wbic1:
You have not stated what unit operation you are referring to. I have stated that I suspect you are referring to a pipe (and/or vessel) purging operation where you are using an inert gas (nitrogen) to "sweep" away and out any hydrocarbon vapors residing in the system in order to avoid a flammable/explosive atmosphere. This would allow you to have a subsequent inspection and/or repair of the system. Am I correct? Or are you referring to something else? Please be explicit, because we don't need to waste time, words, and effort on something that is that simple and direct.
I have used steam in the past to purge out hazardous gases from a piped system. I've used steam in order to economize. A nitrogen sweep can be expensive if the system is relatively large. However, in using steam you will create a lot of water condensate within the system and you will subject the entire system to a heat-up - which will necessitate a cool-down. Subsequent water removal is always a problem - and sometimes may not be tolerated or allowed.
I still don't understand why you persist in using the term "barrier". There is no such thing as a barrier in a purging operation. I have a problem visualizing how one can "maintain a positive pressure differential between the nitrogen and another gas". What do you mean by "blocking out hydrocarbon gas in piping"? How is this done? Why don't you just tell us what the actual operation is?