Overview
ASME B16.5 covers pipe flanges and flanged fittings from NPS 1/2 through NPS 24 within its stated scope. It addresses pressure-temperature ratings, materials, dimensions, tolerances, marking, testing, and methods of designating openings. The standard includes multiple pressure classes and flange types, but it does not mean every material, type, and size is available in every class.
“ANSI flange sizes” is common legacy search language. Current technical purchasing should reference the applicable ASME standard, required edition, nominal size, class, type, facing, material, bore, and inspection requirements.
Why It Matters for Pipe Components
A Class 150 flange is not defined by one fixed pressure value. Allowable pressure changes with material group and temperature. The design engineer must use the correct pressure-temperature table and piping code.
ASME B16.5 dimensions apply only within the standard’s scope. Larger NPS sizes can fall under ASME B16.47 or another standard. A flange can have the correct outside diameter but the wrong bore, facing, bolt circle, hole size, thickness, or material.
The standard also does not select the gasket, bolting material, pipe schedule, welding procedure, corrosion allowance, or service suitability for the purchaser. These items must be coordinated in the complete joint specification.
Methods, Parameters, or Process
Use ASME B16.5 as the flange dimensional and rating framework, then add project-specific material and joint data.
| Order field | What it defines | Common omission |
|---|---|---|
| Edition | Contractual requirements and table basis | Using an uncontrolled catalog |
| NPS and class | Selects dimensional and rating tables | Writing only OD or “150 lb” |
| Flange type | Weld neck, slip-on, blind, threaded, socket weld, lap joint | Omitting connection method |
| Facing | RF, FF, RTJ, or another covered arrangement | Not matching gasket or mating flange |
| Material | Forging, casting, or plate specification as applicable | Confusing material grade with class |
| Bore/schedule | Internal match to connected pipe | Missing weld-neck bore |
| Documents/tests | Certificates and project acceptance evidence | Assuming the standard defines every project test |
Supplier and Inspection Checklist
- Confirm ASME B16.5 is the correct flange standard and size range.
- State the required standard edition.
- Specify NPS, class, flange type, facing, and material.
- Provide pipe schedule or bore where relevant.
- Check OD, thickness, hub, drilling, facing, bore, and markings.
- Verify pressure-temperature suitability for material and design temperature.
- Confirm gasket and bolting as separate joint components.
- Review material certificate, heat treatment, tests, and traceability.
- Define coating restrictions on faces, threads, and weld ends.
- Do not use an ANSI or supplier chart without confirming its ASME source and edition.
Application to Pipe Fittings, Valves, and Flanges
ASME B16.5 is widely used for weld-neck, slip-on, blind, threaded, socket-weld, and lap-joint flanges in process, power, oil and gas, chemical, and utility piping. Flanged valves and fittings may use compatible end dimensions but have their own product standards for body design and face-to-face length.
For NPS above the B16.5 range, the engineer should review ASME B16.47 or the applicable project standard. For gray-iron Classes 25, 125, and 250, ASME B16.1 is a different standard and should not be treated as a direct class conversion.
FAQ
What size range does ASME B16.5 cover?
The ASME scope page states NPS 1/2 through NPS 24. Confirm the contractually required edition and detailed tables.
Is ASME B16.5 the same as ANSI B16.5?
ANSI previously approved standards developed by ASME, which is why legacy language persists. Current purchasing should use the published ASME designation.
What does Class 150 mean?
It is a pressure-temperature class designation, not a universal 150 psi limit.
Does B16.5 specify flange material?
It includes material requirements and rating groups within its scope, but the purchaser must select the exact material specification and grade.
Where are flange bolt sizes found?
The standard dimensional tables provide drilling and bolting data. Use a licensed current table and verify the exact size and class.
Next Steps
Write the full ASME B16.5 flange description on the RFQ and verify the current project-required edition. Use licensed tables for dimensions and pressure-temperature ratings.
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