OXYGEN SYSTEM DESIGN How to select pressure control components for oxygen-enriched aerospace applications - Emerson
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REFE RE NC E GUI DE
OXYGEN SYSTEM DESIGN
I
f it can ignite, it can burn. In mission- materials. This combination will ensure the
critical aerospace applications, even the safety of high-pressure oxygen equipment
How to select pressure smallest source of contamination can in applications such as astronaut breathing
control components lead to dangerous combustion. This threat support and rocket engine fuel pressing.
increases in oxygen-rich environments,
for oxygen-enriched where the steady supply of oxygen can Meet enhanced cleanliness standards
aerospace applications. easily support the ignition and sustained Oxygen is highly reactive in nature so any
burning of certain materials. Minimize components or systems operating in the
By Ryan Kirchner these risks by selecting pressure control presence of liquid or gaseous oxygen must
components that are verifiably cleaned be verifiably cleaned. Meticulous cleaning
and designed with oxygen-compatible is fundamental to ensuring the safe opera-
Credit: Adobe Stock
Since the birth of the space program,
Emerson has met the pressure control
needs of aerospace customers.
2022 REFERENCE GUIDE | AerospaceManufacturingAndDesign.com 27
REF E R E N C E G U I D E
IEST-STD-CC1246E level (maximum particle count)
Min (µm) Max (µm) 25 50 100 200 300 400 500 750 1,000
5 15 19 141 1,519
15 25 2 17 186 2,949
25 50 1 6 67 1,069 6,433
50 100 0 1 9 154 926 3,583 10,716
100 250 0 0 1 15 92 359 1,073 8,704
250 500 0 0 0 0 2 8 25 205 983
500 750 0 0 0 0 0 0 1 7 33
750 1,000 0 0 0 0 0 0 0 1 3
1,000 1,250 0 0 0 0 0 0 0 0 1
TESCOM manifolds and other products are cleaned
per CGA G-4.1 and ASTM G93. Emerson offers Particulate cleanliness levels
enhanced, in-house cleaning for critical applications.
Choose the right materials Autoignition temperature is the tem-
Just because a material is oxygen-cleaned perature at which a material autoignites
tion of an oxygen system by ridding the and free of combustible residue and FOD in the presence of pressurized oxygen.
equipment of foreign object debris (FOD) doesn’t mean it can’t ignite. Selecting suit- Materials with a high autoignition tem-
and combustible residue that could serve able materials is as important as thorough perature are preferred for oxygen service.
as an ignition source. cleaning processes. When it comes to pres- Materials such as Teflon and PCTFE are
ASTM G93, ASTM International’s sure control components, it’s important to preferred, as they have high autoignition
current cleanliness standard for equipment consider a material’s oxygen index, autoigni- temperatures.
in oxygen-enriched environments, and Com- tion temperature, and heat of combustion. Heat of combustion is the amount
pressed Gas Association (CGA) G-4.1, which Oxygen index is the minimum con- of energy released by a material when it
outlines the methods for cleaning equipment centration of oxygen needed for a material burns in oxygen. Materials with a low heat
for oxygen service, are accepted industry to continue to burn on its own once it of combustion, such as Teflon, PCTFE,
standards that must be met for basic-level ignites at atmospheric pressure. Materials and Vespel SP21, are preferred.
oxygen cleaning. However, many mission- with a high oxygen index are preferred for For metals, the minimum burn pres-
critical aerospace applications involving high- oxygen service; the higher the oxygen in- sure is critical since it’s the minimum
pressure oxygen and other oxidizers require dex, the lower the propensity of a material oxygen pressure where a metal will
enhanced and verifiable levels of cleanliness. to ignite and burn. Conversely, the lower continue to burn on its own after ignition.
For these critical applications, TES- the oxygen index, the higher the propen- Burn-resistant metals like Monel and brass
COM offers enhanced cleaning options sity of a material to ignite and burn. Soft are highly preferred for oxygen service.
including IEST-STD-CC1246E, the goods such as Teflon, polychlorotrifluoro- Stainless steels and aluminum have very
industry standard for enhanced cleaning for ethylene (PCTFE) and fluoroelastomers low minimum burn pressures and gener-
critically clean applications. This standard, (FKM) are generally accepted due to their ally are not recommended in oxygen-rich
issued by the Institute of Environmental high oxygen index. environments, even at relatively low pres-
Sciences and Technology (IEST), specifies
and determines product cleanliness levels SOFT GOODS
for contamination-critical products by fo- Autoignition Heat of
Material Oxygen index (%)
cusing on contaminants that impact prod- temperature (°C) combustion (cal/g)
uct performance. It also covers stainless PTFE Teflon 100 434 1,524
steel, high-strength alloys, specialty metals, PCTFE (KEL-F) 100 388 1,475
brass, aluminum, plastics, and elastomers.
Vespel SP-21 ~57 343 1,817
The current IEST-STD-CC1246E
standard is a revision of MIL-STD-1246 Tefzel 60 250 3,535
in an effort to expand its usefulness beyond PEEK 35 300 7,762
military applications. Unlike the MIL stan- Viton A 57 275 3,600
dard, the IEST specification defines the
Buna-N 20 173 9,900
cleanliness levels for products that include
various components and fluids. Oxygen index, autoignition temperature, and heat of combustion of various elastomers.
28 AerospaceManufacturingAndDesign.com | 2 0 2 2 R E F E R E N C E G U I D E
REFE RE NC E GUI DE
MATERIAL PRESSURE (PSI)
TESCOM
Monel >10,000 Since the birth of the space
program more than 50 years ago,
Brass >7,000 Emerson has offered pressure
controls for aerospace customers.
Inconel 625 2,500 Its TESCOM brand continues to
deliver regulators, valves, manifolds,
Elgiloy 2,000 and systems according to strict
industry standards. TESCOM
316 stainless steel 200 engineers and technical support
teams are trained in the safe use of
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