A continuous rolling and welding integrated process for steel pipe of booster station

Abstract

The application discloses a continuous rolling and welding integrated process for a booster station steel pipe and relates to the technical field of metal forming and welding. The process comprises the following steps: continuously rolling a steel plate and differentially rolling the edge area on both sides of the longitudinal seam at a predetermined position to form a residual compressive stress zone; supporting and limiting the edge of a cylindrical blank to keep the longitudinal seam opening in an incompletely closed state; alternately forming a first positioning weld seam and a second positioning weld seam along the longitudinal seam direction, and remelting the first positioning weld seam and keeping the second positioning weld seam connected across the seam during the cooling period of the current weld seam section during the main welding process; and simultaneously using welding heat input and cooling shrinkage to promote the folding of the groove roots on both sides to a target root gap. The application can reduce the forced closing load, reduce the longitudinal seam edge deviation, roundness deviation and residual tensile stress of the weld toe, reduce the post-weld straightening workload, and improve the forming stability and welding quality of the continuous manufacturing of the booster station steel pipe.

Description

Technical Field

[0001] This invention relates to the field of metal forming and welding technology, and in particular to an integrated process for continuous rolling and welding of steel pipes for booster stations. Background Technology

[0002] With the development of larger and heavier substation structures, steel pipe components are gradually evolving towards larger diameters, thicker walls, and higher strength. Their manufacturing typically involves processes such as cutting medium and thick steel plates, beveling, rolling in multiple stages using a plate rolling machine, joint positioning welding, longitudinal seam submerged arc welding, and post-weld straightening. Existing processes mainly control the roundness of steel pipes, longitudinal seam misalignment, and welding defects by improving rolling accuracy, adding internal and external supports, strengthening positioning welding constraints, and optimizing welding heat input. Some production lines are also equipped with automatic jointing and online inspection devices to improve the continuity and stability of thick-walled steel pipe manufacturing.

[0003] However, existing processes such as rolling, joining, tack welding, and main welding are mostly implemented as independent sequential procedures. For large-diameter, thick-walled substation steel pipes, if the longitudinal seam is forcibly pressed to the target root gap before the main welding, high elastic strain is likely to accumulate at the edge of the bevel and in the area near the weld toe. If equal-strength tack welding is used to maintain the assembly state, the positioning constraint cannot be released in an orderly manner according to the welding process when the main welding molten pool passes through. The displacement of the weld seam after cooling and shrinkage is also difficult to be stably transferred to the area to be welded in front. Ultimately, this can easily lead to misalignment of the longitudinal seam, increased roundness deviation, and high residual tensile stress at the weld toe. Summary of the Invention

[0004] This invention provides an integrated process for continuous rolling and welding of steel pipes for substations, comprising the following steps: S1. Continuously roll the steel plate, and perform differential pressing and rolling on both sides of the predetermined position of the longitudinal seam to form a residual compressive stress zone. The width of the edge zone is 2.0 to 3.0 times the thickness of the steel plate. S2. Roll and support the cylindrical blank and limit its edges. Keep the edges of the longitudinal seam opening on both sides incompletely closed. The preset elastic opening between the two sides is 0.08 to 0.13 times the thickness of the steel plate and is greater than the root gap of the main welding target. S3. Perform tack welding at the opening of the longitudinal seam, and alternately form the first tack weld and the second tack weld along the longitudinal seam direction. The cross-sectional area of ​​the molten metal deposited by the first tack weld is 55% to 68% of the cross-sectional area of ​​the molten metal deposited by the second tack weld. S4. Perform main welding along the longitudinal seam. The main weld pool remelts the first locating weld. The second locating weld remains connected across the seam during the cooling of the current weld segment. The edges of the base material on both sides of the longitudinal seam form a heat-affected zone plastic deformation section. Before the leading edge of the root forming weld pool reaches the current position to be welded, the root gap of the bevel on both sides is closed to the root gap of the main weld target. S5. Under the support of the rolling support, edge limit and second positioning weld, the main weld is cooled. The residual compressive stress in the residual compressive stress zone is superimposed on the tensile stress in the weld toe area in the opposite direction to form a longitudinal seam with low residual tensile stress, and the substation steel pipe is obtained.

[0005] Preferably, in S1, the inner support roller and the outer pressure roller are used to differentially press and roll the edge areas on both sides of the predetermined position of the longitudinal seam. The pressing amount of the predetermined area of ​​the outer weld toe is greater than the pressing amount of the predetermined area of ​​the inner weld toe, and the differential pressing amount is 0.03 to 0.06 times the thickness of the steel plate.

[0006] Preferably, in S2, the edge springback amount of the cylindrical blank after the rolling pressure is released is measured, and the preset elastic opening amount is determined based on the root gap of the main welding target, the transverse shrinkage compensation amount of the weld and the edge springback amount. The preset elastic opening amount is 0.08 to 0.13 times the thickness of the steel plate; wherein, the root gap of the main welding target is 1.2 to 2.0 mm.

[0007] Preferably, in S2, an inner support roller supports the inner wall of the cylindrical blank, an outer pressure roller presses the outer wall of the cylindrical blank, and two edge limiting blocks are respectively attached to the outer sides of the longitudinal seam opening. By adjusting the distance between the two edge limiting blocks, a preset elastic opening amount is obtained.

[0008] Preferably, in S3, the first positioning weld and the second positioning weld are arranged alternately along the main welding direction, and the center distance between adjacent positioning welds is 150-220mm.

[0009] Preferably, the weld length of the first positioning weld is 30mm, the weld length of the second positioning weld is 45mm, and the weld leg height of the first positioning weld is less than the weld leg height of the second positioning weld.

[0010] Preferably, in S4, the width of the main weld pool is adjusted to cover the bevel section where the first locating weld is located, the end deposited metal of the second locating weld remains outside the boundary of the current main weld pool, the first locating weld is incorporated into the main weld pool, and the second locating weld maintains the cross-seam connection of the two sides of the longitudinal seam opening during the cooling of the current weld segment.

[0011] Preferably, the tack welding is performed using flux-cored wire gas shielded welding, the main welding is performed using submerged arc welding, and the main welding is performed along the axial direction of the cylindrical blank.

[0012] Preferably, in S5, after the main welding heat source leaves the current weld segment, the rolling support, edge limiting and second positioning weld continue to maintain the positioning state of the current weld segment, and the edge limiting is released after the temperature of the temperature measuring point on the outer surface of the weld toe of the current weld segment drops below 300°C.

[0013] The beneficial effects of this invention are: By differentially pressing and rolling the edges of the longitudinal seam, the pre-welding stress state of the predetermined area of ​​the outer weld toe is changed in advance; by retaining a preset elastic opening amount larger than the root gap of the main weld target, the lateral cooling and shrinkage displacement of the solidified weld behind can be used to pull the front weld area to gradually close; by setting a first positioning weld and a second positioning weld with different effective connecting cross-sectional areas, the first positioning weld is preferentially remelted in the root forming weld, and the second positioning weld continues to cross the seam during the cooling of the current weld section. This reduces the forced closing load, while reducing the longitudinal seam misalignment, roundness deviation and residual tensile stress of the weld toe, reducing the amount of post-weld straightening work, and improving the forming stability and welding quality of the continuous manufacturing of the substation steel pipe. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the coordination between alternating tack welding and main welding in Example 1. Detailed Implementation

[0016] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0017] The steel pipe of this invention for the substation is a low-alloy structural steel straight-seam welded steel pipe used for supporting the steel structure of the substation, supporting the equipment foundation, connecting the platform, or as a pipe pile component. This type of steel pipe is usually formed into a cylindrical blank by rolling medium-thick steel plate or thick steel plate, and then performing tack welding, root forming welding, root cleaning welding, filling welding, and cover welding along the longitudinal seam. Preferably, the thickness of the steel plate is 32-50 mm, and the outer diameter of the steel pipe is 1800-4000 mm.

[0018] The process apparatus used in this invention includes a rolling roller group, an edge differential pressing mechanism, an inner support roller, an outer pressure roller, two edge limiting blocks, a positioning welding device, a submerged arc welding device, and a temperature detection device.

[0019] The rolling roller assembly is used to continuously roll steel plates into a cylindrical blank; the inner support roller is set inside the cylindrical blank and supports the inner wall of the cylindrical blank; the outer pressure roller is set outside the cylindrical blank and presses the outer wall of the cylindrical blank; two edge limiting blocks are respectively attached to the outer sides of the longitudinal seam opening, and the preset elastic opening amount between the bevel roots on both sides of the longitudinal seam opening is controlled by adjusting the distance between the two edge limiting blocks.

[0020] The edge differential pressing mechanism includes an outer bending pressing roller, an inner straightening roller, and a servo displacement detection device connected to the outer bending pressing roller and the inner straightening roller respectively; the two edges of the steel plate are respectively subjected to outer bending pressing and inner springback correction.

[0021] The outer bending reduction refers to the radial pressing displacement of the outer bending pressure roller relative to the outer circle envelope of the steel pipe target; The inner correction amount refers to the radial correction displacement of the inner correction roller relative to the inner circle envelope of the steel pipe target; the differential reduction amount refers to the difference between the outer bending reduction amount and the inner correction amount.

[0022] The same differential pressing method is used on both sides of the steel plate; the outer bending pressing amount is greater than the inner correction amount, so that the edge area has undergone bending and reverse springback correction. After the steel plate is unloaded, a residual compressive stress state is formed in the near-surface layer of the predetermined area of ​​the outer weld toe, which can be confirmed by detection; the differential compression amount is directly read by two sets of servo displacement detection devices.

[0023] The predetermined area for the outer weld toe refers to the strip-shaped area on the outer surface of the steel pipe that is 10 to 35 mm away from the edge of the outer bevel. The inner weld toe predetermined area refers to the strip-shaped area on the inner surface of the steel pipe that is 10 to 35 mm away from the edge of the inner bevel; the outer weld toe predetermined area and the inner weld toe predetermined area are located on the outer surface side and the inner surface side in the thickness direction of the steel plate, respectively.

[0024] The edge region refers to the steel plate area located on both sides of the predetermined position of the longitudinal seam, used for beveling, edge differential pressing, tack welding and main welding; the width of each edge region is measured from the root of the beveling after processing towards the main body of the steel plate, and is preferably 2.0 to 3.0 times the thickness of the steel plate.

[0025] The width of the edge region is 2.0 to 3.0 times the thickness of the steel plate, and is determined based on the influence range of the beveling process, the predetermined location of the outer weld toe area, and the curvature transition length after differential compression. When the width is less than 2.0 times, the differential pressing range cannot cover the main deformation zone from the root of the bevel to the outer weld toe, and the transition length between the edge area and the main arc of the steel plate is insufficient. When the width is greater than 3.0 times, the differential pressing action extends excessively to the rolled arc of the steel plate body, which can easily damage the roundness of the body.

[0026] The preset elastic opening amount refers to the distance measured at the middle position of the steel plate thickness between the two bevel roots when the edges of the longitudinal seam opening are not completely closed before the root forming weld. The preset elastic opening amount is maintained by the rolling support, edge limit and steel plate springback. Before the root forming weld heat source arrives, the edges on both sides of the longitudinal seam are allowed to undergo recoverable closing displacement under the action of welding heat input and the transverse cooling and shrinkage displacement of the weld seam behind.

[0027] The preset elastic opening amount = the root gap of the main welding target + the transverse shrinkage compensation amount of the weld + the springback amount of the cylindrical blank edge; and is greater than the root gap of the main welding target; in the range of 32 to 50 mm steel plate, the preset elastic opening amount is preferably 0.08 to 0.13 times the thickness of the steel plate.

[0028] The range of 0.08 to 0.13 times mentioned above is used to limit the controlled closing stroke. When it is less than 0.08 times, the available closing compensation stroke in the area to be welded is insufficient, making it difficult to stably reach the root gap of the main weld target through the shrinkage displacement of the weld seam behind. When it is more than 0.13 times, the closing stroke that needs to be completed in front of the root forming weld pool is too large, which can easily lead to uneven displacement of the two sides and increased misalignment.

[0029] The root gap of the main welding target refers to the gap maintained by the root of the bevel on both sides to achieve stable fusion before the leading edge of the root forming weld pool reaches the current welding position; the root gap of the main welding target is preferably 1.2 to 2.0 mm. The root gap detection position during the production process is located in the welding area 100 to 150 mm in front of the root forming weld pool.

[0030] Both the first and second locating welds are set across the longitudinal seam opening. The length of the locating weld refers to the transverse dimension of the locating weld extending from the edge of the steel plate on one side of the longitudinal seam across the opening of the longitudinal seam to the edge of the steel plate on the other side, perpendicular to the longitudinal seam direction; the first locating weld and the second locating weld are alternately set along the longitudinal seam direction, and the center distance between adjacent locating welds is measured along the longitudinal seam direction.

[0031] The cross-sectional area of ​​the tack weld metal refers to the effective connection cross-sectional area of ​​the tack weld; the effective connection cross-sectional area refers to the minimum continuous load-bearing cross-sectional area formed by the tack weld metal on the longitudinal macro-section perpendicular to the transverse extension direction of the tack weld and passing through the center of the tack weld.

[0032] The effective connection cross-sectional area of ​​the tack weld is determined by a process test plate of the same material and thickness. After the tack weld on the process test plate is cut, embedded, ground and etched, the minimum continuous load-bearing cross-sectional area of ​​the deposited metal is measured on the macroscopic section. The transverse length of the tack weld is used to measure the transverse coverage relationship of the tack weld relative to the root forming weld pool.

[0033] The effective connection cross-sectional area of ​​the first locating weld is smaller than that of the second locating weld. The effective connection cross-sectional area of ​​the first locating weld is preferably 55% to 68% of the effective connection cross-sectional area of ​​the second locating weld. This range is used to balance the connection stability of the first locating weld before the heat source of the root forming weld arrives and the priority remelting ability after the heat source arrives. When the percentage is below 55%, the stability of the first locating weld connection is insufficient, and the edge to be welded is prone to premature relative displacement; when it is above 68%, the first locating weld is difficult to remelt sufficiently and preferentially when the root forming weld pool passes through, which will impose additional constraints on the current weld segment.

[0034] During the root forming weld, the deposited metal of the first locating weld is almost completely remelted by the root forming weld pool and becomes part of the main weld metal after the pool solidifies.

[0035] The upper deposited metal and a middle portion of the second locating weld enter the root forming weld pool. The effective throat below the root forming weld depth boundary and the continuous fusion areas at both transverse ends are not completely remelted, thus maintaining a solid connection across the edges of the longitudinal weld during the solidification and cooling of the root forming weld.

[0036] The main weld pool refers to the weld pool formed by the root forming weld on the outer side of the longitudinal seam; after the root of the longitudinal seam is formed and cooled and solidified, the exposed end of the second positioning weld that has not been completely remelted is removed, and then the inner root cleaning weld, filler weld and cover weld are performed. The graded remelting and connection maintenance of the first and second locating welds occur during the root forming weld stage.

[0037] The current weld segment refers to the longitudinal seam area located between the center lines of two adjacent second positioning welds along the longitudinal seam direction; when the first positioning weld and the second positioning weld are set alternately, the length of the current weld segment is twice the center distance between the adjacent positioning welds.

[0038] When the heat source of the root forming weld approaches the current weld section, the temperature of the area to be welded increases, and the local deformation resistance of the edges on both sides of the longitudinal weld decreases. The weld that has already solidified behind the heat source of the root forming weld generates a transverse contraction displacement during the cooling process. This displacement is transmitted to the area to be welded in front through the continuous steel plate edges on both sides of the longitudinal weld and the second positioning weld that has not yet been completely remelted.

[0039] The term "closing" refers to the process where, under the condition that the inner support roller, outer pressure roller, and edge limiting block maintain their set positions, the root of the bevel on both sides of the area to be welded within 100-150mm in front of the root forming welding heat source gradually decreases from a preset elastic opening amount to the root gap of the main welding target. The driving force comes from the lateral cooling and shrinkage displacement of the solidified weld and the reduction of the edge local deformation resistance caused by the welding heat input. The closing endpoint is when the root gap of the bevel on both sides reaches the root gap of the main welding target.

[0040] The pre-weld residual compressive stress state formed by differential pressure is relaxed and redistributed during the welding thermal cycle; the pre-weld residual compressive stress state reduces the net residual tensile stress ultimately formed in the weld toe region by changing the stress redistribution process in the predetermined area of ​​the outer weld toe after the welding thermal cycle.

[0041] The thickness of the steel plate was verified and measured using a calibrated ultrasonic thickness gauge and vernier calipers; at least five points were measured on both sides of the predetermined position of the longitudinal seam for each steel plate, and the average value was taken as the basis for calculating the thickness of the steel plate.

[0042] The outer diameter of the steel pipe is measured using a π ruler and a laser diameter measuring device. For each section, a measurement section is selected at both ends and the middle. Three diameter values ​​are measured at 60° intervals between each section. The average value of the measured values ​​is taken as the average outer diameter of the section.

[0043] The roundness deviation of the steel pipe is calculated by dividing the difference between the maximum and minimum diameters within the same cross section by the outer diameter; the roundness deviation of each section is calculated separately at both ends and the middle section, and the maximum value among the three sections is taken as the maximum roundness deviation of that section; the roundness deviation in the table is the average of the maximum roundness deviations of the three sections.

[0044] The longitudinal seam misalignment is measured using a weld misalignment gauge, with measurements taken every 500mm along the longitudinal seam direction. The maximum value among all measuring points for each section is taken as the maximum misalignment for that section. The longitudinal seam misalignment is the average of the maximum misalignment of the three sections.

[0045] The residual stress at the weld toe was determined using the blind hole method, and some measuring points were verified using X-ray diffraction. Three measuring points were set on both sides of the outer weld toe for each test section, for a total of six measuring points per section, and a total of eighteen measuring points were set for each set of examples or comparative examples. The residual tensile stress at the weld toe was the average value of the eighteen measuring points in the direction perpendicular to the weld.

[0046] The cylinder sections for which pre-weld and post-weld residual stress testing is performed using the blind hole method are specially manufactured process qualification cylinder sections and are not delivered as product cylinder sections. Product cylinder sections are subject to quality control through non-destructive testing, dimensional inspection, and process parameters confirmed by process qualification.

[0047] The temperature of the outer surface of the weld toe is measured by a contact thermocouple. The temperature measuring point is located 10 mm outside the outer weld toe, and at least three temperature measuring points are arranged for each cylinder section. The edge limit is released based on the highest temperature among all temperature measuring points. When all temperature measuring points are lower than the set release temperature, the edge limit is released.

[0048] Weld quality is evaluated using ultrasonic and radiographic testing; the first-pass yield rate refers to the proportion of longitudinal weld lengths that meet acceptance requirements without rework to the total inspected weld lengths; cracks and lack of fusion are recorded separately and are not replaced by a first-pass yield record after partial rework.

[0049] Three test cylinder sections were fabricated for each set of examples and comparative examples; except for the first-pass yield, which is based on the actual weld length tested, the maximum misalignment, maximum roundness deviation and residual stress data listed in each table are the average results of the three test cylinder sections.

[0050] The line energy of root forming weld is calculated as 60UI / 1000V, where U is the arc voltage, I is the welding current, and v is the welding speed; this value is used for comparing process records between different test conditions.

[0051] Example 1, referring to Figure 1 ; This embodiment uses Q355 grade low alloy structural steel plate. Under standard parameter conditions of 3200mm outer diameter, 40mm steel plate thickness, edge area width of 2.5 times steel plate thickness, differential reduction of 0.045 times steel plate thickness, and preset elastic opening of 0.105 times steel plate thickness, the technical solution of this invention is verified to control the misalignment of longitudinal seams, roundness deviation, residual tensile stress at weld toe, and first-pass yield of longitudinal seams in the substation steel pipe.

[0052] In this embodiment, three process evaluation cylinder sections were manufactured. Each cylinder section has an outer diameter of 3200mm, a length of 12000mm, a steel plate thickness of 40mm, a diameter-to-thickness ratio of 80, and a target outer circle rolling radius of 1600mm. The unfolded dimensions of the steel plate after edge processing are 9955mm × 12000mm × 40mm, and the average outer diameter after rolling is 3200mm.

[0053] The steel plate adopts an asymmetrical X-shaped bevel, with an outer bevel angle of 50° and an inner bevel angle of 30°, and a blunt edge height of 4.0mm. After beveling, oxide scale, oil stains and burrs are removed mechanically.

[0054] After the steel plate enters the rolling roll group, it is first rolled into a circle, and then the outer edge area on both sides of the longitudinal seam is bent and the inner edge area is corrected respectively; the width of each edge area is 100mm. The outer bending reduction is 3.2mm, the inner correction reduction is 1.4mm, and the differential reduction is 1.8mm, which is equivalent to 0.045 times the thickness of the steel plate.

[0055] Pre-welding residual stress testing was conducted on a process verification section of the same material and thickness. The average residual stress in the predetermined area of ​​the outer weld toe perpendicular to the longitudinal seam direction was -96MPa. This test was used to confirm the pre-welding stress state formed by differential pressure rolling.

[0056] After the cylindrical blank enters the support and limiting position, the inner support roller supports the inner wall of the cylindrical blank, the outer pressure roller presses the outer wall of the cylindrical blank, and the two edge limiting blocks are respectively attached to the outer edges of the longitudinal seam opening.

[0057] After the rolling pressure is released, the springback of the cylindrical blank edge is 0.9mm; the transverse shrinkage compensation of the weld measured on the same material and thickness process test plate is 1.7mm; the root gap of the main welding target is 1.6mm; the preset elastic opening amount is set to 0.105 times the thickness of the steel plate, specifically 4.2mm.

[0058] For tack welding, a flux-cored wire with a diameter of 1.2 mm and a carbon dioxide shielding gas are used. The tack welding current is 220-250 A, the arc voltage is 24-27 V, the welding speed is 180-220 mm / min, and the shielding gas flow rate is 18-22 L / min.

[0059] The first and second positioning welds are alternately arranged along the longitudinal direction. The center distance between adjacent positioning welds is 180mm, the center distance between two adjacent second positioning welds is 360mm, and the length of the current weld segment is 360mm.

[0060] The first locating weld has a transverse length of 30mm perpendicular to the longitudinal seam and a weld leg height of 4.0mm; the second locating weld has a transverse length of 45mm perpendicular to the longitudinal seam and a weld leg height of 5.6mm.

[0061] The effective connection cross-sectional area of ​​the first locating weld was measured to be 24.7 mm², and the effective connection cross-sectional area of ​​the second locating weld was 40.5 mm². The effective connection cross-sectional area of ​​the first locating weld was 61% of the effective connection cross-sectional area of ​​the second locating weld.

[0062] For root forming welding, a 4.0 mm diameter submerged arc welding wire is used, and the flux is dried at 350℃ for 2 hours before use. The wire extension length is 28-32 mm, the welding current is 620-680 A, the arc voltage is 31-34 V, the welding speed is 380-420 mm / min, and the line energy is 2.7-3.6 kJ / mm.

[0063] The width of the root forming weld pool in the transverse direction perpendicular to the longitudinal seam is 32-34 mm, and the length in the longitudinal seam direction is 48-55 mm. The 30mm transverse length of the first locating weld is within the transverse coverage area of ​​the root forming weld pool.

[0064] The second locating weld has a transverse length of 45 mm, with both ends located outside the transverse boundary of the root forming weld pool, and its lower part of the effective throat located below the boundary of the root forming weld depth. During the root forming weld, the second locating weld is partially remelted, and the continuous effective throat that is not remelted remains solid-state connected during the cooling of the current weld segment.

[0065] The root gap is 1.5-1.7 mm at 100-150 mm in front of the root forming weld pool; when the root forming weld speed is calculated at 400 mm / min, the time required for the welding heat source to pass through one current weld segment is 54 s.

[0066] After the welding heat source passes through the second positioning weld, the time required for the temperature measurement point on the outer surface of the weld toe to drop from the peak temperature to 300℃ is 96 to 108 seconds; the remaining part of the second positioning weld is not ground during this period, and its solid connection time is longer than the time required for the temperature of the outer surface of the weld toe to drop to 300℃.

[0067] When the edge limiters of the three cylindrical sections are released, the highest temperatures on the outer surface of the weld toe are 297℃, 298℃ and 299℃ respectively. After all the temperature measurement points are below 300℃, the two edge limiters are released first, then the outer pressure roller is released, and finally the inner support roller is removed.

[0068] After the edge limit is released, remove the remaining end of the second positioning weld located outside the outer bevel edge, mechanically clean the inner side of the longitudinal seam, and then perform two inner submerged arc welds, six outer filler welds, and two outer capping welds; the welding current of subsequent welds is 680-760A, the arc voltage is 32-36V, and the welding speed is 320-380mm / min.

[0069] After testing, the average maximum misalignment of the three cylinder sections was 1.1 mm, the average maximum roundness deviation was 0.32%, and the average residual tensile stress at the weld toe was 78 MPa.

[0070] The total inspected length of the longitudinal seams of the three cylinder sections was 36m; no cracks or lack of fusion were found; among them, 0.50m of welds were repaired due to local porosity or scattered slag inclusions exceeding the acceptance limit, and the proportion of weld lengths that were qualified without repair was 98.6%.

[0071] To evaluate the impact of the overall process combination and key process actions on the longitudinal seam forming quality and residual tensile stress at the weld toe under standard parameter conditions, comparative examples 1-1 to 1-5 were set up.

[0072] Comparative Example 1-1 is a conventional overall process, which eliminates edge differential pressing, does not set a preset elastic opening amount greater than the target root gap, and sets all positioning welds to the same effective connection cross-sectional area; only a 1.6mm assembly root gap is retained before welding; this comparative example is used to evaluate the overall effect of the overall process combination of the present invention relative to the conventional rolling joint welding process.

[0073] Comparative Examples 1-2 were performed with only the edge differential compression removed; all other conditions were the same as in Example 1. Comparative Examples 1-3 retain the differential compression and preset elastic opening amount, but set the first locating weld and the second locating weld to have the same effective connection cross-sectional area; Comparative Examples 1-4 set the preset elastic opening amount to 0.05 times the thickness of the steel plate, i.e., 2.0 mm, and other conditions were the same as in Example 1; Comparative Examples 1-5 set the preset elastic opening amount to 0.16 times the thickness of the steel plate, i.e., 6.4 mm, and other conditions were the same as in Example 1; Table 1: Detection results of Example 1 and Comparative Examples 1-1 to 1-5 Main differences Standard process Conventional overall process Cancel differential pressure Equal cross-sectional area tack welding Opening volume 0.05t Opening volume 0.16t Differential reduction / t 0.045 0 0 0.045 0.045 0.045 Should a preset flexible opening amount be set? yes no yes yes yes yes Preset elastic opening amount / t 0.105 — 0.105 0.105 0.05 0.16 Pre-welding assembly root gap / mm — 1.6 — — — — The effective connection cross-sectional area ratio of the first / second locating weld / % 61 100 61 100 61 61 Maximum misalignment average value / mm 1.1 2.4 1.8 2.1 1.9 2.8 Average value of maximum roundness deviation / % 0.32 0.76 0.58 0.63 0.51 0.88 Average residual tensile stress at weld toe / MPa 78 226 168 151 136 142 Post-weld rounding time / min 18 52 40 43 36 58 Longitudinal seam first pass rate / % 98.6 92 94.5 93.8 95.1 90.4 As shown in Table 1, under the conditions of setting edge differential pressure, preset elastic opening amount, graded positioning weld and cooling limit, Example 1 simultaneously achieved lower maximum misalignment, roundness deviation and residual tensile stress at the weld toe, and the post-weld rounding time and longitudinal seam repair workload were reduced accordingly.

[0074] Comparative Example 1-1 simultaneously eliminated edge differential pressing, preset elastic opening amount, and graded positioning weld, representing a conventional rolling joint welding process. Compared with Example 1, the maximum misalignment of Comparative Example 1-1 increased from 1.1 mm to 2.4 mm, the maximum roundness deviation increased from 0.32% to 0.76%, and the residual tensile stress at the weld toe increased from 78 MPa to 226 MPa, indicating that the overall combination of the various process actions of the present invention can simultaneously improve the longitudinal seam forming accuracy and the post-weld stress state.

[0075] Comparative Examples 1-2 only eliminated edge differential pressure, and their preset elastic opening amount, positioning weld structure and root forming weld conditions were the same as those in Example 1. The residual tensile stress at the weld toe in Comparative Examples 1-2 increased to 168 MPa, indicating that the pre-weld stress state formed by differential pressure can affect the stress redistribution after welding thermal cycle and reduce the residual tensile stress eventually formed in the weld toe area.

[0076] In Comparative Examples 1-3, the first and second locating welds were set to have the same effective connection cross-sectional area. When the root forming weld pool passed through, the two types of locating welds could not form different remelting states of first releasing the connection and then maintaining the connection. The constraints on both sides of the longitudinal seam were not released evenly, and the maximum misalignment and roundness deviation were higher than those in Example 1.

[0077] The preset elastic opening amount of Comparative Examples 1-4 is less than 0.08 times the thickness of the steel plate, and the closing compensation stroke provided by the two sides of the longitudinal seam opening is insufficient; the area to be welded in front of the root forming weld cannot make full use of the shrinkage displacement of the solidified weld behind to complete the closure, and the maximum misalignment, roundness deviation and residual tensile stress of the weld toe are all higher than those of Example 1.

[0078] The preset elastic opening amount of Comparative Examples 1-5 is 0.13 times higher than the thickness of the steel plate. The closing stroke required to be completed by the two sides of the longitudinal seam opening in front of the root forming weld pool is too large. The local displacement of the edge is prone to unevenness, resulting in a significant increase in the maximum misalignment and the maximum roundness deviation. The first-pass yield of the longitudinal seam drops to 90.4%.

[0079] To evaluate the effect of the edge restraint temperature release on the cooling and shaping of the current weld segment, comparative examples 1-6 to 1-9 were set up; each comparative example only changed the edge restraint temperature release, and the other conditions were the same as in Example 1.

[0080] Comparative Examples 1-6 show that the edge restraint is released when the highest temperature on the outer surface of the weld toe is 420°C. Comparative Examples 1-7 show that the edge restraint is released when the highest temperature on the outer surface of the weld toe is 350°C. Comparative Examples 1-8 show that the edge restraint is released when the highest temperature on the outer surface of the weld toe is 320°C. Comparative Examples 1-9 remove edge restraints when the highest temperature on the outer surface of the weld toe is 280°C.

[0081] Table 2: Detection results at different release edge limiting temperatures Releasing edge limit temperature / ℃ 298 420 350 320 280 Maximum misalignment average value / mm 1.1 2.3 1.9 1.5 1.1 Average value of maximum roundness deviation / % 0.32 0.71 0.58 0.44 0.31 Average residual tensile stress at weld toe / MPa 78 174 148 112 80 Longitudinal seam first pass rate / % 98.6 92.8 94.7 96.5 98.4 Table 2 shows that when the edge restraint is removed at the outer surface temperature of the weld toe of 420℃ and 350℃, the current weld segment still has a large high-temperature deformation capacity. After the restraint is removed, springback and uneven shrinkage are likely to occur. The maximum misalignment, roundness deviation and residual tensile stress of the weld toe are significantly higher than those in Example 1.

[0082] Comparative Examples 1-8 showed that the edge restraint was removed at 320℃, and its various indicators were improved compared to the removal condition at 350℃, but still did not reach the level of removal below 300℃, indicating that the cooling and shaping of the current weld segment at 320℃ was not yet fully stable.

[0083] Example 1 released the edge constraint at 298℃, while Comparative Examples 1-9 released the edge constraint at 280℃. The maximum misalignment, maximum roundness deviation, residual tensile stress at the weld toe, and first-pass yield were similar in both examples. This result indicates that when the outer surface temperature of the weld toe drops below 300℃, the further improvement caused by extending the edge constraint holding time is small. Therefore, using all temperature measurement points below 300℃ as the criterion for releasing the edge constraint can balance the cooling and shaping effect with the production cycle.

[0084] Example 2 This embodiment uses Q355 grade low alloy structural steel plate. Under the lower limit parameter combination conditions of outer diameter 2800mm, steel plate thickness 36mm, edge area width 2.0 times steel plate thickness, differential reduction 0.03 times steel plate thickness, and preset elastic opening amount 0.08 times steel plate thickness, the feasibility of the technical solution of the present invention under the corresponding lower limit parameter conditions and the longitudinal seam forming effect are verified.

[0085] In this embodiment, three cylindrical sections are manufactured; each cylindrical section has an outer diameter of 2800mm, a length of 10000mm, a steel plate thickness of 36mm, a diameter-to-thickness ratio of 77.8, and a target outer circle rolling radius of 1400mm; The unfolded dimensions of the steel plate after processing are 8710mm×10000mm×36mm, and the average outer diameter after rolling is 2800mm.

[0086] The width of each edge area is 72mm; the differential reduction is 1.08mm, which is equivalent to 0.03 times the thickness of the steel plate; the root gap of the main welding target is 1.2mm, the edge springback is 0.65mm, and the transverse shrinkage compensation of the weld is 1.0mm.

[0087] The sum of the root gap of the main welding target, the edge springback amount, and the transverse shrinkage compensation amount of the weld is 2.85mm; 0.08 times the thickness of the steel plate is 2.88mm. Therefore, in accordance with the requirement that the preset elastic opening amount is not less than 0.08 times the thickness of the steel plate, the process setting value is adjusted upward to 2.88mm.

[0088] The transverse lengths of the first locating weld and the second locating weld are 30mm and 45mm respectively, the center distance between adjacent locating welds is 150mm, and the length of the current weld segment is 300mm; the effective connection cross-sectional area of ​​the first locating weld is 55% of the effective connection cross-sectional area of ​​the second locating weld.

[0089] The root forming welding current is 560-620A, the arc voltage is 30-33V, the welding speed is 400-450mm / min, the line energy is 2.2-3.1kJ / mm, and the transverse width of the molten pool is 30-32mm.

[0090] The time required for the outer surface temperature of the weld toe to drop from its peak to 300℃ is 82-94 seconds. The time for the second locating weld to remain in solid connection is longer than the above cooling time. The edge limit is released after all temperature measurement points are below 300℃.

[0091] According to the test results, the average value of the maximum misalignment in this embodiment is 1.3 mm, the average value of the maximum roundness deviation is 0.39%, the average value of the residual tensile stress at the weld toe is 92 MPa, and the first-pass yield rate of the longitudinal seam is 97.8%.

[0092] To evaluate the effects of edge region width, differential reduction, preset elastic opening amount, effective connection cross-sectional area ratio of locating welds, and center distance of locating welds on the longitudinal seam forming quality under the lower limit parameter conditions, comparative examples 2-1 to 2-5 were set.

[0093] Comparative Example 2-1 sets the width of the edge region to 1.5 times the thickness of the steel plate; Comparative Example 2-2 sets the differential reduction to 0.015 times the thickness of the steel plate; Comparative Examples 2-3 set the preset elastic opening amount to 0.06 times the thickness of the steel plate; Comparative Examples 2-4 set the effective connection cross-sectional area of ​​the first locating weld to 48% of the effective connection cross-sectional area of ​​the second locating weld; Comparative Example 2-5 sets the center distance between adjacent locating welds to 120mm.

[0094] Table 3: Detection results of Example 2 and Comparative Examples 2-1 to 2-5 Main differences Lower limit parameter combination 1.5t in the edge area Differential compression amount: 0.015t Opening volume 0.06t Cross-sectional area ratio 48% Center distance 120mm Edge area width / t 2 1.5 2 2 2 2 Differential reduction / t 0.03 0.03 0.015 0.03 0.03 0.03 Preset elastic opening amount / t 0.08 0.08 0.08 0.06 0.08 0.08 The effective connection cross-sectional area ratio of the first / second locating weld / % 55 55 55 55 48 55 Center distance between adjacent locating welds / mm 150 150 150 150 150 120 Maximum misalignment average value / mm 1.3 1.9 1.6 1.8 2 1.7 Average value of maximum roundness deviation / % 0.39 0.59 0.52 0.57 0.61 0.49 Average residual tensile stress at weld toe / MPa 92 139 143 132 126 134 Longitudinal seam first pass rate / % 97.8 94.8 95.6 95 94.2 95.4 As shown in Table 3, under the condition that the edge area width, differential reduction, preset elastic opening amount and the ratio of the effective connection cross-sectional area of ​​the first positioning weld are all close to the corresponding lower limits, Example 2 can still obtain a lower maximum misalignment, maximum roundness deviation and residual tensile stress of the weld toe. This indicates that the set of lower limit parameters can meet the matching requirements of continuous rolling, graded positioning and root forming welding.

[0095] In Comparative Example 2-1, the width of the edge region on each side is reduced to 1.5 times the thickness of the steel plate; the differential pressing range is too narrow, the transition length between the edge region and the rolling curvature of the main body of the steel plate is insufficient, the stress adjustment range of the predetermined area of ​​the outer weld toe is reduced, and the maximum misalignment and the maximum roundness deviation are significantly increased.

[0096] In Comparative Example 2-2, when the differential reduction was reduced to 0.015 times the thickness of the steel plate, the stress state formed in the predetermined area of ​​the outer weld toe after rolling was weakened, and the residual tensile stress of the weld toe increased from 92 MPa in Example 2 to 143 MPa. This result shows that when the differential reduction is less than 0.03 times the thickness of the steel plate, its effect on regulating the redistribution of stress after welding is insufficient.

[0097] In Comparative Examples 2-3, the preset elastic opening amount was reduced to 0.06 times the thickness of the steel plate; the closing allowance available for shrinkage displacement traction in the area to be welded in front of the root forming weld was smaller, the root gap adjustment capability decreased, and the maximum misalignment and maximum roundness deviation were higher than those in Example 2.

[0098] In Comparative Examples 2-4, the effective connection cross-sectional area of ​​the first locating weld is only 48% of that of the second locating weld; the connection stability of the first locating weld is insufficient before the heat source of the root forming weld arrives, and the relative displacement of the edge occurs prematurely in a local area, resulting in the maximum misalignment increasing to 2.0 mm, and the first-pass yield of the longitudinal weld decreasing to 94.2%.

[0099] In Comparative Examples 2-5, the center distance between adjacent locating welds was reduced to 120 mm, the number of locating welds per unit longitudinal weld length increased, and the continuous constraint on both sides of the longitudinal weld was enhanced. During the root forming weld, the welding shrinkage displacement was difficult to be uniformly released between adjacent locating welds, and the residual tensile stress at the weld toe and the maximum misalignment were both higher than in Example 2.

[0100] Example 3 This embodiment uses Q420 grade low alloy structural steel plate. Under the upper limit parameter combination conditions of outer diameter 4000mm, steel plate thickness 50mm, edge area width 3.0 times steel plate thickness, differential reduction 0.06 times steel plate thickness, and preset elastic opening amount 0.13 times steel plate thickness, the feasibility of the technical solution of the present invention under the corresponding upper limit parameter conditions and the longitudinal seam forming effect are verified.

[0101] In this embodiment, three cylindrical sections were manufactured. Each cylindrical section has an outer diameter of 4000mm, a length of 12000mm, a steel plate thickness of 50mm, a diameter-to-thickness ratio of 80, and a target outer circle rolling radius of 2000mm. The unfolded dimensions of the steel plate after processing are 12440mm×12000mm×50mm, and the average outer diameter after rolling is 4000mm.

[0102] The width of each edge area is 150mm; the differential reduction is 3.0mm, which is equivalent to 0.06 times the thickness of the steel plate; The root gap of the main welding target is 2.0mm, the edge springback is 1.2mm, the transverse shrinkage compensation of the weld is 3.3mm, and the preset elastic opening is 0.13 times the thickness of the steel plate, specifically 6.5mm.

[0103] The transverse lengths of the first and second locating welds are 30mm and 45mm respectively, the center distance between adjacent locating welds is 220mm, and the length of the current weld segment is 440mm; the effective connection cross-sectional area of ​​the first locating weld is 68% of the effective connection cross-sectional area of ​​the second locating weld.

[0104] The root forming welding current is 700-760A, the arc voltage is 34-37V, the welding speed is 330-370mm / min, the line energy is 3.9-5.1kJ / mm, and the transverse width of the molten pool is 36-38mm.

[0105] The time required for the outer surface temperature of the weld toe to drop from its peak to 300℃ is 118–134 seconds. The time for the second locating weld to remain in solid connection is longer than the above cooling time. The edge restraint is released after all temperature measurement points are below 300℃.

[0106] According to the test results, the average maximum misalignment in this embodiment is 1.5mm, the average maximum roundness deviation is 0.44%, the average residual tensile stress at the weld toe is 105MPa, and the first-pass yield rate of the longitudinal seam is 97.0%.

[0107] To evaluate the impact of edge region width, differential reduction, preset elastic opening amount, effective connection cross-sectional area ratio of locating welds, and center distance of locating welds on the longitudinal seam forming quality under the upper limit parameter conditions, comparative examples 3-1 to 3-5 were set.

[0108] Comparative Example 3-1 sets the width of the edge region to 3.5 times the thickness of the steel plate; Comparative Example 3-2 sets the differential reduction to 0.075 times the thickness of the steel plate; Comparative Example 3-3 sets the preset elastic opening amount to 0.15 times the thickness of the steel plate; Comparative Examples 3-4 set the effective connection cross-sectional area of ​​the first locating weld to 75% of the effective connection cross-sectional area of ​​the second locating weld; Comparative Example 3-5 sets the center distance between adjacent locating welds to 260mm.

[0109] Table 4: Detection results of Example 3 and Comparative Examples 3-1 to 3-5 Main differences Upper limit parameter combination 3.5t in the edge area Differential compression amount: 0.075t Opening volume 0.15t Cross-sectional area ratio 75% Center distance 260mm Edge area width / t 3 3.5 3 3 3 3 Differential reduction / t 0.06 0.06 0.075 0.06 0.06 0.06 Preset elastic opening amount / t 0.13 0.13 0.13 0.15 0.13 0.13 The effective connection cross-sectional area ratio of the first / second locating weld / % 68 68 68 68 75 68 Center distance between adjacent locating welds / mm 220 220 220 220 220 260 Maximum misalignment average value / mm 1.5 1.9 2.3 2.6 2.2 2.4 Average value of maximum roundness deviation / % 0.44 0.56 0.72 0.84 0.67 0.74 Average residual tensile stress at weld toe / MPa 105 132 118 148 138 145 Longitudinal seam first pass rate / % 97 95.4 93.8 91.6 93.5 92.9 As shown in Table 4, under the condition that the edge area width, differential reduction amount, preset elastic opening amount and the ratio of the effective connection cross-sectional area of ​​the first positioning weld are all at the corresponding upper limit, Example 3 can still obtain a stable longitudinal seam closure and cooling and shaping effect.

[0110] In Comparative Example 3-1, the width of the edge region increased to 3.5 times the thickness of the steel plate; the differential pressing range extended excessively into the main body of the steel plate, and the curvature transition between the edge bending area and the main body rolled arc was uneven, with the maximum roundness deviation increasing from 0.44% to 0.56%.

[0111] In Comparative Example 3-2, the differential reduction was increased to 0.075 times the thickness of the steel plate. The larger differential reduction did not reduce the residual tensile stress at the weld toe, but instead increased the degree of local overbending at the edge, making the springback correction after unloading more difficult, and significantly increasing the maximum misalignment and the maximum roundness deviation. This result shows that an excessively large differential reduction is not conducive to the control of edge geometric accuracy.

[0112] In Comparative Example 3-3, the preset elastic opening amount was increased to 0.15 times the thickness of the steel plate; the closing stroke required to be completed in front of the root forming weld pool at the root of the longitudinal seam bevel on both sides was too large, and the displacement of the weld cooling and shrinkage could not be stably and evenly transmitted to all the edges to be welded. The maximum misalignment increased to 2.6 mm, the maximum roundness deviation increased to 0.84%, and the first-pass yield of the longitudinal seam decreased to 91.6%.

[0113] In Comparative Examples 3-4, the effective connection cross-sectional area of ​​the first locating weld is increased to 75% of that of the second locating weld; the first locating weld fails to fully form a preferential remelting state when it passes through the root forming weld pool, and its residual connection imposes additional constraints on the current weld segment, resulting in uneven release of shrinkage displacement on both sides of the longitudinal weld edge.

[0114] In Comparative Examples 3-5, the center distance between adjacent locating welds was increased to 260 mm, and the local support distance between adjacent second locating welds was increased; the edge to be welded is prone to local misalignment and torsion in a longer unlocating connection section, and the maximum misalignment, maximum roundness deviation and residual tensile stress at the weld toe are all higher than in Example 3.

[0115] Example 4 This embodiment uses Q460 grade low alloy high strength steel plate. Under the conditions of an outer diameter of 3600mm and a steel plate thickness of 45mm, the applicability of the technical solution of the present invention to steel plates of different strength grades is verified.

[0116] In this embodiment, three cylindrical sections are manufactured; each cylindrical section has an outer diameter of 3600mm, a length of 10000mm, a steel plate thickness of 45mm, a diameter-to-thickness ratio of 80, and a target outer circle rolling radius of 1800mm. The unfolded dimensions of the steel plate after processing are 11200mm×10000mm×45mm, and the average outer diameter after rolling is 3600mm.

[0117] The width of each edge area is 108mm, which is equivalent to 2.4 times the thickness of the steel plate; the differential reduction is 1.8mm, which is equivalent to 0.04 times the thickness of the steel plate; the root gap of the main welding target is 1.8mm; the edge springback is 1.0mm; the weld transverse shrinkage compensation is 2.2mm; and the preset elastic opening is 0.111 times the thickness of the steel plate, specifically 5.0mm.

[0118] The center distance between adjacent locating welds is 190mm, and the length of the current weld segment is 380mm; the effective connection cross-sectional area of ​​the first locating weld is 62% of the effective connection cross-sectional area of ​​the second locating weld.

[0119] The root forming welding current is 650-710A, the arc voltage is 32-35V, the welding speed is 350-390mm / min, the line energy is 3.2-4.3kJ / mm, and the transverse width of the molten pool is 34-36mm.

[0120] According to the test results, the average maximum misalignment in this embodiment is 1.4 mm, the average maximum roundness deviation is 0.41%, the average residual tensile stress at the weld toe is 96 MPa, and the first-pass yield rate of the longitudinal seam is 97.5%.

[0121] To evaluate the effects of differential pressing and graded positioning welds on the longitudinal seam forming quality of Q460 grade steel plates, Comparative Example 4-1 and Comparative Example 4-2 were set up.

[0122] Comparative Example 4-1: Differential compression winding was omitted; other conditions were the same as in Example 4. Comparative Example 4-2 sets the first and second locating welds to have the same effective connection cross-sectional area, and other conditions are the same as in Example 4.

[0123] Table 5: Detection results of Example 4 and Comparative Examples 4-1 and 4-2 Main differences Q460 steel standard process Cancel differential pressure Equal cross-sectional area tack welding Differential reduction / t 0.04 0 0.04 The effective connection cross-sectional area ratio of the first / second locating weld / % 62 62 100 Maximum misalignment average value / mm 1.4 1.9 2.2 Average value of maximum roundness deviation / % 0.41 0.6 0.66 Average residual tensile stress at weld toe / MPa 96 176 149 Longitudinal seam first pass rate / % 97.5 94 93.4 As shown in Table 5, for Q460 grade low alloy high strength steel plates, the process of the present invention can still achieve lower maximum misalignment, maximum roundness deviation and residual tensile stress at the weld toe, indicating that the present invention does not depend on a single steel plate grade.

[0124] After the differential pressure rolling process was cancelled in Comparative Example 4-1, the predetermined area of ​​the outer weld toe before welding did not form the same stress state as in Example 4. The residual tensile stress of the weld toe increased from 96MPa to 176MPa, and the maximum misalignment and roundness deviation also increased accordingly.

[0125] Comparative Example 4-2 sets the first and second locating welds to have the same effective connection cross-sectional area. When the root forming weld pool passes through the locating weld, the first locating weld can no longer preferentially remelt while the second locating weld continues to maintain the connection, resulting in a maximum misalignment of 2.2 mm and a maximum roundness deviation of 0.66%.

[0126] The above results demonstrate that for Q460 grade steel plates with high yield strength, the pre-weld stress state formed by differential compression and the graded remelting relationship of the two types of locating welds can still play a role, making the process of the present invention applicable to different steel plate strength grades.

[0127] Example 5 This embodiment uses Q355 grade low alloy structural steel plate. Under the condition of a small diameter steel pipe with an outer diameter of 1800mm and a steel plate thickness of 32mm, the applicability of the technical solution of the present invention to different steel pipe diameters and diameter-to-thickness ratios is verified.

[0128] In this embodiment, three cylindrical sections were manufactured. Each cylindrical section has an outer diameter of 1800mm, a length of 8000mm, a steel plate thickness of 32mm, a diameter-to-thickness ratio of 56.3, and a target outer circle rolling radius of 900mm. The unfolded dimensions of the steel plate after processing are 5580mm×8000mm×32mm, and the average outer diameter after rolling is 1800mm.

[0129] The width of each edge area is 73.6 mm, which is equivalent to 2.3 times the thickness of the steel plate; the differential reduction is 1.28 mm, which is equivalent to 0.04 times the thickness of the steel plate; the root gap of the main welding target is 1.4 mm; the edge springback is 0.55 mm; the transverse shrinkage compensation of the weld is 1.35 mm; and the preset elastic opening is 3.3 mm, which is equivalent to 0.103 times the thickness of the steel plate.

[0130] The center distance between adjacent locating welds is 170mm, and the length of the current weld segment is 340mm; the effective connection cross-sectional area of ​​the first locating weld is 60% of the effective connection cross-sectional area of ​​the second locating weld.

[0131] The root forming welding current is 520-580A, the arc voltage is 29-32V, the welding speed is 420-470mm / min, the line energy is 1.9-2.7kJ / mm, and the transverse width of the molten pool is 30-32mm.

[0132] According to the test results, the average value of the maximum misalignment in this embodiment is 0.9 mm, the average value of the maximum roundness deviation is 0.30%, the average value of the residual tensile stress at the weld toe is 72 MPa, and the first-pass yield rate of the longitudinal seam is 99.0%.

[0133] To evaluate the impact of conventional integral process, elimination of differential pressure reduction, and complete remelting of the second positioning weld on the longitudinal seam forming quality under the condition of small diameter steel pipe, comparative examples 5-1 to 5-3 were set up.

[0134] Comparative Example 5-1 adopts the conventional integral process, eliminates differential compression, does not set a preset elastic opening amount, and uses locating welds with the same effective connection cross-sectional area; Comparative Example 5-2 only omits the differential compression winding process; all other conditions are the same as in Example 5. Comparative Example 5-3 maintains the effective connection cross-sectional area ratio of the first locating weld and the second locating weld at 60%, but adjusts the root forming weld current to 760-800A and the welding speed to 300-330mm / min, thereby increasing the transverse width of the root forming weld pool to 40-44mm, increasing the penetration depth, and completely remelting the effective throat of the second locating weld.

[0135] Table 6: Detection results of Example 5 and Comparative Examples 5-1 to 5-3 Main differences Standard process for small diameter steel pipes Conventional overall process Cancel differential pressure The second locating weld was completely remelted. Differential reduction / t 0.04 0 0 0.04 Should a preset flexible opening amount be set? yes no yes yes The effective connection cross-sectional area ratio of the first / second locating weld / % 60 100 60 60 The second locating weld remains connected during cooling. yes no yes no Maximum misalignment average value / mm 0.9 1.8 1.4 1.9 Average value of maximum roundness deviation / % 0.3 0.62 0.46 0.59 Average residual tensile stress at weld toe / MPa 72 204 151 119 Longitudinal seam first pass rate / % 99 94.2 96 94.8 As shown in Table 6, the process of the present invention can still be stably implemented on small-diameter steel pipes with an outer diameter of 1800 mm and a diameter-to-thickness ratio of 56.3. The maximum misalignment, maximum roundness deviation and residual tensile stress at the weld toe are all lower than those of the comparative examples.

[0136] Comparative Example 5-1 adopts the conventional integral process, while eliminating differential pressing, preset elastic opening amount and graded positioning weld. Compared with Example 5, the maximum misalignment of Comparative Example 5-1 increased from 0.9 mm to 1.8 mm, the maximum roundness deviation increased from 0.30% to 0.62%, and the residual tensile stress at the weld toe increased from 72 MPa to 204 MPa.

[0137] Comparative Example 5-2, which only eliminated differential pressing and rolling, had a higher maximum misalignment, roundness deviation, and residual tensile stress at the weld toe than Example 5. This indicates that even if the diameter of the steel pipe is reduced, the pre-weld stress state formed by differential pressing can still affect the stress redistribution in the weld toe area after welding.

[0138] Comparative Example 5-3 maintains the initial effective connection cross-sectional area relationship between the first and second locating welds, but by increasing the heat input of the root forming weld, the second locating weld is completely remelted by the root forming weld pool; the second locating weld cannot continue to maintain a solid connection during the cooling of the current weld segment, the edges on both sides of the longitudinal weld lose segmented restraint, and the maximum misalignment and maximum roundness deviation both increase significantly.

[0139] The results show that the difference in effective connection cross-sectional area between the first and second locating welds needs to be matched with the transverse width and penetration depth of the root forming weld pool; simply setting different initial effective connection cross-sectional areas without adjusting the remelting degree of the root forming weld to the second locating weld cannot achieve the same cooling and shaping effect as the present invention.

[0140] Verification Example 1 This verification example uses the same steel plate material, bevel structure, tack welding material, and root forming welding parameters as in Example 1 to verify the different remelting states, connection holding time, and local longitudinal seam edge displacement of the first and second tack welds during the root forming welding process.

[0141] On a full-size process evaluation cylinder section, three first positioning welds and three second positioning welds were selected as the measurement objects; A set of laser displacement sensors is arranged on the edges of the steel plates on both sides of the center of each locating weld to measure the relative displacement between the edges of the bevels on both sides after the root forming weld pool passes through the corresponding locating weld.

[0142] The springback of the longitudinal seam opening during cooling refers to the maximum value of the relative separation displacement of the two bevel edges from the rear edge of the weld pool to the outer surface temperature of the weld toe after the root forming weld pool passes through the corresponding locating weld and leaves the center of the locating weld from the corresponding locating weld.

[0143] After welding is completed, macroscopic metallographic specimens are cut at the corresponding positions of the first and second locating welds to measure the effective connection cross-sectional area ratio of the locating welds remelted by the root forming weld pool, the effective throat area of ​​the unremelted welds, and the length of the transverse end retained.

[0144] Table 7: Verification Results of Remelting State and Local Displacement of Tack Welds Horizontal length / mm 30 45 Effective connection cross-sectional area / mm² 24.7 40.5 Relative to the effective connection cross-sectional area of ​​the second locating weld / % 61 100 Percentage of effective joint cross-sectional area remelted by root forming weld pool / % 96 62 Unremelted continuous effective throat area / mm² 1 15.2 Length retained at one lateral end / mm 1 6.5 Maintain solid-state connection time / s 6 125 Local opening rebound during cooling / mm 0.42 0.11 As shown in Table 7, the effective connection cross-sectional area of ​​the first locating weld is small, and its 30mm transverse length is within the transverse coverage of the root forming weld pool. After the root forming weld pool passes through, approximately 96% of the effective connection cross-sectional area of ​​the first tack weld is remelted, leaving only 1.0 mm² of unremelted continuous effective throat area. 2 Its independent cross-seam connection state is released.

[0145] The effective connection cross-sectional area and transverse length of the second locating weld are both greater than those of the first locating weld; the root forming weld pool only remelts about 62% of the effective connection cross-sectional area of ​​the second locating weld, and its lower part still retains a continuous effective throat of 15.2 mm², and each of the transverse ends retains a solid connection area of ​​about 6.5 mm.

[0146] The solid connection holding time of the second locating weld is 125s, which is longer than the time required for the outer surface temperature of the weld toe to drop to 300℃. During this period, the opening springback of the local longitudinal joint section where the second locating weld is located is 0.11mm, which is lower than the 0.42mm of the local longitudinal joint section where the first locating weld is located.

[0147] The above results show that the difference in the effective connection cross-sectional area and transverse length of the first and second locating welds causes them to form different remelting states after the root forming weld pool passes through. The first locating weld preferentially releases the cross-weld connection, while the second locating weld continues to maintain the connection during the cooling of the current weld segment, thereby limiting the relative springback displacement of the two sides of the longitudinal weld.

[0148] Verification Example 2 This verification example is used to analyze the relationship between the pre-weld stress state formed under differential pressure and the residual tensile stress at the weld toe after welding.

[0149] This verification example uses the same batch of process qualification cylinder sections corresponding to Example 1, Comparative Example 1-2 and Comparative Example 1-1 to compare and analyze their residual stress data before and after welding.

[0150] Example 1 uses differential compression, preset elastic opening amount and graded positioning welds for the corresponding cylinder section; In Comparative Examples 1-2, the differential compression of the corresponding cylinder sections is eliminated, while the preset elastic opening amount and graded positioning welds are retained. Comparative Example 1-1 uses a conventional integral process for the corresponding cylinder section.

[0151] Table 8: Comparison of pre-weld stress state and post-weld residual stress under differential pressure Differential reduction / t 0.045 0 0 Should a preset flexible opening amount be set? yes yes no The effective connection cross-sectional area ratio of the first / second locating weld / % 61 61 100 Residual stress in the predetermined area of ​​the outer weld toe before welding / MPa -96 -18 12 Residual tensile stress at the weld toe after welding / MPa 78 168 226 Maximum misalignment average value / mm 1.1 1.8 2.4 Average value of maximum roundness deviation / % 0.32 0.58 0.76 It should be noted that the residual tensile stress, maximum misalignment, and maximum roundness deviation data in Table 8 are taken from the same batch of test cylinder sections corresponding to Table 1, and do not constitute another set of independent repeated test data.

[0152] As shown in Table 8, the residual stress in the predetermined area of ​​the outer weld toe before welding of the test section corresponding to Example 1 after differential pressure is -96MPa; the residual stress before welding of the test section corresponding to Comparative Example 1-2, which cancels differential pressure, is -18MPa; and the residual stress before welding of the test section corresponding to Comparative Example 1-1, which adopts conventional integral process, is 12MPa.

[0153] After welding, the residual tensile stress at the weld toe of the test section corresponding to Example 1 was 78 MPa, which was lower than 168 MPa in Comparative Examples 1-2 and 226 MPa in Comparative Example 1-1. This result shows that the pre-weld stress state formed under differential pressure can participate in the stress relaxation and redistribution after welding thermal cycling, and reduce the residual tensile stress eventually formed in the weld toe area.

[0154] The main difference between Example 1 and Comparative Examples 1-2 lies in whether differential pressure is applied. Both examples have a preset elastic opening amount and a graded positioning weld. Therefore, the difference in residual stress between the two examples can reflect the influence of differential pressure on the post-weld stress state.

[0155] Comparative Example 1-1 simultaneously eliminated differential pressure reduction, preset elastic opening amount, and graded positioning weld, and its results were used to characterize the conventional overall process. The maximum misalignment, roundness deviation, and residual tensile stress at the weld toe of this comparative example were the highest among the three groups of tests, indicating that there is a mutual coordination relationship between differential pressure reduction, preset elastic opening amount, and graded positioning weld.

[0156] The above results illustrate how the pre-weld stress state formed under differential pressure alters the stress redistribution process after the welding thermal cycle.

[0157] As can be seen from the above embodiments and verification examples, the present invention performs differential pressing on the edge areas on both sides of the longitudinal seam during continuous rolling, retains a preset elastic opening amount larger than the root gap of the main welding target before root forming welding, and sets a first positioning weld and a second positioning weld with different transverse lengths and effective connection cross-sectional areas.

[0158] During the root forming weld, the deposited metal of the first locating weld is almost completely remelted, while the second locating weld is only partially remelted and remains a continuous solid connection during the cooling of the current weld segment. The transverse shrinkage displacement generated by the solidified rear weld is transmitted to the front welding area through the edges of the steel plates on both sides of the longitudinal weld and the second positioning weld, so that the root of the bevel on both sides approaches the root gap of the main welding target before the front edge of the root forming weld pool arrives.

[0159] Releasing the edge limit after all temperature measurement points on the outer surface of the weld toe are below 300℃ helps to reduce the amount of longitudinal seam misalignment and roundness deviation; the pre-weld stress state formed by differential pressure changes the stress redistribution after the welding thermal cycle, which reduces the net residual tensile stress ultimately formed in the weld toe area.

[0160] The steel plate grade, steel pipe diameter, cylinder section length, bevel size, welding current, arc voltage, welding speed, molten pool size, and test results listed in the above embodiments are all used to illustrate the specific implementation process of the present invention. Those skilled in the art can make corresponding adjustments within the parameter relationships defined in the present invention based on the design diameter of the substation steel pipe, steel plate thickness, steel plate yield strength, and welding process evaluation results.

Claims

1. A continuous rolling and welding integrated process for steel pipes used in booster stations, characterized in that, Includes the following steps: S1. Continuously roll the steel plate, and perform differential pressing and rolling on both sides of the predetermined position of the longitudinal seam to form a residual compressive stress zone. The width of the edge zone is 2.0 to 3.0 times the thickness of the steel plate. S2. Roll and support the cylindrical blank and limit its edges. Keep the edges of the longitudinal seam opening on both sides incompletely closed. The preset elastic opening between the two sides is 0.08 to 0.13 times the thickness of the steel plate and is greater than the root gap of the main welding target. S3. Perform tack welding at the opening of the longitudinal seam, and alternately form the first tack weld and the second tack weld along the longitudinal seam direction. The cross-sectional area of ​​the molten metal deposited by the first tack weld is 55% to 68% of the cross-sectional area of ​​the molten metal deposited by the second tack weld. S4. Perform main welding along the longitudinal seam. The main weld pool remelts the first locating weld. The second locating weld remains connected across the seam during the cooling of the current weld segment. The edges of the base material on both sides of the longitudinal seam form a heat-affected zone plastic deformation section. Before the leading edge of the root forming weld pool reaches the current position to be welded, the root gap of the bevel on both sides is closed to the root gap of the main weld target. S5. Under the support of the rolling support, edge limit and second positioning weld, the main weld is cooled. The residual compressive stress in the residual compressive stress zone is superimposed on the tensile stress in the weld toe area in the opposite direction to form a longitudinal seam with low residual tensile stress, and the substation steel pipe is obtained.

2. The integrated continuous rolling and welding process for substation steel pipes according to claim 1, characterized in that, In S1, the inner support roller and the outer pressure roller are used to differentially press and roll the edge areas on both sides of the predetermined position of the longitudinal seam. The pressing amount of the predetermined area of ​​the outer weld toe is greater than the pressing amount of the predetermined area of ​​the inner weld toe. The differential pressing amount is 0.03 to 0.06 times the thickness of the steel plate.

3. The integrated continuous rolling and welding process for substation steel pipes according to claim 1, characterized in that, In S2, the edge springback amount of the cylindrical blank after the rolling pressure is released is measured. Based on the root gap of the main welding target, the transverse shrinkage compensation amount of the weld, and the edge springback amount, the preset elastic opening amount is determined. The preset elastic opening amount is 0.08 to 0.13 times the thickness of the steel plate. The root gap of the main welding target is 1.2 to 2.0 mm.

4. The integrated continuous rolling and welding process for substation steel pipes according to claim 1, characterized in that, In S2, an inner support roller supports the inner wall of the cylindrical blank, an outer pressure roller presses the outer wall of the cylindrical blank, and two edge limiting blocks are respectively attached to the outer sides of the longitudinal seam opening. By adjusting the distance between the two edge limiting blocks, the preset elastic opening amount is obtained.

5. The integrated continuous rolling and welding process for substation steel pipes according to claim 1, characterized in that, In S3, the first locating weld and the second locating weld are arranged alternately along the main welding direction, and the center distance between adjacent locating welds is 150-220mm.

6. The integrated continuous rolling and welding process for substation steel pipes according to claim 5, characterized in that, The weld length of the first locating weld is 30mm, the weld length of the second locating weld is 45mm, and the weld leg height of the first locating weld is less than the weld leg height of the second locating weld.

7. The integrated continuous rolling and welding process for substation steel pipes according to claim 1, characterized in that, In S4, the width of the main weld pool is adjusted to cover the bevel section where the first locating weld is located. The end deposited metal of the second locating weld remains outside the boundary of the current main weld pool. The first locating weld is incorporated into the main weld pool. The second locating weld maintains the cross-seam connection of the two sides of the longitudinal seam opening during the cooling of the current weld segment.

8. The integrated continuous rolling and welding process for substation steel pipes according to claim 1, characterized in that, The tack welding is performed using flux-cored wire gas shielded welding, and the main welding is performed using submerged arc welding, with the main welding being performed along the axial direction of the cylindrical blank.

9. The integrated continuous rolling and welding process for substation steel pipes according to claim 1, characterized in that, In S5, after the main welding heat source leaves the current weld segment, the rolling support, edge limit and second positioning weld continue to maintain the positioning state of the current weld segment, and the edge limit is released after the temperature of the temperature measuring point on the outer surface of the weld toe of the current weld segment drops below 300°C.

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