Ductile iron pipes are pipes made from ductile iron castings commonly used for the transmission and distribution of drinking water. This type of pipe is a direct development of the previous cast iron pipe, which has been replaced. The ductile iron used to produce pipes is characterized by the spheroidal or nodular properties of graphite in iron. Typically, pipes are produced using centrifugal casting in metal molds or lined resins. Internal protective coatings and external coatings are often applied to ductile iron pipes to inhibit corrosion: standard internal layers are cement mortar and a standard external layer including bonded zinc, asphalt or water-based paint. In a highly corrosive environment, loose polyethylene coating (LPS) for pipe wrapping can also be used. The hope of living an unprotected ductile iron pipe depends on the presence of corrosive soil and tends to be shorter where the soil is highly corrosive. However, a life span of more than 100 years has been estimated for ductile iron pipelines installed using "rolling practice evolved", including the use of properly installed LPS (polyethylene wrapping). Environmental impact studies of ductile iron pipes have different findings on emissions and energy consumed. The ductile iron pipes manufactured in the United States have been certified as sustainable products by the Institute for Market Transformation to Sustainability.
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Dimensions
The ductile iron pipe is sized in accordance with the dimensionless term known as Pipe Size or Nominal Diameter (known by its French abbreviation DN). This is roughly equivalent to the internal diameter of the pipe in inches or millimeters. However, it is the external diameter of the pipe that is constantly maintained between changes in wall thickness, to maintain compatibility in joints and fittings. As a result, the internal diameter varies, sometimes significantly, from its nominal size. The size of the nominal pipes varies from 3 inches to 64 inches, with an increase of at least 1 inch, in the United States.
The pipe dimensions are standardized to the incompatible AWWA C151 (US Standard Unit) in the United States, ISO 2531/EN 545/598 (metric) in Europe, and AS/NZS 2280 (metric) in Australia and New Zealand. Although both metrics, Europe and Australia are not compatible and pipes with identical nominal diameters have very different dimensions.
North America
Pipe dimensions according to American AWWA C-151
Europe
The European pipes are standardized to ISO 2531 and derived specifications EN 545 (drinking water) and EN 598 (waste). The European pipe is approximately roughly in line with the internal diameter of the pipe, following the internal layer, to the nominal diameter. ISO 2531 maintains dimensional compatibility with older German cast iron pipes. Older British pipes, however, that use an incompatible imperial standard, BS 78, require a piece of adapter when connecting to a newly installed pipe. Incidentally, British harmonization with European pipe standards occurs at about the same time as the transition to ductile iron, so almost all cast iron pipes are imperial and all ductile pipes are metric.
Other European standards provide specifications on more dedicated products:
EN 15655: 2009 - Pipes, ductile iron fittings and accessories - Internal polyurethane coating for pipes and fittings - Requirements and test methods
EN 877: 1999/A1: 2006 - Pipes and castings, connections and accessories for water evacuation of buildings - Requirements, test methods, and quality assurance
CEN/TR 15545: 2006 - EN 545 usage guide
CEN/TR 16017: 2010 - EN 598 usage guide
EN 877: 1999 - Pipes and castings, connections and accessories for water evacuation of buildings - Requirements, test methods, and quality assurance
EN 877: 1999/A1: 2006/AC: 2008 - Pipes and iron fittings, their connections and accessories for water evacuation of buildings - Requirements, test methods and quality assurance
EN 598: 2007 A1: 2009 - Ductile iron pipes, fittings, accessories and connections for sewerage applications - Requirements and test methods
EN 12842: 2012 - Ductile iron equipment for PVC-U or PE piping systems - Requirements and test methods
CEN/TR 16470: 2013 - Environmental aspects of ductile iron pipe systems for water and sewage applications
EN 14628: 2005 - Pipes, ductile iron fittings and accessories - External polyethylene coating for pipes - Requirements and test methods
EN 15189: 2006 - Ductile iron pipes, fittings and accessories - External polyurethane coatings for pipes - Requirements and test methods
EN 14901: 2014 - Ductile iron pipes, fittings and accessories - Epoxy coating (heavy duty) of ductile iron fittings and fixtures - Test requirements and methods
EN 969: 2009 - Ductile iron pipes, fittings, accessories and connections for gas pipelines - Requirements and test methods
EN 15542: 2008 - Pipes, ductile iron fittings and accessories - External mortar cement layer for pipes - Requirements and test methods
EN 545: 2010 - Ductile iron pipes, fittings, accessories and connections for piped water - Requirements and test methods
EN 14525: 2004 - Large melt clutch and ductile iron flange adapter for use with pipes of various materials: ductile iron, Gray iron, Steel, PVC-U PE, Fiber-cement
Australian Australia & amp; New Zealand
Australian and New Zealand pipes are up to independent specifications, AS/NZS 2280, which are not compatible with European pipes even though the same nomenclature is used. Australia adopted at the starting point of the British cast iron casting standard of the UK 78 standard, and when it was retired on the adoption of British ISO 2531, rather than similar harmonization with Europe, Australia voted for 'soft' conversion from imperial unit to metric, published as AS/NSZ 2280 , with outside physical diameter remaining unchanged, allowing continuity of manufacture and backward compatibility. Therefore, the inner diameter of the lined pipe is very different from the nominal diameter, and the hydraulic calculations require knowledge of the pipe standards.
Maps Ductile iron pipe
Joints
The individual length of the ductile iron pipe is joined either by flanges, couplings, or some form of tap and socket settings.
Flanges
Flanges are flat rings around the ends of pipes that are paired with equivalent flanges from other pipes, both held together by bolts usually passed through holes drilled through flanges. A formable gasket, usually an elastomer, is placed between the raised faces on the mating flanges that give the seal. Flanges are designed for a large number of different specifications due to dimensional variations in pipe size and pressure requirements, and due to the development of independent standards. In the US flange, either welded or welded to the pipe. In European market flanges are usually welded into pipes. In the US flanges are available in a standard 125 pound bolt pattern as well as a 250 lb (and heavier) bolting pattern (steel bolt pattern). Both are usually rated 250 psi (1,700 kPa). The joints are rigidly flexed and can withstand tension and compression as well as limited shear and bending rates. It can also be dismantled after assembled. Due to the stiffness of the joints and the risk of excessive bending moments being imposed, it is recommended that flat piping is not buried.
Current flange standards used in the water industry are ANSI B16.1 in the US, EN 1092 in Europe, and US/NZS 4087 in Australia and New Zealand.
Spygots and sockets
Spigots and sockets involve the tip of a normal pipe, a spigot, which is inserted into a socket or bell from another pipe or fitted with a seal made between the two inside the socket. Sphinces and normal sockets do not allow direct metal contact with metal with all the power transmitted through elastomer seals. They can consequently flex and allow several degrees of rotation, allowing the pipe to shift and eliminate the pressure caused by ground motion. A reasonable consequence is that spigots and uncontrolled socket connections essentially do not emit compression or tension along the pipe axis and are slightly sliding. Any bend, tees or valves therefore require blocked or, more commonly, thrust blocks, which transmit forces as compression to the surrounding soil.
A large number of different sockets and seals exist. The most modern is 'push-joint' or 'slip-joint', in which sockets and rubber seals are designed to allow the pipe spigot to become, after lubrication, simply pushed into the socket. Push the joints stay exclusive design. Also available gasket locking system. This gasket locking system allows the pipe to be pushed together but does not allow the connection to be released without the use of special tools or torches on the gasket.
The tap pipe and the earliest cast iron socket are connected by filling the socket with a mixture of water, sand, iron powder and sal-ammonia (ammonium chloride.) A gasket ring is pushed into the tap-spin socket to hold the powdered mixture into the socket by means of caulking and then pointed. It takes several weeks to set up and produce a really stiff connection. Such piping systems are often seen in nineteenth-century churches in heating systems.
Age and corrosion
In the late 1950s, ductile iron pipes were introduced to the market, displaying higher strength and similar corrosion resistance compared to cast iron. According to a 2004 study, the expected duration of 100 years is likely for ductile iron pipes, based on test results, field inspections and operations in service for 50 years. In 2012, the American Water Works Association reported that ductile iron pipes on benign ground or mounted on more aggressive soils using "evolving spawn practices" have a life expectancy of up to 110 years, based on a national water pipeline analysis in the US.
Like most iron materials, ductile iron is susceptible to corrosion, therefore its useful life depends on corrosion impact. Corrosion can occur in two ways in a ductile iron pipe: graphitization, the discharge of iron content through corrosion leading to generally weakened pipe structures, and pitting corrosion, which is a more local effect also causes weakening of the pipe structure.
Over the past 100 years, the average thickness of iron pipes has declined as metal strength increases, through better metallurgical advances and casting techniques.
Methods to reduce corrosion
The corrosion potential, which causes pipe failure, is significantly influenced by soil corrosivity. Unprotected pipes in highly corrosive soils tend to have shorter life spans. The lifespan of the ductile iron pipe is installed in an aggressive environment without proper protection possible between 21 and 40 years. The introduction of corrosion mitigation methods for ductile pipes, including the use of polyethylene sleeving, can reduce corrosion by controlling the effects of corrosive soil on piping.
In the United States, the American National Standards Institute and the American Water Works Association have established standards for the use of polyethylene sleeving to protect ductile iron pipes from corrosion effects. A 2003 report by researchers from the National Research Council of Canada notes that "good and bad performance" of polyethylene coatings has been reported. However, a study at the Ductile Iron Pipe Research Association test site in Florida found that, compared to uncoated pipe exposed to corrosive environments, the pipes wrapped in loose polyethylene coatings were "in excellent condition". Based on a 2005 meta-analysis of 1,379 pipe specimens, loose polyethylene coatings were found to be very effective at reducing corrosion. The only environment in which the analysis found that polyethylene derailment did not provide effective corrosion control was for a "unique heavy" environment, a rare but highly corrosive classification of the environment. The analysis found that a 37-year lifespan can be expected in this "unique" environment.
Pipes manufactured under International Standards for Standardization (ISO) standards are usually coated with zinc, to provide corrosion protection. In more aggressive soil samples, polyethylene coating is mounted on a zinc-plated pipe to provide additional protection.
Cathodic protection can also be used to prevent corrosion and is likely to be recommended by corrosion engineers for pipes in corrosive soils in addition to external dielectric coatings.
Engineers and water authorities in the United States are divided into the use of different coatings or cathodic protection. Mixed results have been found for all protection methods. However, this may be due to the influence of variations in land vacancies and local temperatures or by damage occurring during installation, which may affect the effectiveness of the protective layer.
Internal coating
Ductile iron pipes are somewhat resistant to internal corrosion in drinking water and less aggressive waste forms. However, even where the loss of pipe material and consequently the reduction of the pipe wall is slow, the deposition of corrosion products on the internal pipe wall can reduce the effective internal diameter. Various coatings are available to reduce or eliminate corrosion, including cement mortar, polyurethane and polyethylene. Of these, the cement mortar layer is by far the most common.
Polyurethane (PUR)
Polyurethane is an option offered as an internal layer for ductile iron pipes in lieu of cement mortar. However, since PUR only provides passive protection, it is very important that the coating is not damaged during handling and installation. The manufacturer will establish strict handling, transport and installation procedures to ensure that the PUR layer is protected. If the pipe undergoes a Polyurethane elasticity deformation, in some situations allows the coating to remain intact. Corrosion Expert
Polyurethane coatings were first used in 1972. Compared to other layers, internal polyurethane layers exhibit high resistance to a variety of different media such as drinking water, wastewater, de-mineralized water, industrial water and gases, as well as aggressive solutions such as sulfuric acid.
Polyurethane is a thermosetting plastic without solvents, with a three-dimensional molecular structure connected to provide mechanical stability. The polyurethane layers used for internal coating have the following standard properties standardized by EN 15655: 2009 (Ductile iron pipes, fixtures and accessories - Internal polyurethane linings for pipes and fittings - Test requirements and methods).
Mortar cement
The main form of the coating for water applications is the mortar cement applied during manufacturing. Mortar cement consists of a mixture of cement and sand with a ratio between 1: 2 and 1: 3.5. For drinking water, portland cement is used; for waste is common to use sulfate resisting or high alumina cement.
The cement mortar layer has been found to dramatically reduce internal corrosion. The DIPRA survey has shown that the Hazen-Williams factor of the cement layer remained between 130 and 151 with only a slight reduction with age.
External layer
Unsafe ductile iron, just like cast iron, is intrinsically resistant to corrosion in most, though not all, soils. However, due to the frequent lack of information about soil aggressiveness and to prolong the life of buried pipe installation, ductile iron pipes are generally protected by one or more external layers. In the US and Australia, loose polyethylene release is preferred. In Europe, the standard recommends a more sophisticated system of directly bonded zinc coated by a finishing layer used in conjunction with polyethylene sleeving.
Polyethylene Sleeving Loose (LPS)
The loose polyethylene coating was first developed by CIPRA (since 1979, DIPRA) in the US in 1951 for use on highly corrosive soils. It was used more widely in the US in the late 1950s and first worked in England in 1965 and Australia in the mid-1960s. Loose Polyethylene Sleeving (LPS) remains one of the most cost effective corrosion protection methods available today with a proven track record for reliability and effectiveness.
LPS consists of loose sleeves of polyethylene that actually wrap the pipe, including the bells of each joint. The sleeving inhibits corrosion with a number of mechanisms. Physically separate the pipe from the soil particles, preventing direct galvanic corrosion. By providing a watertight barrier, the arm also inhibits oxygen diffusion to ductile iron surfaces and limits the availability of electrolytes that will accelerate corrosion. This provides a homogeneous environment along the pipe surface so that corrosion occurs evenly over the pipe. The sleeve also limits the availability of nutrients that can support sulphate reducing bacteria, inhibiting microbial induced corrosion. LPS is not designed to be completely impermeable but rather to limit the movement of water to and from the surface of the pipe. Water is present under the arm and in contact with the pipe surface is rapidly deoxygenated and depleted of nutrients and forms a stable environment where limited further corrosion occurs. The improperly installed sleeves that continue to allow free flow of groundwater are ineffective in inhibiting corrosion.
The polyethylene arm is available in a number of materials. The most common contemporary compositions are linear low-density polyethylene films requiring a thickness of 8 mil or 200 μm thickness and high density polyethylene cross-laminate films requiring only 4 mil or 100 μm thickness. The latter may or may not be reinforced with an incognito layer.
Polyethylene sleeving does have its limitations. In European practice, its use in the absence of additional zinc and epoxy protective coatings is not recommended where natural soil resistivity is below 750 ohm/cm. Where resistivity is below 1500 ohms/cm and where the pipe is installed at or below the water table, where there is additional artificial soil contamination and especially the longer wild currents it is recommended to be used in addition to zinc and epoxy coating. Because the susceptibility of polyethylene to UV degradation, sleeving, or armpits should not be kept in the sun, although carbon pigments included in sleeving may provide limited protection.
Polyethylene sleeving is standardized according to ISO 8180 internationally, AWWA C105 in the US, BS 6076 in the UK and US 3680 and US 3681 in Australia.
Zinc
In Europe and Australia, ductile iron pipes are usually made with a zinc coated layer of asphalt, polymer, or epoxy. EN 545/598 mandates a minimum zinc content of 200 g/m 2 (at 99.99% purity) and an average final coating thickness of 70 Âμm (with local minimum 50 Âμm). AS/NZS 2280 mandates a minimum zinc content of 200 g/m 2 (with local minimum of 180 g/m 2 at 99.99% purity) and a minimum settlement average of thickness layer 80 Âμm.
There is no current AWWA standard available for bonded coatings (zinc, coal tar epoxy, ribbon wrap systems as seen on steel pipes) for ductile iron pipes, DIPRA does not support bonded coatings, and AWWA M41 generally finds them unfavorable, recommends they are used only in relation to cathodic protection.
bituminous coating
Zinc coating is not generally used in the US. To protect the ductile iron pipe prior to installation, the pipe is supplied with a thick layer of asphalt 1 mile or 25 Âμm. This coating is not intended to provide protection after the pipe is installed.
Water-based pipe layer
Water-based pipe coating, is an eco-friendly coating applied on the inside & amp; the outer diameter of the ductile iron pipe. They protect against corrosion from the outside and inside, and also protect the product from contamination. The coating is an emulsion manufactured using asphaltene and water primarily, with other raw materials according to the manufacturer's specifications.
They began to be used in the early 1990s, replacing coatings based on harmful and environmentally harmful solvents, such as benzene, toluene, hexane and other volatile organic compounds.
Industry and market association
In the United States, the Ductile Iron Pipe Research Association represents the producers of ductile iron pipes. This association provides research and promotes the use of ductile iron pipes in utility projects (water and sewerage), focusing on its strength, recycling and lifecycle costs compared to alternative products such as PVC. The US industry is also represented by the National Association of Pipe Fabricators. Outside the US, the ductile iron pipe industry is supported by associations including the European Association for the Ductile Iron Pipe System.
After the 2008 financial crisis, the whole plumbing industry, sales declined in the US as the city government delayed the replacement of waterways and the reduction of new home construction. According to a report published by The Freedonia Group in 2011, the economic recovery from the 2008 crisis will likely expand the market share of ductile iron in large diameter pipe markets.
Environment
Ductile iron pipes in developed countries are usually produced exclusively from recycled materials including scrap steel and recycled iron. Pipes can be recycled after use. In terms of environmental impact, several studies have compared the impact of ductile pipes on the environment with other pipe materials. A study by Jeschar et al. in 1995 compared to energy use and carbon dioxide emissions (CO2) produced in the manufacture of pipes of various materials including concrete, ductile iron, cast iron and PVC, based on pipes with a nominal diameter of 100mm to 500mm. The energy consumed in the manufacture of ductile iron pipes is 19.55 MJ per kg and the volume of emissions released during manufacture is 1,430 kg CO2 per kg, compared to 68.30 MJ per kg of energy and 4,860 kg CO2 per kg of emissions for PVC pipes; 1.24 MJ per kg and 0.148 kg CO2 per kg for concrete pipes of the same diameter. Another study the following year, by Forschungsinstitut fÃÆ'¼r Chemie und Umwelt, had similar findings. However, it also considers the lifetime of the pipe. The study found an increase in environmental performance for ductile iron pipes in terms of energy consumed and emissions generated during manufacture due to longer life. A more recent study, published in August 2012, by Du et al., Performed a life cycle analysis on six types of materials used for water and wastewater pipes, including ductile iron, PVC, high-density polyethylene (HDPE) and concrete. They found that in diameter <= 24 in, ductile iron pipes had the highest "global warming potential" based on emissions from manufacturing, transportation and installation. In larger diameters,> = 30 in, ductile iron pipes have a lower "global warming potential", whereas PVC has the highest. According to a 2008 study by Koo et al., Ductile iron pipes have the lowest impact on natural resource depletion, compared to HDPE pipes and PVC pipes. In November 2012, the ductile iron pipes manufactured in the United States received certification as a sustainable product of the Institute for Market Transformation for Sustainability.
Note
External links
- The Official Website of the Ductile Iron Pipes Research Association
- Jindal Saw Official Website - Ductile Global Iron Manufacturer
- Official Website of the Australian Water Services Association
- Official Website of PENTAIR AIR SOLUTION
- Ductile Iron Pipe and Fittings Range
- SAINT-GOBAIN PAM Official Website
- The Official Website of vonRoll hydro AG - Swiss Supplier for Ductile Iron & amp; Equipment
- Official Web Site Electrosteel Castings Ltd. - Indian Supplier for Ductile Iron & amp; Equipment
- The Official Website of China National Building Group Corporation (CNBM). - Chinese Suppliers for Ductile Iron & amp; Equipment
- Official Website of Lipetsk Pipelines Svobodny Sokol - Russian Supplier for Ductile Iron Pipes and Fittings
Source of the article : Wikipedia
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