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Non-destructive condition monitoring of aged ethylene-propylenecopolymer cable insulation samples using dielectric spectroscopy and NMR spectroscopy
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
University of Bologna.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.ORCID iD: 0000-0003-3049-7225
University of Bologna.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The causes of changes in dielectric response as a result of thermal and irradiative ageingof a cable insulation of ethylene propylene copolymer rubber containing 38 wt.% filler wereinvestigated. Samples were aged in three different combinations of irradiation dose rate andtemperature, 0.42 kGy h–1 at 85 °C, and 1.58 kGy h–1 at 55 and 85 °C, and subsequentlystudied by dielectric spectroscopy, NMR spectroscopy using a portable spectrometer andtensile testing. The extractable mass fraction and density were determined, and related to theimaginary part of the dielectric permittivity at 100 kHz. The ageing led to an increase in thedielectric permittivity, stiffness, density and degree of oxidation, together with a decrease inboth strain-at-break and relaxation time, as revealed by NMR spectroscopy. Except for thestrain-at-break, the properties changed in a linear fashion with increasing imaginary part ofthe dielectric permittivity at 100 kHz, with a particularly good agreement with respect to thedensity. As these properties are affected by the degree of oxidation, the results show that bothNMR using a portable spectrometer and dielectric spectroscopy can be used as conditionmonitoring techniques to detect the degree of oxidation in complex systems such as filledcopolymers.

Keyword [en]
Ethylene propylene rubber, Radiation ageing, Thermal ageing, Dielectric response, Portable NMR spectrometer, Condition monitoring
National Category
Textile, Rubber and Polymeric Materials
Identifiers
URN: urn:nbn:se:kth:diva-168192OAI: oai:DiVA.org:kth-168192DiVA: diva2:814647
Funder
EU, FP7, Seventh Framework Programme
Note

QS 2015

Available from: 2015-05-27 Created: 2015-05-27 Last updated: 2015-05-29Bibliographically approved
In thesis
1. Polymeric materials in nuclear power plants: Lifetime prediction, condition monitoring and simulation of ageing
Open this publication in new window or tab >>Polymeric materials in nuclear power plants: Lifetime prediction, condition monitoring and simulation of ageing
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nuclear power plants generate a significant part of the world’s electrical power consumption. However, many plants are nearing the end of their designed lifetime, and to extend the lifetime it is important to verify that every component can withstand the added service time. This includes polymeric materials, which become brittle with time. By predicting their lifetime and monitoring their condition, unnecessary downtime of the plant can be avoided, and secure operation can be ensured. The lifetime can be predicted by extrapolating results from accelerated ageing to service conditions, or by simulation of the degradation process.

In this study, lifetime predictions through extrapolation were performed on samples of a polyvinyl chloride (PVC) core insulation and an acrylonitrile butadiene rubber (NBR) membrane, which were thermally aged in air. The lifetime of the PVC cable was predicted using Arrhenius extrapolation, and using a method based on Langmuir, Clausius-Clapeyron, and Kirchhoff’s equations.

The lifetime of the NBR membrane was predicted using extrapolation in the temperature domain using an Arrhenius approach coupled with an extrapolation in pressure-domain, yielding realistic lifetimes.

Two cable insulations, one made from crosslinked polyethylene (XLPE) and the other from ethylene propylene rubber (EPR) were aged under the simultaneous effect of elevated temperature and γ-radiation investigated using several condition monitoring techniques. In particular, two non-destructive techniques, dielectric spectroscopy and nuclear magnetic resonance, showed promising results be developed and used in situ.

Finally, a computer model simulating the diffusion and consumption of oxygen in XLPE was developed, based on assumptions that diffusion, consumption and solubility were dependent on the total degree of oxidation. The model showed promise for further development.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. 75 p.
Series
TRITA-CHE-Report, ISSN 1654-1081 ; 2015:29
National Category
Textile, Rubber and Polymeric Materials
Identifiers
urn:nbn:se:kth:diva-168193 (URN)978-91-7595-587-2 (ISBN)
Public defence
2015-06-11, K2, Teknikringen 28, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20150529

Available from: 2015-05-29 Created: 2015-05-27 Last updated: 2015-05-29Bibliographically approved

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Pourmand, Payam

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