【正文】 al standard without any alteration. Uptodate lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions (English, French, German). 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, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit233。fung – Dichtheitspr252。 Crit232。les d39。 — monitor related international and European developments and promulgate them in the UK. A list of anizations represented on this mittee can be obtained on request to its secretary. Crossreferences The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled ―International Standards Correspondence Index‖, or by using the ―Search‖ facility of the BSI Electronic Catalogue or of British Standards Online. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. This British Standard, having been prepared under the direction of the Engineering Sector Committee, was published under the authority of the Standards Committee and es into effect on 15 November 1999 169。 — present to the responsible European mittee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed。ISCHE NORM ICS English version Nondestructive testing Leak testing Criteria for method and technique selection (includes amendment A1:2022) Essais non destructifs Contr244。it233。rungsfreie Pr252。lt 196。isches Komitee f252。 the operating temperature. The suitability of the system for a given task is indicated by the functional tightness. NOTE 3 : To take into account factors that are unquantifiable, it may be advisable to adopt leak tightness values lower than this by a factor from three to ten. 7 Leak testing The actual gas flow through the leaks of the test object, which has been determined in a leak test, shall be converted to the leakage rate with that under operating conditions. The following considerations shall be applied to all methods by which leakage rates are determined. A review of the methods and techniques is given in table 1. Page 6 EN 1779:1999 Table 1: Leak testing Criteria for method and technique selection Flow direction Extent of test Applicability Techniques gas flow out of object gas flow into object local area total area local area total area location measurement location measurement location measurement location measurement , , , , , , , , , , , , , , , , Utilization of the table: 1) choose the appropriate flow direction for test。 5) check any practical difficulties associated with the test. NOTE: Some techniques used for location can also give an estimate of the leakage size, but they are not allowed to demonstrate the pliance with the specifications. Techniques for leak location and techniques for measurement It is usually not possible to establish in one step the total leakage of a ponent (or a system) and the location of the leaks. Two techniques shall, therefore, be considered: measurement of the overall leakage rate or location of leaks for possible elimination. Examples of total (or integral) techniques include the measurement of the pressure variation with time within the object and the accumulation of gas escaping from the object over a period of time. One technique for leak location involves probing the object with a suitable tracer gas or sniffing the surface of an object filled with tracer gas. NOTE: In the selection of an appropriate technique for leak assessment, the conditions of the test (pressure, vacuum, type of gas, etc.) should be carefully considered. Some guidance is given in clause 8. Time dependence (in tracer gas techniques) The measuring device shall be placed on the opposite side of the boundary to that probed with tracer gas. The tracer gas can be detected only when it has crossed the boundary. Time shall be allowed, therefore, for stabilization. The time taken by the gas to cross the boundary depends on the nature of gas, the pressure difference and the geometry of the leak path. It also depends on the temperature, the cleanliness of the object, etc. NOTE: Small leaks can require a long stabilization time. If the flow through the leak is impeded by successive obstacles, such as multiple seals or double weld beads, the test time can be very long. Page 7 EN 1779:1999 B 2 A 1 A 1 p p 1 p p p p Influence of flow conditions The usual laws governing gas flow shall be used to calculate variation in leakage rate, as a function of pressure, temperature and type of gas. NOTE: In quantitative leak detection two different flow regimes are normally considered. These are the regimes of viscous laminar or molecular flow. The boundaries between these regimes are not precisely defined. Care s