An Overview of ASME B16.5 – Pipe Flanges and Flanged Fittings
NPS ½ Through NPS 24 Metric/Inch Standard
ASME B16.5 covers pressure-temperature ratings, materials, dimensions, tolerances, marking, and testing for pipe flanges and flanged fittings in sizes NPS ½” to NPS 24″ for Classes 150, 300, 400, 600, 900, 1500, 2500. It includes flanges with raised face, flat face, ring joint, lap joint, and other configurations.
The code is structured into the following key sections:
- Scope & Definitions
- Pressure Temperature Ratings (Table 1A/1B)
- Materials (Table 1A/1B, Appendix A)
- Dimensions (Tables 2 to 11)
- Tolerances
- Bolting Requirements
- Markings & Testing
Key Sections of ASME B16.5
Pressure-Temperature Ratings
- Defines maximum allowable pressures for different materials at various temperatures.
- Ratings are given for Classes: 150, 300, 400, 600, 900, 1500, and 2500.
Materials
- Lists acceptable materials for flanges (carbon steel, stainless steel, alloy steel, etc.).
- Includes specifications like ASTM A105, A182, A350, etc.
Dimensions & Tolerances
- Covers flange types: Weld Neck, Slip-On, Socket Weld, Lap Joint, Threaded, Blind. Provide tables for;
- Flange outside diameter (OD)
- Bolt circle diameter
- Number of bolt holes
- Bolt hole size
- Flange thickness
- Hub dimensions (for weld neck flanges)Raised face height/diameter
Marking & Testing
- Flanges must be marked with material grade, pressure class, size, and manufacturer’s name.
- Hydrostatic testing requirements for fittings.
Facing & Surface Finish
- Specifies raised face (RF), flat face (FF), and ring-type joint (RTJ) facings.
- Surface finish requirements for gasket seating.
Flange Types Covered
- Weld Neck (WN) – High-stress applications.
- Slip-On (SO) – Easy alignment, lower cost.
- Socket Weld (SW) – Small sizes, high pressure.
- Lap Joint (LJ) – Used with stub ends.
- Threaded (THD) – For low-pressure piping.
- Blind (BL) – To close pipe ends.
| Type | Description | Common Use |
|---|---|---|
| Weld Neck (WN) | Long tapered hub, butt-welded | High pressure/temp |
| Slip-On (SO) | Fits over pipe, fillet-welded | Low pressure systems |
| Blind (BL) | Solid disc, blocks flow | Isolation, testing |
| Socket Weld (SW) | Pipe sits in socket, fillet-weld | Small-bore, high pressure |
| Threaded (THD) | Internal threads, no welding | Low pressure, maintenance |
| Lap Joint (LJ) | Two-piece, with stub-end | Frequent disassembly |
| Ring Type Joint (RTJ) | Groove for metal ring gasket | High-pressure sealing |
Integration with Other Codes
Often used in conjunction with:
- ASME B31.3 for Process Piping
- ASME Section VIII for Pressure Vessels
- API standards in oil & gas applications
ASME B16.5 Flange Dimensions
Standard weld neck flange dimensions per ASME B16.5 showing key measurements (A: Flange OD, B: Bolt Circle, C: Bolt Hole, T: Thickness, RF: Raised Face)
Note: Pressure ratings decrease at higher temperatures. Dimensions remain constant but maximum allowable working pressure (MAWP) varies with temperature and material.
Notes:
- Dimensions shown are for weld neck flanges per ASME B16.5 standard
- All dimensions are in inches (primary) with millimeter equivalents in parentheses
- Pressure ratings vary by material grade and temperature - refer to ASME B16.5 Table 2-1.1 for exact values
- RF = Raised Face diameter (typically 1/16" height for Classes 150-300, 1/4" for Classes 400-2500)
- For other flange types (slip-on, socket weld, etc.), dimensions may vary slightly