How to select a sealing gasket?

There are many kinds of gasket, different materials, different shapes of gasket have different functions. If the wrong gasket is selected, it will not only not seal well, but also become a potential safety hazard, which may occur at any time. Do you know what are the sealing gaskets and what are their characteristics?

Contents:

Industrial rubber gaskets

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Natural rubber is suitable for water, sea water, air, inert gas, alkali, salt water solution and other media, but it is not resistant to mineral oil and non-polar solvents. Its long-term use temperature is not more than 90 ℃, and its low-temperature performance is excellent. It can be used above – 60 ℃.
NBR is suitable for petroleum products, such as petroleum, lubricating oil, fuel oil, etc., with a long-term service temperature of 120 ℃, 150 ℃ in hot oil and – 10 ~ – 20 ℃ in low temperature.
Chloroprene rubber is suitable for sea water, weak acid, weak alkali and salt solution. It has excellent oxygen and ozone resistance. Its oil resistance is inferior to that of nitrile rubber and superior to other general rubber. Its long-term service temperature is lower than 90 ℃, the maximum service temperature is not higher than 130 ℃, and the low temperature is – 30 ~ – 50 ℃.

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There are many kinds of fluororubber, which have good acid resistance, oxidation resistance, oil resistance and solvent resistance. It can be used in almost all acid media and some oils and solvents. The long-term use temperature is lower than 200 ℃.
As flange gasket, rubber plate is mostly used for manholes and handholes which are often disassembled, and the pressure is not more than 1.568mpa. Among all kinds of gasket, rubber gasket is the softest and has good adhesion performance, so it can play a sealing effect under small preload. Because of this, when bearing the internal pressure, the gasket is easy to be extruded because of its thickness or low hardness.
When rubber sheet is used in benzene, ketone, ether and other organic solvents, it is easy to swell, increase weight, become soft and sticky, resulting in sealing failure. Generally, it can not be used when the swelling degree is more than 30%.
Under the condition of low pressure (especially under 0.6MPa) and vacuum, rubber pad is suitable. Rubber material has good compactness and low air permeability. For example, fluororubber is the most suitable sealing gasket for vacuum vessels, with a vacuum degree of up to 1.3 × 10-7pa. When the rubber pad is used in the vacuum range of 10-1 ~ 10-7pa, it needs to be baked and pumped.
Asbestos rubber gaskets

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Compared with other gaskets, the price is lower and it is convenient to use. The biggest problem is that although rubber and some fillers are added to the gasket materials, they still can not completely fill those small pores which are in collusion, and there is a small amount of penetration. Therefore, in the highly polluting medium, even if the pressure and temperature are not high, it can not be used.
When it is used in some high-temperature oil media, usually in the later stage of use, due to the carbonization of rubber and filler, the strength is reduced, and the material becomes loose, and then there is penetration in the interface and gasket, resulting in coking and smoke. In addition, the asbestos rubber plate is easy to bond on the flange sealing surface under high temperature, which brings a lot of trouble to replace gasket.
In the heating state, the pressure of gasket in various media depends on the strength retention rate of gasket material. There are crystal water and adsorbed water in asbestos fiber materials. At 110 ℃, 2 / 3 of the adsorbed water between the fibers has been separated out, and the tensile strength of the fibers is reduced by about 10%; at 368 ℃, all the adsorbed water is separated out, and the tensile strength of the fibers is reduced by about 20%; when the temperature is over 500 ℃, the crystallized water begins to separate out, and the strength is lower. The medium also has a great influence on the strength of asbestos rubber sheet.
For example, in aviation lubricating oil and aviation fuel oil, the transverse tensile strength of 400 oil resistant asbestos rubber plate is 80% different, which is because the swelling of aviation fuel to rubber in the plate is more serious than that of aviation lubricating oil. Considering the above factors, the recommended safe use range of domestic asbestos rubber plate xb450 is: temperature 250 ℃ ~ 300 ℃, pressure 3 ~ 3.5Mpa; the use temperature of 400 oil resistant asbestos rubber plate should not exceed 350 ℃.
Asbestos rubber sheet contains chloride ion and sulfide, which is easy to form corrosive primary battery with metal flange after absorbing water, especially the sulfur content of oil resistant asbestos rubber sheet is several times higher than that of ordinary asbestos rubber sheet, so it is not suitable for use in non oil medium. Gasket will swell in oil and solvent medium, but in a certain range, it has little effect on sealing performance.
For example, No. 400 oil resistant asbestos rubber plate shall be soaked in aviation fuel oil at normal temperature for 24 hours, and the increase of oil absorption weight shall not exceed 15%.
There is a certain gap between domestic asbestos rubber sheet and foreign famous brand products. Statistics of a certain unit show that in the oil medium above 350 ℃, most of the products that do not leak when asbestos rubber plate is used are imported products. Japanese petroleum industry standard jpi-7s-71 standard for use of asbestos rubber sheet in petroleum industry, with a service life of about one year.
Teflon gaskets

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Polytetrafluoroethylene is easy to cold flow and creep under pressure and high temperature, so it is generally used for medium with low pressure, medium temperature, strong corrosion and no pollution, such as strong acid, strong alkali, halogen, medicine, etc. The safe use temperature is 150 ℃, and the pressure is less than 1MPa. Although the strength of filled polytetrafluoroethylene is higher, the service temperature is not more than 200 ℃, and the corrosion resistance is decreased. The maximum service pressure of PTFE gasket is generally not more than 2MPa.
Due to the temperature rise, the material creep, resulting in a significant drop in sealing pressure. Even if the temperature does not rise, with the extension of time, the compression stress of the sealing surface will decrease, resulting in “stress relaxation phenomenon”. This phenomenon will occur in all kinds of gaskets, but the stress relaxation of PTFE gasket is serious, which should be noted.
The friction coefficient of polytetrafluoroethylene is small (the compression stress is greater than 4MPa, and the friction coefficient is 0.035 ~ 0.04). The gasket is easy to slide outwards when preloading, so it is better to use concave convex flange face. When the flat flange is used, the outer diameter of the gasket can be contacted with the bolt to prevent the gasket from sliding outside.
Because the glass equipment is sintered after spraying a layer of enamel on the metal surface, the glaze layer is very brittle, and the spraying is uneven and the glaze layer flows, the flatness of the flange surface is poor. It is easy to damage the glaze layer by using the metal composite gasket, so it is recommended to use the PTFE gasket with the core material of asbestos board and rubber. The packing pad is easy to fit with the flange surface and resistant to corrosion, with good application effect.
There are many factories in the temperature, pressure is not high in the strong corrosive medium, using asbestos rubber plate wrapped with polytetrafluoroethylene raw material belt, used for the often dismantled manholes, pipes. It is popular because of its convenient production and use.
Asbestos resin board and impregnated asbestos board gasket
It is mainly used for pipelines, pumps, valves, inlet and outlet flanges of various sour media, with the service temperature of 80 ℃ and the pressure below 0.6MPa.
Asbestos gasket is suitable for low pressure and high temperature conditions with pressure below 0.1MPa and temperature not exceeding 800 ℃. And according to the specific requirements of the equipment, it can be woven into gaskets without width, thickness and diameter.
Or cut off the asbestos tape and apply it directly on the flange surface. The utility model is used in large sulfuric acid, nitric acid oxidation furnace and some unprocessed equipment interfaces, and the effect is far more than the original asbestos rope.
Metal covered asbestos gaskets

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The asbestos sheet or asbestos rubber sheet is covered by metal sheet, so that it does not contact with the medium directly, so that the strength of asbestos fiber is avoided to decline, and the leakage phenomenon is overcome, so as to expand the scope of use of asbestos rubber sheet.
Generally, the service temperature of metal clad asbestos pad is 450 ℃ (some of them are 600-700 ℃. For example, in the flue gas of atmospheric pressure ~ 0.16mpa), the service pressure is 4MPa, and the maximum is 6Mpa. If the pressure increases again, the gasket is prone to cross flow, and the core material is extruded from the lap joint.
Because the metal clad asbestos pad needs a large bolt tightening force, even when the use pressure is lower than 2.45mpa, it is not allowed to use the flange below pg25kg. Otherwise, the rigidity of flange and bolt is not enough, resulting in deformation and sealing failure. Some people think that if the core material is changed to synthetic rubber with better elasticity, its tightening force will decrease.
In fact, because the fastening force is absorbed by the core material after the core material is softened, the fastening force required for the metal plate to fit on the flange surface cannot be provided, and the packing pad is easily damaged. In addition, in the medium with more chloride ions and acid medium, the lap joint of stainless steel and iron clad pad is prone to crevice corrosion.
When the temperature is higher than 450 ℃, ceramic fiber or carbon fiber can be used as core material. The metal clad ceramic fiber gasket was used in a steel plant at 1100 ℃ for two years. Flexible graphite is the most suitable core material. At present, the flexible graphite pad for metal cladding has been mass produced in China. Its application effect is better than that of asbestos pad.
The metal packing pad can be made into various shapes and is widely used in various heat exchangers, large covers of reactors, loading and unloading holes, manhole flanges, etc. The iron clad pad with a diameter of 2m has been made in China, which is in good condition.
A layer of flexible graphite sheet is pasted on the surface of the metal gasket. Compared with the same kind of metal gasket which is not coated on the surface, the preload ratio is smaller and the sealing performance is better.
At present, there is no such product in China, so some units stick the existing flexible graphite wrinkly belt on the surface of metal packing pad, metal flat pad, tooth shaped pad or even asbestos rubber pad, which solves many leakage problems. For example, the pressure of the heat exchanger in a factory is 5.88MPA, the temperature is 450 ℃, and the medium is hydrogen / oil gas.
Once used the metal flat pad, the tooth shape pad, has the leakage. After that, the flexible graphite wrinkly belt was pasted on the flat pad, which solved the problem. It should be pointed out that this gasket form is a simple measure to solve the leakage of flange gasket. The working quality of the flexible graphite tape directly affects the normal operation of the equipment. If a layer of glue is applied on the back of the strip, the coating quality can be improved.
Metal Spiral wound gaskets

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Spiral wound gasket is a kind of sealing gasket widely used at present. It is the gasket with the best resilience in the semi-metallic sealing gasket. It is made of V-shaped or W-shaped thin steel strip alternately wound with various fillers. It can withstand high temperature, high pressure and adapt to the conditions of ultra-low temperature or vacuum. By changing the material combination of gasket, the problem of chemical corrosion of gasket caused by various media can be solved. Its structure is dense The degree can be made according to different locking force requirements. In order to strengthen the main body and accurate positioning, spiral wound gasket is equipped with metal inner reinforcing ring and outer positioning ring. The inner and outer steel rings are used to control the maximum degree of compression. The surface accuracy requirements of flange sealing surface contacted by gasket are not high.
Main uses
The metal spiral wound gasket with good resilience can automatically adjust the pressure thermal cycle and vibration of the pipeline system, especially for the occasions with uneven load, easy relaxation of joint force, periodic change of temperature and pressure, impact or vibration. It is the static sealing element of flange joints of valves, pumps, heat exchangers, towers, Manholes, handholes, etc. it is widely used in petrochemical, mechanical, electric power, metallurgy, shipbuilding, medicine, atomic energy, aerospace and other departments.
In the flange gasket appearance design, for the convenience of installation, according to the gasket diameter, 2-8 positioning belts are welded on the periphery of the gasket to make the positioning belt buckle on the flange hole, so as to prevent the gasket from shifting or falling off during installation, saving the auxiliary materials and working hours. Generally, they are divided into the following types:
The spiral wound gasket is made of high-quality SUS304, SUS316 (V-shaped or W-shaped) metal tape and other alloy materials alternately overlapped with graphite, asbestos, polytetrafluoroethylene, non asbestos and other soft materials. The metal tape is fixed by spot welding at the beginning and end. Spiral wound gasket is the best elastic gasket in the semi-metallic gasket. The structural density of spiral wound gasket can be made according to different locking force requirements, and the maximum degree of compression can be controlled by using inner and outer steel rings. The surface accuracy of the flange sealing surface contacted by spiral wound gasket is not high. Spiral wound gasket is especially suitable for the occasion of uneven load, easy relaxation of joint force, periodic change of temperature and pressure, impact or vibration. Spiral wound gasket is an ideal static sealing element for flange joints of valves, pumps, heat exchangers, towers, manholes and handholes.
Application scope of spiral wound gasket:
The flange joints of pipes, valves, pressure vessels, condensers, heat exchangers, towers, Manholes, handholes and other industries such as petroleum, chemical industry, metallurgy, electric power, shipbuilding and machinery are sealed.
Type of spiral wound gasket:
 产品剖面
Profile
产品名称
Products
代号
Style
适用
Flange
表示示例
For example
 
基本型金属缠绕垫
Basic type SWG
TD-SW700
榫槽面
Tongue and Groove
304/PTFE
 
带内环金属缠绕垫
SWG with inner ring
TD-SW700 IR
凹凸面
Male and Female
304 304/FG
 
带外环金属缠绕垫
WG with outer ring
TD-SW700OR
突面
Raise face Flat face
304/ASB CS
 
带内外环金属缠绕垫
SWG with inner & outer rings
TD-SW700IOR
304 304/FG CS
 
换热器用金属缠绕垫
SWG for heat exchanger
TD-SW700 H
换热器
Heat exchanger
 
 
异型金属缠绕垫
Special shape SWG
TD-SW700 S
异形
Special
 
Structural materials of spiral wound gasket:
Filling material
Steel strip
Inner ring
Outer ring
Asbestos winding
SUS304
碳钢
碳钢
Graphite winding
SUS316
SUS304
SUS304
Tetrafluoroethylene winding
SUS316L
SUS316
SUS316
 
 
SUS316L
SUS316L
Filling material
Temperature (°C)
Maximum operating pressure (kg/cm2)
Graphite winding
-200~550
250
Asbestos winding
-150~450
100
Tetrafluoroethylene winding
240~260
100
The following table is used for material selection of inner ring and wound metal:
 Trade name
AISI
Hardness (HB/HV)
Temperature (°C)
304
304
130~180
-250~+550
316
316
130~180
-100~+550
316L
316L
130~190
-100~+550
The outer ring is usually made of corrosion-resistant carbon steel.
Flange type and spiral wound gasket form:
Flange type
Shape of spiral wound gasket
Flat flange
Spiral wound gasket with outer ring only
Spiral wound gasket with inner and outer ring
 
Convex flange
Spiral wound gasket with outer ring only
Spiral wound gasket with inner and outer ring
 
Concave flange
Basic spiral wound gasket
Spiral wound gasket with inner ring only
 
Groove flange
Basic spiral wound gasket
Spiral wound gasket with inner ring only
 
Flat and grooved flanges
Basic spiral wound gasket
Spiral wound gasket with inner ring only
 
Thickness tolerance of spiral wound gasket:
Project
Thickness (mm)
Tolerance (mm)
Thickness of gasket
4.5,3.2
+0.2
-0.1
Thickness of ring
3.0,2.0
±0.24
Main technical parameters of spiral wound gasket:
Coefficient of spiral wound gasket
m=2.5-4
Service pressure of spiral wound gasket
≤25MPa
Service temperature of spiral wound gasket
-196-700(No higher than 600 ℃ in oxidizing medium)
Minimum preload of spiral wound gasket
y=68MPa

How to order spiral wound gasket?

When ordering spiral wound gasket, the following parameters shall be indicated, for example:

  • 1. Type of spiral wound gasket: a B C D
  • 2. Flange standard: ASME b16.20
  • 3. Pipe diameter and pressure rating: 2 “150lbs
  • 4. Material type: inner ring SS316; metal winding belt SS316; packing belt: graphite; outer ring: carbon steel

* the actual application conditions are different, and the above parameters are only for reference without any guarantee requirements.
Type of spiral wound gasket:

  • (I) basic metal winding gasket
  • (II) spiral wound gasket with outer ring
  • (III) spiral wound gasket with inner ring
  • (IV) spiral wound gasket with inner and outer rings
  • (V) for heat exchanger (with reinforcement)
  • (VI) special shaped metal winding gasket

Spiral wound gasket (basic type) is made of high-quality SUS304, SUS316 (“V” shape or “W” shape) metal belt and other alloy materials and soft materials such as graphite, asbestos, polytetrafluoroethylene, non asbestos, which are overlapped and spirally wound. At the beginning and end, the metal belt is fixed by spot welding.
1. Metal belt material

  • A. 08F, 0Cr13, 0cr18ni19ti, 0Cr18Ni9Ti, 00Cr18Ni10, 0Cr18Ni12Mo2Ti, 00cr17ni14mo2201304316 and other cold-rolled steel strips with thickness of 0.15mm ~ 0.25mm shall be adopted, or determined by both parties through negotiation.
  • B. the metal belt shall be preformed V-type or W-type narrow band, with smooth and clean surface, free from rough, uneven, crack, scratch, pit, rust spot and other defects
  • C. hardness value of stainless steel HV ≤ 200
  • D. the width of general steel strip is 3.2mm, 4.5mm, 8mm. W-type steel strip can be thicker.

2. Non metallic belt material

  • A. the non-metallic filler is specially made asbestos tape, flexible graphite tape, polytetrafluoroethylene tape, non asbestos fiber tape, ceramic fiber and mica tape, etc. The thickness of the tape is 0.3-1.0mm.
  • B. loss on ignition of special asbestos must be ≤ 25%
  • C. chloride ion content of nonmetal belt ≤ 100ppm
  • D. recommended operating temperature and pressure of various media and non-metallic tapes
  • E. the width of general steel strip is 3.2mm, 4.5mm and 8mm

3. Inner and outer ring materials
Commonly used are 304SS, 316LSS, 321ss, 347ss, carbon steel, titanium, copper
Scope of use:

  • 1. Service temperature: – 196 ℃ – 650 ℃ 1, the use of temperature: – 196 ° C – 650 ° C
  • (oxidation medium does not exceed 450 ℃)
  • 2. Use pressure ≤ 26mpa 2, the use of pressure ≤ 25MPa
  • 3. Gasket thickness: 2.5-4.5mm 3, gasket thickness: 2.5-4.5mm

Performance:

  • 1. Wide range of application. Able to withstand high temperature, high pressure and adapt to ultra-low temperature or vacuum.
  • 2. Strong application compensation ability. In the high temperature and high pressure fluctuating station, the sealing performance is stable and the reliability is strong.
  • 3. Good sealing performance.
  • 4. Easy to use and install.

Standards of spiral wound gasket:

  • Hg20610-97 European system of Ministry of chemical industry
  • Hg20631-97 American system of the Ministry of chemical industry
  • GB / t4622.2-97 national standard
  • JB / t4719-92 standard of Ministry of machinery
  • Sh3407-96 Petrochemical Enterprise
  • ASME b16.20 American Standard
  • DIN German standard
  • JIS b2404-1999 JIS ts-1998
  • BS 3381-1999 British Standard

Interpretation of ASME standard size code for spiral wound gasket


SWGSketch - How to select a sealing gasket?
tabel1swg - How to select a sealing gasket?
tabelboreswgasmeb16.5flange - How to select a sealing gasket?

Octagonal gasket and elliptical gasket

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Octagonal gasket and elliptical gasket (commonly known as “earth steel ring” in oil refining industry) used for trapezoidal groove face flange have good sealing performance. On the conical surface of the groove, the octagonal pad is in face contact while the elliptical pad is in line contact.
Therefore, the elliptical pad has a good fit under low tightening force, but it needs to be tightened twice, while the octagonal pad is not easy to leak after being tightened once. The disadvantage of them is that they require large bolt tightening force. When they are used in low pressure and high temperature conditions, the flange grade must be above pg25kg.

How to selection of gasket material?

The choice of gasket material mainly depends on the following three factors: temperature, pressure and medium.
I. Material of metal gasket
1. Carbon steel:
It is recommended that the maximum operating temperature should not exceed 538 ℃, especially when the medium is oxidizing. High quality carbon steel plate is not suitable for the equipment used to manufacture inorganic acid, neutral or acid salt solution. If the carbon steel is under the stress, the equipment accident rate under hot water condition is very high. Carbon steel gasket is usually used for high concentration of acid and many alkali solutions. Brinell hardness is about 120.
2. 304 stainless steel
18-8 (chromium 18-20%, nickel 8-10%), the recommended maximum operating temperature is not more than 760 ℃. In the temperature range of – 196 ~ 538 ℃, stress corrosion and grain boundary corrosion are easy to occur. Brinell hardness 160.
3.304L stainless steel
Carbon content shall not exceed 0. 03%. The recommended maximum operating temperature shall not exceed 760 ℃. Corrosion resistance similar to 304 stainless steel. The low carbon content reduces the precipitation of carbon from the lattice, and the resistance to grain boundary corrosion is higher than that of 304 stainless steel. Brinell hardness is about 140.
4.316 stainless steel
18-12 (chromium 18%, nickel 12%) in 304 stainless steel increased about 2% molybdenum, when the temperature increased its strength and corrosion resistance improved. When the temperature increases, it has higher creep resistance than other ordinary stainless steel. The recommended maximum operating temperature shall not exceed 760 ℃. Brinell hardness is about 160.
5. 316L stainless steel
The recommended maximum continuous working temperature is not more than 760 ℃ ~ 815 ℃. The carbon content is not more than 316 stainless steel with better stress and grain boundary corrosion resistance. Brinell hardness is about 140.
6.20 alloy
45% iron, 24% nickel, 20% chromium and a small amount of molybdenum and copper. The recommended maximum operating temperature is not more than 760 ℃ ~ 815 ℃. Especially suitable for manufacturing sulfuric acid resistant equipment, Brinell hardness is about 160.
7. Aluminum
Aluminium (not less than 99%). Aluminum has excellent corrosion resistance and processing performance, suitable for manufacturing double clamp gasket. Brinell hardness is about 35. The recommended maximum continuous working temperature shall not exceed 426 ℃.
8. Red copper
The composition of red copper is close to that of pure copper, which contains a small amount of silver to increase its continuous working temperature. The recommended maximum continuous working temperature shall not exceed 260 ℃. Brinell hardness is about 80.
9. Brass
(Cu 66%, Zn 34%) has good corrosion resistance under most working conditions, but it is not suitable for acetic acid, ammonia, salt and acetylene. The recommended maximum continuous working temperature shall not exceed 260 ℃. Brinell hardness is about 58.
10. Hastelloy B-2
(26-30% Mo, 62% Ni and 4-6% Fe). The recommended maximum operating temperature shall not exceed 1093 ℃. It has excellent heat resistance and hydrochloric acid corrosion resistance. It also has excellent resistance to wet hydrogen chloride gas corrosion, sulfuric acid, phosphoric acid and reducing salt solution corrosion. High strength at high temperature. Brinell hardness is about 230.
11. Hastelloy C-276
16-18% molybdenum, 13-17.5% chromium, 3.7-5.3% tungsten, 4.5-7% iron and the rest are nickel). The recommended maximum operating temperature shall not exceed 1093 ℃. It has excellent corrosion resistance. It has excellent corrosion resistance to cold nitric acid or boiling nitric acid with concentration up to 70%, good corrosion resistance to hydrochloric acid and sulfuric acid, and excellent stress corrosion resistance. Brinell hardness is about 210.
12. Inconel 600
Nickel base alloys (77% nickel, 15% chromium and 7% iron). The recommended maximum operating temperature shall not exceed 1093 ℃. It has high strength under high temperature, and is usually used in equipment to solve stress corrosion problem. At low temperature, it has excellent processability. Brinell hardness is about 150.
13. Monel 400
(the recommended maximum continuous working temperature of copper 30% and nickel shall not exceed 815 ℃. In addition to strong oxidizing acids, it has excellent corrosion resistance to most acids and bases. It is easy to produce stress corrosion crack in the medium of fluorine acid, mercuric chloride and mercury, so it is not suitable for the above medium. It is widely used in hydrofluoric acid manufacturing equipment. Brinell hardness is about 120.
14. Titanium
The recommended maximum operating temperature shall not exceed 1093 ℃. Under high temperature, it has excellent corrosion resistance. It is well known that it is resistant to the corrosion of chloride ions and has excellent resistance to nitric acid corrosion in a wide range of temperature and concentration. Titanium is rarely used in most alkaline solutions and is suitable for oxidation conditions. Brinell hardness is about 216.
II. Non metallic gasket materials
1. Natural Rubber NR
It has good corrosion resistance to weak acid and alkali, salt and chloride solution, and poor corrosion resistance to oil and solvent. It is not recommended for ozone medium. The recommended working temperature is – 57 ℃ ~ 93 ℃.
2. Neoprene Cr
Chloroprene rubber is a kind of synthetic rubber, which is suitable for medium corrosion resistance of acid, alkali and salt solution. It has good corrosion resistance to commercial oil and fuel. However, the corrosion resistance of strong oxidizing acid, aromatic hydrocarbon and chlorinated hydrocarbon is poor. The recommended working temperature is – 51 ℃ ~ 121 ℃.
3. NBR
Cyanobutylene rubber is a kind of synthetic rubber, which has good corrosion resistance to oil, solvent, aromatic hydrocarbon, basic hydrocarbon, oil and natural gas in a wide temperature range. It has good corrosion resistance to hydroxides, salts and nearly neutral acids. However, the corrosion resistance of ketones and lipids is poor in strong oxidizing media and chlorinated hydrocarbons. The recommended operating temperature is 51 ℃ ~ 121 ℃.
4. Fluororubber
Fluororubber compound is composed of binary and ternary raw fluororubber filled with mixture and curing agent. In addition to excellent heat resistance, medium resistance and good physical and mechanical properties, it also has low compression set, good elasticity and long service life. Fluororubber has outstanding heat resistance (200-250 ℃) and oil resistance. It can be used to make cylinder liner seal ring, rubber bowl and rotary lip seal ring, which can significantly improve the service time. The recommended working temperature is – 40 ℃ ~ 232 ℃.
5. Chlorosulfonated polyethylene synthetic rubber
It has good corrosion resistance to acid, alkali and salt solution, and is not affected by climate, light, ozone and commercial fuels (such as diesel oil and kerosene). But it is not suitable for aromatic hydrocarbon, chlorinated hydrocarbon, chromic acid and nitric acid. The recommended working temperature is – 45 ℃ ~ 135 ℃.
6. Silicone rubber
Silicone rubber has outstanding high and low temperature resistance, can be used for a long time at 150 ℃ without performance change; it can be used for 10000 hours continuously at 200 ℃, and can maintain its unique use elasticity, ozone resistance, weather resistance and other advantages within the working temperature range of – 70 ~ 260 ℃. It is suitable for making the sealing gasket needed in the hot mechanism, such as sealing lining ring, valve gasket, oil seal (suitable for water medium), etc, Special silicone rubber can make oil seal.
7. Ethylene propylene rubber
It has good corrosion resistance to strong acid, alkali, salt and chloride solution. But it is not suitable for oil, solvent, aromatic hydrocarbon and hydrocarbon. The recommended working temperature is – 57 ℃ ~ 176.
8. graphite
All graphite material without resin or inorganic substance can be divided into graphite material with or without metal element. The material can be bonded to produce pipe gasket with diameter over 600mm. It has excellent corrosion resistance to many acids, alkalis, salts, organic compounds, heat transfer solutions and even high temperature solutions. It can’t melt, but it will sublime when it exceeds 3316 ℃. Under the high temperature condition, the material should be used carefully in the strong oxidizing medium. In addition to gasket, the material can also be used to make packing and non-metallic spiral wound tape in spiral wound gasket.
9. Ceramic fiber
Ceramic fiber is a kind of excellent gasket material suitable for high temperature and low pressure working conditions and light flange conditions. The recommended working temperature is 1093 ℃, which can be used to make non-metallic spiral wound gasket.
10. Polytetrafluoroethylene
Polytetrafluoroethylene combines the advantages of most plastic gasket materials, including temperature resistance from – 95 ℃ ~ 232 ℃. In addition to free fluorine and alkali metals, it has excellent corrosion resistance to chemicals, solvents, hydroxides and acids. PTFE material can fill glass, its purpose is to reduce the cold fluidity and creep of PTFE.

How to choose the appropriate thickness of non-metallic gasket?

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How to choose the appropriate thickness of non-metallic GASKET? Why do different thickness of gasket appear in various standards? Why choose a gasket of this thickness?
This is a series of problems that the market bothers users.
According to the understanding and experience of sealing, yaang summarized:
1. The thickness, material, size and form of gasket are closely related to sealing medium and flange surface form
The smaller the longitudinal section of most non-metallic gasket, the smaller the medium penetration. However, in order to compensate for the uneven flange surface, the gasket usually chooses a larger thickness to compensate.
The minimum thickness of gasket depends on the roughness of flange surface, compression ratio of gasket itself, gasket stress, deflection degree of flange, etc.
If the flange is absolutely parallel, the thickness formula of the non-metallic gasket is:
T (thickness min.) = 2 x larger thickness of flange concave convex x 100 / C (where C is the maximum compression ratio of gasket).
2. Under the same bolt load, the narrower the gasket width, the higher the gasket stress, and the higher the inherent pressure of the gasket.
However, the selection of the width must consider that the gasket will not be torn and crushed, and the length of the necessary radial sealing channel and enough anti blowing force must also be considered.
Under different nominal diameter and pressure, the width of gasket will not be the same.
When the rough surface of the flange is very low, the width of non-metallic gasket shall be increased appropriately to prevent blowing out.

How to install the gasket correctly?

Gasket installation procedure
I. tools for installation:

Cleaning and fastening requires a variety of specific tools. In addition, standard installation equipment and good safe operation methods must always be used.

The following equipment shall be prepared before installation:

2014032800384383 - How to select a sealing gasket?

>Calibrated torque wrench, hydraulic tightening wrench, or other tightening tools;
>Steel wire brush, brass brush is better;
Helmet >
>Eye protection;
>Lubricants;
>Other factory specified tools, etc
 
II. Gasket installation steps:

1. Inspection and cleaning:

2014032800393428 - How to select a sealing gasket?

>Remove all foreign impurities and fragments from gasket pressing surface, various fasteners (bolts, studs), nuts and gaskets;
>Check the fastener, nut and gasket for burr, crack and other defects;
>Check the flange surface for warpage, radial scratch, deep tool bruise, or other defects affecting the correct seating of gasket;
>If the defective original is found, it should be replaced in time. If you have any questions about whether to replace it, you can contact yaang in time.

2. Align flange:

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>Align the flange face with the bolt hole;
>In case of any situation where positive information cannot be obtained, a report shall be made in a timely manner.
3. Install gasket:
>Confirm that the gasket conforms to the specified size and material;
>Check the gasket to make sure there is no defect;
>Carefully insert the gasket between the two flanges;
>Confirm that the gasket is in the central position between the flanges;
>Unless the gasket installation instructions require the use of adhesive or anti adhesive, it shall not be used without permission;
>Align flange faces to ensure gasket is not punctured or scratched.
4. Lubricate the stressed surface:
>Only the specified or approved lubricants are allowed to be used for the lubrication area;
>Apply sufficient lubricant to all threads, nuts and bearing surfaces of gasket;
>Ensure lubricant does not contaminate flange surface or gasket surface.

5. Install and tighten bolts:

2014032800401595 - How to select a sealing gasket?

>Always use the right tools
Use the calibrated torque wrench or other tightening tools that can control the function;
>Consult yaang engineering for torque requirements and regulations;
>Tighten the nut according to the “cross symmetry principle”;
Tighten the nut according to the following 5 steps:
The first step: the initial tightening of all nuts is carried out by hand, and the larger nut can be tightened with the aid of a small hand wrench;
Step 2: tighten each nut to about 30% of the required torque;
Step 3: tighten each nut to 60% of the required torque;
Step 4: use “cross symmetry principle” again to tighten each nut to achieve 100% of the required torque of the whole wood
Note: large diameter flange can use more times to carry out the above steps;
Step 5: tighten all nuts one by one in clockwise direction at least once to reach all required torque.
6. Tighten the bolt again:
>Note: consult with Sunway seal or engineering for guidance and advice on retightening the bolts;
>The non asbestos gasket and the gasket containing rubber components that have been used at high temperature shall not be tightened again (unless otherwise specified);
>After receiving the fastener of corrosion heat cycle, it needs to be tightened again;
>Re tightening shall be carried out at ambient temperature and atmospheric pressure.

Source: China Gaskets Manufacturer – Yaang Pipe Industry (www.metallicsteel.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@metallicsteel.com

Where do you place a spiral wound gasket?

The outer centering ring controls the compression and holds the gasket centrally within the bolt circle. The inner retaining ring increases the axial rigidity and resilience of the gasket. Spiral wound gaskets should always be in contact with the flange and should not protrude into the pipe or project from the flange.

What is the purpose of a flange gasket?

Flange gaskets are used to create a static seal between two flanges faces, at various operating conditions, with varied pressure and temperature ratings. A gaskets fills the microscopic spaces and irregularities of the flange faces, and then it forms a seal that is designed to keep liquids and gases.

How does a spiral wound gasket work?

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.

What is the difference between a gasket and a seal?

The terms “gaskets” and “seals” are often used interchangeably. The fundamental difference is that a gasket is a physical piece that goes between two flanges to create a seal at a joining point between two components. A gasket is a seal. “Seals” is a category that encompasses many types of seals.

Summary
how to select a sealing gasket - How to select a sealing gasket?
Article Name
How to select a sealing gasket?
Description
There are many kinds of gasket, different materials, different shapes of gasket have different functions. If the wrong gasket is selected, it will not only not seal well, but also become a potential safety hazard, which may occur at any time. Do you know what are the sealing gaskets and what are their characteristics?
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Publisher Name
www.metallicsteel.com
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