Abstract: The ELEKTROAPPARAT Company developed the multifunctional monitoring systems for extended facilities which indicate in on-line mode oil and other liquids, gas and multiphase leaks as far as third party activity in the protected zone using a fibre optic cable (FOC) as a sensing element. The Leak Detection and Activity Control System (ELEKTROAPPARAT Argus-EA LDACS) provides precise detection of location and nature of vibrations, spatial displacements and change of temperature characteristics on and around extended facilities such as pipelines, oil wells, railways, highways and power lines. Having equipped in the Transneft Company more than 5028 km of pipelines with the similar Leak Detection and Activity Control System, the Company is in permanent search of ways of improvement of the FOC monitoring technologies, which have been developed worldwide for nearly 40 years but still are considered to have significant deficiencies.

Ker words: Leak detection in Pipelines, Innovative development, Argus-EA system, FOC.

LDS: “MORE THOUGHT IS REQUIRED”
A recently published study of the U.S. Department of Transportation, Pipeline and Hazardous Materials Safety Administration appeals to a series of past incidents and concludes that only a small percentage of leaks has been detected and confirmed by existing pipeline leak detection systems worldwide (1).


LDACS Server in preparation to the test trials.

Referring to numerous technical reports the authors of the paper defend the view that “far more thought is required in dealing with leak alarms, and the solution may be multiple redundant independent LDS, and training controllers to understand the physical principles causing the alarm in more detail”.

It is the point that has been realized by scientific and development departments of the ELEKTROAPPARAT Company striving to reduce the probability of unmotivated leak alarms still occurring on equipped oil pipelines. The Argus-EA concept envisaged till now the use of two distributed sensing units designed respectively for leak detection and activity control – the DTS (Distributed Vibration Sensor) and the DVS (Distributed Vibration Sensor).

Besides traditional internally based methods analyzing the volume balance and the rate of change in pressure and flow of the transported media four mainstream technologies corresponding to different ideological approaches to leak detection are available: the FOC based sensing, the real time transient model (RTTM), the statistical analysis (SA) and the negative pressure wave analysis (NPWA).

The RTTM represents a hydraulic model of boundary conditions provided by field instruments at several facilities such as supply/delivery points and pumping and compressor stations while the SA deals with a series of different pipeline signals from which the flow, pressure and temperature remain the most significant. The NPWA looks into pressure wave configuration and intensity generated by a leak, and FOC based methods use the ability of the optic cable to register deviation in the acoustic field and


The Fibre Optic Cable serves as the LDACS sensing element.

temperature ranges around the pipeline (or other extended facilities).

THE FOC BASED LEAK DETECTION SYSTEMS DILEMMA
The general perception confirmed by the mentioned U.S. study is that none of the methods available is perfect. “Each of the above methods has its advantages and disadvantages, for example, most of the externally based technologies are able to detect small leaks and locate them accurately but it may not be feasible to retrofit cables or tubes to existing pipelines, sensors and cameras can only detect leaks within the sensing or line of sight distance, Mrs. Jun Zhang of the ATMOS International said at the 2013 PSIG Conference in Prague (2). - Thus most of the externally based methods are used for routine surveillance of pipelines rather than continuous monitoring. A leak may remain undetected until the next survey”.

The latter point evoked vivid discussion and catalyzed a new direction for the ELEKTROAPPARAT Company research in the desire to improve the leak detection precision and to minimize the unmotivated leak alarms rate. To achieve this goal the scientists did their best to use of one of the basic advantages of the ELEKTROAPPARAT systems, which consists in the combination of both the DTS and DVS in the LDACS. The idea was quite simple – to confirm a leakage signal obtained from temperature sensing with the signal on the change in the acoustic field of the corresponding pipeline location, and thus to improve the whole system`s reliability cardinally.

Another generally excepted deficiency of FOC based pipeline based monitoring systems is the fact that it is really difficult to test them. To persuade eventual skeptics ELEKTROAPPARAT uses specially designed pipes with valves which can be opened or partially opened remotely. There are other methods to change the temperature around the piping during test trials, f.e. even very simple water spillage.

AN INTEGRATED SOLUTION: DTS AND DAS SENSING FOR LEAKS
Formerly the Company successfully tested a similar device at the DRUZHBA oil pipeline near the Russian city of Bryansk. Using terminology backed by colleagues both in Europe and America the ELEKTROAPPARAT describes the new product as Distributed Acoustic Sensor (DAS).

The difference really matters: the ELEKTROAPPARAT DAS is able to measure and reproduce for the dispatcher the true acoustic field on two 50 km arms to each side of the Logical Module. The unit sends an optical signal into the fibre and watches the naturally occurring reflections that are scattered back along the preinstalled FOC. Analyzing these reflections and measuring the time between the laser pulse being launched and the signal received, the DAS measures the acoustic signal at all points along the fibre optic sensor.


The ELEKTROAPPARAT Argus-EA test at Transneft.

The mentioned test trial confirmed that possessing new qualities the new DAS based LDACS will have at least following characteristics: maximum coverage range with optical amplifier - 50 km, length of the virtual measuring channel: 5 m and less, sensitivity of phase change: - 0.1 – 0.2 radian, range of analyzed frequencies - 1–500 Hz under pulse recurrence of 1 kHz.

Like in the case of the DVS the newly developed ELEKTROAPPARAT DAS architecture makes the FOC work as a set of virtual microphones and as the transmission medium for measurement information. The DAS utilizes Coherent Optical Time Domain Reflectometry (COTDR) to analyze the backscattered Rayleigh light and to record vibrations in multiple virtual channels the number of which can be up to tens of thousands with the interference sensitivity and an accuracy of the impact location +/- 5m. Hundreds of events can be detected and “heard” simultaneously and independently. For shorter monitoring projects the traditional 5 meter length of the virtual microphone can be decreased to 3 meters since the new device provides wide possibilities to vary the working parameters. So reducing the spatial resolution the “signal–noise” interrelation can be improved bringing down the noise disturbance.

ELEKTROAPPARAT DAS: A STEP TOWARDS NEW QUALITIES AND APPLICATIONS
In the new linear DAS device is characterized by smaller physical size and the use of a breakthrough optoelectronics design. It is implemented to measure the backscattered signal with significantly higher precision and speed, which allows acoustic recording of the registered events converting if necessary the FOC into an acoustic antenna with extremely high sensitivity and frequency response. This would both facilitate new options in event tracking and make it possible to implement the technology in other monitoring fields. The latter fact opens new horizons for the ELEKTROAPPARAT Company which is ready to work not only with oil and gas pipelines, but with railways, power lines and specially protected perimeters as well.


One of the DAS options is the monitoring of 5 pigs simultaneously. While moving through the pipeline the pig meets welded pipe joints, and in the chart recorder each disturbance wave creates a λ-formed image.

Meanwhile having historically set the oil and gas pipelines monitoring as main priority ELEKTROAPPARAT is going to make better use of the newly developed DAS system to make the leak detection and physical event localization more secure and fast. The main of the new abilities of the LDACS is the duplication of the leak signal provided by both the Distributed Temperature Sensor and the DAS. To this pioneering purpose in collaboration with leading scientists from the prominent Moscow State University a special library of the gas and fluid leaks acoustic fields is being created. One of the factors resulting in better leaks and other events recognition is the linearity of frequency phase as far as the stability of the amplitude-frequency characteristics around the 1–2 kHz diapason. So the linear DAS based device is able to preserve the shape of the incoming backscattered signal and to implement the morphological features recognition.

One of the generally recognized DVS deficiencies is the difficulty of fine tuning of each length channel, therefor in many cases the same event can be depicted with different amplitudes. The presence of virtual acoustic microphones distributed along the FOC and possessing preset characteristics allows the normalization of all signals in every length channel. This is the key not only to very precise event recognition, but a way toward the solution of another important task – the calculation of the distance between the established event and the piping. This “2D” technology opens the door towards recognition of significant impacts developing not only along the pipeline, but perpendicular to it as well (f.e. pedestrians or car movement). On the second phase of the algorithmical event analysis the dispatcher can follow the event in development, and the LDACS is ready to filter out natural events not jeopardizing the pipeline and its technical facilities.

One more practical advantage of the ELEKTROAPPARAT DAS is the extension of the working temperature diapason of the LDACS from +5….+25° C in case of the DVS up to +5….+40° C. Due to the fact that many pipeline projects in the Middle East and Latin America cannot provide cooled and air conditioned shelters for the equipment installation, this will bring down the installation and power consumption costs. The extended possibility to implement the Argus-EA DAS on onshore/overland and underwater pipelines is another important marketing feature of the new system.

An awareness that the new version of the LDACS will register even smaller leaks can be enhanced by its integration with parametric LDS`s of any kind, which is important due to the corresponding technical requirements or the legislation of several countries.

Extending the catalog of advantages of the DAS based Leak Detection and Activity Control System, the responsible and environmentally-oriented pipeline operator would remark, that the DAS is not sensitive to any fluid property changes and not affected by pipeline transients. Leak location on gas, liquid and multi-phase pipelines is fast and accurate, multiple leaks can be registered with the same high precision. –0--

LITERATURE

• 1/ U.S. Department of Transportation, Pipeline and Hazardous Materials Safety Administration, Final Report No. 12-173, “Leak Detection Study – DTPH56-11-D-000001”, Dr. David Shaw, Dr.Martin Phillips, Ron Baker, Eduardo Munoz, Hamood Rehman, Carol Gibson, Christine Mayernik, December 10, 2012.
• 2/ Review of Pipeline Leak Detection Technologies.Jun Zhang, Andy Hoffman, Keefe Murphy, John Lewis, Michael Twomey – ATMOS International. Report at the PSIG Conference in Prague, 2013.
• 3/ 3R International, Technical Journal for Piping System Integrity and efficiency, Vulkan-Verlag, Essen Germany, Special 2/2012, p.63-65.