N2 purging and N2/helium detection

Nitrogen purging is the standard technique for replacing hazardous or undesirable atmospheres with an inert dry atmosphere. The two most common methods of purging are displacement and dilution. The geometry of the process system determines which method is used. 

For a simple system, displacement purging is usually more effective in terms of time and cost, but dilution purging is used for a more complex system. 

Nitrogen can also be used for leak tests as a part of facility pre-commissioning services or after facility maintenance where flanges were disturbed, to confirm facility leak tightness. This is done by pressurizing the system with nitrogen gas and identifying leaks by applying a soapy solution on tapped flanges after puncturing it. The pressurized nitrogen gas escaping from the punctured tape will indicate if there is a leak on the flange. 

Nitrogen Leak Testing is to confirm the integrity of a system where water may not be used and has been During Commissioning, the LT is achieved by pressurizing the process system or component to be tested to their design pressure with a test medium comprising of 99% Nitrogen and 1% Helium. To obtain 1% Helium in a Nitrogen gas mixture, the liquid Nitrogen is pumped from the Nitrogen storage tanks at the rate of say 1000 scf/min. And then mixed with the Helium which is pumped by the Helium boost pump at the rate of 10 scf/min supplied from a quad of Helium cylinders. To carry out the leak testing, all flanges are taped so that any gas leaking past the gaskets or seals is collected in the space between the outer edge of the gasket and the tape. Leak detection is performed by puncturing the tape with the remote probe. This in turn is connected to the portable Helium mass spectrometer. Hence, any Helium gas that has collected beneath the tape is sampled, detected, and quantified.Nitrogen/Helium leak testing offers the advantages of reducing the oxygen content of a process plant; systems are tested close to their operating pressure; all leaks are detected and repaired before usage; and an inert nitrogen blanket can be left in the system before start-up