Last updated: April 2026
A spiral wound gasket is a semi-metallic flange seal made by alternately winding a thin V-section metal strip with a soft non-metallic filler — usually flexible graphite or PTFE — bounded by a centring ring that locates the gasket in the flange and acts as a compression stop. The wound construction gives exceptional elastic recovery: as bolt load fluctuates through thermal cycling, pressure spikes, or creep relaxation, the windings spring back and maintain the seal.
Spiral wound gaskets are the default sealing element for ASME B16.5 raised-face flanges from Class 150 through Class 2500, manufactured to ASME B16.20 / API 601. They are used everywhere process pressure has to be contained reliably: refineries, petrochemical plants, power generation, gas processing, and chemical reactors.
What Does a Spiral Wound Gasket Actually Do?
Two machined flange faces, no matter how well finished, are never perfectly flat at the microscopic level. Tiny channels remain between the peaks and valleys of the surface roughness. The soft filler in a spiral wound gasket is compressed into those channels by the bolt load, while the metal winding provides the structural backbone — preventing the filler from extruding outward and supplying the recovery force that keeps the seal under varying load. Three things have to happen for the joint to stay leak-tight:
- Seating. Enough compressive stress on the gasket to initially force the filler into the flange surface (the y factor in ASME VIII Appendix 2 — typically ~25,000 psi / 175 MPa for graphite-filled spiral wound).
- Operating. Enough residual stress to keep the seal during service as internal pressure tries to blow the joint apart (the m factor — ~3.0 for graphite-filled spiral wound).
- Retention. The bolt load must not drop below the operating stress despite creep, thermal cycling, or vibration loosening — this is where the elastic recovery of the winding earns its keep.
How Is a Spiral Wound Gasket Constructed?
| Component | Typical materials | Role |
|---|---|---|
| Centring (outer) ring | Carbon steel (zinc-plated), 304SS, 316SS | Locates gasket in flange, limits compression, protects winding |
| Winding metal | 304SS, 316L, 321, Monel, Inconel 625, Hastelloy C-276 | V-section strip provides elastic recovery and corrosion resistance |
| Filler | Flexible graphite, PTFE, mica, ceramic | Fills micro-surface irregularities; carries the seal |
| Inner ring (optional) | Matches winding alloy | Prevents filler erosion / inward buckling on Class 600+ duties |
What Pressure and Temperature Can a Spiral Wound Gasket Handle?
The flange class — ASME 150, 300, 600, 900, 1500, 2500 — sets the cold working pressure. The winding alloy and filler then determine the temperature envelope.
| Filler | Continuous max temp (°C) | Peak temp (°C) | Typical service |
|---|---|---|---|
| Flexible graphite | 450 (oxidising) / 650 (inert) | 800 | Steam, hydrocarbons, refinery |
| PTFE | 260 | 280 | Acids, alkalis, solvents, high-purity |
| Mica | 800 | 1000 | Flue gas, regenerator, fire-safe |
| Ceramic | 1000 | 1200 | Reformer, exhaust, very-high-temp |
Stainless windings (304SS, 316SS) handle most refinery and chemical service. Above ~650°C continuous, or in sour gas / high-H₂ environments, switch to Inconel 625 or Hastelloy C-276 windings to avoid creep and stress-corrosion cracking.
How Is a Spiral Wound Gasket Selected?
Selection comes down to matching six constraints against the catalogue:
| Constraint | Drives your choice of |
|---|---|
| Media (chemical compatibility) | Filler — PTFE for aggressive chemicals, graphite for hydrocarbons / steam, mica for fire-safe |
| Operating temperature | Filler upper limit and winding alloy (stainless vs Inconel) |
| Flange class & pressure | Centring ring thickness; inner ring required at Class 600+ |
| Flange surface finish | Filler thickness and seating-stress target |
| Service requirement | Fire-safe, sour service (H₂S), high-H₂ — drives winding alloy |
| Bolt load available | Gasket seating stress vs available bolt preload |
For practical guidance, see our filler selection guide and the bolt torque calculator for converting target seating stress into bolt-up torque.
Where Are Spiral Wound Gaskets Used?
- Oil & gas refining — fractionation, hydroprocessing, crude preheat, FCC.
- Petrochemical — reactor manways, corrosive lines, polymer-grade duties.
- Power generation — HP steam lines, turbine bypass, boiler feedwater.
- LNG & cryogenic — graphite-filled SWGs perform down to -200°C.
- Gas processing — sour gas (H₂S), amine units, dehydration.
How Long Does a Spiral Wound Gasket Last?
Correctly selected and bolted up, a spiral wound gasket lasts the design life of the flange — often 10 to 20 years on a static joint with stable temperature. Three things shorten that life: under-compression (bolts not seated to the gasket's y factor), thermal cycling (loss of bolt preload through creep relaxation), and media attack (graphite oxidation in oxidising service above ~450°C, or PTFE swelling in certain solvents). Following ASME PCC-1 bolt-up procedures and selecting a gasket rated for the full duty envelope eliminates most premature failures.
Frequently Asked Questions
A spiral wound gasket is a flange seal made by alternately winding a thin V-section metal strip with a soft filler such as flexible graphite or PTFE, bounded by a metal centring ring. When bolts are tightened the soft filler is compressed into the flange surface to seal the joint, while the metal winding springs back to maintain the seal as load fluctuates. It is the default sealing element for ASME B16.5 flanges from Class 150 to 2500.
A soft-cut gasket (sheet rubber, PTFE, CNAF) is one piece of soft material — cheap and simple but limited in pressure and recovery. A spiral wound gasket adds a metal winding for elastic recovery and higher pressure capability — the standard choice for refinery flanges. A ring-joint (RTJ) gasket is a solid metal ring that seals by metal-to-metal contact in a machined flange groove; it is used at very high pressure (Class 900+) and on API 6A wellhead flanges, but requires a different flange face entirely.
For general refinery, steam, and hydrocarbon service to 450°C, flexible graphite is the default. For aggressive acids, alkalis, solvents, or high-purity media (food, pharma) where graphite contamination is unacceptable, choose PTFE — limit 260°C. For very high temperatures above 800°C or fire-safe duties where graphite would oxidise, mica or ceramic fillers are used. See our filler selection guide for chemical-compatibility specifics.
Inner rings are mandatory at Class 600 and above per ASME B16.20 to prevent filler erosion and inward winding buckling. Below Class 600 they are optional but recommended for vacuum service, high-velocity media, thermal-cycling duties, or any time the filler is at risk of being eroded by the process. The inner ring should match the winding alloy.
Target assembly stress for a flexible-graphite-filled spiral wound gasket is typically 175 MPa (25,400 psi). Convert to bolt preload by multiplying by gasket contact area, then to torque using the nut factor K for your lubricant (≈0.20 dry, 0.16 with anti-seize). Follow ASME PCC-1 four-pass cross-pattern bolt-up. Our bolt torque calculator handles the conversion.
Related Articles
- Filler selection — graphite, PTFE, mica, ceramic
- Bolt-up to ASME PCC-1
- Spiral wound vs ring-joint (RTJ)
- Bolt torque calculator
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Sources
- ASME B16.20 — Metallic Gaskets for Pipe Flanges: Ring-Joint, Spiral-Wound, and Jacketed
- ASME Section VIII Division 1, Appendix 2 — Gasket m & y factors
- ASME PCC-1 — Guidelines for Pressure Boundary Bolted Flange Joint Assembly
- API 601 — Metallic Gaskets for Raised-Face Pipe Flanges