In industry, often used flangeconnections. They must ensure the tightness and strength of the assembled structures. The role of quality connection is important, because fragile bonding can lead to large losses and endanger the staff. The main connection element is a flange. This part is a metal disk and provides a strong and tight detachable connection. The flange found its application in the industry of pipeline transport, public utilities. Through the use of various materials for its manufacture, it becomes almost a universal element of pipeline structures.
Types of flanges
For process pipelines developedA large number of designs of this detail. All flange connections consist of the following elements - flanges, gaskets, fasteners. The main task entrusted to this node is to unite parts of the pipeline or to connect additional equipment to the pipes. Flanges are divided into types depending on various parameters. By design, they are divided into:
The difference is that solid flangestogether with the body undergo respectively the same load. They are made together with the fittings in the process of casting or stamping, also the combination can be produced by welding. As for the free, they represent a disk that is attached to the welded flange or flanged edge of the pipe. Both species have both disadvantages and advantages. Loose flanges are easy to assemble, their design makes it easy to align the holes for the studs. The disadvantage is lower strength and rigidity than solid flanges.
Flange separation by purpose:
- For fittings and pipelines. Flanged connections of pipelines of this type are used for all types and branches of pipe, transport and housing and communal services.
- For vessels and apparatus, such compounds are used for the distillation of oil, equipment of heat supply systems, as well as containers for reservations.
Standards
All flanges are divided into several types depending on GOST and execution:
- Molded flanges are made as one piece with the body. They can be cast from steel or cast iron.
- Steel flanges that are threaded on the neck. This type has rather limited use and is mainly used for low pressure pipelines.
- Collar flanges.Represent a product from steel which is received by end-to-end welding. The purpose of the collar flange is to connect pipelines with high and medium pressure. The advantage of this type is the ease of installation and economy. Compared with flat welded flanges, which we consider the next item, they reduce the labor intensity of manufacturing by an average of 20% and the volume of welding work by half.
- Flanges are flat welded. They are made of steel and used such flange connections for process pipelines.
- Loose flanges. This species has its own characteristics and is divided into three subspecies:
- with a collar, they are used for pipelines with aggressive media from which the collar protects the flange itself;
- on flanged pipe;
- on a welded ring, they are used for pipelines from non-ferrous metals - copper and its alloys, aluminum, and also stainless steel;
Connection selection options
- The shape of the flange connection. Flanges can be: round, oval or rectangular.
- Conditional pass. Its size corresponds to the internal cross section of the flange through which the medium will flow.
- The design. This parameter regulates flange connections, GOST 12815-80 includes 9 different categories of performance.
- Pressure. Connections can withstand the maximum conditional pressure, it depends on the performance and the geometric dimensions of the flange. This parameter is also provided for in the main regulatory document.
- Material.Used for the manufacture of cast iron, carbon, alloyed, stainless steel. The material is selected according to the application environment used. Expensive metals can also be used.
Electrically insulating compound
Insulating flange connection has a numberdifferences from other types and carries the task of preventing the passage of electric current, as well as protection from electrochemical corrosion. Most pipelines are laid under the ground, where the likelihood of stray currents. In general, they do not pose a hazard to the entire pipeline at the inlet, but they are very dangerous at the exit point. Such an impact can lead to the destruction of the metal, the formation of cracks and leakage of the transported liquid or gas, the insulating flange connection provides the necessary security. It consists of flanges, special insulated gaskets, bushings and fasteners. Apply this connection in the following cases:
- on the border of the pipeline and its transition from the supplier to the consumer;
- when the flange connection of pipes provides a combination of different materials from which they are made;
- on pipelines that are laid in the field of sources of stray currents;
- at the outlet of an isolated pipeline network that is connected to an uninsulated pipeline;
- on land sites of gas distribution stations.
Other types of flange connections
- Measuring flange connections. They provide the connection of pipeline networks with additional equipment and measuring devices.
- Compounds working under high pressure. Such nodes are subject to variable loads fromoperating mechanisms. Therefore, to ensure the density and strength, as well as durability, you should observe a number of technological nuances during installation. Twisting the studs is done gradually in a circle and in a certain sequence. Flange connections can be made stronger by using a lens-type gasket. To use this type of gaskets, you must first sand the surface and gaskets and pipes directly. The best option for this type are threaded flange connections. Can also be used along with the lens gasket, flat metal.
Maximum flange density is ensured by using materials for flat gaskets such as copper or aluminum.
- Flange lock. This connection is by design completely.corresponds to the flange, the difference lies in the fact that instead of the usual fasteners - bolts and studs, uses a special design in the form of a strip, which compresses the flanges and tightens the bolts. In such connections, the holes on the diameter of the flanges are missing. This view has proven itself in nodes that require fast and periodic disconnection-connection. It is possible to use in this case flat welded flanges or welded end-to-end.
Flange fasteners
For mounting flange connections requiredneed fasteners. For fastening pipelines used such fasteners: bolt, nut, stud and washer. Since the flange connections of pipelines are a rather responsible construction, requirements are made to the fastener in accordance with the following parameters:
- Wednesday. She can be aggressive and not.Based on this environment setting, fasteners are selected. For aggressive environments, steel with anti-corrosion properties is preferred. It is also possible to use special coatings that prevent corrosion.
- Температура.Here the role is played by the temperature of the liquid or gas that will be transported through this pipeline, as well as the ambient temperature regime. Each material has a working temperature range, according to which the product is selected. If the environment does not exceed –30 ºС, conventional steels may be used, cold-resistant grades are used for lower temperatures.
- Pressure. The higher the working pressure, the higher the parameters should be used the material from which the studs for flanged connections.
- Fastener performance: thread type, pitch, length.
- Material. Steel, which is used in the manufacture of fasteners for flanged connections, can be classified into four categories:
- carbon steel of general purpose, the working temperature should not exceed 200 ºС, and the maximum diameter - 48 mm;
- carbon steel used for products of high accuracy, the work temperature can not be higher than 300 ºС;
- carbon steel with high quality, fasteners of this material can be used at temperatures above 450 ºС;
- alloyed steels that have heat-resistant and anti-corrosion properties.
The limited use of fasteners
The choice of fasteners due to the above parameters, but there are some limitations:
- Крепежи, эксплуатируемые при рабочем давлении до 25 kgf / cm, not limited to the choice of the type of product. As for pressure, which exceeds this figure, only studs for flange connections can be used, the use of bolts is prohibited.
- Steel grade for a pair of "pin-nut" can be selected as the same or different. If one material is used, the strength of the nut should be lower than the strength of the stud by 20 units.
Существует специальный ГОСТ шпильки для фланцевых connections in accordance with which the nominal dimensions of the fastener are selected. The choice of dimensions depends on the working pressure to which the stud will be exposed.
Gaskets
This part is included in an insulated flange.connection in order to ensure the required density between the flanges. Gaskets are divided into different types of certain parameters. Depending on the material from which they are made, there are categories:
- metal;
- non-metallic;
- combined.
Gasket distribution by elasticity:
This property predetermines the material from whichmade gaskets for flange connections. Elastic are obtained from combined and non-metallic species. Rigid pads are mainly metal, as well as non-metallic, obtained from materials such as fiber, hard rubber, paronite, etc.
Gasket design features
On this basis, gaskets for flange connections are divided into:
- Flat (can be either metal,non-metal and combined), they are used in compounds with flat surfaces. The inner diameter of the flat gaskets should be 1-3 mm larger than the pipe diameter.
- Lens gaskets are made of carbon and alloy steels, they can be both rigid and elastic.
- Oval provide reliable sealing, withThis load on the bolts is quite moderate. The contact of the gasket product occurs on the outer and inner circumference with the flange. The material for these gaskets is carbon or stainless steel.
- Гофрированные прокладки могут быть как metal, and nonmetallic. They are made from a thin sheet of copper, mild steel, asbestos cardboard or paper is used as a non-metallic material. The inner diameter corresponds to the diameter of the flange, and the outer diameter is adjusted by the location of the bolts.
- Spiral are elastic gaskets. Such a gasket consists of three elements - the spiral part and two restrictive rings.
- Gear pads, material for these padsserves mild or alloy steel. Insulated flange connection with this type of gasket can be operated at temperatures not exceeding 480 ºС.
Calculation of flange connections
After determining the type of flange, depending onits purpose, the type of gasket product, as well as the materials from which the product will be made, the designers select the required dimensions of the part according to special tables. They are presented in the relevant State Standards. Despite the fact that flanges are standard parts, very often there is a need to design an individual product. The calculation system includes the following items:
- The calculation of plastic deformation at the base of the sleeves, this applies to compounds operating at low temperatures and pressures.
- Accounting for external bending moment arising from the load on the bolts. This parameter defines the strength characteristics of the flange.
- The calculation of the resulting stresses, especially for products that are obtained by welding.
- Selection of bolt pitch, an incorrectly defined parameter may cause deflection of the flange rings between the bolts.
The calculation of flange connections should take into accountkind of load. Two options are possible - in the first case, the load from the bolts is transferred to the gasket, in the second - the load is evenly distributed between the gasket and the support ring.
