MACHINERY | STANDARDS & TESTING


Multiple methods to analyse surfaces


At the Profiles conference in Cologne in November, Michael Schiller, of HMS Concept, told delegates that various analysis methods can be very revealing when studying the surface of PVC profiles and other products. He said that a range of techniques – including colour measurement, FTIR and Raman spectroscopy and X-ray fluorescence (XRF) can pinpoint specific problems, including pinking,


pitting and various reasons behind weathering damage. In one case, FTIR helped to identify


that pitting on PVC pipe – which contained calcium-zinc stabilisers – was caused by sublimation of pentae- rythritol in vacuum ventilation. FTIR was also used to identify oxalic acid salts during natural and artificial weathering of white PVC window profiles. One possible source of oxalic


surface embrittlement, which causes cracking and later failure. “The goal is to determine the effect of ClO2 on


crack initiation time depth,” he said.


In tests, samples were exposed to ClO2 and tested using the cracked round bar (CRB) and compact tension tests – as well as by essential work of fracture (EWF). They were also studied with electron microscopy. Bredacs said that the advantages of the new model included a reasonable testing time – of a few months – that was ideal for material ranking and development. It also allowed extrapolation to relevant conditions. The EWF technique showed promising preliminary results, he said, and could lead to more accurate material ranking.


Cracking with age Benjamin Rabaud, materials cluster manager at Suez, said that chlorinated chemicals have an ageing effect on pipe – including cracking of the inner pipe wall and blistering of the inner surface. The effects can be serious, he said – pointing out the chlorine dioxide caused very high degradation in 30% of HDPE in tests. “For some water networks, a 50-year life expec- tancy is questioned,” he said. While networks in northern Europe fared much


better (with chlorine and ammonium chloride causing only “moderate degradation” in 4% of samples), he said that sustainable growth of plastic pipe water networks required new types of material: while a pipe made from ‘best quality’ standard PE resin had twice the projected lifetime of one made from the ‘worst standard resin’, he said that a grade with ‘chlorine resistance’ showed a 425% improvement. “HDPE with disinfectant resistance should be implemented for demanding networks,” he said.


26 PIPE & PROFILE EXTRUSION | April 2020


acid is pollen. “In some cases, using different methods might help to understand the source of the problem,” said Schiller. n The next Profiles conference from AMI is held in Cleveland, USA on 2-3 November 2020. For more details, contact Stephanie Hume (stephanie. hume@ami.international) on +1 610 478 0800.


Saving time and energy Juergen Wuest, deputy managing director of the German Plastics Center (SKZ), explained an energy- and time-saving method for qualifying PE pipe grades for long term applications at 40°C, using a high-pressure autoclave test (HPAT). While a typical oven test takes more than 5,000


hours, a typical HPAT test will take around 1,000 hours, he said – and uses around one-seventh of the energy. An HPAT test is typically carried out at high


temperatures (60-90°C) in an aqueous medium of variable pH. The sample ages due to the high temperature, and the presence of oxygen. Samples are removed after specific exposure periods and subjected to tensile testing. Results are extrapolated to ‘normal’ conditions – such as 40°C and atmospheric pressure. “With oven ageing, no estimation is possible after


four years, as the test is still running,” he said. “With HPAT, the lifetime estimation with activation


energies meets the literature values in an acceptable time.” n Due to the Coronavirus pandemic, this year’s Plastic Pipes in Infrastructure conference has been rescheduled – and will now take place on 27-28 October in Hamburg, Germany. For details, contact organiser Nicola Charlesworth


(nicola.charlesworth@ami.international) on +44 (0)117 314 8111, or visit the conference website.


CLICK ON THE LINKS FOR MORE INFORMATION: � www.plasticpipe.org � www.ami.international � www.pccl.at � www.suez.com � www.skz.de � www.hms-concept.net


www.pipeandprofile.com


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