A nuclear island main equipment safety end non-isolation layer magnetic control narrow gap welding method

Abstract

The application is a kind of nuclear island main equipment safety end non-isolation layer magnetic control narrow gap welding method, including the following steps S1, the tungsten electrode end part on the welding gun is cut into a pyramid tip structure; S2, the tungsten electrode is placed at a specific height in the groove width center, and TIG welding is carried out in the groove; after adjusting the deflection angle of the tip structure of the tungsten electrode and adjusting the welding parameters, the welding is started, so that the arc generated by the tungsten electrode swings to the two side walls of the groove, and the highest space boundary swept by the arc swing is higher than the molten pool liquid surface at the corresponding moment, wherein the deflection angle is the angle of the tungsten electrode tip vertex rotating in the safety end direction, and the welding parameters include excitation frequency, welding current, duty ratio, wire feeding speed, excitation current and welding speed. The application overcomes the influence of the asymmetric magnetic field in the structure of ferromagnetic material and non-ferromagnetic material on the magnetic control narrow gap TIG welding arc, realizes the efficient butt welding of non-isolation layer pipe connection and safety end, greatly improves the welding efficiency and ensures the weld quality.

Description

Technical Field

[0001] This invention belongs to the field of welding technology, and in particular relates to a magnetically controlled narrow-gap welding method for the safety end of the main equipment of a nuclear island without an isolation layer. Background Technology

[0002] The connection between the nozzles and stainless steel safety ends of the main equipment in the nuclear island (such as the reactor pressure vessel and steam generator) is a typical dissimilar steel welded joint. The nozzle body is usually made of low-alloy steel (such as SA508 Gr.3), which is ferromagnetic; the safety end is made of austenitic stainless steel (such as F316L), which is non-ferromagnetic or weakly magnetic. To mitigate the problems of carbon migration, thermal stress, and corrosion resistance degradation caused by direct welding of dissimilar steels, current nuclear power plant construction standards generally adopt a welding process of "isolation layer welding plus narrow gap butt welding". This welding process usually involves first welding a stainless steel weld overlay on the inner wall of the nozzle, then aligning and assembling the nozzle and safety end with a narrow gap bevel, then welding a nickel-based alloy isolation layer on the nozzle end face, and finally butt welding the isolation layer to the stainless steel safety end after heat treatment. Figure 1 As shown, the isolation layer uses imported nickel-based alloy materials, which are expensive. After the isolation layer is welded, it still needs to undergo processing and non-destructive testing, which not only prolongs the product manufacturing cycle but also increases the quality risk in the manufacturing process. This traditional welding process has inherent defects such as lengthy process, high cost, and the easy occurrence of carbon migration at the weld interface during post-weld heat treatment to form a carburized / decarburized brittle layer.

[0003] Magnetically controlled narrow-gap TIG welding is an advanced welding method that uses an externally applied transverse alternating magnetic field to drive an electric arc to oscillate within a narrow-gap groove, achieving reliable sidewall fusion. It offers advantages such as no mechanical wear, adjustable oscillation frequency, and controllable spatial distribution of arc energy, theoretically making it highly suitable for replacing narrow-gap welding of thick-walled dissimilar steels with isolation layers. Magnetically controlled narrow-gap TIG welding features fewer welding passes, high thermal and welding efficiency, and excellent sidewall fusion. It exhibits a significant improvement in welding efficiency for non-ferromagnetic materials (titanium alloys). If this technology could be applied to welding safety ends without isolation layers, manufacturing efficiency would be dramatically improved. However, for safety end structures without isolation layers, the significant difference in magnetic permeability between the base materials on both sides of the groove leads to severe asymmetry in arc oscillation. Summary of the Invention

[0004] The purpose of this invention is to provide a method for magnetically controlled narrow-gap welding of the safety end of the main equipment of a nuclear island without an isolation layer. This method overcomes the influence of asymmetric magnetic fields in ferromagnetic and non-ferromagnetic material structures on the magnetically controlled narrow-gap TIG welding arc, and achieves efficient single-layer single-pass butt welding of the pipe without an isolation layer and the safety end, which greatly improves the welding efficiency and ensures the weld quality.

[0005] This invention is achieved through the following technical solution: A method for magnetically controlled narrow-gap welding without an isolation layer at the safety end of a nuclear island main equipment includes the following steps: S1. The tungsten electrode tip on the welding torch is shaped into a pyramidal tip structure. The pyramidal tip structure includes a first inclined surface and two second inclined surfaces symmetrically arranged on both sides of the first inclined surface. The first inclined surface intersects the axial generatrix of the tungsten electrode to form an angle, and the two second inclined surfaces meet at the tip apex. S2. Place the tungsten electrode at a pre-set height at the center of the bevel width, and perform TIG welding within the bevel: After adjusting the deflection angle of the tip structure of the tungsten electrode and adjusting the welding parameters, start the arc and begin welding, so that the arc generated by the tungsten electrode swings to the two side walls of the bevel, and the highest spatial boundary swept by the arc during the swing is higher than the molten pool surface at the corresponding moment. The deflection angle is the angle at which the tip of the tungsten electrode rotates towards the safe end. The welding parameters include excitation frequency, welding current, duty cycle, wire feed speed, excitation current, and welding speed.

[0006] Furthermore, The step of performing TIG welding within the groove includes: S21. Perform the root pass welding: The area between the top of the weld overlay and the bottom of the bevel is taken as the root welding area. The deflection angle of the tungsten electrode is adjusted to 0°. After adjusting the welding parameters, the arc is started to perform the root welding. S22. Perform layered filler welding: The deflection angle of the tungsten electrode is adjusted to 30°, and the welding parameters are adjusted. The arc is started to perform welding fill. In each layer of fill welding, the arc is driven by the magnetic field to swing back and forth along the bevel in a continuous circle to complete one layer of fill welding. After each layer of welding is completed, the temperature needs to be lowered to the preset temperature before the next layer of fill welding is performed. S23. Perform cover welding: Adjust the deflection angle of the tungsten electrode to 30° and adjust the welding parameters; initiate arc welding for the capping surface.

[0007] Furthermore, in the steps of performing the root pass welding and the layered fill welding, the welding direction and arc initiation position are changed for each layer.

[0008] Further, in step S21, the excitation frequency is adjusted to 1.5 Hz, the welding current is 300 A, the duty cycle is 50%, the wire feed speed is 26 mm / s, the excitation current is +5.5 A on the safety end side and -5.5 A on the weld overlay side, and the welding speed is 1 mm / s.

[0009] Further, in step S22, the excitation frequency is adjusted to 1.5 Hz, the welding current is 300 A, the duty cycle is 60%, the wire feed speed is 26 mm / s, the excitation current is +5.5 A on the safety end side and -1.5 A on the pipe side, and the welding speed is 1 mm / s.

[0010] Further, in step S23, the excitation frequency is adjusted to 1.5 Hz, the welding current is 300 A, the duty cycle is 60%, the wire feed speed is 33 mm / s, the excitation current is +5.5 A on the safety end side and -1.5 A on the pipe side, and the welding speed is 1 mm / s.

[0011] Furthermore, in the step of performing TIG welding within the groove, uphill welding is adopted.

[0012] Furthermore, The method further includes: S3. After welding, the connecting pipe and safety end are subjected to post-heating, and then slow cooling is performed. S4. After the connector and safety end have cooled to room temperature, the connector and safety end are subjected to heating, heat preservation and cooling processes.

[0013] Furthermore, in step S3, the post-heating temperature is 250-400℃, and the time is 2 hours. In step S4, the heat preservation temperature is 595-620℃, the heat preservation time is 2h, and the heating and cooling rates are less than or equal to 55℃ / h.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By changing the direction of the electric arc through the tip structure, installation position, and deflection angle of the tungsten electrode tip structure, the asymmetric sway of the electric arc caused by uneven magnetic field distribution and differences in magnetic properties of the base materials on both sides is actively compensated; In addition, the optimal matching of the electric arc boundary-molten pool surface-weld shape is achieved by adjusting parameters such as excitation frequency, welding current, tungsten electrode height, duty cycle, wire feeding speed, excitation current and welding speed, ensuring good fusion between the current layer weld and the side wall, and achieving pre-melting of the side wall during subsequent layer welding, reducing the energy requirement of the oscillating electric arc; The above-mentioned adjustment of the deflection angle of the tungsten electrode tip structure and welding process parameters ensures that the electric arc has sufficient climbing height on the side wall, and also ensures that the oscillating electric arc has sufficient overlapping area, ensuring fusion between layers in the vertical direction; (2) A single-layer, single-pass magnetic oscillation filling strategy is adopted. The electric arc oscillates continuously in the groove for one revolution to complete one layer of filling welding. In addition, in terms of weld performance control, the welding parameters are optimized and the welding current and wire feeding speed are related and work together. Under the premise of ensuring a specific molten pool-arc shape by using a larger current, a large number of cold welding wires are introduced into the molten pool to reduce the temperature of the molten pool, thereby avoiding overheating of the molten pool and ensuring weld performance. At the same welding speed, the single-layer deposition thickness is larger, the number of welding passes is significantly reduced, the welding efficiency is improved, and the full fusion between layers and the sidewall can still be guaranteed. The efficiency is better than that of interlaced welds with two passes per layer. (3) An unconventional arc-starting position is adopted to achieve compensation of the oscillating arc in the direction of molten pool depth when the arc height is increased and the heat input remains unchanged. The principle is that the penetration depth of TIG welding on the uphill slope is greater than that on the downhill slope. The fundamental principle is the coupling effect of molten pool flow and arc heating efficiency under the action of gravity. Specifically, the backward flow of the molten pool driven by gravity changes the heat transfer conditions between the arc and the base material. At the same time, the "isolation effect" of the forward flow of the molten pool on the arc during downhill welding further reduces the penetration depth. Attached Figure Description

[0015] Figure 1 A schematic diagram of the welding process for existing isolation layer overlay welding and narrow gap butt welding; Figure 2 This is a flowchart illustrating the steps of the magnetically controlled narrow-gap welding method for the safety end of the main equipment in the nuclear island of the present invention, which involves welding without an isolation layer. Figure 3 This is a schematic diagram of the alignment and assembly of the nozzle and the safety end in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island without an isolation layer according to the present invention; Figure 4 This is a schematic diagram of the welding of the nozzle and the safety end in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island without an isolation layer according to the present invention; Figure 5 This is a schematic diagram of the tungsten electrode structure in the magnetically controlled narrow-gap welding method for the safety end of the main equipment of the nuclear island in this invention; Figure 6 This is a side view of the tungsten electrode in the magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment of the present invention, without an isolation layer. Figure 7 This is a schematic diagram of the deflection of the tungsten electrode during the root pass welding in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island without an isolation layer according to the present invention; Figure 8 This is a schematic diagram of the arc oscillation during the root pass welding in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island without an isolation layer according to the present invention; Figure 9 This is a schematic diagram of the deflection of the tungsten electrode during layered filling welding in the non-isolation layer magnetic narrow gap welding method for the safety end of the main equipment of the nuclear island of the present invention; Figure 10This is a schematic diagram of arc oscillation during layered fill welding in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island without an isolation layer, according to the present invention. Figure 11 This is a first schematic diagram of the uphill welding method used in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island of the present invention, which involves welding with no isolation layer. Figure 12 This is a second schematic diagram of the upslope welding method used in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island in this invention; Figure 13 This is a schematic diagram illustrating the change of welding direction and arc initiation position in the magnetically controlled narrow gap welding method for the safety end of the main equipment of the nuclear island without an isolation layer according to the present invention. Figure 14 This is a weld surface image of the nozzle and the safety end welded using the magnetically controlled narrow gap welding method for the safety end of the nuclear island main equipment without an isolation layer, as described in this invention. Figure 15 The image shows the surface PT (Position Tolerance) pattern of the weld between the nozzle and the safety end, obtained by the magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment without an isolation layer, according to the present invention. Figure 16 This is a diagram showing the results of radiographic inspection of the weld. Figure 17 This is a macroscopic metallographic image of the weld cross-section.

[0016] In the figure, 1-connector, 2-safety end, 3-isolation layer, 4-butt weld, 5-weld overlay, 6-narrow gap bevel, 7-tungsten electrode, 8-first bevel, 9-second bevel, 10-bevel centerline, 11-left arc, 12-weld surface profile, 13-original bevel boundary, 14-right arc, 15-arc overlap area, 16-fusion line, 17-highest spatial boundary of arc, 18-first weld, 19-weld, 20-penetration area, 21-welding direction, 22-wire feed direction. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0018] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0019] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0020] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0021] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] Please see Figures 2 to 6 , Figure 2 This is a flowchart illustrating the steps of the magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment without an isolation layer, as described in this invention. Figure 3 This is a schematic diagram illustrating the alignment and assembly of the nozzle and the safety end in the magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment of the present invention. Figure 4 This is a schematic diagram of the welding of the nozzle and the safety end in the magnetically controlled narrow-gap welding method for the safety end of the main equipment in the nuclear island of the present invention. Figure 5 This is a schematic diagram of the tungsten electrode structure in the magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment of the present invention. Figure 6 This is a side view of the tungsten electrode used in the magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment without an isolation layer, according to the present invention. The present invention provides a magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment without an isolation layer, comprising the following steps: S1. The tungsten electrode tip on the welding torch is shaped into a pyramidal tip structure. The pyramidal tip structure includes a first inclined surface and two second inclined surfaces symmetrically arranged on both sides of the first inclined surface. The first inclined surface intersects with the axial generatrix of the tungsten electrode to form an angle, and the two second inclined surfaces meet at the tip apex. S2. Place the tungsten electrode at a pre-set height at the center of the bevel width and perform TIG welding within the bevel: After adjusting the deflection angle of the tungsten electrode tip structure and adjusting the welding parameters, start the arc and begin welding, so that the arc generated by the tungsten electrode swings to the two side walls of the bevel, and the highest spatial boundary swept by the arc during the swing is higher than the molten pool surface at the corresponding moment. The deflection angle is the angle at which the apex of the tungsten electrode tip rotates towards the safe end. The welding parameters include excitation frequency, welding current, duty cycle, wire feed speed, excitation current, and welding speed.

[0023] In step S1 above, the narrow gap bevel for the connection between the nozzle and the safety end is machined and formed. The narrow gap bevel adopts a variable angle U-shaped bevel. The surface oxide scale, oil, rust, and carburized layer are removed from the sidewalls, root, and area to be welded. Anhydrous ethanol is used to wipe the narrow gap bevel and the base material area on both sides of ≥50mm. After wiping, it is allowed to air dry. The bevel size, blunt edge thickness, and gap width are checked. Areas with out-of-tolerance dimensions are machined and ground to meet the drawing requirements. After completion, a penetrant test is used to check for microcracks and slag inclusions on the bevel surface. Assembly can only proceed if there are no surface defects. Then, the nozzle and the safety end are horizontally aligned and assembled, controlling the gap at the root of the narrow gap to be 0-1mm and the misalignment to be no more than 1mm. Nuclear-grade ERNiCrFe-7 welding rods are used to perform reverse tack welding at the contact position between the nozzle and the safety end. The tack weld length is ≥100mm / segment, with an interval of about 100mm, and evenly distributed on the outer circumference. Then, a φ4.0 cerium-tungsten electrode is taken, and the tungsten electrode shape is pre-treated by grinding the tip of the tungsten electrode into a pyramidal pointed structure, such as... Figure 3 and Figure 4As shown, the angle formed by the intersection of the first inclined plane and the axial generatrix of the tungsten electrode can be set to 30°, and the angle formed by the interaction of the two second inclined planes is 60°. During welding, the electric arc points towards the workpiece along the tip direction. The purpose of shaping the tungsten electrode tip into a pyramidal shape is to change the direction of the electric arc. This is because when using magnetically controlled narrow-gap TIG welding (Tungsten Inert Gas Welding, also known as tungsten inert gas welding or GTAW), the magnetic sidewall attracts the magnetic field that induces the arc oscillation. Even with increased excitation current or the number of turns of the excitation coil, it is difficult to achieve effective oscillation of the GTAW welding arc within the magnetic groove. It is impossible to completely oscillate the arc towards the non-magnetic stainless steel safety end through the magnetic field. Therefore, by changing the direction of the tungsten electrode tip and tilting the tip structure towards the stainless steel safety end, a reverse compensation for the arc position is achieved. This guides the arc offset, actively compensates for the influence of the asymmetric magnetic field on the oscillation of the magnetically controlled arc, reduces the dependence on the oversized magnetic control system, provides a prerequisite for good sidewall welding fusion, and ensures fusion on the stainless steel safety end side.

[0024] In step S2 above, the tungsten electrode is placed at the center of the narrow gap groove width, with the centerline of the tungsten electrode coinciding with the centerline of the narrow gap groove. At this time, the tip of the tungsten electrode is located at the center of the narrow gap groove width. Different molten pool-arc morphology control schemes are used for different areas of the groove. That is, by adjusting the deflection angle of the tip structure of the tungsten electrode and the welding parameters, a specific molten pool-arc morphology is obtained during the welding process. This is used to actively compensate for the asymmetrical sway of the arc caused by the difference in magnetic permeability of the base materials on both sides of the narrow gap groove and the uneven spatial distribution of the magnetic field. This allows the arc generated by the tungsten electrode to swing left and right to the sidewalls of the low-alloy steel nozzle and the safety end of the stainless steel on both sides of the groove, thereby forming a heating area on the sidewalls of the low-alloy steel nozzle and the safety end of the stainless steel on both sides of the groove. The heating area and energy density formed by the arc on the sidewalls of the nozzle and the safety end tend to be symmetrical, achieving optimal matching of arc boundary-molten pool surface-weld morphology. The deflection angle of the tungsten electrode is the angle at which the tip of the tungsten electrode rotates towards the safe end. Specifically, the deflection angle is the angle formed between the deflection line and the center line of the bevel. The deflection line is a horizontal straight line passing through the tip, and the vertical plane containing this horizontal line bisects the first inclined plane. Inert gas protection is used during welding; the inert gas is high-purity argon (Ar) ≥ 99.999%.

[0025] Additionally, the tungsten electrode is placed at a specific height at the center of the bevel width, a pre-set height, such as 6mm. Throughout the welding process, an arc height higher than that used in conventional narrow-gap TIG welding is employed, matched with a wire feed speed appropriate to the arc height. By controlling the arc's oscillation pattern, the molten pool level is ensured to remain below the highest spatial boundary actually swept by the arc under magnetic field drive during any weld pass. This allows the arc to directly cross the molten pool surface during oscillation, scanning the bevel sidewalls and areas not covered by the molten pool on the surface of the previous weld pass, achieving bevel sidewall and interlayer remelting. Simultaneously, the abundant use of cold welding wire reduces molten pool overheating, thus preventing overheating and ensuring weld performance.

[0026] Please refer to the following: Figure 11 and Figure 12 Furthermore, in the TIG welding process within the bevel, an uphill welding method is adopted. Specifically, the tungsten electrode is offset at a certain angle from the vertical direction to form an uphill welding mode. The fundamental principle lies in the coupling effect between the molten pool flow under gravity and the arc heating efficiency, which compensates for the penetration depth. Figure 12 As shown. Specifically, the tungsten electrode is offset vertically upwards by 10°, as... Figure 11 As shown, when welding from bottom to top, gravity continuously pulls the molten pool metal backward (i.e., towards the solidified weld). This synergistic effect displaces the high-temperature molten metal directly below the arc, allowing the arc to act directly on the cooler solid base material, greatly improving the efficiency of heat transfer from the arc to the workpiece, thus forming a deeper molten pool. This creates a virtuous cycle: the arc efficiently melts the new base material, while the newly formed molten metal is immediately displaced backward by gravity. In other words, the gravity-driven backward flow of the molten pool alters the heat transfer conditions between the arc and the base material.

[0027] In step S2 above, the TIG welding process within the groove includes: S21. Perform the root pass welding: The area between the top of the weld overlay and the bottom of the bevel is taken as the root pass welding area. The deflection angle of the tungsten electrode is adjusted to 0°, and the welding parameters are adjusted before arcing is started for root pass welding. S22. Perform layered filler welding: Adjust the deflection angle of the tungsten electrode to 30° and adjust the welding parameters; start the arc to perform welding filler. In each layer of filler welding, the arc continuously oscillates back and forth along the bevel under the drive of the magnetic field to complete one layer of filler welding. After each layer of welding is completed, wait for the temperature to drop to the preset temperature before performing the next layer of filler welding. S23. Perform cover welding: Adjust the deflection angle of the tungsten electrode to 30° and adjust the welding parameters; initiate arc welding for the cover plate.

[0028] In step S21 above, since the inner wall of the connector is covered with a stainless steel weld overlay, and this stainless steel weld overlay, like the safety end, is non-ferromagnetic or weakly magnetic, there is no need to compensate for the asymmetrical arc sway caused by uneven magnetic field distribution. Therefore, the area of ​​the stainless steel safety end of the stainless steel weld overlay within the bevel is used as the root pass welding area. The root pass welding area is controlled according to the symmetrical magnetic field arc sway pattern, and the deflection angle of the tungsten electrode is adjusted to 0°. Figure 7 The welding process parameters were adjusted as follows: specifically, the excitation frequency was adjusted to 1.5 Hz, the welding current to 300 A, the duty cycle to 50%, the wire feed speed to 26 mm / s, the excitation current at the safety end side and the weld overlay side to +5.5 A and -5.5 A respectively, and the welding speed to 1 mm / s. Alternating magnetic control was activated to initiate the arc and perform the root pass welding. Figure 8 The process involves controlling the molten pool-arc morphology, where the arc oscillates continuously, uniformly, and symmetrically perpendicular to both sides of the bevel. The arc's rise height is equal on both the weld overlay side and the safety end side of the bevel. During the arc's oscillation driven by the magnetic field, there is still an overlapping area between the arc and the bevel's extreme heights. The spatial boundary swept by the arc during its oscillation is higher than the corresponding molten pool surface. After each layer of welding is completed, laser cleaning is used to remove surface oxide scale. Visual inspection reveals no porosity, weld oxidation, dimensional inconsistencies, or cracks.

[0029] In step S22 above, layered filler welding is performed within the narrow gap groove after the initial root pass. The area between the low-alloy steel connector and the stainless steel safety end within the groove is the filler welding area. Since the connector is made of low-alloy steel and is ferromagnetic, the layered filler welding is controlled according to the asymmetric magnetic field arc oscillation pattern. This requires adjusting the deflection angle of the tungsten electrode tip structure to change the arc direction, guiding the arc to the non-magnetic material side, and actively compensating for the asymmetric arc oscillation caused by uneven magnetic field distribution and differences in the magnetic properties of the base materials on both sides. Therefore, the deflection angle of the tungsten electrode is adjusted to 30°. Figure 9 As shown, adjust the welding parameters, specifically: adjust the excitation frequency to 1.5 Hz, welding current to 300 A, duty cycle to 60%, wire feed speed to 26 mm / s, excitation current at +5.5 A on the safety end side and -1.5 A on the pipe side, and welding speed to 1 mm / s. Then initiate arc welding and perform layered filler welding, according to... Figure 10The diagram illustrates the control of the molten pool-arc morphology, where the arc continuously and asymmetrically oscillates perpendicular to both sides of the bevel. However, the arc's climbing height remains consistent on both the weld overlay side and the safe end side of the bevel. Furthermore, during the arc's oscillation driven by the magnetic field, there is still an overlapping area when it reaches the extreme heights on both sides of the bevel. The spatial boundary swept by the arc during its oscillation is higher than the corresponding molten pool surface. In layered filler welding, the interlayer thickness is controlled at 4mm. Welding is stopped after each layer is completed to clean the interlayer oxide scale and spatter. The next layer is welded only after the workpiece's interlayer temperature drops to 150℃. The welding direction and arc initiation position are changed with each layer. A continuously applied magnetically controlled magnetic field is used to refine the as-cast structure of the weld by stirring and oscillating the magnetic field, inhibiting the continuous growth of columnar crystals, and improving weld performance. There is no isolation layer surfacing step throughout the process; the base metal and filler metal are directly metallurgically bonded. Each layer is completed using a single-layer, single-pass magnetic oscillation mode. That is, during the welding process of this layer, the electric arc is driven by the magnetic field to continuously oscillate back and forth along the bevel once to complete the welding of one layer. The layer is no longer divided into multiple passes or an interlaced oscillation path is used.

[0030] Furthermore, controlling the uniformity of the overall welding deformation of the nozzle ensures the consistency of the bevel width at the same depth, guaranteeing that the molten pool-arc morphology control scheme is not distorted. During the root pass and layered filler welds, the welding direction and arc initiation position are changed with each layer. Specifically, the welding direction is changed sequentially at 0°, 180°, 90°, and 360°, and each two weld layers are grouped together. The arc initiation position of the next layer is symmetrical to the arc initiation position of the previous layer about the axis of the nozzle's vertical section. Figure 13 As shown, the first time is 0° to the right, the next time is 180° to the left, then 90° to the right, and finally 360° to the left.

[0031] In step S23 above, the area of ​​the low-alloy steel connector and the stainless steel safety end on the bevel surface is the cap welding area. During cap welding, molten pool-arc morphology control is also required, specifically the same as in step S23. Figure 9 and Figure 10 As shown, to actively compensate for the asymmetrical arc deflection caused by uneven magnetic field distribution and differences in the magnetic properties of the base materials on both sides, the deflection angle of the tungsten electrode was adjusted to 30° by changing the direction of the electric arc. Then, the welding process parameters were adjusted, specifically: the excitation frequency was adjusted to 1.5 Hz, the welding current to 300 A, the tungsten electrode height to 6 mm, the duty cycle to 60%, the wire feed speed to 33 mm / s, the excitation current to +5.5 A on the safety end side and -1.5 A on the pipe side, and the welding speed to 1 mm / s. Cover welding was performed within the narrow gap groove after filling, and the cover weld smoothly transitioned to the sidewalls of the base material on both sides to avoid stress concentration at sharp corners.

[0032] After welding is completed, non-destructive testing and performance verification are carried out, such as visual inspection, dimensional inspection, penetrant testing, radiographic testing, and ultrasonic testing, to check for internal and surface cracks, slag inclusions, porosity, and sidewall incomplete fusion defects in the weld. Welded specimens with the same process are taken for mechanical property testing, intergranular corrosion testing, and metallographic observation to verify that the mechanical properties and corrosion resistance of the welded joint without isolation layer meet the design standards of the main equipment of the nuclear island.

[0033] This invention relates to a magnetically controlled narrow-gap welding method for the safety end of the main equipment in the nuclear island. This method utilizes a pyramidal tip structure for the tungsten electrode, and adjusts the installation position and deflection angle of the tungsten electrode tip to alter the arc direction, actively compensating for asymmetrical arc sway caused by uneven magnetic field distribution and differences in the magnetic properties of the base materials on both sides. Furthermore, different molten pool-arc morphology control schemes (specific combinations of parameters such as excitation frequency, welding current, tungsten electrode height, duty cycle, wire feed speed, excitation current, and welding speed) are used for different areas of the structure. These schemes collectively achieve optimal matching of the arc boundary, molten pool surface, and weld morphology, ensuring good fusion between the current weld layer and the sidewall, and enabling pre-melting of the sidewall during subsequent welding layers, thus reducing the energy requirements of the oscillating arc. The aforementioned molten pool-arc morphology control scheme ensures sufficient arc climbing height on the sidewall and adequate oscillating arc energy. The overlapping areas ensure vertical fusion between layers; a single-layer, single-pass magnetic oscillation filling strategy is adopted, where the arc oscillates continuously within the groove in a specific molten pool-arc pattern to complete one layer of filling welding. In addition, in terms of weld performance control, welding parameter matching is optimized, and welding current and wire feed speed are correlated and work together. Under the premise of ensuring a specific molten pool-arc pattern with a larger current, a large amount of cold welding wire is introduced into the molten pool to reduce the temperature of the molten pool, thereby avoiding overheating of the molten pool and ensuring weld performance. At the same welding speed, the single-layer deposition thickness is larger, the number of weld passes is significantly reduced, and the welding efficiency is improved, while still ensuring sufficient fusion between layers and sidewalls. The efficiency is better than that of interlaced welds with two passes per layer. At the same time, an unconventional arc starting position setting is adopted to achieve compensation of the oscillating arc in the molten pool depth direction when the arc height is increased and the heat input remains unchanged.

[0034] Furthermore, the magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment of the present invention, which involves welding without an isolation layer, also includes: S3. After welding, perform post-heating on the connector and safety end, and then perform slow cooling. S4. After the connector and safety end have cooled to room temperature, perform heating, heat preservation and cooling treatments on the connector and safety end.

[0035] In steps S5 and S6 above, the nozzle and safety end are post-heated using an electric heating device at a temperature of 250-400℃ for 2 hours (h / min), where h represents hours and min represents the minimum value. The minimum post-heating time is 2 hours. After post-heating, slow cooling is performed. Once the nozzle and safety end have cooled to room temperature, they are placed into a heat treatment furnace and subjected to heating, holding, and cooling treatments according to nuclear-grade equipment heat treatment specifications. The holding temperature is 595-620℃ for 2 hours, and the heating and cooling rates are less than or equal to 55℃ / h to eliminate residual welding stress.

[0036] Please refer to the following: Figures 14 to 17 This invention relates to a magnetically controlled narrow-gap welding method for the safety end of the main nuclear island equipment, which achieves the welding of a simulated safety end component without an isolation layer in a certain project. This method yields a direct butt joint between a low-alloy steel connector and a stainless steel safety end component without an isolation layer. Figures 14 to 17 As shown, the welding process was stable, the weld formation was good, and no defects such as sidewall incomplete fusion or poor interlayer bonding were found. The weld's non-destructive testing, mechanical properties, macro- and micro-structure all met the design requirements.

[0037] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Therefore, any simple modifications, equivalent changes and alterations 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 shall still fall within the scope of the technical solution of the present invention.

Claims

1. A method for magnetically controlled narrow-gap welding without an isolation layer at the safety end of a nuclear island main equipment, characterized in that, Includes the following steps: S1. The tungsten electrode tip on the welding torch is shaped into a pyramidal tip structure. The pyramidal tip structure includes a first inclined surface and two second inclined surfaces symmetrically arranged on both sides of the first inclined surface. The first inclined surface intersects the axial generatrix of the tungsten electrode to form an angle, and the two second inclined surfaces meet at the tip apex. S2. Place the tungsten electrode at a pre-set height at the center of the bevel width, and perform TIG welding within the bevel: After adjusting the deflection angle of the tip structure of the tungsten electrode and adjusting the welding parameters, start the arc and begin welding, so that the arc generated by the tungsten electrode swings to the two side walls of the bevel, and the highest spatial boundary swept by the arc during the swing is higher than the molten pool surface at the corresponding moment. The deflection angle is the angle at which the tip of the tungsten electrode rotates towards the safe end. The welding parameters include excitation frequency, welding current, duty cycle, wire feed speed, excitation current, and welding speed.

2. The method for non-isolated, narrow-gap magnetic welding of the safety end of the main equipment of the nuclear island according to claim 1, characterized in that, The step of performing TIG welding within the groove includes: S21. Perform the root pass welding: The area between the top of the weld overlay and the bottom of the bevel is taken as the root welding area. The deflection angle of the tungsten electrode is adjusted to 0°. After adjusting the welding parameters, the arc is started to perform the root welding. S22. Perform layered filler welding: The deflection angle of the tungsten electrode is adjusted to 30°, and the welding parameters are adjusted. The arc is started to perform welding fill. In each layer of fill welding, the arc is driven by the magnetic field to swing back and forth along the bevel in a continuous circle to complete one layer of fill welding. After each layer of welding is completed, the temperature needs to be lowered to the preset temperature before the next layer of fill welding is performed. S23. Perform cover welding: Adjust the deflection angle of the tungsten electrode to 30° and adjust the welding parameters; initiate arc welding for the capping surface.

3. The method for non-isolated, narrow-gap magnetic welding of the safety end of the main equipment of the nuclear island according to claim 2, characterized in that, In the steps of performing the root pass welding and the layered fill welding, the welding direction and arc initiation position are changed for each layer.

4. The method for non-isolated, narrow-gap magnetic welding of the safety end of the main equipment of the nuclear island according to claim 2, characterized in that, In step S21, the excitation frequency is adjusted to 1.5 Hz, the welding current is 300 A, the duty cycle is 50%, the wire feed speed is 26 mm / s, the excitation current is +5.5 A on the safety end side and -5.5 A on the weld overlay side, and the welding speed is 1 mm / s.

5. The method for non-isolated, narrow-gap magnetic welding of the safety end of the main nuclear island equipment according to claim 2, characterized in that, In step S22, the excitation frequency is adjusted to 1.5 Hz, the welding current is 300 A, the duty cycle is 60%, the wire feed speed is 26 mm / s, the excitation current is +5.5 A on the safety end side and -1.5 A on the pipe side, and the welding speed is 1 mm / s.

6. The method for non-isolated, narrow-gap magnetic welding of the safety end of the main equipment of the nuclear island according to claim 2, characterized in that, In step S23, the excitation frequency is adjusted to 1.5 Hz, the welding current is 300 A, the duty cycle is 60%, the wire feed speed is 33 mm / s, the excitation current is +5.5 A on the safety end side and -1.5 A on the pipe side, and the welding speed is 1 mm / s.

7. The method for magnetically controlled narrow-gap welding without isolation layer at the safety end of the main equipment of the nuclear island according to claim 1, characterized in that, In the step of performing TIG welding within the groove, uphill welding is adopted.

8. The method for magnetically controlled narrow-gap welding without isolation layer at the safety end of the main equipment of the nuclear island according to claim 1, characterized in that, The method further includes: S3. After welding, perform post-heating on the connector and safety end, and then perform slow cooling. S4. After the connector and safety end have cooled to room temperature, the connector and safety end are subjected to heating, heat preservation and cooling processes.

9. The method for non-isolated, narrow-gap magnetic welding of the safety end of the main equipment of the nuclear island according to claim 7, characterized in that, In step S3, the post-heating temperature is 250-400℃, and the time is 2 hours. In step S4, the heat preservation temperature is 595-620℃, the heat preservation time is 2h, and the heating and cooling rates are less than or equal to 55℃ / h.

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