Filtern
Dokumenttyp
- Zeitschriftenartikel (11)
- Beitrag zu einem Tagungsband (6)
- Vortrag (3)
Sprache
- Englisch (20) (entfernen)
Schlagworte
- LH2 (5)
- Release (5)
- BLEVE (3)
- RPT (3)
- Atmospheric boundary layer (2)
- Distributed acoustic sensing (2)
- Fragments (2)
- Gas dispersion (2)
- Hasard assessment (2)
- Hydrogen (2)
Organisationseinheit der BAM
- 2 Prozess- und Anlagensicherheit (20) (entfernen)
Eingeladener Vortrag
- nein (3)
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.
A steel pipeline segment of 2.5 m length was subjected to quasi-static four-point bending load in three steps for studying the initial cracking and damage accumulation based on the Acoustic Emission (AE) technique and by the direct current potential drop (DCPD) technique. For the latter, a new post-test analysis method was established.
AE is found more sensitive to crack initiation than DCPD. Formation of mesoscopic and macroscopic cracks as well as their closure and the resulting friction generate weighted peak frequencies below 400 kHz, whereas microscopic cracking produces AE with broad band spectra identifiable by weighted peak frequencies above 400 kHz. Critical states alike the maximum load level and the leak opening were accompanied by peak amplitudes above 85 dBAE. This rather fundamental study provides a data base for possibly developing advanced strategies of detection and alarm systems based on acoustic monitoring of pipelines, or at least, steel structures.
In order to reduce the human footprint of CO2 emissions and limit global warming effects hydrogen combustion is becoming increasingly important. To enable fuel cells and gas turbines to operates this carbon free fuel, unprecedently large amounts of hydrogen need to be produced and safely transported and stored. The investigation of the effects of accidents involving hydrogen is therefore becoming of outmost importance. Since hydrogen is usually stored and transported under pressure, one scenario to be considered is the release of hydrogen from a leakage with subsequent ignition. The resulting jet flame must be characterized with respect to the thermal radiation emitted into the environment to define safety regulations. Various models that characterize the resulting flame shape and radiation already exist in the literature, but these are mainly based on empirical data from hydrocarbon jet flames.[1-4] To verify these models, a H2 Jet Flame project conducted at BAM, is investigating the safety of momentum driven hydrogen jet flames. For this purpose, large-scale tests are carried out at the Test Site Technical Safety (BAM-TTS). The object of the investigations is to assess the effects of real scale release scenarios regarding flame geometry and the thermal radiation emitted. Parameters such as release angle, leakage diameter (currently 1 mm to 10 mm), pressure (currently up to max. 250 bar) and mass flow (up to max. 0.5 kg/s) are varied. In addition, influences such as the type of ignition, ignition location as well as delayed ignition can also be investigated. The gained knowledge will be compared with existing jet flame models, to validate these and identify a possible need for further development. In particular, the focus will be laid on the thermal radiation of hydrogen flames. The challenge here is the visualization and characterization of the flame geometry in an open environment. Visualization is performed using infrared (IR) camera systems from at least two viewing angles. Measurements of the heat radiation of jet flames, which can be found in the literature, are mostly based on unsteady outflow conditions. The experimental setup used here allows for the generation of a steady-state outflow for several minutes and thus a direct comparability with existing (steady-state) models. Furthermore, the tests can be carried out for comparative measurements with hydrocarbons (methane, etc.) as well as mixtures of hydrogen and hydrocarbons.
For hazard Assessment purposes we need models to predict what would happen in case of an accident.
The challenge in hazard assessment consists not only in choosing the right model, but beforehand to define the correct scenario .If models can be found for the physical effect to be simulated, the validation of these models is the next challenge.
Even if experimental data can be found it should always be checked, if these data are correct, even if in general experimental data are considered as “failsafe” or “the absolute truth”.
For hazard Assessment purposes we need models to predict what would happen in case of an accident.
The challenge in hazard assessment consists not only in choosing the right model, but beforehand to define the correct scenario. For hydrogen applications the validity of the models has to be checked, as well as the kind of scenario to assume for accidental releases of hydrogen. Open questions on these topics will be adressed and the newly founded competecne centre for Hydrogen Saftey at BAM will be presented.
Experimental investigation of the consequences of release of liquified hydrogen onto and under water
(2022)
Large-scale experiments have been performed to investigate the possible consequences of realistic amounts of liquified hydrogen (LH2) encountering water. The tests were performed at the Test Site Technical Safety of the Bundesanstalt für Materialforschung und –prüfung (BAM) in Horstwalde, Germany.
The experiments aimed at investigating that upon contact with water, the evaporation rate of LH2 can be that high that physical explosions or even rapid phase transitions (RPTs), could occur. RPTs can generate air and underwater blast pressures which could damage adjacent plant or structures (which has been demonstrated when releasing LNG).
The tests were performed in a 10 m x 10 x 1.5 m basin filled with water. LH2 releases with mass flows ranging from approximately 0.25 kg/s to approximately 0.8 kg/s were established releasing directly from a trailer carrying LH2. The LH2 was released through a 46 m long flexible double vacuum insulated transfer line (inner diameter 39 mm). The releases occurred from a height of 50 cm above the water surface pointing downwards, 30 cm under the water surface pointing downwards and 30 cm under the water surface pointing along the water surface. The release system allowed for an initial phase to release flashed LH2 into the air before redirecting the flow towards the water surface for liquid release. A thermocouple inserted near the nozzle is used to indicate the presence of LH2 at the nozzle. The nozzle could be moved up and downwards relative to the water surface and also moved into the water. The release system was purged with helium before starting a release. A mouthpiece at the end of the release line as well as a manually operated valve at the trailer were used to vary the release rate.
The temperature of the water and the air was measured at multiple locations. The temperature of the air was also measured at H2 concentration probe locations. In addition, the temperature in the filling line was measured (1 at the outlet and 1 further down into the filling line). The pressure in the filling line was also measured at 3 locations, one located directly at the outlet. The release rate was determined based on the weight loss rate of the road tanker. To this end the trailer was placed onto load cells. Special blast pressure sensors were used to measure the shock waves generated by the rapid evaporation or other phenomena both in the water and in the air. At several locations the gas concentration development in time was measured. Heat radiation was measured at 3 distances from the point of release. High speed, Infra-Red (IR) cameras and normal cameras were used to record events and to follow the gas cloud behaviour in time. This includes cameras mounted on a drone and an underwater camera. Two weather stations were used to measure wind speed, wind direction, temperature and humidity during all tests performed.
All investigated release configurations resulted in a very chaotic LH2-water mixing zone, causing considerable evaporation and resulting in minor over pressures. The main phenomenon observed was an ignition of the released gas cloud, resulting in significant blast wave overpressures and heat radiation to the surroundings. The ignition occurred in all under-water releases and in about 90 % of the releases above the water surface. The location of the ignition occurred in free air at some distance from the instrumentation and release location.
Large-scale experiments have been performed to investigate the possible consequences of realistic amounts of liquified hydrogen (LH2) encountering water. The experiments aimed at simulating an accidental release of LH2 during especially the fuelling of a ship. For liquified natural gas (LNG) it has been demonstrated that when spilled onto water the evaporation rate can be that high that physical explosions occur which are referred as rapid phase transitions (RPTs). It cannot be excluded that RPTs are also possible in the case of LH2. The tests were performed in a 10 m x 10 m x 1.5 m basin filled with water, at the Test Site Technical Safety of the Bundesanstalt für Materialforschung und –prüfung (BAM) in Horstwalde, Germany within a research cooperation between BAM and Gexcon as part of
the SH2IFT program. LH2 releases were established releasing directly from a trailer carrying LH2 through a long flexible double vacuum insulated transfer line. The releases occurred from a height of 50 cm above and 30 cm under the water surface both pointing downwards and 30 cm under the water surface pointing along the water surface too. The release rate was determined based on the weight loss rate of the road tanker which was placed onto load cells. Special blast pressure sensors were used to measure the shock waves generated by the release processes both in the water and in the air. At several locations the gas concentration was measured. Heat radiation was measured at 3 distances from the point of release. High speed,
Infrared (IR) and normal cameras were used to record events and to follow the gas cloud behaviour in time. This includes cameras mounted on a UAV and underwater cameras. Two weather stations were used to measure wind speed, wind direction, temperature and humidity during all tests performed. All investigated release configurations resulted in a very chaotic LH2-water mixing zone, causing considerable evaporation but only minor over pressures.
The main phenomenon observed was an ignition of the released gas cloud, resulting in significant blast wave overpressures and heat radiation to the surroundings. The location of the ignition occurred in free air at some distance from the instrumentation and release location.
When handling flammable or toxic liquids or liquefied gases, the occurrence of a leakage and formation of a liquid pool is a scenario to be considered for risk assessment. Several models are available for the estimation of the evaporating mass flow, but only a very reduced number of experimental data is available for Validation purposes.
In the last years, the Federal Institute for Materials Research and Testing (BAM) in Berlin, Germany, carried out pool Evaporation experiments with different substances in basins with a Diameter ranging from 0,50 m to 1 m mainly on open air test sites with a built up (inner city) and a non-built-up (flat terrain) topography, but also in an enclosed space. The resulting experimental data sets cover a range of vapor pressures from 0,1 bar to 0,94 bar.
The aim of this work is to make the füll data set publicly available and to provide a description of the experimental boundary conditions.
Based on these data, a Validation of existing pool Evaporation models has been carried out and eventually led to a new formulation of an evaporation model, which is also presented here, covering the whole ränge from low wind speeds up to high vapor pressures.
Pipe integrity is a central concern regarding technical safety, availability, and environmental compliance of industrial plants and pipelines. A condition monitoring system that detects and localizes threats in pipes prior to occurrence of actual structural failure, e.g., leakages, especially needs to target transient events such as impacts on the pipe wall or pressure waves travelling through the medium. In the present work, it is shown that fiber-optic distributed acoustic sensing (DAS) in conjunction with a suitable application geometry of the optical fiber sensor allows to track propagating acoustic waves in the pipeline wall on a fast time-scale. Therefore, short impacts on the pipe may be localized with high fidelity. Moreover, different acoustic modes are identified, and their respective group velocities are in good agreement with theoretical predications. In another set of experiments modeling realistic damage scenarios, we demonstrate that pressure waves following explosions of different gas mixtures in pipes can be observed. Velocities are verified by local piezoelectric pressure transducers. Due to the fully distributed nature of the fiber-optic sensing system, it is possible to record accelerated motions in detail. Therefore, in addition to detection and localization of threatening events for infrastructure monitoring, DAS may provide a powerful tool to study the development of gas explosions in pipes, e.g., investigation of deflagration-to-detonation-transitions (DDT).
Large Scale Experiments have been performed to determine whether a storage vessel containing liquid hydrogen (LH2) and caught in a fire engulfing the vessel can result in a BLEVE (Boiling Liquid Expanding Vapour Explosion) and if so its consequences. The tests were performed at the Test Site Technical Safety of the Bundesanstalt für Materialforschung und –prüfung (BAM) in Germany at the Hydrogen Test Area (H2TA) within a research cooperation between BAM and Gexcon as part of the SH2IFT program. Three tests were performed using double-walled vacuum insulated vessels of 1 m3 volume. The cylindrical Vessels differed in orientation (horizontal or vertical) and the insulation material used (perlite or multi-layer insulation (MLI)). The degree of filling of the vessels was approximately 35-40 % in each of the tests performed. The fire load was provided by a propane fed burner-system positioned under the storage vessel and designed to give a homogeneous fire load. The conditions in the vessel (temperatures and pressure) as well as external effects (heat radiation, blast waves, flame ball development and fragmentation) were measured. All vessels were equipped with K-type thermocouples at several locations at the inner and outer vessel shell. The pressure inside the inner vessel and in the space between the inner and outer vessels (vacuum pressure) was measured. Bolometers were used to measure the heat radiation generated by both the propane fire and that generated by a possible fireball/BLEVE. To measure blast generated by the vessel burst/BLEVEs blast pencils were positioned at up to three locations. Further several cameras were used to monitor the events: normal cameras, infrared (IR)-cameras, high-speed cameras also on board of an UAV. Two of these vessels, a horizontal and a vertical vessel both insulated with perlite withstood the fire loading for 1 hour 20 minutes and 4 hours respectively without catastrophic failure. A horizontal vessel insulated with MLI failed by bursting after 1 hour and 6 minutes resulting in a fireball, fragments, and blast wave.