ASTM D7194-19(2024)
(Specification)Standard Specification for Aerospace Parts Machined from Polychlorotrifluoroethylene (PCTFE)
Standard Specification for Aerospace Parts Machined from Polychlorotrifluoroethylene (PCTFE)
ABSTRACT
This specification establishes the requirements for parts intended for aerospace use and machined from polychlorotrifluoroethylene (PCTFE) homopolymers. This specification, however, does not cover parts machined from PCTFE copolymer, PCTFE film or tape, or modified PCTFE. Material covered by this specification is on four types, differentiated based on intended uses and exposures: Types I (high service pressure) and II (low service pressure) for use in air and oxygen media, Type II for use in inert and reactive media, and Type IV for use in other media. The parts shall be manufactured from virgin, unplasticized, pure PCTFE homopolymer, and the use of recycled polymer or regrind shall be prohibited. The base material shall be free of defects and contaminants. The finished parts shall be white or gray in color with a natural translucent appearance, and shall be free of voids, scratches, fissures, inclusions, or entrapped air bubbles. Tests for specific gravity, melting point, tensile strength and elongation, deformation under load, zero strength time, mechanical impact (in ambient liquid oxygen and pressurized liquid and gaseous oxygen environments), and dimensional stability shall be performed and shall conform to the requirements specified.
SCOPE
1.1 This specification is intended to be a means of calling out finished machined parts ready for aerospace use. Such parts may also find use in selected commercial applications where there are clear benefits derived from the use of parts with high molecular weight, good molecular weight retention during processing, dimensional stability, controlled crystallinity, and tightly controlled engineering tolerances.
1.2 This specification establishes requirements for parts machined from virgin, unplasticized, 100 % polychlorotrifluoroethylene (PCTFE) homopolymers.
1.3 This specification does not cover parts machined from PCTFE copolymers, PCTFE film or tape less than 0.25-mm (0.010-in.) thick, or modified PCTFE (containing pigments or plasticizers).
1.4 This specification does not allow parts containing recycled material.
1.5 The specification does not cover PCTFE parts intended for general use applications, in which control of dimensional stability, molecular weight, and crystallinity are not as important. For machined PCTFE parts intended for general use, use Specification D7211.
1.6 This specification classifies parts into three classes based upon intended uses and exposures: oxygen-containing media, reactive media, and inert media.
1.7 Application—PCTFE components covered by this specification are virgin, 100 % PCTFE resin, free of plasticizers and other additives. The components are combustion resistant in oxygen, dimensionally stable, and meet other specific physical characteristics appropriate for their end use. They are used in valves, regulators, and other devices in oxygen, air, helium, nitrogen, hydrogen, ammonia, and other aerospace media systems. The components typically are used as valve seats, o-rings, seals, and gaskets. They are removed and replaced during normal maintenance procedures. The components provide reliable sealing surfaces resulting in proper closure of valves and related devices and no leakage from the system into the environment. They will experience static mechanical loading, cyclic mechanical loading, temperatures ranging from cryogenic to 71°C (160°F), and pressures up to 68.9 MPa (10,000, psig) for oxygen and air media, and 103.4 MPa (15,000 psig) for inert media.
1.8 The values stated in SI units are to be regarded as standard. The values in parentheses are for information only.
1.9 The following precautionary caveat pertains only to the test methods portion, Section 13, of this specification: 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, health, and environmental pra...
General Information
Relations
Standards Content (Sample)
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: D7194 − 19 (Reapproved 2024)
Standard Specification for
Aerospace Parts Machined from Polychlorotrifluoroethylene
(PCTFE)
This standard is issued under the fixed designation D7194; 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 during normal maintenance procedures. The components pro-
vide reliable sealing surfaces resulting in proper closure of
1.1 This specification is intended to be a means of calling
valves and related devices and no leakage from the system into
out finished machined parts ready for aerospace use. Such parts
the environment. They will experience static mechanical
may also find use in selected commercial applications where
loading, cyclic mechanical loading, temperatures ranging from
there are clear benefits derived from the use of parts with high
cryogenic to 71°C (160°F), and pressures up to 68.9 MPa
molecular weight, good molecular weight retention during
(10,000, psig) for oxygen and air media, and 103.4 MPa
processing, dimensional stability, controlled crystallinity, and
(15,000 psig) for inert media.
tightly controlled engineering tolerances.
1.8 The values stated in SI units are to be regarded as
1.2 This specification establishes requirements for parts
standard. The values in parentheses are for information only.
machined from virgin, unplasticized, 100 % polychlorotrifluo-
1.9 The following precautionary caveat pertains only to the
roethylene (PCTFE) homopolymers.
test methods portion, Section 13, of this specification: This
1.3 This specification does not cover parts machined from
standard does not purport to address all of the safety concerns,
PCTFE copolymers, PCTFE film or tape less than 0.25-mm
if any, associated with its use. It is the responsibility of the user
(0.010-in.) thick, or modified PCTFE (containing pigments or
of this standard to establish appropriate safety, health, and
plasticizers).
environmental practices and determine the applicability of
1.4 This specification does not allow parts containing re-
regulatory limitations prior to use.
cycled material.
NOTE 1—There is no known ISO equivalent to this standard.
1.5 The specification does not cover PCTFE parts intended
1.10 This international standard was developed in accor-
for general use applications, in which control of dimensional
dance with internationally recognized principles on standard-
stability, molecular weight, and crystallinity are not as impor-
ization established in the Decision on Principles for the
tant. For machined PCTFE parts intended for general use, use
Development of International Standards, Guides and Recom-
Specification D7211.
mendations issued by the World Trade Organization Technical
1.6 This specification classifies parts into three classes
Barriers to Trade (TBT) Committee.
based upon intended uses and exposures: oxygen-containing
2. Referenced Documents
media, reactive media, and inert media.
2.1 ASTM Standards:
1.7 Application—PCTFE components covered by this speci-
D618 Practice for Conditioning Plastics for Testing
fication are virgin, 100 % PCTFE resin, free of plasticizers and
D638 Test Method for Tensile Properties of Plastics
other additives. The components are combustion resistant in
D792 Test Methods for Density and Specific Gravity (Rela-
oxygen, dimensionally stable, and meet other specific physical
tive Density) of Plastics by Displacement
characteristics appropriate for their end use. They are used in
D883 Terminology Relating to Plastics
valves, regulators, and other devices in oxygen, air, helium,
D1204 Test Method for Linear Dimensional Changes of
nitrogen, hydrogen, ammonia, and other aerospace media
Nonrigid Thermoplastic Sheeting or Film at Elevated
systems. The components typically are used as valve seats,
Temperature
o-rings, seals, and gaskets. They are removed and replaced
D1430 Classification System for Polychlorotrifluoroethylene
(PCTFE) Plastics
This specification is under the jurisdiction of ASTM Committee D20 on
Plastics and is the direct responsibility of Subcommittee D20.15 on Thermoplastic
Materials. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2024. Published April 2024. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 2005. Last previous edition approved in 2019 as D7194 - 19. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/D7194-19R24. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7194 − 19 (2024)
D1600 Terminology for Abbreviated Terms Relating to Plas- molecular weight retention during molding, whereby as-
tics (Withdrawn 2024) polymerized resin, typically powder or coarse granular
D1708 Test Method for Tensile Properties of Plastics by Use material, is thermoformed into semi-finished rod or sheet stock,
of Microtensile Specimens typically by extrusion or compression molding.
D2512 Test Method for Compatibility of Materials with
4.2 Given the relatively low glass transition temperature of
Liquid Oxygen (Impact Sensitivity Threshold and Pass-
PCTFE (T ≈ 55°C (130°F)), the second intention of this
g
Fail Techniques) (Withdrawn 2023)
specification is to ensure good dimensional stability of finished
D3045 Practice for Heat Aging of Plastics Without Load
articles subjected to temperature excursions during service that
D4591 Test Method for Determining Temperatures and
approach or exceed the T .
g
Heats of Transitions of Fluoropolymers by Differential
4.3 Because the crystallinity can vary widely in PCTFE,
Scanning Calorimetry
which in turn can affect the performance of a finished PCTFE
D7211 Specification for Parts Machined from Polychlorotri-
part in its intended application, nonmandatory guidance is
fluoroethylene (PCTFE) and Intended for General Use
given in Appendix X1. This guidance cites recommended
G86 Test Method for Determining Ignition Sensitivity of
ASTM Test Methods that measure the specific gravity
Materials to Mechanical Impact in Ambient Liquid Oxy-
(X1.1.4), melting point (X1.1.5), and tensile properties
gen and Pressurized Liquid and Gaseous Oxygen Envi-
(X1.1.6) of PCTFE. Control of these properties is used to
ronments
established consistency between different lots of finished parts
2.2 Federal Standards
where either the starting resin, molding method, thickness of
NASA-STD-6001B Flammability, Offgassing, and Compat-
the semifinished article, or machining method change.
ibility Requirements and Test Procedures—Mechanical
Impact for Materials in Ambient Pressure LOX (Test 13A) 4.4 Finished parts are categorized based on whether anneal-
and Mechanical Impact for Materials in Variable Pressure
ing of the finished parts is not performed (Method A), or is
GOX and LOX (Test 13B) performed (Methods B and C), depending on the dimensional
stability of a statistical sample of unannealed finished parts.
3. Terminology
5. Classification
3.1 Definitions:
3.1.1 Terms are defined in accordance with Terminologies
5.1 Part shape and size shall be defined by the applicable
D883 and D1600 unless otherwise indicated.
purchase order.
3.1.2 air media, n—liquid air, pressurized air, and breathing
5.2 The type of product shall be categorized by the intended
air.
use category:
3.1.3 cognizant engineering organization, n—the company,
5.2.1 Type I for use in air and oxygen media (see 3.1.2 and
agency, or other authority responsible for the system or
3.1.5) at service pressures above 11.4 MPa (1650 psi) that
component in which aerospace grade PCTFE is used. This, in
require batch testing.
addition to design personnel, may include personnel from
5.2.2 Type II for use in (1) air and oxygen media (at service
material and process engineering, or quality groups and others
pressures below 11.4 MPa (1650 psi), or at service pressures
as appropriate.
above 11.4 MPa (1650 psi) that do not require batch testing);
or (2) inert and reactive media up to the pressures specified in
3.1.4 inert media, n—gaseous helium (GHe) and gaseous
nitrogen (GN ) up to 103.4 MPa (15,000 psig). 3.1.4 and 3.1.7.
5.2.3 Type III for use in media other than air, oxygen, GHe,
3.1.5 oxygen media, n—liquid oxygen (LOX) and gaseous
GN , ammonia, GH and LH , at service pressures specified by
2 2 2
oxygen (GOX) up to 68.9 MPa (10,000 psig).
the cognizant engineering organization.
3.1.6 processing route, n—the method whereby a thermo-
plastic is taken above its melting point and processed into a
6. Ordering Information
semifinished article, typically sheet or rod stock. For PCTFE,
6.1 All parts covered by this specification shall be ordered
the common processing methods are extrusion and compres-
by Specification D7194, Type, as listed in Section 5, or as listed
sion molding.
on the purchase contract or order when Type is not specified
3.1.7 reactive media, n—ammonia (NH ) up to 3.5 MPa
explicitly.
(500 psig), gaseous hydrogen (GH ) up to 46.2 MPa (6700
psig), and liquid hydrogen (LH ) up to 2.8 MPa (400 psig). 7. Apparatus
7.1 Oven—A convection oven capable of maintaining a
4. Significance and Use
temperature of 100 to 200 6 2°C.
4.1 Given the thermal instability of PCTFE in the melt, the
primary intention of this specification is to ensure adequate
8. Materials and Manufacture
8.1 Parts shall be made from as-polymerized resin meeting
The last approved version of this historical standard is referenced on
all requirements of Classification System D1430. Type I, II and
www.astm.org.
III parts shall be fabricated from as-polymerized resin classi-
Available from U.S. Government Printing Office, Superintendent of
fied as meeting Classification System D1430, Group 01, Class
Documents, 732 N. Capitol St., NW, Washington, DC 20401-0001, http://
www.access.gpo.gov. 1, Grade 3.
D7194 − 19 (2024)
8.2 Parts shall be made from virgin, unplasticized, 100 % ity of PCTFE semi-finished articles and parts machined there-
polychlorotrifluoroethylene (PCTFE) homopolymer. from subject to this specification, refer to Nonmandatory
Appendix X1.
8.3 No recycled polymer or regrind shall be permitted.
8.4 The base material shall be free of all defects or con-
11. Specific Requirements
taminants that would be detrimental to final fabrication or
11.1 Specific requirements for Type I, II and III material are
performance of the finished parts.
summarized in Table 1.
9. Property Requirements
11.2 Type I—Each batch or lot of parts, or semifinished
articles from which the finished parts are made, shall meet the
9.1 Numerical values listed in this specification for proper-
test and criteria of 13.4 or 13.5 in accordance with NASA-
ties or property changes are minimum values.
STD-6001B and Test Methods D2512 and G86 according to
9.2 All requirements stipulated in Sections 9 and 10 shall be
the discretion of the procuring agency. Finished parts meeting
met, unless otherwise specified in the purchase contract or
the criteria of 13.4 or 13.5 shall be assigned a unique dash
order. Any exceptions to the requirements stipulated in Sec-
number or part number.
tions 9 and 10 shall be noted in 14.2.1.12.
11.3 Types II and III—No requirements exist either for
9.3 Any nonmandatory tests or data, such as those cited or
mechanical impact testing and assigning of a unique dash
alluded to in the nonmandatory Appendix X1, shall be speci-
number or part number.
fied at the time of the order.
12. Test Specimens and Number of Tests
10. General Requirements
NOTE 2—Unless otherwise specified in the purchase contract or order,
12.1 In cases where measured values depend on orientation,
the molder producing the semifinished article from which finished parts
for example, tensile properties and dimensions of test speci-
are made is responsible for insuring the requirements in 10.4 are met. All
mens made from extruded material, the extrusion direction
other requirements listed in Section 10 pertain to the finished part, and
relative to the measurement direction shall be tracked.
therefore, are the responsibility of the supplier of the finished, machined
part.
12.2 When the number of test specimens is not stated in the
10.1 Finished parts shall have a natural translucent appear-
test method, a single determination may be made. If more than
ance. The color shall be white or gray with no yellowing or
a single determination or determinations on separate portions
other unnatural color.
10.2 Finished parts shall be free of voids, scratches, fissures,
A
TABLE 1 Type I, II and III Material Requirements
inclusions, or entrapped air bubbles that will affect serviceabil-
Assign Unique
ity. No particles (for example, black specks) shall be visible to
Service
Mechanical Part Number or
Pressure
the naked eye.
Type Media Impact Test Dash Number
(MPa (psi)) and
Required for the
10.3 Finished parts shall be made from semifinished articles
affected parts
Finished Part
having a zero strength time (ZST ) of 300 to 450 s (Grade 3)
stock
I >11.4 (1650): oxygen, air yes yes
when determined in accordance with 13.1.
only parts
for which
10.4 The maximum allowable ZST drop, ∆ZST, shall be
mechanical
<20 % as determined in 13.1.4.
impact
testing is
10.5 No critical engineering dimension in a finished part
required
II oxygen, air: oxygen, air, no no
shall change by more than 0.01 mm/mm (0.01 in./in.) when
< 11.4 (1650): inert, reactive
measured at 23 6 2°C (73.4 6 3.6°F) after being held for a
all parts
predetermined time at 100 6 2°C (212 6 3.6°F) as determined
> 11.4 (1650):
only parts
in accordance with 13.2.
for which no
10.6 Finished parts meeting the general requirements of mechanical
impact
10.1 to 10.5 shall be categorized as parts suitable for Method A
testing is
(no annealing required).
required
He:
10.7 Finished parts meeting the general requirements of
inert, reactive:
10.1 to 10.4, but which fail general requirement 10.5 (∆L > 1.0
pressures
specified
%), shall be categorized as Method B parts (annealing required
in 3.1.4 and
to achieve best dimension stability) or Method C parts (anneal-
3.1.7:
ing required to achieve best engineering tolerances). Annealing
all parts
B
III all pressures other no no
for Methods B and C parts shall be performed in accordance
and parts
(for example,
with 13.3.
nitrox)
A
10.8 For nonmandatory requirements; namely, specific Finished parts made from Type
...
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