ASME B16.5 Flange Pressure Class Rating Reference
Class 150, 300, 600 and so on are pressure classes, not pressure values. The allowable pressure depends on material group and temperature. This table gives the ambient values buyers and engineers look up most often.
| Material group | Typical material | Class | Rating at 38 C (psi) | Rating at 38 C (bar) | Shell test, 1.5 x (psi) |
|---|---|---|---|---|---|
1.1 | A105, A216 WCB | 150 | 285 | 19.6501 | 428 |
1.1 | A105, A216 WCB | 300 | 740 | 51.0212 | 1,110 |
1.1 | A105, A216 WCB | 600 | 1,480 | 102.0424 | 2,220 |
1.1 | A105, A216 WCB | 900 | 2,220 | 153.0637 | 3,330 |
1.1 | A105, A216 WCB | 1500 | 3,705 | 255.4509 | 5,558 |
1.1 | A105, A216 WCB | 2500 | 6,170 | 425.4067 | 9,255 |
2.1 | A182 F304, A351 CF8 | 150 | 275 | 18.9606 | 413 |
2.1 | A182 F304, A351 CF8 | 300 | 720 | 49.6423 | 1,080 |
2.1 | A182 F304, A351 CF8 | 600 | 1,440 | 99.2845 | 2,160 |
2.1 | A182 F304, A351 CF8 | 900 | 2,160 | 148.9268 | 3,240 |
2.1 | A182 F304, A351 CF8 | 1500 | 3,600 | 248.2114 | 5,400 |
2.1 | A182 F304, A351 CF8 | 2500 | 6,000 | 413.6856 | 9,000 |
Ambient (38 C / 100 F) values only, rounded as commonly published. Ratings fall as temperature rises, and each material group has its own curve. Always confirm against the current edition of ASME B16.5 before ordering or design. Test pressure shown is a simple 1.5 x multiple for orientation; the standard sets the actual hydrostatic test rules.
Flange attributes in your ERP
Optional: a short review of how class, facing and group are stored on your item master.
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How to use the table
Search by class or material grade, then read the ambient working pressure in psi and bar. The shell test column applies 1.5 times the rating, the multiple widely used for hydrostatic shell tests of flanged components. Use the table for early sizing, quote review and checking purchase order lines. For design, pull the full pressure-temperature table for your group and your actual design temperature.
- Find the material group from the forging or casting grade
- Read the ambient rating for a quick check
- Look up the derated value at design temperature in the standard
- Match flange class to the mating valve and gasket
What the standard covers
ASME B16.5 covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24 in classes 150, 300, 400, 600, 900, 1500 and 2500. It defines ratings, dimensions, tolerances, marking, materials groups and testing. Larger sizes fall under ASME B16.47. Class 400 is rarely stocked and is omitted here.
Reading the numbers
A Class 300 carbon steel flange handles about 740 psi at ambient, but the same flange at 400 degrees C is rated far lower. A Class 150 flange is not a 150 psi flange. Mistaking class for pressure causes both over-spec and unsafe under-spec purchases, especially in sour or high temperature service where derating is steep.
Common mistakes and ERP notes
Frequent errors include mixing B16.5 with B16.47 series A or B for large sizes, mating a raised face flange to a flat face cast iron flange without precautions, and ordering by class without the facing. In your ERP item master, hold class, facing, material group and standard edition as separate attributes so buyers cannot substitute a lower rating by description.
Frequently Asked Questions
What pressure is a Class 150 flange rated for?
For Group 1.1 carbon steel at ambient temperature, about 285 psi (19.6 bar). The rating drops as temperature rises, so the class number is not a working pressure.
Why do stainless flanges show lower ratings?
Each material group has its own allowable stress curve. Group 2.1 austenitic stainless has a lower ambient rating than Group 1.1 carbon steel in the standard tables, for example 275 versus 285 psi in Class 150.
Do these ratings apply to flanges above NPS 24?
No. ASME B16.47 covers NPS 26 to 60 with its own ratings and series A and B. Check that standard for large diameter flanges.
Is this a substitute for the standard?
No. It is a quick reference for ambient values. Design and procurement decisions need the full pressure-temperature tables in the current edition of ASME B16.5.
Netray can help structure flange and valve attributes in your item master so purchasing catches class mismatches before they reach the floor. The table itself is free to use.
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