A method for handling subsea pipelines during buoyancy.
By pressurizing and venting, segmented dredging, and laying curved concrete cover plates, the engineering safety issues caused by the floating of the subsea pipeline were resolved, the pipeline's stable settlement was achieved, the service life of the anti-corrosion layer was extended, and material costs and ecological impacts were reduced.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SDC WATERWAY CONSTR
- Filing Date
- 2026-05-21
- Publication Date
- 2026-06-30
AI Technical Summary
Submarine pipelines rise to the surface due to buoyancy, threatening the safe operation of the project. Existing methods suffer from high material costs, significant ecological impact, easy damage to pipeline anti-corrosion coatings, and poor stability.
By pressurizing and venting the gas inside the pipe, dredging is carried out in sections and laying arc-shaped concrete covers, combined with underwater positioning and sealing technology, to ensure the stable settlement of the pipeline.
It effectively eliminates buoyancy, reduces material costs, minimizes ecological impact, extends the lifespan of pipeline anti-corrosion coatings, and ensures pipeline stability and operational safety.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to a method for handling subsea pipelines during their ascent. Background Technology
[0002] Due to the lack of comprehensive understanding of the on-site construction conditions by the operation and management unit, and the poor communication mechanism with the project department, information transmission was delayed and inaccurate. This led to errors in the water source scheduling process, resulting in insufficient initial water supply pressure and excessively large openings of the drain valves at the end of the flushing process. This operation prevented the air vent valve at the highest point of the tunnel section from timely expelling air from the pipe, causing a large amount of air to enter the subsea pipeline with the water flow. As gas accumulates inside the pipe, the 800-meter-long pipeline at the starting point of the lake in the sea floats to the surface due to buoyancy. The current conventional approach is to use specialized equipment to dredge and excavate the lower part of the pipeline, removing the accumulated silt and loose mud from the bottom and surrounding areas, eliminating the "buoyancy support layer" that causes the pipeline to float. This allows the pipeline to settle smoothly to the design elevation under its own weight and subsequent ballast measures, and then cover it with soil. However, this method has several drawbacks. After dredging, the silt accumulates back into the pipeline quickly. After covering it with soil, the pipeline is subject to long-term erosion from the rising and falling tides. The soil covering the pipeline and the mud in the trench are prone to loosening and loss, reducing the soil density. When the buoyancy of the seawater exceeds the sum of the pipeline's own weight and the weight of the soil covering, the pipeline is very likely to float a second time and become exposed, seriously threatening the safe operation of the project.
[0003] Therefore, a method for handling subsea pipelines during their ascent is provided to address how to sink the floating pipeline to a designated location and maintain its continuous stability. Summary of the Invention
[0004] To address the aforementioned problems in the existing technology, this invention provides a method for handling subsea pipelines during their ascent, thereby suppressing the ascent and increasing the pipeline's stability on the seabed.
[0005] The technical solution to achieve the above objectives is: A method for handling a subsea pipeline during its ascent, comprising: Step S1, Pipeline gas discharge and reset: When the laid subsea pipeline rises abnormally, the subsea pipeline is pressurized to allow the gas inside the pipe to flow back to the onshore section and be discharged through the onshore section exhaust valve, so that the pipeline falls back to the initial installation elevation. Step S2, trench dredging and pipeline leveling: use an underwater excavator to excavate along both sides of the pipeline to below the design elevation of the bottom of the pipeline, and simultaneously use a mud pump to pump the silt to a mud transport ship, transport it to the designated seepage prevention treatment site, and check the dredging quality. If the pipeline is suspended, use graded sand and gravel to pave and level it. Step S3, Precast Concrete Cover Plate Fabrication: C30 commercial concrete is used, with 3% of a composite anti-corrosion and rust-inhibiting agent added to the cementitious materials to fabricate precast concrete cover plates. Step S4, underwater positioning and cover plate installation preparation: set underwater positioning stakes every 20m along the center line of the exposed pipeline and mark the edge line for cover plate installation; Step S5, Installation of precast concrete cover plate: Use an underwater excavator to lift the cover plate to the designated position using the lifting rings on the cover plate; Step S6, End sealing: At the beginning and end of the exposed section of the pipeline, MU30 rubble masonry retaining walls are built, followed by underwater non-dispersible C30 concrete for sealing.
[0006] Preferably, in step S2, the trench dredging and pipe leveling specifically include: Excavate the pipe trench in 20-30m sections, and use an underwater excavator to excavate within a 50cm range on both sides of the pipe to 10cm below the design elevation of the bottom of the pipe. It is forbidden for the bucket teeth to directly contact the pipe body. Simultaneously, mud pumps are used to pump the silt onto a mud transport vessel and transport it to the designated seepage prevention treatment site. Divers inspect the dredging quality underwater, requiring that the thickness of residual silt at the bottom of the pipe be ≤5cm and the flatness deviation of the pipe trench be ≤10cm / 2m. If the pipe is suspended (i.e., the suspension height is greater than 2cm), graded sand and gravel should be used to pave and level it to make the pipe stable at the bottom.
[0007] Preferably, in step S3, the precast concrete cover plate has an arc-shaped structure that matches the curvature of the outer wall of the submarine pipeline. The precast concrete cover plate has HRB400 grade epoxy resin coated main reinforcement, HPB300 grade epoxy resin coated stirrups and Q235 round steel, and is equipped with lifting rings with PVC anti-corrosion sleeves.
[0008] Preferably, in step S5, the installation of the precast concrete cover plate specifically includes: The cover plate is lifted by an underwater excavator using lifting rings on the cover plate. The cover plate is lined with rubber pads, and 2-ton hand-operated hoists are installed at both ends of the lifting device for fine-tuning the position. Slowly lift the cover plate and move it above the installation position using RTK positioning; Divers guide the process underwater, aligning the curved inner wall of the cover plate with the outer wall of the pipe. The cover plate should be lowered at a speed of ≤0.3m / min and stopped when it is 10cm away from the pipe. The position of the cover plate should be finely adjusted by a hand-operated hoist to make the axis of the cover plate parallel to the axis of the pipe. The gap between the end face and the adjacent cover plate should be ≤20mm and the fit gap should be ≤5mm.
[0009] Preferably, in step S6, underwater non-dispersible C30 concrete is poured for sealing, with the pouring height exceeding the top of the cover plate by 10cm and the width by 50cm, and the divers compact it underwater.
[0010] Compared with the prior art, the beneficial effects of the present invention are: This invention uses controlled pressurization to direct gas back to the onshore section for discharge, avoiding secondary displacement of the pipeline caused by traditional explosive venting, completely removing gas from the pipe, eliminating buoyancy sources, and reducing material costs compared to traditional counterweight ballast methods. Segmented excavation reduces the impact of large-area excavation on the seabed ecosystem; non-contact dredging and the prohibition of bucket teeth from touching the pipe body reduce the damage rate of the pipeline's anti-corrosion layer; graded sand and gravel combined with diver verification ensure uniform support at the pipe bottom; and precast concrete covers are made using C30 commercial concrete with 3% composite anti-corrosion and rust-inhibiting agent added to reduce the chloride ion diffusion coefficient. The covers also incorporate HRB400 grade epoxy resin coated main reinforcement, HPB300 grade epoxy resin coated stirrups, and Q235 round steel, and are reinforced with PVC. The lifting rings of the anti-corrosion sleeve extend the life of the cover plate, and the arc-shaped fitting design reduces the impact of water flow; the dual-control positioning of RTK + hand-operated hoist reduces the deviation of the installation position; the end sealing body is dense and undamaged, there is no obvious sludge backflow in the pipe trench, and the pipeline is in good operating condition. Attached Figure Description
[0011] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of a method for handling a subsea pipeline during its buoyancy, according to the present invention. Figure 2 This is a schematic diagram of the precast concrete cover plate in this invention. Detailed Implementation
[0012] 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.
[0013] like Figure 1 As shown, a method for handling a subsea pipeline during its ascent includes: Step S1, Gas Discharge and Reset in the Pipeline: When the laid subsea pipeline rises abnormally, the subsea pipeline is pressurized to allow the gas inside to flow back to the onshore section and be discharged through the exhaust valve in the onshore section, so that the pipeline falls back to the initial installation elevation.
[0014] Step S2, trench dredging and pipeline leveling: Use an underwater excavator to excavate along both sides of the pipeline to below the design elevation of the bottom of the pipeline. Simultaneously use a mud pump to pump the silt to a mud transport ship and transport it to the designated seepage prevention treatment site. Check the dredging quality. If the pipeline is suspended, use graded sand and gravel to pave and level it.
[0015] In this embodiment, the dredging of the pipe trench and the leveling of the pipe specifically include: Excavate the pipe trench in 20-30m sections, and use an underwater excavator to excavate within a 50cm range on both sides of the pipe to 10cm below the design elevation of the bottom of the pipe. It is forbidden for the bucket teeth to directly contact the pipe body. Simultaneously, mud pumps are used to pump the silt onto a mud transport vessel and transport it to the designated seepage prevention treatment site. Divers inspect the dredging quality underwater, requiring that the thickness of residual silt at the bottom of the pipe be ≤5cm and the flatness deviation of the pipe trench be ≤10cm / 2m (meaning that the maximum allowable height deviation is 10cm within a 2-meter length of the pipe trench). If the pipe is suspended (i.e., the suspension height is greater than 2cm), graded sand and gravel should be used to pave and level it to make the pipe stable at the bottom.
[0016] Step S3, Precast Concrete Cover Plate Fabrication: C30 commercial concrete is used, with 3% of a composite anti-corrosion and rust-inhibiting agent added to the cementitious materials to fabricate the precast concrete cover plate.
[0017] In this embodiment, the precast concrete cover plate has an arc-shaped structure to match the curvature of the outer wall of the submarine pipeline. The precast concrete cover plate contains HRB400 grade epoxy resin coated main reinforcement, HPB300 grade epoxy resin coated stirrups, and Q235 round steel, and is fitted with lifting rings using PVC anti-corrosion sleeves. Figure 2 As shown.
[0018] Step S4, underwater positioning and cover plate installation preparation: set underwater positioning stakes every 20m along the center line of the exposed pipeline and mark the edge line for cover plate installation.
[0019] Step S5, Installation of precast concrete cover plate: Use an underwater excavator to lift the cover plate to the designated position using the lifting rings on the cover plate.
[0020] In this embodiment, the installation of the precast concrete cover plate specifically includes: The cover plate is lifted by an underwater excavator using lifting rings on the cover plate. The cover plate is lined with rubber pads, and 2-ton hand-operated hoists are installed at both ends of the lifting device for fine-tuning the position. Slowly lift the cover plate (lifting speed ≤ 0.5m / min), and move the cover plate to the installation position using RTK positioning (deviation ≤ 5cm). Divers guide the process underwater, aligning the curved inner wall of the cover plate with the outer wall of the pipe. The cover plate should be lowered at a speed of ≤0.3m / min and stopped when it is 10cm away from the pipe. The position of the cover plate should be finely adjusted by a hand-operated hoist to make the axis of the cover plate parallel to the axis of the pipe. The gap between the end face and the adjacent cover plate should be ≤20mm and the fit gap should be ≤5mm.
[0021] Step S6, End sealing: At the beginning and end of the exposed section of the pipeline, MU30 rubble masonry retaining walls are built, followed by underwater non-dispersible C30 concrete for sealing.
[0022] In this embodiment, underwater non-dispersible C30 concrete is poured for sealing, with the pouring height exceeding the top of the cover plate by 10cm and the width by 50cm. Divers then compact the concrete underwater.
[0023] Finally, it should be noted that the above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for the treatment of a pipeline during its floating on the sea bed, characterised in that, include: Step S1, Pipeline gas discharge and reset: When the laid subsea pipeline rises abnormally, the subsea pipeline is pressurized to allow the gas inside the pipe to flow back to the onshore section and be discharged through the onshore section exhaust valve, so that the pipeline falls back to the initial installation elevation. Step S2, trench dredging and pipeline leveling: use an underwater excavator to excavate along both sides of the pipeline to below the design elevation of the bottom of the pipeline, and simultaneously use a mud pump to pump the silt to a mud transport ship, transport it to the designated seepage prevention treatment site, and check the dredging quality. If the pipeline is suspended, use graded sand and gravel to pave and level it. Step S3, Precast Concrete Cover Plate Fabrication: C30 commercial concrete is used, with 3% of a composite anti-corrosion and rust-inhibiting agent added to the cementitious materials to fabricate precast concrete cover plates. Step S4, underwater positioning and cover plate installation preparation: set underwater positioning stakes every 20m along the center line of the exposed pipeline and mark the edge line for cover plate installation; Step S5, Installation of precast concrete cover plate: Use an underwater excavator to lift the cover plate to the designated position using the lifting rings on the cover plate; Step S6, End sealing: At the beginning and end of the exposed section of the pipeline, MU30 rubble masonry retaining walls are built, followed by underwater non-dispersible C30 concrete for sealing.
2. A method for the treatment of a pipeline during its floating to the surface from the bottom of the sea according to claim 1, characterized in that, In step S2, the dredging of the pipe trench and the leveling of the pipe specifically include: Excavate the pipe trench in 20-30m sections, and use an underwater excavator to excavate within a 50cm range on both sides of the pipe to 10cm below the design elevation of the bottom of the pipe. It is forbidden for the bucket teeth to directly contact the pipe body. Simultaneously, mud pumps are used to pump the silt onto a mud transport vessel, which then transports it to the designated seepage prevention treatment site. Divers inspect the dredging quality underwater, requiring that the thickness of residual silt at the bottom of the pipe be ≤5cm and the flatness deviation of the pipe trench be ≤10cm / 2m. If the pipe is suspended (i.e., the suspension height is greater than 2cm), graded sand and gravel should be used to pave and level it to make the pipe stable at the bottom.
3. The method for handling a subsea pipeline during its ascent according to claim 1, characterized in that, In step S3, the precast concrete cover plate has an arc-shaped structure that matches the curvature of the outer wall of the submarine pipeline. The precast concrete cover plate has HRB400 grade epoxy resin coated main reinforcement, HPB300 grade epoxy resin coated stirrups and Q235 round steel, and is equipped with lifting rings with PVC anti-corrosion sleeves.
4. The method for handling a subsea pipeline during its ascent according to claim 1, characterized in that, In step S5, the installation of the precast concrete cover plate specifically includes: The cover plate is lifted by an underwater excavator using lifting rings on the cover plate. The cover plate is lined with rubber pads, and 2-ton hand-operated hoists are installed at both ends of the lifting device for fine-tuning the position. Slowly lift the cover plate and move it above the installation position using RTK positioning; Divers guide the process underwater, aligning the curved inner wall of the cover plate with the outer wall of the pipe. The cover plate should be lowered at a speed of ≤0.3m / min and stopped when it is 10cm away from the pipe. The position of the cover plate should be finely adjusted by a hand-operated hoist to make the axis of the cover plate parallel to the axis of the pipe. The gap between the end face and the adjacent cover plate should be ≤20mm and the fit gap should be ≤5mm.
5. A method for handling a subsea pipeline during its ascent according to claim 1, characterized in that, In step S6, underwater non-dispersible C30 concrete is poured for sealing, with the pouring height exceeding the top of the cover plate by 10cm and the width by 50cm. Divers then compact the concrete underwater.