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Eingeladener Vortrag
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The feasibility study „AGIFAMOR. Ageing infrastructures – distributed acoustic monitoring of pipes” is an interdisciplinary research project at BAM internally financed from 2015 to 2018. Therefore, the quite young fibre optic sensing technology of distributed acoustic sensing (DAS) was investigated to possibly be extended towards a global condition monitoring system for pipelines operating in real time.
DAS is a highly dynamic fibre optic sensing technology based on the method of coherent optical time domain reflectometry (C-OTDR). DAS allows capturing strain changes in the range of kHz. For the experimental work, the most suitable application yielding an optimum sensitivity was proven by wrapping a standard single-mode silica fibre around the pipe.
The DAS sensitivity was investigated regarding the detection of 1) incidents that initiate propagation of acoustic waves in the pipe wall, 2) changes inside the pipeline causing altered flow and 3) damage development in the pipe wall. Therefore, several testing setups in laboratory as well as in real scale were realized. For comparison purposes, experiments were accompanied by acoustic emission analyses and by measurements with accelerometers.
DAS was found to be very sensitive to gas ignition and its propagation across the pipe. Furthermore, the ability of DAS to detect and localize acoustic signals associated with pipeline leakage was demonstrated. The detection of crack formation and propagation within the pipe wall by means of DAS was studied during bending tests on several pipe segments, but was not proven so far with certainty. As expected, these studies turned out as the most difficult challenge due to the random occurrence and transient nature of microscopic damage phenomena.
Es wird ein Überblick über die Technik der faseroptischen Sensorik zur Zustandsüberwachung von Rohrleitungen gegeben. Im ersten Teil des Vortrages werden einige Verfahren der verteilten faseroptischen Sensorik, insbesondere die akustische verteilte faseroptische Sensorik, sowie der Stand der Technik in Bezug auf die Rohrleitungsüberwachung vorgestellt. Anschließend werden im zweiten Teil die Hauptergebnisse des Themenfeldprojektes AGIFAMOR zusammengefasst und in Hinblick auf weiterführende Untersuchungen diskutiert.
Im Vortrag wird das im Themenfeldprojekt AGIFAMOR eingesetzte verteilte faseroptische Messverfahren DAS (distributed acoustic sensing) vorgestellt, und die im Projekt erzielten Ergebnisse am unbeschädigten Rohr werden vorgestellt. Dazu gehören die Optimierung der Sensorapplikation sowie die Beobachtung von Schallwellen im Rohrmantel und von sich im Rohr ausbreitenden Druckwellen.
Here we present the BAM-project AGIFAMOR - Application of distributed acoustic and fibre optic sensors for continuous monitoring of pipes. Special attention is paid to the optimal application of the fibre optic sensor for achieving high sensitivity towards acoustic signals. First results of real scale bending tests are presented, where cracks developing in the pipe material were initialized and analyzed with respect to their acoustic characteristics.
In der Prozessindustrie werden häufig gefährliche Stoffe eingesetzt, so dass auch kleinste Leckagen der medienführenden Anlagenteile zu Gefährdungen der Arbeitnehmer sowie zur Belastung der Umwelt führen können. Für die Gewährleistung einer dauerhaften Verfügbarkeit der Infrastruktur ist die frühzeitige Erkennung und Ortung von potentiell gefährlichen Veränderungen an den Wandungen von Rohrleitungen und Behältern (in Form von Rissen, Pittings und Ablagerungen) erforderlich. Am Beispiel von Rohrleitungen, sollen im Rahmen des Projekts AGIFAMOR an der Bundesanstalt für Materialforschung und -prüfung (BAM), im Sinne einer Machbarkeitsstudie die Verfahren der verteilten akustischen und faseroptischen Sensorik zur kontinuierlichen Überwachung und Detektion potentiell gefährlicher Veränderungen in Industrieanlagen erprobt und qualifiziert werden. Dabei sollen die Applikation der optischen Sensorfasern hinsichtlich der Signalübertragung auf den Sensor optimiert und die Erkennung der für dieses Anwendungsgebiet relevanten Schallsignaturen entwickelt werden. Mithilfe eines solchen Messsystems können mit geringem Aufwand ausgedehnte Strukturen, auch unter erschwerten Bedingungen (z.B. hohe Temperatur, Einfluss von Chemikalien) kontinuierlich überwacht werden.
Pipelines and industrial piping systems are particularly relevant regarding technical safety, availability and maintenance. Large flow rates of hazardous substances imply that even smallest leakages can lead to high environmental impacts. Therefore, and to ensure the availability of infrastructure, an early detection and localization of potentially hazardous degradations to the walls (e.g. cracks, pittings, sedimentation, etc.) of the containments is necessary. However, in many cases it is not feasible to equip pipelines with a large number of point sensors at reasonable expense.
The principle of distributed fibre optic sensing relies on one single optical fibre, which simultaneously acts as a spatially continuous sensor as well as the signal transducer. Therefore, extensive structures can be provided with this type of sensor with comparatively low efforts.
As a consequence, monitoring oil and gas pipelines using distributed fibre optic sensors is on the upswing. Besides the established methods to measure temperature and strain, distributed acoustic sensing (DAS) has lately received considerable attention as a means to detect and localize third party threats to pipelines (approach of vehicles, digging, mechanical manipulation).
The so far not utilized potential of DAS as a means for continuous condition monitoring of pipes by detecting and localizing acoustic signals that point to certain damage scenarios, is currently under investigation in an interdisciplinary research project at BAM (AGIFAMOR, Ageing Infrastructures – Fibre Optic Monitoring of Pipes).
In order to qualify distributed acoustic fibre optic sensors for this application area, we especially focus on detecting and identifying the relevant acoustic emissions of interesting degradations as well as on the optimal way of application of the optical fibres to the specimen to achieve an optimal signal transmission of acoustic signals.
Condition monitoring of industrial infrastructures using distributed fibre optic acoustic sensors
(2017)
Distributed fibre optic acoustic sensing (DAS) can serve as an excellent tool for real-time condition Monitoring of a variety of industrial and civil infrastructures. In this paper, we portray a subset of our current Research activities investigating the usability of DAS based on coherent optical time-domain reflectometry (C-OTDR) for innovative and demanding condition Monitoring applications. Specifically, our application-oriented Research presented here aims at acoustic and vibrational condition monitoring of pipelines and piping systems, of rollers in industrial heavy-duty conveyor belt systems and of extensive submarine power cable installations, respectively.
Distributed Fibre Optic Acoustic and Vibration Sensors for Industrial Monitoring Applications
(2017)
We investigate the usability of distributed fibre optic acoustic sensing (DAS) for innovative and advanced monitoring applications in industrial and civil infrastructure installations. In this paper, we report on our ongoing application-oriented research activities regarding the utilization of DAS based on coherent optical time-domain reflectometry (C-OTDR) for condition monitoring of a variety of infrastructures. Specifically, our research presented here aims at acoustic condition monitoring of and fault detection in pipelines and industrial piping systems, at acoustic condition monitoring of rollers in industrial conveyor belt installations, and at acoustic condition monitoring of and threat detection in extensive submarine power cables, respectively. Furthermore, we show a method to mitigate the effect of sensitivity fading of C-OTDR based DAS due to unstable environmental conditions via the modification of the sensor fibre. This can help to provide a continuous adequate sensor functionality for a number of different industrial monitoring applications.
Industrial piping systems are particularly relevant to public safety and the continuous availability of infrastructure. However, condition monitoring systems based on many discrete sensors are generally not well-suited for widespread piping systems due to considerable installation effort, while use of distributed fibre-optic sensors would reduce this effort to a minimum. Specifically distributed acoustic sensing (DAS) is employed for detection of third-party threats and leaks in oil and gas pipelines in recent years and can in principle also be applied to industrial plants. Further possible detection routes amenable by DAS that could identify damage prior to emission of medium are subject of a current project at BAM, which aims at qualifying distributed fibre optic methods such as DAS as a means for spatially continuous monitoring of industrial piping systems. Here, first tests on a short pipe are presented, where optical fibres were applied directly to the surface. An artificial signal was used to define suitable parameters of the measurement system and compare different ways of applying the sensor.