Furnace and exhaust duty is heat, movement and grit at almost no pressure at all. That combination has exactly one good answer, and it is the one product on this site that is deliberately not pressure-tight.
What this service does to a hose
The heat is obvious. What is less obvious is that a corrugated hose loses most of its pressure rating long before it reaches its temperature limit — at 550 °C a 304L assembly is working at about 43 % of its cold rating. On a duty that carries no pressure, paying for that rating and then losing it makes no sense.
Then there is the particulate. Flue gas, foundry extraction and kiln exhaust all carry solids, and solids erode a corrugation valley from the inside until the wall is thin enough to split. Interlock does not have that problem in the same way because it has no valleys to scour.
Finally there is the movement, which on hot ducting is large, slow and repeated. A strip-wound hose absorbs it kinematically — the coils slide over one another — rather than by stretching a membrane, so it does not fatigue the way corrugated does.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | Helical strip-wound interlock, DN6–DN200 | Kinematic flexibility, and no valleys for grit to scour |
| Grade | SS 304 to 700 °C; SS 321 to 800 °C | 321 is titanium-stabilised, which is why it goes higher |
| Packing | Ceramic, cotton or none, chosen against temperature | Packing is what actually limits the assembly, not the strip |
| Ends | Welded or flanged to suit the ducting | It is a duct connection, not a process joint |
What we would not fit, and what happens
A braided corrugated hose, unless the line genuinely holds pressure. It costs more, it flexes less, and at these temperatures the thing that kills it is thermal fatigue at the crest, not pressure.
304L held for long periods above about 450 °C where the medium is aggressive. Sustained heat in that band precipitates chromium carbides at the grain boundaries and leaves the material open to intergranular attack. That is what 321 exists to solve, and it is covered on the material grades page.
What we need to size it
| We need | Because |
|---|---|
| Gas temperature, continuous and peak | The peak decides the grade; the continuous decides the packing |
| What is in the gas | Particulate, sulphur and chlorides each change the answer |
| Movement — how much, in which direction, how often | Interlock takes lateral and angular well, axial poorly |
| Whether any pressure is present at all | If yes, this may be the wrong family entirely |
| Duct size and how it is connected | Weld, flange or clamp, and the mating face |