Filtern
Dokumenttyp
Sprache
- Englisch (5)
Schlagworte
- Adiabatic compression (5) (entfernen)
Organisationseinheit der BAM
The Oxygen Pressure Surge Test (OPST) is considered to be best practice for evaluating the burn out safety of plant components and testing the compatibility of nonmetallic materials for oxygen service. Nevertheless, there are only a few laboratories worldwide performing the OPST. The Federal Institute for Materials Research and Testing (BAM) already operates oxygen pressure surge test facilities with maximum OPST pressures of 450 bar.
However, to ensure technical innovation and to enhance research and development, the decision was made to develop a new and large-scale oxygen pressure surge test facility. Due to the size and the high potential impact energies, the test facility is located outside of Berlin at BAM Test Site for Technical Safety (TTS), where large scale testing is carried out. In addition to an intended maximum OPST pressure of 750 bar, there is the possibility of testing industrial equipment with large inner volumes and diameters. The new quick opening valve constitutes the core of the system and was developed by BAM. It allows to perform tests with the standardized pressure rise times of 15 ms to 20 ms or with adjustable pressure rise times at higher or lower values. As a result, it is possible to provide customized test parameters for specific practical applications as well as research projects.
This presentation shows the status quo of this unique test facility, its performance, its technical specifications, and its new possibilities for research and development for a long term enhancement of burn out safety in oxygen application.
Adiabatic compression testing of components in gaseous oxygen is a test method that is utilized worldwide and is commonly required to qualify a component for ignition tolerance under its intended service. This testing is required by many industry standards organizations and government agencies; however, a thorough evaluation of the test parameters and test system influences on the thermal energy produced during the test has not yet been performed. This paper presents a background for adiabatic compression testing and discusses an approach to estimating potential differences in the thermal profiles produced by different test laboratories. A "thermal profile test fixture" (TPTF) is described that is capable of measuring and characterizing the thermal energy for a typical pressure shock by any test system. The test systems at Wendell Hull and Associates, Inc., in the United States and at the BAM Federal Institute for Materials Research and Testing in Germany are compared in this manner and some of the data obtained are presented. The paper also introduces a new way of comparing the test method to idealized processes to perform system-by-system comparisons. Thus, the paper introduces an "idealized severity index" (ISI) of the thermal energy to characterize a rapid pressure surge. From the TPTF data a "test severity index" can also be calculated so that the thermal energies developed by different test systems can be compared to each other and to the ISI for the equivalent isentropic process. Finally, a "service severity index" is introduced to characterize the thermal energy of actual service conditions. This paper is the second in a series of publications planned on the subject of adiabatic compression testing.
This work investigates the ignition of tetrafluoroethylene induced by the adiabatic compression that can arise by activating a high speed valve separating two portions of a pipeline with a high pressure difference. In the tests performed the high pressure zone contained tetrafluoroethylene at pressures between 15 and 30 bar. For the low pressure zone, experiments with nitrogen, air and tetrafluoroethylene were carried out. The pressure range in the low pressure zone was comprised between 0.05 and 1 bar. The pipe diameters analyzed were 15 and 20 mm. For the analyzed geometries, special conditions were required in order to reach reproducible ignitions, namely air at temperatures of at least 105 °C had to be present in the compression pipe. Furthermore, a minimum length of the compression pipe had to be used. The current work describes the experimental setup employed for the tests and discusses the achieved results. Numerical simulations were performed in order to clarify unexpected findings.
Adiabatic compression of gases can work as an ignition source and is still one of the main causes of accidents in chemical plants processing tetrafluoroethylene (Reza and Christiansen, 2007). The ignition of tetrafluoroethylene induced by adiabatic compression has been studied experimentally with a setup which allowed for the rapid opening of a high speed valve connecting two portions of a pipeline at different initial pressures. Due to the fast opening time and to the high pressure difference, a shock wave in the pipeline was generated. The propagation of the shock wave and its reflection at the end of the pipeline caused pressure and temperature increase. This led to some ignitions in the experiments performed. Nonetheless, in some test an ignition was not achieved, even if this was expected according to the theoretical temperatures predicted by the Rankine-Hugoniot equations. In order to understand the discrepancy between the experimental results and the theoretical predictions, shock wave simulations have been carried out with COMSOL Multiphysics. The 'High Mach Flow' interface was used, since it solves the heat and impulse equations for fast flows. Figure 1 and Figure 2 show, respectively, the velocity and temperature distribution over time for a simulation in a 0.2 m pipeline of 20 mm in diameter with the following settings:
- high pressure section: nitrogen initially at 20 bar;
- low pressure section: nitrogen initially at 1 bar;
- initial temperature of the system: 20 °C;
- adiabatic walls with slip condition for the flow;
- laminar flow.
As from Figure 1 and Figure 2 the shock wave generation and propagation has been properly computed and the physical properties of the shock wave reflected the prediction of the Rankine-Hugoniot equation. Nonetheless, divergence problem occurred when trying to add turbulence to the system and strange temperature and profiles after the shock wave reflection were achieved if the no slip condition at the walls was chosen. Despite these limitations, it was possible to perform a parametric study and to analyze the effect of the pipe diameter and length on the shock wave evolution. Here simulations with constant wall temperature were carried out, in order to account for the heat losses to the pipe surroundings. Figure 3 shows that the temperature of the reflected wave is maintained for a longer time, if the pipe diameter is larger, due to minor heat losses. On the other hand, Figure 4 shows that higher average temperatures are achieved and maintained for a longer time if the pipe length increases. These results suggest that in the experiments performed by Meyer (2009) the pipe geometry was probably not optimal for the achievement/conservation of high temperatures and might explain the difficulty in inducing ignitions by adiabatic compression.
Two different test apparatuses are used at BAM to evaluate the safety of oxygen components: First, the promoted ignition combustion test according to ASTM G 124 [1] and to EIGA IGC Doc 13/02/E [2], and second, the new metallic disk ignition test that has not been standardized yet. The standard test method ASTM G 124 allows a ranking of metallic materials for use at high pressure oxygen. However, the transfer of those test results to valves and fittings in real-life situations is rather complex. The metallic disk ignition test, developed at BAM, is more practice oriented and uses metallic disks of different thicknesses of the investigated material. A commonly used nonmetallic sealing ring is placed in front of this disk and serves as an igniter. This test array is then exposed to high pressure gaseous oxygen impacts in a standardized pneumatic impact tester according to DIN EN 1797 [3].