Spiral Wound Gaskets

Spiral Wound Gaskets Demystified

Spiral Wound Gaskets are what you reach for when a regular gasket won’t do the job. Regular flat gaskets seal parallel flanges with good surface finish. Over time though, those properties deteriorate and the joint becomes harder to seal. That’s when it’s time to go spiral-wound.

Spiral wound gaskets also work well in high-temperature and high pressure conditions and with corrosive media. That’s why they’re the gasket of choice in many petrochemical plants where their long life helps reduce downtime.

Edge Sealing

Most gaskets are cut from sheet material and that means they seal on their flat surfaces. When flanges are out of parallel the gap between them varies, forcing the use of thicker material. Where the gap is smaller the material must compress more. Pretty quickly the material reaches the limits of what it can do.

In contrast, the spiral wound gasket seals on its edges rather than a flat surface. To do this a long thin strip of gasket material is coiled up to create a ring. Placed between flanges, it’s the sides of the strip that make the seal.

Built-In Spring

To add elastic recovery, ensuring that a seal is maintained regardless of how the joint moves, the gasket material is interleaved with a metal strip. The combined materials are then formed into an approximate ‘V’ section during the coiling process. That metal ‘V’ acts like a spring, pushing outwards against the flanges.

Spiral Wound Gasket Material Options

The choice of gasket material is critical. Usually a spiral-wound gasket is made from PTFE or graphite, both of which come in various grades. In addition, the metal is also selected for the appropriate degree of springiness combined with corrosion resistance and durability.

Spiral-wound gaskets usually come with both an inner metal core and an outer metal ring. These are thinner than the coiled gasket material, so limiting how much the gasket can compress. The inner core also increases blowout resistance; one reason this design works well with high pressures.

For ease of identification, the outer edge of every spiral-wound gasket is color-coded. These codes follow an ASME standard, make it easy to identify and order the replacement part before the joint is taken apart. That helps minimize downtime!

Ask About Going Spiral Wound

The spiral-wound gasket was invented by Flexitallic back in 1912 but today there are a number of manufacturers. The gaskets follow ASME standards but are not all the same as each company has their own materials and designs.

If you have a challenging joint to seal, ask if a spiral-wound gasket would be a good option. If you’re replacing an existing spiral-wound gasket, check the color-code and order the new part before taking the joint apart.  As a spiral wound gasket supplier, Hennig Gasket stocks a large variety of spiral wound gaskets ready to ship.  Contact us today.

The Difference Between Soft, Semi-Metallic and Metallic Gaskets

Gasket selection is driven by the needs of the application. Temperature, environment, media and pressure dictate the gasket required. While there are many different types, to aid selection they are usually separated into three classes:

  • Soft
  • Semi-metallic
  • Metallic

Soft gaskets

These are made from materials that compress easily, such as elastomers like nitrile, (NBR,) EPDM and silicone, as well as graphite, PTFE and fibrous materials. Their corrosion resistance is good but they are limited in the temperatures they can handle. Nitrile gaskets for example only work from -60 to 250°F (-51 to 121°C) and EPDM is only slightly better with a range of -70°F to 350°F (-57°C to 177°C). Silicone gaskets will however go up to 500°F (260°C) and PTFE is effective from cryogenic temperatures up to 450°F (232°C).

Soft gaskets are also limited in their ability to handle high pressures. The best applications are those involving sealing variable gaps as might be found around the doors of an electrical enclosure.

Semi-metallic gaskets

Bridging the gap between metallic gaskets and soft gaskets, the semi-metallics combine features of each. The two main types are spiral-wound and metal-jacketed, although other forms exist. Spiral wound gaskets are made from a ribbon of soft material like PTFE or graphite layered with metal, usually in a ‘V’ form to provide compressibility. Jacketed gaskets consist of a metal cover over a filler material.

Semi-metallic gaskets can handle a wide range of temperatures and pressures up to 6,000 psi, (based on ANSI pressure class 2,500,) so are used in applications ranging from refineries and chemical processing plants to aerospace.

Metallic gaskets

As the name implies, this type of gasket is made from metal. That allows it to resist pressures as high as 10,000 psi but also means it has virtually no compression. Very high bolt loads are needed to create enough deformation for joint sealing.

Metallic gaskets are vulnerable to galvanic corrosion. To minimize problems the gasket metal should be close to the flange material on the electrochemical scale. Alternatively, the material should be chosen to make the gasket the sacrificial element.