Weld Neck (WN) Flanges
Features: Long tapered hub for stress distribution
Pressure: Class 150 to Class 2500
Applications: High-pressure/temperature systems
Standards: ASME B16.5, B16.47
Welding: Requires butt welding to pipe
Slip-On (SO) Flanges
Features: Slides over pipe with two fillet welds
Pressure: Up to Class 600
Applications: Low-pressure systems
Advantages: Easier alignment, lower cost
Note: Requires 360° welding
Blind (BL) Flanges
Features: Solid disc for pipe end closure
Pressure: All classes
Applications: Maintenance, future expansion
Special: No bore, used with all flange facings
Threaded (TH) Flanges
Features: Internal NPT threads
Pressure: Up to Class 300
Applications: Low-pressure threaded pipe
Limitations: Not for cyclic loading
Note: Seal weld often required
Socket Weld (SW) Flanges
Features: Counterbore for pipe insertion
Pressure: Class 300-600
Applications: Small-bore high-pressure lines
Welding: Single fillet weld required
Gap: Must maintain 1/16" expansion gap
Lap Joint (LJ) Flanges
Features: Two-piece (stub end + backing flange)
Pressure: Class 150-900
Advantages: Easy alignment, rotatable
Applications: Systems requiring frequent disassembly
Materials: Stub end matches pipe material
Technical Comparison Table:
| Type | Max Pressure | Welding Required | Cost Factor | Best For |
|---|---|---|---|---|
| WN | 2500# | Butt Weld | High | Critical service |
| SO | 600# | Fillet Weld | Low | General purpose |
| BL | 2500# | None | Medium | Isolation |
| TH | 300# | Optional | Low | Threaded pipe |
| SW | 600# | Fillet Weld | Medium | Small bore HP |
| LJ | 900# | Butt Weld | Medium | Frequent maintenance |
Selection Considerations:
Pressure/Temperature requirements
Corrosion potential
Fatigue loading conditions
Installation/maintenance needs
Total cost of ownership
All types comply with ASME B16.5 dimensional standards and are available in various materials (carbon steel, stainless, alloys) with multiple face finishes (RF, FF, RTJ).
