materials feature | Polyolefin developments


There are short-term destructive tests, which include a variety of tensile tests on small specimens cut from the weld, impact tests, pressure tests and tensile tests on whole pipe assemblies. Long-term tests include creep tests on full thickness specimens, Full Notch Creep Tests (FNCTs) and pressure tests on the pipe assembly. The key to success for the project has been the


evaluation of test methods to fully understand short- and long-term properties of the welds. An important aim was to evaluate welds in large diameter, thick walled pipe with a range of wall thicknesses. This was done by short term, long term and Full Notched Creep testing.


A PE100+ project aimed to evaluate butt fusion test methods for large PE pipe


whereas the life expectancy of polyolefin pipes has been discussed for many years, a definitive conclusion has never been determined. Excavated pipes that were tested had already been in


use for up to 40% of their proposed in-service lifetime. The tests showed that no excessive deterioration or degradation has occurred over this time. “Although the oldest excavated pipes were manufac-


tured using ‘first generation’ material formulations, a residual lifetime of more than 50 years was calculated,” said Calton. “And we should also bear in mind that current formulations offer even greater lifetime performance than those earlier materials.” Other key factors investigated in project were found


not to affect life expectancy adversely. These included: the chemical composition of the sewer water; the temperature profile of sewer flows; and variations in the kind of installation practices used. The influence of higher concentrations of sewer effluent that are typically associated with structured wall pipe systems was also examined. The full technical report and a summary technical


Dow’s Hyper- therm 2399


PE-RT material allows


installers to bend water lines at turning joints to ease installation


report are available on Teppfa’s website, as is a four-page leaflet outlining the project scope. The project was co-ordinated by Teppfa in conjunction with LyondellBasell, Borealis and TGM (Austria).


Joining assessment PE 100+, the industry organisation for suppliers PE 100 pipe materials, recently carried out a project to assess the joining – and testing – of large diameter, thick- walled PE pipe. It has been working to further develop test methods and harmonise global standards for butt fusion procedures, and endorse their suitability for this type of pipe. “Test methods for butt fusion welds are potentially


misleading, and they exist in ISO, European and many national and industry standards,” said Steve Beech, who led the butt fusion harmonsation project.


12 PIPE & PROFILE EXTRUSION | March 2015 www.pipeandprofile.com The minimum service life of the butt welds tested


was estimated in accordance with Vogt et al. A maxi- mum longitudinal stress of 4MPa, a result of the maximum design hoop stress of 8MPa for an unre- strained PE 100 pipeline, gives a conservatively estimated lifetime of 215 years at 20°C in water. Based on this calculation, it can be safely concluded that for water and gas applications at 20°C, a properly made PE 100 butt fusion joint is predicted to achieve a service life well in excess of 100 years. Overall, the results of the project indicate that


rationalisation and some harmonisation of the three procedures could take place – if the industry is willing to do this, said Beech.


Bending round corners Dow has launched Hypertherm 2399, a polyethylene resin for domestic and commercial hot and cold water plumbing pipes. The PE-RT material enhances pipe flexibility, allowing installers to bend water lines at turning joints to ease installation. “Turning joints have always been a challenge when


installing copper, steel and rigid plastic pipe,” said Oray Talu, market manager for Dow pipe and irrigation


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