Checking the tightening of bolted connections. Checking the presence and condition of screws Bolted contact connections

As is known, depending on the design, purpose, method of connecting materials, area of application and other factors, contact connections are distinguished: bolted, welded, soldered and made by crimping (crimped and twisted).
Contact connections include remote wire spacers.

When operating contact connections made by welding, the causes of defects in them may be: deviations from the specified parameters, undercuts, bubbles, cavities, lack of fusion, sagging, cracks, slag and gas inclusions(sinks), unfilled craters, burnt conductor wires, misalignment of connected conductors, incorrect choice tips, lack protective coatings on connections, etc.
Thermal welding technology does not provide reliable operation welded connectors for large cross-section wires (240 mm2 and more). This is due to the fact that due to insufficient heating during the welding process of the connected wires and the uneven approach of their ends, the outer layers of the wires are burned out, lack of penetration, and shrinkage cavities and slags appear at the welding site. As a result, the mechanical strength of the welded joint decreases. When mechanical loads are less than the design ones, a wire break (burnout) occurs in the anchor support loop, which leads to emergency shutdowns of overhead lines with a short service life. If in welded joint When individual wire conductors break, this leads to an increase in the contact resistance and an increase in its temperature.
The rate of development of the defect in this case will significantly depend on a number of factors: the value of the load current, wire tension, wind and vibration influences, etc.
Based on the experiments conducted, it was found that:

a reduction in the active cross-section of a wire by 20 - 25% due to the breakage of individual conductors may not be detected when carrying out IR inspection from a helicopter, which is due to the low emissivity of the wire, the distance of the thermal imager from the route by 50 - 80 m, the influence of wind, solar radiation and other factors;
when rejecting defective contact connections made by welding using a thermal imager or pyrometer, it must be borne in mind that the rate of development of a defect in these connections is much higher than that of bolted contact connections with pressure;
defects in contact connections made by welding, identified by a thermal imager during inspection of overhead lines from a helicopter, must be classified as dangerous if their excess temperature is 5 °C;
steel bushings not removed from welded area wires can create a false impression of possible heating due to the high emissivity of the annealed surface.

In contact connections made by crimping, there is an incorrect selection of tips or sleeves, incomplete insertion of the core into the tip, insufficient degree of crimping, displacement of the steel core in the wire connector, etc. As you know, one of the ways to control crimped connectors is to measure their DC resistance.
The criterion for an ideal contact connection is the equality of its resistance to the resistance of an equivalent section of the whole wire. A crimped connector is considered suitable for use if its resistance is no more than 1.2 times higher than the equivalent section of the whole wire. When the connector is crimped, its resistance drops sharply, but with increasing pressure it stabilizes and changes slightly.
The connector resistance is very sensitive to the condition of the contact surface of the wires being pressed. The appearance of aluminum oxides on contact surfaces leads to a sharp increase in the contact resistance of the connector and increased heat generation.
Minor changes in the contact resistance of the contact connection during their crimping process, as well as the associated low heat generation in the contact connection, indicate insufficient efficiency in detecting defects in them immediately after installation using infrared equipment. During the operation of pressed contact connections, the presence of defects in them will contribute to a more intense formation of oxide films and increase the contact resistance, which can lead to the appearance of local heating. Therefore, we can assume that IR inspection of new crimped contact connections does not allow identifying crimping defects and should be carried out for connectors that have worked for a certain period of time (1 year or more).
The main characteristics of crimped connectors are the degree of crimping and mechanical strength. As the mechanical strength of the connector increases, its contact resistance decreases. The maximum mechanical strength of the connector corresponds to the minimum electrical contact resistance.

Contact connections made using bolts most often have defects due to the lack of washers at the junction of the copper core with a flat terminal made of copper or aluminum alloy, the absence of disc springs, direct connection of the aluminum tip to the copper terminals of equipment in rooms with aggressive or humid environment, as a result of insufficient tightening of bolts, etc.
Bolted contact connections of aluminum busbars for high currents (3000 A and above) are not stable enough in operation. If contact connections for currents up to 1500 A require tightening the bolts once every 1 - 2 years, then similar connections for currents of 3000 A and above require annual overhaul with the obligatory cleaning of the contact surfaces. The need for such an operation is due to the fact that in high-ampere busbars (busbars of power plants, etc.) made of aluminum, the process of formation of oxide films on the surface of contact joints occurs more intensively.
The process of formation of oxide films on the surface of bolted contact joints is facilitated by different temperature coefficients of linear expansion of steel bolts and aluminum busbars. Therefore, when a short-circuit current passes through the busbar, when it operates with an alternating current load, deformation (compaction) of the contact surface of the aluminum bus occurs in it over a long distance as a result of vibration influences. In this case, the force tightening the two contact surfaces of the busbar weakens, the lubricant layer between them evaporates, etc.
Due to the formation of oxide films, the contact area of the contacts, i.e. the number and size of contact pads (number of points) through which current passes decrease and, at the same time, the current density increases, which can reach thousands of amperes per square centimeter, as a result of which the heating of these points increases greatly.
The temperature of the last point reaches the melting temperature of the contact material, and a drop of liquid metal forms between the contact surfaces. The temperature of the drop, rising, reaches a boil, the space around the contact connection is ionized, and there is a danger of a multiphase short circuit in the switchgear. Under the influence of magnetic forces, the arc can move along the switchgear busbars with all the ensuing consequences.
Operating experience shows that, along with multi-ampere busbars, single-bolt contact connections also have insufficient reliability. The latter, in accordance with GOST 21242-75, are allowed for use at a rated current of up to 1,000 A, but are damaged already at currents of 400 - 630 A. Increasing the reliability of single-bolt contact connections requires taking a number of technical measures to stabilize their electrical resistance.
The process of development of a defect in a bolted contact connection, as a rule, takes quite a long time and depends on a number of factors: load current, operating mode (stable load or variable), exposure chemical reagents, wind loads, bolt tightening forces, contact pressure stabilization, etc.
The transient resistance of a bolted contact connection depends on the duration of the current load. The contact resistance of contact connections gradually increases up to a certain point, after which a sharp deterioration of the contact surface of the contact connection occurs with intense heat generation, indicating an emergency condition of the contact connection.
Similar results were obtained by specialists from Inframetrix (USA) during thermal tests of bolted contact joints. The increase in heating temperature during testing was gradual throughout the year, and then there was a period of sharp increase in heat release.

Failures of contact connections made by twisting occur mainly due to installation defects. Incomplete twisting of wires in oval connectors (less than 4.5 turns) leads to the wire being pulled out of the connector and breaking. Uncleaned wires create high contact resistance, resulting in overheating of the wire in the connector with possible burnout. There have been repeated cases of the lightning protection cable AZhS-70/39, twisted at a smaller number of turns, being pulled out from the oval connector brand SOAS-95-3 air lines 220 kV.

Rice. Photo of the place where the remote spacer is attached with a break in the conductors as a result of vibration effects (a) and a diagram of the flow of load currents in the two-wire phase of an outdoor switchgear or overhead line when the conductors are broken at the place where the distance spacers are attached (b)

Distance spacers.

Unsatisfactory design of some designs of spacers, exposure to vibration forces and other factors can lead to chafing of the wire conductors or their break (Fig. 34). In this case, a current will flow through the spacer, the value of which will be determined by the nature and degree of development of the defect.

Analysis of the results of thermal imaging inspection of contact connections

Welded contact connections.

During thermal imaging testing of contact connections, assessment of their condition in accordance with the “Scope and Standards of Testing of Electrical Equipment” can be carried out by the defectiveness coefficient or by the value of excess temperature. Experiments conducted by Yuzhtechenergo revealed the insufficient efficiency of the thermal imaging method for detecting a defect in a welded contact joint at an early stage of development, especially when monitoring contact connections of overhead line wires from a helicopter. For welded contact joints, it is preferable to assess their condition by the value of excess temperature.

Pressed contact connections.

At one time, the values of defectiveness coefficients were used as criteria for assessing the condition of pressed contact connections on outdoor switchgear and overhead lines, i.e. the ratio of the measured resistance or voltage drop across a connector to the resistance of an identical section of a whole wire.
With the advent of CT devices, the condition of pressed contact connections can be assessed by the value of excess temperature or by the defectiveness coefficient.
The question arises about the degree of effectiveness of each of these methods for assessing the condition of pressed contact connections. To solve this problem, Mosenergo carried out load tests on a section of ASU-400 wire with serviceable and defective connectors.
Defect ratios were preliminarily determined for DC(Kx - 9) and by voltage drop (K2 = 5). The results of load tests (Table 1) showed that for crimped connectors, the most preferable method for assessing contact connections is based on the excess temperature value.

Current value	Heating temperature, "C			Coefficient
load, A		proper contact connection	defective contact connection	defectiveness

Thus, at a current of (0.3 - 0.4)/nom, the excess temperature is 7-16 °C, which is quite reliably recorded by the ICT device.
The results of the experiments are in good agreement with the recommendations of the “Scope and standards of testing of electrical equipment.” When assessing the condition of pressed contact connections based on the values of defectiveness coefficients, it is necessary to keep in mind that at the initial stage of manufacture (during installation) contact connections have a defectiveness coefficient of 0.8 - 0.9.

Failure of a crimped contact connection develops gradually and largely depends on compliance with the crimping technology and the pressure developed during this process. The optimal condition is considered to be one in which the maximum degree of compression corresponds to the minimum value of the contact resistance of the contact connection.

Bolted contact connections.

In both domestic and foreign practice, the most widespread assessment of the condition of a bolted contact joint is based on the value of excess temperature.
The process of defect development in a bolted contact connection was studied by Inframetrix (USA) on an existing connection at a load current of 200 A. The experiment showed that the process of defect development in the absence of external climatic, vibration and other factors and a load stable over time can proceed for a very long time .
Based on the test results, the company proposed the following limit values of excess temperature at rated current:
A)< 10 °С - нормальная периодичность тепловизионного контроля;
b) 10 - 20 °C - frequent thermal imaging control;
c) 20 - 40 °C - thermal imaging control every month;
d) > 40 °C - emergency heating.
The system proposed by the company for assessing the condition of bolted contact connections based on heating temperature, in principle, does not differ from that regulated by the “Scope and standards of testing of electrical equipment.”

Rice. 2. Dependence of the excess temperature of the bolted contact connector on the load current:
1 - with a reduction in the contact area of the contact surfaces by 40%; 2 - the same, 80%

The effect of heating temperature of bolted contact joints on the degree of defect development was studied by Yuzhtekhenergo. For this purpose, load tests were carried out on bolted contact connections by simulating a reduction of 40 and 80% in the area of contact of the contact surfaces (Fig. 35). The possibility of detecting defects of this kind during thermal imaging control was confirmed and it was shown that defects at an early stage of development can be clearly detected at load currents (0.3 - 0.4)/nom.
Cyclic long-term tests of bolted contact connections show that the stability of their contact transient resistance is largely determined by the design of the fastening fittings (the presence of spring washers, etc.). When carrying out thermal imaging monitoring, identifying contact connections with increased heating requires taking certain stabilization measures, for example, shutdown or temporary load reduction. In the latter case, the current /admissible permissible for a given defective contact connection can be determined from the relation

Controlled nodes
	heating temperature, °C		temperature rise, "C
1. Current-carrying (except for contacts and contact connections) and non-current-carrying metal parts:
not insulated and not in contact with insulating materials
insulated or in contact with insulating materials of heat resistance classes according to GOST 8865-93:






2. Copper and copper alloy contacts: uncoated (in air/in insulating oil)
with applied silver plates (in air/in insulating oil)
silver or nickel plated (in air/in insulating oil)
with silver coating with a thickness of at least 24 microns

3. Metal-ceramic contacts containing tungsten and molybdenum in insulating oil based on copper/silver
4. Hardware leads made of copper, aluminum and their alloys, intended for connection to external conductors of electrical circuits:
without cover
tin, silver or nickel plated
5. Bolted contact connections made of copper, aluminum and their alloys:
uncoated (in air/in insulating oil)
with tin coating (in air/in insulating oil)
Controlled nodes		Highest allowed value
		temperature heating, “C		exceeding temperature, "C
coated with silver or nickel (in air/in insulating oil)
6. Fuses alternating current for voltage 3 kV and higher:
compounds made of copper, aluminum and their alloys (in air without coating/with tin coating):
with detachable contact connection made by springs
with dismountable connection (pressing with bolts or screws), including fuse terminals
metal parts used as springs:

of phosphor bronze and similar alloys
7. Insulating oil in the top layer of switching devices
8. Built-in current transformers:

magnetic cores
9. Bolted connection of current-carrying terminals of removable inputs (in oil/in air)
10. Connections of on-load tap-changer devices of power trans
formers made of copper, its alloys and copper-containing compositions without silver coating when operating in air/oil:
with pressing bolts or other elements that provide rigidity to the connection
with spring pressure and self-cleaning during shifting
with spring pressure and not self-cleaning during shifting
11. Current-carrying conductors of power cables in long-term / emergency mode with insulation:
made of polyvinyl chloride plastic and polyethylene

Controlled nodes	Highest allowed value
Controlled nodes	heating temperature, °C	temperature rise, “C
made of vulcanizing polyethylene
made of rubber
made of rubber with increased heat resistance
with impregnated paper insulation with viscous / lean impregnation and rated voltage, kV:





12. Collectors and slip rings, unprotected and protected with insulation of heat resistance classes:


13. Sliding/rolling bearings

Note. The data given in the table applies if other standards are not established for specific types of equipment.
where /load, ΔTmeas - current and temperature rise of the measured contact connection, respectively; ΔTnorm - excess temperature of a contact connection, regulated by the “Scope and Standards of Electrical Equipment Testing”, depending on the type of coating of the contact surfaces and the environment in which they are located.
Evaluation of the thermal state of electrical equipment and live parts, depending on their operating conditions and design, can be carried out: by standardized heating temperatures (temperature rises), excess temperature, defectiveness coefficient, dynamics of temperature changes over time, with changes in load, by comparing measured temperature values within phases and between phases with temperature values in known good areas.
Limit values of heating temperature for /nom and its excess are given in table. 16.

For contacts and bolted contact connections, the standards given in table. 16 should be used at load currents (0.6 - 1.0)/nom after appropriate recalculation. Recalculation of the excess of the measured temperature value to the normalized value is carried out according to the relation

where ΔTnom - temperature rise at /nom; ΔTrab - the same, at g
slave-
Thermal imaging monitoring of electrical equipment and live parts at load currents of 0.3/nom and below does not help identify defects at an early stage of their development.
For contacts and bolted contact connections at load currents (0.3 - 0.6)/nom, their condition is assessed based on excess temperature. The temperature value recalculated to 0.5/nom is used as a standard.
For recalculation, the ratio is used

where ΔT0.5 is the excess temperature at a load current of 0.5/nom.
When assessing the condition of contacts and bolted contact connections based on excess temperature at a load current of 0.5/nom, the following areas are distinguished according to the degree of malfunction:

excess temperature 5-10 °C. The initial degree of malfunction, which should be monitored and corrective action taken during scheduled repairs;
excess temperature 10 - 30 °C. Developed defect. Measures should be taken to eliminate the malfunction at the next time the electrical equipment is taken out of service;
excess temperature more than 30 °C. Emergency defect. Requires immediate elimination.

It is recommended to assess the condition of welded and crimped contact connections based on excess temperature or defectiveness coefficient.
When assessing the thermal state of live parts, the following degrees of malfunction are distinguished, based on the given values of the defectiveness coefficient:
No more than 1.2................................................... ... Initial degree of malfunction, Forward

6.2.16.1 Tightening control bolted connections nodal linings of aluminum dome roofs are carried out when dismantling the cards to carry out inspection of beams and support crowns (Table 6.4, lines 12 and 27 and Table 6.5, line 20). Additionally, the tightening of bolted connections in four node linings is checked according to the diagram shown in Figure 6.18.

Figure 6.18 – Diagram of places for dismantling the hub caps (top view of the dome roof)

6.2.16.2 Before checking the tightening, the protective caps must be dismantled and a visual inspection of the bolted connection must be carried out. The surface of bolts, nuts and washers should be free of cracks, scale, rust, burrs, dents and nicks on the threads. The bolts must have a marking that indicates the tensile strength, the symbol of the heat number, the manufacturer's mark, and the marking of the bolts of the HL climatic version (according to GOST 15150) must contain the designation “HL”.

6.2.16.3 The tightness of bolted connections is checked by measuring the tightening torque with a torque wrench and a feeler gauge. The number of controlled bolted connections in a unit must be at least:

If the number of bolts in a connection is up to four – all bolts;

From five to nine - at least three bolts;

From 10 or more - 10% of bolts, but not less than three in each connection.

If one bolted connection is detected with non-standard tightening
(subclause 6.2.16.6), double the number of bolted connections is subject to control. If one bolt with abnormal tightening is detected during re-inspection, all bolts in all inspected units must be checked, bringing the tightening torque of each to the required value.

6.2.16.4 To carry out tightening control threaded connections with a controlled tightening torque of high-strength bolts of the upper node linings, torque wrenches of scale and limit types and probes are used that meet the requirements given in table 6.10.

Table 6.10 – Requirements for means of monitoring bolted connections

Torque wrenches for monitoring the tightening of high-strength bolts must be calibrated at least once per shift in the absence of mechanical damage, as well as after each replacement of the control measuring instrument or repair of the wrench, in accordance with SNiP 3.03.01-87 (clause 4.27).

6.2.16.5 Before inspecting a bolted connection, it is necessary to set on a torque wrench the torque specified in the design documentation, upon reaching which a click will occur. In the absence of data established in the design documentation, the torque M, Nm, is determined by the formula:

M = K∙P∙d, (6.11)

where K is the average value of the torque coefficient established for each batch of bolts in the manufacturer’s certificate or determined at the installation site using control measuring instruments. For bolts according to GOST R 52644 K = 0.18;

P – design bolt tension specified in the working drawings, N (kgf). In the absence of design data, the calculated bolt tension is determined according to SNiP 2.03.06-85, 8.10 using the formula:

Р = Rbh×Abn, (6.12)

where R bh is the calculated tensile strength of a high-strength bolt, determined by the formula:

R bh = 0.7∙R bun , (6.13)

where R bun is the minimum tensile strength of the bolt, taken according to
SNiP II-23-81* (Table 6.1) and given in Table 6.12.

A bn – cross-sectional area of the bolt, accepted in accordance with GOST 9150, GOST 8724 and
GOST 24705, adopted from the values given in SNiP II-23-81* (see table 6.2) and are shown in table 6.11.

Table 6.11 – Value of the minimum tensile strength of a bolt

Table 6.12 – Sectional areas of bolts

d, mm
A bn, cm 2	1,57	1,92	2,45	3,03	3,52	4,59	5,60	8,16	11,20	14,72

6.2.16.6 The criterion for compliance with the tightening of a bolted connection is the absence of rotation of the nut or bolt.

6.2.16.7 The tightness of the tie between the top assembly lining and the aluminum profile at the joints should be checked with a 0.3 mm thick feeler gauge, which should not pass between the assembled parts to a depth of more than 20 mm according to (SNiP 3.03.01-87). A diagram for checking the junction of the upper assembly lining and the aluminum profile with a probe is shown in Figure 6.19.

1 – junction of the upper nodal lining and the aluminum profile

Figure 6.19 – Scheme for checking with a feeler gauge (this place is indicated by the number 1) at the junction of the upper assembly lining and the aluminum profile

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LOAD-LOADING AND ENCLOSING STRUCTURES - BUILDING STANDARDS AND RULES - SNiP 3-03-01-87 (approved by the Decree of the USSR State Construction Committee dated 04-12-87... Relevant in 2017

Mounting connections with high-strength, tension-controlled bolts

4.20. Workers who have undergone special training, confirmed by an appropriate certificate, may be allowed to make tension-controlled bolt connections.

4.21. In shear-resistant connections, the contacting surfaces of the parts must be processed in the manner provided for in the design.

Oily contamination must first be removed from surfaces that are and are not subject to steel brush treatment.

The condition of surfaces after treatment and before assembly should be monitored and recorded in a log (see mandatory Appendix 5).

Before assembling the connections, the treated surfaces must be protected from dirt, oil, paint and ice formation. If this requirement is not met or the assembly of the joint begins more than 3 days after preparing the surfaces, their treatment should be repeated.

4.22. The difference in surfaces (deplanation) of the joined parts of more than 0.5 and up to 3 mm must be eliminated by mechanical processing by forming a smooth bevel with a slope no steeper than 1:10.

If the difference is more than 3 mm, it is necessary to install gaskets of the required thickness, processed in the same way as the connection parts. The use of gaskets is subject to agreement with the organization that developed the project.

4.23. The holes in the parts must be aligned during assembly and secured against displacement with plugs. The number of plugs is determined by calculating the effect of installation loads, but they must be at least 10% when the number of holes is 20 or more and at least two when there are fewer holes.

In the assembled package, fixed with plugs, blackness (mismatch of holes) is allowed, which does not interfere with the free installation of bolts without distortion. A gauge with a diameter 0.5 mm larger than the nominal bolt diameter must fit into 100% of the holes in each connection.

It is allowed to clean the holes of tightly tightened bags with a drill whose diameter is equal to the nominal diameter of the hole, provided that the blackness does not exceed the difference between the nominal diameters of the hole and the bolt.

The use of water, emulsions and oil when cleaning holes is prohibited.

4.24. It is prohibited to use bolts that do not have a factory marking of tensile strength on the head, a manufacturer's mark, a symbol of the heat number, and on bolts of the HL climate version (according to GOST 15150-69) - also the letters "HL".

4.25. Bolts, nuts and washers must be prepared before installation.

4.26. The bolt tension specified by the design should be ensured by tightening the nut or rotating the bolt head to the calculated tightening torque, or by turning the nut at a certain angle, or in another way that guarantees that the specified tension force is obtained.

The tensioning order should prevent the formation of leaks in the bags being tightened.

4.27. Torque wrenches for tensioning and monitoring the tension of high-strength bolts must be calibrated at least once per shift in the absence of mechanical damage, as well as after each replacement of the control device or repair of the wrench.

4.28. The calculated torque M required to tension the bolt should be determined by the formula

where K is the average value of the twist coefficient established for each batch of bolts in the manufacturer’s certificate or determined at the installation site using control instruments;

P - design bolt tension specified in the working drawings, N (kgf);

d- nominal diameter bolt, m.

4.29. The tension of the bolts according to the angle of rotation of the nut should be done in the following order:

manually tighten all the bolts in the connection to failure using a mounting wrench with a handle length of 0.3 m;

turn the bolt nuts at an angle of 180° ± 30°.

This method is applicable for bolts with a diameter of 24 mm with a package thickness of up to 140 mm and the number of parts in the package up to 7.

4.30. One washer in accordance with GOST 22355-77 must be installed under the head of a high-strength bolt and a high-strength nut. It is allowed, if the difference between the diameters of the hole and the bolt is no more than 4 mm, to install one washer only under the element (nut or bolt head), the rotation of which ensures the tension of the bolt.

4.31. Nuts that have been tightened to the design torque or turned to a certain angle should not be secured with anything additional.

4.32. After tensioning all the bolts in the connection, the senior assembly worker (foreman) is obliged to put a mark (a number or sign assigned to it) in the designated place.

4.33. The bolt tension should be controlled:

when the number of bolts in a connection is up to 4 - all bolts, from 5 to 9 - at least three bolts, 10 or more - 10% of bolts, but not less than three in each connection.

The actual torque must be no less than the calculated one, determined by formula (1), and not exceed it by more than 20%. Deviation of the nut rotation angle is allowed within ± 30°.

If at least one bolt is detected that does not meet these requirements, double the number of bolts is subject to inspection. If, during re-inspection, one bolt is detected with a lower torque value or with a smaller angle of rotation of the nut, all bolts must be checked to bring the tightening torque or angle of rotation of each nut to the required value.

The 0.3 mm thick feeler gauge should not fit into the gaps between the connection parts.

4.34. After checking the tension and acceptance of the connection, all outer surfaces of the joints, including bolt heads, nuts and parts of the bolt threads protruding from them must be cleaned, primed, painted, and cracks in places where there is a difference in thickness and gaps in the joints must be puttied.

4.35. All tensioning and tension control work should be recorded in a tension controlled bolting log.

4.36. Bolts in flange connections must be tensioned to the forces specified in the working drawings by rotating the nut until the calculated tightening torque. 100% of bolts are subject to tension control.

The actual torque must be no less than the calculated one, determined by formula (1), and not exceed it by more than 10%.

The gap between the contacting planes of the flanges at the locations of the bolts is not allowed. A 0.1 mm thick feeler gauge should not penetrate into an area with a radius of 40 mm from the bolt axis.

In accordance with the document “MDS 12-22.2005. Recommendations for the application in construction industry of the requirements of regulatory legal and other regulations containing state and regulatory requirements labor protection" Appendix 5, all data relating to construction and installation work in production should be entered into the log of installation connections using tension-controlled bolts. This requirement cannot be ignored or ignored. In the event of any legal proceedings, this journal will have legal weight and be treated as an official document.

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Title page:
- name of the organization performing the work
- name of the construction site
- position, surname, initials and signature of the person responsible for performing the work and maintaining a journal
- the organization that developed project documentation, KM drawings
- project code
- the organization that developed the work project
- project code
- an enterprise that developed KMD drawings and manufactured structures
- order code
- customer (organization), position, surname, initials and signature of the head (representative) of technical supervision

Sections 1
List of link workers (installers) involved in installing bolts.

Graphs log of installation connections using tension-controlled bolts:

2. Assigned rank

3. Assigned number or sign

4-5. Qualification certificate

date of issue

Issued by

6. Note

Main part

Fields to fill out:
1. Date
2. KMD drawing number and name of the node (joint) in the connection
3-6. Installing bolts
- number of bolts supplied in the connection
- certificate number for bolts
- method of processing contact surfaces
- calculated torque or angle of rotation of the nut

7-12. Control results
- treatment of contact surfaces
- number of bolts checked
- results of checking the tightening torque or angle of rotation of the nut
- stamp number, foreman’s signature
- signature of the person responsible for installing the bolts
- signature of the customer representative

In the document "MDS 12-22.2005. Recommendations for use in construction industry requirements of regulatory legal and other regulations containing state regulatory requirements for labor protection" states:
1.5. Data on construction and installation work should be entered daily into

INDUSTRY STANDARD

BUILDING STEEL STRUCTURES. INSTALLATION

CONNECTIONS WITH HIGH STRENGTH BOLTS

Typical technological process

OST 36-72-82

By order of the Ministry of Installation and Special Construction Works of the USSR dated December 7, 1982, the implementation period was set from July 1, 1983.

APPROVED AND ENTERED INTO EFFECT BY ORDER OF THE Ministry of Installation and Special Construction Works of the USSR dated December 7, 1982, No. 267

Performers: VNIPI Promstalkonstruktsiya

K.I. Lukyanov, Ph.D., A.F. Knyazhev, Ph.D., G.N. Pavlova

Co-executors: Central Research Institute Projectstalconstruction

B.G. Pavlov, Ph.D., V.V. Volkov, Ph.D., V.M. Babushkin

B.M. Weinblat, Ph.D.

Introduced for the first time

This standard applies to a typical technological process for making shear-resistant installation connections on high-strength bolts in structural steel structures.

The standard establishes technical requirements for the materials used, structural elements to be connected, tools, as well as the sequence of operations of the technological process, quality control, and basic safety precautions.

1. GENERAL PROVISIONS

1.1. High-strength bolts, nuts and washers should be used in accordance with the instructions of the working (DM) or detailing (DM) drawings of the steel structures of the object being installed.

1.2. Work execution plans (WPP) must contain work execution diagrams or technological maps, which provide for the execution of connections with high-strength bolts in the specific conditions of the facility being installed.

1.3. Preparation, assembly and acceptance of connections with high-strength bolts should be carried out under the supervision of a person (master, foreman) appointed by the order of the installation organization responsible for performing this type of connection at the site.

1.4. Installers who are at least 18 years old and have undergone special theoretical and practical training, confirmed by a personal certificate for the right to perform these works, issued by the installation organization, are allowed to make connections with high-strength bolts.

2. TECHNICAL REQUIREMENTS

2.1.1. High-strength bolts, nuts, washers must be supplied to the site being installed in batches, equipped with certificates in accordance with the requirements of GOST 22353-77, GOST 22354-77, GOST 22355-77, GOST 22356-77.

2.1.2. For sandblasting (shot blasting) treatment of contact surfaces of connected structural elements, quartz sand should be used in accordance with GOST 8736-77 or shot made of cast iron or steel in accordance with GOST 11964-81 E.

2.1.3. To form an adhesive friction coating on the contact surfaces of the linings, glue based on epoxy-dian resin ED-20 in accordance with GOST 10587-76 and carborundum powder of grades KZ and KCH, fractions No. 8, 10, 12 in accordance with GOST 3647-80 should be used.

2.1.4. For gas-flame treatment of surfaces, acetylene should be used in accordance with GOST 5457-75 and oxygen in accordance with GOST 6331-78. Acetylene and oxygen must be supplied to the work site in steel cylinders in accordance with GOST 15860-70.

2.2.1. The possibility of free supply of high-strength bolts and screwing of nuts using impact wrenches and torque wrenches should be ensured constructive solution connections.

2.2.2. Installation of connections is not allowed if there are burrs on structural elements around and inside the holes, as well as along the edges of the elements.

The contact surfaces of the elements are not subject to priming or painting. The distance between the axis of the bolts of the last row and the primed surface should not be less than 70mm.

2.2.3. It is not allowed to use elements in connections that have dimensional deviations that do not comply with the requirements of SNiP III-18-75 “Rules for production and acceptance of work. Metal structures.” The difference between the planes of elements connected by overlays should not exceed 0.5 mm inclusive.

2.2.4. In connections made of rolled sections with non-parallel surfaces of shelves, leveling spacers must be used.

2.2.5. The nominal diameters and blackness of holes (mismatch of holes in individual parts of the assembled package) must not exceed the requirements specified in chapter SNiP III-18-75 “Rules for production and acceptance of work. Metal structures”.

2.2.6. Control and calibration torque wrenches must be numbered, calibrated and provided with calibration graphs or tables. Pneumatic and electric impact wrenches must meet the passport requirements.

3.1.1. Preparatory operations include: re-preservation and cleaning of high-strength bolts; preparation of structural elements; control and calibration check of tools.

3.1.2. High-strength bolts, nuts, washers must be cleaned of factory preservation, dirt, rust and covered with a thin layer of lubricant. Re-preservation and cleaning are carried out using the following technology.

3.1.3. Place high-strength bolts, nuts and washers weighing no more than 30 kg in lattice containers.

3.1.4. Immerse the lattice container filled with hardware into a tank of boiling water for 8 - 10 minutes (see drawing).

3.1.5. After boiling, rinse hot hardware in a mixture consisting of 85% unleaded gasoline in accordance with GOST 2084-77 and 15% machine oil (type autol) in accordance with GOST 20799-75 by immersing 2 - 3 times, followed by drying.

3.1.6. Place the processed bolts, nuts and washers separately in closed boxes with handles with a capacity of no more than 20 kg for transferring them to the workplace.

3.1.7. On the portable container, indicate the standard sizes, number of bolts, nuts and washers, processing date, certificate and batch numbers.

3.1.8. Cleaned bolts, nuts and washers should be stored in closed boxes for no more than 10 days, after which it is necessary to re-process in accordance with paragraphs. 3.1.4 and 3.1.5.

3.1.9. Burrs found around and inside holes, as well as along the edges of elements, must be completely removed. Removal of burrs around holes and along the edges of elements should be done using pneumatic or electric grinding machines without forming a recess that disrupts the contact of the contacting surfaces, and if there are burrs inside the hole, with a drill whose diameter is equal to the diameter of the bolt.

3.1.10. If the difference between the planes of the connected elements is more than 0.5 to 3.0 mm inclusive, it is necessary to make a bevel on the protruding element using a pneumatic or electric machine at a distance of up to 30.0 mm from the edge of the element. If the difference between planes is more than 3.0 mm, leveling spacers should be used.

3.1.11. Calibration (checking calibration) of control and calibration torque wrenches should be done once per shift before starting work on special stands or devices in accordance with recommended Appendix 1. Calibration of impact wrenches is carried out in accordance with recommended Appendix 2.

1 - heating element; 2 - lattice container for bolts; 3 - water tank;

4 - drain plug

3.2.1. The main technological operations include:

Treatment of contact surfaces;

Assembly of connections;

Installation of high-strength bolts;

Tension and control of bolt tension.

3.2.2. The method of processing contact surfaces is selected in accordance with the friction coefficient indicated in the KM or KMD drawings, and chapter SNiP II-23-81 " Steel structures. Design standards".

Installed following methods processing of contact surfaces performed at the installation site: sandblasting (shot blasting); gas-flame; metal brushes; adhesive friction.

3.2.3. Sandblasting (shot blasting) of the contact surfaces of the joined elements should be carried out using sandblasting or shot blasting machines in accordance with GOST 11046-69 (ST SEV 3110-81).

When sandblasting (shot blasting) processing of contact surfaces, mill scale and rust must be completely removed until a uniform light gray surface is obtained.

3.2.4. Gas-flame treatment of contact surfaces must be carried out with wide-cut gas-flame burners GAO-60 or GAO-2-72 according to GOST 17357-71.

Gas-flame processing is allowed for metal thickness of at least 5.0 mm.

The burner movement speed is 1 m/min for metal thicknesses of more than 10 mm and 1.5-2 m/min for metal thicknesses up to 10 mm inclusive.

Combustion products and scale should be swept away with soft wire brushes and then with hair brushes.

The surface after flame treatment must be free from dirt, paint, oil stains and easily peelable scale. Complete removal of mill scale is not necessary.

The equipment of the gas-flame processing post and a brief technical characteristics of the equipment are given in the recommended appendix3.

3.2.5. Treatment of contact surfaces with metal brushes should be carried out using pneumatic or electric cleaning machines, the brands of which are indicated in the recommended Appendix 4.

It is not allowed to bring the contact surfaces to be cleaned to a metallic shine.

3.2.6. The adhesive friction coating on the contact surfaces of the linings is usually applied at manufacturing plants of metal structures.

The technological process for producing adhesive friction coating includes:

Treatment of contact surfaces of linings in sandblasting (shot blasting) machines in accordance with GOST 11046-69 (ST SEV 3110-81);

Application of epoxy-polyamide glue to the treated contact surfaces of the pads;

Applying carborundum powder over uncured glue.

The safety of the adhesive friction coating must be ensured by packaging the linings for the entire period of their loading, transportation, unloading and storage at the construction site.

The shelf life of linings with adhesive friction coating is unlimited.

The composition of the adhesive friction coating is given in recommended Appendix 5.

Before assembly, the contact surfaces of the main connected elements must be treated with metal brushes in accordance with clause 3.2.5.

3.2.7. Metallization treatment of the contact surfaces of connected structural elements (galvanizing, aluminizing), as a rule, is carried out at manufacturing plants of metal structures.

3.2.8. Treated surfaces must be protected from dirt, oil, and ice formation. The shelf life of structures treated by sandblasting (shot blasting), gas flame methods or metal brushes before assembly should not exceed three days, after which the surfaces should be re-treated in accordance with paragraphs. 3.2.3 -3.2.5.

Surfaces treated by sandblasting (shot blasting) can be cleaned using a gas flame method when re-processed.

3.2.9. Contact surfaces without treatment must be cleaned of dirt and loose scale with metal brushes; from oil - unleaded gasoline, from ice - chipping.

3.2.10. Assembling connections with high-strength bolts includes the following operations:

Aligning the holes and fixing the connection elements in the design position using assembly plugs, the number of which should be 10% of the number of holes, but not less than 2 pcs.;

Installation of high-strength bolts in holes free from assembly plugs;

Tight seal of the package;

Tension of installed high-strength bolts to the force specified in the KM and KMD drawings;

Removing the assembly plugs, inserting high-strength bolts into the vacated holes and tensioning them to the design force;

Primer of the connection.

3.2.11. Under the heads and nuts of high-strength bolts it is necessary to place only one heat-treated washer in accordance with GOST 22355-77.

The protruding end of the bolt must have at least one thread above the nut.

3.2.12. If the holes do not coincide, their drilling in elements with machined surfaces should be done without using coolants.

3.2.13. Pre- and final tensioning of high-strength bolts must be carried out from the middle of the connection to the edges or from the most rigid part of the connection towards its free edges.

3.2.14. The method of tensioning high-strength bolts must be specified in the KM or KMD drawings.

3.2.15. In the absence of instructions, the tensioning method is selected by the installation organization according to the recommended Appendix 2.

4.1. After completing the assembly connection on high-strength bolts, the foreman is required to put a personal stamp (a set of numbers) on the connection and present the finished connection to the person in charge.

4.2. After inspection and verification, the responsible person (master, foreman) must present the finished connection to the customer’s representative. If the customer has no comments, the connection should be considered accepted and the responsible person enters all necessary information about it in the journal for making installation connections on high-strength bolts (see mandatory Appendix 6).

4.3. After acceptance, the finished connection should be primed and painted. Soil grades and paint and varnish material accepted according to the “List of polymer materials and products approved for use in construction”, approved by the USSR Ministry of Health, the same as for priming and painting metal structures. The grades of primer and paint must be indicated in the KM and KMD drawings.

4.4. The responsible person checks the quality of connections made with high-strength bolts through operational control. Subject to control:

Quality of processing of contact surfaces;

Compliance of the installed bolts, nuts and washers with the requirements of GOST 22353-77, GOST 22354-77, GOST 22355-77, GOST 22356-77, as well as other requirements specified in the KM and KMD drawings;

The presence of washers under the bolt heads and nuts;

The presence of manufacturer's marks on the bolt heads;

The length of the protruding part of the bolt thread above the nut;

The presence of the mark of the foreman in charge of the assembly of the unit.

4.5. The quality of processing of contact surfaces is checked by visual inspection immediately before assembling the connections. The control results must be recorded in a journal (see mandatory Appendix 6).

4.6. The compliance of the bolt tension with the design one is checked depending on the tension method. The deviation of the actual tightening torque from the moment specified in the KM and KMD drawings should not exceed 20%.

The angle of rotation of the nut is determined by the position of the marks on the protruding end of the bolt and nut. With two-stage bolt tensioning, the deviation of the rotation angle should be within ±15°, with single-stage tensioning - ±30°.

Bolts whose mark positions are outside the specified limits must be loosened and tightened again.

4.7. The tension of high-strength bolts is checked with a torque wrench or a calibrated control wrench.

The tension of the bolts should be controlled by spot checking: with the number of bolts in a connection up to 5 inclusive, 100% of the bolts are controlled, with the number of bolts from 6 to 20 - at least 5, with a larger number - at least 25% of the bolts in the connection.

4.8. If the inspection reveals at least one bolt whose tension does not meet the requirements of clause 4.6 of this standard, then 100% of the bolts in the connection are subject to inspection. In this case, the tension of the bolts must be brought to the required value.

4.9. The density of the compressed bag is controlled with 0.3 mm probes. The probe should not pass between the planes along the contour of the elements being connected.

4.10. The documentation presented upon acceptance of the finished object, except for the documentation provided for in Chapter SNiP III-18-75 “Rules for production and acceptance of work. Metal structures”, must contain:

Log of installation connections using high-strength bolts;

Certificates for bolts, nuts and washers;

Certificates for materials for the formation of adhesive friction coatings.

5. SAFETY REQUIREMENTS

5.1. The organization of the site for the enlarged assembly of structures with assembly connections on high-strength bolts should ensure the safety of workers at all stages of the work.

Work on the installation of structures on high-strength bolts must be carried out in accordance with the PPR, which contains the following safety solutions:

Organization of workplaces and passages;

Sequence of technological operations;

Methods and devices for safe work installers;

Location and coverage areas of installation mechanisms;

Storage methods building materials and structural elements.

5.2. The placement of work equipment and the organization of workplaces must ensure the safety of evacuation of workers during emergency situations taking into account current building codes.

5.3. All work at height to make installation connections using high-strength bolts should be carried out from a scaffold that provides free access to the connection with the tool.

Scaffolding means and other devices that ensure the safety of work must comply with the requirements of chapter SNiPIII-4-80 “Rules for the production and acceptance of work. Safety in construction”, GOST 12.2.012-75, GOST 24259-80 and GOST 24258-80.

5.4. Electrical safety on installation site must be provided in accordance with the requirements of GOST 12.1.013-78.

5.5. When processing contact surfaces with sandblasting (shot blasting) devices, the “Rules for the design and safety of operation of pressure vessels” approved by the USSR State Mining and Technical Supervision Authority should be followed.

5.6. The sandblasting (shot blasting) work area should be fenced and appropriate warning signs and notices should be posted near it.

5.7. Materials for sandblasting (shot blasting) surfaces (sand, shot, metal sand) should be stored in containers with a tightly closed lid.

5.8. The operator of the sandblasting (shot blasting) machine and the auxiliary worker are equipped with spacesuits or helmets with a forced supply of clean air.

5.9. The air supplied to the spacesuit must first be passed through a filter to remove dust, water and oil.

5.10. An audio or light alarm must be provided between the operator's and auxiliary worker's workstations located near the sandblasting (shot blasting) machine.

5.11. When treating contact surfaces with metal brushes (manual and mechanical), workers must be provided with safety glasses in accordance with GOST 12.4.003-80 or masks, mittens and respirators.

5.12. When processing contact surfaces using the gas-flame method, it is necessary to comply with the requirements of chapter SNiP III-4-80 “Rules for production and acceptance of work. Safety in construction", as well as sanitary rules when welding and cutting metals approved by the USSR Ministry of Health.

5.13. Places where gas-flame works are carried out must be cleared of combustible materials within a radius of at least 5 m, and from explosive materials and installations (including gas cylinders and gas generators) - within a radius of 10 m.

5.14. It is not allowed to carry out work on gas-flame treatment of the surfaces of structural elements in rainy weather outside the premises without installing a canopy.

5.15. When performing gas-flame treatment of contact surfaces, workers must be provided with closed-type safety glasses with filter glasses of grades G-1 or G-2.

Auxiliary workers must be provided with safety glasses with filter glasses of grades B-1 or B-2.

5.16. The application of an adhesive friction layer to the surface of the linings, as a rule, should be carried out at manufacturing plants. In this case, the safety requirements in accordance with GOST 12.3.008-75, GOST 12.3.016-79 and GOST 10587-76 must be observed, as well as safety rules when working with synthetic adhesives.

5.17. The preparation of glue and the application of adhesive friction coatings must be carried out in separate room, equipped with exchange and local ventilation.

5.18. Persons working with epoxy-diane resins must be provided with protective clothing and gloves.

To protect the skin from the effects of epoxy-diane resins, protective pastes and ointments based on lanolin, petroleum jelly or castor oil should be used.

5.19. The room for applying adhesive friction coatings must be provided with fire extinguishing means - carbon dioxide and foam fire extinguishers.

5.20. Removal of bolts, nuts and washers should be carried out in an open area with a canopy.

5.21. When boiling hardware in water, the bath must be grounded. Workers re-preserving hardware should not have direct contact with the boiling and lubricating baths. The loading process must be mechanized.

5.22. When performing assembly operations, the alignment of holes and checking their coincidence in the mounted structural elements must be carried out using special tool- conical mandrels, assembly plugs, etc. It is not allowed to check the alignment of the holes with your fingers.

5.23. Operation of mechanisms, small-scale mechanization, including Maintenance, must be carried out in accordance with the requirements of chapter SNiP III-4-80 “Rules for production and acceptance of work. Safety precautions in construction" and instructions from manufacturers.

5.24. When using manual machines, you must comply with the safety rules provided for by GOST 12.1.012-79 (ST SEV 1932-79, ST SEV 2602-80) and GOST 12.2.010-75, as well as the instructions of the manufacturers.

5.25. The labor regime when working with hand-held electric and pneumatic machines and impact wrenches should be established in accordance with the “Recommendations for the development of Regulations on the labor regime of workers in vibration-hazardous professions,” approved in December 1971 by the All-Russian Central Council of Trade Unions, the USSR Ministry of Health, State Committee Council of Ministers of the USSR for Labor and wages, as well as manufacturer’s instructions for performing work with specific types of machines.

5.26. Priming and painting of finished connections on high-strength bolts should be done at the metal structures assembly site.

5.27. Only workers who know the rules for safe handling of the equipment and materials used and are familiar with fire safety rules are allowed to work on priming connections.

5.28. Workers engaged in priming and painting joints must undergo a medical examination in accordance with the requirements of Order No. 400 of the USSR Ministry of Health dated May 30, 1969 “On conducting preliminary upon employment and periodic medical examinations of workers.”

5.29. Temporary production and auxiliary premises must be provided with ventilation and lighting, and also equipped with fire extinguishing means in accordance with the requirements of GOST 12.4.009-75.

ANNEX 1

An example of calibration of a torque wrench type KTR-3 1

_________________

1 KTR-3 keys are manufactured by installation organizations according to the drawings of the Central Research Institute ProektStalkonstruktsiya.

Torque wrenches are calibrated on special calibration stands or by hanging a load of a given size to its handle. A torque wrench is hung on a hexagonal mandrel or a tightened high-strength bolt so that its handle is in a horizontal position (see drawing).

At a fixed point at the end of the key, a load weighing

Where M h - calculated torque;

Δ M z- moment equal to the product of the mass of the key and the distance from its center of gravity to the axis of the mandrel or bolt;

l- the distance from the center of gravity of the load to the axis of the mandrel or bolt.

When the load is suspended, the countdown is carried out using a recording device, for example, a dial indicator ICH 10 mm according to GOST 577-68. The measurement is carried out 2-3 times until a stable result is obtained. The calibration results are recorded in the key calibration log (see mandatory appendix 7).

1 - welded hexagon or tightened high-strength bolt;

2 - rigid support; 3 - indicator; 4 - calibrated wrench; 5-tared load

APPENDIX 2

M h , necessary for tensioning high-strength bolts, is determined by the formula:

M z= kPd,

k- the average value of the torque coefficient for each batch of bolts according to the certificate or established using control devices at the installation site;

R- bolt tension force specified in the KM and KMD drawings;

d- nominal diameter of the bolt.

1.2. To pre-tighten the nuts, pneumatic or electric impact wrenches specified in recommended Appendix 4 and torque wrenches should be used.

1.3. When tensioning the bolt, the head or nut should be held from turning with a mounting wrench. If turning does not stop as the bolt is tensioned, then the bolt and nut must be replaced.

1.4. The torque should be recorded as the wrench moves in the direction that increases tension.

Tightening should be done smoothly, without jerking.

1.5. Torque wrenches must be numbered and calibrated. They should be calibrated at the beginning of the shift.

2.1. High-strength bolts must be installed in holes free of assembly plugs and tightened with a wrench adjusted to a tightening torque of 800 N ⋅ m. Each bolt must be tightened until the nut stops rotating. After removing the assembly plugs and replacing them with bolts, the latter must be tightened to a tightening torque of 800 N⋅ m.

2.2. To control the angle of rotation of the nuts, it is necessary to apply marks on them and the protruding ends of the bolts using a combined center punch (see drawing) or paint.

Combined center punch

1 - center punch; 2 - nut; 3 - high-strength bolt; 4 - package

2.3. The final tightening is carried out with a wrench adjusted to a torque of 1600 N ⋅ m, in this case the nut should turn at the angle indicated in the table.

Number of gaps in the package	Package thickness, mm	Rotation angle, degrees

3.1. Calibration of impact wrenches should be carried out using a special calibration package consisting of three bodies with a number of holes of at least 20.

High-strength bolts are inserted into the holes of the calibration package and tightened with a wrench until the nut stops rotating. A group of bolts (calibration bolts) in an amount of at least 5 pcs. don't delay.

The calibration bolts must be manually tightened with a mounting wrench with a handle length of 0.3 m until failure (initial position).

3.2. The wrench is calibrated using the prepared calibration bolts.

3.3. The compressed air pressure is set so that when the nut is turned through an angle of 180±30° from its original position, the wrench fails.

Air pressure must be checked periodically.

Air pressure should be monitored using a GOST 2405-72 pressure gauge installed at the point where the impact wrench hose is connected to the line.

3.4. When calibrating the impact wrench (to monitor the angle of rotation of the nut), marks must be placed on its replaceable head.

3.5. The impact wrench is considered calibrated if the angle of rotation of the nut during the process of tensioning all bolts at the moment of failure of the impact wrench is 180 ± 30°.

3.6. The results of the impact wrench calibration must be entered into the impact wrench calibration log (see mandatory appendix 8).

3.7. If the compressed air pressure changes after eliminating a malfunction in the impact wrench, it is necessary to carry out a control calibration.

APPENDIX 3

Name of equipment
Burner GAO-60, GAO-2-72 GOST 17357-71 (1 piece)	Wide-cut, multi-flame, working width 100 mm.
Oxygen cylinders (3 pcs.)
Acetylene cylinders (2 pcs.)
	Maximum overpressure at inlet - 1962 ⋅ 10 4 Pa; working excess pressure - 78.48⋅ 10 4 Pa; throughput at maximum pressure - 23m 3/h
	Maximum excess pressure at the inlet - 245.25 ⋅ 10 4 Pa; working excess pressure - from 0.981⋅ 10 4 Pa to 14.715 ⋅ 10 4 Pa; bandwidth - 5 m 3/h
Rubber-fabric hoses for oxygen supply (GOST 9356-75) with an internal diameter of 9.0, external diameter - 18 mm	Operating overpressure 147.15 ⋅ 10 4 Pa

APPENDIX 4

Equipment, mechanisms and tools used to connect elements and tension high-strength bolts

The vibration levels of electric and pneumatic hand-held grinding machines and impact wrenches (Table 1) do not exceed those established in GOST 16519-79 (ST SEV 716-77) and GOST 12.1.012-78.

Table 1

Name	Brand, standard	Purpose
Electric Impact Hand Wrenches	IE-3115A IE-3119U2 IE-3112A
Pneumatic Impact Hand Wrenches	GOST 15150-69 IP-3106A IP-3205A GOST 10210-74
Wrenches
Electric hand grinders	IE-2004UZ	For stripping work
Electric hand-held angle grinders	IE-2102A
Pneumatic manual stripping machines		For cleaning metal surfaces from rust and scale
Gas burners	GAO-2-72 GOST 17357-71	For processing contact surfaces

The noise levels of electric and pneumatic hand-held grinding machines and impact wrenches do not exceed those established in GOST 12.1.003-76. The vibration parameters and noise characteristics of electric and pneumatic hand-held machines used in processing the contact surfaces of connected elements and for tensioning high-strength bolts are given in Table 1, respectively. 2 and 3.

table 2

Vibration parameters

Brand


IE-3115A
IE-3119U2
IE-3112A
IE-3120A
IE-2009
IE-2004AUZ
IE-2102A

Table 3

Noise characteristics

Brand
cars
	Sound power level, dB
IE-3115A
IE-3119U2
IE-3112A
IE-3120A
IP-3106A
IP-3205A

APPENDIX 5

Name		Cooking method
Epoxy-polyamide adhesive
	Hardener I-5M (I-6M) according to VTU OP-2382-65-60 (50 parts by weight) Accelerator UP-606-2 according to MRTU 6-09-6101-69 (2 - 3 parts by weight)
Abrasive material
Solvent	Acetone according to GOST 2768-79

APPENDIX 6

mandatory

Headquarters

_______________________________________

Object name

_______________________________________

Manufacturer of structures, order no.

Monitoring log of installation connections on high-strength bolts

date	KMD drawing number and name of the node, joint in the connection	Number of supplied bolts in connection	Bolt certificate numbers	Method of processing contact surfaces	Standard tightening torque or angle of rotation of the nut	Control results
date		Number of supplied bolts in connection	Bolt certificate numbers	Method of processing contact surfaces	Standard tightening torque or angle of rotation of the nut	Treatment of contact surfaces	Number of bolts checked	Torque test results	Brand number, foreman’s signature	Brand number, signature of the person in charge	Signature of the customer representative

Ch. installation engineer ________________________________________________

Print location

assembly room

organizations

APPENDIX 7

mandatory

_______________________________________

Headquarters

_______________________________________

Object name

Magazine 1 control calibration of keys for tension and control of tension of high-strength bolts

______________

1 The log is drawn up for all keys used when making installation connections at each facility.

During the control calibration, the log must be kept by the responsible person performing the work.

The responsible person fills out the log after each control calibration of the keys. The log is kept until the object is handed over.

date	Change	Key		Torque	Indications on the key device	Signature of the responsible person who carried out the calibration
		type	number

Ch. installation engineer _

Print location

installation organization

APPENDIX 8

mandatory

Headquarters

________________________________________

Installation organization (trust, management)

________________________________________

Object name

Magazine 1 calibration of impact wrenches for tensioning high-strength bolts with control of forces by the angle of rotation of the nut or by axial tension

________________

1 The log is issued for all impact wrenches used when making installation connections at each facility, designed to tension high-strength bolts by the angle of rotation of the nut or by axial tension.

When calibrating impact wrenches, the log must be kept by the responsible person performing the work.

The responsible person fills out the log after each control calibration of the impact wrenches.

The log is kept until the object is handed over.

date	Change	Excessive pressure of compressed air at the inlet of the impact wrench, Pa	A set of plates in a tightly sealed bag	Initial tension key	Angle of rotation of the nut with a wrench	Signature of the responsible person who performed the calibration

This magazine has __________________ pages laced and numbered

Print location

assembly room

organizations

Content

1. General Provisions

2. Technical requirements

3. Contents of the technological process

4. Acceptance rules and control methods

5. Safety requirements

Applications

1. Example of calibration of a torque wrench type KTR-3

2. Methods for tensioning high-strength bolts

3. Fire cleaning station equipment

4. Equipment, mechanisms and tools used for processing contact surfaces, connected elements and tensioning high-strength bolts

5. Composition of the friction coating

6. Monitoring log of installation connections on high-strength bolts

7. Log of control calibration of wrenches for tension and control of tension of high-strength bolts

8. Calibration journal for impact wrenches for tensioning high-strength bolts with control of forces by the angle of rotation of the nut or by axial tension

I APPROVED

Director___________________

___________ .___________________

1. GENERAL PROVISIONS

1.1. High-strength bolts, nuts and washers should be used in accordance with the instructions of the working (DM) or detailing (DM) drawings of the steel structures of the object being installed.

1.2. Work execution plans (WPP) must contain work execution diagrams or technological maps that provide for the execution of connections with high-strength bolts in the specific conditions of the facility being installed.

1.3. Preparation, assembly and acceptance of connections with high-strength bolts should be carried out under the supervision of a person (foreman, foreman) appointed by the order of the installation organization responsible for performing this type of connection at the site.

2. TECHNICAL REQUIREMENTS

2.1. Requirements for the materials used

2.1.1. High-strength bolts, nuts, washers must be supplied to the site being installed in batches provided with certificates in accordance with the requirements of GOST 22353-77, GOST 22354-77, GOST 22355-77, GOST 22356-77.

2.2. Requirements for connected structural elements and tools

2.2.1. The possibility of free supply of high-strength bolts and screwing of nuts using impact wrenches and torque wrenches should be ensured by the design of the connections.

2.2.2. Installation of connections is not allowed if there are burrs on structural elements around and inside the holes, as well as along the edges of the elements.

The contact surfaces of the elements are not subject to priming or painting. The distance between the axis of the bolts of the last row and the primed surface should not be less than 70 mm.

2.2.3. It is not allowed to use elements in connections that have dimensional deviations that do not meet the requirements of SNiP III-18-75 “Rules for production and acceptance of work. Metal constructions". The difference between the planes of elements connected by overlays should not exceed 0.5 mm inclusive.

2.2.4. In connections made of rolled sections with non-parallel surfaces of shelves, leveling spacers must be used.

2.2.6. Control and calibration torque wrenches must be numbered, calibrated and provided with calibration graphs or tables. Pneumatic and electric impact wrenches must meet the passport requirements.

3.1. Preparatory operations

3.1.1. Preparatory operations include: re-preservation and cleaning of high-strength bolts; preparation of structural elements; control and calibration check of the tool.

3.1.2. High-strength bolts, nuts, washers must be cleaned of factory preservation, dirt, rust and covered with a thin layer of lubricant. Depreservation and cleaning are carried out using the following technology.

3.1.3. Place high-strength bolts, nuts and washers weighing no more than 30 kg in lattice containers.

3.1.4. Immerse the lattice container filled with hardware into a tank of boiling water for 8 - 10 minutes (see drawing).

3.1.6. Place processed bolts, nuts and washers separately in closed boxes with handles with a capacity of no more than 20 kg for transferring them to the workplace.

3.1.7. On the portable container, indicate the standard sizes, number of bolts, nuts and washers, processing date, certificate and batch numbers.

3.1.8. Cleaned bolts, nuts and washers should be stored in closed boxes for no more than 10 days, after which it is necessary to re-process in accordance with paragraphs. 3.1.4 and 3.1.5.

3.1.10. If the difference between the planes of the joined elements is more than 0.5 to 3.0 mm inclusive, it is necessary to make a bevel on the protruding element using a pneumatic or electric stripping machine at a distance of up to 30.0 mm from the edge of the element. If the difference between planes is more than 3.0 mm, leveling spacers should be used.

Equipment for boiling high strength bolts, nuts and washers

1 - heating element; 2 - lattice container for bolts; 3 - water tank;

4 - drain plug

3.2. Basic technological operations

3.2.1. The main technological operations include:

Treatment of contact surfaces;

Assembly of connections;

Installation of high-strength bolts;

Tension and control of bolt tension.

3.2.2. The method of processing contact surfaces is selected in accordance with the friction coefficient specified in the KM or KMD drawings and chapter SNiP II-23-81 “Steel structures. Design standards".

The following methods for processing contact surfaces, carried out at the installation site, have been established: sandblasting (shot blasting); gas-flame; metal brushes; adhesive friction.

When sandblasting (shot blasting) processing of contact surfaces, mill scale and rust must be completely removed until a uniform light gray surface is obtained.

3.2.4. Gas-flame treatment of contact surfaces must be carried out with wide-cut gas-flame burners GAO-60 or GAO-2-72 in accordance with GOST 17357-71.

Gas-flame processing is allowed with a metal thickness of at least 5.0 mm.

The burner movement speed is 1 m/min for metal thicknesses of more than 10 mm and 1.5-2 m/min for metal thicknesses up to 10 mm inclusive.

Combustion products and scale should be swept away with soft wire brushes and then with hair brushes.

The surface after flame treatment must be free from dirt, paint, oil stains and easily peelable scale. Complete removal of mill scale is not necessary.

Equipment for gas-flame treatment post and brief technical specifications equipment are given in recommended Appendix 3.

3.2.5. Treatment of contact surfaces with metal brushes should be carried out using pneumatic or electric cleaning machines, the brands of which are indicated in the recommended Appendix 4.

It is not allowed to bring the contact surfaces to be cleaned to a metallic shine.

3.2.6. The adhesive friction coating on the contact surfaces of the linings is usually applied at manufacturing plants of metal structures.

The technological process for producing adhesive friction coating includes:

Treatment of contact surfaces of linings in sandblasting (shot blasting) machines in accordance with GOST 11046-69 (ST SEV 3110-81);

Application of epoxy-polyamide glue to the treated contact surfaces of the pads;

Applying carborundum powder over uncured glue.

The safety of the adhesive friction coating must be ensured by packaging the linings for the entire period of their loading, transportation, unloading and storage at the construction site.

The shelf life of linings with adhesive friction coating is unlimited.

The composition of the adhesive friction coating is given in recommended Appendix 5.

Before assembly, the contact surfaces of the main connected elements must be treated with metal brushes in accordance with clause 3.2.5.

3.2.7. Metallization treatment of the contact surfaces of connected structural elements (galvanizing, aluminizing), as a rule, is carried out at manufacturing plants of metal structures.

Surfaces treated by sandblasting (shot blasting) can be cleaned using a gas flame method when re-processed.

3.2.9. Contact surfaces without treatment must be cleaned of dirt and loose scale with metal brushes; from oil - unleaded gasoline, from ice - by chipping.

3.2.10. Assembling connections with high-strength bolts includes the following operations:

Aligning the holes and fixing the connection elements in the design position using assembly plugs, the number of which should be 10% of the number of holes, but not less than 2 pcs.;

Installation of high-strength bolts in holes free of assembly plugs;

Tight seal of the package;

Tension of installed high-strength bolts to the force specified in the KM and KMD drawings;

Removing the assembly plugs, inserting high-strength bolts into the vacated holes and tensioning them to the design force;

Primer of the connection.

3.2.11. Under the heads and nuts of high-strength bolts it is necessary to place only one heat-treated washer in accordance with GOST 22355-77.

The protruding end of the bolt must have at least one thread above the nut.

3.2.12. If the holes do not coincide, their drilling in elements with machined surfaces should be done without using coolants.

3.2.13. Pre- and final tensioning of high-strength bolts must be carried out from the middle of the connection to the edges or from the most rigid part of the connection towards its free edges.

3.2.14. The method of tensioning high-strength bolts must be specified in the KM or KMD drawings.

3.2.15. In the absence of instructions, the tensioning method is selected by the installation organization according to the recommended Appendix 2.

4. ACCEPTANCE RULES AND CONTROL METHODS

4.2. After inspection and verification, the responsible person (master, foreman) must present the finished connection to the customer’s representative. If the customer has no comments, the connection should be considered accepted and the person in charge enters all the necessary information about it into the journal for performing installation connections on high-strength bolts (see mandatory Appendix 6).

4.3. After acceptance, the finished connection should be primed and painted. The grades of primer and paint and varnish material are accepted according to the “List of polymeric materials and products approved for use in construction”, approved by the USSR Ministry of Health, the same as for priming and painting metal structures. The grades of primer and paint must be indicated in the KM and KMD drawings.

4.4. The responsible person checks the quality of connections made with high-strength bolts through operational control. Subject to control:

Quality of processing of contact surfaces;

The presence of washers under the bolt heads and nuts;

The presence of manufacturer's marks on the bolt heads;

The length of the protruding part of the bolt thread above the nut;

The presence of the mark of the foreman in charge of the assembly of the unit.

4.6. The compliance of the bolt tension with the design value is checked depending on the tension method. The deviation of the actual tightening torque from the torque specified in the KM and KMD drawings should not exceed 20%.

Bolts whose mark positions are outside the specified limits must be loosened and tightened again.

4.7. The tension of high-strength bolts is checked with a torque wrench or a calibrated control wrench.

4.9. The density of the compressed bag is controlled with 0.3 mm probes. The probe should not pass between the planes along the contour of the elements being connected.

4.10. Documentation presented upon acceptance of the finished object, except for the documentation provided for by Chapter SNiP III-18-75 “Rules for production and acceptance of work. Metal structures" must contain:

Log of installation connections using high-strength bolts;

Certificates for bolts, nuts and washers;

Certificates for materials for the formation of adhesive friction coatings.

5. SAFETY REQUIREMENTS

5.1. The organization of the site for the enlarged assembly of structures with assembly connections on high-strength bolts should ensure the safety of workers at all stages of the work.

Work on the installation of structures on high-strength bolts must be carried out in accordance with the PPR, which contains the following safety solutions:

Organization of workplaces and passages;

Sequence of technological operations;

Methods and devices for safe work of installers;

Location and coverage areas of installation mechanisms;

Methods for storing building materials and structural elements.

5.2. The placement of work equipment and the organization of workplaces must ensure the safety of evacuation of workers in emergency situations, taking into account current building codes.

5.3. All work at height to make installation connections using high-strength bolts should be carried out from a scaffold that provides free access to the connection with the tool.

Scaffolding means and other devices that ensure the safety of work must comply with the requirements of Chapter SNiP III-4-80 “Rules for the production and acceptance of work. Safety in construction", GOST 12.2.012-75, GOST 24259-80 and GOST 24258-80.

5.4. Electrical safety at the installation site must be ensured in accordance with the requirements of GOST 12.1.013-78.

5.6. The sandblasting (shot blasting) work area should be fenced and appropriate warning signs and notices should be posted near it.

5.7. Materials for sandblasting (shot blasting) surfaces (sand, shot, metal sand) should be stored in containers with a tightly closed lid.

5.8. The operator of the sandblasting (shot blasting) machine and the auxiliary worker are equipped with spacesuits or helmets with a forced supply of clean air.

5.9. The air supplied to the spacesuit must first be passed through a filter to remove dust, water and oil.

5.10. Between the workplaces of the operator and the auxiliary worker located near the sandblasting (shot blasting) machine, a sound or light alarm must be provided.

5.11. When treating contact surfaces with metal brushes (manual and mechanical), workers must be provided with safety glasses in accordance with GOST 12.4.003-80 or masks, mittens and respirators.

5.12. When processing contact surfaces using the gas-flame method, it is necessary to comply with the requirements of chapter SNiP III-4-80 “Rules for production and acceptance of work. Safety precautions in construction”, as well as sanitary rules for welding and cutting metals, approved by the USSR Ministry of Health.

5.14. It is not allowed to carry out work on gas-flame treatment of the surfaces of structural elements in rainy weather outside the premises without installing a canopy.

5.15. When performing gas-flame treatment of contact surfaces, workers must be provided with safety glasses closed type with filter glasses of grades G-1 or G-2.

Auxiliary workers must be provided with safety glasses with filter glasses of grades B-1 or B-2.

5.17. The preparation of glue and the application of adhesive friction coatings must be carried out in a separate room equipped with exchange and local ventilation.

5.18. Persons working with epoxy-diane resins must be provided with protective clothing and gloves.

To protect the skin from the effects of epoxy-diane resins, protective pastes and ointments based on lanolin, petroleum jelly or castor oil should be used.

5.19. The room for applying adhesive friction coatings must be provided with fire extinguishing means - carbon dioxide and foam fire extinguishers.

5.20. Removal of bolts, nuts and washers should be carried out in an open area with a canopy.

5.21. When boiling hardware in water, the bath must be grounded. Workers re-preserving hardware should not have direct contact with boiling and lubricating baths. The loading process must be mechanized.

5.22. When performing assembly operations, alignment of holes and checking their coincidence in mounted structural elements must be done using a special tool - conical mandrels, assembly plugs, etc. It is not allowed to check the coincidence of holes with your fingers.

5.23. The operation of mechanisms and small-scale mechanization equipment, including maintenance, must be carried out in accordance with the requirements of chapter SNiP III-4-80 “Rules for production and acceptance of work. Safety precautions in construction" and instructions from manufacturers.

5.25. The labor regime when working with manual electric and pneumatic machines and impact wrenches should be established in accordance with the “Recommendations for the development of Regulations on the labor regime of workers in vibration-hazardous professions,” approved in December 1971 by the All-Russian Central Council of Trade Unions, the USSR Ministry of Health, and the State Committee of the USSR Council of Ministers on Labor Issues and wages, as well as instructions from manufacturers for performing work with specific types of machines.

5.26. Priming and painting of finished connections on high-strength bolts should be done at the metal structures assembly site.

5.27. Only workers who know the rules for safe handling of the equipment and materials used and are familiar with fire safety rules are allowed to work on priming connections.

An example of calibration of a torque wrench type KTR-3 1

_________________

1 KTR-3 keys are manufactured by installation organizations according to the drawings of the Central Research Institute ProektStalkonstruktsiya.

At a fixed point at the end of the key, a load weighing

Where M z- calculated torque;

D M z- a moment equal to the product of the mass of the key and the distance from its center of gravity to the axis of the mandrel or bolt;

l- the distance from the center of gravity of the load to the axis of the mandrel or bolt.

Torque wrench calibration diagram

1 - welded hexagon or tightened high-strength bolt;

2 - rigid support; 3 - indicator; 4 - calibrated wrench; 5 - calibrated load

Tensioning Methods for High Strength Bolts

1. Tension of high-strength bolts by tightening torque

1.1. High-strength bolts should be tensioned to the design force by tightening the nuts with a torque wrench to the design torque value. Torque value M z required to tension high-strength bolts is determined by the formula:

M z = kPd,

k- the average value of the torque coefficient for each batch of bolts according to the certificate or established using control devices at the installation site;

R- bolt tension force specified in the KM and KMD drawings;

d- nominal diameter of the bolt.

1.2. To pre-tighten the nuts, pneumatic or electric impact wrenches specified in recommended Appendix 4 and torque wrenches should be used.

1.3. When tensioning the bolt, the head or nut should be held against turning with a mounting wrench. If turning does not stop as the bolt is tightened, the bolt and nut must be replaced.

1.4. The torque should be recorded as the key moves in the direction that increases tension.

Tightening should be done smoothly, without jerking.

1.5. Torque wrenches must be numbered and calibrated. They should be calibrated at the beginning of the shift.

2. Tension of high-strength bolts according to the angle of rotation of the nut

2.1. High-strength bolts must be installed in holes free of assembly plugs and tightened with a wrench adjusted to a tightening torque of 800 N × m. Each bolt must be tightened until the nut stops rotating. After removing the assembly plugs and replacing them with bolts, the latter must be tightened to a tightening torque of 800 N × m.

2.2. To control the angle of rotation of the nuts, it is necessary to apply marks on them and the protruding ends of the bolts using a combined center punch (see drawing) or paint.

Combined center punch

1 - center punch; 2 - nut; 3 - high-strength bolt; 4 - package

2.3. The final tightening is carried out with a wrench adjusted to a tightening torque of 1600 N × m, and the nut should turn to the angle indicated in the table.

3. Calibration of impact wrenches according to the angle of rotation of the nut

3.1. Calibration of impact wrenches should be carried out using a special calibration package consisting of three bodies with a number of holes of at least 20.

The calibration bolts must be manually tightened with a mounting wrench with a handle length of 0.3 m until failure (initial position).

3.2. The wrench is calibrated using the prepared calibration bolts.

3.3. The compressed air pressure is set so that when the nut is turned through an angle of 180±30° from its original position, the wrench fails.

Air pressure must be checked periodically.

Air pressure should be monitored using a GOST 2405-72 pressure gauge installed at the point where the impact wrench hose is connected to the line.

3.4. When calibrating the impact wrench (to monitor the angle of rotation of the nut), marks must be placed on its replaceable head.

3.5. The impact wrench is considered calibrated if the angle of rotation of the nut during the process of tensioning all bolts at the moment of failure of the impact wrench is 180 ± 30°.

3.6. The results of the impact wrench calibration must be entered into the impact wrench calibration log (see mandatory appendix 8).

3.7. If the compressed air pressure changes after eliminating a malfunction in the impact wrench, it is necessary to carry out a control calibration.

APPENDIX 3

Fire cleaning station equipment

Name of equipment	Brief technical characteristics
Burner GAO-60, GAO-2-72 GOST 17357-71 (1 pc.)	Wide-cut, multi-flame, working width 100 mm.
Oxygen cylinders (3 pcs.)
Acetylene cylinders (2 pcs.)
Cylinder oxygen reducer DKD15-65 or RKD-15-81	Maximum excess pressure at the inlet - 1962 × 10 4 Pa; working excess pressure - 78.48 × 10 4 Pa; throughput at maximum pressure - 23 m 3 / h
Acetylene balloon reducer RD-2AM, DAP-1-65	The maximum excess pressure at the inlet is 245.25 × 10 4 Pa; working excess pressure - from 0.981 × 10 4 Pa to 14.715 × 10 4 Pa; throughput - 5 m 3 / h
Rubber-fabric hoses for oxygen supply (GOST 9356-75) with an internal diameter of 9.0 and an external diameter of 18 mm	Operating overpressure 147.15 × 10 4 Pa

APPENDIX 4

Equipment, mechanisms and tools used for processing contact surfaces, connecting elements and tensioning high-strength bolts

The vibration levels of electric and pneumatic hand-held grinding machines and impact wrenches (Table 1) do not exceed those established in GOST 16519-79 (ST SEV 716-77) and GOST 12.1.012-78.

Table 1

Name	Brand, standard	Purpose
Electric Impact Hand Wrenches		For tightening high-strength bolts during installation and assembly work
Pneumatic Impact Hand Wrenches	GOST 15150-69 GOST 10210-74
Wrenches		For pre-assembly of connections
Electric hand grinders		For stripping work
Electric hand-held angle grinders
Pneumatic manual stripping machines		For the cleaning metal surfaces from rust and scale
Gas burners	GOST 17357-71	For processing contact surfaces

The noise levels of electric and pneumatic hand-held grinding machines and impact wrenches do not exceed those established in GOST 12.1.003-76. The vibration parameters and noise characteristics of electric and pneumatic manual machines used in processing the contact surfaces of connected elements and for tensioning high-strength bolts are given in Table 1, respectively. 2 and 3.

table 2

Vibration parameters



Logarithmic levels of vibration velocity values, dB

Table 3

Noise characteristics

	Geometric mean frequencies of octane bands, Hz

	Sound power level, dB

Composition of adhesive friction coating

Name		Cooking method
Epoxy-polyamide adhesive	Epoxy resin ED-20 according to GOST 10587-76 (100 parts by weight)	A hardener and an accelerator are added to the epoxy resin; the resulting mixture is thoroughly mixed
	Hardener I-5M (I-6M) according to VTU OP-2382-65-60 (50 parts by weight) Accelerator UP-606-2 according to MRTU 6-09-6101-69 (2 - 3 parts by weight)
Abrasive material	Carborundum powder grade KZ or KCh
Solvent	Acetone according to GOST 2768-79

Types of bolts. Bolts are usually used to connect metal, less often reinforced concrete structures. The following types of bolts are used to connect metal structures: normal, rough, high precision and high-strength with corresponding nuts and washers.

Rough precision bolts are stamped from round carbon steel with a diameter of no more than 20 mm. They are placed in holes with a gap of 2-3 mm. Such bolts have increased deformability and do not perform well in shear in multi-bolt connections; therefore, their use in connections with alternating forces is not allowed. Rough precision bolts are used, as a rule, in units where one element rests on another, with transmission through a support table, as well as in connections where they do not work or work only in tension.

High-precision bolts are processed by turning lathe with a tolerance of + 0.1 mm. Such bolts are made with a diameter of 10-48 mm and a length of up to 300 mm.

High-strength bolts (otherwise known as friction bolts) are designed to transfer forces acting on a connection through friction. Such bolts are made from high-strength steels and are heat-treated in finished form. The bolts are placed in holes 2-3 mm larger than the diameter of the bolt, but the nuts are tightened with a calibration wrench. Such connections are simple, but quite reliable and are used in critical structures.

The diameters for high-precision bolts are assigned equal to the nominal diameters of the bolts. The holes for such bolts have only positive deviations, which ensures installation of the bolt without difficulty. Unlike normal and rough precision bolts working part The high-precision bolt shaft is not threaded, which ensures fairly complete filling of the hole and good shear performance. To distinguish high-strength bolts from others, raised markings are applied to their heads.

Assembling connections. The assembly of bolted joints includes the following operations: preparing the joining surfaces, aligning the holes for the bolts, preliminary tightening the joint parts to be joined, drilling the holes (if necessary) to the design size, installing the bolts and final assembly.

Preparation of mating surfaces involves cleaning the mating elements from rust, dirt, oil and dust. In addition, they straighten irregularities, dents, and bends, and also remove burrs on the edges of parts and holes with a file or chisel. These operations are performed especially carefully when connecting parts with high-strength bolts, where the tight junction of all joined elements is one of the main conditions for the reliable operation of a bolted connection.

The surfaces to be joined are cleaned with dry quartz or metal sand using a sandblasting machine; roasting gas burners, steel brushes, chemical treatment.

Sandblasting is more effective than other methods, as it provides a high coefficient of friction for the mating surfaces, but this method is the most labor-intensive.

The most commonly used fire processing method is using universal burners that work both natural gas, and on an oxygen-acetylene mixture, and create a temperature of 1600-1800 ° C, which ensures the burning of grease stains and peeling off scale and rust.

One way to clean bolts, nuts and washers is to immerse them in a tank of boiling water and then into a container filled with unleaded gasoline with 10-15% mineral oil. After the gasoline evaporates, a thin continuous film of lubricant remains on the surface of the hardware.

Accurate alignment of the holes of the mounting parts is achieved using pass-through mandrels, which are a rod with cylindrical parts. The diameter of the mandrels should be 0.2-0.5 mm less than the diameter of the hole.

To fix the relative position of the mounted elements and prevent their shifting, 1/10 of the total number of holes is filled with plugs with a diameter equal to the diameter of the holes. The length of the plugs must exceed the total thickness of the elements being connected. After installing the plugs, the mandrels are knocked out. Packages of connected elements are tightened with permanent or temporary bolts, which are placed through every third hole, but at least every 500 mm.

Holes are drilled using manual pneumatic and electric machines.

Pneumatic machines can be straight, used for working in places where there are no size restrictions, and angular, adapted for working in tight spaces. Pneumatic installations are used to drill holes with a diameter of up to 20 mm.

Electric machines operate from an alternating current network with a voltage of 220 V. In the open air, such machines are used complete with a protective switching device, and in closed, dry rooms they are grounded; the installer works with electric tools wearing gloves and standing on a rubber mat. The safest machines are those with double insulation; they can be used without additional protective measures and when working outdoors.

After drilling holes free of assembly bolts, the bolts are unscrewed and permanent bolts are installed in their place.

The nuts of all bolts (permanent and temporary) are tightened with hand wrenches (regular or ratchet). In this case, one worker holds the bolt head from rotating, and the second one tightens the nut. On bolts of normal and high precision, washers are installed - one under the bolt head and no more than two under the nut. When there are a large number of bolts in one connection, electric impact wrenches are used. The bolts are installed from the middle of the joint to the edges. There should be at least one thread with a full profile on the nut side. The quality of tightening is checked by tapping the bolts with a hammer weighing 0.3-0.4 kg. In this case, the bolts should not move or shake.

The nuts are protected from self-unscrewing by locknuts or spring washers. However, under dynamic and vibration loads, these measures are not enough, therefore, during operation, the condition of the installation connections should be systematically monitored and the nuts on loose bolts should be tightened.

Connections with high-strength bolts are shear-resistant and with load-bearing bolts. In shear-resistant connections, bolts are not directly involved in the transmission of forces: all forces applied to the mating elements are perceived only due to the friction forces arising between the shear planes. In connection with load-bearing bolts, along with the friction forces between shear planes, the bolts themselves also participate in the transmission of forces, which makes it possible to increase the load-bearing capacity of one bolt by 1.5-2 times compared to a bolt in shear-resistant connections.

The surfaces of the elements to be connected in these cases are treated as for conventional bolted connections. Before installing bolts, washers and nuts, remove preservative grease. To do this, they are dipped in a lattice container into boiling water, and then into a container with a mixture of 15% mineral oil and 85% unleaded gasoline.

During assembly and installation of metal structures Special attention pay attention to the tension of the elements being connected. There are several ways to determine bolt tension. On construction site A method is often used to indirectly estimate the tension forces through the torque that must be applied to the nut.

Torque M is determined from the expression: M = KR·a, where P - Bolt tension force, N; d - nominal bolt diameter, mm; K is the bolt torque coefficient.

The tension of the bolts is controlled selectively: with the number of bolts in a connection up to 5 - all bolts, with 6-20 - at least 5 bolts and with a larger number - at least 25% of the bolts in the connection. If during inspection it is discovered that at least one bolt does not meet the established requirements, then all bolts are checked. The heads of the checked bolts are painted, and all connections are puttied along the contour.