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Lifetime prediction : different strategies by example
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2009 (English)In: POLYMER DEGRADATION AND PERFORMANCE / [ed] Celina MC; Wiggins JS; Billingham NC, 2009, Vol. 1004, 159-169 p.Conference paper, Published paper (Refereed)
Abstract [en]

Two different approaches for lifetime prediction are presented. The underlying lifetime limiting processes have been identified in two cases. Mathematical expressions of chemical/physical relevance were used for the lifetime predictions for PE hot-water pipes and cables insulated with plasticized PVC. Accelerated testing, extrapolation and validation of the extrapolation by assessment of the remaining lifetime of objects aged during service conditions for 25 years were successfully applied to cables insulated with chlorosulfonated polyethylene. Polyolefin pipes exposed to chlorinated water showed a very complex deterioration scenario and it was only possible to find a method suitable for predicting the time for the depletion of the stabilizer system.

Place, publisher, year, edition, pages
2009. Vol. 1004, 159-169 p.
Series
ACS Symposium Series, ISSN 0097-6156 ; 1004
National Category
Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-14092DOI: 10.1021/bk-2009-1004.ch014ISI: 000280805100014Scopus ID: 2-s2.0-84904786450ISBN: 978-0-8412-6978-1 (print)OAI: oai:DiVA.org:kth-14092DiVA: diva2:329650
Conference
Symposium on Polymer Performance Degradation and Materials Selection held at the ACS Spring Meeting
Note
QC 20110408Available from: 2010-07-13 Created: 2010-07-13 Last updated: 2011-04-08Bibliographically approved
In thesis
1. Long-term Performance of PVC and CSPE Cables used in Nuclear Power Plants: the Effect of Degradation and Plasticizer migration
Open this publication in new window or tab >>Long-term Performance of PVC and CSPE Cables used in Nuclear Power Plants: the Effect of Degradation and Plasticizer migration
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Enormous amounts of low voltage cables installed in a Swedish nuclear power plant are reaching their expected lifetimes. Since the cables are crucial to operational safety, it is of great importance that the actual condition of the installed cables is determined. In this study, cables based on poly(vinyl chloride) plasticized with di(2-ethylhexyl)phthalate (DEHP) were examined with respect to the degradation mechanisms responsible for the ageing of the insulation. This was achieved by studying samples that underwent accelerated ageing by different analytical methods, such as indenter modulus measurements, tensile testing, infrared spectroscopy, differential scanning calorimetry and liquid chromatography, to assess the condition of the cables. The results were unambiguous; the main deterioration mechanism differed for the jacket and the core insulation. The immediate increase in stiffness of the jacket insulation suggests that loss of plasticizer was the dominant cause for degradation. The core insulation on the other hand showed much smaller changes in the mechanical properties due to thermal ageing with an activation energy of the change in the   indenter modulus matching that of the dehydrochlorination process. The electrical functionality during high-energy line break accident was correlated to the mechanical properties of the cable and this correlation was used to establish a lifetime criterion. The mechanical data showed Arrhenius temperature dependence with activation energies of 80 kJmol-1 and 100 kJmol-1 for the jacketing and 130 kJmol-1 for the core insulation. These activation energies were used to extrapolate the lifetimes to service temperatures (20 °C to 50 °C). Plasticizer migration was determined as the lifetime controlling mechanism at the service temperatures. Experimental data, obtained by extraction of DEHP followed by liquid chromatography, were analysed by numerical methods to gain a better understanding of the migration. The analysis showed that the transport of DEHP to the surrounding environment was diffusion controlled at temperatures between 120 °C and 150 °C, with an activation energy of 89 kJmol-1. At lower temperatures, HTML clipboard ≤100 °C, the loss of plasticizer was controlled by evaporation, with an activation energy of 99 kJmol-1. Under the latter conditions, the rate of plasticizer loss from the PVC cable was very similar to that from the pure plasticizer, suggesting that a film of plasticizer was formed on the PVC surface. The evaporation of DEHP showed a clear dependence on the rate of ventilation of the gas phase surrounding the cable. The ability to monitor the condition of the installed cables is dependent on good techniques for the remaining lifetime assessment. The condition monitoring technique, Line Resonance Analysis, was applied to chlorosulfonated polyethylene cables. A clear correlation between LIRA and indenter modulus data obtained and LIRA and tensile testing results was found. This is of interest since existing lifetime criteria used in the nuclear plants are based on these two testing techniques.

 

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 59 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2009:53
Keyword
PCV, CSPE, cables, ageing, mechanical properties, plasticizer migratio, LIRA, life time prediction
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-11286 (URN)978-91-7415-452-8 (ISBN)
Public defence
2009-10-29, E1, Lindstedtsvägen 3, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100713Available from: 2009-10-14 Created: 2009-10-14 Last updated: 2010-07-16Bibliographically approved

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