Enhanced pulse TIG automatic welding process method for two sides of circumferential weld of metal pipeline

Abstract

The invention relates to the technical field of pipeline welding, and particularly discloses a metal pipeline circumferential weld two-side enhanced pulse TIG (Tungsten Inert Gas) automatic welding process method which comprises the following steps: when filling and covering wire filling welding are carried out around a pipeline, a welding torch tungsten needle swings back and forth in a preset welding groove at a constant speed; when the tungsten needle swings to the positions, close to the slope surfaces on the two sides, of the groove, the TIG automatic welding machine triggers instantaneous pulse enhanced current to increase the area of an electric arc bell jar, and the residence time on the two sides is shortened so as to reduce the fusion depth; and when the tungsten needle begins to swing towards the middle position of the groove, the TIG automatic welding machine instantaneously reduces the current so as to maintain arc combustion and continuously melt the welding wire. According to the process, a dynamic current cooperative control welding method that end points on the two sides of arc swing trigger instantaneous enhanced current is innovated, and the defects that a direct-current automatic welding process is low in welding speed, strict in alignment requirement, fine in parameter setting, frequent and complex in on-site parameter adjustment and not beneficial to the welding seam forming quality are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of pipeline welding, and particularly relates to an enhanced pulsed TIG automatic welding process method for both sides of the circumferential weld of metal pipelines. Background Art

[0002] With the progress of welding technology, the automatic welding technology for pipeline circumferential welds is gradually being applied. At present, MAG pipeline automatic welding equipment has been applied in the welding construction of metal pipelines with larger diameters. This equipment usually requires certain technical conditions, such as a high-precision on-site beveling machine, a high requirement for butt joint accuracy, and cooperation with internal and external automatic welding machines. The weld formation is beautiful and the quality is reliable. However, for small-diameter pipelines such as butt-joint pipelines with a diameter less than DN150, since there is no suitable internal welding machine to enter the pipeline for welding, only the single-sided welding method can be used. The MIG automatic welding method cannot be applied to the butt-joint welding construction of small-diameter pipelines at present.

[0003] The TIG welding method has the characteristics of single-sided welding with double-sided formation, and the weld pool is intuitive and the quality is controllable. Therefore, applying the DC TIG welding method to the automatic welding of small-diameter pipelines has certain advantages. However, since buried pipelines must be welded and connected on the ground for a certain length and then connected in the ditch, only the welding machine can be used to perform 360° circumferential welding around the butt joint pipe orifice.

[0004] The TIG circumferential weld automatic welding machine generally adopts a C-shaped structure. Among them, the argon arc welding torch installed on the rotating turntable makes a circular motion around the weld under the drive of a program-controlled motor, and at the same time, welding actions such as tungsten electrode oscillation and arc voltage tracking are completed through a sliding module, and the action of filling the welding material is completed through a wire feeder.

[0005] The welding method of the TIG circumferential weld automatic welding machine has two characteristics: First, the tungsten needle always points in the direction of the center of the circle. During root welding, the tungsten needle does not oscillate or oscillates with a short distance. During filling and capping welding, the tungsten needle oscillates vertically and cannot change the welding angle. Second, different welding positions are transformed into circumferential segmented welding. Usually, it is divided into 3 or 4 segments according to the pipe diameter, and the welding direction is simplified to the downward welding direction and the upward welding direction. Different welding parameters are selected for the same welding direction and different welding positions as shown in the appendix. Figure 1 as follows

[0006] Determined by the characteristics of the welding method of the TIG circumferential weld automatic welding machine, there are problems of "inner convex" at the flat welding position and "inner concave" at the overhead welding position of the root weld layer caused by the continuous DC welding current and the gravity drop of the weld pool in the TIG automatic weld formation. Patent CN116000415A proposes an automatic pulsed TIG argon arc welding process, which is a combined process of pulsed backing + DC filling and capping. The "pulsed backing" process solves the above problems existing in the root pass weld bead. However, the "DC filling and capping" process can only be solved by increasing the arc residence time on both sides to melt the two sides' surfaces and fuse them with the filler metal. This will bring new problems: 1. To ensure good fusion between the molten pool and the two sides of the groove surface, the arc must stay on both sides during oscillation. If the welding speed is to be increased, it is necessary to increase the welding current and the welding line energy. Under the condition of high heat input, if the DC arc residence time on both sides is too long, the temperature of the molten pool will be too high, making it impossible for the molten iron to solidify quickly. The molten iron will flow towards the center of the weld due to gravity. There are three results: First, during the welding of the filling weld layer, it will cause the center of the weld at the 12 o'clock to 3 o'clock position of the downhand weld bead to sink and the center of the weld at the 9 o'clock to 12 o'clock position of the uphand weld bead to bulge. The molten pool that sinks at the 12 o'clock to 3 o'clock position will block the arc, making it difficult for the filling molten pool to fuse with the groove surface. The weld bead that bulges at the 9 o'clock to 12 o'clock position will form an angle with the root of the groove surface, causing trouble for the welding of the capping weld layer; Second, during the welding of the capping weld layer, it will also cause the penetration on both sides to be too deep due to the long arc residence time on both sides, and the "undercut" problem will occur at the 9 o'clock to 11:30 and 12:30 to 3 o'clock positions of the capping weld layer due to the high temperature of the molten pool sinking, as shown in the attachment Figure 2 ; Third, if the arc residence time on both sides is too long, it will cause the penetration of the groove surface to be too large, resulting in grain coarsening in the heat affected zone and affecting the mechanical properties of the weld.

[0007] 2. If the welding current is reduced and the residence time on both sides is decreased to increase the solidification speed of the molten pool in order to avoid the occurrence of the above problems, the welding speed will be reduced, affecting the construction efficiency, and it is easy to occur the defect of "incomplete fusion with the groove surface".

[0008] Although the DC filling and capping process proposed in the existing patent CN116000415A does not solve the sidewall control problem during the oscillating welding of filling and capping, it is also difficult to increase the welding speed.

[0009] The vast majority of single-well pipelines in oilfields have a diameter less than DN150. According to investigations, 70-80% of the parts where the pipeline corrodes and perforates are concentrated in the weld area. This is because the field welding construction environment is harsh and there is a shortage of highly skilled welders, so it is very difficult to ensure the weld quality. Taking the Shengli Oilfield as an example, there are 2.5 hidden dangers per kilometer of single-well pipelines on average, and it is very difficult to maintain the pipeline life for more than 3 years. Some pipelines perforate within less than one year of operation. The economic losses caused by pipeline maintenance and environmental pollution due to corrosion exceed 200 million yuan per year, and the economic losses caused by repeated construction are even incalculable. This is also one of the reasons for the high oilfield production costs. Therefore, providing an advanced TIG automatic welding process equipment for small-diameter pipelines to replace highly skilled welders has a huge market demand. Summary of the Invention

[0010] The purpose of the present invention is to provide an enhanced pulse TIG automatic welding process method for both sides of the circumferential weld of metal pipelines in view of the defects existing in the prior art.

[0011] The technical solution of the present invention is: an enhanced pulse TIG automatic welding process method for both sides of the circumferential weld of metal pipelines, including the following steps: When filling and capping wire welding around the pipeline, the tungsten needle of the welding torch swings back and forth uniformly in the preset groove for welding; When the tungsten needle swings to the position near the side slopes of the groove, the instantaneous pulse enhanced current of the TIG automatic welding machine increases the area of the arc bell, reducing the residence time on both sides; When the tungsten needle starts to swing towards the middle position of the groove, the TIG automatic welding machine instantaneously reduces the current to maintain the arc combustion and continuously melt the welding wire.

[0012] Compared with the prior art, the present invention has the following advantages: 1. This process uses a continuous and controllable pulsed current to penetrate the root of the groove surface of the butt joint pipe orifice and fuse with the filled welding wire to form a root welding bead connected by a uniform weld bead, preventing the occurrence of the "inner convex" phenomenon at the flat welding position and the "inner concave" phenomenon at the overhead welding position of the root welding layer caused by the gravity drop of the molten pool. The welding layer is formed with single-sided welding and double-sided forming, and there are no defects in the back welding bead; 2. This process uses a relatively large instantaneous enhanced current to quickly melt the surface of the side slopes on both sides and form a filler welding layer with the filled welding wire, and uses a relatively small arc-maintaining current to maintain the arc combustion, accelerating the condensation speed of the molten pool and avoiding the surface depression of the weld bead at the downhand welding position and the surface protrusion of the weld bead at the uphill welding position caused by the overheating of the molten pool at the weld center; 3. The instantaneous pulse enhanced current on both sides of this process increases the area of the arc bell, improving the fusion area of the side walls of the filler / capping layer groove, relatively reducing the welding line energy, refining the grains in the heat affected zone, and ensuring the mechanical properties of the weld zone; 4. In this process, the instantaneous pulse enhanced current on both sides can be set, making the penetration depth on both sides of the arc controllable, avoiding the occurrence of the defect of "incomplete fusion between the filling weld layer and the groove surface", eliminating the "undercut" defect of the cover weld layer, and achieving a smooth transition on the weld layer surface. 5. Since this process adopts the instantaneous enhanced current on both sides, the residence time on both sides of the arc is reduced. Without increasing the heat input, a relatively large instantaneous welding current can be appropriately selected to improve the welding speed.

[0013] 6. This process innovates the dynamic current collaborative control welding method that triggers the instantaneous enhanced current at both endpoints of the arc swing, making up for the deficiencies of the DC automatic welding process, such as slow welding speed, strict butt joint requirements, fine parameter settings, frequent and complex on-site parameter adjustment, and being unfavorable to the weld forming quality. It has the advantages of convenient parameter storage and call, simple operation, fast welding speed, and reliable weld quality, and has great popularization value for oilfield pipeline construction. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of the circumferential segmentation and welding direction of TIG automatic welding; Figure 2 It is a schematic diagram of weld undercut; Figure 3 It is a schematic diagram of weld layer distribution; Figure 4 It is a chart of welding process parameters; Figure 5 It is a weld diagram of a ∅76×7mm seamless steel pipe; Figure 6 It is a schematic diagram of the microscopic structure of the weld specimen; Figure 7 It is a diagram of the bending test and radiographic image of the welded part; Figure 8 It is a schematic diagram of butt joint with misalignment. Detailed Implementation Modes

[0015] The following further describes the present invention in conjunction with the drawings and embodiments. Embodiment 1

[0016] The enhanced pulse TIG automatic welding process method for the circumferential welds on both sides of metal pipelines includes the following steps: S1: Open a bevel groove at the butted pipe orifices of two sections of steel pipes to form a V-shaped groove; S2: Use a pipe-wrapping type TIG automatic welding machine to operate on the groove, and divide the butted V-shaped groove from deep to shallow into a root weld layer, a filling weld layer, and a cover weld layer, as Figure 3 shown, and weld them in sequence from deep to shallow; S3: When performing wire filling welding for the root welding layer, start the welding program at the arc starting position about 5 mm from the bottom along the central axis where the tungsten needle of the TIG automatic welding torch extends into the groove. When welding around the pipe, the tungsten needle does not swing. The welding current starts automatic welding with the set pulsed current, and the pulsed current changes periodically between the base value and the peak value, for example, 3 times per second. S4: When performing wire filling welding for filling and capping around the pipe, the tungsten needle arc of the welding torch swings back and forth uniformly in the V-shaped groove at the pipe orifice butt joint. When the tungsten needle swings to the positions near the two side slopes of the groove, the TIG automatic welding machine instantaneously triggers a pulsed enhanced current to increase the arc bell area to improve the cladding rate, reduce the residence time on both sides to reduce the penetration depth of the two side groove faces and increase the cladding speed. When the tungsten needle starts to swing towards the middle position of the groove, the TIG automatic welding machine instantaneously reduces the current to maintain the arc combustion and continuously melt the welding wire.

[0017] This process uses a relatively large instantaneous enhanced current to quickly melt the surfaces of the two side groove faces and form a filling welding layer with the filled welding wire, and uses a relatively small arc maintaining current to maintain the arc combustion, which speeds up the molten pool condensation speed and avoids the surface depression of the weld bead in the downhand welding position and the surface protrusion of the weld bead in the uphill welding position caused by overheating of the molten pool at the weld center. It improves the fusion area of the side walls of the filling / capping layer groove, relatively reduces the welding line energy, refines the grains in the heat affected zone, and ensures the mechanical properties of the weld zone. In this process, the settable instantaneous pulsed enhanced current on both sides makes the penetration depth on both sides of the arc controllable, avoids the occurrence of the defect of "incomplete fusion with the groove face" in the filling welding layer, eliminates the "undercut" defect in the capping welding layer, and the surface of the welding layer has a smooth transition. Example 2

[0018] This example conducts experiments using the enhanced pulsed TIG automatic welding process method for both sides of the circumferential weld of metal pipes in the above example, specifically as follows: The experimental steel pipe selects a 20 steel seamless steel pipe with a diameter of ∅76×7 mm. Use a sanding wheel to clean the inner and outer surfaces within about 10 mm of the pipe orifice. Use an inverter DC pulsed welding power source, equipped with a TIG automatic welding head, and the shielding gas is Ar gas. Pipe orifice alignment and positioning: Use wire filling argon arc welding for positioning welding. The length of each positioning weld bead is not less than 15 mm, and they are evenly distributed on the circumference and not less than 3 places. Control the height of the positioning weld bead not to exceed 1.5 mm. If the weld bead height is too high, it needs to be ground to the required height to ensure that the positioning weld bead can be remelted into a part of the root weld bead during root welding. The opening angle of the V-shaped groove is 30°.

[0019] As Figure 2As shown in the figure, the circumferential all-position welding of the girth weld includes: flat welding position, overhead welding position, vertical welding position, including 2 welding directions of vertical up and vertical down. Therefore, it is necessary to change the welding parameters in different circumferential partitions and divide into multiple regions for parameter setting.

[0020] The root pass layer is divided into four regions. The first region is from 1° to 90°, the second region is from 90° to 180°, the third region is from 180° to 240°, and the fourth region is from 240° to 370°. The base values of the welding current in the four regions are the same, and the peak values of the welding current in the first region and the fourth region are higher than those in the other two regions.

[0021] The filler and cap pass layers are divided into three regions. The first region is from 1° to 120 degrees, the second region is from 120° to 240°, and the third region is from 240° to 365°. When welding the filler pass layer, the base value of the welding current in the second region is higher than that in the first region and the third region, and the peak value of the welding current in the second region is lower than that in the first region and the third region. When welding the cap pass layer, the peak values of the welding current in the three regions are the same, and the base value of the welding current in the second region is higher than that in the first region and the third region.

[0022] The specific set parameters are as Figure 4 shown. The reason for setting the starting arc angle and ending arc angle is as follows: Starting the arc at a position a little after 12 o'clock, due to the lag of wire feeding and the gravity drop, the molten pool formed by the filler wire will flow towards the 1 o'clock direction. The starting point of the weld bead to the highest point of the weld bead will be in a gentle slope shape, which is also the best shape of the starting weld bead and is conducive to the lap joint with the terminal of the weld bead. Due to the above reasons, the terminal of the weld bead must cross the starting arc position, otherwise the girth weld bead cannot be lap jointed to form a continuous weld bead.

[0023] Weld the seamless steel pipe of 20 steel with ∅76×7mm in sequence according to the above welding parameters for the root pass layer, filler pass layer, and cap pass layer. As Figure 5 shown, the weld surface is regular and compact; Visual inspection during welding: The appearance of the molten pool of each weld layer has no defects and is well fused with the groove surface of the base pipe.

[0024] Visual inspection after welding: The weld reinforcement is about 1.0mm, the cap pass layer is well fused with both sides of the base pipe, and no "undercut" phenomenon is seen.

[0025] Prepare a weld specimen and observe and analyze its microstructure as Figure 6 shown; It can be observed that: 1. On one side of the fusion zone of the filler weld, the organizational structure is uniform, and fine ferrite, pearlite, and granular bainite structures can be seen. This is because after continuous automatic welding, the subsequent weld layer heats the previous weld layer, causing phase transformation and recrystallization phenomena. This kind of structure is conducive to maintaining the toughness of the weld. 2. The fusion depth of the weld fusion zone is relatively shallow, and the carbon enrichment phenomenon on the base metal side is weak.

[0026] The butt welds of the experimental welded parts passed the radiographic inspection and mechanical property tests. Among them, there were 6 radiographic images in total, the inspection ratio was 100%, and all the evaluation levels were Class Ι. Among them, the results of the tensile test, bending test, impact test, and notched hammer break test carried out according to the SY / T0452[3] standard were 100% qualified. The bending test of the welded part and the radiographic image are as Figure 7 shown.

[0027] In addition, to verify the adaptability of the "two-side reinforcement" pulsed automatic welding on site, test pieces were specially made. The ∅76×7 and ∅76×8 were butt-welded with misalignment, and the butt gap on one side was intentionally positioned at 0 mm and about 1.5 mm at the other end. Welding experiments were carried out using the above automatic welding parameters, as Figure 8 shown. The experimental results show that: This welding process does not require precise adjustment of welding parameters and has strong adaptability to changes in the on-site welding environment.

[0028] The present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the purpose of the present invention, and the changed content still belongs to the protection scope of the present invention.

Claims

1. The enhanced pulsed TIG automatic welding process method for both sides of the circumferential weld of metal pipelines, characterized in that: It includes the following steps: When filling and surfacing wire feeding welding are carried out around the pipeline, the tungsten needle of the welding torch swings back and forth uniformly in the preset groove for welding; When the tungsten needle swings to the positions near the two side slopes of the groove, the instantaneous pulse enhanced current of the TIG automatic welding machine increases the arc bell cover area and reduces the residence time on both sides; When the tungsten needle starts to swing towards the middle position of the groove, the TIG automatic welding machine instantaneously reduces the current to maintain the arc combustion and continuously melt the welding wire.

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