Leak testing

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. 

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. 

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. 

STANDARD LEAK TEST PRESSURE setting 3 PERCENT... 

In addition, they are usually constructed without isolation valves on the fuel supply lines. As a result the final connection in the pipework cannot be leak-tested. In practice, it is tested as far as possible at the manufacturer s works but often not leak-tested on-site. Reference 32 reviews the fuel leaks that have occurred, including a major explosion at a CCGT plant in England in 1996 due to the explosion of a leak of naphtha from a pipe joint. One man was seriously injured, and a 600-m chamber was lifted off its foundations. The reference also reviews the precautions that should be taken. They include. selecting a site where noise reduction is not required or can be achieved w ithout enclosure. If enclosure is essential, then a high ventilation rate is needed it is often designed to keep the turbine cool and is far too low to disperse gas leaks. Care must be taken to avoid stagnant pockets. 

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... 

Figure 14-2. The check valves (nonreturn valves NRV) prevented a leak test of the equipment to the left of them. During startup a leak occurred at the point indicated.

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). 

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. 

Leaks of R.717 usually make themselves apparent and motivate staff to search out the leak and repair it. In the case of the halocarbons, a regular leak test should be part of the general maintenance schedule. 

Staff should be forbidden to smoke while leak testing or repairing. Many operatives are ignorant of the danger to their health if smoking in the presence of traces of the halocarbons. 

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. 

The accident investigation found that the leak test should have been conducted with a hydraulic procedure and not air and that the vessel should have been protected with a relief device. In addition, the fitters should have taken more time to check out the gauge to ensure that it was correct for this application. 

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... 

Drying of the plant to be sterilized by evacuation down to 1 or 10 mbar 2, several injections of H202 each followed by an evacuation 3, several times venting of the plant with sterile air 4, leak test of the plant before the start of 2 (VHP is a process of AMSCO International, Apex, North Carolina 27502 USA Figure from [2.12]). 

A. The filter system shall include a- series redundant-parallel Chemical Biological Radiological (CBR) filter assembly with a capability of placing a detector between the adsorber banks to warn of "breakthrough". The system shall provide accessibility to filters for repairs, maintenance and leak testing. 

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