A Critical Analysis of Adiabatic Compression Test Methods

Industry test methods such as ASTM G74, Standard Test Method for Ignition Sensitivity of Nonmetallic Materials and Components by Gaseous Fluid Impact; ASTM G175, Standard Test Method for Evaluating the Ignition Sensitivity and Fault Tolerance of Oxygen Pressure Regulators Used for Medical and Emergency Applications; ISO 10297, Gas Cylinders—Cylinder Valves—Specification and Type Testing; ISO 21010, Cryogenic Vessels—Gas/Material Compatibility; and ISO 10524, Pressure Regulators for Use with Medical Gases, have been used for many years to evaluate nonmetallic materials and components for use in high-pressure oxygen. However, the severity of the test methods is widely overestimated compared with the actual temperatures or enthalpy increases that occur in practice. This paper provides a critical analysis of the thermodynamic energy developed by the test approach and summarizes research performed to measure and evaluate the severity of the internationally standardized gaseous fluid impact test apparatus. This paper demonstrates that the “adiabatic compression test,” as embodied in the international standards, is not “adiabatic” despite the rapid pressurization controls and that heat losses are significant and strongly dependent on the surface area to volume ratio of the impact tube. This paper also demonstrates that the current tests are more severe than most service conditions, but not by the large margin that is usually estimated