Pressure Pipe Developments

10-Nov-09
The global market for HDPE pressure pipes will grow from 4010,000 tons in 2008 to 4992,000 tone in 2013, according to SABIC. The major geographic regions using this type of pipe are Europe, Northeast Asia and North America. The main growth in Europe will be in PE100 materials in Central, Eastern, Russia and the CIS states. These figures were discussed at the October 2009 AMI conference, Plastic Pressure Pipes 2009. HDPE pipes have advantages over traditional materials in burst and slip lining and are gaining market share. In France, Veolia Water has encountered some problems with failure of 25 and 32 mm PE pipes of limited wall thickness in contact with chlorine dioxide disinfectant. The ClO2 has strong free radical activity, which depletes the antioxidants in the pipe inner wall, leading to PE oxidation and longitudinal pipe cracking. Glynwed Pipes and Aliaxis have developed a multilayer solution, Excel-Plus® pipes, introduced on the market during 2009 and successfully installed. It has an inner PVDF layer, then adhesives, and mechanical strength from the HDPE outer layer. PVC4Pipes has investigated the performance of PVC pipes in contact with different disinfectants. Initially 4 different PVC materials were examined for resistance to chlorine dioxide – the disinfectant level was kept constant. At normal temperatures and disinfectant levels, no effect was seen on the PVC pipes. At raised temperature (40C) and higher disinfectant levels there was limited attack on the PVC surface. In separate tests, PVC pipes were found to withstand sodium hypochlorite at levels of 1,000 ppm without adverse effect. Exova (formerly the Bodycote Testing Group) has been studying chlorine oxidative resistance since 1992. There are ASTM methods for PEX and PE. High stress and temperature dependency have been issues in testing pipe materials and further work needs to be done on the methods. Mobile NMR has been used in non-destructive testing of HDPE pipes, in studies by RWTH Aachen University. Morphological changes induced by annealing, chemical ageing and deformation can be followed and quantified by the NMR-MOUSE. The VMW water company has 11,500 km of PVC and HDPE pipes now compared to only 5,400 in 1990. It has been looking at new developments like the Krah system of winding PE glass fibre reinforced tape on a core. Becetel findings support the use of this kind of reinforced PE pipes up to 10 bar and for diameter ranges up to DN 4000. The pipe is being tested for durability, installation methods and joining technology. There is a new 3-layer PE pipe from egeplast Werner Strumann, with an outer layer of PE100-RC which is “gas-proof”, a middle layer of stretched PE100 to improve pressure strength, and an inner PE layer, all of which weld together. It has been tested for a year in gas pressure applications by E.ON Ruhrgas up to 35 bar, and in water pipe relining. Wellstream spoolable flexible unbonded pipes operate in more extreme circumstances, for example as risers for offshore oil and gas. A metal carcass provides collapse resistance, a sealing barrier layer is provided by polymer (HDPE, PA11/PA12, PVDF), insulation comes from syntactic PP and the outer shield preventing sea water ingress is of HDPE or PA11/12. The pipe is being tested for ultra-deep water at depths of over 2,000m. Skinned pipes are one of the products of Radius Systems (formerly Uponor Ltd). The skin is a sacrificial, peelable outer layer of 0.8–1.5 mm and the colour depends on the utility, with stripes to show that it can be peeled back, for example at joints. The core pipe is PE100. Samples were tested in the Arizona desert and it was shown that the skin protected the pipe from UV degradation. The pressure strength is also raised by the skin layer. FIRAT Plastik A.S. had production of 300,000 MT in 2008 including profiles. It produces standard PE80 and PE100 pipes, and has recently introduced a spiral wound, reinforced pipe. Projects included a water pipe under the Bosphorus to supply drought areas, with a record wall thickness of 109.1mm. The pipe conveys 300,000 cubic meters of water per day. The company also towed 500m lengths of PE100 pipes across the Aegean and Mediterranean seas to Libya for a desalination plant. Reinforced HDPE pipe has been installed in a dam reservoir supplying Istanbul. There are innovations in PVC water pipe technology, with Molecor selling oriented PVC pipe production technology, including improved environmental credentials in production. In one case study using Solvin resin, Ca/Zn stabiliser from Chemson, 4 pp calcium carbonate, blue colour,and 11% own recyclate, the output rate was 580 kg/h. PVC formulation is changing across Europe as lead stabilisers are phased out. Shin-Etsu PVC has looked at the effects on pipe performance when a Ca/Zn alternative stabiliser is used. The new system requires co-stabilisers, has a narrower processing window, gives more plate-out, and the lubricant package is less well established. Rehau compared the two materials and found that lead-stabilised PVC pipe performed better in tests such as creep and balloon rupture. However, when the Ca/Zn material is aged it matches the Pb more closely. The Netherlands installed uPVC in gas pipes from 1955 to around 1975. Kiwa Gastec has retrieved some of this pipe to assess long-term performance. Spontaneous fracture is very rare: the concern is impact loading, which occurs when contractors are working in the area or during maintenance. Chemical ageing can take place prior to installation, for example due to UV exposure. Carbon dioxide and water uptake in soil also affect performance. Water uptake was shown to be very slow, and emulsion PVC absorbs more than suspension PVC; carbon dioxide uptake was even slower. The carbon dioxide is expected to have a plasticising effect. Since 1975 high impact PVC has been used, with modifiers of butyl acrylate or chlorinated PE. HESSEL Ingenieurtechnik is looking at designing pipe systems for service life of 100 years in gas and water applications. Failure occurs from factors such as stretching (causing ductile failure), stress cracking (causing brittle failure) and thermal ageing (affected by oxygen levels, temperature, stabilisers, fluid flow rate and strain). Tests have been devised and extrapolated to 100 years using the Arrhenius method. PE100-RC material showed high stress crack resistance and outstanding creep-rupture performance with potential for 100 year usage. Univation (a 50:50 joint venture between The Dow Chemical Company and ExxonMobil Chemical) licences the UNIPOL polyethylene production process and PRODIGY BMC-200 bimodal catalyst. Qenos is Australia’s only manufacturer of polyethylene and is using the single-reactor method to produce bimodal PE100. This HDPE has been tested for rapid crack propagation performance by the S-4 test (ISO 13477), and had higher output in extrusion tests than other comparable materials. Reducing energy consumption cuts costs and the carbon footprint. Cincinnati Extrusion is developing technology in this field: the KroSys extrusion line starts melt cooling in the pipe head, followed by intensive air and water cooling of the outer pipe surface then intensive cooling of the inner pipe surface by air sucked against the extrusion direction, and reclaiming and reusing of energy from the cooling process. Pressure pipes are used in critical applications like water and gas, and performance standards are constantly being improved. At the same time there are economic factors driving down costs. The plastics pipe industry and its suppliers are coordinating efforts to produce high quality, standardised, safe products.
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