Etienne Werlen

Vacuum Superinsulated Liquid Oxygen Piping and Vessels

Vacuum superinsulation is commonly used in industrial applications for liquid oxygen transfer piping and liquid oxygen vessels as an alternative to other solid insulation materials such as perlite or Foamglass®, which have lower thermal performances. Tests have been conducted on insulation materials according to ASTM D2512 (equivalent to ISO 11114–3, EN 1797) in LOX as well as according to ASTM G72 (equivalent to EN 1797) in GOX. The superinsulation materials that have been tested are a number of layers of aluminum foils of various thicknesses each being separated by intermediate nonmetallic layers of various nature. Based on experience and incidents in the industry, this paper is intended to discuss the recent test results in pure oxygen and the possible ignition of superinsulation material in the interspace and mechanism of propagation as well as the consequences of a fire. Recommendations regarding material selection for vacuum superinsulation materials in LOX applications are also provided.

Ignition of Contaminated Aluminum by Impact in Liquid Oxygen—Influence of Oxygen Purity

Impact tests in liquid oxygen and oxygen enriched liquids have been conducted on aluminum foils (0.2 mm thick) used for heat exchangers of air separation units (ASUs). Some adaptations to the ASTM Standard D2512, “Standard Test Method for Compatibility of Materials with Liquid Oxygen,” have been done to ensure the good control of oxygen content in the cryogenic liquid and to get reproducible results in aluminum ignition with hydrocarbon coating. Modified striker pins with a cavity on the contact surface have been used. The vertical guiding and the centering of the striker pins have been ensured by using two machined guides. Test samples were three layers of aluminum foil, two corrugated and one flat, contaminated by various quantities of hexadecane. The criteria for the identification of aluminum ignition (positive tests) have been validated by performing Scanning electron microscope surface analysis on residuals of a few impact tests performed in copper cups. Criteria have also been defined to check that hexadecane combustion took place in negative tests. A sufficient number of tests have been performed to plot the probability of ignition of the aluminum samples as a function of the average thickness of hexadecane coating and as a function of the oxygen content in the cryogenic liquid varying from 50 % to above 99.95 %. The remaining part in the cryogenic liquid was nitrogen and 2.3 % argon except for one series of tests where the influence of the absence of argon could be identified. The results of these tests can be used to assess the risk of ignition of some aluminum exchangers or structures used in ASU.