Integral 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. 

An important precondition for applying the BTM-method is a very vacuum-tight design of the chamber. This is the only way to ensure that the rise in pressure caused by a possible leak in the chamber remains negligible compared to the rise in pressure caused by the accumulating water vapour. For this reason, the integral leak rate of the drying chamber must be <10" mbarls". ... 

Containment integrated leak rate testing (Type A) The containment is pressurised with clean, dry air and the leak rate from the containment stmcture is established. Type A testing uses temporary equipment connected through penetration COl. 

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. 

The integral leak test, i.e. the total leak rate for all individual leaks, facilitates the detection of microscopic and sponge-like distributed leaks which altogether result in leakage losses similar to those for a larger individual leak. 

Associated tests to include are leak rate and vacuum integrity tests. Both tests are based on the pressure rise of a sealed chamber and condenser that are isolated from the vacuum pumping system. A detailed presentation on the subject is covered in various technical publications on vacuum technology [3,4], Each of these tests, briefly described in the following paragraphs, is well suited to be stand-alone protocols. 

Kirsch, L.E. Nguyen, L. Moeckly, C.S. Pharmaceutical container/closure integrity I Mass spectrometry-based helium leak rate detection for rubber-stoppered glass vials, PDA. J. Pharm. Sci. Technol. 1997, 51, 187-195. 

During the last 25 years, the plug-type gas sensors have shown a greater mechanical integrity than other types of zirconia-based sensors of similar construction, and thus have lower leak rates and greater resistance to thermal and/or mechanical shock, factors which produce long sensor lifetimes and enable in-situ oxygen probes to be used in applications found to be beyond the capability of the other zirconia-based probes. 

Kirsch, L. E., L. Nguyen, and R. Gerth. 1997c. Pharmaceutical container/closure integrity III Validation of helium leak rate method for rigid pharmaceutical containers. PDA J. Pharm. Sci. Technol. 51 (5) 203-207. 

However, in future, the integrity of the floor liner and other structures must be confirmed for all sodium leak rates and ventilation conditions, focusing on the temperature rise of the floor liner and its thinning by corrosion. 

The leak rate in the fabricated valves was approximately 1.4 nl/min or less. Leak rates of this low level are necessary for reproducible measurements in micro-TAS, and to achieve this, particle filters and valves designed to prevent particle trapping must be integrated in future systems. 

If resilient seals (such as elastomeric seals or electrical cable penetrations) or expansion bellows are used with penetrations, they shall be designed to have the capability for leak testing at the contaimnent design pressure, independent of the determination of the leak rate of the contaimnent as a whole, to demonstrate their continued integrity over the lifetime of the plant. 

If pi > P2, then air will flow from the proportional bellows through the integral restrictor and through the leak. As the rate of change of pressure in the bellows is proportional to this difference is pressure,... 

The rate of change of pressure in the integral bellows due to the leak is, however, half that due to flow through the integral restrictor, or ... 

If the normalized salt rejection is low or the normalized permeate flow is high, the integrity of the membrane may be in question. The vacuum decay test is a direct test for the integrity of a spiral wound RO membrane module. The test is best used to identify leaks within the membrane modules rather than leaks due to chemical attack. The test requires the isolation of an individual membrane module or the entire pressure vessel. A vacuum is then pulled on the membrane(s) and the rate of decay in pressure is observed. A decay of greater than 100 millibar per minute is indicative of a leaky membrane. Refer to ASTM Standards D39235 and D69086 for a more detailed review of the technique. 

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