A design method for the curvature radius of submarine pipelines

Abstract

The present invention relates to the technical field of submarine pipeline design, and is a design method for the curvature radius of a submarine pipeline, comprising the following steps: establishing a pipeline model, using a continuous beam unit for the pipeline, using hinged boundaries at both ends of the pipeline, loading a uniformly distributed load perpendicular to the pipeline axis, using the Newton-Raphson method, performing nonlinear calculations, and obtaining the stress and displacement of the pipeline; when the stress of the pipeline reaches the allowable stress, the uniformly distributed load at this time is the limit load that the pipeline towing can withstand, and the limit wave load that the pipeline can withstand is calculated by considering the pipeline wave force reduction, and the limit wave load is brought into the Morrison equation to obtain the limit wave height under different wave periods; the curvature radius is calculated once for each three adjacent points, so as to find the minimum curvature radius of the pipeline under different limit wave heights. The present invention systematically provides a solution method for the minimum curvature radius, and the steps are simple, the operation is convenient, and the effect is good.

Description

Technical Field

[0001] The invention relates to the technical field of submarine pipeline design, in particular to a method for designing a submarine pipeline curvature radius. Background Art

[0002] Since marine drift pipes are only a few kilometers offshore, they are mostly installed using the pipe dragging method. During the installation process, the pipes bend and deform under the action of external environmental loads. When the bending deformation is too large, that is, the pipe curvature radius is too small, the pipe will be damaged. Therefore, the minimum curvature radius of the drift pipe during the installation process is extremely important.

[0003] The current specification requires the minimum radius of curvature when laying steel pipes to be 1200D~1500D, where D is the outer diameter of the steel pipe. At the same time, the pipeline strength requirements must be met. The minimum radius of curvature requirement is determined based on installation experience, and the steel pipe laying condition is a long-term condition, which is different from the short-term condition of ocean drift pipe towing. At present, there is little research on the minimum radius of curvature when towing ocean drift pipes. Summary of the invention

[0004] The purpose of the present invention is to provide a design method for the curvature radius of a submarine pipeline in view of the fact that there is currently little research on the minimum curvature radius of a marine drift pipe when towing, and the requirement for the minimum curvature radius of existing steel pipes is determined based on installation experience.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A method for designing the curvature radius of a submarine pipeline, wherein the pipeline is a steel pipeline, and the design method comprises the following steps:

[0007] Establish a pipeline model. The length of the pipeline is greater than or equal to 120m. The pipeline adopts continuous beam units and hinged boundaries at both ends of the pipeline. A uniformly distributed load perpendicular to the pipeline axis is applied. The Newton-Raphson method is used for nonlinear calculation to obtain the stress and displacement of the pipeline.

[0008] When the stress of the pipeline reaches the allowable stress, the uniformly distributed load at this time is the ultimate load that the pipeline towing can withstand. Considering the reduction of pipeline wave force, the ultimate wave load that the pipeline can withstand is calculated. By substituting the ultimate wave load into the Morrison equation, the ultimate wave height under different wave periods is obtained.

[0009] The minimum curvature radius is found by calculating the curvature radius once for every three adjacent points. Suppose the three adjacent points are (x1, y1), (x2, y2), and (x3, y3), and the corresponding three sides are a, b, and c. The curvature radius R is obtained according to the cosine theorem.

[0010]

[0011] Calculate the minimum curvature radius of the pipeline under different extreme wave heights.

[0012] By adopting the design method of the curvature radius of a submarine pipeline described in the present invention, a suitable wave theory and a pipeline model are selected according to sea condition parameters, and the Morrison equation is used to calculate the extreme wave height. The curvature radius is calculated once for every three adjacent points under the extreme wave height, and the minimum value thereof is the minimum curvature radius. A solution method for the minimum curvature radius is systematically given, and the value of the solved minimum curvature radius is basically accurate, which is more in line with installation requirements than the minimum curvature radius determined by existing experience. The design method has simple steps, is easy to operate, and has good effects.

[0013] As a preferred technical solution of the present invention, the deformation data within 20 m at both ends of the pipeline are removed, and the minimum value is selected from the remaining curvature radius results.

[0014] As a further preferred technical solution of the present invention, for a pipeline with a length of 1008 m, the minimum radius of curvature R is 800D, where D is the outer diameter of the pipeline.

[0015] As a further preferred technical solution of the present invention, the wave period includes 5s, 6s, 7s and 8s.

[0016] As a further preferred technical solution of the present invention, the initial uniformly distributed load is 1500 N / m, and according to the stress calculation result, it is increased by 100 N / m each step until the stress of the pipeline reaches the allowable stress of the material 170 MPa.

[0017] As a preferred technical solution of the present invention, Midas is used to establish a pipeline model.

[0018] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0019] The design method of the curvature radius of a submarine pipeline described in the present invention selects suitable wave theory and pipeline model according to sea condition parameters, and uses Morrison equation to calculate the extreme wave height. The curvature radius is calculated once for every three adjacent points under the extreme wave height, and the minimum value is the minimum curvature radius. A method for solving the minimum curvature radius is systematically given, and the value of the solved minimum curvature radius is basically accurate, which is more in line with installation requirements than the minimum curvature radius determined by existing experience. The design method is simple in steps, easy to operate, and has good effects. . BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 To numerically analyze the equivalent stress cloud diagram of the discharge pipe at 20 miles and 2m of lifting height;

[0021] Figure 2 For numerical analysis of the displacement cloud diagram of the discharge pipe at 20 miles with a lifting height of 2m;

[0022] Figure 3 It is a schematic diagram of the numerical analysis results of the discharge pipe;

[0023] Figure 4 This is a schematic diagram of the displacement curve of the test 20 mileage lifting height;

[0024] Figure 5 It is a comparison chart of lifting displacement curve;

[0025] Figure 6 It is a schematic diagram of the minimum curvature radius analysis under different tube lengths;

[0026] Figure 7 It is a schematic diagram of the analysis of the minimum radius of curvature under different diameters;

[0027] Figure 8 It is a schematic diagram of the minimum curvature radius analysis under different wall thicknesses;

[0028] Fig. 9 It is a schematic diagram of the analysis of the minimum curvature radius under different elastic moduli;

[0029] Fig.10 It is the stress cloud diagram of the pipeline when the uniform force loading is close to the allowable stress of the pipeline;

[0030] Fig.11 It is the displacement cloud diagram of the pipeline when the uniformly distributed force loading is close to the allowable stress of the pipeline. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with test examples and specific implementation methods. However, this should not be understood as the scope of the above subject matter of the present invention being limited to the following embodiments, and all technologies realized based on the content of the present invention belong to the scope of the present invention.

[0032] Unless otherwise specified, in the description of the specific embodiments of the present invention, the terms indicating the orientation or position relationship such as "up", "down", "left", "right", "center", "inside", "outside", etc. are all expressions based on the orientation or position relationship shown in the drawings, or are the orientation or position relationship when the invented product / equipment / device is usually used. These terms of orientation or position relationship are only for the convenience of describing the scheme of the present invention or simplifying the description in the specific embodiments, so as to facilitate the technicians to quickly understand the scheme, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific position relationship, and therefore cannot be understood as a limitation on the present invention.

[0033] In addition, if the terms "horizontal", "vertical", "overhanging", "parallel" and the like appear, it does not mean that the corresponding devices / components / elements are required to be absolutely horizontal or vertical or overhanging or parallel, but may be slightly tilted or have deviations. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but may be slightly tilted. Alternatively, it can be simplified to mean that the corresponding devices / components / elements are set in directions such as "horizontal", "vertical", "overhanging", "parallel", etc., and can have an error / deviation of ±10% relative to the corresponding direction setting, more preferably an error / deviation within ±8%, more preferably an error / deviation within ±6%, more preferably an error / deviation within ±5%, and more preferably an error / deviation within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its role in the scheme of the present invention.

[0034] In addition, the expressions “first”, “second”, “third”, etc., which appear in the terms, are merely used to distinguish the description of the same or similar components and should not be understood as emphasizing or implying the relative importance of specific components.

[0035] In addition, in the description of the embodiments of the present invention, "several", "plurality" and "a number" represent at least 2. It can be any number such as 2, 3, 4, 5, 6, 7, 8, 9, and even more than 9.

[0036] In addition, in the description of the technical solution of the present invention, unless otherwise clearly specified / defined / restricted, the terms "set", "install", "connect", "connected", "provided with", "laid", and "arranged" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection, and can be welding, riveting, bolting, threading, and other commonly used connection means in the field. This connection can be a mechanical connection, an electrical connection, or a communication connection; it can be a direct connection, or an indirect connection through an intermediate medium, and it can be the internal connection of two elements.

[0037] In the related art, since the marine drift pipe is only a few kilometers offshore, most of the pipes are installed by the pipe dragging method. During the installation process, the pipe bends and deforms under the action of the external environmental load. When the bending deformation is too large, that is, the pipe curvature radius is too small, the pipe will be damaged. Therefore, the minimum curvature radius of the drift pipe during the installation process is extremely important. The current specification requires the minimum curvature radius of 1200D~1500D when laying steel pipes, and the pipeline strength requirements must also be met. The minimum curvature radius requirement is determined based on installation experience, and the steel pipe laying condition is a long-term condition, which is different from the short-term condition of the marine drift pipe towing. There is currently little research on the minimum curvature radius when towing marine drift pipes. For this reason, the technical solution of the present application was produced, and the following is combined with Figures 1 to 11 To elaborate.

[0038] Example 1

[0039] like Figure 1 As shown, a method for designing the curvature radius of a submarine pipeline according to the present invention comprises the following steps:

[0040] Step 1: Study on the radius of curvature

[0041] 1. Modeling

[0042] Midas was used to establish the analysis model. The ocean discharge pipe (i.e., submarine pipeline) was simulated using beam units, and the ground was simulated using compression spring supports. The model was divided according to the size of the grid unit 1m, and a 120m long pipeline model was established. At the node 20m away from the end of the pipe, the node displacement was used to simulate and analyze the working conditions of 20m away from the pipe section and the suspension heights of 1m, 1.5m, and 2m.

[0043] 2. Numerical analysis results

[0044] The analysis results show that with the increase of the lifting height, the maximum stress of the pipeline also increases, and the maximum stress appears at the minimum displacement of the pipe joint. When the 20-mile lifting height is 2m, the maximum stress of the pipe joint is 143.2MPa; the maximum displacement appears at the pipe head, and its displacement increases with the increase of the lifting height. When the 20-mile lifting height is 2m, the maximum displacement of the pipe head is 3m. Figures 1 to 3 shown.

[0045] 3. Calculation of curvature radius

[0046] The minimum curvature radius is found by calculating the curvature radius once for every three adjacent points. Suppose the three adjacent points are (x1, y1), (x2, y2), and (x3, y3), and the corresponding three sides are a, b, and c. The curvature radius R is obtained according to the cosine theorem. Calculate the minimum curvature radius of the pipeline at different lifting heights.

[0047]

[0048] Extract the displacement data, substitute it into the curvature radius formula, calculate the curvature radius of three adjacent points, and select the minimum value in the curvature radius results to obtain the minimum curvature radius. The minimum curvature radius of the pipeline under different hanging heights is shown in Table 1.

[0049] Table 1. Minimum curvature radius of the discharge pipe at different hanging heights

[0050]

[0051] The results of curvature radius analysis show that as the lifting height increases, the curvature radius of the pipeline decreases. When the lifting height is 2m, the curvature radius reaches a minimum of 896D. At this time, the corresponding maximum stress of the pipeline is 143.2MPa, that is, the smaller the curvature radius, the greater the stress of the pipeline itself. At this time, the minimum curvature radius is lower than the 1200D~1500D required by the specification. Therefore, when the stress of the pipeline itself reaches the allowable stress, the corresponding minimum curvature radius is the minimum allowable curvature radius of the pipeline.

[0052] Step 2: Verify the curvature radius

[0053] 1. Test methods

[0054] The object of the curvature radius test is a 120m long discharge pipe section. The pipe section is arranged on the leveled site, and the lifting point is marked at a position 20 miles away from the pipe head. During the test, the pipe section is lifted by a single point of a truck crane at 20 miles away from the pipe head. The truck crane slowly lifts the pipe at 20 miles, and lifts it by 1m, 1.5m and 2m respectively. At this time, the pipe section is bent and deformed. The height from the ground within 60m in front of the pipe section is measured in turn, with a measurement interval of 5m. Based on the measurement data, a pipeline lifting bending deformation curve is drawn, such as Figure 4 shown.

[0055] 2. Test results

[0056] The test results show that as the lifting height at 20 miles increases, the maximum height of the pipe head from the ground increases, and the curvature of the pipe increases. When the lifting height at 20 miles is 2.5m, the maximum height of the pipe head from the ground is 2.9m. The lifting force of the crane hook increases slightly, from 21t to 23t. This is because the increase in the lifting height of the pipe head reduces the support force of the ground on the pipeline, resulting in an increase in the lifting force.

[0057] Comparing the displacement data measured in the test with the displacement results in the numerical analysis, such as Figure 5 As shown in the figure, the test results are basically consistent with the numerical analysis results. The test measurement data is slightly larger than the numerical analysis results, with the maximum difference being about 9%. This is caused by errors in the test measurement. Therefore, it can be determined from the test results and numerical analysis that when the pipeline is bent and deformed, the smaller the radius of curvature, the greater the stress on the pipeline itself.

[0058] Step 3: Analysis of factors affecting curvature radius

[0059] In order to obtain the multi-parameter influence law of the minimum radius of curvature of the pipeline when the ocean discharge pipe is towed, it is necessary to conduct a numerical analysis of the towing process of the ocean discharge pipe. When the ocean discharge pipe is towed, the head end of the pipe section is mainly towed forward, and the tail end is towed to the tail. Therefore, the two ends of the pipe can be simplified as hinged boundaries. Due to the large slenderness of the pipeline, the pipeline is greatly deformed and low stress at sea, which belongs to a geometric nonlinear analysis problem. The main environmental load on the pipeline is the wave load. In order to facilitate the analysis of the change law of the discharge pipe, a regular wave perpendicular to the pipeline axis is loaded in the numerical analysis. The dynamic analysis time is set to 3600s. The multi-parameter influence analysis table is shown in Table 2. After the dynamic analysis, the maximum equivalent stress of the discharge pipe is checked. When the maximum equivalent stress is less than the allowable stress, the wave height is increased until the ocean discharge pipe reaches the allowable stress. At this time, the minimum radius of curvature of the discharge pipe is read.

[0060] Table 2. Analysis of the influence of multiple parameters on the radius of curvature

[0061]

[0062]

[0063] 1. The influence of pipeline length on curvature radius

[0064] In order to understand the effect of pipeline length on the minimum allowable radius of curvature, six lengths of marine drift pipes were analyzed, namely 200m, 300m, 400m, 500m, 600m and 700m. The minimum allowable radius of curvature and its variation law of pipelines at different lengths were analyzed. The results are as follows: Figure 6 shown.

[0065] The analysis results of the minimum radius of curvature under different pipeline lengths show that the pipe length is related to the minimum radius of curvature. The longer the pipe length, the smaller the minimum allowable radius of curvature, so it can withstand greater bending deformation. When the pipe length is 200m, the minimum allowable radius of curvature is 1390D, and when the pipe length is 700m, the minimum allowable radius of curvature is 878D. This is because the longer the pipe length, the stronger the nonlinearity, and the smaller the deformation and stress under the same load.

[0066] 2. The influence of pipe diameter on curvature radius

[0067] In order to obtain the influence of different pipe diameters on the minimum allowable curvature radius, the steel pipe with a wall thickness of 16 mm is used as the benchmark, and six pipes with inner diameters of 800 mm, 900 mm, 1000 mm, 1100 mm, 1200 mm and 1300 mm are compared with the same wall thickness. The minimum allowable curvature radius and its variation law of pipes with the same wall thickness and different inner diameters are analyzed. The results are shown in the figure. Figure 7 shown.

[0068] The analysis results of the minimum curvature radius under different pipe diameters show that the minimum allowable curvature radius of the pipe is related to the pipe diameter. When the wall thickness remains unchanged, the larger the pipe diameter, the larger the minimum curvature radius of the pipe. When the inner diameter of the pipe is 800mm, the minimum allowable curvature radius is 810D, and when the inner diameter of the pipe is 1300mm, the minimum allowable curvature radius is 1135D.

[0069] 3. The influence of pipe wall thickness on the curvature radius

[0070] In order to obtain the influence of different pipe wall thickness on the minimum allowable curvature radius, the steel pipe with an inner diameter of 1000mm was used as the benchmark, and six pipes with different wall thicknesses, 10mm, 12mm, 14mm, 16mm, 18mm and 20mm, were compared respectively. The minimum allowable curvature radius of the pipe with the same inner diameter and different wall thickness was analyzed. The results are shown in the figure. Figure 8 shown.

[0071] The analysis results of the minimum radius of curvature under different pipe wall thicknesses show that when the inner diameter remains unchanged, the minimum allowable radius of curvature increases with the increase of wall thickness. When the pipe wall thickness is 10mm, the minimum allowable radius of curvature is 830D, and when the pipe wall thickness is 20mm, the minimum allowable radius of curvature is 1010D. This is because under the same inner diameter, the greater the wall thickness, the greater the rigidity of the pipe, the stronger the resistance to bending deformation, resulting in a larger minimum allowable radius of curvature of the pipe.

[0072] 4. Influence of elastic modulus on curvature radius

[0073] In order to obtain the influence of different elastic modulus on the minimum allowable curvature radius of pipes, three different pipe materials (elastic modulus) were compared, HDPE pipe, FRP pipe and steel pipe, with elastic modulus of 950MPa, 16900MPa and 212000MPa respectively, with the inner diameter of 1000mm and wall thickness of 16mm as the benchmark. The minimum allowable curvature radius of the pipe under different elastic moduli was analyzed. The results are shown in the figure. Fig. 9 shown.

[0074] The analysis results of the minimum radius of curvature under different elastic moduli of pipes show that when the inner diameter and wall thickness are the same, as the elastic modulus increases, the minimum allowable radius of curvature increases. When the pipe is HDPE with an elastic modulus of 950MPa, the minimum allowable radius of curvature is 43D; when the pipe is FRP with an elastic modulus of 169000MPa, the minimum allowable radius of curvature is 121D; when the pipe is steel with an elastic modulus of 212000MPa, the minimum allowable radius of curvature is 952D. This is because under the same inner diameter and wall thickness, the smaller the elastic modulus, the greater the flexibility of the pipe, the stronger the bending deformation ability, and the smaller the minimum allowable radius of curvature of the pipe.

[0075] Step 4: Analysis of curvature radius of discharge pipe (1008m)

[0076] During the towing process at sea, the drain pipe is subjected to wind, wave and current loads, which will cause bending deformation. For a 1008m long drain pipe, the deformation of the pipe is analyzed when the stress of the drain pipe reaches 0.72[σ]. Based on the pipe deformation results, the minimum curvature radius of the pipe is calculated.

[0077] 1. Analytical model

[0078] When the pipeline is towed at sea, the front and rear are connected to the tugboat by cables. Since the cables cannot withstand bending moments, the cables can be simulated as hinges and loaded with uniform loads. The Newton-Raphson method is used to perform nonlinear calculations to obtain the stress and displacement of the pipeline. When the stress of the pipeline reaches 0.72[σ]=170MPa, the pipeline deformation data at this time is obtained.

[0079] 2. Finite element analysis

[0080] The pipeline is simplified into a continuous beam unit, with simply supported constraints at both ends and uniformly distributed force loaded. Midas Civil is used for calculation and the calculation results are mutually verified.

[0081] The geometric nonlinear factors are taken into account in the calculation, and the Newton-Raphson method is used for solution. The initial uniformly distributed load is 1500N / m. According to the stress calculation results, the load is increased by 100N / m each step until the stress of the pipeline reaches the allowable stress of the material 170MPa.

[0082] When the uniform force is applied to 1900 N / m, the pipeline stress is close to the allowable stress of 170 MPa. At this time, the stress and displacement of the pipeline are as follows: Fig.10 and Fig.11 shown.

[0083] When the uniformly distributed force is loaded to 1900N / m, the pipeline stress is 171MPa and the maximum deformation is 8.09m, located in the middle of the pipeline.

[0084] At this time, the pipeline stress is close to the allowable stress. The uniformly distributed load at this time is the ultimate load that the pipeline towing can withstand. Considering the reduction of pipeline wave force, the ultimate wave load that the 1008m long discharge pipe can withstand is 3700N / m. Taking this load as the wave load limit, substitute it into the Morrison equation to obtain the ultimate wave height under wave periods of 5s, 6s, 7s and 8s. The results are as follows:

[0085] 1) Wave period 5s, extreme wave height 2.8m;

[0086] 2) Wave period 6s, extreme wave height 3.5m;

[0087] 3) Wave period 7s, extreme wave height 4.3m;

[0088] 4) Wave period 8s, extreme wave height 4.9m.

[0089] 3. Calculation of curvature radius

[0090] Extract the deformation data calculated in the software, calculate the curvature radius once for every three adjacent nodes, and find out the minimum curvature radius of the pipeline.

[0091] Substitute the deformation data into the above formula, extract the calculation result list, remove the deformation data within 20m at both ends of the pipeline, select the minimum value from the remaining curvature radius results, and after calculation, the minimum curvature radius R is about 800D (D is the outer diameter of the pipeline).

[0092] A design method for the curvature radius of a submarine pipeline described in this embodiment selects a suitable wave theory and pipeline model according to sea condition parameters, and uses the Morrison equation to calculate the extreme wave height. The curvature radius is calculated once for every three adjacent points under the extreme wave height, and the minimum value among them is the minimum curvature radius. A solution method for the minimum curvature radius is systematically given, and the value of the solved minimum curvature radius is basically accurate, which is more in line with installation requirements than the minimum curvature radius determined by existing experience. The design method has simple steps, is easy to operate, and has good effects.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for designing the curvature radius of a submarine pipeline, wherein the pipeline is a steel pipeline, characterized in that: The design method includes the following steps: Midas was used to establish a pipeline model. The length of the pipeline was greater than or equal to 120m. The pipeline used continuous beam units and hinged boundaries at both ends of the pipeline. A uniformly distributed load perpendicular to the pipeline axis was applied. The Newton-Raphson method was used for nonlinear calculation to obtain the stress and displacement of the pipeline. When the stress of the pipeline reaches the allowable stress, the uniformly distributed load at this time is the ultimate load that the pipeline towing can withstand. Considering the reduction of pipeline wave force, the ultimate wave load that the pipeline can withstand is calculated. By substituting the ultimate wave load into the Morrison equation, the ultimate wave height under different wave periods is obtained. The minimum curvature radius is found by calculating the curvature radius once for every three adjacent points. Suppose the three adjacent points are (x1, y1), (x2, y2), and (x3, y3), and the corresponding three sides are a, b, and c. The curvature radius R is obtained according to the cosine theorem. Calculate the minimum curvature radius of the pipeline under different extreme wave heights; Remove the deformation data within 20m at both ends of the pipeline, and select the minimum value from the remaining curvature radius results; For a 1008m long pipeline, the minimum radius of curvature R is 800D, where D is the outer diameter of the pipeline; Wave periods include 5s, 6s, 7s and 8s; The initial uniformly distributed load is 1500N / m. According to the stress calculation results, it is increased by 100N / m each step until the stress of the pipeline reaches the allowable stress of the material 170MPa.

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