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What are gaskets

What are gaskets?

The gaskets are made of stainless steel, rubber or copper alloy and placed between two planes to strengthen the sealing. In order to prevent fluid leakage, the sealing element set between the static sealing surfaces is usually used to prevent pressure, corrosion and natural thermal expansion, cold contraction and leakage of the pipeline between two objects.
Gaskets are indispensable for all detachable structures of equipment and pipelines in industrial plants. As an important sealing element, the gasket can give better play to its efficiency, prolong its service life and ensure safety.

Gasket sealing plays a very important role in modern industrial enterprises. The quality of sealing is directly related to the continuity of production, property safety, energy conservation and environmental protection, as well as people’s physical and mental health. Therefore, people pay more and more attention to the development of gasket. With the rise of modern industry, especially modern petroleum, chemical industry, atomic energy industry and large-scale power stations, pressure vessels are developing towards high temperature, high pressure, high vacuum, cryogenic, large-scale and multi series. New requirements are constantly put forward for gasket sealing. Various new materials and new structures are emerging, and their sealing performance is also very different. In addition, the fluctuation of pressure, the change of temperature, the relaxation of bolt preload, the inclination and dislocation of flange, the defects of sealing surface and the corrosion of medium will have a great impact on the sealing effect. Therefore, how to correctly select the appropriate sealing gasket according to the working conditions and how to correctly install it are the key to ensure the sealing effect.

Materials of Gaskets

Metal gasket material

1. Carbon steel
The maximum operating temperature is recommended not to exceed 538 ℃, especially when the medium is oxidizing. High quality thin carbon steel plate is also not suitable for equipment manufacturing inorganic acid, neutral or acid salt solution. If carbon steel is subjected to stress, the equipment accident rate under hot water condition is very high. Carbon steel gaskets are usually used for high concentrations of acid and many alkali solutions. Brinell hardness is about 120.
2. 304 stainless steel
18-8 (chromium 18-20%, nickel 8-10%), and the recommended maximum operating temperature shall not exceed 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
The carbon content shall not exceed 0. 03%。 The recommended maximum operating temperature shall not exceed 760 ℃. Corrosion resistance is similar to 304 stainless steel. The low carbon content reduces the precipitation of carbon from the lattice, and the grain boundary corrosion resistance is higher than that of 304 stainless steel. Brinell hardness is about 140.
4. 316 stainless steel
18-12 (chromium 18%, nickel 12%), add about 2% molybdenum in 304 stainless steel. When the temperature increases, its strength and corrosion resistance improve. When the temperature increases, it has higher creep resistance than other ordinary stainless steels. The recommended maximum operating temperature shall not exceed 760 ℃. Brinell hardness is about 160.
5. 316L stainless steel
The recommended maximum continuous operating temperature shall not exceed 760 ℃ ~ 815 ℃. Compared with 316 stainless steel, it has better stress resistance 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 shall not exceed 760 ℃ ~ 815 ℃. It is especially suitable for manufacturing equipment resistant to sulfuric acid corrosion, with Brinell hardness of about 160.
7. Aluminum
Aluminum (content not less than 99%). Aluminum has excellent corrosion resistance and processability, which is suitable for manufacturing double clip gaskets. Brinell hardness is about 35. The recommended maximum continuous operating temperature shall not exceed 426 ℃.
8. Red copper
The composition of red copper is close to pure copper, which contains a small amount of silver to increase its continuous working temperature. It is recommended that the maximum continuous working temperature should not exceed 260 ℃. Brinell hardness is about 80.
9. Brass (copper 66%, zinc 34%)
Under most working conditions, it has good corrosion resistance, but it is not suitable for acetic acid, ammonia, salt and acetylene. It is recommended that the maximum continuous working temperature should not exceed 260 ℃. Brinell hardness is about 58.
10. Hastelloy B-2 (26-30% molybdenum, 62% nickel and 4-6% iron)
The recommended maximum operating temperature shall not exceed 1093 ℃. It has excellent heat resistance and hydrochloric acid corrosion performance. It also has excellent resistance to wet hydrogen chloride gas corrosion, sulfuric acid, phosphoric acid and reducing salt solution corrosion. It has 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 a concentration of 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 alloy (77% nickel, 15% chromium and 7% iron)
The recommended maximum operating temperature shall not exceed 1093 ℃. It has high strength under high temperature conditions and is usually used for equipment to solve stress corrosion problems. At low temperature, it has excellent same processing properties. Brinell hardness is about 150.
13. Monel 400
It is recommended that the maximum continuous operating temperature should 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 cracks in fluoric acid, mercuric chloride and mercury media, so it is not suitable for the above media. It is widely used in the manufacture of hydrofluoric acid. Brinell hardness is about 120.
14. Titanium
The recommended maximum operating temperature shall not exceed 1093 ℃. It has excellent corrosion resistance at high temperature. It is well known that it is resistant to chloride ion corrosion and has excellent nitric acid corrosion resistance in a wide temperature and concentration range. Titanium is rarely used in most alkali solutions and is suitable for oxidation conditions. Brinell hardness is about 216.

Non metallic gasket material

1. Natural rubber
It has good corrosion resistance to weak acid, alkali, salt and chloride solutions, but poor corrosion resistance to oil and solvent. It is not recommended to be used in ozone medium. The recommended operating temperature is – 57 ℃ ~ 93 ℃.
2. Neoprene

Neoprene is a kind of synthetic rubber, which is suitable for the corrosion of medium corrosive acid, alkali and salt solutions. It has good corrosion resistance to commercial oils and fuels. However, the corrosion resistance of strong oxidizing acids, aromatic hydrocarbons and chlorinated hydrocarbons is poor. The recommended operating temperature is – 51 ℃ ~ 121 ℃.
3. Cyano butadiene rubber 

Cyano butadiene rubber is a kind of synthetic rubber, which is suitable for good corrosion resistance to oil, solvent, aromatic hydrocarbon, alkaline hydrocarbon, oil and natural gas in a wide temperature range. It has good corrosion resistance to hydroxide, salt and near neutral acid. However, in strong oxidizing medium, chlorinated hydrocarbons, ketones and lipids, their corrosion resistance is poor. The recommended working temperature is 51 ℃ ~ 121 ℃.
4. Fluororubber
Fluororubber is made by mixing binary and ternary fluororubber with compounding agent and vulcanizing agent. In addition to excellent heat resistance, medium resistance and good physical and mechanical properties, it also has low compression set, good elasticity and ultra long service life. Fluororubber has outstanding heat resistance (200 ~ 250 ℃) and oil resistance. It can be used to manufacture cylinder liner sealing ring, rubber bowl and rotating lip sealing ring, which can significantly improve the service time. The recommended operating temperature is – 40 ℃ ~ 232 ℃.
5. Chlorosulfonated polyethylene synthetic rubber
It has good corrosion resistance to acid, alkali and salt solutions, and is not affected by climate, light,, ozone and commercial fuels (such as diesel and kerosene). However, it is not suitable for aromatic hydrocarbons, chlorinated hydrocarbons, chromic acid and nitric acid. The recommended operating temperature is – 45 ℃ ~ 135 ℃.
6. Silicone rubber
Silicone rubber has outstanding high and low temperature resistance, and can be used for ultra long time at 150 ℃ without performance change; It can be used continuously at 200 ℃ for 10000 hours. It can maintain its unique use elasticity, ozone resistance and weather resistance in the working temperature range of – 70 ~ 260 ℃. It is suitable for making sealing gaskets required in thermal mechanism, such as sealing lining ring, valve gasket and oil seal (suitable for water medium). Special silicone rubber can make oil seal.
7. Ethylene propylene rubber
It has good corrosion resistance to strong acid, alkali, salt and chloride solutions. However, it is not suitable for oils, solvents, aromatic hydrocarbons and hydrocarbons. The recommended operating temperature is – 57 ℃ ~ 176 ℃.
8. Graphite
The material is an all graphite material without resin or inorganic matter, which can be divided into graphite materials with or without metal elements. The material can be bonded to produce pipe gaskets with a diameter of more than 600mm. It has excellent corrosion resistance to many acids, bases, salts, organic compounds, heat transfer solutions and even high temperature solutions. It cannot melt, but will sublimate above 3316 ℃. Under high temperature conditions, the material should be used carefully in strong oxidizing medium. In addition to gaskets, the material can also be used to make non-metallic winding tapes in fillers and spiral wound gaskets.
9. Ceramic fiber
The ceramic fiber formed on the strip is an excellent gasket material suitable for high temperature and low pressure conditions and light flange conditions. The recommended working temperature is 1093 ℃, which can be used to make non-metallic winding tape in wound gasket.
10. Polytetrafluoroethylene
It integrates 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 be filled with glass to reduce the cold fluidity and creep of PTFE.

Types of gaskets

There are many kinds of gaskets, which can be divided into three categories: non-metallic, semi-metallic and metal gaskets according to the subject materials of their structure.

Non metallic gasket

The non-metallic gasket is soft, corrosion-resistant and cheap, but it has poor temperature and pressure resistance. It is mainly used for flange sealing of medium and low pressure vessels or pipelines at normal and medium temperature.
Non metallic gaskets include rubber gasket, asbestos gasket, asbestos rubber gasket, flexible graphite gasket and PTFE gasket.

  • ① Rubber plate. The main materials for making rubber plate gaskets are natural rubber, nitrile rubber, neoprene, etc. in addition, special rubber such as fluororubber has also been applied. Rubber is widely used in the sealing of containers and pipelines because of its compact structure, soft texture, good resilience, easy to cut into various shapes, cheap and easy to buy. However, it is not resistant to high pressure, easy to dissolve and expand in mineral oil, and is not corrosive. It is easy to age at high temperature and lose resilience.
  • ② Asbestos. Asbestos materials include wet asbestos and blue asbestos. Wet asbestos has good heat and alkali resistance, high tensile strength and poor acid resistance. Most asbestos rubber sheets are made from it; Blue asbestos not only has good heat resistance, but also has good acid resistance, so it is mostly used to manufacture acid resistant asbestos rubber sheet. The normal service temperature of asbestos board is below 550 ℃. Asbestos tape or asbestos rope can be used for low-pressure vessels with large diameter. When asbestos rope is used, it is usually impregnated with water glass. Such gaskets can also be used for acid, alkali, solvent and other media.
  • ③ Asbestos rubber sheet. Asbestos rubber sheet is made of asbestos, rubber and filler. General asbestos fiber accounts for 60% – 85%. According to its matching process, performance and use, it mainly includes high-pressure asbestos rubber plate, medium and low-pressure asbestos rubber plate and oil resistant asbestos rubber plate.
  • Asbestos rubber sheet has suitable properties such as strength, elasticity and flexibility. It is convenient and cheap to make gasket with it. Therefore, it has been rapidly popularized and applied in chemical enterprises.
  • ④ Flexible graphite. Flexible graphite is a novel sealing material with good resilience, flexibility and temperature resistance. It has been rapidly popularized and applied in chemical enterprises.
  • ⑤ Polytetrafluoroethylene (PTFE). Polytetrafluoroethylene is known as the “king of plastics” because of its chemical resistance, heat resistance, cold resistance and oil resistance. It is not easy to age, does not burn and has almost zero water absorption. The structure is compact and the molecular structure is non-polar. As a gasket, the contact surface can be flat and smooth without adhesion to the metal flange. In addition to being eroded by molten alkali metal and fluorine-containing element gas, it can resist the corrosion of a variety of acid, alkali, salt and grease solution media. PTFE gasket includes pure PTFE, filled PTFE or expanded PTFE, etc.

Semi metallic gasket (also known as metal composite gasket)

Non metallic materials have the advantages of good flexibility, compressibility and low bolt load capacity. But its main determination is that the strength is not high, the resilience is poor, and it is not suitable for high pressure and high temperature occasions. Therefore, the combined metal material has high strength and good resilience. Capable of withstanding high temperatures. Form a gasket that combines the two. They are semi-metallic gaskets.
Semi metallic gaskets mainly include metal clad gaskets, metal wound gaskets, metal corrugated gasket, metal tooth shape gasket, etc.
① Metal clad gasket (metal composite gasket). The gasket takes non-metal as the material core and is wrapped with a metal sheet with a thickness of 0.25-0.5mm. According to the coating state, it can be divided into full coating, semi coating, waveform coating and double-layer coating.
The metal sheet is selected according to the elastic-plastic, heat resistance and corrosion resistance of the material. Mainly copper, galvanized iron sheet, stainless steel, titanium, Monel alloy, etc. Copper, galvanized iron sheet and stainless steel are widely used.
As the core material of metal pad, heat resistance is the main assessment index. Asbestos board or low rubber asbestos board, carbon fiber or porcelain fiber with good high temperature resistance and flexible graphite plate are generally used.
Another feature of the metal coated pad is that it can be made into various types of gaskets. It can meet the sealing needs of various heat exchanger tube boxes and non-circular pressure vessels, but other composite gaskets can not.
② Spiral wound gasket. The metal spiral wound gasket is made by alternately winding the thin metal corrugated belt and non-metallic materials such as asbestos or flexible graphite into a spiral shape, and welding the beginning and end points of the metal belt. It is also called spiral gasket abroad.

Metal gasket

Under harsh operating conditions such as high temperature, high pressure and frequent load cycles, various metal materials are still the preferred materials for sealing gaskets. Commonly used materials include copper, aluminum, low carbon steel, stainless steel, chromium nickel alloy steel, titanium Monel alloy, etc. In order to reduce the bolt load and ensure the compact structure, in addition to the narrow width of the metal flat pad, various ring pad structures with line contact characteristics are the preferred forms.

Spiral wound gasket

Spiral wound gasket generally adopt and steel tape of the same material as to meet the requirements of pipeline corrosion medium is usually better than that of a pipe or flange material, according to the standard requirements to carry metal winding is fixed on the inner ring and with metal winding belt with graphite, asbestos, PTFE, non asbestos etc. Nonmetal overlapping spiral wound coil alternates with continuously, at the end of the metal belt fixed in spot welding way. The inner ring is also called the reinforcing ring to avoid the loose ring that wraps around the gasket.

Spiral wound gasket with carbon steel inner ring - What are gaskets

Type and code of construction of spiral wound gasket and flange category:
The basic pattern Code name Applicable French sealing face Thickness (mm)
V-shaped basic body/ring W basic body/ring
Basic Type A or R Tenon and groove surface, concave and convex surface, plane and groove surface 3.2; 4.5 4.8; 5.5; 7.5
Take inner ring type Type B or rirs Tenon and groove surface, concave and convex surface, plane and groove surface 3.2/2
4.5/3
4.8/3.0
5.5/4.0
7.5/5.0
With outer ring Type C or CG A flat or convex surface
With inner ring and outer ring type Type D or CGI A flat or convex surface
Material:
1. Metal tape with inner ring metal wound gasket
A. Use sus304,sus316L, SUS321 cold-rolled steel strips with thickness from 0.15mm to 0.25mm, or be determined by negotiation between the supply and demand parties.
B. Metal strip shall be preformed v-shaped or W-shaped narrow strip with smooth surface. Clean, there should be no rough. Defects such as cracks, scratches, pits and rust spots
C. The hardness of stainless steel HV≤200

2. Non-metallic gasket with inner ring non-metallic tape.

A. Non-metallic filling is specially made asbestos tape, flexible graphite tape, ptfe tape, non-asbestos fiber tape, mica tape, etc. The thickness of the belt is 0.3-1.0mm.

B. Loss of fire of specially made asbestos shall be ≤25%.

C. Chloride ion content of non-metallic tape shall be ≤100PPM D. Recommended operating temperature and pressure for all kinds of media and non – metallic tape.

Main technical parameters of spiral wound gasket
material Identification code Temperature ℃ *** High work pressure Applicable medium Compression ratio % Resilient rate % Stress relaxation rate %
Expanded graphite F.G.
-220–550
250 BAR Corrosive medium
18-30
P 17 18 or less
Special asbestos tape ASB -150–450 100 BAR Like the air tightness 18-30 P 19 28 or less
Teflon PTFE – 200-250 100 BAR Corrosive medium 18-30 15 or more 13 or less
Asbestos free material NAF -100–350 100 BAR General air tightness 18-30 P 19 28 or less
Cloud mother MICA -150–800 100 BAR High temperature, 18-30 P 19  
Tao porcelain CER -200–1090 100 BAR Ultra high temperature 18 to 40 P 19  

The following table is used for material selection of inner ring and winding metal:

The name of the material Abbreviations tag Hardness (HB) Temperature (° C)
SUS 304 304 130 ~ 180 – 195 ~ + 550
SUS 316L 316L 130 ~ 180 – 100 ~ + 550
SUS 321 321 130 ~ 190 – 195 ~ + 760
HASTELLOR-B2 HASTB 215 – 185 ~ + 1090
INCONEL-600 INC600 150 – 100 ~ + 1090
MONEL-400 MON 150 – 130 ~ + 820
titanium TI 215 – 195 ~ + 1090

Basic body thickness tolerance:

project Thickness (mm) Tolerance (mm)
The thickness of the gasket 4.5, 3.2 + 0.2
0.1
The thickness of the ring 3.0 + / – 0.25

The following table is the spiral wound gasket diameter tolerance (i.e. the nominal pipe diameter used for flanges) :

  DIN (mm) ANSI B16.5
BS1560 (mm)
Mss sp-44
API 605 The tolerance
The inner diameter
Gasket inside diameter
< = 600 < = 24″ >=26″ and <=34″ + / – 0.5
>600 and <=800 >24″ and <=34″ >=36″ and <=60″ + / – 0.9
>800 and <=1600 >34″ and <=60″   + / – 1.3
> 1600 > 60″   + / – 1.6
Gasket diameter < = 600 < = 24″ < = 24″ + / – 0.9
>600 and <=16000 >24″ and <=60″ >24″ and <=60″ + / – 1.8
1600 > 60″   + / – 2.2
Outer diameter     >=1/2″ and <=60″ + / – 0.9
< = 600 < = 24″   0-1.0
>600 and <=1000 >24″ and <=34″   0-1.8
>1000 and <=1600″ >34″ and <=60   0-2.2

Main performance parameters:

Wound gasket coefficient M = 2.5 4
Wound gasket using pressure 25 mpa or less
Service temperature of wound gasket -196℃-700℃(not higher than 600℃ in oxidizing media)
Wound gasket *** small preload specific pressure y=68MPa

Toothed composite gasket

Toothed composite gasket tooth shape metal composite gasket belongs to a kind of metal composite gaskets, commonly used special precision lathe or milling machine first in the two aspects of metallic flat gasket processed into concentric waveform 90 degrees Angle of sawtooth groove, is due to contact with other sealing surface of multiple concentric line contact, so have labyrinth seal effect, according to the different medium and conditions, You can choose flexible graphite, PTFE, non-asbestos board or some other soft metal, paste on the two sides of the gasket, using the advantages of the sealing of the soft covering layer and the strength and elasticity of the metal, in order to achieve 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 to choose the newly launched excellent performance of the expanded tetrabluoride paste layer, generally do not need a lot of compression force, can achieve sealing effect. Toothed gasket can also be used directly without a covering seal layer, which can also achieve good sealing effect, but it is easy to damage the surface of the flange in high-pressure situations. Therefore, it is generally required that the roughness of the sealing surface is above RA1.6um. Special working conditions such as extremely high temperature, strong corrosion and other need special material metal tooth shape combination gasket we can also produce some of the following special materials can be required: Stainless steel 304L,321,316TI, 309,347,410, duplex steel (2205,31803), MONEL (400), INCOLOY (800,825), HASTELLO (B2, C276), titanium (T2) and other special stainless steel or alloy materials. 1. Low preload, good sealing effect even in high pressure environment, especially suitable for high temperature, high pressure, alternating conditions of the occasion is the ideal substitute of traditional metal wound gasket and metal coated gasket. 2. The metal toothed gasket does not damage the sealing surface and is easy to disassemble. 3. The metal teeth can be reused for larger gaskets or gaskets of special materials, such as heat exchanger gaskets. Application range: Toothed gasket is mainly used in petroleum, chemical, metallurgy, electric power, ship, machinery and other industries of medium, high pressure and high temperature pressure vessels, heat exchanger, condenser and pipe flange joint sealing.

Type and code of construction of toothed gasket and flange category:
The basic pattern  Code name Applicable French sealing face Thickness (mm)
The seal body Adhesive layer (single side)
basic ZD-1900A Tenon and groove surface, concave and convex surface, plane and groove surface 3,4,5 0.5-1.0
With outer ring (fixed) ZD-1901C A flat or convex surface 3,4,5 0.5-1.0
Outband ring (active) ZD-1902C A flat or convex surface 3,4,5 0.5-1.0
Bring earrings ZD-1903C A flat or convex surface 3,4,5 0.5-1.0
Main technical parameters of various non-metallic materials:
material Identification code Temperature ℃ *** High work pressure Applicable medium Compression ratio % Resilient rate % Stress relaxation rate %
inflationgraphite F.G. -220–550 250 BAR Corrosive medium
18-30
P 17 18 or less
Teflon PTFE – 100-200 100 BAR Corrosive medium 18-30 15 or more 13 or less
Expanded ptfe EPTFE -100–260 200 BAR Corrosive medium 25-35 25 or higher 13 or less
Asbestos free material NA -100–350 100 BAR General air tightness 18-30 P 19 28 or less
Cloud mother MICA -150–800 100 BAR High temperature, 18-30 P 19  
Ceramic fiber CER -200–1090 100 BAR Ultra high temperature 18 to 40 P 19  

The following table is used for material selection of metal skeleton of common toothed gasket combination:

The name of the material Abbreviations tag Hardness (HB) Limit temperature (°C)
Carbon steel CRS 120 – 40 ~ + 540
304 stainless steel 304 130 ~ 180 – 195 ~ + 760
304 l stainless steel 304L 130 ~ 180 – 195 ~ + 760
316 l stainless steel 316L 130 ~ 180 – 100 ~ + 760
317 l stainless steel 317L   – 100 ~ + 760
321 stainless steel 321 130 ~ 190 – 195 ~ + 760
347 stainless steel 321   – 185 ~ + 760
20CB-3(ALLOY 20) A-20   – 185 ~ + 1090
HASTELLOY-B2 HAST B 215 – 185 ~ + 1090
HASTELLOY-C276 HAST C   – 185 ~ + 1090
INCOLOY-800 IN 800   – 100 ~ + 870
INCOLOY-825 IN 825   – 100 ~ + 870
INCONEL-600 INC 600 150 – 100 ~ + 1090
INCONEL-625 INC 625   – 100 ~ + 1090
INCONEL-X750 INX   – 100 ~ + 1090
MONEL-400 MON 150 – 130 ~ + 820
NICKEL – 200 (ni) NI   – 195 ~ + 760
TITANIUM (ti) TI 215 – 195 ~ + 1090

Size limit deviation of toothed gasket: 

Tooth seal internal diameter D1 Tooth seal internal diameter D2 Outer diameter of outer ring D3 The thickness of the T
+ 1.5
0
0
0.75
+ 1.5
0
+ 0.25
0

Performance parameters of toothed combination gasket

Coefficient of gasket  M = 4.25
Gasket used pressure 25 mpa or less
Service temperature of gasket -196℃-650℃(not higher than 450℃ in oxidizing medium)
Gasket *** small preload ratio pressure y=50MPa

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

Octagonal gasket

The metal gasket is made of metal material by forging and heat treatment and machining into cross section shape is the entity of octagon metallic gasket, have radial since the tight sealing effect, is a standard type R a kind of metal ring gasket, its action principle is cushion for leaning on is with flange type ladder groove (mainly the lateral) out of contact, and through the pressure sealing function to form.

asme b16.20 ss316l octagonal ring gasket type r45 6 inch 900lb - What are gaskets

The Octagonal gasket is installed in the ladder ring groove of the flange face. When tightening the connecting bolt, it is tightly connected with the upper and lower ladder groove by axial compression, resulting in plastic deformation, forming a ring seal belt and establishing the initial seal. After pressure boost, under the action of medium pressure, the ring pad radial expansion. Gasket and trapezoidal groove of the inclined plane more closely, resulting in self-tightening. However, the rise of medium pressure will also deform the flange and connecting bolt, resulting in the relative separation between sealing surfaces, gasket sealing ratio relative decline, therefore, ring gasket can be considered as semi-self-sealing.
Octagonal gasket and flange groove match is mainly surface contact, compared with the oval ring pad, although it is not easy to achieve close with the flange groove, but it can be used again, and because the section is made of straight lines easy to process. At the same time, the hardness of Octagonal gasket should be lower than the flange surface of 15~20HB.
Performance characteristics of octagonal gasket
1, high temperature and high pressure resistance, suitable for high pressure flange;
2, durable and reliable sealing;
3. Adapt to the working conditions with fluctuation of pressure and temperature;

Application range of octagonal gasket

Usually used in high temperature and high pressure steam, gas, solvent pipe flange, tower groove, pressure vessel, high speed joint surface, high temperature and high pressure valve, cover. Sealing of wellhead units and production trees in the oil and gas industry

The metal gasket originated from the United States, and was used in the field of boilers in the 1920s. It was later used for manhole covers and the sealing of other Windows of autoclasts. After that, it received special attention in the petroleum production and refining industry. As the temperature and pressure of steam power plant increase, the use of metal gasket becomes more and more extensive.

R oval gaskets, standard oval metal ring gaskets are used for flanges with standard grooves.
Type R octagonal gaskets, standard octagonal metal ring gaskets are used on flanges with standard grooves.
RX octagonal gasket, pressure up to 700bar This gasket is first used with the outer sealing surface and flange contact, high system pressure will produce high base stress. RX type metal gasket is interchangeable with standard R type ring pad.
Type BX octagonal gasket, high pressure resistant (up to 1500bar) type BX gasket is self-sealing controlled by internal system pressure generated by increasing gasket base pressure on flange contact surface. Gaskets are suitable for API BX flanges and mortise flanges.

Material selection of octagonal gasket

material * * * great hardness mark Temperature ℃
Brinell HB Rocknell HB Min Max
Soft Iron 90 56 P – 40 540
Low C/S 120 68 S – 60 500
SS410 170 86 S410 – 40 850
SS304 160 83 S304 – 250. 540
SS316 160 83 S316 – 200. 815
SS347 160 83 S347 – 200. 870
0.5% 4-6% Cr, Mo, 130 72 F5 – 40 650
Copper 80 C – 100. 315
Aluminum 35 A – 200. 425
Inconel 600 150 78 Y – 100. 1095
Inconel 825 150 78 W – 100. 1095
Monel 400 150 78 M – 100. 760
Titanium 215 77 T – 200. 540
Nikel 200 110 58 N – 200. 760
Hastelloy B2 230 121 X1 – 100. 1095
Hastelloy C276 210 110 X2 – 100. 1095

Size limit deviation of octagonal gasket

Name of size Generation of no. Limit deviation
Pitch diameter of ring pad P + / – 0.18
Width of ring pad A + / – 0.20
Height of ring pad H + / – 0.4 creates
Bottom width of octagonal ring pad C + / – 0.2
23 ° Angle   + / – 0.5 °
Fillet radius of ring pad R + / – 0.4
1) The limit deviation of ring pad height (H) can be +1.2mm as long as the height difference between any two points of ring pad does not exceed 0.4mm

Main performance parameters of octagonal gasket

Coefficient of gasket M = 5.50 to 6.50
Gasket operating pressure 42 mpa or less
Service temperature of gasket – 196 ℃ to 1000 ℃
*** Small preload ratio pressure Y = 126.6-182.8 MPa

Standards of Gaskets

The most common standards are:

  • BS10:2009: British standard specification for flanges and bolting for pipes, valves and fittings.
  • DIN Deutsches Institut für Normung): the German Institute for Standardisation.
  • ANSI: the American National Standards Institute.
  • ASA: the American Standards Association (Now ANSI).
  • ASME: the American Society of Mechanical Engineers. The ASME B16.47 Series A and B took over from MSS SP-44 (Series A) and API 605 (Series B).
  • ISO: International Organisation for Standardisation.
  • JIS: Japanese Industrial Standards.

British and European Standards

The current standard for use in the UK and Europe is BS EN 1514-1:1997. This standard took over from BS 4865-1:1989 for PN flanges.

Other standards include

  • BS EN 12560-1:2001: Flanges and their joints. Gaskets for Class-designated flanges. Non-metallic flat gaskets with or without inserts
  • BS EN 12560-2:2013: Flanges and their joints. Dimensions of gaskets for Class-designated flanges. Spiral wound gaskets for use with steel flanges
  • BS EN 12560-3:2001: Flanges and their joints. Gaskets for Class-designated flanges. Non-metallic PTFE envelope gaskets
  • BS EN 14772:2005: Flanges and their joints. Quality assurance inspection and testing of gaskets in accordance with the series of standards EN 1514 and EN 12560

Gasket installation requirements

  1. The sealing gasket and flange sealing surface should be cleaned, and there should be no defects such as scratches and spots that affect the connection sealing performance.
  2. The outer diameter of the gasket should be smaller than the flange sealing surface. The inner diameter of the gasket should be slightly larger than the inner diameter of the pipe. The difference between the two inner diameters is generally 2 times the thickness of the gasket to ensure the gasket after pressing. The inner edge does not protrude into the container or conduit to prevent interference with the flow of fluid in the container or conduit.
  3. The pre-tightening force of the gasket should not exceed the design regulations, so as to avoid the excessive compression of the gasket and the rebound ability.
  4. When the gasket is pressed, it is best to use a torque wrench. For large bolts and high strength bolts, hydraulic tensioners are preferred. The tightening torque should be calculated according to the compression of a given gasket. The hydraulic pressure of the hydraulic tensioner should also be determined by calculation.
  5. When installing the gasket, tighten the nuts in order. However, the design value should not be reached once. Generally, it should be circulated for at least 2 to 3 times so that the stress distribution of the gasket is uniform.
  6. For pressure vessels and pipelines with flammable and explosive media, safety tools should be used when replacing gaskets to avoid sparks caused by the collision of tools with flanges or bolts, resulting in fire or explosion accidents. 
  7. If the pipeline leaks, it must be replaced after the pressure reduction treatment or adjust the installation of the gasket. It is strictly forbidden to operate with pressure.

Special installation requirements for sealing gasket

  • 1. When installing the sealing spiral wound gasket matched with the raised plane flange, pay attention to ensure that the seal is concentric with the pipe. Generally, the external stiffening ring is in contact with the inner circumferential surface of the bolt for positioning, and eccentric installation is not allowed. When installing the basic spiral wound gasket in the sealing surface flange of tenon and groove surface, pay attention to keep the gap consistent with the groove wall surface.

  • 2. When installing the metal clad gasket with narrow width, place a certain thickness of steel plate on the outside of the gasket, and then press the flange, so as to avoid expanding the interface (or lap) of the metal shell and damaging the metal clad gasket after the clad filler in the metal gasket is pressed.

  • 3. When the working temperature of the flange is higher than 200 ℃, sealant shall be applied between the flange sealing surface and the sealing gasket to prevent sintering between the sealing gasket and the flange sealing surface under high temperature, which will increase trouble for maintenance and replacement of the sealing gasket.

  • 4. If the sealing surface is not flat, apply sealant on the sealing surface before installing the sealing gasket. Sealant is generally composed of manganese dioxide, lead, graphite powder and boiled linseed oil (dry oil). The corresponding type and brand of liquid sealant can be selected according to the sealing medium, working temperature and medium pressure.

  • 5. For the installation of octagonal metal ring gasket, when the processing of metal ring gasket and flange sealing groove is not ideal, the tight fit can be achieved by matching and grinding. For large-diameter metal ring gasket, it is difficult to match and grind. In order to fill the small unevenness on the metal surface, sealant can be used.

How to choose a gasket?

Important factors affecting gasket selection

Gasket selection is not an easy task, especially in the selection of gasket sealing materials, many factors should be considered. The variables at the flange connection seem to be endless, and all these uncertain factors affect the sealing effect of the gasket. In the past, “temp” (temperature, application, medium, pressure) seemed to be sufficient. However, today, the sealing effect of gasket is affected by flange processing quality, bolt thread embedding amount, flange rotation amount, bolt tension amount, medium filler and flange surface treatment. Therefore, we must comprehensively consider various parameters in order to make an appropriate choice.
(1) Temperature
In most selection processes, fluid temperature is the primary consideration. This will quickly narrow the selection, especially from 200 ° f (95 ° C) to 1000 ° f (540 ° C). When the system operating temperature reaches the limit of the maximum continuous operating temperature of a specific gasket material, a higher level of material should be selected. This should also be the case at some low temperatures.
(2) Apply
The most important parameters in application are the type of flange and the bolts used. The size, number and grade of bolts in the application determine the payload. The effective area compressed is calculated from the contact size of the gasket. The effective gasket sealing pressure can be obtained from the load of the bolt and the contact surface of the gasket. Without this parameter, we will not be able to make the best choice among many materials.
(3) Medium
There are thousands of fluids in the medium, and the corrosivity, oxidation and permeability of various fluids are very different. The materials must be selected according to these characteristics. In addition, the cleaning of the system must also be taken into account to prevent the gasket from being eroded by the cleaning fluid.
(4) Pressure
Each gasket has its maximum limit pressure. The pressure bearing performance of the gasket decreases with the increase of material thickness. The thinner the material, the greater the pressure bearing capacity. The selection must be based on the fluid pressure in the system. If the pressure fluctuates frequently and violently, you need to know the details in order to make a choice.
(5) PT value
The so-called Pt value is the product of pressure (P) and temperature (T). The pressure resistance of each gasket material is different at different temperatures, which must be considered comprehensively. In general, the manufacturer of the gasket will give the maximum Pt value of the material.

Selection steps

(1) Determine the standard used for the gasket
Generally speaking, the standard of gasket is the same as that of flange. Commonly used standards include: Chinese national standard (GB), machinery industry standard (JB / T), chemical industry standard (Hg), international standard (ISO), etc.
(2) Determine the nominal diameter and pressure of the gasket
The nominal diameter and nominal pressure of the gasket are the same as those of the flange. For example: DN100-PN25.
(3) Determine the type of gasket
The type of gasket used shall be determined according to the nominal pressure and the maximum temperature of the medium. It is mainly divided into flexible graphite, polytetrafluoroethylene, rubber, asbestos free fiber gasket and spiral wound gasket, waveform live pressure gasket, elliptical gasket and octagonal gasket. Because asbestos gaskets are phased out due to environmental protection and health reasons, they are not recommended in this paper.
(4) Determine the forms of gaskets
The forms of gaskets are mainly divided into four categories: non-metallic soft gasket, spiral wound gasket, metal composite gasket and metal gasket. The specific gasket form shall be selected according to the flange form and with reference to the technical parameters provided by various manufacturers.
(5) Determine the material and model of gasket
The material of the gasket shall be determined according to the temperature, pressure and corrosion performance of the medium, and then the model of the gasket shall be determined according to the above contents. The model of gasket generally includes six parts: gasket form, material, nominal diameter, nominal pressure, standard number, manufacturer or brand.

Reference for selection of seals

Temperature and pressure

 

Material is qualitative Seal form Seal characteristics For note
The temperature of 80 ℃ or less

In the low pressure resistance

 

Medium pressure asbestos sheet

Oil resistant asbestos sheet

Aramid non – asbestos sheet

 

Flat gasket Pipe with flange interface, water, gas, oil, acid and alkali dilute liquid Asbestos materials are becoming obsolete and are not recommended
Rubber adhesive Add skeleton in flat gasket When the pressure increases, the steel is flexible
Hydraulic transmission seal, pressure and friction resistance parts available polyurethane products

 

Flat gasket outsourcing
Teflon
 
Resistant to medium and low pressure and strong corrosive medium
The temperature of 120 ℃ or less – 260 ℃

Resistance to high pressure in the

 

Nitrile butadiene rubber Inner and outer skeleton oil seal, all kinds of V, U, Y O rings, under high pressure cloth rubber products Hydraulic transmission seal, all kinds of oil or pipe valve interface seal There are other special rubber such as: epDM, chloroprene, chlorophenol butyl, butadiene and so on for special working conditions
Silicone rubber Hydraulic transmission seal, high temperature gas, food medical special
Fluorine rubber Hydraulic transmission seal, harsh acid and alkali environment
Asbestos fiber, rubber, copper wire Disk root Pump valve seal 250 KGF/cm 60 ℃
550 ℃ 200 KGF/cm
The asbestos fiber 250 KGF/cm 60 ℃
450 ℃ 150 KGF/cm
Aramid fibre (asbestos free) Resistance to corrosion and friction Asbestos fiber immersion F4 and silicone oil coil are economic substitutes of aramid fiber F4 coil
Teflon Disk root Corrosion resistance, wire speed (GFO)
Packed modified filler All kinds of dynamic and static sealing and machine accessories  
Flat gasket Pipe with flange interface, insulation, anti-aging, suitable for all kinds of gas strong acid and alkali liquid seal
The steel frame is coated with graphite Flat gasket Pipe flange interface to replace asbestos gasket upgrading products
Stainless steel F4 winding Basic model with inner and outer ring Pipe with flange interface, suitable for strong corrosive medium
High temperature and high pressure Walka sheet (asbestos, non-asbestos) Flat gasket, large size within 3000 Corrosion-resistant 550℃ 60kGF /cm pipe with flange interface, suitable for a wide range of media  
Graphite winding of stainless steel Basic model with inner and outer ring Suitable for various media  
Flexible graphite Packing ring Pump, valve, stem, shaft seal  
Graphite and nickel wire braided Disk root Pump, valve, rod, shaft seal: ≤600℃ 150kgf/cm  
Carbon fiber braid Disk root Low carbon 280 ℃ 150 KGF/cm  
High carbon 600 ℃ 300 KGF/cm
Carbon fiber resin Forming by hot pressing mechanism Piston valve seal ≤600℃ 200~600kgf/cm  
Graphite resin Forming by hot pressing mechanism All kinds of dynamic and static sealing and machine accessories  
All kinds of metal Stainless steel Flat gaskets, toothed gaskets, (and composite graphite), octagonal, elliptical, lens gaskets Excellent pressure resistance  
Carbon steel  
Purple copper  
Pure aluminium  
Pure titanium  

How do I order gaskets?

When ordering, try to provide real samples so that we can measure the material, measure the size and provide the most accurate products.
Provide drawings or pictures, and indicate the product name, material, shape, size and other requirements of the required products. For example, ordering gaskets: indicate the gasket product name (such as spiral wound gasket, with outer ring), material (such as #316 steel), size (outer diameter of outer ring × Outer diameter of winding part × internal diameter × Thickness of winding part × Thickness of stiffening ring (mm).
Gasket size representation:

  • Basic 1 – outside diameter × internal diameter × Thickness (mm);
  • With inner ring 2 – outer diameter × internal diameter × Inner ring inner diameter × Thickness (mm);
  • With outer ring 3 – outer ring diameter × Outer diameter of winding part × internal diameter × Thickness of winding part × Thickness of stiffening ring (mm);
  • With inner and outer ring 4 – outer ring outer diameter × Outer diameter of winding part × Inner diameter of winding part × Inner ring inner diameter × Thickness of winding part × Thickness of stiffening ring (mm).

Provide working conditions, such as operating temperature, pressure and medium corrosivity, maintenance conditions, environmental requirements, price and cost. We can fax the data to our company, and we can provide real samples according to the working conditions until the customer’s trial is successful.
For the gasket used at the flange connection, if the size cannot be determined, be sure to confirm the form of flange butt joint: flat flange (including flat flange with convex table) Butt joint; concave convex flange; tenon and grooved flange. At the same time, confirm which country and standard this flange is applicable to. How to reasonably use and purchase seals? Media, temperature, pressure and working conditions should be important factors. For example, when the working pressure is small, use plastic flange (PN < 6kg), if hard seals, such as F4 or metal materials, are selected, leakage will occur due to improper material selection. If graphite materials are used, better results will be achieved due to flexible effects, and vice versa.
For another example, in the working environment of chemical media, it is necessary to reasonably match different sealing media to achieve good results, otherwise unpredictable chemical changes are easy to occur. Therefore, any deviation in the selection of seals will lead to unimaginable consequences.
The following general gasket structures are available for reference:
1. Most used for flange connection are:
a. Flat gasket: it is made of medium pressure asbestos, non asbestos, oil resistant asbestos, polytetrafluoroethylene, graphite gasket or reinforced graphite gasket, metal flat gasket, special metal gasket, etc.
b. Spiral wound gasket: spiral wound gasket with outer ring or with inner and outer ring (convex flat flange is widely used); spiral wound gasket with inner ring (concave convex flange is commonly used); basic type (without inner and outer ring) and grooved flange have narrow sealing surface and wide sealing surface on flat welded full plane flange, which is equivalent to spiral wound gasket with inner and outer ring. Attention must be paid to which standard flange from which country.
2. Various fillers are used for rotating and pulling shaft seal, such as flexible graphite ring (with or without opening), packing (or packing ring) woven from various materials, inner and outer skeleton oil seal YX ring and O-ring of various materials, etc.
3. Sealing products for special parts. Common ones include various sealing strips, Teflon ball valve seat, graphite ring, rubber parts, butterfly valve ring, etc.

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

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