What Is an ASME B16.20 Spiral-Wound Gasket?
A spiral-wound gasket is a semi-metallic sealing element formed by winding a preformed V-shaped metallic strip together with a soft filler strip in a spiral. ASME B16.20 (Part SW) defines the dimensions, tolerances, materials and marking of spiral-wound gaskets used with flanges per ASME B16.5 (NPS 1/2 through NPS 24) and ASME B16.47. The metal winding provides recovery under cycling load, while the soft filler fills the flange surface micro-irregularities.
Construction
- Winding strip — 304, 316, 321, 347, Inconel 600/625, Monel 400
- Filler — flexible graphite, PTFE, or non-asbestos fibre
- Inner ring — required for high classes to support the windings and control bolt compression (per B16.20 para. SW-2.5)
- Centering (outer) ring — aligns the gasket on the flange face
Dimensions — B16.20 Table SW-2.1-1 (mm)
Gasket inside diameter (ID), gasket outside diameter (OD) and centering-ring OD for use with ASME B16.5 flanges, NPS 1/2 through NPS 24. An em-dash (—) means no size listed for that class (refer to the standard notes). Inch dimensions are given in the standard.
Gasket Outside Diameter (mm)
| NPS | Gasket OD, Classes 150/300/400/600 (mm) | Gasket OD, Classes 900/1500/2500 (mm) |
|---|---|---|
| 1/2 | 31.8 | 31.8 |
| 3/4 | 39.6 | 39.6 |
| 1 | 47.8 | 47.8 |
| 1 1/4 | 60.5 | 60.5 |
| 1 1/2 | 69.9 | 69.9 |
| 2 | 85.9 | 85.9 |
| 2 1/2 | 98.6 | 98.6 |
| 3 | 120.7 | 120.7 |
| 3 1/2 | 133.4 | — |
| 4 | 149.4 | 149.4 |
| 5 | 177.8 | 177.8 |
| 6 | 209.6 | 209.6 |
| 8 | 263.7 | 257.3 |
| 10 | 317.5 | 311.2 |
| 12 | 374.7 | 368.3 |
| 14 | 406.4 | 400.1 |
| 16 | 463.6 | 457.2 |
| 18 | 527.1 | 520.7 |
| 20 | 577.9 | 571.5 |
| 22 | 625.5 | — |
| 24 | 685.8 | 679.5 |
Inside Diameter of Gasket by Class (mm)
| NPS | ID Class 150 | ID Class 300 | ID Class 400 | ID Class 600 | ID Class 900 | ID Class 1500 | ID Class 2500 |
|---|---|---|---|---|---|---|---|
| 1/2 | 19.1 | 19.1 | — | 19.1 | — | 19.1 | 19.1 |
| 3/4 | 25.4 | 25.4 | — | 25.4 | — | 25.4 | 25.4 |
| 1 | 31.8 | 31.8 | — | 31.8 | — | 31.8 | 31.8 |
| 1 1/4 | 47.8 | 47.8 | — | 47.8 | — | 39.6 | 39.6 |
| 1 1/2 | 54.1 | 54.1 | — | 54.1 | — | 47.8 | 47.8 |
| 2 | 69.9 | 69.9 | — | 69.9 | — | 58.7 | 58.7 |
| 2 1/2 | 82.6 | 82.6 | — | 82.6 | — | 69.9 | 69.9 |
| 3 | 101.6 | 101.6 | — | 101.6 | 95.3 | 92.2 | 92.2 |
| 3 1/2 | 114.3 | 114.3 | — | 104.8 | — | — | — |
| 4 | 127.0 | 127.0 | 120.7 | 120.7 | 120.7 | 117.6 | 117.6 |
| 5 | 155.7 | 155.7 | 147.6 | 147.6 | 147.6 | 143.0 | 143.0 |
| 6 | 182.6 | 182.6 | 174.8 | 174.8 | 174.8 | 171.5 | 171.5 |
| 8 | 233.4 | 233.4 | 225.6 | 225.6 | 222.3 | 215.9 | 215.9 |
| 10 | 287.3 | 287.3 | 274.6 | 274.6 | 276.4 | 266.7 | 270.0 |
| 12 | 339.9 | 339.9 | 327.2 | 327.2 | 323.9 | 323.9 | 317.5 |
| 14 | 371.6 | 371.6 | 362.0 | 362.0 | 355.6 | 362.0 | — |
| 16 | 422.4 | 422.4 | 412.8 | 412.8 | 412.8 | 406.4 | — |
| 18 | 474.7 | 474.7 | 469.9 | 469.9 | 463.6 | 463.6 | — |
| 20 | 525.5 | 525.5 | 520.7 | 520.7 | 520.7 | 514.4 | — |
| 22 | 593.8 | 577.9 | 577.9 | 577.9 | — | — | — |
| 24 | 628.7 | 628.7 | 628.7 | 628.7 | 628.7 | 616.0 | — |
Outside Diameter of Centering Ring by Class (mm)
| NPS | Centering Ring OD Class 150 | Centering Ring OD Class 300 | Centering Ring OD Class 400 | Centering Ring OD Class 600 | Centering Ring OD Class 900 | Centering Ring OD Class 1500 | Centering Ring OD Class 2500 |
|---|---|---|---|---|---|---|---|
| 1/2 | 47.8 | 54.1 | — | 54.1 | — | 63.5 | 69.9 |
| 3/4 | 57.2 | 66.8 | — | 66.8 | — | 69.9 | 76.2 |
| 1 | 66.8 | 73.2 | — | 73.2 | — | 79.5 | 85.9 |
| 1 1/4 | 76.2 | 82.6 | — | 82.6 | — | 88.9 | 104.9 |
| 1 1/2 | 85.9 | 95.3 | — | 95.3 | — | 98.6 | 117.6 |
| 2 | 104.9 | 111.3 | — | 111.3 | — | 143.0 | 146.1 |
| 2 1/2 | 124.0 | 130.3 | — | 130.3 | — | 165.1 | 168.4 |
| 3 | 136.7 | 149.4 | — | 149.4 | 168.4 | 174.8 | 196.9 |
| 3 1/2 | 161.9 | 165.1 | — | 161.9 | — | — | — |
| 4 | 174.8 | 181.1 | 177.8 | 193.8 | 206.5 | 209.6 | 235.0 |
| 5 | 196.9 | 215.9 | 212.9 | 241.3 | 247.7 | 254.0 | 279.4 |
| 6 | 222.3 | 251.0 | 247.7 | 266.7 | 289.1 | 282.7 | 317.5 |
| 8 | 279.4 | 308.1 | 304.8 | 320.8 | 358.9 | 352.6 | 387.4 |
| 10 | 339.9 | 362.0 | 358.9 | 400.1 | 435.1 | 435.1 | 476.3 |
| 12 | 409.7 | 422.4 | 419.1 | 457.2 | 498.6 | 520.7 | 549.4 |
| 14 | 450.9 | 485.9 | 482.6 | 492.3 | 520.7 | 577.9 | — |
| 16 | 514.4 | 539.8 | 536.7 | 565.2 | 574.8 | 641.4 | — |
| 18 | 549.4 | 596.9 | 593.9 | 612.9 | 638.3 | 704.9 | — |
| 20 | 606.6 | 654.1 | 647.7 | 682.8 | 698.5 | 755.7 | — |
| 22 | 660.4 | 704.9 | 701.8 | 733.6 | — | — | — |
| 24 | 717.6 | 774.7 | 768.4 | 790.7 | 838.2 | 901.7 | — |
Pressure Classes
Spiral-wound gaskets are supplied for flanges of Class 150 through Class 2500. Per B16.20 Table SW-2.1-1 notes, no sizes are listed for Class 400 in NPS 1/2 through 3 1/2 (use Class 600) and for Class 900 in NPS 1/2 through 2 1/2 (use Class 1500).
Related Standards
- ASME B16.20 — Metallic Gaskets (Parent Standard)
- ASME B16.20 RTJ Ring Joint Gaskets
- ASME B16.20 Metal Jacketed Gaskets
- ASME B16.5 — Pipe Flanges (NPS 1/2–24)
- ASME B16.47 — Large-Diameter Flanges (NPS 26–60)
- Our Metallic Gasket Range
- Our PTFE Gasket Range
- ASTM A105 Carbon Steel
- ASTM A182 F304 Stainless Steel
FAQ
What is a spiral-wound gasket used for?
It is the standard semi-metallic gasket for raised-face flanges in high-temperature, high-pressure and cyclic service — oil & gas, petrochemical and power piping.
When is an inner ring required?
Inner rings are required for higher classes and for larger pipe sizes, to prevent winding buckling and to spread bolting load. B16.20 para. SW-2.5 lists the required minimum pipe wall for gaskets with inner rings.
Graphite or PTFE filler — which is better?
Flexible graphite handles the highest continuous temperatures; PTFE is chosen for strong chemical resistance up to about 260°C. Tell us your medium and temperature and we will select the winding/filler combination.
What sizes does B16.20 cover?
NPS 1/2 through NPS 24 for ASME B16.5 flanges (Table SW-2.1-1), and NPS 26 through NPS 60 for B16.47 Series A/B flanges (Tables SW-2.1-2/2.1-3).
Which flange face does a spiral-wound gasket fit?
Raised-face (RF) flanges. The gasket itself sits inside the bolt circle; the centering ring aligns it over the flange face.
Need This Standard for Your Project?
We manufacture and export flanges, fittings and gaskets to ASME standards. Send your standard, size, material, and quantity — we reply within 24 hours.