MATERIALS | PEX
lution hyperspectral IR images of cross-sectional slices of unused virgin, used in-service, and cracked PEX pipe,” said the researchers in a paper published in Applied Materials & Interfaces. This way, the researchers could extract detailed
information on the changes that occur during aging, degradation, and cracking in PEX pipe. “This study shows how representation learning by deep generative modelling can enhance the analysis of high-resolution IR images of complex heterogene- ous samples,” the researchers concluded.
Above: Tecnomatic has supplied an extrusion line to help a European pipe producer make five-layer PEX pipe
layers) and the number of layers. At the same time, the short flow path reduces residence time and allows rapid material and colour changes. The line has a working range of 8-32mm and
produces pipe at 60 m/min. It comprises an Atlas 60.30 Evo as the main extruder, which has been further optimised for higher output, melt homoge- neity and energy consumption. Mizar and Atlas 30 models act as co-extruders and are used for adhesive, EVOH and external layers. The extruders are integrated and fed by a
gravimetric system for a total of eight dosing components. An ultrasonic wall thickness station continuously controls pipe parameters such as eccentricity, wall thickness, diameter and ovality. Pipes are coiled using a high-speed automatic coiler from FB Balzanelli.
Cracking results PEX is becoming more heavily researched – not only in order to assess its physical attributes, but also in order to understand whether it has any potentially harmful effects such as leaching. One recent paper, by researchers at the Univer-
sity of Guelph in Canada, used a new way to model infrared (IR) images in order to assess cracking in PEX pipes. Hyperspectral infrared (IR) images contain lots of
information about the chemical composition of a sample. However, analysing this data can be challenging because of the spectroscopic and spatial complexity of the data. The researchers implemented a ‘deep genera- tive modelling’ approach in order to ‘disentangle’ data that was collected on PEX pipe. “We identify three distinct physicochemical factors of aging and degradation – learned by the model – and apply the trained model to high-reso-
38 PIPE & PROFILE EXTRUSION | September 2023
Burst strength A recent paper in the International Journal of Pressure Vessels and Piping investigates the long-term rupture pressure in PEX-Al-PEX compos- ite pipes. This type of pipe is widely used in a building’s
hydronic heating and cooling and plumbing systems. It comprises three main layers: outer and inner layers of PEX, and an aluminium (Al) middle layer. A polyethylene adhesive is typically used between the layers to prevent slipping of the polymer layers over the Al layer. One of the most vital parameters in making these pipes is the tolerated internal long-term hydrostatic pressure, say the Iran-based research- ers. The rupture pressure of composite pipes depends on operating temperature and time – as well as each layer’s dimensions (inner polymer, outer polymer, and aluminium layer), the mechani- cal properties of the layers, and the welding types of the aluminium layer. The researchers measured the long-term life behaviour of PEX multi-layer pipes for up to 1000 hours – for different diameters and welding types. The hoop and radial stress of the pipe layers are calculated analytically, based on classical elasticity theory. The pressure that can be tolerated by each layer was defined as a function of long-term hydro- static pressure, size, and mechanical properties of both the aluminium and PEX layers in the pipe. The results showed that the pressure bearing by the aluminium layer is 84-91% of the pipe’s hydrostatic pressure. The PEX outer layer pressure bears less than 3% of the hydrostatic pressure – with the rest taken up by the PEX inner layer.
Leaching effects Several recent research projects have addressed the issue of substances leaching from PEX into water. Researchers from the German Environment Agency recently used gas and liquid chromatography to assess leaching of a particular chemical that “repeat- edly occurs in the migration waters of PEX pipes”.
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