What is a Spiral Wound Gasket?

ASME B16.20 spiral wound gasket is a type of semi-metallic gasket designed specifically for sealing flange joints in high-pressure, high-temperature (HPHT) environments. It is constructed by spirally winding two distinct materials: a thin metallic strip (the “winding strip”) and a non-metallic filler material (the “filler strip”). The winding process creates a series of alternating layers of metal and filler, forming a flexible yet robust sealing structure. This unique design also allows them to withstand extreme operating conditions, making them a favorable choice for critical applications in oil and gas, petrochemical, power generation, and other heavy industries.

Key Components of a ASME B16.20 Spiral Wound Gasket

To understand how a spiral wound gasket works, it’s essential to acknowledge their core components. A typical spiral wound gasket consists of three main parts:

Winding Strip (Metallic Core)

The winding strip is the backbone of the spiral wound gasket, providing structural strength, pressure resistance, and temperature stability. It is usually made from thin, corrosion-resistant metal sheets that can withstand high stress without deforming permanently.

Common materials for the winding strip:

①304/304L Stainless Steel: The most widely used option, suitable for general-purpose applications and moderate corrosion resistance.

②316/316L Stainless Steel: Performs enhanced corrosion resistance, ideal for acidic or chloride-rich environments (e.g., marine, chemical processing).

Filler Strip (Non-Metallic Sealant)

The filler strip is the sealing element of the flange connection, responsible for filling in minor irregularities on flange surfaces and creating a tight barrier against leakage. It is made from compressible, heat-resistant non-metallic materials that can conform to flange textures under compression.

Common filler materials include:

①Flexible Graphite: The most popular filler, offering excellent high-temperature resistance (up to 650°C), chemical inertness, and resilience. It is applied in most industrial applications.

②PTFE: Known for its exceptional chemical resistance and low friction. Suitable for low to moderate temperatures (up to 260°C).

③Ceramic Fiber: Designed for ultra-high temperatures (up to 1,200°C), and suitable for boiler flanges and furnace connections etc.

Inner/Outer Rings (Optional Reinforcements)

Many flange gaskets include optional inner and/or outer metal rings (called “centering rings” or “anti-extrusion rings”) to enhance performance:
    – Outer Ring: Prevents the gasket from extruding between flange bolts under high pressure. It’s also helpful to center the gasket on flange face.
    – Inner Ring: Provides additional support for the inner diameter of the gasket, preventing deformation and improving sealing integrity in large-diameter flanges or high-pressure applications.

Applications of ASME B16.20 Spiral Wound Gasket

Thanks to its versatility and ability to withstand harsh conditions, spiral wound gasket is used in a wide range of industries and applications:

• Oil & Gas Industry: Pipeline flanges, wellheads, refineries, and petrochemical plants (handling crude oil, natural gas, and petrochemical products).
• Power Generation: Boiler flanges, turbine connections, and steam pipelines (withstanding high-temperature steam and pressure).
• Chemical Processing: Reactors, distillation columns, and chemical storage tanks (resisting corrosive acids, bases, and solvents).
• Pharmaceutical & Food Processing: Sanitary flanges (using FDA-approved fillers like PTFE to ensure product purity).
• Marine Industry: Shipboard piping systems (resisting saltwater corrosion and vibration).

In general, spiral wound gaskets are the go-to choice whenever a reliable seal is required. For example, when pressure up to 20,000 psi, temperature up to 1,200°C, or corrosive media.

Advantages of Spiral Wound Gasket

①Excellent Sealing Performance: 

The multi-layer sealing construction forms a robust barrier that prevents gas and liquid leakage in harsh industrial flange connections.

②High Temperature & Pressure Resistance: 

Ideal for extreme HPHT conditions, ranging from cryogenic temperatures to ultra-high temperatures (up to 1000°C or higher) and from vacuum to high pressure (typically up to 25MPa or more).

③Corrosion Resistance: It compensates for flange displacement caused by temperature and pressure fluctuations, maintaining long-term sealing integrity without performance degradation.

④Flexibility & Resilience: The spiral design provides flexibility, and allows gasket to adapt to flange movement without losing sealing integrity.

⑤Cost-Effective Reliability: Spiral wound gaskets realize a perfect balance between all-metal gaskets (lower cost) and non-metallic gaskets (higher durability).

Important Considerations When Choosing Flange Connection

To select the suitable spiral wound gasket under ASME B16.20, following factors should be considered:

• Operating Conditions: Determine the maximum temperature, pressure, and type of media (e.g., corrosive, non-corrosive) the gasket will be exposed to. This helps to choose the winding and filler materials.
• Flange Type: Match the gasket type to the compatible flange design (e.g., Type BX for RTJ flanges, Type RX for raised-face flanges).
• Size & Dimensions: Ensure the gasket’s inner diameter, outer diameter, and thickness match the flange specifications by strictly following ASME B16.20 standards.
• Material Compatibility: Verify that the winding and filler materials are compatible with the process media to avoid corrosion or degradation.

Key Installation Steps to Ensure Sealing Performance

• Preparation: Clean the flange sealing surface to remove scratches, rust, or residues of former gaskets—any impurities may compromise the sealing integrity.
• Inspection: Verify the gasket type and material to ensure they match the application requirements; check for any damage (e.g., cracks, deformations) before installation.
• Centering: Align the gasket accurately with the flange hole. Avoid forced insertion.
• Pre-tightening: Tighten the bolts gradually in a diagonal sequence to 30%-50% of the specified preload force, ensuring initial uniform compression.
• Final Fastening: Re-tighten the bolts to the designed torque value in multiple steps (at least 3 steps) in a diagonal sequence again, ensuring uniform stress distribution across the flange.
• Hot Tightening (if necessary): For high-temperature operating conditions, shutdown for re-inspection or hot-state re-fastening may be required after the system heats up to maintain sealing performance.

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The spiral wound gasket has good sealing performance. Its spiral winding structure allows the metal belt and filling material to fit tightly on the sealing surface when the gasket is under pressure, filling the tiny unevenness of the sealing surface, thereby effectively preventing medium leakage.Spiral wound gaskets are widely used in the sealing of flange connections of pipelines, valves, pressure vessels, condensers, heat exchangers and other equipment in the petroleum, chemical, metallurgy, electric power, shipbuilding, machinery and other industries.

ASME B16.20 Standard

This Standard covers materials,dimensions, tolerances, and markings for metal ring-joint gaskets, spiral-wound metal gaskets, metal-jacketed gaskets, and grooved metal gaskets with covering layers. These gaskets are dimension ally suitable for use with flanges described in reference flange standards ASME B16.5,ASME B16.47, API Specification 6A, and ISO 10423.

Spiral Wound Gasket 

Spiral wound gasket, including centering ring and inner ring (paras.3.2.4 and 3.2.5), are identified by flange size (NPS),pressure class, and the appropriate flange standard(ASME B16.5 or ASME B16.47).

Dimensions and Tolerances

Dimensions and tolerances for spiral wound gasket, centering rings, and inner rings shall be in accordance with Tables 9 through 14 (Tables I-4through I-9 of Mandatory Appendix I) and as specified in this section (see also Figs. 1 and I-1).

Construction

Spiral-wound gaskets shall be constructed as alternate plies (circular layers counted as revolutions)of preformed metal windings and pliant fillers that are spirally wound. For the finished gasket,the filler shall be essentially flush with, but not below,the metal winding on both contact faces of the gasket.The metal strip in the winding shall be 0.15-mm(0.006-in.)to 0.23-mm(0.009-in.) thick.The filler material thickness shall be determined by the manufacturer.

Spiral Wound Gasket Color Codes

Spiral Wound Gasket Dimension

Installation of Spiral Wound Gaskets

Before installing the spiral wound gasket, you need to carefully check the integrity of the gasket. Check whether the metal belt is damaged or broken, whether the filling material has fallen off, etc.

It is very important to thoroughly clean the sealing surface and the gasket installation area. Remove impurities such as oil, rust, dust, etc. on the sealing surface.

Place the spiral wound gasket correctly on the sealing surface. Make sure that the center of the gasket is aligned with the center of the sealing surface.

When installing the bolts, a symmetrical and gradual tightening method should be adopted. First, lightly screw all the bolts into the screw holes to initially position the gasket. Then follow the diagonal order and tighten the angle a small amount each time to gradually increase the tightening force of the bolts.

After installation, you need to check the installation of the gasket again. Check whether the gasket is still in the correct position without offset or distortion.

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There are many types of gasket, such as Industrial Rubber Sheet, Asbestos Rubber Sheet, PTFE Gasket,  Spiral Wound Gasket and so on.

Industrial Rubber Sheet

Natural Rubber

Natural rubber is suitable for water, seawater, air, inert gas, alkali type, salt water solution and other media, but not resistant to mineral oil and non-polar solvents. The working temperature is no more than 90 ℃ for long-term usage. Low temperature application can reach above -60 ℃.

NBR

NBR applies to petroleum products, such as oil, lubricants, fuel oil, etc.. Working temperature for long-term use is 120 ℃. But in hot oil it can withstand 150 ℃. Low working temperature is -10~-20℃.

Neoprene

Neoprene is suitable for seawater, weak acid, weak alkali, salt solution. It has excellent oxygen-resistance and ozone aging performance. The oil-resistance is secondary to nitrite rubber but better than other general-purpose rubbers. Working temperature for long-term use is less than 90 ℃, the maximum working temperature of not more than 130 ℃, lower working temperature is -30~-50℃.

Fluorine Rubber

Fluorine rubber has a number of varieties. They have good acid resistance, oxidation resistance, oil resistance,and solvent resistance. They may suit for all acid media and some oil or solvents media, working temperature for long-term use is less than 200 ℃.

Rubber Sheet

As a flange gasket, the rubber sheet is used for the pipe or the manhole, hand hole, and the pressure is no more than 1.568MPa. Among various gaskets, the rubber gasket is the softest, has good laminating performance. Under small pre-tension, it can play the sealing role. But when it is subjected to internal pressure, it is easily extruded because the gasket is too thick and has low hardness. Rubber sheet appears swelling, weight gain, soft, sticky in organic solvents like benzene, ketone, and ether, which can lead to sealing failure. General speaking, it should be replaced when the swelling degree is more than 30%.

Conclusion

Rubber cushion is more suitable in the low pressure (especially under 0.6MPa), and vacuum condition. The rubber material has good compactness and low permeability. For example, fluorine rubber, the most suitable gasket for vacuum container sealing, the highest degree of vacuum can reach 1.3×10-7pa. The rubber cushion is used in the 10-1~10-7PA vacuum range and is processed by baking and gas extraction.

Industrial Rubber Sheet

Asbestos Rubber Sheet

Polluting Medium

It is the most cheaper gasket and is convenience. The biggest problem of this gasket is its materials. Although it contains rubber and some fillers, it still can not fully fill the small pores of the collusion, then leads to the traces of infiltration. Therefore, with a highly polluting medium, even if the pressure, temperature is not high it can not be used.

High-Temperature Oil Medium

In some high-temperature oil medium, the rubber and filler will be carbonizationin late period, so strength becomes less and material becomes loose, then in the interface and gasket internal will find infiltration, coking and smoke phenomenon happens. In addition, asbestos rubber board is easily bonded to the flange sealing surface at high temperature, causing a lot of troubles to replace the gasket.

Heating Condition

Under the condition of heating, the pressure of the gasket in different mediums depends on the strength retention rate of the gasket material.

Crystalline water and adsorbed water exist in the asbestos fiber.

• At 110 ° C, 2/3 adsorbed water precipitated. Fiber tensile strength is about 10%.
• At 368℃, adsorbed water all precipitated. Fiber tensile strength reduces about 20%.
• More than 500 ℃, crystalline water began to precipitate. The intensity is lower.

Dielectric

The dielectric also has a great influence on the strength of the asbestos rubber sheet.

For example, applied NO. 400 oil-resistant asbestos rubber sheet to aviation lubricants and aviation fuels, the horizontal difference of tensile strength is 80%. This is due to the plate rubber is easier swelling in aviation fuel.

Taking into account the above factors, the recommended safe usage range of domestic asbestos rubber sheet XB450 is

• Temperature 250℃~300℃,
• Pressure 3~3.5mpa;
• Working temperature of 400 oil-resistant asbestos rubber plate should beside 350 ℃.

Oil Medium

Asbestos rubber sheet containing chloride ions and sulfides, easily absorbs and rusts with metal flanges after water absorption. Especially the oil-resistant asbestos rubber plate has several times the sulfur content of the ordinary asbestos rubber plate, is not suitable for the Non-oil medium application. Swelling will occur in oil and solvent medium, but it has no impact on sealing performance.

For example, soaking the NO. 400 oil-resistant asbestos rubber sheet in aviation fuel at ambient temperature for 24 hours, the oil absorption does not exceed 15% of the weight that requirement. To be honest, there is a gap between domestic asbestos rubber plate and foreign famous brand products. Statistics show that in petroleum media application above 350 °C, the asbestos rubber sheets are mostly imported.

PTFE Gasket

PTFE is prone to occor cold flow and creep under high pressure and high temperature. It is generally common for low pressure, medium temperature and strong corrosion conditions. It is not allowed to contact with contaminated media, such as acid, alkali and drugs.

Safe usage condition is under temperature 150 ℃, pressure 1Mpa. Although the strength of PTFE filler is higher, but the working temperature is no more than 200 ℃.

The Maximum working pressure is generally no more than 2MPa. With increas of temperature, the decline of sealing pressure is obviously. Even if without heating, the compressive stress of sealing surface will decrease with the prolonging of time, resulting in “stress relaxation phenomenon.” This phenomenon is general actually, but PTFE gasket ismore serious and attracts you attention.

PTFE Gasket Application

The friction coefficient of PTFE is small (the compression stress is greater than 4MPa, the friction coefficient is 0.035~0.04). So the gasket is easy to slip when preloading, and the concave flange surface is the best choice.

When the plane flange is adopted, the outside diameter of gasket can be contacted with bolts, in order to prevent the gasket from slipping. Because the glass-lined is sprayed on the surface with a brittle glaze layer, and the spraying may be uneven and the glaze layer will flow, so the surface is irregularity.

Metal composite gaskets would damage the glaze layer, so it is recommended to adopt PTFE gasket with . This kind of cushion is easy to match with the flange surface with corrosion resistance. It is popular because of the easy production and usage.

PTFE Gasket

Asbestos Resin Board and Impregnated Asbestos Sheet Gasket

It is used for a variety of acidic media pipelines, pumps, valves, import and export flange, the use of temperature in 80 ℃, pressure under 0.6MPa. The Asbestos preparation gasket is suitable for under the pressure 0.1MPa, the temperature does not surpass 800 ℃ low pressure, the high temperature working condition. And according to the specific requirements of equipment, woven into the width, thickness, diameter of the gasket. or cut the asbestos strip directly to the flange surface. The working fields are large sulfuric acid, nitric acid oxidation furnace and some raw equipment interface, the effect is far more than the original asbestos rope.

Spiral Wound Gasket 

Spiral Wound Gasket skillfully utilizes the heat resistance, resilience and strength of the metal and the softness of non-metallic materials. So it has better sealing performance, and the performance of the stainless steel tape winding Flexible graphite mat is the best.

The metal strip uses 0cr13 more often, while the other media is 1cr18ni9ti.

Gas Medium

In the gas medium it usually uses stainless steel with flexible graphite winding pad, working pressure is 14.7MPa (domestic is up to 19.6MPa).

Liquid Medium

In the liquid, the pressure can be 30Mpa, temperature is -190~ 600 ℃ (available to 1000 ℃ in the case of anaerobic and low-pressure).

Low-Temperature Medium

The low-temperature resistance of PTFE is good. Its yield strength at low temperature is much higher than that at ambient temperature. Therefore, PTFE winding pad suits for low-temperature medium, such as liquid hydrocarbon. At the same time, due to the addition of metal belt to improve the thermal conductivity, PTFE winding pad working temperature is up to 250 ℃. And in the acidic medium it can be 9MPa, 200 ℃. The winding pad is suitable for the heat exchanger, reactor, pipe, and valve for pressure and temperature fluctuation system. For the conditions that more than 300 ℃, it is better use inner ring, outer ring or inner ring. If use concave-convex flange, the winding cushion effect is better with the inner ring.

Good Sealing Effect

It can get a good sealing effect by sticking flexible graphite plate on both sides of flexible graphite winding pad. The key equipment with high temperature and high pressure such as the waste heat boiler of a large chemical fertilizer plant, is better use gasket with flexible graphite winding pad with outer ring. It can prevent leakage when full and reducing load.

Spiral Wound Gasket

Octangon Gasket and Elliptical Gasket

The octagonal cushion and ellipse pad (commonly known as “Earth rims”) for trapezoidal groove flanges are well sealed. On the cone of the groove, the octagonal mat is contact with the surface and the ellipse pad is the line contact. Therefore, the ellipse cushion under the low fastening force of good adhesion, but need to carry out two times fastening, and the octagonal pad is generally once fastening, not easy to leak. Their deficiencies are to require a larger bolt tightening force, when use it in low temperature conditions, the flange grade must be above pg25 kg level

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