Inner hole welding process method for small-diameter thick-wall heat exchange pipe

Abstract

The invention relates to a small-diameter thick-wall heat exchange pipe inner hole welding process method which comprises the steps that S1, an inner hole welding pipe plate is prepared, and a groove is machined in a to-be-welded joint of a boss of the pipe plate; s2, an inner hole welding heat exchange tube is prepared, and a groove is machined in a to-be-welded joint at the tube end; and S3, the inner hole welded pipe plate and the heat exchange pipe are assembled, so that the groove at the joint to be welded is Y-shaped. According to the inner hole welding process method for the small-diameter thick-wall heat exchange tube, a full-penetration high-quality welding process method can be provided for a butt joint structure of the small-diameter thick-wall heat exchange tube and a tube plate, and the defect that an existing inner hole welding gun can only be used for welding a thin-walled tube is overcome; the quality problem of non-penetration type butt welding seams generated when an existing inner hole welding gun is used for welding a thick-wall pipe is effectively solved, the bearing strength of a connector can be remarkably improved, an ideal full-penetration thick-wall inner hole welding connector is obtained, and the service life of equipment is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of welding, and in particular to a process for welding inner holes of a small-diameter thick-walled heat exchange tube. Background Art

[0002] In the field of modern industrial manufacturing, welding technology, as a key connection process, is widely used in many industries such as petrochemical, nuclear power, aerospace, etc. With the continuous development of industry, more and more stringent requirements are put forward on the quality, reliability and production efficiency of welding joints.

[0003] In the petrochemical industry, many equipment need to handle high temperature, high pressure and highly corrosive media. As one of the core equipment, the heat exchanger has a connection quality between the tube sheet and the heat exchange tube that is directly related to the equipment's operating stability and service life. The traditional heat exchanger's tube sheet and heat exchange tube connection structure has many disadvantages when dealing with such working conditions. Due to the structural characteristics of the welding part, the ordinary fillet weld welding method is prone to weld cracking, leakage and other problems under the action of long-term thermal stress, mechanical vibration and medium corrosion. This will not only lead to production interruptions and huge economic losses, but may also cause safety accidents and pose a serious threat to personnel and the environment. Therefore, in some important equipment or special working conditions in the industry, the internal hole welded tube sheet and heat exchange tube butt weld structure has been gradually introduced to improve the reliability of the heat exchanger and extend its service life.

[0004] The butt weld of the inner hole welding structure cannot be welded from the outside of the tube because the heat exchange tube is a close-packed structure with a small interval between the tubes. Therefore, a welding gun is currently used to insert the tube hole on the tube sheet side, and the tungsten electrode of the welding gun is inserted into the connection between the tube sheet boss and the heat exchange tube group. The welding gun starts the arc to melt the tube sheet parent material and the heat exchange tube parent material at the connection to form a butt joint. However, this method of inner hole welding has great limitations: due to the small diameter of the inner hole welding tube and the heat exchange tube diameter, the inner hole welding gun barrel size on the market is currently small, which is difficult to withstand the high current welding process, and there is no integrated filling wire function, so only TIG arc self-melting can be used to weld some thin-walled heat exchange tubes with full penetration structures. If thick-walled heat exchange tubes are further welded, non-full penetration butt joints will be formed, which seriously affects the service life of the heat exchanger. The limitations of the inner hole welding limit the industrial application of small-diameter thick-walled heat exchange tubes, and affect the design concept of using thick-walled heat exchange tubes to improve the connection strength and extend the service life of the equipment.

[0005] There is no effective inner hole welding process method for a small-diameter thick-walled heat exchange tube inner hole full penetration butt joint. Summary of the invention

[0006] The purpose of the present invention is to provide a small diameter thick wall heat exchange tube inner hole welding process method, the problem to be solved is to provide a thick wall heat exchange tube and tube sheet butt joint welding from the inside of the tube, and form a full penetration weld, characterized in that it includes the following steps:

[0007] S1. Prepare the inner hole welding tube sheet and process the groove at the joint to be welded on the tube sheet boss;

[0008] S2, prepare the inner hole welding heat exchange tube, and process the groove at the joint to be welded at the end of the tube;

[0009] S3. Assemble the inner hole welded tube sheet and the heat exchange tube so that the groove at the joint to be welded is Y-shaped;

[0010] S4. Use an internal welding gun to completely melt the blunt edge of the Y-shaped groove by TIG self-fusion welding;

[0011] S5. Prepare a straight welding wire, and bend the straight welding wire into an open circular ring welding wire according to the inner diameter size at the root of the Y-shaped groove notch;

[0012] S6, pre-setting the annular welding wire into the inner side of the V-shaped groove welded in step S4;

[0013] S7, insert the inner hole welding gun into the pre-set circular welding wire on the inner wall of the hole again and start arc welding, so that the molten welding wire fills the V-shaped gap, forming a final full-penetration joint connecting the inner hole welded tube plate and the heat exchange tube;

[0014] After the above steps, a full penetration inner hole weld is formed between the tube sheet and the thick-walled small-diameter heat exchange tube, and the weld thickness of the butt joint is filled in the form of a pre-set welding wire ring to form a full penetration weld, ensuring the connection strength of the joint. The total number of welding passes is 2;

[0015] If the thickness of the joint is further increased and steps S4 to S5 cannot fill the V-shaped gap, repeat the pre-setting of the circular welding wire to the gap and perform TIG welding again until the entire thickness is filled, thereby ensuring the quality of the fully penetrated welded joint.

[0016] Preferably, the tube sheet boss described in S1 is processed with a groove at the joint to be welded, leaving a groove. Figure 2 The blunt edge p in the figure is processed with a groove angle α. The size of the blunt edge p is the thickness that a conventional thin-walled heat exchange tube can be melted through at one time, and the thickness range is 1.2 to 2.5 mm. The groove angle α is usually set to 30 to 40° according to the size of the thick-walled heat exchange tube, in order to meet the needs of different engineering applications.

[0017] If the blunt edge is too thick, the inner hole welding gun cannot completely melt the blunt edge through, resulting in defects. If the blunt edge is too thin, the inner hole welding gun cannot replenish the liquid metal enough to form a weld. If the groove angle is too large, the joint metal is insufficient, multiple preset wire rings are required, and the number of welding times is increased, affecting the welding efficiency. If the groove angle is too small, the blunt edge cannot be completely melted through.

[0018] Preferably, the tube sheet boss described in S1 is processed with a groove at the joint to be welded, with Figure 2 The purpose of the locking bottom step is to facilitate the positioning of the heat exchange tube assembly during product welding and improve product manufacturing efficiency; at the same time, it is beneficial to solve the problem of liquid metal gravity during welding. Figure 3 The problem of weld depression formed at the upper end of the 90° circumferential joint is compensated by the molten liquid metal from the lock bottom step to compensate for the problem of insufficient weld filling.

[0019] Preferably, the groove is processed at the joint to be welded at the end of the heat exchange tube as described in S2 to prepare Figure 2 The purpose of the blunt edge p and groove angle α is to ensure that they match the groove form at the boss of the tube sheet in S1, forming a welded joint with symmetrical angles and equal thickness of blunt edges, which is beneficial to the first TIG autogenous welding of the inner hole, and the quality of the fully penetrated weld is excellent, avoiding the problem of asymmetric melting of the parent material on both sides of the groove.

[0020] Preferably, the inner hole welded tube plate and the thick wall heat exchange tube are assembled in S3, and a Y-shaped groove is formed at the welding joint, in order to clean the factors affecting the welding quality such as oil, rust, dust, etc. on the groove and edge, so as to further ensure that the welding joint does not produce welding defects.

[0021] Preferably, the blunt edge of the Y-shaped groove is completely melted through by TIG self-fusion welding using an inner hole welding gun as described in S4, which is the first weld between the small-diameter thick-walled inner hole welded heat exchange tube and the tube sheet;

[0022] Preferably, as described in S5, a straight welding wire is prepared, and the straight welding wire is bent into an open circular ring welding wire according to the inner diameter size at the root of the Y-shaped groove notch, such as Figure 4 The outer diameter of the bent wire ring is larger than the inner diameter of the tube hole. By utilizing the tension of the wire ring itself expanding outward, when the wire ring is inserted into the V-shaped notch at the joint, the circumferential tension of the wire ring itself makes it firmly fixed in the notch and will not fall or tilt. The purpose of the wire ring opening L is to reduce the outer diameter of the wire ring and place the wire ring in the tube plate hole by external force.

[0023] Preferably, the circular welding wire is pre-set and inserted into the inner side of the V-shaped groove welded in step S4 in step S6. At this time, the first weld has been fully penetrated by the inner hole welding gun, and there is no metal in the remaining gap. The strength of the weld joint is insufficient, the weld thickness is insufficient, and the weld joint cannot meet the service requirements. The purpose of pre-setting the welding wire ring here is to prepare for the second weld in step S7. Figure 3 It is placed in the orientation shown, with the wire ring opening L placed just below 270°. This is to ensure that the tungsten electrode of the welding gun starts arc welding from one end of the wire ring opening during the second welding, and to prevent the wire ring from being interrupted when welding from other positions, affecting the release of the wire ring tension, resulting in the problem of the wire ring falling off and shifting during welding. This is the key to the success of the second weld.

[0024] Preferably, as described in S7, the inner hole welding gun is again inserted into the pre-installed circular ring welding wire on the inner wall of the hole and arc welding is started, so that the molten welding wire fills the V-shaped notch to form a final full-penetration joint connecting the inner hole welded tube plate and the heat exchange tube; the reason is that the gravity of the molten pool itself during welding will affect the solidification and formation of the weld. In this position, the orientation of the welding wire ring notch is conducive to ensuring that the welding wire is at the bottom when the arc is closed and will not fall or shift, so that the thickness of the weld bead is uniform in the circumferential direction, and the formed full-penetration butt joint is of excellent quality and meets the service requirements.

[0025] The beneficial effects of the present invention are as follows: the inner hole welding process method of the small-diameter thick-walled heat exchange tube of the present invention can provide a full-penetration high-quality welding process method for the butt joint structure of the small-diameter thick-walled heat exchange tube and the tube sheet, overcomes the deficiency that the existing inner hole welding gun can only weld thin-walled tubes, effectively solves the quality problem of non-penetration butt welds produced by the existing inner hole welding gun welding thick-walled tubes, can significantly improve the bearing strength of the joint, obtain an ideal full-penetration thick-wall inner hole welding joint, and extend the service life of the equipment;

[0026] This design can be directly adapted to existing inner hole welding guns, and can be used to weld small diameter thick wall heat exchange tubes, making up for the problem that existing automatic wire feeding welding equipment cannot be adapted to small diameter thick wall heat exchange tubes. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the inner hole welding gun welding of the present invention;

[0028] Figure 2 It is a schematic diagram of the groove structure on the tube sheet boss and the heat exchange tube of the present invention;

[0029] Figure 3 It is a schematic structural diagram of the positional relationship between the welding wire and the groove of the present invention;

[0030] Figure 4 It is a schematic diagram of the relationship between the dimensions of the annular welding wire and the tube sheet boss of the present invention;

[0031] Figure 5 It is a schematic diagram of the structure of the circular welding wire.

[0032] Figure numerals: tube sheet boss 1, heat exchange tube 2, full penetration inner hole weld 3, inner hole welding gun 4, welding gun tungsten electrode 5, bottom locking step 6, welding wire ring opening 7. DETAILED DESCRIPTION

[0033] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings.

[0034] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0035] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The term "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor does it refer to a separate or selective embodiment that is mutually exclusive with other embodiments.

[0036] Secondly, the present invention is described in detail with reference to the schematic diagram. When describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional diagrams showing the device structure will not be partially enlarged according to the general scale, and the schematic diagrams are only examples, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional dimensions of length, width and depth should be included.

[0037] like Figures 1 to 5 As shown, the present invention proposes a small diameter thick wall heat exchange tube inner hole welding process method, small diameter thick wall heat exchange tube inner hole welding steps:

[0038] S1, prepare the inner hole welding tube sheet, and process the groove at the joint to be welded on the tube sheet boss 1;

[0039] S2, prepare the inner hole welding heat exchange tube 2, and process the groove at the joint to be welded at the end of the tube;

[0040] S3, align the inner hole welded tube plate and the heat exchange tube 2, so that the groove at the joint to be welded is Y-shaped;

[0041] S4. Use an internal welding gun to completely melt the blunt edge of the Y-shaped groove by TIG self-fusion welding;

[0042] S5. Prepare a straight welding wire, and bend the straight welding wire into an open circular ring welding wire according to the inner diameter size at the root of the Y-shaped groove notch;

[0043] S6, pre-setting the annular welding wire into the inner side of the V-shaped groove welded in step S4;

[0044] S7, insert the inner hole welding gun into the pre-set circular welding wire on the inner wall of the hole again and start arc welding, so that the molten welding wire fills the V-shaped gap, forming a final full-penetration joint connecting the inner hole welded tube plate and the heat exchange tube;

[0045] After the above steps, a full penetration inner hole weld is formed between the tube sheet and the thick-walled small-diameter heat exchange tube, and the weld thickness of the butt joint is filled in the form of a pre-set welding wire ring to form a full penetration weld, ensuring the connection strength of the joint. The total number of welding passes is 2;

[0046] If the thickness of the joint is further increased and steps S4 to S5 cannot fill the V-shaped gap, repeat the pre-setting of the circular welding wire to the gap and perform TIG welding again until the entire thickness is filled, thereby ensuring the quality of the fully penetrated welded joint.

[0047] Preferably, the tube sheet boss described in S1 is processed with a groove at the joint to be welded, leaving a groove. Figure 2 The blunt edge p in the figure is processed with a groove angle α. The size of the blunt edge p is the thickness that a conventional thin-walled heat exchange tube can be melted through at one time, and the thickness range is 1.2 to 2.5 mm. The groove angle α is usually set to 30 to 40° according to the size of the thick-walled heat exchange tube, in order to meet the needs of different engineering applications.

[0048] If the blunt edge is too thick, the inner hole welding gun cannot completely melt the blunt edge through, resulting in defects. If the blunt edge is too thin, the inner hole welding gun cannot replenish the liquid metal enough to form a weld. If the groove angle is too large, the joint metal is insufficient, multiple preset wire rings are required, and the number of welding times is increased, affecting the welding efficiency. If the groove angle is too small, the blunt edge cannot be completely melted through.

[0049] The tube sheet boss described in S1 is processed with a groove at the joint to be welded, and the locking bottom step 6 is convenient for positioning when assembling and aligning the heat exchange tube during welding, thereby improving product manufacturing efficiency; at the same time, it is beneficial to solve the problem of weld depression formed on the upper mouth of the 90° circumferential joint due to the gravity of the liquid metal during welding, and the liquid metal melted by the locking bottom step 6 can compensate for the problem of insufficient weld filling.

[0050] As described in S2, a groove is machined at the joint to be welded at the end of the heat exchange tube to prepare Figure 2 The purpose of the blunt edge p and groove angle α is to ensure that they match the groove form at the boss of the tube sheet in S1, forming a welded joint with symmetrical angles and equal thickness of blunt edges, which is beneficial to the first TIG autogenous welding of the inner hole, and the quality of the fully penetrated weld is excellent, avoiding the problem of asymmetric melting of the parent material on both sides of the groove.

[0051] The inner hole welded tube plate and the thick wall heat exchange tube are assembled as described in S3, and a Y-shaped groove is formed at the welding joint, in order to clean the factors affecting the welding quality such as oil, rust, dust, etc. on the groove and edge, so as to further ensure that no welding defects occur in the welding joint.

[0052] As described in S4, the blunt edge of the Y-shaped groove is completely melted through by TIG self-fusion welding using an inner hole welding gun. This is the first weld between the small-diameter thick-walled inner hole welded heat exchange tube and the tube sheet.

[0053] As described in S5, a straight welding wire is prepared, and the straight welding wire is bent into an open circular ring welding wire according to the inner diameter size at the root of the Y-shaped groove notch;

[0054] The outer diameter of the bent welding wire ring is larger than the inner diameter of the tube hole. By utilizing the tension of the welding wire ring itself expanding outward, when the welding wire ring is inserted into the V-shaped notch at the joint, the circumferential tension of the welding wire ring itself makes it firmly fixed in the notch and will not fall or tilt. The purpose of the welding wire ring opening L is to facilitate the reduction of the outer diameter of the welding wire ring and place the welding wire ring in the tube plate hole by external force.

[0055] As described in S6, the circular welding wire is pre-set and inserted into the inner side of the V-shaped groove welded in step S4. At this time, the first weld has been fully penetrated by the inner hole welding gun, and there is no metal in the remaining gap. The strength of the weld joint is insufficient, the weld thickness is insufficient, and the weld joint cannot meet the service requirements. The purpose of pre-setting the welding wire ring here is to prepare for the second weld in S7. Figure 3 It is placed in the orientation shown, with the wire ring opening L placed just below 270°. This is to ensure that the tungsten electrode of the welding gun starts arc welding from one end of the wire ring opening during the second welding, and to prevent the wire ring from being interrupted when welding from other positions, affecting the release of the wire ring tension, resulting in the problem of the wire ring falling off and shifting during welding. This is the key to the success of the second weld.

[0056] As described in S7, the inner hole welding gun is again inserted into the pre-placed circular welding wire on the inner wall of the hole and arc welding is started, so that the molten welding wire fills the V-shaped notch to form a final full-penetration joint connecting the inner hole welded tube plate and the heat exchange tube; the reason is that the gravity of the molten pool itself during welding will affect the solidification and formation of the weld. In this position, the orientation of the welding wire ring notch is conducive to ensuring that the welding wire is at the bottom when the arc is closed and will not fall or shift, so that the thickness of the weld bead is uniform in the circumferential direction, and the formed full-penetration butt joint is of excellent quality and meets the service requirements.

[0057] The angle between the groove and the tube sheet boss 1 and the inner wall of the heat exchange tube 2 is α. The remaining thickness of the shell of the heat exchange tube 2 excluding the groove is the blunt edge p. The size of the blunt edge p is the thickness that a conventional thin-walled heat exchange tube can be melted through at one time, and the thickness range is 1.2 to 2.5 mm. The groove angle α is usually set to 30 to 40° according to the size of the thick-walled heat exchange tube.

[0058] A notch is provided on the circular welding wire, and the width of the welding wire ring opening 7 is L (unit: mm):

[0059] L = π*(Φ3-Φ1)-3;

[0060] The inner diameter of the tube sheet boss 1 is Φ1, the maximum diameter of the groove is Φ2, and the outer diameter of the circular welding wire is Φ3.

[0061]

[0062] T is the thickness of the heat exchange tube 2, p is the remaining thickness of the shell of the heat exchange tube 2 excluding the groove, and r is the radius of the welding wire;

[0063] The two ends of the wire ring opening 7 are respectively the starting point and the end point. During welding, the arc can be started from the starting point. Since the width of the wire ring opening 7 is sufficient, the end point of the welding wire will not melt, so that the stress of the welding wire can be released during welding, and no serious deformation will occur to affect the welding quality. After the welding wire melts and solidifies, a full penetration inner hole weld 3 is formed.

[0064] The inner hole welding gun 4 extends into the inner side of the tube sheet boss 1 , and a welding gun tungsten electrode 5 is installed on the inner hole welding gun 4 . A locking bottom step 6 is provided on one side of the tube sheet boss 1 , and the locking bottom step 6 is sleeved with the heat exchange tube 2 .

[0065] 1. Example 1 (Φ40×3.5mm thick-walled heat exchange tube):

[0066] Experimental parameters:

[0067]

[0068]

[0069] Welding strategy:

[0070] The first pass penetrates 2.0 mm blunt edge;

[0071] Preset 1 layer of welding wire ring (filling 1.5mm);

[0072] Quality comparison:

[0073] index The present invention Traditional crafts Relative penetration rate 100％ 42％ Weld reinforcement 0.5-1mm Unformed Width of welding heat affected zone 1.2mm 3.5mm Pressure test (10MPa) No leakage 5% leakage rate

[0074] 2. Example 2 (5×2.5 mm thick-walled heat exchange tube):

[0075] Experimental parameters:

[0076] parameter Numeric Heat exchange tube outer diameter Φ30mm Wall thickness 2.5mm Blunt edge 1.5mm Groove angle α 35° Wire ring outer diameter Φ27.2mm Welding current (TIG autogenous welding) 85A

[0077] Welding strategy:

[0078] The first pass melts through the 1.5mm blunt edge;

[0079] Preset 1 layer of welding wire ring (filling 1.5mm);

[0080] Weld formation: full penetration, no pores or cracks;

[0081] Mechanical properties: tensile strength ≥ 95% of the base material; comparison group (traditional inner hole welding process):

[0082] Full penetration is not possible, and the unfused rate at the weld root is >4%; the joint strength is only 75% of the parent material.

[0083] 3. Example 3 (Φ15×1.8 mm micro heat exchange tube): Extreme working condition verification:

[0084] Challenge Parameters Solution Tube hole inner diameter Φ13.6mm Wire ring outer diameter Φ14.0mm (interference 0.4mm) Welding gun tungsten electrode diameter 0.8mm (special micro gun) Wire ring opening positioning accuracy ±0.1mm (robot preset)

[0085] Microscopic analysis data:

[0086] Detection location Weld line width Microhardness(HV) Weld center - 185 Heat affected zone 50μm 210 Parent material area - 175

[0087] The results show that there are no micro cracks and the fusion line is continuous and uniform; Comprehensive comparison table:

[0088]

[0089]

[0090] Design description of the embodiment

[0091] Gradient verification: covers typical pipe diameters of Φ15 to 40 mm, with wall thicknesses of 1.8 mm to 3.5 mm, to verify the universality of the process;

[0092] Limit test: verify the feasibility of miniaturization implementation in the minimum specification of Φ15mm;

[0093] Efficiency analysis: Through the optimization of weld passes, the welding time of 3.5mm wall thickness can be controlled within 12 minutes;

[0094] Failure mode: The traditional process generates stress concentration due to incomplete penetration, while the present invention returns the failure position to the parent material through the full penetration structure;

[0095] The data is based on ASME Section IX welding procedure assessment standards, and the test environment is a pressure vessel manufacturing workshop (humidity ≤ 60%, temperature 20±5℃).

[0096] Small diameter thick wall heat exchange tube refers to thick wall heat exchange tube with inner diameter less than 120mm.

[0097] It will be appreciated that in the development of any actual implementation, as in any engineering or design project, numerous implementation-specific decisions may be made. Such a development effort may be complex and time-consuming, but will be a routine task of design, fabrication, and production for those of ordinary skill having the benefit of this disclosure without undue experimentation.

[0098] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A small diameter thick wall heat exchange tube inner hole welding process, characterized in that: Small diameter thick wall heat exchange tube inner hole welding steps: S1, preparing an inner hole welding tube sheet, and processing a groove at the joint to be welded on the tube sheet boss (1); S2, preparing an inner hole welded heat exchange tube (2), and processing a groove at the joint to be welded at the end of the tube; S3, aligning the inner hole welded tube plate and the heat exchange tube (2) so that the groove at the joint to be welded is Y-shaped; S4. Use an internal welding gun to completely melt the blunt edge of the Y-shaped groove by TIG self-fusion welding; S5. Prepare a straight welding wire, and bend the straight welding wire into an open circular ring welding wire according to the inner diameter size at the root of the Y-shaped groove notch; S6, pre-setting the annular welding wire into the inner side of the V-shaped groove welded in step S4; S7, insert the inner hole welding gun into the pre-set circular welding wire on the inner wall of the hole again and start arc welding, so that the molten welding wire fills the V-shaped gap, forming a final full-penetration joint connecting the inner hole welded tube plate and the heat exchange tube; After the above steps, a full penetration inner hole weld is formed between the tube sheet and the thick-walled small-diameter heat exchange tube, and the weld thickness of the butt joint is filled in the form of a pre-set welding wire ring to form a full penetration weld, ensuring the connection strength of the joint. The total number of welding passes is 2; If the thickness of the joint is further increased and steps S4 to S5 cannot fill the V-shaped gap, repeat the pre-setting of the circular welding wire to the gap and perform TIG welding again until the entire thickness is filled, thereby ensuring the quality of the fully penetrated welded joint.

2. The method for inner hole welding of a small diameter thick wall heat exchange tube according to claim 1, characterized in that: The angle between the groove and the tube sheet boss (1) and the inner wall of the heat exchange tube (2) is α. The remaining thickness of the shell of the heat exchange tube (2) after removing the groove is the blunt edge p. The size of the blunt edge p is the thickness that can be melted through in one time for a conventional thin-walled heat exchange tube, and the thickness range is 1.2 to 2.5 mm. The groove angle α is usually set to 30 to 40° according to the size of the thick-walled heat exchange tube.

3. The method for inner hole welding of a small diameter thick wall heat exchange tube according to claim 2, characterized in that: A notch is provided on the annular welding wire, and the width of the notch is L: L = π*(Φ3-Φ1)-3; The inner diameter of the tube plate boss (1) is Φ1, the maximum diameter of the groove is Φ2, and the outer diameter of the circular ring welding wire is Φ3.

4. The method for inner hole welding of a small diameter thick wall heat exchange tube according to claim 1, characterized in that: An inner hole welding gun (4) extends into the inner side of the tube sheet boss (1), a welding gun tungsten electrode (5) is mounted on the inner hole welding gun (4), and a bottom locking step (6) is arranged on one side of the tube sheet boss (1), and the bottom locking step (6) is sleeved with the heat exchange tube (2).

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