1、Non-destructive testing - Leak testing Bubble emission techniques English version of DIN EN 1593 DIN - EN 1593 EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN 1593 September 1999 ICs 19.100 English version Non-destructive testing - Leak testing Bubble emission techniques Essais non destructifs
2、- Contrle dtanchit - Contrle la bulle Zerstrungsfreie Prfung - Dicht- heitsprfung - Blasenprfverfahren This European Standard was approved by CEN on 1999-08-1 6. CEN members are bound to comply with the CENKENELEC Internal Regulations which stipulate the conditions for giving this European Standard
3、the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national stand- ards may be obtained on application to the Central Secretariat or to any CEN member. The European Standards exist in three official versions (English, French, Ger
4、man). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, the Czech Republic, Denmar
5、k, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland, and the United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassa
6、rt 36, B-1050 Brussels O 1999. CEN - All rights of exploitation in any form and by any means reserved worldwide for CEN national members. Ref. No. EN 1593: 1999 E Page 2 EN 1593 : 1999 Contents Foreword 1 Scope 2 Normative references 3 Definitions 4 Personnel qualification 5 Principle 6 General requ
7、irements 7 Intederences 8 Immersion technique 9 Liquid application technique 1 O Test report Annex A (informative) Example of quantitative evaluation of leakage rate Annex ZA (informative) Clauses of this European Standard addressing essential requirements or other provisions of EU Directives Page 2
8、 3 3 3 3 3 4 5 5 6 7 9 11 Foreword This European Standard has been prepared by Technical Committee CENTTC 138 “Non- destructive testing“, the secretariat of which is held by AFNOR. This European Standard shall be given the status of a national standard, either by publication of an identical text or
9、by endorsement, at the latest by March 2000, and conflicting national standards shall be withdrawn at the latest by March 2000. This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association, and supports essential requirement
10、s of EU Directive(s). For relationship with EU Directive(s), see informative Annex ZA, which is an integral part of this standard. According to the CENKENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this European Standard: Austria,
11、 Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom. Page 3 EN 1593: 1999 1 Scope This European Standard describes procedures for the detection and location of leaks
12、 by the bubble emission techniques. The sensitivity depends on techniques and materials used. Two techniques are described: a) immersion technique: quantitative measurements can be made using this b) liquid application technique. procedure with particular devices (see informative annex A). This stan
13、dard can be used for equipment which can be evacuated or pressurised. 2 Normative references This standard incorporates by dated or undated reference, provisions from other publications. These normative references are cited at the appropriate places in the text and the publications are listed hereaf
14、ter. For dated references, subsequent amendments to or revisions of any of these publications apply to this standard only when incorporated in it by amendment or revision. For undated references the latest edition of the publication referred to applies. EN 473 Qualification and certification of NDT
15、personnel - General principles EN 1330-8 Non-destructive testing - Terminology - Part 8 - Terms used in leak tightness testing EN 1779:1999 Non-destructive testing - Leak testing - Criteria for method and technique selection 3 Definitions For the purposes of this standard, the definitions given in E
16、N 1330-8 apply. 4 Personnel qualification It is assumed that leak testing is performed by qualified and capable personnel. In order to prove this qualification, it is recommended to certify the personnel in accordance with EN 473 or equivalent. 5 Principle The techniques involve the establishment of
17、 a pressure difference across the object wall and the observation of bubble formation in a liquid medium located on the low pressure side. The minimum detectable leakage rate by these techniques depends on the pressure difference, the gas and the liquid used for testing. Page 4 EN 1593 : 1999 6 Gene
18、ral requirements The position of the leak shall be visible directly or indirectly in order to check if it is a real leak in the area to be tested. 6.1 Gases The test gas is normally air. Inert gases may however be used. When inert gases are used, the safety aspects of oxygen deficient atmospheres sh
19、all be considered. 6.2 Pressure limits Verification shall be obtained that the object has been designed to withstand the test pressure difference. The test conditions shall be such that the object is not permanently deformed nor should the test be a hazard for the operators. 6.3 Stabilization time (
20、for immersion technique) Prior to examination, the test pressure in the sealed object shall be maintained for a time appropriate for the establishment of bubble emission. For small leaks, this may take several minutes. 6.4 Surface temperature Normally the temperature of that part of the surface of t
21、he object that is to be examined shall not be below 278 K (5 OC) nor above 323 K (50 OC), throughout the examination. Local heating or cooling is permitted provided the temperatures remain within this range. Where it is impractical to comply with the foregoing temperature limitations, other temperat
22、ures may be used provided that the procedure has been shown to be suitable. 6.5 Direct visual examination Direct visual examination is usually made when the surface can be viewed directly at a distance not exceeding 0,6 m at an angle not less than 1/6 rad (30 degrees). Mirrors may be used to improve
23、 the angle of vision, and aids such as magnifying lenses may also be used to assist examinations. The component or area under immediate examination should be illuminated, if necessary with a flashlight or other auxiliary lighting, to attain an appropriate light level. Recommended illumination is 350
24、 lux to 500 lux. 6.6 Indirect visual examination In some cases indirect visual examination may have to be substituted for direct examination. This may involve the use of visual aids such as mirrors, endoscopes, telescopes or other suitable instruments. These should have a resolution capability at le
25、ast equivalent to that obtainable by a direct visual observation. Page 5 EN 1593 : 1999 7 Interferences The test object should be thoroughly cleaned. Surface contamination, e.g. grease, rust, weld slag, etc., on the test object surface can mask or cause bubble formation and give a false indication.
26、Contaminated detection liquid or one that foams spontaneously on application may cause spurious surface bubbles on the test object and should be avoided. 8 Immersion technique 8.1 General This technique (see EN 1779:1999, table A.2, technique C.l) is applicable to the examination of objects that can
27、 be completely immersed in a container of detection liquid, including sealed or temporary sealed ones during the test, and the pressure in any part of the test object shall be greater than in the liquid and should be known. 8.2 Variations 8.2.1 Direct pressurization of the object The object is press
28、urized and placed in the selected detection liquid. The surface, ater the stabilization (soak) time, is observed for a minimum period which depends on the test specification (e.g. allowable leakage rate, pressure, liquid type) and the type of test object. A stream of bubbles originating from any iso
29、lated point shall be interpreted as a leakage. 8.2.2 Use of detection liquid at elevated temperature If the object is sealed close to an atmospheric pressure, its internal pressure can be increased by placing it in the detection liquid held at an elevated temperature. The test time depends on the in
30、ternal volume of the object and shall be sufficient to allow a suitable pressure increase within the object (according to the equation of state of ideal gases). The efficiency of this test can be increased by introducing, before sealing, a liquid with a boiling point lower than the test temperature.
31、 A stream of bubbles originating from any isolated point shall be interpreted as a leakage. 8.2.3 Use of vacuum The sealed object is completely immersed in the detection liquid in a vacuum chamber, with a viewing port (see figure 1). Pressure in the vacuum chamber is reduced to a level which depends
32、 on the detection liquid, to prevent excessive loss of liquid by evaporation. A series of bubbles originating from any isolated point shall be interpreted as a leakage. Page 6 EN 1593 : 1999 8.3 Detection liquids used in immersion technique Various liquids may be used for the detection, provided tha
33、t they are transparent enough and do not adversely affect the objects being tested. Comrnonly-used are water with suitable wetting agents, ethylene glycol or low-viscosity mineral oil. An analysis of the detection fluid should be carried out to determine the presence of undesirable components, such
34、chlorine, fluorine, sulfur, etc. Mineral oil is the most suitable liquid for the vacuum technique, but degreasing of the test object may be necessary. When the vacuum technique is used the liquid should be previously degassed. 9 Liquid application technique 9.1 General This technique involves the ap
35、plication of a liquid film to the surface of the test object. It is applicable to any object in which a pressure differential can be created across the boundary to be examined. This technique may be used for open components and for those objects for which immersion would be impractical. 9.2 Variatio
36、ns 9.2.1 Direct pressurization of the object This procedure (see EN 1779:1999, table A.2, technique C.2) refers to objects that can be pressurized. A suitable liquid surfactant is applied on the low pressure side (by brush, spray or other methods). Afterwards, wait for a sufficiently long inspection
37、 time to realice even slow production of foam from small leaks. From large leaks the test fluid may be blown away and no foaming may occur. A growing foam originating from any isolated point shall be interpreted as a leakage. 9.2.2 Use of vacuum for unpressurized (open) objects This technique (See E
38、N 1779:1999, table A.2, technique C.3) is suitable for open objects e.g. unfinished parts, objects not accessible on the rear side or large objects for which the pressurization is impractical. The method involves the attachment of a suitable vacuum box with a top viewing port to those parts of the t
39、est object under investigation, the latter having been previously covered with surfactant liquid (see figure 2). Care shall be taken in the design and construction of the vacuum box to prevent implosion. Page 7 EN 1593 : 1999 The required pressure can be attained in the box by any convenient method,
40、 e.g. a vacuum pump. Care should be taken in the sealing of the vacuum box, particularly on the weld reinforcement (crown). The pressure should be progressively reduced until the specified test pressure, e.g. 20 kPa or 50 kPa, has been reached. This value has to be maintained for the specified time,
41、 at least 30 s. A minimum vacuum box overlap of 50 mm for adjacent test areas is necessary. 9.3 Detection liquids used in liquid application technique Suitable surfactant liquids shall be used. They shall be nonvolatile (they shall not dry at test temperature during the inspection time), viscous and
42、 shall not foam under reduced pressure. Commercial fluids not specific for leak testing shall not be used unless their suitability has been previously demonstrated on that type of test, by comparison with the characters of a specific bubble test fluid. In the presence of gas leakage however the bubb
43、les which form should persist for the duration of the test. For vertical surface tests, the test fluid viscosity may be increased, if necessary, by suitable methods. The compatibility of the test fluids with the materials of the test objects has to be ensured. 10 Test report If procedures require a
44、test report, this shall include the following information: a) technique used; b) internal andior low side pressure; cj liquid type; d) test temperature; e) soaking time; f) duration of the test; gj operator certification; h) test results. Page 8 EN 1593 : 1999 N 8 c Page 9 EN 1593 : 1999 Annex A (in
45、formative) Example of quantitative evaluation of leakage rate The bubble test is generally specified for the location of leaks and in this context the leakage rate is not required as any bubble formation means rejection. In some cases, e.g. a valve with a metallic gasket, the maximum specified leaka
46、ge may be accepted. In this case the leakage can be evaluated by bubble counting or can be measured by accumulating the escaping gas in a graduated tube. A typical test arrangement for the determination of the leakage rate is shown in figure A.1. The gas escaping from the object (.e. a safety relief
47、 valve) is led through a small tube to bubble in a transparent cup or collected and accumulated in a graduated tube. Before starting the bubble count, the test pressure shall be applied for a period in a range depending on the object size. Air at approximately ambient temperature should be used. Usi
48、ng table A.1, the leakage rate can be estimated from the size and number of bubbles per unit time. Table A.l Page 1 O EN 1593 : 1999 t 3 II 1 seal 2 cover plate 3 pressure NOTE: The cover plate should be fitted with a suitable device to relieve body pressure in case of accidental popping of the valv
49、e seal. Figure A.l Test apparatus for valve seat leak testing Page 11 EN 1593: 1999 Essential requirements or provisions of Directive Annex ZA (informative) Clauses of this European Standard addressing essential requirements or other provisions of EU Directives Qualifying remarkshotes This European Standard has been prepared under a mandate given to CEN by the European Commission and the European Free Trade Association and supports essential requirements or provisions of EU Directive : Directive 97/23/EC of the European Parliament and of the Council of 29 May 1997 on the ap
