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
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.
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.
A wide selection of HDPE pipe can meet the needs for any oil field applications.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.
Polyethylene has products specifically for the oil and gas industry for gas gathering, crude transmission, water lines and auxiliary lines.
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.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.
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.”
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.
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.
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.
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.
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.