Pipe Flange Gasket Types: Selection Guide & Material Comparison

What is a pipe flange gasket?

Flange gaskets are seals used between two flanges in pipe flange connections. The selection of a flange gasket directly depends on the media, pressure, and temperature of the application. Gaskets are mainly divided into non-metallic, semi-metallic, and metallic types.

Flange Gasket Types Overview:

The following table provides a quick comparison of the three main gasket categories:

Gasket Category	Common Types	Characteristics	Typical Applications
Non-metallic	Rubber, asbestos rubber, PTFE, flexible graphite	Soft, good sealing, limited by pressure/temperature	Low pressure, non-corrosive media, clean services
Semi-metallic	Spiral wound, metal jacketed, corrugated composite	Combines metal strength with non-metallic sealing	Medium/high pressure, temperature fluctuations, chemical/power industries
Metallic	Ring joint (octagonal/oval), toothed, lens	High strength, excellent for extreme conditions	High pressure/high temperature, critical service, rarely disassembled

Detailed Guide to Common Gasket Types:

1. Non-metallic Gaskets

These gaskets are made from materials like asbestos, rubber, synthetic resin, or PTFE. They are generally soft and provide good sealing at lower pressures and temperatures.

PTFE Coated Gasket: A composite soft gasket with a PTFE envelope for corrosion resistance and a non-metallic insert (often asbestos rubber sheet). It is suitable for raised face (RF) and flat face (FF) steel flanges, with a nominal pressure PN 0.6~5.0MPa and temperature 0~150°C.

● Forms: Cut type (S), machined type (M), and folded type (F). The folded type is made from a 0.4~0.8mm thick PTFE film, with ends heat-sealed and wrapped around a core, making it suitable for larger flange sizes.

2. Semi-metallic Gaskets

These combine metal and non-metallic materials to offer improved strength and resilience over non-metallic gaskets.

Metal Spiral Wound Gasket: Made by spirally winding a metal strip (V or W-shaped) with a non-metallic filler. It offers excellent compression and rebound, multi-path sealing, and can handle pressure/temperature fluctuations and vibration.

● Forms: Basic type, with inner ring, with outer ring, and with both inner and outer rings. The inner ring prevents buckling under high pressure, and the outer ring aids centering and prevents blowout.

● Filler Materials: Common fillers include flexible graphite, PTFE, and asbestos, selected based on the media and temperature.

Metal-Jacketed Gasket: A non-metallic core (e.g., asbestos) covered with a thin metal sheet (0.25~0.5mm). It combines the sealing of the core with the strength and heat resistance of the metal jacket.

● Forms: Flat type (F) and corrugated type (C). The corrugated type provides better elasticity and sealing performance.

Metal Punched Tooth Plate Flexible Graphite Composite Gasket: Made from a punched metal plate and flexible graphite particles. It offers high strength, excellent resistance to temperature, corrosion, and radiation. Requires less preload force than metal gaskets and can seal on imperfect flange surfaces.

● Forms: Suitable for RF, MFM (male/female), and TG (tongue and groove) flange faces. RF type gaskets can be equipped with a stainless steel or carbon steel inner edge (RF-E type) for added strength.

Metal Corrugated Composite Gasket: A metal plate (corrugated) covered with flexible graphite on both sides. It provides metal strength and corrugated elasticity.
● Specifications: Maximum temperature 650°C, maximum pressure 26MPa.
● Forms: Basic type, with positioning ring, and with spacer.

3. Metallic Gaskets

These are solid metal gaskets used for extreme high-pressure and high-temperature services. They require high bolt preload and are typically used in applications where disassembly is rare.

Metal Ring Gasket: A solid metal gasket with an octagonal or oval cross-section. It provides a radial self-tightening seal by contacting the flange's ring joint groove.
● Octagonal Ring: Surface contact, reusable, easier to machine.
● Oval Ring: Line contact, better sealing performance, but not reusable and requires higher precision.

● Pressure Range: PN 2.0~42.0MPa.

Metal Toothed Gasket: A solid metal gasket with concentric V-shaped teeth (t=1.5~2mm, tooth height h=0.65~0.85mm, tip width C=0.2~0.3mm) on the sealing surface. The number of teeth is typically 7 to 16, depending on the gasket size. The multiple line contacts provide reliable sealing with less preload than plain metal gaskets.
● Forms: Basic type, with outer ring, with inner ring, and with both inner and outer rings.
● Pressure Range: PN 1.6~25.0MPa.
Note: May leave indentations on flange faces, so best for infrequent disassembly. This also means the flange sealing surface must be re-machined each time the gasket is replaced, adding to maintenance costs.

How to Select the Right Gasket?

Use the following quick guidelines to choose a gasket type for your application:

Quick Selection Guide:

By Media:
Water, air, low-corrosivity: Non-metallic gaskets (rubber, PTFE).
Acids, alkalis, chemicals: PTFE coated, or semi-metallic (spiral wound with suitable filler like PTFE).

Hydrocarbons, steam, high-temp: Semi-metallic (flexible graphite spiral wound) or metal gaskets.

By Pressure & Temperature:
Low pressure (PN ≤ 1.6 MPa) & low temperature (≤ 120°C): Non-metallic flat gaskets (ordinary rubber gaskets are suitable for <120°C; asbestos rubber for <450°C in steam or <350°C in oil, under 5MPa).
Medium/high pressure (PN 2.5~10 MPa) & fluctuating temperature: Semi-metallic (spiral wound).

High pressure (PN > 10 MPa) & high temperature (T > 350°C): Metallic (ring joint, toothed).

By Flange Type:
Raised Face (RF): Compatible with most gasket types (non-metallic, semi-metallic, metal toothed).
Ring Joint Face (RTJ): Must use metal ring gaskets.
Flat Face (FF): Use full-face non-metallic gaskets.
Tongue & Groove (T/G) or Male/Female (M/F): Use matching semi-metallic or metal gaskets designed for these faces.

Frequently Asked Questions (FAQ):

Q1: What type of gasket is best for a raised face (RF) flange?

A: RF flanges are the most common. You can use non-metallic flat gaskets, semi-metallic gaskets (like spiral wound), or metal toothed gaskets, depending on your pressure/temperature requirements.

Q2: When should I use a spiral wound gasket?

A: Spiral wound gaskets are ideal for applications with fluctuating temperatures and pressures, or where cyclic loading occurs (e.g., heat exchangers, piping with vibration). They offer excellent resilience.

Q3: Can I reuse a spiral wound or metal gasket?

A: Generally, no. Gaskets deform to create a seal. Reusing them is highly risky and likely to leak. Metal ring gaskets (oval type) are also not reusable; octagonal rings may be reused in some cases but it is not recommended for critical services.

Q4: Why are inner and outer rings used on spiral wound gaskets?

A: The outer ring (centering ring) helps position the gasket in the flange bolt circle. The inner ring prevents the gasket from buckling or collapsing inward under high internal pressure.

Related Resources:
[Steel Flange Dimensions Chart (ASME B16.5 & B16.47)]

[Pipe Flange Size Guide: Types, Classification & How to Select]

Need help selecting the right gasket for your specific application? 

Contact our team for expert advice: sales@hu-steel.com