Tube-to-tubesheet sealing weld of a steam generator and welding method thereof

Abstract

The present invention belongs to the field of welding technology and provides a tube-to-tubesheet sealing weld of a steam generator and a welding method. The weld is filled with wire using a welding head with a transverse oscillation and variable diameter rotation function; the weld includes a backing layer, a filling layer, and a capping layer; the backing layer covers the tube sheet groove and the tube end, and has a penetration depth; the width of the backing layer is 5.3 - 5.7 mm, and the thickness is 1.3 - 1.7 mm; the penetration depth is 0.3 - 0.7 mm; the filling layer covers the backing layer; the width of the filling layer is 4.8 - 5.2 mm, and the thickness is 1 - 1.4 mm; the capping layer covers the filling layer; the width of the capping layer is 6.8 - 7.2 mm, and the thickness is 1.3 - 1.7 mm. The present invention can effectively solve the problems of root cracks, weld throat size, and necking in the nickel-based tube-to-tubesheet sealing weld.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a tube-to-tube sheet sealing weld of a steam generator and a welding method therefor. Background Art

[0002] The main steam tube sheet of the high-temperature gas-cooled reactor steam generator is made of Incoloy 800H forgings, the heat exchange tubes are made of Incoloy 800H tubes, the heat exchange tube specifications are φ19×3, and the tube-to-tube sheet needs to be sealed by welding (sealing weld). After welding, it is necessary to ensure that the inner diameter of the tube hole is not less than φ12.3, the weld throat size ≥ 1e (tube wall thickness), and the weld thickness size control range is only 0.35 mm. Excessive convexity inside the weld will cause the expansion rod to be unable to enter during the subsequent hydraulic expansion process, and no convexity inside the weld will result in insufficient designed weld throat size.

[0003] Since the Incoloy 800H nickel-based alloy is a single-phase austenitic structure, it has characteristics such as poor fluidity of liquid metal and shallow penetration of weld metal, and there is a tendency for hot cracks. Crystalline cracks are likely to occur during the welding process. The generation of hot cracks in nickel-based materials is mainly due to the relatively large linear expansion coefficient and small thermal conductivity, resulting in the segregation and accumulation of impurity elements and low-melting-point substances at the grain boundaries, forming a low-melting-point eutectic. In order to prevent hot cracks, reasonable welding joint designs are usually adopted in the design, such as reducing the structural restraint degree and reducing the welding stress. Technologically, while ensuring good weld fusion, it is necessary to reduce the temperature of the molten pool as much as possible to shorten the high-temperature residence time. The parameters related to the molten pool temperature mainly include heat input and filler metal amount. That is to say, it is necessary to use a small heat input and a large filler metal amount to avoid overheating of the molten pool, thereby reducing the sensitivity to hot cracks.

[0004] In addition, for the tube-to-tube sheet sealing weld structure, due to the initial assembly gap at the weld root, the root is in an I-type (opening type) crack state. This gap can be regarded as the initial crack source, where obvious stress concentration will occur, which will lead to a sharp decline in the structural strength. Even small stresses and strains will cause crack initiation and propagation. Therefore, the weld root region is the weakest point in the entire structure both during the welding process and during the subsequent operation of the product.

[0005] In the field of nuclear power, in the prior art, the tube-to-tubesheet seal weld of the main equipment steam generator in the nuclear island is usually welded by the Polysoude tube-to-tubesheet welding head. This is the most mature process at present, with good process stability. The welding equipment mainly includes TS25 (autogenous), TS34 (autogenous), and TS2000 (fillet welding). However, for the tube-to-tubesheet seal weld structure of the new generation of nuclear power high-temperature gas-cooled reactor steam generator, higher requirements are imposed on strength and tightness, and the weld throat size requirement is ≥ 1e (3 mm). Therefore, the autogenous welding method cannot be adopted (the penetration cannot meet the requirements). Moreover, the existing TS2000 equipment itself has certain limitations. The structure of this welding head is simple, the position of the tungsten electrode relative to the workpiece is fixed and cannot be automatically adjusted, and it is impossible to achieve oscillating welding and variable-diameter welding, etc. Therefore, the degree of freedom for adjusting the weld size is low, and the weld forming size is strongly correlated with the welding parameters (current, voltage, speed). Especially under the condition of specifying the welding heat input, the weld forming shape has strong regularity (under the same heat input condition, the width increases, the thickness decreases, and the penetration decreases).

[0006] Under the limitation of the above conditions, when welding with TS2000, if multi-layer single-pass welding is adopted, considering that the weld needs to have sufficient internal convexity to ensure the weld throat requirement of 1e, the weld forming will be as Figure 1 shown. The root pass weld is wide and thin, with shallow penetration and insufficient thickness, reducing the crack resistance at the root. This is not only unfavorable for meeting the minimum weld throat requirement but also increases the cracking risk. If multi-layer multi-pass welding is adopted, the theoretical weld forming will be as Figure 2 shown. In this state, both the weld throat and crack problems can be satisfied simultaneously; however, in reality, due to the minimum arc diameter of the TS2000 equipment being 4 - 5 mm, it is impossible to achieve the weld bead arrangement as Figure 2 shown. Even if the bead arrangement is forced without considering the welding quality, it will result in excessive internal convexity of the weld, thus not meeting the requirement of the inner diameter of the tube hole after welding; at the same time, the weld bead arrangement of multi-layer multi-pass increases the transverse tensile stress perpendicular to the gap, making it more prone to crack propagation.

[0007] Based on the above defects, it is necessary to propose a new seal weld and its welding method for the tube-to-tubesheet of the steam generator to improve the crack problem of the seal weld of the tube-to-tubesheet. Summary of the Invention

[0008] In order to overcome the above-mentioned drawbacks of the prior art, the object of the present invention is to provide a tube-to-tubesheet seal weld of a steam generator, which can effectively solve the root crack problem of the tube-to-tubesheet.

[0009] The technical solution adopted by the present invention to solve its technical problems is:

[0010] The sealing weld of the tube and tube sheet of a steam generator is filled with wire using a welding head with a cross swing and variable diameter rotation function; the weld includes a backing layer, a filling layer, and a capping layer;

[0011] The backing layer covers the groove of the tube sheet and the end of the tube, and has a penetration depth; the width of the backing layer is 5.3 - 5.7 mm, the thickness is 1.3 - 1.7 mm; the penetration depth is 0.3 - 0.7 mm;

[0012] The filling layer covers the backing layer; the width of the filling layer is 4.8 - 5.2 mm, the thickness is 1 - 1.4 mm;

[0013] The capping layer covers the filling layer; the width of the capping layer is 6.8 - 7.2 mm, the thickness is 1.3 - 1.7 mm.

[0014] Preferably, the surface of the backing layer is inclined from the side of the tube sheet to the side of the tube, and the outer end of the groove of the tube sheet is not covered by the backing layer.

[0015] Preferably, the filling layer only covers the surface of the backing layer, and a part of the surface of the backing layer is exposed, and the exposed part is located at one end far from the inner hole of the tube;

[0016] Along the radial direction from outside to inside, the surface of the filling layer is curved, and its thickness first gradually increases and then gradually decreases, and the position of the maximum thickness is at the end of the tube.

[0017] Preferably, the capping layer covers the groove of the tube sheet, the backing layer, and the filling layer, and the direct welding part between the groove of the tube sheet and the capping layer has a penetration depth;

[0018] The capping layer protrudes from the surface of the tube sheet.

[0019] Another object of the present invention is to provide a welding method for obtaining the above weld structure.

[0020] A method for sealing and welding the tube and tube sheet of a steam generator is filled with wire using a welding head with a cross swing and variable diameter rotation function, and a groove is pre - machined inside the tube sheet seal; the method includes the following steps:

[0021] S1. Weld the backing layer at the groove of the tube sheet and the end of the tube; the width of the backing layer is controlled within 5.3 - 5.7 mm, the thickness is controlled within 1.3 - 1.7 mm; the backing layer has a certain penetration depth, and the penetration depth is controlled within 0.3 - 0.7 mm;

[0022] S2. Weld the filling layer on the backing layer; the width of the filling layer is controlled within 4.8 - 5.2 mm, the thickness is controlled within 1 - 1.4 mm;

[0023] S3. Weld the capping layer on the backing layer; the width of the capping layer is controlled within 6.8 - 7.2 mm, and the thickness is controlled within 1.3 - 1.7 mm.

[0024] In a preferred embodiment of the present invention, before welding, perform positioning expansion joint treatment on the inner hole of the pipe to eliminate the gap between the pipe and the tube sheet; after the expansion joint treatment is completed, clean the expansion joint area and the welding area.

[0025] In a preferred embodiment of the present invention, before formal welding, first edit the welding program, input the welding parameters, and position the pipe holes.

[0026] Subsequently, adjust the angle, position, and rotation radius of the welding headstock according to the position of the inner hole of the pipe; adjust and fix the position of the wire feeding elbow of the welding equipment to ensure the relative position and distance between the fed welding wire and the tungsten electrode.

[0027] Preferably, during the welding process, pay attention to the deviation between the actual value and the input set value of the welding parameters in real time, and the fluctuation range shall not exceed 2%.

[0028] In a preferred embodiment of the present invention, during the welding of the backing layer, when the welding headstock reaches the 3 o'clock and 9 o'clock positions of the seal, the residence time on the pipe side and the tube sheet side is equal; when the welding headstock reaches the 6 o'clock position of the seal, the residence time on the pipe side is shorter than that on the tube sheet side; when the welding headstock reaches the 12 o'clock position of the seal, the residence time on the pipe side is longer than that on the tube sheet side.

[0029] In a preferred embodiment of the present invention, the surface of the backing layer is inclined along the direction from the tube sheet groove to the end of the pipe.

[0030] When welding the filling layer, the residence time of the welding headstock on the tube sheet side is shorter than that on the pipe side.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] The present invention provides a reasonable weld bead shape and size for the backing layer, filling layer and capping layer, which significantly improves the sealing welding effect of the tube-to-tube sheet of the steam generator. In particular, the matching method of the bead forming size can effectively solve the problems of root cracks, weld throat size and necking in the sealing weld of nickel-based tubes and tube sheets. Moreover, the welding head with a swing function and a variable diameter rotation function is applied to the sealing welding of the tube-to-tube sheet, so that the width of each weld bead is not limited by the specification of the filler metal and the heat input, realizing precise control of the bead forming size, freely controlling the width and thickness of the weld bead, and obtaining good weld bead formation (the weld bead is flat, has a small convexity, a large thickness and a suitable penetration depth) under the same heat input level; in addition, the swing function makes the molten pool shape more symmetrical, so that the weld surface is smoother, the quality is better, the influence on the welding pass arrangement of the subsequent layer is reduced, and no surface treatment is required; during the swing welding process, the arc also stirs the molten pool, which helps to discharge the gas, thereby reducing the generation of pores. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0034] Figure 1 Schematic diagram of a weld bead for multi-layer single-pass welding using TS2000 (the red filled area in the figure represents the weld bead, and the dotted circle range is the theoretical weld throat).

[0035] Figure 2 Schematic diagram of a weld bead for multi-layer multi-pass welding using TS2000 (the red filled area in the figure represents the weld bead, and the dotted circle range is the theoretical weld throat).

[0036] Figure 3 Schematic diagram of the sealing weld of the tube-to-tube sheet of the steam generator of the present invention.

[0037] Figure 4 Actual forming effect diagram of the sealing weld of the tube-to-tube sheet of the steam generator of the present invention.

[0038] Wherein:

[0039] 1 - tube sheet, 2 - tube, 3 - backing layer, 4 - filling layer, 5 - capping layer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] In order to more clearly understand the above objects, features and advantages of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, without conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. In the following description, many specific details are set forth in order to fully understand the present invention. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0041] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0042] See Figure 3 - Figure 4 , this embodiment discloses a seal weld of a tube and tube sheet of a steam generator, and a wire filling welding is carried out by using a welding head with a transverse oscillation and variable diameter rotation function; the weld includes a root pass layer 3, a filling layer 4 and a capping layer 5; the root pass layer 3 covers the groove of the tube sheet 1 and the end of the tube 2 and has a penetration depth; the width W1 of the root pass layer 3 is 5.3 - 5.7 mm, and the thickness h1 is 1.3 - 1.7 mm; the penetration depth is 0.3 - 0.7 mm; the filling layer 4 covers the root pass layer 3; the width W2 of the filling layer 4 is 4.8 - 5.2 mm, and the thickness h2 is 1 - 1.4 mm; the capping layer 5 covers the filling layer 4; the width W3 of the capping layer 5 is 6.8 - 7.2 mm, and the thickness h3 is 1.3 - 1.7 mm.

[0043] Furthermore, the surface of the root pass layer 3 is inclined from the side of the tube sheet 1 to the side of the tube 2, and the root pass layer 3 does not cover the outer end of the groove of the tube sheet 1. Such a root pass layer 3 facilitates the subsequent row of the filling layer 4. It is inclined and relatively flat, making the welding of the filling layer 4 more flexible and easy. Moreover, for solving the crack problem of the tube and tube sheet, the root pass layer 3 is particularly important. In this embodiment, a certain penetration depth is generated at the groove position of the tube sheet 1 and the end of the tube 2 when welding the root pass layer 3, so that the weld of the root pass layer 3 has a more reliable stress effect on the tube sheet 1 and the tube 2, can effectively improve the joint stress state, and avoid the continuous action of the welding residual stress generated in the subsequent layer and the root gap from inducing cracks and expansion.

[0044] Furthermore, the filling layer 4 only covers the surface of the backing layer 3, and a part of the surface of the backing layer 3 is exposed. The exposed part is located at one end far from the inner hole of the tube 2. Along the radial direction from the outside to the inside, the surface of the filling layer 4 is curved, and its thickness first gradually increases and then gradually decreases. The position of the maximum thickness is at the end of the tube 2.

[0045] More importantly, in this embodiment, when welding the filling layer 4, taking advantage of the relatively flat surface structure of the backing layer 3, the welding of the filling layer 4 is made more convenient, and the surface of the filling layer 4 is made close to being flush with the tube sheet 1 during welding, thus providing favorable conditions for the welding of the capping layer 5 later.

[0046] Furthermore, the capping layer 5 covers the groove of the tube sheet 1, the backing layer 3 and the filling layer 4, and there is a penetration depth at the direct welding position between the groove of the tube sheet 1 and the capping layer 5; the capping layer 5 protrudes from the surface of the tube sheet 1. The capping layer 5 is in contact with the tube sheet 1, the backing layer 3 and the filling layer 4, forming a function of mutual aggregation to enhance the crack prevention ability, which is beneficial to making the strength of the whole weld seam greater and further avoiding the appearance of cracks.

[0047] This embodiment also discloses a welding method for obtaining the above weld structure. This welding method uses a welding head with a transverse oscillation and variable diameter rotation function for wire filling welding. The transverse oscillation function of the welding head can be realized by adding a motor drive and is controlled by a corresponding software system during welding. And a groove is pre-machined on the inner side of the seal of the tube sheet 1. The angle between the groove and the end face is 40°, and the depth of the groove is 3 - 3.5 mm; the method includes the following steps:

[0048] S1. Weld the backing layer 3 at the groove of the tube sheet 1 and the end of the tube 2; the width W1 of the backing layer 3 is controlled within 5.3 - 5.7 mm, and the thickness h1 is controlled within 1.3 - 1.7 mm; the backing layer 3 has a certain penetration depth, and the penetration depth is controlled within 0.3 - 0.7 mm;

[0049] S2. Weld the filling layer 4 on the backing layer 3; the width W2 of the filling layer 4 is controlled within 4.8 - 5.2 mm, and the thickness h2 is controlled within 1 - 1.4 mm;

[0050] S3. Weld the capping layer 5 on the backing layer 3; the width W3 of the capping layer 5 is controlled within 6.8 - 7.2 mm, and the thickness h3 is controlled within 1.3 - 1.7 mm.

[0051] Furthermore, before welding, positioning and expansion joint treatment is carried out on the inner hole of the tube 2 to eliminate the gap between the tube 2 and the tube sheet 1; after the expansion joint treatment is completed, the expansion joint area and the welding area are cleaned. Expansion joint is carried out on the position of the inner hole of the tube 2 close to the tube sheet 1, and the expansion joint distance is 15 - 30 mm.

[0052] Further, before formal welding, first edit the welding program, input the welding parameters, and position the holes of the pipe 2. The positioning can be carried out by means of visual photography. Subsequently, adjust the angle, position and rotation radius of the welding head according to the position of the inner hole of the pipe 2; adjust and fix the position of the wire feeding elbow of the welding equipment to ensure the relative position and distance between the fed welding wire and the tungsten electrode. After welding is completed, visual inspection of the weld surface, weld size, weld penetration, weld radiography and destructive tests of witness pieces shall be carried out.

[0053] Further, during the welding of the root pass 3, when the welding head reaches the 3 o'clock and 9 o'clock positions of the seal, the residence time on the side of the pipe 2 and the side of the tube sheet 1 is equal; when the welding head reaches the 6 o'clock position of the seal, the residence time on the side of the pipe 2 is shorter than the residence time on the side of the tube sheet 1; when the welding head reaches the 12 o'clock position of the seal, the residence time on the side of the pipe 2 is longer than the residence time on the side of the tube sheet 1. For example, when the welding head is at the 9 o'clock and 3 o'clock positions, the residence time on the side of the pipe 2 and the side of the tube sheet 1 is 0.2 s; when the welding head reaches the 12 o'clock position, the residence time on the side of the pipe 2 is 0.4 s, and the residence time on the side of the tube sheet 1 is 0.2 s. When the welding head reaches the 6 o'clock position, the residence time on the side of the pipe 2 is 0.2 s, and the residence time on the side of the tube sheet 1 is 0.4 s. Weld the root pass 3 in this way to resist the influence of gravity on the formation of the molten pool, ensure that the filling metal amount in the entire circumferential area is quite the same, the weld roundness is better, the dimensions are consistent, and at the same time, it also avoids the influence of uneven residual stress after welding on the root gap and reduces the cracking risk.

[0054] Further, the surface of the root pass 3 is inclined along the direction from the groove of the tube sheet 1 to the end of the pipe 2; when welding the filling layer 4, the residence time of the welding head on the side of the tube sheet 1 is shorter than the residence time on the side of the pipe 2. Through the above setting of the residence time parameters of the welding head, the weld surface of the filling layer 4 is flatter after welding, so that the convex amount of the weld can be better controlled (when the weld surface is an inclined plane, the molten iron of the molten pool flows along the slope direction of the groove under the influence of gravity, and it is not easy to control the convex amount of the weld), making the subsequent pass arrangement simpler and easier to control the balance between the weld throat and the convex size of the weld, so as to meet the requirements of the weld throat and the weld convexity at the same time.

[0055] In addition, during the welding process, pay attention to the deviation between the actual value and the input set value of the welding parameters in real time, and the fluctuation range shall not exceed 2%.

[0056] The welding parameters of this embodiment can be seen in the following table data:

[0057]

[0058] In the table, "T" represents the initial centering position of the welding head; "left stop" means the welding head stays on the side of the tube 2; "right stop" means the welding head stays on the side of the tube sheet 1.

[0059] This embodiment gives a reasonable weld bead shape and size for the root pass 3, filler pass 4 and cover pass 5, which significantly improves the sealing welding effect of the tube and tube sheet of the steam generator and effectively solves the problem of weld cracks. And the welding head with a swing function and a variable diameter rotation function is applied to the sealing welding of the tube and tube sheet, so that the width of each weld bead is not limited by the specification of the filler metal and the heat input, realizing free control of the weld bead width and thickness. Under the same heat input level, good weld bead formation is obtained (the weld bead is flat, has a small convexity, a large thickness and a proper penetration depth); in addition, the swing function makes the molten pool shape more symmetrical, so that the weld surface is smoother, the quality is better, the influence on the welding bead arrangement of the subsequent layer is reduced, and no surface treatment is required; during the swing welding process, the arc also stirs the molten pool, which helps to discharge the gas, thus reducing the generation of pores. At the same time, combined with the above welding parameters, the welding molten pool temperature is controlled, which is beneficial to reducing the high-temperature residence time of the molten metal in the molten pool and avoiding the generation of hot cracks.

[0060] Through the weld joint and welding method of this embodiment, the internal convexity of the formed weld meets the requirements, thus meeting the requirements of the inner hole diameter of the tube 2 after welding; at the same time, it solves the problem that the welding bead arrangement of multiple layers and multiple passes increases the transverse tensile stress perpendicular to the gap, thus solving the problem of crack propagation.

[0061] The above is only a preferred embodiment of the present invention, and does not impose any form of limitation on the present invention. Therefore, any modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A tube sheet sealing weld of a steam generator, characterized in that: A welding head with a swing and diameter-changing rotation function is used for wire-filling welding; the weld includes a base layer, a filling layer and a cover layer; The base layer covers the tube sheet groove and the tube end and has a penetration depth; the width of the base layer is 5.3-5.7 mm, the thickness is 1.3-1.7 mm; the penetration depth is 0.3-0.7 mm; The filling layer covers the base layer; the width of the filling layer is 4.8-5.2 mm, and the thickness is 1-1.4 mm; The cover layer covers the filling layer; the width of the cover layer is 6.8-7.2 mm, and the thickness is 1.3-1.7 mm; The surface of the primer layer is inclined from one side of the tube sheet to one side of the tube, and the primer layer does not cover the outer end of the groove of the tube sheet; The filling layer only covers the surface of the base layer, and the surface of the base layer is partially exposed, and the exposed portion is located at an end away from the inner hole of the pipe; From the outside to the inside in the radial direction, the surface of the filling layer is curved, and its thickness gradually increases and then gradually decreases, and the maximum thickness is located at the end of the tube; The cover layer covers the tube sheet groove, the base layer and the filling layer, and the direct welding point between the tube sheet groove and the cover layer has a fusion depth; The cap layer protrudes from the surface of the tube sheet.

2. A welding method for obtaining the sealing weld of the tube sheet of the steam generator according to claim 1, characterized in that: The welding head with the function of swaying and reducing diameter rotation is used for wire welding, and the groove is pre-processed on the inner side of the tube sheet seal; the following steps are included: S1. Welding a base layer at the groove of the tube sheet and the end of the tube; the width of the base layer is controlled at 5.3-5.7 mm, and the thickness is controlled at 1.3-1.7 mm; the base layer has a certain penetration depth, and the penetration depth is controlled at 0.3-0.7 mm; S2, welding a filling layer on the base layer; the width of the filling layer is controlled to be 4.8-5.2 mm, and the thickness is controlled to be 1-1.4 mm; S3, welding a capping layer on the base layer; the width of the capping layer is controlled to be 6.8-7.2 mm, and the thickness is controlled to be 1.3-1.7 mm.

3. The welding method according to claim 2, characterized in that: Before welding, the inner hole of the tube is positioned and expanded to eliminate the gap between the tube and the tube sheet; after the expansion treatment is completed, the expansion area and the welding area are cleaned.

4. The welding method according to claim 3, characterized in that: Before formal welding, edit the welding procedure, enter the welding parameters, and locate the pipe hole; Subsequently, the angle, position and rotation radius of the welding head are adjusted according to the position of the inner hole of the pipe; the wire feeding elbow position of the welding equipment is adjusted and fixed to ensure the relative position and distance between the fed welding wire and the tungsten electrode.

5. The welding method according to claim 3, characterized in that: During the welding process, pay real-time attention to the deviation between the actual value of the welding parameter and the entered set value. The fluctuation range shall not exceed 2%.

6. The welding method according to claim 3, characterized in that: During the welding of the base layer, when the welding head reaches the 3 o'clock and 9 o'clock positions of the seal, the residence time on the tube side and the tube sheet side is equal; when the welding head reaches the 6 o'clock position of the seal, the residence time on the tube side is shorter than the residence time on the tube sheet side; when the welding head reaches the 12 o'clock position of the seal, the residence time on the tube side is longer than the residence time on the tube sheet side.

7. The welding method according to claim 6, characterized in that: The surface of the base layer is inclined along the direction from the tube sheet groove to the tube end; When welding the filling layer, the residence time of the welding head on the tube sheet side is shorter than that on the tube side.

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