Plastics in Underground Pipes

Plastics are extensively used in Underground Pipes as discussed at the May 2008 AMI conference in Houston, Texas. With renewal and rehabilitation of aging systems, this is a sizeable market. Earthquakes cause devastating damage: in 1994 in the Northridge quake, there were 1500 water pipeline failures due to tectonic movement and wave passage. Camille Rubeiz of the Plastic Pipe Institute outlined the benefits of ductile materials such as PE and the use of flexible joints to minimise disruption. In the Tsunami in Thailand, many PE pipes were exposed but performed well and being flexible, conformed to the new lay of the land. Gene Palermo has reviewed the latest material developments for plastic pipes. Bimodal polyethylene has been used in Europe for some time where it is known as PE100. It has more recently arrived in North America where it is known as PE 4710: it has high stress crack growth resistance and very high rapid crack growth (RCP) resistance. ISO4437 covers RCP and the ASTM is developing its own standard. WL Plastics described PE 4710 as having higher pressure and flow capacity reducing material and operating costs. There is a newer MDPE for gas applications (PE 2708). Reinforced thermoplastic (RTP) composite pipe comprises and outer and inner layer of HDPE with an intermediate reinforcement such as glass fiber. It can be used at pressures up to 1500 psig. KWH Pipe has extensive expertise in PE pipes, with solid wall pipe from ¾" to 63" diameter and profile (hollow) walled pipe from 18" to 132". Profile wall pipe can be buried from 2-35 feet and is field welded: it is an alternative in low pressure applications to steel, GRP and concrete with the advantage of low weight. The AB-Hayat Kerman Industrial Group (Iran) has developed software to predict structural integrity of polyethylene pipe in underground applications. The software has been developed to assist in water pipeline development. Ingenieurbüro Röper GmbH has developed an EPS foam bedding system to protect pipes during installation, which is particularly effective in twin-bedding projects. A complete cover can be used to protect the pipe when backfilling. Pipe Coil Technology has technology to reduce ovality and preserves pipe. Factors affecting ovality are temperature, bend radius, wall thickness and coil torque. Introducing controlled ovality into pipe in the opposite plane prior to coiling can be effective. Wavin was established as a PVC pipe producer by the Dutch water authority in 1955. PVC has particularly good chemical resistance and can protect water being transported through contaminated soil. Wavin has just has licensed oriented PVC (O-PVC) pipe production technology to Amanco Colombia to produce lower weight, stronger pipes. Ipex has bell and spigot PVC "Terrabrute" pipe for trenchless technology with a minimum pressure rating of 235 psi and very high pull strength. Reamers and pull heads are used to drag the pipe into place and joining and installation technology have been established and tested. The pipe is used for sewer and water applications. PA 11 gives high pressure performance (up to 200 psig) and has high chemical resistance. It is also being used as liner to rehabilitate existing pipe. Arkema has been testing its Rilsan material over 6 years in gas pipelines. More than 15,000 miles have been installed in Australia since the mid 1970s. In the US it is awaiting government approval to move to full commercialization. Steven Cianfarini has examined gas mains replacement options. UV cured liners can rehabilitate a 12", 400 foot cast iron pipe in a few hours. Chicago is planning to use nearly 10 miles of plastic pipe in gas mains, either as liner or direct burial. There are also projects using plastic pipe to transport landfill gas. Thermoplastic lining systems are commonly used in pipeline rehabilitiation, such as those from Agru America. In Germany there is estimated to be leakage in the sewer mains of 100 billion cubic meters per year with around 55 billion euros required for repairs. 7% is due to corrosion by chemicals such as sulfuric acid. PE and PP are effective linings in this situation. Systems have been tested worldwide including a deep tunnel system in Singapore where an HDPE liner was installed. Oren Lever of Central Plastics (now part of the Georg Fischer Group) talked about designing piping systems using Finite Element Analysis to predict performance during manufacturing and after installation. It can be used to "determine the location of stress concentrations, displacement due to external loads, minor flow losses through any fitting, or any other physical effect". Ernest Lever has looked at lifetime prediction by examining the stress intensification factors in fittings: the critical factors are material properties, good manufacturing and knowledge of the behavior of different designs under load. McElroy Manufacturing provides pipe joining equipment worldwide. Its latest HDPE butt fusion technology improved joint rates for 20-24" pipe from 10-16 to 18-20/10 hour day. Fast Fusion is a company with mobile fast HDPE pipeline joining technology designed to limit the stress on the pipe during the procedure. The pipe is offloaded and the machine moves along lifting it and forming the joints. Manufacturing is critical to pipe integrity. Cincinnati Extrusion has a variety of equipment for both PVC, PP and PE pipe including corrugated and foam core pipe. The Argos extruders are used for O-PVC pipe. Molecor is another company with O-PVC pipe production technology. Plastics are well established in subsurface systems and can extend the lifespan of existing systems, reducing cost in rehabilitation and replacement of more traditional materials. Higher performance thermoplastics have been developed and this will drive market growth with expansion into new sectors.