An automatic pipe-to-pipe butt welding process for hydraulic stainless steel pipelines

Abstract

The present invention discloses an automatic pipe-to-pipe butt welding process for hydraulic stainless steel pipelines. The present invention utilizes a technical solution using a fixing or a steel threaded air inlet joint with a clamping sleeve to achieve automatic butt welding of pipe joints and steel pipes of any clampable length, achieving a 100% automatic welding ratio for hydraulic pipelines. The present invention also utilizes a tungsten electrode gap gauge and a technical solution for adjusting the relative position of the tungsten electrode and the center of the groove to stabilize welding quality, resolve the issue of weld deviation from the center of the groove, and achieve a single-sided welding and double-sided forming effect. The present invention also utilizes a technical solution for debugging welding parameters through an algorithm, which can quickly predict reasonable welding parameters when product specifications change, thereby reducing the number of welding tests. By rationally adjusting the process parameters, the single-sided welding and double-sided forming effect can be achieved for hydraulic pipelines of equal or unequal diameters with a thickness of 2 to 4 mm.

Description

Technical Field

[0001] The invention relates to the technical field of pipeline welding, in particular to an automatic pipe-to-pipe butt welding process for hydraulic stainless steel pipelines. Background Art

[0002] Currently, domestic application of automatic pipe-to-pipe butt welding processes is primarily focused on high-precision tubing in the aviation sector, with limited experience in chassis hydraulic piping. Chassis piping primarily includes suspension hydraulic system piping, steering hydraulic system piping, engine piping, transmission piping, brake piping, and drive piping. These piping systems are primarily made of stainless steel. Due to the low thermal conductivity of stainless steel, using the same welding parameters during girth welds results in poor initial penetration and high weld temperatures later, which can easily cause burn-through. Most automatic pipe welding processes utilize stepwise decreasing process parameters, making parameter adjustment increasingly difficult as pipe diameter decreases and wall thickness increases. Aviation pipe wall thicknesses range from 0.6 to 1 mm, while chassis piping has a thicker wall thickness range of 2 to 4 mm and a wide diameter range of 6 to 38 mm. Consequently, chassis piping places even greater demands on heat input control during welding. Due to the increase in wall thickness, the difficulty of weld formation increases accordingly due to the heavier molten pool in vertical and overhead welding positions. Therefore, when achieving the same welding quality, the welding of chassis hydraulic pipelines is more difficult.

[0003] Automatic welding equipment requires a certain linear distance on either side of the weld to meet the equipment's clamping requirements, hereinafter referred to as the clamping length. For closed-type pipe welding clamps, the clamping length must be equal to or greater than the distance between the tungsten electrode and the outer wall of the clamp. Open-type welding equipment requires greater space on either side of the weld, requiring room for the welding torch to rotate. To meet the assembly requirements of various chassis systems, hydraulic pipelines have diverse shapes, often resulting in distortion of the steel pipe near the weld seam and a corresponding shortening of the joint length. Due to the limited operating space available for welding equipment, common open-type welding equipment cannot perform automated welding, while closed-type pipe welding clamps are generally unsuitable for pipes thicker than 3mm, requiring the use of both types of equipment alternately. Manual welding requires high worker skill and difficult to control weld quality. Furthermore, the parameter tuning method for multi-stage welding processes is complex, requiring multiple test welds for verification, which wastes significant manpower and material resources. Therefore, achieving and controlling consistent weld quality is a major new challenge facing chassis piping production.

[0004] Document CN103962684B discloses an automatic welding method for hydraulic rigid pipe assemblies, but it also has certain shortcomings. The welding method described in the document achieves an automatic welding rate of 85.6%, failing to fully implement automatic welding of hydraulic pipelines. Because closed welding tongs can only weld pipes with a wall thickness of less than 2mm, pipes with a wall thickness greater than 2mm require a closed welding tongs for base welding, followed by a filler wire weld using open automatic welding equipment. This requires two welding processes using two different pieces of equipment, making the production process complex. Furthermore, the joints must be machined to the same inner and outer diameters as the conduit before welding can proceed, which increases the processing steps and fails to provide a solution for butt welding of unequal-diameter joints.

[0005] In conventional argon arc welding, the center of the tungsten electrode points to the center of the groove. However, when welding hydraulic pipelines, the center of the tungsten electrode deviates from the center of the weld seam on both the front and back sides. The width of the back weld seam ranges from 1 mm to 4 mm. When the back weld seam deviates significantly from the center of the groove, it can result in incomplete weld penetration at the root. To ensure full weld penetration on the back side, the relative position of the tungsten electrode and the groove center must be adjusted. There is currently no consensus on the mechanism of this deviation, and there is no effective solution to compensate for it.

[0006] In summary, the existing technology lacks effective solutions for the problems of how to achieve fully automatic welding of hydraulic pipelines, how to achieve the goals of single-sided welding and double-sided forming of chassis hydraulic pipelines and single-sided welding and double-sided forming of unequal diameter joints in one welding process. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, the present invention provides an automated pipe-to-pipe butt welding process for hydraulic stainless steel pipelines. This process is capable of welding pipe joints and steel pipes of any clampable length, achieving a 100% automated welding ratio. The automated welding process provided by the present invention enables single-sided welding and double-sided formation of pipe joints of equal or unequal diameters and steel pipes, achieving Class I welds as specified in QJ2865A-2014, "Technical Requirements for Conduit Welding." The technical solutions employed by the present invention are as follows:

[0008] A pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines, comprising the following steps:

[0009] The first step is to saw the stainless steel conduit into pieces.

[0010] The second step is to flatten the end of the catheter.

[0011] The third step is to bend the conduit after the flat end with a hydraulic pipe bender.

[0012] Step 4: Clean the catheter.

[0013] The fifth step is to spot weld the conduit and the welded pipe joints. Use an argon arc welder and do not use filler wire for positioning welding. Before welding, clean the welds of the conduit and joints to be welded with industrial acetone wipes.

[0014] Step 6: Install the welding clamp on the welding clamp bracket. The welding clamp is a closed pipe welding clamp. A fixing piece for clamping the pipeline is installed on the welding clamp bracket, or a steel threaded air inlet connector with a clamping end is directly clamped on the welding clamp. The fixing piece is selected from a flat clamp or a concave clamp, and the flat clamp or concave clamp respectively includes upper and lower semicircles. The pipeline includes a pipe joint and a stainless steel conduit. The pipe joint includes a joint body and a pipe joint nut.

[0015] Step 7: Place the tungsten electrode gap gauge in the welding clamp, and position the tungsten electrode after dropping it to the middle diameter position of the gap gauge.

[0016] The eighth step is to place the pipeline into the welding clamp, adjust the relative position of the pipeline groove center and the tungsten electrode according to the comparison results of the size and material of the joint body and the conduit, clamp the pipeline, and clamp the pipeline by adjusting the height of the set screw on the upper half of the clamp.

[0017] When the pipeline is too long, the other side of the steel pipe is placed on the steel pipe bracket.

[0018] The ninth step is to install the air inlet and outlet devices of the protective gas in the pipeline.

[0019] The tenth step is to use the formula to estimate the average heat input based on the diameter and wall thickness of the joint body, calculate the heat input value of each segment based on the average heat input, set the welding speed and pulse time, and after deducing the peak and base welding current values ​​from the formula, enter the welding program for a test weld, and then adjust the parameters according to the welding results until the welding quality is qualified.

[0020] The eleventh step is to automatically weld the batch-welded conduits and pipe joints.

[0021] Preferably, the stainless steel hydraulic pipeline is made of austenitic stainless steel, and its outer diameter ranges from 6 to 38 mm, and the wall thickness is 2 to 4 mm; one side of the butt-jointed pipeline is a pipe joint, and the other side is a stainless steel conduit, and at least one of the outer diameter, inner diameter and wall thickness of the pipe joint body and the conduit must be the same; when the diameters are equal or the outer diameters are equal and the inner diameters are unequal, a flat-end pipe joint is selected, and when the difference between the outer diameter of the pipe joint and the outer diameter of the conduit is greater than or equal to 1 mm, a bevel pipe joint is selected; the outer diameter, inner diameter and wall thickness of the steel pipe and the pipe joint that are butt-jointed on both sides must be the same; when the wall thickness is the same, the difference between the outer diameter and the inner diameter is not greater than 2 mm; when one of the outer diameter or the inner diameter is the same, the wall thickness difference is not greater than 1 mm.

[0022] In the sixth step, the tungsten electrode is installed on the rotor gear of the welding clamp. Its axial direction cannot be adjusted, and a suitable fixing part needs to be selected before installing the pipeline.

[0023] The method of clamping a steel threaded air inlet joint with a clamping end on the welding clamp is simple and convenient; in order to directly perform a more stable clamping at the joint of the pipe joint, a flat clamp or a concave clamp can be used, and the concave clamp includes a first-level indented concave clamp and a second-level indented concave clamp. The first-level indented concave clamp is indented into the clamp body to 0~0.5mm before the thread of the fastening bolt hole, and the indented diameter is larger than the maximum outer diameter of the pipe joint nut; the second-level indented clamp moves the fastening bolt hole out of the clamp, and the fastening bolt hole is arranged radially.

[0024] Preferably, when the clampable length of the pipe joint is less than the distance from the tungsten electrode to the outer wall of the welding clamp, a first-stage indented concave clamp or a second-stage indented concave clamp is used according to the degree of reduction in the clampable length; the center hole of the concave clamp is the same as the outer diameter of the pipe joint or the steel pipe, and when the distance from the tungsten electrode to the outer wall of the welding clamp is the total length of the joint or the clamping position is at the nut part of the pipe joint, a steel threaded air inlet joint with a clamping end is clamped on the welding clamp.

[0025] Further preferably, when the pipe joint can clamp a pipe with a length greater than the distance from the tungsten electrode to the outer wall of the welding clamp, a flat clamp is selected, and the center hole of the clamp is the same as the outer diameter of the pipe joint or the steel pipe; at this time, a larger clamping area can be guaranteed, and the clamping point is coplanar with the clamp, and the clamping force is greater.

[0026] When the clampable length of the steel pipe is less than the distance from the tungsten electrode to the outer wall of the welding clamp, it is impossible to use a clip clamp. At this time, a card clamp is used. The card clamp includes two U-shaped card plates, one of which is an aluminum alloy card plate and the other is a high-temperature resistant flame-retardant nylon card plate; the aluminum alloy must be in contact with the conduit and the welding clamp to achieve a conductive effect; the high-temperature resistant flame-retardant nylon card plate is placed outside the aluminum alloy card plate and crosses the aluminum alloy card plate to prevent air leakage; the nylon card plate is clamped on the welding clamp with an insulating clip for fixation.

[0027] In step 7, the tungsten electrode gap gauge used is a stepped cylindrical structure, with the middle cylinder used to locate the radial position of the tungsten electrode. The middle diameter is determined as follows: Middle Diameter = Side Diameter + 2 × Tungsten Electrode Gap. The side diameters represent the outer diameter of the pipe fitting or the outer diameter of the conduit. When the outer diameters of the pipe are different, the larger diameter is used. The tungsten electrode gap is the distance from the tungsten electrode tip to the outer diameter of the larger pipe. The tungsten electrode gap h is a function of the pipe wall thickness, and the formula for h is: h = 0.5 * δ ;

[0028] Where δ is the wall thickness. When the wall thicknesses on both sides of the pipeline are different, the value is the one with the larger wall thickness. The unit is mm.

[0029] In step 8, the tungsten electrode is used as a reference to locate the center of the groove. The relative position of the groove center relative to the tungsten electrode tip is within a range of ±0.5mm. Since the tungsten electrode is now fixed, the relative position of the groove center and the tungsten electrode tip is adjusted by adjusting the pipe position. The relative position of the tungsten electrode and the groove center is adjusted based on the size and material comparison between the fitting body and the conduit. When the wall thickness of the fitting body and conduit is different, the tungsten electrode is offset toward the thicker wall by (0, 0.5) mm. When the wall thickness is the same, the tungsten electrode is offset toward the larger outer diameter by (0, 0.5) mm. When the wall thickness is different, the thicker wall requires more energy to melt the parent material. When the wall thickness is the same, the larger outer diameter side has a transition groove, and the groove surface slope causes the arc to deflect downward. To ensure that the inner wall of the smaller inner diameter side is fully melted and forms a transition connection with the inner wall of the larger inner diameter side, the tungsten electrode should be offset toward the larger outer diameter side.

[0030] Specifically, the relative position of the tungsten electrode and the center of the groove is adjusted by moving the pipeline. When the wall thickness of the joint body and the pipe is different, the pipeline is moved to make the tungsten electrode deviate to the side with the larger wall thickness, with an offset of (0, 0.5] mm; when the wall thickness is the same, the pipe is moved to make the tungsten electrode deviate to the side with the larger outer diameter, with an offset of (0, 0.5] mm; when welding with equal diameters (when the inner diameter and outer diameter on both sides of the weld are equal), the tungsten electrode should be deviated to the side with higher silicon content. Based on the silicon content of the pipeline being 0.3% to 0.4%, when When the silicon content of the joint body is less than 0.3%, the pipeline is moved so that the tungsten electrode is deflected toward the guide tube (0, 0.3] mm); when the silicon content of the joint body and the steel pipe is both within the range of 0.3-0.4%, the tungsten electrode is not deflected; when the silicon content of the joint body is higher than 0.4%, the pipeline is moved so that the tungsten electrode is deflected toward the joint body (0, 0.3] mm). The silicon content can be estimated by the appearance of the weld. When the silicon content is less than 0.3%, the weld has a bright surface, and when the silicon content is higher than 0.4%, the weld has a matte surface.

[0031] In the ninth step, the structure of the air inlet side of the in-pipe protective gas supply device can be: a perforated silicone plug plus a steel conduit, the silicone plug is conical, the minor diameter is more than 3 mm smaller than the inner diameter of the pipe joint, and the major diameter is more than 1 mm larger than the inner diameter of the pipe joint; the structure of the air inlet side of the in-pipe protective gas supply device can also be: a steel threaded air inlet joint is connected to the air supply pipe through a quick-connect joint; the steel threaded air inlet joint is connected by the air inlet joint and the threaded sleeve through H / n matching, and the threaded sleeve is threadedly matched with the outer nut of the pipe joint; the air inlet joint is stepped, one end can be connected to the air supply pipe with a quick-connect joint, and the outer diameter of the other end is 0.5 mm smaller than the inner diameter of the pipe joint, and is inserted into the inner diameter of the pipe joint during installation. There is a wire mesh in the air inlet joint to achieve a uniform air outlet effect.

[0032] Specifically, when the pipe joint can be clamped, a silicone plug is used to supply air, the air supply steel pipe is connected to the air supply hose through a quick-connect connector, the air supply steel pipe is inserted into the silicone plug, and the silicone plug is installed in the pipe joint.

[0033] The tenth step includes the following steps:

[0034] (1) The method of estimating the mean heat input using the formula based on the diameter and wall thickness of the joint body is as follows: record the welding parameters of at least five groups of pipe joints and pipes with different diameters and wall thicknesses under the same material conditions, list the diameter, wall thickness, and mean heat input, use the mean heat input as the dependent variable, and the diameter and wall thickness as the independent variables to fit the diameter, wall thickness, and mean heat input using a linear formula, and derive the relationship between the mean heat input and the diameter and wall thickness:

[0035] ;

[0036] in, —Estimated mean heat input; D—Outer diameter of the pipe. When the outer diameters on both sides are different, the larger value shall be taken. Unit: mm;

[0037] a, b, c—constants obtained from the fitting formula;

[0038] δ—Pipeline wall thickness. When the pipes have equal diameters but unequal wall thicknesses, the average wall thickness is taken. When the pipes have equal thicknesses but unequal diameters, δ=wall thickness+0.5 radius difference, unit: mm.

[0039] (2) The method for calculating the heat input value of each section from the mean heat input is as follows: according to the number of sections and the heat input value of each section of at least five known groups of pipeline penetration welding parameters, a decreasing linear formula is fitted to obtain the decreasing coefficient k of the heat input of each section, and the mean value of the decreasing coefficient of the heat input of each section is calculated;

[0040] The heat input of each section decreases step by step, and is converted into a segment function through fitting method, and the Qn formula is obtained: Qn=k*n+b;

[0041] Where Qn is the heat input of the nth stage; k is the slope, which is the constant obtained from the fitting formula, that is, the decreasing coefficient of heat input;

[0042] b—intercept, which is the constant obtained from the fitting formula;

[0043] n—number of segments;

[0044] The fitting method is: record the qualified welding parameters under different diameters and wall thicknesses, calculate the heat input of each section, and perform linear fitting between the number of sections and the welding heat input of each section;

[0045] Then average the k values ​​of different formulas to get the mean of the decreasing coefficient ;

[0046] Combined mean heat input formula: ; Input the estimated mean heat Data Substitution formula;

[0047] Where n is the number of stages, Qn is the heat input of the nth stage,

[0048] and Qn= *n+Q1, calculate Q1, and thus calculate the estimated heat input Qn of each section;

[0049] (3) Calculate the peak heat input and base heat input of each section based on the following formula:

[0050] Since the average heat input of each section is equal to the sum of the peak current heat input and the base current heat input, the heat input of the nth section Qn=Qp*[Tp / (Tp+Tb)]+Qb*[Tb / (Tp+Tb)];

[0051] Wherein, Qp is peak heat input, Qb is base heat input, Tp is peak pulse time, Tb is base pulse time, Tb: Tp is selected from 1 to 3, preferably 1;

[0052] The peak heat input to base heat input ratio range Qp:Qb is 2 to 5, preferably 3;

[0053] (4) Calculate the peak current and base current based on the following formula:

[0054] Heat input formula: Q=η*I*U / V / 1000;

[0055] Where, Q is welding input, unit is KJ / mm;

[0056] η—Effective utilization rate of arc heat power, which is 0.9 for argon arc welding according to experience;

[0057] I—welding current, peak current is marked by Ip, base current is marked by Ib, unit is A; Ip:Ib is 2~5;

[0058] U—welding voltage, the peak voltage is marked by Up, the base voltage is marked by Ub, the unit is V;

[0059] V—welding speed, unit: mm / s; the welding speed adjustment range is 1~2.5mm / s;

[0060] The voltage formula is obtained by fitting. The formula is universal for the same type of welding equipment. When changing the equipment brand or model, it is necessary to re-fit:

[0061] U=d×h+e×I+f;

[0062] Where, h is the tungsten electrode gap, which is the distance from the tungsten electrode tip to the outer diameter of the pipeline. When the outer diameters of the two sides of the pipeline are different, the outer diameter of the pipeline referred to is the larger one, in mm.

[0063] For the same type of welding equipment, d, e, and f are constants;

[0064] The fitting method is: record the voltage values ​​fed back by the device at different tungsten electrode gaps and current values, and then perform a linear fit on the corresponding relationship between tungsten electrode height, current value, and voltage value to derive the voltage calculation formula;

[0065] The tungsten electrode gap h is a function of the pipe wall thickness, and the h formula is: h=0.5*δ ;

[0066] Among them, δ is wall thickness. When the wall thickness on both sides of the pipeline is different, the value is taken from the side with larger wall thickness. The unit is mm.

[0067] The peak heat input Qp and base heat input Qb of each section are calculated, and then substituted into the voltage formula, the peak current Ip and base current Ib of each section can be calculated by setting the tungsten electrode gap value and welding speed;

[0068] Preferably, the heat input is inversely proportional to the sulfur content in the material. As the sulfur content decreases, the welding current can be increased or the welding speed can be decreased as a whole to ensure full penetration, with an adjustment range of ±10%.

[0069] Write the welding current calculation formula into the EXCEL table, and use the single variable solution and macro command loop statements to quickly calculate the peak and base welding currents of each segment and generate a welding parameter table.

[0070] Preferably, the welding procedure is divided into 5 to 9 segments, starting from 3 o'clock and welding clockwise, segment 1 is the arc starting segment, the arc starting segment is 10°, the middle is the welding segment, the angle is 40°~80°, and the last segment is the arc ending segment**, which is not counted in the number of welding segments, the arc ending angle is 90°~120°, and the current decays to zero.

[0071] Furthermore, the present invention also adopts the technical solution of a welding clamp bracket and a steel pipe bracket, which has the effect of facilitating the positioning and clamping of steel pipes and providing auxiliary support for over-long steel pipes.

[0072] Compared with the prior art, the present invention has the following beneficial effects:

[0073] 1. This invention utilizes various concave clips, clamps, or steel threaded air inlet connectors to achieve automatic butt welding of pipe connectors of any clampable length to steel pipes, achieving 100% automated welding of hydraulic pipelines. This technology utilizes a single piece of equipment and achieves single-sided welding and double-sided forming in a single weld. It can meet the clamping and welding requirements of common brands of weldable hydraulic pipe connectors with 24° cone heads and 37° ball heads (e.g., Eaton and Suqiangge). It is compatible with enclosed pipe welding equipment from various brands, including AMI, MK, Huaheng, and Poly Sudi.

[0074] 2. The technical means of adjusting welding parameters through algorithms is adopted. It can quickly predict reasonable welding parameters when changing materials or pipeline specifications, quickly adjust appropriate process parameters, and reduce the number of welding tests. By reasonably adjusting the process parameters, the effect of single-sided welding and double-sided forming of hydraulic pipelines with equal or unequal diameters of (2~4) mm thickness can be achieved;

[0075] 3. The present invention also adopts the technical means of back-side air supply device and air outlet device, which can fully protect the back weld and use the principle of air pressure difference to support the flat weld, so as to achieve the effect of flat and even weld appearance without collapse on the top;

[0076] 4. This invention utilizes a tungsten electrode gap gauge and a technical solution for adjusting the relative position of the tungsten electrode to the center of the groove, which stabilizes welding quality, resolves the problem of weld deviation from the center of the groove, and achieves a double-sided weld effect. This adjustment process includes the seventh step of adjusting the radial diameter of the tungsten electrode based on the pipe joint and the outer diameter of the steel pipe, and the eighth step of adjusting the tungsten electrode offset by adjusting the axial position of the pipe based on the pipe size and material composition. BRIEF DESCRIPTION OF THE DRAWINGS

[0077] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0078] Figure 1 This is a process flow chart for automatic pipe-to-pipe butt welding of hydraulic stainless steel pipelines;

[0079] Figure 2 Schematic diagram of the hydraulic stainless steel piping structure; Figure (a) is a schematic diagram of the hydraulic stainless steel piping structure with equal outer diameters and unequal inner diameters; Figure (b) is a schematic diagram of the hydraulic stainless steel piping structure with equal wall thickness and unequal outer and inner diameters;

[0080] Among them, 001 is the pipe joint, 002 is the steel pipe to be welded, and 003 is the tungsten electrode;

[0081] Figure 3 Schematic diagram of hydraulic pipe clamping; 301 is the clampable length of the pipe joint, 302 is the distance from the tungsten electrode to the outer wall of the welding clamp, 303 is the clampable length of the steel pipe; 004 is the welding clamp;

[0082] Figure 4 (a) to Figure 4 (f) show the clamping solutions for different pipe sizes.

[0083] Figure 4 (a) shows the solution when the flat clip-joint length can be clamped;

[0084] Figure 4 (b) shows a solution for a level 1 indented concave clamp with a small clamping length.

[0085] Figure 4 (c) shows a 2-stage indentation concave clamping piece with a small clamping length.

[0086] Figure 4 (d) shows the clamping position of the steel threaded air inlet joint with the clamping end above the pipe joint nut;

[0087] Figure 4 (e) shows a solution for a steel threaded air inlet connector with a clamping end where the clamping position is outside the pipe connector.

[0088] Figure 4 (f) shows a clamping solution for the steel pipe with a plate fixture that does not have a straight-edge conduit to hold;

[0089] Among them, 005 is the upper clamp and 006 is the lower clamp;

[0090] 401-threaded hole; 402-clamping sleeve, 403-threaded sleeve, 404-air inlet connector, 405-reserved clamping length for pipe joint nut installation and removal, 406-clamping position, 407-outer diameter of pipe joint nut, 408-aluminum alloy clamping plate, 409-high temperature resistant flame retardant nylon clamping plate, 410-insulating clamp;

[0091] Figure 5 Schematic diagram of the use of welding clamp bracket and steel pipe bracket; 501- welding clamp bracket, 502- pipe bracket, 503- rotating handle, 504- rotating support plate;

[0092] Figure 6 is a schematic diagram of a tungsten electrode gap gauge and its use; Figure (a) is a schematic diagram of a tungsten electrode gap gauge, and Figure (b) is a schematic diagram of the use of a tungsten electrode gap gauge; 601 is the middle diameter position, and 602 is the tungsten electrode gap gauge;

[0093] Figure 7 shows an in-pipe protective gas inlet device; Figure (a) shows an in-pipe protective gas inlet device with a silicone plug and a steel pipe, and Figure (b) shows an in-pipe protective gas inlet device with a steel threaded joint; 701 is a silicone plug, 702 is an air supply steel pipe, 703 is a quick-connect connector, 704 is an air supply hose, and 705 is a steel mesh.

[0094] Figure 8 It is a protective gas outlet device in the pipe; wherein, 801 is the inner core part, 802 is the limit part, and 803 is the handle part;

[0095] Figure 9 This is a schematic diagram of welding current partitioning;

[0096] Figure 10 Metallographic test photos of welded joints; (a) is the metallographic sample, (b) is the joint structure, 200×, (c) is the fusion zone structure, 500×;

[0097] Figure 11 This is the fitting diagram of tungsten electrode height, current and voltage. DETAILED DESCRIPTION

[0098] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention belongs.

[0099] In a typical embodiment of the present invention, the process flow chart is as follows Figure 1 The pipeline structure diagram is shown in Figure 2 The following diagrams illustrate the connection between pipe fittings and conduits. Figure (a) illustrates the connection between equal outer diameters and unequal inner diameters; Figure (b) illustrates the connection between equal wall thicknesses and unequal outer and inner diameters. One side of the butted pipe is a pipe fitting 001, and the other side is a steel pipe 002 to be welded. The steel pipe to be welded is a stainless steel hydraulic conduit made of austenitic stainless steel, with an outer diameter ranging from 8 mm to 38 mm and a wall thickness of 2 to 4 mm. For equal diameters or equal outer diameters with unequal inner diameters, a flat-end pipe fitting is used. For a difference of 1 mm or greater between the outer diameter of the pipe fitting and the outer diameter of the conduit, a beveled pipe fitting is used. The butted pipe and pipe fitting must have at least one of the same outer diameter, inner diameter, or wall thickness. When the wall thickness is the same, the difference between the outer diameter and inner diameter should not exceed 2 mm. When either the outer diameter or inner diameter is the same, the wall thickness difference should not exceed 1 mm.

[0100] The main process steps are:

[0101] The first step is to saw the stainless steel pipe into pieces. The cutting methods can be: portable pipe cutting machine, metal circular saw with coolant, laser pipe cutting machine;

[0102] The second step is to flatten the catheter with a flattening machine. The flatness of the tube end after flattening should be ≤0.2mm.

[0103] The third step is to bend the conduit after flattening with a data hydraulic pipe bender. In order to meet the clamping requirements of the equipment, an extension section is set on the conduit. After forming, the extension section is sawed. Automatic or manual sawing is selected according to the structural form. After sawing, the conduit is flattened again. The conduit with a clampable length that can be clamped by the flattening machine is flattened with a flattening machine. The flatness of the pipe end after flattening is ≤0.2mm; if the length is less than 10mm, an electric grinder or file is used for flattening. The flatness of the pipe end after flattening is ≤0.5mm.

[0104] The fourth step is to use a pneumatic pipe cleaning gun to fire a high-density polyurethane bullet that is about (10-30)% larger than the inner diameter of the pipe into the pipe. The bullet will remove excess objects in the pipe during its movement, and clean the dust in the pipe, fine iron filings brought in during the cutting process, and other dirt. The cleaning frequency is repeated until the dirt on the surface of the sponge bullet is removed;

[0105] The fifth step is to use an argon arc welding machine to perform positioning welding on the formed conduits and welded pipe joints without filling wire. Before welding, use industrial acetone wipes to clean the welds of the conduits and joints to be welded; positioning welding points (3~4) points are required to be evenly distributed around the pipe, with a welding point diameter of (3~4) mm and a welding point height not exceeding 0.3 mm from the surface of the parent material. If it exceeds, it should be ground with a file; after positioning, the maximum butt gap is less than 0.5 mm, and the maximum misalignment is less than 0.5 mm.

[0106] Step 6: Install the welding clamp on the welding clamp bracket. Figure 5 As shown; for butt joints of unequal diameters, use clips with different inner diameters on both sides to clamp; for the clampable length of the pipe joint (the clampable length of the pipe joint is as shown Figure 3 301) is greater than the distance from the tungsten electrode to the outer wall of the welding clamp (as shown in Figure 3 302 in the figure), the technical solution of using flat clamps is shown in Figure 4 (a). A flat-end set screw is installed in the threaded hole 401 of the upper clamp 005. The effect is that the protruding screw presses the pipeline after the upper clamp 005 and the lower clamp 006 are closed; for the pipeline whose clamping length of the joint is less than the distance from the tungsten electrode to the outer wall of the welding clamp, as shown in Figure 4 (b), a first-level or second-level indented concave clamp is used to clamp it on the welding clamp according to the degree of reduction in the clampable length. For example, the clampable length of the reducer is slightly less than that of the ordinary reducer. The through joint adopts the technical solution of one-stage indented concave clip. The center axes of the upper clip 005 and the lower clip 006 of the one-stage indented concave clip are indented inward to 0.5mm in front of the thread of the fastening bolt hole 401, and the indented diameter is larger than the maximum outer diameter of the pipe joint nut; the clamping position of the clip is located at the connection between the joint and the nut of the pipe joint. The effect is that the indented part avoids the nut and the diameter reduction part, so that the groove of the pipe joint is closer to the tungsten electrode, and the concave clip is chamfered to avoid the rounded corner of the diameter reduction part of the reducer.

[0107] As shown in Figure 4 (a), a workpiece error of 3 to 5 mm is generally reserved between the clip and the pipe joint nut to overcome the cumulative dimensional error of the workpiece components and positioning welding.

[0108] If the total length of the pipe joint is short, a two-stage indented concave clip technology solution is adopted, as shown in Figure 4 (c). A two-stage indented clip is used, and the first stage is indented 1.5 mm before the clip installation surface. The indented diameter is larger than the maximum outer diameter of the pipe joint nut. The second stage indentation moves the fastening threaded hole 401 outside the clip. The inner diameter of the center hole of the concave clip is the same as the outer diameter of the pipe joint and the steel pipe. The clamping position of the clip is located at the outer periphery of the pipe joint. The effect is that the threaded hole is retracted into the welding clamp, so that the clamping position is closer to the tungsten electrode, providing a larger avoidance distance between the pipe joint nut and the diameter change.

[0109] If the welding clamp width of the welding equipment is large and the clamping length of the pipe joint is less than the distance from the tungsten electrode to the outer wall of the welding clamp, a steel threaded air inlet joint with a clamping end can also be used. When the clamping position of the clamp is above the nut of the pipe joint, a steel threaded air inlet joint 404 with a clamping sleeve is used, as shown in Figure 4 (d). The clamping sleeve and the threaded sleeve are matched with H / n. The outer diameter of the clamping sleeve 402 is the same as the inner diameter of the flat clamp. The effect is that the clamping sleeve replaces the outer diameter part of the pipe for clamping; the inner diameter of the clamping sleeve 402 is larger than The outer diameter of the pipe joint nut is 407, which enables the pipe joint nut to be screwed onto the threaded sleeve 403; the length of the clamping sleeve 402 after installation must not cover the outer nut of the pipe joint, and a mounting and dismounting clamping length 405 of the pipe joint nut and the threaded sleeve is set, which facilitates the installation and disassembly of the pipe joint nut and the steel threaded air inlet joint with the clamping end; the clamping position 406 in the figure is the clamping sleeve nut. The clamping sleeve and the threaded sleeve, as well as the threaded sleeve and the air inlet joint adopt H / n matching, which has the effect of ensuring air tightness by matching.

[0110] The gas outlet structure of the in-pipe protective gas supply device is a stepped steel rod. The inner core part penetrates into the pipe joint and has a diameter smaller than the inner diameter of the steel pipe (1~1.5) mm, which plays a flow-blocking role. The limiting part is larger than the inner diameter of the pipe joint, and the handle part has no limit on diameter and can be equal to the inner core.

[0111] When the clamp is outside the pipe joint, that is, the pipe joint is inside the welding clamp, a steel threaded air inlet joint 404 with a clamping end is used, as shown in Figure 4 (e). When the clamping position of the welding clamp clamp is outside the length range of the pipe joint, the threaded sleeve is added with a clamping end. The outer diameter of the clamping end is the same as the inner hole of the flat clamp. The effect is that the clamping end is used to replace the joint clamping. The threaded sleeve with the clamping end can be processed into a stepped shape according to the requirements of the clamp.

[0112] For the situation where one side of the steel pipe cannot be clamped due to the small distance between the bend and the weld, a technical solution of clamping with a pallet clamp is adopted, as shown in Figure 4 (f). The pallet clamp used is two U-shaped pallets. The inner width of the U-shaped pallet is the same as the diameter of the steel pipe. The effect is that the distance from the steel pipe to the clamping side is no longer restricted by the concentricity requirement of the clamp; one of the two pallets is made of aluminum alloy and the other is made of high-temperature resistant flame-retardant nylon. The aluminum alloy pallet 408 is grounded and in contact with the conduit and the welding clamp to achieve a conductive effect. The high-temperature resistant flame-retardant nylon pallet 409 is placed outside the aluminum alloy pallet and is arranged crosswise with the aluminum alloy pallet to prevent air leakage. The nylon pallet is clamped on the welding clamp with an insulating clip 410 for fixation, which prevents short circuit between the clips.

[0113] The seventh step is to place the tungsten electrode gap gauge 602 in the welding clamp, and position the tungsten electrode after dropping the tip of the tungsten electrode 003 to the middle diameter position 601. The traditional method is to visually locate the radial position of the tungsten electrode. Due to the large error, the inventor designed a tungsten electrode gap gauge 602 as shown in Figure 6 (a). The tungsten electrode gap gauge 602 is a cylinder with a stepped structure. The cylinders at both ends are supported and fixed by the lower half of the clamp. The middle cylinder is used to locate the radial position of the tungsten electrode, as shown in Figure 6 (b), which is used to quickly and accurately locate the tungsten electrode gap. The middle diameter size is determined by the following method: when the outer diameters on both sides are the same, the middle diameter D = the diameters on both sides + 2 × tungsten electrode gap h. The tungsten electrode gap h is the distance from the tip of the tungsten electrode to the outer diameter of the pipeline. When the outer diameters on both sides of the pipeline are different, the outer diameter of the pipeline referred to is the larger outer diameter side. The tungsten electrode gap h is a function of the pipeline wall thickness, and the formula is: h = 0.5*δ ; δ—wall thickness. When the wall thicknesses on both sides of the pipeline are different, the value is taken from the side with the larger wall thickness, unit: mm. Regarding the tolerance of 0.2mm, if it is less than Ф16mm, 0.2mm does not need to be added. If it is greater than or equal to Ф16mm, 0.2mm needs to be added. Its effect is that the appropriate tungsten electrode gap can avoid tungsten sticking during welding and improve the stability of welding quality. The smaller the tungsten electrode gap, the closer the arc is to the molten pool, the greater the arc stiffness, and the weld center deviation caused by material composition is reduced, thus avoiding the back weld from deviating from the groove.

[0114] The tungsten electrode is preferably made of cerium tungsten. Cerium tungsten, thorium tungsten, and lanthanum tungsten have no difference in effect on welding quality and stability. The cerium tungsten electrode with high durability and no radiation is preferred. The structure of the cerium tungsten electrode is as follows: its tip should be ground to (30~35) degrees along the axial direction, the end plane diameter is (0.2~0.3) mm, the grinding pattern should be consistent with the axial direction, and a tungsten electrode grinding machine with an angle scale should be used for grinding.

[0115] Step 8: Place the pipe into the welding clamp. If the pipe is too long, place the other side of the pipe on the pipe bracket. The pipe bracket can be adjusted in height. The welding clamp bracket 501 (the anti-collision frame and support are removed in the figure) and the pipe bracket 502 are placed as shown in the figure. Figure 5 As shown, the pipeline bracket 502 is provided with a rotating handle 503 for adjusting the height, and a V-shaped rotatable support plate 504 is provided at the top of the pipeline bracket 502. The effect is that if the pipeline has a complex shape, the appropriate height can keep the pipeline in a horizontal position in the welding clamp, reducing the stress on the welding clamp.

[0116] Move the steel pipe in the welding clamp and adjust the relative position of the groove center and the tungsten electrode tip according to the size and material composition of the pipe joint and steel pipe. The reason is that there are deviations between the position of the tungsten electrode tip, the center of the front weld (outer weld center), and the center of the back weld (inner weld center). The width of the back weld can be as small as 1mm. When the back weld formation position deviates greatly from the groove center, the root will not be fully melted. To ensure full melt of the back weld, the relative position of the groove center and the tungsten electrode tip must be adjusted. The groove center should be within ±0.5mm of the tungsten electrode tip. The relative position between the center of the groove and the tip of the tungsten electrode is adjusted according to the size of the pipeline. The method is as follows: when the wall thickness of the pipe joint and the steel pipe is different, the tungsten electrode is offset to the side with larger wall thickness, with an offset of (0, 0.5] mm; when the wall thickness is the same, the tungsten electrode is offset to the side with larger outer diameter, with an offset of (0, 0.5] mm, as described in Examples 5 and 6. The principle is that when the wall thickness is different, the side with larger wall thickness requires more energy to melt the parent material; when the wall thickness is the same, the inner wall of the side with larger inner diameter needs to melt and flow to the inner wall of the side with smaller inner diameter to form a transition connection.

[0117] The composition of steel pipes and joints has a significant impact on welding results. Generally, steel pipes purchased from the same manufacturer have stable composition, while pipe joints have different compositions according to standards or selected manufacturers. Even if they all meet national standards, it is difficult to ensure that the composition of joints and steel pipes is exactly the same due to different manufacturers, different processing methods, and non-uniform raw materials. Tungsten inert gas arc welding without filler wire is more sensitive to material composition. In order to ensure full penetration of the back weld root, the following method is used to adjust the pointing position of the tungsten electrode tip:

[0118] Adjust the pointing position of the tungsten electrode tip according to the material composition of the pipe joint and the steel pipe. The method is: when welding with equal diameters (when the inner diameter and outer diameter on both sides of the weld are equal), the tungsten electrode should be tilted toward the side with higher silicon content. Taking the silicon content of the steel pipe as the benchmark, when the silicon content of the joint is less than 0.3%, the tungsten electrode should be tilted toward the steel pipe (0, 0.3] mm); when the silicon content of the joint and the steel pipe is similar, both within the range of 0.3%~0.4%, the tungsten electrode should not be offset; when the silicon content of the joint is higher than 0.4%, the tungsten electrode should be tilted toward the pipe joint (0, 0.3] mm. The silicon content can be estimated by the appearance of the weld. When the silicon content is less than 0.3%, the weld has a bright surface, and when the silicon content is higher than 0.4%, the weld has a matte surface. As described in Example 7, Comparative Example 2 and Example 4. The principle is that when the silicon content on both sides is different, the side with higher silicon content generates higher SiO2 due to deoxidation. SiO2 is an oxidizing agent that can make the surface tension temperature coefficient of the molten pool positive. At the same time, since SiO2 is a non-metallic oxide with poor conductivity, the anode spot area of ​​the molten pool and the arc conductive path are reduced, causing the arc to shrink, causing the arc to deflect toward the side with lower silicon content (Bian Chunhong et al., Measurement of Surface Tension of Stainless Steel A-TIG Welding Pool and Research on the Mechanism of Increased Penetration [D]. Lanzhou: Lanzhou University of Technology, 2020: 0-61), causing the back weld to tilt toward the side with lower silicon content. Therefore, to ensure root penetration, the tungsten electrode should be tilted toward the side with higher silicon content.

[0119] The ninth step is to install the air inlet and outlet devices of the protective gas in the pipeline.

[0120] The air inlet and outlet devices are selected according to the product size; the protective gas is argon with a purity of ≥99.99%; the protective gas flow rate outside the tube is (30~40) cubic feet / hour, the protective gas flow rate inside the tube is (15~20) cubic feet / hour, the advance gas supply time is (10~15) seconds, and the delayed gas supply time is (20~35) seconds.

[0121] For the in-pipe shielding gas inlet device installed on the pipeline, a silicone plug gas supply technology solution can be used when the pipe joint 001 can be clamped. As shown in Figure 7 (a), the gas supply steel pipe 702 is connected to the gas supply hose 704 via a quick-connect connector 703. The gas supply steel pipe 702 is inserted into the silicone plug 701, and the silicone plug 701 is installed into the pipe joint 001. The silicone plug has a smaller diameter than the inner diameter of the pipe joint by at least 3mm, and a larger diameter than the inner diameter of the pipe joint by at least 1mm. The silicone plug is inexpensive, securely installed, quick to replace, and easy to purchase. The in-pipe shielding gas inlet device can also be made of a steel threaded connector, as shown in Figure 7 (b). One end of the steel threaded connector is connected to the pipe joint and the other end is connected to the gas supply connector. A steel mesh 705 is provided at the end of the gas supply connector. The other end of the gas supply connector is connected to the shielding gas inlet pipe via a quick-connect connector. Its effectiveness lies in its secure installation and resistance to falling off. The internal steel mesh 705 allows for more uniform exhaust of air from the pipe, making it suitable for larger diameter pipes. However, it requires threaded engagement, making it less convenient than a silicone plug solution. When pipe joints cannot be clamped, a clamping steel threaded air inlet joint is used. The structure is shown in Figure 4(d)(e). This solution satisfies air delivery requirements while also providing a clamping solution.

[0122] Place the protective gas outlet device on the other side of the pipeline, the structure is as follows Figure 8 As shown, the placement method is as follows Figure 5 As shown. The characteristic feature of the in-pipe shielding gas supply device is that its outlet structure is a stepped steel rod, comprising a sequentially connected inner core portion 801, a stopper portion 802, and a handle portion 803. The inner core portion 801 extends deep into the pipe joint and has a diameter smaller than the inner diameter of the pipe joint (1-1.5) mm. The stopper portion 802 is larger than the inner diameter of the pipe joint. The handle portion 803 has an unlimited diameter (it can be equal to the inner core diameter). This facilitates installation by allowing the in-pipe shielding gas supply device to be simply placed into the pipe without requiring threaded connections. The outlet device has a diameter smaller than the inner diameter of the pipe joint (1-1.5) mm, blocking a portion of the pipe opening to act as a flow barrier. The outlet volume is smaller than the inlet volume, creating a positive pressure within the pipe. Combined with the in-pipe shielding gas flow rate, this can adjust weld formation.

[0123] Welding current partitioning Figure 9As shown, the angle is divided into nine sections, approximately one and a half circles around the weld pipe. Different current levels exist within each section. Starting from the 3 o'clock position, welding proceeds clockwise. At the 6 o'clock position, the weld seam is only one-quarter closed, and the low pressure inside the pipe does not affect weld formation. By the 12 o'clock position, the weld seam is three-quarters closed. At this point, the pressure inside the pipe can exceed the pressure outside. This positive pressure supports the molten pool metal during the horizontal position, preventing weld collapse near 12 o'clock. After the 9th section, the current gradually decreases to zero. Set the pre-gas supply time (10-15 seconds) and the delayed gas supply time (20-35 seconds). The principle behind this is that pre-gas supply expel air from the welding clamp and the pipe, ensuring an inert gas atmosphere during welding. Delayed gas supply accelerates weld cooling. A simulation of welding a 20-mm diameter pipe was performed, with a starting position of 0 degrees. Welding ended at 33 seconds, and at 50 seconds, the tungsten electrode returned to its starting position, and delayed gas supply began. When delayed gas supply begins, the maximum temperature of the weld is already below 450°C. Austenitic stainless steel no longer experiences intergranular corrosion below 450°C. After cooling for another 20 to 35 seconds, the temperature drops to around 300°C, at which point the weld will not oxidize or discolor when exposed to air.

[0124] The tenth step is to use the formula to estimate the average heat input based on the composition, diameter, and wall thickness of the weld joint. Calculate the heat input value of each segment based on the average heat input, set the welding speed and pulse time, and deduce the peak and base welding current values ​​from the formula. Then enter the welding program for a test weld, and then adjust the parameters according to the welding results until the welding quality is qualified.

[0125] Mean heat input formula: ;

[0126] Where n is the number of stages; Qn is the heat input of the nth stage;

[0127] Heat input for the nth section Qn=Qp*[Tp / (Tp+Tb)]+Qb*[Tb / (Tp+Tb)];

[0128] Where, Qp—peak heat input;

[0129] Qb—base heat input; Tp—peak pulse time; Tb—base pulse time; f—pulse frequency, f=1 / (Tp+Tb).

[0130] According to Welding Handbook 3rd Edition Volume 1 Page 149 Figure 5-2 9. The ratio of base value to peak pulse time Tb:Tp is generally 1 to 3, and is taken as 1 in the present invention. The pulse time is a function of the wall thickness Tp = Tb = δmax / 10;

[0131] Wherein, δ is the pipe wall thickness. When the wall thicknesses on both sides of the pipe are different, δ takes the larger value δmax, in mm.

[0132] Stainless steel pulse argon arc welding is generally low-frequency pulse. As the wall thickness increases, increasing the pulse time, that is, reducing the pulse frequency, can increase the penetration depth and improve the arc stability.

[0133] The welding speed adjustment range is (1 to 2.5) mm / s;

[0134] According to Table 5-2 on page 149 of Volume 1 of the third edition of the Welding Handbook, the welding speed V and pulse frequency f must match each other to ensure a certain amount of overlap in the welds and obtain a continuous and dense weld. The pulse frequency and speed correspondence table is calculated using the interpolation method. The corresponding pulse frequency speed adjustment range within the patented wall thickness range is (1 to 2.5) mm / s.

[0135] The peak heat input and base heat input ratio range Qp:Qb is 2-5.

[0136] According to the heat input formula, heat input is proportional to current. Therefore, the relationship between the peak and base heat input ratios can be the same as the current ratio relationship. According to the welding manual, the pulse amplitude ratio F=Ip:Ib is generally 5 to 10. Since the pipe wall thickness welded by this patent is relatively large, the maximum current that can be output by the closed pipe welding machine is generally not higher than 200 amperes. In order to reduce the peak current value while maintaining the welding heat input value that can penetrate, the pulse amplitude ratio is reduced, and the Ip:Ib value range is 2 to 5. Since heat input is a function of current, the Qp:Qb ratio range refers to the current ratio and is taken as 2 to 5;

[0137] The estimated mean heat input is converted into a function of diameter and wall thickness by a fitting method, .

[0138] Where D is the outer diameter of the pipe. When the outer diameters on both sides are different, the larger value shall be taken. The unit is mm.

[0139] a, b, c—constants obtained from the fitting formula;

[0140] δ—Pipeline wall thickness. When the pipes have equal diameters but unequal wall thicknesses, take the average wall thickness. When the pipes have equal thicknesses but unequal diameters, δ=wall thickness+0.5 radius difference, unit: mm.

[0141] The fitting method is as follows: record the qualified welding parameters of several different diameters and wall thicknesses of pipe joints and conduits under the same material conditions, calculate their mean heat input value, and then use a linear formula to fit the diameter, wall thickness, and mean heat input to obtain the formula of mean heat input with respect to diameter and wall thickness.

[0142] The estimated heat input of each section is piecewise decreasing, which can be converted into a segment function by fitting method to obtain Qn 估 Formula: Qn=k*n+b.

[0143] k—slope, which is the constant obtained from the fitting formula, i.e., the decreasing coefficient of heat input;

[0144] b—intercept, which is the constant obtained from the fitting formula.

[0145] The fitting method is: record the qualified welding parameters under different diameters and wall thicknesses respectively, calculate the heat input of each section, and perform linear fitting between the number of sections and the welding heat input of each section.

[0146] Then average the k values ​​of different formulas to get the mean of the decreasing coefficient The estimated mean heat input calculated based on diameter and wall thickness According to the decreasing coefficient and the number of sections, the estimated heat input Qn of each section can be calculated by reverse calculation.

[0147] The voltage formula is obtained by fitting, and the formula is universal for welding equipment of the same model. When the equipment brand or model is changed, it needs to be refitted.

[0148] For example, the voltage formula of MK-200 pipe welding machine is: U=0.775×h+0.048×I+5.9;

[0149] h—Tungsten electrode gap, the distance from the tungsten electrode tip to the outer diameter of the pipe. When the outer diameters on both sides of the pipe are different, the outer diameter of the pipe referred to is the larger one, unit: mm

[0150] The fitting method involves recording the voltage values ​​fed back by the device at different current values ​​at different tungsten electrode gaps. A linear fit is then performed on the corresponding relationship between tungsten electrode height, current, and voltage to derive the voltage calculation formula. For example, at 1, 1.2, 1.5, and 2 mm, the corresponding voltage values ​​at currents ranging from 140 amps to 20 amps are recorded, and the software then performs a linear fit to derive the formula.

[0151] The tungsten electrode gap h is a function of the pipe wall thickness, and the h formula is: h=0.5*δ ;

[0152] δ—Wall thickness. When the wall thickness on both sides of the pipeline is different, the value is taken from the side with larger wall thickness. Unit: mm.

[0153] Reducing the tungsten electrode gap helps improve arc stability. If the tungsten electrode gap is too small, there is a risk of tungsten sticking during welding. According to the tolerance of the parts and the welding wall thickness range of this patented product, the welding quality is relatively stable when the tungsten electrode gap is within the range of half the wall thickness.

[0154] By Qn 估 The peak heat input Qp and base heat input Qb of each section are calculated based on the ratio of the peak to base heat input. Then, the peak current Ip and base current Ib of each section can be calculated by substituting the voltage formula, setting the tungsten electrode gap value and welding speed.

[0155] The heat input is inversely proportional to the sulfur content in the material. As the sulfur content decreases, the welding current can be increased or the welding speed can be decreased to ensure full penetration, with an adjustment range of ±10%.

[0156] The eleventh step is to automatically weld the batch-welded conduits and pipe joints.

[0157] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0158] Example 1: Automatic welding is performed using an MK-200 pipe welding machine and a chassis hydraulic pipeline as an example. The pipe joint material is SUS304, and the steel pipe material is 1Cr18Ni9Ti.

[0159] Example 2: Automatic welding is performed using an AMI-M207A pipe welding machine and a chassis hydraulic pipeline as an example.

[0160] The difference between Example 2 and Example 1 is that the welding clamp of the AMI-M207A pipe welding machine used in Example 2 is wider, and the clamping length required for clamping is larger.

[0161] Table 1 Ratio of automatic welding of chassis hydraulic pipelines using MK-200

[0162]

[0163] Table 2 Ratio of automatic welding of chassis hydraulic pipelines using AMI-M207A

[0164]

[0165] It can be seen from Table 1 and Table 2 that when the clamping length is zero, this process has automatic welding solutions using different welding equipment, and can achieve a 100% automatic welding ratio.

[0166] The performance test of the welded joint in Example 1 was carried out:

[0167] 1) Visual inspection: After welding, the welds are uniform and full, with no defects visible to the naked eye, and the weld concavity does not exceed 25% of the wall thickness. When the welds of pipelines No. 2 and No. 3 are sectioned, it is found that both single-sided welding and double-sided forming effects can be achieved in the cases of equal-diameter and unequal-diameter welding, and the weld transition is uniform.

[0168] 2) Oil pressure test: Pressurize at 25MPa for 10 minutes, maintain pressure for 30 minutes, and the pipeline welds are intact without oil leakage.

[0169] 3) Radiographic Inspection: X-ray inspection of the joints revealed no welding defects such as porosity and slag inclusions, meeting the requirements for Class I welds as specified in QJ2865A-2014, "Technical Requirements for Conduit Welding." Inspection films of Ø20 and Ø10 pipes showed uniform brightness within the welds, with no circular or strip-shaped shadows, indicating excellent weld quality.

[0170] 4) Tensile test: The full-tube tensile test results of steel pipes with a diameter less than φ38 are shown in Table 3. The results meet the tensile strength requirements of GB / T14976-2002 "Seamless Stainless Steel Pipes for Fluid Transportation". The fracture position is the weld joint.

[0171] 5) Metallographic test: attached Figure 10 (a) is the sample with phase 6, the molten pool is clearly visible, indicating that the weld is fully penetrated. Figure 10 (b) is a microscopic photograph of the weld joint. The upper right corner of the figure shows the weld structure, the lower left corner shows the base metal structure, and the middle transition area shows the fusion zone structure. White represents austenite structure, and black represents δ-ferrite structure. A certain amount of δ-ferrite in austenitic stainless steel welds can cut the directionality of austenite columnar crystals, improving the toughness and resistance to hot cracking. Figure 10 (c) shows a relatively uniform structure in the fusion zone, with no coarse columnar crystals along the fusion line, which is beneficial to the overall mechanical properties of the welded joint. The metallographic structure is good, free of pores and cracks, and is composed of austenite and ferrite.

[0172] Table 3 Full tube tensile test results

[0173]

[0174] In order to enable those skilled in the art to more clearly understand the technical solution of the protective gas outlet device of the present invention, the technical solution of the present invention will be described in detail below in combination with specific Example 3 and Comparative Example 1.

[0175] Example 3: Butt connection between φ12×2 pipe joint and steel pipe

[0176] Use an in-line shielding gas flow rate of 15-20 cubic feet per hour, a pre-gas supply time of 10-15 seconds, and a delayed gas supply time of 20-35 seconds. Use silicone plugs for the in-line shielding gas supply device and the in-line shielding gas outlet device.

[0177] Comparative Example 1: Butt connection between φ12×2 pipe joint and steel pipe

[0178] The difference between Comparative Example 1 and Example 3 is that Comparative Example 1 does not use the protective gas outlet device in the tube.

[0179] According to the welding forming effect diagrams of Comparative Example 1 and Example 3, it can be seen that when the shielding gas flow rate in the pipe is 15-20 cubic feet per hour, the weld in the flat welding position collapses due to gravity without the shielding gas outlet device in the pipe, while the weld in the flat welding position is lifted by the gas pressure and the surface is flattened when the shielding gas outlet device in the pipe is used.

[0180] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention regarding the relationship between heat input and sulfur content, the technical solution of the present invention will be described in detail below in conjunction with specific Example 4 and Comparative Example 2.

[0181] Example 4 A φ16×2 pipe joint (SUS316L, sulfur content 0.0165%) and a φ16×2 (1Cr18Ni9Ti) steel pipe were butt-jointed.

[0182] Comparative Example 2 A φ16×2 pipe joint (SUS316L sulfur content 0.0015%) and a φ16×2 (1Cr18Ni9Ti) steel pipe were butt-jointed.

[0183] The difference between Comparative Example 2 and Example 4 is that the sulfur content of the joint in Comparative Example 2 is low, the two sets of pipelines are welded using the same welding parameters, Example 4 uses an overall 3% reduction in current for welding, and Comparative Example 2 uses a 9% increase in current for welding.

[0184] According to the welding forming effect diagrams of Comparative Example 2 and Example 4, it is found that both pipelines are internally melted through and the welding effect is the same, indicating that the same weld forming effect is achieved. The heat input used in Example 4 is 12% less than that in Comparative Example 2, proving that the higher the sulfur content, the less heat input is required. It is difficult to measure the material composition during the welding production process. By trial welding the first piece and adjusting the welding current or welding speed of each section according to the welding effect, the heat input can be increased or decreased as a whole to achieve a full penetration welding effect.

[0185] The principle is that sulfur increases the surface tension of the molten pool. When the sulfur content is high, the molten metal flows toward the center of the pool, carrying heat with it toward the center of the weld. This heat is then transferred toward the wall thickness, increasing the weld depth while reducing the weld width. When the sulfur content is low, the surface tension is low. As the temperature rises, the liquid metal flows toward the periphery of the pool, dispersing the heat, reducing the weld depth, and widening the weld.

[0186] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention for aligning the pipeline size and the tungsten electrode, the technical solution of the present invention will be described in detail below in conjunction with specific Examples 5 and 6.

[0187] Example 5 A φ22×2 pipe joint (SUS304) and a φ20×2 (1Cr18Ni9Ti) steel pipe were butt-jointed, with the tungsten electrode offsetting the pipe joint by 0.3 mm.

[0188] Example 6 A φ20×2.5 pipe joint (SUS304) and a φ20×2 (1Cr18Ni9Ti) steel pipe were butt-jointed, with the tungsten electrode offsetting the pipe joint by 0.3 mm.

[0189] In Example 5, the tungsten electrode is positioned toward the larger outer diameter during pipe welding. The relative positions of the tungsten electrode and weld after welding and the internal weld formation diagram after sectioning reveal that the tungsten electrode is offset toward the joint, causing the centers of the inner and outer welds to shift toward the steel pipe due to the groove slope. This offset allows for a single-sided weld with a double-sided formation. In Example 6, the tungsten electrode is positioned toward the larger wall thickness during pipe welding. The relative positions of the tungsten electrode and weld after welding reveal that the center of the outer weld is aligned with the tungsten electrode. The internal weld formation diagram after sectioning reveals that the center of the inner weld shifts toward the steel pipe due to melting transition. This offset allows for a single-sided weld with a double-sided formation.

[0190] In order to enable those skilled in the art to more clearly understand the technical solution of aligning the material composition and the tungsten electrode of the present invention, the technical solution of the present invention will be described in detail below in combination with specific Example 7, Example 4 and Comparative Example 2.

[0191] Example 7 A φ16×2 pipe joint (SUS304) and a φ16×2 (1Cr18Ni9Ti) steel pipe were butt-jointed, and the tungsten electrode was aligned.

[0192] Comparative Example 2 A φ16×2 pipe joint (SUS316L) and a φ16×2 (1Cr18Ni9Ti) steel pipe were butt-jointed, with the tungsten electrode deviating 1.1 mm from the pipe joint.

[0193] Example 4: A φ16×2 pipe joint (SUS316L) and a φ16×2 (1Cr18Ni9Ti) steel pipe are butt-jointed, with the tungsten electrode offset from the pipe joint by 0.7 mm.

[0194] The difference between Example 7 and Example 4 and Comparative Example 2 is that the silicon content of the joints is different, while the difference in the silicon content of the steel pipes is relatively small; the main components of the materials are shown in Table 4, and the welding effect records are shown in Table 5.

[0195] Table 4 Connector and catheter components

[0196]

[0197] Table 5 Silicon content and weld offset record

[0198]

[0199] In Example 7, when welding the pipeline, the tungsten electrode points to the center of the groove. After welding is completed, it can be seen that the center of the outer weld is biased towards the steel pipe. After cutting, the internal weld formation diagram shows that the center of the inner weld is further biased towards the steel pipe. This shows that when welding equal diameters, the tungsten electrode should be biased towards the side with higher silicon content to ensure that the center of the back weld is in the center of the groove.

[0200] In comparative example 2, the tungsten electrode deviated from the pipe during pipeline welding. The silicon content in the pipe joint was not much different from that in the steel pipe. After welding, it was found that the center of the outer weld was deviated toward the joint. After sectioning, the internal weld formation diagram showed that the center of the inner weld was further deviated toward the joint. At this time, the tungsten electrode was deviated toward the steel pipe. Although the offset was too large, the back groove could still be covered by the weld. This also shows that the tungsten electrode should be deviated toward the side with higher silicon content during equal-diameter welding.

[0201] In Example 4, the tungsten electrode deviated from the pipe during pipe welding. The silicon content in the pipe joint was similar to that of the steel pipe. After welding, the center of the outer weld seam deviated slightly toward the joint, with a small offset. A cross-section of the internal weld formation revealed that the inner and outer weld seams had the same center, but the weld position partially deviated from the joint, a phenomenon only seen on the pipe. This indicates that when the silicon content is similar, the weld center offset is small, and the tungsten electrode offset should be limited.

[0202] The principle is that when the silicon content on both sides is different, the side with higher silicon content generates higher SiO2 due to deoxidation. SiO2 is an oxidizing agent that can make the surface tension temperature coefficient of the molten pool positive. At the same time, since SiO2 is a non-metallic oxide with poor conductivity, the anode spot area of ​​the molten pool and the arc conductive channel are reduced, causing the arc to shrink, causing the arc to deviate to the side with lower silicon content, causing the back weld to tilt toward the side with lower silicon content. Therefore, in order to ensure root penetration, the tungsten electrode should be biased toward the side with higher silicon content.

[0203] In order to enable those skilled in the art to more clearly understand the technical solution of estimating welding parameters of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiment 9.

[0204] Example 9 The welding parameters of a pipe joint of equal diameter 20×2.5 made of 316L and a steel pipe of equal diameter 20×2 made of 1Cr18Ni9Ti were estimated by formula, and the welding effect of the estimated data was tested.

[0205] 1) For example, given several pipe penetration welding parameters, the parameters are organized and listed as diameter, wall thickness, and mean heat input (see Table 6). Based on Table 6, Minitab was used to fit the relationship between mean heat input and pipe diameter and wall thickness. Using multiple regression, the equation was found to be: Mean heat input (kJ / mm) = -0.1776 + 0.0074 × diameter + 0.1526 × wall thickness.

[0206] Table 6 Heat input data of penetration weld

[0207]

[0208] 2) Input the pipe diameter and wall thickness into the formula to obtain the average heat input = -0.1776 + 0.0074 × 20 + 0.1526 × 2.25 (the average of wall thickness 2.5 and wall thickness 2.0 is 2.25) = 0.314 (KJ / mm)

[0209] 3) Based on the known number of sections and heat input values ​​for several known pipeline penetration welding parameters, a decreasing linear formula was fitted to derive the decrease coefficient k for each section. The average of the decrease coefficients for each section was also calculated, as shown in Table 6. Assuming welding is performed in nine sections, the heat input for each section can be calculated using the decrease coefficients, as shown in Table 7.

[0210] 4) Take the peak-to-base heat input ratio as 3 (the empirical data ratio is between 2-5, and 3 is often taken for ease of calculation). According to the average heat input, the heat input of each section is equal to the sum of the peak heat input and the base heat input. The peak and base heat input values ​​of each section can be calculated, as shown in Table 7.

[0211] 5) Calculate the relationship between the equipment voltage, current, and tungsten electrode gap. Fit the equation based on the welding equipment data. For example, for an MK-200 pipe welder, fit the voltage parameters for currents from 140 amps to 20 amps at tungsten electrode heights of 1, 1.2, 1.5, and 2 mm to obtain the voltage formula: U (V) = 0.775 × tungsten electrode gap (mm) + 0.048 × current (A) + 5.9. Select the Linear model in Polynomial, set the exponents for X (tungsten electrode height) and Y (current) to 1, and select LAR for the robust type. The fitting graph is shown below. Figure 11 As shown:

[0212] 6) The relationship between pulse time and plate thickness is: peak pulse time (s) = base pulse time (s) = wall thickness / 10 (mm), and the ratio of peak pulse time to base pulse time, i.e., pulse width ratio, is 1. Furthermore, the relationship between heat input, welding current, and voltage is: welding input (kJ / mm) = 0.9 × welding current (A) × welding voltage (V) / welding speed (mm / s) / 1000; the welding current adjustment range is: base current (15-90)A, peak current 45-180A; the welding voltage is a function of welding current and tungsten electrode gap.

[0213] Set the welding speed to 2.4 mm / s, the peak / base value welding time to 0.25 s (welding time = wall thickness / 10 = 2.5 / 10 = 0.25 s), and the tungsten electrode gap to 1.5 (tungsten electrode gap = (0.5 × wall thickness) = (0.5 × 2.5) =1.4 Take 1.5) and use EXCEL to reversely solve the heat input formula and voltage formula to obtain the peak base current, as shown in Table 7.

[0214] Table 7 Peak and base heat inputs derived from mean heat input

[0215]

[0216] 7) The generated welding parameters were input into the welding equipment and a trial weld was performed. Endoscopic inspection showed that the pipe weld was fully penetrated, but the weld was slightly concave. The welding current was fine-tuned and a trial weld was performed again. The final generated parameters are shown in Table 8. The predicted parameters can be used to obtain the appropriate welding parameters in just two welding tests.

[0217] Table 8 Welding parameters

[0218]

[0219] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0220] 1) Compared with the prior art, the present invention has the following advantages: by adopting the technical means of designing concave clips, clamps or steel threaded air inlet joints of different specifications, 100% automatic welding of hydraulic pipelines can be achieved, and single-sided welding and double-sided forming of equal-diameter and unequal-diameter pipe joints and steel pipes can be achieved, achieving the effect of using only one piece of equipment and welding in one go.

[0221] 2) The present invention uses a technical means of adjusting welding parameters through an algorithm, thereby achieving the effect of quickly adjusting appropriate process parameters when changing materials or pipeline specifications.

[0222] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A pipe-to-pipe automatic welding process for hydraulic stainless steel pipes, characterized in that the steps include: The first step is to saw the stainless steel conduit into pieces; The second step is to flatten the end of the catheter; The third step is to bend the conduit after the flat end; Step 4: Clean the catheter; The fifth step is to position weld the conduit and the welding pipe joint: use argon arc welding machine and position weld without filling wire; Step 6: Install the welding clamp on the welding clamp bracket. The welding clamp is a closed pipe welding clamp. A fixing piece for clamping the pipeline is installed on the welding clamp bracket, or a steel threaded air inlet connector with a clamping end is directly clamped on the welding clamp. The fixing piece is selected from a flat clamp or a concave clamp, and the flat clamp or concave clamp respectively includes upper and lower semicircles. The pipeline includes a pipe joint and a stainless steel conduit. The pipe joint includes a joint body and a pipe joint nut. Step 7: Place the tungsten electrode gap gauge in the welding clamp, and position the tungsten electrode after dropping it to the middle diameter position of the gap gauge. Step 8: Place the pipe into the welding clamp; adjust the relative position of the pipe groove center and the tungsten electrode according to the comparison results of the size and material of the pipe joint body and the pipe, and clamp the pipe; The ninth step is to install the inlet and outlet devices of the protective gas in the pipeline; Step 10: Use the formula to estimate the average heat input based on the joint body diameter and wall thickness. Calculate the heat input value for each segment from the average heat input. Set the welding speed and pulse time. After deducing the peak and base welding current values ​​for each segment from the formula, enter the welding program and conduct a test weld. Adjust the parameters based on the welding results until the welding quality is satisfactory. The eleventh step is to automatically weld the batch-welded conduits and pipe joints.

2. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1 is characterized in that: The stainless steel conduit is made of austenitic stainless steel, with an outer diameter ranging from 6 to 38 mm and a wall thickness of 2 to 4 mm. One side of the butted pipe is a pipe joint, and the other side is a stainless steel conduit. The outer diameter, inner diameter, and wall thickness of the pipe joint body must be identical to those of the conduit in at least one dimension. A flat-end pipe joint is used when the diameters are equal or the outer diameters are equal but the inner diameters are unequal. A beveled pipe joint is used when the difference between the outer diameter of the pipe joint and the outer diameter of the conduit is greater than or equal to 1 mm.

3. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1 is characterized in that: In the sixth step, the concave clip includes a first-stage indented concave clip and a second-stage indented concave clip. The first-stage indented concave clip is indented into the clip body to 0-0.5 mm before the thread of the fastening bolt hole, and the indented diameter is larger than the maximum outer diameter of the pipe joint nut; the second-stage indented concave clip moves the fastening bolt hole out of the clip. The fastening bolt hole is arranged radially, and the inner diameter of the center hole of the concave clip is the same as the outer diameter of the pipe joint or steel pipe. When the pipe joint can be clamped for a length shorter than the distance from the tungsten electrode to the outer wall of the welding clamp, a first-stage indented concave clamp or a second-stage indented concave clamp is used according to the degree of reduction in the clamping length. When the pipe fitting can clamp a pipe with a length greater than the distance from the tungsten electrode to the outer wall of the welding clamp, choose a flat clamp with the center hole of the clamp having the same outer diameter as the pipe fitting and the steel pipe.

4. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1 is characterized in that: When the clampable length of the steel pipe is less than the distance from the tungsten electrode to the outer wall of the welding clamp, a card clamp is used. The card clamp includes two U-shaped card plates, one of which is an aluminum alloy card plate and the other is a high-temperature resistant flame-retardant nylon card plate; the aluminum alloy card plate is in contact with the conduit and the welding clamp; the high-temperature resistant flame-retardant nylon card plate is placed outside the aluminum alloy card plate and crosses the aluminum alloy card plate; the high-temperature resistant flame-retardant nylon card plate is clamped on the welding clamp with an insulating clip.

5. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1 is characterized in that: In the seventh step, the tungsten electrode gap gauge used is a stepped cylinder, and the middle cylinder is used to locate the radial position of the tungsten electrode; the middle diameter size is determined by the following method: middle diameter = diameter on both sides + 2 × tungsten electrode gap, where the diameter on both sides represents the outer diameter of the pipe joint body or the outer diameter of the conduit. When the outer diameters on both sides of the pipeline are different, the outer diameter of the larger side is used for the diameter on both sides; the tungsten electrode gap refers to the radial distance from the tip of the tungsten electrode to the outer diameter of the pipeline with the larger diameter.

6. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1 is characterized in that: In the eighth step, the relative position of the tungsten electrode and the center of the groove is adjusted according to the comparison results of the size and material of the joint body and the conduit. When the wall thickness of the joint body and the conduit is different, the tungsten electrode is offset to the side with larger wall thickness, with an offset of (0, 0.5) mm; when the wall thickness is the same, the tungsten electrode is offset to the side with larger outer diameter, with an offset of (0, 0.5) mm; when welding equal diameters, the tungsten electrode should be offset to the side with higher silicon content. Based on the silicon content of the pipe being between 0.3% and 0.4%, when the silicon content of the joint body is less than 0.3%, the pipe is moved so that the tungsten electrode is offset to the conduit by (0, 0.3) mm; when the silicon content of both the joint body and the conduit is within the range of 0.3-0.4%, the tungsten electrode is not offset; when the silicon content of the joint body is higher than 0.4%, the pipe is moved so that the tungsten electrode is offset to the joint body by (0, 0.3) mm.

7. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1 is characterized in that: In the ninth step, the air inlet device for the protective gas in the pipe adopts a silicone plug or a steel threaded joint to supply air; when the pipe joint can be clamped, the silicone plug is used to supply air, and the air supply steel pipe is connected to the air supply hose through a quick plug joint, the air supply steel pipe is inserted into the silicone plug, and the silicone plug is installed in the pipe joint.

8. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1, characterized in that: The tenth step includes the following steps: (1) The method of estimating the mean heat input using the formula based on the diameter and wall thickness of the joint body is as follows: record the welding parameters of at least five groups of pipe joints and pipes with different diameters and wall thicknesses under the same material conditions, list the diameter, wall thickness, and mean heat input, use the mean heat input as the dependent variable, and the diameter and wall thickness as the independent variables to fit the diameter, wall thickness, and mean heat input using a linear formula, and derive the relationship between the mean heat input and the diameter and wall thickness: ； in, —Estimated mean heat input; D—Outer diameter of the pipe. When the outer diameters on both sides are different, the larger value shall be taken. Unit: mm; a, b, c—constants obtained from the fitting formula; δ—Pipeline wall thickness. When the pipes have equal diameters but unequal wall thicknesses, the average wall thickness is taken. When the pipes have equal thicknesses but unequal diameters, δ=wall thickness+0.5 radius difference, unit: mm. (2) The method for calculating the heat input value of each section from the mean heat input is as follows: according to the number of sections and the heat input value of each section of at least five known groups of pipeline penetration welding parameters, a decreasing linear formula is fitted to obtain the decreasing coefficient k of the heat input of each section, and the mean value of the decreasing coefficient of the heat input of each section is calculated; The heat input of each section decreases step by step, and is converted into a segment function through fitting method, and the Qn formula is obtained: Qn=k*n+b; Where Qn is the heat input of the nth stage; k is the slope, which is the constant obtained from the fitting formula, that is, the decreasing coefficient of heat input; b—intercept, which is the constant obtained from the fitting formula; n—number of segments; The fitting method is: record the qualified welding parameters under different diameters and wall thicknesses, calculate the heat input of each section, and perform linear fitting between the number of sections and the welding heat input of each section; Then average the k values ​​of different formulas to get the mean of the decreasing coefficient ; Combined mean heat input formula: ; Input the estimated mean heat Data Substitution formula; Where n is the number of stages, Qn is the heat input of the nth stage, and Qn= *n+Q1, calculate Q1, and thus calculate the estimated heat input Qn of each section; (3) Calculate the peak heat input and base heat input of each section based on the following formula: Since the average heat input of each section is equal to the sum of the peak current heat input and the base current heat input, the heat input of the nth section Qn=Qp*[Tp / (Tp+Tb)]+Qb*[Tb / (Tp+Tb)]; Wherein, Qp is the peak heat input, Qb is the base heat input, Tp is the peak pulse time, Tb is the base pulse time, and Tb:Tp is selected from 1 to 3; The peak heat input to base heat input ratio range Qp:Qb is 2 to 5; (4) Calculate the peak current and base current based on the following formula: Heat input formula: Q=η*I*U / V / 1000; Where, Q is welding input, unit is KJ / mm; η—Effective utilization rate of arc heat power, which is 0.9 for argon arc welding according to experience; I—welding current, peak current is marked by Ip, base current is marked by Ib, unit is A; Ip:Ib is 2~5; U—welding voltage, the peak voltage is marked by Up, the base voltage is marked by Ub, the unit is V; V—welding speed, unit: mm / s; the welding speed adjustment range is 1~2.5mm / s; The voltage formula is obtained by fitting. The formula is universal for the same type of welding equipment. When changing the equipment brand or model, it is necessary to re-fit: U=d×h+e×I+f; Where, h is the tungsten electrode gap, which is the distance from the tungsten electrode tip to the outer diameter of the pipeline. When the outer diameters of the two sides of the pipeline are different, the outer diameter of the pipeline referred to is the larger one, in mm. For the same type of welding equipment, d, e, and f are constants; The fitting method is: record the voltage values ​​fed back by the device at different tungsten electrode gaps and current values, and then perform a linear fit on the corresponding relationship between tungsten electrode height, current value, and voltage value to derive the voltage calculation formula; The tungsten electrode gap h is a function of the pipe wall thickness, and the h formula is: h=0.5*δ ; Among them, δ is wall thickness. When the wall thickness on both sides of the pipeline is different, the value is taken from the side with larger wall thickness. The unit is mm. The peak heat input Qp and base heat input Qb of each section are calculated, and then the voltage formula is substituted. The peak current Ip and base current Ib of each section can be calculated by setting the tungsten electrode gap value and welding speed.

9. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1, characterized in that: The heat input is inversely proportional to the sulfur content in the material. As the sulfur content decreases, the welding current is increased or the welding speed is decreased to ensure full penetration, with an adjustment range of ±10%.

10. The pipe-to-pipe automatic welding process for hydraulic stainless steel pipelines according to claim 1, characterized in that: The welding procedure is divided into 5 to 9 sections. Starting from 3 o'clock, welding is carried out clockwise. Section 1 is the arc starting section with an angle of 10°. The middle section is the welding section with an angle of 40° to 80°. The last section is the arc ending section, which is not counted in the number of welding sections. The arc ending angle is 90° to 120°, and the current decays to zero.

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