Leaks, testing for

This section introduces a five-step procedure developed by Tracer Research Corporation for conducting the leak testing for an underground storage tank. 

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). 

Figure 2-16. Pressure drop of the background leak test for the current test setup...

Check the unit once a year on air velocity a leak test for HEPA or ULPA filters is easy to perform by an expert. 

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]. 

Fire-Resistant Hydraulic Fluids. Fire-resistant hydrauhc fluids are used where the fluid could spray or drip from a break or leak onto a source of ignition, eg, a pot of molten metal or a gas flame (17). Conditions such as these exist in die-casting machines or in presses located near furnaces. Specific tests for fire resistance are conducted by Factory Mutual in the United States. 

R. C. McMaster, ed., "Leak Testing," Nondestructive Testing Handbook, Vol. 1, 2nd ed.. The American Society for Nondestmctive Testing, Columbus, Ohio, and The American Society for Metals, Metals Park, Ohio, 1982. 

When constmction is complete, the pipeline must be tested for leaks and strength before being put into service industry code specifies the test procedures. Water is the test fluid of choice for natural gas pipelines, and hydrostatic testing is often carried out beyond the yield strength in order to reHeve secondary stresses added during constmction or to ensure that all defects are found. Industry code limits on the hoop stress control the test pressures, which are also limited by location classification based on population. Hoop stress is calculated from the formula, S = PD/2t, where S is the hoop stress in kPa (psig) P is the internal pressure in kPa (psig), and D and T are the outside pipe diameter and nominal wall thickness, respectively, in mm (in.). 

Testing for leaks in heat exchangers was discussed by Rubin [Chem. Eng., 68, 160-166 (July 24, 1961)]. 

The enclosure must be tested for one minute, with an inside air pressure equal to a head of about 1 in of water. No air should leak during the lest. Air leakage may be detected by submerging the enclosure in water, with the Just covering the enclosure. 

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. 

The hydrostatic testing is the first test used on the lube system. The system is tested while assembled or partially assembled, based on the particular system. A test pressure of VA times the maximum allowable working pressure, a minimum of 20 psi for the oil side, is used for the test. For the oil-wetted parts, the test fluid should be light oil, which is normally the recommended lubricant for the compressor train. The test period is the length of time needed to inspect for leaks, or a minimum ol thirty minutes. Acceptance is based on the lack of leaks as visually observed or the lack of a drop in the test pressure. 

If a gas leak test is called for, the test can take place shortly after the hydrotest, especially on the reciprocator cylinder or centrifugal or rotary compressors, where the gas is tested without end seals. 

Each PR valve must be installed so that the bonnet vent does not allow released vapors to impinge on lines or equipment, or towards personnel walkways. Where necessary, a short nipple and elbow should be added to direct flow away from such areas. In these cases, the vent piping should discharge horizontally to avoid entry of rainwater and debris, and should terminate in a position which is accessible for leak testing. 

Air in leakage, depending on the quantity, can create an explosive mixture in some process reaction systems therefore, the system should be tested for air leaks and kept as tight as practical. 

Factory-built equipment will be constructed to the relevant Standards and will be pressure tested for safety and leaks at the works. In cases of doubt, a test certificate should be requested for all such items. 

Site-erected pipework, once complete, must be pressure tested for safety and freedom from leaks. Pressures will be 1.3 times the... 

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. 

Where fluid pressure is carried by a capillary tube, such as with the thermostatic expansion valve or pressure switches, the tube should be installed with due attention to the risk of it chafing against metal edges and wearing through. Tubes to manometers are usually in plastic, but may be copper. These must be carefully tested for leaks, as they are transmitting very low pressures. 

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