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Developments in plastics usage in underground pipes |
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AMI recently conducted a conference on Plastics in Underground Pipes in May 2009.
Some of the developments in pipe use and technology highlighted at the conference are:
Polyethylene pipes have been in use in North America since the 1950s when they were introduced in the oilfields. Dr Gene Palermo reviewed the issues for the industry including rapid crack propagation (RCP), which is a fast fracture of around 200 m/second with a sinusoidal path. The factors involved include internal pressure, wall thickness, temperature, pipe processing and material.
ISO 4437 is a standard for PE gas pipes incorporating RCP. The American Gas Association requested that this be included in the ASTM D 2513 standard. According to the Plastic Pipe Institute, there are 0.5 million miles of US water transmission pipes and 0.6 million miles of wastewater systems.
The cost of replacing one mile of water mains is around US$D56400 compared to US$24600 to repair (data from Corpro). There is a massive benefit in the carbon footprint of projects using trenchless technology (around 90%), partly due to the minimal traffic disruption and the shorter project duration. Costing of a sewer replacement project in the city of Troy gave around 25% savings using trenchless technology. There is an urgent need for rehabilitation of water mains pipes.
An average US city loses 17% of its potable water and this is still a priority for state funding. Insituform Technologies has reviewed the options including tight-fit HDPE, polyester reinforced PE and cured-in-place pipe (CIPP). More than 25,000 miles of CIPP has been installed in the last 38 years. There are two types of pipe liner - independent of the host pipe, and interactive (reliant on radial support from the outer pipe). The American Water Works Association (AWWA) has four classifications of trenchless liner products: non-structural (cement or epoxy/PU lining), semi-structural (CIPP, modified epoxy), and fully structural (sliplining, CIPP and polyester-reinforced PE).
Insitumain is in the latter class and is suitable for potable pressure pipe rehabilitation. It has a PE inner layer surrounded by layers of epoxy reinforced with polyester or glass fibre. In one project in Michigan there was a 61-97% increase in flow: the old iron pipe was cleaned and lined. HDPE pipe was used in a sliplining project - the pipe was temporarily shrunk during lining and then restored in situ. Trenchless technology is a key application for PE pipes from Chevron Phillips Chemical Co Performance Pipe.
Around 12,000 ft of 30in pipe was used to slipline an ageing iron pipe in Dallas. In King County, 42 in HDPE pipe was used to replace 30 in concrete. ASTM F1962 covers directional drilling of PE pipe: one project in Fort Wayne used 37,000 ft of 6 in and 8 in pipe by horizontal direct drilling (HDD). The gas industry in the US has installed 526,000 miles of polyethylene mains pipe. Sanitary sewer overflow is mainly due to pipe breakage or blockage. Around 70% of US sewerage pipe is now rehabilitated using trenchless technology. Ultraliner has used PVC and PE pipes in sliplining - the advantages are cost-efficiency and minimal disruption; the disadvantages can include a reduced flow.
A folded PE pipe can be placed inside an ageing pipe and then unfolded in situ: this is still quite rare in North America. Spiral wound PVC is used for pipe sizes ranging from 24-108in. HDPE grout-in-place pipe liner ranges from 8-144in; sheets are pre-manufactured and the grout quality is checked on site. Solid-wall HDPE pipe can be butt fused up to 63in in diameter according to KWH Pipe, and profile-wall or solid-wall pipe can be joined by handheld extrusion welding up to 132in diameter. Plastic pipe is very lightweight: 163ft of 60in Weholite pipe weighs in at less than 15000lb. It has a low resistance to flow so even in sliplining flow can increase. Corrosion resistance is
another benefit. Applications for large diameter pipe include sanitary sewer, canal enclosure, hydroelectric power and relining. Lyondellbasell has collaborated with KWH Pipe in producing pipes suitable for a nickel mine in Finland. PE 100 was used because of its resistance to cold, chemical resistance against 10% sulphuric acid, good flexibility, wear behaviour and weldability. Hostalen CRP 100 black was used for fresh water and solution transport. Irrigation pipe was made from LLDPE and corrugated drainage pipe was constructed from PE-HD.
Univation Technologies has a new HDPE material for pipes: single-reactor bimodal PE-100. It has worked with Qenos in Australia to produce this material, which has been tested in pipe up to 900mm in diameter. Polybutylene (PB) pipe was tested for longevity using standard methods and marketed with a 50-year lifespan: failures were mainly due to shear at fitting (67%) with 7% each for longitudinal and circumferential split. The main cause appeared to be oxidative degradation.
The University of Illinois has been examining failure of underground pipes. The three main causes are: ductile failure at high stress, brittle fracture at intermediate stress and environmental stress cracking. The researchers have concluded that extrapolation of accelerated aging can be misleading and need to be combined with field experience to generate realistic lifetime predictions.
The Polymer Competence Centre Leoben has examined failure behaviour of pressurised PE pipes and lifespan. Slow crack growth was the main cause. It has looked at new test methods to get results in a reasonable time from higher performance materials, quick material rankings can be obtained by cyclic fatigue tests. Pipecoil noted that some of the top causes of HDPE pipe failure are due to joints: the material itself is only responsible for 12.5%.
Risks can be reduced by cutting the number of joins (using longer pipe) and making sure that the pipe is round when it is fused. Pipe coilers and trailers have been developed to transport longer pipes and the company has equipment for straightening pipe using rollers on site. In 2002, an attempt was made to integrate the higher performing PE100 grades from Europe into North America, where PE3408 was prevalent. The ASTM standards had to be revised to include these new materials.
In 2006, PE3608/PE4710 was introduced to the North American pipe market. Polypipe has studied material selection and specification of pipe for different applications using resources such as the Plastic Pipe Institute Polyethylene Design Handbook and the AWWA Manual M55 (PE Pipe Design and Installation). Factors include pipe diameter and working pressure ratings. Utah in the western US is very dry and the Colorado river is a key resource. The Huntington-Cleveland Irrigation Company had targets of increasing the area under irrigation during dry periods, improving water delivery efficiency from 35% to at least 75%, and reducing salinity in the Colorado and adjacent rivers by 70,000 US tons pa.
ISCO Industries became involved in fabrication of the 145 miles of PE3408/3608 HDPE pressure-rated pipelines (pipe was supplied by WL Plastics, JM Manufacturing and Performance Pipe). There were issues with the high liquid load under the arid surface, which gave trenches a short lifetime and meant that concrete bearing pads under junctions would sink. However, the HDPE pipe was flexible enough to tolerate the instability during construction. Tri-Environmental has worked with AASHTO on a project to produce corrugated drainage pipe from recyclate: the pipe manufacturers participating were ADS, Blue Diamond Industries and Lane Enterprises. Tests were carried out using virgin resin mixed with either post-consumer (PCR) or industrial waste (PIR), varying the proportion of recyclate and overall formulation.
Results to date suggest that 50-year lifetimes are possible with up to 60 per cent PCR. Joining technology for pipes includes solvent welding as well as fusion technologies. IPS Corporation has been manufacturing solvent cements and primer for pipe for more than 50 years. Key applications are on PVC, cPVC and ABS pipes. The application determines the choice - for example, there are potable water grades. The surface is softened with primer and sufficient cement is added to ensure a tight joint.
Omya has new direct addition technologies for calcium carbonate in rigid PVC pipes, which is used in applications such as municipal sewer and drain, waste and vent (DWV). A new PVC dry-blend mixer unit allows the mineral to be added directly to the extruder, potentially saving US$130,000 pa for a sewage pipe producer. Cincinnati Extrusion has new Krosys energy saving technology for pipe production, best suited for high-output, large-diameter pipes. It can be used for extrusion of smooth mono- and multi-layer PE and PP pipes from 110-2,000mm with wall thickness up to 150mm. There is cooling of the pipe head in the tool of up to 25% and air and water cooling of the pipe inside and outside. The overall extrusion line can be much shorter and the vacuum and spray tanks can be smaller.
The latest development in PVC pipe production is the molecular orientation system developed by Molecor Tech in Spain. The material is almost metallic in behaviour in stress-strain tests and energy use is reduced during production compared to HDPE and conventional PVC pipes. The company is in partnership with Cincinnati Extrusion and Solvin. The industry is working on improving performance of pipe, reducing the carbon footprint and bringing long-term benefits to water and gas utilities.
(Source: Processingtalk) |
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