Reference charts for valve pressure ratings at operating temperatures. Understand how temperature affects the maximum allowable working pressure for PN and ANSI Class rated valves.
Every industrial valve carries a pressure rating — either a PN (Pression Nominale) rating under European DIN/EN standards, or a Class rating under the American ASME/ANSI system. These ratings define the maximum allowable working pressure of the valve at a specific reference temperature.
As temperature increases, the tensile strength of metallic materials decreases. This means a valve rated at PN40 (40 bar) at 20°C cannot safely operate at 40 bar when the temperature rises to 200°C or above. The pressure must be derated — reduced to a lower maximum allowable working pressure that accounts for the weakened material strength.
The tables below show how pressure ratings decrease across the operating temperature range. Always ensure your system's maximum operating pressure and temperature combination falls within the rated envelope.
The PN number indicates the maximum allowable pressure in bar at the reference temperature of 20°C. For example:
PN ratings are defined by EN 1092-1 (flanges) and the relevant valve product standards.
ANSI/ASME Class ratings are defined by ASME B16.34 and do not directly correspond to a pressure in psi or bar — instead, they define a pressure-temperature envelope. The reference temperature is 100°F (38°C). Common classes include:
Maximum allowable working pressure in bar for carbon steel (ASTM A216 WCB / EN 1.0619) valves at elevated temperatures. Based on EN 1092-1 and EN 12516.
| Temperature | PN10 | PN16 | PN25 | PN40 |
|---|---|---|---|---|
| −10°C to 120°C | 10.0 bar | 16.0 bar | 25.0 bar | 40.0 bar |
| 150°C | 9.5 bar | 15.2 bar | 23.8 bar | 38.0 bar |
| 200°C | 8.9 bar | 14.2 bar | 22.2 bar | 35.5 bar |
| 250°C | 8.0 bar | 12.8 bar | 20.0 bar | 32.0 bar |
| 300°C | 7.1 bar | 11.4 bar | 17.8 bar | 28.5 bar |
| 350°C | 6.3 bar | 10.1 bar | 15.8 bar | 25.2 bar |
Maximum allowable working pressure in bar for stainless steel 316 (ASTM A351 CF8M / EN 1.4408) valves at elevated temperatures.
| Temperature | PN10 | PN16 | PN25 | PN40 |
|---|---|---|---|---|
| −10°C to 120°C | 10.0 bar | 16.0 bar | 25.0 bar | 40.0 bar |
| 150°C | 9.3 bar | 14.9 bar | 23.3 bar | 37.2 bar |
| 200°C | 8.5 bar | 13.6 bar | 21.3 bar | 34.0 bar |
| 250°C | 7.9 bar | 12.6 bar | 19.8 bar | 31.6 bar |
| 300°C | 7.3 bar | 11.7 bar | 18.3 bar | 29.2 bar |
| 350°C | 6.8 bar | 10.9 bar | 17.0 bar | 27.2 bar |
Stainless steel 316 retains a greater proportion of its room-temperature strength at elevated temperatures compared to carbon steel, which is why the derating curve is flatter.
Maximum allowable working pressure in bar for carbon steel (ASTM A216 WCB) and stainless steel 316 (ASTM A351 CF8M) valves. Based on ASME B16.34 Table 2-1.1 and 2-3.1.
| Temperature | Class 150 | Class 300 | Class 600 |
|---|---|---|---|
| −29°C to 38°C | 19.6 bar | 51.1 bar | 102.1 bar |
| 100°C | 17.7 bar | 46.6 bar | 93.2 bar |
| 150°C | 15.8 bar | 43.8 bar | 87.6 bar |
| 200°C | 13.8 bar | 40.7 bar | 81.5 bar |
| 250°C | 12.1 bar | 37.6 bar | 75.2 bar |
| 300°C | 10.2 bar | 34.5 bar | 69.0 bar |
| 350°C | 8.4 bar | 31.0 bar | 62.1 bar |
| Temperature | Class 150 | Class 300 | Class 600 |
|---|---|---|---|
| −29°C to 38°C | 19.6 bar | 51.1 bar | 102.1 bar |
| 100°C | 17.2 bar | 44.8 bar | 89.6 bar |
| 150°C | 15.5 bar | 40.5 bar | 81.0 bar |
| 200°C | 13.8 bar | 36.5 bar | 73.0 bar |
| 250°C | 12.7 bar | 33.4 bar | 66.9 bar |
| 300°C | 11.8 bar | 31.0 bar | 62.1 bar |
| 350°C | 11.0 bar | 29.0 bar | 58.0 bar |
Carbon steel is the most widely used valve body material for high-pressure and high-temperature applications. It offers excellent mechanical strength and is cost-effective. However, carbon steel is susceptible to corrosion in wet or chemically aggressive environments and should not be used for seawater, brine, or acidic media without protective coatings.
Maximum service temperature: Approximately 425°C. Above 425°C, carbon steel is subject to graphitisation, which reduces its structural integrity.
316 stainless steel provides superior corrosion resistance compared to carbon steel, particularly against chloride-bearing media, seawater, and many acids. It retains a greater proportion of its strength at elevated temperatures (note the flatter derating curve in the tables above). It is widely used in chemical processing, food and beverage, pharmaceutical, and marine applications.
Maximum service temperature: Approximately 550°C in non-corrosive environments. However, sensitisation (carbide precipitation) can occur between 450–850°C, reducing corrosion resistance.
For extreme conditions — very high temperatures, highly corrosive media, or sour gas (H₂S) environments — exotic alloys may be required:
UK Valves Direct can source valves in all of these materials. Contact our technical team for lead times and pricing on exotic alloy valves.
The following table provides an approximate cross-reference between DIN/EN PN ratings and ANSI/ASME Class ratings. Note that these are not exact equivalents — the pressure-temperature envelopes differ between standards.
| PN Rating | Approx. ANSI Class |
|---|---|
| PN10 | — |
| PN16 | — |
| PN20 | Class 150 |
| PN50 | Class 300 |
| PN100 | Class 600 |
PN10 and PN16 do not have direct ANSI equivalents. Class 150 most closely aligns with PN20, though flange dimensions differ between EN 1092-1 and ASME B16.5.
Not sure which pressure class or material grade you need? Our technical team can review your system parameters and recommend the correct valve specification.