Pipes with diameter from 500 mm to 2000 mm are typically considered as large diameter PE pipes. In the past, these pipes would have been manufactured from ductile iron or glass-reinforced plastics (GRP) but they are now increasingly specified in PE. As per Borouge, large diameter PE pipes are being used for many applications, including: • Water and raw water transportation mains – typical of these is the 8.5 km of 710 mm diameter main laid by Abu Dhabi Distribution Centre (ADDC) to Residence City in Abu Dhabi • Irrigation water mains, which can be up to 1000 mm diameter • Cooling water supply lines to industrial plants – a good example is the 25 km of 1600 mm pipe installed at the Borouge 2 site in Ruwais, Abu Dhabi • Sea water intake and outfall lines • Transportation of mining slurries – in countries with a large mining industry such as South Africa and Australia these pipes can be 1000 mm or more in diameter • Desalination plant intakes and outflow pipes – a good example is the 1200 mm intake and outflow pipes used at Khorfakkan, Sharjah • Sewage and treated effluent pumping mains Usually, these large pipelines are critical elements within a network or an industrial complex and premature failures will be extremely costly. Therefore, it is even more important that only fully tested and approved precompounded PE materials such as BorSafe™ HE3490-LS are used in these projects. It has been demonstrated that large diameter thick walled pipes made from these compounds fully comply with the standards and are equal in performance to smaller diameter PE pipes. In many cases for large diameter projects, the cost of the PE pipe will be higher than the equivalent ductile iron or GRP pipe and therefore it is essential that the client is made aware of the “Whole Life Cost” benefits of PE. By making use of narrow trenches or trenchless techniques such as insertion or directional drilling, the overall project costs can be substantially lower using PE. It is also well proven that the operational and maintenance costs of modern PE systems are lower than those of ductile iron or GRP pipes. Third generation PE100 materials such as BorSafe HE3490-LS can also cope better with operating at higher ambient temperatures than other materials. Since the ISO specification allows the designer to use of the actual pressure characteristics of the material, the pressure reduction factors used in the design can be lower, which means that a thinner wall pipe can be used. In supplying large diameter PE pipe projects, pipe manufacturers are required to keep up with the speed of installation. It is extremely important that the extruder maintains a consistently high output rate. The quality and homogeneity of the melt at a relatively low melt temperature (circa. 190°C) is extremely important for consistent output of good quality pipe. In general, extruders with the latest design of barrier flight screw and with grooved feed bushes tend to provide the best melt homogeneity. The lower melt temperature also helps with pipe dimensioning. In the die head, it is also important to maintain the same low even temperature distribution through the complete melt. For producing high quality large diameter PE pipes, pre-drying the pre-compounded material is even more important for thick walled pipe production as it is very difficult for any trapped water vapour to vent. In addition, a constant feed of warm PE material will improve the melt consistency and throughput of the machine. The speed and quality of cooling in a well designed vacuum calibration system is critically important in reducing wall. Large diameter thick walled PE pipes are heavy and need to be handled and stored correctly. The use of the correct lifting equipment in the factory and on site is extremely important. A well trained and experienced team is required to joint and install all PE pipe systems. In most regions, there are a number of reputable fusion training courses available. Pipe ovality and wall thickness variations need to be minimised as it is not good to have a step across a butt joint. This step can be minimised by rotating the pipes until the best match is obtained using the print line on the pipe as a reference mark. All welds should be produced under cover to protect the joint area and the free ends of the pipe should be covered to prevent a “chimney effect”, which will cool the heater plate. The heater plate temperature distribution should be checked and the heating capacity of the plate should be sufficient to maintain the set temperature throughout the heating cycle. When jointing the pipe lengths it is important to support the pipe on rollers to reduce the drag force. Thanks to the excellent track record of large diameter PE pressure pipes, they are now becoming the norm for water transportation and many other applications in the Middle East. The use of modern wall thickness control equipment also reduces overweight by minimising the actual wall thickness tolerance and can also significantly reduce start up scrap by bringing the pipe quickly into specification. The last element in the line is the haul off and it is important that this operates smoothly, even at the low line speeds which are common in large diameter pipe extrusion. Sag always happens with large diameter thick walled pipe production and is the flow of the material to the bottom of the pipe before it has been frozen off by the cooling water. This can be corrected to some extent by offsetting the die but this takes time and always leads to the use of additional material. For BorSafe PE100 materials, the molecular weight distribution has been adjusted to increase the viscosity at low shear rates, which reduces the sag that will take place, while allowing the same material to be used for smaller diameter pipes. When setting up for large diameter pipe production for the first time, choose the right material and work closely with your raw material supplier for the best results. Inspect the weld beads, which should be of even width and shape, as they give a good indication of weld quality. The inspection plan should include taking regular samples for tensile and reverse bend testing – a reasonable testing frequency would be 1% of the joints. Usually the external bead is not removed, but in some circumstances (e.g. close fit insertion) bead removal is required. If the correct tooling is used, the bead may be easily removed without any detrimental effect to the strength of the joint. Many projects do not require many fittings with the exception of air venting and isolation valves. The steel valves are usually connected to the PE pipe using flanges and the PE pipes should be anchored with concrete blocks to minimise the risk of leakage at the flange gasket due to temperature changes in the valve pit. Bends and tees can be fabricated in the factory from pipe using specially designed butt fusion equipment. For maintenance and repair of electrofusion couplers are available up to 900 mm in diameter and mechanical couplings can be used for larger size.