ASTM E498/E498M-11(2017)

Standard Practice for Leaks Using the Mass Spectrometer Leak Detector or Residual Gas Analyzer in the Tracer Probe Mode

SIGNIFICANCE AND USE
6.1 Test Method A is the most frequently used in leak testing components which are structurally capable of being evacuated to pressures of 0.1 Pa (approximately 10−3 torr). Testing of small components can be correlated to calibrated leaks, and the actual leak rate can be measured or acceptance can be based on a maximum allowable leak. For most production needs acceptance is based on acceptance of parts leaking less than an established standard which will ensure safe performance over the projected life of the component. Care must be exercised to ensure that large systems are calibrated with reference leak at a representative place on the test volume. Leak rates are determined by calculating the net gain or loss through a leak in the test part that would cause failure during the expected life of the device.  
6.2 Test Method B is used for testing vacuum systems either as a step in the final test of a new system or as a maintenance practice on equipment used for manufacturing, environmental test or for conditioning parts. As the volume tends to be large, a check of the response time as well as system sensitivity should be made. Volume of the system in liters divided by the 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 a few seconds makes leak detection difficult.  
6.3 Test Method C is to be used only when there is no convenient method of connecting the leak detector to the outlet of the high vacuum pump. If a helium leak detector is used and the high vacuum pump is an ion pump or cryopump, leak testing is best accomplished during the roughing cycle as these pumps leave a relatively high percentage of helium in the high vacuum chamber. This will obscure all but large leaks, and the trace gas will quickly saturate the pumps.
SCOPE
1.1 This practice covers procedures for testing and locating the sources of gas leaking at the rate of 1 × 10 −8 Pa m3/s (1 × 10−9  Std cm 3/s)3 or greater. The test may be conducted on any object to be tested that can be evacuated and to the other side of which helium or other tracer gas may be applied.  
1.2 Three test methods are described:  
1.2.1 Test Method A—For the object under test capable of being evacuated, but having no inherent pumping capability.  
1.2.2 Test Method B—For the object under test with integral pumping capability.  
1.2.3 Test Method C—For the object under test as in Test Method B, in which the vacuum pumps of the object under test replace those normally used in the leak detector.  
1.3 Units—The values stated in either SI or std-cc/sec units are to be regarded separately as standard. The values stated in each system may not be exact equivalents: therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.  
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.  
1.5 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.

General Information

• Status: Historical
• Publication Date: 31-May-2017
• ICS: 19.100 - Non-destructive testing
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.08 - Leak Testing Method

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: E498/E498M − 11 (Reapproved 2017)
Standard Practice 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/E498M; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope* 2. Referenced Documents
1.1 This practice covers procedures for testing and locating 2.1 ASTM Standards:
−8 3
the sources of gas leaking at the rate of 1×10 Pa m /s E1316Terminology for Nondestructive Examinations
−9
3 3
(1×10 Std cm /s) or greater. The test may be conducted on
2.2 Other Documents:
any object to be tested that can be evacuated and to the other
SNT-TC-1A Recommended Practice for Personnel Qualifi-
side of which helium or other tracer gas may be applied.
cation and Certification in Nondestructive Testing
ANSI/ASNT CP-189ASNT Standard for Qualification and
1.2 Three test methods are described:
Certification of Nondestructive Testing Personnel
1.2.1 Test Method A—For the object under test capable of
being evacuated, but having no inherent pumping capability.
3. Terminology
1.2.2 Test Method B—Fortheobjectundertestwithintegral
pumping capability. 3.1 Definitions—For definitions of terms used in this
1.2.3 Test Method C—For the object under test as in Test practice, see Terminology E1316, Section E.
MethodB,inwhichthevacuumpumpsoftheobjectundertest
4. Summary of Practice
replace those normally used in the leak detector.
4.1 The tests in this practice require a helium leak detector
1.3 Units—The values stated in either SI or std-cc/sec units
−9 3
that is capable of detecting a leak of 1×10 Pa m /s
are to be regarded separately as standard. The values stated in
−10
3 3
(1×10 Stdcm /s).
each system may not be exact equivalents: therefore, each
system shall be used independently of the other. Combining
4.2 Test Method A—This test method is used to helium leak
values from the two systems may result in non-conformance
test objects that are capable of being evacuated to a reasonable
with the standard.
testpressurebytheleakdetectorpumpsinanacceptablelength
1.4 This standard does not purport to address all of the of time. This requires that the object be clean and dry.Also to
cope with larger volumes or relatively “dirty” devices, auxil-
safety concerns, if any, associated with its use. It is the
iary vacuum pumps having greater capacity than those in the
responsibility of the user of this standard to establish appro-
mass spectrometer leak detector (MSLD) may be used in
priate safety and health practices and determine the applica-
conjunction with the MSLD. The leak test sensitivity will be
bility of regulatory limitations prior to use.
reduced under these conditions.
1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
4.3 Test Method B—This test method is used to leak test
ization established in the Decision on Principles for the
equipmentthatcanprovideitsownvacuum(thatis,equipment
Development of International Standards, Guides and Recom-
that has a built-in pumping system) at least to a level of a few
mendations issued by the World Trade Organization Technical
hundred pascals (a few torr) or lower.
Barriers to Trade (TBT) Committee.
4.4 Test Method C—When a vacuum system is capable of
−2 −4
producing internal pressures of less than 2×10 Pa (2×10
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
torr) in the presence of leaks, these leaks may be located and
structive Testing and is the direct responsibility of Subcommittee E07.08 on Leak
Testing Method.
CurrenteditionapprovedJune1,2017.PublishedJuly2017.Originallyapproved
in 1973. Last previous edition approved in 2011 as E498-95 (2011). DOI: For referenced ASTM standards, visit the ASTM website, www.astm.org, or
10.1520/E0498_E0498M-11R17. contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
(Atmospheric pressure external, vacuum internal). This document covers the Standards volume information, refer to the standard’s Document Summary page on
Tracer Probe Mode described in Terminology E1316. the ASTM website.
The gas temperature is referenced to 0°C. To convert to another gas reference AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
temperature, T , multiply the leak rate by (T +273) ⁄273. 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
ref ref
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E498/E498M − 11 (2017)
evaluatedbytheuseofeitheraresidualgasanalyzer(RGA)or 7.1.2 Double O-rings.
by using the spectrometer tube and controls from a conven-
7.1.3 Threaded joints.
tional MSLD, provided, of course, that the leakage is within
7.1.4 Ferrule and flange-type tubing fittings.
thesensitivityrangeoftheRGAorMSLDundertheconditions
7.1.5 Casings with internal voids.
existing in the vacuum system.
7.1.6 Flat polymer gaskets.
7.1.7 Unvented O-ring grooves.
5. Personnel Qualification
5.1 It is recommended that personnel performing leak test- 7.2 In general, the solution is in proper design to eliminate
theseconditions;however,whendoublesealsmustbeused,an
ing attend a dedicated training course on the subject and pass
a written examination.The training course should be appropri- accessportbetweenthemshouldbeprovidedforattachmentto
the MSLD. Leaks may then be located from each side of the
ate for NDT level II qualification according to Recommended
Practice No. SNT-TC-1A of theAmerican Society for Nonde- seal and after repair, the access port can be sealed or pumped
continuously by a “holding” pump (large vacuum systems).
structive Testing or ANSI/ASNT Standard CP-189.
7.3 Temporarily plugged leaks often occur because of poor
6. Significance and Use
manufacturing techniques. Water, cleaning solvent, plating,
6.1 TestMethodAisthemostfrequentlyusedinleaktesting
flux, grease, paint, etc., are common problems. To a large
components which are structurally capable of being evacuated
extent,theseproblemscanbeeliminatedbyproperpreparation
−3
to pressures of 0.1 Pa (approximately 10 torr). Testing of
of the parts before leak testing. Proper degreasing, vacuum
smallcomponentscanbecorrelatedtocalibratedleaks,andthe
baking, and testing before plating or painting are desirable.
actualleakratecanbemeasuredoracceptancecanbebasedon
7.4 In a device being tested, capillary tubing located be-
a maximum allowable leak. For most production needs accep-
tween the leak and the leak detector can make leak testing
tance is based on acceptance of parts leaking less than an
extremely difficult as test sensitivity is drastically reduced and
established standard which will ensure safe performance over
responsetimeincreased.Ifthereisavolumeateachendofthe
the projected life of the component. Care must be exercised to
capillary, each such volume should be attached to the leak
ensure that large systems are calibrated with reference leak at
detector during testing. If this is impossible, the device should
a representative place on the test volume. Leak rates are
be surrounded with a helium atmosphere while attached to the
determinedbycalculatingthenetgainorlossthroughaleakin
leak detector for a long time to assure leak tightness. When
thetestpartthatwouldcausefailureduringtheexpectedlifeof
unusually long pumping times are necessary, the connections
the device.
to the leak detector (and all other auxiliary connections) that
6.2 TestMethodBisusedfortestingvacuumsystemseither
are exposed to the helium should be double-sealed and the
as a step in the final test of a new system or as a maintenance
space between the seals evacuated constantly by a small
practice on equipment used for manufacturing, environmental
auxiliary roughing pump to avoid allowing helium to enter the
test or for conditioning parts.As the volume tends to be large,
system through seals that are not a part of the device to be
a check of the response time as well as system sensitivity
tested.
should be made. Volume of the system in liters divided by the
speed of the vacuum pump in L/s will give the response time
TEST METHOD A—HELIUM LEAK TESTING OF
to reach 63% of the total signal. Response times in excess of
SMALL DEVICES USING THE MSLD
a few seconds makes leak detection difficult.
8. Apparatus
6.3 Test Method C is to be used only when there is no
convenientmethodofconnectingtheleakdetectortotheoutlet
8.1 Helium Mass Spectrometer Leak Detector, having a
ofthehighvacuumpump.Ifaheliumleakdetectorisusedand
minimumdetectableleakrateasrequiredbythetestsensitivity.
the high vacuum pump is an ion pump or cryopump, leak
8.2 Auxiliary Pumps, capable of evacuating the object to be
testingisbestaccomplishedduringtheroughingcycleasthese
tested to a low enough pressure so that the MSLD may be
pumps leave a relatively high percentage of helium in the high
connected.
vacuum chamber.This will obscure all but large leaks, and the
trace gas will quickly saturate the pumps.
NOTE 1—If the object under test is small and clean and the MSLD has
a built-in roughing pump, the auxiliary pumps are not required.
7. Interferences
8.3 Suitable Connectors and Valves, to connect to the
7.1 Series leaks with an unpumped volume between them
MSLD test port. Compression fittings and metal tubing should
present a difficult if not impossible problem in helium leak
be used in preference to vacuum hose.
testing. Although the trace gas enters the first leak readily
enough since the pressure difference of helium across the first 8.4 Standard Leaks of Both Capsule Type (Containing its
leak is approximately one atmosphere, it may take many hours own Helium Supply) and Capillary Type (an Actual Leak which
to build up the partial pressure of helium in the volume is Used to Simulate the Reaction of the Test System to Helium
betweenthetwoleakssothatenoughheliumentersthevacuum Spray)—The leak rate from the capsule-type leak should be
system to be detected by the MSLD. This type of leak occurs adequate to demonstrate the minimum allowable sensitivity of
frequently under the following conditions: the MSLD. The capillary type should be slightly smaller than
7.1.1 Double-welded joints and lap welds. the test requirement.
E498/E498M − 11 (2017)
8.5 Vacuum Gage, to read the pressure before the MSLD is valve and partially closing the MSLD inlet valve or by
connected. reducing the sensitivity of the leak detector itself if more
convenient. If the unknown leak still produces an o
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E498/E498M − 11 E498/E498M − 11 (Reapproved 2017)
Standard Practice 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/E498M; 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope*
−8 3 −9
1.1 This practice covers procedures for testing and locating the sources of gas leaking at the rate of 1 × 10 Pa m /s (1 × 10
3 3
Std cm /s) or greater. The test may be conducted on any object to be tested that can be evacuated and to the other side of which
helium or other tracer gas may be applied.
1.2 Three test methods are described:
1.2.1 Test Method A—For the object under test capable of being evacuated, but having no inherent pumping capability.
1.2.2 Test Method B—For the object under test with integral pumping capability.
1.2.3 Test Method C—For the object under test as in Test Method B, in which the vacuum pumps of the object under test replace
those normally used in the leak detector.
1.3 Units—The values stated in either SI or std-cc/sec units are to be regarded separately as standard. The values stated in each
system may not be exact equivalents: therefore, each system shall be used independently of the other. Combining values from the
two systems may result in non-conformance with the standard.
1.4 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 and health practices and determine the applicability of regulatory
limitations prior to use.
1.5 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.
2. Referenced Documents
2.1 ASTM Standards:
E1316 Terminology for Nondestructive Examinations
2.2 Other Documents:
SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive Testing
ANSI/ASNT CP-189 ASNT Standard for Qualification and Certification of Nondestructive Testing Personnel
3. Terminology
3.1 Definitions—For definitions of terms used in this practice, see Terminology E1316, Section E.
4. Summary of Practice
−9 3 −10
4.1 The tests in this practice require a helium leak detector that is capable of detecting a leak of 1 × 10 Pa m /s (1 × 10
3 3
Std cm /s).
This practice is under the jurisdiction of ASTM Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.08 on Leak Testing
Method.
Current edition approved July 1, 2011June 1, 2017. Published July 2011July 2017. Originally approved in 1973. Last previous edition approved in 20062011 as E498 - 95
(2006).(2011). DOI: 10.1520/E0498_E0498M-11.10.1520/E0498_E0498M-11R17.
(Atmospheric pressure external, vacuum internal). This document covers the Tracer Probe Mode described in Terminology E1316.
The gas temperature is referenced to 0°C. To convert to another gas reference temperature, T , multiply the leak rate by (T + 273) ⁄273.
ref ref
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E498/E498M − 11 (2017)
4.2 Test Method A—This test method is used to helium leak test objects that are capable of being evacuated to a reasonable test
pressure by the leak detector pumps in an acceptable length of time. This requires that the object be clean and dry. Also to cope
with larger volumes or relatively “dirty” devices, auxiliary vacuum pumps having greater capacity than those in the mass
spectrometer leak detector (MSLD) may be used in conjunction with the MSLD. The leak test sensitivity will be reduced under
these conditions.
4.3 Test Method B—This test method is used to leak test equipment that can provide its own vacuum (that is, equipment that
has a built-in pumping system) at least to a level of a few hundred pascals (a few torr) or lower.
−2 −4
4.4 Test Method C—When a vacuum system is capable of producing internal pressures of less than 2 × 10 Pa (2 × 10 torr)
in the presence of leaks, these leaks may be located and evaluated by the use of either a residual gas analyzer (RGA) or by using
the spectrometer tube and controls from a conventional MSLD, provided, of course, that the leakage is within the sensitivity range
of the RGA or MSLD under the conditions existing in the vacuum system.
5. Personnel Qualification
5.1 It is recommended that personnel performing leak testing attend a dedicated training course on the subject and pass a written
examination. The training course should be appropriate for NDT level II qualification according to Recommended Practice No.
SNT-TC-1A of the American Society for Nondestructive Testing or ANSI/ASNT Standard CP-189.
6. Significance and Use
6.1 Test Method A is the most frequently used in leak testing components which are structurally capable of being evacuated to
−3
pressures of 0.1 Pa (approximately 10 torr). Testing of small components can be correlated to calibrated leaks, and the actual
leak rate can be measured or acceptance can be based on a maximum allowable leak. For most production needs acceptance is
based on acceptance of parts leaking less than an established standard which will ensure safe performance over the projected life
of the component. Care must be exercised to ensure that large systems are calibrated with reference leak at a representative place
on the test volume. Leak rates are determined by calculating the net gain or loss through a leak in the test part that would cause
failure during the expected life of the device.
6.2 Test Method B is used for testing vacuum systems either as a step in the final test of a new system or as a maintenance
practice on equipment used for manufacturing, environmental test or for conditioning parts. As the volume tends to be large, a
check of the response time as well as system sensitivity should be made. Volume of the system in liters divided by the 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 a few seconds
makes leak detection difficult.
6.3 Test Method C is to be used only when there is no convenient method of connecting the leak detector to the outlet of the
high vacuum pump. If a helium leak detector is used and the high vacuum pump is an ion pump or cryopump, leak testing is best
accomplished during the roughing cycle as these pumps leave a relatively high percentage of helium in the high vacuum chamber.
This will obscure all but large leaks, and the trace gas will quickly saturate the pumps.
7. Interferences
7.1 Series leaks with an unpumped volume between them present a difficult if not impossible problem in helium leak testing.
Although the trace gas enters the first leak readily enough since the pressure difference of helium across the first leak is
approximately one atmosphere, it may take many hours to build up the partial pressure of helium in the volume between the two
leaks so that enough helium enters the vacuum system to be detected by the MSLD. This type of leak occurs frequently under the
following conditions:
7.1.1 Double-welded joints and lap welds.
7.1.2 Double O-rings.
7.1.3 Threaded joints.
7.1.4 Ferrule and flange-type tubing fittings.
7.1.5 Casings with internal voids.
7.1.6 Flat polymer gaskets.
7.1.7 Unvented O-ring grooves.
7.2 In general, the solution is in proper design to eliminate these conditions; however, when double seals must be used, an access
port between them should be provided for attachment to the MSLD. Leaks may then be located from each side of the seal and after
repair, the access port can be sealed or pumped continuously by a “holding” pump (large vacuum systems).
7.3 Temporarily plugged leaks often occur because of poor manufacturing techniques. Water, cleaning solvent, plating, flux,
grease, paint, etc., are common problems. To a large extent, these problems can be eliminated by proper preparation of the parts
before leak testing. Proper degreasing, vacuum baking, and testing before plating or painting are desirable.
7.4 In a device being tested, capillary tubing located between the leak and the leak detector can make leak testing extremely
difficult as test sensitivity is drastically reduced and response time increased. If there is a volume at each end of the capillary, each
E498/E498M − 11 (2017)
such volume should be attached to the leak detector during testing. If this is impossible, the device should be surrounded with a
helium atmosphere while attached to the leak detector for a long time to assure leak tightness. When unusually long pumping times
are necessary, the connections to the leak detector (and all other auxiliary connections) that are exposed to the helium should be
double-sealed and the space between the seals evacuated constantly by a small auxiliary roughing pump to avoid allowing helium
to enter the system through seals that are not a part of the device to be tested.
TEST METHOD A—HELIUM LEAK TESTING OF SMALL DEVICES USING THE MSLD
8. Apparatus
8.1 Helium Mass Spectrometer Leak Detector, having a minimum detectable leak rate as required by the test sensitivity.
8.2 Auxiliary Pumps, capable of evacuating the object to be tested to a low enough pressure so that the MSLD may be
connected.
NOTE 1—If the object under test is small and clean and the MSLD has a built-in roughing pump, the auxiliary pumps are not required.
8.3 Suitable Connectors and Valves, to connect to the MSLD test port. Compression fittings and metal tubing should be used
in preference to vacuum hose.
8.4 Standard Leaks of Both Capsule Type (Containing its own Helium Supply) and Capillary Type (an Actual Leak which is
Used to Simulate the Reaction of the Test System to Helium Spray)—The leak rate from the capsule-type leak should be adequate
to demonstrate the minimum allowable sensitivity of the MSLD. The capillary type should be slightly smaller than the test
requirement.
8.5 Vacuum Gage, to read the pressure before the MSLD is connected.
8.6 Helium Tank and Regulator, with attached helium probe hose and jet.
9. Calibration of MSLD
9.1 Attach the capsule leak to the MSLD and tune the MSLD to achieve maximum sensitivity in accordance with the
manufacturer’s instruction. Allow sufficient time for the flow rate from the capsule leak to equilibrate. The capsule leak should be
stored with the shutoff valve (if present) open, and the leak should be allowed to equilibrate to ambient temperature for several
hours.
9.2 MSLD calibration shall be performed prior to and upon completion of testing.
10. Procedure
10.1 Evacuate the device to be tested until near equilibrium pressure is reached on the rough vacuum gage. Open the valve to
the leak detector and close the valve to the roughing pumps.
NOTE 2—This procedure will be automatic where the device is relatively small and clean and where an automatic MSLD is used without external
pumps. Do not allow the pressure in the spectrometer tube to exceed the manufacturer’s recommendation. This means in some cases that the MSLD inlet
valve can only be partially opened. Maximum test sensitivity will be achieved with the inlet valve completely open and the auxiliary pump valve
completely closed. However, testing at reduced sensitivity levels can be done as long as the inlet valve can be opened at all.
10.2 Adjust the helium probe jet so that a small flow of helium is coming from the tip.
10.3 Set the leak detector on the appropriate lowest range.
10.4 Pass the tip of the helium probe by the end of the standard capillary leak at a rate similar to the scan rate at which the object
under test will subsequently be tested. Note the deflection of the leak detector output meter. If the probing rate is increased, the
test sensitivity will be decreased, and if the probing rate is decreased, the test sensitivity will be increased. Consequently, when
a leak is indicated during leak testing, it will be necessary to move the probe slowly backward until a maximum signal occurs.
The approximate leak size can be determined by multiplying the size of the standard leak by the maximum reading obtained from
the located leak and dividing by the maximum reading obtained when the helium was applied directly to the standard leak.
10.5 Starting at the most suspect part of the object to be tested, spray the smallest amount of helium on the part that will give
a signal when sprayed on the capillary leak. If there are drafts, work up opposite to the direction of air flow.
10.6 When a leak is pinpointed, it should be first evaluated if desired, then sealed either permanently (preferable) or temporarily
in such a manner as to allow repair at a later time, before proceeding to look for additional leaks. If the leak is so large that the
MSLD output saturates (that is, goes to the top of the highest range), it can be evaluated by reducing the sensitivity of the test until
the signal from the standard leak is barely readable. This can be done by opening the roughing valve and partially closing the
MSLD inlet valve or by reducing the sensitivity of the leak detector itself if more convenient. If the unknown leak still produces
an off-scale signal, it will be necessary to use a larger standard leak and far less test sensitivity or to use a reduced percentage of
helium in the probe. (For instance, a probe gas concentration of 1 % helium and 99 % nitrogen would reduce the apparent
sensitivity
...