A welding backshield tool and a welding backshield method

Abstract

The application discloses a kind of welding back protection tool and welding back protection method, it is related to welding auxiliary device field, protection tool is used for pipeline welding, including air extraction device and the pedestal with round plate at both ends, with protection space between two the round plate;The outer wall of the round plate is sleeved with the outward annular air bag that can produce deformation;Two end faces of the round plate are slidably connected with support plate, the sliding direction of the support plate is along the radial direction of round plate, and outward annular air bag is located between support plate, to realize the outward annular air bag with support plate along the radial direction of round plate sliding;The air inlet of the air extraction device is communicated with protection space, and the air outlet of the air extraction device is communicated with outward annular air bag;One-way valve is arranged between the air extraction device and outward annular air bag.The application can greatly reduce welding back protection cost, ensure that the sealing space at welding back is sealed stably, improve the application range of tool.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of welding auxiliary device, in particular to a welding back protection tool and a welding back protection method. BACKGROUND

[0002] When welding pipes, especially when building oil and gas pipelines, the butt weld of two single pipes is usually welded by tungsten inert gas welding or hot wire TIG welding. In order to prevent the oxidation of the back of the weld and the occurrence of harmful defects in the weld metal structure, inert gas insulation or air replacement protection measures are needed for the back of the weld.

[0003] The current method is as described above, which usually uses inert gas to replace the oxygen-containing air at the back of the weld. For example, the Chinese utility model patent with publication number CN206216096U discloses a welding back gas protection device, which seals the butt welding position by two soft circular plates and introduces inert gas into the sealed space to replace the oxygen-containing air in the sealed space, so as to protect the back of the weld from being oxidized. However, in practice, inert gas is usually obtained from air, and the main gas component in air is nitrogen, so the content of inert gas is low and the cost of preparation is high. Therefore, the cost of using inert gas to replace the oxygen-containing air at the welding position to protect the back of the weld from being oxidized is high. Moreover, when a large amount of inert gas is filled into the sealed space at the back of the weld, the internal pressure increases, which can easily cause the position of the sealing components (such as the soft circular plates in CN206216096U) at both ends of the sealed space to deviate, resulting in sealing failure and oxidation of the back of the weld. Finally, when forming a sealed space at the back of the weld, the tool can only be used for pipes of corresponding size after the design size of the protection tool is determined, so the application range is low. SUMMARY

[0004] The present application aims to provide a welding back protection tool and a welding back protection method, which can greatly reduce the cost of welding back protection, ensure the sealing stability of the sealed space at the back of the weld, and improve the application range of the tool.

[0005] The technical scheme adopted by the present application is as follows: a back surface protection tool for pipe welding, comprising an air extraction device and a base with circular plates at two ends, and a protection space between the two circular plates; an outward annular air bag capable of deforming is sleeved on the outer wall of the circular plate; a support plate is slidably connected to each end surface of the circular plate, the sliding direction of the support plate is along the radial direction of the circular plate, and the outward annular air bag is located between the support plates, so that the outward annular air bag slides along the radial direction of the circular plate with the support plates; the air inlet end of the air extraction device is communicated with the protection space, and the air outlet end of the air extraction device is communicated with the outward annular air bag; a one-way valve is arranged between the air extraction device and the outward annular air bag.

[0006] Further, a plurality of sliding grooves are arranged on the two end surfaces of the circular plate, the support plates are slidably connected with the sliding grooves, the sliding direction of the sliding grooves is along the radial direction of the circular plate, and the plurality of sliding grooves are uniformly distributed.

[0007] Further, the cross section of the sliding groove is dovetail-shaped, and the shape of the connection position of the support plate with the sliding groove matches the shape of the sliding groove.

[0008] Further, a sealing groove is arranged on the side surface of the support plate, and the sealing grooves on the support plates connected to the same end surface of the circular plate are nested in the same sealing ring, and the sealing ring has a deforming ability.

[0009] Further, a branch air pipe is communicated between the two outward annular air bags, the air outlet end of the air extraction device is connected with the branch air pipe through the main air pipe, and the one-way valve is arranged on the main air pipe.

[0010] Further, an exhaust pipe is connected to the branch air pipe, and an exhaust valve is arranged on the exhaust pipe.

[0011] Further, a hand holding rod is fixed to one end of the base, the exhaust pipe passes through the hand holding rod, and the exhaust pipe is arranged outside the hand holding rod.

[0012] Further, a support rod is arranged between the support plates in the protection space, and the support rod is parallel to the axis of the circular disc; or / and further comprising a welding auxiliary tool capable of reducing the pressure at the position corresponding to the welding front surface of the protection space, the welding auxiliary tool comprising two mutually parallel inward annular air bags and an air extraction device, a high-strength cylinder is fixed between the two inward annular air bags, and the outer sides of the two inward annular air bags are fixedly connected with the inner wall of the cylinder, and a welding space is formed between the cylinder and the two inward annular air bags; the air inlet end of the air extraction device is communicated with the welding space, the air outlet end of the air extraction device is communicated with the inward annular air bags, and a one-way valve is arranged between the air extraction device and the inward annular air bags.

[0013] Further, an oxygen concentration measurer is arranged on the base and located in the protection space.

[0014] A welding back face protection method using the protection tool comprises the following steps:

[0015] S1: placing the protection tool into the pipe so that the welding back face is located in the protection space;

[0016] S2: starting the air pumping device to pump the air in the protection space to the outward annular air bag at two ends of the base and / or the protection space;

[0017] S3: increasing the pressure in the outward annular air bag, increasing the volume, and tightly adhering the outward annular air bag to the inner wall of the pipe to seal the protection space;

[0018] S4: under the actions of S2 and S3, no oxygen or low-concentration oxygen exists in the protection space, so that the metal of the welding back face is not oxidized, and the protection of the welding back face is realized.

[0019] As described above, the present application has the following advantages:

[0020] 1. The present application provides a new idea for welding back face protection, which is to pump the oxygen-containing air at the welding back face to reduce or eliminate oxygen, so as to avoid the oxidation of the metal of the welding back face and achieve the purpose of protecting the welding back face;

[0021] 2. The present application does not need to introduce a large amount of inert gas into the protection space to replace the oxygen-containing air in the protection space, thereby reducing the production or purchase cost of inert gas, further reducing the protection cost of the welding back face, and improving the efficiency;

[0022] 3. The present application can expand the outward annular air bag by air pressure while pumping the protection space at the welding back face position, so that the outward annular air bag tightly adheres to the inner wall of the pipe to achieve the purpose of sealing the protection space, ensure the sealing of the protection space, and keep the protection space in an oxygen-free or low-oxygen state, thereby improving the protection quality of the welding back face;

[0023] 4. The present application can adapt to pipes with different diameters by sliding the outward annular air bag and the support plate radially outward along the circular plate, thereby improving the application range of the tool. BRIEF DESCRIPTION OF DRAWINGS

[0024] The present application will be described by examples and with reference to the accompanying drawings, in which:

[0025] Figure 1 Fig. 1 is a structural schematic view of the protection tool disclosed by the present application;

[0026] Figure 2A connection diagram of the circular plate and the supporting block disclosed in the present application;

[0027] Figure 3 A connection diagram of the circular plate and the supporting block disclosed in the present application; Figure 1 An enlarged diagram of A in the middle;

[0028] Figure 4 A connection diagram of the outward annular air bag and the supporting plate disclosed in the present application;

[0029] Figure 5 A structure diagram of the welding auxiliary tool disclosed in the present application;

[0030] Figure 6 A structure diagram of the welding auxiliary tool disclosed in the present application;

[0031] Markings in the figure: 1-base; 11-circular plate; 111-sliding groove; 112-supporting plate; 12-outward annular air bag; 13-sealing ring; 14-supporting rod; 15-protection space; 2-welding auxiliary tool; 21-inward annular air bag; 22-cylinder; 23-welding space; 3-pumping device; 31-one-way valve; 32-branch air pipe; 33-main air pipe; 4-oxygen concentration measurer; 6-exhaust pipe; 5-handheld rod; 7-exhaust valve; 8-restraint rope; 9-pipe. DETAILED DESCRIPTION

[0032] All features disclosed in this specification, and / or all steps of any methods or processes disclosed, can be combined in any combination, except combinations where at least some of the features and / or steps are mutually exclusive.

[0033] Any feature disclosed in this specification, unless stated otherwise, can be replaced by any other feature serving the same, or a similar, purpose.

[0034] Embodiment 1

[0035] As Figures 1-6As shown, a back welding protection tool for pipe 9 welding, comprising an air extractor 3 and a base 1, the base 1 comprises a connecting rod and two circular plates 11, the two circular plates 11 are respectively fixedly connected to the two ends of the connecting rod, the circumferential cross-sectional area of the two circular plates 11 is larger than the cross-sectional area of the connecting rod, so that the two circular plates 11 have a protection space 15 between them, and the back welding is located in the protection space 15 during use; the outer wall of the circular plate 11 is sleeved with an outward annular air bag 12, the outward annular air bag 12 is made of rubber material which can be elastically deformed, and the outward annular air bag 12 can be inflated and enlarged when pressure air is filled into the outward annular air bag 12; eight support plates 112 are slidably connected to the two end faces of the circular plate 11, the sliding direction of the eight support plates 112 is along the radial direction of the circular plate 11, and the outward annular air bag 12 is located between the support plates 112, so as to realize that the outward annular air bag 12 carries the support plates 112 and slides outward along the radial direction of the circular plate 11; the air inlet end of the air extractor 3 is communicated with the protection space 15, and the air outlet end of the air extractor 3 is communicated with the outward annular air bag 12; a one-way valve 31 is arranged between the air extractor 3 and the outward annular air bag 12, and the one-way valve 31 only allows air to enter the outward annular air bag 12 from the air extractor 3.

[0036] In this embodiment, the specific working mode for pipe 9 welding is as follows:

[0037] The air extractor 3 extracts the oxygen-containing air in the protection space 15 into the outward annular air bag 12, the outward annular air bag 12 has pressure air, so that the outward annular air bag 12 inflates, and due to the constraint of the support plates 112, the outward annular air bag 12 can only inflate along the radial direction of the circular plate 11, so that the support plates 112 slide outward along the radial direction of the circular plate 11 under the carrying of the outward annular air bag 12, until the support plates 112 and the outer wall of the outward annular air bag 12 are tightly attached to the inner wall of the pipe 9, thereby isolating the two sides of the outward annular air bag 12 and further isolating the protection space 15; after the oxygen-containing air in the protection space 15 is exhausted by the air extractor 3, when the pipe 9 is welded, there is almost no oxygen at the back welding position, thereby avoiding the oxidation of the metal at the back welding position, achieving the purpose of protecting the back welding position; it is not necessary to introduce a large amount of inert gas into the protection space 15 to replace the oxygen-containing air in the protection space 15, thereby reducing the production or purchase cost of inert gas, further reducing the protection cost of the back welding position, and improving the efficiency; it is suitable for pipes 9 of different diameters, and the application range of the tool is improved.

[0038] It should be noted that the support plates 112 can move along the radial direction of the circular plate 11, and in this embodiment, at least the following effects exist:

[0039] The two end faces of the outward annular airbag 12 can always be constrained so that the outward annular airbag 12 can maintain deformation in the free direction of the outside (radial direction of the circular plate 11), thereby achieving the purpose of adapting to the application of various pipe diameters and sealing the protective space 15 under the action of air pressure.

[0040] Furthermore, in this embodiment, regarding the connection between the outward annular airbag 12 and the support plate 112, there are several implementation methods as follows.

[0041] like Figure 1 As shown, a first feasible embodiment is provided in which a friction layer for increasing friction is provided on the surface of the support plate 112 that contacts the outward annular airbag 12. When pressurized air exists inside the outward annular airbag 12, the friction between the outer surface of the outward annular airbag 12 and the support plate 112 increases with the increase of pressure, thereby causing the outward annular airbag 12 to move along the radial direction of the circular plate 11 under the action of the high friction force between the support plate 112 and the outward annular airbag 12.

[0042] like Figure 4 As shown, a second feasible embodiment is provided with a restraint rope 8 between adjacent support plates 112 connected on the two end faces of the same circular plate 11, and both ends of the restraint rope 8 are fixedly connected to the support plate 112. The restraint rope 8 is located on the outside of the outward annular airbag 12 and crosses the outward annular airbag 12 along the radial direction of the outward annular airbag 12, that is, the restraint rope 8 restrains the outward annular airbag 12; when the outward annular airbag 12 expands, it pushes the restraint rope 8 to diffuse around the circular plate 11, and the restraint rope 8 carries the support plate 112, thereby realizing that the outward annular airbag 12 carrier supports movement along the radial direction of the circular plate 11.

[0043] In this embodiment, the side surface of the support plate 112 can be configured to be arc-shaped to reduce the travel gap when the side surface of the support plate 112 contacts the inner wall of the pipe 9 .

[0044] In this embodiment, the air extraction device 3 can be a gas transportation power device such as an air pump.

[0045] Example 2

[0046] like Figures 1-2 、 Figure 4 As shown, based on any one of the implementation methods in Example 1, a feasible specific implementation method is further proposed.

[0047] A feasible embodiment is that, in order to realize the sliding connection between the support plates 112 and the circular plate 11, eight sliding grooves 111 are arranged on each end face of the circular plate 11, and the support plates 112 are in sliding connection with the sliding grooves 111; the stroke direction of the sliding grooves 111 is along the radial direction of the circular plate 11, and a plurality of sliding grooves 111 are uniformly distributed, so as to realize that the sliding direction of the support plates 112 is along the radial direction of the circular plate 11; the uniform distribution can satisfy that the support force distribution of the support plates 112 is uniform, and satisfy that the outward annular air bag 12 is uniformly deformed under the action of air pressure.

[0048] Further, in the above embodiment, under the condition that space permits, the more the number of the support plates 112 is, the better; the more the support plates 112 are, the more dense the arrangement of the support plates 112 is, and the better the constraint ability and constraint effect of the support plates 112 to the two end faces of the outward annular air bag 12 are; the constraint effect mainly reflects that the outward annular air bag 12 is constrained from deforming along the radial direction.

[0049] A feasible embodiment is that the cross section of the sliding groove 111 is dovetail-shaped, and the shape of the position on the support plate 112 where the sliding groove 111 is connected is matched with the shape of the sliding groove 111, so as to enable the sliding groove 111 to constrain the support plate 112, avoid the support plate 112 from being separated from the sliding groove 111 in the direction perpendicular to the stroke direction of the sliding groove 111, and enable the support plate 112 to only slide along the radial direction of the circular plate 11.

[0050] A feasible embodiment is that, when the support plate 112 is in contact with the inner wall of the pipeline 9, there will inevitably be a gap between the support plate 112 and the inner wall of the pipeline 9; although the outward annular air bag 12 can be tightly pressed against the inner wall of the pipeline 9 after expansion to form a seal, in order to further ensure the stability of the sealing performance, a sealing groove is arranged on the side surface of the support plate 112, and the sealing grooves on the support plates 112 connected to the same end face of the circular plate 11 are nested in the same sealing ring 13, and the sealing ring 13 has a deformation ability; as the support plate 112 moves along the radial direction of the circular plate 11 and outwardly, the support plate 112 can tightly press the sealing ring 13 against the inner wall of the pipeline 9, so that the sealing ring 13 fills the gap between the support plate 112 and the inner wall of the pipeline 9, and further seals the space 15; the sealing of the sealing ring 13 and the sealing of the outward annular air bag 12 realize double sealing.

[0051] It should be noted that the sealing ring 13 does not constrain the movement of the support plate 112, and the effect is due to the fact that the sealing ring 13 can be deformed; thus, in the embodiment, the sealing ring 13 is preferably elastic rubber.

[0052] Embodiment 3

[0053] As Figure 1 , Figure 3 ,Figure 4 On the basis of any one of the embodiments 1-2, further feasible specific embodiments are proposed.

[0054] In a feasible specific embodiment, the gas pressures in the two outward annular air bags 12 are equal, so that the two outward annular air bags 12 expand to the same extent, so that the axes of the two outward annular air bags 12 (or the circular plate 11) are collinear with the axis of the pipeline 9, and this effect is due to the fact that the two outward annular air bags 12 are kept in communication through the branch air pipe 32, the gas outlet end of the air extraction device 3 is connected with the branch air pipe 32 through the main air pipe 33, and the one-way valve 31 is arranged on the main air pipe 33. The one-way valve 31 controls the flow direction of the gas in the main air pipe 33, thereby avoiding the backflow of the gas in the outward annular air bag 12 to the protection space 15, and ensuring that the protection space 15 remains in an oxygen-free state during welding.

[0055] As shown in Figure 3 In a feasible specific embodiment, the exhaust pipe 6 is connected to the branch air pipe 32, and the exhaust valve 7 is arranged on the exhaust pipe 6. The exhaust valve 7 is in a normally closed state during use. After the welding is completed, the exhaust valve 7 is opened, and the pressure gas in the outward annular air bag 12 flows out from the exhaust valve 7 through the branch air pipe 32 and the exhaust pipe 6. There is no pressure gas acting on the outward annular air bag 12, the outward annular air bag 12 returns to the deformed state, and the support plate 112 is reset. Therefore, the device can be easily detached from the protection position, and the device can be repeatedly used.

[0056] In a feasible specific embodiment, the hand-held rod 5 is fixed to one end of the base 1, and the exhaust pipe 6 passes through the hand-held rod 5 and is arranged outside the hand-held rod 5. The hand-held rod 5 is arranged to facilitate the operator to put the protection tool into the pipeline 9 and to extract the protection tool from the pipeline 9. The exhaust valve 7 is arranged outside the hand-held rod 5 to facilitate the operator to operate the exhaust valve 7.

[0057] Embodiment 4

[0058] As shown in Figures 1-6 On the basis of any one of the embodiments 1-3, further feasible specific embodiments are proposed.

[0059] In a feasible specific embodiment, the support rods 14 are arranged between the support plates 112 in the protection space 15, and the two ends of each support rod 14 are connected with the support plates 112. The support rods 14 are parallel to the axis of the circular plate.

[0060] Specifically, the support rod 14 is parallel to the axis of the disc in the initial state. Since the two outward annular airbags 12 described in Example 3 are connected through the bronchus 32, the pressure in the two outward annular airbags 12 is the same, and the degree of expansion and deformation of the outward annular airbags 12 is the same, so that the relative position between the support plates 112 remains unchanged, that is, the support rod 14 can always remain parallel to the axis of the disc, so that the support rod 14 can be close to the inner wall of the pipe 9 under the action of the support plate 112, so that the welding position can be supported by the support rod 14 on all sides (the supporting force of the support rod 14 comes from the support plate 112, and the reason why the support plate 112 can play a supporting role is due to the expansion and deformation of the outward annular airbags 12). The support rod 14 supports the back side of the weld, which can reduce the deformation of the back side of the weld caused by factors such as pressure difference and thermal expansion, and maintain the original shape of the pipe 9 as much as possible.

[0061] It should be noted that since the pressure in the protective space 15 is extremely low during welding, the pipeline 9 with sufficient strength can resist the pressure difference by itself or with the assistance of the support rod 14; for the pipeline 9 with insufficient strength, welding can also be performed with the cooperation of the welding auxiliary tool 2.

[0062] like Figures 5-6 As shown, a welding auxiliary tool 2 includes two mutually parallel inward annular airbags 21 and an air extraction device, a high-strength cylinder 22 is fixed between the two inward annular airbags 21, and the outer sides of the two inward annular airbags 21 are fixedly connected to the inner wall of the cylinder 22, and a welding space 23 is formed between the cylinder 22 and the two inward annular airbags 21; the air inlet end of the air extraction device is connected to the welding space 23, and the air outlet end of the air extraction device is connected to the inward annular airbags 21, and a space 23 is formed between the air extraction device and the inward annular airbags 21. A one-way valve 31 is provided; when in use, the pipe 9 passes through the two inward annular airbags 21, and the air extraction device draws the air in the welding space 23 into the inward annular airbags 21, and the inward annular airbags 21 expand. On the one hand, the expanded annular airbags support the cylinder 22 so that the welding space 23 has operating space. On the other hand, under its own constraints, the inward annular airbags 21 are pressed tightly against the outer surface of the pipe 9 to form a seal, so that the welding space 23 maintains a low pressure state, thereby reducing the pressure difference between the front and back of the welding position, and reducing the damage to the welding position caused by the pressure difference.

[0063] It should be noted that when using the welding auxiliary tool 2, the high-strength cylinder 22 withstands atmospheric pressure, avoiding the pressure difference at the welding position, thereby reducing the adverse effects of the pressure difference at the welding position on the pipeline 9; and, the inward annular airbag 21 expands under the action of the pressurized gas, and the contact area with the pipeline 9 is much larger than the area of ​​the welding position. According to the pressure-pressure formula, the pressure on the pipeline 9 can be greatly reduced.

[0064] Furthermore, the two inward annular airbags 21 may also be connected via an air conduit to ensure that the pressures in the two inward annular airbags 21 are the same.

[0065] Furthermore, the air conduit is connected to an exhaust valve 7 , which can release the gas pressure in the inward annular airbag 21 after welding is completed, thereby facilitating the disassembly of the welding auxiliary tool 2 .

[0066] Furthermore, a glove hole is opened on the cylinder 22, and a glove is sealedly connected to the glove hole. The glove is inserted into the welding position. Before use, the welding tool can be placed in the welding space 23, and then the operator can perform the welding operation. The purpose of providing the glove and sealing the connection is, on the one hand, to facilitate the operator to perform the welding operation and ensure the sealing performance of the welding space 23; on the other hand, it can also prevent the splashing of materials generated during the welding operation from causing damage to the operator's hands.

[0067] In this embodiment, the upper surface of the support rod 14 used can be covered with aluminum foil. Under oxygen conditions, the aluminum foil is oxidized first before the material of the pipe 9. Therefore, even if there is extremely low oxygen in the protection space 15, the oxygen can be oxidized first with the aluminum foil, thereby avoiding the oxidation of the pipe on the back side of the weld, thereby achieving the purpose of protecting the back side of the weld.

[0068] Example 5

[0069] like Figure 1 、 Figure 4 、 Figure 6 As shown, based on any one of the implementation methods in Examples 1-4, a feasible specific implementation method is further proposed.

[0070] An oxygen concentration meter 4 is provided on the base 1 and is located in the protective space 15. The oxygen concentration meter 4 can measure the oxygen concentration in the protective space 15 and play a monitoring role. The oxygen concentration meter 4 is connected to a controller via a wireless signal or a wired signal. The controller can be a PC, so that the operator can easily obtain oxygen concentration data.

[0071] Example 6

[0072] like Figures 1-6 As shown, a method for protecting the back side of welding, using any one of the protection tools described in Examples 1-5, comprises the following steps:

[0073] S1: Place the protection tool into the pipe 9 by holding the rod 5 so that the back of the weld is located in the protection space 15;

[0074] S2: Start the air extraction device 3 to transport the air in the protection space 15 into the outward annular airbag 12;

[0075] S21: At the same time as step S2, for the insufficient strength pipeline 9, the welding auxiliary tool 2 is used, the pipeline 9 is passed through the welding auxiliary tool 2, so that the welding position is located in the welding space 23, the air in the welding space 23 enters the inward annular air bag 21, the inward annular air bag 21 is inflated under the action of the pressure gas, the inner ring of the inward annular air bag 21 is tightly attached to the outer wall of the pipeline 9 to form a seal, and the high-strength cylinder 22 bears the atmospheric pressure, so that the pressure difference borne by the welding position is avoided, and the adverse effect of the pressure difference of the welding position on the pipeline 9 is reduced;

[0076] S3: The pressure in the outward annular air bag 12 is increased, the volume is increased along the radial direction of the circular plate 11 under the constraint of the support plate 112, and the outward annular air bag 12 is tightly attached to the inner wall of the pipeline 9 to complete the sealing of the protection space 15;

[0077] S4: Under the action of steps S2 and S3, there is no oxygen or low-concentration oxygen in the protection space 15, so that the metal on the back of the welding does not oxidize, and the protection of the back of the welding can be realized.

[0078] The present application is not limited to the foregoing specific embodiments. The present application extends to any novel one, or any new combination, of the characteristics disclosed in this specification, as well as to any novel method or process disclosed in any step or any new combination.

Claims

1. A tool for welding back protection, characterized by: Used for welding pipelines (9), comprising an exhaust device (3) and a base (1) with circular plates (11) at both ends, wherein a protective space (15) is provided between the two circular plates (11); an outward annular airbag (12) capable of generating deformation is sleeved on the outer wall of the circular plate (11); support plates (112) are slidably connected to both end faces of the circular plate (11), the sliding direction of the support plates (112) is along the radial direction of the circular plate (11), and the outward annular airbag (12) is located between the support plates (112) so as to enable the outward annular airbag (12) to slide along the radial direction of the circular plate (11); the air inlet end of the exhaust device (3) is connected to the protective space (15), and the air outlet end of the exhaust device (3) is connected to the outward annular airbag (12); a one-way valve (31) is provided between the exhaust device (3) and the outward annular airbag (12).

2. The back protection tool for welding according to claim 1, characterized in that: Both end surfaces of the circular plate (11) are provided with a plurality of sliding grooves (111), and the support plate (112) is slidably connected to the sliding grooves (111); the travel direction of the sliding grooves (111) is along the radial direction of the circular plate (11), and the plurality of sliding grooves (111) are evenly distributed.

3. The back protection tool for welding according to claim 2, characterized in that: The cross section of the chute (111) is dovetail-shaped, and the shape of the connection position of the support plate (112) with the chute (111) matches the shape of the chute (111).

4. The back side protection tool for welding according to claim 1, characterized in that: A sealing groove is provided on the side of the support plate (112), and a same sealing ring (13) is nested in the sealing groove on the support plate (112) connected to the same end face of the circular plate (11), and the sealing ring (13) has deformation capability.

5. The back side protection tool for welding according to claim 1, characterized in that: A bronchus (32) is connected between the two outward annular air bags (12), an air outlet end of the air extraction device (3) is connected to the bronchus (32) via a main air pipe (33), and the one-way valve (31) is arranged on the main air pipe (33).

6. The back side protection tool for welding according to claim 5, characterized in that: The bronchus (32) is connected to an exhaust pipe (6), and an exhaust valve (7) is provided on the exhaust pipe (6).

7. The back side protection tool for welding according to claim 6, characterized in that: A hand-held rod (5) is fixedly mounted on one end of the base (1), the exhaust pipe (6) passes through the hand-held rod (5), and the exhaust pipe (6) is arranged outside the hand-held rod (5).

8. The welding back side protection tool according to claim 1, characterized in that: A support rod (14) is provided between the support plates (112) located in the protective space (15), and the support rod (14) is parallel to the axis of the disc; or / and further includes a welding auxiliary tool (2) capable of reducing the pressure at the welding front position corresponding to the protective space (15), the welding auxiliary tool (2) including two mutually parallel inward annular airbags (21) and an air extraction device, a high-strength cylinder (22) is fixed between the two inward annular airbags (21), and the outer sides of the two inward annular airbags (21) are fixedly connected to the inner wall of the cylinder (22), and a welding space (23) is formed between the cylinder (22) and the two inward annular airbags (21); the air inlet end of the air extraction device is connected to the welding space (23), the air outlet end of the air extraction device is connected to the inward annular airbag (21), and a one-way valve (31) is provided between the air extraction device and the inward annular airbag (21).

9. The back side protection tool for welding according to claim 1, characterized in that: An oxygen concentration measuring device (4) is provided on the base (1), and the oxygen concentration measuring device (4) is located in the protective space (15).

10. A method for protecting the back side of welding, using the protection tool according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1: Place the protection tool into the pipe (9) so that the back of the weld is located in the protection space (15); S2: activating the air extraction device (3) to transport the air in the protective space (15) into the outward annular air bag (12); S3: The pressure inside the outward annular airbag (12) increases, the volume becomes larger, and the outward annular airbag (12) and the inner wall of the pipe (9) are tightly attached to complete the sealing of the protective space (15); S4: Under the action of steps S2 and S3, there is no oxygen or low-concentration oxygen in the protection space (15), so that the metal on the back side of the weld will not be oxidized, thereby achieving protection of the back side of the weld.

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