Aluminum and its alloys are the preferred material in air separation units (ASUs) and are submitted to strict cleanliness requirements to avoid combustion reactions in oxygen. Linde Engineering Division has investigated the role of particle contamination for the ignition of aluminum pipes in high pressure oxygen. Tests were carried out with oil coated aluminum pipes in combination with a particle contamination. Accumulations of following particle types were tested: molecular sieve 13X, filter deposits (rust), perlite, quartz sand, and aluminum swarf. The contaminated pipes were pressurized with oxygen up to 150 bar and fractured in a hydraulic apparatus. The conditions and probability of an ignition reaction compared with oiled pipes without particles were of interest. Additionally, similar high pressure tests with a mixture of liquid and gaseous oxygen were performed. A combination of oil and particles enhanced the probability of an ignition at elevated temperatures. The results indicated that temperature is the dominating factor for an oil ignition, not the oxygen pressure. At room temperature, an oil/aluminum ignition could never be initiated. The results give a good understanding regarding the mechanism of an aluminum ignition and help to clarify causes of damage in the ASU industry.
