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  • Optical Fiber Senses Spills

Photonics Spectra
Jul 1999
Robert C. Pini

MANCHESTER, UK — The rapid, pinpoint accuracy of optical time domain reflectometry could find new use in detecting pipeline leaks and spills. Energy and chemical companies now visually examine pipelines from a vehicle or helicopter, but finding leaks can be difficult. To stop spills quickly, an ideal solution would be a sensor that directs workers to the problem.

An optical fiber sensor could signal pipeline leaks.

Frank Kvasnik of the Manchester University of Science and Technology thinks he may have such a solution -- an optical fiber sensor. Unlike telecommunications fiber, which is protected by cable that keeps the environment out, this optical fiber is wrapped with cladding doped to react chemically with the material in the pipeline. If a leak or spill occurs, the chemical reaction in the cladding degrades the fiber, and reflectometry can tell precisely where, leading repair crews rapidly to the scene.

Sensors based on electrochemical or semiconductor cells are also being tested. They are accurate but monitor single points, whereas an optical fiber sensor monitors the pipeline from end to end. "One kilometer of sensing fiber would be functionally equivalent to 1000 individually addressable sensors," Kvasnik said.

Catching ammonia leaks

Moreover, if the fiber doesn't break, it could signal numerous leaks at the same time. Leaks can be catastrophic failures or small holes that typically occur around joints. For these, Kvasnik said, an optical fiber sensor could alert a repair crew in time to prevent a major failure.

In designing the sensor, he used cladding reagents to absorb light at a near-IR wavelength that matches the operation of commercially available reflectometers. Research trials have shown that the sensor effectively signals leaks of ammonia, which is used in the steel production process and as a refrigerant in food production and on fishing ships.

Kvasnik is working on applications with sensing lengths up to 1 km. He said the concept could be extended to 5 km, giving a 10-km spacing for the instrumentation, with potential application in chemical and process industries, gas and oil storage, and waste management. A prototype could be developed for field trial within six to 12 months after finding a commercial sponsor. Meanwhile, Kvasnik is working to develop cable structures that protect the sensing fibers and allow the target chemicals to reach the fiber.

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