Socket Weld Flange
Socket weld flanges feature a socket (recessed bore) into which the pipe is inserted before being fillet welded at the hub. This design provides good flow characteristics for small-diameter piping where internal weld protrusion is manageable. Socket weld flanges are primarily used in sizes DN50 (NPS 2) and smaller, though they are available up to DN100 for certain applications.
The socket design provides accurate alignment without the need for tack welding during fit-up. A gap is intentionally left between the pipe end and the socket bottom before welding to accommodate thermal expansion of the pipe within the socket. Our socket weld flanges are forged to ASME B16.5 and are commonly specified for chemical injection lines, instrument connections, steam tracing, and small-bore high-pressure process piping in Classes 150 through 1500.
ASME B16.5
ASTM A105
DN15-DN100, Class 150-1500
Applications
- Small-bore chemical injection lines
- High-pressure instrument connections
- Steam tracing and utility lines
- Hydraulic and pneumatic systems
- Small-diameter process piping
Quality Assurance
All Socket Weld Flange products undergo NDT testing with MTC per EN 10204 3.1. Third-party inspection by SGS, BV, TUV available.
Socket Weld Flange Technical Specifications
Socket weld flanges (SW flanges) have a counterbore that receives the pipe, with a single fillet weld on the outside. They are designed for small-bore, high-pressure piping in ASME B31.3 severe service and are used extensively in process instrumentation and hydraulic systems.
| Parameter | Specification |
|---|---|
| Standard | ASME B16.5 / EN 1092-1 Type 11 / JIS B2220 |
| Size Range | DN15 (1/2") to DN100 (4") - small bore only |
| Pressure Class | Class 150, 300, 600, 900, 1500, 2500 |
| Bore Type | Counterbore to match pipe OD + 1/16" gap |
| Face Type | Raised Face (RF), RTJ for high pressure |
| Material Grades | ASTM A105, A350 LF2, F304/F316/L, F22, F91 |
Manufacturing Process
Socket weld flanges require precision counterbore machining to ensure proper pipe fit-up:
- Forging: Upset forging creates the flange blank with hub for welding.
- Counterbore Machining: Precision boring to ASME B16.5 counterbore dimensions (bore depth, diameter, and shoulder).
- Gap Control: Counterbore depth includes 1.6mm (1/16") allowance for pipe-to-shoulder gap, preventing weld shrinkage stress.
- Bolt Hole Drilling: CNC drilling to ASME B16.5 patterns.
- Face Machining: Raised face or RTJ groove finishing.
- NDT: Magnetic particle and dye penetrant testing on machined surfaces.
Installation & Critical Gap Requirement
The single most important installation requirement for socket weld flanges is maintaining the 1.6mm (1/16") gap between the pipe end and the counterbore shoulder:
- Why the gap matters: Without the gap, weld shrinkage during cooling pulls the pipe tight against the shoulder, creating high residual stress and potential cracking in corrosive service.
- Gap verification: Before welding, insert a feeler gauge or wire to confirm the pipe is not bottomed out in the socket.
- Welding: Single fillet weld on the outside, leg size equal to 1.4x pipe wall thickness.
- Limitation: The gap creates a crevice that can trap corrosive media; socket welds are not recommended for services with severe corrosion or crevice corrosion potential (e.g., stainless steel in chloride environments).
- Hydrotesting: ASME B31.3 requires hydrotest at 1.5x design pressure before service.
Socket weld flanges are the standard for high-pressure, small-diameter piping in refineries, chemical plants, and hydraulic systems where their compact size and reliable sealing offer advantages over threaded connections.