Method for controlling butt welding straightness of thick-wall stainless steel pipes

Abstract

The invention belongs to the field of nuclear power, and discloses a method for controlling butt welding straightness of a thick-wall stainless steel pipe, which comprises the following steps of: processing a welding groove of the stainless steel pipe; the machined steel pipe is assembled; spot welding and fixing; rotating the workpiece to measure the rotation jerk value of the workpiece, and recording a first displacement value; backing welding is conducted on a weld joint; repeating displacement value measurement again to obtain a second displacement value; the two displacement values are compared, and the straightness deformation direction and size after one weld joint is welded are determined; the welding starting position is adjusted to the reverse side where the welding deformation direction is determined; carrying out filling welding; and repeating the second displacement value acquisition until the stainless steel pipe is welded. A special weld groove is used, gapless assembly is performed, and a specific spot welding process is matched; according to the method, an automatic argon arc welding method is used, welding deformation of each welding seam is monitored in the welding process, and the direction of an arcing point of the next welding seam is controlled according to the current deformation direction, so that the straightness of the large-wall-thickness stainless steel pipe after butt welding is controlled.

Description

Technical Field

[0001] The invention belongs to a steel pipe welding method in the field of nuclear power, and relates to a method for controlling the straightness of thick-walled stainless steel pipes after butt welding. Background Art

[0002] Since stainless steel has the characteristics of high melting point, large thermal expansion coefficient, large heat affected zone, etc., it is very easy to cause post-weld deformation, stress concentration and other problems after welding. The thermal expansion coefficient of austenitic stainless steel is about 1.5 times that of low carbon steel. Stainless steel is more affected by thermal expansion and is more prone to deformation.

[0003] Two tube sheets of a nuclear power heat exchanger are connected by a 304 stainless steel pipe with a length of 2200mm, a diameter of 210mm and a thickness of 20mm. There are at least three joint welds on this stainless steel pipe. To ensure the smooth insertion of the heat exchange tube, the straightness error of the tube sheet shall not exceed 0.5mm.

[0004] In the nuclear power field, only mature welding methods are generally used. The butt weld of thick-walled stainless steel pipes usually uses a V-shaped groove with a single-side angle of 30°. During assembly, the groove is opened with a gap of 2-3mm, and multi-layer and multi-pass welding is performed using manual argon arc welding or arc welding.

[0005] When using the above commonly used welding grooves for assembly, the straightness of the thick-walled pipe cannot be guaranteed; the straightness deformation is large after the gap is opened for welding; at the same time, the welding speed is slow and uneven when using processes such as manual argon arc welding and arc welding, and the welding deformation cannot be effectively controlled during the multi-layer and multi-pass welding process; the final welding deformation is unpredictable, and it is impossible to manufacture a pipeline that meets the straightness requirements. Therefore, it is necessary to develop a thick-walled stainless steel pipe welding process with small deformation for this structure. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides a method for controlling the straightness of butt welding of thick-walled stainless steel pipes, which can ensure the straightness.

[0007] In order to achieve the above object, the technical solution of the present invention is to provide a method for controlling the straightness of a butt weld of a stainless steel pipe, the steps are as follows:

[0008] (1) Processing the welding groove of stainless steel pipe, the groove angle of the welding groove is 15°-30°;

[0009] (2) Tightly assemble the two stainless steel pipes obtained in step (1) and control the straightness after assembly to be within 0.1 mm;

[0010] (3) Spot welding the assembled grooves at symmetrical positions of the workpiece without adding welding wire;

[0011] (4) moving the workpiece fixed by spot welding in step (3) to an automatic welding machine, rotating the workpiece to measure its rotational runout, and recording the first displacement value;

[0012] (5) Adjust the welding head and perform base welding on the weld of the stainless steel pipe;

[0013] (6) After the base welding in step (5), step (4) is repeated again to obtain the second displacement value;

[0014] (7) Compare the first displacement value with the second displacement value to determine the straightness deformation direction and deformation magnitude of the stainless steel pipe after welding a weld;

[0015] (8) Adjust the position of the automatic welding gun so that the welding start position is adjusted to the opposite side of the welding deformation direction determined in step (7);

[0016] (9) Performing filler welding;

[0017] (10) Repeat steps (6) to (9) until the stainless steel pipe is welded;

[0018] (11) Measure the straightness of the stainless steel pipe after welding.

[0019] According to the present invention, the stainless steel pipe in step (1) is further processed to form a welding groove with a blunt edge thickness of 2 mm, a straight section of 2 mm, a fillet of R3 mm, and a groove angle of 15°, thereby facilitating the realization of a high-precision assembly weld groove.

[0020] According to the present invention, further, in the step (4), the stainless steel pipe fixed by spot welding is transferred to a horizontal automatic argon arc welding machine, one end of the stainless steel pipe is fixed, the stainless steel pipe is rotated, and the rotational runout is measured with a dial indicator at the other end of the stainless steel pipe.

[0021] According to the present invention, further, the rotational runout of a whole circle is controlled within 0.1 mm, and the first displacement values ​​measured at 0°, 60°, 120°, 180°, 240°, and 300° are obtained.

[0022] According to the present invention, further, the spot welding position of step (3) is vertical welding, the spot welding current is 60-80A, the voltage is 9-12V, and the spot welding length is 5-8mm; after one position positioning is completed, the workpiece is rotated 90° and spot welding is performed in the same way; and the welding of 8 evenly distributed positioning points is completed by analogy. The welding current is 60-80A, and the spot welding fixing process of 8 points is evenly and symmetrically spot welded without adding welding wire; a method of using fast automatic argon arc welding to obtain a more uniform welding deformation.

[0023] According to the present invention, further, the base welding in step (5) is a single-sided welding and double-sided forming welding method, and the base welding adopts a pulse welding process; wherein, the current parameter peak value: 200-240A, base value: 140-180A, voltage 10-13V, pulse frequency 4-6Hz, welding speed: 160-200mm / min.

[0024] According to the present invention, further, the filling welding in step (9) adopts a pulse welding process, and the welding parameters are peak value: 220-260A, base value: 160-200A, voltage 12-14V, pulse frequency 4-6Hz, and welding speed: 160-200mm / min.

[0025] The beneficial effects of the present invention are:

[0026] The present invention uses a special weld groove, gapless assembly, and a specific spot welding process; uses an automatic argon arc welding method, monitors the welding deformation of each weld during the welding process, and controls the arc starting point orientation of the next weld according to the current deformation orientation, thereby achieving control of the straightness of heavy-walled stainless steel pipes after butt welding.

[0027] The present invention provides a weld groove that is conducive to high-precision assembly;

[0028] The present invention provides a spot welding fixing process which is beneficial to preventing welding deformation;

[0029] According to the fast backing welding process provided by the present invention, with the corresponding groove, backing welding of single-sided welding and double-sided forming of stainless steel material can be realized, with low welding difficulty and small weld deformation;

[0030] The present invention provides a method for quickly and effectively monitoring welding deformation using a dial indicator;

[0031] According to the process provided by the present invention, the welding starting position is adjusted by the deformation direction, thereby effectively correcting the deformation during the welding process, and the straightness error of the thick-walled stainless steel pipe after butt welding can be effectively controlled. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the stainless steel groove and assembly dimensions of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0034] See also Figure 1 , which is a schematic diagram of the stainless steel groove and assembly dimensions of the present invention; a method for controlling the straightness of a stainless steel pipe butt weld disclosed in an embodiment of the present application, wherein the welding steps are as follows:

[0035] (1) Process the stainless steel pipe with a blunt edge thickness of 2 mm, a straight section of 2 mm, a fillet of R3 mm, and a welding groove angle of 15°;

[0036] (2) Tightly assemble two stainless steel pipes with grooves processed, and control the straightness after assembly to within 0.1 mm;

[0037] (3) Spot welding is performed on the assembled grooves at the symmetrical positions of the workpieces without adding welding wire. The spot welding position is vertical welding, the spot welding current is 60-80A, the voltage is 9-12V, and the spot welding length is 5-8mm. After one position positioning is completed, the workpiece is rotated 90° and spot welding is performed in the same way. Similarly, welding is completed at 8 evenly distributed positioning points.

[0038] (4) Transfer the spot-welded stainless steel pipe to a horizontal automatic argon arc welding machine, fix one end of the stainless steel pipe with a chuck, rotate the stainless steel pipe, and measure the rotation runout with a dial indicator at the other end of the stainless steel pipe; wherein a visual sensor can also be used to monitor the rotation runout signal of the stainless steel pipe, and the value is fed back to a display system;

[0039] (5) Adjust the clamping mechanism so that the full circle runout is within 0.1 mm, and record the displacement values ​​measured by the dial indicator at 0°, 60°, 120°, 180°, 240°, and 300°;

[0040] (6) Adjust the welding head, perform single-sided welding and double-sided forming base welding on the weld of the stainless steel pipe, the base welding adopts pulse welding process, and uses a faster welding speed to achieve smaller and more uniform deformation by reducing the heat input; wherein, the current parameter peak value: 200-240A, base value: 140-180A, voltage 10-13V, pulse frequency 4-6Hz, welding speed: 160-200mm / min;

[0041] (7) After a full circle of welding is completed, the stainless steel pipe is rotated again and the displacement values ​​measured by the dial indicator in the six directions in step (5) are recorded;

[0042] (8) Compare the displacement data before and after welding in the six directions in step (7) and step (5) to determine the straightness deformation direction and deformation magnitude of the stainless steel pipe after welding a weld;

[0043] (9) Adjust the position of the automatic argon arc welding gun and adjust the welding start position to the opposite side of the welding deformation direction determined in step (8) (i.e., rotate 180°);

[0044] (10) Performing filler welding, which also uses a pulse welding process and a faster welding speed to achieve smaller and more uniform deformation by reducing the heat input; wherein the welding parameters are peak value: 220-260A, base value: 160-200A, voltage 12-14V, pulse frequency 4-6Hz, and welding speed: 160-200mm / min;

[0045] (11) Repeat steps (7) to (10) until the stainless steel pipe is welded;

[0046] (12) Measure the straightness of the stainless steel pipe after welding.

[0047] The above is only a preferred embodiment of the present invention, and is not any formal or substantial limitation of the present invention. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the present invention, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any technician familiar with this profession, without departing from the spirit and scope of the present invention, can make some changes, modifications and equivalent changes made by using the technical content disclosed above, which are equivalent embodiments of the present invention; at the same time, any changes, modifications and evolutions of any equivalent changes made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for controlling the straightness of a stainless steel pipe butt weld, characterized in that: Here are the steps: (1) Processing the welding groove of stainless steel pipe, the groove angle of the welding groove is 15°-30°; (2) Tightly assemble the two stainless steel pipes obtained in step (1) and control the straightness after assembly to be within 0.1 mm; (3) Spot welding the assembled groove at the symmetrical position of the workpiece without adding welding wire; (4) moving the workpiece fixed by spot welding in step (3) to an automatic welding machine, rotating the workpiece to measure its rotational runout, and recording the first displacement value; (5) Adjust the welding head and perform base welding on the weld of the stainless steel pipe; (6) After the base welding in step (5), step (4) is repeated again to obtain the second displacement value; (7) Compare the first displacement value with the second displacement value to determine the straightness deformation direction and deformation magnitude of the stainless steel pipe after welding a weld; (8) Adjust the position of the automatic welding gun so that the welding start position is adjusted to the opposite side of the welding deformation direction determined in step (7); (9) Performing filler welding; (10) Repeat steps (6) to (9) until the stainless steel pipe is welded; (11) Measure the straightness of the stainless steel pipe after welding.

2. A method for controlling the straightness of a stainless steel pipe butt weld according to claim 1, characterized in that: The stainless steel pipe in step (1) is processed to form a welding groove with a blunt edge thickness of 2 mm, a straight section of 2 mm, a rounded corner R of 3 mm, and a groove angle of 15°.

3. A method for controlling the straightness of a stainless steel pipe butt weld according to claim 1, characterized in that: In the step (4), the spot-welded stainless steel pipe is transferred to a horizontal automatic argon arc welding machine, one end of the stainless steel pipe is fixed, the stainless steel pipe is rotated, and the rotational runout is measured with a dial indicator at the other end of the stainless steel pipe.

4. A method for controlling the straightness of a stainless steel pipe butt weld as claimed in claim 3, characterized in that: The rotational runout of the entire circle is controlled within 0.1 mm, and the first displacement values ​​measured at 0°, 60°, 120°, 180°, 240°, and 300° are obtained.

5. A method for controlling the straightness of a stainless steel pipe butt weld according to claim 1, characterized in that: The spot welding position of step (3) is vertical welding, the spot welding current is 60-80A, the voltage is 9-12V, and the spot welding length is 5-8mm; after one position positioning is completed, the workpiece is rotated 90° and spot welding is performed in the same manner; and the welding of 8 evenly distributed positioning points is completed in the same manner.

6. A method for controlling the straightness of a stainless steel pipe butt weld according to claim 1, characterized in that: The base welding in step (5) is a single-sided welding and double-sided forming welding method, and the base welding adopts a pulse welding process; wherein, the current parameter peak value is: 200-240A, the base value is: 140-180A, the voltage is 10-13V, the pulse frequency is 4-6Hz, and the welding speed is: 160-200mm / min.

7. A method for controlling the straightness of a stainless steel pipe butt weld according to claim 1, characterized in that: The filling welding in step (9) adopts a pulse welding process, and the welding parameters are peak value: 220-260A, base value: 160-200A, voltage 12-14V, pulse frequency 4-6Hz, and welding speed: 160-200mm / min.

Images