Leak detection advances using fibre optics

Fibre-optic technology is making it possible to monitor pipeline its entire length with thousands of monitoring points providing a near real-time picture of what’s actually happening.

Fibre-optic technology used in monitoring has been available for quite some time; however, new technical advances have led to improved readout systems and better strain and temperature sensing fibres.

To monitor profiles over long distances means this technology represents a very efficient way to perform leak detection.

Distributed temperature or strain sensing using Brillion-based systems can identify leakages, verify pipeline operational parameters, prevent failures due to slope failures or fault zones, optimise oil production from wells and detect temperature anomalies usually indicating blockages or pipeline wear.

Often pipelines stretch several kilometres, crossing a multitude of terrains which are often composed of various geologies, meaning that a pipeline may be subject to landslide, settlement or heave factors.

Faults can cause lateral deflections leading to shear strains resulting in changes in curvature of the buried pipeline. These sorts of hazards lead to long-term deformations and altered stress/strain states and ultimately, leakage.

Ecological or environmental disasters can be avoided or minimised if pipeline leaks are detected early.

Often pipelines are under high pressure, meaning any presence of leaks great or small may produce a massive negative impact. Moreover, such events lead to lost revenue due to downtime and in some cases greater financial loss for remediation.

Recent developments into health monitoring of a pipeline based on a distributed optical fibre strain and temperature promise to provide cost-effective tools allowing structural monitoring over kilometric distances.

Thus, using a limited number of very long sensors it will be possible to monitor structural and functional behaviour of flowlines with a reasonable measurement and spatial resolution.

The development of SmarTape, Smartcord and temperature sensing cable when configured correctly provides monitoring of structural parameters such as average strains, average curvatures and deformed shape of the pipeline.

The Smartcord is made of a sensing optical fibre integrated into a fibre-reinforced plastic cord. Its aim is to monitor the strain changes in the soil.

The aim of the Temperature Sensing Cable is to monitor temperature, compensate the strain measurements for temperature and detect and localise leakages through the cooling that results from gas decompression or water leakage and conversely the local warming anomaly produced by crude oil.

Detection of leakage along pipelines, which is obviously an important part of the maintenance activity, has always been a difficult task.

Most of the time, a visual inspection of the pipeline is required to attest to the absence of leakage. In the case of buried pipeline, where an inspection is not possible, the presence of a leak is identified by a drop of the pressure.

Moreover, pressure tests are periodically performed to check the integrity of the pipeline even though the reliability of the test is relatively poor due to the influence of temperature differences along the pipeline.

As a result, pipeline operators have been looking at new solutions for the detection of leakage through the monitoring of the pipeline surrounding temperature.

The aim is to produce cost-effective integrated systems which may include combining conventional sensors, fibre optics, vibrating wire and vibration monitoring. Although commonly used in structural monitoring detection and dam seepage projects, pipeline leak detection is now becoming one of the most popular applications for this technology.

The key benefits for monitoring are:

• Monitoring ensures long-term quality;
• Allows structural management through improved maintenance and repair strategies;
• Optimisation of design through feedback leading to improved safety margins;
• Precise remediation reducing insurance premiums;
• Reduction of uncertainties;
• Increase in safety and knowledge.

Other useful applications for monitoring using this technique are on structures like bridges, towers, buildings, power plants, dams, roads and harbours, and the shutting down of high-speed railways in case of structural damage caused by earthquakes.

Distributed systems can pick up early hot spots of strain on a slope or open-pit face. Geotechnical engineers use this information to mitigate the slope, improving safety.

Advantages over existing technologies include a greater spatial coverage with enhanced reliability. Fibre-optic technology is passive, meaning it’s unaffected by transient currents and, importantly, unlikely to be damaged by lightning.

The beauty of the system is that the readout or interrogator is fully transportable. This portability means it can be used at different locations or even completely separate projects.

Typically, the fibre is fixed, glued or clamped to the surface or structure. If the system needs to be expanded, it’s simply a matter of running new fibres. The system is robust and fully integrated, including hardware, interrogator and software.

Monitoring provides real data regarding condition of the structure, its behaviour or response, monitoring changes caused by loading or induced stress, effects of aging and detection of new degradations.

The best results are managed when monitoring systems are implemented during the early construction phase, providing information on the structure's initial state, performance and evolution.

Environmental Systems & Services
www.esands.com