Reciprocal connection of pipeline fittings type ach. Types of fittings for connecting to a pipeline. Advantages of threaded connections for pipeline fittings

One of the main issues when choosing pipeline fittings is the type of connection to the system. Usually the existing pipeline system itself dictates to us which type of connection to choose. But if you are faced with the task of designing such a system, then it is important to know all the possible types of connecting pipeline fittings to the system in order to choose the ideal option for your conditions. From our article you will learn about all types, their pros and cons, and you will better understand the types of connections. We'll start with the most popular ones.

Flange connection

This is a connection using two metal plates adjacent to each other. The plates have holes through which bolts or studs pass and are tightened with nuts on the other side, thus pressing the flanges together. For greater reliability and tightness of the connection, protrusions, grooves, etc. are made on the plates, and gaskets are installed between the metal plates. Most often the plates have a rounded shape, but this is not necessary. Occasionally you can find square flanges, rectangular or with three corners, but their production is more expensive. Such forms of flanges are used only when strictly necessary, for example, if space limitations require it. Used on industrial pipelines with a diameter of DN 50 mm.

The word “flange” comes from the German flansch, which means the same thing as in Russian – a flat metal plate with holes.

Flange connection is one of the most popular connections in pipeline fittings. For the manufacture of flanges, cast iron is most often used - gray or malleable, as well as steel of various grades. Gray cast iron is the most inexpensive solution, but ductile iron can generally withstand a greater range of pressures and temperatures. An even more expensive and durable solution is cast steel flanges. But at the same time, steel is more susceptible to plastic deformation than cast iron, which is brittle but holds its shape well.

Video: installing a flanged LD ball valve on a pipe using

Advantages of flange connection of pipeline fittings

• Strong, reliable connection.
• Withstands high pressure.
• High tightness. But it depends on the seals used.
• Can be mounted and dismantled many times.

Flaws

• Large overall dimensions of the flange connection. Large mass.
• High metal consumption and labor-intensive production, and therefore the price.
• The bolts holding the flanges together must be tightened periodically to ensure proper tightness. This is especially important in systems where the pipe is subject to vibration (solved by installation in front of the flange connection) or temperature changes.

Threaded, coupling connection

Also one of the most popular types of connections, but for pipeline systems of small diameter (usually up to DN 50) and low pressures (up to 1.6 MPa). Very often found in household pipeline fittings, for example for. Its essence is simple: the pipe has a thread and the fittings have a thread, the latter is screwed onto the former.

You can cut a thread on a pipe using special tools if it does not exist and the equipment has not been installed before. Threaded pipeline fittings at one end are made in the form of a hexagon for gripping with an adjustable wrench and screwing the fittings onto the pipe thread.

Video: how to cut a thread on a metal pipe and install a threaded ball valve

There are various options for making threaded connections: internal or external thread. The fittings can have an internal thread on one side and an external thread on the other, or the same type on both sides. There are also different thread standards, for example ISO 228/1 or DIN 2999. You need to take this into account when choosing.

The word “muff” comes from the Dutch word mouw, meaning “sleeve”.

To ensure the tightness of threaded types of connections, additional sealants are used in them - special FUM tapes, flax thread, as well as especially thick lubricants on top of them. All this is applied to the external thread.

Union connection

This is a subtype of threaded connection, which is used on taps of tiny sizes - up to DN 5. When connecting, the threaded fittings are tightened to the threads on the pipe with a union nut. Used for pipes for narrow purposes, such as laboratory pipes. Also used for implanting various measuring devices into pipelines.

Advantages of threaded connections for pipeline fittings

• Low price.
• They do not require additional parts for installation, such as the flange type.
• Easy to install, even easier to replace.

Flaws

• Not suitable for high pressures.
• The larger the diameter, the more effort must be applied to screw the fittings onto the threads with a seal.

Welded connection

If the ends of the pipeline fittings look simply like pipes without any additions, then they are connected to the system by welding. This is the most reliable and hermetically sealed connection, and if done correctly, you can obtain absolute structural compliance of the materials. By welding a valve or tap to a pipe, you will not have to tighten the bolts, as with a flange connection, and the cost and weight of such fittings will be significantly less.

This type of connection can often be found on pipeline systems transporting liquids and gases hazardous to health, where the slightest leaks cannot be allowed and absolute tightness is required. For a welded joint, the saying “set it and forget it” is typical. The main thing is to properly connect the pipe to the fittings so that the welding point is not weaker than the pipe wall.

The ends of the pipes must be prepared before welding, and each metal is prepared differently. We offer you a video with the simplest welding method.

Advantages of a welded connection

• Absolute tightness when the welding procedure is performed correctly.
• Low cost of fittings.
• Light weight.
• Small size, the connection does not take up much space.

Flaws

• Qualified personnel are needed, which increases the final cost of installing such fittings.
• A labor-intensive dismantling process, such valves or taps must be installed once and for all.

Clamp quick release connection (Tri-Clamp)

A modern quick-release connection for pipeline fittings, used mainly in the food industry, pharmacology and other industries where sterility and cleanliness are important. After all, this type of connection allows you to regularly remove, clean, and disinfect the equipment installed with this mount.

The clamp connection consists of two fittings, a seal and a clamp. The clamp presses the two fittings against the seal and against each other, resulting in a tight connection. We suggest you study what such a clamp is in the video.

The word “flange” came into the Russian language from the German language along with the flange itself, and was not assigned on the basis of some analogies. In German, the noun Flansch means exactly the same thing as the Russian word “flange” derived from it, ─ a flat metal plate at the end of a pipe with holes for threaded fasteners (bolts or studs with nuts). It is more common when this plate is round, but the shape of the flanges is not limited to one disk. For example, square and triangular flanges are used. But round ones are easier to make, so the use of rectangular or triangular flanges can be justified for really compelling reasons.

The material, types and design features of the flanges are determined by the nominal diameter, pressure of the working medium and a number of other factors.

For the manufacture of pipeline valve flanges, gray and ductile cast iron and different types of steel are used.

Ductile iron flanges are designed to withstand higher pressures and a wider temperature range than flanges made from gray cast iron. Cast steel flanges are even more resistant to these factors. Welded steel flanges, while easily withstanding high temperatures, are inferior to cast flanges in the maximum permissible pressure.

Design features of flanges may include the presence of projections, chamfers, spikes, annular recesses, etc.

The prevalence of flanged connections for pipeline fittings is due to their many inherent advantages. The most obvious of them is the possibility of repeated installation and dismantling. The temptation to add the adjective “easy” to the noun “installation” is somewhat diminished if we remember how many bolts will need to be unscrewed and tightened when disassembling and joining flanges of large diameters (flange connections are usually used for pipe diameters of 50 mm or more). Although in this case, the complexity of installation work will not go beyond reasonable limits.

Flange connections are durable and reliable, which allows them to be used to complete pipeline systems operating under high pressure. Subject to certain conditions, flange connections provide very good tightness. To do this, the flanges being joined must have similar connecting dimensions that do not exceed the permissible error. Another condition is mandatory periodic tightening of joints, which allows maintaining the “grip” of bolted joints at the proper level. This is especially important when they are constantly exposed to mechanical vibrations or there are significant fluctuations in ambient temperature and humidity. And the larger the diameter of the pipeline, the more relevant this is, because as it increases, the force on the flanges increases. The tightness of flange connections largely depends on the sealing ability of the gaskets installed between the flanges.

Deformations cannot be discounted. Moreover, flanges made of different materials are susceptible to them to different degrees, therefore the material from which it is made is the most important parameter of the flange. Thus, ductile steel flanges are deformed more easily than those made of cast iron, which is more brittle but holds its shape much better.

The disadvantages of flanged fittings are a continuation of its advantages. High strength results in significant overall dimensions and weight, which, in turn, mean increased metal consumption (in the manufacture of large-sized flanges, it is necessary to use a thick metal sheet or round profiles of large diameter) and labor-intensive production.

Weld fittings

Welding of reinforcement is resorted to when the reliability and tightness of other types of connections is considered unsatisfactory. Welding is especially in demand when constructing pipeline systems in which the working environment is toxic, poisonous or radioactive liquids and gases. In this case, a welded connection, which, if properly executed, provides 100 percent tightness, may be the optimal, and often the only acceptable solution. It is only important that such a section of the system does not require frequent dismantling of equipment, the implementation of which will each time lead to complete destruction of the welded joints.

Thanks to welding, which combines fragments of the pipeline system into a single whole, it is possible to ensure harmony, or, in technical terms, structural compliance between all its elements - pipes and pipeline fittings. The main thing is that, due to differences in the mechanical properties of the welded joint and other components of the pipeline system, it does not become its weak link.

The connecting ends of the reinforcement are prepared for welding by leveling and grinding the surface of the welded fragments, removing the required chamfers.

Welded joints can be made in socket and butt. In the first case, the welding seam is located on the outside of the pipe. This option is usually used for steel fittings of relatively small diameter, installed in pipelines operating at high pressure and temperature of the working environment.

In the second case, the connection can be supplemented with a backing ring, which prevents distortion of the parts being connected. It is precisely these connections, characterized by reliability and absolute tightness, that are used when installing pipeline systems of hazardous production facilities, for example, power units of nuclear power plants.

Important advantages of welded connections, especially compared to flanged ones, are minimal weight, compactness and space saving.

Coupling fittings

One of the most common in technology is the coupling connection of reinforcement.

It is used for various types of valves of small and medium diameter, operating at low and medium pressures, the body of which is made of cast iron or non-ferrous alloys. If the pressure is high, then it is preferable to use pin fittings.

In the connecting pipes of coupling fittings, the thread is on the inside. As a rule, this is a pipe thread ─ inch thread with a fine pitch. It is formed in various ways - knurling, cutting, stamping. It is important that with a fine thread pitch, the height of the teeth does not depend on the diameter of the pipeline.

On the outside, the connecting ends are designed in the form of a hexagon to make it convenient to use the key.

The word “coupling” came into Russian from German, and possibly from Dutch, where mouw means sleeve. The coupling, like the valve, is an example of how tailoring and the production of pipeline fittings each use in their special terminology words that sound the same, but carry different meanings. In engineering, a coupling is not a sleeve, but a short metal tube that provides connections to the cylindrical parts of machines.

The fine thread of the coupling connection plus the use of special viscous lubricants, flax strands or fluoroplastic sealing material (FUM tape) guarantee its high tightness. A coupling connection does not require the use of additional fasteners (for example, bolts or studs, as in a flange connection). But one cannot ignore that screwing a coupling onto a thread with a seal requires considerable effort, the greater the larger the diameter of the pipeline.

Union fittings

The German origin of the term “fitting” from the verb stutzen (to trim, cut) even reveals its sound. This is the name given to the muskets used to arm armies up until the 19th century, due to the presence of a rifled barrel. In modern technology, this noun is used to define a short piece of pipe (in other words, a sleeve) with threads on both ends, used to connect pipes and pipeline fittings to units, installations and tanks. In a fitting connection, the connecting end of the valve with external thread is pulled to the pipeline using a union nut. It is used for fittings of small and ultra-small (with a nominal diameter of up to 5.0 mm) diameters. As a rule, this is laboratory or other special fittings. For example, reducers installed on compressed gas cylinders. Using a fitting connection, various control and measuring instruments (I&I) are “implanted” into pipeline networks, evaporators, thermostats, and many types of equipment that are part of chemical production lines are installed.

Pin fittings

The term “pin joint” came into widespread use at the end of the 19th century. Its main attributes for pipeline fittings are connecting pipes with external threads and the presence of a collar. The end of the pipeline with the flange is pressed against the end of the fitting pipe using a union nut.

The pin connection is used for small-sized high-pressure fittings, in particular, instrumentation devices. It is effective when screwing fittings into the body of vessels, devices, installations or machines. Its tightness is ensured by the presence of gaskets and special lubricants.

An example of a pin connection would be the connection of a fire hose to a fire hydrant.

All threaded connections have such advantages as a minimum number of connecting elements, low metal consumption and, accordingly, low weight, and manufacturability. Effective installation of threaded connections requires matching internal and external threads and the use of soft or viscous materials for sealing. But it should be taken into account that threading reduces the thickness of the pipe wall, so this type of connection is not suitable for thin-walled pipes.

In addition to those listed, there are other ways to connect fittings. Thus, durite compounds can be used in pipeline systems. These are connections through cylindrical couplings, consisting of several layers of rubberized fabric (in simple words, fragments of hoses), pushed onto protrusions made on the pipes and fixed with metal clamps.

Another method of connecting fittings is soldering, which is used for copper pipes with a small diameter. The end of the pipeline, treated with solder, is inserted into the groove made in the pipe.

The functionality, operability and reliability of a pipeline system is determined not only by the parameters of the fittings included in its composition, but also by the quality ofdone reinforcement connection , the selection and implementation of which should always be given special attention.

In apartment buildings, residents mainly use the central heating network to heat the premises. The quality of these services is influenced by many factors: the age of the house, wear and tear of equipment, the condition of the heating main, etc. A special scheme for connecting to the heating network is also of significant importance in the heating system.

Connection types

Connection schemes can be of two types: dependent and independent. Connecting using the dependent method is the simplest and most common option. An independent heating system has gained popularity recently and is widely used in the construction of new residential areas. Which solution is more effective for providing warmth, comfort and coziness to any room?

Dependent

This connection scheme, as a rule, provides for the presence of in-house heating points, often equipped with elevators. In the mixing unit of the heating station, superheated water from the main external network is mixed with the return water, thereby acquiring a sufficient temperature (about 100°C). Thus, the internal heating system of the house is completely dependent on external heat supply.

Advantages

The main feature of this scheme is that it provides for the supply of water to the heating and water supply systems directly from the heating main, and the price pays off quite quickly.

Flaws

Along with the advantages, such a connection also has some disadvantages:

• uneconomical;
• temperature control is significantly difficult during weather changes;
• overconsumption of energy resources.

Connection methods

Connection can be made in several ways:

Independent

An independent heat supply system allows you to save consumed resources by 10-40%.

Operating principle

The consumer heating system is connected using an additional heat exchanger. Thus, heating is carried out by two hydraulically isolated circuits. The external heating circuit heats the water of the closed internal heating network. In this case, mixing of water, as in the dependent version, does not occur.

However, such a connection requires considerable costs for both maintenance and repair work.

Water circulation

The movement of the coolant is carried out in the heating mechanism thanks to circulation pumps, due to which there is a regular supply of water through the heating devices. An independent connection circuit may have an expansion vessel containing a supply of water in case of leaks.

Components of an independent system.

Scope of application

Widely used to connect multi-storey buildings or structures to the heating system, which require an increased level of reliability of the heating mechanism.

For facilities that have premises where access to outside service personnel is undesirable. Provided that the pressure in return heating systems or heating networks is higher than the permissible level - more than 0.6 MPa.

Advantages

Negative points

• high price;
• difficulty of maintenance and repair.

Comparison of the two types

The quality of heat supply according to a dependent scheme is significantly affected by the operation of the central heat source. This is a simple, cheap method that does not require special maintenance or repair costs. However, the advantages of a modern independent connection scheme, despite the financial costs and complexity of operation, are obvious.

Ball valve is one of the most popular types of pipeline fittings. One of its main classifying features is the method of attachment. “Coupled”, “flange”, “welded” are commonly used attachments for ball valves. Less commonly used are “pin”, “nozzle”, “nipple”, “solder”.

Types of connections for industrial pipeline fittings are defined in the current interstate standard GOST 24856-81(analogous to ISO 6552-80). In the “description” cell of the GOST table of terms and definitions regarding types of connections there is a dash; there is only a graphic sketch. It is understood that the meaning of the term should be clear literally from the name. However, for a person who is not interested in technology, the marking “socket ball valve” or “flanged ball valve” may be incomprehensible.

Ball valves by connection type

Coupling

The coupling ball valve is connected using internal threads cut into the body along the edges. A coupling is a connecting part of pipelines that has the shape of a hollow cylinder with a thread cut inside.
Socket ball valves often used in both the domestic and industrial and public sector. They are very convenient, since installation requires only a pair of wrenches (open-end, pipe, adjustable) depending on the installation location. To prevent leakage, the threads of the coupling valve are packed with strands of flax with Unipack, FUM tape, sealing thread or anaerobic sealant. Installation of a coupling ball valve is quick, and the fittings themselves are relatively inexpensive. The most commonly used sizes are corresponding to the connecting thread ½, ¾, 1, 1 ¼, 1 ½, 2 inches. Also on the market there are smaller diameters - ¼, ⅜ inches, large ones - 2 ½, 3, 4 inches.

Flanged

The connection of a flanged ball valve is made in the form of a flat, most often round, part located perpendicular to the axis, with holes for fasteners (bolt and nut). There are always two flanges in the connection. One on the pipe, the second on the fittings. The flange connection is highly reliable. The thickness of the flange and the number of holes depends on the maximum pressure for which the ball valve is designed. In the domestic sector, flanged ball valves are practically not used, except when connecting to a central water supply or gas pipeline. Such shut-off valves are mainly used in public utilities and industry.

Welded

Weld-on ball valves are mounted on the pipeline by welding. The connecting pipes of such fittings are made in the shape of a pipe and do not have threads or connecting parts. They are often also called (as GOST 24856-81 regulates) “ball valves for welding.” Weld-on ball valves can be made of carbon, low-alloy, stainless steel, and have a one-piece or collapsible design. The scope of application of welded fittings is industry and public utilities.

Fittings

Union ball valves are similar in design to coupling valves, with the only difference being that the thread on the connecting pipe is not internal, but external. The selection of a coupling or fitting product is made based on the thread on the mating part. Sellers, installers, and many manufacturers call such fittings “nipple taps,” which is the same thing. Their distinctive feature is connections with external threads. The price of a coupling ball valve is lower than that of a nipple valve. The installation and standard sizes of such fittings are mostly similar.
A ball valve with external thread can be equipped with half-bends on one or both sides. Such a connection will be dismountable and the valve can be removed for replacement or maintenance. The half fitting can be threaded or welded. Reinforcement with a half-bend on one side is often called “ American crane ”.

Tsapkovye

The pin-type ball valve has connecting pipes (one or both) with external threads and a collar. Such products are intended for installation directly on the tank, equipment ( boiler, boiler), etc. An example of pin-type cranes can be seen below. For example, these are taps with a fitting for irrigation, water taps, drainage taps.

Solderable

Connection of ball valves is also possible by soldering. Basically, such fittings are placed on copper and polypropylene systems. The use of solder ball valves makes the connection more durable and aesthetically pleasing; the use of additional fittings is not required. It should be noted that it is correct to use the word “welding” when referring to polypropylene, but “soldering” is more often used among installers and consumers.

Names of ball valves

It just so happens that the standard establishes certain terms for fittings, installers and designers use others, and Chinese manufacturers use others. Here are some commonly used names and their meanings:

• ball valve NN - fittings on both sides with external thread (other names, “male-male”, “fitting on both sides”, “nipple”);
• ball valve BB - fittings on both sides with internal thread (“female-female”, “coupling”);
• ball valve VN has an external thread on one side and an internal thread on the other (“male-female”);
• faucet with a gander - pin-type water dismounting with a fitting for a hose;
• American tap - fittings with a collapsible connection (with a half-fitting).

Threaded and other shut-off valves can be the same type of connecting pipes or different - combined. For example, a ball valve has an internal thread on one side and an external thread on the other (VN). Or one connection is flanged and the other is welded.

Large selection of ball valves in our UniDim online store. Our brands - GIACOMINI,RBM,WATTS.