ASME B16.5 · Material Group 1.1 · Carbon Steel
Find the maximum allowable working pressure for a flange class at a given operating temperature.
Classes per ASME B16.5: 150, 300, 400, 600, 900, 1500, 2500
Understand ASME B16.5 pressure-temperature ratings and material group classifications
This calculator uses Material Group 1.1 ratings per ASME B16.5 Table 2-1.1, applicable to:
| Service | Cycles | Factor |
|---|---|---|
| Normal | ≤1,000 | 1.00 |
| Moderate | 1,001–7,000 | 0.80 |
| Severe | >7,000 | 0.67 |
Per ASME B31.3 Para. 300.2, severe cyclic conditions apply when N > 7,000 and stress exceeds 0.8×Sa.
Linear interpolation between tabulated temperatures is permitted per ASME B16.5. Interpolation between pressure classes is not permitted—always round up to the next class.
Pressure ratings for flanges are inversely related to temperature. As operating temperature rises, the material's yield strength decreases, requiring a "derating" of the maximum allowable working pressure. This calculator uses the specific derating factors from ASME B16.5 Table 2-1.1 for Carbon Steel.
| Temp | Cl 150 | Cl 300 | Cl 400 | Cl 600 | Cl 900 | Cl 1500 | Cl 2500 |
|---|---|---|---|---|---|---|---|
| 100°F | 285 | 740 | 990 | 1480 | 2220 | 3705 | 6170 |
| 200°F | 260 | 675 | 900 | 1350 | 2025 | 3375 | 5625 |
| 400°F | 200 | 635 | 845 | 1270 | 1900 | 3170 | 5280 |
| 600°F | 140 | 550 | 730 | 1095 | 1640 | 2735 | 4560 |
| 800°F | 80 | 410 | 550 | 825 | 1235 | 2060 | 3430 |
| 1000°F | 20 | 50 | 70 | 105 | 155 | 260 | 430 |
Source: ANSI/ASME B16.5 · For intermediate temperatures, use calculator above for interpolated values.
Carbon steel flanges above 800°F approach the creep range. For sustained high-temperature service, consider chrome-moly (ASTM A182 F11/F22) or stainless steel (F304/F316) flanges with appropriate material group ratings.
Learn about P-T rating derivation, material groups, and flange selection criteria
Pipe Flanges and Flanged Fittings: NPS ½ Through NPS 24
Valves—Flanged, Threaded, and Welding End
Process Piping (Cyclic Service Requirements)
Carbon Steel Forgings for Piping Applications
ANSI flange pressure ratings are standardized pressure-temperature limits per ASME B16.5. Classes include 150, 300, 400, 600, 900, 1500, and 2500, with actual pressure ratings varying by material group and temperature.
Class 150 flanges have lower pressure ratings than Class 300. At 100°F, Class 150 = 285 psig while Class 300 = 740 psig for carbon steel. The class number doesn't directly equal pressure rating.
Use ASME B16.5 pressure-temperature tables for your material group. Linear interpolation between tabulated temperatures is permitted. As temperature increases, pressure rating decreases due to material strength reduction.
Material Group 1.1 covers carbon steel including ASTM A105 (forgings), A216 WCB (castings), A350 LF2 (low temp), and A515/A516 Grade 70 (plate materials) commonly used in flanges.
Higher temperatures reduce material yield strength and tensile properties. ASME B16.5 incorporates temperature derating factors to maintain safe operation as metals weaken at elevated temperatures.