Authors: Schmacke, Saskia
Title: Investigations of Polyethylene Materials by Means of X-ray Diffraction
Other Titles: Artificial Ageing of Polyethylene Gas Pipes
Language (ISO): en
Abstract: This work deals with the investigation of polyethylene gas pipes by means of x-ray diffraction, which have been in use for 35 years for the supply of gas. A lifetime of 50 years was predicted for these polyethylene (PE) pipes of first generation. A remaining life time of 15 years for all gas pipes installed in the seventies has thus to be expected. In order to prevent expensive and complex replacement of pipes after failure, parts of the pipes are removed from the gas grid. Afterwards, so-called creeping tests are conducted, which serve as a simulation method for the ageing behaviour and for the estimation of the remaining life time. Ageing processes are atomic modifications, for which creeping tests are in- sensitive. In order to gain a more detailed insight into these ageing processes and to identify indicators for ageing, pipe parts have been exposed to high temperatures and pressures. This procedure leads to an artificial ageing of the material additionally to the natural ageing due to the 35 years period of use. Sample slices have been prepared out of these artificially aged pipe parts and out of the corresponding natural aged pipe, in order to analyse the material's structure depending on the position within the pipe wall and to compare the results. X-ray diffraction, small angle x-ray scattering and x- ray tomography experiments have been conducted at di erent experimental stations to investigate the materials structure on nanometre and micrometre length scales. The sample's crystallinity of the semicrystalline material turned out to be the searched indicator for ageing. With increasing age, the material becomes more crystalline and thus more brittle. Furthermore, this change was the most pronounced at the inner surface of the pipe wall. Texture analysis showed moreover a preferred orientation of unit cells parallel to the long axis of the pipe, which is also stronger pronounced at the inner surface than for the rest of the pipe wall. These are thus most vulnerable for material failure.
Subject Headings: Polyethylen
X-ray diffraction
Powder diffraction
Small angle x-ray scattering
Creeping tests
Remaining lifetime
Issue Date: 2011-01-21
Appears in Collections:Experimentelle Physik I

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