PE Manufacture
Worldwide Use
Polyethylene (PE) materials were initially introduced in the UK in 1933 and have progressively been used in the pipeline industry since the late 1930s. The physical properties of the PE materials have been continually upgraded with improvements in crack propagation resistance, increased hydrostatic pressure resistance, ductility and elevated temperature resistance resulting from developments in the methods of polymerisation. These developments have resulted in increased applications of PE in the pipeline industry in such areas as gas reticulation, water supply, mining slurries, irrigation, sewer and general industrial applications.
The well recognised attributes of high impact resistance, ease of installation, flexibility, smooth hydraulic flow characteristics, high abrasion resistance, and excellent chemical reagent resistance have resulted in PE pipeline systems being routinely specified and used in a wide range of applications in pipe sizes up to 1600 mm diameter.
Australian Use
PE pipe extrusion commenced in Australia in the mid-1950s where small diameter pipes were used in irrigation, rural and industrial applications.
The Australian Standards for PE pressure pipes were initially developed as ASK119 in 1962, and progressively improved and metricated as AS1159 PE Pipes for Pressure Applications in 1972 to include 1000mm diameter. These specifications provided the engineering basis for the approval and use of PE as approved pipeline materials in such applications as potable water and natural gas reticulation by gas and water utilities throughout Australia. Subsequent developments at Standards Australia resulted in the progressive development of Standard Specifications for PE compounds, PE gas pipes, PE fittings, irrigation systems, drainage, sewer and PE pipeline system installation guidelines.
Ongoing international developments in PE polymer grades led to review of these specifications, culminating in the publication of the PE Standards AS/NZS 4130 – PE Pipes for pressure applications, AS/NZS 4131 – PE Compounds for pressure pipe and fittings and AS/NZS 4129 – Fittings for PE pipes for pressure applications. These Standards have introduced the latest International developments and terminologies, and also provided uniform specifications throughout Australasia.
Polymer developments have resulted in PE80B materials, which have improved ductility and thermal stability and PE100 with improved strength. PE pipelines have now become the preferred solution in many applications where the unique properties of PE provides the most cost effective solution. Vinidex provide Australia wide manufacturing and supply services for PE pipeline systems in a wide range of end use applications for pipes up to 1000 mm diameter.
Pipe Extrusion
Vinidex PE pipes are extruded using sophisticated, highly controlled manufacturing processes and technologies. The PE raw materials used in extrusion are compounded into pelletised form containing precise amounts of polymer, lubricants, stabilisers, antioxidants and pigments for the specific end product application. The PE compound (1) is preheated to remove moisture and volatiles and is conveyed into the extruder by a controlled rate feeder (2). The extruder (3), consists of a single screw configuration which melts and conveys the PE material along the length of the extruder barrel. The design of the extruder barrel/screw is complex and takes into account the properties of the various types of PE material grades used in pipe applications. Various zones exist along the length of the screw and act to melt, mix, de-gas and compress the PE compound. External electrical heater bands along the barrel, together with the frictional heat generated as the PE material passes through the gaps between barrel and screw provide the energy needed to fully melt the PE compound materials. The total heat input is carefully controlled to ensure full melting of the PE without thermal degradation.
After passing through a mixing zone at the tip of the extruder, the PE melt then feeds into a head and die combination (4), where the melt is formed into the size of pipe required. The correct design of the head and die is essential to permit the production of pipe to Australian Standards requirements and to ensure retention of the physical properties of the PE materials. Once the molten PE pipe form leaves the die, it enters the sizing system (5), where it is initially cooled to the required dimensions. This is performed using an external vacuum pressure system where the pipe surfaces are cooled with refrigerated water sprays whilst in contact with precision machined sizing sleeves. The initially cooled pipe is then progressively passed through a series of water spray cooling tanks (6) to reduce the PE material to ambient temperature, and to finalise the pipe dimensions. As the pipe passes along the extrusion line, it is pulled along at a constant speed using a caterpillar track haul off (7). This haul off speed is closely co-ordinated with the speed of the extruder output using closed loop process controllers, to minimise built in stress in the pipe.
The pipe information of size, material, class, and batch data required by Australian Standards, or by specific client specification, is then marked on the pipe by an in-line printer (8) to provide continuous branding at specified intervals. The completed pipe is then cut to standard or required length by an in-line saw (9), and then packed into stillages, or for large diameter pipes stored (10). Small diameter pipes are either cut to standard length, or coiled (11), and the finished coils are strapped in standard coil sizes.
