What are metal serrated gaskets?

What are metal serrated gaskets?

Metal serrated gaskets belong to a kind of metal composite gaskets. Generally, the zigzag grooves with 90 degree angle of concentricity are machined on the two sides of metal flat gaskets by precision lathe or special milling machine. Because the contact with other sealing surfaces is a linear contact of many concentric circles, they have labyrinth sealing effect. Flexible graphite can be selected according to different media and working conditions. PTFE, asbestos-free board or some other soft metals are pasted on the two sides of the gasket, making use of the sealing property of the soft covering layer and the strength and elasticity of the metal to achieve a better sealing effect. In most cases, we recommend graphite as the sealing layer. When the medium reacts to graphite or requires a clean environment, we recommend that we choose the newly introduced expander IV with excellent performance. Fluorine as adhesive layer, generally do not need a lot of pressure, can achieve sealing effect.

Type & Cross Section of Metal Serrated Gasket Application Range of Metal Serrated Gasket
History and Development of Metal Serrated Gasket Sealing Principle of Metal Serrated Gasket
Technical standard for metal serrated gaskets How to Order Serrated Gaskets

SERRATED METAL GASKET - What are metal serrated gaskets?
Serrated gaskets can also be directly used without covering sealing layer, and can achieve good sealing effect, but in high-pressure situations, flange surface is easily damaged. Therefore, the roughness of the sealing surface is generally required to be above Ra 1.6um.
Special working conditions such as extreme high temperature, strong corrosion, etc. require special material Metal serrated gaskets, we can also produce the following special materials can be required:
Stainless steel 304L, 321, 316TI, 309, 347, 410, duplex steel (2205, 31803), Monel MONEL (400), INCONEL (600, 625), INCOLOY (800, 825), HASTELLO (B2, C276), Titanium (T2) and other special stainless steel or alloy materials.
Performance characteristics of metal serrated gaskets:

  1. Lower pre-tightening force, even in high pressure environment, has a good sealing effect, especially suitable for high temperature, high pressure, alternating working conditions of the occasion is an ideal substitute for traditional metal-wound gaskets and metal-clad gaskets.
  2. Metal serrated gaskets do not damage the sealing surface and are easy to disassemble.
  3. The metal tooth shape part can be reused, which is of great significance for larger gaskets or gaskets of special materials, such as heat exchanger gaskets.

p27 2 - What are metal serrated gaskets?

pg27 1 - What are metal serrated gaskets?

Ret ring with concentric serrations made of various types of metal. Used when bolting force is not sufficient to seal a flat gasket, because it contacts flange face only at serration peaks. Commonly used on valve bannets and flanges attached to equipment. 3 types of cross section as per right table are available.

Type & Cross Section

Type

Cross Section

Basic(A)

pg27 - What are metal serrated gaskets?

With outer Ring(B)

With inner and Outer ring(C)

Depth of Serration(t)

Width

4.5mm

3.0mm

Cross Section

Less than 10mm

Inner diameter less than 200mm;0.75mm

0.5mm

p27 - What are metal serrated gaskets?

10mm and above

1.0mm


























Application Range of Metal Serrated Gaskets:

Tooth-shaped gaskets are mainly used in medium, high pressure and high temperature pressure vessels in petroleum, chemical, metallurgical, electric power, shipping, machinery and other industries, as well as in the sealing of heat exchangers, condensers and pipeline flanges.

History and Development of Metal Serrated Gaskets

Metal toothed composite gaskets are toothed composite gaskets with overburden. It was first developed and applied in Europe. Its toothed cross section was developed in Germany and was incorporated into the German pipe flange standard DIN2697 (DN10-400, PN 63, 100, 160, 250, 320, 400) about 40 years ago. Flange gaskets are widely used in heat exchangers and pressure vessels to replace metal-clad gaskets.
This gasket has been used in the high-pressure equipment of 480,000 tons/year urea plant (design pressure is 16.6 Mpa) designed by ourselves for a long time. At the end of the 20th century, it has also been used in many industrial plants in the United States to replace metal-wound gaskets and metal-clad gaskets. Over the years, the original design has been improved many times.

Sealing Principle of Metal Serrated Gasket

The soft material (flexible graphite or PTFE) covered on the two teeth surfaces of the metal tooth gasket not only fills the uneven defects on the contact surface of the flange easily, but also is pressed into many concentric circular grooves on the surface of the metal core. The compressive stress during the pre-tightening increases the density of the covering material (such as flexible graphite) in the groove and on the top of the teeth. Under the compressive stress of 200 Mpa, the density can be increased to about 2.27g/cm3.
When the average compressive stress of pre-tightening is very low, the compressive stress of flexible graphite at the top of the tooth will be very high, and it can still reach a high density. Thus, a multi-channel concentric high density seal ring is formed on the contact cross section between the flange and the gasket. Even if the cyclic variation of operating temperature, uneven thermal expansion and fluctuation of pressure lead to the change of bolt load and average compressive stress on gasket, graphite at the top of tooth can still maintain a high density state, and the springback of metal core can make gasket withstand the change of various loads and maintain a good sealing effect.
20190621235030 80234 - What are metal serrated gaskets?

The structural form and code number of the serrated gasket and the type of flange used are:

fundamental type

Code name

Applicable flange sealing surface

Thickness (mm)

Seal body

Paste layer (single side)

Basic type

YA-G410A

Tenon groove surface, concavo convex surface, plane and groove face

3, 4, 5

0.5-1.0

Outer ring (fixed)

YA-G420C

Plane or convex surface

3, 4, 5

0.5-1.0

Outer ring (activity)

YA-G421C

Plane or convex surface

3, 4, 5

0.5-1.0

Earring

YA-G422C

Plane or convex surface

3, 4, 5

0.5-1.0

Main technical parameters of various non-metallic materials for serrated gaskets:

Material Science

Identification code

Temperature c

Maximum working pressure

Applicable medium

Compression ratio%

Rebound percentage

Stress relaxation rate%

expand graphite

F.G.

-220–550

250 BAR

Corrosive medium


18–30

More than 17

Less than 18

Teflon

PTFE

-100– 200

100 BAR

Corrosive medium

18–30

More than 15

Less than 13

Expanded polytetrafluoroethylene

EPTFE

-100–260

200 BAR

Corrosive medium

25–35

More than 25

Less than 13

Asbestos free material

NA

-100–350

100 BAR

General tightness

18–30

More than 19

Less than 28

mica

MICA

-150–800

100 BAR

Extra high temperature

18–30

More than 19

 

ceramic fiber

CER

-200–1090

100 BAR

Ultrahigh temperature

18–40

More than 19

 

The following table is used for material selection of metal skeleton of commonly used serrated gaskets.

Material name

Abbreviation mark

Hardness (HB)

Limit temperature (C)

Carbon steel (Carbon steel)

CRS

One hundred and twenty

-40~+540

304 stainless steel

Three hundred and four

130~180

-195~+760

304L stainless steel

304L

130~180

-195~+760

316L stainless steel

316L

130~180

-100~+760

317L stainless steel

317L

 

-100~+760

321 stainless steel

Three hundred and twenty-one

130~190

-195~+760

347 stainless steel

Three hundred and twenty-one

 

-185~+760

20CB-3 (ALLOY 20)

A-20

 

-185~+1090

HASTELLOY-B2

HAST B

Two hundred and fifteen

-185~+1090

HASTELLOY-C276

HAST C

 

-185~+1090

INCOLOY-800

IN 800

 

-100~+870

INCOLOY-825

IN 825

 

-100~+870

INCONEL-600

INC 600

One hundred and fifty

-100~+1090

INCONEL-625

INC 625

 

-100~+1090

INCONEL-X750

INX

 

-100~+1090

MONEL-400

MON

One hundred and fifty

-130~+820

NICKEL-200 (nickel)

NI

 

-195~+760

TITANIUM (titanium)

TI

Two hundred and fifteen

-195~+1090

Dimensional limit deviation of serrated gaskets:

Internal diameter of toothed seal D1

The outer diameter of the toothed seal is D2

Outer ring outer diameter D3

Thickness T

+1.5
Zero

Zero
-0.75

+1.5
Zero

+0.25
Zero

The main parts of the serrated gaskets are performance parameter :

Gasket coefficient

M=4.25

Use of gaskets pressure

Less than 25MPa

Service temperature of gaskets

-196 C -650 C (no more than 450 C in oxidizing medium)

Minimum preload specific pressure of gasket

Y=50MPa

Customers choose different skeleton materials and adhesive layers according to different working conditions. Generally, the performance of the adhesive layer is the main reference, such as the requirement of high temperature resistant graphite and corrosion resistance of tetrafluoroethylene.

Technical standard for metal serrated gaskets:

  1. The foreign standards of metal serrated gaskets are: ASME B 16.5, BS1560, ASME B 16.47, BS EN1092, DIN2697, JIS and NF..
  2. Domestic standard has JB/T 88-1994 pipe flange metal serrated gasket mechanical part standard.
  • HB 6474-1990| toothed washer Aerospace Standards
  • Serrated gaskets for HG20611-2009 steel pipe flanges
  • Serrated gaskets for HG20632-2009 steel pipe flanges: American Ministry of chemical industry

How to Order Serrated Gaskets?

  1. Nominal pipe size or specific gasket dimensions
  2. Pressure rating
  3. Winding and filler materials
  4. Centering / outer ring or inner ring material

Source: China Serrated Gaskets Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

If you want to have more information about the article or you want to share your opinion with us, contact us at sales@steeljrv.com

Please notice that you might be interested in the other technical articles we’ve published:

References:

  • https://www.yaang.com

Summary
what are metal serrated gaskets - What are metal serrated gaskets?
Article Name
What are metal serrated gaskets?
Description
Metal serrated gaskets belong to a kind of metal composite gaskets. Generally, the zigzag grooves with 90 degree angle of concentricity are machined on the two sides of metal flat gaskets by precision lathe or special milling machine.
Author
Publisher Name
www.steeljrv.com
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