A method having a welding residual stress control and a crack prevention function

Abstract

The application discloses a method with welding residual stress control and crack prevention functions, comprising the following steps: before welding, according to the strength, stress state, welding method and welding parameters of the workpiece material, determining the preheating temperature and holding time; segmentally welding the annular large-thickness weld of the workpiece material; adopting repeated multi-pass welding to perform mid-way welding and reserving a final blocking segment for welding; in the welding process, performing real-time temperature monitoring on the welding area, and according to the real-time temperature data, adjusting the welding parameters to control the welding temperature and welding speed; after welding, performing cooling treatment on the welded joint. The application is used for solving the technical problems that the existing method for controlling welding stress and preventing welding cracks cannot well adapt to the welding requirements and control welding stress of different workpieces, and welding cracks still exist, so as to improve the welding quality and control the welding residual stress.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and more specifically to a method with functions of controlling residual welding stress and preventing cracks. Background Technology

[0002] Welding is a widely used manufacturing process. Also known as fusion welding, it is a manufacturing process and technology that joins metals or other thermoplastic materials such as plastics by heating, high temperature, or high pressure. During welding, the workpiece and the filler metal melt to form a molten zone, and the weld pool cools and solidifies to form a bond between the materials. Pressure is usually applied during this process. There are many energy sources for welding, including gas flames, electric arcs, lasers, electron beams, friction, and ultrasound.

[0003] In the field of marine engineering construction, welding is a key technology, especially in the construction of jacket structures for ultra-deepwater large offshore oil platforms. Circumferential closed welds exhibit high restraint and residual stress, making them prone to transverse cracks. While various methods for controlling welding stress and preventing welding cracks have been proposed in existing technologies, the following problems still exist:

[0004] (1) Existing methods for controlling welding stress and preventing welding cracks have many limitations in practical use, and therefore cannot well meet the welding requirements of different workpieces.

[0005] (2) Existing methods for controlling welding stress still have design flaws, thus failing to effectively control welding stress;

[0006] (3) Existing methods for preventing welding cracks reduce the number of welding cracks after welding, but welding cracks still exist. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, this invention provides a method with welding residual stress control and crack prevention functions. This method addresses the technical problems that existing methods for controlling welding stress and preventing welding cracks cannot adequately meet the welding requirements of different workpieces and control welding stress, and that welding cracks still exist. This method aims to improve welding quality and control welding residual stress.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0009] A method for controlling welding residual stress and preventing cracks includes the following steps:

[0010] Before welding, the preheating temperature and holding time are determined based on the strength, stress state, welding method and welding parameters of the workpiece material;

[0011] The annular thick-walled weld seam of the workpiece material is welded in sections.

[0012] The process involves repeated multi-pass welding, with a final sealing section reserved for welding.

[0013] During the welding process, the temperature of the welding area is monitored in real time, and the welding parameters are adjusted according to the real-time temperature data to control the welding temperature and welding speed.

[0014] After welding, the welded joint is cooled.

[0015] In a preferred embodiment of the present invention, when performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included:

[0016] The annular thick-walled weld is divided into several segments, which are then welded in sequence. The later segments are the stress relief holes of the earlier segments.

[0017] In a preferred embodiment of the present invention, when performing intermediate welding using repeated multi-pass welding, the following is included:

[0018] The segments are repeatedly welded in multiple layers and passes in the same direction, with one end of each segment being a free end that can be freely contracted.

[0019] In a preferred embodiment of the present invention, the multi-layer multi-pass welding is a three-layer multi-pass welding.

[0020] In a preferred embodiment of the present invention, the size range of the final sealing segment is 50-100mm.

[0021] In a preferred embodiment of the present invention, when welding is performed on a pre-reserved final sealing section, the following is included:

[0022] SMAW or FCAW welding is used, and the parameters are taken as the lower limit of the process requirements.

[0023] In a preferred embodiment of the present invention, before welding, the following is further included:

[0024] The workpiece material is surface cleaned and prepared for docking, and the conformity and gap of the weld joint are checked.

[0025] In a preferred embodiment of the present invention, when performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included:

[0026] The front and rear ends of the welded seam are not restricted and can freely contract.

[0027] In a preferred embodiment of the present invention, when performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included:

[0028] Segmented welding is performed using SMAW or FCAW.

[0029] As a preferred embodiment of the present invention, the specific process parameters for segmented welding using FCAW include:

[0030] The electrode diameter is 1.2mm, the welding current is 210-240A, the welding voltage is 25-28V, and the heat input is 1.0-2.0kJ / mm.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] (1) The method provided by the present invention can effectively control welding residual stress, reduce the risk of deformation and cracking of welded joints, and improve the quality and service life of welded joints;

[0033] (2) This method of residual stress control and crack prevention can also be adapted to the welding requirements of different workpieces and can achieve good results in practical applications:

[0034] (3) The method provided by the present invention improves welding quality, increases work efficiency, and shortens construction period.

[0035] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0036] Figure 1 - This is a schematic diagram of the design and welding sequence of the stress relief hole of the reinforcing ring during horizontal manufacturing according to an embodiment of the present invention;

[0037] Figure 2 - This is a schematic diagram of the design and welding sequence of the stress relief hole of the reinforcing ring during vertical manufacturing in an embodiment of the present invention;

[0038] Figure 3 - This is a flowchart illustrating the method steps for controlling welding residual stress and preventing cracks according to an embodiment of the present invention.

[0039] Explanation of the symbols in the attached diagram: 1. Large steel pipe; 2. Reinforcing ring. Detailed Implementation

[0040] The method provided by this invention, which has the functions of controlling welding residual stress and preventing cracks, such as... Figure 3 As shown, it includes the following steps:

[0041] Step S1: Before welding, determine the preheating temperature and holding time based on the strength, stress state, welding method, and welding parameters of the workpiece material;

[0042] Step S2: Perform segmented welding on the annular thick-walled weld of the workpiece material;

[0043] Step S3: Use repeated multi-pass welding for intermediate welding, and reserve a final sealing section for welding;

[0044] Step S4: During the welding process, the temperature of the welding area is monitored in real time, and the welding parameters are adjusted according to the real-time temperature data to control the welding temperature and welding speed.

[0045] Step S5: After welding, the welded joint is cooled.

[0046] The method of this invention involves segmenting the circumferential, thick-walled weld seam and designing stress relief holes within each segment. By employing repeated multi-pass welding, segmental sealing, appropriate preheating and heat preservation, real-time temperature monitoring, and cooling treatment, residual welding stress is effectively controlled, reducing the risk of deformation and cracking in the welded joint and improving its quality and service life. Furthermore, this method can also utilize composite welding techniques to achieve even better weld quality and control of residual welding stress.

[0047] In step S1 above, an appropriate preheating temperature and holding time are determined based on the actual selection of workpiece material and welding process, so that the temperature of the workpiece material is evenly distributed during the welding process, thereby reducing stress concentration during the welding process.

[0048] In step S2 above, when performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included:

[0049] The annular thick-walled weld is divided into several segments, which are welded in sequence. The later segments are the stress relief holes of the earlier segments.

[0050] In step S3 above, when performing intermediate welding using repeated multi-pass welding, the following is included:

[0051] The segments are repeatedly welded in multiple layers and passes in the same direction, with one end of each segment being a free end that can be freely contracted.

[0052] Specifically, when performing multi-layer, multi-pass welding, ensuring that one end of each segment is a free end allows residual welding stress to be released through the free end. This, combined with the stress release hole design in the segmented welding and the free end design in the intermediate welding process, further controls residual welding stress.

[0053] Furthermore, multi-layer multi-pass welding is transformed into three-layer multi-pass welding.

[0054] Specifically, this invention allows for a wider range of adjustments to heat input and welding speed during multi-layer, multi-pass welding, thereby enabling better control of residual welding stress. Furthermore, multi-layer, multi-pass welding offers advantages such as lower heat input and reduced defects. The interlayer microstructure in multi-layer, multi-pass welding undergoes multiple heat inputs, resulting in finer and more uniform grains after remelting. This is because the longitudinal heat input to the bottom weld layer continuously increases, leading to vertical growth under the thermal action of subsequent welds. The finer grains increase the material's hardness, thus improving weld quality.

[0055] In step S3 above, the final sealing segment has a size range of 50-100mm.

[0056] Specifically, the purpose of reserving a final sealing segment is to ensure that one end of the segment remains free during the final segment welding. This allows the heat input and thermal stress generated during the final segment welding to be released from the final sealing segment, thereby controlling residual welding stress. Generally, the larger the reserved final sealing segment, the better the residual welding stress can be released. However, a problem arises with a larger final sealing segment: after completing the segment welding, the final sealing segment needs to be sealed with welding. A larger final sealing segment at this stage results in greater heat input and thermal stress from the sealing welding. This invention, by controlling the size of the final sealing segment within the range of 50-100mm, ensures stress release during segment welding while preventing excessive heat input and thermal stress during sealing welding.

[0057] In step S3 above, when welding is performed on the reserved final sealing section, the following steps are included: welding is performed using SMAW or FCAW, with parameters taken as the lower limit of the process requirements.

[0058] Specifically, when welding the final sealing section, the parameters are set to the lower limit of the process requirements. During welding, the higher the process parameters are set, the greater the heat input and thermal stress will be. This invention reduces heat input and thermal stress, and lowers overall residual stress, by setting the parameters to the lower limit of the process requirements, while ensuring that welding requirements are met.

[0059] Furthermore, before welding, the process also includes: cleaning the surface of the workpiece material and preparing for the butt joint, and checking the conformity and gap of the weld joint.

[0060] In step S2 above, when performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are taken: the front and rear ends of the weld are not constrained and can shrink freely.

[0061] Specifically, by releasing the front and rear ends of the pre-welded weld, the present invention ensures that stress transmission does not form a closed loop throughout the welding process, and there are always stress release points, thereby helping to minimize residual welding stress.

[0062] In step S2 above, when performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included:

[0063] Segmented welding is performed using SMAW or FCAW. Furthermore, the specific process parameters for segmented welding using FCAW include: electrode diameter of 1.2 mm, welding current of 210-240 A, welding voltage of 25-28 V, and heat input of 1.0-2.0 kJ / mm.

[0064] Furthermore, SAW+FCAW can be used for segmented welding.

[0065] Specifically, manual arc welding (SMAW) is an arc welding method that uses a welding electrode manually. SMAW uses a welding electrode and the workpiece as two electrodes; the metal being welded is called the workpiece or base metal. During welding, the high temperature and blowing force of the arc cause localized melting of the workpiece, forming an elliptical pit filled with molten metal on the workpiece; this pit is called the molten pool. As the welding electrode moves, the molten pool cools and solidifies, forming the weld. The slag covering the weld surface is called slag. The distance from the molten end of the welding electrode to the surface of the molten pool is called the arc length; the distance from the surface of the workpiece to the bottom of the molten pool is called the penetration depth. SMAW is characterized by its flexibility and adaptability, making it suitable for welding various metal materials in different structures and positions. Due to its high flexibility, SMAW allows for real-time adjustment of welding parameters based on real-time temperature data, effectively controlling the welding temperature and speed, thereby reducing thermal stress in the weld area.

[0066] FCAW (Flux-Cored Arc Welding), also known as gas-shielded flux-cored arc welding, is an arc welding method using flux-cored electrodes, belonging to the category of arc welding technology. The key feature of FCAW is the addition of a metal oxide inside the electrode, with an antioxidant layer on the outside. The arc melts the metal, completing the weld in a single pass. Therefore, it is an automated welding method achieved through arc welding technology, and it is an arc welding technology that does not require external gas shielding.

[0067] The basic principle of FCAW welding is to use an electric arc to melt the metal particles within the welding strip, creating a molten pool that eliminates oxides, impurities, and other materials at the weld joint, thus forming a tight weld. The welding electrode itself is a composite material encased in a metal outer layer, containing metal oxides and antioxidants. As the electrode melts, the metal oxides act as a shielding gas for the arc, enabling welding without the need for external gas protection.

[0068] The basic characteristics of the FCAW welding method are: high welding speed, high efficiency, ability to weld various materials, and the ability to achieve automated welding. During welding, the welding current and welding voltage can be adjusted to achieve seamless welding. Thus, residual welding stress can be controlled by adjusting the welding current and welding voltage during the welding process.

[0069] The FCAW welding method also has the following advantages:

[0070] (1) It can achieve automated welding and improve welding efficiency; (2) It can achieve seamless welding; (3) Welding current and welding voltage can be adjusted during welding; (4) It can weld various materials to meet the diverse needs of industry; (5) It has fast welding speed and high efficiency.

[0071] In step S4 above, the welding parameters are adjusted in real time based on the real-time temperature data, which can effectively control the welding temperature and welding speed, thereby reducing the thermal stress in the welding area.

[0072] In step S5 above, after welding is completed, the welded joint is subjected to appropriate cooling treatment so that the temperature of the welded area gradually decreases, thereby effectively avoiding stress concentration and cracking caused by excessively rapid cooling.

[0073] Furthermore, the method of the present invention can also employ a composite welding approach, which involves dividing the weld seam into segments and combining various welding methods and welding materials to achieve better welding quality and control of residual welding stress.

[0074] The following is one embodiment of the present invention, for reference only. The parameters and process parameters provided in the embodiment should not be considered as limiting the scope of the present invention.

[0075] Example (Control of residual stress in guide leg reinforcing ring welding and prevention of transverse weld cracks)

[0076] 1. Workpiece preparation:

[0077] Prepare a large steel pipe 1 and a thick-walled reinforcing ring 2, and weld them using FCAW. The material is DH36, the pipe diameter is φ2800mm, the wall thickness is 80mm, and the thickness of the reinforcing ring is 60mm.

[0078] 2. Welding process:

[0079] (1) Clean the surface of the workpiece and prepare for docking, and check the conformity and gap of the welding joint;

[0080] (2) FCAW is used for horizontal segmented welding. The electrode diameter is φ1.2mm, the welding current is 210-240A, the welding voltage is 25-28V, and the heat input is 1.0-2.0kJ / mm.

[0081] (3) Segmented Welding: During horizontal manufacturing, the circumferential weld of the reinforcing ring 2 of the large steel pipe 1 is divided into three parts (segment A, segment B, and segment C), with segment C, approximately 50mm, serving as the final stress relief hole. The welding sequence of each weld segment is as follows: Figure 1 As shown; in Figure 1 In the process of welding section A, the unwelded sections B and C serve as stress relief holes for section A; similarly, when welding section B, the unwelded section C serves as a stress relief hole for section B. Alternatively, vertical manufacturing can be employed, dividing the circumferential weld into two sections (section D and section E), as shown below. Figure 2 As shown, segment E is approximately 50mm; in Figure 2 In the process of welding section D using submerged arc welding, section E, which is still unwelded, is the stress relief hole of section D. Finally, section E is completed using carbon dioxide shielded welding.

[0082] (3) Repeated multi-pass welding is used for intermediate welding. Each section of welding uses three layers of multi-pass welding. One end is a free end that can shrink freely. The residual welding stress can be released through the free end.

[0083] (4) The final sealing section is reserved with 50mm, and FCAW is used for welding. The parameters are taken as the lower limit of the process requirements to reduce heat input and thermal stress, thereby reducing the overall residual stress.

[0084] (5) Before welding, determine the appropriate preheating temperature and holding time based on factors such as the strength of the workpiece material, stress state, welding method and welding parameters, so as to make the workpiece temperature evenly distributed and reduce stress concentration during the welding process.

[0085] (6) During the welding process, the temperature of the welding area is monitored in real time, and the welding parameters are adjusted according to the real-time temperature data to control the welding temperature and speed and reduce the thermal stress in the welding area.

[0086] (7) After welding, the welded joint should be cooled appropriately to gradually reduce the temperature of the welded area and avoid stress concentration and cracking caused by excessive cooling rate.

[0087] Welding results: Using the welding method described in the above embodiment, the weld surface of the large steel pipe 1 is smooth, free of porosity, inclusions, and defects. No deformation or cracks appeared in the welded joint, and the residual welding stress was effectively controlled, meeting the design requirements.

[0088] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0089] (1) The method provided by the present invention can effectively control welding residual stress, reduce the risk of deformation and cracking of welded joints, and improve the quality and service life of welded joints;

[0090] (2) This method of residual stress control and crack prevention can also be adapted to the welding requirements of different workpieces and can achieve good results in practical applications:

[0091] (3) The method provided by the present invention improves welding quality, increases work efficiency, and shortens construction period.

[0092] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method having a function of controlling welding residual stress and preventing cracks, characterized by, Includes the following steps: Before welding, the preheating temperature and holding time are determined based on the strength, stress state, welding method and welding parameters of the workpiece material. The annular thick-walled weld seam of the workpiece material is welded in sections. The process involves repeated multi-pass welding, with a final sealing section reserved for welding. During the welding process, the temperature of the welding area is monitored in real time, and the welding parameters are adjusted according to the real-time temperature data to control the welding temperature and welding speed. After welding, the welded joint is cooled. When welding is performed on the reserved final sealing section, the following is included: SMAW or FCAW welding is used, and the parameters are taken as the lower limit of the process requirements.

2. The method of claim 1, wherein the method is characterized by: When performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included: The annular thick-walled weld is divided into several segments, which are then welded in sequence. The later segments are the stress relief holes of the earlier segments.

3. The method of claim 1, wherein the method is characterized by: When using repeated multi-pass welding for intermediate welding, including: The segments are repeatedly welded in multiple layers and passes in the same direction, with one end of each segment being a free end that can be freely contracted.

4. The method for controlling welding residual stress and preventing cracks according to claim 3, characterized in that, The multi-layer multi-pass welding is a three-layer multi-pass welding.

5. The method for controlling welding residual stress and preventing cracks according to claim 1, characterized in that, The size range of the final sealing segment is 50-100mm.

6. The method for controlling welding residual stress and preventing cracks according to claim 1, characterized in that, Before welding, it also includes: The workpiece material is surface cleaned and prepared for docking, and the conformity and gap of the weld joint are checked.

7. The method for controlling welding residual stress and preventing cracks according to claim 1, characterized in that, When performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included: The front and rear ends of the welded seam are not restricted and can freely contract.

8. The method for controlling welding residual stress and preventing cracks according to claim 1, characterized in that, When performing segmented welding on the annular thick-walled weld of the workpiece material, the following steps are included: Segmented welding is performed using SMAW or FCAW.

9. The method for controlling welding residual stress and preventing cracks according to claim 8, characterized in that, The specific process parameters for segmented welding using FCAW include: The electrode diameter is 1.2mm, the welding current is 210-240A, the welding voltage is 25-28V, and the heat input is 1.0-2.0kJ / mm.

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