HELICOPTER-BORNE LASER METHANE DETECTION SYSTEM A NEW TOOL FOR EFFICIENT GAS PIPELINE INSPECTION Werner Zirnig E.ON Ruhrgas AG, Germany Matthias Ulbricht Adlares GmbH, Germany Andreas Fix and Hans Klingenberg German Aerospace Center DLR, Germany ABSTRACT Together with the German Aerospace Centre DLR and the Brandenburg-based company Adlares, E.ON Ruhrgas has developed a novel infrared laser remote sensing equipment which can be used during routine aerial inspections by helicopter to check natural gas pipelines for tightness, particularly in built-up areas. In combination with the E.ON Ruhrgas satellite reference service ascos, which provides Germany-wide reference data for highly accurate satellite-based surveying, and geographic information systems with digital maps containing detailed data on pipeline routes, this development offers new, highly flexible and efficient ways of looking after natural gas pipeline systems. 1
BACKGROUND E.ON Ruhrgas is Germany's leading gas transmission company and the largest natural gas importer in Europe. It has a total gas sendout of approx. 640 billion kilowatt hours and operates a high-pressure gas transmission system totalling some 11,200 km of pipeline. This pipeline system covers the whole of Germany, providing the central link in the integrated European natural gas grid (Figure 1). E.ON Ruhrgas Pipeline System Figure 1. E.ON Ruhrgas pipeline system within the integrated European gas grid Being the owner of the pipeline system, E.ON Ruhrgas is also responsible for monitoring the system as required by law. This is done by way of walking or mobile surveys or aerial inspections of the pipeline corridors by helicopters. While surveillance by air is the best way of preventing third-party interference and detecting gas leakinduced discolouring of the vegetation in the countryside, leaks below sealed surfaces in built-up areas (Figure 2) can, with today's technology, best be detected by walking surveys involving the use of mobile leak detectors. These monitoring methods help prevent developments or events that could jeopardise pipeline integrity or cause hazards in the immediate vicinity of the pipeline route or put supply security at risk, while at the same time ensuring a high level of safety for pipeline operation. Yet using these methods, which have come to be standard throughout the world, usually entails high operating costs, which is why gas companies are keen to develop more cost-efficient solutions. The key to the success of new monitoring techniques lies in being able to swiftly translate innovative solutions into usable 2
applications. One of these monitoring techniques with a particularly high potential is optical remote sensing [1]. Figure 2. Helicopter view of buried high-pressure natural gas pipeline (dashed white line) in a built-up area. To use this efficiency-enhancing potential, E.ON Ruhrgas teamed up with the German Aerospace Centre DLR and the Brandenburg-based systems developer Adlares to develop a novel, infrared-based remote sensing equipment which has come to be known as the CHARM (CH 4 Airborne Remote Monitoring) system. This system can be used during routine aerial surveys by helicopter to also detect pipeline leaks [2, 3]. THE MEASUREMENT PRINCIPLE BEHIND REMOTE GAS SENSING Gas detection systems which are used to prove that buried natural gas pipelines are tight must be designed to detect leaks in the ppm range. Any remote detection system capable of performing a task of this kind must therefore be able to identify very small methane flows of as little as 10 l/hr. In Japan, the UK, France and Germany, considerable progress has been made in recent years in developing mobile and vehicle-based laser systems for remote gas detection [4,, 6]. Other experimental helicopter-borne sensing techniques to detect major gas leaks from long-distance transmission pipelines have undergone trials in the US and Russia [7, 8, 9]. Yet these gas detection systems are essentially designed for helicopter inspection in the open country and therefore lack the flexibility in measurement 3
beam control, detection speed and gas sensitivity specified for the CHARM system, which is designed for the more densely populated areas in western Europe. The Differential Absorption Lidar (DIAL) measurement principle employed in the CHARM project to develop the new technique is a laser based active optical detection method used successfully throughout the world for analysing trace gases in the earth's atmosphere [10]. The Lidar (Light detecting and ranging) technique involves sending out a laser light in the ultraviolet, visible or infrared spectral range and detecting and analysing the light back-scattered by the atmosphere or a solid target object. Trace gas concentrations can be determined by tuning the laser wavelength to the spectral signature and the absorption characteristics of the gas to be measured. In order to eliminate atmospheric and backscatter effects on the measurement signal, the DIAL technique uses light pulses of two different wavelengths. The pulses of one wavelength (λ on ) are absorbed by the gas while the others (λ off ) are not absorbed and serve as the reference (Figure 3). The trace gas concentration determined this way is the value integrated over the measurement path. The unit is ppm m. Backscatter area Figure 3. The Differential Absorptions Light detection and ranging (DIAL) principle. In order to be able to measure hydrocarbons like methane, which is the main constituent of natural gas, with a sufficiently high sensitivity from distances of 80 m to 10 m (the altitude of helicopters), the laser has to emit a wavelength at which these gases have an appropriate absorption line. Moreover, care must be taken to ensure that especially for gases with a finite background concentration such as methane (~ 1.8 ppm) 4
there are no saturation effects and there is no interference with the absorption lines of water vapour. MEASUREMENT SYSTEM INTEGRATION INTO HELICOPTER In a number of laboratory experiments over a two-year development and trial period, the measuring method was tuned to the light scatter on the ground, the use of the mobile helicopter platform and the main constituent of natural gas, i.e. methane. In a next step, a number of measurements were conducted under near-field conditions to determine the performance range of the remote sensing system. The tests showed that the very small methane leakage flows specified for this project can best be detected on a variety of surfaces by using an 100 Hz double-pulse laser system at distances of 80 m to 10 m. The measuring system is currently installed on a type MD00E helicopter. The entire equipment is accommodated in an external container attached to the cargo hook below the cabin between the skids (Figures 4 and ). Figure 4. Remote methane detection system attached to cargo hook between the skids of the MD00E helicopter. Particular care was needed to install the laser system such that it would not be subjected to major shocks and to ensure appropriate thermal control of all electronic components. The only prerequisites defined for the helicopter were a 320 kg load-
carrying capacity and the need for its on-board power supply system to provide some 1.8 kw. 1 2 3 1 Scanner & telescope 4 6 7 2 Double pulse laser 3 Opening for cargo hook 4 Laser cooling system Data acquisition system 6 Navigation system 7 Mains supply for laser Figure. System integration into on-board container (container sized 2.3 m x 1.1 m x 0. m). At an altitude of 10 m, the measuring points of the eye-safe infrared laser have a diameter of about 1 m on the ground. Since the gas leaking from a pipeline will not necessarily exit the soil directly above the pipe defect, the measuring beam scans a corridor of up to 18 m in width along the pipeline route. This involves the use of a newly developed scanning system designed to distribute the measuring points equally across the width of the corridor (Figure 6). In addition, to ensure proper beam positioning onto the pipeline corridor, a series of control devices have been implemented to ensure that the effects of helicopter movement are compensated. 10 10 direction of travel 0 0 0-10 0 20-10 0 10 0 20 10 20 20 30 40 - - -10-10 Figure 6. Example of scanning pattern within the pipeline corridor checked (scanned width of corridor is up to 18 m. The diameter of the measuring points on the ground is approx. 1 m; 100 measuring points per second). 6
A video camera records the image of the pipeline corridor, which is transmitted to a computer screen in the cabin. If natural gas is detected, it is shown on screen and there is an acoustic signal. Test flights of more than 100 hours have shown that even the smallest simulated gas leak can be detected from the helicopter at normal travelling speeds and altitudes (Figure 7). The detection system is currently undergoing further testing by E.ON Ruhrgas as part of the routine aerial inspection of pipelines in the open country and in built-up areas in preparation for a company-wide use. On these test flights, an additional operator on board can use the video image to manually direct the scanning field of the beam onto the pipeline corridor using the computer's control panel box. 7 6 Methankonzentration ppm 4 3 2 1 0 1 11 21 31 41 1 61 71 81 91 101 111 121 131 141 D atenpunkte Figure 7. Typical methane detection signal. A series of measurement points indicates presence of methane. Further system development will enable automatic positioning of the beam along the corridor. The coordinates of the E.ON Ruhrgas pipeline system are available in a geographic information system with an accuracy of 1 m to 3 m. The position of the helicopter can be determined using satellite-aided positioning (GPS) along with the E.ON Ruhrgas satellite reference service ascos which has an accuracy better than 1 m. Combining these highly accurate positioning system data for the pipeline and the helicopter in real time makes it possible to automatically direct the beam onto the pipeline corridor during the flight. ASCOS, THE SATELLITE-BASED REFERENCE SYSTEM OF E.ON RUHRGAS E.ON Ruhrgas has reproduced its 11,000 km natural gas transmission network in a geographic information system. The extensive land surveying required was based on data provided by the US Global Positioning System (GPS) and the Russian GLONASS system (Global Navigation Satellite System). For this purpose, E.ON Ruhrgas has set up its own reference network using stationary reference locations at its field sites. This network 7
provides real-time Germany-wide correction data for surveying work via a mobile telephone connection. Known as "ascos - ruhrgas positioning services" [11], this correction data service is also available to other organisations for general use. In combination with SAPOS, the positioning system used by the German Land Surveying Service, ascos can now offer consistent, highly accurate correction data for surveying tasks across Germany, which allows satellite-based surveying with an accuracy as high as 2 cm. CONCLUSIONS The successful completion of developments for a helicopter-borne methane measurement system has provided a natural gas leak detection method that can be used on small helicopters for routine monitoring of natural gas pipelines particularly in built-up areas. This new technique stands a good chance of replacing the costly manual gas detection method presently used. In combination with geographic information systems, whose digital maps include details on pipeline routes, as well as modern, highly-accurate satellite surveying systems, the new technique now makes it possible to geographically automatically allocate the reported locations in a straight forward, unambiguous way. Ground vehicles using similar navigation systems can then be directed to the locations detected from the air. This enables new highly flexible and efficient ways of looking after gas pipeline networks, allowing a swift and well-targeted response to alarms from central network monitoring systems. REFERENCES CITED [1] Zirnig, W.; Hausamann, D.; Schreier, G.: A concept for natural gas transmission pipeline monitoring based on new high-resolution remote sensing technologies. Proceedings 2001 International Gas Research Conference, Amsterdam, The Netherlands, November 2001. [2] Zirnig, W.; Ulbricht, M.: Innovative Technologies improve environmental protection - detection of gas leaks by helicopter-borne infrared laser system. Proceedings 22 nd World Gas Conference, Tokyo, Japan, June 2003. [3] Fix, A.; Ehret, G.; Hoffstädt, A; Klingenberg, H., H.; Lemmerz, C; Mahnke, P.; Ulbricht, M.; Wirth, M.; Wittig, R.; Zirnig, W.: CHARM - A Helicopter-borne Lidar System for Pipeline Monitoring, Proceedings of the 22nd International Laser Radar Conference (ESA SP-61), 2004. [4] Fabiano, A.G.; Green, B.D.: Development of a remote methane leak detector. Proceedings GTI's Conference and Exhibition on Natural Gas Technologies, Orlando/Florida October 2002. [] Hodgkinson, J.; Pride, R.; Smith, J.; Sutton, S.: GLIDE a new portable gas leak detection instrument. Proceedings GTI's Conference and Exhibition on Natural Gas Technologies, Orlando/Florida October 2002. [6] Iseki, T.; Miyaji, M.: A portable remote methane detector using a tuneable diode laser. Proceedings 22 nd World Gas Conference, Tokyo, Japan, June 2003. [7] McRae, T.G.: Evaluation of a new aerial leak survey approach. GRI Summary Report 1996 (GRI-96/0376). 8
[8] Philippov, P.G., et al.: DIAL-Infrared lidar for monitoring of main pipelines and gas industry objects. In: Optical remote sensing for industry and environmental monitoring, Proceedings of Beijing meeting 1998 (SPIE Proceedings, Vol. 304), p.119-127. [9] Degtiarev, E.V.; Geiger, A.R.; Richmond, R.D.: Compact mid-infrared DIAL lidar for ground-based and airborne pipeline monitoring. Proceedings SPIE 9 th International Symposium on Remote Sensing, Crete/Greece 2002. [10] Weidauer, D.; Rairoux, P.; Ulbricht, M.; Wolf, J.P.; Wöste, L.: Ozone, VOC, NO 2 and Aerosol Monitoring in Urban and Industrial Areas Using a Mobile DIAL System. In: Ansman, A., et al.: (Eds.): Advances in Atmospheric Remote Sensing with Lidar, 18 th ILRC Berlin, Germany 1996, pp. 423-426, Springer 1996. [11] Loef, P.: Die Vorteile des Ruhrgas Satelliten-Referenzdienstes kann jetzt jedes Unternehmen nutzen. In: VDV-Schriftenreihe, Band 19: Der Vermessungsingeieur in der Praxis, Verlag Chmielorz, Wiesbaden/Germany 2001. 9