The short answer
Nitrogen is used wherever oxygen has to be excluded. Its major applications are purging and inerting vessels and pipelines, blanketing flammable and oxidisable liquids, modified-atmosphere food packaging, assist gas for laser cutting, controlled-atmosphere heat treatment, pressure and leak testing, and pneumatic service where dry inert gas is specified.
The common thread is chemical inertness. Nitrogen makes up 78% of the air we breathe and reacts with essentially nothing at ordinary temperatures, so introducing it is the simplest way to remove oxygen from a space without introducing a new hazard.
Purging and inerting
Before a vessel, reactor or pipeline is opened for maintenance — or started up afterwards — the flammable or oxygen-bearing atmosphere inside must be displaced. Nitrogen is the standard medium because it neither burns nor supports burning.
On flammable-gas plant this is not optional. An acetylene plant is purged with dry nitrogen and never with air, because compressing an acetylene-air mixture is hazardous at any pressure. The purge is verified by sampling at the outlet and testing for residual oxygen before the plant is started.
Blanketing and padding
- ✓Storage tanks holding flammable solvents and fuels — a nitrogen layer above the liquid keeps the vapour space out of its flammable range
- ✓Edible oils, which oxidise and go rancid on contact with air
- ✓Resins, adhesives and paints that skin or cure prematurely when exposed to oxygen
- ✓Pharmaceutical intermediates and fine chemicals sensitive to oxidation
- ✓Transformer oil and other insulating fluids
Food and beverage
Modified-atmosphere packaging replaces the air in a pack with nitrogen — sometimes alongside carbon dioxide — so the product does not oxidise and the pack keeps its shape. This is why a bag of crisps is inflated: the nitrogen is both preservative and cushioning.
Nitrogen also blankets beverages during filling to keep oxygen out of the bottle, purges lines between production runs, and provides dispense pressure where CO₂ alone would over-carbonate. Food-grade nitrogen is a distinct product from industrial nitrogen, supplied to food-contact requirements.
Laser cutting and metalworking
Nitrogen is the assist gas of choice for laser cutting stainless steel and aluminium. Because it is inert, the cut edge comes out clean and bright with no oxide layer — which means no secondary cleaning before welding or finishing. Cutting the same material with oxygen assist is faster and cheaper but leaves an oxidised edge.
In heat treatment, nitrogen-based controlled atmospheres allow bright annealing, sintering and hardening without scaling the surface of the work.
The full range of applications
| Application | Why nitrogen | Typical grade |
|---|---|---|
| Purging and inerting vessels | Displaces oxygen without introducing a fire hazard | Industrial 99.5%+ |
| Tank blanketing | Keeps the vapour space below the flammable range | Industrial |
| Laser cutting assist | Oxide-free cut edge on stainless and aluminium | High purity 99.99%+ |
| Modified-atmosphere packaging | Stops oxidation and supports the pack | Food grade |
| Bright annealing / heat treatment | Prevents surface scaling | High purity |
| Pressure and leak testing | Inert test medium | Industrial |
| Beverage dispense and blanketing | Pressure without over-carbonation | Food grade |
| Analytical carrier gas | Unreactive baseline for instruments | Ultra-high purity 99.999% |
| Tyre inflation | Dry and inert — stable pressure, no internal corrosion | Industrial |
| Fire prevention in coal and grain handling | Reduces oxygen below the level supporting ignition | Industrial |
| Electronics manufacture | Oxide-free soldering and reflow | High to ultra-high purity |
| Cryogenic freezing (as liquid) | Very rapid freezing at −195.8 °C | Food grade liquid |
Choosing the grade
Over-specifying nitrogen purity is one of the most common ways an industrial gas budget is wasted. Purging and blanketing rarely need better than standard industrial grade. Laser cutting and bright annealing do need high purity, because residual oxygen shows directly on the work. Analytical instruments need ultra-high purity because they measure at the level the impurities sit.
Tell your supplier the application rather than a purity figure, and let the specification follow from it.