Steam is the duty where the catalogue number and the real answer are furthest apart. A hose rated 16 bar is not a 16 bar steam hose. On saturated steam the pressure and the temperature are the same variable, so the moment you name the pressure you have also named the derating factor. On a typical header the rating you are actually allowed to use is about two-thirds of the one on the front of the datasheet, and on a superheated line it is less than half.
What this service does to a hose
Saturated steam at 10 barg is at 184 °C. At 16 barg it is 204 °C. You cannot have one without the other, and the stainless does not care which of them you wrote on the enquiry — it loses proof stress at that temperature either way. The derating table puts 316L at 0.62 around 200 °C, so a hose rated 30 bar cold is good for about 18 bar on that line. Size the hose on the cold rating and it is under-specified from the first hour, in a way that will not show up for a year.
The second mechanism is condensate. Steam lines do not carry dry steam — they carry steam with water in it, and that water collects in the corrugation valleys of a hose that sits low or slopes the wrong way. When a slug of it is picked up and driven down the line at steam velocity, the hose sees a pressure spike that has nothing to do with the working pressure. Water hammer is what splits steam hoses, far more often than steady pressure does.
The third is cycling. A steam line that is put on and taken off shift by shift moves a great deal as it heats and cools, and it does so in a hose whose ends are usually bolted to something rigid. That is thermal expansion arriving as a fatigue load. See movement types for how to let it move instead.
What we would fit
| Element | What we would supply | Why |
|---|---|---|
| Hose | 321 annular corrugated where the line cycles hot; 316L where it is steady and below 300 °C | 321 is stabilised, so sustained time in the sensitisation range does not cost it intergranular resistance |
| Braid | Matching grade, sized on the derated pressure | The rating that matters is the hot one, not the catalogue one |
| Liner | Fitted where velocity is high or the line carries wet steam | It keeps the flow off the convolutions and stops condensate pooling in the valleys |
| Ends | Flanged or butt weld; we would avoid threads on live steam | A threaded joint on steam is a maintenance item forever |
| Length | Sized on live length with the hot movement included | The run grows before the hose is asked to flex |
What we would not fit, and what happens
Interlock hose. The seam is mechanical, not welded. It is not pressure-tight and it never was — on steam it simply vents. See interlock construction.
A PTFE liner on high-pressure steam. The PTFE sets a ceiling well below the stainless and steam finds it. Where a smooth bore is genuinely needed, tell us the temperature first and we will say honestly whether it can be done.
A hose that traps condensate. A steam hose looped below the line becomes a water trap. Route it so it drains, and put the trap where a trap belongs.
A worked example
Given. A DN50 assembly on a saturated steam header at 10 barg, so 184 °C. Single-braid 316L is rated 30 bar at 20 °C.
Factor. 316L at 184 °C interpolates to 0.64.
Result. 30 × 0.64 = 19.2 bar, against a line at 10 barg — our ratings are gauge figures, so those numbers compare directly, and there is margin for the swings. If the same line ran at 16 barg and 204 °C the factor falls to 0.62, giving 18.6 bar, and the margin has largely gone. That is the point at which we would move you to double braid rather than argue about it. This is an illustration of the method, not a rating for your line — send us the duty and we will work it properly.
What we need to size it
| We need | Because |
|---|---|
| Steam pressure, and whether it is saturated or superheated | On saturated steam the pressure tells us the temperature; on superheated it does not |
| Superheat temperature where applicable | This is the number the derating runs on |
| Whether the line hammers, surges or is quick-valved | Halve the working pressure before anything else |
| How often it is put on and taken off | Daily cycling is a fatigue duty, not a static one |
| Flow velocity, or bore and flow rate | Above 45 m/s the bore needs a liner |
| End connections and whether the ends are anchored | Anchored ends mean the movement has to go into the hose |
Check it yourself
The derating calculator takes the grade and the temperature and returns the factor and the derated pressure, from the same table we quote from. The thermal expansion calculator will tell you how far the run grows.