Pressure leak test

G. Rawls, IES Pressure/Leak Test data Sheet, Job SRNL-HPL-2006-3830, Record 12891... 

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). 

The leak detection methods described above for pressure leak testing also apply for vacuum leak testing. More sensitive methods use an easily detectable tracer gas. Excellent detailed reviews of leak testing and leak detection techniques are available elsewhere (315, 345). 

Vacuum Leak Test. The vacuum leak test is similar in concept to the internal pressure leak test in that the result is a pass/fail for the detection of bubbles emanating from the package while submersed in a water bath. The method is described in ASTM D3078, Standard Test Method for Leaks in Heat-Sealed Flexible Packages. The pressure differential is obtained by evacuating the chamber, causing the package to expand. 

SUMMA canisters are cleaned by alternatively filling them with humidified air, venting them, and then pulling a very low vacnnm (<0.05 mm Hg) for a total of three cycles. Sometimes the canisters require heating during the process to remove less volatile compounds. On the last cycle they are filled with humidified air, and each canister must be analyzed to certify that it is clean of VOCs. A pressurized leak test is also required. The cleaned canisters are then evacuated and ready for sampling. 

Piping required to have a sensitive leak test shall be tested by the gas- and bubble-formation testing method specified in Art. 10, Sec. V of the ASME Code or by another method demonstrated to have equal or greater sensitivity. The sensitivity of the test shall be at least (100 Pa mL)/s [(10 atm mL)/s] under test conditions. If a hydrostatic pressure test is used, it shall be carried out after the sensitive leak test. 

After catalyst charging and the flow vs. RPM measurement is done, the reactor should be closed and flushed out with nitrogen while the impeller runs, until O2 drops below a few tenths of a percent. Then a static pressure and leak test should be made by turning off the forward pressure controller and the flow controller. If an observable drop of pressure occurs within 15 minutes, all joints and connections should be checked for leaks and fixed before progressing any fijither. 

Immediately after the running test, any compressor intended for toxic, hazardous, flammable, or hydrogen-rich service should be gas tested with an inert gas to the maximum seal design pressure. The test is held at least 30 minutes and the casing and its joints checked for leaks, using a soap bubble method or other suitable means for leak detection. When no leaks are detected, the compressor will be considered acceptable. 

STANDARD LEAK TEST PRESSURE setting 3 PERCENT... 

It is possible that the employees concerned did not understand the difference between a pressure test, normally carried out with water, and a leak test, often carried out with compressed air at a pressure well below the test pressure. 

When a plant was being leak-tested with nitrogen after a shutdown, a leak was found on a manhole joint on the side of a vessel. The pressure was blown off, and a fitter was asked to remake the... 

Similarly, pressure tests (at pressures above design, as distinct from leak tests at design pressure) are intended to detect defects. Defects may be present—if we were sure there were no defects, we would not need to pressure-test—and therefore we must take suitable precautions. No one should be in a position where he or she may be injured if the vessel or pipework fails (see Section 19.2). 

Hesitation continues until no pressure leak-off is observed. A further test of about 500 psi over the final injection pressure will indicate the end of the injection process. Usually, well-cementing perforations will tolerate pressures above the formation fracture pressure, but the risk of fracturing is increased. 

The test pressure should be maintained for at least an hour. In this period a thorough test is made of each joint with soapy water. This method is no more tedious than a refrigerant leak test and saves the time and loss of refrigerant. Targe leaks will be heard. 

For gaseous sterilization procedures, elevated temperatures are monitored for each sterilization cycle by temperature probes, and routine leak tests are performed to ensure gas-tight seals. Pressure and humidity measurements are recorded. Gas concentration is measured independently of pressure rise, often by reference to weight of gas used. 

Leaks are, besides loss of power, the most unwanted events during freeze drying (see the end of this chapter about defects). Therefore it is recommended, to make a leak test before each freeze drying run, though this routine test does not have to follow the procedure described above. If the leak rate is measured once, the pressure as a function of time during the evacuation period can be recorded and compared with the evacuation plot of the... 

The above test provides a basis for evaluating a seal material s capability at the desired operating temperature. However, in realistic stack conditions, a seal material is under a shear stress. A double tube arrangement can be used to study the seal behavior. A disc can be sealed on both sides, and both tube enclosures can be pressurized to the same level. Such condition will eliminate the flexing of the membrane causing the seal to delaminate at a fairly low pressure when tested above Tg. In fact, a repeat test of the above seal with a double-tube arrangement showed that the seal could withstand 20 psi pressure before a small leak developed. 

The internal line shall be leak tested on the basis of the internal or external design pressure, whichever is more critical. This test must be performed before the jacket is completed if it is necessary to provide visual access to joints of the internal line as required by para. IP-10.6.3(a). 

The jacket shall be leak tested in accordance with para. IP-10.6.1 on the basis of the jacket design pressure unless otherwise specified in the engineering design. 

A piping system containing expansion joints shall be leak tested without temporary joint or anchor restraint at the lesser of 150% of design pressure for a bellows-type expansion joint or the system test pressure determined in accordance with para. IP-10.6. In no case shall a bellows-type expansion joint be subjected to a test pressure greater than the manufacturer s test pressure. 

If a combination hydrostatic-pneumatic leak test is used, the requirements of para. IP-10.8 shall be met, and the pressure in the liquid-filled part of the piping shall not exceed the limits stated in para. IP-10.7. 

Leak Testing Location of through wall defects and flaws while under pressure or vacuum. Various fluids and gases are used for pressure testing several types of leak detectors are used to locate a leak. 

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