ASTM G74-13

4.1 This test standard describes how to evaluate the relative sensitivity of materials and components to dynamic pressure impacts by various gaseous fluid media (can include gas mixtures).

4.2 Changes or variations in test specimen configurations, thickness, preparation, and cleanliness can cause a significant change in their impact ignition sensitivity/reaction. For material tests, the test specimen configuration shall be specified on the test report.

4.3 Changes or variation in the test system configuration from that specified herein may cause a significant change in the severity produced by a dynamic pressure surge of the gaseous media.

4.4 A reaction is indicated by an abrupt increase in test specimen temperature, by obvious changes in odor, color, or material appearance, or a combination thereof, as observed during post-test examinations. Odor alone is not considered positive evidence that a reaction has occurred. When an increase in test specimen temperature is observed, a test specimen reaction must be confirmed by visual inspection. To aid with visual inspection, magnification less than 10× can be used.

4.5 When testing components, the test article must be disassembled and the nonmetallic materials examined for evidence of ignition after completion of the specified pressure surge cycles.

4.6 Ignition or precursors to ignition for any test sample shall be considered a failure and are indicated by burning, material loss, scorching, or melting of a test material detected through direct visual means. Ignition is often indicated by consumption of the non-metallic material under test, whether as an individual material or within a component. Partial ignition can also occur, as shown in Fig. 3a, b, and c, and shall also be considered an ignition (failure) for the purpose of this test standard.

4.7 For material testing, the prescribed procedure is conducted on multiple samples until a statistically significant number of ignitions or no-ignitions, or both, are achieved at various test pressures. The data is then analyzed by a procedure that calculates the median failure pressure (i.e., the 50 % reaction pressure) or the functional form of the ignition probability versus pressure by logistic regression analysis. Materials tested in a similar configuration can be ranked against each other by either of these two criteria. The initial test gas temperature may be varied as required depending on the requirements of the test.

4.8 For component testing, a specified number of pressure surge cycles are conducted at a defined test pressure, usually specified by a particular industry test standard. Usually, this pressure is 1.2 times the maximum allowable working pressure of the component. The initial test gas temperature may be varied depending on the requirements of the test; however, most commonly the initial test gas temperature is 60 ± 3 °C.

1.1 This test method describes a method to determine the relative sensitivity of nonmetallic materials (including plastics, elastomers, coatings, etc.) and components (including valves, regulators flexible hoses, etc.) to dynamic pressure impacts by gases such as oxygen, air, or blends of gases containing oxygen.

1.2 This test method describes the test apparatus and test procedures employed in the evaluation of materials and components for use in gases under dynamic pressure operating conditions up to gauge pressures of 69 MPa and at elevated temperatures.

1.3 This test method is primarily a test method for ranking of materials and qualifying components for use in gaseous oxygen. The material test method is not necessarily valid for determination of the sensitivity of the materials in an “as-used” configuration since the material sensitivity can be altered because of changes in material configuration, usage, and service conditions/interactions. However, the component testing method outlined herein can be valid for determination of the sensitivity of components under service conditions. The current provisions of this method were based on the testing of components having an inlet diameter (ID bore) less than or equal to 14 mm (see Note 1).

1.4 A 5 mm Gaseous Fluid Impact Sensitivity (GFIS) test system and a 14 mm GFIS test system are described in this standard. The 5 mm GFIS system is utilized for materials and components that are directly attached to a high-pressure source and have minimal volume between the material/component and the pressure source. The 14 mm GFIS system is utilized for materials and components that are attached to a high pressure source through a manifold or other higher volume or larger sized connection. Other sizes than these may be utilized but no attempt has been made to characterize the thermal profiles of other volumes and geometries (see Note 1).

1.6 Many ASTM, CGA, and ISO test standards require ignition testing of materials and components by gaseous fluid impact, also referred to as adiabatic compression testing. This test method provides the test system requirements consistent with the requirements of these other various standards. The pass/fail acceptance criteria may be provided within other standards and users should refer to those standards. Pass/fail guidance is provided in this standard such as that noted in section 1.7 The criteria used for the acceptance, retest, and rejection, or any combination thereof of materials and components for any given application shall be determined by the user and are not fixed by this method. However, it is recommended that at a minimum the 95 % confidence interval be established for all test results since ignition by this method is inherently probabilistic and should be treated by appropriate statistical methods.

1.8 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.9 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.