Pipeline front opening circle blanking method

Abstract

The invention relates to a pipeline front opening circle blanking method which comprises the steps that four points A1, A2, A3 and A4 are marked on the inner side of a pipe opening in one end of a pipeline in the circumferential direction, and four points B1, B2, B3 and B4 are marked on the inner side of a pipe opening in the other end of the pipeline in the circumferential direction; measuring the lengths of A1 and B1, the lengths of A2 and B2, the lengths of A3 and B3, and the lengths of A4 and B4; measuring the lengths of A1 and B3, the lengths of A2 and B4, the lengths of A3 and B1, and the lengths of A4 and B2; establishing a three-dimensional space coordinate system; calculating and marking coordinates of A1, B1, A2, B2, A3, B3, A4 and B4; determining a point E on the X axis, and calculating the projection of the point E on the line segments L1, L2, L3 and L4; and respectively carrying out position analysis on A1, B1, A2, B2, A3, B3, A4 and B4. The method has the advantages that accurate data used for drawing the shape of the pipeline front opening circle can be obtained, the front opening circle finding error is reduced, the alignment and construction conditions are improved, and therefore the operation construction quality in pipeline construction, transformation and operation is improved.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas pipeline construction, and in particular to a pipeline round blanking method. Background Art

[0002] During the construction of oil and gas pipelines, it is often necessary to trim the pipe ends into unique shapes. These shapes are drawn and cut based on the right-end circle on the pipe. Currently, there are two main ways to draw the right-end circle of the pipe:

[0003] 1) The pipe wall is wrapped with a band, and the edge formed by the band on the weather can be considered as the normal mouth circle of the pipe;

[0004] 2) Draw through a ferrule flange. The inner diameter of the flange is slightly approximately the outer diameter of the pipe. Use a right-angle ruler to make the flange plane perpendicular to the outer wall line of the pipe. Draw along the flange plane on the outer wall of the pipe, which can be considered as the normal mouth circle of the pipe.

[0005] Since the square circle found by the above two methods is significantly different from the real square circle in shape, the connection gap often fails to meet the construction requirements, resulting in operation failure or forceful assembly, which poses a major safety hazard to production operations.

[0006] Based on this, it is necessary to develop a method for cutting pipe round mouth to overcome the above technical problems. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a method for cutting pipe round ends, which effectively overcomes the defects of the prior art.

[0008] The technical solution of the present invention to solve the above technical problems is as follows:

[0009] A method for cutting a pipe round mouth, comprising the following steps:

[0010] Step 1: Mark four points (A1, A2, A3, A4) along the circumferential direction on the inner side of the pipe opening at one end of the pipeline, and mark four points (B1, B2, B3, B4) along the circumferential direction on the inner side of the pipe opening at the other end of the pipeline, and make A1 and B1, A2 and B2, A3 and B3, A4 and B4 fall on the same straight line in the axial direction respectively;

[0011] Step 2: Measure the length of line segment L1 between A1 and B1, the length of line segment L2 between A2 and B2, the length of line segment L3 between A3 and B3, and the length of line segment L4 between A4 and B4; and the plane where line segments L1 and L3 are located intersects with the plane where line segments L2 and L4 are located, and the intersection line coincides with the axis of the pipeline;

[0012] Step 3, measure the length of line segment S1 between A1 and B3, the length of line segment S2 between A2 and B4, the length of line segment S3 between A3 and B1, and the length of line segment S4 between A4 and B2;

[0013] Step 4: Establish a three-dimensional space coordinate system with the midpoint of the vertical line segment between line segments L1 and L3 as the origin, where the X-axis points to the axial direction of the pipeline, the Y-axis points to the radial direction of the pipeline and is perpendicular to line segment L1, and the Z-axis points to the radial direction of the pipeline and is perpendicular to line segment L2:

[0014] Step 5: Use the above three-dimensional space coordinate system and the measured line segment data to calculate and mark the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4;

[0015] Step 6: Determine a point E on the X-axis, calculate the projections of point E on line segments L1, L2, L3 and L4, and record them as F1, F2, F3, F4 respectively;

[0016] Step 7. Use the coordinates F1, F2, F3, and F4 to perform position analysis with A1, B1, A2, B2, A3, B3, A4, and B4, respectively, to obtain the position relationship between the normal mouth circle and each characteristic point in the axial direction of the pipeline.

[0017] Based on the above technical solution, the present invention can also be improved as follows.

[0018] Furthermore, in the above step 4, the method of establishing the three-dimensional space coordinate system is as follows:

[0019] S11. Take four points A, B, C, and D on the plane A1A3B1B3, where A and B fall on line segment L1, C and D fall on line segment L3, and the intersection of line segments AD and BC is O;

[0020] S12. Assuming that the length of line segment AO is known, then OD = AD-AO;

[0021] S13, calculate the length of BO, BO = AO * BC / AD;

[0022] S14, calculate the length of OC, OC = BC-BO;

[0023] S15. Calculate ∠AOB using the law of cosines;

[0024] S16. Calculate ∠COD using the law of cosines;

[0025] S17, by ∠AOB=∠COD, obtain the equation system and solve it to obtain the length of AO;

[0026] S18, line segment AB and line segment CD are parallel, and the vertical distance between them is the pipe diameter length;

[0027] S19. In plane ABCD, specify the midpoint of the perpendicular line segment between line segment AB and line segment CD as the origin, establish a coordinate system in the X-axis direction, and use basic geometric principles to obtain the coordinates of A, B, C, and D;

[0028] S20, using the values ​​of A2, A4, B2, B4 in the Y-axis direction being 0, and the values ​​of A1, A3, B1, B3 in the Z-axis direction being 0, the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4 in the established three-dimensional space coordinate system can be obtained;

[0029] Among them, the lengths of line segments L1, L2, L3, L4, S1, S2, S3, S4 and the diameter of the pipeline are known parameters for measurement.

[0030] Furthermore, the above four points A1, A2, A3 and A4 are distributed at equal intervals along the circumferential direction.

[0031] Furthermore, the four points A1, A2, A3 and A4 are arranged in a clockwise direction, and the point A1 is at the 12 o'clock direction.

[0032] Furthermore, in the above step 7, using the coordinates of F1, F2, F3, and F4, the position analysis can be performed with A1, B1, A2, B2, A3, B3, A4, and B4 respectively, specifically including:

[0033] S111, calculating the length data of line segments A1F1, A2F2, A3F3, and A4F4, which are used for cutting the pipe orifice where the characteristic point A1 is located;

[0034] S112, calculating the length data of line segments B1F1, B2F2, B3F3, and B4F4, which are used for cutting the pipe mouth circle where the characteristic point B1 is located.

[0035] Furthermore, the position of the above-mentioned point E is close to any end of the pipeline.

[0036] Furthermore, the method also includes step eight of drawing the circular shape of the pipe mouth.

[0037] Furthermore, the method also includes step nine, cutting the pipe mouth circle according to the shape and coordinate data.

[0038] Furthermore, in the above step 1, the above A1, A2, A3, A4 and B1, B2, B3, B4 are respectively aligned and marked using the highest point principle.

[0039] Furthermore, in the above step six, take another point different from E on the X-axis, then calculate the projection of the end on the line segments L1, L2, L3 and L4, mark the projection point, and then use the method of step seven to perform another analysis and verification.

[0040] The beneficial effects of the present invention are as follows: the length between the characteristic points of the inner wall of the pipe body at both ends is measured by combining the pipe wall to perform relevant spatial calculations, so as to obtain accurate data for drawing the shape of the pipe mouth circle, which can improve the matching and construction conditions by reducing the error in finding the mouth circle, thereby improving the construction quality of pipeline construction, transformation and operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the distribution of characteristic points of the pipe orifice and four length data involved in the method for blanking the pipe orifice of the present invention;

[0042] Figure 2 It is a schematic diagram of four length data measured on the pipeline involved in the pipeline normal round blanking method of the present invention;

[0043] Figure 3 It is a geometrical schematic diagram of the calculation principle involved in the pipe normal round blanking method of the present invention;

[0044] Figure 4 It is a schematic diagram of a three-dimensional space coordinate system involved in the pipe round blanking method of the present invention;

[0045] Figure 5 It is a schematic diagram of the square circle involved in the method for cutting the square circle of the pipe of the present invention. DETAILED DESCRIPTION

[0046] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0047] Example: Figure 1 , 2 As shown in , 3, 4, and 5, the pipe round blanking method of this embodiment includes the following steps:

[0048] Step 1: Mark four points (A1, A2, A3, A4) along the circumferential direction on the inner side of the pipe opening at one end of the pipe, and mark four points (B1, B2, B3, B4) along the circumferential direction on the inner side of the pipe opening at the other end of the pipe, and make A1 and B1, A2 and B2, A3 and B3, A4 and B4 fall on the same straight line in the axial direction; wherein, the above A1, A2, A3, A4 and B1, B2, B3, B4 are respectively aligned and marked using the highest point principle;

[0049] Step 2: Measure the length of line segment L1 between A1 and B1, the length of line segment L2 between A2 and B2, the length of line segment L3 between A3 and B3, and the length of line segment L4 between A4 and B4; and the plane where line segments L1 and L3 are located intersects with the plane where line segments L2 and L4 are located, and the intersection line coincides with the axis of the pipeline;

[0050] Step 3, measure the length of line segment S1 between A1 and B3, the length of line segment S2 between A2 and B4, the length of line segment S3 between A3 and B1, and the length of line segment S4 between A4 and B2;

[0051] Step 4: Establish a three-dimensional space coordinate system with the midpoint of the vertical line segment between line segments L1 and L3 as the origin, where the X-axis points to the axial direction of the pipeline, the Y-axis points to the radial direction of the pipeline and is perpendicular to line segment L1, and the Z-axis points to the radial direction of the pipeline and is perpendicular to line segment L2: The method for establishing the three-dimensional space coordinate system is as follows:

[0052] S11. Take four points A, B, C, and D on the plane A1A3B1B3, where A and B fall on line segment L1, C and D fall on line segment L3, and the intersection of line segments AD and BC is O;

[0053] S12. Assuming that the length of line segment AO is known, then OD = AD-AO;

[0054] S13, calculate the length of BO, BO = AO * BC / AD;

[0055] S14, calculate the length of OC, OC = BC-BO;

[0056] S15. Calculate ∠AOB using the law of cosines;

[0057] S16. Calculate ∠COD using the law of cosines;

[0058] S17, by ∠AOB=∠COD, obtain the equation system and solve it to obtain the length of AO;

[0059] S18, line segment AB and line segment CD are parallel, and the vertical distance between them is the pipe diameter length;

[0060] S19. In plane ABCD, specify the midpoint of the perpendicular line segment between line segment AB and line segment CD as the origin, establish a coordinate system in the X-axis direction, and use basic geometric principles to obtain the coordinates of A, B, C, and D;

[0061] S20, using the values ​​of A2, A4, B2, B4 in the Y-axis direction being 0, and the values ​​of A1, A3, B1, B3 in the Z-axis direction being 0, the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4 in the established three-dimensional space coordinate system can be obtained;

[0062] Among them, the lengths of line segments L1, L2, L3, L4, S1, S2, S3, S4 and the diameter of the pipeline are known parameters for measurement;

[0063] Step 5: Use the above three-dimensional space coordinate system and the measured line segment data to calculate and mark the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4;

[0064] Step 6: Determine a point E on the X-axis, calculate the projections of point E on line segments L1, L2, L3 and L4, and record them as F1, F2, F3, F4 respectively;

[0065] Step 7: Use F1, F2, F3, F4 coordinates to analyze the position with A1, B1, A2, B2, A3, B3, A4 and B4 respectively to get the position relationship between the right mouth circle and each characteristic point in the pipeline axis, as follows:

[0066] S111, calculating the length data of line segments A1F1, A2F2, A3F3, and A4F4, which are used for cutting the pipe orifice where the characteristic point A1 is located;

[0067] S112, calculating the length data of line segments B1F1, B2F2, B3F3, and B4F4, which are used for cutting the pipe mouth circle where the characteristic point B1 is located.

[0068] Example 2

[0069] The pipe round blanking method of this embodiment comprises the following steps:

[0070] Step 1: Mark four points (A1, A2, A3, A4) along the circumferential direction on the inner side of the pipe opening at one end of the pipe, and mark four points (B1, B2, B3, B4) along the circumferential direction on the inner side of the pipe opening at the other end of the pipe, and make A1 and B1, A2 and B2, A3 and B3, A4 and B4 fall on the same straight line in the axial direction; wherein, the above A1, A2, A3, A4 and B1, B2, B3, B4 are respectively aligned and marked using the highest point principle;

[0071] Step 2: Measure the length of line segment L1 between A1 and B1, the length of line segment L2 between A2 and B2, the length of line segment L3 between A3 and B3, and the length of line segment L4 between A4 and B4; and the plane where line segments L1 and L3 are located intersects with the plane where line segments L2 and L4 are located, and the intersection line coincides with the axis of the pipeline;

[0072] Step 3, measure the length of line segment S1 between A1 and B3, the length of line segment S2 between A2 and B4, the length of line segment S3 between A3 and B1, and the length of line segment S4 between A4 and B2;

[0073] Step 4: Establish a three-dimensional space coordinate system with the midpoint of the vertical line segment between line segments L1 and L3 as the origin, where the X-axis points to the axial direction of the pipeline, the Y-axis points to the radial direction of the pipeline and is perpendicular to line segment L1, and the Z-axis points to the radial direction of the pipeline and is perpendicular to line segment L2: The method for establishing the three-dimensional space coordinate system is as follows:

[0074] S11. Take four points A, B, C, and D on the plane A1A3B1B3, where A and B fall on line segment L1, C and D fall on line segment L3, and the intersection of line segments AD and BC is O;

[0075] S12. Assuming that the length of line segment AO is known, then OD = AD-AO;

[0076] S13, calculate the length of BO, BO = AO * BC / AD;

[0077] S14, calculate the length of OC, OC = BC-BO;

[0078] S15. Calculate ∠AOB using the law of cosines;

[0079] S16. Calculate ∠COD using the law of cosines;

[0080] S17, by ∠AOB=∠COD, obtain the equation system and solve it to obtain the length of AO;

[0081] S18, line segment AB and line segment CD are parallel, and the vertical distance between them is the pipe diameter length;

[0082] S19. In plane ABCD, specify the midpoint of the perpendicular line segment between line segment AB and line segment CD as the origin, establish a coordinate system in the X-axis direction, and use basic geometric principles to obtain the coordinates of A, B, C, and D;

[0083] S20, using the values ​​of A2, A4, B2, B4 in the Y-axis direction being 0, and the values ​​of A1, A3, B1, B3 in the Z-axis direction being 0, the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4 in the established three-dimensional space coordinate system can be obtained;

[0084] Among them, the lengths of line segments L1, L2, L3, L4, S1, S2, S3, S4 and the diameter of the pipeline are known parameters for measurement;

[0085] Step 5: Use the above three-dimensional space coordinate system and the measured line segment data to calculate and mark the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4;

[0086] Step 6: Determine a point E on the X-axis, calculate the projections of point E on line segments L1, L2, L3 and L4, and record them as F1, F2, F3, F4 respectively;

[0087] Step 7: Use F1, F2, F3, F4 coordinates to analyze the position with A1, B1, A2, B2, A3, B3, A4 and B4 respectively to get the position relationship between the right mouth circle and each characteristic point in the pipeline axis, as follows:

[0088] S111, calculating the length data of line segments A1F1, A2F2, A3F3, and A4F4, which are used for cutting the pipe orifice where the characteristic point A1 is located;

[0089] S112, calculating the length data of line segments B1F1, B2F2, B3F3, and B4F4, which are used for cutting the pipe orifice where the characteristic point B1 is located;

[0090] Step 8: Draw the circular shape of the pipe mouth.

[0091] Example 3

[0092] The pipe round blanking method of this embodiment comprises the following steps:

[0093] Step 1: Mark four points (A1, A2, A3, A4) along the circumferential direction on the inner side of the pipe opening at one end of the pipe, and mark four points (B1, B2, B3, B4) along the circumferential direction on the inner side of the pipe opening at the other end of the pipe, and make A1 and B1, A2 and B2, A3 and B3, A4 and B4 fall on the same straight line in the axial direction; wherein, the above A1, A2, A3, A4 and B1, B2, B3, B4 are respectively aligned and marked using the highest point principle;

[0094] Step 2: Measure the length of line segment L1 between A1 and B1, the length of line segment L2 between A2 and B2, the length of line segment L3 between A3 and B3, and the length of line segment L4 between A4 and B4; and the plane where line segments L1 and L3 are located intersects with the plane where line segments L2 and L4 are located, and the intersection line coincides with the axis of the pipeline;

[0095] Step 3, measure the length of line segment S1 between A1 and B3, the length of line segment S2 between A2 and B4, the length of line segment S3 between A3 and B1, and the length of line segment S4 between A4 and B2;

[0096] Step 4: Establish a three-dimensional space coordinate system with the midpoint of the vertical line segment between line segments L1 and L3 as the origin, where the X-axis points to the axial direction of the pipeline, the Y-axis points to the radial direction of the pipeline and is perpendicular to line segment L1, and the Z-axis points to the radial direction of the pipeline and is perpendicular to line segment L2: The method for establishing the three-dimensional space coordinate system is as follows:

[0097] S11. Take four points A, B, C, and D on the plane A1A3B1B3, where A and B fall on line segment L1, C and D fall on line segment L3, and the intersection of line segments AD and BC is O;

[0098] S12. Assuming that the length of line segment AO is known, then OD = AD-AO;

[0099] S13, calculate the length of BO, BO = AO * BC / AD;

[0100] S14, calculate the length of OC, OC = BC-BO;

[0101] S15. Calculate ∠AOB using the law of cosines;

[0102] S16. Calculate ∠COD using the law of cosines;

[0103] S17, by ∠AOB=∠COD, obtain the equation system and solve it to obtain the length of AO;

[0104] S18, line segment AB and line segment CD are parallel, and the vertical distance between them is the pipe diameter length;

[0105] S19. In plane ABCD, specify the midpoint of the perpendicular line segment between line segment AB and line segment CD as the origin, establish a coordinate system in the X-axis direction, and use basic geometric principles to obtain the coordinates of A, B, C, and D;

[0106] S20, using the values ​​of A2, A4, B2, B4 in the Y-axis direction being 0, and the values ​​of A1, A3, B1, B3 in the Z-axis direction being 0, the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4 in the established three-dimensional space coordinate system can be obtained;

[0107] Among them, the lengths of line segments L1, L2, L3, L4, S1, S2, S3, S4 and the diameter of the pipeline are known parameters for measurement;

[0108] Step 5: Use the above three-dimensional space coordinate system and the measured line segment data to calculate and mark the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4;

[0109] Step 6: Determine a point E on the X-axis, calculate the projections of point E on line segments L1, L2, L3 and L4, and record them as F1, F2, F3, F4 respectively;

[0110] Step 7: Use F1, F2, F3, F4 coordinates to analyze the position with A1, B1, A2, B2, A3, B3, A4 and B4 respectively to get the position relationship between the right mouth circle and each characteristic point in the pipeline axis, as follows:

[0111] S111, calculating the length data of line segments A1F1, A2F2, A3F3, and A4F4, which are used for cutting the pipe orifice where the characteristic point A1 is located;

[0112] S112, calculating the length data of line segments B1F1, B2F2, B3F3, and B4F4, which are used for cutting the pipe orifice where the characteristic point B1 is located;

[0113] Step 8: Draw the shape of the pipe mouth;

[0114] Step 9: Cut the pipe mouth circle according to the shape and coordinate data.

[0115] Example 4

[0116] In this embodiment, based on embodiments 1, 2, and 3, in step six, another point different from E is taken on the X-axis, and then the projection of the end on the line segments L1, L2, L3, and L4 is calculated, and the projection point is marked, and then the method of step seven is used to perform another analysis and verification.

[0117] The rest is the same as in Examples 1, 2, and 3.

[0118] It should be particularly emphasized that: based on the above-mentioned embodiments 1, 2, and 3, the four points A1, A2, A3, and A4 are equally spaced along the circumferential direction, that is, the distance between A1 and A2 is 90° at the central angle, the distance between A3 and A2 is 90° at the central angle, the distance between A4 and A3 is 90° at the central angle, and the distance between A1 and A4 is 90° at the central angle.

[0119] It should be particularly emphasized that the above-mentioned four points A1, A2, A3 and A4 are arranged in a clockwise direction (from a normal viewing angle at one end of the pipeline), and point A1 is at the 12 o'clock direction.

[0120] It should be particularly emphasized that the position of the above-mentioned point E is close to either end of the pipeline.

[0121] In the description of the present invention, it is to be understood that the terms “center”, “longitudinal”, “lateral”, “length”, “width”, “thickness”, “up”, “down”, “front”, “back”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inside”, “outside”, “clockwise”, “counterclockwise”, “axial”, “radial”, “circumferential”, etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0122] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0123] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0124] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0125] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0126] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for cutting pipe round mouth, characterized in that: The following steps are involved: Step 1: Mark four points (A1, A2, A3, A4) along the circumferential direction on the inner side of the pipe opening at one end of the pipeline, and mark four points (B1, B2, B3, B4) along the circumferential direction on the inner side of the pipe opening at the other end of the pipeline, and make A1 and B1, A2 and B2, A3 and B3, A4 and B4 fall on the same straight line in the axial direction respectively; Step 2: Measure the length of line segment L1 between A1 and B1, the length of line segment L2 between A2 and B2, the length of line segment L3 between A3 and B3, and the length of line segment L4 between A4 and B4; and the plane where line segments L1 and L3 are located intersects with the plane where line segments L2 and L4 are located, and the intersection line coincides with the axis of the pipeline; Step 3, measure the length of line segment S1 between A1 and B3, the length of line segment S2 between A2 and B4, the length of line segment S3 between A3 and B1, and the length of line segment S4 between A4 and B2; Step 4: Establish a three-dimensional space coordinate system with the midpoint of the vertical line segment between line segments L1 and L3 as the origin, where the X-axis points to the axial direction of the pipeline, the Y-axis points to the radial direction of the pipeline and is perpendicular to line segment L1, and the Z-axis points to the radial direction of the pipeline and is perpendicular to line segment L2: Step 5: Use the above three-dimensional space coordinate system and the measured line segment data to calculate and mark the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4; Step 6: Determine a point E on the X-axis, calculate the projections of point E on line segments L1, L2, L3 and L4, and record them as F1, F2, F3, F4 respectively; Step 7. Use the coordinates F1, F2, F3, and F4 to perform position analysis with A1, B1, A2, B2, A3, B3, A4, and B4, respectively, to obtain the position relationship between the normal mouth circle and each characteristic point in the axial direction of the pipeline.

2. A method for cutting pipe round mouth according to claim 1, characterized in that: In step 4, the method of establishing a three-dimensional space coordinate system is as follows: S11. Take four points A, B, C, and D on the plane A1A3B1B3, where A and B fall on line segment L1, C and D fall on line segment L3, and the intersection of line segments AD and BC is O; S12. Assuming that the length of line segment AO is known, then OD = AD-AO; S13, calculate the length of BO, BO = AO * BC / AD; S14, calculate the length of OC, OC = BC-BO; S15. Calculate ∠AOB using the law of cosines; S16. Calculate ∠COD using the law of cosines; S17, by ∠AOB=∠COD, obtain the equation system and solve it to obtain the length of AO; S18, line segment AB and line segment CD are parallel, and the vertical distance between them is the pipe diameter length; S19. In plane ABCD, specify the midpoint of the perpendicular line segment between line segment AB and line segment CD as the origin, establish a coordinate system in the X-axis direction, and use basic geometric principles to obtain the coordinates of A, B, C, and D; S20, using the values ​​of A2, A4, B2, B4 in the Y-axis direction being 0, and the values ​​of A1, A3, B1, B3 in the Z-axis direction being 0, the coordinates of A1, B1, A2, B2, A3, B3, A4 and B4 in the established three-dimensional space coordinate system can be obtained; Among them, the lengths of line segments L1, L2, L3, L4, S1, S2, S3, S4 and the diameter of the pipeline are known parameters for measurement.

3. A method for cutting pipe round mouth according to claim 1, characterized in that: The four points A1, A2, A3 and A4 are distributed at equal intervals along the circumferential direction.

4. A method for cutting pipe round mouth according to claim 3, characterized in that: The four points A1, A2, A3 and A4 are arranged in a clockwise direction, and point A1 is at the 12 o'clock direction.

5. A pipe round blanking method according to claim 1, characterized in that: In step 7, using the coordinates of F1, F2, F3, and F4, the position analysis can be performed with A1, B1, A2, B2, A3, B3, A4, and B4 respectively, specifically including: S111, calculating the length data of line segments A1F1, A2F2, A3F3, and A4F4, which are used for cutting the pipe orifice where the characteristic point A1 is located; S112, calculating the length data of line segments B1F1, B2F2, B3F3, and B4F4, which are used for cutting the pipe mouth circle where the characteristic point B1 is located.

6. A method for cutting pipe round mouth according to claim 1, characterized in that: The location of point E is close to either end of the pipeline.

7. A method for cutting pipe round mouth according to any one of claims 1 to 6, characterized in that: It also includes step eight, drawing the circular shape of the pipe mouth.

8. A method for cutting pipe round mouth according to claim 7, characterized in that: Features: The method also includes step nine, cutting the pipe mouth circle according to the shape and coordinate data.

9. A method for cutting pipe round ends according to any one of claims 1 to 6, characterized in that: In the step 1, A1, A2, A3, A4 and B1, B2, B3, B4 are aligned and marked respectively using the highest point principle.

10. A method for cutting pipe round ends according to any one of claims 1 to 6, characterized in that: In step six, take another point different from E on the X-axis, then calculate the projection of the end on line segments L1, L2, L3 and L4, mark the projection point, and then use the method of step seven to analyze and verify again.

Images