Tightening force for flange bolts. How to properly connect steel pipes with flanges? Design features of flanges

ment indicated in the table below.
a The table below applies to the bolts shown in fig. BUT.

2. Table of tightening torques for flange bolts
a Unless otherwise specified, use the norm"
mats below.

3. Table of tightening torques for O-ring pipe fittings
a Unless otherwise specified, when tightening the grommets of the tubing connectors with sealing
ring, use the guidelines below.

4. Table of tightening torques for O-ring plugs
a Unless otherwise specified, use O-ring plugs to tighten
the standards below.

5. Tightening torque table for hoses (with conical and mechanical seals)
a Unless otherwise specified, when tightening hoses (with conical and mechanical seals)
use the rules below
a The points below apply when applying engine oil to the threads.

6. Table of tightening torques for mechanical seal connections
a Tighten the mechanical seal connections (flare nuts) on low
pressure from clad steel used on engines, up to moments, represented by "
shown in the following table.
a Apply the following tightening torques to mechanical seal connections,
having previously applied a layer of engine oil to their threaded sections.

Reference: Depending on the specific specifications connections are used with
mechanical seal, the dimensions of which are indicated in brackets ().

7. Torque table for 102, 107 and 114 series motors (bolts and nuts)
a Unless otherwise specified, when tightening bolts and nuts with metric threads on

8. Torque table for motors series 102, 107 and 114 (swivel joints)
a Unless otherwise specified, when tightening metric swivel joints on
For 102, 107 and 114 series engines, use the specifications below.

9. Torque table for 102, 107 and 114 series motors (Tapered screws)
carving)
a Unless otherwise specified, when tightening screws with a tapered thread (unit: inch) by
For 102, 107 and 114 series engines, use the specifications below.

Flange is a way of connecting pipes, valves, pumps and other equipment to form a piping system. This connection method provides easy access for cleaning, inspection or modification. Flanges are usually threaded or welded. The flange connection consists of two flanges fixed with bolts and a gasket between them to ensure tightness.

Pipe flanges are made from various materials. Flanges are surface machined, cast iron and nodular iron, but the most commonly used material is forged carbon steel.

The most used flanges in the oil and chemical industry:

• with welding neck
• through flange
• welded with a recess for welding
• welded overlap (free-rotating)
• threaded flange
• flange plug

All types of flanges, except free, have a reinforced surface.

Special flanges
With the exception of the flanges mentioned above, there are a number of special flanges, such as:

• diaphragm flange
• long welded collar flanges
• expansion flange
• adapter flange
• ring plug (part of the flange connection)
• disc plugs and intermediate rings (part of the flange connection)

Flange materials
The most common materials used for the manufacture of flanges are carbon steel, stainless steel, cast iron, aluminum, brass, bronze, plastic, etc. In addition, flanges, like fittings and pipes for special applications, are sometimes internally coated with a layer of material of a completely different quality than the flanges themselves. These are lined flanges. The material of the flanges is most often set when selecting pipes. As a rule, the flange is made of the same material as the pipes themselves.

Example of a 6" collar weld flange - 150#-S40
Each ASME B16.5 flange has a number of standard sizes. If a designer in Japan, or a person preparing a project for a start-up in Canada, or a pipeline installer in Australia, talks about a 6"-150#-S40 welding flange according to ASME B16.5, then he means the flange, which is shown below.

In the case of ordering a flange, the supplier would like to know the quality of the material. For example, ASTM A105 - Forged Flange carbon steel, while A182 is a stamped alloy steel flange. Thus, by regulation, both standards must be specified for the supplier: Weld Flange 6"-150#-S40-ASME B16.5/ASTM A105.

PRESSURE CLASS

The pressure class or rating for flanges will be in pounds. Different names are used to indicate the pressure class. For example: 150 Lb or 150Lbs or 150# or Class 150, mean the same thing.
Forged steel flanges have 7 main classifications:
150 lbs - 300 lbs - 400 lbs - 600 lbs - 900 lbs - 1500 lbs - 2500 lbs

The concept of flange classification is clear and obvious. A Class 300 flange can handle higher pressures than a Class 150 flange because a Class 300 flange has more metal and can withstand higher pressures. However, there are a number of factors that can affect the flange pressure limit.

EXAMPLE
Flanges can withstand different pressures at different temperatures. As the temperature rises, the pressure class of the flange decreases. For example, a Class 150 flange is rated for approximately 270 PSIG in environment, 180 PSIG at 200°C, 150 PSIG at 315°C, and 75 PSIG at 426°C.

Additional factors are that flanges can be made from various materials such as alloy steel, cast and ductile iron, etc. Each material has different pressure classes.

PARAMETER "PRESSURE-TEMPERATURE"
The pressure-temperature class defines the operating, maximum allowable overpressure in bar at a temperature in degrees Celsius. For intermediate temperatures, linear interpolation is allowed. Interpolation between notation classes is not allowed.

Temperature-pressure classifications
The Temperature-Pressure class is applicable to flanged connections that comply with the limits on bolted connections and gaskets that are made in accordance with good practice for assembly and alignment. Use of these classes for flange connections that do not meet these limits is the responsibility of the user.

The temperature shown for the corresponding pressure class is the temperature of the inner shell of the part. Basically, this temperature is the same as that of the contained liquid. In accordance with the requirements of current codes and regulations, when using a pressure class corresponding to a temperature different from the flowing liquid, all responsibility lies with the customer. For any temperature below -29°C, the rating must be no higher than when used at -29°C.

As an example, below you will find two tables with material groups in accordance with ASTM and two other tables with the temperature-pressure class for these materials in accordance with ASME B16.5.

Materials ASTM group 2-1.1
Nominal designation	Stamping	Casting	plates
C-Si	A105(1)	A216 Gr.WCB(1)	A515 Gr.70(1)
C-Mn-Si	A350 Gr.LF2(1)	-	A516 Gr.70(1),(2)
C-Mn-Si-V	A350 Gr.LF6 Cl 1(3)	-	A537 Cl.1(4)
3½ Ni	A350 Gr.LF3	-	-
REMARKS: (1) When exposed to temperatures above 425°C for a long time, the carbide phase of the steel may be converted to graphite. Permissible, but not recommended for prolonged use above 425°C. (2) Do not use above 455°C (3) Do not use above 260°C (4) Do not use above 370°C

Temperature-Pressure Class for ASTM Group 2-1.1 Materials Operating pressure by class
Temperature °C	150	300	400	600	900	1500	2500
from 29 to 38	19.6	51.1	68.1	102.1	153.2	255.3	425.5
50	19.2	50.1	66.8	100.2	150.4	250.6	417.7
100	17.7	46.6	62.1	93.2	139.8	233	388.3
150	15.8	45.1	60.1	90.2	135.2	225.4	375.6
200	13.8	43.8	58.4	87.6	131.4	219	365
250	12.1	41.9	55.9	83.9	125.8	209.7	349.5
300	10.2	39.8	53.1	79.6	119.5	199.1	331.8
325	9.3	38.7	51.6	77.4	116.1	193.6	322.6
350	8.4	37.6	50.1	75.1	112.7	187.8	313
375	7.4	36.4	48.5	72.7	109.1	181.8	303.1
400	6.5	34.7	46.3	69.4	104.2	173.6	289.3
425	5.5	28.8	38.4	57.5	86.3	143.8	239.7
450	4.6	23	30.7	46	69	115	191.7
475	3.7	17.4	23.2	34.9	52.3	87.2	145.3
500	2.8	11.8	15.7	23.5	35.3	58.8	97.9
538	1.4	5.9	7.9	11.8	17.7	29.5	49.2

Temperature-Pressure Class for ASTM Group 2-2.3 Materials Operating pressure by class
Temperature °C	150	300	400	600	900	1500	2500
from 29 to 38	15.9	41.4	55.2	82.7	124.1	206.8	344.7
50	15.3	40	53.4	80	120.1	200.1	333.5
100	13.3	34.8	46.4	69.6	104.4	173.9	289.9
150	12	31.4	41.9	62.8	94.2	157	261.6
200	11.2	29.2	38.9	58.3	87.5	145.8	243
250	10.5	27.5	36.6	54.9	82.4	137.3	228.9
300	10	26.1	34.8	52.1	78.2	130.3	217.2
325	9.3	25.5	34	51	76.4	127.4	212.3
350	8.4	25.1	33.4	50.1	75.2	125.4	208.9
375	7.4	24.8	33	49.5	74.3	123.8	206.3
400	6.5	24.3	32.4	48.6	72.9	121.5	202.5
425	5.5	23.9	31.8	47.7	71.6	119.3	198.8
450	4.6	23.4	31.2	46.8	70.2	117.1	195.1

FLANGE SURFACE

The shape and design of the flange surface will determine where the sealing ring or gasket will be located.

Most used types:

• raised surface (RF)
• flat surface (FF)
• o-ring groove (RTJ)
• with male and female thread (M&F)
• tongue and groove (T&G)

PROPERTIES (RF-Raised Face)

Raised face, the most applicable type of flange, easy to identify. This type is so called because the surface of the gasket protrudes above the surface of the bolted joint.

Diameter and height are defined in accordance with ASME B16.5 using pressure class and diameter. In the pressure class up to 300 Lbs, the height is about 1.6 mm, and in the pressure class from 400 to 2500 Lbs, the height is about 6.4 mm. The pressure class of the flange determines the height of the raised face. The purpose of an (RF) flange is to concentrate more pressure on a smaller gasket area, thereby increasing the pressure limit of the joint.

For the height parameters of all flanges described in this article, dimensions H and B are used, with the exception of the lap joint flange, this must be understood and remembered as follows:

In pressure classes 150 and 300 Lbs, the protrusion height is approximately 1.6 mm (1/16 inch). Almost all suppliers of flanges in these two classes list dimensions H and B in their brochures or catalogues, including the face (see Fig.1 below)

In pressure classes 400, 600, 900, 1500 and 2500 Lbs, the protrusion height is 1/4 in. (6.4 mm). In these classes, many suppliers list the H and B dimensions, not including the protrusion height (see Fig.2 above)

In this article you will find two sizes. The top row of dimensions does not include protrusion height, and the dimensions in the bottom row include protrusion height.

FLAT SURFACE (FF - Flat Face)
For a flat face (full face) flange, the gasket is in the same plane as the bolted connection. Most often, flat face flanges are used where the mating flange or fitting is cast.

A flat face flange never connects to a raised flange. According to ASME B31.1, when connecting cast iron flat flanges to carbon steel flanges, the protrusion on the steel flange must be removed and the entire surface must be sealed with a gasket. This is done to keep the thin, brittle cast iron flange from cracking due to the protrusion of the steel flange.

FLANGE WITH ROOT FOR O-RING SEAL (RTJ - Ring Type Joint)
RTJ flanges have grooves cut into their surface, into which steel o-rings are inserted. The flanges are sealed due to the fact that when the bolts are tightened, the gasket between the flanges is pressed into the grooves, deformed, creating close metal-to-metal contact.

The RTJ flange may have a lip with an annular groove made in it. This protrusion does not serve as a seal of any kind. For RTJ flanges that are sealed with O-rings, the raised faces of the mated and tightened flanges may come into contact with each other. In this case, the compressed gasket will no longer carry additional loads, bolt tightening, vibration and displacement will no longer crush the gasket and reduce the tightening force.
Metal o-rings are suitable for use at high temperatures and pressures. They are made with the right choice of material and profile and are always used in the appropriate flanges, providing a good and reliable seal.

O-rings are designed so that sealing occurs by means of a "leading line of contact" or wedging between the mating flange and the gasket. By applying pressure to the seal through the bolting, the softer metal of the gasket penetrates the fine structure of the stiffer flange material, and creates a very tight and effective seal.

Most used rings:

Type R-Oval according to ASME B16.20
Suitable for ASME B16.5 flanges pressure class 150 to 2500.

Type R-Octagonal according to ASME 16.20
An improved design over the original R-Oval. However, they can only be used for flat flanges with a groove. Suitable for ASME B16.5 flanges pressure class 15 to 2500.

FLANGES WITH SEALING AND SURFACE TYPE LUG-VESSEL (LMF - Large Male Face; LFF - Large Female Face)


Flanges of this type must match. One flange face has an area that extends beyond the normal flange face limits ( dad). The other flange or counter flange has a corresponding recess ( mother) made in its surface.

Semi-loose laying

• The depth of the undercut (notch) is usually equal to or less than the height of the protrusion to prevent metal-to-metal contact when the gasket is compressed
• Depth of notch is typically no more than 1/16" greater than the height of the lip

FLANGE WITH SEALING SURFACE
(Protrusion - Tounge Face - TF; Depression - Groove Face - GF)


Flanges of this type must also match. One flange has a ring with a protrusion (thorn) made on the surface of this flange, while a groove is machined on the surface of the counterpart. Such surfaces are commonly found on pump covers and valve covers.

Fixed gasket

• Gasket dimensions are the same or less than the height of the groove
• Gasket wider than groove no more than 1/16"
• The dimensions of the gasket will match the dimensions of the groove
• When disassembling, the connection must be unclenched separately

Basic flange surfaces such as: RTJ, T&G and F&M are never joined together.

FLAT SURFACE AND GROOVE


Fixed gasket

• One surface is flat, the other is notched
• For applications where precise control of gasket compression is required
• Only resilient gaskets are recommended - spiral, hollow ring, pressure actuated and metal sheath gaskets

FLANGE SURFACE FINISHING
ASME B16.5 requires that the flange surface (raised face and flat face) have a certain roughness so that this surface, when aligned with the gasket, provides a good seal.

The final fluting, either concentric or spiral, requires 30 to 55 grooves per inch, resulting in a roughness between 125 and 500 micro inches. This will allow flange manufacturers to process any class of metal flange gasket.

For pipelines transporting substances of groups A and B technological facilities I category of explosion, it is not allowed to use flange connections with a smooth sealing surface, except for the use of spiral wound gaskets.

MOST USED SURFACES

Roughing

The most commonly used in the machining of any flange because it is suitable for almost all common operating conditions. When compressed, the soft surface of the gasket will engage the machined surface, which will help create a seal, and there will be a high level of friction between the connected parts. Finishing for these flanges is done with a 1.6mm radius cutter at a feed rate of 0.88mm per revolution for 12". For 14" and larger, machining is done with a 3.2mm radius cutter at a 1.2mm feed vice versa.

Spiral notch
This can be a continuous or phonographic spiral groove, but differs from roughing in that the groove is obtained by using a 90 degree cutter that creates a V-profile with a 45° fluted angle.

Concentric notch.
As the name suggests, the machining consists of concentric grooves. A 90° cutter is used and the rings are distributed evenly over the entire surface.

Smooth surface.
Such processing does not visually leave traces of the tool. Such surfaces are typically used for metal faced gaskets such as double sheath, flat steel, or corrugated metal. A smooth surface helps create a seal and depends on the flatness of the opposite surface. Typically, this is achieved by a gasket contact surface formed by a continuous (sometimes called phonographic) helical groove made with a 0.8 mm radius cutter, at a feed rate of 0.3 mm per revolution, 0.05 mm deep. This will result in a roughness between Ra 3.2 and 6.3 micrometers (125-250 micro inches)

GASKETS
In order to make a tight flange connection, gaskets are needed.

Gasket is compressed sheets or rings used to create a waterproof connection between two surfaces. Gaskets are manufactured to withstand extreme temperatures and pressures and are available in metallic, semi-metallic and non-metallic materials.
For example, the sealing principle may be to compress a gasket between two flanges. The gasket fills the microscopic spaces and surface irregularities of the flanges and then forms a seal that prevents leakage of liquids and gases. Proper and careful gasket installation is required to prevent leakage in the flange connection.

This article will describe gaskets conforming to ASME B16.20 (Metallic and Semi-Metallic Pipe Flange Gaskets) and ASME B16.21 (Non-Metallic, Flat Pipe Flange Gaskets)

BOLTS
Bolts are required to connect two flanges to each other. The number will be determined by the number of holes in the flange, and the diameter and length of the bolts will depend on the type of flange and its pressure class. The most commonly used bolts in the oil and chemical industry for ASME B16.5 flanges are studs. The stud consists of a threaded rod and two nuts. Another type of bolt available is the regular hex bolt with one nut.

Dimensions, dimensional tolerances, etc. have been defined in ASME B16.5 and ASME B18.2.2, materials in various ASTM standards.

TORQUE

To obtain a tight flange connection, the gasket must be properly installed, the bolts must have the correct tightening torque, and the total tightening stress must be evenly distributed over the entire flange.

The necessary stretching is carried out due to the tightening torque (applying a preload to the fastener by turning its nut).

The correct torque of the bolt allows the best use of its elastic properties. To do its job well, a bolt must behave like a spring. During operation, the tightening process places an axial, pre-load on the bolt. Of course, this tensile force is equal to the opposing compressive forces applied to the assembly components. It may be referred to as tightening force or tensile force.

TORQUE WRENCH
A torque wrench is a generic name for a hand tool that is used to apply precise torque to a joint, be it a bolt or a nut. This allows the operator to measure the rotational force (torque) applied to the bolt, which must match the specification.

Choosing the right flange bolt tightening technique requires experience. The correct application of any of the techniques also requires the qualifications of both the tool to be used and the specialist who will do the work. Below are the most commonly used bolt tightening methods:

• tightening by hand
• pneumatic wrench
• hydraulic torque wrench
• manual torque wrench with rocker or gear
• hydraulic bolt tensioner

LOSS OF TORQUE
Torque loss is inherent in any bolted connection. The combined effect of bolt loosening (about 10% during the first 24 hours after installation), gasket creep, vibration in the system, thermal expansion, and elastic interaction during bolt tightening contribute to torque loss. When the torque loss reaches a critical level, the internal pressure exceeds the compression force that holds the gasket in place, in which case leakage or blowout may occur.

The key to reducing these effects is proper gasket placement. When installing the gasket, it is necessary to bring the flanges together and smoothly and parallel, with the least tightening torque, tighten the 4 bolts, following the correct tightening sequence. This will reduce operating costs and improve safety.

The correct thickness of the gasket is also important. The thicker the gasket, the higher its creep, which in turn can lead to loss of tightening torque. The ASME standard for serrated flanges generally recommends a 1.6 mm gasket. Thinner materials can operate at higher gasket loads and therefore higher internal pressures.

LUBRICATION REDUCE FRICTION
Lubrication reduces friction during tightening, reduces bolt shedding during installation, and increases service life. A change in the coefficient of friction affects the amount of preload achieved at a given tightening torque. A larger coefficient of friction results in less conversion of torque into preload. The value of the coefficient of friction provided by the lubricant manufacturer must be known in order to accurately set the required torque value.

Grease or anti-seize compounds must be applied to both the surface of the bearing nut and the male thread.

TIGHTENING SEQUENCE
First pass, lightly tighten the first bolt, then the next one opposite it, then a quarter turn in a circle (or 90 degrees) to tighten the third bolt and, opposite it, the fourth. Continue this sequence until all bolts are tightened. When tightening four-bolt flanges, use a criss-cross pattern.

PREPARATION OF FIXING THE FLANGE
In order to achieve tightness in flange connections, it is necessary that all components are accurate.

Before starting the connection process, the following steps must be taken to avoid problems in the future:

• Clean flange surfaces and check for scratches, surfaces must be clean and free from any defects (bumps, pits, dents, etc.)
• Inspect all bolts and nuts for damage or thread corrosion. Replace or repair bolts or nuts as needed
• Remove burrs from all threads
• Lubricate the threads of the bolts or studs and the surfaces of the nuts adjacent to the flange or washer. In most applications, hardened washers are recommended.
• Install the new gasket and make sure it is centered. DO NOT USE AN OLD GASKET, or use multiple gaskets.
• Check flange alignment per ASME B31.3 process piping standard
• Adjust the position of the nuts to make sure that 2-3 threads are above the top of the thread.

Regardless of which tightening method is used, all checks and preparations must first be made.

The tightness of the flange connection is achieved by proper installation of the gasket, ensuring the correct tightening torque for the bolts, and the distribution of the total stress from the tightening must be uniform over the entire area of ​​the flange.

With the correct tightening torque of the bolt, it becomes possible to realize its elastic properties. The bolt should behave like a spring when tightened, this allows it to fully perform its task.

torque wrench

A torque wrench is a generic name for a hand-held screwdriving tool and is used to accurately tighten nuts or bolts.

The following tools are used to tighten bolted joints:

• Manual key
• Pneumatic Impact Wrench
• ring key
• Hydraulic Torque Wrench
• Torque wrench with adjustable torque limit
• Hydraulic Bolt Tensioner

Loss of Torque (Loose Torque)

Loss of torque is possible in any type of bolted connection. The combined effect of bolt settling and creep is approximately 10% of the total tightening in the first 24 hours after installation, gasket misalignment, system vibration, thermal expansion and elastic interaction during bolt tightening also contribute to torque loss.

When the torque loss reaches its limit, the internal pressure exceeds the compressive force holding the gasket in place and causes the gasket to leak or rupture.

A key factor in reducing the impact of these effects is the correct installation of the gasket. Accurate flange assembly, parallel gasket installation, fixed with a minimum of four bolts using the correct torque, provided the correct mounting sequence, increases the possibility of reducing operating costs and increasing safety.

Choosing the right gasket thickness is also important. If the gasket is thicker than necessary, this can cause the gasket to slip, and this increases the chance of losing torque. A 1.6mm thick gasket is recommended for ASME faceted flanges. A thinner gasket will take on a greater load, and, therefore, the internal pressure will increase.

Friction Reducing Lubricant

Lubrication reduces friction during bolt tightening, reduces bolt installation problems and increases bolt life. Changing the coefficient of friction affects the level of preload achieved at a given torque. High level friction results in less preload torque.

The coefficient of friction provided by the used lubricants, it is necessary to calculate as accurately as possible, as this will help to set the desired torque value.

Lubrication must be applied to both surfaces of both the nut being screwed and the thread.

Flange tightening sequence

First you need to tighten the first bolt, then go to 180 ° and tighten the second bolt, then go ¼ turn in a circle (90 °) and tighten the third bolt, go to the bolt opposite - the fourth - and tighten. Continue the sequence until they are all twisted in a circle.

When using a flange with four bolt holes, the bolts are tightened "crosswise".

Method for Calculating Torques for Bolted Flange Connections Part II

A measure of the load required to stretch a bolt is the yield strength. By acting within it, we allow the bolt to return to its original length. Overloading the bolt can overshoot the yield strength and actually reduce the loads on the gasket due to additional stresses generated inside the flange joint. In this case, continuing to tighten the bolts does not necessarily increase the load on the gasket. Most likely, instead of preventing leakage, the bolt may fail.

A bolt can lose its compressive function if it is not stretched enough and the system loosens following its tightening. It is recommended to load the bolt at 50-60% of its yield strength in order for it to stretch sufficiently. In some cases, however, this value can be reduced, in particular if the load could damage the gasket or bend it.

Bolts are made from a variety of materials, each with a different yield strength. Right choice of the bolt is critical to the effectiveness of the assembled flange connection.

So, we have a torque wrench to measure torque and a formula that allows us to calculate this moment based on the required gasket compression force. The question is, how hard do you have to compress the gasket to ensure a tight seal?

The force exerting pressure on the gasket consists of several components:

The first component is to compress and hold the gasket in place. The load generated by the bolt compresses the gasket and it takes the shape of the flange face. The hydrostatic pressure that occurs inside the vessel or pipeline, on the contrary, tends to squeeze the gasket out of the connection weld flanges. The compression of the gasket must be sufficient to hold it in place while compensating for internal pressure. It also requires some residual load to hold the gasket in place after the pressure is released.

The force required to create a tight seal depends on the type or shape of the gasket, the fluid in the system, and the temperature and pressure. ASME standards list the main factors that affect a gasket, but it's always best to get advice from the gasket manufacturer.

The equation for determining the minimum force on the gasket is as follows:

Wm2 = (π b G)

The first combination of parameters is the effective area of ​​the pad based on its width b and the load diameter G, which reflects the backlash of the pad. Deriving numerical values ​​for all gasket types and compression configurations is beyond the scope of this article. However, this data can be found in the documentation for the boilers or pressure vessels.

It should be noted that some manufacturers use a more conservative approach, in particular, they propose to equate the gasket area to the sealing surface as much as possible. However, the above formula allows you to calculate the minimum loads.

To get the final compression Wm2, it is necessary to multiply all this by the coefficient of laying y. The larger the coefficient y, the more effort is required to “settle” the gasket.

Flange connection is the most vulnerable and weak point of the pipeline.

The assembly of pipes with flanges is one of the most common and critical operations in the manufacture and installation of pipelines, since the breakdown of the flange connection makes it necessary to disconnect the pipeline.

Passes of the medium through leaks in flange connections during testing and operation of pipelines occur due to weak tightening of the flanges, distortions between the planes of the flanges, poor cleaning of the sealing surfaces of the flanges before installing a new gasket, improper installation of the gasket between the flanges, use of poor-quality gasket material or material that does not comply medium parameters, defects on the sealing surfaces (mirrors) of the flanges.

The process of assembling a flange connection consists of installing (grooving), aligning and fastening flanges at the ends of pipes, installing a gasket and connecting two flanges with bolts or studs. Before assembling the flange connection, the pipe sections to be connected are checked for the straightness of their axes.

When fitting flanges onto pipes in accordance with SNiP ST.9-62, the following requirements must be met.

Flange deviation P to the axis of the pipe (skew), measured along the outer diameter of the flange (Fig. 99, a) should not exceed 0.2 mm for every 100 mm diameter of the pipeline designed to work under pressure up to 16 kgf / cm 2, 0,1 mm- under pressure from 16 kgf / cm 2 up to 64 kgf / cm 2 and 0.05 mm under pressure above 64 kgf / cm 2.

It is necessary to install the flanges so that the holes for the bolts and studs are located symmetrically to the main axes (vertical and horizontal), but do not coincide with them (Fig. 99.6). Offset bolt holes in flanges t relative to the axis of symmetry should not exceed ± 1 mm with hole diameter 18-25 mm,±1.5 mm- at 30-34 mm and ±2 mm- at 41 mm.

The displacement of the axes of the flange holes along the circumference of the pipe is checked using a plumb line or level, along which the vertical or horizontal axis is found, and then the displacement of the holes is controlled with a ruler.

The perpendicularity of the flange is checked with a control square (Fig. 100) and a probe. Gap between flange 2 and square 1 measured at points diametrically opposite to the points of contact.

For tapping on pipes with nominal bore up to 200 mm flat and butt-welded flanges with their centering along the inner diameter of the pipe, use the device shown in fig. 101. The device consists of a lever device 1 mounted on a rod 3, and disk 5 . For flange installation 6 the lever mechanism is inserted into the pipe 2. When the rod is rotating 3 clockwise the levers diverge, pressing the slats 4 to the pipe wall, while the disk is installed strictly perpendicular to the pipe axis. Flat flanges are mounted on the tool disk (position 1 ), and butt-welded - along the end of the pipe and fixture bars (position II). After reconciling the position of the flange, it is seized by electric arc welding.

Rice. 99. The position of the flange when installed on the pipe:

a - deviation from the perpendicularity of the flange to the main. pipes,
b - displacement of the axes of the bolt holes in the flanges relative to the axis of symmetry

Rice. 100. Control square:

I- square, 2 - flange, 3 - pipe

Rice. 101. Device for fitting flanges centered on the inner diameter of the pipe:

1 - lever device 2 - pipe, 3 - rod with a collar, 4 - bar, 5 - disk, 6 - flange

When assembling elements and assemblies of pipelines on assembly stands, special mobile devices are used for fitting flanges.

For lining up butt-weld flanges with nominal bore up to 500 mm The most rational device shown in Fig. 102, a. The welded flange is mounted on replaceable control pins 1 manufactured to match the bolt hole diameter of the flange. These pins with a double lead screw 2 and handles 3 spread and fix the position of the bolt holes of the flange symmetrically to the vertical axis. The perpendicularity of the flange of the longitudinal axis of the pipe is achieved by pressing its mirror to the plane of the mounting carriage 4. The coincidence of the flange axis with the pipe axis is achieved by moving the carriage with the flange vertically using screw 5 and the handle 6. The fixture is mounted on guide rollers 7, and after assembly and tacking of the element, it is easily rolled back.

When assembling a flat flange on such a device, an adjusting ring is inserted inside it so that the pipe does not reach the end of the carriage (flange plane) by the required amount. The disadvantage of this design is the need for individual centering of the inner hole of the flange and pipe during assembly.

On fig. 102.6 shows a device for tapping flat flanges with nominal bore up to 500 mm. It differs from the one described above in that a mandrel is fixed on the mounting carriage along with the control pins. 8, having a series of cylindrical protrusions, the diameters of which correspond to inner diameters assembled flanges. The width of the protrusions is taken taking into account the value to which the flange is not adjusted. The end surfaces of the protrusions are machined strictly perpendicular to the longitudinal axis. The flange is put on the pipe and pressed with a mirror to the end surface of the mandrel. The installation carriage is moved with the help of screw 5 so that it is on the same axis with the pipe in height.

Rice. 102. Devices for fitting flanges:

a- welded butt, b- flat welded; 1 - control pin 2 - double screw
3, 6 - handles, 4 - installation carriage, 5 - screw, 7 - guide rollers 8 - mandrel

If the flange is not skewed or the amount of skew is acceptable, the final assembly of the connection is carried out with the installation of gaskets. Soft gaskets (from paronite, cardboard, asbestos) are moistened with water before installation and rubbed on both sides with dry graphite. It is impossible to lubricate the gaskets with mastics or graphite diluted in oil, since the mastic and oil burn to the flange mirrors and spoil their surface.

The tightness of a flanged connection largely depends not only on the cleanliness of the surface of the flange mirrors, the quality and dimensions of the gasket, but also on the careful and skillful assembly and tightening of the nuts. Before assembling flanged joints with a lip and a socket, make sure that the lip of one flange freely enters the socket of the flange mating with it, and the gasket does not have offsets in one direction or another.

The assembly of pipes with loose flanges on a welded ring or flanged pipe is no different from the above and boils down mainly to preparing the end of the pipe.

Correcting the misalignment of flanges during their assembly by tightening bolts or studs, as well as eliminating gaps by installing wedge gaskets, is not allowed. This tension causes one-sided compression of the gasket and unacceptable stretching of the bolts or studs, as a result of which the connection becomes loose. Overtightened bolts or studs may break during operation.

Nuts of flange connections with paronite gaskets are tightened using the crosswise bypass method. First, one pair of oppositely lying bolts is tightened, then the second pair, which is at an angle of 90 ° to the first. Gradually, by transverse tightening of the nuts, all the bolts are tightened. With this sequence of tightening the nuts, distortions are not formed in the flange connections.

Nuts with metal spacers are tightened according to the circular bypass method, i.e., with a three- or four-fold circular bypass, all nuts are evenly tightened. The nuts of the flange connection are tightened with manual and mechanized ratchet wrenches. Power tools include electric or pneumatic driven wrenches. Uniformity of tightening and the amount of cold interference of flanged connection studs and valve covers on pipelines high pressure control with torque wrenches - by measuring the elongation of the stud during tightening. The allowable size of the cold tension of the studs is in the range from 0.03 to 0.15 mm for every 100 mm pin length.