Leak detection sampling systems

Sampling systems are centrally located leak-detection systems that use a pump or aspirator to pull samples from various locations into an instrument for analysis. They can be used to detect both toxic or flammable materials. The instruments used may sample and analyze a single point or multiple points, depending on the application. Additionally, some of these systems will allow detection of up to five components. 

Fume detectors should be employed to detect leaks from the sampling system, especially when the fumes are toxic or flammable. 

Use of the chromatograph with gas samples at an absolute pressure of 1 mm Hg has been possible. This has allowed in some special cases the detection of leaks in a system that could not be evacuated to a better pressure than this. The manway between the inner and outer shells of one of the dewars had such a leak. Since the inner shell was filled with nitrogen at the time and the outer flange would leak air, a sample analysis readily provided information that an inner flange leak was present. 

Steam generator leak detection system (SGLDS) has been provided to detect small steam/water leak (few mg/s to few g/s) into sodium. This is a diffusion type meter wherein sodium sample from SG is passed through nickel tubes of 0.3 mm thick. Vacuum is maintained outside the tube with the help of sputter ion pump (SIP) and partial pressure of hydrogen is measured with the help of Quadra pole mass spectrometer (MSM) and SIP current. 

It is not likely that one can find this type of leak by sampling for amine strength at different points in the refinery. The entire amine system volume may circulate through the scrubber and regenerator 20 times a day. A small loss in amine strength per pass cannot be detected by the lab. This small loss in strength is, however, multiplied by 20 each day. 

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). 

Compounds not detected or detected in lower-than-expected concentrations. First, make sure that the problem is definitely due to a problem with the model mouth. For example, the cause of the problem may be due to the analytical equipment (e.g., gas chromatograph or mass spectrometer), inconsistencies in the food sample, and/or extraction errors. If volatile compounds are not detected or are detected in far lower-than-expected concentrations, there may be a gas leak somewhere in the system. All connections should be checked with a leak detector as described for the RAS. 

The common problems in HPLC concern pressure (high, low, or unstable, or none), leaks, quantitation (detection problems, injection problems, sample problems or data-system problems), chromatogram (peak shape), and hardware. 

Exposures to ethyl acrylate monomer are most likely to occur in an occupational environment via skin contact and inhalation. However, the closed systems used during manufacture and transportation will limit worker exposures to those that may occur during routine process maintenance, periodic plumbing leaks, and the collection of quality control samples. Under these conditions, exposures are further limited by the use of industrial hygiene controls and personal protective equipment. The acrid odor of ethyl acrylate, which can be detected at 0.001-0.005 ppm, also serves to limit exposure. Studies of monomer production workers have indicated that... 

Johansson and Granat (1984) conducted research on pressure differences between the outside atmosphere and air within a chamber using a tilted water manometer, which indicated that pressure differences were below detectable limits (0.2 mm H2O). Arkinson (2003) conducted research on temperature difference between the outside atmosphere and air within the chamber. The results indicate that temperature differences are < 0.4°C. The out-flowing gas also flows through a Teflon FEP sample line and is directed into a temperature controlled mobile laboratory, which houses the analytical instruments and data acquisition system. Here, the sample is analyzed continuously for content of the gas of interest. A vent line is fitted to the exiting sample line to prevent pressurization and was periodically bubble tested to check for under pressurization and/or leaks in the enclosed system. Sample lines do not exceed 10 meters. 

---