What are flange connections? Types of flange connections. Flanged connections in industry

Flange connections are often used in industry. They must ensure the integrity and strength of the assembled structures. The role of a quality connection is important, because a fragile bond can lead to large losses and threaten the service staff. The main element of the connection is the flange. This part is a metal disc and provides a durable and tight detachable connection. The flange has found its application in the field of pipeline transport, municipal services. Due to the use of various materials for its manufacture, it becomes an almost universal element of pipeline structures.

Types of flanges

For technological pipelines , a large number of designs of this part have been developed. All flange connections consist of the following elements - flanges, gaskets, fasteners. The main task that is entrusted to this unit is the unification of parts of the pipeline or the addition of additional equipment to the pipes. Flanges are divided into types depending on various parameters. By design, they are divided into:

• Whole;
• Free.

The difference lies in the fact that the integral flanges together with the body undergo respectively the same load. They are produced together with the armature in the process of casting or stamping, also the combination can be made by welding. As for free, they are a disk that is attached to a welded flange or flanged pipe edge. Both types have both shortcomings and dignities. Free flanges are easy to assemble, their design makes it easy to combine holes for studs. The disadvantage is the lower strength and stiffness than that of the integral flanges.

Separation of flanges to their intended use:

• 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 distillation of oil, equipment for heat supply systems, and also reservoirs for reservation.

Standards

All flanges are divided into several types, depending on GOST and performance:

1. Molded flanges, are made as a single unit with the body. They can be cast out of steel or cast iron.
2. Steel flanges that have a thread on the neck. This type has a rather limited application and is mainly used for low pressure pipelines.
3. Collar flanges. They are a product made of steel, which is obtained by butt welding. The purpose of the collar flanges is to connect the pipelines with high and medium pressure. The advantage of this type is that it is easy to install and economical. In comparison with flat welded flanges, which we consider with the following point, they reduce the labor input of manufacturing by an average of 20% and the amount of welding work is doubled.
4. Flanges are flat welded. They are made of steel and such flanged connections are used for process pipelines.
5. Free 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 a flanged pipe;
• On the weld ring, they are used for pipelines of non-ferrous metals - copper and its alloys, aluminum, and stainless steel;

Connection Selection Options

1. The shape of the flange connection. Flanges can be round, oval or rectangular.
2. Conditional pass. Its size corresponds to the internal section of the flange, through which the medium will flow.
3. Constructional design. This parameter regulates flange connections, GOST 12815-80 includes 9 different performance categories.
4. Pressure. The connections can withstand the maximum conditional pressure, it depends on the design and geometric dimensions of the flange. This parameter is also provided for by the main normative document.
5. Material. For the production of cast iron, carbon, alloy, stainless steel is used. The material is selected in accordance with the used environment. Can also be used and expensive metals.

Electrical insulating connection

The insulating flange connection has a number of differences from other types and carries the task of preventing the passage of electric current, as well as protection against electrochemical corrosion. Most of the pipelines are laid underground, where the possibility of stray currents is possible . In general, they do not pose a threat to the entire pipeline at the entrance, but are very dangerous at the exit site. Such an impact can lead to the destruction of the metal, the formation of cracks and leakage of the transported liquid or gas, the isolating flange connection ensures the necessary safety. 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 ensures the matching of different materials from which they are made;
• On pipelines, which are laid in the field of sources of stray currents;
• At the outlet of an isolated pipeline network, which is connected to an uninsulated pipeline;
• On ground sections of gas distribution stations.

Other types of flange connections

• Measuring flange connections. They provide docking of pipeline networks with additional equipment and measuring devices.
• Compounds operating under high pressure. Such nodes undergo variable loads from operating mechanisms. Therefore, in order to ensure density and strength, as well as durability, a number of technological nuances must be observed during installation. Twisting of the studs is made gradually in a circle and in a certain sequence. Flange joints can become more durable through the use of a lens-type gasket. To use this kind of gaskets, it is first necessary to sand the surface and gaskets and pipes directly. The best option for this type are threaded flange connections. Also can be used along with the lens gasket, flat metal.
  The maximum density of the flange connection is ensured by the use of such materials for flat gaskets, such as copper or aluminum.

• Flange lock. This connection according to the design fully corresponds to 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 tightens with bolts. In such joints there are no holes along the diameter of the flanges. This kind of well proven in the nodes that require a quick and periodic disconnection-connection. Use in this case can be flat welded flanges or welded end to end.

Flange fasteners

Mounting of flange connections is always necessary fasteners. For fixing pipelines, fasteners such as bolts, nuts, pins and washers are used. Since flange connections of pipelines are a fairly responsible design, requirements are imposed on fasteners in accordance with the following parameters:

1. Wednesday. It can be aggressive and not. Based on this environment parameter, the fastener is selected. For corrosive media, preference is given to steel with anti-corrosive properties. It is also possible to use special coatings to prevent corrosion.
2. Temperature. Here, the temperature of the liquid or gas that will be transported through this pipeline, as well as the temperature regime of the environment, play a role. Each material has a working temperature range, according to which the product is selected. If the environment does not exceed -30 ° C, conventional steel grades are possible , cold temperatures are used for lower temperatures.
3. Pressure. The higher the value of the working pressure, the higher the parameters used should be the material used, from which the studs for flange connections are made.
4. Indicators of fasteners: thread type , pitch, length.
5. Material. Steel that is used in the manufacture of fasteners for flange joints can be classified into four categories:

• Carbon steel for general use, the operating temperature should not exceed 200 ° C, and the maximum diameter - 48 mm;
• Carbon steel, used for products of increased accuracy, the operating temperature can not be higher than 300 ° C;
• Carbon steel with increased quality, fasteners from this material can be operated at temperatures above 450 ° C;
• Alloy steel, which 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:

1. Fasteners operated at an operating pressure of up to 25 kgf / cm are not limited to the choice of product type. As for the pressure that exceeds this figure, only studs for flange connections can be used, the use of bolts is prohibited.
2. The steel grade for the pair "hairpin-nut" can be chosen as the same, or different. If one material is used, the strength of the nut must be below the strength of the stud by 20 units.

There is a special GOST pin for flange connections, according to which the nominal dimensions of the fastener are chosen. The choice of dimensions depends on the working pressure to which the stud will be exposed.

Gaskets

This part comes in an insulated flange connection 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, the following categories are distinguished:

• Metal;
• Non-metallic;
• Combined.

Distribution of gaskets by elasticity:

• Elastic;
• Hard.

This property determines the material from which the gaskets for flange connections are made. Elastic are obtained from combined and non-metallic species. Rigid gaskets are mainly metallic, as well as nonmetallic, obtained from materials such as fiber, hard rubber, paronite, etc.

Design features of gaskets

For this reason, the gaskets for flange connections are divided into:

• Flat (can be both metallic, non-metallic and combined), they are used in connections with flat surfaces. The internal diameter of the flat gaskets must be greater than the pipe diameter by 1-3 mm.
• Lens gaskets are made of carbon and alloy steels, they can be both rigid and elastic.
• Oval provides a reliable seal, while the load on the bolts is quite moderate. The contact of the gasket product takes place along the outer and inner circumference with the flange. The material for these gaskets is carbon or stainless steel.
• Corrugated gaskets can be both metallic and non-metallic. They are made of a thin sheet of copper, soft steel, as non-metallic material is used asbestos cardboard or paper. The internal diameter corresponds to the diameter of the flange, and the outer diameter is corrected by the arrangement of the bolts.
• Spiral refers to elastic gaskets. This gasket consists of three elements - a spiral part and two restrictive rings.
• Toothed gaskets, the material for these gaskets is a low-carbon or alloyed steel. An insulated flange connection with this type of gaskets can be operated at temperatures not exceeding 480 ° C.

Calculation of flange connections

After determining the type of flange, depending on its purpose, the type of gasket products, as well as the materials from which the product will be manufactured, the designers select the necessary dimensions of the part by special tables. They are presented in the corresponding GOSTs. Despite the fact that flanges are standard parts, very often there is a need for the design of an individual product. The calculation system includes the following items:

1. Calculation of plastic deformations at the base of the sleeves, this applies to compounds operating at low temperatures and pressures.
2. Accounting for the external bending moment arising from the load on the bolts. This parameter determines the strength characteristics of the flange.
3. Calculation of the arising stress, especially for products that are welded.
4. The choice of the bolt pitch, incorrectly defined this parameter can cause deflection of the flange rings between the bolts.

Calculation of flange connections should take into account a variety of load. There are two options - in the first case, the load from the bolts is transferred to the gasket, in the second case, the load is evenly distributed between the gasket and the support ring.