HDPE USES AND APPLICATIONS

3.1       Introduction

The effect of installation procedures on the field performance of existing high-density polyethylene (HDPE) pipe used for drainage applications on highway projects was investigated. A total of 45 HDPE pipes were inspected at sites in South Carolina that were statistically selected based on geographical location, pipe diameter, use, and age. The condition of each pipe was not known prior to selection for inspection. Both the external and internal conditions of the pipe were evaluated with respect to AASHTO and ASTM specifications, measurements of pipe deflection with a mandrel set to 5% deflection, and visual inspections of the pipe interior using a video camera. The video camera inspections revealed circumferential cracks in 18% of the pipes, localized bulges in 20% of the pipes, and tears or punctures in 7% of the pipes. Deflections greater than 5% were observed in 20% of the pipes. Installation problems such as poor preparation of bedding soils, inappropriate backfill material, and inadequate backfill cover contributed to the excessive deflection and observed internal cracking in pipes with observed damage. Appropriate construction procedures are essential in achieving a proper installation.

·         Gas Gathering

·         Crude Oil Flow

·         Water Flood

·         Saltwater Disposal

·         Supply Water

·         Fuel Transfer

·         Main Lines

3.2       Fluid and Gas Flow

Polyethylene pipes are used extensively in gas distribution applications worldwide. In USA and Canada over 90% of the natural gas distribution system is in plastics pipes with polyethylene representing 99% of the installations. The use of polyethylene in natural gas distribution systems is growing rapidly.

PE is lightweight, flexible and available in long coils minimizing the number of joints. It is ideally suited for a wide range of service conditions requiring very little maintenance. It has good abrasion resistance, flexible not effected by soil shift and temperature fluctuations.

Polyethylene pipe is recommended by PIPA for use in compressed air installations.

3.3              Fluid Flow

Polyethylene has an extremely smooth surface resulting in a very low coefficient of friction and a minimal loss of head pressure due to frictional losses. This, combined with excellent corrosion and abrasion properties, results in excellent flow characteristics throughout the life of the pipe. for pressurized systems, a Hazen-Williams "C" factor of 150 is used.PE3408/3608 Extra High Molecular Weight (EHMW) Black Pipe - a premium quality, high density, extra high molecular weight, and polyethylene pipe specifically designed for the rigors of the oil field. It is produced from PE3408/3608 resin containing not less than two percent (2%) carbon black for superior resistance to UV degradation. This pipe offers outstanding environmental stress crack resistance (ESCR), the best chemical resistance of any polyethylene pipe and high impact resistance. Polyethylene^® oil field products are available in diameters from 1/2" CTS to 6" IPS coiled and straight lengths from 1/2" through 65" IPS.

3.4              Oil Field

 

Moving fluids through pipe in the oil field demands the utmost in flexibility, reliability and performance. That is why Polyethylene is the best choice for the energy business. High-density polyethylene (HDPE) pipe provides superior flow characteristics, extended life, durability, and reduced maintenance than traditional piping materials, anywhere in the oil patch.

A wide selection of HDPE pipe can meet the needs for any oil field applications.

Polyethylene has products specifically for the oil and gas industry for gas gathering, crude transmission, water lines and auxiliary lines.

Polyethylene will not rust, rot, pit or corrode because of chemical, electrolytic or galvanic action. Chemicals that pose potentially serious problems for polyethylene are strong oxidizing agents or certain hydrocarbons. These chemicals may reduce the pressure rating for the pipe or be unsuitable for transport. Either can be a function of service temperature or chemical concentration. Continuous exposure to hydrocarbons can lead to permeation through the material or electrometric gaskets used at joints. The degree of permeation is a function of pressure, temperature, the nature of the hydrocarbons and the polymer structure of the piping material. The chemical environment may also be of concern where the purity of the fluid within the pipe must be maintained. Hydrocarbon permeation may affect pressure ratings and hinder future connections.

High Density Polyethylene (HDPE) is available for all pipe applications. Being non-chlorinated, requiring fewer additives, and having a much higher recycling rate, it is considered a more benign plastic than PVC. PVC is more resistant to combustion, but smolders at a lower temperature than HDPE and releases toxic hydrochloric gases before combustion. Cross-linked polyethylene (PEX) is a polyethylene similar in many characteristics to HDPE but with molecules cross-linked to improve its ability to handle higher temperatures. Copper is highly recyclable but copper leaching into water supplies can be harmful to aquatic life. Copper also has significant life cycle problems in its mining, manufacture. Concrete, iron and steel have significant embodied energy usage, and their manufacture is not environmentally benign. However, all of them (with the exception of ABS) are generally considered environmentally superior to PVC.  Aside from concrete, the primary PVC free alternatives are consistent with state government and professional association Environmentally Preferable Purchasing (EPP) guidelines (http://www.apwa.net/Documents/GovtAffairs/Policies/SolidWaste/solid-environpolicy.pdf). Steel, HDPE and copper pipe or conduit may all contain recycled content in the product. Quantities and post consumer content will vary with application and manufacturer. Alternative materials comparison issues The long-term durability of piping systems depends on many factors, including the soil environment, proper installation, material properties such as corrosion resistance, chemical resistance and strength and the performance of joints. Each of the primary PVC free materials has benefits that have kept them as significant market players.

3.5       Water SUPPLIES

The use of plastics pipes in potable water supply applications has been growing rapidly. Both PVC and Polyethylene pipe have major advantages over competitive materials and as polymer technology, keeps improving the choice of plastics pipes for water supply infrastructure projects keeps increasing.

Plastics pipes have design life in excess of 100 years during which they provide excellent performance and trouble free service life. They are corrosion resistant and because of their relatively lightweight are easy to handle, transport and install. Plastics pipes are flexible and fatigue resistant and can withstand repetitive pressure surges. Plastics pipes provide a smooth biological growth free bore through the life of the product eliminating flow restrictions common to other materials.

Water mains typically operate at pressures from 100 to 150 lbs per sq. in. (psi), while distribution lines operate between 40 and 100 psi. Service connection lines are usually a diameter of 1" or less and can be made of various materials: polyethylene, PVC, iron or copper pipe. Currently, PVC has a dominant share of the market for small diameter pipe in the water main (4” - 12”), sanitary sewer and storm sewer (4”-15”) markets, while traditional materials (ductile iron and concrete) continue to have majority market share in the larger diameter pipe. According to the Plastics News (July 16, 2001) the demand for large diameter pipe plastic pipe has increased 8.3% between 1990 and 2000.

The smaller tube sizes used for in building distribution are primarily split between PVC, copper, and iron. There is limited data on the breakdown of market share. Polyethylene is just beginning to penetrate the market for all sizes. The use of galvanized steel and Polyethylene has declined due to corrosion problems with galvanized and catastrophic failures with Polyethylene One of the key design concerns for drinking water infrastructure design and installation is leakage. When one turns on the tap for potable water, there is a cost associated with the acquisition, treatment, and supply (pumping) of the waster. If a water distribution system leaks, the lost water can become an extremely high cost. In arid areas, where costs to acquire water can be exorbitant, leaks can be an expensive proposition. A 4-inch leak in their 24-inch diameter iron pipe can result in the loss of 3 to 5 million gallons of water per day.

HDPE has a slight advantage in leak resistance over PVC. This is because it can be delivered in longer lengths, minimizing the quantity of joints. Furthermore, the butt or electro-fusion processes used to join HDPE provides stronger, tighter, more leak proof joints compared to the bell and spigot joints used in PVC pipe for mains or the solvent glue joints used for smaller distribution. The longer length of HDPE can require longer trenches to be open at a time, but its length and flexibility can allow for trench less procedure, particularly in sewer replacement. HDPE’s greater flexibility and resilience (particularly at lower temperatures) also make it less susceptible to surge and hammer shocks or to damage from digging. HDPE’s flexibility and resilience has made it increasingly popular in earthquake territory or other areas where soils can shift. For larger diameters, the fusion technique requires a fusion machine, which might be problematic in cramped spaces. For smaller diameter pipes, a handheld device can be used to weld/melt the pipe lengths together. Mechanical couplings are available for HDPE, though some of these couplings may be made of PVC.

PEX is another form of polyethylene that retains HDPE’s flexibility and chemical resistance while providing resistance to higher temperatures for which HDPE is not suitable. It is coupled with either fusion techniques or mechanical crimp couplings. Due to its higher temperature ratings it was initially used in radiant and district heating system applications, but is now also beginning to be used more widely in water supply and gas distribution systems.

Ductile Iron (DI) has significantly higher tensile strength, making it more capable of handling higher pressures, crushes and hammer than PVC. DI does not lose strength at high or low temperatures as PVC does. Ductile iron is impermeable to hydrocarbons and other groundwater contamination unlike PVC or other plastic pipe. “There has been much debate over the durability and expected lifespan of each of these materials. The life of a pipe system depends on not only the material, but also the installation and the surrounding environment. All these types of pipe have been on the market for over 30 years, and while there are examples of pipe failures for each of them, this study did not find conclusive evidence to suggest that one material has a significantly different lifespan from the other. When properly designed and installed, pipe systems of any of these materials can be sufficiently durable to withstand many decades of services.”

3.6       Sewerage and Drainage

The use of plastics pipes for both pressure and a gravity sewer is extensive. In addition, there is rapid growth in the use of plastics liners for repair of old and leaking sewer installations.

Availability of large diameter plastics pipes at competitive prices gives design engineers an opportunity to select products on cost and performance basis. Long life expectancy, low maintenance requirements are major advantages in the use of plastics pipes for sewage and drainage applications.

As in water main pipe, HDPE is a comparable alternative to PVC pipe in sewer systems. HDPE sewer pipes are also available in diameters ranging from 4 inches to 36 inches, although for storm sewer, much of the demand is for 10 to 15 inch, while for sanitary 8 to 12 inch are popular diameters. At larger diameters, the major market share is held by concrete, primarily due to cost.

Prior to the 1960s most sewer systems were combined sewers, that is, carried both sanitary and storm water. The system had to be designed to carry large volumes of water during rain events, but otherwise the capacity was little used. In addition, when it did rain the flood of relatively fresh water often negatively impacted water treatment. Design changed so that by the mid 1960s sanitary and storm systems were designed and constructed separately. Storm sewers collect water from roof drains, parking lots and streets. Unlike sanitary sewers, storm wastewater is not typically treated and the flow is directly discharged into a receiving body of water.

Similar to water distribution use, PVC is dominant in the smaller size sewer pipe market with HDPE just beginning to seriously compete. These smaller lines are commonly used in the collection network of subdivisions. In this segment, the competing concrete pipe is non-reinforced concrete pipe in 8" and 10" sections. The smallest diameter reinforced concrete pipe is usually 12" pipe.

The flow formula for smooth pipe should be used to compute the gas flow rate through Polyethylene. It has been found that the Mueller formula for smooth wall pipe describes the flow characteristics of Polyethylene.

3.7       Plumbing

PVC pipes and fittings for plumbing and drainage applications is the choice of plumber’s word wide. Low cost, lightweight, long life expectancy usually for the life of the installation is the overwhelming advantages. PVC does not corrode internally or externally eliminating the possibility of pipe failures or blockages. Cross-linked polyethylene, polypropylene and Polyethylene pipes are used in hot and cold-water reticulation in domestic, commercial and industrial installations. Ease of installation using compression fittings is providing a cost advantage.

Polyethylene, like other plastics, has a thermal coefficient of expansion higher than metals. When subjected to a temperature change, unrestrained (not buried) polyethylene pipe will experience expansion and contraction.

The coefficient of thermal expansion/contraction for Polyethylene is 1.0 x 10^-4 in/in/°F. As a general allowance, 1" per 100' of pipe per 10°F change in temperature.

Forces due to thermal expansion and contraction can be significant. Proper system design should be used to account for the compressive and tension stresses that can be generated.

When pipe is used in pressure applications, the longitudinal stress created by the sum of the bending radius, internal pressure and other stress loads on the pipe should not exceed the material’s design stress rating. Severe but acceptable bends in polyethylene pipelines should be buried or properly restrained.

3.8       Agriculture, Irrigation & Drainage

A variety of alternatives to PVC are used both for water delivery and for drainage. Irrigation sprinkler, drip and drainage systems have long been available in HDPE and have significant advantages in resilience against compression, shovel attack and ground movement. Corrugated steel, concrete and HDPE are all competitive alternatives for drainage.  HDPE drainage pipe is now available in formulations with high-recycled content. Plastic pipe has carved a hunk of the huge market previously dominated by concrete and steel. Highway drainage is a fast growing market for HDPE.  Recently, the Corrugated Polyethylene Pipe Association initiated a third party certification system, which allows for increased acceptance of their product by the American Association of State Highway and Transportation Officials. Footing and under slab drains are all available in HDPE.

3.9              Agricultural and Rural

Water is a lifeline for all farming operations and the security of water is essential. Plastics pipes are available for the wide range of farming applications. Pressure pipes for irrigation, plant watering and potable water reticulation. Non-pressure pipes for irrigation, stock watering, micro-irrigation and general water reticulation systems.

Low cost, wide range of pipe sizes, flexible and easy to handle and transport are all advantages important to the farmers.

3.10     Industrial and Chemical

Corrosion resistance and resistance to attack by many industrial chemicals make plastics pipes the obvious choice for chemical plant installations. Like with all materials used in the construction of chemical plants care must be taken in selecting the correct plastics pipes and fittings that will withstand the operating conditions.

The wide range of polymers used in manufacture of plastics pipes and fittings provide a good range of products from which to select the appropriate material. PVC piping systems are widely used in water, wastewater and chemical transfer. Polyethylene piping systems are well suited to installation in difficult industrial situations. Their high strength and ease of installation also makes them ideal for compressed air reticulation.

    Electrical and Communications

PVC is ideally suited for telecommunication and power conduits due to its high impact strength, smooth internal bore and large range of diameters. Flexibility and corrosion resistance characteristics of PVC conduits make them ideal for a wide range of installation conditions.

High-density polyethylene (HDPE) is ideal for pipe lining and cable encasing, which makes it perfect for communications cables. Although polypropylene pipes are used mainly for plumbing and sewerage applications, they can also be effectively used as conduits.

INTRODUCTION OF POLYETHYLENE

1.1    introduction of Polyethylene

Since its discovery in 1933, polyethylene (also known as polythene) has grown to become one of the world’s most widely used and recognized thermoplastic materials . The versatility of this unique plastic material is demonstrated by the diversity of its use. The original Application for polyethylene (PE) was as a substitute for rubber in electrical insulation during World War II. Polyethylene has since become one of the world’s most widely utilized thermoplastics. Today’s modern polyethylene resins are highly engineered for much more rigorous applications such as pressure-rated gas and water pipe, automotive fuel tanks and other demanding applications. Polythene’s use as a piping material was first developed in the mid 1950’s. In North America, its original use was in oil field production where a flexible, tough and lightweight piping product was needed to fulfill all the needs of a rapidly developing oil and gas production industry. The success of polyethylene pipe in these installations quickly led to its use in natural gas distribution where a coil able, corrosion-free piping material could be fusion joined in the field to assure a “leak free” method of transporting natural gas to homes and businesses. Polyethylene’s success in this critical application has not gone without notice and today it is the material of choice for the natural gas distribution industry. Sources now estimate that nearly 95% of all new gas distribution pipe installations in North America that are 12” in diameter or smaller are polyethylene piping 

The performance benefits of polyethylene pipe in these original oil and gas related applications have led to its use in equally demanding piping installations such as potable water distribution, industrial and mining pipe, force mains and other critical applications where a tough, ductile material is needed to assure long-term performance. It is these applications, representative of the expanding use of polyethylene pipe that are the principal subject of this article. In the chapters that follow, we shall examine all aspects of design and use of polyethylene pipe in a broad array of applications. From engineering properties and material science to fluid flown and burial design; from material handling and safety considerations to modern installation practices such as horizontal directional drilling and/or pipe bursting; from potable water lines to industrial slurries, all these things have led to the growing use of polyethylene pipes in the world 

1.2              Features and Benefits of HDPE Pipe

When selecting pipe materials, designers, owners and contactors specify materials that provide reliable, long-term service durability, and cost-effectiveness. Solid wall polyethylene pipes provide a cost-effective solution for a wide range of piping applications including gas, municipal, industrial, marine, mining, electrical and communications duct applications. Polyethylene pipe is also effective for above ground, buried, trench less, floating and marine installations. According to David A. Willoughby, P.O.E., “…one major reason for the growth in the use of the plastic pipe is the cost savings in installations, labor and equipment as compared to traditional piping materials. Add to this the potential for lower maintenance costs and increased service life and plastic pipe is a very competitive product. 

Natural gas distribution was among the first applications for medium-density polyethylene (MDPE) pipe. In fact, many of the systems, currently in use, have been in continuous service since 1960 with great success. Today, polyethylene pipe represents over 95% of the pipe installed for natural gas distribution in diameters up to 12” in the U.S. and Canada. PE pipe has been used in potable water applications for almost 50 years and has been continuously gaining approval and growth in municipalities. The production, quality assurance and testing of PE gas pipes, including joints, are carried out according to international AWWA, NSF, and ASTM standards. The fear often expressed in the early days that HDPE would have insufficient resistance to the aromatics contained in natural gas (such as tetrahydrothiophene (THT), concomitant substances and condensates) has not been confirmed, either by laboratory tests, or by practical experience. Other material alternatives do not share PE’s advantages. For instance, there are about 23,000 fractures and corrosion failures of iron mains across the United Kingdom each year. Of these events, the majority are located and dealt with in a safe manner. However, on average, about 600 of these results in the leakage of gas into buildings and annually this results in 3 to 4 major incidents involving fire.

1.3       History of Polyethylene Pipe

The history of the polyethylene (PE) pipe began with early civilization's attempts to find a suitable transport medium that could move water and other fluids from one place to another. Concrete has, in some form or another, been around since the Assyrians, Babylonians and Egyptians, while steel was first patented in 1855. Plastic piping, on the other hand, beginning with polyvinyl chloride or PVC in 1926, dates back to the 1930s, when it was utilized for sanitary drainage. PE was first developed in 1933 as a flexible, low-density coating and insulating material for electrical cables.

HDPE, however, is quite a bit different material from the PE used in the 1930s. LDPE was discovered in 1935 and it was not until nineteen years later in 1954 that commercially available quantities of HDPE appeared on the scene. As a relative newcomer in the piping industry, PE is constantly making its way into applications normally reserved for the older piping technologies. Since the late 1950s and early 1960s, PE has made its way into every corner of our lives launching a multi-billion dollar industry. It is currently the largest volume plastic in the world. This is partly due to the fact that there are certain characteristics (or combinations of characteristics) of HDPE that make it an attractive alternative. Whether it is an issue of installing a new piping system or rehabilitating an existing system, there are certain requirements placed on the piping material: that it be simple to install, that it doesn't leak or cost a lot to maintain, and will last a very long time.

1.4       What is Polyethylene

Polythene resins are milky white, translucent substances derived from ethylene (CH₂=CH₂). Its chemical formula is [─CH₂─CH₂─]_n (where n denotes that the chemical formula inside the brackets repeats itself to form the long chains of plastic molecules).

n CH₂=CH₂       ¾¾¾¾¾®       [─CH₂─CH₂─]_n

When Hogan and Banks first created a reaction between ethylene and benzaldehyde using two thousand atmospheres of internal pressure, their experiment went askew when all the pressure escaped due to a leak in the testing container. On opening the tube, they were stunned to find a white waxy substance that looked a lot like some form of plastic. After repeating the experiment, they discovered that the loss of pressure was not due to a leak at all, but was a result of the polymerization process. The residue polyethylene (PE) resin was a milky white, translucent substance derived from ethylene (CH₂=CH₂). Polyethylene was produced with either a low or a high density.

Low-density polyethylene (LDPE) has a density ranging from 0.91 to 0.93 g/cm3 (0.60 to 0.61 oz/cu in). The molecules of LDPE have a carbon backbone with side groups of four to six carbon atoms attached randomly along the main backbone. LDPE is the most widely used of all plastics, because it is inexpensive, flexible, extremely tough, and chemical-resistant. LDPE is molded into bottles, garment bags, frozen food packages, and plastic toys.

High-density polyethylene (HDPE) has a density that ranges from 0.94 to 0.97 g/cm3 (0.62 to 0.64 oz/cu in). Its molecules have an extremely long carbon backbone with no side groups. As a result, these molecules align into more compact arrangements, accounting for the higher density of HDPE. is stiffer, stronger, and less translucent than low-density polyethylene. HDPE is formed into grocery bags, car fuel tanks, packaging, and, of course, piping.

1.5       Polyethylene Pipe

The history of the polyethylene (PE) pipe begins with early civilization's attempts to find a suitable transport medium that could move water and other fluids from one place to another. It is no secret that plastic is relatively a new kid on the block as a piping material. Concrete has, in some form or another, been around since the Assyrians, Babylonians and Egyptians, while steel was first patented in 1855. Plastic piping, on the other hand, beginning with polyvinyl chloride or PVC in 1926, dates back to the 1930s, when it was utilized for sanitary drainage. Polyethylene was first developed in 1933 as a flexible, low-density coating and insulating material for electrical cables. It played a key role during World War II -- first as an underwater cable coating and then as a critical insulating material for such vital military applications as radar insulations. Because of its lightweight, radar equipment was easier to carry on a plane, which allowed the out-numbered Allied aircraft to detect German bombers under difficult conditions such as nightfall and thunderstorms.

1.6       Polyethylene Time Line

1862 - Parkesine, the first synthetic plastic

1866 - Celluloid by John Wesley Hyatt

1891 - Rayon is used to make Cellophane

1900 - Celluloid is used for Film

1907 - Bakelite, the first thermosetting synthetic resin.

1918 - Polystyrene

1926 - PVC or Polyvinyl Acetate

1927 - Nylon - synthetic silk for stockings in 1939

1933 - Polyethylene

1935 - Low Density Polyethylene

1938 - Teflon

1951 - High Density Polyethylene

1957 - Velcro and Silly Putty

1.7              Life Cycle Cost Savings

For municipal applications, the life cycle cost of HDPE pipe can be significantly less than other pipe materials. The extremely smooth inside surface of HDPE pipe maintains its exceptional flown characteristics and butt fusion joining eliminates leakage. This has proven to be a successful combination for reducing total system operating costs.

1.8              LEAKS Free, Fully Restrained Joints HDPE

Heat fusion joining forms leak-free joints as strong as, or stronger than, the pipe itself. For municipal applications, fused joints eliminate the potential leak points that exist every 10 to 20 feet when using the bell and spigot type joints associated with other piping products such as PVC or ductile iron. As a result of this, the “allowable water leakage” for HDPE pipe is zero as compared to the water leakage rates of 10% or greater typically associated with other piping products. HDPE pipe’s fused joints are also self-restraining, eliminating the need for costly thrust restraints or thrust blocks while still insuring the integrity of the joint and the fl own stream. Notwithstanding the advantages of the butt fusion method of joining, the engineer also has other available means for joining HDPE pipe and fittings such as electro fusion and mechanical fittings. Electro fusion fittings join the pipe and/or fittings together using embedded electric heating elements. In some situations, mechanical fittings may be required to facilitate joining to other piping products, valves or other system appurtenances. Specialized fittings for these purposes have been developed and are readily available to meet the needs of most demanding applications.

1.9              Corrosion & Chemical Resistance

HDPE pipe will not rust, rot, pit, corrode, tube roulade or support biological growth. It has superb chemical resistance and is the material of choice for many harsh chemical environments. Although unaffected by chemically aggressive native soil, installation of PE pipe (as with any piping material) through areas where soils are contaminated with organic solvents (oil, gasoline) may require installation methods that protect the PE pipe against contact with organic solvents. Protective installation measures that assure the quality of the fluid being transported are typically required for all piping systems that are installed in contaminated soils

.

1.10          Fatigue Resistance and Flexibility HDPE

Pipe can be field bent to a radius of 30 times the nominal pipe diameter or less depending on wall thickness (12” HDPE pipe, for example, can be cold formed in the field to a 32-foot radius). Willoughby, D. A. (2002). Plastic Piping Handbook, McGraw-Hill Publications, New York.

1.11          Seismic Resistance 

The physical attributes that allow HDPE pressure pipe to safely ac commodate repetitive pressure surges above the static pressure rating of the pipe, combined with HDPE’s natural flexibility and fully restrained butt fusion joints, make it well suited for installation in dynamic soil environments and in areas prone to earthquakes or other seismic activity.

1.12          Construction Advantages HDPE

Pipe’s combination of lightweight, flexibility and leak-free, fully restrained joints permits unique and cost-effective installation methods that are not practical with alternate materials. Installation method such as horizontal directional drilling, pipe bursting, slip lining, plow and plant, and submerged or floating pipe, can save considerable time and money on many installations. At approximately one-eighth the weight of comparable steel pipe, and with integral and robust joining methods, installation is simpler, and it does not need heavy lifting equipment. Polyethylene pipe is produced in straight lengths up to 50 feet and coiled in diameters up through 6”. Coiled lengths over 1000 feet are available in certain diameters. Polyethylene pipe can withstand impact better than PVC pipe, especially in cold weather installations where other pipes are more prone to cracks and breaks.

1.13          Durability OF Polyethylene

Polyethylene pipe installations are cost-effective, have long-term cost advantages due to the pipe’s physical properties, leak-free joints, and reduced maintenance costs. The polyethylene pipe industry estimates a service life for HDPE pipe to be, conservatively, 50-100 years if the system has been properly designed, installed and operated in accordance with industry established practice and the manufacturer’s recommendations. This longevity confers savings in replacement costs for generations to come. Properly designed and installed PE piping systems require little on-going maintenance. PE pipe is resistant to most ordinary chemicals and is not susceptible to galvanic corrosion or electrolysis.

1.14          Hydraulically Efficient

For water applications, HDPE pipe’s Hazen Williams C factor is 150 and does not change over time. The C factor for other typical pipe materials such as PVC or ductile iron systems declines dramatically over time due to corrosion and tuberculation or biological build-up. Without corrosion, tuberculation, or biological growth HDPE pipe maintains its smooth interior `all and its flown capabilities indefinitely to insure hydraulic efficiency over the intended design life.

1.15          Temperature Resistance

PE pipe’s typical operating temperature range is from -40°F to 140°F for pressure service. Extensive testing at very low ambient temperatures indicates that these conditions do not have an adverse effect on pipe strength or performance characteristics. Many of the polyethylene resins used in HDPE pipe are stress rated not only at the standard temperature, 73° F, but also at an elevated temperature, such as 140°F. Typically, HDPE materials retain greater strength at elevated temperatures compared to other thermoplastic materials such as PVC. At 140°F, polyethylene materials retain about 50% of their 73°F strength, compared to PVC which loses nearly 80% of its 73°F strength when placed in service at 140°F [5]

As a result, HDPE pipe materials can be used for a variety of piping applications across a very broad temperature range. The features and benefits of HDPE are quite extensive, and some of the more notable qualities have been delineated in the preceding paragraphs.  

1.16     Ductility

Ductility is the ability of a material to deform in response to stress without fracture or, ultimately, failure. It is also sometimes referred to as trainability and it is an important performance feature of PE piping, both for above and below ground service. For example, in response to earth loading, the vertical diameter of buried PE pipe is slightly reduced. This reduction causes a slight increase in horizontal diameter, which activates lateral soil forces that tend to stabilize the pipe against further deformation. This yields a process that produces a soil-pipe structure that is capable of safely supporting vertical earth and other loads that can fracture pipes of greater strength but lower strain capacity. With its unique molecular structure, HDPE pipe has a very high strain capacity thus assuring ductile performance over a very broad range of service conditions. Materials with high strain capacity typically shed or transfer localized stresses through deformation response to surrounding regions of the material that are subject to lesser degrees of stress. Because of this transfer process, stress intensification is significantly reduced or does not occur, and the long-term performance of the material is sustained. Materials with low ductility or strain capacity respond differently. Strain sensitive materials are designed based on a complex analysis of stresses and the potential for stress intensification in certain regions within the material. When any of these stresses exceed the design limit of the material, crack development occurs which can lead to ultimate failure of the part or product. However, with materials like polyethylene pipe that operate in the ductile state, a larger localized deformation can take place without causing irreversible material damage such as the development of small cracks. Instead, the resultant localized deformation results in redistribution and a significant lessening of localized stresses, with no adverse effect on the piping material. As a result, the structural design with materials that perform in the ductile state can generally be based on average stresses, a fact that greatly simplifies design protocol. To ensure the availability of sufficient ductility (strain capacity) special requirements are developed and included into specifications for structural materials intended to operate in the ductile state; for example, the requirements that have been established for “ductile iron” and mild steel pipes. Similar ductility requirements have also been established for PE piping materials. Validation requirements have been added to PE piping specifications that work to exclude from pressure piping any material that exhibits insufficient resistance to crack initiation and growth when subjected to loading that is sustained over very long periods of time, i.e. any material that does not demonstrate ductility or strain ability. The PE piping material validation procedure is described in the chapter on Engineering Properties of Polyethylene.

1.17     Visco-Elasticity

Polyethylene pipe is a visco-elastic construction material [6]. Due to its molecular nature; polyethylene is a complex combination of elastic-like and fluid-like elements. As a result, this material displays properties that are intermediate to crystalline metals and very high viscosity fluids. The visco-elastic nature of polyethylene results in two unique engineering characteristics that are employed in the design of HDPE water piping systems, creep and stress relaxation. Creep is the time dependent viscous flown component of deformation. It refers to the response of polyethylene, over time, to a constant static load. When HDPE is subjected to a constant static load, it deforms immediately to a strain predicted by the stress-strain modulus determined from the tensile stress-strain curve. At high 12 introduction loads, the material continues to deform at an ever decreasing rate, and if the load is high enough, the material may finally yield or rupture. Polyethylene piping materials are designed in accordance with rigid industry standards to assure that, when used in accordance with industry recommended practice, the resultant deformation due to sustained loading, or creep, is too small to be of engineering concern. Stress relaxation is another unique property arising from the visco-elastic nature of polyethylene. When subjected to a constant strain (deformation of a specific degree) that is maintained over time, the load or stress generated by the deformation slowly decreases over time. This stress relaxation response to loading is of considerable importance to the design of polyethylene piping systems. As a visco-elastic material, the response of polyethylene piping systems to loading is time-dependent. The effective modulus of elasticity is significantly reduced by the duration of the loading because of the creep and stress relaxation characteristics of polyethylene. An instantaneous modulus for sudden events such as water hammer can be as high as 150,000 psi at 73°F. For slightly longer duration, but short-term events such as soil settlement and live loadings, the short-term modulus for polyethylene is roughly 110,000 to 120,000 psi at 73° F, and as a long-term property, the modulus is reduced to something on the order of 20,000-30,000 psi. As will be seen in the chapters that follow, this modulus is a key criterion for the long-term design of polyethylene piping systems. This same time-dependent response to loading also gives polyethylene its unique resiliency and resistance to sudden, comparatively short-term loading phenomena. Such is the case with polyethylene’s resistance to water hammer phenomenon, which will be discussed in more detail in subsequent sections of this article.

1.18          GENERAL

Polyethylene (PE) is a thermoplastic material produced from the polymerization of ethylene. PE plastic pipe is manufactured by extrusion in sizes ranging from ½" to 63". PE is available in rolled coils of various lengths or in straight lengths up to 40 feet. Generally small diameters are coiled and large diameters (>6" OD) are in straight lengths. PE pipe is available in many varieties of wall thicknesses, based on three distinct dimensioning systems:

• Pipe Size Based on Controlled Outside Diameter (DR)
• Iron Pipe Size Inside Diameter, IPS-ID (SIDR)
• Copper Tube Size Outside Diameter (CTS)

PE pipe is available in many forms and colors such as the following:

• Single extrusion colored or black pipe
• Black pipe with co extruded color striping

Black or natural pipe with a co extruded colored layer

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.