Welding method of cylindrical non-bearing accessory structure beneficial to improvement of fatigue performance

Abstract

According to the welding method of the cylindrical non-bearing accessory structure beneficial to improving the fatigue performance, the transition angle of the base metal bottom plate side of the annular fillet weld is controlled, and the welding fillet width of the annular fillet weld on the base metal bottom plate side is controlled; therefore, optimal control over the stress concentration effect of the cylindrical non-bearing accessory during load transmission is achieved. According to the welding method of the cylindrical non-bearing accessory structure beneficial to improving the fatigue performance, the research and development team of the applicant finds that the fatigue performance of the accessory welding structure can be conditionally improved along with the improvement of the strength level of the base metal of the whole part; on the basis that a fatigue strength characteristic value specified in a non-standard is irrelevant to a material characteristic, a stress concentration factor in optimization factors which the new discovery depends on is disclosed for a specific optimization scheme of a welding structure of the cylindrical non-bearing accessory.

Description

Technical Field

[0001] The present invention belongs to the technical field of welding, and particularly relates to a welding method for a cylindrical non-load-bearing accessory structure beneficial to improving fatigue performance. Background Art

[0002] For the fatigue S-N curve of welded joints in the original welded structural member fatigue design standard, the basic guiding cognition behind its determination is that the fatigue strength level of the welded joints of steel materials is not related to the material strength level, but only related to the joint form design, welding quality grade, and post-weld treatment state. For example: the mainstream EN1993 standard, IIW-2259-15 standard, and DNV-RP-C203 standard all give a set of S-N curves for fatigue design according to different design forms and quality grades of steel materials under this basic guiding cognition.

[0003] For general dynamic load service structural members, in addition to direct load-bearing butt joints or fillet joints, for the purposes of pipeline or cable layout and fixation, operation monitoring and maintenance, decoration, etc., various-shaped accessories are often welded on the overall structure, mainly rectangular plate-shaped accessories and cylindrical accessories with a central hole. The welds of the accessories themselves do not bear direct fatigue loads, but due to the strong stress concentration at the weld toes or weld roots during the load transfer process, the fatigue performance of the overall structure will be significantly reduced.

[0004] However, the research team of the applicant found through research that: with the increase in the strength level of the base material of the overall part, the fatigue performance of the welded accessory structure will also be conditionally improved, rather than the fatigue strength characteristic value specified in the standard being independent of the material characteristics. This discovery after research makes it possible to apply high-strength steel for the design and lightweight reduction of dynamic load structural members, including the main body butt joint structure and the non-load-bearing accessory structure. Based on this, it is necessary to disclose the specific optimization scheme of the stress concentration factor in the optimization factors on which this new discovery depends for this kind of welded structure of cylindrical non-load-bearing accessories.

[0005] The invention application with the application number: CN2006100155949 discloses "a spray fusing method for improving the fatigue performance of welded structures", which uses a spray welding or laser spray fusing method to coat the weld toes of the welded structure with a spraying material to form a smooth-transition metal coating layer with a coating thickness between 1 mm and 6 mm at the weld toes, and the coating thickness at the weld toes is thicker than that in the nearby area, and the spraying material is in a molten state. Summary of the Invention

[0006] To achieve the above technical objectives, the present invention provides a welding method for a cylindrical non-load-bearing accessory structure beneficial to improving fatigue performance, and its technical solution is as follows:

[0007] A welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance

[0008] By establishing the control of the transition angle on the base plate side of the circumferential fillet weld and the control of the weld leg width of the circumferential fillet weld on the base plate side of the base metal, an optimized control of the stress concentration effect during the transfer of load by the cylindrical non - load - bearing accessory is formed.

[0009] Furthermore,[[]]

[0010] The establishment of the control of the transition angle on the base plate side of the circumferential fillet weld and the establishment of the control of the weld leg width of the circumferential fillet weld on the base plate side of the base metal are specifically as follows:

[0011] During the welding process, by controlling and reducing the turbulence intensity of the molten pool and cooperating with the set oscillating welding process, the control of the spreading uniformity of the weld toe on the base metal side is established;

[0012] And the welding is completed by satisfying the constraint of the established angle control of the transition angle on the base plate side of the circumferential fillet weld, satisfying the constraint of the established width control of the weld leg width of the circumferential fillet weld on the base plate side of the base metal, satisfying the uniformity constraint of the established transition angle on the base plate side of the circumferential fillet weld in the circumferential space distribution of the circumferential fillet weld, and satisfying the uniformity constraint of the established weld leg width of the circumferential fillet weld on the base plate side of the base metal in the circumferential space distribution of the circumferential fillet weld.

[0013] Furthermore,[[]]

[0014] The control of reducing the turbulence intensity of the molten pool is achieved by setting groove welding and controlling the groove angle and root face size;

[0015] The groove angle is controlled within 10° - 25°;

[0016] The root face size is controlled within 1 / 3t - 3 / 5t and greater than 4mm,

[0017] where t: the thickness of the cylindrical non - load - bearing accessory, unit: mm.

[0018] Furthermore,[[]]

[0019] The set oscillating welding process is specifically as follows:

[0020] In a way that controls the angle between the welding torch and the base plate of the base metal in the horizontal direction to be less than 20° and is close to the horizontal welding position, the dry elongation of the welding wire is controlled within 15 - 24mm, and it oscillates asymmetrically up and down at the edge of the circular groove; during the oscillation process, the oscillation width is formed with the limit of covering the upper groove edge, and at the same time, the control of the residence time for the upper edge and the lower edge is established respectively according to the influencing factor of the molten pool gravity.

[0021] Furthermore,[[]]

[0022] The establishment of the control over the residence time of the upper edge specifically involves controlling the residence time within the range of 0.5 to 2 s;

[0023] The establishment of the control over the residence time of the lower edge specifically involves controlling the residence time to be less than 0.5 s.

[0024] Furthermore,

[0025] The constraint on the angular control of the transition angle of the circumferential fillet weld on the base plate side of the parent material is specifically: setting the transition angle to be greater than 155°.

[0026] Furthermore,

[0027] The constraint on the width control of the fillet weld width of the circumferential fillet weld on the base plate side of the parent material is specifically: setting the fillet weld width to fall within the range of 9 - 20 mm and be greater than 2 / 5t;

[0028] where t: the thickness of the cylindrical non - load - bearing accessory, unit: mm.

[0029] Furthermore,

[0030] By establishing the control over the penetration depth of the circumferential fillet weld on the base plate side of the parent material and the penetration depth in the thickness direction of the cylindrical non - load - bearing accessory, to ensure meeting the constraint on the angular control of the transition angle of the circumferential fillet weld on the base plate side of the parent material and ensuring meeting the constraint on the width control of the fillet weld width of the circumferential fillet weld on the base plate side of the parent material.

[0031] Furthermore,

[0032] The establishment of the control over the penetration depth of the circumferential fillet weld on the base plate side of the parent material is specifically: controlling the penetration depth on the base plate side of the parent material within the range of 1.2 - 3.5 mm;

[0033] The establishment of the control over the penetration depth of the circumferential fillet weld in the thickness direction of the cylindrical non - load - bearing accessory is specifically: controlling the penetration depth in the thickness direction of the accessory within the range of 2.6 - 7.5 mm, and the penetration depth in the thickness direction of the accessory should be greater than 2.2 times the penetration depth on the base plate side of the parent material.

[0034] Furthermore,

[0035] The control over the penetration depth of the circumferential fillet weld on the base plate side of the parent material and the control over the penetration depth in the thickness direction of the cylindrical non - load - bearing accessory are achieved by the set swing welding process in cooperation with the establishment of the control over the wire diameter, the control over the welding voltage, the control over the welding current, and the control over the welding speed.

[0036] Furthermore,

[0037] The wire diameter described is set to 1.2 mm;

[0038] The welding voltage described is controlled within 24 - 30 V;

[0039] The welding current described is controlled within 200 - 260 A;

[0040] The welding speed described is controlled within 210 - 320 mm / min.

[0041] Furthermore,

[0042] The establishment of the uniformity constraint on the transition angle of the circumferential fillet weld on the base plate side of the parent material is specifically as follows:

[0043]

[0044] In the above formula,

[0045] θ i : The transition angle of each of the 6 set distribution points of the weld in the circumferential space distribution. The determination process of these 6 set distribution points is as follows: Taking the center of the projection of the cylindrical accessory on the plane of the base plate of the parent material as the center, two distribution points are determined with the center line formed parallel to the length direction of the base plate of the parent material, and the other four distribution points are determined by rotating this center line clockwise by 45° and counterclockwise by 45° respectively;

[0046] θ: The average value of the transition angles of the 6 set distribution points.

[0047] Furthermore,

[0048] The establishment of the uniformity constraint on the weld leg width of the circumferential fillet weld on the base plate side of the parent material is specifically as follows:

[0049]

[0050] In the above formula,

[0051] l pi : The weld leg width of each of the 6 set distribution points of the weld in the circumferential space distribution. The determination process of these 6 set distribution points is as follows: Taking the center of the projection of the cylindrical accessory on the plane of the base plate of the parent material as the center, two distribution points are determined with the center line formed parallel to the length direction of the base plate of the parent material, and the other four distribution points are determined by rotating this center line clockwise by 45° and counterclockwise by 45° respectively;

[0052] The average value of the transition angles of the 6 set distribution points.

[0053] Furthermore,

[0054] Taking the center of the projection of the cylindrical non-load-bearing accessory on the plane of the base metal floor as the center, a center line is formed parallel to the length direction of the base metal floor. The center line is rotated clockwise by 45° to form a first oblique line, and the center line is rotated counterclockwise by 45° to form a second oblique line. The vertical angle area formed by the first oblique line and the second oblique line in the direction with the center line as the angular bisector is set as the main influence area for positive transmission of load, and welding is carried out with the starting and ending arc positions controlled to avoid the main influence area.

[0055] Furthermore,

[0056] By setting a circulating water cooling device on the back of the base metal floor, a contact conduction heat exchange with the circulating water temperature less than 45°C during the welding process is provided, and accordingly, a control of less than 5° for the structural angular deformation is established.

[0057] A welding method for a cylindrical non-load-bearing accessory structure beneficial to improving fatigue performance according to the present invention is based on the discovery by the applicant's R & D team that as the strength level of the base metal of the integral part increases, the fatigue performance of the welded accessory structure will also be conditionally improved, rather than the fatigue strength characteristic value stipulated in the standard being independent of the material characteristics. The specific optimization scheme of the stress concentration factor in the optimization factors relied on by this new discovery for this kind of welded structure of cylindrical non-load-bearing accessories is disclosed. Brief Description of the Drawings

[0058] Figure 1 It is a schematic front view of the structure of the base metal floor and the cylindrical non-load-bearing accessory before welding in the present invention;

[0059] Figure 2 is Figure 1 the top view of;

[0060] Figure 3 is Figure 1 the detailed schematic diagram of the large depth-width ratio annular groove in;

[0061] Figure 4 It is a schematic diagram of the characteristic parameters of the circumferential fillet weld of the cylindrical non-load-bearing accessory in the present invention;

[0062] Figure 5 It is a schematic diagram of the measuring points of the characteristic parameters of the circumferential fillet weld of the cylindrical non-load-bearing accessory in the present invention;

[0063] Figure 6 It is a schematic diagram of the position of the welding torch for the circumferential fillet weld of the cylindrical non-load-bearing accessory in the present invention;

[0064] Figure 7 It is a front view of the welded structure of the central opening cylindrical accessory on the Q500MD high-strength steel floor in the embodiment of the present invention;

[0065] Figure 8 is Figure 7 the top view of

[0066] In the figure,

[0067] 1 - Base material bottom plate;

[0068] 2 - Central opening cylindrical accessory;

[0069] 3 - Large depth - width ratio annular groove;

[0070] 4 - The center line formed parallel to the length direction of the base material bottom plate with the center of the projection of the cylindrical non - load - bearing accessory on the plane of the base material bottom plate as the center;

[0071] 5 - The first oblique line formed by rotating the center line clockwise by 45°;

[0072] 6 - The second oblique line formed by rotating the center line counterclockwise by 45°;

[0073] 7 - Welding torch;

[0074] 8 - Large depth - width ratio circumferential fillet weld. Specific implementation mode

[0075] Next, according to the accompanying drawings of the specification and the specific implementation mode, a welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance of the present invention will be further specifically described.

[0076] To fully understand this technical solution, the following will be elaborated in turn from three parts: the setting background of this technical solution, the overall overview of this technical solution, and the specific process of this technical solution.

[0077] The setting background part of this technical solution:

[0078] A welding method for a cylindrical non-load-bearing accessory structure beneficial to improving fatigue performance, based on the discovery by the applicant's R & D team that as the strength level of the base material of the integral part increases, the fatigue performance of the welded accessory structure will also be conditionally improved, rather than the fatigue strength characteristic value specified in the standard being independent of the material characteristics. The specific optimization scheme of the stress concentration factor in the optimization factors relied on by this new discovery for this welded structure of cylindrical non-load-bearing accessories is disclosed. Through this technical solution, the control and optimization of stress concentration are realized, and then combined with the control and optimization of the initial fatigue crack source formed by macroscopic or microscopic defects in the weld seam, and the control and optimization of the welding residual tensile stress. Based on these three control and optimizations, a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base material is formed, realizing the conversion of the welding fatigue characteristics to follow a relationship positively correlated with the static load strength. The establishment of the control and optimization of the initial fatigue crack source formed by macroscopic or microscopic defects in the weld seam mentioned above refers to forming the microzone cyclic plastic strain fatigue crack initiation stage controlled by the yield strength of the base material through the control of microscopic or macroscopic defects; the establishment of the control and optimization of the welding residual tensile stress is achieved by establishing a welding process that can reduce the welding residual tensile stress and then cooperating with the established optimization of the peak value of the welding residual tensile stress. Here, the establishment of the optimization of the peak value of the welding residual tensile stress refers to controlling the duration of the residual stress relaxation effect generated by the superposition of the welding residual tensile stress and the external load to meet the set time.

[0079] The overall overview part of this technical solution:

[0080] In order to optimize the stress concentration of the cylindrical non-load-bearing accessory during the transfer of load during service, so that it meets the stress concentration factor in the fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base material through the control and optimization of three factors (that is, establishing a response to the stress concentration influencing factor among the three factors). This technical solution establishes the control of the transition angle on the base plate side of the circumferential fillet weld and the control of the weld leg width of the circumferential fillet weld on the base plate side of the base material. Based on the control of these two factors, the optimization control of stress concentration is realized. Specifically: during the welding process, by controlling and reducing the turbulence intensity of the molten pool and cooperating with the set weaving welding process, the control of the spreading uniformity of the weld toe on the base material side is established; and the welding is completed by meeting the constraint of the established angle control of the transition angle on the base plate side of the circumferential fillet weld, meeting the constraint of the established width control of the weld leg width of the circumferential fillet weld on the base plate side of the base material, meeting the uniformity constraint of the established transition angle on the base plate side of the circumferential fillet weld in the circumferential space distribution of the circumferential fillet weld, and meeting the uniformity constraint of the established weld leg width of the circumferential fillet weld on the base plate side of the base material in the circumferential space distribution of the circumferential fillet weld.

[0081] The control in the above reduces the turbulence intensity of the molten pool, which is achieved by setting up a groove weld and controlling the groove angle and root face size; the groove angle is controlled within 10° to 25°; the root face size is controlled within 1 / 3t to 3 / 5t and greater than 4 mm, where t is the thickness of the cylindrical non-load-bearing accessory, unit: mm. This setting provides better conditions and possibilities for the normal flow of the molten pool, and then cooperates with controlling the torch angle to perform welding operations in a way close to the horizontal fillet welding, forming the effect of automatically draining the liquid molten pool, and then cooperating with the specifically set weaving welding process to ensure smooth transition and uniform spreading on the base plate side of the fillet weld parent material. The specifically set weaving welding process described here is: in a way close to the horizontal fillet welding with the angle between the torch and the base plate of the parent material in the horizontal direction less than 20°, control the wire dry elongation at 15 - 24 mm, and swing asymmetrically up and down at the edge of the circular groove; during the swinging process, form the swinging width with the limit of covering the upper groove edge, and at the same time, establish the control of the dwell time for the upper edge and the lower edge respectively according to the influencing factor of the molten pool gravity. The internal mechanism of the influence of the molten pool gravity here is: during the welding process at a position close to the horizontal fillet welding, the molten pool tends to flow downward due to the action of gravity, so increase the dwell time at the upper edge, use the arc force to hold back the molten pool, thereby appropriately increasing the amount of clad metal at this position and appropriately offsetting the amount of clad metal flowing downward under the action of gravity; while at the lower edge, due to the action of gravity, there has already been an accumulation of the amount of clad metal, and if the dwell time at the edge is too long, the increased amount of clad metal will be excessive, resulting in too high and convex weld reinforcement at this position, exacerbating the sharp transition and stress concentration at the adjacent weld toe position between the lower part of the fillet weld and the high-strength steel parent material, which is not conducive to the fatigue performance of the welded structure of this accessory.

[0082] The established constraint on the angle control of the transition angle on the base plate side of the circumferential fillet weld parent material is specifically: set the transition angle to be greater than 155°. The established constraint on the width control of the weld leg width of the circumferential fillet weld on the base plate side of the parent material is specifically: set the weld leg width to fall within the range of 9 - 20 mm and greater than 2 / 5t; where, t is the thickness of the cylindrical non-load-bearing accessory, unit: mm. On this basis, further establish the control of the penetration depth of the circumferential fillet weld on the base plate side of the parent material and the penetration depth in the thickness direction of the cylindrical non-load-bearing accessory to ensure meeting the established constraint on the angle control of the transition angle on the base plate side of the circumferential fillet weld parent material and ensuring meeting the established constraint on the width control of the weld leg width of the circumferential fillet weld on the base plate side of the parent material. Further, the specific control of the penetration depth is achieved by controlling the wire diameter, welding voltage, welding current, and welding speed.

[0083] The establishment of the uniformity constraint on the transition angle of the circumferential fillet weld on the base plate side in the circumferential spatial distribution of the circumferential fillet weld, and the establishment of the uniformity constraint on the weld leg width of the circumferential fillet weld on the base plate side in the circumferential spatial distribution of the circumferential fillet weld, as described above, are achieved by establishing control over the volatility of the transition and spreading quality of the circumferential fillet weld toe to control the overall spreading uniformity, thereby facilitating the control of additional stress concentration during the load transfer process. The specific control and implementation of these two constraints are ensured through all the settings starting from the self-groove form design described in the text to the welding series operation methods.

[0084] To better serve the technical purpose of this technical solution, some precautions are also set on the basis of the above settings. Specifically: to avoid starting and ending arcs near the main area of positive load transfer, the starting and ending arc positions are set on the side of the accessory. To control the overall structural deformation angle to be less than 5°, a circulating water cooling device based on contact conduction heat exchange is set on the back of the base plate of the base material, and forced cooling is formed during the welding of the accessory through the device to reduce the influence of welding heat on the overall structural deformation.

[0085] The specific process part of this technical solution:

[0086] A welding method for a cylindrical non-load-bearing accessory structure beneficial to improving fatigue performance according to the present invention is directed to a non-load-bearing cylindrical accessory structure in a large-thickness steel structure serving in a dynamic load fatigue scenario. By establishing the design of the cylindrical accessory joint form, the design of the characteristic parameters and size uniformity of the circumferential fillet weld of the accessory, and the optimization of the semi-automatic welding process technology based on gas-shielded flux-cored wire, etc., the problems of local sharp transition and uneven spreading of the fillet weld caused by the continuous change of curvature and the random volatility of short weld bead formation during the welding process of the cylindrical accessory are solved, achieving the effect of reducing the stress concentration in the positive load transfer during the service of the steel structure and meeting the purpose of establishing control and optimization of stress concentration as described above. Starting from the dimension of optimizing the forming quality and uniformity of the circumferential fillet weld of the cylindrical accessory, through the design of the center-opening cylindrical accessory joint form, the design of the characteristic parameters and size uniformity of the circumferential fillet weld of the accessory, and the optimization of the semi-automatic welding process technology based on gas-shielded flux-cored wire, etc., a circumferential fillet weld of the cylindrical accessory with smooth overall transition and uniform spreading is obtained. While reducing the stress concentration in the positive load transfer during the service of the steel structure, the fatigue performance of the non-load-bearing cylindrical accessory welding structure is significantly improved, and the circumferential fillet weld of the accessory is prevented from becoming a weak link in the fatigue service of the overall steel structure.

[0087] The specific technical solution is as follows:

[0088] Step 1: Design of the center-opening cylindrical accessory joint form

[0089] For the commonly used center - opened cylindrical appendages of large - scale steel structures under dynamic loads, considering their inherent characteristics such as short fillet welds at the angular joints, small operating space, and large curvature changes during the welding process, in order to ensure the forming quality of the weld toes on the base - plate side of the circumferential fillet welds that play a positive role in load transfer, a center - opened cylindrical appendage with a large depth - to - width ratio annular groove is designed. Thus, when performing fillet welding with the base - plate of the parent material, by operating near the horizontal welding position, the effect of automatically draining the liquid molten pool in the annular groove is achieved, thereby appropriately increasing the operating space for the fillet weld, avoiding the severe impact on the weld toes on the parent - material side caused by the formation of unidirectional turbulence in the liquid molten pool in a short time. Through the normal flow of the molten pool and the oscillation of the welding torch, the spreading quality of the weld toes on the parent - material side is ensured. At the same time, this design form is conducive to increasing the penetration depth of the fillet weld in the thickness direction of the cylindrical appendage, while reducing the penetration depth on the base - plate side of the parent material, which is beneficial to avoiding undercut and uneven transition of the weld toes on the base - plate side of the parent material and is conducive to obtaining a circumferential fillet weld with uniform overall forming for the appendage. Figure 1 、 2 The structural schematic diagrams of the center - opened cylindrical appendage 2, the large depth - to - width ratio annular groove 3, and the base - plate 1 of the parent material are shown. Figure 3 The schematic diagram of the characteristic parameters of the large depth - to - width ratio annular groove 3 is shown. In order to achieve the effect of a large depth - to - width ratio and ensure the welding quality of the fillet welds of the subsequent cylindrical appendage, the opening angle ɑ of the annular groove is limited to 10 - 25°, the root face size f is 1 / 3 - 3 / 5t, and f > 4mm, where t represents the thickness of the center - opened cylindrical appendage.

[0090] Step 2: Design of the characteristic parameters and dimensional uniformity of the circumferential fillet weld of the appendage

[0091] Figure 4 The schematic diagram of the characteristic parameters of the circumferential fillet weld of the center - opened cylindrical appendage is shown. In the figure, 8 represents the large depth - to - width ratio circumferential fillet weld. From the perspective of reducing the stress concentration effect during load transfer in service, the larger the transition angle θ on the base - plate side of the circumferential fillet weld, the more beneficial it is. Considering the actual forming situation of the fillet weld, θ > 155° is limited. Under certain welding conditions, the weld leg width l of the circumferential fillet weld on the base - plate side of the parent material p has a great influence on the stress concentration effect during load transfer in service. If it is too narrow, the welding operation is difficult, and it is not conducive to controlling the transition angle θ; if it is too wide, the stress concentration effect will be significantly increased. Generally speaking, l p is limited to 9 - 20mm, and l p > 2 / 5t, where t represents the thickness of the center - opened cylindrical appendage. In order to ensure the smooth transition and uniform spreading of the circumferential fillet weld on the base - plate side of the parent material, the penetration depths of the circumferential fillet weld in the thickness directions of the base - plate of the parent material and the appendage need to be controlled. If the penetration depth d on the base - plate side of the parent material p satisfies the design requirements, the penetration depths of the circumferential fillet weld in the thickness directions of the base - plate of the parent material and the appendage need to be controlled. If the penetration depth d on the base - plate side of the parent material band the penetration depth d in the thickness direction of the attachment is too large or too small, the liquid molten pool is likely to form a one-way turbulent flow on the base metal bottom plate side and cause a severe impact on the formation of the weld toe on this side, which is not conducive to ensuring the transition angle θ and the weld leg width l on the base metal bottom plate side. In view of this, the following restrictions are imposed on the penetration depths on both sides of the circumferential fillet weld: d a = 1.2 - 3.5 mm, d p = 2.6 - 7.5 mm, and d b > 2.2d a a b .

[0092] The characteristic parameters of the circumferential fillet weld of the attachment, especially the uniformity design of the transition angle θ and the weld leg width l on the base metal bottom plate side, are also very important. If the quality fluctuation of the weld toe transition and spreading of the circumferential fillet weld is very large, it is also easy to additionally increase the stress concentration effect during the transmission of the load, which is not conducive to improving the fatigue performance of the overall structure. In view of this, for θ and l p , taking the average value of the measured values of the cumulative six characteristic parameters at the four intersection positions of the circumferential fillet weld at an angle of 45° with the transverse and longitudinal central axes and the two intersection positions of the longitudinal central axis and the circumferential fillet weld as the measurement index, as p shown at six points A, B, C, D, E, and F, that is, taking the center of the projection of the cylindrical attachment on the base metal bottom plate plane as the center, determining two distribution points with the center line formed parallel to the length direction of the base metal bottom plate, and determining the other four distribution points by rotating this center line clockwise and counterclockwise by 45° respectively, and making the following restrictions: As Figure 5 shown

[0093] Here, l pi and θ i are the measured values of the two characteristic parameters of the circumferential fillet weld of the attachment at six different circumferential positions respectively, and i = 6.

[0094] Step 3. Optimization based on the semi-automatic welding process technology of gas shielded flux-cored wire

[0095] Considering the operating habits and implementation convenience in the field of large steel structure parts manufacturing, the circumferential fillet weld of the center-opening cylindrical attachment structure is welded by using semi-automatic welding with a gas shielded flux-cored wire. From the perspective of ensuring the overall quality uniformity of the circumferential fillet weld, the following restrictions are imposed on the implementation process of the circumferential fillet weld welding process for the center-opening cylindrical attachment structure:

[0096] (1) Avoid starting and stopping arcs in the main area where the load is transmitted in the forward direction and its vicinity, that is Figure 5 ​​The F - A - B area and the C - D - E area shown. The starting arc and ending arc positions should both be located on the side of the accessory; that is, centered on the center of the projection of the cylindrical non - load - bearing accessory on the plane of the base material bottom plate, a center line 4 is formed parallel to the length direction of the base material bottom plate. Rotate this center line clockwise by 45° to form the first oblique line 5, and rotate it counterclockwise by 45° to form the second oblique line 6. The vertical - angle area formed by the first oblique line and the second oblique line in the direction with the center line as the angular bisector is set as the main influence area for positive load transfer, and welding is carried out by controlling the starting arc and ending arc positions to avoid the main influence area.

[0097] (2) By means of Figure 3 the large depth - to - width ratio annular groove form of the center - hole cylindrical accessory shown. In order to ensure the smooth transition and uniform spreading of the circumferential fillet weld on the side of the base material bottom plate, the welding process is made close to the horizontal welding position by adjusting the welding gun angle. The wire extension length is controlled within 15 - 24 mm, and it swings asymmetrically up and down at the edge of the large depth - to - width ratio annular groove. The swinging width needs to cover the upper groove edge. The residence time at the upper edge is 0.5 - 2 s, and the residence time at the lower edge is 0 - 0.5 s. As Figure 6 shown, control the angle β between the welding gun 7 and the high - strength steel base material bottom plate in the horizontal direction to be less than 20°;

[0098] (3) A circulating water cooling device is arranged on the back of the base material bottom plate to ensure that the circulating water temperature is less than 45°C. Through forced cooling during the welding process of the accessory structure, the influence of welding heat on the deformation of the overall structure is reduced, and the angular deformation of the overall structure is controlled to be less than 5°.

[0099] The AWS A5.29 E71T1 gas - shielded flux - cored wire commonly used in the industrial field is adopted, with a diameter of 1.2 mm. The following optimized welding process parameters are applied:

[0100] The welding current I = 200 - 260 A, the welding voltage U = 24 - 30 V, the welding speed v = 210 - 320 mm / min. The welding shielding gas uses an argon - rich mixed gas of 80% Ar + 20% CO 2 and the gas flow rate g f = 18 - 28 L / min.

[0101] Example

[0102] As described above, by establishing the optimization control of stress concentration, combining the optimization control of fatigue crack sources, and the optimization control of welding residual tensile stress, a fatigue strength mechanism characterized by the cumulative damage of local microzone cyclic plastic strain controlled by the yield strength of the base material can be formed, thereby converting the welding fatigue characteristics into a relationship that is positively correlated with the static load strength. To verify whether the technical solution established for the cylindrical non-load-bearing accessory in the present invention meets the optimization of stress concentration control, based on ensuring the optimization control of fatigue crack sources and the optimization control of welding residual tensile stress, a fatigue test will be carried out on the welded structure after being processed by the welding process for stress concentration optimization of the present invention.

[0103] A fatigue test was carried out on the welding method of a cylindrical non-load-bearing accessory structure beneficial to improving fatigue performance of the present invention. The base plate of Q500MD high-strength steel with a wall thickness of 20 mm was used as the base material. According to the specific steps described in the present invention, the joint form design of the cylindrical accessory, the design of the circumferential fillet weld characteristic parameters and size uniformity of the accessory, and the optimization of the semi-automatic welding process technology based on gas-shielded flux-cored wire were completed in sequence to obtain a welded structure of a center-opening cylindrical accessory with good welding quality. For this welded accessory structure, a pull-pull dynamic load fatigue performance evaluation test was carried out under the conditions of stress ratio R = 0.5 and fatigue stress range Δσ = 80 MPa. The test stop condition was that the specimen generated fatigue cracks resulting in a significant decrease in the test frequency or the fatigue cycle number reached 1*10 7 times. By comparing and contrasting the test results under this fatigue test condition with the current mainstream standard design values, the improvement effect of the method described in the present invention on the fatigue performance of the welded accessory structure was comprehensively evaluated.

[0104] Figure 7 、 8 The figure shows a schematic diagram of the type and dimensions of the fatigue evaluation specimen of the welded structure of the center-opening cylindrical accessory located on the Q500MD high-strength steel base plate. Figure 7 In the figure, 1 is the base plate of the base material, 2 is the center-opening cylindrical accessory, and 8 is the circumferential fillet weld with a large depth-width ratio. The Q500MD thick-wall base plate of the base material was machined to ensure that the surface roughness Ra of the two cross-sections parallel to the loading direction was ≤ 3.2. The cylindrical accessory was also machined to ensure the flatness of the contact surface between the bottom of the accessory and the thick-wall base plate of the base material, and the fitting gap was less than 1 mm. To ensure the welding quality of the subsequent circumferential fillet weld of the cylindrical accessory, the relevant areas including the thick-wall base plate and the accessory were polished and cleaned before welding to remove rust, oil and other pollutants that may cause a decrease in weld quality. The area to be welded showed obvious metallic luster.

[0105] In this embodiment, considering the operating habits and implementation convenience in the field of large steel structure manufacturing, the semi-automatic welding with flux-cored wire of gas shielded arc welding is adopted to complete the welding of the circumferential fillet weld of the cylindrical accessory welding structure. From the perspective of ensuring the overall quality uniformity of the circumferential fillet weld, the following principles are followed during the implementation process of the welding process for the circumferential fillet weld of the cylindrical accessory structure with a central opening:

[0106] (1) Starting and stopping arcs are avoided in the main area and its vicinity where the load is transferred in the forward direction, that is, Figure 4 in the F—A—B area and C—D—E area shown, the starting and stopping arc positions are both located on the side of the accessory;

[0107] (2) In order to ensure smooth transition and uniform spreading of the circumferential fillet weld on the base metal floor side, the welding process is made close to the horizontal welding position by adjusting the welding torch angle. The wire extension length is controlled at 16 - 19 mm, and it swings asymmetrically up and down at the edge of the large depth-to-width ratio annular groove. The swing width needs to cover the upper groove edge, with a residence time of 1.0 - 1.5 s at the upper edge and 0 - 0.5 s at the lower edge. As Figure 6 shown, the included angle β between the welding torch and the high-strength steel floor in the horizontal direction is limited to < 20°;

[0108] (3) A circulating water cooling device is set on the back of the base metal floor to ensure that the circulating water temperature is less than 45°C. Through forced cooling during the welding process of the accessory structure, the influence of welding heat on the overall structure deformation is reduced, and the overall structure angular deformation is controlled to be less than 5°.

[0109] The commonly used AWS A5.29 E71T1 gas shielded flux-cored wire in the industrial field with a diameter of 1.2 mm is adopted. The optimized welding process parameters are as follows: welding current I = 210 - 230 A, welding voltage U = 26 - 29 V, welding speed v = 230 - 270 mm / min, and the welding shielding gas adopts an argon-rich mixed gas of 80% Ar + 20% CO 2 with a gas flow rate gf = 21 - 24 L / min.

[0110] Table 1 shows the design of the joint forms of three groups of centrally - perforated cylindrical appendages and the examples of the characteristic parameters of the circumferential fillet weld series obtained. Table 2 shows the conditional fatigue life of the welded structures of the three groups of centrally - perforated cylindrical appendages when the stress ratio R = 0.5 is obtained. It can be seen that under the fatigue test conditions with the design stress range Δσ = 80 MPa, which is commonly used in current mainstream standards, the fatigue cycle times of the welded structure of the appendages in the examples are much higher than the corresponding cycle times in the design standards. By implementing the welding method of the non - load - bearing centrally - perforated cylindrical appendage structure described in the present invention and comparing the fatigue performance data under specific conditions with the design values of current mainstream standards, it is confirmed that the welding method of the non - load - bearing centrally - perforated cylindrical appendage structure described in the present invention can improve the overall fatigue performance of structural members under certain conditions.

[0111] Table 1 Examples of the design of the appendage joint form and the characteristic parameters of the circumferential fillet weld series obtained

[0112]

[0113] Table 2 Conditional fatigue life of the welded structures of the three groups of appendage examples

[0114]

[0115] Note: The corresponding cycle times in the design standard are the cycle times corresponding to the fatigue stress range Δσ = 80 MPa on the fatigue S - N curve of typical rectangular appendages specified in the EN 1993 standard. This stress range value is also commonly used in the fatigue design of structural members.

Claims

1. A welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance, characterized in that: By establishing control over the transition angle on the base plate side of the circumferential fillet weld and establishing control over the weld leg width of the circumferential fillet weld on the base plate side of the base material, an optimized control of the stress concentration effect during load transfer of the cylindrical non - load - bearing accessory is formed.

2. The welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 1, characterized in that: The establishment of control over the transition angle on the base plate side of the circumferential fillet weld and the establishment of control over the weld leg width of the circumferential fillet weld on the base plate side of the base material are specifically as follows: During the welding process, by controlling and reducing the turbulence intensity of the molten pool and cooperating with the set oscillating welding process, control over the spreading uniformity of the weld toe on the base material side is established; And welding is completed by satisfying the constraints of the established angle control of the transition angle on the base plate side of the circumferential fillet weld, satisfying the constraints of the established width control of the weld leg width of the circumferential fillet weld on the base plate side of the base material, satisfying the uniformity constraint of the transition angle on the base plate side of the circumferential fillet weld in the circumferential space distribution of the circumferential fillet weld, and satisfying the uniformity constraint of the weld leg width of the circumferential fillet weld on the base plate side of the base material in the circumferential space distribution of the circumferential fillet weld.

3. The welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 2, characterized in that: The control of reducing the turbulence intensity of the molten pool is achieved by setting groove welding and controlling the groove angle and root face size; The groove angle is controlled within 10° - 25°; The root face size is controlled within 1 / 3t - 3 / 5t and greater than 4 mm, where t: the thickness of the cylindrical non - load - bearing accessory, unit: mm.

4. The welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 3, characterized in that: The set oscillating welding process is specifically as follows: In a way that controls the angle between the welding torch and the base plate of the base material in the horizontal direction to be less than 20°, close to horizontal welding, control the wire dry elongation to be 15 - 24 mm, and swing asymmetrically up and down at the edge of the circular groove; during the swinging process, form a swing width limited by covering the upper groove edge, and at the same time, establish control over the dwell time of the upper edge and the lower edge respectively according to the influencing factor of the molten pool gravity.

5. The welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 4, characterized in that: The establishment of control over the dwell time of the upper edge is specifically to control the dwell time within 0.5 - 2 s; The establishment of control over the dwell time of the lower edge is specifically to control the dwell time to be less than 0.5 s.

6. The welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 2, characterized in that: The constraint of the established angle control of the transition angle on the base plate side of the circumferential fillet weld is specifically: set the transition angle to be greater than 155°.

7. The welding method for a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 2, It is characterized in that: The established constraint on the width control of the fillet weld width on the base plate side of the circumferential fillet weld is specifically: the fillet weld width is set to fall within the range of 9 - 20 mm and is greater than 2 / 5t; wherein, t: the thickness of the cylindrical non - load - bearing accessory, unit: mm.

8. The welding method of a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 2, It is characterized in that: By establishing the control of the penetration depth of the circumferential fillet weld on the base plate side of the base metal and the penetration depth in the thickness direction of the cylindrical non - load - bearing accessory, to ensure meeting the established constraint on the angle control of the transition angle of the circumferential fillet weld on the base plate side of the base metal and ensuring meeting the established constraint on the width control of the fillet weld width on the base plate side of the circumferential fillet weld.

9. The welding method of a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 8, It is characterized in that: The established control of the penetration depth of the circumferential fillet weld on the base plate side of the base metal is specifically: controlling the penetration depth on the base plate side to be within the range of 1.2 - 3.5 mm; The established control of the penetration depth of the circumferential fillet weld in the thickness direction of the cylindrical non - load - bearing accessory is specifically: controlling the penetration depth in the thickness direction of the accessory to be within the range of 2.6 - 7.5 mm, and the penetration depth in the thickness direction of the accessory should be greater than 2.2 times the penetration depth on the base plate side of the base metal.

10. The welding method of a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 9, It is characterized in that: The control of the penetration depth of the circumferential fillet weld on the base plate side of the base metal and the control of the penetration depth in the thickness direction of the cylindrical non - load - bearing accessory are realized by the set swing welding process in cooperation with the establishment of the control of the wire diameter, the control of the welding voltage, the control of the welding current, and the control of the welding speed.

11. The welding method of a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 10, It is characterized in that: The wire diameter is set to 1.2 mm; The welding voltage is controlled within 24 - 30 V; The welding current is controlled within 200 - 260 A; The welding speed is controlled within 210 - 320 mm / min.

12. The welding method of a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 2, It is characterized in that: The established constraint on the uniformity of the transition angle of the circumferential fillet weld on the base plate side of the base metal in the circumferential spatial distribution of the fillet weld is specifically: In the above formula, θ i : The transition angle of each of the 6 set distribution points of the weld in the circumferential space distribution. The determination process of the 6 set distribution points is as follows: Taking the center of the projection of the cylindrical accessory on the plane of the base material bottom plate as the center, two distribution points are determined by the center line formed parallel to the length direction of the base material bottom plate, and the other four distribution points are determined by rotating this center line clockwise by 45° and counterclockwise by 45° respectively; The mean of the transition angles of the 6 set distribution points.

13. The welding method of a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 2, It is characterized in that: The established constraint on the uniformity of the fillet weld width of the circumferential fillet weld on the base plate side in the circumferential spatial distribution of the circumferential fillet weld is specifically: In the above formula, l pi : The fillet weld widths of six set distribution points in the circumferential space distribution of the weld seam. The determination process of these six set distribution points is as follows: Taking the center of the projection of the cylindrical accessory on the plane of the base material bottom plate as the center, two distribution points are determined with the center line formed parallel to the length direction of the base material bottom plate. The other four distribution points are determined by rotating this center line clockwise by 45° and counterclockwise by 45° respectively. The mean of the transition angles of the 6 set distribution points.

14. The welding method of a cylindrical non - load - bearing accessory structure beneficial to improving fatigue performance according to claim 1, It is characterized in that: Taking the center of the projection of the cylindrical non-load-bearing accessory on the plane of the base metal bottom plate as the center, a center line is formed parallel to the length direction of the base metal bottom plate. The center line is rotated clockwise by 45° to form a first oblique line, and the center line is rotated counterclockwise by 45° to form a second oblique line. The vertical angle region formed by the first oblique line and the second oblique line in the direction with the center line as the angular bisector is set as the main influence area for positive transmission of load, and welding is carried out with the starting and ending arc positions controlled to avoid the main influence area.

15. A welding method for a cylindrical non-load-bearing accessory structure beneficial to improving fatigue performance according to claim 1, characterized in that: By providing a circulating water cooling device on the back of the base metal bottom plate to provide contact conduction heat exchange with the circulating water temperature less than 45°C during the welding process, a control of the angular deformation of the structure less than 5° is established accordingly.

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