Spiral wound gaskets are a vital component in many industries, from oil and gas to chemical processing. They are a semi-metallic gasket known for their exceptional sealing capabilities under a wide range of pressures, temperatures, and media. Choosing the wrong spiral wound gasket doesn’t just cause a leak it can shut down a production line, trigger an environmental compliance issue, or put a maintenance crew at risk. This guide will walk you through everything you need to know about spiral wound gaskets, including their construction, types, applications, filler and winding material selection, ASME B16.20 dimensions and colour coding, pressure-temperature limits, installation torque practices, common failure causes and how a spiral wound gasket compares to ring joint, PTFE and rubber gaskets so you can specify the right gasket the first time.
What Is a Spiral Wound Gasket?
A spiral-wound gasket is a semi-metallic gasket made by winding a V-shaped (or W-shaped) metal strip with a soft, non-metallic filler material into a continuous spiral. The metal strip supplies mechanical strength and a spring-like recovery action; the filler fills the microscopic irregularities on the flange face and provides the actual seal. The outer and inner rings of the gasket, often made of carbon steel or stainless steel, provide structural stability and prevent the gasket from over-compressing. The inner ring also protects the windings from the process media, preventing erosion and corrosion.
This hybrid construction is why spiral-wound gaskets are used wherever a flanged joint needs to maintain a seal under pressure surges, thermal cycling and vibration conditions that flat, purely soft gaskets can’t reliably handle over time.
What a Spiral Wound Gasket Is Made Of
A spiral wound gasket has up to three components, depending on style:
1. The Winding Element: This is the heart of the gasket, formed by spirally winding alternating layers of a pre-formed metallic strip and a soft filler material.
2. The Inner Ring (Compression Stop Ring): While optional, this component is highly recommended, especially for challenging conditions involving high pressure, vacuum, or turbulent flow.
- Its Role: The inner ring acts as a protective barrier, preventing the inner windings from buckling inwards into the pipe bore, which could lead to filler erosion and premature failure. It also serves as a crucial compression stop, preventing the gasket from being over-compressed during installation.
- Material: Typically made from the same material as the winding strip for compatibility.
3. The Outer Ring (Centering/Guiding Ring): This solid metal ring is your visual guide and added protection.
- Its Role: It ensures the gasket is perfectly centered within the flange’s bolt circle, provides an additional compression stop to prevent over-compression and shields the winding element from external damage and corrosion. It significantly contributes to the gasket’s radial strength.
- Material: Typically carbon steel with a protective coating, or stainless steel for environments with corrosive external conditions.
Compression and Sealing Mechanism
The effectiveness of a spiral wound gasket lies in its unique ability to convert axial bolt load into a radial sealing force. When the flange bolts are tightened, the axial compressive force is applied to the gasket. The outer ring (and inner ring, if present) acts as a controlled compression stop, ensuring the winding element is compressed to a precise thickness.
During compression, the softer filler material is forced to flow and conform to the irregularities of the flange facing, creating a primary seal against leakage. Simultaneously, the metallic winding strip provides the necessary resilience, acting like a spring. This spring-like action allows the gasket to recover from minor fluctuations in joint stress caused by thermal expansion/contraction, pressure variations, or vibration. This dynamic recovery is what makes SWGs so effective in maintaining a leak-tight seal over extended periods, even under fluctuating operating conditions. The stored energy in the compressed metal windings continuously pushes the filler material against the flange faces, maintaining the seal.
Types of Spiral Wound Gaskets
| Style | Description | Best used for |
|---|---|---|
| Style CG (with outer ring) | Standard style with a carbon steel centring ring | Raised-face flanges, general industrial service |
| Style CGI (with inner + outer ring) | Adds an inner ring for extra support | High-pressure/high-temperature service, erosive or turbulent media, larger diameters |
| Style R (basic, no rings) | Windings only, seats into a groove | Ring-type-joint (RTJ) or grooved flanges |
| Style RIR (with inner ring) | Ring style with added inner ring | RTJ flanges in more demanding service |
If you’re unsure which style fits your flange, the safest default for most raised-face industrial flanges is Style CGI; the outer ring protects against blowout and mishandling and the inner ring guards against buckling at higher pressure classes.
Filler Material Selection Matrix
The filler is the single biggest factor in temperature and chemical compatibility. This is usually where selection mistakes happen.
| Filler | Max Temperature (approx.) | Chemical Resistance | Typical Use Case |
|---|---|---|---|
| Flexible Graphite | ~450°C (higher in non-oxidising/inert atmospheres) | Excellent, except in strong oxidising acids | Oil & gas, refining, steam service, power generation |
| PTFE | ~260°C | Excellent — resists most acids, alkalis, solvents | Chemical processing, pharma, food-grade, corrosive media |
| Mica | ~1000°C | Good, but more brittle | Very high-temperature service where graphite oxidation is a concern |
Graphite vs PTFE, in practice: Graphite wins on temperature range and is the default for hydrocarbon and steam service. PTFE wins where the media is strongly oxidising or where graphite’s trace chloride/sulphur content would be a contamination risk (e.g., stainless steel piping in nuclear or high-purity chemical service). Always cross-check the manufacturer’s chemical compatibility chart against your actual process fluid — “acid resistant” is not one property, it depends on concentration and temperature.
Winding Material Selection: SS304 vs SS316 vs Inconel vs Monel
| Winding Material | Corrosion Resistance | Typical Application |
|---|---|---|
| SS304 | Good general resistance | Mild service, non-corrosive fluids, cost-sensitive projects |
| SS316L | Better resistance to chlorides and pitting | Standard choice for oil & gas, chemical and marine-adjacent service |
| Inconel 600/625 | Excellent at high temperature, resists oxidation and many acids | High-temperature, high-stress, or cyclic thermal service |
| Monel | Strong resistance to hydrofluoric acid and seawater | Specific chemical service, offshore/marine applications |
SS316L is the default winding material for most industrial flange applications in India because it balances corrosion resistance and cost. Inconel and Monel are specified when the process chemistry or temperature genuinely demands it — not as a default upgrade.
Standards Governing Spiral Wound Gaskets
Spiral wound gaskets are manufactured and tested to internationally recognised standards, which is what makes them interchangeable across manufacturers and compatible with standard flanges:
- ASME B16.20 — the primary standard for dimensions, tolerances, materials and markings of spiral wound, ring-joint and jacketed gaskets, designed to mate with ASME B16.5 and B16.47 flanges.
- API 601 / API 6A — referenced for gaskets used in wellhead and piping equipment.
- EN 1514-2 — the European dimensional standard, used where flanges follow DIN/EN sizing.
- BS 3381 / BS 4865-2 — British dimensional and material standards.
- JIS B2404 — Japanese Industrial Standard for gasket dimensions.
- MSS SP-44 — standard for large-diameter steel pipe flanges.
Specifying “ASME B16.20 compliant” on a purchase order is not enough by itself; always also confirm the flange standard (B16.5 vs B16.47 Series A or B), the pressure class and the nominal bore, since dimensions differ across these.
ASME B16.20 Colour Codes Explained
ASME B16.20 assigns a colour to the outer ring edge (winding colour) and a colour to the filler stripe, so the gasket’s material composition can be identified visually after installation, without needing paperwork on hand.
| Winding Material | Outer Ring Colour |
|---|---|
| Carbon Steel | Silver / Grey |
| SS304 | Yellow |
| SS316 | Green |
| SS316L | Green with yellow stripe |
| Monel | Orange |
| Inconel | Gold/Beige |
| Filler Material | Stripe Colour |
|---|---|
| Graphite | Grey |
| PTFE | White |
| Mica | Yellow |
Always verify colour codes against the current edition of ASME B16.20, as some manufacturers use house-standard colour variants. The outer ring colour and filler stripe together should always be cross-checked against the mill test certificate before installation, and not relied on visually alone for critical service.
Spiral Wound Gasket Dimensions
Dimensions are governed by nominal pipe size (NPS), flange pressure class and flange standard (ASME B16.5 for NPS ½”–24″, ASME B16.47 Series A or B for NPS 26″–60″). Key dimensions to confirm before ordering:
- Inside diameter (ID) — matched to bore, slightly oversized to avoid flow restriction
- Outside diameter of winding (OD) — sized to the flange raised face
- Outer ring OD — sized to the bolt circle, without fouling bolt holes
- Thickness — commonly 3.2 mm (⅛”) or 4.5 mm (3/16″), with 4.5 mm generally preferred above Class 600 for better recovery
Because dimensional errors are one of the most common causes of installation problems, always match the gasket to the exact flange standard, pressure class and facing type (raised face, flat face, or tongue-and-groove) rather than assuming NPS alone is sufficient.
Pressure and Temperature Ratings
Spiral wound gasket ratings are a function of the winding material, filler and flange pressure class, not a single fixed number. As a general reference:
| Flange Class | Typical Max Pressure (non-shock, ambient) |
|---|---|
| Class 150 | ~19.6 bar (285 psi) |
| Class 300 | ~51 bar (740 psi) |
| Class 600 | ~102 bar (1480 psi) |
| Class 900 | ~153 bar (2220 psi) |
| Class 1500 | ~256 bar (3705 psi) |
These figures drop as temperature rises, per ASME B16.5 pressure-temperature tables. Always size the gasket using the actual pressure-temperature rating table for the specific flange class and material, not a generic figure — this is one area where under-specifying has serious safety consequences.
Installation Best Practices and Torque Guidance
Correct installation determines whether a correctly specified gasket actually performs. General best practices:
- Inspect the flange faces — clean, undamaged, free of old gasket material, radial scoring, or corrosion.
- Check gasket dimensions and markings against the flange size, class and service before installing.
- Centre the gasket precisely within the bolt circle — the outer ring is designed to help with this.
- Lubricate bolt threads and nut faces (not the gasket face) to ensure accurate torque translates into actual bolt load.
- Tighten bolts in a cross (star) pattern, in at least 3–4 passes, gradually increasing to final torque — never tighten sequentially around the flange.
- Torque to the flange and gasket manufacturer’s stated value for that bolt size, class, and gasket combination — spiral wound gasket seating stress typically falls in the range of 20,000–35,000 psi (138–241 MPa), but always follow the specific manufacturer’s data sheet or ASME PCC-1 guidance rather than a generic number.
- Re-check torque after initial system pressurisation and thermal cycling where the service allows a hot re-torque.
Common Installation Mistakes
- Reusing a gasket after it has been compressed once
- Over-torquing in an attempt to “guarantee” a seal, which can crush the filler and cause loss of resilience
- Uneven, sequential (non-star-pattern) bolt tightening, causing flange distortion
- Skipping flange face inspection, leaving old gasket residue or scoring under the new gasket
- Mismatched gasket ID/OD or pressure class for the flange
- Ignoring bolt lubrication, which causes torque readings to under-represent actual clamping force
Common Causes of Leakage and Gasket Failure
| Cause | What Happens |
|---|---|
| Insufficient seating stress | Filler doesn’t compress enough to fill flange irregularities |
| Over-compression | Filler is crushed beyond its resilient range, losing recovery ability |
| Wrong filler for the media | Chemical attack degrades the filler over time |
| Flange face damage or misalignment | Gasket can’t form a continuous seal across the face |
| Thermal cycling beyond the material’s rating | Repeated expansion/contraction fatigues the winding |
| Incorrect bolt torque or sequence | Uneven load distribution creates local leak paths |
| Vibration without adequate bolt load retention | Gradual loosening reduces seating stress over time |
If a joint develops a chronic, recurring leak after every re-torque, the root cause is almost always one of the first three: filler-media mismatch, wrong seating stress, or flange face condition — rather than the gasket itself being defective.
Explore our spiral wound gasket range or contact us for application-specific selection support.
Spiral Wound Gasket vs Ring Joint Gasket
| Factor | Spiral Wound Gasket | Ring Joint Gasket |
|---|---|---|
| Construction | Metal winding + soft filler | Solid metal ring (oval or octagonal) |
| Flange type | Raised face, flat face | Grooved (RTJ) flanges only |
| Pressure rating | High | Very high (typically Class 600 and above) |
| Flexibility/recovery | Good, spring-like recovery | Minimal — relies on plastic deformation |
| Reusability | Not recommended after compression | Never reusable |
| Typical use | General high-pressure/high-temp service | Extreme-pressure wellhead, high-class flanges |
Choose a ring joint gasket when the flange is RTJ-grooved and the pressure class exceeds what a standard SWG can comfortably handle. Choose a spiral wound gasket for raised-face flanges across most industrial pressure classes it’s the more versatile, more commonly stocked option.
Spiral Wound Gasket vs PTFE Gasket
| Factor | Spiral Wound Gasket | PTFE (Envelope/Skived) Gasket |
|---|---|---|
| Chemical resistance | Good with PTFE filler; excellent with graphite in non-oxidising service | Excellent, near-universal chemical resistance |
| Pressure rating | Higher | Lower — more suited to moderate pressure |
| Temperature range | Higher (graphite filler) | Lower, PTFE limit ~260°C |
| Cost | Higher | Generally lower |
PTFE gaskets are the better choice for highly corrosive, low-to-moderate pressure chemical service. Spiral wound gaskets are the better choice once pressure and temperature move into more demanding territory.
Spiral Wound Gasket vs Rubber Gasket
| Factor | Spiral Wound Gasket | Rubber Gasket |
|---|---|---|
| Temperature range | High | Low to moderate |
| Pressure range | High | Low to moderate |
| Chemical resistance | Depends on filler/winding | Depends on elastomer, generally narrower range |
| Typical use | Oil & gas, chemical, power, high-spec piping | Water lines, HVAC, low-pressure general service |
Rubber gaskets are appropriate where pressure and temperature are modest and cost is the primary driver. They are not a substitute for a spiral wound gasket in hydrocarbon, high-temperature, or safety-critical service.
Applications by Industry
- Oil & Gas — pipelines, wellheads, separators, compressor stations
- Petrochemical & Chemical Processing — reactors, distillation columns, heat exchangers
- Power Generation — steam lines, turbines, boiler flanges
- Refining — high-temperature, high-pressure process piping
- Pharmaceutical & Food Processing — hygienic, non-contaminating sealing (with appropriate filler selection)
- Water Treatment — large-diameter, moderate-pressure flanged connections
How to Choose the Right Spiral Wound Gasket
Work through these questions in order:
- What is the flange type and pressure class? (Raised face vs RTJ narrows your style choice immediately.)
- What is the maximum operating temperature and pressure, including upset conditions?
- What is the process media and is it oxidising, corrosive, or high-purity? (This decides the filler.)
- Is the environment corrosive externally (marine, chemical washdown)? (This affects winding and outer ring material.)
- Is the application prone to vibration, thermal cycling, or pressure surges? (Favour CGI style with inner ring.)
- Does the project specification mandate a particular standard (ASME, DIN, JIS)?
If you’re specifying gaskets in bulk across a facility, standardising on SS316L winding with graphite filler as the default for hydrocarbon service and PTFE filler as the default for corrosive chemical service simplifies stocking without compromising performance in most standard applications.
Frequently Asked Questions
What is a spiral wound gasket used for?
It’s used to create a leak-tight seal between two flanges in piping systems that experience high pressure, high temperature, thermal cycling, or vibration common in oil & gas, chemical and power generation piping.
What material is best for a spiral wound gasket?
It depends on the service. SS316L winding with graphite filler is the most common default for hydrocarbon and general industrial service. PTFE filler is preferred for corrosive or high-purity chemical media. Inconel or Monel windings are reserved for extreme temperature or specific chemical resistance needs.
Can a spiral wound gasket be reused?
No. Once compressed, the filler has already deformed to seal the flange faces and won’t perform a second time reliably. Always fit a new gasket at every flange break.
What temperature can a spiral wound gasket withstand?
This depends on the filler: graphite handles up to roughly 450°C, PTFE up to roughly 260°C and mica up to roughly 1000°C in specialised applications.
What pressure class can a spiral wound gasket support?
Spiral wound gaskets are used across the full range of ASME flange classes, from Class 150 through Class 2500, provided the winding material, filler and style (particularly the presence of an inner ring) are matched to the class.
When should an inner ring be used?
Use an inner ring (Style CGI) for higher pressure classes, larger diameters, erosive or turbulent media, or where buckling resistance is important.
What filler should I choose for chemical service?
PTFE is generally preferred for strongly acidic, alkaline, or oxidising chemical media, due to its broad chemical resistance.
How do I prevent gasket leakage?
Match the gasket to the correct flange class and dimensions, select the right filler and winding for the media and temperature, inspect flange faces before installation and torque bolts to the manufacturer’s specification using a star pattern.
Which industries use spiral wound gaskets?
Oil & gas, petrochemical, chemical processing, power generation, refining and, with the right filler, pharmaceutical and food processing.
What’s the difference between Style CG and Style CGI?
Style CG has an outer centring ring only. Style CGI adds an inner ring for extra support in higher-pressure or erosive applications.
Do spiral wound gaskets need a specific torque value?
Yes, torque depends on bolt size, gasket size and target seating stress (typically 20,000–35,000 psi for the filler material). Always use the manufacturer’s torque chart or follow ASME PCC-1 guidelines rather than a generic figure.
What standards govern spiral wound gasket dimensions?
Primarily ASME B16.20 in North America and Indian industrial projects following ASME specifications, with EN 1514-2, BS 3381 and JIS B2404 used where European or Japanese flange standards apply.
Can spiral wound gaskets be custom-made?
Yes. Manufacturers can produce custom sizes, non-standard shapes and specific material/filler combinations to match unique flange or process requirements.
Why does my spiral wound gasket keep leaking after re-torquing?
A recurring leak after re-torquing usually points to filler-media incompatibility, incorrect seating stress, or flange face damage rather than a defective gasket. Inspect the flange face and confirm the material specification before re-ordering.
