Direct answer: A Class 150, 300 or 600 nickel-alloy flange does not have one fixed pressure rating. Under ASME B16.5, the allowable pressure is selected from the table for the exact material group, flange class and metal temperature. The completed joint may require a lower limit because of the gasket, bolting, piping code, corrosion allowance or service condition.
How to Determine the Rating
- Identify the exact forging specification and grade, such as an ASTM B564 nickel-alloy grade.
- Find that material in the applicable ASME B16.5 material group.
- Select the flange Class and design metal temperature.
- Read the pressure from the correct pressure–temperature table and edition.
- Check all notes, temperature restrictions and interpolation rules.
- Verify the full flange joint and governing piping code.
What ASME B16.5 Covers
The 2025 edition covers pressure–temperature ratings, materials, dimensions, tolerances, marking and testing for NPS 1/2 through NPS 24 within its class ranges. Larger flanges may fall under ASME B16.47 or an engineered design.
| Common mistake | Correct approach |
|---|---|
| Class 300 means 300 psi | Class is a designation; table pressure varies by material and temperature |
| All nickel alloys share one table | Use the group assigned to the exact material grade |
| Ambient rating applies at high temperature | Use design metal temperature |
| Flange rating equals joint rating | Check gasket, bolting, facing, assembly and piping code |
RFQ Checklist
State alloy/UNS, forging standard and grade, B16.5 or B16.47 edition, NPS, Class, flange type, facing, bore, schedule, design pressure, design temperature, bolting, gasket, NACE/PED requirements, NDE, PMI and certificate type.
FAQ
What pressure can a Class 150 Alloy 625 flange hold?
The answer requires the precise material group, temperature, code edition and joint details. “150 psi” is not a valid general answer.
Can I interpolate between temperatures?
Use only the method and restrictions permitted by the governing edition and project specification.
Does corrosion resistance increase pressure rating?
No. Corrosion resistance and code allowable stress are different selection factors.
Primary References
Engineering note: Values and acceptance criteria must be checked against the edition of the governing standard named in the purchase order. Application-specific design approval remains the responsibility of the purchaser or project engineer.
Post time: Sep-11-2026