Flanged joints are often used in industry . They must ensure the tightness and strength of the assembled structures. The role of a high-quality connection is important, because loose bonding can lead to large losses and threaten maintenance personnel. The main element of the connection is the flange. This part is a metal disk and provides a solid and tight detachable connection. The flange has found its application in the pipeline transport industry and public utilities. Through the use of various materials for its manufacture, it becomes an almost universal element of pipeline structures.
Types of Flanges
A large number of designs of this part have been developed for process pipelines . All flange connections consist of the following elements - flanges, gaskets, fasteners. The main task that is assigned to this unit is the union of the pipeline parts or the addition of additional equipment to the pipes. Flanges are divided into types depending on various parameters. By design, they are divided into:
The difference lies in the fact that the integral flanges together with the body undergo the same loads, respectively. They are made together with fittings during the casting or stamping process, and the combination can also be done by welding. As for the free ones, they are 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 combine the holes for the studs. The disadvantage is less strength and stiffness than solid flanges.
Purpose of flange separation:
- For fittings and pipelines. Flange connections of pipelines of this type are used for all types and industries of pipe, transport and housing and communal services.
- For vessels and apparatuses, such compounds are used for distillation of oil, equipment of heat supply systems, as well as tanks for reservation.
Standards
All flanges are divided into several types depending on state standard specification and execution:
- Cast flanges are made as a unit with the body. They can be cast from steel or cast iron.
- Steel flanges that have a thread on the neck. This type has a rather limited application and is mainly used for low pressure pipelines.
- Collar flanges. They are a product of steel, which is obtained by butt welding. The purpose of the collar flanges is to connect pipelines with high and medium pressure. The advantage of this type is its ease of installation and cost-effectiveness. Compared to flat welded flanges, which we will consider in the next paragraph, they reduce the manufacturing complexity by an average of 20% and the amount of welding work by half.
- Flat welded flanges. They are made of steel and such flange joints are used for process pipelines.
- Loose flanges. This species has its own characteristics and is divided into three subspecies:
- with collar, they are used for pipelines with aggressive environments, from the impact of which the collar itself protects the flange;
- on a flanged pipe;
- on a welded ring, they are used for pipelines of non-ferrous metals - copper and its alloys, aluminum, as well as stainless steel;
Connection selection options
- Flange joint shape. Flanges can be: round, oval or rectangular.
- Conditional pass. Its size corresponds to the internal section of the flange through which the medium will flow.
- Constructive execution. This parameter regulates flange connections, GOST 12815-80 includes 9 different performance categories.
- Pressure. Connections can withstand the maximum nominal pressure, it depends on the design and geometric dimensions of the flange. This parameter is also provided by the main regulatory document.
- Material. For the manufacture of cast iron, carbon, alloy, stainless steel. The material is selected according to the environment used. Expensive metals can also be used.
Electrical insulating compound
The insulating flange connection has a number of differences from other types and bears the task of preventing the passage of electric current, as well as protection against electrochemical corrosion. Most pipelines are laid underground where
stray currents are likely to occur
. In general, they do not pose a danger to the entire pipeline at the inlet, but are very dangerous at the exit point. Such an impact can lead to the destruction of the metal, the formation of cracks and leaks of the transported liquid or gas, the insulating flange connection provides the necessary safety. It consists of flanges, special insulated gaskets, bushings and fasteners. Such a compound is used in the following cases:
- at the border of the pipeline and its transition from supplier to consumer;
- when the flange connection of pipes ensures the combination of different materials of which they are made;
- on pipelines that are laid in the field of stray current sources;
- at the outlet of an insulated pipeline network that connects to an uninsulated pipeline;
- on land sections 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.
- High pressure connections. Such nodes are exposed to variable loads from operating mechanisms. Therefore, to ensure density and strength, as well as durability, a number of technological nuances should be observed during installation. The twisting of the studs is carried out gradually in a circle and in a certain sequence. Flange connections can become more durable through the use of a lens type of gasket. To use this type of gaskets, you must first grind the surface and gaskets, and pipes directly. The best option for this type are threaded flange connections. It can also be used along with a lens gasket, flat metal.
Maximum flange density is ensured by the use of materials for flat gaskets such as copper or aluminum.
- Flange lock. This connection by design is fully consistent with the flange, the difference is that instead of the usual fasteners - bolts and studs, a special design is used in the form of a strip that compresses the flanges and is tightened with bolts. In such joints, there are no holes in the diameter of the flanges. This type has proven itself in nodes that require quick and periodic disconnection-connection. In this case, flat welded flanges or butt welded can be used.
Flange fasteners
Fasteners are required for mounting flange connections. For fastening pipelines, the following fasteners are used: bolt, nut, stud and washer. Since flange connections of pipelines are a rather responsible design, the requirements for fasteners are made in accordance with the following parameters:
- Wednesday. She can be aggressive and not. Based on this environmental parameter, hardware is selected. For aggressive environments steel with anticorrosion properties is preferred. It is also possible to use special coatings that prevent corrosion.
- Temperature. Here, the temperature of the liquid or gas that will be transported through this pipeline plays a role, as well as the temperature regime of the environment. Each material has an operating temperature range in accordance with which the product is selected. If the environment does not exceed –30 º, the use of ordinary steel grades is possible , cold-resistant grades are used for lower temperatures.
- Pressure. The higher the working pressure indicator, the higher parameters the material used should be, from which the studs for flange joints are made.
- Indicators of fasteners: type of thread, pitch, length.
- Material. The steel used in the manufacture of fasteners for flange connections can be classified into four categories:
- general purpose carbon steel, the operating temperature should not exceed 200 º, and the maximum diameter is 48 mm;
- carbon steel used for high precision products; operating temperature cannot be higher than 300 º;
- carbon steel with high quality, fasteners made of this material can be used at temperatures above 450 º;
- alloy steels that have heat resistant and anti-corrosion properties.
Limited use of fasteners
The choice of fasteners is due to the above parameters, but there are some limitations:
- Fasteners operated at operating pressures up to 25 kgf / cm are not limited to the choice of product type. As for pressure that exceeds this figure, only studs for flange connections can be used, the use of bolts is prohibited.
- The steel grade for the stud – nut pair can be selected either 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.
There is a special GOST stud for flange connections, in accordance with which the nominal dimensions of the fastener are selected. The choice of sizes depends on the working pressure to which the stud will be subjected.
Gaskets
This part is included in an insulated flange joint in order to provide the necessary density between the flanges. Gaskets are divided into different types according to certain parameters. Depending on the material from which they are made, there are categories:
- metal;
- non-metallic;
- combined.
The distribution of gaskets by elasticity:
This property determines the material from which the gaskets for flange joints are made. Elastic are obtained from combined and non-metallic species. Rigid gaskets are mainly metal, as well as non-metallic, obtained from materials such as fiber, hard rubber, paronite, etc.
Design features of gaskets
On this basis, gaskets for flange connections are divided into:
- Flat (can be both metallic, non-metallic and combined), they are used in conjunction with flat surfaces. The inner diameter of the flat gaskets should be 1-3 mm larger than the diameter of the pipe.
- Lens pads are made of carbon and alloy steels, they can be both rigid and elastic.
- Oval provide a reliable seal, while the load on the bolts is quite moderate. The contact of the cushioning product occurs on the outer and inner circumference with the flange. The material for these gaskets is carbon or stainless steel.
- Corrugated gaskets can be either metallic or non-metallic. They are made of 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 is adjusted by the location of the bolts.
- Spiral are elastic gaskets. Such a gasket consists of three elements - a spiral part and two restrictive rings.
- Toothed gaskets, the material for these gaskets is mild steel or alloy steel. Insulated flange connection with this type of gaskets can be operated at temperatures not exceeding 480 º.
Calculation of flange connections
After determining the type of flange, depending on its purpose, type of cushioning product, as well as the materials from which the product will be manufactured, designers select the necessary 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:
- Calculation of plastic deformations at the base of the bushings, this applies to joints operating at low temperatures and pressures.
- Taking into account the external bending moment arising from the load on the bolts. This parameter determines the strength characteristics of the flange.
- Calculation of arising stresses, especially for products obtained by welding.
- The choice of the pitch of the bolts, if this parameter is incorrectly defined, can cause a deflection of the flange rings between the bolts.
Calculation of flange connections should take into account the type of load. Two options are possible - in the first case, the load from the bolts is transferred to the gasket, in the second - there is an even distribution of loads between the gasket and the support ring.