Helium leak test

Leaks in medical sources and seeds are detected by a vacuum immersion leach test. Because the internal volume of the medical sources is so small (3.6 x 10 mL, in the case of the ALC-P4C seed), the conventional helium leak test is not a valid leak test procedure. About 45 minutes is required to pump down the system before helium measurement is begun. If the internal volume of the test specimen is small, trapped helium would escape before helium assay begins. Therefore, leaks in encapsulated medical sources are detected by measuring the alpha activity of a nitric acid penetrant solution in which the source had been immersed. After immersion, pressure above the liquid is decreased to 2.5 psia for 3 min before venting to atmosphere. This procedure is repeated twice, then the sources remain in acid a minimum of 16 h at 20°C. 

Helium leak tests were carried out under load pressure up to 4 MPa and surface temperature of the models up to 500°C. All cormections were installed in a vacuum electric furnace, and leak rates were measured with a helium leak detector. Table 2 shows the leak rates obtained at 500°C in the third times at the heat cycle up to 5()()°C, and Table 3 obtained under 2()°C after the leak measurement at 500°C shown in Table 2. In these tables, line loads and seating stresses (tightening forces) are also indicated. As seen these tables, although the tightening forces under 500°C decreased down to less than... 

Fine and gross helium leak testing will detect any marginal or bad seals through which moisture and other contaminants can enter the package. 

Hydrotest Pneumatic Test Soap Bubble Test Helium Leak Test Performance Test Acoustic Emission Test Hardness Test Ferrite Check Copper Sulfate Test PMI... 

Vendor should perform the leak tests as per standard practice for all components which should operate under high vacuum—main vessel, evaporator and absorber (helium leak test may be asked for), etc. 

The hermeticity of a sintered ceramic is particularly important in electronic components. Fine size, open porosity or surface cracks in sintered ceramics can be characterized by the bubble test or by dye penetration. The hermeticity of closed-porosity sintered ceramics can be characterized using the helium leak test. ... 

Electron-beam welding requires a vacuum, while laser welding can be done in air or in an inert environment. Argon and helium mixtures are often the preferable inert laser-welding gas for protective purposes. Moreover, helium is the ideal gas for helium-leak testing. 

The requirement of a helium-leak test for a MEMS device package with an internal volume of around 0.001 cc or below for chronic implantation (>10 years) is definitely beyond the capability of any current helium-leak detector. That is where getter materials come into play. A getter material can absorb various gaseous species and can be used to extend the effective lifetime of a medical device by absorbing moisture and other detrimental gas species, such as hydrogen [104—106] and oxygen [40]. 

After fabrication, the units were subjected to 50 primary-side thermal cycles covering temperature changes more severe than those likely to be encountered in subsequent operation. The units were then helium-leak-tested at atmospheric pressure with mass-spectrometer equipment capable of detecting leakage lower than 0.1 cc of helium at STP per day. Leaks were repaired and the thermal-cycle test and leak test w ere repeated until no leakage w as detectable. 

The helium leak detector is a common laboratory device for locating minute leaks in vacuum systems and other gas-tight devices. It is attached to the vacuum system under test a helium stream is played on the suspected leak and any leakage gas is passed into a mass spectrometer focused for the helium-4 peak. The lack of nearby mass peaks simplifies the spectrometer design the low atmospheric background of helium yields high sensitivity helium s inertness ensures safety and its high diffusivity and low adsorption make for fast response. 

Object to be tested 2, helium leak detector L, slit with a fixed conductivity (Fig. 10 from [2.27]). 

The leak rate which is no longer tolerable in accordance with the acceptance specifications is known as the rejection rate. Its calculation is based on the condition that the test specimen may not fail during its planned utilization period due to faults caused by leaks, and this to a certain degree of certainty. Often it is not the leak rate for the test specimen under normal operating conditions which is determined, but rather the throughput rate of a test gas - primarily helium - under test conditions. The values thus found will have to be converted to correspond to the actual application situation in regard to the pressures inside and outside the test specimen and the type of gas (or liquid) being handled. 

Where a vacuum is present inside the test specimen (p < 1 mbar), atmospheric pressure outside, and helium is used at the test gas, one refers to standard helium conditions. Standard helium conditions are always present during helium leak detection for a high vacuum system when the system is connected to a leak detector and is sprayed with helium (spray technique). If the specimen is evacuated solely by the leak detector, then one would say that the leak detector is operating in the direct-flow mode. If the specimen is itself a complete vacuum system with its own vacuum pump and if the leak detector is operated in parallel to the system s pumps, then one refers to partial-flow mode. One also refers to partial stream mode when a separate auxiliary pump is used parallel to the leak detector. 

Today leak tests for vacuum systems are usually carried out with helium leak detectors and the vacuum method (see Section 5.7.1). The apparatus is evacuated and a test gas is sprayed around the outside. In this case it must be possible to detect (on the basis of samplings inside the apparatus) the test gas which has passed through leaks and into the apparatus. Another option is to use the positive-pressure leak test. A test gas (helium) is used to fill the apparatus being inspected and to build up a slight positive pressure the test gas will pass to the outside through the leaks and will be detected outside the device. The leaks are located with leak sprays (or soap suds, 5.4.5) or - when using He or H2 as the test gas - with a leak detector and sniffer unit (5.7.2). 

Table 5.3 Comparison of bubble test method (immersion technique) wit helium leak...

Where the size of the vacuum vessel or the leak makes it impossible to evacuate the test specimen to the necessary inlet pressure, or where this would simply take too long, then supplementary pumps will have to be used. In this case the helium leak detector is operated in accordance with... 

Here the points suspected of leaking at the pressurized test specimen (see Fig. 5.4, d) are carefully traced with a test gas probe which is connected with the leak detector by way of a hose. Either helium or hydrogen can be detected with the INFICON helium leak detectors. The sensitivity of the method and the accuracy of locating leaky points will depend on the nature of the sniffer used and the response time for the leak detector to which it is connected. In addition, it will depend on the speed at which the probe is passed by the leak points and the distance between the tip of the probe and the surface of the test specimen. The many parameters which play a part here make it more difficult to determine the leak rates quantitatively. Using sniffer processes it is possible, virtually independent of the type of gas, to detect leak rates of about 10 mbar l/s. The limitation of sensitivity in the detection of helium is due primarily to the helium in the atmosphere (see Chapter 9, Table VIII). In regard to quantitative measurements, the leak detector and sniffer unit will have to be calibrated together. Here the distance from the specimen and the tracing speed will have to be included in calibration, too. 

N cuum envelope tests are integral leak tests using helium as the test gas, in which the test specimen is enclosed either in a rigid (usually metal) enclosure or in a light plastic envelope. The helium which enters or leaves (depending on the nature of the test) the test specimen is passed to a helium leak detector, where it is measured. Envelope tests are made either with the test specimen pressurized w/ith helium (Fig. 5.4c) or with the test specimen evacuated (Fig. 5.4a). In both cases it may be necessary to convert the helium enrichment figure (accumulation) to the helium standard leak rate. 

When the test specimen, pressurized with helium, is placed in a rigid vacuum chamber, connected to a helium leak detector, the integral leak rate can be read directly at the leak detector. 

Immediately following the initial assembly (and at any other time leaks are suspected), the box and purification train should be tested for leaks. A quick test for leaks is to pressurize the dry box until the gloves stick straight out. The gloves should remain in this position for several hours if no leaks are present. If leaks are indicated, testing is most easily accomplished while the box is pressurized. If the inert atmosphere is helium, the preferred method is the helium sniff test. All joints, welds, and connections should be checked. In the absences of a helium-sensitive probe or if the inert atmosphere is other than helium, the bubble method may be used a small amount of soapy water is placed on leak-prone welds and joints and the appearance of any bubbles is noted. 

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