Annex 2: Test methods used by the Federal Institute of Materials Research and -testing (BAM) for evaluating the compatibility of nonmetallic materials for oxygen service

The following test methods refer only to the reactivity of materials with oxygen.

1   Testing of materials for ignition sensitivity to gaseous oxygen impacts

For testing, solid materials are divided and liquids are applied onto ceramic fibers. A sample mass of ca. 0.1 g to 0.5 g is placed into a heatable sample tube of 15 cm3 in volume.
The sample tube is connected by a pipe and a pneumatically operated quick opening valve to a high-pressure oxygen accumulator. After the pipe and sample tube are at initial pressure pa (generally ambient pressure) and the sample has reached the test temperature, the quick opening valve is opened and preheated oxygen (generally 60 °C) of final pressure pe flows abruptly into the pipe and sample tube.
In this way, the oxygen in the sample tube is almost adiabatically compressed from initial pressure pa to final pressure pe and heated. A possible reaction of the sample with oxygen is indicated by a steep temperature rise in the sample tube.
Assessment criterion:
If there is a reaction, further test series are performed at a lower pressure ratio pe/pa until the compression ratio is found, where no reaction of the sample with oxygen can be detected in a series of five consecutive gaseous impacts. If this result is confirmed in a second test series of five consecutive oxygen impacts, the tests can be finished or continued at a different test temperature.

2   Autogenous ignition temperature (AIT) in high pressure oxygen

For testing, solid materials are divided and liquids are applied onto ceramic fibers. A sample tube that contains a sample mass of ca. 0.1 g to 0.5 g is placed into an autoclave of 34 cm3 in volume. A low-frequency heater allows to heat the sample inductively in an almost linear way at a rate of 110 °C/min.
A thermocouple on the bottom of the sample tube measures the temperature. The pressure is measured by means of a pressure transducer.
Assessment criterion:
The ignition of the sample can be recognized by a sudden rise in temperature and pressure.
Usually, the maximum use temperature of the sample is fixed at a value that is 100 °C below the determined AIT. This safety margin considers the fact, that the AIT is not a constant and depends on test method, sample preparation, and other parameters. Publications in literature as well as researches in BAM confirm this fact.
The safety margin of 100 °C has been proven over many decades. For use temperatures up to 60 °C, and depending on the intended purpose, BAM only performs oxygen impact tests (test method 1) or flange tests (test method 4).

3   Testing of materials for aging resistance

A sample with known mass is exposed to high pressure oxygen at elevated temperature, usually 25 °C above the intended use temperature, in an autoclave for 100 hours.
Assessment criterion:
The aged sample shall not show substantial changes in mass, autogenous ignition temperature, and appearance. Otherwise, the test has to be repeated at lower pressures or temperatures.

4   Testing of flange gaskets for gaseous oxygen service

The test apparatus mainly consists of two steel pipes, each approximately 1 m in length, with corresponding standard flanges welded to each pipe. Both pipes are sealed with a disk of the gasket material to be tested. The test apparatus is then pressurized with oxygen up to the desired test pressure. The flange is heated by heating sleeves up to the test temperature, at least 50 °C lower than the ignition temperature of the gasket material. An electrical filament ignites intentionally that part of the gasket disk that projects into the pipe.
Assessment criterion:
It is decisive how the gasket material behaves after intentional ignition. If the gasket disk burns with such a hot flame that the fire is transmitted to the steel of the flanges or the pipes, the gasket material is considered unsuitable right from the beginning. In a positive test result, only those parts of the gasket disk burn that project into the pipes and the gasket disk does not burn between the flanges. If this test result is confirmed in four additional tests, there are no objections with regard to technical safety to use the gasket material up to the test pressure and test temperature.
If the flange connection leaks because the gasket material burns between the flanges or becomes soft, the test has to be repeated at lower temperatures or pressures until finally a positive result is achieved in five tests.

5   Testing of materials for reactivity with liquid oxygen on mechanical impact

Approximately 0.5 g of the divided sample is placed into a sample cup, made of 0.01 mm copper foil. Liquid oxygen is poured into the cup over the sample until it is immersed in liquid. The sample is then exposed to the mechanical impact of a plummet with a mass of 76.5 kg. The drop height and in this way the impact energy of the plummet can be varied.
A flame and a more or less strong noise of an explosion usually indicate a reaction of the sample with liquid oxygen. In varying the drop height of the plummet, the impact energy, at which no reaction occurs, is determined in a series of ten tests.
Assessment criterion:
The material is not compatible with liquid oxygen, if reactions occur at impact energies of 125 Nm or less.

6   Examples for scope of testing

The following table shows for some particular fields of application what tests are required:
Intended purpose of materialAutogenous ignition temperatureGaseous oxygen impactAging resistanceLiquid oxygenFlange
Lubricant+1+ +2 
Flange Gasket+1 +1+2+
Thread Sealent
– Tape, Cord+1++1+2 
– Liquid, Paste+1+ +2 
Seat Seal+1++1+2 
Piston Ring++++2 
Filling Liquids
– for Vacuum Pumps+    
– for Measuring Instruments++   
1) for use temperatures greater than 60 °C
2) only if required
The maximum use conditions of a material regarding pressure and temperature are the result of the overall assessment that takes into account the results of all separate tests.

7   Standards of the Test methods

ASTM G 114-14: Standard Practices for Evaluating the Age Resistance of Polymeric Materials used in Oxygen Service
EN 1797:2002: Cryogenic vessels – Gas/material compatibility
ISO 21010:2017-12: Cryogenic vessels – Gas/materials compatibility