(6) All stainless steel fittings shall be austenitic stainless
steel in accordance with either MIL-F-5509 for AN fittings or MIL-F-18866 for
industrial fittings. These specifications shall be qualified so that the
fittings shall have a minimum burst strength of 20,000 psig. To prevent
interchanging these two types of fittings, all of the fittings for a single
contract shall be of the same type as in the rest of the system.
Note:
Although the instruction does not specifically refer to
pump diaphragms, it can be inferred that since the
instruction applies to all parts of a piping system in
contact with high-pressure oxygen, it also applies to
oxygen pump parts.
MIL-STD-777, Schedule of Piping, Valves, Fittings, and Associated Piping
Components for Naval Surface Ships (Reference 8) contains guidance for the use
of copper alloy materials with liquid and gaseous oxygen. The types of
service are shown in Table 5-3.
TABLE 5-3
Oxygen Systems Contained in MIL-STD-777
Category
System
Maximum
and
Pressure,
Temperature,
Group
Service
psig
F
MIL-STD-777
K-1
Gaseous oxygen outside hull
3000
150
K-2
Gaseous oxygen inside hull
3000
ambient
K-3
Gaseous oxygen
100
ambient
K-4
Liquid oxygen and nitrogen
6000
-
K-5
Liquid oxygen and nitrogen
250
-
b.
Compatibility with Seawater. The compatibility of piping materials
with seawater, when seawater is the contained fluid, will not normally
represent a threat to personnel safety. A number of piping materials are
compatible with seawater; however, seawater can cause corrosion and
malfunctioning of moving parts, such as are contained in valves, and
avoidance of this situation is a design problem. MIL-STD-777 (Reference 8)
and MIL-STD-889 Dissimilar Metals (Reference 5) contain guidance for the use
of materials in piping systems containing seawater.
c.
Compatibility with Other Materials. Most of the fluids in
hyperbaric chamber piping systems other than oxygen and seawater do not
present significant compatibility problems. MIL-STD-777 (Reference 8) and
MIL-STD-889 (Reference 5) contain guidance for the selection of materials for
use with air, nitrogen, helium, and fresh water.
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