MACHINERY | COMPUTER MODELLING SOFTWARE
tensile load on the selected HDPE conduit, as compared to its allowable Safe Pull Strength. The calculator gives users the options of HDPE conduit manufactured from a standard strength HDPE resin or higher strength HDPE resin.
Users can select conduit diameter and wall thickness type from a menu with three pre-loaded sizing systems. All conduit dimensions and properties are in accordance with industry stand- ards such as ASTM F2160, NEMA TC 7, and UL 651A. Once inputs have been entered, the calcula- tor shows the Safety Factor for the selected wall type, and potential alternatives, in a Results Table. A Safety Factor greater than 1.0 indicates that the displayed wall thickness types will have sufficient tensile strength to meet the calculated tensile forces for the given installation. “As long as the jobsite conditions are known, the
calculation for a given installation can be complet- ed in two to three minutes for most projects,” said Lance MacNevin, director of engineering for PPI’s building and construction division. The software can be downloaded from
www.conduitcalc.com.
Eccentric modelling Researchers at Borealis and Borouge have used heat transfer simulations – in addition to physical experiments – to assess how the shape of an extruded HDPE pipe affects the development of residual stresses. The researchers said that these types of studies
are typically done on regular, concentric pipe. However, factors such as sagging cause pipe shape to become slightly eccentric after it leaves the die. This can lead to uneven wall thickness, for instance. For this reason, the researchers created – and simulated – several ‘eccentric’ HDPE pipes, that
PPI’s free software tool calculates the most appropriate wall thickness of HDPE conduit installed via HDD
would typically be used in pressurised water and gas applications. They were looking to understand how eccentric-
ity affected cooling, residual stress and hydrostatic pressure resistance in the final pipe. Heat transfer simulations – for pipe entering a cooling bath – were carried out using the Ansys Polyflow CFD software package. Non-isothermal, time-dependent, 2D geometry models were developed for one concentric and three eccentric cases for pipes with an outside diameter of 110mm and average wall thickness of 10mm. In the simulation, the temperature profile of the concentric pipe was colder at the outer surface and increased gradually through the wall thickness towards the inner surface. However, the tempera- ture profile of eccentric pipes around the circum- ference at a given radius was not homogenous and differed depending on the angular location. Temperature distribution along the radius of an eccentric pipe – at the top and bottom – increase in line with eccentricity. “It is clear that with increase in pipe eccentricity, the temperature difference between inner and outer surfaces of pipes increases at maximum wall thickness and decreases at minimum wall thickness locations,” said the researchers. They found that net residual stress increased at
the thicker side of an eccentric pipe and decreased at the thinner wall. “Such manipulations in the total stress state of the pipe during solidification will lead to significant changes in morphology and mechanical properties of pipes – which is the subject of our next research paper,” said the authors. Results were published in the January 2021 issue of Polymer Testing.
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PIPE & PROFILE EXTRUSION | March 2021
www.pipeandprofile.com
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