Saturated or superheated: which one sets your steam hose rating
Saturated steam carries a temperature fixed by its pressure. Superheated steam does not, and that is how a line reading well under 10 bar can still be too hot for a one-braid rubber hose.
Flexihose rubber steam hose: one wire braid 145 PSI / 10 BAR, −40 °C to +195 °C, 1/2" to 2" · two wire braid 250 PSI / 17 BAR, −40 °C to +232 °C, 1/2" to 1-1/4" · EPDM tube and cover · brass-coated steel wire braid
Quick answer
For a rubber steam hose, saturated steam is the simple case: pressure fixes its temperature, so at the one-braid grade’s 10 bar working pressure it sits near 184 °C, inside the +195 °C limit. Superheated steam breaks that link. It can pass +195 °C while the gauge still reads well under 10 bar, so on a superheated line the temperature reading, not the pressure, usually decides the grade.
Most steam hose enquiries we receive give us one number: the pressure. That is enough when the line carries saturated steam, because a steam table turns the pressure into a temperature. It is not enough when the steam is superheated, which is the normal supply for turbines and is sometimes used for process heating in hydrocarbon plants. We make rubber steam hose in two grades, and the difference between them is as much about temperature as pressure. This guide covers how saturated, wet and superheated steam differ, why superheat can take a hose past its temperature rating first, how to read your line at the hose point, and what to do when conditions fall outside the rubber range.
How saturated, wet and superheated steam differ at the hose
All three are the same water vapour. What separates them is where they sit against the boiling point for their pressure, and that position decides whether a pressure gauge alone can tell you how hot the hose will get. Spirax Sarco’s engineering pages define all three and are our reference throughout (Spirax Sarco, What is steam).
Three steam conditions and what each one means for a rubber steam hose.
| Condition | Temperature at a given pressure | What the gauge tells you | Typical source | For the hose |
|---|---|---|---|---|
| Wet steam | At the saturation temperature, carrying water droplets. Spirax Sarco gives an example of steam at 6 bar g with a dryness fraction of 0.94, meaning 6% water by mass. | Enough. Temperature follows pressure. | Any main that loses heat on its way to the user | Read pressure |
| Dry saturated steam | Exactly the boiling point for its pressure: 170 °C at 7 bar g in the Spirax Sarco table. | Enough. A steam table gives the temperature. | Boilers without a superheater, and most process heating lines | Read pressure |
| Superheated steam | Above the saturation temperature, by any amount. No fixed link to pressure. | Not enough. You must measure temperature. | Superheater outlets, turbine supply mains, and steam after a large pressure drop | Read both |
Definitions and the 0.94 dryness example: Spirax Sarco, What is steam. Superheater: the Boilers Act, 2025, s.2(d), defines it as equipment that raises steam "beyond the saturation temperature at that pressure". Pressure drop as a source of superheat: Spirax Sarco, Superheated steam, Example 2.3.5.
Wet and saturated steam behave the same way for hose selection: both sit at the saturation temperature, so pressure is the only number you need. Wet steam matters for other reasons. The water it carries is condensate, and our EPDM tube is chosen because it holds up in both steam and the hot condensate that forms with it.
Superheated steam is different in kind. Spirax Sarco notes that it has no direct temperature to pressure relationship, so at one pressure it can exist over a wide range of temperatures. It is the steam a turbine wants, and Spirax Sarco observes that hydrocarbon processing plants sometimes use it for process heating simply because it is already on site from power generation, even though saturated steam transfers heat better (Spirax Sarco, Superheated steam). That is one route by which superheat can reach a hose station in a refinery.
The saturation figures below are the ones we use in the rest of this guide. Each comes straight from a published steam table, and the source column says which.
Saturation temperature by gauge pressure, read from two published steam tables.
| Gauge pressure | Saturation temperature | Against the rubber grades | Table |
|---|---|---|---|
| 0 bar g | 100 °C | Inside both | Spirax Sarco |
| 3 bar g | 144 °C | Inside both | Spirax Sarco |
| 5 bar g | 159 °C | Inside both | Spirax Sarco |
| 7 bar g | 170 °C | Inside both | Spirax Sarco |
| 145 psig (10.0 bar g) | 363.4 °F (184.1 °C) | One-braid pressure limit, 11 °C under its +195 °C ceiling | Milwaukee Valve |
| 190 psig (13.1 bar g) | 383.7 °F (195.4 °C) | Saturated steam only reaches +195 °C here, above the one-braid pressure limit | Milwaukee Valve |
| 250 psig (17.2 bar g) | 406.0 °F (207.8 °C) | Two-braid pressure limit, about 24 °C under its +232 °C ceiling | Milwaukee Valve |
0 to 7 bar g: Spirax Sarco Table 2.2.2, What is steam. psig rows: Milwaukee Valve steam temperature pressure table (Rev 01/18), printed in psig and °F; our conversions use 1 bar = 14.504 psi and °C = (°F − 32) / 1.8. Highlighted rows fall on our published working pressures of 145 PSI and 250 PSI.
Why superheated steam can push a steam hose past its temperature rating before its pressure rating
Start with saturated steam, because it shows why the problem never arises there. Our one-braid grade is rated 145 PSI / 10 BAR and +195 °C. Saturated steam at 145 psig is 184.1 °C by the Milwaukee Valve table, so a saturated line at full rated pressure is still 11 °C under the temperature ceiling. Saturated steam does not reach 195 °C until about 190 psig, which is 13.1 bar g and already over the pressure rating. The same holds one grade up: at 250 psig saturated steam is 207.8 °C, well inside the two-braid ceiling of +232 °C. On saturated service, pressure always runs out first, and the published pressure rating is the only limit you are likely to meet.
Superheat removes that safety net. Because its temperature is free of its pressure, a superheated line can sit at a comfortable gauge reading and still be hotter than a grade allows. A buyer who orders on pressure alone will choose the one-braid grade, and the hose will run above its temperature rating from the first day.
1. A worked example at 7 bar g
Take a hose point downstream of a reducing station where the gauge reads 7 bar g and a thermometer on the line reads 210 °C. That reading is an illustration we have chosen for the arithmetic, not a measurement from any plant. Everything else in the example comes from the published tables.
- Step 1Look up saturation7 bar g saturates at 170 °C (Spirax Sarco).
- Step 2Find the superheat210 − 170 = 40 °C above saturation.
- Step 3Check pressure7 bar is under 10 bar. The one-braid grade passes.
- Step 4Check temperature210 °C is over +195 °C. The one-braid grade fails.
- ResultTwo-braid gradeInside 17 bar and +232 °C, in 1-1/4" or smaller.
Saturation temperature from Spirax Sarco Table 2.2.2. The 210 °C line reading is illustrative. Grade limits from the FLEXI HOSE Product Catalogue 2026-2027.
The pressure check in step 3 passes with room to spare, which is exactly why this case catches people out. The 40 °C of superheat is what fails the one-braid grade. If the bore needed is 1-1/2" or 2", the two-braid grade is not catalogued in those sizes, so the answer is a conversation with us before ordering, not a larger one-braid hose.
2. The chart that shows both limits at once
The figure below puts the two grade envelopes on one plane with the saturation curve drawn through the table points above. Saturated steam can only ever sit on that curve, and the curve leaves the one-braid box through its top edge, the pressure limit, never through its right edge. Superheated steam sits anywhere to the right of the curve, and that is the only way to reach the right-hand edge of either box below its pressure limit.
Hose grade envelopes against the saturation curve. Points to the right of the curve are superheated.
- 17 bar g, 170 °C. Saturated, from Spirax Sarco Table 2.2.2, as are the small points from 0 to 6 bar g.
- 2145 psig (10.0 bar g), 184.1 °C. Saturated steam at the one-braid working pressure, inside the box.
- 3190 psig (13.1 bar g), 195.4 °C. Where saturated steam first reaches +195 °C, already above 10 bar.
- 4250 psig (17.2 bar g), 207.8 °C. Saturated steam at the two-braid working pressure.
- 5Worked example, 7 bar g at 210 °C. An illustrative reading 40 °C to the right of point 1: out of the one-braid box, inside the two-braid box.
- 60 bar g (1.013 bar a) at 250 °C. A state listed in Spirax Sarco’s superheated steam table. Zero gauge pressure, yet hotter than both rubber grades.
Envelopes: FLEXI HOSE Product Catalogue 2026-2027. Saturation curve drawn only through the listed table points: Spirax Sarco Table 2.2.2 (0 to 7 bar g) and the Milwaukee Valve table (points 2 to 4, converted from psig and °F). Point 6: Spirax Sarco superheated steam table at 1.013 bar a. Point 5 is an illustration, not a table value.
3. Point 6 is the warning
Spirax Sarco’s superheated table lists steam at atmospheric pressure, 1.013 bar a or 0 bar g, at 200 °C and at 250 °C. The gauge on such a line would read zero. A hose rated by pressure would look massively over-specified, yet 250 °C is beyond our two-braid ceiling of +232 °C and close to PTFE’s catalogued limit of +260 °C. Low pressure is not evidence of a mild duty once superheat is possible.
This is the reason we ask for the temperature and the steam type alongside the pressure on every enquiry. If you want to see how the two rubber grades are built and where each one is used, our steam hose page lists both with their mean outside diameters, and our guide to the types of steam hose sets them beside the other hose families.
Reading your line conditions at the hose point
The numbers that matter are the ones at the hose coupling, not at the boiler and not on the design sheet for the main. Four checks give you a reading you can order against.
1. Read the gauge after any reducing station
A hose fed through a reducing valve sees the downstream pressure. Note whether the figure is gauge or absolute. Spirax Sarco points out that saturated steam tables generally give gauge pressure while superheated tables give absolute pressure, so 0 bar g in one table is 1.013 bar a in the other. Mixing them shifts your saturation temperature by several degrees.
2. Measure the temperature on the line
Do not infer temperature from pressure unless you know the steam is saturated. A thermometer or temperature transmitter close to the hose point settles it. Compare the reading with the saturation temperature for your gauge pressure from a steam table. If the reading is higher, the steam is superheated by the difference.
3. Expect superheat after a large pressure drop
Reducing pressure can create superheat even from steam that started slightly wet. Spirax Sarco’s Example 2.3.5 takes steam with a dryness fraction of 0.98 from 10 bar g down to 1 bar g and finds it superheated at 136 °C against a saturation temperature of 120 °C (Spirax Sarco, Superheated steam). The same physics applies at higher pressures, which is why a hose station below a big reducing valve deserves a thermometer.
4. Record the worst case, not the average
Readings at start-up, at changeover or during an upset can differ from the normal running figure. Send us the highest pressure and the highest temperature the hose point can see, with the steam type. That pair, not the running average, decides the grade.
- ReadGauge pressureDownstream of any reducing valve. Note bar g or bar a.
- MeasureLine temperatureAt or near the hose point, not inferred.
- CompareAgainst the tableHigher than saturation means superheated.
- SendThe worst-case pairHighest pressure, highest temperature, steam type.
Gauge and absolute convention, and Example 2.3.5: Spirax Sarco, Superheated steam.
When steam conditions fall outside a rubber steam hose’s range
Our two rubber grades together cover up to 250 PSI / 17 BAR and +232 °C. Beyond that, or in bores we do not catalogue at the grade you need, the answer changes. We would rather tell you that than sell a hose that runs past its rating.
Where the rubber range ends, and what we suggest instead.
| Your condition at the hose | Rubber steam hose | What we suggest |
|---|---|---|
| Above +195 °C, up to +232 °C, bore 1-1/4" or less | Two-braid grade | The two wire braid grade, provided pressure is within 17 BAR. |
| Above +195 °C, bore 1-1/2" or 2" | Not catalogued | Enquire before ordering. We do not quote the two-braid grade in these bores. |
| Above +232 °C, up to +260 °C | Outside range | PTFE hose, catalogued −65 °C to +260 °C, with pressure read at your bore: 250 BAR at 1/8" down to 30 BAR at 2". |
| Above 17 BAR | Outside range | PTFE hose, rated 30 BAR even at 2", or stainless steel corrugated hose rated at your size and confirmed at your temperature. |
| Bore above 2" | Outside range | Stainless steel corrugated hose to EN ISO 10380, 6 to 150 mm. The catalogue prints no service temperature, so we confirm it against your duty. |
All figures from the FLEXI HOSE Product Catalogue 2026-2027. Rubber grades exceed IS 10655 Type 2 and Type 3; neither holds a BIS licence.
Two cases fall outside every rubber steam hose regardless of temperature. Hot oil and thermal fluid lines attack EPDM, so they need a different product even at modest temperatures. A fixed main, superheated or not, should be rigid pipe; a hose is not a substitute for fixed piping. Our guide to rubber versus stainless steel steam hose compares the three hose families in more depth for the duties where rubber is close to its limits.
Measure the temperature at the hose before you choose a steam hose grade
On saturated steam, the pressure rating is the limit you will meet first, and a steam table proves it. On superheated steam, temperature can cross the one-braid ceiling while the gauge reads 7 bar, or even zero. Read the gauge, measure the line, compare it with the table, and send us the worst-case pair with the bore. We will tell you which steam hose grade fits, or that neither rubber grade does. That is how we work at Flexihose.
FAQ
What are the hazards associated with steam?
Burns are the main hazard, and steam holds far more heat than its temperature suggests. Spirax Sarco's table gives saturated steam at 7 bar g about 2,048 kJ of latent heat per kilogram, released as it condenses, on top of 721 kJ in the hot water. A hose failure releases that energy at once.
What are the three types of steam?
Wet, saturated and superheated. Wet steam carries water droplets: Spirax Sarco's example at 6 bar g has a dryness fraction of 0.94, meaning 6% of the mass is water. Saturated steam holds no water and sits exactly at its boiling point. Superheated steam has been heated beyond that point.
How do you know if a steam is superheated or saturated?
Measure the pressure and the temperature at the same point, then look up the saturation temperature for that pressure in a steam table. A reading at the table figure is saturated steam; a higher reading is superheated. Check whether the table uses gauge or absolute pressure before comparing the two numbers.
What is the difference between saturated vapor and superheated vapor?
Saturated vapour is at the boiling point for its pressure, so any heat it loses turns some of it straight into water. Superheated vapour must first lose its superheat. Spirax Sarco shows steam throttled from 10 bar g to 1 bar g arriving at 136 °C, against 120 °C saturation at that pressure.
What is the temperature range of a steam hose?
It depends on the grade. Our one wire braid steam hose is rated from minus 40 °C to plus 195 °C, and the two wire braid grade from minus 40 °C to plus 232 °C. ISO 6134:2024, the international rubber steam hose specification, sets its two types at 164 °C and 210 °C.
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