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The gasket is the main seal part of the flange connection, so the correct choice of the flange gaskets is also the key to ensure that the flange connection does not leak. There are many types of gaskets, depending on the materials used to make them. In addition to the type of gasket, gasket identification and selection is also very important! Today, as a professional gasket manufacturer, we will show you how to mark and choose flange gaskets.

Gaskets’ Construction

Gaskets used in industry is generally composed of sealing element and inner and outer rings. The sealing element also called gasket body is the key part to prevent leakage. The material for the sealing element is usually non-metallic material such as flexible graphite, PTFE, non-asbestos, etc. In addition, the material also can be rigid or soft metal which is commonly used in higher pressure and temperature environment.

As for non-metallic sealing elements, it’s usually reinforced with a metallic material to make it strong enough for some application, especially for fragile material like pure flexible graphite.

The reinforced metallic material can be thin sheet or wire, and the thin sheet is always tanged to provide better sealing and resilience force. By using a binder and rolling, the graphite can be closely sticking to the sheet. Besides, an anti-sticking agent can be applied on the surfaces of the finished sheet to provide better sealing function and avoid stick with the flange’s surface.

The inner and outer rings are always solid metal, and their functions are as below:

– Work as a center ring during installation.

– Avoid the sealing element’s damages under extra pressure.

– Avoid the gasket’s blow-out and minimize the flanges’ turns.

– The outer ring is always made of carbon steel as it’s not in contact with the sealing medium and not required to be resistant to corrosive medium. It can also be integrated with the sealing element, such as metal kammprofile or metallic grooved gaskets.

– The inner ring’s material should be considered to be corrosion resistant as it’s in contact of the sealing medium. The inner ring is to prevent the fluid flow in the gap of sealing element and container or pipe flange and the impact on gasket resulted from the fluid flow.

Gaskets types:

We classify the various gasket into three types based on the different materials:

Non-metallic gasket, semi-metallic gasket, and metallic gaskets. please see below chart:

And you can also refer to our blog: Gasket Material to have a look at the materials.

Below we are going to talk about the most commonly used gaskets in the above three types:

Type 1: Non-metallic gasket: PTFE envelope rubber Gasket

*What is PTFE envelope Gasket?

It’s a kind of non-metallic composite gaskets made up of a PTFE envelope and an insert rubber gasket. The PTFE envelope protects the insert gasket from corrosion while the insert gaskets are always made from asbestos-free jointing sheets of EPDM rubber.

The gaskets are mainly used for full-faced or raised faced flanges and suitable for the nominal pressure of PN0.6 to 5Mpa and working temperature from 0~150℃ environment with corrosive medium and medium with high requirements for cleanliness.

*What is the construction of PTFE envelope Gasket?

This flange gasket can be classified into three types base on different manufacturing methods: Fin type or called split type, M type or machined type and F type or folded type.

Type 2: Semi-metallic Gasket

It is made from stainless steel strip with non-metallic tape and the formed metal steel strip works as a spring to provide better compressibility when under pressure. It is a kind of semi-metallic gasket.

Characteristics of the spiral wound gaskets:

1. Good compressibility and resilience.
2. It can provide multiple sealing.
3. Non-sticky and easy installation & easy to remove.
4. Low requirement for the flange surface’s perfectness.
5. It can partially eliminate the influence from pressure, temperature and mechanical vibration.
6. It can keep its excellent sealing performance under high temperature, low pressure, high vacuum, vibration and other severe conditions.

Construction of Spiral wound Gasket:

We provide four types of spiral wound gasket: Basic type, Spiral wound gasket with inner ring (RIR type), Spiral wound gasket with outer ring (CG type), Spiral wound gasket with inner and outer ring (CGI type).

Please refer to our blog How to choose a suitable spiral wound gasket for your flange to get more information.

Mark on the Spiral wound gasket:

• Take the picture on left as example (CGI type)
• The inner ring material is carbon steel;
• The outer ring material is 316L;
•  Winding material is 316L;
•  Filler material is Graphite;
•  Gasket size: 2”3-600#
•   Manufacturer: Ginseal
•   Gasket Standard: ASME B16.20

It’s made from a thin metal jacketed with a non-metallic filler always in graphite or non-asbestos.

Commonly the thin metal jacket’s thickness is 0.25~0.5mm.

The most commonly used metal jacketed gasket is double jacketed gasket with flat surface.

• SS tanged Graphite Gasket

It’s also called SS reinforced graphite gasket which is cut from tanged graphite sheet. It is comprising two outer layers of graphite foil with a central tanged stainless steel core of 0.1mm thick. The graphite layers are mechanically pressed together and won’t be delaminated during punching, storage, and use.

This gasket has good resistance to high and low temperature, to corrosion and can work under conditions of high pressure.

Its pre-tightening force required is less than the use of metal gaskets and spiral wound gaskets. Due to the graphite’s flexibility and filling property, it’s unnecessary to precision machining on the flange’s surface while underuse, and also it’s also suitable for the flanges with waterline groove. So the tanged graphite gasket is an economical choice when comparing to other gaskets.

It’s made up of a serrated metal core with a soft material usually in graphite or PTFE.

The gasket composes of the metal’s strength and serrated elasticity and soft material’s resilience. It’s suitable for high pressure and high temperature when the soft material is graphite.

There are three types for kammprofile gasket/metal grooved gasket: Basic type, Kammprofile gasket with loose outer ring, and kammprofile gasket with an integral outer ring. Please refer to Kammprofile Gasket-Grooved Gasket to know more about it.

Type 3: Metal Gasket

It is a metallic gasket with its cross-section machined to octagonal or oval shape. It provides sealing function by contacting with the inside and outside of the flange’s groove under pressing.

Octagonal type Ring joints are a face to face seal while oval type Ring joints are line seal. Based on the different sealing way, the oval type can provide better sealability but require high machining precision and cannot be re-used which result in higher cost compared with octagonal ring type joints.

The ring joints’ recommended working pressure is 2.0~42.0Mpa.

The choice made on the gaskets:

When choosing a suitable flange gasket, we should base on below basic information:

• Flange face type and dimensions
• Nominal diameter of flange or gasket
• Nominal pressure of flange or gasket
• Temperature of the fluid
• Characteristics of the fluid

And we also need to have knowledge of below:

• If the gasket can provide good compressibility and resilience and if it can adapt to the influence of temperature and pressure.
• If the gasket flexible enough to fit well with the flange face.
• For some metal flanges sensitive to stress corrosion, the gaskets’ material shall not contain excessive impurities which will lead to various corrosion, for example, we should take a note of the content of chloride ions in the material as it will corrode the flange.
• The gaskets’ material should not contaminate the fluid media.
• For sealing highly toxic chemicals, we should request the maximum safeness from the gaskets. For sealing in the pipes carrying flammable liquids, we should consider to choose gaskets suitable for the maximum pressure and temperature.
• The gaskets should have good machining performance and easy to install.
• The gaskets should be easy to remove and no-adhesive to flange.

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