Dichtheitsprüfung

Leakage Tests — Flexible packaging in food processing and pharmaceutical industry Extended storage life for food products or better protection against environmental influences increases the demand for more accurate leak detection methods. Flexible, and therefore more fragile packaging is even more complicated when it comes to the commonly required non destructive leak testing. The main focus when testing flexible packaging is on welded seams. They represent the weakest point in flexible packaging. Today, there are several leak detection methods used to perform tests on flexible packaging. The most common ones are waterbath, pressure/vacuum decay and tracer gas based leak detection. All of which have their strength and weaknesses wheras the desired reject leak rate is mostly influencig the decision process. To measure very small leaks (<10 μ oder 10^‐5 mbar l/s) or to enable very short test cycles, trace gas leak detection is the way to go. On top of high accuracy, tracer gas leak detection also allows the precise localization of the leak. Nevertheless, the mechanical stress applied to the flexible packaging due to the vacuum required for tracer gast testing is not an easy task to cope with.     

High sensitivity leak testing for critical nuclear components

Quality Assurance on leak tightness performance of systems and components that handle hazardous, toxic/radioactive fluids is to be ensured through a well chosen leak testing method. It is very much essential for components and systems used in such applications to be subjected to high sensitive leak testing methods capable of detection of leaks of the order of 10⁻¹¹ Pa.m³/sec. due to the fact that a minutest leakage to the environment is likely to pose serious consequences. The choice of a particular leak testing method and technique depends on the degree of leak tightness required and the service requirements of the components. Mass spectrometer leak detection method is the only technique which possesses matching sensitivity requirements for the purpose of ensuring the leak tightness of this magnitude, thus well suited for testing of critical components required for Fast Reactor, Cryogenic systems, ultrahigh and high vacuum applications etc. Large number of components required for such applications have been subjected to a very stringent leak tightness requirements with a sensitivity of the order of 10⁻¹³ Pa.cu.m/sec. This paper outlines the approach, planning and execution of helium leak testing of a few critical components with varying complexities. The details of the difficulties experienced, particularly in attaining higher vacuum and suggestions to achieve highest sensitivity are also discussed.     

比较法校准氦真空参考漏孔漏率及合成不确定度评定

直接比对法是氦质谱检漏仪在稳定工作和引入气体相同条件下,将参考漏孔流出的氦气和标准漏孔提供的已知流量的氦气分别引入校准室中,用氦质谱检漏仪分别测量氦气产生的离子流,通过比较两次离子流的测量值计算出参考漏孔漏率的一种校准方法。这种校准范围为1×10-7Pa.m3/s~1×10-10Pa.m3/s。对同一参考漏孔,采用同样的校准测量,可以采用高斯分布统计的方法获得校准不确定度,其他不确定度分量由氦质谱检漏仪组成的校准装置决定,其合成相对不确定度可达到10%。     

基于分子流传感元件的真空腔体漏率测量方法

本文介绍了一种基于分子流传感元件的真空腔体漏率测量方法,该方法通过分子流传感元件测量真空腔体整体漏率,采用的测量装置由气体流量测量系统、真空抽气系统、恒温系统等部分组成.在测量系统中,流经传感元件的气流处于分子流状态,通过测量传感元件两端的差压,计算质量流量,可以得到真空腔体的整体漏率.实验中对多个真空腔体漏率的测量结...     

氦质谱非真空积累检漏法中几个问题的研究

氦质谱非真空积累检漏法被广泛应用于航天器的总漏率测试中,因此研究氦质谱非真空检漏法具有重要的工程实际意义。本文首次详细给出了氦质谱非真空积累检漏法计算公式的详细推导过程,同时讨论了采用柔性收集室技术可能产生的一些问题。研究结果表明:氦质谱非真空积累检漏法有着严格的理论依据;柔性收集室的技术在理论上是可行的。本文的研究结论可以为氦质谱非真空积累检漏法的工程应用提供理论依据。     

Measurement of helium leaks 10 times better than the sensitivity of a mass spectrometer leak detector

The actual limit of helium leak detection is given by the highest sensitivity to helium of a mass spectrometer leak detector and can be considered to be 10⁻¹⁰ atm cc/sec. The output of such a leak detector is strongly influenced by the vacuum created at the height of the spectrometer tube. In this paper a method is proposed which permits the range of leak measurements to be extended by a factor of 10⁻⁵ over the actual limit of mass spectrometer leak measurements. The method is based on the accumulation of a leak, compared to the accumulation of a background over the same time. The rather complex manipulations are explained and justified so that the reader of the paper becomes familiar with this technique.     

Real time calibration for ultrasensitive leak detection

A variable reference leak rate system is developed for real time calibration of ultrasensitive leak detection. It is based on the molecular flow characteristics of the platinum wire-glass leak element combined with a helium pressure adjustable device. Helium reference leak rate range from 10⁻¹⁴ to 10⁻¹⁰ Pa m³/s is provided and has been used for real time calibration of ultrasensitive mass spectrometer leak detection system.     

基于压电传感器的管道泄漏信号可靠性识别技术研究

管道泄漏检测的可靠性主要取决于泄漏信号的信噪比,泄漏信号信噪比的提高主要由传感器和对信号的处理方法决定。在定量分析的基础上,得出了基于压电传感器的管道泄漏检测方法具有比基于压力传感器的负压波法更高的泄漏信号信噪比。通过信号分析,论证了平滑滤波对于提高泄漏信号信噪比的必要性,提出了用区间信号能量来突出泄漏信号的方法。分析比较了实际检测信号幅值、区间信号能量和区间信号平均能量的平方3种方法下泄漏信号的信噪比,提出了用基于区间信号平均能量平方的顺序能量比率法进行管道泄漏信号识别的方法。结果表明该方法可以极大地提高泄漏信号信噪比和泄漏检测可靠性。     

Einführung in die industrielle Dichtheitsprüftechnik

The industrial leak test technology is today mainly based on the h gas mass spectrometer test method and, according to the specifications, on pressure and air measure techniques (delta pressure increase, pressure decrease, differential pressure etc.) The machines for the industrial leak test technique are manufactured according to customers and product specifications and are applied for the detection of components and component parts, which are produced in great numbers in the capital goods industry. As the kind of machines must meet very severe industrial standards and complex rules, a highly specialized field for testing and measure technology has been developed during the last years in cooperation with the relevant machine manufactures. As typical examples two automatic industrial leak test machines are presented below — automatic leak test machine for hermetic compressors with a cycle time of 12 sec. — automatic leak test machine for drums and barrels with a cycle time of 5 sec.     

Mass Point Leak Rate Technique with Uncertainty Analysis

The mass point leak rate technique is often the methodology of choice for quantifying leak rates as it uses simple elementary measurements, applies to gas systems of low mass, proves effective for low leak rates, and does not rely on test-gas conversions. In this methodology, a number of instantaneous mass measurements are calculated through samples of volume, pressure, gas composition, and temperature measurements over time. A regression analysis of the corresponding mass-time sample set yields the leak rate of the system. A detailed uncertainty analysis is paramount for a complete, experimental characterization of the leak rate and previously was not fully implemented in the mass point leak rate method. Recent advancements in regression uncertainty analysis by propagation of errors afford the ability to quantify the uncertainty with estimates of covariance in the regression results. The mass point leak rate technique with the associated detailed measurement uncertainty analysis offers the ability to quantify both the leak rate and the uncertainty associated with the leak rate value. Detailed herein is the development of the methodology and a detailed uncertainty analysis that includes both precision (repeatability) and bias (systematic) error. Alternative leak rate methods are also discussed for comparison purposes. An example in the methodology is presented.     

A probabilistic simulation of fluid leakage in multiple cracks situation

ABSTRACT In pressure vessels and piping the leak‐before‐break (LBB) assessment method is employed to avoid any catastrophic failure prior to a detectable leakage. One of the most important parameter, the leak rate, is investigated in the present paper by means of the Monte Carlo method. A brief review is carried out with emphasis on aspects such as crack growth, crack size with detectable leakage, crack opening area and leak rate. Issues concerning the property and behaviour of multiple cracks are also covered along with a review of the characteristics of leak rate through distributed multiple cracks using a statistical simulation method. The simulation results show that the effect of multiple cracks is quite significant to the LBB concept. Both the relationship between leak rate and crack length (or time) and the statistical characteristics of the leak rate are considerably different for different initial crack conditions.     

Industrielle Vakuumlecksuche mit intelligenten Gas‐Leckdetektoren: nicht nur ein Massenspektrometer. Industrial Vacuum Leak Detection with Intelligent Gas Leak Detectors: not only a Mass Spectrometer

In recent years, the requirements on reliability and lifetime of industrial components have increased significantly. This is due both to customer requirements and the Total Quality philosophy that has been introduced much more widespread. This development has had an impact especially on industrial leak detection since this is one of the non‐destructive testing techniques that has been at a rather low level both regarding the involved technologies and the training of personnel. Modern leak detectors that use test gases, especially helium, for testing components and systems have addressed these needs. In a most important first step, already 20 years ago, helium leak detectors got rid of liquid nitrogen traps by introducing counter flow technology. This together with the replacement of manual valves by electromagnetic ones controlled by a microprocessor enabled operation by relatively unskilled persons in industrial processes. In the following years efforts concentrated on lowering the detection limit and the helium signal response time of the new method. The introduction of dry pumping systems (required by the semiconductor industry) was an additional challenge to be mastered in parallel to those efforts. With the latest instruments, and that is the major concern of this article, operation under industrial conditions was optimized now also focusing on background signal handling which is mandatory for a quick pump‐down of large vessels (up to 100 liters of volume) and unambiguous detection of leaks under contamination conditions. Reaching the leak rate range below 1x10^–9mbarl/s within a few minutes when pumping a 100 liter vessel is one of the specifications to be achieved. Several 1000ppm of ambient helium background or contamination of elastomer gaskets must not produce long waiting times with no value added. It is not surprising that beside new pumping technologies software is more and more an important part of modern leak detectors. There are ways of dealing with signal instabilities to increase the detection limit for leak rates, it is possible to reduce the effect of water vapour desorption on the pump‐down time for large volume vessels without LN2, there are more and more sophisticated ways of “ZERO” functions and non‐linearity compensations for high total pressure operation. These developments are explained and demonstrated with some examples of modern leak detectors recently introduced into the market.     

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.     

A New Calibration Apparatus of Port Quick Leak Detector for Spacecraft

The leak rate of spacecraft port must meet certain standards during the opening and closing processes. The port quick leak detector can be used to on-line measure leak rates of spacecraft port. In this work, a new calibration apparatus is designed and investigated. It can work at different temperatures with different gases in a wide leak rate range. This apparatus consists of the standard leak rate system, calibration system, temperature control system, gas supply and pumping system, which is designed on the basis of direct comparison calibration method and pressure-rising method with a constant volume, and the leak rates are provided by the standard leak rate system. The calibration range of the calibration apparatus is from 2 × 10 ^–6 to 2 × 10 ^–2 Pa m³/s. Its combined standard uncertainty is about 4.7%, and its calibration temperature is from ? 50 to 20 °C. Within the above leak rate and temperature ranges, the correction factor of the port quick leak detector is about 0.88–1.09.     

Moderne Lecksucher mit Vakuumtechnik

Modern leak detectors in vacuum technology In many areas of industrial manufacturing, quantitative leak tightness measurements are required in order to analyze product quality. This article examines three approaches to vacuum leak testing, which utilize different measuring principles and completely different working pressures. The processes are divided into “non-gas selective”, “single gas selective” and “double gas selective”. The pressure rise method does not work gas-selectively. In so-called foil test chambers the pressure rise measurement is used in optimized design and is particularly suitable for leak testing in the food industry. The classic test gas vacuum leak detection is a gas-selective method. The test gas is selectively detected and the chamber is pumped independently of the type of gas. Major innovations in current device solutions are the extension of the measuring range and improved convenience in use. To achieve a detection limit of less than 10⁻¹² mbar·l/s, a double gas selective operation is used, residual gases from the test chamber are selectively pumped, additionally, the test gas detection is selective.     

On the plant-specific impact of different pressurization rates in the estimation of containment failure mode probabilities

The explicit consideration of different pressurization rates (e.g. fast and slow) in estimating the probabilities of containment failure modes (e.g. leak, rupture, and/or catastrophic rupture) might have a profound effect on the confidence of the containment performance evaluation that is so critical for risk assessment of nuclear power plants. We have performed a bounding analysis for the impact of different pressurization rates on the leak and rupture mode probabilities using models for fast and slow pressurizations. The present models are based on the evaluations of probability distributions that are characterized with the median pressures and their standard deviations, for individual mechanisms of structural failure modes and the nominal break sizes. As a result, we have obtained a quantitative and plant-specific estimate of the impact of the pressurization rates on the leak and rupture containment failure probabilities. The present study showed that the impact was not significant for the specific cases considered in this study and confirmed that the treatment used in the specific cases was conservative.     

压漏孔校准装置性能测试

正压漏孔校准装置可采用定容法和定量气体动态比较法进行正压漏孔的校准。定容法的校准范围是１００～５ × １０~（－３） Ｐａ· Ｌ／ｓ,不确定度小于９．１０％;定量气体动态比较法的校准范围是１×１０~（－２）～５×１０~（－５）Ｐａ·Ｌ／ｓ,不确定度小于１４．２０％。     

Development of vacuum technology market in Russia. Entwicklung des Marktes für Vakuumtechnik in Russland

Scientific investigations of leak detection problems are being carried out in several directions. The most significant are metrology problems. Mathematical modeling of working processes in new types of leak detectors is also being developed. Mass spectrometer leak detectors remain the most popular for high accuracy measurements. Other types of leak detectors, such as halogen, manometer, and gas discharge, are also developing. Different types of gas discharge leak detectors are being manufactured.     

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。     

R32制冷剂泄漏位置对浓度分布与室内安全性的实验研究

本文通过实验研究的方法,对比分析了R32制冷剂在泄漏量为3.6 kg,不同泄漏位置时,R32气体在室内不同平面的浓度扩散规律,并通过典型平面首次达到可燃下限（LFL）的时间和可燃风险时间来分析室内的安全性影响。结果表明：随着泄漏位置高度的增加,制冷剂浓度扩散速率在沿高度方向上逐渐趋于一致,浓度上升速率和浓度下降速率分别保持在约0.5%/min和0.06%/min。当制冷剂气体从房间上部水平方向泄漏改变为垂直向下泄漏时,泄漏口附近平面处最大浓度及浓度扩散速率均减小约50%,可燃危险时间减少了约78%;房间下部的的可燃危险时间随泄漏位置高度的升高而逐渐增大。当泄漏位置位于房间上部和顶部时,房间底部区域最先达到LFL值,其余位置处泄漏口附近平面处最先达到LFL值。