Use Nitrogen Cylinders Without Pressure Regulator

No personal N2 purge experience, but I would advise you use a pressure regulator anyway to reduce potential risks. That and ensure you are safely venting the natural gas into an open, safe area to mix and dissipate into the atmosphere safely away from people and ignition sources.

on EVERY gas piping system that we have has a regulator to control pressure, an in-line orifice to control maximum flowrate, and a pressure relief valve set below the burst limit of the weakest link in the system.

just some of the questions our safety team would ask before a safety permit for the procedure would be issued:

piping diameter? what material it the pipe and "hose" is made of? pressure ratings? what is the vessel that you are purging this much nitrogen into made of? what is pressure rating of the tank/room being purged? is the tank/room pressure tested on a periodic basis and when was it last tested? how large is the exhaust port (which could be considered a system orifice for this much flow)? does the tank have a rupture disc and what pressure is it rated for?

the only thing that i can think of that is similar to a system that you are talking about would be a hood fire suppression system, i haven't looked at these systems very carefully but i would assume they have an orifice set to the exhaust rate of the room/hood at the very least, but i do not know.

without anymore info, i would not get near this setup.

Thank you all for your replies.

piping diameter: 24" , piping is a part from gas transportation system

piping material: API 5L X65M PSL2, wt 14,27mm

hose material: synthetic rubber reinforced with steel wires, hose nominal dia: 1/2"

no vessel, only piping is being purged

no periodic pressure test is required for piping, working pressure is typically 45 bar

exhaust port is 2"

My main worries is about the freezing. Could the low temperature make the shut off valve unable to operate, or the hose fail?

It's no good asking a bunch of anonymous strangers on the internet, as none is liable if the procedure goes wrong.

The questions above need to be asked of the individuals involved in the activity instead. If unwilling to do so, then walk away from it, and FFS don't sign anything!

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I would be concerned first about ventilation of the area...second I would be concerned about the pressure in the tank if a rupture in the purge line should occur...Yes and the valve freezing in open position, or ice accumulation in the line someplace causing a blockage...Definitely need a pressure gauge on the tank outlet, and would like one at the end of the pipe...would be good to monitor the tank outlet for frost, and throttle back if necessary...Emergency oxygen available, just in case....

...is the right answer.

I don't understand why you need to purge at such a high rate?

there are many standard techniques to purge a system, i am no expert in fast purging.

Mr. Bernoulli has a principal that you may work to your advantage using less nitrogen. but you would need a port on the nitrogen side of the system for atmosphere to enter.

and for your valve, there are cryogenic valves that will work, you may want to investigate that option?

The piping is not one simple pipe. There are pipe branches (diameter 24") , and so we cannot rely on letting gas in from one point (diameter 1/2") and getting it out from an other point (diameter 2"), because that would let all the "blind" branches almost without purging. So dilution by pressurising and depressurising (by venting to atmosphere) is more effective to remove the gas from "blind" branches and to ensure that the gas concentration will be lower than e.g. 20 %LEL (which is the target)

The available time for this operation is limited to about 8 hour, hence the need for high flow rate.

When you disconnect each N₂ cylinder to attach the next, air from the large pipe will flow back through the hose, unless there is another valve. If there is, then the hose/piping between the two valves could conceivably be exposed to 200 bar, say if someone forgets to open the downstream valve before the cylinder valve.

Even so, I doubt that the expressed fears are justified. The hose and any small piping to the large pipe will get cold, but the N₂ inside won't freeze.

If the price of a regulator is a problem, consider renting one.