TPI DETECTION ON PIPELINE ROUTE BY USING EXISTING FIBRE OPTIC CABLES

Transcription

1 TPI DETECTION ON PIPELINE ROUTE BY USING EXISTING FIBRE OPTIC CABLES G. Re and A. Colombo Snam Rete Gas Italy ABSTRACT A significant and cost-effective technology for industry employing advanced, distributed fibre optic sensors is offered on the market. This technology provides an innovative tool for detecting and locating Third Party Interference (TPI) in security areas by using, as sensor, a fibre optic cable installed in proper position around the area to be protected. As a matter of fact and since several years, most European gas companies lay a fibre optic cable parallel to big-inch transmission pipelines, to take advance both of the signal transmission possibility and the minimum additional cost of the work taking into account that a big trench must be in any case excavated for pipe laying. Now, the idea of using cable fibres for detecting TPI on pipeline route turns out to be a logic new application of the system. However cable type and lay conditions were not made for the purpose of security monitoring system, detecting TPI, tampering and illegal tapping attempts: that s why the immediate system transfer and its behaviour were not so certain. Due to the novelty of the system and its promising performance, a joint study among seven companies of the Groupe Europeen de Recherches Gazieres (GERG), Program Committee Transmission and Storage, plus Tokyo Gas Co., Ltd. was started in order to evaluate the system performance with field tests, discuss the results and equally share related costs. The test location was selected along a big inch transmission pipeline located in North-East Italy transporting to Italy natural gas from Russia. The region is very populated, industrial and therefore generating different types of background noises like those deriving from wheeled traffic, railways, river crossings etc.: one big concern was in fact the discrimination of true alarms in a noisy ambient not penalising its sensitivity. This paper explores the merits of the selected system for monitoring TPI after a first series of field tests carried out in Italy on a 35 km long pipe section, in June In addition, the paper describes the principles of TPI detection in fibre optic cables, the system installation characteristics and the series of tests carried out in field giving a general system evaluation. 1

2 1. INTRODUCTION Optical fibres are dielectric wave guiding devices used to confine and guide light. Figure (1) illustrates a cross-sectional view of a typical optical fibre. n cladding Core µm n core Cladding 125 µm Buffer 250 or 900 µm θ n core θ 1 φ c n cladding Cross-Section Figure 1. Cross-sectional view of typical optical fibre. Due to high bandwidth, low attenuation and mechanical properties, each fibre is capable of replacing over 1000 copper wires in telecommunication systems and due to these characteristics, optical fibres have become the most affordable and efficient medium available in the field of communications. Fibre Optic Sensing However, optical fibres can be more than mere signal carriers. Light that is launched into and confined to the fibre core propagates along the length of the fibre unperturbed unless acted upon by an external influence. Specialised sensing instrumentation may be configured such that any disturbance of the fibre that alters some of the characteristics of the guided light (i.e. amplitude, phase, wavelength, polarisation, modal distribution and time-of-flight) can be monitored, and related to the magnitude of the disturbing influence. Such modulation of the light makes possible the measurement of a wide range of events and conditions; many of which are useful for monitoring engineered structures and machinery. Fibre optic sensors offer significant operational advantages over conventional techniques: they can cover, as sensor, long distances, in addition their composition turns out in an insensitivity to electromagnetic fields and corrosive environments. Hence, fibres are now replacing the role of conventional electrical devices in sensing applications to the extent where we are now seeing a multitude of sensing techniques and applications being explored for practical gain. Therefore, fibre optic sensors offer a radically different approach to continuous, online condition monitoring. In addition, fibre optic sensors are particularly well suited for condition monitoring applications in that they are lightweight, durable, sensitive to several 2

3 parameters while insensitive to many disturbances, and can be incorporated within equipment and structures without being intrusive. Furthermore, the strong developments of this technology for communications, the continuous research and new achievements obtained worldwide are leading to significantly reduce the cost and complexity of future sensing systems with immediate benefits on systems adopting these principles. The vibration and movement sensing characteristics of fibre optic sensors makes them a good candidate for new applications where tampering or interference needs to be monitored. Such applications vary from monitoring the integrity of cables carrying sensitive data or industrial process control signals to monitor the integrity of asset perimeters. Fibre optic cables, when used as sensors, can be applied to many types of fences and walls, rooftops, or air-conditioning ducts, or they can be buried in gravel or under lawns. Their application in monitoring pipeline right-of-way (ROW) and in detecting TPI intrusions for lengths of tenths of kilometers is a new field of use therefore requiring validation. 2. SYSTEM DESCRIPTION The system is effectively a fibre optic microphone, combining the characteristics of a piezoelectric transducer and strain gauge sensor, designed to detect disturbances generated by TPI activities, while discriminating between normal ambient conditions. For practical purposes, system monitors signals from 1 Hz to 100 KHz. This is in contrast to most conventional TPI detection systems, which tend to operate as a trip wire style system, where damage has to be done to the fibre optic cable or copper wire, so the OTDR (Optical Time Domain Reflectometer) or TDR (Time Domain Reflectometer) can locate the damage. This is often too late and the cable would have to be repaired after each incident. The system tested in our project is real time and should be looked at as a preventive alarm as well, since it can detect early stages of set up of an excavator or other equipment as well as, earth movement caused by, landslide, earthquakes, floods or stream scour. A further expected advantage is that the system can utilise any existing optical fibre communications cable as the sensor. The system employs an optical fibre cable laid alongside or above the pipeline as a uniform sensing device to continuously monitor, in real-time, any physical disturbances or TPI activity near the pipeline. The system is very sensitive to the frequencies of the sound or pressure waves generated by TPI and these can be isolated from other environmental signals for clear identification. The system comprises an optical fibre cable laid in close proximity, above or adjacent to the pipeline (within one to three meters) and an industrial hardware platform (the Locator ), containing the optoelectronics, data acquisition hardware and signal processing software, installed at one end of the pipeline section to be monitored. The system can operate in a stand-alone mode or interfaces can be provided for the industrial control systems usually encountered in pipeline management operations. 3

4 The pipeline industry has been installing fibre optic cable along their pipelines for several years. If the cable has three single mode fibres that are not in use, system could use the existing cable. This would reduce installation costs; its sensitivity, on the other hand, is not significantly affected. If fibre is not available or not installed near the pipe, then an inexpensive, direct burial cable can be installed above or adjacent to the pipeline using an approved ploughing method. The cable would be installed from 300 mm to 1.5 meters below the ground surface. Cable depth is dependent on the end user requirements i.e. early detection of excavation by hand tools or the approach of a truck or excavation equipment would require 300 mm positioning. If early detection of excavation by hand tools is not a requirement, then the cable could be positioned at a greater depth. System does not require the optical fibre to be in intimate contact with the pipeline for effective TPI detection. The system comprises only two major components an industrial hardware platform that houses all the intelligence and the external optical fibre cable. The use of an industrial PC-based, software-controlled system provides useful flexibility in analysing and reporting pipeline TPI s. For example, a response action may be deferred on a TPI alarm, if the operator knows there is scheduled maintenance activity or repair works at the particular alarm location. Should another activity occur at a different location, then the alarm can be acknowledged and the end user s response team can take the appropriate action. TPI data can also be stored for later analysis so that a profile can be established of any ad hoc environmental factors or incidents that might falsely be assessed as a TPI event. In this way, the system can learn to adapt to its environment. The Locator feature will also allow the detection of TPI signals to be treated differently according to their location, further minimising potential false alarms. Concerning false alarms, one particular benefit of fibre-optic based systems is their immunity to both radio frequency interference (RFI) and electrical interference (EMI), particularly important for installations near high voltage electrical equipment or in areas subject to lightning strikes. The system can be interfaced directly to a SCADA System via LAN/Ethernet that provides a complete package. The overall system also has the flexibility to interface to a wide variety of local or remote pipeline management systems so that it can interact with supporting security technologies such as video display systems, CCTV, Access Control systems and visual and audible alarms. Its interfacing capabilities include Ethernet TCP/IP, UDP, SMTP and RS SYSTEM CONFIGURATION The system deploys an industrial platform as the system controller. For this application, no optical amplifiers are required, as the test section is less than 50 km long. 4

5 Locator in ISTRANA compressor station Fibre optic cable buried near pipe CABLE LENGTH m ODERZO 29.1C VALVE STATION END SENSOR Not to scale Buried Pipeline Figure 2. System installation schematic. A field termination unit (end sensor) will be required and housed in a fibre dome and suitable pit. The system controller & fibre terminating equipment are in rack-mount configuration and must be installed in a suitable cabinet in a temperature-controlled environment, typical of today s modern control rooms. The ideal operating temperature is +20 C ± 5 C.As part of the system, there will be one System Controller with a standard Graphical User Interface (GUI) to receive, identify and acknowledge alarms. The system s standard controller screens (GUI as shown in Figure 3) are predefined with some customisation available to display the customer s logo or other minor changes. This display is the primary interface for the operator to receive, identify and acknowledge alarms. Another software allows to have the alarms displayed on a site map (Figure 4), which provides a pictorial representation of the pipeline, valves, etc. When a TPI incident occurs the location of the event is immediately displayed on the site map at the same time as an audible alarm is triggered. The operator needs to acknowledge the alarm to disarm the system. The setting up of alarm control limits and any environmental filters would be undertaken initially at each section controller. After initial system set-up, management of control limits and filters would be undertaken from the controller. Resetting of alarm status would also be carried out from this controller or remotely by using appropriate programmes. The system will operate over three unused single mode fibres in the communications optical fibre cable installed near the pipeline. The cable is approximately 1.5 meters below the surface in close proximity to the pipeline. 5

6 Figure 3. Screen supplied with System 4. THE EXPERIMENTATION 4.1 General Project Plan The project objective is to evaluate system performance in detecting and locating TPI. The system installation, which does not include installation of the optical fibre cable, is carried out in accordance with ISO 9001 quality assurance requirements and include factory and site acceptance testing. There were eight (8) distinct phases involved in the project for which GERG experts, Snam Rete Gas operative centres of Pordenone and Montebelluna and company s engineers contributed in their specific field to carry out the experimentation. Phase No. Table (1). Project Phase 1 System purchase 2 On-site assembly of the equipment 3 In site calibration and commissioning 4 Training 5 TPI testing (first phase)- preliminary report 6 Pig run test 7 System behaviour evaluation 8 Final report 6

7 Being available a suitable length of fibre optic cable in Italy along the 48 import pipeline from Russia and in order to minimise overall costs, Snam Rete Gas proposed to the companies group as project leader and suggested to perform scheduled tests in the pipe section comprised between Istrana and Oderzo with a corresponding cable length of meters. Participating companies have approved the solution as proposed and a contractual agreement has been signed. The experimentation was therefore aimed to evaluate the sensitivity and performance of the selected system. 4.2 Test Execution The testing activities were carried in Italy from May 26 th to December For test purposes, three fibres of the fibre optic cable buried along a 48 OD Russian gas import pipeline in North East Italy have been used and more precisely a section from Istrana (Compressor station positioning of the controller) to Oderzo (installation of passive reflector) two towns located in the regions Veneto and Friuli Venezia Giulia. The cable, armoured, was buried directly in the ground without conduit at the beginning of the eighties; it stretches along a typical alluvial soil mainly composed of a superficial layer of cultivated humus with a depth varying from 50 to 120 mm; beyond this depth stones of different sizes mixed in sand are present. Water is also present and need drainage works in field to facilitate its flow downwards: for this scope many drain trencher machines are used in the area even on pipeline R.O.W. Figure 4. Pipeline route with alarm sections displayed on the map 7

8 The length of the sensor cable section is 36,286 km. This length of sensor will allow testing of the locator functions; no amplifiers were necessary; the quality of the fibre and splices determine this capability. The section of used f.o. cable and the relevant fibre position and connections is reported in Figure 4. Channel 1 Channel 2 Locator Figure 5. Connections schematic on existing f.o. cable Preliminary attenuation measures were made by Snam Rete Gas engineers and communicated in advance to system manufacturer. The test protocol was executed in these phases: 1 system background noise calibration 2 system length calibration 3 system TPI detection capability 4 PIG tracking 5 normal operation. 4.3 System Background Noise Calibration In this phase the system must learn and do not recognise as alarms the typical background noises of the examined pipe section. The testing/calibration also determined the following: - Ambient background levels. - Non-threatening events such as vehicle traffic on nearby roads. - Railway traffic, if situated near the site. - Sensitivity to weather events, e.g. thunder storms. 4.4 System Length Calibration The length of the fibre optic cable may differ from pipeline length: it is important, in order to fix the exact event location, to synchronise the two lengths. The measurements carried out with an O.T.D.R. (f.o. cable) and previous recorded pig runs reported the following: 48 OD PIPE SECTION LENGTH: m F.O. CABLE LENGTH : m ( m) A simple equation was produced in order to correct distance error when displayed on the map. 8

9 4.5 System TPI Detection Capability The capability and the sensitivity of the system to detect different kind of interference have been checked in controlled conditions. The testing includes all of the following TPI in three different locations: 1 Dropping of various weights. This provides an indication of equipment or materials being unloaded on the ROW. 2 Manual excavation of the site. 3 Different types of vehicles driven on the ROW, e.g. motorcycles, 4WD vehicle, and rubber tired backhoe on trailer, excavation equipment. 4 Horse riding. 5 Mechanical excavation with a rubber tired backhoe. 6 Agricultural activity, i.e. tractor with plough, drain trencher. 7 Gas leak. 8 Pig run tracking. The results of the activity carried out from May 26 th to June 3 rd report; this is how tests procedure was carried out: were gathered in a 1 Material drop. A series of weights (5, 10, 15, 20 and 25 kg) was dropped one at a time from a 1 meter height starting at a horizontal distance of 5 meters from the pipeline and reduce the distance by one meter until the drop point is above the pipeline. 2 Manual excavation. The test was performed with individual digging with spades and pickaxes, starting 5 meters from the pipeline and reducing the distance a meter at a time until the excavation was above the pipeline. 3 Drive over test. Motorcycle (dirt bike), ATV, 4WD and a typical vehicle used for pipeline inspection were driven parallel to the direction of the pipeline at several distances, say 10 m, 6m, 3m and 1 m, at typical speeds. Vehicles were also driven across the pipeline position, one at a time. 4 Horse riding. Horse riding along the pipeline was organised in order to verify system sensitivity to this peculiar event. 5 Backhoe Test. Once the equipment has been put in place the bucket was raised and dropped from varying heights and distances from the pipeline. The drop height varied from 1 to 3 meters and the distance started from 10 meters from the pipeline and reduced in 1 m steps until the equipment was one meter from the pipeline. The backhoe excavated a pit 1 meter deep at the 10 meter mark and again every 2 meters until it was within 2 meters of the sensor. 6 Agricultural activities. A drain trencher (Fig. 6) and a tractor with plough operated at different depths and distances from the pipe. 7 Gas Leak. A gas leak was simulated by opening of a vent valve in a secure area. 9

10 8 Pig run tracking. A cleaning pig was launched from the trap point of San Giorgio running at the usual average speed of 2/3 m/s and recovered in Istrana Compressor station. Figure 6. The drain trencher perpendicularly crossing pipeline route during test 4.6 Normal Operation Figure 7. Cleaning PIG The system has been tested in normal operational conditions for a sufficiently long period (8 months) which allowed a good comprehension of its behaviour in different situations. 10

11 Its control was made in remote conditions, thru internal LAN which stretches all over Italy and directly in Milan Snam Rete Gas headquarters, about 250 km away. 5. RESULTS This peculiar type of terrain composition together with an important cable burial depth turned out in a system sensitivity tuned in detecting big operating machines only, for which the information of their presence on pipeline R.O.W. was appreciated by the operative maintenance area centre. The location of the interference has been obtained with an accuracy precise enough to intervene quickly and effectively. The accuracy in locating the event is higher when the number of elementary signals is high, i.e. the perturbation is noticeable and the event lasts long time. It can also be improved by a better alignment of the pipe and the cable lengths. In our test the system was not able to track the PIG with enough accuracy and reliability. During the normal operation phase of the test, some alarms were caused by big operating machines as in the preliminary tests. The long period of system testing, evaluation and trials, permitted system amelioration thanks also to a constant and active presence of system manufacturer. System stability to background noises, one of main concerns considering the very populated and industrialised region, was shown to be one of the best system performance. Particular attention was paid to the temperature of the HW component and in particular of the laser which must be as constant as possible and around 20 C. 6. CONCLUSIONS In the limits of a single installation, the final evaluation of the experts of the GERG working group is positive. Future activities for improving the knowledge of the system could be oriented in evaluating this technology with different kind of cables, e.g. non-armoured f.o. cable in conduit, and in different terrains. Furthermore additional system improvements could be envisaged as software development in order to permit alarm type recognition as well as the pig tracking possibility, a very useful information to monitor pig position at any time. 11