Valve Pressure-Temperature Rating Chart: ASME B16.34 & EN PN Quick Reference
Quick Answer
A valve pressure-temperature rating defines the maximum allowable working pressure at a given temperature for a specific material and class. For ASME B16.34, Class 150 carbon steel is good for about 285 psig at 100 deg F but only about 80 psig at 800 deg F. EN standards express the same concept as PN (e.g. PN 16, PN 40). Pick the class or PN that covers your worst-case pressure and temperature combination, and apply the material correction factor for alloys other than carbon steel.
Why Pressure-Temperature Ratings Matter
The body of a valve does not fail because of pressure alone. It fails when pressure and temperature together exceed the material allowable stress. As temperature rises, the allowable working pressure falls. A valve rated Class 300 at ambient temperature may be overstressed if you apply the same pressure at 600 deg F. Reading the rating chart correctly is the difference between a safe spec and a field failure.
ASME B16.34 Class Rating Chart — Carbon Steel (Group 1.1)
The table below shows allowable working pressures in psig for Group 1.1 carbon steel (A105, WCB, WCC) by ASME B16.34 class. This is the most common reference for North American steel valves.
| Temperature (deg F) | Class 150 | Class 300 | Class 600 | Class 900 | Class 1500 | Class 2500 |
|---|---|---|---|---|---|---|
| 100 | 285 | 740 | 1480 | 2220 | 3705 | 6170 |
| 200 | 260 | 675 | 1350 | 2025 | 3375 | 5625 |
| 300 | 230 | 655 | 1310 | 1965 | 3275 | 5460 |
| 400 | 200 | 635 | 1270 | 1905 | 3180 | 5300 |
| 500 | 170 | 600 | 1200 | 1800 | 3000 | 5000 |
| 600 | 140 | 550 | 1100 | 1650 | 2750 | 4585 |
| 650 | 125 | 535 | 1070 | 1605 | 2675 | 4460 |
| 700 | 110 | 500 | 1000 | 1500 | 2500 | 4165 |
| 750 | 95 | 450 | 900 | 1350 | 2250 | 3750 |
| 800 | 80 | 370 | 740 | 1110 | 1850 | 3100 |
| 900 | 50 | 270 | 540 | 810 | 1350 | 2250 |
| 1000 | 20 | 165 | 330 | 495 | 825 | 1375 |
Note: Values are representative of ASME B16.34 Group 1.1 carbon steel for comparison. The current edition of the standard governs project specifications. For the full standard background and flange pairings, see our valve standards comparison guide.
Material Group Correction Factors
Carbon steel (Group 1.1) is the baseline. Other materials carry different allowable stresses, so the same class yields a different pressure. Representative multipliers relative to Group 1.1 at 100 deg F:
| Material Group | Example Grade | Relative Allowable |
|---|---|---|
| 1.1 Carbon steel | A105, WCB, WCC | 1.00 |
| 1.2 Low alloy | WC6, WC9 | 0.90 to 1.05 |
| 1.3 Stainless | CF8, CF8M | 0.85 to 1.00 |
| 1.4 High alloy | CN7M, alloy 20 | 0.80 |
| 1.9 Nickel alloy | Alloy 400, Alloy 600 | 0.95 |
These are approximate ratios for orientation. Always use the material-specific table in the current ASME B16.34 edition for the actual allowable pressure.
EN PN Ratings (European System)
European flanges and valves use the PN system. PN roughly corresponds to the pressure in bar at ambient temperature, but like Class ratings, the allowable pressure drops with temperature. Representative PN ratings:
| PN | Approx. max bar at ambient | Common use |
|---|---|---|
| PN 10 | 10 bar | Low-pressure water, HVAC |
| PN 16 | 16 bar | General process, water |
| PN 25 | 25 bar | Process, low steam |
| PN 40 | 40 bar | Higher-pressure process |
| PN 63 | 63 bar | High-pressure, hydraulic |
| PN 100 | 100 bar | Severe service |
Class 150 and PN 20 are close at ambient temperature but not identical, and they diverge as temperature rises. Do not treat them as interchangeable across the full range.
Temperature Conversion Quick Reference
Because standards mix deg F (ASME) and deg C (EN), keep this conversion handy:
- 100 deg F = 38 deg C
- 200 deg F = 93 deg C
- 300 deg F = 149 deg C
- 400 deg F = 204 deg C
- 500 deg F = 260 deg C
- 600 deg F = 316 deg C
- 800 deg F = 427 deg C
How to Select the Right Class
- Identify the worst-case coincident pressure and temperature in your service.
- Read down the temperature row in the chart to the pressure column.
- Choose the lowest class whose allowable pressure at that temperature meets or exceeds your required pressure, with margin.
- Apply the material correction factor if the body is not carbon steel.
- Confirm the flange standard matches the adjacent piping. See our valve standards comparison for flange pairings, and our valve selection guide for type selection.
Common Rating Mistakes
- Using the ambient-temperature class pressure at elevated temperature. The real allowable is far lower.
- Assuming Class 150 equals PN 20 at all temperatures.
- Ignoring the material factor when specifying stainless or alloy bodies.
- Mixing flange ratings between connected components.
Where to Verify Real Product Ratings
Charts are a starting point. For project specifications, confirm actual product pressure-temperature data against the manufacturer data sheet. The ValveSpecs Pro database includes dimensional and pressure-temperature information for more than 1,000 valve products across 90 plus brands. Browse valve specifications by brand to compare real ratings before you specify.
References
This chart references ASME B16.34 pressure-temperature tables, EN 1092 and EN 12516, and manufacturer data sheets. Consult the current edition of the applicable standard for binding values.
Frequently Asked Questions
What is a valve pressure-temperature rating?
A pressure-temperature rating is the maximum allowable working pressure a valve body can sustain at a given temperature for a specified material and class. As temperature rises, the allowable pressure falls because the material strength decreases. Ratings are published in standards such as ASME B16.34 (Class) and EN (PN).
How do I read an ASME B16.34 rating table?
Find the service temperature in the leftmost column, then read across to the pressure class you are considering. The number at that intersection is the maximum allowable working pressure in psig for carbon steel. For other materials, apply the material correction factor from the standard.
What is the difference between Class and PN ratings?
Class (ASME B16.34) and PN (EN) are two ways to express the same idea, allowable pressure at temperature. Class uses named steps (150, 300, 600) in psig at the reference temperature, while PN uses bar at ambient. Class 150 and PN 20 are close at ambient temperature but diverge at higher temperatures, so they are not fully interchangeable.
Does allowable pressure decrease as temperature rises?
Yes. For essentially all valve materials, the allowable working pressure drops as temperature increases because the material loses strength. A Class 300 carbon steel valve rated about 675 psig at 200 deg F is limited to about 165 psig at 1000 deg F.
How do I choose the right valve class for my service?
Take your worst-case coincident pressure and temperature, find that temperature row in the rating chart, and pick the lowest class whose allowable pressure meets or exceeds your requirement with margin. If the body is not carbon steel, apply the material correction factor, and confirm the flange rating matches the connected piping.