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Cylinder valves for oxygen service that meet the standard DIN EN ISO 10297 should be safe, if properly handled by the user. In the last few years, however, the number of incidents with oxygen valves that has been reported to Federal Institute for Materials Research and Testing (BAM) has increased. According to the incident reports, incorrect handling can be ruled out. People were seriously injured and in most cases, the causes of these incidents were not clear. Very often, such incidents occurred during opening and closing of the valves. Therefore, the technical-scientific community has put the existing test methods for type testing more and more into question. Besides other mandatory tests, the above-mentioned standard allows to perform the endurance test with air or with nitrogen. This is appropriate for all other gases but not for oxygen. Up to now, this test does not consider the fact that cylinder valves also contain nonmetallic seat materials and lubricants that may react with oxygen in a dangerous way. Because of this unsatisfactory situation, BAM initiated a research project to perform endurance testing of cylinder valves for oxygen service much more practice related with oxygen. This test simulates very well real life situations when the cylinder valve is opened or closed. The first part of this project was the development of a new oxygen operated endurance tester in accordance with DIN EN ISO 10297. In a second part, endurance testing of valves with air and with oxygen was performed and the results were compared. In addition, another mandatory test of the standard, the oxygen pressure surge test was carried out on new valves and on valves that had undergone endurance tests with air or oxygen, to see the influence on the burn-out safety of such pre-stressed valves. This paper presents the main results of the project. The findings clearly speak for implementing the oxygen endurance test not only to DIN EN ISO 10297 but also to various other standards to increase the burn-out safety of oxygen cylinder valves.
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].
The new promoted ignition combustion test apparatus at BAM matches the requirements of ASTM test method G 124 [ASTM G 124, Standard Test Method for Determining the Combustion Behavior of Metallic Materials in Oxygen-Enriched Atmospheres, 2003] and of EIGA publication, IGC Doc 13/02/E [EIGA Gas Association Document IGC Doc 13/02/E, Oxygen Pipeline Systems, 2003]. The test apparatus is most likely the only one in Europe. The test chamber allows investigations with pure oxygen or oxygen mixtures at pressures up to 500 bar and at temperatures up to 400°C at static or flowing gas conditions. The ignition device consists of an electrical ignition wire and a promoter. IR-sensors, distributed over the whole length of the rod, measure and record the burning temperature and allow measurement of the burn rate. A video system records the experiment for visual characterization of the burning behavior. BAM test results are compared with published data. Results on investigations with coated rods are presented. Ceramic coatings seem to be a solution for the use of certain less compatible metallic materials at higher oxygen pressures.