A welding process for offshore wind power pipe pile ultra-high strength steel thick steel plate

Abstract

The present application belongs to the technical field of offshore wind power pipe pile manufacturing, and particularly relates to a welding process for offshore wind power pipe pile ultra-high-strength steel thick steel plate, which controls the process by designing a reasonable groove form and adopting flux-cored wire arc welding (FCAW) + automatic submerged arc welding (SAW) welding process to guarantee the welding quality of thick plate high-strength steel. The present application adopts a composite process of flux-cored wire arc welding and automatic submerged arc welding, FCAW is used for positioning welding and backing welding, the arc is stable, the forming is beautiful, and the operation is convenient; SAW is used for filling and surfacing, the weld quality is stable, there is no smoke dust, the labor conditions are good, the welding efficiency is high, and it is suitable for the demand of ultra-thick plate large filling amount. The K-type asymmetric groove is suitable for the characteristics of S460ML high-strength steel thick plate, reduces the welding stress concentration, reduces the crack tendency, and guarantees the full-thickness fusion quality.

Description

Technical Field

[0001] This invention belongs to the field of offshore wind power pipe pile manufacturing technology, specifically relating to a welding process for ultra-high strength steel thick steel plates for offshore wind power pipe piles. Background Technology

[0002] With the continuous development of offshore wind power, the industry is gradually transitioning from shallow to deep sea areas. The megawattage of offshore wind turbines is also increasing, and as the main supporting structure, the steel plates used in the pipe piles are becoming increasingly thick, placing higher demands on the steel. Offshore wind turbine pipe piles are a typical large-scale welded engineering structure, characterized by its complex structure, large base material thickness, and high welding requirements. To cope with complex sea conditions, a portion of the pipe pile's base material uses super high-strength steel (according to the authoritative marine engineering structure manufacturing standard DNV-OS-C401, its yield strength exceeds 420MPa, classifying it as super high-strength steel), grade S460ML, with a thickness exceeding 100mm.

[0003] For welding super high-strength steel thick plates, the large filler volume and high stress accumulation make them prone to defects such as cracks. To reduce the stress generated during welding and the resulting cracks, most thick plates undergo post-weld heat treatment after prefabrication. In recent years, with the development of fracture mechanics, evaluation methods based on fracture mechanics assessment (CTOD test) have been applied in marine engineering. These methods can replace post-weld heat treatment in construction, greatly reducing production time and costs.

[0004] In actual industrial production, the continuous welding of ultra-high strength steel thick plates involves a large volume of work. The welding thermal cycle easily leads to the deterioration of the metallographic structure and the decline of mechanical properties of the weld joint, generating high residual welding stress. In severe cases, this can cause cracking and failure of the weld and heat-affected zone, making the weld joint a weak link in the overall structure of the pipe pile. Therefore, optimizing the welding process of high-strength steel thick plates, stabilizing and controlling welding quality, and improving the low-temperature impact toughness and fracture resistance of the weld joint are important factors in improving the overall structural stability, durability, and service safety of offshore wind turbine pipe piles, and ensuring the safe operation of offshore wind turbine units. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of large welding volume of thick steel plates, deterioration of weld joint microstructure and properties, excessive welding residual stress, easy cracking defects, resulting in the welded area of ​​the pipe pile becoming a weak part of the structure, insufficient low-temperature fracture toughness, and difficulty in meeting the safe operation requirements of offshore wind turbine units. The invention provides a welding process for ultra-high strength steel thick steel plates for offshore wind turbine pipe piles.

[0006] This invention is achieved through the following technical solution: A welding process for ultra-high strength steel plates for offshore wind turbine pipe piles is described. This process involves designing a reasonable bevel shape and employing flux-cored wire arc welding (FCAW) combined with automatic submerged arc welding (SAW) to control the process. The specific steps are as follows: a. For welding of ultra-high strength steel plates of European standard EN10025-4S460ML with a thickness of T=110mm, the processing bevel type is K, the bevel angle is 40° / 50°, the bevel depth is T1=63mm on one side and T2=45mm on the other side, and the blunt edge dimension is 2mm. b. Grind the bevel and the area within 25mm around it to remove oxide scale and impurities; c. Test piece assembly: The assembly gap is 2mm. The positioning welding is performed using flux-cored wire arc welding (FCAW). The preheating temperature for positioning welding is not lower than 100℃. d. Root pass welding: Use flux-cored wire arc welding (FCAW) for the root pass welding, keep the preheating temperature not lower than 100℃, and use a welding wire with a diameter of 1.2mm. e. Automatic Submerged Arc Welding (SAW): When using automatic submerged arc welding for filler and capping, first bake the flux at a temperature of 300-350℃ for 1 hour, and then heat the test plate with a flame to a temperature of not less than 100℃. The preheating temperature and interpass temperature are controlled at 100-250℃. f. After welding one side of the bevel (40° side), perform carbon arc gouging to clean the root on the other side of the bevel (50° side). The preheating temperature during gouging should not be lower than 100°. g. Grind the area after air gouging; h. After grinding, use automatic submerged arc welding (SAW) to fill and cover the surface until the welding is complete; i. After welding, cover the weld with rock wool to allow it to cool slowly and evenly to room temperature.

[0007] As a further technical solution of the present invention, the welding parameters for flux-cored wire arc welding (FCAW) are: current 200A~240A, voltage 26V~28V, and speed 280mm / min~320mm / min.

[0008] As a further technical solution of the present invention, the automatic submerged arc welding (SAW) welding parameters are: current 550A~650A, voltage 28V~33V, and speed 380mm / min~420mm / min.

[0009] As a further technical solution of the present invention, the welding position of the root pass welding is at the flat weld (PA) position, and the thickness of the root pass weld is ≥5mm.

[0010] As a further technical solution of the present invention, the preheating temperature and interlayer temperature are measured at a distance of 75mm from the bevel, using a contact thermometer or an infrared thermometer gun, and the temperature is measured on the back side of the heating side.

[0011] As a further technical solution of the present invention, the interlayer needs to be cleaned during the welding process to remove oxide scale, keep the pre-welding clean, and ensure good fusion between layers.

[0012] As a further technical solution of the present invention, after welding is completed, non-destructive testing is performed on the weld, and mechanical property testing is carried out on the welded joint in accordance with the DNV-OS-C401 standard.

[0013] As a further technical solution of the present invention, fracture mechanics evaluation (CTOD test) is performed on the welded joint. The CTOD test uses full thickness sampling to cover the weld zone and the heat-affected zone.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention employs a composite process of flux-cored wire arc welding (FCAW) and submerged arc welding (SAW). FCAW is used for tack welding and root pass welding, resulting in a stable arc, aesthetically pleasing weld formation, and convenient operation. SAW is used for filler and cover pass welding, resulting in stable weld quality, no smoke or dust, good working conditions, and high welding efficiency, making it suitable for the large filler requirements of ultra-thick plates.

[0015] 2. In this invention, the K-type asymmetric bevel is adapted to the characteristics of S460ML high-strength steel thick plates, reducing welding stress concentration, reducing crack tendency, and ensuring full-thickness fusion quality.

[0016] 3. This invention uses conventional mechanical properties and CTOD fracture mechanics assessment as the core acceptance methods, replacing traditional post-weld heat treatment, significantly shortening the production cycle and reducing manufacturing costs. The weld and heat-affected zone exhibit excellent crack resistance and fatigue performance. Attached Figure Description

[0017] Figure 1 Schematic diagram of the beveling and assembly process for welding S460ML high-strength steel thick plates; Figure 2 : Schematic diagram of welding on the first side (40° bevel side); Figure 3 : Schematic diagram of welding on the second side (50° bevel side). Detailed Implementation

[0018] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below. Example 1

[0020] like Figure 1-3 As shown, the base material and bevel are made of EN10025-4S460ML steel plate with a thickness of T=110mm. It is machined into a K-type bevel: one side has a bevel angle of 40° and a bevel depth T1=63mm; the other side has a bevel angle of 50° and a bevel depth T2=45mm; the blunt edge is 2mm. The bevel and the surrounding 25mm are ground to remove rust, oil, and oxide scale.

[0021] The assembly gap between the assembly and tack welding is 2mm. FCAW tack welding is used, with a preheating temperature of 120℃. Welding parameters: current 220A, voltage 27V, welding speed 300mm / min. Tack weld length ≥50mm, spacing 200mm, to ensure dimensional stability of the assembly.

[0022] For the root pass, use a 1.2mm diameter welding wire, flat welding position (PA), and preheat to 120℃. Parameters: current 220A, voltage 27V, speed 300mm / min. The root pass should be 6mm thick to ensure root penetration and strength.

[0023] Automatic submerged arc welding (SAW) is used for filler and cover passes, with flux baked at 350℃ for 1 hour. Preheating is 120℃, interpass temperature is 150–200℃, and the temperature measurement point is 75mm from the bevel, measured on the back side of the heating process. Parameters: current 600A, voltage 30V, speed 400mm / min. Oxide scale is removed after each pass to ensure good interpass fusion.

[0024] Carbon arc gouging for root cleaning and reverse welding: First, complete the 40° side welding; for the 50° side, perform carbon arc gouging for root cleaning, preheating to 120°C before gouging. After root cleaning, grind until the metal luster is exposed, then use SAW to complete the reverse filling and capping. Immediately after welding, cover completely with rock wool and allow to cool slowly to room temperature.

[0025] Then, the weld was subjected to non-destructive testing (48 hours post-weld), mechanical property testing, and fracture mechanics assessment (CTOD test). Mechanical property testing was conducted according to DNV-OS-C401 standards, including tests for side bending, transverse tensile strength, low-temperature impact, macroscopic properties, and hardness. For the side bending test, a 50mm diameter indenter was used to bend the weld joint specimen to 180°, and the surface of the specimen was checked for cracks. The low-temperature impact test was conducted at -50℃, requiring an impact energy ≥50J. In the CTOD test, the entire thickness was used as the CTOD specimen thickness, effectively overcoming the shortcomings of "thin plate sampling and layered sampling." In the actual test, CTOD specimens were taken from the weld and heat-affected zone of the weld test plate, and tests were conducted separately, with three specimens taken from each area. Example 2

[0026] The base material and bevel are made of EN10025-4S460ML steel plate with a thickness of T=110mm. The K-type bevel parameters remain unchanged, and the bevel area is ground clean.

[0027] The assembly and tack welding gap is 2mm. FCAW tack welding, preheated to 150℃. Parameters: current 240A, voltage 28V, speed 320mm / min.

[0028] For the root pass (FCAW), preheat to 150℃, use 1.2mm diameter welding wire, and position PA. Parameters: current 240A, voltage 28V, speed 320mm / min. Root pass thickness 7mm.

[0029] Submerged arc welding (SAW) filler / cap coat flux is baked at 300℃ for 1 hour. Preheating temperature is 150℃, and interpass temperature is 180–250℃. Parameters: current 650A, voltage 33V, speed 420mm / min. Strict slag removal is required between passes.

[0030] Carbon arc gouging and reverse welding are performed with root cleaning preheating at 150°C, followed by grinding and SAW welding until completion.

[0031] Immediately after welding, cover the entire area with rock wool and allow it to cool slowly to room temperature.

[0032] Then, the weld was subjected to non-destructive testing, mechanical property testing, and fracture mechanics evaluation (CTOD test) according to the method in Example 1. Example 3

[0033] The base material and bevel are made of EN10025-4S460ML steel plate with a thickness of T=110mm. The K-type bevel parameters remain unchanged, and the bevel area is ground clean.

[0034] The gap between assembly and tack welding is 2mm. FCAW positioning, preheated to 100℃. Parameters: current 200A, voltage 26V, speed 280mm / min.

[0035] For the root pass (FCAW), preheat to 100℃, use 1.2mm diameter welding wire, and position PA. Parameters: current 200A, voltage 26V, speed 280mm / min. Root pass thickness 5mm.

[0036] Submerged arc welding filler / cap coat flux baked at 330℃ for 1 hour. Preheating temperature 100℃, interpass temperature 100–180℃. Parameters: current 550A, voltage 28V, speed 380mm / min.

[0037] Carbon arc gouging and reverse welding gouging are preheated to 100℃. After root cleaning and grinding, SAW welding is completed across the entire cross-section. Immediately after welding, the entire surface is covered with rock wool and allowed to cool slowly to room temperature.

[0038] Then, the weld was subjected to non-destructive testing, mechanical property testing, and fracture mechanics evaluation (CTOD test) according to the method in Example 1.

[0039] The detection results of Examples 1-3 are as follows:

[0040] As shown in the table above, the non-destructive testing, mechanical properties, and fracture mechanics evaluation results of the three sets of embodiments of the present invention comprehensively verify the reliability and technological superiority of the welded joints. Non-destructive testing shows that after 48 hours post-weld, visual inspection, magnetic particle testing, and ultrasonic testing revealed no harmful defects such as cracks, lack of fusion, porosity, or slag inclusions, indicating stable weld formation and internal quality.

[0041] In terms of mechanical properties, the joint exhibited excellent plasticity after being bent 180° with a 50mm indenter in a side bending test. The transverse tensile strength ranged from 504MPa to 531MPa, all exceeding the standard requirement of 490MPa, and the joint strength met the design specifications of the S460ML base material. The impact energy at -50℃ was significantly greater than 50J, with excellent impact performance in the weld center, fusion line, fusion line +2mm, and root region. The joint also demonstrated sufficient low-temperature toughness, making it suitable for harsh marine environments. Macroscopic testing revealed good fusion between the weld and the heat-affected zone, resulting in a dense microstructure. The HV10 hardness value ranged from 174 to 245, far below the upper limit of 420HV10, indicating no hard or brittle microstructure and reliable crack resistance.

[0042] The CTOD test, conducted at -10℃ with full-thickness sampling, showed that the weld and heat-affected zone values ​​were both ≥0.25mm, indicating that the fracture toughness met the standard and could effectively replace post-weld heat treatment. Overall results demonstrate that the FCAW+SAW composite process, K-groove design, and full-process temperature control employed in this invention ensure that the joint strength, plasticity, low-temperature toughness, hardness, and fracture resistance fully meet the DNV-OS-C401 standard. This guarantees the long-term safe operation of offshore wind turbine piles while eliminating the need for post-weld heat treatment, significantly improving efficiency and reducing costs.

Claims

1. A welding process for ultra-high strength steel thick plates for offshore wind power pipe piles, characterized in that, By designing a reasonable bevel shape, and employing a flux-cored wire arc welding (FCAW) + automatic submerged arc welding (SAW) welding process, the process is controlled. The specific steps are as follows: a. For welding of ultra-high strength steel plates of European standard EN10025-4S460ML with a thickness of T=110mm, the process is to fabricate a K-type bevel: one side bevel angle is 40°, bevel depth T1=63mm; the other side bevel angle is 50°, bevel depth T2=45mm; and the blunt edge is 2mm. b. Grind the bevel and the area within 25mm around it to remove oxide scale and impurities; c. Test piece assembly: The assembly gap is 2mm. Use flux-cored wire arc welding (FCAW) for tack welding. The tack welding preheating temperature is not lower than 100℃. d. Root pass welding: Use flux-cored wire arc welding (FCAW) for the root pass welding, maintaining a preheating temperature of not less than 100℃. The diameter of the welding wire used for the root pass welding is 1.2mm. FCAW welding parameters: current 200A~240A, voltage 26V~28V, speed 280mm / min~320mm / min. e. Automatic Submerged Arc Welding (SAW): For filling and capping welding, first bake the flux at 300-350℃ for 1 hour. For the welding test plate, heat it with a flame to a temperature not lower than 100℃. The preheating temperature and interpass temperature are controlled at 100-250℃. Automatic submerged arc welding (SAW) welding parameters: current 550A~650A, voltage 28V~33V, speed 380mm / min~420mm / min. f. After welding one side of the 40° bevel, then perform carbon arc gouging on the other side of the 50° bevel. The preheating temperature during gouging should not be lower than 100°. g. Grind the area after air gouging; h. After grinding, use an automatic submerged arc welding (SAW) machine to fill and cover the surface until welding is complete; i. After welding, cover the weld with rock wool to allow it to cool slowly and evenly to room temperature.

2. The welding process of ultra-high strength steel thick steel plate for offshore wind power pipe piles as described in claim 1, characterized in that, The welding position for the root pass is at the PA position of the flat weld, and the thickness of the root pass weld is ≥5mm.

3. The welding process of ultra-high strength steel thick steel plate for offshore wind power pipe piles as described in claim 1, characterized in that, The preheating temperature and interlayer temperature are measured within 75mm of the bevel, using a contact thermometer or infrared thermometer, and the temperature is measured on the back side of the heating side.

4. The welding process of ultra-high strength steel thick steel plate for offshore wind power pipe piles as described in claim 1, characterized in that, During the welding process, it is necessary to clean between layers, remove oxide scale, keep the area clean before welding, and ensure good fusion between layers.

5. The welding process of ultra-high strength steel thick steel plate for offshore wind power pipe piles as described in claim 1, characterized in that, After welding is completed, non-destructive testing is performed on the weld, and mechanical property testing is carried out on the welded joint in accordance with DNV-OS-C401 standard.

6. The welding process of ultra-high strength steel thick steel plate for offshore wind power pipe piles as described in claim 1, characterized in that, Fracture mechanics assessment of the welded joint was performed using the CTOD test, which involved full-thickness sampling covering both the weld zone and the heat-affected zone.

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