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Geophysical applications of optical fibers for distributed temperature, strain, and acoustic sensing challenges their reliability due to harsh environmental conditions. Which may include high temperature, pressure, presence of hot steam, hydrogen, and other aggressive chemicals. Robustness of silica-based optical fibers is primarily governed by the thermal and environmental stability of their polymer coatings. Among different types of coatings, polyimide materials exhibit favorable properties, such as durability at elevated temperatures, protection against solvents, and long-term mechanical reliability. In this work we investigate optical fibers employed with a novel polyimide coating. Extensive environmental testing was performed, comparing fibers with a standard and the novel coating. Fiber samples were aged in dry air (up to 380 °C), high temperature/pressure water, paraffin oil, crude oil, hydrogen scavenging cable gel and isopropyl alcohol (all up to 300 °C/2000 psi). Mechanical strength of the aged fibers was used as a measure of their performance at harsh conditions. In addition, we studied an adhesion that develops at elevated temperatures between the fibers and a stainlesssteel tube interior. Thermal stability of the polyimides was also evaluated via thermogravimetric analysis. Based on the obtained results, the novel polyimide coating shows a 35 – 38 °C improvement over the standard coating. The findings indicate the superiority of the new coating, which should extend the useful temperature range for this class of optical fibers.
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