Nitrogen and argon are inert, dry and unreactive. Nothing in an assembly is under chemical attack and the pressures are ordinary. These lines still fail, and when they do it is almost always because something got in — air through a joint, moisture from a badly purged line, or particulate from an assembly that was never cleaned. On inert gas duty the hose is not protecting itself, it is protecting the process on the other end.
What this service does to a hose
Ingress, not egress. On most duties on this site a leak is product going out. On a blanketing or shielding line at low pressure it is often air coming in, and a few hundred parts per million of oxygen is enough to discolour a weld, spoil a blanket or ruin a heat treatment. That makes joint quality and permeability the specification even though the pressure is low.
Moisture. A line that has stood open collects water vapour on its internal surface, and the corrugation valleys of an unlined hose have a great deal more internal surface than a tube of the same bore. On dry-gas duty that surface has to be purged out, and it takes longer than people expect. Where dryness is specified to a dewpoint, tell us — it changes how the assembly is cleaned, dried, capped and packed.
Particulate. Shielding gas carries whatever is in the line to the weld pool. An assembly that was cut, braided and ferruled in an ordinary workshop and then fitted straight to a welding line will deliver its own manufacturing debris into the first few welds.
Asphyxiation. Inert gas displaces air, and it does so without any warning property at all. In a confined space that is the actual hazard on this duty; it is not a hose issue, but it is the reason a leak here is taken seriously.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 316L annular corrugated. 304L where cost matters and the environment is dry and indoor | Neither gas attacks either grade |
| Braid | 304 wire, single braid at cylinder-header pressures and below | Pressure is rarely the constraint; check it against the pigtail page for cylinder duty |
| Ends | Metal-to-metal seal faces or welded, in preference to threads with tape | Threads and tape are an ingress path and a particulate source |
| Cleaning | Degreased, dried and capped where a dewpoint or purity level is specified | The internal surface of a corrugation holds far more moisture than a tube |
| Packing | Capped both ends and not opened until fitting | An assembly cleaned and left on a bench is no longer clean |
What we would not fit, and what happens
Interlock hose. Not pressure-tight, so it leaks both ways.
PTFE tape on a joint feeding a dry or high-purity line. It sheds, and what it sheds ends up in the process.
An uncapped assembly delivered for a dry-gas duty. It arrives wet inside and nobody will know until the dewpoint reading is wrong.
An ordinary production assembly on a semiconductor or analytical line. That is a high-purity duty and it is built differently.
What we need to size it
| We need | Because |
|---|---|
| Gas and what it is doing — purge, blanket, shielding, instrument feed | It decides how much of the cleanliness specification you need |
| Working pressure, and whether it is cylinder-fed or from a bulk vessel | Cylinder-fed means the pigtail question upstream of the regulator |
| Any dewpoint or purity specification | It changes the cleaning, drying and packing route |
| Whether the line feeds a weld or an analyser | Particulate and moisture become the acceptance criteria |
| Bore and flow rate | So the assembly is not throttling the supply |
| End connections at both ends | Metal-face fittings if purity matters, threads if it genuinely does not |