Choosing Between Metallic and Non-Metallic Gaskets

Curious which type of gasket is better for your needs?

According to Thomas Net:

Gaskets serve as essential components in a full range of industries and applications allowing for a tight seal between two joined parts. Their primary purpose is to fill in gaps between parts whose surface tolerances would otherwise cause leakage from or into the joined objects while under compression.

Containing pressure while minimizing the risk of contamination, gaskets ensure high performance and safety in applications involving fluid or gas systems that operate under pressure. These versatile components can also withstand high compressive loads, assuring their longevity.

Types of Gaskets

Gasket designs vary based on intended use, cost considerations, anticipated exposure to chemicals or corrosives, and physical parameters such as material. Common types include:

  • solid-material gaskets
  • spiral-wound gaskets
  • double-jacketed gaskets
  • flange gaskets

Gasket Materials

Typically produced from a flat material, gaskets are commonly created from materials such as:

  • paper
  • rubber
  • silicone
  • metal
  • cork
  • felt
  • neoprene
  • nitrile rubber
  • fiberglass
  • PTFE
  • plastic polymers

Before selecting a specific material to use for an application, it’s important to have a solid understanding of metallic vs. non-metallic gaskets and their unique features and benefits.

Metallic Gasket Options and Applications

Metallic gaskets are fabricated from a single metal or a combination of metals, which allows for surface sealing of a higher-quality than can be achieved with their non-metallic counterparts. These gaskets are ideal for medium- and high-pressure applications, and are designed to resist extreme temperatures and pressures, as well as chemical exposure.

Metallic gaskets often are of the ring-type-joint variety, also called ring gaskets. Ring-type-joint (RTJ) gaskets are commonly used in offshore oil and gas pipelines where high-pressure conditions are prevalent. Featuring a solid metal ring construction, these gaskets come in different cross-sections, such as oval, round, and octagonal. They are also available with a passage hole that permits pressure equalization on both sides of the sealing surfaces. These gaskets seal via initial line contact, a wedging action between the gasket and the mating flange. The softer metal of the gasket applies pressure on the seal interface through bolt force, and it flows into the microfine structure of the harder mating flange, creating a very tight — and, therefore, very effective — seal.

Other common metallic gasket types include:

  • Camprofile (grooved) gaskets
  • Spiral-wound gaskets
  • Corrugated metal gaskets
  • Metal-jacketed gaskets

Metallic gaskets can be produced in a wide range of material combinations to accommodate all types of applications, such as use in heat exchangers, compressors, condensers, pumps, valves, and turbines.

Non-Metallic Gasket Options and Applications

Non-metallic gaskets, on the other hand, are usually made from composite sheet materials such as aramid fiber, glass fiber, or PTFE, and are used with flat-face and raised-face flanges in low-pressure applications. No metals are used in their construction.

Commonly available materials include:

  • Biaxially oriented (filled) PTFE
  • Flexible graphite sheet
  • Mica sheet
  • Ceramic fiber
  • Elastomeric and fiber sheet
  • Compressed non-asbestos sheet
  • Expanded PTFE sheet
  • Glass-filled/reprocessed PTFE sheet

Full-face non-metallic gaskets are suitable for use with flat-face flanges; flat-ring gaskets are used with raised-face flanges. Non-metallic gaskets — also called soft gaskets — are easily compressed under bolt load. Since they don’t contain metal, they offer superior corrosion resistance, but can only handle a limited range of temperature and pressure.

Non-metallic gaskets are commonly used in pipe flanges, heat exchangers, compressors, and bonnet valves. These gaskets are available in a variety of cut shapes.

The In-Between Option: Semi-Metallic Gaskets

Semi-metallic gaskets bridge the divide between metallic and non-metallic gaskets. As their name implies, semi-metallic gaskets are made of both metal and non-metallic materials. The metal offers strength and resiliency, while the non-metallic portion allows for easy conforming and sealing. Spiral-wound gaskets are commonly comprised of semi-metallic materials.

These unique properties make semi-metallic gaskets suitable for the widest range of operating conditions. Used on raised face, male-and-female, and tongue-and-groove flanges, semi-metallic gaskets are ideal for high-temperature and high-pressure applications.

Choosing the Best Gasket for Your Application

Gaskets may be tiny components, but they play a crucial role in equipment and system operations.  As selecting the wrong gasket configuration or material can impact operational reliability, great care should be taken during the design and material selection process. Be sure to partner with a trusted supplier who will be able to carefully evaluate your specific needs and guide you throughout every step of the process.

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