Helium‐Testlecks

Helium test leaks Leak localization and tightness control with Helium provides a very sensitive testing method. Frequently, the sensitivity of a leak has to be testspecified quantitatively. In particular, quality control requires a reliable verification of the sensitivity. For this purpose, test leaks with well‐known leakage are used. In the article, various types of test leaks and their properties are described. Test leaks are commercially available over a wide range of leak rates. Their leakage flow can be calibrated with good accuracy. In the usage of the test leaks, the temperature‐dependency of the leak rate has to be taken into account, as well as the slow decrease of the leak rate due to the continuous loss of gas from the reservoir.     

Prüflecks für Schnüffel‐Lecksucher

In the testing of leak tightness and in the localisation of leaks by means of a test gas, proper operation and sensitivity of the employed instrument must be checked by a certified reference leak. In the so‐called sniffer mode of operation, the component under test is filled to overpressure with the test gas, so that in case of a leak there is a gas flow from the component to atmosphere. The atmospheric gas is sucked by the instrument and probed for its test gas content. For checking the instruments performance, commercial test leaks are available for various gas species, which deliver a well‐defined leakage. Construction and properties of such a test leak are described. The leak has an internal gas reservoir and a capillary as leak element. Because the inlet pressure at the capillary is kept constant by a pressure controller, the leakage remains constant over several years despite the gradual pressure decrease in the gas reservoir. The calibration of the leakage via the volume flow rate is described in detail. The volume flow rate can be measured by a liquid drop in a measuring capillary as well as a displacement piston in a dosing syringe.     

Stabilität der Leckrate von Helium-Testlecks

The stability of the bak rate of Helium test leaks For the sensitivity calibration of Helium leak detectors, test leaks with known Helium throughput are used. Widespread is the type of test leak with internal gas reservoir from which the gas is delivered by permeation through a wall. In case of constant temperature, one expects a constant gas throughput except for a gradual minor decrease due to gas loss (typically ?1% per year). This behavior is in fact found for test leaks with quartz wall. In contrast, substatial scattering is observed for test leaks with plastic wall which is not yet understood. In the paper also reaction times of the leak rate on changes of temperature and reservoir pressure are reported for test leaks with quartz and plastic wall.     

Kalibrierung von Schnüffel‐Testlecks

Calibration of reference leaks for testing leak sniffers Functionality, safety and environment protection require the tightness of equipment against atmosphere. To check for possible leaks, commercial leak sniffers are commonly used. In order to warrant the reliability of leak testing, the sniffers must work properly with correct sensitivity at usage. To prove the proper operation of the leak sniffer, test leaks with known leak rates are used. The present paper deals with design and calibration of the test leaks, in particular for very small leakage.     

Reliability Enhancement in Nondestructive Evaluation: Development of Practical Rules for Vacuum Type Helium Leak Tests

In helium leak testing, reliability is an important factor and while attempting to improve this, lot of challenges are being faced. There are contributors for bringing in variations in leak meter readings obtained during system sensitivity check and actual leak test which ultimately affect the final measured leakage rate of test object and they need to be controlled for obtaining reliable results. Response times of leaks are affected by vacuum side volumes, contaminations in vacuum side, leaked gas travel path restrictions on vacuum side and nature of actual leak paths and their gas flow impedances. Hence, actual consideration of real responses of leaks is to be practiced for a reliable test. The traditional concept of using estimate for percentage helium concentration in test hoods is modified by a novel method for its exact determination which improves reliability in tests. Also, practical rules are derived for the reliable identification of leak locations from response time concept. Spurious indications caused by leaks in temporary test rig joints or due to leaks from joints or passages not in the scope of test are other impediments for a reliable test. The response of system changes instantly by spurious indications and hence they require elimination by adopting innovative methods.     

氦质谱检漏仪现场校准方法研究

目前,用户采用单只标准漏孔对氦质谱检漏仪进行校准,由于受检漏仪线性范围的影响限制,不能对其全量程范围进行校准。为了满足对氦质谱检漏仪全量程范围内的现场校准,将一系列不同量级漏率的薄膜渗氦型标准漏孔分别接入氦质谱检漏仪,得到一组标准漏孔检漏仪示值,通过对标准漏孔漏率值与检漏仪示值的关系曲线进行数学拟合,得到氦质谱检漏仪全量程测量范围示值与漏率值之间的拟合公式。其校准过程简单,能够提高氦质谱检漏质量。     

基于Fluent薄带钢桶气体泄漏数值分析

目的探究钢桶气体泄漏的射流流场对桶身激励产生声发射信号的基本原理和特性。方法利用计算流体力学Fluent软件分析钢桶气体泄漏流场状态,介绍钢桶气体泄漏的射流模型及产生机理,利用计算流体力学有限元方法建立数学模型,建立钢桶泄漏的几何模型和边界条件,设置仿真分析的相关参数,得到不同内压、不同漏孔直径和多漏孔情况下的钢桶泄漏仿真结果,并讨论钢桶泄漏气流速度场、压力场等参数的分布情况。结果钢桶发生泄漏时的气流速度对声发射信号起主导作用,内压对气流速度影响较大,孔径和漏孔数量带来的影响较小。结论该分析为探讨钢桶的泄漏机理与声发射激励信号的检测提供了参考。     

金属压扁型正压漏孔不同压力下的漏率研究

在不同入口和出口压力条件下,正压漏孔的漏率值会发生变化,在使用时需要对正压漏孔的校准值进行修正。对2支金属压扁型正压漏孔在多种压力条件下进行漏率测量,给出了测量结果,然后根据管道流导理论推导出正压漏孔漏率随压力变化的修正公式,并对修正结果与实验测量数据进行了研究分析。     

多级漏孔泄漏分析及其漏率预测方法研究

为了评估气体介质经多级漏孔的泄漏量,指导多道密封结构的安全设计,有必要研究气体经多级漏孔的泄漏特性。通过建立双级与多级漏孔的数学模型,在不同的初始条件下对多级漏孔的泄漏特性进行了计算分析。结果表明:多级漏孔的稳定漏率仅与各级独立漏孔漏率有关,与中间空腔体积无关,其倒数等于各级漏孔漏率的倒数之和。影响稳定时间的因素包括末级漏孔的漏率、其余各级漏孔组成的多级漏孔漏率以及中间空腔的容积。利用分析结果,提出了多级漏孔漏率的预测方法。     

蒸气压缩式制冷系统压力试验的研究与应用

通过对蒸气压缩式制冷系统现场检漏的观测,发现保压试验满足国家标准GB50274-98《制冷设备、空气分离设备安装工程施工及验收规范》的合格判据时,发泡试验还有检出漏孔的可能.针对这一现象,对发泡和保压试验的不同作用,以及“GB50274-98”关于保压试验的漏率判据进行分析.结果表明,“GB50274-98”关于测定压力降不大于试验压力值的1％为合格的相对漏率判据对系统整体泄漏的限制要求偏低,也不能有效控制大容积被测系统粗漏漏孔的出现几率.进一步研究指出,通过保压试验可以直接评价系统整体漏率和对制冷系统运行中的制冷剂非事故耗损进行评估.同时提出现场保压试验应提高压力表精度和延长保压时间,以获得更准确的试验数据.研究可为提高制冷系统现场检漏质量和改进评定方法提供参考.     

Kältemittel‐Schnüffler

Testing refrigerant sniffers The technical generation of coldness is typically done by machines based on a closed thermodynamic process using a refrigerant. As refrigerants usually halogenated hydrocarbons are used since these have good thermodynamic properties. Unfortunately, the halogens are harmful to the environment: They destroy the ozone layer. Therefore, the machines must be tight and must not loose the refrigerant. To check a machine for leakage, mobile leak sniffers are available which can be reliably and quantitatively controlled by test leaks.     

Simple models for evaluating effects of small leaks on the gas barrier properties of food packages

A detailed theoretical analysis and calculations were made for providing a simple and explicit means to evaluate the effects of small leaks on the barrier properties of food packages. Small leaks, such as pinholes and channel leaks, were approximated as cylindrical pores with diameters of 50–300 μm. The first part of the current study proposes a simple mathematical model based on Fick's law of diffusion, which accounts for both the gas leakage across small leaks and the gas permeation across package walls. The model uses an effective permeability that depends on leak dimensions, type of diffusing gas, type of packaging material and gas conditions around the leak ends. In the second part of the study, three practical cases are presented to illustrate the application of the proposed model in examining the significance of leaks. These demonstrate in a simple and explicit manner that for LDPE packages: (a) leaks affect the oxygen transfer more than the water vapour transfer; (b) leak effects are more significant at lower storage temperatures; and (c) that for high gas barrier packages, the effect of leaks is very important and should not be neglected. The model can be also used to arrive at conclusions about the significance of leaks in other packaging situations (e.g. other than LDPE packaging materials) and to correct the shelf‐life estimation of gas‐ and water vapour‐sensitive foods for errors from package leaks. Copyright © 2003 John Wiley & Sons, Ltd.     

Method of calibration of leak detectors over the entire effective range

A method for calibrating leak detectors that makes it possible to reproduce a sufficiently large number of calibration points over the entire effective range of the device using only two leaks is described. Because calibration is discrete, a situation that is appropriate to the relationship between the flows of both leaks, it is possible to regulate the flow of the test gas from the leaks into an analytic chamber. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 23–24, June, 1998.     

供水管道泄漏声信号及其传播特性

相关仪利用供水管道泄漏时产生的泄漏声波对漏点定位。泄漏信号验证为高斯分布,泄漏声波主要是在管道里的水中传播,与管壁发生流固耦合作用,引起管壁振动。用FIR滤波器对管道系统建模,采用最小均方误差(LMS)自适应系统辨识方法得到管道的冲激响应函数,与线性相位FIR滤波器的冲激响应相比较,表明泄漏声波在传播过程中存在频散。泄漏声信号受各种噪声干扰,根据互谱相位谱信息估计泄漏信号的频带范围,对信号滤波后作时延估计,结果表明,提高了泄漏定位的置信度。     

Leakproofness of dangerous goods packagings—comparison of worst‐case limit leakage rates and sensitivity of the bubble test

This work focuses on the question if the bubble test prescribed in the Dangerous Goods Regulations has sufficient sensitivity to detect leakage rates, which could result in the formation of explosive atmospheres during transport. The sensitivity of the bubble test is not directly comparable with other leak testing methods because of its different flow conditions. Therefore, a normalized minimum detectable leakage rate under Helium test conditions is calculated for the bubble test. This sensitivity of the bubble test under reference conditions is compared with limit leakage rates for a worst‐case transport scenario. The sensitivity of the bubble test is not sufficient to prove the limit leakage rates for 6‐L packagings. The formation of explosive vapour‐air‐mixtures cannot be excluded. Therefore, more sensitive leak testing methods should be considered for smaller packaging design types.     

Frost-Point Measurement Error Due to a Leak in a Sampling Line

When measuring low dew-point temperatures, a leak from the sampling tubing to ambient may cause a significant error due to back-diffusion of water vapor. In the work reported in this article, the significance of this error was studied experimentally and theoretically. The effects of leaking VCR^® and Swagelok^® connectors were studied experimentally and analyzed by comparing the results to the outcomes of experiments with actual leak holes. Theoretical calculations with a simplified combined convection–diffusion model were used to evaluate the results. Calculations were successfully carried out to predict the minimum leak flow rate required to prevent any water vapor from back-diffusing into the tubing. It was concluded that, in many cases, maintaining gauge pressure in a sampling line prevents penetration of water vapor into the line. Tiny leaks, however, can be a route for harmful back-diffusing of water vapor. VCR connectors were shown to be more sensitive to leaks compared with Swagelok connectors.     

Leak calibration by comparison with reference standard leaks

A study of the calibration of leaks by comparison with reference standard leaks calibrated at a National Metrology Laboratory is presented. The simplicity and efficiency of the method make it suitable for calibrations of leaks carried out at the industrial level. A commercial leak tester equipped with a mass spectrometer tuned to helium is used for the comparison. The main origins of uncertainties and their contributions to the expanded uncertainty are presented. In particular, discussion is devoted to the long-term stability, shift, or depletion of the reference standard leaks and the resulting impact on the expanded uncertainty. Results of application of the procedure for calibration of a leak of similar metrological characteristics to the reference standard leaks are also presented.     

Verkürzen der Messzeit eines Lecksuchers

Reducing the measuring times of a leak detector With individual as well as routine helium leak detection tests, rapid response times and fast signal decay times are of great interest for the quick and distinct localization of leaks. The effects of additional pumps connected in different setups to the recipient are described by means of a real test assembly. The operation of a high‐vacuum pump series connected with the leak detection unit is presented as method of choice for reducing the response time during leak detection.     

Quantification of the UN leakproofness test method

In this paper a theoretical model is described for the UN leakproofness test, which is one of the test methods of the UN test programme for the type testing of packaging for liquids for the transport of dangerous goods. The test is also required for every single packaging produced. Quantification was thought necessary in order to be able to evaluate production line leakproofness test methods which should be as effective. The model was verified with an experimental programme which was performed with leaks of the pinhole type. The results show that the process of bubble formation and flow of the UN leakproofness test method can be modelled assuming laminar flow and taking into account capillary pressure and bubble frequency. For a leak of the pinhole type and a realistic set of parameters the detection limit of the method can be indicated as being in the order of 20 μm of hole diameter. It is discussed whether analysis of the concept of leakproofness testing might be necessary.     

大型真空系统氦检漏率的快速准确检测方法

大型真空系统检漏往往耗时长、效率低。本文分析了氦气通过漏孔进入氦质谱检漏仪形成检漏信号的规律,并据此建立检漏信号数学模型,确定漏孔的最终稳态泄漏信号。基于上述分析,提出漏孔漏率的一种快速预测方法。该方法用于大型真空系统检漏能准确预测被检部位的漏率,能显著缩短检漏时间,提高检漏效率。