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Title: Morphology and residual strains in PE100 polyethylene pipes
Author: Perridge, R. J.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1999
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The morphologies of four polyethylene resins for pipeline applications were investigated, each material having been cooled at three different rates. Salt water quenching (at -10°C) was used since this was found to cool the sample more rapidly than quenching in liquid nitrogen. After quench cooling two of the resins were found to be spherulitic and the other resins showed some signs of spherulitic behaviour. At the slower cooling rates the BP, Borealis and Hostalen resins had non-spherulitic morphologies but the Solvay resin retained a spherulitic morphology. Atomic force microscopy proved a useful technique for the imaging of bulk PE, providing complementary data to the SEM and confirming the general observations. The through thickness released microstrains, which can be related to the residual stresses in a pipe, were measured for a BP PE100 SDR11 180mm diameter pipe cooled from the outer surface and a Borealis PE100 SDR11 250mm diameter pipe cooled from both the inside and outside. The released microstrains were measured using strain gauges, following a technique modified from that developed by Boot and Guan. The dual cooling of the Borealis PE100 pipe was found to give rise to lower released microstrains (and hence probably residual stresses) when compared with mono cooled pipes. This is thought to be due to lower thermal gradients through the pipe thickness during cooling as the morphological distributions were found to be similar between mono and dual cooled pipes. The morphologies of all the pipe samples were non-spherulitic with the lamellar lengths in both pipes increasing as the distance from the inner surface increased indicating that cooling was also more rapid from the outside in the dual cooled pipe. The through thickness distributions of released microstrains were found to be more complicated in the dual cooled pipe.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available