Offshore converter station jacket and LMU folding welding construction process

Abstract

The invention relates to an offshore converter station jacket and LMU folding welding construction process. The method comprises the steps of groove arrangement, wherein the groove of the cylinder wall of the lower end of an LMU is 30 degrees, and the groove of the cylinder wall of an upper opening of a jacket is 15 degrees; mounting a liner: pre-mounting the steel liner on the inner side of the cylinder wall at the lower end of the LMU; wedge-shaped cushion blocks are welded on the cylinder wall of the upper opening of the jacket at intervals; hoisting: enabling the cylinder wall of the lower end of the hoisted LMU and the cylinder wall of the upper opening of the jacket to form a qualified butt joint through the matching of a guide block and a steel liner; fixing the code plate; preheating is conducted, and multi-layer and multi-pass welding is adopted for groove welding seams; and detecting. The method has the advantages that the risk of incomplete fusion of a lower groove is reduced by selecting the groove angle with the large upper part and the small lower part; the steel liner is adopted to facilitate fusion of the root of a welding seam, the welding difficulty of single-face welding and double-face forming is reduced, butt joint is more accurate, the wedge-shaped cushion block is adopted to facilitate high-precision control over hoisting assembly gaps, and high-precision assembly and high-quality welding are completed.

Description

Technical Field

[0001] This invention relates to the field of merging the jacket of an offshore converter station with the LMU, and specifically to a welding construction process for merging the jacket of an offshore converter station with the LMU. Background Technology

[0002] With the large-scale development of offshore wind power in my country, the output of offshore wind power is becoming increasingly important, and its investment share is also increasing. Offshore wind power output generally has two options: AC and DC. AC output requires the construction of offshore booster stations, while DC output requires the construction of offshore converter stations.

[0003] The LMU (Leg Coupling Unit) is a crucial component connecting the jacket structure and superstructure of large offshore converter stations. Its assembly with the jacket structure is typically completed at sea. Affected by wind, waves, and tides, the LMU is prone to swaying during hoisting, leading to misalignment. Furthermore, controlling the precise dimensions of the closure joint is difficult, and irregular assembly gaps and excessive misalignment significantly impact welding quality. Additionally, since access to the jacket structure and LMU is impossible, only single-sided welding is possible. The components have significant wall thickness, the welding position is horizontal, and the bevel angle affects the accessibility of the welding torch and the welding field of vision. Full penetration of the weld is required, making the overall welding process quite challenging. The offshore converter station jacket and LMU closure welding construction process provided by this invention achieves high-precision assembly and high-quality welding of the jacket structure and LMU. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a welding construction process for the closure of the jacket and LMU of an offshore converter station. This process can solve the problems in the prior art, such as the easy shaking during the hoisting of the LMU leading to misalignment, the difficulty in controlling the precision of the joint dimensions of the closure seam, the significant impact of irregular assembly gaps and excessive misalignment on welding quality, the impact of the bevel angle of the jacket and LMU on the accessibility of the welding torch, the welding field of vision, and the overall difficulty of welding.

[0005] To solve the above technical problems, the technical solution of the present invention includes the following steps: S1, bevel arrangement: the V-shaped bevel of the lower end cylinder wall of the LMU is set at 30°, and the V-shaped bevel of the upper end cylinder wall of the guide frame is set at 15°; S2. Gasket Installation: During LMU fabrication in the workshop, the steel gasket is pre-installed on the inner side of the lower end cylinder wall of the LMU, and welded continuously around the entire circle. The bottom of the steel gasket extends downwards towards the lower end cylinder wall of the LMU. S3. Pad installation: Weld 6 wedge-shaped pads at intervals on the upper end wall of the guide frame. The 6 wedge-shaped pads are evenly distributed around the entire circumference of the upper end wall of the guide frame. The wedge-shaped pad is set to correspond to the bevel of the upper opening of the guide frame. The inclination angle of the bottom surface of the wedge-shaped pad is 75°. After the wedge-shaped pad is installed with the guide frame, it fills the bevel position to make it a plane. S4. Lifting: After the LMU is ready, the hook is raised and the crane is rotated to the position of the main leg of the jacket frame. The guide block is placed on the outside of the lower end cylinder wall of the LMU and the upper end cylinder wall of the jacket frame. With the cooperation of the steel liner on the inside of the lower end cylinder wall of the LMU, a qualified butt joint is formed between the lower end cylinder wall of the LMU and the upper end cylinder wall of the jacket frame. S5. Mounting plate installation: The LMU and the guide frame are pre-fixed by rectangular mounting plates. The mounting plates are welded to the outer side of the LMU cylinder wall and the guide frame cylinder wall respectively. After the LMU and the guide frame are pre-fixed by welding the mounting plates, the hooks are released. S6. Pre-welding preparation: Non-destructive testing is performed on the entire continuous weld of the steel liner to ensure that the weld is free of any defects; S7. Preheating before welding: Preheating is performed before welding, with a preheating temperature ≥120℃; S8. Welding: Welding is carried out using FCAW method. The bevel weld is multi-layer and multi-pass welding, and the joints of each layer of weld are staggered by 30~50mm. After welding, post-heating is performed immediately, with a post-heating temperature of 180℃~220℃. After heat preservation for at least 1 hour, the weld is covered with insulation cotton to slow cooling. The closed weld is divided into 8 segments, and each segment is welded symmetrically in pairs. The 4 segments of the semicircle are welded alternately. S9. Visual inspection and non-destructive testing.

[0006] Furthermore, in step S3, the wedge-shaped pad is welded to the upper cylinder wall of the guide frame on three sides. After the circumferential seam is welded to 1 / 3 of the plate thickness, it is removed. After removal, the weld is repaired to ensure continuity and pass the flaw detection before the remaining weld is welded. The top of the wedge-shaped pad is 6-8mm higher than the upper cylinder wall of the guide frame.

[0007] Furthermore, in step S5, 15 rectangular code plates of 250mm*800mm*20mm are selected, and the 15 code plates are evenly distributed around the outside of the LMU and the guide frame.

[0008] Furthermore, in step S6, before welding, oxides, moisture, oil stains and impurities within 20mm of the welding bevel and both sides of the edge are cleaned; a stable and safe construction platform is built at the welding point, and strict wind and rain protection measures are taken to avoid excessive wind speed and rain water soaking during the welding process, which would cause the weld to cool too quickly and crack.

[0009] Furthermore, in step S7, preheating is performed using electric heating. A fixed hook is installed on the outer side of the lower end cylinder wall of the LMU, and an electric heating element is installed on the fixed hook. The electric heating element extends to the outer side of the upper end cylinder wall of the lower guide frame. The outer side of the lower end cylinder wall of the LMU and the upper end cylinder wall of the guide frame are preheated by the electric heating element. The preheating width of the upper side of the lower end cylinder wall of the LMU and the lower side of the upper end cylinder wall of the guide frame is ≥150mm.

[0010] Further, in step S8, the welding material selected is low-hydrogen flux-cored wire T554T1-1C1A, and the welding parameters are: DC reverse polarity, current 200-260A, voltage 24-30V, welding speed 200-300mm / min, shielding gas is CO2 with purity ≥99.9% and flow rate 15-25L / min; the minimum interpass temperature is 120℃ and the maximum interpass temperature is 200℃, and all welding is carried out within this temperature range; after each weld is completed, the slag is thoroughly removed, and the weld quality is checked and confirmed to be qualified before starting the next weld; Each section should be welded within one shift. If welding is interrupted due to severe weather, post-heating insulation measures should be taken, and preheating should be carried out again before welding resumes.

[0011] Furthermore, in step S9, visual inspection: the weld surface must not have cracks, porosity, arc craters, or slag inclusions. Non-destructive testing: Ultrasonic testing shall be used, and there shall be no defects exceeding the standard within the effective weld thickness.

[0012] The advantages of this invention are: high-precision assembly and high-quality welding of the offshore converter station jacket and LMU are achieved through reasonable welding process. Due to the thick plate and the fact that only a single-sided V-groove can be used, the selection of a groove angle that is larger at the top and smaller at the bottom helps to reduce the risk of incomplete fusion of the bottom groove during horizontal welding, while avoiding other defects such as porosity and nodules caused by the molten pool falling due to an excessively large bottom groove. Using steel backing is beneficial to the fusion at the root of the weld, reduces the welding difficulty of single-sided welding and double-sided forming, and the steel backing limits the connection between the lower end cylinder wall of the LMU and the upper end cylinder wall of the guide frame, making the connection more precise and avoiding misalignment. Using wedge-shaped pads is beneficial to the high-precision control of the gap of the hoisting assembly, effectively ensuring the quality of the root pass weld. Preheating and post-heat insulation measures can effectively reduce the risk of cold cracking in high-strength steel welding, improve weld quality, and segmented symmetrical welding sequence can effectively reduce welding deformation and stress concentration, thereby improving the fatigue strength of the weld. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the bevel arrangement of the present invention; Figure 2 This is a schematic diagram of the installation of the steel gasket of the present invention; Figure 3 This is a schematic diagram of the wedge-shaped pad structure of the present invention; Figure 4 This is a schematic diagram of the closing joint between the lower end cylinder wall of the LMU and the upper end cylinder wall of the guide frame according to the present invention; Figure 5 This is a schematic diagram showing the distribution of the code plate and wedge-shaped pad on the upper wall of the guide frame according to the present invention; Figure 6 This is a diagram showing the arrangement of the electric heating elements of the present invention; Figure 7 This is a schematic diagram of the welding sequence of the present invention. Detailed Implementation

[0014] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The following embodiments will enable those skilled in the art to more fully understand this invention, but do not limit the invention to the scope of these embodiments.

[0015] This specific implementation adopts the following technical solution: a welding construction process for merging the jacket of an offshore converter station with the LMU, including the following steps: S1. Bevel arrangement: such as Figure 1 As shown, the V-groove of the lower end of the LMU cylinder wall is set at 30°, and the V-groove of the upper end of the jacket is set at 15°. The jacket cylinder wall 1 and the LMU cylinder wall 2 are welded using EH420 high-strength steel as the base material.

[0016] S2. Gasket installation: (e.g.) Figure 2 As shown, when LMU is manufactured in the workshop, the steel liner 3 is pre-installed on the inner side of the lower end cylinder wall of the LMU and welded continuously around the entire circle. The bottom of the steel liner 3 extends downward towards the lower end cylinder wall of the LMU. The pre-installed steel liner 3 in the workshop can be welded in a horizontal or vertical position to improve the welding quality of the first weld at the root of the steel liner 3 and reduce the risk of incomplete fusion when the root of the horizontal weld at the top of the seam is welded at sea.

[0017] S3. Installation of spacers: (e.g., ...) Figure 5 As shown, six wedge-shaped pads 4 are welded at intervals on the upper end wall of the guide frame, and the six wedge-shaped pads 4 are evenly distributed around the entire circumference of the upper end wall of the guide frame. The structure of the wedge-shaped pad 4 is as follows Figure 3 As shown, the wedge-shaped pad 4 is set to correspond to the bevel of the upper opening of the guide frame. The inclination angle of the bottom surface of the wedge-shaped pad 4 is 75°. After the wedge-shaped pad 4 is installed with the guide frame, the bevel position is filled to make a plane. The top of the wedge-shaped pad 4 is 6-8mm higher than the upper opening of the guide frame.

[0018] The wedge-shaped pad 4 is welded to the upper cylinder wall of the jacket on three sides. After the circumferential seam is closed, the entire circumferential seam is welded to 1 / 3 of the plate thickness (the thickness of the jacket and LMU cylinder wall). After the seam is removed, the weld is repaired to ensure continuity and pass the flaw detection before the remaining weld is welded.

[0019] S4. Lifting: After the LMU is ready, the hook is slowly raised. After maintaining a safe distance from the transport ship, the crane rotates to the position of the main leg of the jacket support. The guide block is placed on the outside of the lower end wall of the LMU and the upper end wall of the jacket support. Through the cooperation of the steel liner 3 on the inside of the lower end wall of the LMU, a qualified butt joint is formed between the lower end wall of the LMU and the upper end wall of the jacket support. Figure 4 As shown.

[0020] S5, Plate Installation: (e.g., ...) Figure 5 As shown, the LMU and the jacket are pre-fixed by rectangular code plates 5. Fifteen rectangular code plates 5, each 250mm*800mm*20mm in size, are selected and evenly distributed around the outside of the LMU and the jacket. The top and bottom of the code plates 5 are welded to the outside of the LMU cylinder wall 2 and the jacket cylinder wall 1, respectively. After the LMU and the jacket are pre-fixed by welding the code plates 5, the hooks are released.

[0021] S6. Pre-welding preparation: Non-destructive testing is performed on the entire continuous weld of the steel backing 3 to ensure that the weld is free of any defects; Before welding, clean the weld bevel and the area within 20mm on both sides of the edge to remove oxides, moisture, oil and other impurities. Build a stable and safe working platform at the welding point and take strict measures to prevent wind and rain damage. Avoid excessive wind speed or rain during welding, which could cause the weld to cool too quickly and crack. Welding operations must be carried out in sunny weather; welding is strictly prohibited on windy or rainy days.

[0022] S7. Preheating before welding: Preheating is performed before welding, with a preheating temperature ≥120℃; like Figure 6 As shown, preheating is achieved using electric heating. A fixed hook 6 is installed on the outer side of the lower end cylinder wall of the LMU, and an electric heating element 7 is installed on the fixed hook 6. The electric heating element 7 extends to the outer side of the upper end cylinder wall of the lower guide frame. The electric heating element 7 preheats the outer side of the lower end cylinder wall of the LMU and the upper end cylinder wall of the guide frame. The preheating width of the upper side of the lower end cylinder wall of the LMU and the lower side of the upper end cylinder wall of the guide frame is ≥150mm. If it has been painted, the paint needs to be removed in advance.

[0023] S8. Welding: Welding is carried out using FCAW method. The welding material selected is low-hydrogen flux-cored wire T554T1-1C1A. The welding parameters are: DC reverse polarity, current 200-260A, voltage 24-30V, welding speed 200-300mm / min, shielding gas is CO2 with purity ≥99.9% and flow rate 15-25L / min. The minimum interpass temperature for welding is 120℃, and the maximum interpass temperature is 200℃. All welding is carried out within this temperature range. The bevel weld is made of multiple layers and multiple passes. After each weld is completed, the slag is thoroughly removed and the weld quality is checked and confirmed to be qualified before the next weld is started. The joints of each layer of weld are staggered by 30~50mm. After welding, post-heating is performed immediately, with a post-heating temperature of 180℃~220℃. After heat preservation for at least 1 hour, the weld is covered with insulation cotton to slow down cooling. Welding sequence: Given the weather-related impacts on offshore construction, to ensure weld quality, the closure weld circle needs to be divided into 8 segments, with the 4 segments of each semicircle welded alternately. Figure 7 As shown, the welding is carried out in sections according to the order of ① to ④, with each pair of sections welded symmetrically. Each section should be welded within one shift. If welding is interrupted due to severe weather, post-heating insulation measures should be taken, and preheating should be carried out again before welding resumes.

[0024] S9. Visual inspection and non-destructive testing: Visual inspection: The weld surface shall be free from cracks, porosity, arc craters, and slag inclusions. Non-destructive testing: Ultrasonic testing shall be used, and there shall be no defects exceeding the standard within the effective weld thickness.

[0025] The high-precision assembly and high-quality welding of the jacket and LMU of the offshore converter station were completed by using reasonable welding process. Due to the thickness of the plate, the jacket and LMU could not be accessed. Only single-sided V-groove welding was used. The groove angle of the groove was selected to be larger at the top and smaller at the bottom. This helped to reduce the risk of incomplete fusion of the groove at the bottom when welding in the horizontal position. At the same time, it avoided other defects such as porosity and nodules caused by the molten pool falling due to the groove being too large at the bottom. Using steel backing is beneficial to the fusion at the root of the weld, reduces the welding difficulty of single-sided welding and double-sided forming, and the steel backing limits the connection between the lower end cylinder wall of the LMU and the upper end cylinder wall of the guide frame, making the connection more precise and avoiding misalignment during the hoisting and connection of the LMU. Using wedge-shaped pads is beneficial for the hoisting team to control the joint size of the closure seam with high precision, making it easy to control the precision, effectively ensuring the quality of the root pass weld, and avoiding the impact of irregular assembly gaps and excessive misalignment on the welding quality. Preheating and post-heat insulation measures can effectively reduce the risk of cold cracking in high-strength steel welding, improve weld quality, and segmented symmetrical welding sequence can effectively reduce welding deformation and stress concentration, thereby improving the fatigue strength of the weld.

[0026] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A welding construction process for merging the jacket of an offshore converter station with the LMU, characterized in that: Includes the following steps: S1. Bevel arrangement: The V-bevel of the lower end of the LMU cylinder wall is set at 30°, and the V-bevel of the upper end of the jacket is set at 15°. S2. Gasket Installation: During LMU fabrication in the workshop, the steel gasket is pre-installed on the inner side of the lower end cylinder wall of the LMU, and welded continuously around the entire circle. The bottom of the steel gasket extends downwards towards the lower end cylinder wall of the LMU. S3. Pad installation: Weld 6 wedge-shaped pads at intervals on the upper end wall of the guide frame. The 6 wedge-shaped pads are evenly distributed around the entire circumference of the upper end wall of the guide frame. The wedge-shaped pad is set to correspond to the bevel of the upper opening of the guide frame. The inclination angle of the bottom surface of the wedge-shaped pad is 75°. After the wedge-shaped pad is installed with the guide frame, it fills the bevel position to make it a plane. S4. Lifting: After the LMU is ready, the hook is raised and the crane is rotated to the position of the main leg of the jacket frame. The guide block is placed on the outside of the lower end cylinder wall of the LMU and the upper end cylinder wall of the jacket frame. With the cooperation of the steel liner on the inside of the lower end cylinder wall of the LMU, a qualified butt joint is formed between the lower end cylinder wall of the LMU and the upper end cylinder wall of the jacket frame. S5. Mounting plate installation: The LMU and the guide frame are pre-fixed by rectangular mounting plates. The mounting plates are welded to the outer side of the LMU cylinder wall and the guide frame cylinder wall respectively. After the LMU and the guide frame are pre-fixed by welding the mounting plates, the hooks are released. S6. Pre-welding preparation: Non-destructive testing is performed on the entire continuous weld of the steel liner to ensure that the weld is free of any defects; S7. Preheating before welding: Preheating is performed before welding, with a preheating temperature ≥120℃; S8. Welding: Welding is carried out using FCAW method. The bevel weld is multi-layer and multi-pass welding, and the joints of each layer of weld are staggered by 30~50mm. After welding, post-heating is performed immediately, with a post-heating temperature of 180℃~220℃. After heat preservation for at least 1 hour, the weld is covered with insulation cotton to slow cooling. The closed weld is divided into 8 segments, and each segment is welded symmetrically in pairs. The 4 segments of the semicircle are welded alternately. S9. Visual inspection and non-destructive testing.

2. The construction process for welding the jacket structure and LMU of an offshore converter station according to claim 1, characterized in that: In step S3, the wedge-shaped pad is welded to the upper cylinder wall of the guide frame on three sides. After the circumferential seam is welded to 1 / 3 of the plate thickness, it is removed. After removal, the weld is repaired to ensure continuity and pass the flaw detection before the remaining weld is welded. The top of the wedge-shaped pad protrudes 6-8 mm above the upper opening wall of the guide tube holder.

3. The welding construction process for merging the jacket structure and LMU of an offshore converter station according to claim 1, characterized in that: In step S5, 15 rectangular code plates of 250mm*800mm*20mm are selected, and the 15 code plates are evenly distributed around the outside of the LMU and the guide frame.

4. The welding construction process for merging the jacket structure and LMU of an offshore converter station according to claim 1, characterized in that: In step S6, before welding, the oxides, moisture, oil and impurities within 20mm of the welding bevel and both sides of the edge are cleaned; a stable and safe construction platform is built at the welding point, and strict wind and rain protection measures are taken to avoid excessive wind speed and rain water soaking during the welding process, which would cause the weld to cool too quickly and crack.

5. The welding construction process for merging the jacket structure and LMU of an offshore converter station according to claim 1, characterized in that: In step S7, preheating is performed using electric heating. A fixed hook is installed on the outer side of the lower end cylinder wall of the LMU, and an electric heating element is installed on the fixed hook. The electric heating element extends to the outer side of the upper end cylinder wall of the lower guide frame. The outer side of the lower end cylinder wall of the LMU and the upper end cylinder wall of the guide frame are preheated by the electric heating element. The preheating width of the upper side of the lower end cylinder wall of the LMU and the lower side of the upper end cylinder wall of the guide frame is ≥150mm.

6. The welding construction process for merging the jacket structure and LMU of an offshore converter station according to claim 1, characterized in that: In step S8, the welding material selected is low-hydrogen flux-cored wire T554T1-1C1A. The welding parameters are: DC reverse polarity, current 200-260A, voltage 24-30V, welding speed 200-300mm / min, shielding gas is CO2 with purity ≥99.9% and flow rate 15-25L / min; the minimum interpass temperature is 120℃ and the maximum interpass temperature is 200℃, and all welding is carried out within this temperature range; after each weld is completed, the slag is thoroughly removed, and the weld quality is checked and confirmed to be qualified before starting the next weld. Each section should be welded within one shift. If welding is interrupted due to severe weather, post-heating insulation measures should be taken, and preheating should be carried out again before welding resumes.

7. The welding construction process for merging the jacket structure and LMU of an offshore converter station according to claim 1, characterized in that: In step S9, visual inspection: the weld surface must not have cracks, porosity, arc craters, or slag inclusions. Non-destructive testing: Ultrasonic testing shall be used, and there shall be no defects exceeding the standard within the effective weld thickness.

Images