Volume 6, Issue 8 (September 2009)
Promoted Ignition Testing of Metallic Filters in High-Pressure Oxygen
Currently, no test standard exists for evaluating the ignition tolerance and fault tolerance of metallic filters in high-pressure oxygen. Filters are a critical component in oxygen systems to ensure system cleanliness and mitigate ignitions by particle impact and contamination. However, filters are at risk to these same ignition mechanisms and fires have occurred in service. A new test method was developed using ASTM Standard G175 Phase 2 as a basis. The test subjects a pre-contaminated filter to a forced ignition event using an ignition pill while the filter is maintained at elevated pressure. Prior to testing, contaminant was applied to the filter element and was also placed at the filter inlet. This additional contaminant was based on contaminant that could potentially accumulate in a filter over time. This contaminant consisted of aluminum powder, iron particles, and perfluorinated lubricant. An ignition pill, consistent with ASTM Standard G175 Phase 2, was located on the upstream side of the filter. A back pressure was applied downstream of the ignition pill to ensure that the filter was pressurized during the ignition and burning of the pill. Testing was performed on brass and stainless steel filters of the same design using an oxygen shock to ignite the ignition pill at a test pressure greater than the back pressure applied to the filter. The brass filters safely contained the ignition event without breaching through the filter element or body. For the stainless steel filters, the ignition event kindled the filter element and burned through the filter body. This testing showed that the ignition fault tolerance of the brass filters was far superior to that of the stainless steel filters, which was consistent with the relative flammability of these metallic materials, and therefore verified the test methodology.