What is a sealing gasket?
Sealing gasket is a kind of sealing spare parts used in machinery, equipment and pipeline as long as there is fluid. It uses internal and external materials to seal. Sealing gasket is made of metal or non-metal plate material by cutting, stamping or cutting. It is used for sealing connection between pipelines and between machine parts. According to the material, it can be divided into metal sealing gasket and non-metal sealing gasket. Metals include copper gaskets, stainless steel gaskets, iron gaskets, aluminum gaskets, etc. Non-metallic asbestos gaskets, non-asbestos gaskets, paper gaskets, rubber gaskets, etc.
|Material of Metal Gaskets|
|Material for Non-metallic Gaskets|
|Types of gaskets|
|Standards of Gaskets|
|Selection of Sealing Gaskets|
|Selection reference of sealing gasket|
|Installation of gaskets|
|How to Order Sealing Gaskets|
Selection of raw materials for sealing gaskets
1. Carbon steel:
It is recommended that the maximum operating temperature should not exceed 538 ℃, especially when the medium is oxidizing. High quality thin carbon steel sheet is not suitable for equipment manufacturing inorganic acid, neutral or acid salt solution. If carbon steel is under stress, the equipment accident rate for hot water condition is very high. Carbon steel gaskets are usually used in high concentration acid and many alkali solutions. Brinell hardness is about 120.
2. 304 stainless steel
18-8 (18-20% chromium and 8-10% nickel), recommended maximum operating temperature not exceeding 760 ℃. Stress corrosion and grain boundary corrosion are prone to occur in the temperature range from 196 to 538 ℃. Brinell hardness is 160.
3. 304L Stainless Steel
Carbon content is no more than 0. 03%. It is recommended that the maximum working temperature should not exceed 760 ℃. Corrosion resistance is similar to 304 stainless steel. Low carbon content reduces the precipitation of carbon from the lattice, and the grain boundary corrosion resistance of 304 stainless steel is higher than that of 304 stainless steel. Brinell hardness is about 140.
4. 316 Stainless Steel
18-12 (18% chromium and 12% nickel), about 2% molybdenum was added to 304 stainless steel. The strength and corrosion resistance of 304 stainless steel were improved with the increase of temperature. The creep resistance of stainless steel is higher than that of other common stainless steel when the temperature is increased. It is recommended that the maximum working temperature should not exceed 760 ℃. Brinell hardness is about 160.
5. 316L Stainless Steel
It is recommended that the maximum continuous working temperature should not exceed 760 ~815 ℃. Carbon content no more than 316 stainless steel 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. It is recommended that the maximum operating temperature should not exceed 760 ~815 ℃. Especially suitable for the manufacture of sulfuric acid corrosion resistant equipment, Brinell hardness of about 160.
Aluminum (content not less than 99%). Aluminum has excellent corrosion resistance and processing performance. It is suitable for manufacturing double clip gaskets. Brinell hardness is about 35. It is recommended that the maximum continuous working temperature should not exceed 426 ℃.
The composition of copper is close to that of pure copper, which contains trace 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.
(copper 66%, zinc 34%) has good corrosion resistance under most working conditions, but 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. Harrington B-2
(26-30% molybdenum, 62% nickel and 4-6% iron). It is recommended that the maximum working temperature should not exceed 1093 ℃. It has excellent corrosion resistance to hydrochloric acid at heat concentration. 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. Harrington C-276
16-18% molybdenum, 13-17.5% chromium, 3.7-5.3% tungsten, 4.5-7% iron and the rest are nickel. It is recommended that the maximum working temperature should not exceed 1093 C. It has excellent corrosion resistance. It has excellent corrosion resistance to cold nitric acid or boiling nitric acid with 70% concentration, good corrosion resistance to hydrochloric acid and sulfuric acid, and excellent stress corrosion resistance. Brinell hardness is about 210.
12. Inconel 600
Nickel-based alloys (77% nickel, 15% chromium and 7% iron). It is recommended that the maximum working temperature should not exceed 1093 ℃. It has high strength at high temperature, and is usually used in equipment to solve stress corrosion problems. At low temperature, it has excellent co-processing performance. Brinell hardness is about 150.
13. Monel 400
(Copper 30%, nickel recommended maximum continuous working temperature not exceeding 815 ℃. Except strong oxidizing acid, it has excellent corrosion resistance to most acids and bases. Stress corrosion cracks are easy to occur in fluoric acid, mercuric chloride and mercury media, so they are not suitable for the above media. It is widely used in the manufacture of hydrofluoric acid equipment. Brinell hardness is about 120.
It is recommended that the maximum working temperature should not exceed 1093 ℃. It has excellent corrosion resistance at high temperature. It is well known that it is resistant to chloride ions and has excellent resistance to nitric acid corrosion in a wide range of temperature and concentration. Titanium is rarely used in most alkali solutions and is suitable for oxidation conditions. Brinell hardness is about 216.
Material for Non-metallic Gaskets
1. Natural rubber
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 operating temperature is – 57 ~93 ℃.
2. Chloroprene rubber
Chloroprene rubber is a synthetic rubber, which is suitable for medium corrosion resistance in 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 ℃.
Cyanobutadiene rubber (NBR) is a synthetic rubber, which is suitable for corrosion resistance of oil, solvent, aromatic hydrocarbon, alkaline hydrocarbon, oil and natural gas in a wide temperature range. It has good corrosion resistance to hydroxides, salts and near neutral acids. However, the corrosion resistance of strong oxidizing medium, chlorinated hydrocarbons, ketones and lipids is poor. The recommended operating temperature is 51 ~121 ℃.
Fluorine rubber compound is made by mixing binary and ternary fluorine raw rubber 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 permanent deformation, good elasticity and long service life. Fluororubber has outstanding heat resistance (200-250 ℃) and oil resistance. It can be used to manufacture cylinder liner sealing rings, rubber bowls and rotary lip sealing rings, and can significantly improve the service time. The recommended operating temperature is – 40 ~232 ℃.
5. Chlorosulfonated polyethylene rubber
It has good corrosion resistance to acid, alkali and salt solutions, and is not affected by climate, light, ozone, commercial fuels such as diesel oil and kerosene. But 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 resistance to high and low temperatures and can be used for a long time at 150 ℃ without performance change. It can be used continuously for 10000 hours at 200 ℃. It can maintain its unique use elasticity, ozone resistance and weather resistance within the working temperature range of -70-260 ℃. It is suitable for making sealing gaskets needed in thermal mechanism, such as sealing gaskets, valve gaskets and oil seals (suitable for water media). Special silicone rubber can be used to make oil seals.
7. Ethylene propylene rubber
It has good corrosion resistance to strong acid, alkali, salt and chloride solutions. But it is not suitable for oil, solvent, aromatic hydrocarbon and hydrocarbon. Recommended operating temperature – 57 ~176 ℃.
The material does not contain resin or inorganic matter, and can be divided into metal-doped or non-metal-doped graphite materials. The material can be bonded to make pipeline gaskets with diameters exceeding 600 MM. 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 sublimate when it exceeds 3316 ℃. At high temperature, the material should be used cautiously in strong oxidizing medium. In addition to gaskets, the material can also be used to make fillers and non-metallic winding tapes in winding gaskets.
9. Ceramic fibers,
Ceramic fiber formed on tape 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 winding gasket.
10. Polytetrafluoroethylene (PTFE) concentrates the advantages of most plastic gasket materials, including the temperature resistance from – 95 ℃ to 232 ℃. Except for free fluorine and alkali metals, it has excellent corrosion resistance to chemicals, solvents, hydroxides and acids. PTFE materials can be filled with glass to reduce the cold flow and creep properties of PTFE.
According to its material and structural characteristics, gaskets can be divided into non-metal gaskets, metal gaskets, metal-non-metal composite gaskets, and various types can be subdivided into several types.
- Compressed Non-Asbestos Fibre Gasket (CNAF)
- PTFE Gasket
- Rubber Gasket
Metal-non-metal Composite Gaskets
- Spiral Wound Gaskets
- Camprofile Gaskets
- Metal Jacketed Gasket
Non-metallic gaskets are usually composite sheet materials are used with flat-face and raised-face flanges in low Pressure Class applications. Non-metallic gaskets are manufactured from arimid fiber, glass fiber, elastomer, Teflon® (PTFE), graphite etc.. Full-face gasket types are suitable for use with flat-face flanges. Flat-ring gasket types are suitable for use with raised face flanges.
ASME B16.21 covers types, sizes, materials, dimensions, dimensional tolerances, and markings for non-metallic flat gaskets.
Metal-non-metal composite gaskets are composites of metal and non-metallic materials. The metal is intended to offer strength and resiliency, while the non-metallic portion provides conformability and sealability. Often used semi-metallic gaskets are spiral wound and camprofile, and a variety of metal-reinforced graphite gaskets.
Semi-metallic are designed for almost all operating conditions and high-temperature and pressure applications, and are used on raised face, male-and-female, and tongue-and-groove flanges.
ASME B16.20 covers materials, dimensions, dimensional tolerances, and markings for metallic and semi-metallic gaskets.
Typical Spiral Wound gasket
Metallic gaskets are fabricated from one or a combination of metals to the desired shape and size. Often used metallic gaskets are ring-type-joint gaskets (RTJ). They are always applied to special, accompanying flanges which ensure good, reliable sealing with the correct choice of profiles and material.
Ring Type Joint gaskets are designed to seal by “initial line contact” or wedging action between the mating flange and the gasket. By applying pressure on the seal interface through bolt force, the “softer” metal of the gasket flows into the microfine structure of the harder flange material, and creating a very tight and efficient seal.
ASME B16.20 covers materials, dimensions, dimensional tolerances, and markings for metallic and composite gaskets.
Types of RTJ 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 seals play an important role in modern industrial enterprises. The quality of gasket seals is directly related to the continuity of production, property safety, energy saving and environmental protection, as well as people’s physical and mental health. Therefore, the development of gaskets has attracted more and more attention. With the rise of modern industry, especially modern petroleum, chemical industry, atomic energy industry and large-scale power plants, pressure vessels are developing in the direction of high temperature, high pressure, high vacuum, cryogenic, large-scale and multi-series. New requirements are constantly put forward for gasket sealing. New structures of various new materials are constantly emerging, and their sealing performance is also very different. In addition, the fluctuation of pressure, the change of temperature, the relaxation of bolt pretension, the inclination and dislocation of flange, the defect of sealing surface and the corrosion of medium will have a great influence on the sealing effect. Therefore, how to choose the appropriate gasket and how to install it correctly according to the working condition is the key to ensure the sealing effect.
Type Selection of Sealing Gasket
1.1 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 that appear at the flange connection seem endless, and all these uncertainties affect the sealing effect of gaskets. In the past, “TEMP” (temperature, application, medium, pressure) seemed adequate. But today, the quality of flange processing, the insertion of bolt teeth, the rotation of flange, the tension of bolt, the filler of medium and the surface treatment of flange all affect the sealing effect of gasket. Therefore, various parameters must be taken into account in order to make appropriate choices.
In most selection processes, the temperature of the fluid is the primary consideration. This will rapidly narrow the selection range, especially from 200 °F (95 ℃) to 1000 °F (540 ℃). When the operating temperature of the system reaches the maximum continuous operating temperature limit of a particular gasket material, a higher material should be selected. This should also be true at some low temperatures.
The most important parameters in application are the types of flanges and bolts used. In application, the size, number and grade of bolts determine the payload. The effective area of compaction is calculated by the contact size of gasket. Effective gasket sealing pressure can be obtained from bolt load and gasket contact surface. Without this parameter, it would be impossible to make the best choice among many materials.
There are thousands of fluids in the medium, and the corrosiveness, oxidation and permeability of various fluids are very different. Material selection must be based on these characteristics. In addition, the cleaning of the system must also be taken into account in order to prevent the erosion of the washer by the cleaning fluid.
Each gasket has its maximum limit pressure. The compressive performance of gasket decreases with the increase of material thickness. The thinner the material, the greater the compressive capacity. The selection must be based on the pressure of the fluid in the system. If the pressure often fluctuates violently, you need to know the details in order to make a choice.
(5) PT value
The 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. Generally, the gasket manufacturer will give the maximum PT value of the material.
1.2 Type Selection Steps
(1) Determine the standard used for gaskets
Generally speaking, gaskets adopt the same standard as flanges. The commonly adopted standards are: China National Standard (GB), Machinery Industry Standard (JB/T), Chemical Industry Standard (HG), International Standard (ISO), etc.
(2) Determining the nominal diameter and pressure of gaskets
The nominal diameter and pressure of gaskets are the same as those of flanges. For example: DN100-PN2.5.
(3) Classification of gaskets
The gasket type is determined according to nominal pressure and the highest temperature of the medium. It is mainly divided into flexible graphite, PTFE, rubber, asbestos-free fiber gasket and winding gasket, waveform active pressure gasket, elliptical gasket and octagonal gasket. Because asbestos gaskets are gradually eliminated due to environmental protection and health reasons, so this paper does not recommend the use of asbestos gaskets.
(4) Determining the form of gaskets
The gaskets are mainly divided into four types: non-metallic soft gaskets, winding gaskets, metal composite gaskets and metal gaskets. The specific gasket form should be selected according to the flange form and referring to the technical parameters provided by each manufacturer.
(5) Determine the material and type of gasket
The material of gasket shall be determined according to the temperature, pressure and corrosion performance of medium, and then the type of gasket shall be determined according to the above contents. Gasket models generally include six parts: gasket form, material, nominal diameter, nominal pressure, standard number, manufacturer or brand.
Several factors for attention in selecting flange sealing gaskets
When choosing flange gaskets, the sealing performance, creep, compression and recovery rate are all noticed. These test data can indicate what kind of gasket materials and forms users need to use, and make reference for the selection of gaskets, because these parameters are interrelated and influential, so one or two items can not be considered as reference only in the selection. All these factors should be taken into account.
When choosing flange gaskets, the sealing performance, creep, compression and recovery rate are all noticed. These test data can indicate what kind of gasket materials and forms users need to use, and make reference for the selection of gaskets, because these parameters are interrelated and influential, so one or two items can not be considered as reference only in the selection. All these factors should be taken into account.
1. Compression and Recovery Rate
Compression ratio refers to the influence of thickness under specific loads. Recovery ratio refers to the increase of thickness after the load is removed. The high compression rate of gaskets indicates that gaskets can be used on irregular surfaces, flange surfaces are more adaptable, and can increase friction, so that gaskets are not easily blown out, reducing the probability of leakage.
The recovery rate indicates the elastic performance of gaskets. The gaskets with high recovery rate generally need to exert greater compressive force to maintain a good seal.
2. Sealing capacity
All gasket seals are leaked. The gasket seals are ideal when there is no leakage. Under any circumstances, good sealing performance can reduce product losses, improve safety and save costs. If the gasket has leaked at room temperature, the condition at high temperature may be more serious. Gaskets of 0.8mm thickness can be selected for testing. The thinner the gasket, the better the sealing ability, because the less material the medium can pass through. In practical application, many gaskets with thickness of 1.5mm or 3mm are chosen, together with the influence of temperature, so the leakage rate is higher. If the medium is gas, then the leakage rate is higher, because the gas molecules are smaller and easier to pass through the gasket and around the gasket.
3. Chemical adaptability
Gaskets may be eroded and decomposed by chemical media, resulting in serious leakage, so gaskets must be compatible with the media. Gaskets are rarely eroded because they enter the inner diameter of the pipeline during installation, so gaskets generally do not fail quickly after assembly. It takes a certain amount of time for the medium to pass through the whole gasket. Some gaskets will expand in some media. In this case, even if the gaskets are incompatible with the media, gaskets can still play a sealing role in a relatively short time. The safe choice is that gaskets can not be eroded by media, so most gaskets manufacturers will provide the chemical properties (PH value) of products.
4. Gasket Creep
Creep will lead to load reduction. If the load is reduced or lost, the friction between gasket and flange surface decreases, and the gasket is easy to leak or even blow out. If the gasket creep is large, it needs to tighten the flange regularly to increase the labor intensity.
Temperature is one of the key factors in gasket selection. Temperature has different effects on gaskets of different materials. At high temperature, the filler may evaporate, the elastomer solidifies and hardens; at low temperature, the gasket will easily lose elasticity and become brittle; at low temperature, the fastening flange will not improve the sealing performance, but will break the gasket. Gaskets used at extremely low temperatures should generally be kept clean and dry.
The maximum pressure that gaskets can withstand is closely related to temperature. Most gaskets can not be applied under the condition that both temperature and pressure are at the limit. At high temperature, the pressure bearing capacity of gaskets will be reduced; similarly, at high pressure, the temperature bearing capacity will also be reduced.
7. Gasket thickness
If the chemical adaptability, temperature and pressure have been clearly defined when gaskets are selected, there is still a determination of the maximum thickness of gaskets. In many cases, the thinnest gasket is the best choice. Because the thinner, the smaller the contact area with the medium, the smaller the way the medium leaks through the gasket, and the higher the pressure bearing capacity. And it’s more economical. If the flange surface is rough, we suggest using a thicker gasket to make up for the flange surface unevenness, so as to achieve sealing effect.
Seven factors affecting gasket and packing seal
- (1) Surface condition of the sealing surface: The shape and roughness of the sealing surface have some influence on the sealing performance, and the smooth surface is beneficial to the sealing. Soft gaskets are insensitive to the surface condition because of their easy deformation, while for hard gaskets, the surface condition has a great influence.
- (2) Contact width of sealing surface: The larger the contact width between sealing surface and gasket or filler, the longer the path required for fluid leakage, and the greater the loss of flow resistance, which is conducive to sealing. However, under the same pressure, the greater the contact width, the smaller the specific pressure of the seal. Therefore, the appropriate contact width should be sought according to the material condition of the seals.
- (3) Sealing fluid properties: the viscosity of the liquid has a great impact on the sealing of fillers and gaskets, and the fluid with high viscosity is easy to seal because of its poor fluidity. The viscosities of liquids are much greater than those of gases, so liquids are easier to seal than gases. Saturated steam is easier to seal than superheated steam because it can condense droplets and block the passage of leakage between sealing surfaces. The larger the molecular volume of the fluid, the easier it is to be blocked by the narrow sealing gap, and thus easy to seal. The wettability of liquid to sealing material also has some influence on sealing. The liquid which is easy to soak is easy to leak because of the capillary action of the micropore inside the gasket and filler.
- (4) Temperature of sealing fluid: Temperature affects the viscosity of the liquid, thus affecting the sealing performance. As the temperature increases, the liquid viscosity decreases and the gas viscosity increases. On the other hand, the change of temperature often makes the seal assembly deform and easy to cause leakage.
- (5) Material of sealing gaskets and fillers: Soft materials are easy to produce elastic or plastic deformation under pre-tightening force, thus blocking the passage of fluid leakage, which is conducive to sealing; however, soft materials generally can not withstand the role of high-pressure fluid. The corrosion resistance, heat resistance, compactness and hydrophilicity of sealing materials have certain effects on sealing.
- (6) Specific pressure of sealing surface: The normal force acting on the unit contact surface between sealing surfaces is called the specific pressure of sealing surface. The specific pressure of sealing surface is an important factor affecting the sealing performance of gaskets or fillers. Usually, by applying pre-tightening force to produce a certain specific pressure on the sealing surface, the sealing parts will be deformed to reduce or eliminate the gap between the sealing contact surface and prevent the fluid from passing through, so as to achieve the purpose of sealing. It should be pointed out that the effect of fluid pressure will change the specific pressure of the sealing surface. Although the increase of specific pressure of sealing surface is beneficial to sealing, it is limited by the extrusion strength of sealing material. For dynamic sealing, the increase of specific pressure of sealing surface will also cause the corresponding increase of friction resistance.
- (7) The influence of sealing external conditions: the vibration of pipeline system, the deformation of connecting components and the offset of installation position will exert additional force on the sealing parts, which will have adverse effects on the sealing. In particular, vibration will cause periodic changes in the pressure between the sealing surfaces, which will make the connecting bolts relax, thus causing seal failure. The cause of vibration may be external or internal fluid flow in the system. In order to make the seal reliable, the above factors must be carefully considered, and the manufacture and selection of sealing gaskets and fillers are very important.
1 Inspection before installation
(1) Inspection of gaskets
1) Whether the material, form and size of gasket meet the requirements;
2) No mechanical damage, radial scratch and serious rust are allowed on gasket surface.
Defects such as corrosion, internal and external edge damage, etc.
3) The gasket chosen should be suitable for the flange sealing surface.
(2) Inspection of bolts and nuts
1) Whether the material, form and size of bolts and nuts meet the requirements;
2) The nut should rotate flexibly on the bolt, but not shake.
3) No scratches or burrs are allowed on bolts and nuts.
4) No thread breakage is allowed.
5) Bolts should not be bent.
(3) Inspection of flanges
Check whether the flange forms meet the requirements, whether the sealing surface is smooth, there is no mechanical damage, planer prints, radial notches, serious corrosion, welding scars, tar residues and other defects, if it can not be repaired, specific treatment methods should be studied.
(4) Inspection of Installation Quality of Pipeline and Flange
1) Deviation – Pipeline is not vertical, concentric and flange is not parallel.
The allowable deviation between two flanges should be less than 2 mm when using non-metallic gaskets, less than 1 mm when using metal composite gaskets, elliptical gaskets, octagonal gaskets and flanges connected with equipment.
2) Faults – Pipelines and flanges are perpendicular. But the two flanges do not agree.
If the bolt hole diameter and bolt diameter meet the standard, the bolt can be freely penetrated into the bolt hole without other tools, which is considered qualified.
3) The gap between opening and flange is too large. As shown in Figure 3.
The allowable opening value between two flanges (pre-stretching value of outgoing pipeline and thickness of gasket or blind plate): the opening of pipe flange should be less than 3mm, and the flange connected with equipment should be less than 2mm.
4) staggered hole – concentric flange of pipeline, but screw corresponding to two flanges
The chord distance between bolt holes (or the diameter of the center circle of bolt holes, etc.) is quite different.
(1) The two flanges must be on the same central line and parallel. It is not allowed to use bolts or pointed steel brazing to correct flanges in bolt holes in order to avoid bolts bearing greater stress. Before installation, flange sealing surface and water line (sealing line) should be carefully cleaned. Winding gaskets are best used for flanges without dense sealing lines.
(2) Only one gasket can be added between two flanges, and the method of adding more gaskets is not allowed to eliminate the defect of excessive gap between two flanges. Gaskets must be installed correctly, not deflected, to ensure uniform pressure, but also to avoid the gaskets into the pipeline by medium erosion and cause eddy current.
(3) When the nut is tightened, the moment wrench is used when the nut is below M22, and the pneumatic wrench is used when the nut is above M27.
In order to ensure uniform pressure on gaskets, bolts should be tightened symmetrically and evenly for 2-3 times.
(4) In order to avoid the bending of the bolt when tightening the nut and clamping when loosening the bolt, the flange should be coated with scaly graphite and lubricant at both ends of the bolt, and a light washer should be added under the nut if the back of the flange is rough. The end of the bolt with steel stamp should be exposed at the end which is convenient for inspection.
(5) As the tightening bolt is carried out in the cold state, it will relax when the temperature rises. Where the medium temperature is above 300 and 250 280 the bolt should be hot flanged, when the medium temperature rises to tight. In order to prevent the bolt from being removed during overhaul, when the medium temperature drops to 200-250 ℃, bolt loosening agent is used to loosen the bolt at the joint of bolts and nuts, and then the nut is loosened by 30-60 degrees pre-cyclotron.
3 Concluding remarks
In recent years, the definition of seal has changed fundamentally, and the standard for measuring leakage has increased from a few drops per minute to a few parts per million. Higher and higher standards inevitably require that gaskets be improved in form, material, processing and installation. Faced with a variety of sealing gaskets, only by adopting reasonable selection method and correct installation steps, can the ideal sealing effect be achieved.
Flange Seal and Leakage Seal Processing Method
There are many factors affecting the flange seal. Mainly: bolt preload; sealing surface type; gasket performance; flange stiffness; operating conditions.
For decades, ANSI flanges designed by the National Institute of Standards have provided a suitable sealing technology for the oil and gas industry, and have been effective. However, because the demand of oil and gas industry has changed, the defects of ANSI flange are constantly exposed. Cost-benefit principle, environmental protection and optimal health and safety assurance are three major issues faced by operators and contractors in the 21st century. Therefore, people begin to consider new flange sealing methods.
The sealing principle of ANSI flange is extremely simple: the two sealing surfaces of bolts extrude each other flange gaskets and form a seal. But at the same time, it also leads to the destruction of the seal. In order to keep the seal, a huge bolt force must be maintained. For this reason, bolts have to be made bigger. Larger bolts match larger nuts, which means larger diameter bolts are needed to create conditions for tightening nuts. Little wonder, the bigger the diameter of the bolt, the more flexible the flange will be. The only way is to increase the wall thickness of the flange. The whole device will require enormous size and weight, which becomes a special problem in offshore environment, because in this case, weight is always the main concern of people. Moreover, fundamentally, ANSI flange is an ineffective seal, which requires 50% of the bolt load to be used to extrude gaskets, while only 50% of the load to maintain pressure is left.
However, the main design disadvantage of ANSI flange is that it can not guarantee no leakage. This is the shortcoming of its design: the connection is dynamic, and such as thermal expansion and fluctuating periodic loads will cause the movement between flange surfaces, affect the function of flange, so that the integrity of flange is damaged, and eventually lead to leakage.
New flange developed by YAANG company overcomes the shortcomings of ANSI flange. Compact flange has many advantages: standard flange not only saves space and reduces weight, but also ensures that the joint does not leak. The reason why the size of compact flange decreases is that the diameter of the seal is reduced, which will reduce the cross section of the sealing surface. Secondly, the flange gasket has been replaced by the sealing ring to ensure that the sealing face matches the sealing face. In this way, only a small amount of pressure is required to press the cover tightly. As the required pressure decreases, the size and quantity of bolts can be reduced accordingly. Finally, a new product with small volume and light weight (70%-80% less weight than the traditional ANSI flange) was designed.
Treatment of Flange Leakage Seal
1. Leakage position and condition of connecting flange bolts on both sides of DN150 valve body. Because the gap between flanges is very small, it is impossible to eliminate leakage by injecting sealant into the gap. The leaking medium is steam, the temperature of the leaking system is 400-500 ℃, and the pressure of the system is 4 MPA.
2. Sealing construction method is based on the site survey of the leakage site. In order to achieve limited sealing, fixed fixture method is used to contain the leakage point to form a sealing chamber and inject sealant, so as to eliminate the leakage.
1. Fixture design
Determination of fixture structure
(1) Containing leakage points, the sealing chamber between valve body flange and pipeline flange is established. In order to prevent potential leakage of clearance between valve body and flange from re-leakage due to pressure constraints, annular cavity injection is installed at the outer edge of the clamp and flange of valve body.
(2) In the injection process of different-diameter flange, the fixture is easy to displace to the side of small-diameter flange, so the restriction measure of tooth contact clamping is adopted.
2. Sealant selection and dosage estimation
(1) TXY-18#A sealant is selected according to the temperature of the leaking system and the characteristics of the leaking position. The sealant has excellent heat resistance, medium resistance and injection process performance, and is easy to establish a uniform and compact sealing structure, and the sealing can maintain long-term stability.
(2) Sealant 4.5KG is needed to estimate the leakage point of one side.
3. Construction Operation
(1) Fixture installation, because of the tooth contact, the inner diameter of the tooth tip is smaller, so it is necessary to clamp the clamp with the outer wall of the ring to produce tooth end deformation and clamp the position.
(2) After the fixture and valve body and flange ring cavity are injected into the sealing cavity, the intermediate cavity is injected. The injection process should be balanced, and attention should be paid to reinforcing and pressing to prevent stress relaxation.
(3) After the sealant is solidified, after the effect observation, local reinjection and compression are carried out to prevent stress relaxation, and then the injection hole is sealed.
Sealing gaskets, though small, are of great importance. “Do not lose the overall situation by small profits” should be the first condition for the whole enterprise to make decisions and choose the configuration of sealing gaskets. Modern managers should be very conscious of the serious negative effects of leakage caused by careless selection of sealing gaskets for enterprises. The lessons of countless bloodshed are always warning us that a small gasket with imprudent use contains a huge crisis, and the losses it causes are by no means equal to its value. There are also inestimable loss of raw materials, costs and even the most valuable loss of human life in minutes and seconds.
Faced with a large number of different manufacturers, different performance, different specifications of sealing gaskets, many customers are often helpless, round-trip can not be solved. Or it may cause unnecessary losses due to the inaccurate description of the order requirements. In view of the above problems we often encounter, we recommend that you do your best when ordering: provide real samples, so that we can determine the material, measure the size, and provide the most accurate products.
Provide drawings or pictures, and specify the product name, material, shape and size requirements. For example, order gaskets: specify the name of gaskets (such as winding gaskets, with outer rings) material (such as #316 steel), size (outer ring diameter * outer winding part diameter * inner diameter * thickness of winding part * thickness of reinforcing ring (mm);
Gasket dimension representation method:
- Basic Type 1 – Outer Diameter * Inner Diameter * Thickness (mm)
- Inner Ring 2-Outer Diameter * Inner Diameter * Inner Ring Diameter * Thickness (mm)
- Outer Ring 3-Outer Ring Outer Diameter * Winding Part Outer Diameter * Inner Diameter * Winding Part Thickness * Reinforcement Ring Thickness (mm)
- Outer diameter of outer ring with inner and outer ring 4-Outer diameter of winding part X Outer diameter of winding part X Inner diameter of winding part X Inner diameter of winding part X Thickness of winding part X Thickness of reinforcing ring (mm)
Provide working conditions. For example, the use of temperature, pressure and corrosiveness of media, maintenance conditions, environmental requirements, price and cost can be faxed to our company, we can provide samples according to the working conditions, until the successful trial of customers.
In the case of gaskets used in flange connection, it is necessary to confirm the flange butting form: flat flange (including flat flange with convex platform); concave flange; mortise flange. At the same time, it is necessary to confirm which country and standard this kind of flange is suitable for. How can we rationally use and purchase sealing gaskets? Medium, temperature, pressure and working conditions should be important factors. For example, in the case of low working pressure and using plastic flange butt joint (PN < 6kg), the use of harder sealing gaskets, such as F4 or metal materials, will lead to leakage due to improper selection of materials. If graphite materials are used instead, better results will be achieved due to the special effect of flexibility, and vice versa.
In addition, in the working environment of chemical media, it is necessary to match different sealing media reasonably to achieve good results, otherwise unpredictable chemical changes will easily occur. Therefore, any inconsistency in the choice of sealing gaskets will lead to unimaginable consequences.
The general gasket structure can be referred to as follows:
1. Most of the flanged joints are used
A. Flat gaskets: materials are mostly medium-pressure asbestos, non-asbestos, oil-resistant asbestos, polytetrafluoroethylene, graphite gaskets or reinforced graphite gaskets, metal flat gaskets, special metal gaskets, etc.
B. Winding gasket: with outer ring or inner and outer ring (convex flat flange for multi-purpose); with inner ring (concave and convex flange commonly used); basic type (without inner and outer ring), slotted flange special sealing surface is narrow, flat welded flat flange, the sealing surface is wider, equivalent to the winding gasket with inner and outer ring. We must pay attention to which country and what kind of standard the flange is.
2. Multi-purpose fillers for rotating pull shaft seal. For example, flexible graphite rings (open and non-open), various material braided packing rings (or packing rings), various material inside and outside framework oil seal YX rings and O rings, etc.
3. Sealing products for special parts. Commonly used are various seals, PTFE ball seats, graphite rings and rubber butterfly rings, etc.
What aspects should we pay attention to when installing sealing gaskets?
Do not damage the sealing surface of the gasket or the sealing line of the planar sealing gasket. The sealing performance of the hydraulic sealing gasket depends on the upper and lower ends. The sealing performance of the hydraulic sealing gasket depends on the lip line matched with the hole or shaft. These parts are composed of soft and resilient special materials which are easy to be damaged, such as temperature resistant, corrosion resistant, aging resistant graphite, rubber and plastics, and fibers. In the process of handling, installation and storage, special protection and care should be given. Once damaged, it often leaves a great hidden danger to the sealing parts.
Some sealing gaskets should not be installed forcibly in the groove-shaped packing letter. At this time, they need to be installed tightly. They should not be rough and barbarous in construction. Forced loading with great action will certainly destroy the original prefabricated structure of sealing gaskets, which is like filling the required parts of prefabricated concrete after smashing will inevitably lead to disaster. The installation of such gaskets must be very careful and careful, and the insertion should be carried out step by step.
When installing, it is necessary to balance and symmetrically place the sealing gasket in the position where the effective sealing surface (or lip line) is tightly fastened. After the system is opened and used, further observation and tightening of sealing gaskets are needed to prevent the collapse caused by micro-leakage due to the change of working conditions (such as pressurization) in the process of system operation.
How to properly keep the temporary unused sealing gaskets?
- Anti-aging, light-proof, moisture-proof, flat placement, away from cold and heat sources;
- Do not apply pressure to keep the gasket relaxed naturally, and do not apply external force to change its physical shape.
- Classification and labeling (same shape, different material, use location, applicable standard, purchase date, etc.)
Source: China 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.)
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