Class 300 Flange Temperature Derating
Class 300 flange temperature derating refers to the reduction in maximum allowable pressure as the operating temperature increases above ambient. At room temperature, a Class 300 ASTM A105 carbon steel flange is rated for 740 psig (51.0 barg). At 750°F (399°C), this drops to 505 psig—a 32% reduction. At 1,000°F (538°C), the carbon steel rating falls to just 170 psig, while stainless steel grades retain significantly more capacity.
Class 300 Flange Derating Table
| Temperature | A105 (Group 1.1) | A182 F304 (Group 2.1) | A182 F316 (Group 2.3) | A182 F11 (Group 1.9) |
|---|---|---|---|---|
| -20 to 100°F (-29 to 38°C) | 740 psig | 720 psig | 720 psig | 750 psig |
| 200°F (93°C) | 675 psig | 620 psig | 620 psig | 750 psig |
| 400°F (204°C) | 635 psig | 510 psig | 530 psig | 720 psig |
| 500°F (260°C) | 600 psig | 465 psig | 505 psig | 705 psig |
| 600°F (316°C) | 550 psig | 430 psig | 480 psig | 685 psig |
| 700°F (371°C) | 535 psig | 400 psig | 455 psig | 670 psig |
| 750°F (399°C) | 505 psig | 385 psig | 440 psig | 660 psig |
| 800°F (427°C) | 410 psig | 365 psig | 430 psig | 650 psig |
| 900°F (482°C) | 270 psig | 335 psig | 395 psig | 580 psig |
| 1,000°F (538°C) | 170 psig | 310 psig | 345 psig | 450 psig |
Values from ASME B16.5-2020. A182 F11 is a 1.25Cr-0.5Mo alloy steel used in high-temperature service.
Derating Percentage from Ambient Rating
| Temperature | A105 Derating | F304 Derating | F316 Derating |
|---|---|---|---|
| 200°F | -8.8% | -13.9% | -13.9% |
| 400°F | -14.2% | -29.2% | -26.4% |
| 600°F | -25.7% | -40.3% | -33.3% |
| 800°F | -44.6% | -49.3% | -40.3% |
| 1,000°F | -77.0% | -56.9% | -52.1% |
Carbon steel (A105) loses pressure capacity faster than stainless steel grades at elevated temperatures. Above 800°F, the difference is dramatic: A105 retains only 23% of its ambient rating, while F316 retains 48%.
Key Observations
Carbon steel threshold: For A105 flanges, the derating curve steepens above 750°F due to the rapid decline in carbon steel tensile strength at high temperatures. Class 300 A105 flanges are generally not recommended for continuous service above 800°F.
Stainless steel advantage: A182 F304 and F316 flanges maintain a significantly higher percentage of their ambient rating at elevated temperatures, making them the preferred choice for high-temperature applications such as steam systems and thermal oil loops.
Alloy steel for extreme temperatures: For service above 900°F, chrome-moly alloy steel flanges (A182 F11, F22) offer the best combination of strength retention and cost. These materials are specifically designed for elevated-temperature creep resistance.
Leave a Comment
Have a question or feedback? Send us a message.