A narrow-gap submerged arc welding process for tube sheet flanges

Abstract

This invention discloses a narrow-gap submerged arc welding process for tube sheet flanges, belonging to the field of welding. It includes the following steps: machining a narrow-gap bevel with a bevel angle of 1° to 5° on the areas to be welded on the tube sheet and flange; performing multi-layer, multi-pass welding, wherein the entire bevel filling process is divided into a root region, a middle region, and a capping region. This invention divides the filling process of thick-walled joints into three heat management regions: root, middle, and capping, and formulates a differentiated heat input and weld bead arrangement coordination strategy for each region. This zoned coordinated management avoids the performance unevenness caused by a single heat input, thus optimizing the microstructure and mechanical properties of the joint from the root to the capping.

Description

Technical Field

[0001] This invention relates to the field of welding, and more specifically, to a narrow-gap submerged arc welding process for tube sheet flanges. Background Technology

[0002] In the manufacturing of critical equipment in energy, chemical, and other industries, the tube sheet flange connection is a key structure for pressure bearing and connection, and the welding quality of its circumferential weld directly affects the safety and service life of the equipment. These welds typically feature thick walls, high material strength, and harsh service conditions. While the traditional wide-groove submerged arc welding method is mature and widely used, it suffers from problems such as high filler metal consumption, low welding efficiency, high heat input leading to significant welding deformation and residual stress, and a wide heat-affected zone with significant performance degradation.

[0003] To overcome the aforementioned shortcomings, narrow-gap submerged arc welding (NGA) technology has emerged. This technology, through its narrow bevel design with a small angle (typically ≤7°), significantly reduces the amount of filler metal, improves welding efficiency, and lowers heat input and deformation, making it an important development direction for welding thick-walled components. However, in practical engineering applications, especially for high-requirement circumferential welds such as tube sheet flanges, existing NGA processes still face a series of long-standing technical challenges: the narrow bevel space results in poor accessibility and visibility of the welding torch. Traditional oscillating welding parameters (amplitude, dwell time) are mostly preset fixed values, unable to adapt to microscopic changes in bevel width caused by bevel machining errors, assembly misalignment, and thermal deformation during welding, easily leading to fatal defects such as sidewall incomplete fusion or undercut, making it difficult to guarantee consistent quality. Existing processes often treat multi-layer, multi-pass welding of thick-walled joints as a homogeneous process, with a single heat input control strategy. They fail to implement differentiated, precise energy management and weld bead layout design based on the heat accumulation state, restraint conditions, and performance requirements of different depth regions of the bevel (such as the root, middle, and cap). This can easily lead to problems such as poor root fusion, coarse grains in the middle, or overheating of the cap, affecting the uniformity and reliability of the overall joint performance. Summary of the Invention

[0004] The purpose of this invention is to provide a narrow-gap submerged arc welding process for tube sheet flanges to solve the problems mentioned in the background art.

[0005] Technical solution: A narrow-gap submerged arc welding process for tube sheet flanges, comprising the following steps:

[0006] Narrow-gap bevels with bevel angles of 1° to 5° are machined on the parts of the tube sheet and flange to be welded.

[0007] Multi-layer, multi-pass welding is performed, in which the entire bevel filling process is divided into root region, middle region, and capping region;

[0008] In the root region, single-pass welding is used, with a welding heat input of 18-28 kJ / cm. The welding wire is welded on the center line of the bevel without lateral oscillation, or with a micro-oscillation amplitude of no more than 2 mm.

[0009] In the central region, double-pass parallel welding is employed, with a welding heat input of 15-22 kJ / cm. The welding wire is oscillated laterally, with the oscillation amplitude such that the tip of the welding wire is 1-2 mm from the sidewall of the groove, and it remains on the sidewall for 0.3-0.6 seconds. In the double-pass welding, the overlap rate of the width of the two welds in the central region of the groove is 15%-25%.

[0010] In the covered area, three welding passes are used, with a welding heat input of 12-18 kJ / cm. The welding wire oscillates laterally, driven by a servo mechanism. The oscillation amplitude covers the entire bevel width and pauses for 0.2-0.5 seconds on each side wall.

[0011] Preferably, the root region is the area with a weld thickness of no more than 20 mm from the bottom of the bevel; the cover region is the area with a weld thickness of no more than 15 mm from the top of the bevel; and the portion between the root region and the cover region is the middle region.

[0012] Preferably, during the welding process, the oscillation amplitude of the welding wire is adjusted adaptively by monitoring real-time fluctuations in the welding current, specifically including:

[0013] Welding current signals are acquired at a sampling frequency of 100Hz or higher;

[0014] When the welding wire swings close to one side of the bevel wall, if the values ​​of three or more consecutive current sampling points are continuously higher than the average current value by 8%-15%, it is determined that the distance between the welding wire and the side wall has reached the preset range of 1-2mm.

[0015] If the value of the continuously higher than average current is less than 8%, it is determined that the distance is too large, and the servo mechanism is controlled to increase the swing amplitude by 1-3mm in the next swing; if the value of the continuously higher than average current is more than 15%, it is determined that the distance is too small, and the servo mechanism is controlled to decrease the swing amplitude by 1-2mm in the next swing.

[0016] Preferably, during the multi-layer, multi-pass welding process, a finite element model is used to obtain welding parameter combinations, and a set of welding parameter combinations is selected for welding. The steps are as follows:

[0017] Obtain the geometric parameters of the bevel and the thermophysical parameters of the base material;

[0018] A finite element model of the welding process is established, with the heat input value, the number and arrangement of weld beads as input variables, and the peak temperature and residual stress of the weld area as output variables.

[0019] Iterative calculations are performed in the model to select welding parameter combinations that satisfy all of the following conditions:

[0020] In the root region, the predicted peak temperature of the weld metal is not less than 1400℃;

[0021] In the central region, the area where the previous weld pass is repeatedly heated to no less than 800°C by the subsequent weld pass accounts for more than 50% of its total area.

[0022] In the capping area, the predicted peak temperature of the weld metal shall not exceed 1200℃;

[0023] The selected welding parameter combinations are output as welding process specifications.

[0024] Preferably, the mesh generation of the finite element model for the welding process satisfies the following conditions:

[0025] In the weld zone and the heat-affected zone adjacent to the base material, hexahedral elements are used for meshing, and the side length of the element in this area is no greater than 2mm.

[0026] In areas far from the weld, the unit size can be gradually increased to over 5mm.

[0027] Preferably, the heat source model used in the finite element model is a double ellipsoidal volumetric heat source model, and the energy distribution coefficient ratio of the front and rear halves of the ellipsoid is 1.2:0.8 to 1.5:0.5.

[0028] Preferably, the initial values ​​of the length of the first half of the ellipsoid, the length of the second half of the ellipsoid, the width of the ellipsoid, and the depth of the double-ellipsoidal volumetric heat source model are determined based on the welding heat input and the welding speed using the following empirical formulas:

[0029] Length of ellipsoid: ;

[0030] Ellipsoid width: ;

[0031] Ellipsoid Depth: ;

[0032] in, The heat input per unit length is given by k1, k2, and k3, which are shape coefficients related to the wire diameter and flux type, with values ​​ranging from k1=2.0 to 3.0, k2=1.0 to 1.5, and k3=1.5 to 2.0, respectively.

[0033] Preferably, in the finite element model, the thermophysical parameters of the material are set as functions that vary with temperature, and the thermophysical parameters include at least thermal conductivity, specific heat capacity, density, and elastic modulus.

[0034] Preferably, in the finite element model, convection and radiation heat dissipation boundary conditions are applied to the surface of the component, and the overall heat dissipation coefficient is set to 10-30 W / (m²). 2 •K), used to simulate the heat dissipation environment under flux coverage.

[0035] Compared with the prior art, the advantages of this invention are:

[0036] (1) This invention establishes a closed-loop adaptive control system by monitoring the real-time fluctuations of the welding current and dynamically adjusting the oscillation amplitude of the welding wire accordingly. When the distance between the welding wire tip and the bevel sidewall changes slightly due to various factors, the system can sense it in real time and correct it immediately. This ensures that the welding wire and the sidewall always maintain a preset optimal distance of 1-2mm, ensuring stable heating of the sidewall by the arc. It solves the problem of sidewall incomplete fusion that is very likely to occur in such narrow spaces when welding with traditional fixed parameters, and transforms quality control from relying on operator experience to being guaranteed by the process system itself.

[0037] (2) The present invention divides the filling process of thick-walled joints into three heat management zones: root, middle and cover. Differentiated heat input and weld bead arrangement coordination strategies are formulated for each zone. This zoned coordination management avoids the performance unevenness caused by a single heat input, so that the microstructure and mechanical properties of the joint from the root to the cover are optimized.

[0038] (3) By constructing a precise heat source model, material parameters that change with temperature and a finite element model, this invention can perform digital twin simulation and optimization of the process before welding, which changes the trial-and-error mode that mainly relies on physical experiments and experience, and greatly reduces the material, energy and time costs required for process evaluation. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall process of a narrow-gap submerged arc welding process for tube sheet flanges according to the present invention. Detailed Implementation

[0040] For examples, please refer to Figure 1 A narrow-gap submerged arc welding process for tube sheet flanges includes the following steps:

[0041] Narrow-gap bevels with bevel angles of 1° to 5° are machined on the parts of the tube sheet and flange to be welded.

[0042] Multi-layer, multi-pass welding is performed, in which the entire bevel filling process is divided into root region, middle region, and capping region;

[0043] In the root region, single-pass welding is used, with a welding heat input of 18-28 kJ / cm. The welding wire is welded on the center line of the bevel without lateral oscillation, or with a micro-oscillation amplitude of no more than 2 mm.

[0044] In the central region, double-pass parallel welding is employed, with a welding heat input of 15-22 kJ / cm. The welding wire is oscillated laterally, with the oscillation amplitude such that the tip of the welding wire is 1-2 mm from the sidewall of the groove, and it remains on the sidewall for 0.3-0.6 seconds. In the double-pass welding, the overlap rate of the width of the two welds in the central region of the groove is 15%-25%.

[0045] In the covered area, three welding passes are used, with a welding heat input of 12-18 kJ / cm. The welding wire is oscillating laterally, with the oscillation amplitude covering the entire bevel width, and pausing for 0.2-0.5 seconds on each side wall.

[0046] The root region is the area where the weld thickness does not exceed 20mm from the bottom of the bevel; the cover region is the area where the weld thickness does not exceed 15mm from the top of the bevel; the portion between the root region and the cover region is the middle region.

[0047] During the welding process, the oscillation amplitude of the welding wire is adjusted by monitoring real-time fluctuations in the welding current, specifically including:

[0048] Welding current signals are acquired at a sampling frequency of 100Hz or higher;

[0049] When the welding wire swings close to one side of the bevel wall, if the values ​​of three or more consecutive current sampling points are continuously higher than the average current value by 8%-15%, it is determined that the distance between the welding wire and the side wall has reached the preset range of 1-2mm.

[0050] If the value of the continuously higher than average current is less than 8%, it is determined that the distance is too large, and the servo mechanism is controlled to increase the swing amplitude by 1-3mm in the next swing; if the value of the continuously higher than average current is more than 15%, it is determined that the distance is too small, and the servo mechanism is controlled to decrease the swing amplitude by 1-2mm in the next swing.

[0051] In the process of performing multi-layer, multi-pass welding, a finite element model is used to obtain welding parameter combinations. From the selected welding parameter combinations, a set is chosen for welding. The steps are as follows:

[0052] Obtain the geometric parameters of the bevel and the thermophysical parameters of the base material;

[0053] A finite element model of the welding process is established, with the heat input value, the number and arrangement of weld beads as input variables, and the peak temperature and residual stress of the weld area as output variables.

[0054] Iterative calculations are performed in the model to select welding parameter combinations that satisfy all of the following conditions:

[0055] In the root region, the predicted peak temperature of the weld metal is not less than 1400℃;

[0056] In the central region, the area where the previous weld pass is repeatedly heated to no less than 800°C by the subsequent weld pass accounts for more than 50% of its total area.

[0057] In the capping area, the predicted peak temperature of the weld metal shall not exceed 1200℃;

[0058] The selected welding parameter combinations are output as welding process specifications.

[0059] The mesh generation of the finite element model for the welding process satisfies the following conditions:

[0060] In the weld zone and the heat-affected zone adjacent to the base material, hexahedral elements are used for meshing, and the side length of the element in this area is no greater than 2mm.

[0061] In areas far from the weld, the unit size can be gradually increased to over 5mm.

[0062] The heat source model used in the finite element model is a double ellipsoidal volumetric heat source model, with the energy distribution coefficient ratio of the front and rear halves of the ellipsoid being 1.2:0.8 to 1.5:0.5.

[0063] The initial values ​​of the length of the first half of the ellipsoid, the length of the second half of the ellipsoid, the width of the ellipsoid, and the depth of the double ellipsoidal volumetric heat source model are determined based on the welding heat input and welding speed using the following empirical formulas:

[0064] Length of ellipsoid: ;

[0065] Ellipsoid width: ;

[0066] Ellipsoid Depth: ;

[0067] in, The heat input per unit length is given by k1, k2, and k3, which are shape coefficients related to the wire diameter and flux type, with values ​​ranging from k1=2.0 to 3.0, k2=1.0 to 1.5, and k3=1.5 to 2.0, respectively.

[0068] In the finite element model, the thermophysical parameters of the material are set as functions that vary with temperature, and the thermophysical parameters include at least thermal conductivity, specific heat capacity, density, and elastic modulus.

[0069] When establishing the finite element model, the thermophysical parameters of the material are set as functions of temperature, and the specific values are based on the publicly available material property data of high-strength low-alloy steel (such as Q345R). The thermophysical parameters at least include thermal conductivity, specific heat capacity, density, and elastic modulus. The functional relationships or data points of each parameter varying with temperature are as follows:

[0070] Thermal conductivity λ (unit: W / (m·°C)):

[0071] In the finite element model, the thermophysical parameters of the material are set as functions of temperature, and the thermophysical parameters at least include thermal conductivity, specific heat capacity, density, and elastic modulus.

[0072] When establishing the finite element model, the thermophysical parameters of the material are set as functions of temperature, and the specific values are based on the publicly available material property data of high-strength low-alloy steel (such as Q345R). The thermophysical parameters at least include thermal conductivity, specific heat capacity, density, and elastic modulus. The functional relationships or data points of each parameter varying with temperature are as follows:

[0073] Thermal conductivity λ (unit: W / (m·°C)):

[0074] In the temperature range of 20°C to 1500°C, the specific heat capacity varies with temperature, and the specific values can be determined by the following piecewise function or data points:

[0075] When T ≤ 600°C, c = 420 + 0.504×T;

[0076] When 600°C < T ≤ 800°C, c = 730 + 0.280×(T - 600);

[0077] When T > 800°C, c is taken as 830 J / (kg·°C).

[0078] Where T is the Celsius temperature.

[0079] Density ρ (unit: kg / m³):

[0080] In the solid state (temperature lower than the solidus temperature of about 1480°C), the density varies little with temperature, and a constant of 7850 kg / m³ can be used. To consider the thermal expansion effect, the volume change can also be calculated through the linear expansion coefficient, but the mass density is usually regarded as a constant in thermal analysis.

[0081] Elastic modulus E (unit: GPa):

[0082] In the temperature range of 20°C to 1200°C, the elastic modulus decreases with the increase of temperature, and the specific values can be determined by the following data points:

[0083] At 20℃, E = 210 GPa; at 200℃, E = 195 GPa; at 400℃, E = 175 GPa; at 600℃, E = 150 GPa; at 800℃, E = 80 GPa; at 1000℃, E = 20 GPa; and at 1200℃ and above, E = 5 GPa. Intermediate temperature values ​​can be obtained through linear interpolation.

[0084] In addition, to perform thermo-elastoplastic stress analysis, it is also necessary to set Poisson's ratio (a constant of 0.3 is recommended) and the linear expansion coefficient (a constant of 1.2 × 10⁻⁻⁶ is recommended). 5 The parameters include (temperature / ℃) and yield strength (which decreases with increasing temperature; a corresponding data table is required). Specific values ​​for these parameters can be obtained from standard material databases (such as ASME II, Section D or EN standards) and input into the model based on the actual base material grade used. Those skilled in the art can create material properties in finite element software (such as ANSYS, ABAQUS, etc.) based on the above teachings, defining the relationship between each parameter and temperature through tables or functions, thereby completing the material model setup.

[0085] In the finite element model, convection and radiation heat dissipation boundary conditions are applied to the surface of the component, and the comprehensive heat dissipation coefficient is set to 10-30 W / (m²). 2 ·K), used to simulate the heat dissipation environment under flux coverage.

[0086] During iterative calculations in the model, the model change technique is used to simulate the weld bead filling process.

[0087] When performing iterative calculations in the finite element model to simulate the welding process, the "element birth and death" technique is used to simulate the sequential filling of weld passes. The core of this technique is that, before the calculation begins, the finite element meshes (elements) corresponding to all future weld passes to be filled are pre-established in the model, but defined as "inactive." These "inactive" elements do not initially exist in the model and do not participate in mechanical and thermal calculations, as if they have been "killed." The simulation calculation is performed step-by-step according to the actual welding sequence. At the start of the calculation step corresponding to the beginning of welding a specific weld pass, the program activates the element group corresponding to that weld pass from the "inactive" state to the "active" state. At the moment the element is "activated," it is usually assigned an initial ambient temperature (such as the preheating temperature or the interpass temperature after the previous weld pass was completed). Subsequently, in this calculation step, the welding heat source model is defined and moved on the elements of this newly formed weld pass, calculating the resulting temperature field changes. In subsequent calculation steps, these activated elements will continue to participate in the full-field calculation of heat conduction, heat convection, heat radiation, and the resulting thermo-elasto-plastic stress and strain, just like the original base metal elements in the model. This cycle continues until all weld elements are activated sequentially, ultimately completing the construction of the entire joint model and the simulation of the entire welding process. Through this "element life and death" technique, the finite element model can dynamically and physically realistically reproduce the welding thermal and mechanical processes that accumulate as weld layers are added. This is a key numerical method for accurately predicting the temperature field, stress field, and deformation of multi-layer, multi-pass welds. Those skilled in the art can achieve the above process in the transient thermo-mechanical coupling analysis module of mainstream general-purpose finite element software (such as ANSYS, ABAQUS, etc.) by defining element groups, setting analysis steps, and specifying the activation state and time of each element group.

[0088] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples of the present invention and are not intended to limit the present invention. Various changes and modifications can be made to the present invention without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A narrow-gap submerged arc welding process for tube sheet flanges, characterized in that, Includes the following steps: Narrow-gap bevels with bevel angles of 1° to 5° are machined on the parts of the tube sheet and flange to be welded. Multi-layer, multi-pass welding is performed, in which the entire bevel filling process is divided into root region, middle region, and capping region; In the root region, single-pass welding is used, with a welding heat input of 18-28 kJ / cm. The welding wire is welded on the center line of the bevel without lateral oscillation, or with a micro-oscillation amplitude of no more than 2 mm. In the central region, double-pass parallel welding is employed with a welding heat input of 15-22 kJ / cm. The welding wire oscillates laterally, driven by a servo mechanism. The oscillation amplitude ensures that the tip of the welding wire is 1-2 mm from the bevel sidewall and remains on the sidewall for 0.3-0.6 seconds. In the double-pass welding, the overlap rate of the width of the two welds in the central region of the bevel is 15%-25%. In the covered area, three welding passes are used, with a welding heat input of 12-18 kJ / cm. The welding wire oscillates laterally, driven by a servo mechanism. The oscillation amplitude covers the entire bevel width and pauses for 0.2-0.5 seconds on each side wall. During the welding process, the oscillation amplitude of the welding wire is adjusted by monitoring real-time fluctuations in the welding current, specifically including: Welding current signals are acquired at a sampling frequency of 100Hz or higher; When the welding wire swings close to one side of the bevel wall, if the values ​​of three or more consecutive current sampling points are continuously higher than the average current value by 8%-15%, it is determined that the distance between the welding wire and the side wall has reached the preset range of 1-2mm. If the value of the continuously higher than average current is less than 8%, it is determined that the distance is too large, and the servo mechanism is controlled to increase the swing amplitude by 1-3mm in the next swing; if the value of the continuously higher than average current is more than 15%, it is determined that the distance is too small, and the servo mechanism is controlled to decrease the swing amplitude by 1-2mm in the next swing. In the process of performing multi-layer, multi-pass welding, a finite element model is used to obtain welding parameter combinations. From the selected welding parameter combinations, a set is chosen for welding. The steps are as follows: Obtain the geometric parameters of the bevel and the thermophysical parameters of the base material; A finite element model of the welding process is established, with the heat input value, the number and arrangement of weld beads as input variables, and the peak temperature and residual stress of the weld area as output variables. Iterative calculations are performed in the model to select welding parameter combinations that satisfy all of the following conditions: In the root region, the predicted peak temperature of the weld metal is not less than 1400℃; In the central region, the area where the previous weld pass is repeatedly heated to no less than 800°C by the subsequent weld pass accounts for more than 50% of its total area. In the capping area, the predicted peak temperature of the weld metal shall not exceed 1200℃; The selected welding parameter combinations are output as welding process specifications.

2. The narrow-gap submerged arc welding process for tube sheet flanges according to claim 1, characterized in that, The root region is the area where the weld thickness does not exceed 20mm from the bottom of the bevel; the cover region is the area where the weld thickness does not exceed 15mm from the top of the bevel; the portion between the root region and the cover region is the middle region.

3. The narrow-gap submerged arc welding process for tube sheet flanges according to claim 1, characterized in that, The mesh generation of the finite element model for the welding process satisfies the following conditions: In the weld zone and the heat-affected zone adjacent to the base material, hexahedral elements are used for meshing, and the side length of the element in this area is no greater than 2mm. In areas far from the weld, the unit size can be gradually increased to over 5mm.

4. The narrow-gap submerged arc welding process for tube sheet flanges according to claim 1, characterized in that, The heat source model used in the finite element model is a double ellipsoidal volumetric heat source model, with the energy distribution coefficient ratio of the front and rear halves of the ellipsoid being 1.2:0.8 to 1.5:0.

5.

5. The narrow-gap submerged arc welding process for tube sheet flanges according to claim 4, characterized in that, The initial values ​​of the length of the first half of the ellipsoid, the length of the second half of the ellipsoid, the width of the ellipsoid, and the depth of the double ellipsoidal volumetric heat source model are determined based on the welding heat input and welding speed using the following empirical formulas: Length of ellipsoid: ； Ellipsoid width: ； Ellipsoid Depth: ； in, The heat input per unit length is given by k1, k2, and k3, which are shape coefficients related to the wire diameter and flux type, with values ​​ranging from k1=2.0 to 3.0, k2=1.0 to 1.5, and k3=1.5 to 2.0, respectively.

6. The narrow-gap submerged arc welding process for tube sheet flanges according to claim 1, characterized in that, In the finite element model, the thermophysical parameters of the material are set as functions that vary with temperature, and the thermophysical parameters include at least thermal conductivity, specific heat capacity, density, and elastic modulus.

7. The narrow-gap submerged arc welding process for tube sheet flanges according to claim 1, characterized in that, In the finite element model, convection and radiation heat dissipation boundary conditions are applied to the surface of the component, and the comprehensive heat dissipation coefficient is set to 10-30 W / (m²). 2 ·K), used to simulate the heat dissipation environment under flux coverage.

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