Welding repair and reinforcement technology for cracks in the main frame of wind turbines

Abstract

A welding repair and reinforcement process for cracks in the main frame of a wind turbine includes the following steps: S1, defect detection, using penetrant testing and ultrasonic testing to determine the length, depth, and trend of the defect in the main frame; S2, applying a V-groove to the defective portion of the wind turbine main frame in unobstructed locations; applying a single V-groove to the obstructed portions of the wind turbine main frame, with the opening angle α of the V-groove being 40-50°. Beneficial effects: Compared to existing technologies, this invention, through grinding the V-groove and drilling crack-stopping holes, and by optimizing the interpass temperature, welding heat input, and welding materials based on appropriate preheating, reduces welding stress and improves welding quality. This solves the problem of high weld crack tendency in cast iron main frame components of wind turbines and the difficulty of high-temperature preheating for in-service repairs in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of in-service repair and reinforcement of wind turbine equipment, specifically relating to a welding repair and reinforcement process for cracks in the main frame of a wind turbine. Background Technology

[0002] As the main load-bearing component of a wind turbine generator, the main frame must simultaneously withstand the weight of the generator, gearbox, and wind turbine blades, as well as the complex and variable wind forces in the environment, resulting in harsh operating conditions. Under prolonged alternating loads, the main frame is prone to fatigue cracks, seriously threatening the safe operation of the wind turbine. If not addressed promptly, these cracks will rapidly propagate under external forces, potentially leading to tower collapse. Therefore, timely repair and reinforcement of the main frame cracks are essential. The main frame is primarily made of ultra-low temperature high-toughness ductile iron, such as QT400-18. This type of material possesses good low-temperature toughness and room-temperature mechanical properties, but as a cast iron component, it is prone to defects such as shrinkage porosity, sand holes, insufficient filler, and microcracks during casting and subsequent machining. During use, complex stresses can cause macroscopic cracks to appear in critical stress areas of the workpiece. There are three main methods for welding repair and reinforcement of ductile iron in the existing technology: (1) Hot welding: The workpiece is preheated to 700°C before welding, and the temperature is maintained during the welding process until the welding is completed. After welding, the temperature is slowly reduced. The advantage of this method is that the welding stress is small and cracks are not easy to occur. The disadvantage is that it is difficult to operate under in-service conditions; (2) Semi-hot welding: The casting is preheated to 300~400°C in whole or in part, and the temperature is maintained during the welding process. The advantage of this method is that it improves the difficulty of welding construction, but the white iron area is large and the weld has poor crack resistance; (3) Cold welding: A special process is used without high temperature conditions. The disadvantage is that the welding heating and cooling speed is fast and welding cracks are easy to occur. However, since no preheating is required, it is suitable for welding and repairing key parts of castings of in-service units such as wind power. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problems existing in the prior art and to provide a heterogeneous welding repair and reinforcement process for cracks in the main frame of a wind turbine, which reduces the construction difficulty and facilitates in-service construction while ensuring the quality of crack repair in the main frame of the wind turbine.

[0004] The specific plan is as follows:

[0005] A welding repair and reinforcement process for cracks in the main frame of a wind turbine generator includes the following steps:

[0006] S1, Defect detection: Using penetrant testing and ultrasonic testing methods, the length, depth, and trend of defects in the main frame 10 are determined.

[0007] S2, a V-shaped bevel is used for the defective part of the wind turbine frame in the unobstructed position; a single V-shaped bevel is used for the position of the wind turbine frame with obstruction 20, and the opening angle a of the V-shaped bevel is 40-50°; a Φ5mm crack-stopping hole 12 is drilled at a distance d along the direction of crack extension.

[0008] S3. Before welding, the welding rod should be preheated to 200°C for more than 4 hours. The workpiece should be preheated before welding, and the workpiece temperature should be controlled between 40°C and 70°C. The workpiece should be kept dry and free of oil before welding. The V-shaped bevel position after grinding should be wiped with anhydrous propanol.

[0009] S4. When the welding depth f of the V-groove is greater than 20mm, nickel-based cast iron welding rods are used to perform multi-layer, multi-pass welding of the root and V-groove. When welding in the flat position, a backing plate 16 consistent with the body should be set at the root. The welding thickness e on the body side of the nickel-based cast iron welding rod is ≥7mm. The attached drawing of the nickel-based cast iron welding layer is marked as 15. At least one layer of the final cover is welded with nickel-based cast iron welding rods, and the remaining parts are welded with fine-grained steel welding rods. The attached drawing of the fine-grained steel welding layer is marked as 14.

[0010] If the welding depth f of the V-groove is less than 20mm, nickel-based cast iron welding rods should be used for all welding.

[0011] Welding method: manual electric arc welding, DC reverse polarity, welding speed 140~180 mm / min, interpass temperature 40~70 ℃, welding current for the root and intermediate layers 60~100 A, welding current for the top layer 80~110 A;

[0012] After welding, post-heat treatment at a temperature of 180~200 degrees Celsius should be carried out for no less than 8 hours.

[0013] In step S1, if the crack 11 of the defect penetrates through the root, a gap of 2-4mm needs to be reserved, and a processing pad 16 of the same material as the main frame needs to be added at the root. The thickness of this pad is usually 3-5mm.

[0014] In step S4, the welding sequence for the V-groove is as follows:

[0015] The lowest point of the space corresponding to layer 14 is shown in the attached diagram as area marked "1".

[0016] S42. Welding begins at the lowest point of the fine-grained steel weld layer 14;

[0017] S43. Welding begins at the lowest point of the nickel-based cast iron weld layer 15;

[0018] S44. Welding begins at the lowest point of the fine-grained steel weld layer 14;

[0019] S45. Welding begins at the lowest point of the nickel-based cast iron weld layer 15.

[0020] S46. Welding begins at the lowest point of the fine-grained steel weld layer 14;

[0021] S47. Begin welding the nickel-based cast iron layer 15 at the outermost part of the fine-grained steel weld layer 14.

[0022] In step S4, multi-segment welding is used during welding. Stress is relieved by hammering the weld layer. At this time, the workpiece temperature should be controlled to keep the temperature difference between weld layers within ±10℃.

[0023] In step S4, during reinforcement welding, reinforcement plate 30 is welded to the outside of the weld at the V-groove on the reinforcement plate. The direction of reinforcement plate 30 is perpendicular to the V-groove. Nickel-based cast iron welding rods should be used at the connection position between the V-groove and the workpiece. After the welding surface is flush, dissimilar steels are welded using a process with a fusion ratio of not less than 30%. The weld leg height k of the reinforcement welding is not less than 10mm. If the lap length n of the reinforcement section connected to reinforcement plate 30 is less than 1.5 times the weld cross-sectional width m, then the weld reinforcement height is not less than 13mm.

[0024] The reinforcing plate was welded to the part that cracked first;

[0025] The inner side of the weld between the reinforcing plate 30 and the body is filled with CHE507Ni welding, and the outer side is filled with WE777 welding.

[0026] Beneficial effects: Compared with the prior art, the present invention reduces welding stress and improves welding quality by grinding V-shaped bevels and drilling crack-stopping holes, and by optimizing welding interpass temperature, welding heat input and welding materials on the basis of appropriate preheating. This solves the problem of high welding crack tendency of cast iron parts of wind turbine main frame and difficulty in high-temperature preheating for in-service repair. Attached Figure Description

[0027] Figure 1 This is a schematic diagram A of the V-shaped bevel at the defect repair location of the present invention.

[0028] Figure 2 This is a schematic diagram (B) of the V-shaped bevel at the defect repair location of the present invention.

[0029] Figure 3 This is a schematic diagram of the anti-crack hole.

[0030] Figure 4 This is a schematic diagram of heterogeneous welding filler.

[0031] Figure 5 This is a schematic diagram of the filling sequence for heterogeneous welding.

[0032] Figure 6 This is a schematic diagram of the reinforcement structure. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will now be clearly and completely described with reference to the accompanying drawings.

[0034] like Figure 1-6 A welding repair and reinforcement process for cracks in the main frame of a wind turbine includes the following steps:

[0035] S1, Defect detection: Using penetrant testing and ultrasonic testing methods, the length, depth, and trend of defects in the main frame 10 are determined.

[0036] S2, based on the defect location and the actual working conditions at the repair site, combined with experimental data, a V-shaped bevel (e.g., ...) is applied to the defective part of the wind turbine frame in an unobstructed location. Figure 2 For locations where there are obstacles to the wind turbine frame, a single V-shaped bevel should be used (e.g., ...). Figure 1 The opening angle α of the V-shaped bevel is 40-50°.

[0037] like Figure 4 If the defective crack 11 penetrates to the root, a gap of 2-4mm needs to be reserved, and a processing pad 16 of the same material as the main frame needs to be added to the root. The thickness of this pad is usually 3-5mm.

[0038] like Figure 3 Based on the inspection results of the V-groove, drill a Φ5mm anti-crack hole 12 at a distance d (e.g., 10mm) ahead of the crack extension direction.

[0039] S3. Before welding, the welding rod should be preheated to 200°C for more than 4 hours. The workpiece should be preheated before welding, and the workpiece temperature should be controlled between 40°C and 70°C. The workpiece should be kept dry and free of oil before welding. If necessary, the ground V-groove area should be wiped with anhydrous propane.

[0040] S4, see appendix Figure 4 When the welding depth f of the V-groove is greater than 20mm, nickel-based cast iron electrodes should be used for multi-layer, multi-pass welding of the root and V-groove. For flat welding, a backing plate 16 consistent with the body should be placed at the root. The thickness e of the nickel-based cast iron electrode body side welding (surfacing) should be ≥7mm. The attached drawing of the nickel-based cast iron weld layer is denoted as 15. At least one layer of the final cover layer should be welded with nickel-based cast iron electrodes, and the remaining parts should use fine-grained steel electrodes. The attached drawing of the fine-grained steel weld layer is denoted as 14. If the welding depth f is less than 20mm, all welding should be done with nickel-based cast iron electrodes. The welding method is manual arc welding, DC reverse polarity, welding speed 140~180 mm / min, interpass temperature 40~70 ℃, welding current for the root and intermediate layers 60~100 A, and welding current for the top layer 80~110 A. After welding, a post-heat treatment at 180~200 degrees Celsius should be performed for no less than 8 hours.

[0041] The welding sequence for the V-groove is as follows:

[0042] S41. Welding begins at the lowest point of the nickel-based cast iron weld layer 15 until the height of the weld zone is greater than the lowest point of the corresponding space of the fine-grained steel weld layer 14, see area marked "1" in the attached figure.

[0043] S42. Welding begins at the lowest point of the fine-grained steel weld layer 14, see area marked "2" in the attached figure;

[0044] S43. Welding begins at the lowest point of the nickel-based cast iron weld layer 15, see area marked "3" in the attached figure;

[0045] S44. Welding begins at the lowest point of the fine-grained steel weld layer 14, see area marked "4" in the attached figure;

[0046] S45. Welding begins at the lowest point of the nickel-based cast iron weld layer 15, see area marked "5" in the attached figure;

[0047] S46. Welding begins at the lowest point of the fine-grained steel weld layer 14, see area marked "6" in the attached figure;

[0048] S47. Begin welding the nickel-based cast iron layer 15 at the outermost part of the fine-grained steel weld layer 14, see area marked "7" in the attached figure.

[0049] During welding, multi-segment welding should be used if necessary (the welding length is determined according to the specific temperature, preferably 30~50mm). Due to the large size of the workpiece and good heat dissipation, the welding layer (the first layer at the root must not be hammered) should be hammered to remove stress. At this time, the workpiece temperature should be controlled, and the temperature difference between welding layers should be controlled within ±10℃. Strict control of heat input should be exercised to reduce the internal stress generated by the cooling and shrinkage of the molten pool.

[0050] like Figure 6 Furthermore, during reinforcement welding, a reinforcement plate 30 is welded to the outside of the weld at the V-groove on the reinforcement plate (see attached reference numeral 19). The reinforcement plate 30 is perpendicular to the direction of the V-groove. Nickel-based cast iron welding rods should be used at the connection between the V-groove and the workpiece. After the welding surfaces are flush, dissimilar steels are welded using a fusion ratio of not less than 30%. The weld leg height k of the reinforcement weld is not less than 10mm. If the weld cross-section is affected by the structure, and the lap length n of the reinforcement section connecting to the reinforcement plate 30 is less than 1.5 times the weld cross-section width m, then the weld reinforcement height is not less than 13mm. The reinforcement plate is welded to the location where cracking first occurs.

[0051] like Figure 6 The inner side of the weld between the reinforcing plate 30 and the body (see reference numeral 191) is filled with CHE507Ni welding, and the outer side (see reference numeral 192) is filled with WE777 welding.

[0052] If defects need to be removed during the entire welding process, a grinding wheel should be used; the use of electric alloy steel ball heads or alloy files is strictly prohibited. Fine-grained steel welding electrodes are strictly prohibited from being used on the weld body during the welding process.

[0053] Penetrant testing and ultrasonic testing were conducted 24 hours after welding. The acceptance criteria were as follows: the main body weld was accepted according to NB / T47013.5 and NB / T47013.3, both of which required Class I qualification; the reinforcement weld was accepted according to NB / T47013.5, with Class I qualification.

[0054] Under confidential conditions, the experiment was conducted on the main frame of wind turbines #25 and #29 in a certain wind farm. The overall cost was low, the repair success rate was 100%, and the results were satisfactory after one year of operation.

[0055] The experimental data are as follows:

[0056] A set of welding specimens for a pair of workpieces (400mm × 200mm), made of QT400-18 steel with a thickness of 30mm, are presented. The specimens are made of solid ductile iron and the bevel pattern is shown in the attached diagram (e.g., ...). Figure 1 Welding was performed using WE777 and CHE507Ni welding electrodes, following the welding process parameters in Table 1. UT and PT inspections were conducted 24 hours and 48 hours after welding, and no defects were found.

[0057] Table 1 Welding Repair and Reinforcement Process Parameters

[0058]

[0059] After welding, mechanical specimens were prepared according to NB / T 47014-2011 standard. The average data for the two groups of body tests were: tensile strength 412.7 MPa, elongation after fracture 24.3%, impact energy (0°) 48.2 J, and impact energy (-40°) 12.4 J. The average data for the two groups of machined welded specimens were: 418.4 MPa (base metal at fracture), elongation after fracture 22.4%, impact energy (0°) 44.1 J, 62.4 J (weld, heat-affected zone), and impact energy (-40°) 10.6 J, 18.4 J (weld, heat-affected zone). The experimental data indicate that the mechanical properties of the welded joint specimen are no less than those of the base metal.

[0060] The principle of this invention is to reduce welding stress by optimizing the interpass temperature, welding heat input and welding materials, so as to ensure the quality of welding repair at a lower preheating temperature, reduce the construction difficulty, and enable all-position welding of cracked parts of the wind turbine main frame.

[0061] Other details are available in existing technologies and will not be elaborated further.

[0062] The technical means disclosed in this invention are not limited to those disclosed in the above embodiments, but also include technical solutions composed of any combination of the above technical features. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications are also considered within the scope of protection of this invention.

Claims

1. A welding repair and reinforcement process for cracks in the main frame of a wind turbine generator, characterized in that: The steps include: S1, Defect Detection: Using penetrant testing and ultrasonic testing methods, the length, depth, and trend of defects in the main frame are determined. S2, for unobstructed defects on the wind turbine frame, use a V-shaped bevel; for obstructed areas on the wind turbine frame, use a single V-shaped bevel, with an opening angle a of 40-50°; drill a Φ5mm anti-crack hole at a distance d along the crack extension direction. S3. Before welding, the welding rod should be preheated to 200°C for more than 4 hours. The workpiece should be preheated before welding, and the workpiece temperature should be controlled between 40°C and 70°C. The workpiece should be kept dry and free of oil before welding. The V-shaped bevel position after grinding should be wiped with anhydrous propanol. S4. When the welding depth f of the V-groove is greater than 20mm, nickel-based cast iron welding rods are used to perform multi-layer and multi-pass welding of the root and V-groove. When welding in the flat position, a backing plate consistent with the body should be set at the root. The welding thickness e on the body side of the nickel-based cast iron welding rod is ≥7mm. At least one layer of the final cover is welded with nickel-based cast iron welding rods, and the rest uses fine-grained steel welding rods. If the welding depth f of the V-groove is less than 20mm, nickel-based cast iron welding rods should be used for all welding. Welding method: manual electric arc welding, DC reverse polarity, welding speed 140~180 mm / min, interpass temperature 40~70 ℃, welding current for root and intermediate layers 60~100 A, welding current for cover layer 80~110 A; After welding, a heat treatment at 180-200 degrees Celsius should be performed for no less than 8 hours. In step S1, if the crack of the defect penetrates through the root, a gap of 2-4mm needs to be reserved, and a processing pad of the same material as the main frame needs to be added at the root. The thickness of the pad is usually 3-5mm. In step S4, during reinforcement welding, a reinforcement plate is welded to the outside of the weld at the V-groove on the reinforcement plate. The reinforcement plate is perpendicular to the direction of the V-groove. Nickel-based cast iron welding rods should be used at the connection position between the V-groove and the workpiece. After the welding surfaces are flush, dissimilar steels are welded using a process with a fusion ratio of not less than 30%. The weld leg height k of the reinforcement welding is not less than 10mm. If the lap length n of the reinforcement section connecting the reinforcement plate is less than 1.5 times the weld cross-sectional width m, then the weld reinforcement height is not less than 13mm. The reinforcing plate was welded to the part that cracked first; The inner side of the weld between the reinforcing plate and the main body is filled with CHE507Ni welding, and the outer side is filled with WE777 welding.

2. The welding repair and reinforcement process for cracks in the main frame of a wind turbine generator according to claim 1, characterized in that: In step S4, the welding sequence for the V-groove is as follows: S41. Welding begins at the lowest point of the nickel-based cast iron weld layer until the height of the weld zone is greater than the lowest point of the corresponding space of the fine-grained steel weld layer. S42. Welding begins at the lowest point of the weld layer in fine-grained steel. S43. Welding begins at the lowest point of the nickel-based cast iron weld layer; S44. Welding begins at the lowest point of the weld layer in fine-grained steel. S45. Welding begins at the lowest point of the nickel-based cast iron weld layer; S46. Welding begins at the lowest point of the weld layer in fine-grained steel. S47. Begin welding the nickel-based cast iron layer at the outermost part of the fine-grained steel weld layer.

3. The welding repair and reinforcement process for cracks in the main frame of a wind turbine generator according to claim 1, characterized in that: In step S4, multi-segment welding is used during welding. Stress is relieved by hammering the weld layer. At this time, the workpiece temperature should be controlled to keep the temperature difference between weld layers within ±10℃.

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