ASTM E498-95(2000)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation:E498–95 (Reapproved 2000)
Standard Test Methods for
Leaks Using the Mass Spectrometer Leak Detector or
,
1 2
Residual Gas Analyzer in the Tracer Probe Mode
This standard is issued under the fixed designation E498; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
This specification has been approved for use by agencies of the Department of Defense.
1. Scope ANSI/ASNT CP-189 ASNT Standard for Qualification and
Certification of Nondestructive Testing Personnel
1.1 These test methods cover procedures for testing and
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locating the sources of gas leaking at the rate of 4.5 310
3. Terminology
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mol/s (1 310 Std cm /s) or greater. The test may be
3.1 Definitions—For definitions of terms used in this stan-
conducted on any object to be tested that can be evacuated and
dard, see Terminology E1316, Section E.
to the other side of which helium or other tracer gas may be
applied.
4. Summary of Test Methods
1.2 Three test methods are described:
4.1 Thesetestmethodsrequireaheliumleakdetectorthatis
1.2.1 Test Method A—For the object under test capable of
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capableofdetectingaleakof4.5 310 mol/s(1 310 Std
being evacuated, but having no inherent pumping capability.
cm /s).
1.2.2 Test Method B—Fortheobjectundertestwithintegral
4.2 Test Method A—This test method is used to helium leak
pumping capability.
test objects that are capable of being evacuated to a reasonable
1.2.3 Test Method C—For the object under test as in Test
testpressurebytheleakdetectorpumpsinanacceptablelength
MethodB,inwhichthevacuumpumpsoftheobjectundertest
of time. This requires that the object be clean and dry and
replace those normally used in the leak detector.
usually no larger than a few cubic feet in volume.Also to cope
1.3 This standard does not purport to address all of the
with larger volumes or relatively“ dirty” devices, auxiliary
safety concerns, if any, associated with its use. It is the
vacuum pumps having greater capacity than those in the mass
responsibility of the user of this standard to establish appro-
spectrometer leak detector (MSLD) may be used in conjunc-
priate safety and health practices and determine the applica-
tion with the MSLD. The leak test sensitivity will be reduced
bility of regulatory limitations prior to use. A specific hazard
under these conditions.
statement can be found in 19.2.
4.3 Test Method B—This test method is used to leak test
equipmentthatcanprovideitsownvacuum(thatis,equipment
2. Referenced Documents
that has a built-in pumping system) at least to a level of a few
2.1 ASTM Standards:
4 hundred pascals (a few torr) or lower.
E1316 Terminology for Nondestructive Examinations
4.4 Test Method C—When a vacuum system is capable of
2.2 Other Documents:
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producing internal pressures of less than 2 3 10 Pa
SNT-TC-1A Recommended Practice for Personnel Qualifi-
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5 (2 310 torr) in the presence of leaks, these leaks may be
cation and Certification in Nondestructive Testing
located and evaluated by the use of either a residual gas
analyzer(RGA)orbyusingthespectrometertubeandcontrols
These test methods are under the jurisdiction of ASTM Committee E07 on from a conventional MSLD, provided, of course, that the
Nondestructive Testing and is the direct responsibility of Subcommittee E07.08 on
leakage is within the sensitivity range of the RGA or MSLD
Leak Testing.
under the conditions existing in the vacuum system.
Current edition approved September 10, 1995. Published November 1995.
Originally published as E498–73. Last previous edition E498–94.
5. Personnel Qualification
(Atmospheric pressure external, vacuum internal). This document covers the
Tracer Probe Mode described in Terminology E1316.
5.1 It is recommended that personnel performing leak test-
The gas temperature is referenced to 0°C. To convert to another gas reference
ing attend a dedicated training course on the subject and pass
temperature, T , multiply the leak rate by (T +273)/273.
ref ref
a written examination.The training course should be appropri-
Annual Book of ASTM Standards, Vol 03.03.
Available from American Society for Nondestructive Testing, 1711 Arlingate
ate for NDT level II qualification according to Recommended
Plaza, P.O. Box 28518, Columbus, OH 43228-0518.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E498–95 (2000)
Practice No. SNT-TC-1A of theAmerican Society for Nonde- 7.3 Temporarily plugged leaks often occur because of poor
structive Testing or ANSI/ASNT Standard CP-189. manufacturing techniques. Water, cleaning solvent, plating,
flux, grease, paint, etc., are common problems. To a large
6. Significance and Use
extent,theseproblemscanbeeliminatedbyproperpreparation
6.1 TestMethodAisthemostfrequentlyusedinleaktesting
of the parts before leak testing. Proper degreasing, vacuum
components which are structurally capable of being evacuated
baking, and testing before plating or painting are desirable.
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to pressures of 0.1 Pa (approximately 10 torr). Testing of
7.4 In a device being tested, capillary tubing located be-
smallcomponentscanbecorrelatedtocalibratedleaks,andthe
tween the leak and the leak detector can make leak testing
actualleakratecanbemeasuredoracceptancecanbebasedon
extremely difficult as test sensitivity is drastically reduced and
a maximum allowable leak. For most production needs accep-
responsetimeincreased.Ifthereisavolumeateachendofthe
tance is based on acceptance of parts leaking less than an
capillary, each such volume should be attached to the leak
established standard which will ensure safe performance over
detector during testing. If this is impossible, the device should
the projected life of the component. Care must be exercised to
be surrounded with a helium atmosphere while attached to the
ensure that large systems are calibrated with reference leak at
leak detector for a long time to assure leak tightness. When
a representative place on the test volume. Leak rates are
unusually long pumping times are necessary, the connections
determinedbycalculatingthenetgainorlossthroughaleakin
to the leak detector (and all other auxiliary connections) that
thetestpartthatwouldcausefailureduringtheexpectedlifeof
are exposed to the helium should be double-sealed and the
the device.
space between the seals evacuated constantly by a small
6.2 TestMethodBisusedfortestingvacuumsystemseither
auxiliary roughing pump to avoid allowing helium to enter the
as a step in the final test of a new system or as a maintenance
system through seals that are not a part of the device to be
practice on equipment used for manufacturing, environmental
tested.
test or for conditioning parts.As the volume tends to be large,
a check of the response time as well as system sensitivity
TEST METHOD A—HELIUM LEAK TESTING OF
should be made. Volume of the system in liters divided by the
SMALL DEVICES USING THE MSLD
speed of the vacuum pump in L/s will give the response time
to reach 63% of the total signal. Response times in excess of
8. Apparatus
a few seconds makes leak detection difficult.
8.1 Helium Mass Spectrometer Leak Detector, having a
6.3 Test Method C is to be used only when there is no
minimumdetectableleakrateasrequiredbythetestsensitivity.
convenientmethodofconnectingtheleakdetectortotheoutlet
ofthehighvacuumpump.Ifaheliumleakdetectorisusedand 8.2 Auxiliary Pumps, capable of evacuating the object to be
tested to a low enough pressure so that the MSLD may be
the high vacuum pump is an ion pump or cryopump, leak
testingisbestaccomplishedduringtheroughingcycleasthese connected.
pumps leave a relatively high percentage of helium in the high
NOTE 1—If the object under test is small and clean and the MSLD has
vacuum chamber.This will obscure all but large leaks, and the
a built-in roughing pump, the auxiliary pumps are not required.
trace gas will quickly saturate the pumps.
8.3 Suitable Connectors and Valves, to connect to the
7. Interferences
MSLD test port. Compression fittings and metal tubing should
7.1 Series leaks with an unpumped volume between them be used in preference to vacuum hose.
present a difficult if not impossible problem in helium leak
8.4 Standard Leaks of Both Capsule Type (Containing its
testing. Although the trace gas enters the first leak readily
own Helium Supply) and Capillary Type (anActual Leak which
enough since the pressure difference of helium across the first
is Used to Simulate the Reaction of the Test System to Helium
leak is approximately one atmosphere, it may take many hours
Spray)—The leak rate from the capsule-type leak should be
to build up the partial pressure of helium in the volume
adequate to demonstrate the minimum allowable sensitivity of
betweenthetwoleakssothatenoughheliumentersthevacuum
the MSLD. The capillary type should be slightly smaller than
system to be detected by the MSLD. This type of leak occurs
the test requirement.
frequently under the following conditions:
8.5 Vacuum Gage, to read the pressure before the MSLD is
7.1.1 Double-welded joints and lap welds.
connected.
7.1.2 Double O-rings.
8.6 Helium Tank and Regulator,withattachedheliumprobe
7.1.3 Threaded joints.
hose and jet.
7.1.4 Ferrule and flange-type tubing fittings.
7.1.5 Casings with internal voids.
9. Calibration of MSLD
7.1.6 Flat polymer gaskets.
7.1.7 Unvented O-ring grooves. 9.1 Attach the capsule leak to the MSLD and tune the
7.2 In general, the solution is in proper design to eliminate MSLD to achieve maximum sensitivity in accordance with the
theseconditions;however,whendoublesealsmustbeused,an manufacturer’s instruction. Allow sufficient time for the flow
accessportbetweenthemshouldbeprovidedforattachmentto rate from the capsule leak to equilibrate. The capsule leak
the MSLD. Leaks may then be located from each side of the should be stored with the shutoff valve (if present) open, and
seal and after repair, the access port can be sealed or pumped the leak should be allowed to equilibrate to ambient tempera-
continuously by a “holding” pump (large vacuum systems). ture for several hours.
E498–95 (2000)
10. Procedure there are any materials in the device that are pervious to
helium, doing this step first may build up the helium back-
10.1 Evacuate the device to be tested until near equilibrium
ground to such a degree that subsequent probing would be
pressure is reached on the rough vacuum gage. Open the valve
insuffici
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