Pipeline tests target fiber optic cable for detecting third-party damage

March 3, 2003
Field tests are under way to evaluate the use of fiber optic cable to detect intrusion along a pipeline by third-party excavators, widely documented as the most common source of damage to oil and gas pipelines.

Field tests are under way to evaluate the use of fiber optic cable to detect intrusion along a pipeline by third-party excavators, widely documented as the most common source of damage to oil and gas pipelines.

The US Department of Energy and the Gas Technology Institute, Des Plaines, Ill., are jointly sponsoring the tests.

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In January, the cable was buried along a mile of pipeline operated in northwest Indiana by El Paso Corp. subsidiary ANR Pipeline Co. During the next several months, said a joint release by DOE and GTI, construction equipment will create vibrations in the ground, causing compressions in the soil around the pipeline (Fig. 1).

If the vibrations and soil compressions are sufficiently close to the pipeline, the fiber optic cable will bend slightly. "Even a minute deformation in the cable will change its light transmission and reflection properties and send an early warning of a potentially hazardous encroachment," said the parties.

Other options

Fiber optic cable is among the least costly options for protecting operating pipelines, they said, compared with satellite, ground-based visual, and global positioning system (GPS) monitoring systems. And it can help prevent pipeline damage, not simply detect it after it happens.

GTI will test four different fiber optic cables. Three multi-mode fibers (Hergalite, Corning 62.5/125, and Corning 50/125) and one single-mode fiber (Fibercore Ltd.'s SM600). Technicians have buried the cable approximately 15-50 cm below the surface of the ground.

DOE said construction equipment does not have to break the fiber to be detected. When intrusion is detected, an alarm sounds, alerting the pipeline company of equipment encroaching on its pipe.

"This would enable pipeline companies in the future to take immediate action to stop unauthorized excavation and prevent potential damage to the pipeline," said the research unit.

The fiber optic system not only can warn of approaching construction activity but also help operators pinpoint where along the pipeline the potential hazard is developing. Stresses in the fiber optic cable will cause some of the light to be reflected back to its source, said DOE.

Because the light velocity in the fiber will be known, measuring the time for the reflected light pulse to return can determine the location of the encroaching equipment.

The largest technical barrier to perfecting fiber optic cable technology for pipelines, said DOE, is in developing methods to distinguish between potentially hazardous and benign intrusions into the right-of-way.

Compared to benign activities and noises, such as pedestrian traffic and thunder, large construction equipment will have characteristic signals. One goal of the project is to minimize or eliminate false readings from the cables through all seasons and soil conditions, said DOE.

Results of the project will be ready later this year.