Flange welding deformation control method for FPSO main deck inboard seawater lifting pipe

Abstract

The present application relates to the technical fields of ship pipeline welding, and discloses a FPSO main deck inboard seawater lifting pipe flange welding deformation control method, step S1: reinforcing plate installation, step S2: main weld welding, step S3: process monitoring adjustment, step S4: reinforcing plate removal. The FPSO main deck inboard seawater lifting pipe flange welding deformation control method, by installing temporary reinforcing plate, welding flange on the temporary reinforcing plate, welding main deck below, not welding pipe wall, forming stable rigid constraint, cooperating with symmetric welding sequence from outside to inside and small current process, synergistically controlling welding deformation from constraint condition and heat input, effectively ensuring that the size precision such as flatness, perpendicularity and spacing of the flange after welding meets predetermined requirements.

Description

Technical Field

[0001] This invention relates to the field of marine pipeline welding technology, specifically a method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO. Background Technology

[0002] Seawater riser pipes are important pipeline system components of marine engineering vessels such as floating production storage and offloading (FPSO) vessels. Their top flanges are welded to the main deck and are responsible for the installation and connection of equipment such as seawater lift pumps. The dimensional accuracy of the flanges after welding, such as flatness, verticality, and spacing, directly affects the installation quality and operational reliability of subsequent equipment.

[0003] During the welding process between flanges and pipelines, residual stress and welding deformation are inevitably generated due to factors such as uneven heat input, weld metal shrinkage, and changes in the microstructure of the heat-affected zone of the base material. This welding deformation problem is particularly prominent for structures with closed circumferential welds, such as the top flange of a seawater riser pipe. During the welding process between flanges and pipelines, residual stress and welding deformation are inevitably generated due to factors such as uneven welding heat input, weld metal shrinkage, and changes in the microstructure of the heat-affected zone of the base material. In order to control the welding deformation of flanges, rigid fixation with tooling is generally used. However, the above-mentioned existing technologies are mainly applicable to conventional working conditions. The space inside the FPSO is limited, and large rigid fixation tooling cannot be arranged. Moreover, the corner joints, inner and outer double ring welds, and uneven stiffness distribution of the flanges at the top of the seawater riser make it difficult to control the dimensional accuracy of the flanges after welding. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO, thus solving the problem of difficulty in controlling the dimensional accuracy of the flange after welding mentioned in the background.

[0005] This invention provides the following technical solution: a method for controlling welding deformation of the seawater riser pipe flange inside the main deck of an FPSO, comprising the following steps: Step S1: Reinforcing plate installation. Before welding the top flange of the seawater riser pipe to the seawater riser pipe, several temporary reinforcing plates are symmetrically installed along the arc of the seawater riser pipe. The upper end of the temporary reinforcing plate is welded and fixed to the flange, and the lower end of the temporary reinforcing plate is welded and fixed to the main deck surface. The arc contact surface between the temporary reinforcing plate and the seawater riser pipe is not welded. Step S2: Main weld welding, welding the flange and the seawater riser pipe, first welding the outer side of the flange and the seawater riser pipe, then welding the inner side of the flange and the seawater riser pipe, using low current welding; Step S3: Process monitoring and adjustment. During the welding process, the flatness of the flange is measured in stages. When the flatness exceeds the standard, welding is stopped and adjustments are made. Welding continues after the adjustment is qualified. Step S4: Remove the reinforcing plates. After all welding is completed, remove all the temporary reinforcing plates.

[0006] Preferably, in step S2, the angle joint between the flange and the seawater riser pipe is divided into an outer ring and an inner ring. The outer ring is welded first, followed by the inner ring, according to the left-right symmetrical welding method.

[0007] Preferably, in step S4, before removing all the temporary reinforcing plates, the overall flatness of the flange is re-measured; if the flatness does not meet the requirements, it is corrected first, and then all the temporary reinforcing plates are removed.

[0008] Preferably, in step S4, after removing all the temporary reinforcing plates, the flatness of the flange is checked again; Adjustments are made when the flatness does not meet the requirements until it does.

[0009] Preferably, the flatness requirement is less than 1.5 mm.

[0010] Preferably, the temporary reinforcing plate has a thickness of 25mm to 40mm and a width of 100mm to 120mm.

[0011] Preferably, the temporary reinforcing plate has weld holes on both the top and bottom of the mating surface with the seawater riser pipe.

[0012] Preferably, the radius of the weld hole is 20 mm.

[0013] Preferably, the temporary reinforcing plate is made of steel.

[0014] Preferably, the number of temporary reinforcing plates is 8 to 12.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention, by installing a temporary reinforcing plate, with a flange welded to the top and the main deck welded to the bottom, and the pipe wall left unwelded, forms a stable rigid constraint. Combined with a symmetrical welding sequence from the outside to the inside and a low-current process, welding deformation is controlled in a coordinated manner from both constraint conditions and heat input, effectively ensuring that the dimensional accuracy of the flange flatness, verticality, and spacing after welding meets the predetermined requirements.

[0016] 2. This invention employs a complete closed-loop control process, including pre-welding constraints, in-welding monitoring, pre-disassembly re-inspection, and post-disassembly re-inspection. By measuring and dynamically correcting deviations in stages during the welding process, it avoids the accumulation of deformation. Before disassembly, it utilizes rigid support with reinforcing plates for efficient correction, and after disassembly, it re-inspects and fine-tunes the secondary deformation after stress release, ensuring that the final dimensional accuracy is stable and controllable.

[0017] 3. This invention, by controlling most of the welding deformation within the allowable range during the welding process and by re-inspecting and correcting before removing the reinforcing plate, requires only minor adjustments after removal. This significantly reduces or even avoids the amount of work that requires large-scale corrections by means of mechanical methods or fire correction, thereby reducing labor costs and material consumption and improving construction efficiency. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the process for controlling the welding deformation of the seawater riser flange inside the main deck of an FPSO according to the present invention. Figure 2 This is a schematic diagram of the temporary reinforcing plate connecting flange and the main deck structure of the present invention; Figure 3 This is a schematic diagram of the temporary reinforcing plate distribution structure of the present invention; Figure 4 This is a schematic diagram showing the welding path of the main weld seam of the seawater riser pipe and flange of the present invention.

[0019] In the diagram: 1. Seawater riser pipe; 2. Flange; 3. Main deck; 4. Temporary reinforcing plate; 5. Welding hole. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] Please see Figures 1-4 A method for controlling welding deformation of the seawater lift pipe flange inside the main deck of an FPSO, characterized by the following steps: Step S1: Reinforcing plate installation. Before welding the top flange 2 of the seawater riser pipe 1 to the seawater riser pipe 1, several temporary reinforcing plates 4 are symmetrically installed along the arc of the seawater riser pipe 1. The upper end of the temporary reinforcing plate 4 is welded and fixed to the flange 2, and the lower end of the temporary reinforcing plate 4 is welded and fixed to the main deck 3. The arc contact surface between the temporary reinforcing plate 4 and the seawater riser pipe 1 is not welded. Step S2: Main weld welding, welding flange 2 to seawater riser pipe 1, first welding the outer side of flange 2 to seawater riser pipe 1, then welding the inner side of flange 2 to seawater riser pipe 1, using low current welding. Furthermore, the angle joint between flange 2 and seawater riser pipe 1 is divided into an outer ring and an inner ring. Following the left-right symmetrical welding method, the outer ring is welded first, followed by the inner ring. Step S3: Process monitoring and adjustment. During the welding process, the flatness of flange 2 is measured in stages. When the flatness exceeds the standard, welding is stopped and adjustments are made. Welding continues after the adjustment is qualified. Step S4: Remove the reinforcing plates. After all welding is completed, remove all temporary reinforcing plates 4. Furthermore, before removing all temporary reinforcing plates 4, re-measure the overall flatness of flange 2; if the flatness does not meet the requirements, correct it first, and then remove all temporary reinforcing plates 4. After removing all temporary reinforcing plates 4, recheck the flatness of flange 2. If the flatness does not meet the requirements, make adjustments until it does. The flatness requirement is less than 1.5mm.

[0022] In one specific embodiment: I. Installation of the reinforcing plate: Please see Figure 1 The temporary reinforcing plate 4 is made of steel of grade A or above, with a plate thickness of 25mm to 40mm and a width of 100mm to 120mm. The temporary reinforcing plate 4 is a rectangular plate, which is the most stable to resist the welding deformation of the flange 2 and the stress is more evenly transmitted. Welding holes 5 with a radius of 20mm are opened on the upper and lower surfaces of the rectangular temporary reinforcing plate 4 and the seawater riser pipe 1. Please see Figure 2 Before welding flange 2 to seawater riser pipe 1, temporary reinforcing plates 4 are installed along the circumference of the outer side of seawater riser pipe 1. The number of temporary reinforcing plates 4 is 8 to 12 pieces. The specific number is determined according to the pipe diameter of seawater riser pipe 1. More plates are used when the pipe diameter is large and fewer plates are used when the pipe diameter is small, so as to ensure that the constraint is evenly distributed along the arc. The upper end of each temporary reinforcing plate 4 is welded and fixed to the flange 2, and the lower end of each temporary reinforcing plate 4 is welded and fixed to the main deck 3. The temporary reinforcing plate 4 and the surface of the seawater riser pipe 1 are not welded. That is, only the fillet weld between the temporary reinforcing plate 4 and the flange 2 and the fillet weld between the temporary reinforcing plate 4 and the main deck 3 are welded. The fillet weld between the temporary reinforcing plate 4 and the wall of the seawater riser pipe 1 is not welded.

[0023] After the temporary reinforcing plate 4 is installed, check the welding quality of each temporary reinforcing plate 4 to ensure that the weld is full, without cracks, and without defects such as incomplete fusion, so as to ensure that the temporary reinforcing plate 4 can provide stable and reliable rigid constraints in the subsequent welding process.

[0024] II. Main weld seam welding: After the temporary reinforcing plate 4 is installed and fixed, check the assembly gap and bevel size between the flange 2 and the seawater riser pipe 1. After confirming that they meet the welding process requirements, prepare for welding. like Figure 2 , Figure 3 As shown, the flange 2 and the seawater riser pipe 1 are connected by a corner butt joint. The weld consists of two circumferential welds, an outer ring and an inner ring. During welding, the outer ring is welded first, followed by the inner ring, following a symmetrical welding method. On the outer ring weld, welding is performed simultaneously from two symmetrical starting points, progressing symmetrically from left to right. Figure 3 As shown, weld symmetrically along the arrow lines. After welding line A, weld line B symmetrically until all outer ring welds are completed. After the outer ring welds are completed, use the same left-right symmetrical welding method to weld the inner ring welds.

[0025] Low-current welding is used during the welding process. Specific process parameters such as welding current, welding voltage, and welding speed should be followed according to the approved welding procedure specification. Low-current welding helps reduce heat input, decrease the size of the heat-affected zone, and reduce residual stress levels, thereby controlling welding deformation. Interpass temperature should be controlled during welding to avoid excessive heat input accumulation and increased deformation due to excessively high interpass temperatures. The specific interpass temperature control range should be followed according to the welding procedure specification.

[0026] III. Process Monitoring and Adjustment During the welding process between flange 2 and seawater riser pipe 1, the flatness of flange 2 is measured in stages. Specifically, after completing several welds, such as after completing 1 / 4 or 1 / 2 of the outer ring weld and the corresponding stage of the inner ring weld, the flatness of flange 2 is measured once. The measurement can be performed using a level, laser measuring instrument or other measuring tools with corresponding accuracy. Multiple measuring points are selected along the circumference of flange 2, such as 8 or 12 measuring points are evenly selected along the circumference. The relative height difference of each measuring point is recorded to determine the overall flatness of flange 2.

[0027] Stop work and adjust if the flatness exceeds the predetermined standard: Welding shall be stopped immediately, the cause of the deformation shall be analyzed and corresponding adjustment measures shall be taken. Welding may continue only after the adjustment is qualified. Adjustment measures include, but are not limited to: adjusting the welding sequence of subsequent welds, adjusting welding parameters, and taking appropriate corrective measures at deformed areas. After the adjustments are completed, the flatness of flange 2 should be measured again, and welding can continue only after confirming that it meets the requirements.

[0028] IV. Removal of the reinforcing plate: After all welding work between flange 2 and seawater riser pipe 1 is completed, before removing all temporary reinforcing plates 4, the overall flatness of flange 2 is re-measured. If the re-measured flatness does not meet the predetermined requirements, for example, if the flatness is greater than or equal to 1.5mm, it needs to be corrected until the flatness meets the predetermined requirements. Since the temporary reinforcing plates 4 have not been removed at this time, the main deck 3 provides strong rigid support to flange 2 through the temporary reinforcing plates 4, the correction efficiency is high, and the additional impact on the body of seawater riser pipe 1 is small. The correction method can be mechanical correction or fire correction. The specific correction position and correction amount are determined according to the flatness measurement results. After correction, the flatness is re-measured again. Only after confirming that the requirements are met can the next step be carried out. After the re-inspection is passed, remove all temporary reinforcing plates 4. When removing them, take care to protect the surface quality of flange 2 and main deck 3 to avoid damage caused by the removal operation. Temporary reinforcing plates 4 can be cut off from flange 2 and main deck 3 by means of carbon arc gouging or mechanical cutting. After cutting, grind the remaining weld scars smooth. After all temporary reinforcing plates 4 are removed, the flatness of flange 2 should be checked again. Since the residual welding stress previously constrained by the reinforcing plates is released after removal, the flatness of flange 2 may change slightly. Therefore, a second check is necessary. If the flatness does not meet the predetermined requirements, adjustments should be made until they are met. The deformation at this stage is usually small, and only minor adjustments are generally needed to meet the standards. Appropriate heat treatment methods can be used, and the flatness should be checked again after adjustment.

[0029] After all adjustments are completed, a comprehensive inspection of the flatness, perpendicularity, and spacing of flange 2 will be conducted to ensure that all indicators meet the requirements of the shipowner and process drawings. Once the inspection is passed, the shipowner can submit the application for inspection.

[0030] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for controlling welding deformation of the seawater riser pipe flange inside the main deck of an FPSO, characterized in that, Includes the following steps: Step S1: Reinforcing plate installation. Before welding the top flange (2) of the seawater riser pipe (1) to the seawater riser pipe (1), several temporary reinforcing plates (4) are symmetrically installed along the arc of the seawater riser pipe (1). The upper end of the temporary reinforcing plate (4) is welded and fixed to the flange (2), and the lower end of the temporary reinforcing plate (4) is welded and fixed to the main deck (3). The arc contact surface between the temporary reinforcing plate (4) and the seawater riser pipe (1) is not welded. Step S2: Main weld welding, welding the flange (2) and the seawater riser pipe (1), first welding the outer side of the flange (2) and the seawater riser pipe (1), then welding the inner side of the flange (2) and the seawater riser pipe (1), using low current welding; Step S3: Process monitoring and adjustment. During the welding process, the flatness of the flange (2) is measured in stages. When the flatness exceeds the standard, welding is stopped and adjustment is carried out. Welding continues after the adjustment is qualified. Step S4: Remove the reinforcing plates. After all welding is completed, remove all the temporary reinforcing plates (4).

2. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 1, characterized in that, In step S2, the angle connection between the flange (2) and the seawater riser pipe (1) is divided into an outer ring and an inner ring. According to the left-right symmetrical welding method, the outer ring is welded first and then the inner ring is welded.

3. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 1, characterized in that, In step S4, before removing all the temporary reinforcing plates (4), the overall flatness of the flange (2) is re-measured; if the flatness does not meet the requirements, it is corrected first, and then all the temporary reinforcing plates (4) are removed.

4. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 3, characterized in that, In step S4, after removing all the temporary reinforcing plates (4), the flatness of the flange (2) is checked again; Adjustments are made when the flatness does not meet the requirements until it does.

5. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 4, characterized in that, The flatness requirement is less than 1.5mm.

6. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 1, characterized in that, The temporary reinforcing plate (4) has a thickness of 25mm to 40mm and a width of 100mm to 120mm.

7. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 1, characterized in that, The temporary reinforcing plate (4) has welded holes (5) on both the upper and lower surfaces of its mating surface with the seawater riser pipe (1).

8. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 7, characterized in that, The radius of the weld hole (5) is 20 mm.

9. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 1, characterized in that, The temporary reinforcing plate (4) is made of steel.

10. The method for controlling welding deformation of the seawater riser flange inside the main deck of an FPSO according to claim 1, characterized in that, The number of temporary reinforcing plates (4) is 8 to 12.

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