A welding process for gas turbine flue guard plate

Abstract

The invention provides a welding process for a gas turbine flue guard plate, comprising the following steps: the wall plate of the flue guard plate adopts Q235B, a hot-rolled coil steel with a thickness of 6 mm, and a suitable steel plate width is selected according to the size of the component to reduce the number of splicing welds, and plasma cutting is adopted; the reinforcing rectangular tube and the rib plate are combined into reinforcing ribs, and the combination with the guard plate plate is combined with free docking and then spot welded; after the beam, rib plate and guard plate plate are installed, welding is performed, and segmented lines are drawn, and segmented welding is performed along the center position toward the two ends. The deformation of the flue guard plate is effectively controlled by controlling the welding deformation through welding methods and reasonable welding sequences.

Description

Technical Field

[0001] The invention belongs to the technical field of building construction, and in particular relates to a welding process for a gas turbine flue guard plate. Background Art

[0002] With the rapid development of social economy, the demand for electricity is also increasing. In this context, gas turbine power plants have developed rapidly. Compared with coal-fired units, the construction of more environmentally friendly and flexible gas turbine units has high environmental and economic value. The flue is an important part of the gas turbine unit, usually made of steel plates. During use, the flue gas flows from the combustion chamber through the flue, transferring heat to the medium water driving the steam turbine. Therefore, the good performance and safety of the flue is crucial.

[0003] According to relevant national standards and specifications, the steel plates of the machine flue need to be thin steel plates. During the welding process of thin steel plates, welding will cause uneven local heating of the thin steel plates, which will cause welding deformation and curling of the thin steel plates. The second-order effect caused by welding deformation will reduce the bearing capacity of the thin steel plates, and the welding deformation will greatly reduce the accuracy of structural installation. Therefore, when producing various components of the gas turbine unit, it is inevitable to face and solve the problem of welding deformation of thin steel plates. Summary of the invention

[0004] In order to solve the technical problem of thin steel plate welding deformation in the production of gas turbine units, the present invention provides a welding process for gas turbine flue guard plates. The welding deformation is controlled by welding methods and reasonable welding sequences, so that the deformation of the flue guard plates can be effectively controlled.

[0005] In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is:

[0006] A welding process for a gas turbine flue guard plate comprises the following steps:

[0007] A. Material feeding control

[0008] The wall panels of the flue guard plate are made of Q235B, 6mm thick hot-rolled coil steel. The appropriate steel plate width is selected according to the component size to reduce the number of splicing welds. Plasma cutting is used, and 5-10mm shrinkage is reserved according to the size of the workpiece to ensure that the overall size will not be adjusted due to the size of the weld during the later assembly, thereby avoiding stress concentration caused by excessive weld width and excessive deposited metal.

[0009] The present invention adopts plasma cutting, which can avoid large thermal deformation of the thin plate after flame cutting and improve the processing accuracy of the parts.

[0010] B. Assembly

[0011] After the guard plate is spliced, spot welding is first performed, with an interval of 200mm and 50mm spot welding, and no full welding is temporarily performed;

[0012] Combine the reinforcement rectangular tube and the rib plate into reinforcement ribs. If there are columns or beams attached to the guard plate, combine them first, and then use free docking to combine with the guard plate to ensure good fit. Spot weld at reasonable positions. The spot welding should not exceed 5mm, and 5-10mm shrinkage should be reserved. Do not weld for the time being;

[0013] The present invention first tightens the weld and then welds to enhance the rigidity of the steel plate, thereby controlling the deformation of the weld. Free docking is adopted during the reinforcement process to minimize forced pulling, twisting and squeezing, so that the weld is basically stress-free and the welding deformation is small.

[0014] C. Welding

[0015] After the installation of beams, stiffeners and guard plates is completed, welding is carried out. Lines are drawn in sections and welding is carried out from the center position to both ends. The length of each section is 300-400mm. After the welding of the reinforced surface on the outside of the guard plate is completed, turn it over and weld the inside. The same welding sequence is used. After welding, the shape is adjusted and inspected.

[0016] The welding sequence has an important influence on the post-weld deformation of the plate. If welding is performed without optimizing the welding sequence, the heating and cooling of the plate will be uneven due to the differences in thermal stress and constraint conditions in different local areas, which will lead to increased post-weld deformation.

[0017] In step A of the present invention, the steel plate is first pre-shot blasted and pre-coated with a layer of inorganic zinc-rich primer, and then the steel plate is leveled with a flat machine. Under the impact of the shot blasting machine, the steel plate can effectively remove rust, oil stains and other debris on the surface of the steel plate to prevent the formation of pores, and at the same time, a layer of inorganic zinc-rich primer is pre-coated to prevent rust; and then the flat machine is used for leveling, which can effectively level the deformation and eliminate the stress generated during the shot blasting process.

[0018] In step B of the present invention, the parts are assembled on a flat platform and polished to make the assembly gap no more than 0.5 mm, thereby reducing the welding filling amount.

[0019] Preferably, after the beams and stiffeners are installed, they are spot welded firmly, first welding the vertical welding positions, and then welding the stiffeners, beams, and rectangular tubes in sequence, welding in sections from the center to the outside.

[0020] In step C of the present invention, during the welding process of the reinforced surface, after the welding of the middle position of the guard plate is completed, a counterweight is added to press it down, and the edges are allowed to shrink and stretch freely, so that the stress is released.

[0021] In the step C of the present invention, welding is performed from the center to both ends, and the adjacent sections are welded discontinuously, so that the first welding section can be cooled more naturally, avoiding the influence of high temperature during welding of adjacent sections, causing thermal stress changes in local areas and deformation.

[0022] The present invention adopts carbon dioxide gas shielded welding, and argon gas is used to protect the back of the weld during welding. Using argon gas as back gas protection has a cooling effect on the welding area, helps to reduce the temperature of the welding point, reduces deformation caused by high temperature, and avoids weld oxidation and assists in root forming, reducing the welding workload after root cleaning.

[0023] Preferably, by weight, the welding material is Atlantic flux-cored wire T711, with a wire diameter of 1.2 mm and a wire elongation of 12 mm.

[0024] Preferably, the welding current polarity adopts direct current reverse polarity, the welding current is 120-140A, the arc voltage is 20-22V, the gas flow rate is 10-12L / min, and the welding speed is 500-600mm / min.

[0025] In the weld of thin steel plate, the vertical bending of the weld is very sensitive to the temperature change of the weld. If a large amount of heat appears in the weld, it will cause the weld of the plate to be distorted. Reducing the welding heat can effectively control the welding deformation of thin steel plate. The melting point of Atlantic flux-cored welding wire T711 is 400-500℃. The low melting point can effectively prevent the generation of heat and stress in the weld, thereby reducing the deformation of the weld. The wire diameter is 1.2mm and the wire elongation is 12mm. If the electrode diameter is too large, it will increase the difficulty of welding the weld and it is not easy to control. The wire diameter of 1.2mm is suitable for thin steel plates.

[0026] Select the wire extension value of 12mm. When the wire extension length increases, the wire melting speed increases. At this time, the current decreases, which will reduce the temperature of the molten droplet and the molten pool, resulting in insufficient heat and incomplete welding. In addition, the arc is unstable, difficult to operate, large spatter, poor forming, and easy to produce pores. When the wire extension length becomes shorter, the current increases, the arc length becomes shorter, the melting depth becomes larger, the spatter is easy to adhere to the inner wall of the nozzle, it is difficult to observe the molten pool, and even burn the conductive nozzle.

[0027] The size of the welding current directly affects the temperature distribution and heat input during welding. When the welding current is small, the heat-affected zone is smaller and the microstructure around the weld is less affected. When the welding current gradually increases, the heat-affected zone will gradually expand and the microstructure around the weld will become more complex. It is necessary to fine-tune the welding parameters and processes to obtain the best welding effect.

[0028] The present invention controls the arc voltage at 20-22V. If the voltage is too low, the spatter increases, the weld narrows, and the top wire is easy to appear; if the voltage is too high, the arc length becomes longer, the spatter particle size becomes larger, pores are easy to appear, the weld becomes wider, the penetration depth and the residual height become smaller, and there is a strong blasting sound. The welding speed is controlled at 500-600mm / min. If the speed is too slow, a large amount of heat input will be caused, which is easy to cause deformation and the weld becomes wider; if the welding speed is too fast, the heat input is insufficient, and the weld is easy to have incomplete penetration.

[0029] The present invention adopts direct current reverse polarity, the arc is stable, the welding process is smooth, and the spatter is small. If direct current positive polarity is adopted, the penetration depth is shallow, the residual height is large, and the spatter is large. By observing the spatter condition, the melting condition of the electrode and the shape of the molten pool during the welding process, the optimal current range matching the 20-22V voltage is found to be 120-140A, ensuring that the vibration of the welding gun during the welding process is within the controllable range, and the wire feeding speed of the welding wire is controlled at 500-600mm / min.

[0030] The beneficial effects of the present invention are:

[0031] 1. The flue guard plate of the present invention adopts a 6mm thin steel plate. In view of the characteristics of large welding area, thin steel plate, and overall surface flatness, the quality, size and construction process of the blanking plate are strictly controlled, and the welding deformation is strictly controlled according to the set welding method and reasonable welding sequence, so that the deformation of the flue guard plate is effectively controlled, saving propane used in the later shape correction, as well as some re-welding and grinding consumables that need to be cut to eliminate stress, saving labor time and cost, improving work efficiency and reducing costs while greatly improving product quality.

[0032] 2. The present invention selects suitable welding materials according to the characteristics of thin steel plates and large welding areas. On the basis of carbon dioxide gas shielded welding, argon back gas protection is added, and welding parameters and processes are finely adjusted. A low current of 120-140A and a low voltage of 20-22V are used for welding to ensure a high welding speed of 500-600mm / min, thereby reducing the amount of heat input to obtain the best welding effect and further reduce welding deformation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the welding sequence of the gas turbine flue guard plate of the present invention.

[0034] Figure 2 The figure is a schematic diagram of the assembly of the gas turbine flue guard plate of the present invention. DETAILED DESCRIPTION

[0035] In order to more clearly and in detail illustrate the technical solution of the present invention, the present invention is further described below through relevant embodiments. The following embodiments are only for specific explanation of the implementation method of the present invention, and do not limit the protection scope of the present invention.

[0036] Example 1

[0037] A welding process for a gas turbine flue guard plate comprises the following steps:

[0038] A. Material feeding control

[0039] The wall panels of the flue guard plate are made of Q235B, 6mm thick hot-rolled coil steel. The appropriate steel plate width is selected according to the component size to reduce the number of splicing welds; plasma cutting is used, and 5-10mm shrinkage is reserved according to the size of the workpiece.

[0040] B. Assembly

[0041] After the guard plate is spliced, spot welding is first performed, with a spot welding interval of 50mm at 200mm;

[0042] Combine the reinforcing rectangular tube and the rib plate into reinforcing ribs. If there are columns or beams attached to the guard plate, assemble them first, and then use free docking to combine with the guard plate and then spot weld. The spot welding should not exceed 5mm, leaving 5-10mm shrinkage allowance;

[0043] C. Welding

[0044] After the installation of beams, stiffeners and guard plates is completed, welding is carried out. Lines are drawn in sections and welding is carried out from the center position to both ends. The length of each section is 300-400mm. After the welding of the reinforced surface on the outside of the guard plate is completed, turn it over and weld the inside. The same welding sequence is used. After welding, the shape is adjusted and inspected.

[0045] Example 2

[0046] This embodiment is based on embodiment 1:

[0047] In the step A, the steel plate is firstly pre-shot blasted and pre-coated with a layer of inorganic zinc-rich primer, and then the steel plate is leveled with a flat plate machine.

[0048] In the above-mentioned step B, the parts are assembled on a flat platform and polished to make the assembly gap no more than 0.5 mm, thereby reducing the welding filling amount.

[0049] After the beams and stiffeners are installed, spot weld them firmly. First weld the vertical welding position, then weld the stiffeners, beams, and rectangular tubes in sequence, welding in sections from the center to the outside.

[0050] Example 3

[0051] This embodiment is based on Embodiment 2:

[0052] In the step C described above, during the welding process of the reinforced surface, after the welding of the middle position of the guard plate is completed, a counterweight is added to press it down, and the edges are allowed to shrink and stretch freely, so that the stress is released.

[0053] In step C, welding is performed from the center to both ends, and the adjacent sections are welded discontinuously. Figure 1 As shown, draw lines and mark the segments "1, 3, 5", "2, 4, 6", and press Figure 1 Weld in the order of markings.

[0054] Example 4

[0055] This embodiment is based on Embodiment 3:

[0056] Carbon dioxide gas shielded welding is used, and argon gas is used to protect the back of the weld during welding.

[0057] By weight, the welding material is Atlantic flux-cored wire T711, with a wire diameter of 1.2 mm and a wire elongation of 12 mm.

[0058] The welding current polarity adopts DC reverse polarity, the welding current is 120A, the arc voltage is 20V, the gas flow rate is 10L / min, and the welding speed is 500mm / min.

[0059] Example 5

[0060] This embodiment is based on Embodiment 3:

[0061] Carbon dioxide gas shielded welding is used, and argon gas is used to protect the back of the weld during welding.

[0062] By weight, the welding material is Atlantic flux-cored wire T711, with a wire diameter of 1.2 mm and a wire elongation of 11 mm.

[0063] The welding current polarity adopts DC reverse polarity, the welding current is 140A, the arc voltage is 22V, the gas flow rate is 11L / min, and the welding speed is 550mm / min.

[0064] Example 6

[0065] This embodiment is based on Embodiment 3:

[0066] Carbon dioxide gas shielded welding is used, and argon gas is used to protect the back of the weld during welding.

[0067] By weight, the welding material is Atlantic flux-cored wire T711, with a wire diameter of 1.2 mm and a wire elongation of 12 mm.

[0068] The welding current polarity adopts DC reverse polarity, the welding current is 130A, the arc voltage is 21V, the gas flow rate is 12L / min, and the welding speed is 600mm / min.

[0069] The present invention needs to select suitable welding wire according to the type of steel to be welded, the quality requirements of the welded parts and the welding construction conditions. Carbon dioxide gas shielded welding was used to investigate the welding of hot-rolled coil steel with a diameter of δ=6mm and a size of 300×1500mm with 9 welding wires of different diameters. The welding current polarity adopted direct current reverse polarity, the current was 180A, the arc voltage was 25V, the gas flow rate was 10L / min, and the welding speed was 400mm / min. The dimensions of the 9 groups of samples were measured three times before and after welding, and Table 1 is the comparison result of the mean values ​​of the dimension measurements before and after welding.

[0070] Table 1 Comparison of the dimensions of different welding wires before and after welding

[0071]

[0072] As can be seen from Table 1, when the diameter of the 7th group of flux-cored wire T711 is 1.2, the dimensional shrinkage value after welding is the smallest. This may be because the melting point of Atlantic flux-cored wire T711 is 400-500°C, which has a low melting point and prevents the generation of heat and stress in the weld, thereby reducing weld deformation. Therefore, the present invention uses flux-cored wire T711 as welding material, and further performs argon protection on the back of the weld during welding, and the dimensional shrinkage value after welding is further reduced to 7.8mm.

[0073] Table 2 Dimensional comparison of the embodiment of the present invention before and after welding

[0074]

[0075] As can be seen from Table 2, the present invention adopts a small current of 120-140A, a small voltage of 20-22V, and increases the welding speed by 500-600mm / min, which reduces the amount of heat input and can further control deformation.

[0076] The present invention splices and welds the flue of the 2X9H gas turbine waste heat furnace of Xizi Clean Energy Sichuan Energy Investment Guangyuan Gas, and the length dimension deviation of the guard plate after riveting and welding is in line with Table 3. 70 man-hours of labor are saved in the processes of splicing, welding, calibration, and inspection, and the labor cost is saved by 24,500 yuan based on an average wage of 350 yuan per day. The consumables saved are mainly propane used for local flame heating during shape correction, and welding materials and angle grinders used for re-welding and grinding after some parts need to be cut to eliminate stress, saving 14,220 yuan in consumables. A total of 38,720 yuan is saved.

[0077] The weld surface is smooth and flat, with a smooth transition between the weld and the base material, and there are no defects such as cracks, slag inclusions, pores, lack of fusion and obvious weld bumps on the weld surface. There are no pores or pits on the surface of full-penetration butt welds and fillet welds, and the number of pores or pits per meter of incomplete-penetration fillet welds is no more than 3.

[0078] Table 3 Welding structure length deviation

[0079]

[0080] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A welding process for a gas turbine flue guard plate, characterized in that: The following steps are involved: A. Material feeding control The wall plate of the flue guard plate is made of Q235B, 6mm thick hot-rolled coil steel. The appropriate steel plate width is selected according to the size of the component to reduce the number of splicing welds; plasma cutting is used, and 5-10mm shrinkage is reserved according to the size of the workpiece; B. Assembly After the guard plate is spliced, spot welding is first performed, with a spot welding interval of 50mm at 200mm; Combine the reinforcing rectangular tube and the rib plate into reinforcing ribs. If there are columns or beams attached to the guard plate, assemble them first, and then use free docking to combine with the guard plate and then spot weld. The spot welding should not exceed 5mm, leaving 5-10mm shrinkage allowance; C. Welding After the installation of beams, stiffeners and guard plates is completed, welding is carried out. Lines are drawn in sections and welding is carried out in sections from the center position to both ends. The length of each section is 300-400mm. After the welding of the reinforced surface on the outside of the guard plate is completed, turn it over and weld the inside. The same welding sequence is used. After welding is completed, the shape is adjusted and inspected.

2. The welding process of the gas turbine flue guard plate according to claim 1 is characterized in that: In the step A, the steel plate is firstly pre-shot blasted and pre-coated with a layer of inorganic zinc-rich primer, and then the steel plate is leveled with a flat plate machine.

3. The welding process of the gas turbine flue guard plate according to claim 1 is characterized in that: In the above-mentioned step B, the parts are assembled on a flat platform and polished to make the assembly gap no more than 0.5 mm.

4. The welding process of the gas turbine flue guard plate according to claim 3 is characterized in that: After the beams and stiffeners are installed, spot weld them firmly. First weld the vertical welding position, then weld the stiffeners, beams, and rectangular tubes in sequence, welding in sections from the center to the outside.

5. The welding process of the gas turbine flue guard plate according to claim 1 is characterized in that: In step C, welding is performed from the center toward both ends, and the welding of two adjacent sections is discontinuous.

6. The welding process of the gas turbine flue guard plate according to claim 1 is characterized in that: During the welding process of the reinforced surface, after the welding of the middle position of the guard plate is completed, counterweights are added to press it down, and the edges are allowed to shrink and stretch freely.

7. The welding process of the gas turbine flue guard plate according to claim 1 is characterized in that: Carbon dioxide gas shielded welding is used, and argon gas is used to protect the back of the weld during welding.

8. The welding process of the gas turbine flue guard plate according to claim 7 is characterized in that: The welding material used is Atlantic flux-cored wire T711, with a wire diameter of 1.2 mm and a wire elongation of 12 mm.

9. The welding process of the gas turbine flue guard plate according to claim 7 is characterized in that: The welding current polarity adopts DC reverse polarity, the welding current is 120-140A, the arc voltage is 20-22V, the gas flow rate is 10-12L / min, and the welding speed is 500-600mm / min.

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