Elbow bisector scribing device and elbow bisector scribing method

Abstract

The application relates to the technical field of elbow wall thickness monitoring, and particularly discloses an elbow bisector line marking device and method, which comprises a reference flat plate and a marking straight rod. The upper surface of the reference flat plate is provided with marking paint; the marking straight rod is arranged on the upper surface of the reference flat plate, is perpendicular to the upper surface of the reference flat plate and is in sliding fit with the reference flat plate, and the outer peripheral wall of the marking straight rod is provided with marking paint. The two side surfaces of the elbow are respectively placed on the reference flat plate, thereby forming two lateral marking lines on the two side surfaces of the elbow; the axis of the elbow is adjusted to be parallel to the reference flat plate; the marking straight rod is moved on the reference flat plate, and the marking straight rod is kept in contact with the curved surface of the elbow, thereby drawing a back ridge line and an inner arc line on the elbow, and the back ridge line, the inner arc line and the two lateral marking lines form a four-equal-division line. The problems that a simple marking tool which lacks adaptation to nuclear power overhaul conditions and can stably reproduce a geometric reference and the precision of manual marking is difficult to guarantee are effectively solved.

Description

Technical Field

[0001] This invention relates to the field of elbow wall thickness monitoring technology, and in particular to an elbow bisector marking device and a method for elbow bisector marking. Background Technology

[0002] In the conventional island steam-water system of a nuclear power plant, pipelines are subjected to harsh conditions of high temperature, high pressure, and high-speed fluid erosion for extended periods. Among these conditions, the outer arch ridge area of ​​elbows, due to its unique hydrodynamic characteristics, is the location with the highest risk of accelerated corrosion (FAC) leading to wall thinning. Acid-accelerated corrosion gradually thins the pipeline wall, severely impacting its pressure-bearing capacity and service life. In the event of a pipeline rupture, it will cause enormous economic losses and serious social consequences.

[0003] According to the mandatory requirements of NB / T25033-2014 "Guidelines for Screening Fluid-Accelerated Corrosion-Sensitive Pipelines in Conventional Island of Pressurized Water Reactor Nuclear Power Plants," periodic gridded ultrasonic thickness measurement must be carried out on elbows. By accurately comparing the wall thickness change rate over many years, corrosion of pipelines can be detected in a timely manner, and corrosion risks can be accurately assessed, thereby ensuring the long-term safe operation of the nuclear power plant unit. In this process, ensuring that the measurement points are completely aligned during each major overhaul is crucial. If the measurement points drift, it is highly likely to lead to misjudgment of pipeline corrosion risks, thus threatening the safe and stable operation of the unit.

[0004] Currently, in nuclear power plants, the common method for thickness measurement at bends is to use the geometric ridge line (outer arch generatrix) as the 0° reference, then divide the circumference into four or eight equal parts, and select points at equal intervals along the axial direction for thickness monitoring. However, in practice, the industry mainly relies on manual visual inspection to locate the bend ridge and inner arc reference, using chalk or markers to draw lines by hand. This traditional positioning method has many drawbacks. On the one hand, the accuracy of manual operation is difficult to guarantee, and errors are prone to occur, leading to inaccurate measurement point positions. On the other hand, due to the lack of simple marking tools adapted to nuclear power plant overhaul conditions and capable of stably reproducing the geometric reference, the rigid requirements for high-precision retesting cannot be met. This makes it difficult to ensure the consistency of measurement point positions in different overhaul cycles, posing a significant challenge to accurately assessing pipeline corrosion.

[0005] Therefore, there is an urgent need for a device and method for marking bends to divide lines, in order to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a device and method for marking bisectors on elbows, in order to solve the problem that when measuring the wall thickness of elbows, there is a lack of simple marking fixtures that are suitable for nuclear power plant overhaul conditions and can stably reproduce geometric benchmarks, making it difficult to guarantee the accuracy of manual marking and prone to errors, resulting in inaccurate measurement point positions.

[0007] On one hand, the present invention provides a bend dividing line marking device, the bend dividing line marking device comprising: A reference plate, the upper surface of which is configured to accommodate an elbow, and the upper surface of which is provided with marking paint; A scribing rod is disposed on the upper surface of the reference plate. The scribing rod is perpendicular to the upper surface of the reference plate and slides with the reference plate. The outer peripheral wall of the scribing rod is provided with marking paint.

[0008] As a preferred technical solution for the bend dividing line marking device, the marking rod includes a slider and a rod portion. The slider is disposed on the upper surface of the reference plate and slides in cooperation with the reference plate. The rod portion is inserted into the slider and is perpendicular to the reference plate.

[0009] As a preferred technical solution for the bend dividing line marking device, the rod rotates relative to the slider around the axis of the rod.

[0010] As a preferred technical solution for the bend dividing line marking device, the outer peripheral wall of the rod is covered with a thin layer of flexible sponge, and the thin layer of flexible sponge absorbs marking paint.

[0011] As a preferred technical solution for the bend dividing line marking device, the thickness of the thin flexible sponge layer is h, where 2mm≤h≤3mm.

[0012] As a preferred technical solution for the elbow dividing line marking device, the reference plate includes a support layer and an adsorption layer stacked sequentially. Both the support layer and the adsorption layer are rigid structures. The adsorption layer is configured to support the elbow, and the adsorption layer adsorbs marking paint.

[0013] On the other hand, the present invention provides a method for marking equal bisectors on elbows, used to mark four equal bisectors on the periphery of the elbow, implemented by any of the elbow marking devices described above, specifically including: The elbow is placed on the reference plate, and one side of the elbow abuts against the reference plate and is coated with paint, thereby forming a lateral marking line on one side of the elbow. The elbow is rotated so that the other side of the elbow is placed on the reference plate. The other side of the elbow abuts against the reference plate and transfers paint, thereby forming another lateral marking line. Adjust the axis of the elbow to be parallel to the reference plate; The scribing rod moves on the reference plate while maintaining contact between the scribing rod and the curved surface of the bend, thereby drawing the ridge line and inner arc line on the bend.

[0014] As a preferred technical solution for the method of marking equal bisectors of elbows, adjusting the axis of the elbow to be parallel to the reference plate specifically includes: By adjusting the position of the elbow relative to the reference plate, the axis of the elbow is made parallel to the reference plate.

[0015] As a preferred technical solution for the method of marking bisectors of elbows, adjusting the position of the elbow relative to the reference plate to make the axis of the elbow parallel to the reference plate specifically includes: A level is placed on the bend section and the two straight sections of the bend. If the measurement result 'a' of the level instrument is outside the tolerance range, a shim is inserted between the bend section and the reference plate, and / or between the straight section and the reference plate, so that the measurement results of all the level instruments meet the requirements. If all the measurements 'a' from the level are within the tolerance range, the elbow position will not be adjusted.

[0016] As a preferred technical solution for the method of marking the bisectors of an elbow, before placing the level on the bend section and the two straight sections of the elbow, the reference plate is further adjusted to be in a horizontal position.

[0017] The elbow dividing line marking device and elbow dividing line marking method provided by the present invention have at least the following beneficial effects: The elbow dividing line marking device includes a reference plate and a marking rod. The upper surface of the reference plate is configured to hold the elbow, and the upper surface of the reference plate is coated with marking paint. The marking rod is set on the upper surface of the reference plate, perpendicular to the upper surface of the reference plate and slidingly engaged with the reference plate. The outer peripheral wall of the marking rod is coated with marking paint. The elbow is placed on the reference plate, with one side of the elbow abutting against the reference plate and transferring paint, thus forming a lateral marking line on one side of the elbow. The elbow is rotated so that the other side of the elbow abuts against the reference plate and transfers paint, thus forming another lateral marking line. The axis of the elbow is adjusted to be parallel to the reference plate. The marking rod moves on the reference plate while maintaining contact with the curved surface of the elbow, thus drawing a ridge line and an inner arc line on the elbow.

[0018] In nuclear power plants, where periodic grid-based ultrasonic thickness measurement is required for bends in the conventional island steam-water system pipelines, and given that current methods rely on manual marking for bend ridge and inner arc reference positioning, which is insufficient for high-precision remeasurement, a new device addresses this issue. The marking paint on the upper surface of the reference plate allows lateral markings to be transferred onto the bend's side. Rotating the bend creates two lateral markings. Simultaneously, the device adjusts the bend's axis to be parallel to the reference plate. The marking rod slides with the reference plate, and its outer wall is coated with marking paint, accurately drawing the ridge and inner arc lines during contact with the bend's curved surface. This device effectively solves the problems of insufficient accuracy in manual positioning and difficulty in stably reproducing geometric references. It stably and accurately reproduces the bend's geometric references, ensuring complete overlap of measurement points during major overhauls. This provides a reliable guarantee for accurately comparing wall thickness change rates over many years and accurately assessing pipeline corrosion risks, greatly improving the safety and stability of nuclear power plant unit operation. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the elbow dividing line marking device in an embodiment of the present invention; Figure 2 This is a flowchart of the method for marking equal division lines on elbows in an embodiment of the present invention; Figure 3 This is a flowchart of step S30 in the elbow bisector marking method in an embodiment of the present invention.

[0020] In the picture: 100. Elbow; 101. Bend section; 102. Straight section; 1. Reference plate; 11. Support layer; 12. Adsorption layer; 2. Marking rod; 21. Slider; 22. Rod section; 23. Thin flexible sponge layer. Detailed Implementation

[0021] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. The terms "first position" and "second position" refer to two different positions. Furthermore, "above," "on top of," and "over" the first feature in relation to the second feature includes the first feature directly above and diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "under," and "below" the first feature in relation to the second feature includes the first feature directly below and diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0023] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0024] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0025] like Figure 1As shown, this embodiment provides a bend dividing line marking device, which includes a reference plate 1 and a marking rod 2. The upper surface of the reference plate 1 is configured to place the bend 100, and the upper surface of the reference plate 1 is provided with marking paint. The marking rod 2 is disposed on the upper surface of the reference plate 1, and the marking rod 2 is perpendicular to the upper surface of the reference plate 1 and slides with the reference plate 1. The outer peripheral wall of the marking rod 2 is provided with marking paint. Place elbow 100 on reference plate 1, with one side of elbow 100 abutting against reference plate 1 and transferring paint, thereby forming a lateral marking line on one side of elbow 100; rotate elbow 100 so that the other side of elbow 100 is placed on reference plate 1, with the other side of elbow 100 abutting against reference plate 1 and transferring paint, thereby forming another lateral marking line; adjust the axis of elbow 100 to be parallel to reference plate 1; move scribing rod 2 on reference plate 1, while keeping scribing rod 2 in contact with the curved surface of elbow 100, thereby drawing the ridge line and inner arc line on elbow 100.

[0026] In the context of the need for periodic gridded ultrasonic tracking thickness measurement of elbow 100 in the conventional island steam-water system pipeline of a nuclear power plant, and the current reliance on manual freehand marking for the ridge and inner arc reference positioning of elbow 100 which is difficult to meet the requirements of high-precision retesting, the marking paint on the upper surface of the reference plate 1 can transfer the lateral markings on the side of elbow 100. By rotating elbow 100, two lateral markings can be formed. At the same time, it can adjust the axis of elbow 100 to be parallel to the reference plate 1. The marking rod 2 slides with the reference plate 1 and has marking paint on its outer peripheral wall. The marking rod 2 slides on the upper surface of the reference plate 1 and can contact the inner arc surface and ridge surface of elbow 100. During the movement, the ridge line and inner arc line can be accurately drawn. It effectively solves the problems of insufficient accuracy of manual positioning and difficulty in stably reproducing geometric benchmarks. It can stably and accurately reproduce the geometric benchmark of the 100 bend, ensuring that the positions of the measuring points are completely coincident during each major overhaul. This provides a reliable guarantee for accurately comparing the rate of wall thickness change over many years and accurately assessing the risk of pipeline corrosion, greatly improving the safety and stability of nuclear power plant unit operation.

[0027] The four-section line can effectively and accurately locate each position on the bend, providing a reliable basis for the accurate arrangement of measuring points in subsequent ultrasonic thickness measurement work, ensuring the consistency of measuring point positions in different overhaul cycles, thereby accurately comparing the wall thickness change rate over many years and accurately assessing the corrosion risk of the pipeline.

[0028] Optionally, the scribing rod 2 includes a slider 21 and a rod 22. The slider 21 is disposed on the upper surface of the reference plate 1 and slides in contact with the reference plate 1. The rod 22 is inserted into the slider 21 and is perpendicular to the reference plate 1. In this embodiment, the slider 21 is disposed on the upper surface of the reference plate 1 and slides in contact with the upper surface of the reference plate 1. This design allows the scribing rod 2 to move flexibly on the reference plate 1 and can be quickly adjusted according to different positions and sizes of the elbow 100. The rod 22 is inserted into the slider 21 and is perpendicular to the reference plate 1, ensuring that it maintains a precise perpendicular relationship with the reference plate 1 during movement. Therefore, when in contact with the curved surface of the elbow 100, it can accurately draw the ridge line and inner arc line on the elbow 100 along the required trajectory. This structural design effectively overcomes the shortcomings of traditional manual scribing, such as low accuracy and difficulty in stably reproducing geometric references, and greatly improves the accuracy and stability of the thickness measurement and positioning of the elbow 100.

[0029] Optionally, the rod 22 rotates relative to the slider 21 about its axis. In this embodiment, the rotatable nature of the rod 22 allows it to roll on the inner arc surface and ridge surface of the bend 100. Compared to the rod 22 not being able to rotate about its own axis, this improves the uniformity of the scribing and avoids uneven depths of the inner arc or ridge lines. It also reduces localized wear on the rod 22.

[0030] Optionally, the outer peripheral wall of the rod 22 is covered with a thin flexible sponge layer 23, which absorbs marking paint. In this embodiment, due to the unevenness and curved surface characteristics of the elbow 100, the thin flexible sponge layer 23 of the rod 22 can fit well against the surface of the elbow 100. When the rod 22 rotates around the axis and rolls to draw lines on the curved surface of the elbow 100, it can effectively buffer the contact with the elbow 100 and avoid damage to the surface of the elbow 100 due to rigid contact. At the same time, the marking paint absorbed by the sponge layer can be transferred evenly and continuously to the surface of the elbow 100. On the basis of improving the uniformity of the marking, the drawn ridge line and inner arc line are clearer and more complete, further ensuring the high precision and high quality of the marking.

[0031] Optionally, the thickness of the thin flexible sponge layer 23 is h, where 2mm ≤ h ≤ 3mm. In this embodiment, the sponge layer within this thickness range has good flexibility, enabling it to closely and naturally conform to the irregular curved surface of the elbow 100. This ensures sufficient contact with the elbow 100 surface when the rod 22 rotates around the axis and rolls to draw lines on the elbow 100 surface, effectively avoiding intermittent or uneven lines due to insufficient contact. Simultaneously, this thickness of sponge layer has a suitable ability to absorb and release marking paint. It can absorb enough marking paint to ensure clear and complete lines, and when in contact with the elbow 100, it can evenly and appropriately transfer paint onto the elbow 100 surface, resulting in uniform thickness and consistent color of the drawn ridge lines and inner arc lines.

[0032] Optionally, the value of h can be one of 2mm, 2.5mm and 3mm.

[0033] Optionally, the reference plate 1 includes a support layer 11 and an adsorption layer 12 stacked sequentially. Both the support layer 11 and the adsorption layer 12 are rigid structures. The adsorption layer 12 is configured to support the elbow 100, and it adsorbs marking paint. In this embodiment, the rigid structure of the support layer 11 provides a stable support foundation for the entire reference plate 1, ensuring that the reference plate 1 will not deform or shake during the placement of the elbow 100 and the marking operation, thus guaranteeing the stability and accuracy of the operation. The adsorption layer 12 is also a rigid structure, which can effectively support the elbow 100. Because it adsorbs marking paint, when the elbow 100 is placed on it, the marking paint can be evenly transferred to the side of the elbow 100, forming clear and accurate lateral markings.

[0034] like Figure 2 and 3 As shown, this embodiment also provides a method for marking equal bisectors on elbows, used to mark four equal bisectors on the periphery of elbow 100, implemented by the elbow equal bisector marking device in the above scheme, specifically including: S10: Place elbow 100 on reference plate 1, with one side of elbow 100 abutting against reference plate 1 and transferring paint, thereby forming a lateral marking line on one side of elbow 100.

[0035] In this step, the plane containing the axis of the elbow 100 is the reference plane, and the two sides of the reference plane are the two sides of the elbow 100. The elbow 100 is placed on the reference plate 1, and one side of the elbow 100 abuts against the reference plate 1. At this time, the marking paint on the reference plate 1 will be transferred to one side of the elbow 100, thus forming a lateral marking line on one side of the elbow 100.

[0036] S20: Rotate the elbow 100 so that the other side of the elbow 100 is placed on the reference plate 1. The other side of the elbow 100 abuts against the reference plate 1 and transfers the paint, thereby forming another lateral marking line.

[0037] In this step, the elbow 100 is inverted and placed on the reference plate 1, with the other side of the elbow 100 abutting against the reference plate 1. At this time, the marking paint on the reference plate 1 will be transferred to the other side of the elbow 100, thus forming another lateral marking line on the other side of the elbow 100.

[0038] S30: Adjust the axis of elbow 100 to be parallel to the reference plate 1.

[0039] In this step, after performing the above steps, when the axis of elbow 100 is parallel to the reference plate 1, the position and angle of elbow 100 can be accurately determined based on the reference plate 1, so that the position of the measuring point marked on elbow 100 is more accurate and standardized, avoiding deviation of the measuring point position due to the tilt or offset of elbow 100, thereby ensuring that the measuring point position is completely coincident in different overhaul cycles.

[0040] S40: The scribing rod 2 moves on the reference plate 1 while maintaining contact between the scribing rod 2 and the curved surface of the elbow 100, thereby drawing the ridge line and the inner arc line on the elbow 100.

[0041] In this embodiment, the rod 22 abuts against the inner arc surface of the elbow 100. By pushing the slider 21, the rod 22 moves across the entire inner arc surface to form an inner arc line on the inner arc surface. The rod 22 abuts against the back surface of the elbow 100. By pushing the slider 21, the rod 22 moves across the entire back surface to form a back line on the back surface.

[0042] The inner arc line, the ridge line, and the two lateral markings form the four equal division lines of the 100-degree bend.

[0043] Optionally, S30: Adjusting the axis of the elbow 100 to be parallel to the reference plate 1 specifically includes: By adjusting the position of the elbow 100 relative to the reference plate 1, the axis of the elbow 100 is made parallel to the reference plate 1.

[0044] In this step, the position of elbow 100 is adjusted by setting up adjustment structures such as pads and supports, thereby making the axis of elbow 100 parallel to the reference plate 1. Optionally, adjusting the position of the elbow 100 relative to the reference plate 1, thereby making the axis of the elbow 100 parallel to the reference plate 1, specifically includes: Optionally, S300: Adjust the reference plate 1 to be in a horizontal position.

[0045] This step is a prerequisite for subsequently adjusting the axis of the elbow 100 to be parallel to the reference plate 1 using a level.

[0046] S301: Place a level on the bend section 101 of the elbow 100 and on the two straight sections 102 respectively.

[0047] In this step, the level can measure the vertical height 'a' of the level's location.

[0048] S302: If the level measurement result 'a' is outside the tolerance range, then execute S303; otherwise, execute S304.

[0049] In this step, the tolerance range is a range. When the three measurement results 'a' are within the tolerance range, it indicates that the axis of the elbow 100 is parallel to the reference plane. If at least one measurement result 'a' is outside the tolerance range, it indicates that the axis of the elbow 100 is not parallel to the reference plane.

[0050] S303: Then, a shim is inserted between the bend section 101 and the reference plate 1, and / or between the straight section 102 and the reference plate 1, so that the measurement results of all levels meet the requirements.

[0051] In this step, this operation ensures that the axis of elbow 100 is precisely parallel to the reference plate 1, providing a stable and standard basis for subsequent measurement point positioning, ensuring that the measurement point positions are highly coincident in different overhaul cycles, and avoiding measurement point drift due to elbow 100 tilting or positional deviation.

[0052] For example, when the level of the straight section is within the tolerance range and the level of the bend section 101 is below the tolerance range, a shim can be set between the bend section 101 and the reference plate 1 to adjust the height of the bend section 101 so that the level measurement result a of the bend section 101 is within the tolerance range.

[0053] S304: The 100° elbow position is not adjusted.

[0054] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively describe all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A device for marking equidistant lines on elbows, characterized in that, include: A reference plate (1), the upper surface of which is configured to place an elbow (100), and the upper surface of which is provided with marking paint; A scribing rod (2) is disposed on the upper surface of the reference plate (1). The scribing rod (2) is perpendicular to the upper surface of the reference plate (1) and slides with the reference plate (1). The outer peripheral wall of the scribing rod (2) is provided with marking paint.

2. The bend dividing line marking device according to claim 1, characterized in that, The scribing rod (2) includes a slider (21) and a rod (22). The slider (21) is disposed on the upper surface of the reference plate (1) and slides in cooperation with the reference plate (1). The rod (22) is inserted into the slider (21) and is perpendicular to the reference plate (1).

3. The elbow dividing line marking device according to claim 2, characterized in that, The rod (22) rotates relative to the slider (21) about the axis of the rod (22).

4. The bend dividing line marking device according to claim 2, characterized in that, The outer peripheral wall of the rod (22) is covered with a thin flexible sponge layer (23), and the thin flexible sponge layer (23) adsorbs the marking paint.

5. The elbow dividing line marking device according to claim 4, characterized in that, The thickness of the thin flexible sponge layer (23) is h, where 2mm ≤ h ≤ 3mm.

6. The bend dividing line marking device according to claim 1, characterized in that, The reference plate (1) includes a support layer (11) and an adsorption layer (12) stacked in sequence. Both the support layer (11) and the adsorption layer (12) are rigid structures. The adsorption layer (12) is configured to support the elbow (100) and adsorbs marking paint.

7. A method for marking equal bisectors on a bend, used to mark equal bisectors on the perimeter of the bend (100), characterized in that, The implementation, carried out by the elbow dividing line marking device according to any one of claims 1-6, specifically includes: The elbow (100) is placed on the reference plate (1), and one side of the elbow (100) abuts against the reference plate (1) and is coated with paint, thereby forming a lateral marking line on one side of the elbow (100); Rotate the elbow (100) so that the other side of the elbow (100) is placed on the reference plate (1), and the other side of the elbow (100) abuts against the reference plate (1) and transfers paint, thereby forming another lateral marking line; Adjust the axis of the elbow (100) to be parallel to the reference plate (1); The scribing rod (2) moves on the reference plate (1) while maintaining contact between the scribing rod (2) and the curved surface of the bend (100), thereby drawing the spine line and the inner arc line on the bend (100).

8. The method for marking equal division lines on elbows according to claim 7, characterized in that, Adjusting the axis of the elbow (100) to be parallel with the reference plate (1) specifically includes: By adjusting the position of the elbow (100) relative to the reference plate (1), the axis of the elbow (100) is made parallel to the reference plate (1).

9. The method for marking equal division lines on elbows according to claim 8, characterized in that, Adjusting the position of the elbow (100) relative to the reference plate (1), thereby making the axis of the elbow (100) parallel to the reference plate (1), specifically includes: A level is placed on the bend section (101) and the two straight sections (102) of the elbow (100); If the measurement result a of the level is outside the tolerance range, a pad is inserted between the bend section (101) and the reference plate (1), and / or between the straight section (102) and the reference plate (1), so that the measurement results of all the level meet the requirements. If the measurement results a of all the levels are within the tolerance range, the position of the elbow (100) will not be adjusted.

10. The method for marking equal division lines on elbows according to claim 9, characterized in that, Before placing the level in the bend section (101) and the two straight sections (102) of the elbow (100), the reference plate (1) is adjusted to be in a horizontal position.

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