Inner hole welding protection tooling and inner hole welding method

Abstract

The present invention relates to an inner hole welding protection tool and an inner hole welding method, which relate to the field of inner hole welding of tube joints of shell and tube heat exchangers, and specifically to an inner hole welding protection tool and an inner hole welding method, comprising an upper clamping body and a lower clamping body, wherein the upper clamping body and the lower clamping body are connected to form a hollow cylindrical clamping body, wherein the upper clamping body and the lower clamping body are connected through a sealing structure, wherein a fixing seat is fixedly connected to the outer peripheral surface of the lower clamping body, wherein a pressure rod is connected to the upper clamping body, and a sleeve is connected to the end of the pressure rod away from the upper clamping body; the present invention is reliable to use: the present invention adopts an inner hole welding protection tool on the outer surface of the weld, which can avoid the pipe joint from being welded through and the outer surface of the weld from being oxidized. During welding, high-purity argon or other protective gases are introduced into the inner hole welding protection tool, and a protective gas atmosphere is formed outside the weld through the channel formed by the upper and lower clamps, so that the weld surface is smooth. The operator only needs to install the ventilation, and the operation is safe and practical.

Description

Technical Field

[0001] The invention relates to the field of inner hole welding of a tube joint of a shell and tube heat exchanger, and in particular to an inner hole welding protection tooling and an inner hole welding method. Background Art

[0002] In the fields of petroleum, chemical industry, food, medicine and nuclear industry, heat exchangers are widely used, with various types and structures, among which shell and tube heat exchangers are the most commonly used. This type of heat exchanger has two cavities, and the sealing of the two cavities is mainly ensured by the welded joints (pipe joints) between the heat exchange tubes and the tube sheets. During the design and manufacturing process, the welding quality of the pipe joints directly affects the quality, safety and service life of the heat exchanger. The connection methods of the pipe joints generally include strength welding, strength expansion, strength welding + expansion, inner hole welding and other types.

[0003] The low-pressure reaction water cooler is the core equipment of the ammonium nitrate unit. The feed side of the tube is internal hole welding, and the other side is strength welding. The heat exchange tube specification diameter is 25×2, material S30403, length 11300mm, quantity 2020, tube sheet material S30403Ⅲ. The medium of the tube side is nitrogen oxide, there is a cooling spray at the front end of the inlet, and the axial feed forms a strong corrosive medium boiling acid at the tube sheet, and the chloride ion concentration is concentrated, forming a strong corrosive environment. The pipe joint adopts an internal hole welding structure and is formed on the shell side. It belongs to a butt welding structure. This type of joint has high connection strength, prevents gap corrosion, butt joints can bear large loads, there is no residual stress caused by expansion, there is no stress concentration area of ​​the weld root cut that appears in the end welding joint, and can withstand fatigue loads, etc., with outstanding advantages.

[0004] Common problems are that the welded joint is not fully welded and breaks during use, resulting in mixing of the heat exchanger tube and shell medium; the intergranular corrosion resistance of the welded joint decreases, and it is easy to be corroded and damaged in a corrosive environment, resulting in leakage, affecting the quality of the final product. The structural dimensions of the positioning table, convex ring, stress relief groove, etc. of the inner hole welding structure in this article are closely related to the welding quality. By adopting this structure and matching the welding process parameters, plus the back protection tooling, a fully welded joint can be obtained, which can not only ensure the welding quality, but also ensure the intergranular corrosion resistance of the welded joint, and it is worthy of promotion and application in the same industry. Summary of the invention

[0005] In order to solve the above problems, the present invention provides an inner hole welding protection tool and an inner hole welding method which effectively solve the problems of inner hole welding of tube joints of shell and tube heat exchangers, as well as the problems of incomplete welding, poor protection of the tube joints and oxidation, decreased intergranular corrosion resistance, excessive welding stress, crevice corrosion during use, etc.

[0006] The present invention discloses an inner hole welding protection tool, comprising an upper clamping body and a lower clamping body, wherein the upper clamping body and the lower clamping body are connected to form a hollow cylindrical clamping body, wherein the upper clamping body and the lower clamping body are connected through a sealing structure, wherein a fixing seat is fixedly connected to the outer peripheral surface of the lower clamping body, wherein a pressure rod is connected to the upper clamping body, wherein a sleeve is connected to the end of the pressure rod away from the upper clamping body, wherein a slide rail is fixedly connected to the fixing seat, wherein the sleeve is sleeved on the slide rail and connected to the slide rail through a locking device, and when the sleeve slides on the slide rail, the upper clamping body and the lower clamping body are close to or away from each other;

[0007] The clamp body is also provided with an air inlet pipe, and the air vent pipe is connected with the inside of the clamp body;

[0008] An annular boss is arranged on one end of the clamp body, and the central axis of the annular boss is in the same straight line as the central axis of the clamp body; and a plurality of semicircular gas outlets are evenly distributed on the annular boss.

[0009] Preferably, the sealing structure is a stepped structure, the upper clamp body and the lower clamp body are both semi-cylindrical, the stepped structures are respectively arranged on the two ends of the circumference of the upper clamp body and the lower clamp body, and the stepped structures on the upper clamp body and the lower clamp body are both arranged from the inside of the clamp body to the outside of the clamp body, and the air intake pipe is arranged on the upper clamp body.

[0010] Preferably, the pressure rod is an L-shaped pressure rod, the connection between the L-shaped pressure rod and the upper clamp body is equidistant from both ends of the upper clamp body in the circumferential direction, and the L-shaped pressure rod is formed by argon arc welding at 90°.

[0011] Preferably, the locking device comprises a positioning locking bolt, which is inserted into the sleeve and abuts against the slide rail, and the positioning locking bolt is threadedly connected to the sleeve.

[0012] An inner hole welding method comprises the following steps:

[0013] 1) First, process the through hole of the tube sheet, then process the stress relief ring groove at one end of the through hole on the tube sheet, and finally process the positioning ring stage on the same end of the through hole on the tube sheet. The central axis of the stress relief ring groove, the through hole and the positioning ring stage are in the same straight line, and the inner diameter of the stress relief groove is larger than the outer diameter of the positioning ring stage. The difference between the inner diameter of the stress relief groove and the outer diameter of the positioning ring stage is 0.5mm, and the bottom of the stress relief groove is rounded;

[0014] 2) Use a cleaning agent to clean the tube sheet and the butt end of the heat exchange tube, remove oil stains and return strokes, and keep them clean, using non-woven cloth to wipe;

[0015] 3) Assemble an inner hole welding protection tool and welding gun to connect the butt ends of the tube sheet and the heat exchange tube: extend the butt end of the heat exchange tube into the through hole on the tube sheet and abut against the positioning ring to achieve positioning;

[0016] Assemble an inner hole welding protection tooling, slide the sleeve up and down, drive the upper clamping body and the lower clamping body to move away from or approach each other, after the upper clamping body and the lower clamping body are approached and combined, connect the annular boss on the inner hole welding protection tooling with the stress release groove on the tube sheet, and then tighten the locking device, the inner area of ​​the clamping body is connected to the outside through the semicircular gas discharge holes evenly distributed on the annular boss;

[0017] Install the welding gun, install the positioning block on the other end of the through hole on the tube sheet, adjust the height of the tungsten electrode of the welding gun, the central axis of the welding gun mandrel and the central axis of the through hole on the tube sheet are in a straight line, the height of the tungsten electrode of the welding gun in the radial direction of the through hole on the tube sheet is 16.5-16.9mm, and the tungsten electrode extends out of the positioning ring platform in the axial direction of the through hole on the tube sheet, and is 0.5mm away from the positioning ring platform;

[0018] 4) Welding: weld row by row and tube by tube from the bottom of the tube sheet upwards. Observe the deformation of the tube sheet during welding. If the gap between the heat exchange tube and the positioning ring increases after the heat exchange tube is inserted, it is difficult for the heat exchange tube to penetrate the positioning ring, or the tube sheet is deformed to the naked eye, reinforce it in time;

[0019] Clamp the outer circumference of an inner hole welding protection tooling, and introduce argon gas, and then use a welding gun to perform automatic welding. The welding parameters are shown in the table below. After 6 seconds of welding, remove an inner hole welding protection tooling;

[0020] 5) Inspection: After welding is completed, use an endoscope to visually observe the weld surface, and then perform a water pressure test on each pipe to check the welding quality. If the heat exchange tube is burned through during welding, perform argon arc welding at the burned-through position. After completion, the heat exchange tube must be tested for ammonia leakage in addition to the water pressure test to ensure the welding quality.

[0021] The welding parameters are as follows:

[0022] Serial number Parameter name and unit Specific parameters 1 Advance air supply time (S) 10 2 Delayed air supply time (S) 6 3 Pre-melting time (S) 2 4 Pre-melting current (A) 90 5 Current decay position (°) 370 6 Current decay time (S) 5 7 Peak current (A) 120 8 Peak time (S) 0.2 9 Base current (A) 45 10 Base value time (S) 0.2 11 Welding speed (mm / min) 125 12 Argon gas flow rate (L / min) 12L / min (inside) / 10L / min (outside) 13 120° Current (A) 117 14 240° Current (A) 114 15 Arc voltage (V) 12

[0023] Preferably, the distance between the positioning ring on the tube sheet and the end of the through hole on the tube sheet is 1.5 mm, and the depth of the stress relief groove is 4.5 mm.

[0024] The beneficial effects of the present invention are as follows:

[0025] 1) Reliable use: The present invention adopts an inner hole welding protection tooling on the outer surface of the weld to prevent the pipe joint from being not welded through and the outer surface of the weld from being oxidized. During welding, high-purity argon or other protective gases are introduced into the inner hole welding protection tooling, and a protective gas atmosphere is formed outside the weld through the channel formed by the upper and lower clamps, making the weld surface smooth. The operator only needs to install the ventilation, and the operation is safe and practical.

[0026] 2) Easy to operate: The tube sheet is easy to process and can be processed with ordinary CNC multi-hole drills, and the dimensional accuracy can also meet the requirements. The production of the inner hole welding protection tooling can be completed with a lathe, milling machine, and electric spark cutting machine. When in use, it is easy to install and position, the operation is simple and flexible, and the locking adopts threaded connection, which is easy to disassemble and assemble.

[0027] 3) Good welding quality: During welding, after the heat exchange tube is positioned, the inner hole welding protection tooling is simple to install. After the welding gun is inserted according to the method, automatic welding can be realized to obtain a full penetration welding joint, and the inside and outside are not oxidized and are silver-white.

[0028] 4) Strong applicability: The present invention is applicable to heat exchange tubes with diameters of 25 mm and 19 mm, and similar structural dimensions and welding methods can be used. Heat exchange tubes with outer diameters of 25 mm and 19 mm are commonly used in shell and tube heat exchangers.

[0029] 5) The effect of setting up the inner hole welding protection tooling is remarkable; the main body of the inner hole welding protection tooling is made of red copper, which can form a channel for argon gas and is a good conductor of heat, which can quickly cool the weld and form an austenite structure. The end of the tooling has a notch, which makes it easy for argon gas to flow out and a protective atmosphere to form inside the tooling. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the connection between the tube sheet and the heat exchange tube of the present invention.

[0031] Figure 2 This is a schematic diagram of the hole welding protection tooling structure.

[0032] Figure 3 for Figure 2 Schematic diagram of direction A.

[0033] Figure 4 This is a schematic diagram of the welding process structure.

[0034] Figure markings: 1-tube sheet, 2-positioning ring, 3-stress relief groove, 4-annular boss, 5-heat exchange tube, 6-lower clamping body, 7-upper clamping body, 8-slide rail, 9-sleeve, 10-locking bolt, 11-inlet pipe, 12-pressure rod, 13-welding gun, 14-positioning block, 15-tungsten electrode of welding gun. DETAILED DESCRIPTION

[0035] The present invention discloses an inner hole welding protection tool, comprising an upper clamp body 7 and a lower clamp body 6, wherein the upper clamp body 7 and the lower clamp body 6 are connected to form a hollow cylindrical clamp body, wherein the upper clamp body 7 and the lower clamp body 6 are connected by a sealing structure, wherein a fixing seat is fixedly connected to the outer peripheral surface of the lower clamp body 6, wherein a pressure rod 12 is connected to the upper clamp body 7, wherein a sleeve 9 is connected to the end of the pressure rod 12 away from the upper clamp body 7, wherein a slide rail 8 is fixedly connected to the fixing seat, wherein the sleeve 9 is sleeved on the slide rail 8 and connected to the slide rail 8 by a locking device, wherein when the sleeve 9 slides on the slide rail 8, the upper clamp body 7 and the lower clamp body 6 are close to or away from each other;

[0036] The clamp body is also provided with an air inlet pipe 11, and the air inlet pipe is connected with the inside of the clamp body;

[0037] An annular boss 4 is arranged on one end of the clamp body, and the central axis of the annular boss 4 is in the same straight line as the central axis of the clamp body; and a plurality of semicircular gas outlets are evenly distributed on the annular boss 4 .

[0038] The sealing structure is a stepped structure, and the upper clamp body 7 and the lower clamp body 6 are both semi-cylindrical. The stepped structures are respectively arranged on the two ends of the circumference of the upper clamp body 7 and the lower clamp body 6, and the stepped structures on the upper clamp body 7 and the lower clamp body 6 are arranged from the inside of the clamp body to the outside of the clamp body, and the air intake pipe 11 is arranged on the upper clamp body 7.

[0039] The pressure rod 12 is an L-shaped pressure rod 12, and the connection between the L-shaped pressure rod 12 and the upper clamp body 7 is equidistant from both ends of the upper clamp body 7 in the circumferential direction, and the L-shaped pressure rod 12 is formed by argon arc welding at 90°.

[0040] The locking device comprises a positioning locking bolt 10 , which extends into the sleeve 9 and abuts against the slide rail 8 , and the positioning locking bolt 10 is threadedly connected to the sleeve 9 .

[0041] An inner hole welding method comprises the following steps:

[0042] 1) First, process the through hole of the tube sheet 1, then process the stress release ring groove at one end of the through hole on the tube sheet 1, and finally process the positioning ring stage 2 at the same end of the through hole on the tube sheet 1. The central axes of the stress release ring groove, the through hole and the positioning ring stage 2 are in the same straight line, and the inner diameter of the stress release groove 3 is larger than the outer diameter of the positioning ring stage 2, and the difference between the inner diameter of the stress release groove 3 and the outer diameter of the positioning ring stage 2 is 0.5mm, and the bottom of the stress release groove 3 is rounded;

[0043] 2) Use a cleaning agent to clean the butt ends of the tube sheet 1 and the heat exchange tube 5, remove oil stains and return strokes, and keep them clean by wiping with non-woven fabric;

[0044] 3) Assemble an inner hole welding protection tool and a welding gun 13, and connect the butt ends of the tube sheet 1 and the heat exchange tube 5: extend the butt end of the heat exchange tube 5 into the through hole on the tube sheet 1, and abut against the positioning ring 2 to achieve positioning;

[0045] Assemble an inner hole welding protection tooling as described in any one of claims 1 to 4, slide the sleeve 9 up and down, drive the upper clamp body 7 and the lower clamp body 6 to move away from or approach each other, and after the upper clamp body 7 and the lower clamp body 6 are approached and combined, connect the annular boss 4 on the inner hole welding protection tooling with the stress release groove 3 on the tube sheet 1, and then tighten the locking device, and the inner area of ​​the clamp body is connected to the outside through the semicircular gas discharge holes evenly distributed on the annular boss 4;

[0046] Install the welding gun 13, install the positioning block 14 on the other end of the through hole on the tube sheet 1, adjust the height of the welding gun tungsten electrode 15, the central axis of the welding gun 13 mandrel is in a straight line with the central axis of the through hole on the tube sheet 1, and the height of the welding gun tungsten electrode 15 in the radial direction of the through hole of the tube sheet 1 is 16.5-16.9mm, that is, in the radial direction of the through hole of the tube sheet 1, the distance between one end of the welding gun tungsten electrode 15 extending out of the welding gun and the lower end face of the welding gun, and the tungsten electrode extends out of the positioning ring 2 in the axial direction of the through hole on the tube sheet 1, and is 20.5mm away from the positioning ring;

[0047] 4) Welding: weld row by row and tube by tube from the bottom of the tube sheet 1 upwards. Observe the welding deformation of the tube sheet 1 during the welding process. If the gap between the heat exchange tube 5 and the positioning ring 2 increases after the heat exchange tube 5 is inserted, it is difficult for the heat exchange tube 5 to penetrate the positioning ring 2, or the tube sheet 1 is deformed to the naked eye, etc., reinforce it in time;

[0048] Clamp the outer circumference of an inner hole welding protection tooling, and introduce argon gas, and then use the welding gun 13 to perform automatic welding. The welding parameters are shown in the table below. After 6 seconds after the welding is completed, remove the inner hole welding protection tooling;

[0049] 5) Inspection: After welding is completed, use an endoscope to visually observe the weld surface, and then perform a water pressure test on each pipe to check the welding quality. If the heat exchange tube 5 is burned through during welding, perform argon arc welding at the burned-through position. After completion, the heat exchange tube 5 must be tested for ammonia leakage in addition to the water pressure test to ensure the welding quality.

[0050] The welding parameters are as follows:

[0051] Serial number Parameter name and unit Specific parameters 1 Advance air supply time (S) 10 2 Delayed air supply time (S) 6 3 Pre-melting time (S) 2 4 Pre-melting current (A) 90 5 Current decay position (°) 370 6 Current decay time (S) 5 7 Peak current (A) 120 8 Peak time (S) 0.2 9 Base current (A) 45 10 Base value time (S) 0.2 11 Welding speed (mm / min) 125 12 Argon gas flow rate (L / min) 12L / min (inside) / 10L / min (outside) 13 120° Current (A) 117 14 240° Current (A) 114 15 Arc voltage (V) 12

[0052] The following is an explanation of the welding of a heat exchange tube 5 with an outer diameter of 25 mm. The distance between the positioning ring 2 on the tube sheet 1 and the end of the through hole on the tube sheet 1 is 1.5 mm, the depth of the stress relief groove 3 is 4.5 mm, the radius of the bottom fillet of the stress relief groove 3 is 1.5 mm, the length of the positioning ring 2 along the axial direction of the tube sheet 1 is 1.5 mm, the outer diameter of the positioning ring 2 is 25.2 mm, and the deviation is ±0.05 mm.

[0053] The diameter of the through hole on the tube sheet 1 must match the head positioning block 14, which can not only position the welding gun 13, but also make it convenient for the welding gun 13 to enter and exit the tube hole. The diameter of the through hole on the tube sheet 1 is 23mm, with a deviation of ±0.1mm.

[0054] The inner diameter of the cavity formed by the upper clamp body 7 and the lower clamp body 6 is 27mm, and the outer diameter of the heat exchange tube 5 is 25mm. The rear ends of the upper clamp body 7 and the lower clamp body 6 are tightly fitted with the heat exchange tube 5 to reduce gas leakage. The front ends are inserted into the stress release groove 3, and the thickness of the inserted end is 2mm thinner than the main body and is processed into a semicircular serrated shape to facilitate gas outflow, forming a high-purity argon atmosphere in the cavity to protect the back of the weld and prevent oxidation.

[0055] The upper clamp body 7 and the lower clamp body 6 of the inner hole welding protection tooling are connected by steps to prevent radial rubbing.

[0056] The lower clamp is threadedly connected to the slide rail 8, the slide rail 8 has a diameter of 5mm and a length of 100mm. The upper clamp body 7 is slidably connected to the slide rail 8 through an L-shaped pressure rod 12. A slider is arranged between the L-shaped pressure rod 12 and the slide rail 8. The slider is threadedly connected to the L-shaped pressure rod 12 and the positioning bolt. The L-shaped pressure rod 12 has a diameter of 5mm, and the positioning bolt is M5 and 10mm long.

[0057] The sliding block should be drilled and the processing accuracy should be high, with a roughness of 6.3μm. The ends of the L-shaped pressure rod 12 and the positioning bolt must be processed into arc surfaces with an arc radius of 2.5mm. The L-shaped pressure rod 12 and the slide rail 8 slide smoothly, and the positioning bolt fits in a semicircle with the slide rail 8 to form a circular cross-section with the L-shaped pull rod. The contact area is large during positioning, and the positioning is accurate and firm.

[0058] The upper clamp body 7 and the lower clamp body 6 of the inner hole welding protection tooling are made of red copper, which will not adhere to the weld during use and has a good thermal conductivity. The welding of stainless steel requires rapid cooling, and copper can promote cooling.

[0059] The air inlet pipe 11 on the upper clamp body 7 is connected to the argon gas belt.

[0060] The L-shaped pressure rod 12 is threadedly connected to the upper clamp body 7, and the turning part of the L-shaped pull rod is completed by welding.

[0061] The inner hole welding protection tooling, after the heat exchange tube 5 is accurately positioned, the lower clamp is inserted into the heat exchange tube 5, and the upper clamp is moved down to fasten the position, and then inserted into the stress release groove 3 together to complete the assembly work.

[0062] The tungsten electrode is positioned axially and inserted into the tube hole accurately to facilitate welding. The tungsten electrode should be 0.5mm on the side of the heat exchange tube 5. The inner diameter of the heat exchange tube 5 is 21mm, and a convex shoulder is formed with the through hole on the tube sheet 1. The exposed thickness of the convex shoulder is 1.5mm, which can be used as the deposited metal. High heat is required during welding, so the tungsten electrode should cross the convex shoulder by 0.5mm.

[0063] The radial positioning of the tungsten electrode, the distance between the extreme end of the tungsten electrode and the inner wall of the heat exchange tube 5 are closely related to arc striking and welding, and there is an optimal distance, which should be 0.5 mm. For a heat exchange tube 5 with a diameter of 25 mm × 2 mm, the distance from the bottom of the welding gun 13 to the extreme end of the tungsten electrode is 16.80 mm, and the distance is measured with a vernier caliper.

[0064] The tungsten tip should be ground into a needle tip to facilitate arc starting and welding.

[0065] The above structure, tooling and welding method can realize the inner hole welding of the shell and tube heat exchanger, and a full penetration structure can be obtained, and the weld surface is silvery white.

[0066] The inner hole welding structure and welding method can be extended to similar equipment or structures with inner holes welded inside.

[0067] The beneficial effects of the present invention are as follows:

[0068] 1) Reliable use: The present invention adopts an inner hole welding protection tooling on the outer surface of the weld to prevent the pipe joint from being not welded through and the outer surface of the weld from being oxidized. During welding, high-purity argon or other protective gases are introduced into the inner hole welding protection tooling, and a protective gas atmosphere is formed outside the weld through the channel formed by the upper and lower clamps, making the weld surface smooth. The operator only needs to install the ventilation, and the operation is safe and practical.

[0069] 2) Easy to operate: The tube sheet 1 is easy to process and can be processed with a common CNC multi-hole drill, and the dimensional accuracy can also meet the requirements. The production of the inner hole welding protection tooling can be completed by a lathe, milling machine, and electric spark cutting machine. When in use, it is easy to install and position, the operation is simple and flexible, and the locking adopts threaded connection, which is easy to disassemble and assemble.

[0070] 3) Good welding quality: During welding, after the heat exchange tube 5 is positioned, the inner hole welding protection tooling is simple to install, and after the welding gun 13 is inserted according to the method, automatic welding can be realized to obtain a full penetration welding joint, and the inside and outside are not oxidized and are silver-white.

[0071] 4) Strong applicability: The present invention is applicable to heat exchange tubes 5 with diameters of 25 mm and 19 mm, and similar structural dimensions and welding methods can be used. Heat exchange tubes 5 with outer diameters of 25 mm and 19 mm are commonly used in shell and tube heat exchangers.

[0072] 5) The effect of setting up the inner hole welding protection tooling is remarkable; the main body of the inner hole welding protection tooling is made of red copper, which can form a channel for argon gas and is a good conductor of heat, which can quickly cool the weld and form an austenite structure. The end of the tooling has a notch, which makes it easy for argon gas to flow out and a protective atmosphere to form inside the tooling.

Claims

1. An inner hole welding method, characterized in that: The following steps are involved: 1) First, a through hole of the tube sheet (1) is processed, then a stress relief annular groove is processed at one end of the through hole on the tube sheet (1), and finally a positioning ring stage (2) is processed at the same end of the through hole on the tube sheet (1), wherein the central axes of the stress relief annular groove, the through hole and the positioning ring stage (2) are in the same straight line, and the inner diameter of the stress relief groove (3) is larger than the outer diameter of the positioning ring stage (2), and the difference between the inner diameter of the stress relief groove (3) and the outer diameter of the positioning ring stage (2) is 0.5 mm, and the bottom of the stress relief groove (3) is rounded; 2) Clean the butt ends of the tube sheet (1) and the heat exchange tube (5) with a cleaning agent to remove oil and dust, and keep them clean by wiping with a non-woven cloth; 3) Assembling an inner hole welding protection tool and a welding gun (13) to connect the butt ends of the tube sheet (1) and the heat exchange tube (5): extending the butt end of the heat exchange tube (5) into the through hole on the tube sheet (1) and abutting against the positioning ring (2) to achieve positioning; Assemble an inner hole welding protection tooling, slide sleeves (9) up and down, drive the upper clamp body (7) and the lower clamp body (6) to move away from or approach each other, and after the upper clamp body (7) and the lower clamp body (6) are brought closer to each other and combined, connect an annular boss (4) on an inner hole welding protection tooling with a stress release groove (3) on a tube sheet (1), and then tighten the locking device, so that the inner area of ​​the clamp body is connected to the outside through the semicircular gas discharge holes evenly distributed on the annular boss (4); Install a welding gun (13), install a positioning block (14) on the other end of the through hole on the tube sheet (1), adjust the height of the welding gun tungsten electrode (15), so that the central axis of the welding gun (13) mandrel is in a straight line with the central axis of the through hole on the tube sheet (1), the height of the welding gun tungsten electrode (15) in the radial direction of the through hole on the tube sheet (1) is 16.5-16.9 mm, and the tungsten electrode extends out of the positioning ring platform (2) in the axial direction of the through hole on the tube sheet (1) and is 0.5 mm away from the positioning ring platform (2); 4) Welding: welding the tube sheets (1) row by row and root by root from the bottom of the tube sheet (1) upwards. During the welding process, observe the welding deformation of the tube sheet (1). If the gap between the heat exchange tube (5) and the positioning ring (2) increases after the heat exchange tube (5) is inserted, it is difficult for the heat exchange tube (5) to be inserted into the positioning ring (2), or the tube sheet (1) is deformed to the naked eye, reinforce it in time; Clamping the outer circumferential surface of an inner hole welding protection tooling, and passing argon gas, and then using a welding gun (13) to perform automatic welding, the welding parameters are shown in the following table, and 6 seconds after the welding is completed, removing the inner hole welding protection tooling; 5) Inspection: after welding is completed, the weld surface is visually observed with an endoscope, and then a water pressure test is performed on each pipe to check the welding quality; if the heat exchange tube (5) is burned through during welding, argon arc welding is performed at the burned through position. After completion, the heat exchange tube (5) is subjected to ammonia leakage detection in addition to the water pressure test to ensure the welding quality; The welding parameters are as follows: The advance gas supply time is 10S, the delayed gas supply time is 6S, the pre-melting time is 2S, the pre-melting current is 90A, the current decay position is 370°, the current decay time is 5S, the peak current is 120A, the peak time is 0.2S, the base current is 45A, the base time is 0.2S, the welding speed is 125mm / min, the argon flow rate inside the clamp is 12L / min, the argon flow rate outside the clamp is 10L / min, the 120° current is 117A, the 240° current is 114A, and the arc voltage is 12V; The inner hole welding protection tool comprises an upper clamp body (7) and a lower clamp body (6), wherein the upper clamp body (7) and the lower clamp body (6) are connected to form a hollow cylindrical clamp body, wherein the upper clamp body (7) and the lower clamp body (6) are connected via a sealing structure, wherein a fixing seat is fixedly connected to the outer peripheral surface of the lower clamp body (6), wherein a pressure rod (12) is connected to the upper clamp body (7), wherein a sleeve (9) is connected to the end of the pressure rod (12) away from the upper clamp body (7), wherein a slide rail (8) is fixedly connected to the fixing seat, wherein the sleeve (9) is sleeved on the slide rail (8) and is connected to the slide rail (8) via a locking device, wherein when the sleeve (9) slides on the slide rail (8), the upper clamp body (7) and the lower clamp body (6) move closer to or farther from each other; The clamp body is also provided with an air inlet pipe (11), and the air inlet pipe (11) is connected to the interior of the clamp body; An annular boss (4) is provided on one end of the clamp body, and the central axis of the annular boss (4) is in the same straight line as the central axis of the clamp body; and a plurality of semicircular gas outlets are evenly distributed on the annular boss (4).

2. An inner hole welding method as claimed in claim 1, characterized in that: The sealing structure is a stepped structure. The upper clamp body (7) and the lower clamp body (6) are both semi-cylindrical. The stepped structures are respectively arranged on the two ends of the circumference of the upper clamp body (7) and the lower clamp body (6). The stepped structures on the upper clamp body (7) and the lower clamp body (6) are arranged from the inside of the clamp body to the outside of the clamp body. The air inlet pipe (11) is arranged on the upper clamp body (7).

3. An inner hole welding method as claimed in claim 2, characterized in that: The pressure rod (12) is an L-shaped pressure rod (12), the connection between the L-shaped pressure rod (12) and the upper clamp body (7) is equidistant from both ends of the upper clamp body (7) in the circumferential direction, and the L-shaped pressure rod is formed by argon arc welding at 90°.

4. An inner hole welding method as claimed in claim 3, characterized in that: The locking device comprises a positioning locking bolt (10), wherein the positioning locking bolt (10) is inserted into the sleeve (9) and abuts against the slide rail (8), and the positioning locking bolt (10) is threadedly connected to the sleeve (9).

5. An inner hole welding method as claimed in claim 4, characterized in that: The distance between the positioning ring (2) on the tube sheet (1) and the end of the through hole on the tube sheet (1) is 1.5 mm, and the depth of the stress relief groove (3) is 4.5 mm.

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