4.9
Corrosion
In metal water pipes, corrosion can occur
because chemical reactions cause the pipe to act mildly electrically charged.
This charge can cause it to release ions, causing it to lose strength. This can
be remedied typically by supplying coatings such as tar or enamel.
In sewer pipes, corrosion can occur because of
chemical reactions caused by the biological production of sulfuric acid. In
concrete pipes, the acid reacts with the lime to form calcium sulfate, which
lacks structural strength. The best protection is corrosion resistant pipe such
as vitrified clay or plastic. Concrete pipe can be protected with coatings and
or linings.
4.14 Flexible PIPES
Pipes with higher flexibility, such as PVC and
HDPE (and larger diameter ductile iron) require proper pipe bedding and full
side fill support to resist deflection. The bedding, the side fills and the
walls of these "flexible" pipes must form a structural unit to resist
the pipe deflection caused by overlying soil loads. In practice, this means
that these pipes require increased labor and materials for backfilling and side
filling.
4.15 Joints
There are varieties of ways in which pipes are
joined. These are • Mechanical –
a joint where pipes are joined by bolting or threaded their ends together.
4,15-1 Solvent Cement
Solvents are used to join PVC DWV
pipe. The solvent is used to soften and “glue” two pipe sections together.
Health concerns have been raised about these solvents.
4.15-2 Welded
Both metal and some plastic pipes can be
welded. Plastic pipe uses a hot plate to melt the ends of the plates to be
joined. The plate is removed and the ends are pushed together using joining
machinery, creating a seamless joint.
4.15-3 Bell
4.16 Sliplining
If an older pipe is to be replaced, sliplining
is frequently used to minimize installation costs. Costs are minimized because
no excavation is required. Sliplining involves the placement of newer pipe
inside that of an older, usually failed pipe. As the inside diameter of the
“new’ pipe will be smaller than the old, the new smaller pipe diameter will be
able to carry less flow so this method requires that there be excess capacity
in the older larger pipe. The new pipe, in lengths of 1000m can either be
pushed of pulled through the older pipe. (PM Construction)
4.17 PIPES Bursting
This is a relatively new technique for pipe
placement. It is the only trench less technology that allows for the
replacement pipe to have larger diameter than the original pipe. In this
method, a pneumatic bursting machine is dragged through the existing pipe. Old
pipe fragments are displaced into the surrounding soil and the new larger pipe,
in lengths up to 500 meters, is pulled in behind as replacement.
4.18 Case Studies
The following case studies have been provided
to show examples of where and how PVC alternatives are used. All these case
studies illustrate the use of HDPE, not because it is the preferred alternative
to PVC, but because the other alternatives (ductile iron, copper, concrete)
have already proven themselves in the North American marketplace.
Western Lake Superior
Sanitary District commits to PVC free pipe The
Western Lake Superior Sanitary District (WSLLD) is a regional wastewater
treatment plant located in Duluth ,
Minnesota Lake Superior .
The WLSSD, has adopted a nationally recognized pollution prevention program
which has as its basis a commitment to zero discharge of persistent toxic
substances. This commitment reads:
"The WLSSD as a discharger
to Lake Superior is committed to the goal of
zero discharge of persistent toxic substances and will establish programs to
make continuous progress toward that goal. The District recognizes step-wise
progress is only possible when pollution prevention strategies are adopted and
rigorously pursued. These approaches will focus upon our discharge as well as
indirect sources. WLSSD will work with its users to implement programs,
practices, and policies, which will support the goal.... WLSSD recognizes that
airborne and other indirect sources beyond District control must be addressed
in order for significant reductions to occur."
One component of their P2 program is a PVC free
policy as a means towards dioxin reduction. As a wastewater treatment plant
this policy has been applied to assist in the purchase of PVC-free pipe, an
alternative PVC-free liner for their new anaerobic digestion facility,
preference for PVC alternatives in their master plan development, PVC free
electrical applications, and in the elimination of other uses of PVC such as
office products. www.wlssd.duluth.mn.us
Bow, NH uses HDPE for
roadway drainage. The community of 6,500
residents has 110 miles of roadway, and as old roads are upgraded and new roads
built, the town includes storm drains made of HDPE. The corrugated polyethylene
pipe was chosen for its ability to withstand frost action in the varied soil
conditions beneath the town. "Metal pipe and cement pull apart from heat,
and the freeze-and-contract movement in the winter. If there's a pocket of
clay, water beneath the surface humps it up when it freezes, and that makes
metal pipe come apart at the joints," comments cleverly, the city
engineer, noting that he has not seen any similar problems with corrugated
polyethylene pipe. Additionally, cleverly likes the safety factor HDPE pipe
provides over metal pipe. He describes freshly cut metal pipe ends as,
"razor-sharp," compared to HDPE. "We try to be as
safety-conscious as possible," he says. (CPPA website)
Atlanta Parks &
Recreation uses 4" and 6" perforated polyethylene pipe to improve the hydraulic performance of a series of French
drains running through the park and alongside a ball field. The Arts Group, Decatur , Ga.
4.19
Heat
Fusion and Joining Introduction
An
integral part of any pipe system is the method used to join the system
components. Proper engineering design of a system will take into consideration
the type and effectiveness of the techniques used to join the piping components
and accessories, as well as the durability of the resulting joints. The
integrity and versatility of the joining techniques used for polyethylene pipe
allow the designer to take advantage of the performance benefits of
polyethylene in a wide variety of applications.
There
are three types of heat fusion joints currently used in the industry: Butt,
Saddle and Socket Fusion. Additionally, there are two methods for producing the
socket and saddle fusion joints. In addition to the fusion procedures that
follow, electro fusion is recognized as an acceptable method of producing
socket and saddle fusions but is not addressed here.
The
fusion procedures that follow have been proven to consistently produce sound
fusion joints when used correctly and are recommended for the joining of
Polyethylene® products. The recommended procedures for butt and
saddle fusions are consistent with the Plastic Pipe Institute (PPI) TR-33, Generic Butt
Fusion Procedures and TR-41,
Generic Saddle Fusion Procedures.
4.20
Federal
Regulations
Individuals
who are involved in joining gas-piping systems must note certain qualification
requirements of the U.S. Department of Transportation Pipeline Safety
Regulations. The U.S. Department of Transportation, D.O.T., requires that all
persons who make fusion joints in polyethylene gas piping systems must be
qualified under the operator’s written procedures (49 CFR, Part 192,
§192.293(a)), and require that gas system operators ensure that all persons who
make fusion joints are qualified (49 CFR, Part 192, §192.285(d)).
4.21
Qualification
Procedure
Due
to the requirements of the U.S. Department of Transportation, any person
joining polyethylene gas pipe must receive training in each of the fusion
procedures (49 CFR, Part 192). Each operator should make a sample joint for
each procedure used. Each sample joint must pass the following inspections and
tests:
1.
Pressure and tensile
testing as described in §192.283, CFR,
2.
Ultrasonically
inspected and found to contain no flaws, or
3.
Cut into at least
three (3) strips, each of which is:
·
Visually examined and
found free of voids or discontinuity on the cut surface of the joint.
·
Deformed by bending,
torque or impact, and if failure occurs, must not initiate in the joint area.
·
A person must be re-qualified under an
applicable procedure during a 12-month period for the following conditions:
1.
The individual does
not make any joints under the procedure.
2.
The individual has
three (3) joints or 3% of the joints made, whichever is reater, that are found
to be unacceptable by —192.513, CFR.
Each
operator shall establish a method to determine that each person making a joint
in plastic pipelines in his/her system is qualified in accordance with this
section.
4.22 Heat
Fusion
The
principle behind heat fusion is to heat two surfaces to a designated
temperature, and then fuse them together by application of a sufficient force.
This applied force causes the melted materials to flow and mix, resulting in a
permanent, monolithic fusion joint. When fused according to the recommended
procedures, the fusion or joint becomes as strong as or stronger than the pipe
itself in both tensile and pressure properties. Polyethylene fusion procedures
require specific tools and equipment for the fusion type and for the sizes of
pipe and fittings to be joined.
4.22.1
Butt Fusion
This technique consists of heating the squared
ends of two pipes, a pipe and fitting, or two fittings by holding them against
a heated plate, removing the plate when the proper melt is obtained, promptly
bringing the ends together and allowing the joint to cool while maintaining the
appropriate applied force.
4.22.2 Saddle Fusion
This technique involves melting the concave
surface of the base of a saddle fitting, while simultaneously melting a
matching pattern on the surface of the pipe, bringing the two melted surfaces
together and allowing the joint to cool while maintaining the appropriate
applied force.
4.22.3 Socket Fusion
This technique involves simultaneously heating
the outside surface of a pipe end and the inside of a fitting socket, which is
sized to be smaller than the smallest outside diameter of the pipe. After the
proper melt has been generated at each face to be mated, the two components are
joined by inserting one component into the other. The fusion is formed at the
interface resulting from the interference fit. The melts from the two
components flow together and fuse as the joint cools.
Properly
fused polyethylene joints do not leak. If a leak is detected during hydrostatic
testing, it is possible for a system failure to occur. Caution should be
exercised in approaching a pressurized pipeline and any attempts to correct the
leak should not be made until the system has been depressurized.
Note: Polyethylene cannot be joined by solvent bonding or
threading. Extrusion welding or hot air welding is not recommended for pressure
applications.
4.23
Inclement
Weather
Polyethylene
has reduced impact resistance in sub-freezing conditions. Additional care
should be exercised while handling in sub-freezing conditions. In addition,
polyethylene pipe will be harder to bend or uncoil.
In
inclement weather and especially in windy conditions, the fusion operation
should be shielded to avoid precipitation or blowing snow from contracting pipe
fusion areas and to prevent excessive heat loss from wind chill. The heating
tool should also be stored in an insulated container to prevent excessive heat
loss. Remove all frost, snow or ice from the OD and ID of the pipe; all
surfaces must be clean and dry prior to fusing.
The
time required to obtain the proper melt may increase when fusing in cold
weather. The following recommendations should be followed:
1.
Maintain the specified
heating tool surface temperature. Do not increase the tool surface temperature.
2.
Do not apply
pressure during zero pressure butt fusion heating steps.
3.
Do not increase
the butt fusion joining pressure.
In
butt fusion, melt bead size determines heating time; therefore, the procedure
automatically compensates when cold pipe requires longer time to form the
proper melt size.
The
outside diameter of polyethylene pipe and fittings will contract in cold
weather conditions. This can result in loose fit or slippage in the cold rings.
For best results, clamp one cold ring in its normal position adjacent to the
depth gage. Shim around the pipe behind the clamp with paper, tape, etc., and
place a second cold ring over this area. This cold ring will prevent slippage
while the inner cold ring will allow for the pipe to expand during the heating
cycle of the fusion process.
The
proper cycle time for any particular condition can be determined by making a
melt pattern on a piece of scrap pipe using the recommended standard heating
time. If the melt pattern is incomplete, increase the heating time by three (3)
second intervals until a complete melt pattern is established. Each time the
procedure is repeated, a new piece of scrap pipe should be used. For additional
information concerning cold weather procedures, refer to ASTM D2657, Standard
Practice for Heat Fusion Joining of Polyolefin Pipe and Fittings, Annex A1.
4.24
Fusion
Confidence
Reliable
fusion joints of polyethylene piping systems can be accomplished under reasonable
latitude of conditions. The following is a listing of general notes to help
ensure proper equipment and techniques are utilized:
1. The fusion operator must have adequate training
and understanding of the equipment and tools and the fusion procedure. Improper
understanding of the operation of the equipment and tools can produce a fusion
of poor quality. The operator must understand thoroughly how to use the
equipment and tools, their function and operation. The operator should adhere
to the equipment manufacturer’s instructions.
Contact
pressures and heating/cooling cycles may vary dramatically according to pipe
size and wall thickness. Operators should not rely exclusively on automated
fusion equipment for joint qualification. In addition, visual inspection and
qualification should always be made. If necessary, test fusions should be made
to determine correct pressures and heat/cool cycle times. Destructive test
methods, such as bend back tests, may be necessary to formulate correct
pressures and heat/cool cycle times (refer to Qualification Procedures).
2. Pipe and fitting surfaces must be clean and
properly prepared. Any contaminants present on the surfaces
or poor preparation of the surfaces cannot produce a quality fusion joint.
Ensure that all pipe and fitting surfaces are clean. If surfaces are
reintroduced to contaminants, they should be cleaned again.
3. Heater plates must be cleaning, undamaged and the
correct surface temperature. Heater surfaces are usually coated
with a non-stick material. Cleaning techniques should be used accordingly. If a
solvent is deemed necessary, do not use gasoline or other petroleum products.
Refer to the equipment manufacturer’s instructions for proper cleaning
products.
Recommended
heating tool temperatures are specified for each procedure. This temperature is
indicative of the surface temperature, not the heating tool thermometer. The
surface temperature should be verified daily by using a surface pyrometer. If a
crayon indicator (melt stick) is used, it should not be used in an area that
will be in contact with the pipe or fitting.
If
the heater plate is not in use, it is recommended that it be stored in an
insulated holder. This not only protects the heater surfaces from contaminants,
but it can also prevent inadvertent contact, which can result in serious
injuries.
4. Proper equipment and condition of tools and
equipment for the job. Each type of fusion requires special
tools and equipment. Fusions performed with the incorrect fusion equipment,
materials or tools can result in a poor fusion.
4.25
Fusion
CHECKLISTS
·
Inspect pipe lengths
and fittings for unacceptable cuts, gouges, deep scratches or other defects.
Damaged products should not be used. Refer to Polyethylene Info Brief No.
17 for allowable surface damage according to the Plastics Pipe
Institute (PPI) and the American Gas Association (AGA).
·
Any surface damage at
pipe ends that could compromise the joining surfaces or interfere with fusion
tools and equipment should be removed.
·
Be sure all required
tools and equipment are on site and in proper working order.
·
Pipe and fitting
surfaces where tools and equipment are fitted must be clean and dry. Use clean,
dry, non-synthetic (cotton) cloths or paper towels to remove dirt, snow, water
and other contaminants.
·
Shield heated fusion
equipment and surfaces from inclement weather and winds. A temporary shelter
over fusion equipment and the operation may be required.
·
Relieve tension in the
line before making connections. When joining coiled pipe, making an S-curve
between pipe coils can relieve tension. In some cases, it may be necessary to
allow pipe to equalize to the temperature of its surroundings. Allow pulled-in
pipes to relax for several hours to recover from tensile stresses.
·
Pipes must be
correctly aligned before making connections.
·
Trial fusions. A trial fusion, preferably at the
beginning of the day, can verify the fusion procedure and equipment settings
for the actual jobsite conditions. Refer to Qualification Procedures for
detailed information on the bend back test procedure.
4.26
ADVANTAGES
OF POLYETHYLENE pipe
·
Polyethylene provides
the total system solution
·
Durability, long-term
strength and integrity
·
Flexible and
lightweight
·
Superior corrosion,
chemical & abrasion resistance
·
Non-toxic
environmentally safe (interior and exterior)
·
Indent printed for
easy long-term identification
·
Heat fused, fully
restrained, leak proof joints
·
Improved flow rates
over non-HDPE piping
·
Cost advantages
·
Continuous coiled pipe
available from 1/2" to 6" diameter
·
Straight length pipe
available from 2" to 65" diameter
·
Produced in mm, CTS,
IPS and DIPS sizing systems
4.27 Basic
Features and Benefits of polyethylene Pipe
4.27.1 Lightweight
Polyethylene
HDPE pipe and MDPE pipe is lighter than traditional piping material, and that
results in substantial savings for handling and faster, less costly
installation from both an equipment and labor rationalization.
4.27.2 Flexible
Polyethylene
pipe is produced in straight length or in coils. Since PE is not a brittle
material, it can be installed with bends and over uneven terrain easily in
continuous lengths without additional welds, couplings or costly and
time-consuming fittings.
4.27.3 Tough
Polyethylene
pipe and fittings are well suited for use in slurry applications where its inherent
toughness and abrasion resistance can be fully utilized. PE pipe is very
resilient and resistant to damage caused by external loads, vibrations, and
from pressure surges such as water hammer.
4.27
4.28
Conduit and Ducting
Galvanized steel and aluminum are the
traditional conduit materials. Over the last few decades, PVC has been able to
take a large share of this market. Over the last decade HDPE has seen the
most growth in the conduit sector, and easily competes with PVC. There is
limited data on the breakdown of market share. HDPE’s extremely low coefficient
of friction makes it easy to pull cable through; one reason for its increasing
popularity. Fire code concerns have limited HDPE acceptance for indoor conduit
applications making it the primary alternative to PVC for outdoor and
underground applications. Steel and aluminum conduit are the primary
alternatives to PVC for indoor applications. While PVC is fire resistant, it’s
tendency to smolder and emit hydrochloric gases before combustion is a
particularly dangerous attribute in medium and high voltage conduit
applications. HDPE comes in rolls of several hundred feet while PVC and metal
conduits comes in rigid 20-foot sections. This makes HDPE easier to use for
larger installations and metal easier for smaller installation. Some metal
conduit products may be coated with PVC. It is important to specify those
products that are PVC free.
4.29
Drain Waste and Vent (DWV)
Cast Iron and copper are the traditional DWV
materials. PVC is widely used in residential construction because of the ease
of joining with solvent glues. ABS and PEX have both become popular
alternatives to PVC in years that are more recent. As previously noted, ABS has
serious environmental problems of its own.
Table 4.1
Technical
Comparison of PVC and Ductile Iron Pipe
Technical
Characteristics
|
PVC
|
Ductile Iron
|
Corrosion Resistance
|
Resistant to acids
|
Can corrode; requires protection in some acidic soils and septic
waters
|
Chemical Resistance
|
Can soften/degrade with organic solvents at high concentrations
|
Resistant to organic solvents; requires protection from acids
|
Impact Resistance
|
Moderate
|
High
|
Hydrostatic strength
|
Moderate
|
High
|
Tensile Strength
|
Moderate
|
High
|
Pipe Stiffness
|
Flexible; bends moderately
|
Flexible; bends slightly
|
Installation Factors
|
||
Handling, weight
|
Light (~15 kg/m - 8" DR 18)
|
Heavy (32-36 kg/m - 8" Class 350)
|
Joining
|
Push on joints most common; mechanical and butt-fusion joints
possible
|
Push-on joints most common; accommodates some deflection;
mechanical joints possible
|
Bedding
|
generally requires more side fill support to control deflection
|
more rigid at lower diameters; still requires careful bedding
|
Service
|
||
Durability
|
High
|
High (with corrosion control as required)
|
Joint Integrity
|
Long term reliability
|
Long term reliability
|
Water Flow
|
Smooth walls; low friction factor
|
Slightly higher friction factor; larger internal diameter;
higher flow
|
Lower impact resistance with decreasing temperatures; lower
tensile strength with increasing temperatures
|
Handles very high and low temperatures
|
|
Table 4.2
Technical
Comparison of PVC and HDPE Pipe
Characteristics
|
PVC
|
HDPE
|
Durability
|
Decades
|
Decades
|
Joining
|
bell and spigot push-on
|
butt-fusion above ground mostly, bolted
flange for equipment connections
|
Joint integrity
|
tight seals; low leakage
|
butt-fusion results in tight seals
|
Weight
|
more dense than HDPE
|
less dense than PVC
|
Ductility
|
more stiff than HDPE
|
less stiff then PVC
|
Flexibility
|
rigid
|
flexible
|
Pressure rating
|
more susceptible to surge, hammer shocks
|
less susceptible to surge, hammer shocks
|
Tensile strength
|
PVC has better strength to volume ratio
|
HDPE has less strength to volume ratio
|
Internal wall smoothness
|
close to HDPE
|
close to PVC
|
Abrasion resistance
|
moderate
|
high
|
Chemical resistance
|
moderate
|
very good
|
Impact resistance
|
brittle at very low temperature, glass
transition temperature higher than HDPE
|
better low temperature resistance, glass
transition temperature lower than PVC
|
Fire resistance
|
will not sustain combustion
|
will sustain combustion
|
Tapping
|
mechanical taps
|
fusion or mechanical tapping
|
Table 4.3
Technical
Comparison of PVC and Concrete Sewer Pipe
Technical
Characteristics
|
PVC
|
Concrete
|
Material
Properties
|
||
Corrosion Resistance
|
Resistant
|
resistant
|
Chemical Resistance
|
susceptible to some hydrocarbon solvents
|
susceptible to acids (i.e. sulphuric acid);
solvents may cause dissolution
|
Impact Resistance
|
moderate; reduced at very low temperatures
|
moderate
|
Abrasion Resistance
|
High
|
high; moderate under acidic conditions
|
Tensile Strength
|
moderate; flexible
|
high; rigid sections; flexibility in system
due to shorter lengths
|
Soil Stress Resistance
|
flexible; withstands stress with side fill
support
|
withstands high soil loads
|
Installation
Factors
|
||
Handling, weight
|
light (13 kg/m); long (6.1m) sections
(8" basis)
|
heavy (72 kg/m); short (1.2 m) sections
(8" basis)
|
Joining
|
push on joint
|
push-on joint; more joints
|
Bedding
|
180 bed tamping required
|
lower half support may be necessary
|
Service
|
||
Durability
|
high; long life span expected, not proven
beyond 30 years
|
high; long lifespan
|
Joint Integrity
|
long-term reliability with proper
installation
|
long-term reliability with proper
installation
|
Water Flow
|
smooth walls; low friction
|
smooth walls; low friction
|
lower impact resistance with decreasing temperatures;
flexibility increases with increasing temperatures
|
wide range application
|
|
Table 4.4
Technical
Comparison of PVC and HDPE Sewer Pipe
Characteristic
|
PVC
|
HDPE
|
Durability
|
decades
|
decades
|
Joining
|
bell and spigot push-on
|
bell and spigot push-on, butt-fusion, clam shell
connections
|
Joint integrity
|
tight seals; low infiltration
|
tight seals; low infiltration (higher for clam shell
enclosures)
|
Weight
|
more dense than HDPE
|
less dense than PVC
|
Ductility
|
less ductile than HDPE
|
more ductile than PVC
|
Flexibility
|
flexible
|
flexible
|
Tensile strength
|
better strength/volume ratio
|
lower strength to volume ratio
|
Internal wall smoothness
|
close to HDPE
|
close to PVC
|
Abrasion resistance
|
moderate
|
high
|
Chemical resistance
|
softens with solvents at high concentrations
|
very good
|
Impact resistance
|
Decreases at very low temps., glass transition temp.
higher than HDPE
|
Better low temperature. Resistance, glass transition
temperature. lower than PVC
|
Fire resistance
|
resistant to combustion
|
will sustain combustion
|
4.30 DESIGN AND CONSTRUCTION
The State Rivers & Water Supply Commission (SR&WSC
) carried out all design work and project management for the construction of
the scheme.
The climate in the Northern Mallee district of North
Western Victoria is such that consideration had to be given to possible
elevated ground temperatures for determination of the appropriate pipe pressure
classes. The CSIRO, Merbein Office, reported peak ground temperatures, at a
depth of 20" (500mm) below the surface, ranging from 55°F (13°C) in August
to 80°F (27°C) in February. It was considered that, at 30" (760mm) minimum
depth, no special provision needed to be made for elevated-temperature
operating conditions. That is, ground temperature would not be a limiting
factor in the use of PVC. However, the sporadic rainfall conditions and the
nature of the native soil necessitated consideration of the effects of
potential ground movement. Accordingly, only plastics pipes, with their
inherent flexibility, were considered in sizes below 8" diameter.
With the exception of some pipelines installed by
SR&WSC day labor forces, pipelines were constructed on a "supply and
install" basis by contractors selected by the SR&WSC.
Pipe used in the project were of either PVC or asbestos
cement (AC). Concrete pipes were considered unsuitable due to pressure
restrictions, whilst polyethylene pipes were not an economical proposition. The
use of AC pipes was restricted to diameters 200mm (8") and above due to
concerns about the beam strength being sufficient to cope with possible ground
movement. There were no limitations placed on the use of PVC, which was
subsequently installed in sizes from 20mm to 200mm, (3/4" to 8").
Pipe pressure classes ranged from Class 4.5 to Class 18 (’A’ to ‘F’ under the
now defunct classification system). Pressure classes were selected solely based
on the internal working pressure of the relevant location in the system.
There was no adjustment to the pressure class of pipes for
the many rail and road crossings. The latter included both sealed and unsealed
roads. Pipe lengths were generally 20ft (6m). However, for one contract,
incorporating all sizes up to 8", solvent cement jointed 34 ft (10m)
lengths were used.
The fittings and appurtenances included air valves,
isolating valves, fireplugs (used for scour outlets), and metered services.
Fittings types used in the system were moulded PVC pressure fittings, coated
aluminum, wrapped cast iron gibaults, flanges and tees together with cast iron
and brass valves.
4.31 INSTALLATION
Installation, including handling and storage, pipe laying
and jointing, and pressure testing, was in accordance with SR&WSC
specifications. These specifications were subsequently incorporated into
Australian Standards AS CA 67:1972, and AS 2032:1977. Pipes were installed with
a minimum of 750mm cover, increasing to 900mm at road and rail crossings.
4.32
Trench Conditions
Pipes were surrounded by granular material obtained from
the excavation or, in the case of rock excavation, from nearby. A layer of
granular material was placed beneath the pipe to a minimum depth of 75 mm
throughout the project, including areas of rock excavation.
Typical trench conditions are illustrated in the photo at.
Below.
4.33 Jointing
Whether RRJ or SWJ were used was determined by the
‘in-ground’ cost. Both solvent cement and electrometric seal systems were
approved by the principal. Rubber ring joints were made to the SR&WSC
specification, which required the spigots to be inserted into the sockets to a
witness mark that allowed for subsequent thermal movement. In practice, the
spigots were generally inserted past the witness mark.
Electrometric seal joints as exhumed and subsequently
sectioned are depicted below.
Dark staining is evident on the matching socket and spigot
surfaces where the water would be essentially dormant. This staining is likely
to be due to sulphides reacting with the lead stabiliser in the pipe. The
staining is only a surface effect.
Solvent weld sockets were manufactured to have an
interference fit with the spigot. It was reported that some solvent weld joints
leaked when the lines were first pressure tested. This was attributed to poor
workmanship during installation rather than the quality of the pipes supplied.
Solvent cement jointing for pipes up to 8" dia. was
conducted to the SR&WSC specification using appropriate cements for the
products and environment, plus disposable brushes and containers. These pipes
were usually jointed above the trench and lowered into the trench the following
day.
Pressure Testing Pipelines
were tested to 1.3 times nominal working pressure of the pipe, the time of test
being varied from two hours to 24 hours, depending on the length of pipeline
under test.
4.33
4.34
PERFORMANCE
The first pipeline was put into service in 1970, with
subsequent sections being commissioned as they were completed. The project was
completed in 1975. Sunraysia Water Corporation, the current operator of the
system, has reported the following: Asbestos Cement. - AC pipe joints have been
reported as leaking and subject to tree root intrusion. Pipe barrel failures
due to ground movement have occurred. PVC - No reported leaks in either
elastomeric seal joints or solvent weld joints, with the exception of one 40mm
solvent weld joint failure. The cause of this single failure is not known. No
pipe barrel failures have been reported, other than those resulting from third
party damage.
Valves and Fittings - Corrosion has occurred with some
valves. Air valve blockages due to ants have been reported. Water Quality - As
mentioned above, the possibility of lead extraction adversely affecting the
water quality was investigated and discounted early in the project. Some
pipelines are currently "contaminated" by a grey "sludge",
as can be seen in the photograph shown at right. This material is thought to be
at least partly composed of dead organisms and has had no apparent effect on
the performance of the PVC pipes.
4.35
EXHUMATION AND
TESTING
The
prime objective of the pipe exhumation project was to determine, by physical
testing, whether there had been any deterioration in either the PVC pipes or
joints. This assessment to be made in conjunction with reports of operational
performance. The field performance of the PVC pipes has been excellent, as
described above. The following pipes were exhumed in 1996, after approximately
25 years of service Unless otherwise specified the
tests were performed at 20 ± 2°C.
:
- Resistance to flattening was
carried out by deflecting short sections to 40% of the original diameter
and inspecting for any damage or fracture. Test Method: AS 1462.2Test
laboratories - Vinidex Tubemakers Pty. Ltd., Sunshine, Vic. Iplex
Pipelines, Technical Centre, Gladesville, NSW
- Resistance to impact. Test
Method: AS 1462.3Test laboratories - Vinidex Tubemakers Pty. Ltd.,
Sunshine, Vic. Iplex Pipelines, Technical Centre, Gladesville, NSW
- The gelation level was
measured using a Perkin Elmer differential scanning calorimeter using the
method described by Potente and Schultheis
and Gilbert and Vyvoda .Test laboratories - ICI Australia
Operations Pty. Ltd., Ascot Vale, Vic. Iplex Pipelines, Technical Centre,
Gladesville, NSW
- The dispersion of the resin
in the pipes was assessed on microtomed samples approximately 0.02 mm
thick under low power magnification. Test laboratory - Iplex Pipelines,
Technical Centre, Gladesville, NSW
- Tensile properties of the
PVC were determined on four pipe samples, using the average of five
determinations for each. Test Method: ASTM D638M-1991, using an Instron
4302 Tester. Test laboratory - ICI Australia Operations Pty. Ltd., Ascot
Vale, Vic.
- The fracture toughness of
the pipes was determined using the C-ring method. Test Method: Draft
Australian Standard No. 2570. Test laboratory - CSIRO, DBCE, Highett, Vic.
4.36
CONCLUSIONS
The PVC pipes and joints in the Millewa water scheme in
North Western Victoria are performing well, having been in service for almost
30 years. The pipes were installed in a variety of terrains including sandy
soil and solid limestone. The performance has been satisfactory in all
situations. In addition, the pipes in the system traverse both roads and rail
lines. In neither instance was the pressure class of the pipe upgraded to
accommodate the dynamic loads imposed by passing road traffic or trains.
Nevertheless, no failures have been reported as a consequence of dynamic
loading.
For the four pipes tested, the tensile strength at yield
and elongation-at-break were essentially the same. Moreover, the results are
the same as expected for contemporary pipes tested at the time of manufacture.
Thus it can be concluded there has been no degradation in the strength or
elongation characteristics of the PVC during the service life of the pipes. The
exhumed pipes have not suffered any loss of strength as a consequence of
operating under pressure for almost 30 years.
The fracture toughness of all the samples tested was higher
than the values reported by J. M. Marshall et al and G. P. Marshall et al for
pipe made in the UK at about the same time.
In addition, the fracture toughness exceeded the enhanced
levels specified in the recently revised Australian New Zealand Standard AS/NZS
1477-1999. These results imply there has been no deterioration in the fracture
toughness during a service life approaching 30 years.
Some variability occurred in the impact test results but
this did not appear to be related to a particular manufacturer, pipe size or
pressure class. The variability is possibly due to surface damage caused during
the exhumation, transport or original installation.
Weathering of the pipe during the original storage and
transport period might also have contributed to the variability of the impact
resistance. The field performance of the pipeline has not been adversely
affected by such surface damage.
Flattening test results on the exhumed pipes were also
variable and again it is possible surface damage could be a contributing
factor.
The degree of gelation and the quality of the dispersion
would be expected to be higher with contemporary PVC pipe production.
Nevertheless, the performance of the pipes has not been adversely affected by
these factors.
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