Right: A

snow-melting project in Utah used around 36,000 ft of Rehau’s

Raupex O2 barrier PEX pipe

contributor to overall life cycle toxicity, depending on the PEX brand – particularly for carcinogenic effects,” said the researchers, in a paper published in Science of the Total Environment.

Ageing behaviour Separate to this, French researchers have studied the ageing of silane-crosslinked PEX that has been stabilised with an excess of phenolic antioxidant (Irganox 1076, from BASF). The researchers, from Ensam in Paris, focused on thermal ageing in air at temperatures between 87°C and 130°C. “The purpose was to investigate the role of an

anti-oxidant excess in the stabilisation process of the polymer,” said the researchers, in a paper published in Polymer Degradation and Stability. Comparing oxidation induction periods at 130°C showed that antioxidant excess helps polymer stabilisation during thermal ageing, the researchers concluded.

Freeze resistance The Plastics Pipe Institute (PPI) has published a new technical report on the break-resistance of PEX pipe when fluid inside it becomes frozen. The report (PPI TR-52) explains how proper

installation and protection of piping can prevent freezing of fluids inside PEX, how the inherent material properties of PEX can delay freezing of water, and how PEX can resist breaking if the fluid inside does freeze. “The flexibility of PEX gives excellent freeze-

break resistance,” said Lance MacNevin, director of engineering for PPI’s building and construction division. “If water or fluid-filled PEX pipe freezes, its elasticity typically allows it to expand without cracking or splitting –then to return to its original diameter upon thawing.” However, he said there are installation variables

that can cause PEX to fail in certain situations, which are described in the report. “The relatively low thermal conductivity of PEX

material reduces heat transfer through the pipe wall,” he added. “For similar material thickness, PEX is 68 times less conductive than copper, which can delay the freezing of fluids within PEX tubing – po- tentially preventing freeze events.” PEX tubing remains flexible enough to be bent

at temperatures below -40F (-40°C). “Since water expands upon freezing, this elastic

property is beneficial during a freeze event – as the pipe can expand with the water,” he said. TR-52 includes excerpts from Canadian and US model plumbing and mechanical codes about protecting all pipes from freezing, as well as PPI’s

32 PIPE & PROFILE EXTRUSION | September 2021

recommendations to protect pipes in specific applications.

Winning project In its latest awards, PPI recognised a snow-melting project that makes extensive use of PEX pipe. In the project, Raupex O2

barrier PEX pipe from Rehau

was used as part of the ‘snow melting’ system at a university campus. The system, at the Utah Valley University in Orem, Utah, melts snow on a large pedestrian bridge – which connects the university campus with student housing on the other side of a busy freeway. These types of system are common, and work by running warm glycol through pipes in order to melt surface snow. This latest project was complicated by the fact that the system needed to be incorpo- rated into a bridge. The project is a ‘hybrid’ snow-melt installation because it uses both PP-RCT and PEX. In total, 36,000ft of PEX was installed in a ‘grid’ on the bridge, along with 1,900ft of PP-RCT – in diameters of 2.5-4in.



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