Bolted Connections for Piping, Valves, and Equipment
Flanges provide demountable connections between pipe sections, valves, pumps, vessels, and other equipment. They are the second most common connection type after buttwelds and are essential wherever maintenance, inspection, or future modification access is required.
Flange Types (ASME B16.5 / B16.47)
| Flange Type | Description | Typical Application |
|---|---|---|
| Weld Neck (WN) | Long tapered hub butt-welded to pipe. Transfers stress smoothly | High pressure, high temperature, cyclic service, hazardous fluids |
| Slip-On (SO) | Pipe slips inside flange bore. Two fillet welds (inside and outside) | Lower pressure, non-critical service. Lower cost |
| Socket Weld (SW) | Pipe inserts into socket. One fillet weld | Small bore (≤2″), high pressure |
| Blind (BL) | Solid disc. Closes off a flanged opening | End of pipe run, vessel manway, future connection |
| Lap Joint (LJ) | Used with stub end. No direct weld to pipe | Systems requiring frequent disassembly, costly alloys (flange can be carbon steel with stainless stub end) |
| Threaded (TH) | Screwed onto threaded pipe. No welding | Low pressure, small bore, hazardous areas (no hot work) |
| Orifice (Orifice Flange) | Weld neck or slip-on with pressure tap holes | Metering runs for orifice plates |
| Spectacle Blind / Spade & Spacer | Installed between two flanges. Solid (spade) or open (spacer) | Positive isolation during maintenance |
| Long Weld Neck (LWN) | Extended straight hub | Pressure vessels, columns, nozzle connections |
| Reducing Flange | WN or SO with smaller bore than flange size | Connecting different pipe sizes at flange joint |
| Expander Flange | WN with expanding bore from smaller pipe to larger flange | Reducing number of reducers in the system |
Flange Facing Types
| Facing | Description | Application |
|---|---|---|
| Raised Face (RF) | Serrated raised surface. 1.6mm (1/16″) for ≤600#, 6.4mm (1/4″) for ≥900# | Standard for ASME flanges. Most common in process plants |
| Flat Face (FF) | Full flat face | Cast iron flanges, FRP, low pressure |
| Ring Type Joint (RTJ) | Precision machined groove accepts metal ring gasket | High pressure, high temperature, critical service, API 6A wellheads |
| Male & Female (M&F) | One flange has raised male face, other has matching female recess | Low pressure, small sizes (less common now) |
| Tongue & Groove (T&G) | One flange has raised ring, other has matching groove | Self-aligning, for toxic or expensive fluids |
Applicable Standards
| Standard | Scope | Size Range | Pressure Range |
|---|---|---|---|
| ASME B16.5 | Pipe flanges and flanged fittings | 1/2″ to 24″ | 150# to 2500# |
| ASME B16.47 Series A (MSS SP-44) | Large diameter flanges | 26″ to 60″ | 150# to 900# |
| ASME B16.47 Series B (API 605) | Large diameter flanges | 26″ to 60″ | 150# to 900# |
| ASME B16.36 | Orifice flanges | 1″ to 24″ | 300# to 2500# |
| API 6A | Wellhead and Christmas tree flanges | 1-13/16″ to 30″ | 2,000 to 20,000 psi |
| API 6B | API flanges (superseded by API 6A) | Various | Up to 5,000 psi |
| AWWA C207 | Waterworks flanges | 4″ to 144″ | Class B to Class F |
| MSS SP-44 | Steel pipeline flanges | 12″ to 60″ | 150# to 900# |
Flange Material Options
| Material | ASTM Forging Spec | Service |
|---|---|---|
| Carbon Steel | A105 | General sweet service |
| Carbon Steel (Service) | A105N | Normalized for better toughness |
| Carbon Steel (Low Temp) | A350 LF2 | -46°C applications |
| Carbon Steel (Sour) | A105/A350 (NACE MR0175) | H2S service with hardness control |
| Chrome-Moly (1.25Cr-0.5Mo) | A182 F11 | High temperature |
| Chrome-Moly (2.25Cr-1Mo) | A182 F22 | Higher temperature |
| Stainless 304/304L | A182 F304/F304L | General corrosive |
| Stainless 316/316L | A182 F316/F316L | Chlorides, offshore, sour |
| Stainless 321 | A182 F321 | High temperature (stabilized) |
| Stainless 347 | A182 F347 | High temperature (stabilized) |
| Duplex (2205) | A182 F51 (UNS S31803) | High chlorides |
| Super Duplex (2507) | A182 F53 (UNS S32750) | Extreme chlorides, subsea |
| Inconel 625 | B564 N06625 | Sour HPHT |
| Inconel 825 | B564 N08825 | Sour, acid |