi for pressurized pipelines
= 400 psi for non-pressurized pipelines
q= Load per unit length (Ib/in.)
Note: A common and conservative design objective (in the case on non-pressure pipelines) is to limit the bending
stress to one half of the PE pipe materials HDS for the maximum anticipated operating temperature. For pressure
pipelines, the objective is to limit the bending stress to 1/8th of the HDS. For example, for a PE4710 material
one having an HDS of 1000psi for water for 73F the corresponding bending limits for 73F would be 500
(for non-pressure) and 125psi (for pressure). And, for a different maximum operating temperature these limits
would be modifed in accordance with the temperature adjustment factors given in the Appendix to Chapter 3.
Also, if environment is a factor this should also be recognized.
(9) Load per Unit Length
where
q= Load per unit length (Ib/in)
W = Weight of pipe (Ibs/ft)
= Density of Internal fuid (Ib/ft
3
)
= 3.1416
This calculation gives a conservative estimate of the support span in cases where the
pipe is not completely restrained by the supports. (The pipe is free to move within
the supports.) A more complex analysis of the bending stresses in the pipe may be
performed by treating the pipe as a uniformly loaded beam with fxed ends. The
actual defection that occurs between spans may be determined on the basis of this
type of analysis, as shown in Equation 10.
(10) Simple Beam Defection Analysis
(14,15)
Based on Limiting Defection
d =

f qL
4

E
L
I
where
d= Defection or sag (in)
f = Defection Coeffcient, (Refer to Table 2)
L = Span length (in)
q= Load per unit length (Ib/in)
q = +
W
12 6912
(ID)
2
304-326.indd 321 1/27/09 12:19:27 PM
Chapter 8
Above-Ground Applications for PE Pipe
322 322
= d + y
d =

fqL
4

E
L
I
E
L
= Apparent long-term modulus of elasticity at average long-term temperature from Appendix, Chapter 3
I = Moment of inertia (in
4
)
= ( /64)(OD
4
- ID
4
)
Simple beam analysis refects the defection associated with the proposed support
spacing confguration and the apparant modulus of elasticity at a given service
temperature. It does not take into consideration the increased or decreased defection
that may be attributed to expansion or contraction due to thermal variations. These
phenomena are additive - Equation 11 illustrates the cumulative effect.
(11) Cumulative Defection Effects
Total defection = beam defection + thermal expansion defection
Simple beam analysis assumes one support point at each end of a single span.
Most supported pipelines include more than one single span. Normally, they consist
of a series of uniformly spaced spans with relatively equal lengths. The designer
may analyze each individual segment of a multiple-span suspended pipeline
on the basis of simple beam analysis. However, this approach may prove overly
conservative in the majority of multiple-span supported pipelines. Equation 12
presents a more realistic approach to defection determination on the basis of
continuous beam analysis.
(12) Continuous Beam Analysis
d =

f qL
4

+ 0.5(T)
E
L
I
L
whErE
d = Defection or sag (in)
f = Defection coeffcient (Refer to Table 2 )
q = Load per unit length (lbs/in)
L = Span length (in)
E
L
= Apparent long-term modulus of elasticity at average long-term temperature from Appendix, Chapter 3
I = Moment of inertia (in
4
)
= ( /64)(OD
4
- ID
4
)
The defection coeffcient, f, is a function of the number of spans included and
whether the pipe is clamped securely, fxed, or simply guided (not fxed) within the
supports. Practical values for the defection coeffcient, f, are provided in Table 2.
304-326.indd 322 1/16/09 10:00:39 AM
Chapter 8
Above-Ground Applications for PE Pipe
323
whErE
f = Defection Coeffcient (Refer to Table 2)
q= Load per unit length from Eq. 9 (lbs/in)
L = Span length from Eq. 8 (in)
E
L
= Apparent long-term modulus of elasticity at average long-term temperature from Appendix, Chapter 3
I = Moment of inertia (in.
4
)
= ( /64)(OD
4
- ID
4
)
anchor and Support Design
Proper design of anchors and supports is as important with PE piping as it is with
other piping materials. A variety of factors must be considered.
TablE 2
Defection Coeffcients, f, for Various span Confgurations
(17)
1 Span 2 Spans 3 Spans 4 Spans
N-N N-N-N N-N-N-N N-N-N-N-N
1 2 1 1 2 2 1
f=0.013 f=0.0069 f1=0.0069 f1=0.0065
f2=0.0026 f2=0.0031
FN F-N-N F-N-NN F-N-N-N-N
1 2 1 2 2 1 2 2 2
f=0.0054 f=0.0026 f1=0.0026 f1=0.0026
f2=0.0054 f2=0.0054 f2=0.0054
F-F F-N-F F-N-N-F F-N-N-N-F
1 2 1 1 2 2 1
f=0.0026 f=0.0026 f1=0.0026 f1=0.0026
f2=0.0031 f2=0.0031
F-F-F F-F-F-F F-F-F-F-F
f=0.0026 f=0.0026 f=0.0026
F = Fixed Securely N = Not Fixed
As was the case for simple beam analysis, continuous beam analysis addresses the
defection resulting from a given span geometry at a specifed service temperature.
The equation does not take into consideration the additional defection associated
with expansion or contraction due to temperature variations. Equation 13 combines
the effect of defection due to span geometry (using continuous beam analysis) with
defection resulting from expansion due to a temperature increase. A total span
defection of to 1 inch is generally considered as a maximum.
(13) Total Span Defection Based on Continous Beam Analysis and Thermal Response
Total Defection (in) =

f qL
4

+ L 0.5(T)
E
L
I
304-326.indd 323 1/16/09 10:00:39 AM
Chapter 8
Above-Ground Applications for PE Pipe
324 324
Some installations of PE pipe have the pipe lying directly on the earths surface.
In this type of installation, the surface under the pipe must be free from boulders,
crevices, or other irregularities that could create a point-loading situation on the pipe.
On-grade placement over bed rock or hard pan should be avoided unless a uniform
bed of material is prepared that will cushion the pipe. If the PE pipe rests directly on
a hard surface, this creates a point loading situation and can increase abrasion of the
outer pipe surface as it wanders in response to temperature variations.
Intermittent pipe supports should be spaced properly, using the design parameters
discussed in the preceding pages. Where excessive temperatures or unusual loading
is encountered, continuous support should be considered.
Supports that simply cradle the pipe, rather than grip or clamp the pipe, should be
from one-half to one-pipe diameter in length and should support at least 120 degrees
of the pipe diameter. All supports should be free from sharp edges.
The supports should have adequate strength to restrain the pipe from lateral or
longitudinal defection, given the anticipated service conditions. If the design allows
free movement during expansion, the sliding supports should provide a guide
without restraint in the direction of movement. If on the other hand, the support is
designed to grip the pipe frmly, the support must either be mounted fexibly or have
adequate strength to withstand the anticipated stresses.
Heavy fttings or fanges should be fully supported and restrained for a distance of
one full pipe diameter, minimum, on both sides. This supported ftting represents
a rigid structure within the fexible pipe system and should be fully isolated from
bending stresses associated with beam sag or thermal defection.
Figure 8 includes some typical pipe hanger and support arrangements that are
appropriate for use with PE pipe, and Figure 9 shows some anchoring details and
cradle arrangements.
Pressure-Testing
It is common practice to pressure-test a pipe system prior to placing it in service. For
the above-ground systems described in this chapter, this test should be conducted
hydrostatically. Hydrostatic testing procedures are described in a number of
publications, including PPI Technical Report 31.
(8)
The Plastics Pipe Institute does not
recommend pneumatic pressure testing of an above-ground installation.
(16)
An
ASTM test method for leakage testing of PE pipe installations is under development
and may be applicable. The reader is also advised to refer to Chapter 2 of this
Handbook where the subject of pressure testing of installed PE pipe systems is
covered in greater detail.
304-326.indd 324 1/16/09 10:00:39 AM
Chapter 8
Above-Ground Applications for PE Pipe
325
Figure 8 Typical Pipe Hangers and Supports
Figure 8.1 Pipe Stirrup Support
Figure 8.2 Clam Shell Support
Figure 8.3 Suspended I-Beam or Channel-Continuous Support
Figure 9 Typical Anchoring and Cradling Details
Conclusion
PE pipe has been used to advantage for many years in above-ground applications.
The unique light weight, joint integrity, and overall toughness of PE has resulted in
the above-ground installation of PE pipe in various mining, oil, gas production and
municipal distribution applications. Many of these systems have provided years of
cost-effective service without showing any signs of deterioration.
25


Figure 8 - Typical Pipe Hangers and Supports









Figure 9 - Typical Anchoring and Cradling Details


Pipe Stirrup Support
Clam Shell Support
Suspended I Beam or
Channel Continuous Support
25


Figure 8 - Typical Pipe Hangers and Supports









Figure 9 - Typical Anchoring and Cradling Details


Pipe Stirrup Support
Clam Shell Support
Suspended I Beam or
Channel Continuous Support
25


Figure 8 - Typical Pipe Hangers and Supports









Figure 9 - Typical Anchoring and Cradling Details


Pipe Stirrup Support
Clam Shell Support
Suspended I Beam or
Channel Continuous Support
25


Figure 8 - Typical Pipe Hangers and Supports









Figure 9 - Typical Anchoring and Cradling Details


Pipe Stirrup Support
Clam Shell Support
Suspended I Beam or
Channel Continuous Support
304-326.indd 325 1/16/09 10:00:39 AM
Chapter 8
Above-Ground Applications for PE Pipe
326 326
The key to obtaining a quality above-ground PE piping system lies in careful design
and installation. This chapter is intended to serve as a guide by which the designer
and/or installer may take advantage of the unique properties of PE pipe for these
types of applications. In this way, excellent service is assured, even under the
demanding conditions found with above-ground installations.
references
1. ASTM D2837, Standard Method for Obtaining the Hydrostatic Design Basis for Thermoplastic Materials, Annual
Book of Standards, American Society for Testing and Materials (ASTM), Philadelphia, PA,
2. Plastics Pipe Institute, Report TR-3, Policies and Procedures for Developing Recommended Hydrostatic Design
Stresses, Irving, TX.
3. ASTM D3035, Standard Specifications for PE (PE) Plastic Pipe (DR-PR) Based on Controlled Outside Diameter,
Annual Book of Standards, American Society for Testing and Materials ASTM), Philadelphia, PA,
4. Arctic Town Gets Royal Flush. (1984, January 5). Engineering News Record, New York.
5. Bringing Modern Utilities to Town Beyond the Arctic Circle. (1985, December). Public Works.
6. Plastics Pipe Institute. (1991). Report TR19, Thermoplastic Piping for the Transport of Chemicals,Irving, TX.
7. ASTM D2321, Standard Practice for Underground Installation of Flexible Thermoplastic Sewer Pipe, Annual Book of
Standards, American Society for Testing and Materials (ASTM), Philadelphia, PA,
8. Plastics Pipe Institute. (1988). Report TR-31, Underground Installation of Polyolefin Piping, Irving, TX.
9. Gachter, R., & H. Muller. (1983). Plastics Addition Handbook, McMillan Publishing Co., New York, NY.
10. Parker, J. D., James H. Boggs, & Edward F. Click. (1969). Introduction to Fluid Mechanics and Heat Transfer,
Addison-Wesley Publishing Co., Reading, MA.
11. VanWylen, Gordon J., & Richard E. Sonntag. (1973). Fundamentals of Classical Thermodynamics, John Wiley &
Sons, New York, NY.
12. Ferry, John D. (1982). Viscoelastic Properties of Polymers, John Wiley & Sons, New York, NY, 1980. Pipeline
Anchoring Encyclopedia, A. B. Chance Company Bulletin 30-8201.
13. Pipeline Anchoring Encyclopedia. (1982). A. B. Chance Company bulletin 30-8201.
14. Engineering in Training Reference Manual, 8th edition, M.R. Lindeburg, Professional Publications, Belmont, CA,
2002.
15. Moffat, Donald W. (1974). Plant Engineering Handbook of Formulas, Charts, and Tables, Prentice-Hall, Inc.,
Englewood Cliffs, NJ.
16. Plastics Pipe Institute. (1989). Recommendation B. Thermoplastic Piping for the Transport of Compressed Air
or Other Compressed Cases, Irving, TX.
17. Manual of Steel Construction, 6th Edition, American Institute of Steel Construction, Chicago, IL.
18. Gilroy, H. M., Polyolefin Longevity for Telephone Service, AT&T Bell Laboratories, Murray Hill, NJ.
references, Equations
Eq 1. The Plastics Pipe Institute. (1976). Plastics Piping Manual, Wayne.
Eq 2. Managing Corrosion with Plastics. (1983). Volume 5, National Association of Corrosion Engineers.
Eq 3. Roark Raymond J., & Warren C. Young. (1973). Formulas for Stress & Strain, McGraw-Hill Co., New York, NY.
Eq 4. Ibid.
Eq 5. Baumeister, T., & L. S. Marks. (1967). Standard Handbook for Mechanical Engineers, 7
th
Edition, McGraw-Hill
Book Co., New York, NY.
Eq 6. Roark, Raymond J., & Warren C. Young. (1973). Formulas for Stress & Strain, McGraw-Hill Book Co., New York,
NY.
Eq 7. Crocker. (1945). Piping Handbook, Grunnell Co., Providence, RI.
Eq 8. This is a basic equation utilized to determine the total weight of a pipe filled with fluid.
Eq 9. Shigley, J. E. (1972). Mechanical Engineering Design, 2
nd
Edition, McGraw-Hill Book Co., New York.
Eq 10. Ibid.
Eq 11. Ibid.
Eq 12. Ibid.
304-326.indd 326 1/16/09 10:00:39 AM