FAQs
Installing fibre optic cables
The Sensornet team offers a full solution and will design the entire engineering solution for you. This includes the fibre optic cable required and its installation, the sensing equipment and the monitoring and reporting software. Sensornet has the personnel and equipment to perform fibre optic installations across a number of industries and in the past has carried out installations ranging from inside oil-wells to along the length of pipelines to inside dams.
Each specific installation requires specialised knowledge and equipment as well as dedicated fibre optic cable designs. Sensornet has built this knowledge over a number of years and together with installation partners is able to tackle the most challenging of installations.
The Sensornet team will manage your entire project right through to its handover. We operate to the highest standards of quality; our solution is, after all, about increased safety and security. We are ISO 9001 accredited and meet all Health & Safety Executive requirements.
Types of cables that we offer
In the Sensornet distributed detection system, the fibre is the sensor. Sensornet has developed rigorous quality assurance systems to verify the effectiveness of the fibres that we package into our sensing cables. Depending on the environment of the specific installation the cable will require different levels of protection - varying from the bare fibres which are not much thicker than a hair to very rugged cables where the fibre is encased in a combination of steel tubes and polymers, with design lives of up to 30 years.
Care to be taken when installing fibre optics
Because they are used in a variety of harsh environments, including oil rigs, dams, power stations, refineries and other industrial settings, fibre optic sensors need protection from both mechanical and chemical damage. Mechanical hazards can range from dropped tools to damage from traffic.
Fibre optic sensors offer many advantages over conventional sensors. They are very small and flexible, intrinsically safe, and not susceptible to electromagnetic interference. They are also very strong – an optical fibre can support a weight of 5kg without breaking. But in spite of their strength, the fibres are susceptible to damage and scratches, and micro-cracks can weaken the fibre and lead to errors in measurement data. Although these errors can generally be compensated for, better results will be achieved if the fibre is correctly installed and adequately protected from its environment.
Chemical damage can result from exposure to process chemicals or from exposure to hydrogen, which can diffuse into the fibre and cause darkening. Hydrogen darkening occurs even more rapidly in environments, such as steam injection wells, where the fibre is also exposed to high temperatures and pressures. The darkening reduces the amount of light that can pass through the fibre. This, in turn, reduces the amount of backscattering signal. This not only affects the resolution of temperature measurements but, because the Stokes and anti-Stokes reflections each respond differently, it may also reduce their accuracy, if inappropriate calibration techniques are used.
Fibre protection
To avoid these pitfalls, the fibres need to be protected. The fibre’s first line of protection is a primary coating. This can vary from 10 to 400 microns thick and is usually applied to the surface of the fibre during manufacture. The coating prevents the development of microcracks on the fibre surface resulting from mechanical damage or exposure to the atmosphere. A variety of different materials can be used as coatings. Although the fibre itself can withstand temperatures up to 1200°C, the coating materials generally cannot, and once the coating breaks down it no longer offers any protection to the fibre surface. Therefore the choice of coating material depends on the operating temperatures the fibre will be subjected to.
Although the primary coating provides a good initial layer of protection, in order to survive in harsher environments the fibre optic is generally inserted into a cable, which is specially designed to withstand the hazards of the environment in which the fibre optic will be used. Cable designs can range from thin cables just 1mm thick, to thicker cables rugged enough to ensure a fibre is not damaged if the cable is run over by a tank.
All splices also need to be housed in appropriate splice boxes – these protective environments ensure that the splice is correctly shielded against damage.
Hydrogen protection
Where the fibre is exposed to hydrogen, it is necessary to provide a hermetic layer to prevent hydrogen from entering the core of the fibre. One way to do this is to deposit a carbon or metal coating onto the surface of the fibre. Another is to manufacture a tube around the fibre, and then fill the tube with a hydrogen scavenging gel. These methods normally provide adequate protection against hydrogen darkening, even at elevated temperatures.
However, these precautions are in vain if the cable is damaged during installation. A common installation method involves inserting a conduit into the installation, and then pumping the primary coated fibre into the conduit, a practice which often damages the fibre and reduces the performance of the sensor. To avoid this, Sensornet uses a technique where a well-protected, cabled fibre is injected, rather than pumped, along the conduit.
Want to find out more?
Sensornet Ltd is the technology leader in distributed sensing. To find out more about what our technologies can do for please contact one of our sales representatives.
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