Industrial leak testing of dangerous goods packagings

The Dangerous Goods Regulations currently do not include limit leakage rates or sensitivity requirements for industrial leak testing procedures that are equivalent to the bubble test, which is the prescribed test method for design type testing of dangerous goods packagings. During series production of such packagings, various methods are used, which often do not meet the requirements of the bubble test with regard to important criteria. Sensitivity, flow direction, pressure level and automatability are particularly important factors when selecting a suitable industrial leak testing method. The following methods are in principle both suitable and equally effective as the bubble test: pressure rise test (vacuum chamber), ultrasonic bubble leak detection and gas detection methods (pressure technique by accumulation and vacuum chamber technique). To ensure a uniform test level during design type testing and production line leak testing and therefore a comparable safety level as required by the Dangerous Goods Regulations, it is necessary to include a more precise specification in these regulations. This requires, on the one hand, information about the sensitivity of the bubble test and, on the other hand, the inclusion of a list of suitable, equally effective industrial test methods with their specific boundary conditions.     

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.     

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.     

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.     

Hochempfindliche Dichtheitsprüfung mit Spürgas SF6 und Laser‐Gasnachweis

At the Institute of Technical Physics of the Research Center Karlsruhe, superconducting magnets for fusion reactors are tested in the test tank TOSKA since more than 20 years. A crucial test parameter of the magnets weighing up to 120 metric tons is the tightness at operating conditions down to 2 K temperature and max. 25 bars He‐refrigerant pressure. Because the final tests at cryo‐temperature are costly and time‐consuming, intermediate tests at room temperature are already performed at the stages of manufacturing, certification, assembling, and before cooling‐down. So far, these tightness tests by the sniffermethod have been performed with probe gas Helium employing a conventional mass spectrometer leak detector. The achievable smallest detectable leakage is limited by the He partial pressure in ambient air. Therefore, a new technique of leak measurement was investigated using the probe gas sulphur hexafluoride SF₆ which does not occur in natural air and employing a laser‐acoustical gas detection. The experimental results reveal substantial advantages of the new method with respect to detection sensitivity, testing expenditure, and costs. The results can be transferred to tightness tests in other fields of technology.     

Measurement of Helium Leakage Rates through Closures of Dangerous Goods Packagings for the Assessment of Potentially Explosive Mixtures in Freight Containers

The objective was to find out whether an explosive atmosphere can be created in a freight container by gaseous leakage flow of vapour‐air‐mixture through leaks in the closures of dangerous goods packagings filled with hazardous liquids. Because of high temperatures during intercontinental carriage, there is a gauge pressure in the free vapour phase inside the packagings which can cause a gaseous leakage flow. Two different methods were applied: Helium limit leakage rates for 23 quantitatively important hazardous liquids concerning their lower explosion limit (LEL) were calculated for a worst case transport scenario (Method 1). Helium leakage rates of five closure types of dangerous goods packagings with volumes of approximately 6 l were measured using the pressure technique by accumulation (Method 2). All types of closures of steel packagings were uncritical. The maximum measured leakage was 33% of the limit leakage rate. The leakage rates of screw closures of plastic jerricans can exceed the LEL if there are production‐related patterns such as non‐concentricity of the closures and flashes on the neck. Especially for plastic packagings it is important to minimize gaseous leakage flow, because an explosive atmosphere can also be reached by permeation of the individual filling substance or by a combination of both effects. For the assessment of potentially explosive mixtures in freight containers, both mass transfer mechanisms have to be taken into account. Copyright © 2015 John Wiley & Sons, Ltd.     

Kältemittel‐Leckschnüffler

Refrigerant leak sniffer — testing the detection limit Refrigerators, air‐conditioners, dehumidifiers, water recoolers and other cooling devices generate the coldness by circulating a refrigerating agent in a closed circuit. As refrigerants halogenated hydrocarbons are commonly used due to their good thermo‐physical properties. Unfortunately, these refrigerants are harmful to the environment since they cause a depletion of the ozone layer and thus contribute to the global warming. To avoid a loss of the refrigerant to atmosphere, the refrigeration circuit has to be tight. Law requires the leakage of a total circuit to be smaller than a few grams per year. To test the tightness of appliances and plants, mobile refrigerant detectors are commonly used. The user of a leak sniffer has to prove that his sniffer meet its specified detection limit. The present article deals with testing refrigerant sniffers according to standardized procedures.     

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.     

Heliumlecksuche unter extremen Prüfbedingungen

Among the known leak detection techniques the leak test with helium as the tracer gas has become established as a universal technique in industrial manufacture and in the field of research due to its high sensitivity and versatile applications. There are different standard testing variants carried out at a differential pressure of Δp = 1 bar and at room temperature. A special test setup must be conceived, however, if in special cases a statement is required on the leak tightness of a component under special operating conditions. In this report, two tests under extreme testing conditions (950 °C, 200 mbar differential pressure and ?196 °C, 10 bar test pressure) are presented with the test assemblies provided for this purpose.     

Helium‐Testlecks zur Kalibrierung von Lecksuchern

In order to perform reliable quantitative measurements of leak rates, the used leak detection equipment is calibrated by injection of a known leakage flow delivered by a test leak. Well‐proven are Helium test leaks of the diffusion type with internal gas reservoir. The present paper deals with the construction of such leaks, the temperature dependence and response time of the leak rate, and their calibration. In case of careful handling, the relative uncertainty of the delivered leakage flow can amount to only 3 % (2σ).     

Package performance testing of dangerous goods in high‐altitude shipments

This paper discusses the impact of high‐altitude shipments on package integrity. High‐altitude shipments are encountered when trucks travel over high mountain passes or when cargo and feeder aircraft transport packages in non‐pressurized or partially‐pressurized cargo holds. Both these types of transport methods will result in severe changes in pressure as compared to packages being transported close to sea level. The testing of packages under these conditions is critical since package integrity may be compromised. The current shipping tests performed in test laboratories do not account for pressure changes and vibration together. This study showed that combination packages for dangerous goods and hazardous materials that are tested to existing UN, ICAO and US DOT requirements are limited, and can result in significant number of leaks. Testing under combined vibration and pressure changes is necessary. Copyright © 2003 John Wiley & Sons, Ltd.     

Die Hauptstrommessung als Innovation in der industriellen Helium‐Dichtheitsprüfung

Main flow measurement as an innovation in industrial helium leak testing So‐called main flow measurement with its special vacuum pump stations brings numerous technological advantages to helium leak testing, making it possible to significantly enhance the cost profile and efficiency of industrial inline test systems. The suppression of ambient influences and the achievability of the shortest clock rates are the key factors for the successful automation of test processes. The reduction in helium consumption and the achievable energy savings improve the cost benefits of investing in a test system working on the main flow principle still further. PINK leak test systems are equipped with numerous diagnostic features ranging from continuous self‐monitoring and fully automatic leak rate control to the independent calculation of new test parameters.     

Measurement and Analysis of Physical and Climatic Distribution Environment for Air Package Shipment

There has been a significant growth in the air package shipment business, which involves the multi‐modal movement of a package in transportation and material handling systems that encompass conveyors, carts, trucks, delivery vans and aircrafts of various sizes and shapes. This study was aimed at establishing the ‘air package shipment’ conditions experienced by packages transported by air under ‘normal conditions of transport’. Air package shipment data (temperature, humidity, pressure, shock and vibration) were collected for several domestic and international routes through instrumented packages. The collected data were supplemented by previous research to measure and quantify this multi‐modal shipping environment. This study also compared industry‐accepted American Society for Testing and Materials (ASTM) pre‐shipment test methods with the general requirements of package design qualification testing as outlined in 49 Code of Federal Regulations (CFR) Part 178, Subpart M. This review revealed that the design qualification testing for certain distribution‐related hazard elements is not currently representative of the normal conditions of air transport. The data gathered in this study were analysed to represent the current ‘normal conditions of transport’, i.e. beginning‐to‐end delivery of air packages. The study used the time spent by the package in each of the segments of transportation to determine a ‘single profile’ or ‘test’ that would represent the average and normal expected levels for each hazard element and would serve as the basis of a minimum level for performance testing to establish normal conditions of transport by air. The recommended test methods and levels can be easily adopted by existing distribution packaging testing labs globally. Copyright © 2015 John Wiley & Sons, Ltd.     

Heliumlecktestgeräte für die Qualitätsprüfung von Gehäusen für Vakuumverdichter

Helium leak test devices for the quality inspection of housings for vacuum compressors The well‐known and wide‐spread helium leak test method is a safe and fast quality testing method for construction units of any kind. Due to its safe examination and the short time of examination it is predominantly inserted into automated production lines as e.g. in the automobile supporting industry up to the examination by Airbags and rims of wheel. Likewise in addition, for the construction units, machines and devices of the vacuum engineering. From this the demand results simple and in particular economical devices for the helium leak test of construction units with small numbers of items of under 200 pieces per day. For these manufacturing profiles economical ways for the helium leak test are pointed out.     

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.     

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.     

Investigation of leak detection method by means of measuring the pressure increment in vacuum

Leak detection by measuring the pressure increment in a vacuum has found wide application on pressure vessels, pipes and accessories. However, the reproducibility of the method and the effect of some secondary factors on the results of leak detection have not yet been satisfactorily studied and explained. In this paper, the leak detection method is discussed and the possibility of measuring small leakage rates outlined. Some factors influencing the results, especially the virtual leakage rate and test temperature, which may affect the accurate measurement of small leakage rates, are investigated in detail. In order to improve measurement accuracy, it is suggested that the evacuation time is prolonged and, if possible, the testing system is pre-heated, to eliminate the influence of the virtual leakage rate as far as possible. The research results indicate that both the variation of the ambient temperature and the inconsistency of the temperature of the testing system with that of the gas leaking into the system will introduce errors. Methods for correcting measured results are proposed.     

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.