Aging and long-term performance of elastomers for utilization in harsh environments

Winoj Naveen Balasooriya Arachchige

Research output: ThesisDoctoral Thesis

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Despite remarkable growth in alternative energy sources, the energy requirements in the foreseeable future will still depend on fossil fuels, and the oil and gas industry will have to contend with more and more hostile down-hole conditions to fulfill the future energy demand. Elastomers are an essential class of materials in oil field applications, not only as seals but also in several other crucial components, due to their intrinsic properties. However, the functional properties, the performance and the service life of components are affected by the working conditions, for example, the viscoelastic effects, the surrounding media in high-pressure and high-temperature conditions. Especially, seal damage caused by the rapid gas decompression (RGD) is a well-known failure in high-pressure fluid handling conditions but this is still under discussion and holds financial, safety and environmental implications for the stakeholders. This study concerns the use of hydrogenated nitrile butadiene rubbers (HNBR) as seals in oil and gas field applications and discusses the results under three main topics; (i) thermo-oxidative aging, (ii) swelling induced aging, and (iii) utilization in harsh environments. Accordingly, the aging behavior (at elevated temperatures in the presence of oxygen and in contact with liquids) of HNBR in different conditions was investigated and the effects of intense aging on bulk and surface properties were evaluated. Further, the environmental influences on component level RGD resistance as well as the relevance of additives, especially carbon black (CB), on the development of RGD-improved material grades was investigated. Within the evaluation, the classical test set-ups on tensile, tear, and dynamic mechanical analysis, as well as the special test apparatus on RGD and tribological behavior of seals at the component level, were instrumented. Furthermore, the material composition, composite structure, microstructural changes, and possible damage mechanisms were analyzed. The thermo-oxidative aging deteriorated the mechanical properties, for example, the tensile strength, strain at break, tear resistance and damping properties were decreased, and the stiffness was increased. The different aging temperatures and the exposure times revealed the onset and intensity of property degradations. However, the RGD resistance improved in thermally aged conditions. The elastomers absorbed the fluids in contact and their morphology and subsequently their properties, physically as well as chemically, were changed. Therefore, in the swollen conditions, the bulk, as well as the surface properties, were degraded. However, RGD resistance was enhanced in swollen conditions as both of these phenomena involve fluid absorption and dissolution into the elastomer. The physically altered mechanical properties were regained after fully drying the samples; however, the degree of the swelling irreversibly degraded the surface and deteriorated the tribological properties influencing damage modes and component lifetime. In general, adding CB improves the mechanical properties of elastomer compounds and the surface area of CB is primarily responsible for the size and shape of filler aggregates and agglomerates, which are decisive factors in forming filler-filler and filler-rubber interactions. In the tested higher CB loading conditions, which already deliver a certain level of mechanical properties, the higher surface area CB adversely affected RGD resistance. Apparently, the higher surface area CB created a densified filler network and a lower amount of matrix component around the CB grades, which adversely affected the RGD resistance. Therefore, the environmental factors as well as the material quality and composition influence the RGD resistance. In future work, the information gained in this study will be useful in material modeling and simulation purposes for determining
Translated title of the contributionAlterung und Langzeitverhalten von Elastomeren für den Einsatz in rauen Umgebungen
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Briatico Vangosa, Francesco, Assessor B (external), External person
  • Pinter, Gerald Gerhard, Assessor A (internal)
Publication statusPublished - 2019

Bibliographical note

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  • Oil and gas
  • Elastomers
  • HNBR
  • Thermo-oxidative aging
  • swelling
  • Rapid gas decompression (RGD)
  • Tribology
  • Carbon black

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