Method for screwing together a flange connection

Abstract

In a method for screwing together flanges (1, 2), bolts (5) extend through openings in said flanges, said bolts being supported with respect to the outer side of one flange and also being supported, with a nut screwed onto a threaded portion (5A) of the bolt, with respect to the outer side of the other flange. In order to safely close a gap (10) between the flanges (1, 2), the following is proposed: engaging an axial bolt tightening device such that its tensile force acts on a threaded portion (5A) of the bolt (5) projecting beyond the nut (8); longitudinally extending the bolt (5) by increasing the tensile force, wherein at the same time there is a continuous detecting of the tensile force, a continuous subsequent turning of the nut (8) and a continuous detecting of the rotational angle travelled by the nut (8); for the detected rotational angles or rotational angle equivalents, deriving a geometrical variable characterising the bolt elongation from the rotational angle or rotational angle equivalent in connection with the geometry of the threaded portion (5A); establishing a function which sets the geometric variables characterising the bolt elongation in relation to the detected tensile forces; a comparison operation with comparison of the gradient of the function and the gradient of a predefined reference profile; notification of the result depending on the result of the comparison operation.

Description

[0001] Method for screwing a flange connection

[0002] The invention relates to a method for screwing a flange connection, which consists of a first flange with an outer side and with a first flange surface, a second flange with an outer side and with a second flange surface opposite the first flange surface, mutually aligned openings in the flanges and flange surfaces through which the bolt bodies of bolts extend, wherein the bolts are supported on the one hand against the outer side of the first flange and on the other hand, with a nut screwed onto a threaded section of the bolt body, against the outer side of the second flange.

[0003] EP 3 195 991 A1 discloses hydraulically operated bolt tensioning devices which are used to tighten a plurality of screw connections arranged along a flange connection consisting of two flanges, one after the other or in a specific sequence. Each screw connection consists of a screw bolt which, with a radially expanded bolt head, rests against the flange connection from below, and of a threaded nut screwed onto the threaded section of the screw bolt which rests against the flange connection from above. The connection is retightened by axially stretching the screw bolt and retightening or re-tightening the nut along the bolt thread once a maximum clamping force has been reached. The bolt tensioning cylinder used also has a position sensor which, based on its position signals, can be used to reach a position in axial alignment with the screw connection axis.Such clamping cylinders are used primarily in the assembly of wind turbines. For example, the static basic structure of wind turbines consists of ring segments, each with ring flanges at their ends. The tower segments are connected to the ring flanges by means of screw bolts passing through them to form a flange connection. In practice, the structural components of wind turbines have flange surfaces, i.e. the pressure or contact surfaces of the flanges to be screwed together, which are not always exactly parallel to one another. Due to insufficient dimensional accuracy in previous production processes, the annular flange surfaces often do not fit together over their entire surface, i.e. do not fit together without gaps. Such inaccuracies in dimension, resulting in gaps, can occur both in the circumferential direction of the ring flanges and, to a lesser extent, in the radial direction, i.e. inwards or outwards.The gaps can also have an uneven gap height and thus gap size. However, for the correct design of a bolted connection, it is extremely important to avoid such gaps. If parts of a flange are not yet closed after the tightening process is complete, or if they continue to gap, the bolted connections in this area are subjected to significantly higher loads. During operation of the wind turbine, vibrations in the tower act as an additional bolt force on the individual connections. Those bolts or bolts located in the gap area receive a significantly higher proportion of the additional bolt force, with the result that these bolts may fail or break before reaching their planned service life.

[0004] For safety reasons, the flange gaps must therefore be closed, which can practically only be achieved by appropriately tightening the bolted connections. Also for safety reasons, companies carrying out such work are required to document the closing of the flange gaps that were initially present, so that they can be verified later.

[0005] EP 3 663 034 A1 discloses a method for joining ring flanges, in which the initially actual gap size profile between the two flanges is detected using a large number of individual gap size values. The individual gap size value is the vertical distance between the flange surfaces at a single measuring position. The gap size between the ring flanges thus recorded is closed by the clamping process. The flange surfaces come into complete axial contact by being pulled against each other during the clamping process by means of the screw connections, the individual positions of which are predetermined by the design and thus known. The position values ​​of the individual measuring positions are determined successively for each screw position.The bolt tensioning device with the attached gap detector is moved from one bolted joint to the next, and at each individual position, the respective gap size is measured in addition to the position value. This detection process continues until the gaps have been measured and recorded at all positions.

[0006] EP 3 593 939 A1 also deals with a method for screwing a flange connection and detecting the gaps between the flanges. This is done using a gap measuring device, which has a movement device and may also have a camera directed at the gap. The measurements are taken at the individual screw positions. The movement device used has first and second movement elements. These are designed like probes and are supported for measurement purposes on the opposite outer sides of the flanges to be screwed together.

[0007] DE 10 2018 110 482 B4 deals with the compression of the flanges involved, particularly for the construction of wind turbines, and in this context also mentions the importance of closing residual gaps between the flanges. It describes how, when clamping individual bolts, gaps between the flanges are first closed and only then can a force build up to compress the flanges. The method described in DE 10 2018 110 482 B4 works with continuously determined elongation values ​​that correlate with the actual bolt elongation, the device compression occurring at the clamping device, and the compression of the flanges. This method is complex to implement in practice because, for example, it is necessary to first determine the device-specific compression behavior for the bolt clamping device used in addition to the bolt-typical elongation behavior.

[0008] Furthermore, DE 10 2018 110 482 B4 describes clamping cylinders for bolt tensioning devices. First, a rotatable interchangeable bushing of the clamping cylinder is screwed onto the free end of the bolt that projects beyond the nut. For this purpose, the interchangeable bushing is provided with a corresponding internal thread. The interchangeable bushing is arranged within a hydraulic cylinder housing and surrounded by at least one piston. As part of a hydraulic piston-cylinder unit, the piston is able to axially drive the interchangeable bushing, thereby stretching the threaded bolt. Once the maximum hydraulic force has been reached, the nut is retightened, i.e., turned. The operating parameters actually used in the process, as well as general data relating to the screw connection, can be recorded and documented.

[0009] It is also known to individually identify bolted connections by scanning an individual identifier present on each bolted connection. The identifier thus determined can also be documented, for example, together with the applied tightening force and / or the hydraulic tightening pressure. If the nut is tightened during longitudinal stretching using, for example, a torque wrench, the actual tightening torque applied can also be saved as an additional data record.

[0010] The object of the present invention is to propose a method for tightening screw connections that takes into account the fact that irregular gaps with uneven gap heights often exist between the flanges to be connected when screwing flange connections. The actual closing of initially existing gaps should be verifiable in a technically simple manner and also demonstrable later. Furthermore, appropriate documentation specific to the individual screw connection should be enabled.

[0011] This object is achieved by a method for screwing a flange connection having the features of claim 1. Preferred embodiments of the method are defined in the subclaims.

[0012] The method utilizes an axially operating, preferably hydraulically operated bolt tensioning device. This is applied in such a way that a housing section of the bolt tensioning device surrounding the nut rests against the outside of the corresponding flange, and the tensile force exerted by the bolt tensioning device acts on a threaded portion of the bolt that protrudes beyond the nut. The bolt is then progressively stretched longitudinally by the bolt tensioning device. This occurs by preferably continuously increasing the tensile force exerted by the bolt tensioning device until a maximum tensile force is reached.

[0013] During this longitudinal stretching and until the maximum tensile force is reached, the following occurs: a continuous recording of the tensile force, which can be done e.g. on the basis of the hydraulic pressure acting at the time in conjunction with the piston area of ​​the hydraulic cylinder used in the bolt tensioning device, a continuous re-tightening of the nut by means of a torque exerted on the nut, which can be done e.g. by a rotating sleeve that is coupled to the nut in a rotationally fixed manner and which in turn is continuously driven, preferably by an electric motor and preferably with a torque of constant strength, which can be e.g. 50 Nm, a continuous recording of the angle of rotation covered by the re-tightening or an equivalent angle of rotation. This can be achieved e.g. by using a rotation angle sensor.This can either directly detect the rotational movement of the nut or the rotating sleeve, or a rotational angle equivalent, i.e. a movement in an upstream drive element that is mechanically coupled to the movement of the nut.

[0014] Using the rotation angles or rotation angle equivalents thus determined, a geometric value characterizing the bolt elongation is derived in a further step from the rotation angle or rotation angle equivalent in conjunction with the thread geometry of the threaded section. This thread geometry is preferably the thread pitch, i.e., the length measurement per thread revolution.

[0015] A further step in the process involves setting up a function. The function relates the geometric quantities that characterize the bolt elongation to the tensile forces acting on the bolt.

[0016] Viewed graphically, the function can be designed, for example, such that the abscissa represents the recorded or calculated tensile forces on the bolt, and the ordinate represents a measure of the actual bolt elongation, i.e., the angle of rotation, the equivalent angle of rotation, or an equivalent length value. The resulting function is an ascending line, which, depending on the specific bolting situation, can exhibit functional sections with a linear gradient or with a non-linear or bent gradient. The course of this line and the functional sections, as well as their gradients, allow for a clear interpretation of whether or not the flange connection had a gap in the area of ​​the tightened bolt connection, and whether or not an initially existing gap could be closed.

[0017] Therefore, based on the established function, a comparison operation is performed in a subsequent step. In the comparison operation, the gradient of the function, on the one hand, and the gradient of a given reference curve, on the other, are compared.

[0018] For the reference curve and its derivation, for example, the results of previous experimental or test setups using flanges, bolts and threaded nuts of the same design and material can be used.

[0019] The method according to the invention concludes with the generation of a result message based on the result of the comparison operation. The result message contains information on whether or not the flange connection had a gap in the area of ​​the tightened bolt connection and whether or not an initially existing gap could be closed.

[0020] The generated result message can, for example, be sent directly to the technician involved in the tightening process. This can be done, for example, via a visual display on a control and evaluation unit. The control and evaluation unit monitors the tightening process and coordinates its individual steps, preferably automatically.

[0021] The generated result report can also or additionally become part of a tightening protocol created by the control and evaluation unit for each tightening operation. The tightening protocol records and documents all operating parameters actually used for the tightening process, as well as general data relating to the screw connection, including an identifier for identifying the respective bolt. The basic idea behind the invention is to work with fewer parameters to obtain a meaningful result report, and in particular with parameters that are either easily accessible or that can be reliably recorded or determined with relatively little technical effort.

[0022] In comparison to the method according to DE 10 2018 110 482 B4, for example, instead of a purely calculated elongation value, which is recorded well above the bolt end, the technically easy-to-detect angle of rotation a, which the threaded nut travels, is used. The angle of rotation a is directly related to the bolt elongation via the thread geometry or thread pitch. The evaluation of the angle of rotation a or a rotation angle equivalent offers the advantage that, compared to the prior art, parameters are eliminated, e.g., the influence of compression on the clamping tool used. This is because in the method according to the invention, the recorded angle of rotation a is at most significantly influenced by the compression of the flanges and by the elongation of the screw connection.

[0023] It is important to continuously record the angle of rotation a over the duration of the hydraulic force build-up. This can be achieved, for example, by placing an electric drive, preferably with a structurally integrated angle of rotation sensor, on the pinion of the bolt tensioning device that drives the rotary sleeve with the nut. The electric drive loads the nut with a defined, constant torque, whereby a change in the length of the bolt is directly reflected in the recorded angle of rotation. When determining the torque of the drive acting on the nut, it should be taken into account that the torque should be sufficient to overcome the static friction of the nut at all times without delay, but should not be so great that there is a risk of repeated jamming.

[0024] In practice, the results from measuring the angle of rotation a can be distorted by settlement processes at the beginning of the process. Therefore, it is recommended that the angles of rotation or equivalent angles of rotation be recorded only after calibration. Calibration precedes the step of increasing longitudinal stretching. During calibration, the bolt tensioning device is operated with a calibration tensile force of less than 20% of the maximum tensile force, and the nut is retightened during or after calibration. Preferably, the torque used to retighten the nut during calibration is also used at the same level and without interruption for the subsequent continuous retightening of the nut.

[0025] The following drawings illustrate embodiments of the invention in more detail. They show:

[0026] Fig. 1 Flanges which are clamped against each other by means of screw connections, whereby the individual screw connection consists of a threaded bolt with a threaded nut;

[0027] Fig. 2 shows a longitudinal section through a hydraulically operating bolt tensioning device;

[0028] Fig. 3 shows a perspective view of a bolt tensioning device including an electric drive attached to its housing for retightening the threaded nut;

[0029] Fig. 4 Functional curves of two different screwing situations, where the function relates the dimensions of an actual bolt elongation to simultaneously recorded or calculated bolt tensile forces;

[0030] Fig. 5 shows the functional progression for a third screwing situation.

[0031] Fig. 1 shows a small section of an extensive flange connection between two annular flanges 1, 2. A large number of screw connections are present around the circumference of the flange connection, preferably at equal circumferential distances. Such flange connections are used in wind turbines. For example, the basic static structure of such turbines consists of ring segments, each of which has annular flanges at its end. The tower segments are connected to the ring flanges to form a rigid flange connection by means of screw connections distributed around the circumference, which extend transversely to the flange surfaces. In practice, the flange surfaces 3, 4 intended for mutual contact, i.e. the annular pressure surfaces of the flanges 1, 2 to be screwed together, are not always exactly parallel to one another, which results in gaps 10.This is because, due to insufficient dimensional accuracy in previous production processes, the annular flange surfaces 3, 4 often do not fit together over their entire surface, i.e. there are no gaps. Inadequate dimensional accuracy resulting in such gaps 10 between the flange surfaces 3, 4 can occur both in the circumferential direction of the flanges and, albeit to a lesser extent, in the radial direction, i.e. towards the inside or outside. The gaps 10 can also have an uneven gap height and therefore gap size. For the correct design of a bolted connection, such gaps must be avoided or closed, even retrospectively if necessary. This is because if parts of the flanges involved are not closed after the bolting has been completed or continue to gap, the bolted connections in this area are subject to significantly higher loads. During operation of the wind turbine, vibrations in the tower act as an additional bolt force on the individual connections. These bolts and nuts canBolts located in the gap area receive a significantly higher proportion of the additional screw force, with the result that these screws may fail or break before reaching their planned service life.

[0032] Each of the screw connections consists of a bolt 5, which in the exemplary embodiment consists of an elongated bolt body and a radially expanded bolt head, the bolt head of which rests from below against the outer side 7 of the lower flange 2, and a nut 8 screwed onto the threaded portion of the bolt 6 and rests from above against the outer side 6 of the upper flange 1. Furthermore, Fig. 1 shows a gap 10 between those flange surfaces 3, 4 that should actually be in direct pressure contact. A washer can also be arranged under the nut 8 and / or under the bolt head. Further washers can also be part of the screw connection.

[0033] To tighten and in particular retighten the screw connection, the bolt 5 is axially stretched by pulling on its threaded section 5A projecting beyond the nut 8, and the nut 8 is thereby retightened or re-tightened.

[0034] Fig. 2 shows the basic structure of a usable bolt tensioning device 11. This is of the type of hydraulic tensioning cylinder and is designed to stretch or expand the screw connection by applying an exclusively axial tensile force. In this case, the threaded section 5A of the threaded bolt 5 protruding beyond the nut 8 is stretched longitudinally by axial tension, with the shaft and partially the threaded section stretching in particular. The tensile force applied in this process, which is equivalent to the respective hydraulic pressure, can be automatically saved in a documentation module and is thus available for later testing purposes. While tensile force is exerted on the threaded bolt 5 by activating the hydraulic tensioning cylinder, the nut 8 is tightened by turning. An interchangeable bushing 12, which is arranged centrally in a cylinder housing 17 of the bolt tensioning device 11 and is longitudinally movable, is provided with an internal thread 13.Before the clamping process, the interchangeable bushing 12 is screwed onto the threaded section 5A projecting beyond the threaded nut 8 using the internal thread 13. For this purpose, the interchangeable bushing 12 can be provided with a polygonal drive 14 at its other end.

[0035] During the clamping process, the interchangeable bushing 12 is subjected to axial tension by hydraulic pressure, causing the threaded bolt 5 to expand. This releases the underside of the nut 8, allowing the nut to be rotated with relatively little resistance. This direct rotation is achieved by a rotating sleeve 16 mounted in a support tube 18, which is provided with form-fitting structures on its inside, in particular with a hexagon that positively engages the nut 8. The rotating sleeve 16 is driven by an electric motor, possibly via an intermediate gear.

[0036] Compared to Fig. 2, Fig. 3 also shows the housing of the electric motor 23 driving the rotating sleeve 16 and the intermediate gear. These components are attached as an assembly to the outside of the housing of the bolt tensioning device 11.

[0037] A rotation angle sensor 20 configured to detect rotational movements is preferably also integrated into the assembly comprising the rotary sleeve 16, the electric motor 23, and, if applicable, an intermediate gear. The rotation angle sensor 20 is designed to continuously detect either the rotation angle a traveled by the rotary sleeve 16 and thus the threaded nut, or alternatively, a rotation angle equivalent of the same significance.

[0038] The hydraulic clamping mechanism is enclosed by the pressure-resistant cylinder housing 17. Its rigid downward continuation is the support tube 18 surrounding the nut 8. This can be integral with the cylinder housing 17. The support tube 18 is open on its underside and rests with this underside on the outer side 6 of the flange 1 against which the nut 8 also rests. Located on the outside of the cylinder housing 17 is a hydraulic connection, via which a hydraulic working chamber 21 (Fig. 2) is connected to an external hydraulic supply, for example a hydraulic pump.

[0039] A piston 25 is movably mounted in the cylinder housing 17, sealed from the cylinder inner wall. By feeding hydraulic pressure into the hydraulic working chamber 21, the piston 25 lifts. The piston 25 surrounds the interchangeable bushing 12 in a ring shape. It is provided on its inner edge with a step 27 against which the interchangeable bushing 12 rests. When the hydraulic pump feeds pressurized fluid into the working chamber 21, the piston 25 lifts and axially carries the interchangeable bushing 12 with it. This creates a tensile force on the bolt 5.

[0040] The aim of the method described here is not only to completely close the gap 10 existing between the flanges 1, 2 during the screwing process, but also to detect, signal and possibly document such a closure in a suitable manner.

[0041] First, calibration is performed. This is because the desired results can be distorted in practice by settlement processes at the beginning of the process. Therefore, the rotation angle a or, alternatively, rotation angle equivalents are only recorded after calibration. During calibration, the hydraulic bolt tensioning device 11 is loaded with a calibration tensile force FK of less than 20% of the maximum tensile force F later used. ma x, and during or afterward, the nut 8 is retightened. This minimizes settlement phenomena in the area of ​​the pressure and clamping surfaces involved. Preferably, the torque applied when retightening the nut 8 during calibration, e.g., 50 Nm, is also used at the same level and without interruption for the subsequent, continuous retightening of the nut 8.

[0042] Following calibration, the bolt tensioning device 11 is used to stretch the bolt 5 longitudinally by increasing the hydraulically generated tensile force Fz until a maximum tensile force F applicable to the specific screwing case is reached. ma x. This maximum tensile force F ma x can be, for example, 1000 kN to 1500 kN. During this longitudinal stretching and until the maximum tensile force F ma x is carried out - a continuous recording of the tensile force Fz, by means of a torque exerted on the nut 8 a continuous re-tightening of the nut 8,

[0043] - Continuous detection of the angle of rotation a covered by the nut 8 during re-tightening, or the equivalent angle of rotation. This is achieved by using the angle of rotation sensor 20. This either directly detects the rotational movement of the nut 8 or the rotating sleeve 16, or a rotational angle equivalent, i.e., a movement mechanically coupled to the movement of the nut 8 in an upstream drive element.

[0044] Using the rotation angle a thus determined, a further step involves deriving a geometric variable characterizing the achieved bolt elongation from the rotation angle a and in conjunction with the thread geometry of the bolt 5 at the threaded section 5A. This thread geometry is, in particular, the thread pitch, i.e., the length dimension per thread revolution.

[0045] According to Figures 4 and 5, a further step of the method consists in setting up a function F in which geometric variables that characterize the bolt elongations are related to the increasing tensile forces Fz on the bolt 5. The function curves are each described by increasing lines. The abscissa represents the increasing tensile forces Fz on the bolt 5, and the ordinate the recorded angle of rotation a as a measure of the bolt elongation. Depending on the specific screw connection situation, the function F has functional sections with a linear gradient or with a non-linear or angular gradient. The specific course of the function and in particular the size of the gradients and their arrangement provide information as to whether or not the flange connection had a gap 10 in the area of ​​the tightened bolt connection and whether or not an initially existing gap 10 could be closed.

[0046] Fig. 4 shows the functional curves for two different screwing situations, but with the same dimensions of the flanges and the screws or bolts:

[0047] The largely linearly rising line with a lower gradient shows that the flanges 1, 2 involved are in surface contact from the beginning, i.e., from the beginning of the force application, meaning that no gap 10 was present. The increasing tensile force Fz leads to the compression of the flanges 1, 2. The angle of rotation a shown on the ordinate as a measure of the bolt elongation remains relatively small.

[0048] - The line with a greater gradient, also shown in Fig. 4, shows that in this other case, a gap 10 exists between the flanges 1 and 2 involved, which, however, could not be closed over the entire duration of the force application. The angle of rotation a shown on the ordinate as a measure of the bolt elongation is relatively large, since a significant amount of deformation work had to be performed to reduce the gap.

[0049] Fig. 5 shows the course of the function F for a different screwing situation, but again with the same dimension of the flanges and the screws or bolts:

[0050] - The initially largely straight, rising line with a steeper gradient indicates that a gap 10 existed between the flanges 1 and 2 involved. As the tensile force Fz increases further, the line bends or becomes less steep, ending in a curve with a lower gradient. Thus, what is shown here is a case where an initially existing gap 10 closes as the force builds up.

[0051] - After closing, represented by the bending section of the functional curve, the further increase of the tensile force Fz leads to the compression of the flanges 1, 2. Therefore, Fig. 5 also shows the gap height which initially decreases and then becomes zero in the last third.

[0052] Based on the specifically defined function F, a comparison operation is carried out in a next step. In this comparison operation, the gradient of the function F, and in particular the gradient of the function F towards the end of the increase in the tensile force Fz, on the one hand, and the gradient of a specified reference curve R, on the other hand, are compared. For the reference curve R (Fig. 5) and its derivation, the results of previous experimental or test setups using flanges, bolts, and threaded nuts of the same design and material can be used, for example. It is recommended that the gradient of the reference curve R specified in the comparison operation covers a tolerance range R+, R., i.e., allows for a certain bandwidth.

[0053] Finally, a result message is generated depending on the result of the comparison operation. The result message contains information about whether the flange connection had a gap 10 in the area of ​​the tightened bolt connection, and whether an initially existing gap 10 was closed or not.

[0054] The evaluation of the results can not only provide conclusions about the gap closure. If the gradient of the function F—especially in the last third—does not run smoothly or decreases slowly, but instead increases or reaches zero, this may be an indication of impending plasticization in the screw connection.

[0055] The method also enables an additional determination of the gap width of the gap between the flanges 1, 2. For this purpose, a kink point is determined in the gradient of the function F. Based on the values ​​for the angle of rotation and the thread geometry of the thread section 5A, the kink point is converted into a change in length and / or into a gap length.

[0056] The gap height can also be calculated, whereby this calculation takes into account either the determined or an already known stiffness of the flanges 1 , 2 .

[0057] Furthermore, it is possible for all or some of the determination, calculation, and evaluation steps to be performed using self-learning processes and / or artificial intelligence methods. This allows, for example, statements to be made regarding irregularities in the clamping process, defects in individual sections of the flange connection, or application errors by specific operators. Reference symbols

[0058] 1 flange

[0059] 2 flange

[0060] 3 Flange surface

[0061] 4 Flange surface

[0062] 5 bolts

[0063] 5A threaded section

[0064] 6 Outside

[0065] 7 Outside

[0066] 8 Nut, threaded nut

[0067] 10 gap

[0068] 11 Bolt clamping device

[0069] 12 interchangeable socket

[0070] 13 internal threads

[0071] 14 drive polygon

[0072] 16 rotating sleeve

[0073] 17 cylinder housing

[0074] 18 Support tube

[0075] 20 rotation angle sensor

[0076] 21 hydraulic working chamber

[0077] 23 Electric motor

[0078] 25 pistons

[0079] 27 Level a angle of rotation

[0080] F Function

[0081] FK calibration tensile force

[0082] F m ax maximum force

[0083] Vehicle traction force

[0084] R Reference history

[0085] R+ tolerance range

[0086] R. Tolerance range

Claims

Claims 1. Method for screwing a flange connection made of - a first flange (1) with an outer side (6) and with a first flange surface (3), - a second flange (2) with an outer side (7) and with a second flange surface (4) opposite the first flange surface (3), - mutually aligned openings in the flanges (1, 2), through which the bolt bodies of bolts (5) extend, wherein the bolts (5) are supported on the one hand against the outer side (7) of one of the flanges (2) and on the other hand, with a nut (8) screwed onto a threaded section (5A) of the bolt body, against the outer side (6) of the further flange (1), and comprising the method steps - Attaching an axially operating, preferably hydraulically operated bolt tensioning device (11) to the bolt (5) in such a way that a housing section of the bolt tensioning device (11) surrounding the nut (8) is supported against the outer side (6) of the further flange (1) and the tensile force (Fz) exerted by the bolt tensioning device (11) acts on a threaded section (5A) of the bolt (5) projecting beyond the nut (8), by means of the bolt tensioning device (11) increasing longitudinal stretching of the bolt (5) by increasing the tensile force (Fz) until a maximum tensile force (F ma x), whereby during the longitudinal stretching and until the maximum tensile force (F max) is reached, - a continuous recording of the tensile force (Fz), by means of a torque exerted on the nut (8), a continuous re-tightening of the nut (8), - a continuous recording of the angle of rotation (a) covered by the nut (8) with the subsequent turning or a rotation angle equivalent is carried out, for the recorded angle of rotation (a) or angle of rotation equivalents. Derivation of a geometric variable characterising the bolt elongation from the angle of rotation (a) or angle of rotation equivalent in conjunction with the thread geometry of the threaded section (5A), - Establishing a function (F) which relates the geometrical quantities characterising the bolt elongations to the measured tensile forces (Fz), - performing a comparison operation with comparison of the gradient of the function (F) on the one hand and the gradient of a given reference curve (R) on the other hand, - Generate a result message depending on the result of the comparison operation.

2. Method according to claim 1, characterized in that the result message generated is one of at least three possible result messages, wherein a first result message represents contact of the flange surfaces (3, 4) achieved during the longitudinal stretching of the bolt (5), a second result message represents contact of the flange surfaces (3, 4) not achieved during the longitudinal stretching of the bolt (5), a third result message represents gap-free contact of the flange surfaces (3, 4) from the beginning during the longitudinal stretching of the bolt (5).

3. Method according to claim 1 or 2, characterized in that the angle of rotation (a) or angle of rotation equivalents are only recorded following a calibration preceding the increasing longitudinal stretching, in which the bolt tensioning device (11) is subjected to a calibration tensile force (FK) of less than 20% of the maximum tensile force (F ma x) is operated and the nut (8) is retightened during or after this.

4. Method according to claim 3, characterized in that the torque used during calibration when retightening the nut (8) is also used with the same strength and without interruption for the continuous retightening of the nut (8).

5. Method according to one of the preceding claims, characterized in that the gradient of the reference curve (R) specified in the comparison operation comprises a tolerance range (R+, R.).

6. Method according to claim 1, characterized by an additional determination of the gap width of a gap (10) between the flanges (1, 2) with the method steps - Determination of a break point in the gradient of the function (F) based on the values ​​for the angle of rotation (a) or the angle of rotation equivalent and the thread geometry of the thread section (5A), - Converting the bending point into a change in length and / or a gap length.

7. Method according to claim 1, characterized by an additional calculation of the gap height of the gap (10), wherein the calculation includes the determined or an already known stiffness of the flanges (1, 2).

8. Method according to claim 1, characterized in that all or some of the determination, calculation and evaluation steps are carried out using self-learning methods and / or artificial intelligence methods in order, for example, to make statements about irregularities in the clamping process, errors on individual sections of the flange connection or application errors by specific operators.

9. Method according to one of the preceding claims, characterized in that in the comparison operation, primarily the gradient of the function (F), which it has towards the end of the increase in the tensile force (Fz), is compared with the gradient of the reference curve (R).

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