NASA Technical Reports Server (NTRS) 20030106776: Verification of International Space Station Component Leak Rates by Helium Accumulation Method

6 Pages·0.21 MB·English

by  NASA Technical Reports Server (NTRS)

40fhS pace Congress 2003
International Space Station Advances, Mission Milestones, Mission Operations
I Verification of International Space Station Component Leak Rates by Helium
Accumulation Method
Steve D. Underwood
Boeing Leak Test Engineer
Sherry L. Smith
Boeing Leak Test Engineer
Contact Author:
Steve Underwood
The Boeing Company
Integrated Defense Systems
International Space Station Program
499 Boeing Blvd.
P.O. BOX2 40002, M/S JT-03
Huntsville, AL 35824-6402
Work: [phone]
[email protected] .com
ABSTRACT mode to determine helium leak rates inside a
containment hood installed on the test
Discovery of leakage on several International
Space Station U.S. Laboratory Module
ammonia system quick disconnects (QDs) led
to the need for a process to quantify total component. The method was validated through
leakage without removing the QDs from the extensive developmental testing. Test results
system. An innovative solution was proposed showed the method was viable, accurate and
allowing quantitative leak rate measurement at repeatable for a wide range of leak rates. The
ambient external pressure without QD removal. accumulation method has been accepted by
The method utilizes a helium mass NASA and is currently being used by Boeing
spectrometer configured in the detector probe Huntsville, Boeing Kennedy Space Center and
Boeing Johnson Space Center to test welds and
, . I. \ ’
valves and will be used by Alenia to test the QD leakage. It was determined through a series
Cupola. The method has been used in place of of developmental tests that QD leak rates
more expensive vacuum chamber testing which
requires removing the test component from the
system. could be measure in place, by concentrating QD
TEST METHOD DEVELOPMENT leakage in a containment hood and comparing
peak detector probe responses with those of a
The Space Station Modules have many known leak in the same enclosure. The
components, which are leak tested at the bench developmental test setup is shown in Figure 1.
level before module integration. For various A containment enclosure made of plastic and
reasons it is sometimes necessary to retest the tape is installed over a QD volume simulator.
components in place, after integration. The The helium mass spectrometer is configured for
Laboratory Module Ammonia QDs were detector probe operation and the probe is
originally tested at the manufacturer in a inserted into the bag for initial background
vacuum chamber utilizing a helium mass measurement. Calibrated sources of various
spectrometer. The vacuum chamber is an leak rates are inserted into the bag for a
accurate method for quantifying leak rates and predetermined time period as shown in Figure
verifying the QDs met their leakage requirement 2. At the end of the time period the detector
of 1E-4 helium. However after installation, probe is inserted into the bag and the maximum
SCCS
QD leakage due to seal contamination was mass spectrometer response is recorded.
detected during Lab Module ammonia system Enclosure sensitivity is determined from this
weld testing. The detector probe method used data.
to test the welds is a qualitative method and did
not provide the accuracy needed to quantify the
Helium
Containment Hood
Detector Probe
QD Volume
Simulator
Mass Spectromete
Leak Detector
Figure 1: Accumulation Developmental Leak Test Setup
HHeelliiuumm CCoonnttaaiinnmmeenntt
EEnncclloossuurree
SSttaannddaarrdd LLeeaakk SSoouurrccee
/I < ! Y
QD Volume
Simulator
Figure 2: Enclosure Calibration
DEVELOPMENTAL TESTING RESULTS
Developmental tests were performed to collect 15 minutes the detector probe was inserted into
accumulation data for various enclosure the enclosure and the maximum mass
volumes, leak sizes and accumulation times. spectrometer reading was recorded. The
Initial development tests were performed with enclosure was purged with air before each
the following standard leaks: 1E-6 sccs He, calibration to ensure a consistent helium
4.2E-6 sccs He, 1.OE-4 sccs He, 1.3E-3 sccs background throughout the test. Fig 3 shows
He. Sensitivities were determined for the the mass spectrometer output resulting from
enclosure with each standard leak. Ambient each standard leak. The standard leak size and
background measurements were taken and each the resulting enclosure sensitivity are denoted
standard leak was inserted into the enclosure on the figure. More developmental tests were
for an accumulation time of 15 minutes. After conducted to gather similar accumulation data
on different types and sizes of enclosures, and
longer and shorter accumulation time.s, prior to
applying the method to flight hardware
acceptance testing.
Accumulation Data
I
Standard Leak Response
4
1.00EM2
I I I I I I I
0 10 20 30 40 50 60 70 80
Minutes
Figure 3 : Accumulation Developmental Test Typical Results
FLIGHT HARDWARE ACCEPTANCE
TESTING
Leak testing of the flight QDs on the Lab
Element ammonia system QDs began in May resulting enclosure sensitivity is denoted on the
of 1999. The method has since been utilized graph. Calibration accumulation time was
for leak testing welds, heat exchangers, racks, fifteen minutes. The ammonia system was
hoses, and will be used to test the Space Station pressurized to 500 psig He and allowed to
Cupola Module. Several QD problems were stabilize for three hours. At the end of three
identified and corrected through use of the hours the enclosure was purged with air, which
accumulation method. Figure 4 shows actual began the fifteen minute accumulation period.
data from Lab Element ammonia quick The second response on the graph is from the
disconnect (QD-l), with leakage exceeding the QD leakage and the leak rate was determined to
3E-4 sccs He requirement. The first response be 7.3E-3 sccs. Figure 5 shows data from Lab
on the graph is from the 1E-4 sccs He standard Element ammonia quick disconnect (QD-2),
leak used for the enclosure calibration. The with leakage below the 3E-4sccs He
requirement. The test performed on QD-2 was
identical to QD-1 and the leak rate was
determined to be 5.3E-5 sccs He.
----
1000000 __ - -- - - - - ________ 1
I
I
I
I
- II
OD1 Respona OB1 Leak Rate = 7 3E-3s ccs He i
100000 -
1
t
I
10000 -
,
- I
Standard Leak Response
\
~I
1000 - ,
I
Calibrated Leak 1 E4 sccs t
,
Enclosure Sensitiviy = 4 3E-6 sccs He
I
100 - I I I I I I I I I 1
0 5 10 15 20 25 30 35 40 45 50
Figure 4: QD-1 Test Results
.-
.
. v *
.
* ’
Flight QD-2
6000
I
Acn
C
.0-
‘.>-3 5000 -
s /
4000 1
c
0 j
Q
0
2cn
3000
L - i1I
Uaa,, OD-2 Respo.nse OD-2 Leak Rate = 5.3E-5 sccs He
Ee 2000 I
1
0
a,
Q
u) Standard Leak 1E-4 sccs He
1000
cn
:m Enclosure Sensitivity = 2.2E-8 sccs Held v
j
1
0
0 5 10 15 20 25 30 35 40 45 50
Minutes
Figure 5: QD-2 Test Results
CONCLUSIONS AND SUMMARY
ISS leak test engineers verified that it is
possible to accurately and consistently
quantify the leakage rate of pressurized
components at ambient test conditions,
utilizing a helium mass spectrometer configured
in the detector probe mode. Verification was
performed on volumes ranging from a few cubic
centimeters to 30 cubic feet, and leak rates
ranging from 1E-6 sccs helium up to 1E-2 sccs.
It is not necessary to know the enclosure
volume or the test article volume and it is not
critical that the enclosure have a specific leakage
as this is taken into account when the
sensitivity is determined.