THE ADVANTAGE IN THE FIELD COST EFFECTIVE 2

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 and Spigot

      Bell and spigot joints are often used in gravity lines. With bell and spigot joints, each pipe length has a bell (or larger diameter end piece) end and spigot (or normal diameter) end. The spigot is inserted into the bell via a compression fit. Much sewer work uses bell and spigot joints.

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. It is the largest American point source discharge to 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., installed 1,000 linear feet of perforated pipe down the center of the drains to speed water flow. The smooth interior of the pipe provided greater hydraulic efficiency than ditches alone.

 

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
Temperature Range	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
Temperature Range	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.

:

1. 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
2. Resistance to impact. Test Method: AS 1462.3Test laboratories - Vinidex Tubemakers Pty. Ltd., Sunshine, Vic. Iplex Pipelines, Technical Centre, Gladesville, NSW
3. 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
4. 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
5. 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.
6. 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.