Managing Hydrogen Diffusion
Oil and gas markets provide myriad applications where optical fibers, used as fully distributed sensors, benefit end-users by promising lowest cost per sensor point. Examples include pipeline and borehole monitoring for distributed flow, distributed seismic detection, and leak detection.
Commonly, oil and gas installations include very harsh environments, with temperature extremes (up to 300˚C), high pressures (up to 30,000 psi), and exposure to harsh chemicals. Under these conditions hydrogen will diffuse from the environment, through virtually all materials, and nest in the core of the optical fiber. This build-up of hydrogen causes attenuation to increase and is highly variable, dependent upon temperature, pressure, and hydrogen concentration. (In some oil and gas environments extremes in pressure (up to 30,000 psi) and temperature (up to 300 ˚C) may exist.)
To counter hydrogen diffusion, OFS takes two approaches. In the first case we apply a thin layer of carbon to traditional Germanium (Ge) doped optical fibers during the draw process. We then apply a high temperature coating over the carbon layer for chemical, abrasion, and temperature resistance.
We also offer pure-core single-mode fiber. In this case, we radically redesign the optical fiber, removing Ge as the dopant, leaving pure silica as the core material, thus eliminating H2 nesting sites within the core. During the draw process similar coatings to those described above are applied.
We commonly use PYROCOAT® (polyimide) for harsh environment applications but other coatings are available. We encourage you to contact us to discuss your needs. We will help you select the combination of materials that best matches the unique needs of your application.