ASTM E432-1991(2017)e1 6875 Standard Guide for Selection of a Leak Testing Method《选择检漏法的标准指南》.pdf

1、Designation: E432 91 (Reapproved 2017)1Standard Guide forSelection of a Leak Testing Method1This standard is issued under the fixed designation E432; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A numb

2、er in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1NOTEWithdrawn Terminology replaced with Terminology E1316 editorially in July 2017.1. Scope1.1 This guide2is intended to assist in the selection of a

3、leaktesting method.3Fig. 1 is supplied as a simplified guide.1.2 The type of item to be tested or the test system and themethod considered for either leak measurement or location arerelated in the order of increasing sensitivity.1.3 This standard does not purport to address all of thesafety concerns

4、, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally reco

5、gnized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:E1316 Terminology for

6、 Nondestructive Examinations3. Terminology3.1 DefinitionsThe definitions of terms relating to leaktesting which appear in Terminology E1316 shall apply to theterms in this guide.4. Selection of System4.1 The correct choice of a leak testing method optimizessensitivity, cost, and reliability of the t

7、est. One approach is torank the various methods according to test system sensitivity.4.2 The various testing methods must be individually ex-amined to determine their suitability for the particular systembeing tested. Only then can the appropriate method be chosen.For example, radioactive gases are

8、not generally employed asa tracer for leak location because of the hazards associated withtheir use. However, such gases are employed in leakagedetection equipment when they can be safely added to, andremoved from, a test chamber on a periodic basis.4.3 It is important to distinguish between the sen

9、sitivityassociated with the instrument employed to measure leakageand the sensitivity of the test system followed using theinstrument. The sensitivity of the instrument influences thesensitivity that can be attained in a specific test. The range oftemperatures or pressures, and the types of fluids i

10、nvolved,influence both the choice of instrument and the test system.4.4 The sensitivity of various test systems differ. Forexample, a test utilizing a mass spectrometer leak detectornormally has an ultimate sensitivity of 4.4 1015mol/s whenthe procedure involves the measurement of a steady-state gas

11、leakage rate. The sensitivity of the test may be increased underspecial conditions to 4.4 1019mol/s by allowing an accu-mulation of the leakage to occur in a known volume before ameasurement of leakage is made. In the first case, the sensi-tivity of the test equals the sensitivity of the instrument;

12、whereas in the second case, the sensitivity of the test is 104times greater than that of the instrument. If the test systemutilizes a mass spectrometer operating in the detector-probemode, the sensitivity of the test can be 102to 104smaller thanthat of the mass spectrometer itself.5. Leakage Measure

13、ment5.1 In general, leakage measurement procedures involvecovering the whole of the suspected region with tracer gas,while establishing a pressure differential across the system byeither pressurizing with a tracer gas or by evacuating theopposite side. The presence and concentration of tracer gas on

14、the lower pressure side of the system are determined and thenmeasured.5.2 A dynamic test method can be performed in the shortesttime. While static techniques increase the test sensitivity, thetime for testing is also increased.1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc

15、-tive Testing and is the direct responsibility of Subcommittee E07.08 on Leak TestingMethod.Current edition approved June 1, 2017. Published July 2017. Originally approvedin 1971. Last previous edition approved in 2011 as E432 - 91 (2011). DOI:10.1520/E0432-91R17E01.2For ASME Boiler and Pressure Ves

16、sel Code applications see related Recom-mended Guide SE-432 in the Code.3Additional information may be obtained from Marr, J. W., Leakage TestingHandbook, Report No. CR-952, NASA, Scientific and Technical InformationFacility, P. O. Box 33, College Park, MD 20740 (Organizations registered withNASA) o

17、r Clearing House for Federal, Scientific and Technical Information, Code410.14, Port Royal Road, Springfield, VA 22151.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with interna

18、tionally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15.3 Equipment or devices that are the object of le

19、akagemeasurement fall into two categories: (1) open units, which areaccessible on both sides, and (2) units that are sealed. Thesecond category is usually applied to mass-produced itemsincluding gas and vacuum tubes, transistors, integrated circuitmodules, relays, ordnance units, and hermetically se

20、aled in-struments.5.3.1 Open or Single-Sealed UnitsEither evacuation orpressurization of one side of a unit that is accessible on bothsides, may be employed to test for leakage across a unit.5.3.1.1 Systems Leaking to VacuumIn the order of increas-ing sensitivity for testing an evacuated system, the

21、 methodsinclude: flow measurement, absolute pressure measurement,the alkaline-ion diode halogen detector, and the helium massspectrometer leak detector.(a) The first approach to the testing of units that may beevacuated is to determine if there is an inherent tracer in thesystem. This gas should be

22、utilized if possible.(b) When one side is evacuated, leakage of the tracer intothe vacuum will reach the detector quickly if there is essen-tially no stratification. However, evacuation does not alwaysallow the most sensitive and reliable measurement. If theevacuated region is extremely large, high

23、pumping speeds willbe required and the leakage gas will tend to follow streamlinesto the pump port. The amount of tracer gas that reaches thedetector may then be substantially reduced depending on thelocation of the detector in the evacuated region.(c) When no inherent tracer is available, the next

24、approachshould be to determine if there is a gage in the system thatmight be used for leakage measurement. This gage might be anionization gage or, in some fortunate circumstances, a massspectrometer in the system as part of the analytical instrumen-tation. Consideration should be given not only to

25、gages that arenormally used for leak detection, but to any gas concentrationdetection equipment that may be used for leakage measurementif it happens to be available. Equipment not originally intendedfor pressure measurement may be used; for example, it ispossible to detect the pressure rise in a le

26、aking vacuum tube byoperating the grid at a positive and an anode at a negativepotential, and noting an increase in anode current with time.(d) When there is no inherent tracer or gage within thesystem, a standard testing method must be chosen based on thesensitivity desired.5.3.1.2 Systems Leaking

27、to AtmosphereThe choice of atesting method for systems leaking to atmospheric pressureshould be made in the same manner as suggested for evacuatedFIG. 1 Guide for Selection of Leakage Testing MethodE432 91 (2017)12systems. In the absence of an inherent tracer or a gage, one ofthe standard methods of

28、 making leakage measurements againstatmospheric pressure must be chosen. These are, in the order ofincreasing sensitivity: flow measurement, pressuremeasurement, bubble testing (immersion), helium massspectrometer, infrared analyzer, alkaline-ion diode halogendetector, and radioactive tracer. (Note

29、that the helium massspectrometer method may not be the most sensitive in thissituation where the measurement is to be made at atmosphericpressure.)5.3.2 Multiple-Sealed UnitsIn the testing of sealed units,applicable testing methods are, in the order of increasingsensitivity: bubble testing, flow mea

30、surement, pressuremeasurement, infrared analyzer, alkaline-ion diode halogendetector, helium mass spectrometer, and radioactive tracer. Thelast four methods are applicable to a back pressurizing testingprocedure.(a) Back pressuring, or bombing, is the usual procedureused for applying a tracer gas. I

31、f the leak in the unit isexceptionally large, any tracer gas in the unit will escaperapidly when it is subjected to reduced pressure. Consequently,high-sensitivity tests for this tracer will be ineffective if thetracer gas has already escaped from the system. It is thereforerecommended that all part

32、s be tested for large leaks after thehigh sensitivity tests have been conducted. Tests for large leaksinvolved relatively insensitive procedures. If liquids areemployed, the smaller leaks can easily become clogged andmay not be detected during a subsequent high sensitivity test.5.3.2.1 Evacuated Uni

33、t TestingWith evacuated units, thechoice of a testing procedure is relatively simple. If the systemincludes a gage, this gage may be used to show the presence ofgas contamination. The back pressurizing procedure should beused in the absence of an internal gage. The units should bepassed through a bu

34、bble test after the back pressurizing test tolocate the exceptionally large leaks. If the unit can be openedto the atmosphere, a flow measurement procedure may be used.5.3.2.2 Units Sealed with AirTesting procedures for unitssealed with air may be divided into two categories: lowsensitivity testing

35、by either bubble testing, flow measurement,or pressure measurement, and high sensitivity testing using theback pressurizing technique.5.3.2.3 Units Sealed With Tracer GasUnits sealed withtracer gas may be tested for leakage of the gas out of the unitby dynamic or static procedures. Generally, the pa

36、rtial pressureof tracer gas inside a unit will be higher than it would be if thetracer gas was forced into an evacuated unit through a smallleak as is done in the back pressurizing procedure. Thus,pre-sealing with tracer gas leads to a more sensitive procedureinvolving fewer steps. As in the case wi

37、th the other methods, afinal inspection must be conducted by means of a bubble testprocedure to locate exceptionally large leaks.6. Leak Location6.1 Leak location can be subdivided into a tracer probemode and a detector probe mode. The tracer probe procedure isused when the system is evacuated, and

38、the tracer gas comesfrom a probe located outside the system. The detector probemode is used when the system is pressurized with tracer gasand testing is done at atmospheric pressure. Usually the tracerprobe technique is more rapid because the gas reaches thedetector at a higher concentration, despit

39、e any streamingeffects, than it does with a detector probe which detects tracergas which is highly diluted by atmospheric gases. In thedetector probe mode, a higher pressure differential across thesystem may be used, and therefore leaks of a smaller conduc-tance can be found. In using either mode it

40、 is important thatleak location be attempted only after the presence of a leak hasbeen verified.6.1.1 Testing of Evacuated Systems (Tracer ProbeMode)In the location of leaks in evacuated systems, firstdetermine if there is an inherent detector within the system.This may be a pressure gage; preferabl

41、y a gage that is specificfor some tracer gas which may be used. If such a gage does notexist, the methods to use in the order of increasing sensitivityare: sonic, pressure change, gage response, high-voltagedischarge, alkali-ion diode leak halogen detector, infrareddetector, and mass spectrometer.6.

42、1.2 Testing at Atmospheric Pressure (Detector ProbeMode)In testing a system that is leaking into atmosphere, thefirst consideration is whether or not the leaking fluid may beused as a tracer. This will always be the case when using eitherthe sonic method or the bubble-testing method. However, thetra

43、cer might be of a composition that will also prove satisfac-tory for use with the other testing methods. In order ofincreasing sensitivity these methods for leak location are:chemical testing, gage response, infrared gas analyzer, massspectrometer, and alkali-ion diode halogen detector.6.1.2.1 When

44、using liquid penetrants, the pressure may beatmospheric both inside and outside. Both surfaces must beaccessible. Leaks are detected visually by fluorescence orcoloration.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedi

45、n this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and mu

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