Pressure Pipes 2007 International Conference: Plastic Pipes under Pressure

Pressure Pipes are used in many areas from gas, potable water, sprinkler systems and sewage transport to high end applications such as the chemical industry and oilfield. Plastics are generally lighter, more flexible and less susceptible to corrosion than traditional materials. New grades of plastics are being developed and tested for pressure pipe use and new designs and manufacturing technologies are arising at the same time. Some pipes are single layer; others are multilayer sometimes with the same plastic in different forms to reinforce the pipes. For example, an HDPE core might be wound with an HDPE fibre and coated.
The environment for pipes can vary from domestic interior to exterior, to burial in soil and underwater pipelines. The pressures that pipes are subjected to cover different ranges and may be constant or cyclic. In the case of buried and undersea pipes the pressures are external as well as internal. Drinking water pipes must not contaminate the water supply and there are additional regulations in this area.
Hydrostatic pressure testing is used to predict the safe performance window for new pressure pipes. Testing during pipe development has shown that failure occurs in a variety of ways: ductile failure (ballooning through the weakest point in the pipe wall), brittle mechanical failure (slow crack propagation), and chemical degradation of the pipe material that makes the material brittle and liable to split, often accompanied by discoloration. Specific standards cover critical pipe properties such as creep rupture strength and resistance to stress cracking and rapid crack propagation. (Due to the pressures, cracks in pressure pipes can grow very quickly – rates of propagation of hundreds of meters per second have been recorded.) The standards and testing requirements for pressure pipes are very extensive and ensure safety of pressure pipes in use.
Pipe extruders aim for uniform wall thickness and select cooling methods that minimise residual stresses. New developments by the machinery manufacturers and expert companies working in this field.

Polyethylene (PE) is the dominant material in this market (including HDPE, MDPE, crosslinked PE (PEX), and raised temperature resistant PE (PE-RT)). Historically the density of PE was used as an indication of its strength. Now there are International Standards that give more precise indications of hydrostatic strength, thus PE100 has a minimum required strength (MRS) of 10 MPa and PE80 of 8 MPa. A variety of other plastics are also used in pressure pipes including polyvinyl chloride (PVC) and polypropylene (PP). Higher performance polymers are found in harsher environments, such as polyamide 11, PVDF, ABS and glass-reinforced plastic (GRP).

Additives are used in pipe compounds for a variety of reasons. Colorants are used to code pipes by their contents. Antioxidants are used to slow degradation. Anti-UV agents are needed for above ground exposure. Heat stabilizers are used in high temperature environments and to stabilize materials during processing. Process aids can assist the flow of viscous plastics and improve efficiency.

AMI is pleased to announce a new international conference for the plastic pipes industry. Pressure Pipes 2007 will be held at the Renaissance Hotel, Düsseldorf, Germany, 25-27 June 2007. The conference aims to cover developments in materials, processing technology and applications of Pressure Pipes.

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