Screwed (threaded) flanges are pipe flanges joined by screwing onto externally threaded pipes. They provide a secure connection without welding, making them ideal for low-pressure, low-temperature, or hazardous environments where welding is unsafe. Commonly used in plumbing, fire protection, and industrial systems, these flanges are easy to assemble and disassemble for maintenance. Available in materials like carbon steel, stainless steel, and alloys, they conform to standards such as ASME B16.5 and ASTM specifications. Though convenient, threaded connections are not recommended for high-pressure or vibrating systems due to potential leakage and thread wear.
| Standard | Description | Applicable Materials |
|---|---|---|
| ASME B16.5 | Flanges and Flanged Fittings – Pipe sizes NPS ½” to 24” | Carbon steel, stainless steel, alloy steel |
| ANSI B1.20.1 | Standard for pipe threads (NPT – National Pipe Thread Taper) | Threaded flange connections |
| ASTM A105 | Standard for forged carbon steel piping components | Carbon steel |
| ASTM A182 | Standard for forged stainless and alloy steel flanges | Stainless steel, alloy steel |
| EN 1092-1 | European standard for flanges | Various steels |
| NPS (inches) | Outside Diameter (OD) (mm) | Bolt Circle Diameter (mm) | No. of Bolts | Bolt Size | Flange Thickness (mm) |
|---|---|---|---|---|---|
| ½ | 90 | 60.3 | 4 | ½" | 11.2 |
| 1 | 110 | 76.2 | 4 | ½" | 12.7 |
| 2 | 150 | 120.7 | 4 | ⅝" | 15.9 |
| 3 | 190 | 152.4 | 4 | ⅝" | 19.1 |
| 4 | 230 | 190.5 | 8 | ⅝" | 23.9 |
| 6 | 280 | 241.3 | 8 | ¾" | 25.4 |
| 8 | 345 | 298.5 | 8 | ¾" | 28.4 |
| 10 | 405 | 362.0 | 12 | ⅞" | 30.2 |
| 12 | 485 | 431.8 | 12 | ⅞" | 31.8 |
Screwed flanges are typically available in the following pressure classes:
Higher pressure classes are less common and often not recommended due to limitations of threaded connections.
