When regularly provided with information about the structural and functional condition of a pipeline, monitoring can help to prevent pipeline failure; detect problems and their positions; and, allow maintenance and repair activities to be undertaken when needed. This increases safety, optimises maintenance costs and decreases economic loss. Typical structural parameters to be monitored are strain and curvature, while the most interesting functional parameters are temperature distribution, leakage and third-party intrusion.

Recent developments in distributed optical fibre strain and temperature sensing techniques based on the Brillouin scattering effect promise to provide cost-effective tools that will allow monitoring over kilometric distances. Thus, using a limited number of very long sensors, it is possible to monitor the structural and functional behaviour of pipelines with a high spatial resolution at a reasonable cost.

Leak detection case study

In 2002, the construction of a natural gas storage facility approximately 1,500 m underground commenced near Berlin, Germany.

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Using mining technology, the building of underground caverns for gas storage in large rock-salt formation requires hot water and produces large quantities of water saturated with salt – otherwise known as brine. In most cases the brine cannot be processed onsite and must be transported by pipeline to a location where it can either be used for chemical processes, or injected safely back into the ground. Due to the fact that the brine can be harmful to the environment, the pipeline must be monitored by a leakage detection system.

The Berlin project required a 55 km pipeline to be constructed, and GESO GmbH was selected for the development and installation of the leakage detection system. During the construction phase, the temperature sensing equipment was first placed in the trench and buried in the sand approximately 10 cm beneath the pipeline.

The temperature profiles measured by both DiTeSt instruments are transferred every 30 minutes to a central computer and further processed for leakage detection. Dedicated software performs the leakage detection through a comparison between recorded temperature profiles, looking at abnormal temperature evolutions, and generates an alarm if a leak is detected. The system is able to automatically transmit alarms, generate reports, periodically reset and restart measurements, and requires virtually no maintenance.

Successful detection

Construction on the pipeline was completed in November 2002, with operation commencing in January 2003. In July 2003, the monitoring system detected a leakage. It was later found that the leakage was accidentally caused by excavation work in the vicinity of the pipeline. An alarm was immediately and automatically triggered and the flow was stopped.

A useful leak detection tool

Distributed strain/deformation and temperature sensing for pipeline integrity monitoring is a useful tool that ideally complements the current monitoring and inspection activities, allowing a more dense acquisition of operational and safety parameters. The measurements can be performed at any point along the pipeline. Furthermore, the monitoring is continuous and does not interfere with regular pipeline operation in the way that other maintenance can. The method can also be applied to non-piggable pipes.