Hazards From Low Dew Point Nitrogen?

It depends upon the materials and whether or not they have been correctly selected.

What piping standards are in use, please?

Are you under the impression that the system has to be OK for temperature minus 40° C ? That's probably not the case. Dewpoint is the temperature to which the gas has to be cooled for dew to form. It gives a measure of the water vapour content, the lower the dewpoint the drier the gas. It's not the actual temperature.

You need to consider the actual pressure and temperature to determine material selection.

Codey

Nitrogen is a generally inert gas and will not react with any of the materials in your pipe. It is safe to use as long as you remember that if you breath it exclusively you will die of suffocation.

Thank you all for your answers.

The general piping standard is B31.8.

I should explained it earlier. What makes me ask this question is that having so low humidity in the N2, may be considered as relatively big (bigger than usual) differential concentrations of humidity in areas that are near fluids (atmosphere air, other proccess gases) with higher humidity. Could that be a problem?

Could a non-metallic material, for example, be "dehydrated" and loose some of its functionality?

Normally the specifications of non-metallic material (gaskets, o-ring, membrans, teflon, etc) say nothing about the low limit of the humidity, so that's why I ask this.

How can your dry nitrogen be "near" other gases? They're either separate or mixed, as far as I can see.

But I'd be surprised if there's a problem. Though you still haven't told us the pressure and temperature.

By "near" I mean areas where dry N2 is separated from other fluids by a thin piece of no-metallic material, for example, flanged joints, o-ring sealings, membrane of relief valves.

The nitrogen network has design temperature from -24 to 80 deg C, and design pressure 11 bar.

Absolutely no risk. As I have earlier mentioned, you can treat it like air inside the pipe or buffer vessels. Specifications do not specify about the low limit of the humidity because lower humidity is always better for most of the materials.

OK thanks. Need to ensure the materials are good for the temperature range, the -24°C is likely to be the limiting condition, but nothing directly to do with the nitrogen and its dryness.

Codey

"Could a non-metallic material, for example, be "dehydrated" and loose some of its functionality?"

No, most properties of non-metallics improve as they get drier, especially electrical properties. One of the reasons for using dry gas backfill is to lower the dew point of all the gas trapped in the pipe so there will be no condensation when the pipe temperature drops.

One non-metallic material that is affected by humidity is polyamide (nylon). Different types (6, 6/6, etc) are affected to differing degrees. It will take up and release water from whatever service atmosphere it is in. It is plasticized (softened) by water, so will be more brittle at low humidity. This is not normally an issue in a static condition. It normally surfaces as an issue during assembly or during dynamic loading/unloading. I am not familiar with plumbing specifications, so I don't know if this is a material you would encounter.