ASTM G63-15(2023)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: G63 − 15 (Reapproved 2023)
Standard Guide for
Evaluating Nonmetallic Materials for Oxygen Service
This standard is issued under the fixed designation G63; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.1 This guide applies to nonmetallic materials, (hereinafter
called materials) under consideration for oxygen or oxygen-
2. Referenced Documents
enriched fluid service, direct or indirect, as defined below. It is
intended for use in selecting materials for applications in
2.1 ASTM Standards:
connection with the production, storage, transportation,
D217 Test Methods for Cone Penetration of Lubricating
distribution, or use of oxygen. It is concerned primarily with
Grease
the properties of a material associated with its relative suscep-
D566 Test Method for Dropping Point of Lubricating Grease
tibility to ignition and propagation of combustion; it does not
D1264 Test Method for Determining the Water Washout
involve mechanical properties, potential toxicity, outgassing,
Characteristics of Lubricating Greases
reactions between various materials in the system, functional
D1743 Test Method for Determining Corrosion Preventive
reliability, or performance characteristics such as physical
Properties of Lubricating Greases
aging, degradation, abrasion, hardening, or embrittlement,
D1748 Test Method for Rust Protection by Metal Preserva-
except when these might contribute to an ignition.
tives in the Humidity Cabinet
1.2 When this document was originally published in 1980, it
D2512 Test Method for Compatibility of Materials with
addressed both metals and nonmetals. Its scope has been
Liquid Oxygen (Impact Sensitivity Threshold and Pass-
narrowed to address only nonmetals and a separate standard
Fail Techniques)
Guide G94 has been developed to address metals.
D2863 Test Method for Measuring the Minimum Oxygen
1.3 This standard does not purport to address all of the
Concentration to Support Candle-Like Combustion of
safety concerns, if any, associated with its use. It is the
Plastics (Oxygen Index)
responsibility of the user of this standard to establish appro-
D4809 Test Method for Heat of Combustion of Liquid
priate safety, health, and environmental practices and deter-
Hydrocarbon Fuels by Bomb Calorimeter (Precision
mine the applicability of regulatory limitations prior to use.
Method)
G72 Test Method for Autogenous Ignition Temperature of
NOTE 1—The American Society for Testing and Materials takes no
position respecting the validity of any evaluation methods asserted in Liquids and Solids in a High-Pressure Oxygen-Enriched
connection with any item mentioned in this guide. Users of this guide are
Environment
expressly advised that determination of the validity of any such evaluation
G74 Test Method for Ignition Sensitivity of Nonmetallic
methods and data and the risk of use of such evaluation methods and data
Materials and Components by Gaseous Fluid Impact
are entirely their own responsibility.
NOTE 2—In evaluating materials, any mixture with oxygen exceeding G86 Test Method for Determining Ignition Sensitivity of
atmospheric concentration at pressures higher than atmospheric should be
Materials to Mechanical Impact in Ambient Liquid Oxy-
evaluated from the hazard point of view for possible significant increase
gen and Pressurized Liquid and Gaseous Oxygen Envi-
in material combustibility.
ronments
1.4 This international standard was developed in accor-
G88 Guide for Designing Systems for Oxygen Service
dance with internationally recognized principles on standard-
G93 Guide for Cleanliness Levels and Cleaning Methods for
ization established in the Decision on Principles for the
Materials and Equipment Used in Oxygen-Enriched En-
Development of International Standards, Guides and Recom-
vironments
G94 Guide for Evaluating Metals for Oxygen Service
This guide is under the jurisdiction of ASTM Committee G04 on Compatibility
and Sensitivity of Materials in Oxygen Enriched Atmospheres and is the direct
responsibility of Subcommittee G04.02 on Recommended Practices. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved March 1, 2023. Published March 2023. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1980. Last previous edition approved in 2015 as G63 – 15. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0063-15R23. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G63 − 15 (2023)
2.2 Federal Standard: experience, know how to apply physical and chemical prin-
Fed. Test Method Std. 91B Corrosion Protection by Coating: ciples involved in the reactions between oxygen and other
Salt Spray (Fog) Test
materials.
2.3 Other Standard:
3.2.11 reaction effect—the personnel injury, facility damage,
BS 3N:100: 1985 Specification for General Design Require-
4 product loss, downtime, or mission loss that could occur as the
ments for Aircraft Oxygen Systems and Equipment
result of an ignition.
2.4 Other Documents:
CGA Pamphlet G4.4 Oxygen Pipeline and Piping System
4. Significance and Use
EIGA IGC 13-12 Oxygen Pipeline and Piping Systems
NSS 1740.15 NASA Safety Standard for Oxygen and Oxy-
4.1 The purpose of this guide is to furnish qualified techni-
gen Systems
cal personnel with pertinent information for use in selecting
materials for oxygen service in order to minimize the probabil-
3. Terminology
ity of ignition and the risk of explosion or fire. It is not intended
3.1 Definitions:
as a specification for approving materials for oxygen service.
3.1.1 autoignition temperature—the temperature at which a
material will spontaneously ignite in oxygen under specific test
5. Factors Affecting Selection of Material
conditions.
5.1 General—The selection of a material for use with
3.2 Definitions of Terms Specific to This Standard:
oxygen or oxygen-enriched atmospheres is primarily a matter
3.2.1 direct oxygen service—in contact with oxygen during
of understanding the circumstances that cause oxygen to react
normal operations. Examples: oxygen compressor piston rings,
with the material. Most materials in contact with oxygen will
control valve seats.
not ignite without a source of ignition energy. When an
3.2.2 impact-ignition resistance—the resistance of a mate-
energy-input rate, as converted to heat, is greater than the rate
rial to ignition when struck by an object in an oxygen
of heat dissipation, and the temperature increase is continued
atmosphere under a specific test procedure.
for sufficient time, ignition and combustion will occur. A
3.2.3 indirect oxygen service—not normally in contact with
material’s minimum ignition temperature and the ignition
oxygen, but which might be as a result of a reasonably
sources that will produce a sufficient increase in the tempera-
foreseeable malfunction, operator error, or process disturbance.
ture of the material must therefore be considered. Ignition
Examples: liquid oxygen tank insulation, liquid oxygen pump
temperatures and ignition sources should be viewed in the
motor bearings.
context of the entire system design so that the specific factors
3.2.4 maximum use pressure—the maximum pressure to
listed below will assume the proper relative significance.
which a material can be subjected due to a reasonably
Therefore: material suitability for oxygen service is
foreseeable malfunction, operator error, or process upset.
application-dependent.
3.2.5 maximum use temperature—the maximum tempera-
NOTE 3—For the safe use of materials in oxygen, in addition to the
ture to which a material can be subjected due to a reasonably
flammability and ignitability properties of the material, it is necessary to
foreseeable malfunction, operator error, or process upset.
consider other physical and chemical properties such as mechanical
3.2.6 nonmetallic—any material, other than a metal, or any
properties, potential toxicity, etc. Consequently, because ignition and
composite in which the metal is not the most easily ignited physical (or chemical) properties may be conflicting for selecting a
material, it may be necessary in such cases to perform component tests
component and for which the individual constituents cannot be
simulating the most probable ignition mechanisms (e.g., a rapid pressur-
evaluated independently.
ization test on a valve if heat of compression is analyzed as severe).
3.2.7 operating pressure—the pressure expected under nor-
5.2 Properties of the Material:
mal operating conditions.
5.2.1 Factors Affecting Ease of Ignition—Generally, when
3.2.8 operating temperature—the temperature expected un-
considering a material for a specific oxygen application, one of
der normal operating conditions.
the most significant factors is its minimum ignition temperature
3.2.9 oxygen-enriched—applies to a fluid (gas or liquid) that
in oxygen. Other factors that will affect its ignition include
contains more than 25 mol % oxygen.
relative resistance to various ignition energies, geometry,
3.2.10 qualified technical personnel—persons such as engi-
configuration, specific heat, relative porosity, thermal
neers and chemists who, by virtue of education, training, or
conductivity, preoxidation or passivity, and “heat-sink effect.”
Heat-sink effect is the heat-transfer capacity of the material
Available from U.S. Government Printing Office Superintendent of Documents, relative to that of the material in intimate contact with it,
732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
considering the mass, physical arrangement, and physical
www.access.gpo.gov.
4 properties of each. For instance, a gasket material may have a
Available from British Standards Institute (BSI), 389 Chiswick High Rd.,
London W4 4AL, U.K., http://www.bsi-global.com. relatively low ignition temperature but be extremely resistant
Available from Compressed Gas Association (CGA), 4221 Walney Rd., 5th
to ignition when confined between two steel flanges. The
Floor, Chantilly, VA 20151-2923, http://www.cganet.com.
6 presence of a small amount of an easily ignitable contaminant,
National Aeronautics and Space Administration, Office of Safety and Mission
Assurance, Washington, DC. such as a hydrocarbon oil or a grease film, can promote the
G63 − 15 (2023)
(6) An increase in the likelihood of compression heating ignition, with
ignition of the base material. Accordingly, cleanliness is vital to
the greatest likelihood at the highest pressures.
minimize the risk of ignition (1). See also Practice G93 and
Refs. 2–3. In the case of friction, increased pressure may improve heat
dissipation and make ignition at constant frictional energy
5.2.2 Factors Affecting Propagation—Once a material is
ignited, combustion may be sustained or may halt. Among the input less likely than at lower pressure. Increased pressure also
reduces the likelihood of spark generation at constant electric
factors that affect whether fire will continue are the basic
composition of the material, the presence of heat-sink effects, field strength through increased breakdown voltage values.
the pressure, the initial temperature, the geometric state of the 5.3.2 Temperature—Increasing temperature obviously in-
matter, and whether there is oxygen available to sustain the creases the risk of ignition but does not generally contribute to
reaction. Combustion may also be interrupted by the presence the reaction effect. The material should have a minimum
of a heat sink. ignition temperature, as determined by an acceptable test
5.2.3 Properties and Conditions Affecting Potential Resul- procedure, that exceeds the maximum use temperature (as
tant Damage—The material properties and system conditions defined in 3.2.5) by a suitable safety margin.
that could affect the damage potential if ignition occurs should 5.3.3 Concentration—As oxygen concentration decreases
be taken into account when estimating the reaction effect in from 100 %, the likelihood and intensity of a potential reaction
7.5. These properties and conditions include the material’s heat
also decrease; therefore, greater latitude may be exercised in
of combustion, its mass, the oxygen concentration, flow the selection of materials.
conditions before and after ignition, and the flame propagation
5.4 Ignition Mechanisms—For an ignition to occur, it is
characteristics.
necessary to have three elements present: oxidizer, fuel, and
5.3 Operating Conditions—Conditions that affect the suit-
ignition energy. The oxygen environment is obviously the
ability of a material include pressure, temperature,
oxidizer, and the material under consideration is the fuel.
concentration, flow, and gas velocity, and the ignitability of
Several potential sources of ignition energy are listed below.
surrounding materials. Pressure and temperature are generally
The list is neither all-inclusive nor in order of importance nor
the most significant, and their effects show up in the estimate
in frequency of occurrence.
of ignition potential (5.4) and reaction effect (5.5), as explained
5.4.1 Friction—The rubbing of two solid materials results in
in Section 7.
the generation of heat. Example: the rub of a centrifugal
5.3.1 Pressure—The operating pressure is important, not
compressor rotor against its casing.
only because it generally affects the generation of potential
5.4.2 Heat of Compression—Heat is generated from the
ignition mechanisms, but also because it affects the destructive
conversion of mechanical energy when a gas is compressed
effects if ignition should occur. While generalizations are
from a low pressure to a high pressure. This can occur when
difficult, approximate reaction effects would be as given in
high-pressure oxygen is released into a dead-ended tube or
Table 1.
pipe, quickly compressing the residual oxygen that was in the
tube ahead of it. As the ratio of final pressure to initial pressure
TABLE 1 Reaction Effect Assessment for Typical Pressures
increases, so, too, does the final theoretical temperature gen-
erated from the compression event. Example: a downstream
Reaction Effect
kPa psi
Assessment
valve in a dead-ended high-pressure oxygen manifold.
0–70 0–10 relatively mild
5.4.2.1 Equation—An equation that can be used to estimate
70–700 10–100 moderate
the theoretical maximum temperature that can be developed
700-7000 100–1000 intermediate
7000–20 000 1000–3000 severe when pressurizing oxygen rapidly from one pressure and
Over 20 000 over 3000 extremely severe
temperature to an elevated pressure is as follows:
~n21!/n
T /T 5 @P /P # (1)
f i f i
NOTE 4—While the pressure generally affects the reaction as indicated
where:
in Table 1, tests indicate that it has varying effects on individual
T = final temperature, abs,
f
flammability properties. For example, for many materials, increasing
T = initial temperature, abs,
i
pressure results in the following:
P = final pressure, abs,
(1) An increase in propagation rate, with the greatest increase in rate at
f
P = initial pressure, abs, and
lower pressures but with significant increases in rate at high pressures;
i
C
(2) A reduction in ignition temperature, with the greatest decrease at
n = p
51.40 for oxygen.
low pressure and a smaller rate at high pressure, however, it should be
C
v
noted that increasing autoignition temperatures with increasing pressures
where:
have been reported for selected polymers, due to competing kinetics (4);
C = specific heat at constant pressure, and
(3) An increase in sensitivity to mechanical impact;
p
(4) A reduction in oxygen index, as measured in an exploratory study C = specific heat at constant volume.
v
(5), with sharper initial declines in materials of high oxygen index but
Table 2 gives the theoretical temperatures which could be
with only slight relative declines in general above 10 atmospheres and up
obtained by compressing oxygen from one atmosphere (abso-
to at least 20 atmospheres;
(5) A negligible change in heat of combustion; and
lute) and 20 °C to the pressures shown.
NOTE 5—The final temperature calculated by Eq 1 is conservative
The boldface numbers in parentheses refer to the list of references at the end of because the equation assumes instantaneous pressurization with no heat
this standard. loss (adiabatic). The equation is also conservative because it treats oxygen
G63 − 15 (2023)
TABLE 2 Theoretical Maximum Temperature Obtained When
5.4.6 Electrical Arc—Electrical arcing may occur from
Compressing Oxygen Adiabatically from 20°C and One Standard
motor brushes, electrical control equipment, instrumentation,
A
Atmosphere to the Pressures Shown
lightning, etc. Example: defective pressure switch.
Final Pressure, P Final Temperature, T
f Pressure Ratio f
5.4.7 Resonance—Acoustic oscillations within resonant
P /P
kPa psia f j °C °F
cavities are associated with rapid temperature rise. This rise is
345 50 3.4 143 289
more rapid and achieves higher values where particulates are
690 100 6.8 234 453
present or where there are high gas velocities. Ignition can
1000 145 9.9 291 556
1379 200 13.6 344 653
result. For example: a gas flow into a tee and out of the side
2068 300 20.4 421 789
port when the remaining port presents a resonant cavity.
2758 400 27.2 480 896
3447 500 34.0 530 986 5.4.8 Internal Flexing—Continuous rapid flexing of a ma-
5170 750 51.0 628 1163
terial can generate heat. Such heating may add to environmen-
6895 1000 68.0 706 1303
tal factors and increase the possibility of ignition. For example:
10 000 1450 98.6 815 1499
13 790 2000 136.1 920 1688 a gasket protruding into the fluid flow stream.
27 579 4000 272.1 1181 2158
5.4.9 Other—Since little is known about the actual cause of
34 474 5000 340.1 1277 2330
some oxygen fires or explosions, other mechanisms, not readily
100 000 14 500 986.4 1828 3322
1 000 000 145 000 9883.9 3785 6845 apparent, may be factors in, or causes of such incidents. These
A
might include external sources, such as defective electric
See 5.4.2.
resistance-heating elements, smoking, welding sparks or
spatter, and nearby open flames, or internal sources such as
material fracture.
as an ideal gas, which potentially results in calculated final temperature
5.5 Reaction Effect—The effect of an ignition (and subse-
values being much higher than would be realistic and higher than if
quent combustion propagation, if it should occur) has a strong
calculated using real gas equations.
bearing on the selection of a material. While it is an obviously
5.4.3 Heat From Mass Impact—Heat is generated from the
imprecise and strongly subjective judgment, it must be bal-
transfer of kinetic energy when an object having relatively
anced against factors such as those given in 5.6. Suggested
large mass or momentum strikes a material. Example: hammer
criteria for rating the reaction effect severity are given in Table
striking oxygen-saturated macadam.
3, and a method of applying the rating in a material selection
5.4.4 Heat from Particle Impact—Heat is generated from
process is given in Section 7. The user should keep in mind
the transfer of kinetic and possibly thermal energy when small
that, in many cases, the reaction effect severity rating for a
particles (sometimes incandescent), moving at high velocity,
particular application can be lowered by changing other
strike a material. Example: dirt particles striking a valve seat in
materials that may be present in the system, changing compo-
an inadequately cleaned high-velocity pipeline.
nent locations, varying operating procedures, or using barri-
5.4.5 Static Electric Discharge—Electrical discharge from
cades or shields.
static electricity, possibly generated by high fluid flow under
certain conditions, may occur, especially where particulate 5.6 Extenuating Factors—Performance requirements, prior
matter is present. Example: arcing in poorly cleaned, inad- experience with the material, availability, and cost enter into
equately grounded piping. the decision. For instance, while a particular material may be
TABLE 3 Reaction Effect Assessment for Oxygen Applications
Rating
Effect on Personnel Safety Effect on System Objectives Effect on Functional Capability
Code Severity Level
A Negligible No injury to personnel No unacceptable effect on production, No unacceptable damage to the system
storage, transportation, distribution, or use
as applicable
B Marginal Personnel-injuring factors can be controlled Production, storage, transportation, No more than one component or subsystem
by automatic devices, warning devices, or distribution, or use as applicable is possible damaged. This condition is either
special operating procedures by utilizing available redundant operational repairable or replaceable within an
options acceptable time frame on site
C Critical Personnel injured (1) operating the system, Production, storage, transportation, Two or more major subsystems are
(2) maintaining the system, or (3) being in distribution, or use as applicable impaired damaged—This condition requires
vicinity of the system seriously extensive maintenance
D Catastrophic Personnel suffer death or multiple injuries Production, storage, transportation, No portion of system can be salvaged—total
distribution, or use as applicable rendered loss
impossible—major unit is lost
G63 − 15 (2023)
NOTE 8—Oxygen index data are reported as a volume percent oxygen
rated relatively low based on conventional acceptance criteria,
(0 to 100). However, early work reported the volume fractional oxygen (0
many years of successful safe usage or full-life cycle tests
to 1.0).
might indicate its continued acceptance.
NOTE 9—Experience with oxygen index tests indicates that elevated
temperatures enable combustion in lower oxygen concentrations and that
6. Test Methods
passage of hot combustion products across an unaffected surface may
preheat and promote combustion of materials in concentrations below the
6.1 Heat of Combustion, Test Method D4809—This is a
oxygen index value. In exploratory work to measure oxygen indices at
measurement of the heat evolved per unit of specimen mass
elevated pressures up to 20 atm (2.0 MPa), it was found that the oxygen
when a material is completely burned in 25 atm to 35 atm
index decreased with increasing pressures, but that the ranking of
(2.5 MPa to 3.5 MPa) of oxygen at constant volume. The
materials was unchanged.
results are reported in calories per gram (or megajoules per
6.4 Autogenous Ignition Temperature, Test Method G72—
kilogram). For many materials, measured amounts of combus-
This is a determination of the minimum specimen temperature
tion promoter must be added to ensure complete combustion.
at which a material will spontaneously ignite when heated in an
Heat of combustion is a test readily conducted and many
oxygen or oxygen-enriched atmosphere. Autogenous ignition
differing bomb calorimeter methods provide results with ad-
(commonly called the autoignition temperature) should be
equate accuracy for use with this guide.
measured at or above the maximum anticipated oxygen con-
6.2 Ignition Sensitivity of Materials to Mechanical Impact
centration. The test should be continued up to the ignition point
in Ambient and Pressurized Oxygen Environments, Test
or at least to 100 °C above the maximum use temperature. The
Method G86—This is a determination of the drop-height
temperature that will produce autoignition of materials in
required to produce a reaction when energy from a known mass
configurations that differ from the test configuration may be
is transmitted through a striker pin in contact with a specimen
greater or less than the measured autoignition temperature.
immersed in liquid oxygen or exposed to gaseous oxygen.
System materials and contaminants may catalyze and lower
Results are reported in drop-height and number of reactions in
ignition temperatures. Specimens with large surface area to
20 drops. Test Method G86 is currently the only mechanical
volume ratios (such as powders) typically ignite at lower
impact test that is fully standardized, although other procedures
temperatures. Flammable vapors that evolve at elevated tem-
are used in some laboratories. For this reason, and for the large
peratures may promote lower ignition temperatures, or if
quantity of background data already obtained using this
dissipated, result in higher autoignition temperatures.
procedure, Test Method G86 is the recommended screening
NOTE 10—Pressure has its greatest effect on autoignition temperatures
test to evaluate materials for mechanical impact sensitivity.
at lower pressures. For instance, an autoignition temperature of a typical
elastomer as measured by Test Method G72 may decrease 80 °C between
NOTE 6—Previous mechanical impact data in ambient pressure liquid
1.5 psig and 15 psig (10 kPa and 100 kPa), but may only decrease 10 °C
oxygen may have been obtained following Test Method D2512 proce-
between 150 psig and 750 psig (1000 kPa and 5000 kPa). The autoignition
dures. In 1997, Test Method G86 was updated to include a LOX impact
temperature test measures a highly behavioral property of a material,
test procedure that includes a more strict calibration procedure as an
especially among polymers. Because it depends upon geometry, heating
alternative to Test Method D2512. At a given plummet drop height the
rate, temperature history of the material, trace contaminants and even
pressurized LOX mechanical impact system provides significantly lower
catalytic effects of the environment, data collected on differing appara-
impact energy than the ambient pressure LOX mechanical impact system;
tuses using differing techniques may yield widely differing results. One
however, the relative ranking of materials was maintained.
should therefore not confuse the measured autoignition temperature
NOTE 7—Test Method G86 was developed as a screening technique for
minimum with the minimum temperature at which the material might
selection of nonmetallic materials for use in liquid and gaseous oxygen
ignite in actual hardware.
service components and systems; the test has proven to be consistent in its
rankings. For tests in liquid oxygen, since the material specimen is
6.5 Gaseous Fluid Impact, Test Method G74—This is a test
immersed in liquid oxygen prior to impact, and since the liquid oxygen
in which the material is subjected to a rapid oxygen pressure
surrounding the specimen is maintained at atmospheric pressure, two
concerns must be stated. The first concern relates to the physical changes rise in a closed end tube. The procedure may be used as a
(for example, contraction, sub-T transitions, phase transitions) that occur
g fixed-pressure screening method or to measure a threshold
in a specimen when the temperature is reduced to cryogenic conditions.
pressure.
Sensitivity of selected materials may be significantly affected by such
physical changes. The second concern relates to test severity. Experience
NOTE 11—This test method provides a reliable means for ranking
indicates that most materials are more sensitive to ambient or heated
nonmetallic materials for use in gaseous oxygen service components and
gaseous oxygen environments, as opposed to cryogenic oxygen environ-
systems. The test is configuration dependent and severe. Reaction thresh-
ments. Also, experience shows most materials have a tendency to display
old pressures obtained for most materials are below those pressures that
increasing sensitivity with increasing oxygen pressure. As a result, tests in
would produce ignition in most common systems.
ambient pressure liquid oxygen may not be sufficiently severe to discrimi-
6.6 Additional Candidate Test Methods:
nate materials for use in ambient or elevated temperature, high-pressure
gaseous oxygen systems.
6.6.1 Thermal Analysis Tests—In these tests, a material’s
6.3 Limiting Oxygen Index, Test Method D2863—This is a tendency to undergo exothermic or endothermic activity are
determination of the minimum concentration of oxygen in a observed as temperature is raised. Pilot studies have been
flowing mixture of oxygen and nitrogen at 1 atm (0.1 MPa) that accomplished with Accelerating Rate Calorimeters (ARC) and
will just support flaming combustion from top ignition. The Pressurized Differential Scanning Calorimeters (PDSC), and
minimum oxygen concentration that will support combustion data have been published for autoignition temperatures mea-
of materials in configurations that differ from the test configu- sured by Differential Thermal Analysis (DTA). These tests
ration may be greater or less than the measured oxygen index indicate that material reactions occur at temperatures signifi-
value. cantly different from those measured by Test Method G72.
G63 − 15 (2023)
NOTE 12—Although some thermal analysis tests report lower autoigni-
the context of the necessity to avoid ignition and decide
tion temperatures than Test Method G72, one should not infer that these
whether the material will be acceptable (7.6).
measurements represent the lowest levels at which ignition could con-
ceivably occur in real systems. 7.2 Ignition Probability Assessment—In assessing a materi-
al’s suitability for a specific oxygen application, the first step is
6.6.2 Friction/Rubbing Test—The material is heated by
to review the application for the presence of potential ignition
friction and rubbing resulting from contact between rotating
mechanisms and the probability of their occurrence under both
and stationary test specimens. This test permits evaluation of
normal and reasonably foreseeable abnormal conditions. As
materials under various axial loads while exposed to elevated
shown in the Materials Evaluation Data sheets, Appendix X1,
pressure oxygen or oxygen-enriched environments.
values may be assigned, based on the following probability
NOTE 13—There is no standard friction rubbing test for polymers and
scale:
no plans to develop test. Preliminary tests were conducted by NASA in the
0—Almost impossible
late 1970s, and polymers proved difficult to ignite. At that time, test
1—Remote
development focused on the study of metals which are more likely to
2—Unlikely
experience severe rubs in actual systems. In the case of polymers, in
3—Probable
particular nylon, the polymers melted and flowed from the friction zone.
4—Highly probable
6.6.3 Particle Impact Test—The material is struck by par-
This estimate is quite imprecise and generally subjective, but
ticles while exposed to a flowing oxygen environment.
furnishes a basis for evaluating an application through helping
to focus on the most important properties. These ratings may in
NOTE 14—There is no standard test method for studying the ignition of
nonmetals during particle impact and none is planned. Preliminary tests some cases be influenced by the materials present in the
conducted by NASA suggest that polymers may be more difficult to ignite
system.
than metals under particle impact, possibly due to their ability to cushion
an impact. 7.3 Ignition-Susceptibility Determination—The next step is
to determine its rating with respect to those factors which affect
6.6.4 Promoted Ignition Test—The material is heated by
ease of ignition (5.2.1), assuming the material meets the other
exposure to an electrically-ignited promoter material having a
performance requirements of the application. If required infor-
known heat of combustion. This test method is currently being
mation is not available in published literature or from prior
developed and permits evaluation of materials while subjected
related experience, one or more of the applicable tests de-
to elevated-pressure oxygen or oxygen-enriched environments.
scribed in Section 6 should be conducted to obtain it. The
NOTE 15—Polymers have much lower autoignition temperatures than
application and materials present will play a strong role in
metals and tend to ignite in a range of 150 °C to 450 °C. Further, the
defining the most important criterion in determining the
combustion temperatures of most polymers exceeds the autoignition
ignition susceptibility.
temperature of virtually all polymers. Hence tests to evaluate the ability of
a promoter material or amount of promoter necessary to ignite polymers
NOTE 17—Until an ASTM test method is established for a particular
are not deemed meaningful and rather, the concept of a promoted ignition
test, test results are to be considered provisional.
test is usually applied only to metals for which there are enormous ranges
of ignition temperatures and for which the amount of polymer or metal
7.4 Post-Ignition Property Evaluation—The properties and
necessary to cause ignition is more amenable to experiment.
conditions that could affect potential resultant damage if
6.6.5 Electrical Arc—This test is designed to evaluate the
ignition should occur (5.2.3) should be evaluated. Of particular
arc ignition characteristics of materials in pressurized oxygen
importance is the total heat release potential, that is, the
or oxygen-enriched atmospheres.
material’s heat of combustion times its mass (in consistent
units). When available, other important postignition data of
NOTE 16—There is no standard test method for electrical arc ignition of
interest are the combustion reaction rate and the oxygen index.
nonmetals, and none is planned. Experience in oxygen and limited testing
in air suggests that arc ignition of polymers as a result of static charge
7.5 Reaction Effect Assessment—Based on the evaluation of
separation is unlikely at low pressures, perhaps also at high pressures.
7.4, and the conditions of the complete system in which the
Further, reports on incident studies of NASA suggest that probable arcing
at high pressures in oxygen did not produce ignition. material is to be used, the reaction effect severity should be
assessed using Table 3 as a guide. In judging the severity level
6.6.6 Special Tests—Depending on circumstances, a unique
for entry on the Material Evaluation Data Sheets, Appendix
test may be required to qualify a material for a specific
X1, it is important to note that the severity level is defined by
application, such as a resonance, internal flexing, or hot-wire
the most severe of any of the effects, that is, effect on personnel
ignition test.
safety or on system objectives or on functional capability. The
materials present in the system can affect the reaction effect
7. Material Selection Method
assessments.
7.1 Overview—To select a material for an application, first
7.6 Final Selection—In the final analysis, the selection of a
review the application to determine the probability that the
material for a particular application involves a complex inter-
material will be exposed to significant ignition phenomena in
action of the above steps, frequently with much subjective
service (7.2). Then consider the material’s susceptibility to
judgment, external influences, and compromises involved.
ignition (7.3) and its destructive potential or capacity to
While each case must ultimately be decided on its own merits,
involve other materials (7.4) once ignited. Next, consider the
the following generalizations apply:
potential reaction effects of an ignition on the system environ-
ment (7.5). Finally, compare the demands of the application 7.6.1 Use the least reactive material available consistent
with the level of performance anticipated from the material in with sound engineering and economic practice. Attempt to
G63 − 15 (2023)
maximize autoignition temperature, oxygen index, mechanical above guidelines. Explanatory remarks should be indicated by
impact ignition energy, and gaseous impact pressure threshold. a letter in the “Remarks” column and noted following the table.
Attempt to minimize heat of combustion and total heat release.
7.8 Examples—The following examples illustrate the mate-
Not every test need be conducted for every application, but it
rial selection procedure applied to three different hypothetical
is best to base material selections on more than one test
cases involving valve seats, and one case of a gasket:
method.
7.8.1 High-Pressure Manifold Shutoff Valve:
7.6.1.1 If the damage or personnel injury potential is high
7.8.1.1 Application Description—An ambient-temperature
(Severity Level C or D) use the best (least reactive) practical
1 in. (2.54 cm) stainless steel manifold requires a manual
material available (see Table 3).
shutoff valve located 20 ft (6.1 m) from a primary 5000 psig
7.6.1.2 If the damage or personnel injury potential is low
(34.5 MPa) pressure source. The line is to be located outdoors
(Severity Level A or B) and the ignition mechanism probability
but near attended equipment. A primary pressure valve up-
is low (2 or less) a material with a medium resistance to
stream can be opened rapidly, hence the line might be rapidly
ignition may be used.
pressurized to 5000 psig. A soft-seated valve is desirable to
7.6.1.3 If one or more potential ignition mechanisms have a
allow ease of operation.
relatively high probability of occurrence (3 or 4 on the
7.8.1.2 Ignition Probability Assessment (see 7.2)—Due to a
probability scale, 7.2) use only a material which has a very
small contact area and small quantity of rubbing motion during
high resistance to ignition.
operation, friction ignition is considered to be remote. Though
7.6.2 The higher the maximum use pressure, the more
the valve can be opened rapidly, the maximum velocity of the
critical is the resistance to ignition (see 5.3.1).
seat during closure would be negligible, hence mechanical
7.6.3 Prefer a material whose autoignition temperature in
impact ignition is also rated remote. Since the system is both
oxygen (as determined by 6.4) exceeds the maximum use
clean and dry, neither particle impact nor static electricity is
temperature by at least 100 °C. A larger temperature differen-
considered to be likely. There is no electrical apparatus in the
tial may be appropriate for high use pressures (see 7.6.2) or
equipment, so that arc ignition is thought to be almost
other mitigating factors.
impossible. Since sudden pressurization of the system to
7.6.4 Autoignition temperatures of 400 °C or higher are
5000 psig (34.5 MPa) might occur, the theoretical temperature
preferred; 160 °C or lower are unsuitable for all but the mildest
achievable from heat of compression (Eq 1) would be very
applications (see 6.4).
high, and adiabatic compression ignition is thought to be a
7.6.5 Resistance to ignition by impact from drop heights of
highly probable ignition source. No other ignition sources are
43.3 in. (1100 mm) on repeated trials is preferred, while
identified, but their absence cannot be assumed. The summary
susceptibility to ignition at 6.0 in. (152 mm) or lower would
of ignition probability ratings is:
render a material unsuitable for all but the mildest applications
Friction 1
(see 6.2). Heat of Compression 4
Mechanical Impact 1
7.6.6 Heats of combustion of 2500 cal ⁄g (10.5 MJ ⁄kg) or
Particle Impact 2
less are preferred; heats of combustion of 10 000 cal ⁄g
Static Electricity 2
(41.9 MJ ⁄kg) or higher are unsuitable for all but the mildest Electric Arc 0
Other 1
applications (see 6.1).
7.8.1.3 Prospective Material Evaluations (see
7.6.7 Materials with high oxygen indices are preferable to
7.3)—Nonmetallic seat materials are reviewed, and polytet-
materials with low oxygen indices. For demanding
rafluoroethylene (PTFE) is found to be highly rated with regard
applications, choose a material with an oxygen index above 55.
to resistance to ignition (it has one of the highest ignition
Materials with oxygen indices below 20 are unsuitable for all
temperatures for plastics). A well-documented material, it has
but the mildest applications (see 6.3).
a very low heat of combustion of 1700 cal/g and Liquid
NOTE 18—With respect to guidelines 7.6.3 – 7.6.7, the use of materials
Oxygen (LOX) impact results of passing at a 10 kg-m energy
that yield intermediate test results is a matter of judgment involving
level. Hence, PTFE is considered the best available plastic.
consideration of all significant factors in the particular application.
7.8.1.4 Post-Ignition Property Evaluation (see
7.6.8 Experience with a given material in a similar applica-
7.4)—Though PTFE is found to have a low heat of combustion,
tion or a similar material in the same application frequently
the size of the seat required is quite large. Beyond this, PTFE
forms a sound basis for a material selection. However, discre-
is a relatively dense polymer. As a consequence, ignition of the
tion should be used in the extrapolation of conditions.
seat would be expected to release a small to moderate quantity
7.6.9 Since some materials vary from batch to batch, it may
of heat.
be necessary to test each batch for some applications.
7.8.1.5 Reaction Effect Assessment (see 7.5)—Ignition of the
7.7 Documentation—Table X1.1 (Appendix X1) is a mate- seat might, in turn, ignite the stainless steel valve components
rials evaluation sheet filled out for a number of different and possibly release fire to the surroundings. Since such
applications. It indicates how a materials evaluation is made ignition would most likely occur while personnel are in the
and what documentation is involved. Pertinent information immediate area and since barricading is not feasible, the effect
such as operating conditions should be recorded; estimates of on personnel safety is rated high. Ignition would result in
ignition mechanism probability and reaction effect ratings damage to the valve alone, which could be readily and
filled in; and a material selection made on the basis of the inexpensively replaced. Interruption of the system for the
G63 − 15 (2023)
required repair time is acceptable. Hence the following reac- 7.8.2.4 Post-Ignition Property Assessment (see
tion assessment ratings are assigned: 7.4)—Though PTFE has a low heat of combustion, the mass of
PTFE present in the seat is large and PTFE is rather dense;
Effect of Personnel Safety D
Effect on System Objectives B
complete combustion would represent a large heat release. In
Effect on Function Capability B
contrast, the PTFE is in intimate contact with a massive bronze
Because of the importance of personnel safety, the overall
body and the gas-wetted area is modest. As a result, the very
rating is concluded to be a worst case D. compatible brass body should resist ignition and remain intact.
Ignition of the downstream carbon steel piping is rated unlikely
7.8.1.6 Final Selection (see 7.6)—In view of the overall
because of the 10 diameter isolation section of Monel pipe.
catastrophic reaction effect severity (Code D), only a valve seat
7.8.2.5 Reaction Effect Assessment (see 7.5)—Ignition of the
that is able to function successfully is concluded to be
seat would be unlikely to produce a major release of fire or to
acceptable. Since there is a high probability (rating 3) that a
ignite the pipeline. Since the valve and neighboring pipeline
PTFE seat would be exposed to temperatures due to heat of
are unattended, the effect on personnel safety is rated negli-
compression approaching the ignition point (x °F (y °C)
gible (A). Combustion of the seat in the absence of penetration
predicted using Eq 1), PTFE is concluded to be unacceptable in
would not interrupt oxygen supply to the pipeline, nor would
this application. As a result, a metal seat is selected instead
the combustion products force a long-term process problem.
(refer to X1.1).
Combustion of the seat, when the valve is closed would supply
7.8.2 Pipeline Control Valve:
oxygen to the pipeline, but the system can safely control this
7.8.2.1 Application Description—Automatic flow control is
flow. Hence the effect on system objectives is rated negligible
required in an 8-in. (20.3-cm), 650-psig (4.6-MPa) carbon steel
(A). Finally, since only the valve seat is expected to react, the
above-ground pipeline at ambient temperature. High flow and
effect on functional cap
...