A welding demagnetization method for steel pressure pipeline

Abstract

The invention discloses a welding demagnetization method for a steel pressure pipeline, and relates to the technical field of steel pipeline welding. The method uses a demagnetization auxiliary ruler to quickly identify the original magnetic field direction and magnetic field strength of the steel pressure pipeline, thereby reducing the difficulty of welding demagnetization, and based on Ampere's law, a cable winding and energizing method of a DC welding machine is used to generate a reverse magnetic field to offset the original magnetic field of the steel pressure pipeline, thereby achieving a demagnetization effect. The welding demagnetization method provided by the invention does not require carrying large-scale special demagnetization equipment, but only requires the use of a demagnetization auxiliary ruler with a sophisticated structure and a DC welding machine that is necessary at the construction site to achieve rapid demagnetization and welding of steel pipelines, and has the advantages of simple operation, low cost and strong versatility, and effectively overcomes the defects of the prior art.

Description

Technical Field

[0001] The invention relates to the technical field of steel pipeline welding, and in particular to a welding demagnetization method for a steel pressure pipeline. Background Art

[0002] The main function of steel pressure pipelines is to transport liquid or gaseous media. At the same time, these liquid or gaseous media are generally very dangerous. Once a leak or explosion occurs, the consequences are very serious, so there are high requirements for the quality of pressure pipeline installation and inspection and maintenance. The quality of steel pressure pipeline installation and inspection and maintenance is affected by many factors, but the greatest impact is the welding quality. Generally, the quality of welded joints accounts for about 70%-80% of the quality of steel pressure pipeline installation and inspection and maintenance. The welding quality seriously affects the safety and economy of the use of steel pressure pipelines. Therefore, the welding quality must be strictly controlled during the installation and inspection and maintenance of steel pressure pipelines.

[0003] During the welding construction process of installation, inspection and maintenance of steel pressure pipelines, the steel pressure pipelines may be contaminated by magnetic equipment or tooling during manufacturing, transportation, storage or after installation and commissioning, the pipeline itself is used as a ground wire during welding, the weld is not demagnetized thoroughly after non-destructive testing with magnetic powder, and the groove is not properly polished during installation. This causes magnetic blow during welding, which causes the arc to swing strongly during the welding process and weakens the gas protection atmosphere around the arc. This affects the welding quality at the least and causes welding defects such as porosity and incomplete penetration. At worst, it causes the welding wire to stick and adsorb to the edge of the groove, or the welding arc cannot be ignited, and welding work cannot be carried out, which seriously restricts the production progress.

[0004] The Chinese patent with application number 202120200811.1 discloses a magnetic variable measurement and demagnetization device for natural gas pipeline welds, which wraps the electromagnetic wire around the side wall of the electromagnetic cylinder, inputs current through the demagnetization controller, and adds an external reverse magnetic field to the natural gas pipeline weld to suppress the original magnetic field and reduce the residual magnetic field of the magnetic weld, thereby meeting the welding requirements, and heats the natural gas pipeline weld by setting an electric heating plate to the Curie point to change its metallographic structure and demagnetize it, thereby achieving double demagnetization of the natural gas pipeline weld. However, in actual pipeline welding construction, it is not common for the pipeline to be magnetic, and most of the operations are field operations. Therefore, the above-mentioned special demagnetization device not only has the problems of large size and inconvenience in carrying, but also has the problems of high equipment cost and cumbersome operation.

[0005] Based on this, we provide a welding demagnetization method for steel pressure pipelines to solve the above problems. Summary of the invention

[0006] The invention provides a welding demagnetization method for a steel pressure pipeline, the main purpose of which is to solve the problems existing in the prior art.

[0007] The present invention adopts the following technical solution:

[0008] A welding demagnetization method for a steel pressure pipeline comprises a demagnetization auxiliary ruler, a DC welding machine and two pipelines to be welded; the demagnetization auxiliary ruler comprises a sleeve, a first magnetic column, a second magnetic column and a spring; the first magnetic column and the second magnetic column are slidably arranged at two ends of the length direction of the sleeve, and the spring is connected between the first magnetic column and the second magnetic column; the magnetic poles of the first magnetic column and the second magnetic column are in opposite directions, so that the two ends of the length direction of the demagnetization auxiliary ruler present N poles and S poles with opposite polarities; both ends of the length direction of the sleeve are provided with an observation window for observing the displacement of the first magnetic column and the second magnetic column; the welding demagnetization method comprises the following steps:

[0009] (1) using a demagnetization auxiliary ruler to determine whether a magnetic field exists in the two pipes; if no magnetic field exists, directly welding the two pipes; if a magnetic field exists, performing subsequent steps to perform demagnetization processing;

[0010] (2) Use a DC welding machine to perform preliminary spot welding on the two pipes to connect them firmly;

[0011] (3) Set the pipeline that needs to be demagnetized as the first pipeline and the pipeline that does not need to be demagnetized as the second pipeline. Adjust the direction of the demagnetization auxiliary ruler so that the magnetic pole directions at both ends are opposite to those of the first pipeline, and fix it on the wall of the second pipeline.

[0012] (4) The first magnetic column or the second magnetic column of the demagnetization auxiliary ruler senses the magnetic force of the first pipe and moves. The original magnetic field strength of the first pipe is determined based on the displacement of the first magnetic column or the second magnetic column, thereby preliminarily determining the strength of the external magnetic field;

[0013] (5) Winding the cable of the DC welding machine around the outside of the first pipe, and starting the DC welding machine to perform test welding on a pre-prepared steel test plate, thereby introducing an external magnetic field to demagnetize the first pipe. During the demagnetization process, the welding current or the number of turns of the cable is gradually adjusted until the first magnetic column or the second magnetic column of the demagnetization auxiliary ruler is reset, thereby achieving an optimal demagnetization state;

[0014] (6) Continue to maintain the optimal demagnetization state unchanged and actually weld the two pipelines.

[0015] Furthermore, the number of the DC welding machines is two, including a first welding machine and a second welding machine. In step (2), the first welding machine or the second welding machine is selected to perform preliminary spot welding on the two pipelines. In step (5), the first welding machine is used to demagnetize the first pipeline, and the magnitude of the applied magnetic force is adjusted by adjusting the magnitude of the welding current during the demagnetization process. In step (6), the demagnetization state of the first welding machine is kept unchanged, and the second welding machine is used to actually weld the first pipeline and the second pipeline with the actual current required by the welding process.

[0016] Furthermore, the number of the DC welding machine is 1. In step (5), a test welding is performed on a pre-prepared steel test plate with an actual current required by the welding process. During the test welding, the number of turns of the cable is gradually adjusted until an optimal demagnetization state is reached. In step (6), the current actual current and the number of turns of the cable are maintained, and the DC welding machine is immediately used to actually weld the two pipes.

[0017] Furthermore, in step (3), the degaussing auxiliary ruler is fixed to the pipe wall of the second pipe, and the distance between the degaussing auxiliary ruler and the groove of the first pipe is 1-2 mm.

[0018] Furthermore, in step (2), when the magnetic field is too strong to allow normal spot welding, firstly, the two pipes are fixed with the aid of an external clamp so that the two pipes meet the requirements of the assembly conditions; then, steps (3) to (5) are performed to perform demagnetization, and while maintaining the optimal demagnetization state, the two pipes are spot welded; then, the external clamp is removed, and steps (3) to (6) are repeated to perform demagnetization and actual welding.

[0019] Furthermore, both observation windows are provided with scales.

[0020] Furthermore, both ends of the sleeve are provided with a strip groove, and the first magnetic column and the second magnetic column are both fixed with a slider, which extends into the strip groove and is provided with a pointer for indicating the scale.

[0021] Furthermore, the outer side walls of the first magnetic column and the second magnetic column are provided with a plurality of guide strips; the inner side wall of the sleeve is provided with a plurality of guide grooves matched with the guide strips.

[0022] Furthermore, the sleeve includes a cylinder body and end covers, and the two end covers are respectively arranged at two ends of the cylinder body. In the reset state, the two end covers are respectively supported by the first magnetic column and the second magnetic column.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. The present invention uses a demagnetization auxiliary ruler to quickly identify the original magnetic field direction and magnetic field strength of the steel pressure pipeline, thereby reducing the difficulty of welding demagnetization operations, and based on Ampere's law, uses the cable winding and energizing method of the DC welding machine to generate a reverse magnetic field to offset the original magnetic field of the steel pressure pipeline, thereby achieving a demagnetization effect. It can be seen that the present invention does not need to carry large-scale special demagnetization equipment, but only needs to use a demagnetization auxiliary ruler with a sophisticated structure and a DC welding machine that is necessary at the construction site to achieve rapid demagnetization and welding of steel pipelines. It has the advantages of simple operation, low cost and strong versatility, and effectively overcomes the defects of the prior art.

[0025] 2. The demagnetization auxiliary ruler provided by the present invention can be applied to the welding operation of steel pressure pipelines. It can easily and quickly identify the magnetic field direction and magnetic field strength of steel pressure pipelines, thereby reducing the difficulty of welding demagnetization operations. It is also small and light, easy to carry, simple to use and low in cost, and meets the operating conditions required for steel pressure pipelines. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a structural schematic diagram of the demagnetization auxiliary ruler in the present invention.

[0027] Figure 2 It is a cross-sectional schematic diagram of the demagnetization auxiliary ruler in the present invention.

[0028] Figure 3 It is a partial cross-sectional view of the demagnetization auxiliary ruler in the present invention.

[0029] Figure 4 It is a structural schematic diagram of the guide strip and guide groove of the demagnetization auxiliary ruler in the present invention.

[0030] Figure 5 The working principle of the present invention is shown in FIG. Figure 1 .

[0031] Figure 6 The working principle of the present invention is shown in FIG. Figure 2 .

[0032] In the figure: 1, demagnetizing auxiliary ruler; 11, sleeve; 110, observation window; 111, cylinder; 112, end cover; 113, strip groove; 114, guide groove; 12, first magnetic column; 121, slider; 122, pointer; 123, guide strip; 13, second magnetic column; 14, spring; 2, first pipeline; 3, second pipeline; 4, DC welding machine; 5, steel test plate. DETAILED DESCRIPTION

[0033] The specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0034] Reference Figures 1 to 3The present invention provides a demagnetization auxiliary ruler 1 for pipeline welding, the demagnetization auxiliary ruler 1 comprises a sleeve 11, a first magnetic column 12, a second magnetic column 13 and a spring 14; the first magnetic column 12 and the second magnetic column 13 are slidably arranged at the two ends of the length direction of the sleeve 11, and a spring 14 is connected between the first magnetic column 12 and the second magnetic column 13; the magnetic poles of the first magnetic column 12 and the second magnetic column 13 are in opposite directions, so that the two ends of the length direction of the demagnetization auxiliary ruler 1 present N poles and S poles with opposite polarities; an observation window 110 is provided at both ends of the length direction of the sleeve 11 for observing the displacement of the first magnetic column 12 and the second magnetic column 13. The present invention sets a first magnetic column 12 and a second magnetic column 13 with opposite magnetic pole directions, so that the two ends of the demagnetization auxiliary ruler 1 present N poles and S poles with opposite polarities. When the two ends of the demagnetization auxiliary ruler 1 are respectively close to the magnetic object, the first magnetic column 12 or the second magnetic column 13 close to the magnetic object will be displaced based on the principle of opposite poles repelling each other. When the magnetic field of the magnetic object disappears or the magnetic field intensity decreases, the first magnetic column 12 or the second magnetic column 13 will be reset under the elastic force of the spring 14. Therefore, by observing the displacement change of the first magnetic column 12 or the second magnetic column 13 through the observation window 110, the magnetic field direction and magnetic field intensity of the magnetic object can be clearly and intuitively judged. It can be seen that the demagnetization auxiliary ruler provided by the present invention can be applied to the welding operation of steel pressure pipelines. It can easily and quickly identify the magnetic field direction and magnetic field intensity of steel pressure pipelines, thereby reducing the difficulty of welding demagnetization operation, and has the advantages of being small and light, easy to carry, simple to use and low cost, which meets the operating conditions of steel pressure pipelines.

[0035] Reference Figures 1 to 3 The sleeve 11 includes a cylinder 111 and an end cap 112. The two end caps 112 are respectively arranged at the two ends of the cylinder 111. In the reset state, the two end caps 112 respectively support the first magnetic column 12 and the second magnetic column 13. In other embodiments, the compression state of the spring can be changed so that the first magnetic column 12 and the second magnetic column 13 are at one end away from the end cap 112 in the reset state, and gradually move toward the end cap 112 after inducing the external magnetic field.

[0036] Reference Figures 1 to 3 A transparent observation window 110 is provided at both ends of the cylinder 111, and scales are provided at the two observation windows 110, thereby quantifying the displacement of the first magnetic column 12 and the second magnetic column 13, so as to easily determine the magnetic field strength.

[0037] Reference Figures 1 to 3, a strip groove 113 is provided at both ends of the cylinder 111, and a slider 121 is fixedly provided on the first magnetic column 12 and the second magnetic column 13. The slider 121 extends into the strip groove 113 and is provided with a pointer 122 for indicating the scale. The design of the strip groove 113 and the slider 121 can play a guiding role, ensuring that the first magnetic column 12 and the second magnetic column 13 move in the horizontal direction, and the design of the pointer 122 can play a more obvious indicating role, so that the staff can quickly and easily read the displacement of the first magnetic column 12 and the second magnetic column 13.

[0038] Reference Figure 4 The outer side walls of the first magnetic column 12 and the second magnetic column 13 are provided with a plurality of guide bars 123; the inner side wall of the cylinder 111 is provided with a plurality of guide grooves 114 adapted to the guide bars 123. The design of the guide bars 123 and the guide grooves 114 can also play a guiding role, ensuring that the first magnetic column 12 and the second magnetic column 13 are displaced in the horizontal direction without deflection, thereby improving the sensitivity and accuracy of the first magnetic column 12 and the second magnetic column 13 to the external magnetic field.

[0039] Reference Figures 1 to 3 As a preferred solution, the cylinder 111 and the end cover 112 are both made of transparent material, thereby eliminating the need to provide an additional transparent observation window 110 , allowing the staff to clearly and intuitively observe the displacement changes of the first magnetic column 12 and the second magnetic column 13 .

[0040] Reference Figures 1 to 6 A method for welding demagnetization of a steel pressure pipeline is described below. The method involves a demagnetization auxiliary ruler 1, a DC welding machine 4, and two pipelines to be welded, and specifically includes the following steps:

[0041] (1) Use the demagnetization auxiliary ruler 1 to determine whether there is a magnetic field between the two pipes. If there is no magnetic field, the two pipes are directly welded; if there is a magnetic field, the subsequent steps are performed to perform demagnetization.

[0042] Specifically, the demagnetization auxiliary ruler 1 is placed horizontally beside the two pipes, and the first magnetic column 12 and the second magnetic column 13 are respectively placed close to the two pipes to observe whether the first magnetic column 12 or the second magnetic column 13 is displaced. If the first magnetic column 12 and the second magnetic column 13 are not displaced, it means that there is no magnetic field in the two pipes; if the first magnetic column 12 or the second magnetic column 13 is displaced, it means that there is a magnetic field in the pipe it is close to, and at this time, the direction of the magnetic field can be quickly determined according to the magnetic pole direction of the first magnetic column 12 or the second magnetic column 13, and the magnetic field strength can be roughly determined according to the displacement of the first magnetic column 12 or the second magnetic column 13.

[0043] According to actual experience, during the welding construction of steel pressure pipelines, there are generally only two situations: first, there is no magnetic field in both pipelines; second, there is a magnetic field in one of the pipelines. Therefore, the welding demagnetization method described in this embodiment is for the situation where there is a magnetic field in one of the pipelines.

[0044] (2) Use a DC welding machine 4 to perform preliminary spot welding on the two pipes to connect and fix the two pipes. This step is to prepare for the subsequent demagnetization welding so that the two pipes can meet the assembly condition requirements, thereby ensuring the quality of the actual welding;

[0045] (3) Set the pipeline that needs to be demagnetized as the first pipeline 2, and the pipeline that does not need to be demagnetized as the second pipeline 3. Adjust the direction of the demagnetization auxiliary ruler 1 so that the magnetic pole directions at both ends are opposite to the original magnetic pole directions of the first pipeline 2, and fix it on the pipe wall of the second pipeline 3.

[0046] like Figure 5 As shown, in this embodiment, we set the left end of the original magnetic field of the first pipe 2 as the S pole and the right end as the N pole, then the left end of the degaussing auxiliary ruler 1 should be the N pole and the right end should be the S pole, so the first magnetic column 12 should face the left side. The degaussing auxiliary ruler is fixed on the wall of the second pipe 3, and the distance between the degaussing auxiliary ruler 1 and the groove of the first pipe 2 is 1-2mm, so as to ensure that the first magnetic column 12 can accurately and sensitively sense the magnetic field changes of the first pipe 2.

[0047] (4) If Figure 5 As shown, the first magnetic column 12 of the demagnetization auxiliary ruler 1 senses the magnetic field of the first pipe 2 and moves. The magnetic field strength of the first pipe 2 is judged according to the displacement of the first magnetic column 12, thereby preliminarily determining the magnetic field strength that needs to be applied.

[0048] (5) If Figure 6 As shown, the cable of the DC welding machine 4 is wound around the outside of the first pipe 2, and the DC welding machine 4 is turned on to perform test welding on the pre-prepared steel test plate 5, thereby introducing an external magnetic field to demagnetize the first pipe 2. During the demagnetization process, the welding current or the number of turns of the cable is gradually adjusted until the first magnetic column 12 of the demagnetization auxiliary ruler 1 is reset, thereby achieving the best demagnetization state.

[0049] The demagnetization principle of the present invention is: the cable is wound around a magnetic steel pressure pipe, and a DC welding machine is turned on to put it in a welding state. At this time, DC current passes through the cable. According to the principle of an energized solenoid, the cable wound around the steel pressure pipe with DC current will generate an external magnetic field, thereby offsetting the original magnetic field of the steel pressure pipe.

[0050] At present, the on-site welding of steel pressure pipelines all uses tungsten inert gas arc welding for primer. In order to protect the tungsten electrode from being burned, the DC positive pole method must be used, that is, the tungsten inert gas arc welding gun is connected to the negative pole and the pipeline is connected to the positive pole. This determines the direction of the current and therefore also determines the winding direction of the cable that generates an external reverse magnetic field.

[0051] The strength of the applied magnetic field can be adjusted by adjusting the number of turns of the cable or the output current. However, since there is only one DC welding machine in this embodiment, the actual welding process requires a suitable welding current, so the selected welding current should not be changed at will, and the strength of the applied magnetic field should be changed by changing the number of turns of the cable. Therefore, in this step, the pre-prepared steel test plate should be tested with the actual current required by the welding process, and the number of turns of the cable should be gradually adjusted during the test welding until the best demagnetization state is reached; when the first magnetic column 12 is reset, it means that the strength of the applied magnetic field and the original magnetic field strength can offset each other, and the best demagnetization state has been reached at this time.

[0052] (6) Maintaining the optimal demagnetization state, the two pipelines are actually welded. After the test welding is completed, the current actual current and the number of turns of the cable are maintained, and the two pipelines are immediately welded using the DC welding machine 4 to achieve the effect of demagnetizing and welding at the same time. The actual welding can be performed using conventional welding methods, but it must be performed under the optimal demagnetization state.

[0053] It should be noted that in step (2), when the magnetic field is too strong to allow normal spot welding, the two pipes should first be fixed with the aid of an external clamp so that the two pipes meet the assembly conditions. Then, steps (3) to (5) are performed to demagnetize the pipes, and the two pipes are spot welded while maintaining the optimal demagnetization state. Then, the external clamp is removed, and steps (3) to (6) are repeated to perform demagnetization and actual welding.

[0054] During the renovation process, the air return pipeline of a compressor plant of a certain United Petrochemical Company suffered from severe magnetic blow, and two steel pipes could not be welded normally. The above method took only 3-5 minutes from trial welding to formal welding. It can be seen that the welding demagnetization method provided in this embodiment does not require carrying large-scale special demagnetization equipment, but only requires the use of a sophisticated demagnetization auxiliary ruler 1 and a DC welding machine 4 that is necessary at the construction site to achieve rapid demagnetization and welding of steel pipes. It has the advantages of simple operation, low cost and strong versatility, and effectively overcomes the defects of the prior art.

[0055] Embodiment 2:

[0056] Reference Figures 1 to 6, which is different from the first embodiment, the present embodiment uses two DC welding machines for demagnetization welding, and the two DC welding machines include a first welding machine and a second welding machine, wherein the first welding machine is used for demagnetization and the second welding machine is used for welding. In step (2), the first welding machine or the second welding machine is arbitrarily selected to perform preliminary spot welding on the two pipelines; in step (5), the first welding machine is used to demagnetize the first pipeline 2, the cable of the first welding machine is wound around the outside of the first pipeline 2, and the first welding machine is turned on to perform trial welding on the pre-prepared steel test plate 5, thereby starting demagnetization. During the demagnetization process, the strength of the external magnetic field is preferentially adjusted by adjusting the magnitude of the welding current to achieve the best demagnetization state; in step (6), the demagnetization state of the first welding machine is kept unchanged, and the second welding machine is used to actually weld the first pipeline 2 and the second pipeline 3 with the actual current required by the welding process. In the present embodiment, the first welding machine always maintains the test welding and demagnetization state, and there is no need to frequently change the number of turns of the cable. The strength of the external magnetic field can be adjusted by adjusting the welding current, which is simpler and more convenient to operate.

[0057] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an infringement of the protection scope of the present invention.

Claims

1. A welding demagnetization method for a steel pressure pipeline, characterized in that: The invention comprises a demagnetization auxiliary ruler, a DC welding machine and two pipes to be welded; the demagnetization auxiliary ruler comprises a sleeve, a first magnetic column, a second magnetic column and a spring; the first magnetic column and the second magnetic column are slidably arranged at two ends of the sleeve in the length direction, and the spring is connected between the first magnetic column and the second magnetic column; the magnetic poles of the first magnetic column and the second magnetic column are in opposite directions, so that the two ends of the demagnetization auxiliary ruler in the length direction present N poles and S poles with opposite polarities; both ends of the sleeve in the length direction are provided with an observation window for observing the displacement of the first magnetic column and the second magnetic column; the welding demagnetization method comprises the following steps: (1) using a demagnetization auxiliary ruler to determine whether a magnetic field exists in the two pipes; if no magnetic field exists, directly welding the two pipes; if a magnetic field exists, performing subsequent steps to perform demagnetization processing; (2) Use a DC welding machine to perform preliminary spot welding on the two pipes to connect them firmly; (3) Set the pipeline that needs to be demagnetized as the first pipeline and the pipeline that does not need to be demagnetized as the second pipeline. Adjust the direction of the demagnetization auxiliary ruler so that the magnetic pole directions at both ends are opposite to those of the first pipeline, and fix it on the wall of the second pipeline. (4) The first magnetic column or the second magnetic column of the demagnetization auxiliary ruler senses the magnetic force of the first pipe and moves. The original magnetic field strength of the first pipe is determined based on the displacement of the first magnetic column or the second magnetic column, thereby preliminarily determining the strength of the external magnetic field; (5) Winding the cable of the DC welding machine around the outside of the first pipe, and starting the DC welding machine to perform test welding on a pre-prepared steel test plate, thereby introducing an external magnetic field to demagnetize the first pipe. During the demagnetization process, the welding current or the number of turns of the cable is gradually adjusted until the first magnetic column or the second magnetic column of the demagnetization auxiliary ruler is reset, thereby achieving an optimal demagnetization state; (6) Continue to maintain the optimal demagnetization state unchanged and actually weld the two pipelines.

2. A welding demagnetization method for a steel pressure pipeline as claimed in claim 1, characterized in that: There are two DC welding machines, including a first welding machine and a second welding machine. In step (2), the first welding machine or the second welding machine is selected to perform preliminary spot welding on the two pipelines. In step (5), the first welding machine is used to demagnetize the first pipeline. During the demagnetization process, the magnitude of the external magnetic force is adjusted by adjusting the magnitude of the welding current. In step (6), the demagnetization state of the first welding machine is kept unchanged, and the second welding machine is used to actually weld the first pipeline and the second pipeline with the actual current required by the welding process.

3. A welding demagnetization method for a steel pressure pipeline as claimed in claim 1, characterized in that: The number of the DC welding machine is one. In step (5), a test welding is performed on a pre-prepared steel test plate with an actual current required by the welding process. During the test welding, the number of turns of the cable is gradually adjusted until an optimal demagnetization state is reached. In step (6), the current actual current and the number of turns of the cable are maintained, and the DC welding machine is immediately used to actually weld the two pipes.

4. A welding demagnetization method for a steel pressure pipeline as claimed in claim 1, characterized in that: In step (3), the degaussing auxiliary ruler is fixed to the pipe wall of the second pipe, and the distance between the degaussing auxiliary ruler and the groove of the first pipe is 1-2 mm.

5. A welding demagnetization method for a steel pressure pipeline as claimed in claim 1, characterized in that: In step (2), when the magnetic field is too strong to allow normal spot welding, firstly, the two pipes are fixed with the aid of an external clamp so that the two pipes meet the requirements of the assembly conditions; then, steps (3) to (5) are performed to demagnetize the pipes, and while maintaining the optimal demagnetization state, the two pipes are spot welded; then, the external clamp is removed, and steps (3) to (6) are repeated to perform demagnetization and actual welding.

6. A welding demagnetization method for a steel pressure pipeline as claimed in claim 1, characterized in that: Both observation windows are provided with scales.

7. A welding demagnetization method for a steel pressure pipeline as claimed in claim 6, characterized in that: Both ends of the sleeve are provided with a strip groove, and the first magnetic column and the second magnetic column are both fixed with a slider, which extends into the strip groove and is provided with a pointer for indicating the scale.

8. A welding demagnetization method for a steel pressure pipeline as claimed in claim 1, characterized in that: The outer side walls of the first magnetic column and the second magnetic column are provided with a plurality of guide strips; the inner side wall of the sleeve is provided with a plurality of guide grooves matched with the guide strips.

9. A welding demagnetization method for a steel pressure pipeline as claimed in claim 1, characterized in that: The sleeve comprises a cylinder body and end covers, wherein two end covers are respectively arranged at two ends of the cylinder body, and in a reset state, the two end covers respectively support the first magnetic column and the second magnetic column against each other.

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