Monitoring oil and gas pipelines in order to keep them safe from damages is a major challenge. Especially third party interference is a serious problem.
Fiber optic based monitoring systems represent a solution which substantially reduces the risk of pipeline damages and its devastating impact on the human and natural environment. Some of these systems use the so called Coherent Rayleigh Opticial Time Delay Reflectometer (OTDR) which deploys a standard single mode fiber optic cable into a listening device. They are inexpensive to install, operate largely automated and are designed to:
- Prevent pipeline damages or leaks caused by construction work, farming, illegal tapping, sabotage etc.
- Protect critical assets from third party interference.
The working principle behind the Coherent Rayleigh OTDR is the reflectometry effect. A single mode fiber cable is attached or buried nearby the pipeline or rail track. For telecommunication purposes such cables are very often already installed. As long as a dark fiber is still available it can be used for pipeline monitoring. A short-time laser pulse is generated and sent continuously with a repetition frequency from 1 kHz to 11 kHz and a wavelength of 1.55 µm through the fiber. The laser pulse causes the Rayleigh backscattering signal in form of a reflectogram in which the time delay of the signal is shown as a distance on the cable. After receiving the optical signals, the pattern of these signals are digitalized and analyzed by a computer unit. Using a special algorithm the signals pass through digital filters and will then be compared with samples stored in a library. After categorizing the event, the system sends an alarm with the exact position through the internet via TCP/IP to the system operator and suitable countermeasures can be initiated.