A method for optimizing the stress of a special-shaped butt welding structure and the structure

Abstract

Embodiments of the present disclosure provide a method and a structure for optimizing the stress of a special-shaped butt welding structure. The special-shaped butt welding structure includes a welding joint and a first base material part and a second base material part that are connected to each other through the welding joint, and there is a height difference between the surfaces of the first base material part and the second base material part. The method includes: determining a surfacing area to be surfaced on the surfaces of the welding joint, the first base material part, and the second base material part; the surfacing area to be surfaced continuously covers the welding joint and a part of the surfaces of the first base material part and the second base material part on both sides of the welding joint; forming a surfacing layer in the surfacing area to be surfaced, so that the surfaces of the first base material part, the surfacing layer, and the second base material part are smoothly connected. Embodiments of the present disclosure optimize the appearance line type of the structure through surfacing, reduce the stress concentration level of the structure, thereby reducing the early failure risk of the special-shaped butt welding structure and improving the service safety level of the structure.

Description

Technical Field

[0001] Embodiments of the present disclosure belong to the technical field of special-shaped docking structures, and particularly relate to a method and structure for optimizing the stress of a special-shaped docking and welding structure. Background Art

[0002] On one side is a straight pipe component, and on the other side are special-shaped components such as valves, tees, elbows, etc. with inconsistent structural dimensions at both ends, especially unequal inner and outer wall dimensions and significant thickness differences. Assemblies formed by welding and docking are widely used in engineering practice. For assemblies formed by such special-shaped structural components with inconsistent structural dimensions at both ends of the welded joints, national standards and industry standards have certain regulations on how to transition. However, due to manufacturing and processing capabilities or production reality, there are a large number of special-shaped welded joints with sudden changes in structure shape and wall thickness in engineering practice. In these welded joints, the stress concentration positions at the structural change points of the assembly usually overlap or are adjacent to the fusion zone of the welded joint, making this overlapping or adjacent area the weakest link in the entire assembly structure. During long-term use, especially under the action of additional system stresses, early failure cracking is likely to occur, thus causing safety risks.

[0003] The prior art adopts the method of secondary machining of the special-shaped structure section. The surface of the thick-end base material is turned with a turning tool to form a straight section with a certain dimension length, so that its outer diameter is the same as that of the thinner pipe section, and a slope of 15° - 30° is formed to transition to the outer diameter of the thick end for stress reduction and to avoid the overlap of structural stress and the welding fusion line.

[0004] However, secondary machining on-site for pipeline and pipe fittings equipment requires certain space conditions to mount mechanical turning tools. At the same time, some pipeline and pipe fittings require special fixtures, tools, etc. due to their structures, which further limits their on-site application and makes mechanical turning difficult to achieve. Summary of the Invention

[0005] Embodiments of the present disclosure aim to at least solve one of the technical problems existing in the prior art, and provide a method and structure for optimizing the stress of a special-shaped docking and welding structure.

[0006] One aspect of the present disclosure provides a method for optimizing the stress of a special-shaped docking and welding structure. The special-shaped docking and welding structure includes a welded joint and a first base material part and a second base material part connected to each other through the welded joint, and there is a height difference on the surfaces of the first base material part and the second base material part. The method includes:

[0007] Determine the area to be surfacing on the surfaces of the welded joint, the first base material part, and the second base material part; the area to be surfacing continuously covers the welded joint and a part of the surfaces of the first base material part and the second base material part on both sides of the welded joint;

[0008] A surfacing layer is formed in the area to be surfaced, so that the surfaces of the first base material part, the surfacing layer and the second base material part are smoothly connected.

[0009] Optionally, determining the area to be surfaced includes:

[0010] The excess height of the welded joint is removed by mechanical turning.

[0011] Optionally, the surfaces of the first base material part and / or the second base material part have a slope section, and the bottom end of the slope section is connected to the welded joint;

[0012] Determining the area to be surfaced includes:

[0013] A smooth transition area is formed on the surface of the connecting part between the slope section and the welded joint.

[0014] Optionally, the welded joint is respectively connected to the end of the straight section of the first base material part and the bottom end of the slope section of the second base material part;

[0015] The surface of the first base material part has a first widening area, and the surface of the second base material part has a second widening area;

[0016] The first widening area is the surface of the first base material part that extends from the end of the straight section to the other end of the first base material part with a length of 5 mm to 10 mm; the second widening area is the surface of the second base material part that extends from the top end of the slope section to the other end away from the slope section with a length of 5 mm to 10 mm;

[0017] The area to be surfaced continuously covers the first widening area, the surface of the welded joint, the surface of the slope section and the second widening area.

[0018] Optionally, the included angle between the surface of the surfacing layer and the straight section surface of the first base material part is 15° to 30°.

[0019] Further, the method further includes:

[0020] If the included angle between the surface of the surfacing layer and the straight section surface of the first base material part is greater than 30°, the first widening area is extended to make the included angle reach 15° to 30°.

[0021] Optionally, before forming the surfacing layer in the area to be surfaced, the method further includes:

[0022] Manual arc welding is used to perform crack blocking process welding in the area to be surfaced.

[0023] Optionally, the surfacing layer includes a filling surfacing layer and a capping surfacing layer;

[0024] Forming a surfacing layer in the area to be surfaced includes:

[0025] Performing filling welding in the surfacing area to form a filling surfacing layer;

[0026] Performing capping welding on the surface of the filling surfacing layer.

[0027] Optionally, forming a surfacing layer in the area to be surfaced includes:

[0028] Attenuating the welding current while receiving the weld bead, and moving the welding head to the edge of the groove to stop welding after filling the crater.

[0029] Another aspect of the present disclosure provides a stress optimization structure for a special-shaped butt welding structure, and the structure is obtained by the stress optimization method for a special-shaped butt welding structure described above;

[0030] The structure includes a welding joint and a first base material part and a second base material part connected to each other through the welding joint, and there is a height difference on the surfaces of the first base material part and the second base material part;

[0031] A continuously covered surfacing layer is provided on the welding joint and a part of the surfaces of the first base material part and the second base material part on both sides of the welding joint, and the surfaces of the first base material part, the surfacing layer, and the second base material part are smoothly connected.

[0032] A stress optimization method and structure for a special-shaped butt welding structure according to an embodiment of the present disclosure, through a surfacing method, optimize the appearance line type of the structure, reduce the degree of structural mutation, solve the problem of stress superposition concentration caused by the overlap or proximity of the stress concentration position of the component structure and the fusion zone of the welding joint, reduce the stress concentration level of the structure, thereby reducing the early failure risk of the special-shaped butt welding structure and improving the service safety level of the structure, and has good popularization and application value for the improvement and transformation of the same type of components. Description of the Drawings

[0033] Figure 1 It is a structural schematic diagram of an existing special-shaped butt welding structure;

[0034] Figure 2 It is a flow schematic diagram of a stress optimization method for a special-shaped butt welding structure according to an embodiment of the present disclosure;

[0035] Figure 3 It is a structural schematic diagram of a special-shaped butt welding structure according to another embodiment of the present disclosure;

[0036] Figure 4Structural schematic diagram of a stress optimization structure for a special-shaped butt welding structure according to another embodiment of the present disclosure. Detailed implementation manners

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only a part of the embodiments of the present disclosure, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present disclosure without making creative efforts belong to the scope of protection of the present disclosure.

[0038] In addition, the described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to give a full understanding of the embodiments of the present disclosure. However, those skilled in the art will realize that the technical solutions of the present disclosure can be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, well-known methods, devices, implementations or operations are not shown or described in detail to avoid obscuring various aspects of the present disclosure.

[0039] The flowcharts shown in the accompanying drawings are only illustrative and do not necessarily include all the contents and operations / steps, nor do they necessarily need to be executed in the described order. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined. Therefore, the actual execution order may be changed according to the actual situation.

[0040] It should be understood that although terms such as first, second, and third may be used in the present disclosure to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another. Therefore, the first component described below may be referred to as the second component without departing from the teachings of the concept of the present disclosure. As used in the present disclosure, the term "and / or" includes any one and all combinations of one or more of the associated listed items.

[0041] Those skilled in the art can understand that the accompanying drawings are only schematic diagrams of exemplary embodiments, and the modules or processes in the accompanying drawings are not necessarily essential for implementing the present disclosure, so they cannot be used to limit the protection scope of the present disclosure.

[0042] An embodiment of the present disclosure provides a method for optimizing the stress of a special-shaped butt welding structure. As Figure 1As shown in the figure, the special-shaped butt welding structure includes a welding joint 2 and a first base material part 1 and a second base material part 3 that are connected to each other through the welding joint 2. The first base material part 1 is a straight pipe section, and the second base material part 3 is a special-shaped pipe section. There is a height difference between the surfaces of the first base material part 1 and the second base material part 3. The welding fusion line (area) 21 of the two base materials coincides with the stress concentration point 31 of the butt welding structure. During long-term use, the welding joint is prone to early failure cracking, causing safety risks.

[0043] To solve the above problems, as Figure 2 shown, the stress optimization method for the special-shaped butt welding structure includes:

[0044] Step S21: Determine the surfacing area to be built on the surfaces of the welding joint, the first base material part, and the second base material part.

[0045] Specifically, first measure the surface of the welding joint of the special-shaped butt welding structure to understand the groove structure and width of the welding joint, the pipe diameters and thicknesses of the special-shaped components on both sides of the welding joint, the inclination angle and length of the slope section, etc. Referring to Figure 1 , using the method of mechanical turning processing, such as a ring groove machine, all the remaining height 22 that may exist on the surface to be welded of the welding joint 2 is turned and removed. It is also possible to use a hand-held grinding wheel to grind and remove the remaining height 22 of the welding joint 2 to make the surface to be welded of the welding joint 2 flat. When the surface of the first base material part 1 and / or the second base material part 2 has a slope section 32, and the bottom end of the slope section 32 is connected to the welding joint 2, manual grinding is carried out along the slope section 32.

[0046] As Figure 3 shown in the special-shaped butt welding structure, the welding joint 2 is respectively connected to the end of the straight section of the first base material part 1 and the bottom end of the slope section 32 of the second base material part 3. The surfacing area to be built 4 continuously covers the welding joint 2 and a part of the surfaces of the first base material part 1 and the second base material part 3 on both sides of the welding joint. Specifically, the surface of the first base material part 1 has a first widened area 41, and the surface of the second base material part 3 has a second widened area 42. The first widened area 41 is the surface on the first base material part that extends from the end of the straight section to the other end of the first base material part 1 with a length of 5 mm to 10 mm; the second widened area 42 is the surface on the second base material part 3 that extends from the top end of the slope section 32 to the other end away from the slope section 32 with a length of 5 mm to 10 mm. The surfacing area to be built 4 continuously covers the first widened area 41, the surface of the welding joint 2, the surface of the slope section 32, and the second widened area 42 from the left straight pipe section to the right slope section 32. The widened areas 41 and 42 can be used as the subsequent enlarged cover welding area.

[0047] The manual grinding range of the base material should also extend 20 mm beyond both sides of the surfacing area 4, removing rust and dirt to expose the metallic luster. At the same time, a smooth transition area 43, such as an R5 angle, should be ground on the surface of the connection part between the welded joint 2 and the slope section 32. The upper edge of the slope can also be ground to a smooth transition to facilitate the subsequent surfacing process.

[0048] Finally, macroscopic inspection is used to check the surface quality of the base material within the surfacing area and 20 mm on both sides. After confirming no defects, surfacing welding treatment can be carried out.

[0049] Step S22: Form a surfacing layer in the area to be surfaced, making the surfaces of the first base material part, the surfacing layer, and the second base material part smoothly connected.

[0050] Specifically, taking the 9%Cr - 12%Cr martensitic heat-resistant steel commonly used in high-temperature and high-pressure pipelines of thermal power plants as an example, the welding and heat treatment processes are formulated. Before forming the surfacing layer, check the materials of the welded joint and the base materials on both sides, and conduct material spectrum rechecks to detect and recheck the materials of the above components. According to the component materials and specifications, formulate the welding process and post-weld heat treatment process in accordance with relevant regulations. The welding process parameters are shown in Table 1, and the post-weld heat treatment process parameters are shown in Table 2. Metal parts with other materials and component sizes can refer to this; for some other low-alloy materials, similar effects can be achieved without post-weld heat treatment, and the heat treatment step is not a necessary step.

[0051] Table 1. Welding process parameters

[0052]

[0053] Table 2. Post-weld heat treatment process parameters

[0054]

[0055] The crack blocking process welding is carried out on the surfacing welding layer by shielded metal arc welding (SMAW). On the one hand, by controlling the welding heat cycle of the weld bead, the self-tempering weld bead welding is carried out on the surface weld and its heat affected zone, reducing the crack initiation tendency in the weak area of the weld and playing the role of "blocking" cracks. On the other hand, the way of widening the area to expand the capping weld area is adopted to block the expansion channel parallel to the fusion line after crack initiation and avoid low plasticity and rapid fracture of the joint. The preheating before welding is carried out in accordance with the standards of DL / T 869-2021 and DL / T 819-2019. The preheating temperature for arc welding is 200°C to 250°C. After the temperature rises to the preheating temperature, it is kept warm for at least 0.5 h, and the interpass temperature is controlled at 200°C to 250°C. Electric heating is adopted, and the temperature is measured by thermocouples. The heating width on one side is not less than 4 times the pipe wall thickness and not less than 100 mm.

[0056] Subsequently, a surfacing process is carried out to form a surfacing layer in the area to be surfaced. As Figure 4 shown, by using shielded metal arc welding, the area to be surfaced 4 is gradually surfaced from the straight pipe section side of the first base material part 1 to the special-shaped structure side of the second base material part 3 to form a surfacing layer 5. Specifically, the surfacing weld bead includes filling welding and capping welding. Filling welding is carried out in accordance with the area to be surfaced 4 determined in the previous step S21 to form a filling weld layer, leaving a remaining weld layer thickness of 2 mm to 3 mm. Then, capping welding is carried out on the surface of the filling weld layer. The overall contour after capping welding should be slightly higher than the predetermined surfacing layer for subsequent smooth grinding.

[0057] During the above welding process, filling welding and capping welding should be carried out continuously when the interpass temperature permits. The welding material is selected as AWS E9015-B92. The welding process can be carried out by two people symmetrically. Strictly control the heat input of welding. The way of combining a heat treatment machine for recording and a temperature measuring gun / temperature measuring pen is adopted to control the interpass temperature, and relevant parameter records during the welding implementation process are well done. Multi-layer and multi-pass thin layer welding is adopted. Strictly control the heat input of welding, the width of a single weld bead and the thickness of the weld layer. The thickness of a single weld layer does not exceed 3 mm, and the width of a single weld bead does not exceed 3 times the diameter of the welding electrode. The ratio of the length of the weld bead welded by each complete welding electrode to the melting length of the welding electrode should be greater than 50%. During the welding process, attention should also be paid to the distribution of the weld beads and the arrangement of the arc striking positions to prevent local overheating. The joints of each layer of weld beads should be staggered by 10 mm to 15 mm. At the same time, pay attention to making the weld beads transition smoothly as much as possible to facilitate slag cleaning and avoid "dead corners".

[0058] After each weld pass is completed, slag, spatter and other debris shall be completely removed using an angle grinder or wire brush. Only after the welder's self-inspection is qualified can the next layer of welding be carried out. The treatment of interlayer defects in the welded joint shall be carried out by grinding with an angle grinder, especially at the weld pass joint and the edge of the groove. The molten iron transition adopts free transition. When finishing the welding, special attention should be paid to reducing the welding current. After filling the crater, move to the edge of the groove to stop welding to prevent the generation of crater cracks. The cover welding shall be smoothly transitioned with the base metal, and the crater at the end of welding shall be full, and the joint shall be well fused.

[0059] After the above welding process, finally form a stress optimization structure of the special-shaped butt welding structure as shown in Figure 4 . To meet the engineering stress requirements of the present disclosure, the angle 52 between the surface of the surfacing layer 5 and the straight section surface of the first base metal part 1 shall satisfy 15° to 30°. If it does not meet the requirement and the angle is greater than 30°, when designing the area 4 to be surfaced, extend the widened area distance of the left straight pipe groove in the figure, that is, extend the first widened area described above until the angle 52 meets the requirement of 15° to 30°.

[0060] After welding is completed, the slag and spatter on the weld surface shall be cleaned in time. For the appearance defects exceeding the standard, grinding or repair welding shall be carried out. The repair welding process is the same as the formal welding process. After the appearance inspection is qualified, post-weld heat treatment is prepared.

[0061] According to the post-weld heat treatment process parameter table described in Table 2 above, in order to ensure the reliability of post-weld heat treatment, a zoning precise temperature control method shall be adopted for post-weld heat treatment. The specific process requirements include: the post-weld heat treatment temperature is 750°C - 760°C, the holding time is determined to be 2.5 hours according to the height of the surfacing area of the component, and the heating and cooling rate is not higher than 80°C / h. If the heat treatment cannot be carried out in time, post-heat treatment at 350°C for 2 hours is required.

[0062] After welding and heat treatment are completed, the surfacing layer 5 can be shaped according to the grinding reference line 51 as shown in Figure 4 to further ensure the smooth transition connection between the surface of the surfacing layer 5 and the surfaces of the two side base metals.

[0063] A method for optimizing the stress of a special-shaped butt welding structure according to an embodiment of the present disclosure optimizes the appearance line type of the structure and reduces the degree of structural mutation through surfacing, solves the problem of stress superposition concentration caused by the overlap or proximity of the stress concentration position of the component structure and the fusion zone of the welded joint, reduces the stress concentration level of the structure, thereby reducing the early failure risk of the special-shaped butt welding structure and improving the service safety level of the structure, and has good popularization and application value for the improvement and transformation of the same type of components.

[0064] Another embodiment of the present disclosure provides a stress optimization structure of a special-shaped butt welding structure, and the structure is obtained by the stress optimization method of the special-shaped butt welding structure described in the above embodiment.

[0065] As Figure 4 shown, the structure includes a welded joint 2, and a first base metal part 1 and a second base metal part 3 that are connected to each other through the welded joint 2. There is a height difference on the surfaces of the first base metal part 1 and the second base metal part 3. A continuously covered surfacing layer 5 is provided on a part of the surfaces of the welded joint 2 and the first base metal part 1 and the second base metal part 3 on both sides of the welded joint 2. The surfaces of the first base metal part 1, the surfacing layer 5, and the second base metal part 3 are smoothly connected.

[0066] The specific manufacturing process has been described in detail in the foregoing embodiments and will not be elaborated herein.

[0067] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the present disclosure. However, the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also regarded as the protection scope of the present disclosure.

Claims

1. A stress optimization method for a special-shaped butt welding structure, wherein the special-shaped butt welding structure comprises a welding joint and an end of a straight section of a first parent material part and a bottom end of a slope section of a second parent material part connected to each other by the welding joint, wherein the surfaces of the first parent material part and the second parent material part have a height difference, characterized in that: The method comprises: Determine the area to be surfacing on the surface of the weld joint, the first parent material part and the second parent material part, including using mechanical turning to cut off the excess height of the weld joint, and forming a smooth transition zone between the slope section of the second parent material part and the surface of the connecting part of the weld joint; the area to be surfacing continuously covers the weld joint and a part of the surface of the first parent material part and the second parent material part on both sides of the weld joint; A surfacing layer is formed in the area to be surfacing, so that the surface of the first parent material portion, the surface of the surfacing layer and the surface of the second parent material portion are smoothly connected.

2. The method according to claim 1, characterized in that The surface of the first matrix part has a first widened area, and the surface of the second matrix part has a second widened area; The first widened area is a surface of the first mother material portion extending from the end of the straight section to the other end of the first mother material portion with a length of 5 mm to 10 mm; the second widened area is a surface of the second mother material portion extending from the top of the slope section to the other end away from the slope section with a length of 5 mm to 10 mm; The area to be surfacing continuously covers the first widened area, the surface of the weld joint, the surface of the slope section, and the second widened area.

3. The method according to claim 1, characterized in that: The angle between the surface of the surfacing layer and the surface of the straight section of the first parent material portion is 15° to 30°.

4. The method according to claim 2, characterized in that The method further comprises: If the angle between the surface of the cladding layer and the surface of the straight section of the first parent metal portion is greater than 30°, the first widened area is extended so that the angle reaches 15° to 30°.

5. The method according to claim 1, characterized in that Before forming the surfacing layer in the area to be surfacing, the method further comprises: Manual arc welding is used to perform crack blocking process welding in the area to be clad.

6. The method according to claim 1, characterized in that The surfacing layer includes a filling welding layer and a capping welding layer; The forming of a surfacing layer in the to-be-surfacing area comprises: Performing filling welding in the surfacing area to form a filling welding layer; Cap welding is performed on the surface of the filling welding layer.

7. The method according to claim 1, characterized in that The forming of a surfacing layer in the to-be-surfacing area comprises: While welding the end of the arc, the welding current is attenuated. After the arc pit is filled, the welding head is moved to the edge of the groove to close the arc.

8. A stress optimization structure of a special-shaped butt welding structure, characterized in that: The structure is obtained by the stress optimization method of the special-shaped butt welding structure according to any one of claims 1 to 7; The structure comprises a welding joint and an end of a straight section of a first parent material part and a bottom end of a slope section of a second parent material part connected to each other by the welding joint, and the surfaces of the first parent material part and the second parent material part have a height difference; A continuous cladding layer is provided on the surface of the weld joint and a portion of the first parent material part and the second parent material part on both sides of the weld joint, and the surface of the first parent material part, the surface of the cladding layer and the surface of the second parent material part are smoothly connected.

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