Design method and device for metal sealing structure of underwater wellhead connector, medium and equipment

Abstract

The invention relates to a design method and device for a metal sealing structure of an underwater wellhead connector, a medium and equipment, and the method comprises the steps that S1, under the pre-tightening working condition, mechanical analysis is conducted on a driving piston, a locking block, a Christmas tree body and a metal sealing ring; s2, under the operation working condition, mechanical analysis is conducted on the wellhead connector body and the metal sealing ring; s3, according to the steps S1 and S2, obtaining a theoretical relationship between the operation contact stress of the metal sealing ring and the structural parameters, the radial compression amount and the working pressure; s4, establishing a sealing design criterion of the metal sealing ring according to the step S3; s5, establishing a strength design criterion of the metal sealing ring according to the step S3; s6, establishing a finite element simulation model of the sealing performance of the underwater wellhead connector; s7, analyzing the sealing performance of the metal sealing ring according to the finite element simulation model of the sealing performance of the underwater wellhead connector; and S8, obtaining the contact stress of the sealing surface of the metal sealing ring according to the steps S4, S5 and S7.

Description

Technical Field

[0001] The present invention relates to a design method, device, medium and equipment for a metal sealing structure of an underwater wellhead connector, belonging to the technical field of offshore oil production. Background Art

[0002] In the process of offshore oil and gas production, underwater wellhead connectors are mainly used for connecting the Christmas tree and the wellhead to prevent the leakage of oil and gas media. In order to be used in high-temperature, high-pressure and corrosive environments for a long time, metal sealing rings are generally used for sealing, and the sealing problem is the key technology of underwater wellhead connectors.

[0003] At present, there are no relevant standards and specifications specifically for the sealing design of underwater wellhead connectors, and the sealing mechanism is not yet clear. Moreover, the research and application of underwater production systems in China started relatively late and are still in the stage of R & D and trial application, with less research on underwater wellhead connectors. Summary of the Invention

[0004] In view of the above technical problems, the present invention provides a design method, device, medium and equipment for a metal sealing structure of an underwater wellhead connector. The method conducts a mechanical analysis of the underwater wellhead connector, deduces the theoretical relationship between the contact stress of the metal sealing ring under preloading and operating conditions and the structural parameters and working pressure, and establishes a force analysis method for the metal sealing structure of the underwater wellhead connector through the analysis of sealing design criteria and strength design criteria.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A design method for a metal sealing structure of an underwater wellhead connector includes the following steps:

[0007] S1: Under the preloading condition, conduct a mechanical analysis of the drive piston, locking block, Christmas tree body and metal sealing ring;

[0008] S2: Under the operating condition, conduct a mechanical analysis of the wellhead connector body and the metal sealing ring;

[0009] S3: According to steps S1 and S2, obtain the theoretical relationship between the operating contact stress of the metal sealing ring and the structural parameters, radial compression amount and working pressure;

[0010] S4: According to step S3, establish the sealing design criteria for the metal sealing ring;

[0011] S5: According to step S3, establish the strength design criteria for the metal sealing ring;

[0012] S6: Establish a finite element simulation model for the sealing performance of the underwater wellhead connector;

[0013] S7: Analyze the sealing performance of the metal sealing ring according to the finite element simulation model of the sealing performance of the subsea wellhead connector;

[0014] S8: According to steps S4, S5 and S7, accurately obtain the contact stress of the sealing surface of the metal sealing ring.

[0015] For the design method of the metal sealing structure of the subsea wellhead connector, preferably, in step S4, the calculation formula for the sealing design criterion of the metal sealing ring is as follows:

[0016]

[0017] In the formula, q0 is the pre-tightening contact stress; q is the operating contact stress; E R is the elastic modulus of the metal sealing ring, F R is the cross-sectional area of the metal sealing ring; b is the contact width; Δ is the radial compression of the metal sealing ring; W0 is the axial pre-tightening force; D1 is the inner diameter of the metal sealing ring; δ is the angle between the sealing surface of the metal sealing ring and the vertical direction; f3 is the friction angle between the Christmas tree body and the metal sealing ring; s p is the area under the action of internal pressure; h is the height at the inner diameter of the sealing ring; L1 is the length of the extended part of the wellhead connector; s1 is the cross-sectional area of the extended part of the wellhead connector; E1 is the elastic modulus of the extended part of the wellhead connector;, y p is the sealing specific pressure of the metal sealing ring; p is the internal pressure.

[0018] For the design method of the metal sealing structure of the subsea wellhead connector, preferably, in step S5, the calculation formula for the strength design criterion of the metal sealing ring is as follows:

[0019]

[0020] In the formula, σ1 is the first principal stress; σ2 is the second principal stress; σ3 is the third principal stress; σ s is the yield strength of the metal sealing ring material.

[0021] For the design method of the metal sealing structure of the subsea wellhead connector, preferably, in step S7, the analysis of the sealing performance of the metal sealing ring includes:

[0022] Analyze the influence of different pre-tightening forces on the radial compression, analyze the relationship between the contact stress and the pre-tightening force under different contact widths, analyze the relationship between the contact stress and the contact width under different pre-tightening forces, analyze the relationship between the contact stress and the radial compression under different widths, and analyze the influence of the working pressure on the contact stress under different widths.

[0023] The second aspect of the present invention provides a design device for the metal sealing structure of a subsea wellhead connector, including:

[0024] The first processing unit is used to perform mechanical analysis on the driving piston, the locking block, the production tree body, and the metal sealing ring under the pre-tightening condition;

[0025] The second processing unit is used to perform mechanical analysis on the wellhead connector body and the metal sealing ring under the operating condition;

[0026] The third processing unit is used to obtain the theoretical relationship between the operating contact stress of the metal sealing ring, the structural parameters, the radial compression amount, and the working pressure according to the first processing unit and the second processing unit;

[0027] The fourth processing unit is used to establish the sealing design criterion of the metal sealing ring according to the third processing unit;

[0028] The fifth processing unit is used to establish the strength design criterion of the metal sealing ring according to the third processing unit;

[0029] The sixth processing unit is used to establish a finite element simulation model for the sealing performance of the subsea wellhead connector;

[0030] The seventh processing unit is used to analyze the sealing performance of the metal sealing ring according to the finite element simulation model for the sealing performance of the subsea wellhead connector;

[0031] The eighth processing unit is used to accurately obtain the contact stress of the sealing surface of the metal sealing ring according to the fourth processing unit, the fifth processing unit, and the seventh processing unit.

[0032] In the third aspect of the present invention, there is provided a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, the steps of the design method of the metal sealing structure of the subsea wellhead connector described above are implemented.

[0033] In the fourth aspect of the present invention, there is provided a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the steps of the design method of the metal sealing structure of the subsea wellhead connector described above are implemented.

[0034] Due to the above technical solutions adopted by the present invention, it has the following advantages:

[0035] 1. Currently, the commonly used two-dimensional axisymmetric analysis method separately extracts the metal sealing ring and the wellhead head and the production tree in contact with it for simplified analysis. This simplified method ignores the influence of the contact action between components and does not conform to the actual contact force of the wellhead connector. Using a 1 / 12 of the overall structure in the circumferential direction to establish a three-dimensional model of the overall wellhead connector for contact analysis can more realistically simulate the load transfer between components, making the contact stress transmitted to the sealing surface of the metal sealing ring more accurate.

[0036] 2. The sealing performance of the wellhead connector was analyzed by the finite element method. Effective sealing can be achieved when the pre-tightening force is 892.5 - 1785 kN and the radial compression is 0.1045 - 0.2089 mm. The contact stress of the metal sealing ring increases with the increase of the pre-tightening force and radial compression, and decreases with the increase of the contact width. The operating contact stress q has a linear relationship with the working pressure p of the oil and gas medium. As the working pressure increases, the operating contact stress first decreases and then increases linearly. There is an inflection point in the change of the operating contact stress q with the internal pressure p. At this time, the corresponding operating contact stress value is the smallest, and this inflection point should be particularly concerned about when designing the metal sealing ring.

[0037] 3. Through the mechanical analysis of the underwater wellhead connector, the theoretical relationship between the contact stress of the metal sealing ring and the structural parameters and working pressure under the pre-tightening and operating conditions was derived. On this basis, a design method for the metal sealing structure of the underwater wellhead connector was established, including the sealing design criterion and the strength design criterion, to ensure the sealing performance during long-term use in high-temperature and high-pressure, deep and shallow water, and corrosive environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is the force analysis diagram of the driving piston under the pre-tightening condition provided by an embodiment of the present invention;

[0039] Figure 2 It is the force analysis diagram of the locking block under the pre-tightening condition provided by this embodiment of the present invention;

[0040] Figure 3 It is the force analysis diagram of the production tree body under the pre-tightening condition provided by this embodiment of the present invention;

[0041] Figure 4 It is the force analysis diagram of the metal sealing ring of the wellhead connector under the pre-tightening condition provided by this embodiment of the present invention;

[0042] Figure 5 It is the mechanical analysis diagram of the wellhead connector under the operating condition provided by this embodiment of the present invention;

[0043] Figure 6 It is the force analysis diagram of the metal sealing ring under the action of internal pressure provided by this embodiment of the present invention;

[0044] Figure 7 It is the relationship diagram of the radial compression and the pre-tightening force provided by this embodiment of the present invention, where Figure (a) is the calculation and comparison diagram of the relationship between the radial compression and the pre-tightening force, and Figure (b) is the relative error diagram;

[0045] Figure 8 It is the relationship diagram of the pre-tightening force and the contact stress provided by this embodiment of the present invention, where Figure (a) is the calculation and comparison diagram of the relationship between the pre-tightening force and the contact stress, and Figure (b) is the relative error diagram;

[0046] Figure 9 It is the relationship diagram of contact width and contact stress provided for this embodiment of the present invention. Among them, Figure (a) is the calculation and comparison diagram of the relationship between contact width and contact stress, and Figure (b) is the relative error diagram;

[0047] Figure 10 It is the relationship diagram of radial compression amount and contact stress provided for this embodiment of the present invention. Among them, Figure (a) is the calculation and comparison diagram of the relationship between radial compression amount and contact stress, and Figure (b) is the relative error diagram;

[0048] Figure 11 It is the relationship diagram of working pressure and contact stress provided for this embodiment of the present invention. Among them, Figure (a) is the relationship diagram of working pressure and operating contact stress when W0 = 892.5N, Figure (b) is the relationship diagram of working pressure and relative error when W0 = 892.5N, Figure (c) is the relationship diagram of working pressure and operating contact stress when W0 = 1785kN, and Figure (d) is the relationship diagram of working pressure and relative error when W0 = 1785kN;

[0049] Figure 12 It is the design roadmap of the metal seal structure of the underwater wellhead connector provided for this embodiment of the present invention;

[0050] Figure 13 It is the schematic diagram of the metal seal structure of the underwater wellhead connector provided for this embodiment of the present invention;

[0051] The reference numerals are as follows:

[0052] 1 - indicating mechanism; 2 - Christmas tree body; 3 - metal sealing ring; 4 - locking block; 5 - wellhead connector body; 6 - driving piston; 7 - secondary unlocking piston; 8 - acting ring; 9 - wellhead. Detailed implementation manners

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0054] Unless otherwise defined, the technical terms or scientific terms used in the present invention shall have the ordinary meanings understood by those of ordinary skill in the field to which the present invention pertains. The terms "first", "second", "third", "fourth" and similar terms used in the present invention do not denote any order, quantity or importance, but are only used to distinguish different components. Words such as "comprising" or "including" mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connected" or "coupled" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0055] For the sake of convenience of description, spatial relative relationship terms may be used in the text to describe the relationship of one element or feature shown in the figure relative to another element or feature. These relative relationship terms are, for example, "inner", "outer", "inner side", "outer side", "below", "above", etc. Such spatial relative relationship terms are intended to include different orientations of the device in use or operation other than the orientations depicted in the figure.

[0056] One of the prior arts discloses a test system and method for an underwater wellhead connector. The system includes: an upper test pile for sealing the upper interface of the underwater wellhead connector; a high-pressure wellhead test pile for sealing the lower interface of the underwater wellhead connector, and an oil injection port is provided on the high-pressure wellhead test pile; a hydraulic power loading system connected to the upper test pile for applying a load to the upper test pile; a data acquisition and control system and a hydraulic pump, and the data acquisition and control system is electrically connected to the hydraulic pump. The test system and method have a simple structure and strong repeatability, and can fully test the failure characteristics of the underwater wellhead connector under load in the locked state, ensuring the safety of deepwater oil exploitation. This invention only calculates the mechanical properties in the locked state under the production pressure of oil and gas media, and does not fully analyze the mechanical properties under the pre-tightening condition and the operating condition. Moreover, the test method of this invention does not elaborate on the dimensional relationship between the parts of the wellhead connector, and can only test the mechanical properties of an underwater wellhead connector with a specific size.

[0057] The second prior art discloses a method for predicting the sealing performance of a sealing structure of an underwater pipeline connector, including the following steps: determining the design variables of the sealing structure of the underwater pipeline connector; generating a number of design points through a sampling method, performing finite element simulation calculations on the generated number of design points to obtain a data set; constructing an ANN model with the output parameters as the objective function and constraint conditions based on the data set, and optimizing the model parameters of the ANN model through a genetic algorithm; inputting the design variables into the optimized ANN model to obtain the prediction result of the sealing performance of the sealing structure of the underwater pipeline connector. The present invention optimizes the model parameters of the neural network model by using a genetic algorithm and improves the traditional GA-ANN model. Compared with the traditional GA-ANN model, the fast GA-ANN model of the present invention does not need to be trained multiple times, and while ensuring that the ANN model has good generalization ability, it greatly reduces the required calculation time.

[0058] The third prior art discloses a method for monitoring the fretting fatigue state. First, an acoustic emission device is selected according to the fretting fatigue characteristics; then, acoustic emission sensors are arranged on the test piece; then, the relevant parameters of the acoustic emission equipment are adjusted to accurately monitor the change of the acoustic emission signal during the fretting fatigue test process; finally, the fretting fatigue state and the moment of the initiation of the fretting fatigue crack are judged through the analysis of the change of the acoustic emission signal. The present invention can study the fretting fatigue state under different materials and different connection structures and overcomes the deficiency that it is difficult to judge the initiation life of the fretting fatigue crack, which has important engineering practical significance. The cost of the acoustic emission device is relatively high, and the acoustic emission device is affected by the material characteristics, which will affect the judgment of the actual fretting fatigue life, and it is not universal. The device test design of the present invention pays attention to cost-effectiveness and realizes universality by simplifying the parameters. This method is a prediction of the sealing structure of the underwater pipeline connector, which has similarities with the metal design structure and sealing method of the underwater connector, but the invention does not perform a simulation on the prediction result and lacks real data to compare with the predicted data.

[0059] Since there are currently no clear relevant standards and specifications for the sealing design of underwater wellhead connectors, and the sealing mechanism is not yet clear, the research on underwater wellhead connectors in China started relatively late, and there is less research on underwater wellhead connectors (especially in deep water).

[0060] Based on the above technical problems, the present invention provides a method for designing a metal sealing structure of an underwater wellhead connector. The present invention conducts a mechanical analysis on the underwater wellhead connector and deduces the theoretical relationship between the contact stress of the metal sealing ring under the pre-tightening and operating conditions and the structural parameters and working pressure. On this basis, a design method for the metal sealing structure of the underwater wellhead connector is established, including a sealing design criterion and a strength design criterion, to ensure the sealing performance during long-term use in high-temperature, high-pressure, deep and shallow water, and corrosive environments.

[0061] As shown Figure 13 in the figure, the metal sealing structure of the underwater wellhead connector provided by the present invention includes: an acting ring 8 sleeved on the wellhead 9. The acting ring 8 includes a first acting ring and a second acting ring integrally formed coaxially. The outer diameter of the second acting ring is smaller than that of the first acting ring; a wellhead connector body 5. A trumpet-shaped accommodating cavity penetrating its axis is arranged in the wellhead connector body 5. The small-diameter end of the accommodating cavity is connected to the production tree body 2 through a flange. The large-diameter end of the accommodating cavity is used to accommodate the acting ring 8. The first acting ring is connected to the inner wall of the wellhead connector body 5. A gap is left between the second acting ring and the inner wall of the wellhead connector body 5; a secondary unlocking piston 7 and a driving piston 6, both of which are sleeved on the second acting ring, located in the gap and connected to the inner wall of the wellhead connector body 5. The driving piston 6 is located above the secondary unlocking piston 7; a locking block 4 is sleeved on the wellhead 9 and connected to the lower end surface of the production tree body 2. Teeth meshing with the tooth grooves of the wellhead 9 are arranged on the locking block 4. The outer wall surface of the locking block 4 contacts the upper end inner wall surface of the driving piston 6; a metal sealing ring 3 is assembled on the top of the wellhead 9 and located in the cavity of the production tree body 2 for sealing the wellhead 9 and the production tree body 2.

[0062] The general design life of the underwater wellhead connector of the present invention is 20 years. The sealing ring with a softer texture will creep over time and has poor resilience and is prone to failure. In addition, the oil and gas medium contains sulfur and sand, which causes greater corrosion and erosion to the sealing ring. Soft gaskets or soft metal wires with a softer texture are not applicable. The underwater wellhead connector of the present invention is mainly used for connecting between the production tree and the wellhead to prevent the leakage of oil and gas media. In order to be used in high-temperature, high-pressure and corrosive environments for a long time, metal sealing rings are generally used for sealing.

[0063] During the pre-tightening process of the underwater wellhead connector of the present invention, the locking pressure in the hydraulic cavity pushes the driving piston 6 to move downward. The inclined surface of the driving piston 6 drives the locking block 4 to contract radially. The locking block 4 meshes with the tooth grooves of the wellhead 9; while meshing, the locking block 4 moves downward along the axis, squeezing the acting ring 8. The acting ring 8 moves downward. The acting ring 8 and the wellhead connector body 5 are connected together. The wellhead connector body 5 and the production tree body 2 are also connected together through a flange. Therefore, the acting ring 8 drives the lower end of the production tree body 2 to move downward, squeezing the metal sealing ring 3 to complete the pre-tightening.

[0064] The following conducts a mechanical analysis of the pre-tightening process of the underwater wellhead connector of the present invention to obtain the mechanical relationship between the parts of the underwater wellhead connector under the pre-tightening condition. The force analysis of the driving piston 6 of the present invention under the pre-tightening condition is as Figure 1 shown. Under the action of the control hydraulic pressure P, the driving piston 6 moves downward relative to the locking block 4. The specific calculation formula is as follows:

[0065]

[0066] Among them, P is the control hydraulic pressure; D is the outer diameter of the hydraulic action surface of the driving piston; d is the inner diameter of the hydraulic action surface of the driving piston, α is the angle between the inclined plane of the driving piston and the vertical direction; f1 is the friction angle between the contact surface of the driving piston and the locking block; F L is the locking pressure generated by the control hydraulic pressure; f N1 is the frictional force between the contact surface of the driving piston and the locking block. The mechanical relationship of the normal pressure F N1 exerted by the driving piston 6 on the locking block 4 is obtained through formulas (1)-(3).

[0067] Under the pre-tightening state, the force analysis of the locking block 4 under the pre-tightening condition is as Figure 2 shown. Under the action of the normal pressure F N1 , the locking block 4 shrinks radially, and at the same time drives the wellhead connector body 5 to move downward, compressing the metal sealing ring 3 to achieve pre-tightening seal. The specific calculation formulas are as follows:

[0068]

[0069]

[0070] In the formula, β is the angle between the tooth groove of the locking block and the vertical direction; f is the friction angle between the locking block and the contact surface of the acting ring; f2 is the friction angle between the locking block and the meshing contact surface of the wellhead; f N is the frictional force between the locking block and the contact surface of the acting ring; f N2 is the frictional force between the tooth groove of the locking block and the meshing of the wellhead; F N is the supporting force of the acting ring on the locking block; F N2 is the normal meshing force between the tooth groove of the locking block and the tooth groove of the wellhead; F1 is the resultant force of F N1 and f N1 ; F2 is the resultant force of F N2 and f N2 ; F3 is the resultant force of F N3 and f N3 . The mechanical relationship of F N and F N2 under the pre-tightening state is obtained through formulas (4)-(6).

[0071] Under the pre-tightening state, the force analysis of the Christmas tree body 2 is as Figure 3 shown. When the locking block 4 and the wellhead 9 are locked, under the action of the axial pre-tightening force F N provided by the locking block 4, the Christmas tree body 2 has a tendency to move downward, and the frictional force f N3 of the contact surface is upward, and F X1 is the radial resilience of the metal sealing ring 3 received by the Christmas tree body 2. The specific calculation formulas are as follows:

[0072]

[0073] In the formula, δ is the angle between the sealing surface of the metal sealing ring and the vertical direction; f3 is the friction angle between the Christmas tree body and the metal sealing ring; F N3 is the normal pressure exerted by the Christmas tree on the metal sealing ring; f N3 is the frictional force on the contact surface between the Christmas tree and the metal sealing ring. The mechanical analysis of the friction angle f3 between the Christmas tree body and the metal sealing ring is obtained through formulas (7)-(8).

[0074] Under the pre-tightening state, the mechanical analysis of the metal sealing ring 3 is as Figure 4 shown. The normal pressure exerted by the Christmas tree body 2 on the metal sealing ring 3 is F N3 , and the upper frictional force f of the metal sealing ring 3 N3 is downward. The calculation formula is as follows:

[0075]

[0076] In the formula, D1 is the inner diameter of the metal sealing ring; E R is the elastic modulus of the metal sealing ring, F R is the cross-sectional area of the metal sealing ring; b is the contact width; Δ is the radial compression of the metal sealing ring; W0 is the axial pre-tightening force; The relationship between the contact stress q of the metal sealing ring of the subsea wellhead connector under the pre-tightening condition and the structural parameters and radial compression is calculated through formula (9).

[0077] From the above analysis, it can be seen that the necessary condition for the subsea wellhead connector of the present invention to form an initial seal is that the pre-tightening contact stress is not less than the pre-tightening seal specific pressure. The pre-tightening seal specific pressure can be determined according to the geometric characteristics of the contact surface. The metal sealing ring 3 studied in the present invention can refer to the specified value of the gasket with a circular cross-section. When the gasket material is stainless steel, the pre-tightening seal specific pressure is 179.3 MPa.

[0078] Under the operating condition, in addition to the pre-tightening force acting on the wellhead connector, it is also subjected to the production pressure of the oil and gas medium. Under the action of the pressure, the metal sealing ring 3 has a tendency to "expand" outward, and the wellhead connector body 5 has a tendency to be "lifted up". At this time, the axial force of the wellhead connector body 5 includes: the axial pre-tightening force W0, the axial load W p generated by the "lifting" of the wellhead connector due to the oil and gas medium pressure, the axial load W1' generated by the compression inside the metal sealing ring 3, and the axial load W2' generated by the radial pre-tightening compression rebound of the metal sealing ring 3. The mechanical analysis under the operating condition is as Figure 5 . The specific calculation and analysis are as follows:

[0079] W P =-ps P (10)

[0080] N p = πD1hp (11)

[0081] Wherein, p is the working internal pressure; s p is the area under the action of the internal pressure; N p is the radial self-tightening force generated when the sealing ring expands, N p ; h is the height at the inner diameter of the sealing ring.

[0082] Under the operating conditions, the force analysis of the metal sealing ring 3 is as Figure 6 shown. Under the action of the internal pressure, the metal sealing ring 3 expands, generating a radial self-tightening force N p , and the axial force corresponding to the radial self-tightening force on the sealing surface is W1, and the normal pressing force is F n1 . The radial self-tightening force of the sealing surface of the metal sealing ring 3 is Np. The specific calculation and analysis are as follows:

[0083]

[0084] Wherein, W1 is the axial force, W2 is the axial load, N0' is the radial self-tightening force, D1 is the inner diameter of the metal sealing ring, W'' is the pre-tightening contact pressure, and the mechanical relationship of the operating contact stress q of the metal sealing ring 3 is obtained through formulas (12)-(15). To obtain the theoretical relationship between the contact stress q and the internal pressure p, the unknown quantity Δ' must be calculated first.

[0085]

[0086] Wherein, ΔL1 is the uplift deformation; L1 is the length of the extended part of the wellhead connector; s1 is the cross-sectional area of the extended part of the wellhead connector; E1 is the elastic modulus of the extended part of the wellhead connector. The theoretical relationship between the operating contact stress of the metal sealing ring 3 of the subsea wellhead connector under the operating conditions, the structural parameters, the radial compression amount, and the working pressure is obtained through formulas (16)-(18).

[0087] Through the above mechanical analysis, the present invention deduces the theoretical relationship between the metal sealing parameters and the design parameters of the subsea wellhead connector. It is also necessary to judge whether an effective seal is formed through the seal design criterion, so as to judge whether the designed seal structure parameters are reasonable. At the same time, under the condition of meeting the seal, the strength of the metal sealing ring 3 should also meet the design requirements to avoid excessive equivalent stress in the seal structure.

[0088] The metal seal of the underwater wellhead connector of the present invention can be divided into two stages, namely the preloading condition seal and the operating condition seal. The necessary condition for sealing under the preloading condition is that the preloading contact stress is not less than the preloading seal specific pressure. At this time, the preloading seal specific pressure is mainly determined by the structure and can be determined according to the geometric characteristics of the contact surface. The metal sealing ring 3 studied in this paper can refer to the gasket with a circular cross-section. According to the provisions of GB 150.3-2011 "Pressure Vessels", when the material of the metal sealing ring 3 is stainless steel, the initial preloading seal specific pressure is 179.3 MPa; the seal specific pressure under the operating condition is the product of the gasket factor m of the metal sealing ring 3 and the working pressure p, and the gasket factor m = 6.5.

[0089] On the premise of meeting the seal specific pressure, a continuous seal band with a certain width needs to be formed on the sealing surface of the metal sealing ring 3, and reliable sealing can be achieved when the width of the metal seal band is at least more than 1.5 mm.

[0090] Based on the theoretical derivation results of the previous formulas, the following design criteria for the metal sealing ring 3 in the underwater wellhead connector are established:

[0091]

[0092] In the formula, y p is the seal specific pressure of the metal sealing ring, MPa. When p = 0, y p = 179.3 MPa; when p > 0, y p = mp; q0 is the preloading contact stress; q is the operating contact stress.

[0093] The greater the contact stress on the sealing surface, the more conducive it is to achieving sealing. However, as the contact stress increases, the equivalent stress of the metal sealing ring 3 also increases. When the equivalent stress increases to a certain extent, the metal sealing ring 3 enters the plastic deformation state, and at this time the structural resilience of the sealing ring fails. Therefore, it is necessary to control the upper limit of the contact stress and check the strength of the sealing ring.

[0094] Under the preloading condition, the strength dangerous section of the metal sealing ring 3 is its sealing surface. At this time, taking the sealing surface as the reference plane, the three principal stresses are: the normal stress σ0 on the sealing surface, the shear stress τ0 on the sealing surface, and the circumferential stress σ θ . Their values are respectively:

[0095]

[0096] Under the operating condition, the strength dangerous surface of the metal sealing ring 3 is also its sealing surface. At this time, the three principal stresses taking the sealing surface as the reference plane are: the normal stress σ0' on the sealing surface, the shear stress τ0' on the sealing surface, and the circumferential stress σ θ '. Their values are respectively:

[0097]

[0098] Let σ s be the yield strength of the metal seal ring material. The metal seal ring 3 is checked using the fourth strength theory. The strength design criterion for the metal seal ring 3 is as follows:

[0099]

[0100] After the design of the sealing structure of the underwater wellhead connector of the present invention is completed, the finite element method is used to analyze its sealing performance, as Figure 12 shown.

[0101] Based on the finite element method established according to the present invention, the influence of different pre-tightening forces on the radial compression amount is analyzed. The trends of the finite element and theoretical calculation results are the same. The radial compression amount increases with the increase of the pre-tightening force and is proportional. The finite element calculation result is slightly larger than the theoretical calculation result. The maximum relative error between the theoretical calculation and the finite element calculation of the radial compression amount is 4.9%. The calculation results are as Figure 7 shown.

[0102] The known modeling method is used to establish the finite element simulation model of the sealing performance of the underwater wellhead connector. The model includes the following modules: a three-dimensional model establishment module for establishing the basic three-dimensional model of the structure of the underwater wellhead connector. A finite element model establishment module for establishing the overall structure finite element model of the underwater wellhead connector according to the basic three-dimensional model. The underwater wellhead is installed and fixed on the seabed, and fixed constraints are applied to it, and the circumferential displacements of the two periodic symmetry planes of the wellhead connector are constrained to be zero. The lower part of the Christmas tree body, the wellhead head and the support ring are in a bonded constraint. Since the pre-tightening of the underwater wellhead connector is realized by relying on the driving piston, a displacement load can be applied to the driving surface of the driving piston to realize the finite element simulation of the assembly model. A working condition calculation module for applying different constraint conditions to the finite element model according to the preset working conditions, and analyzing the influence of different constraints on the underwater wellhead connector. In the actual working condition of the underwater wellhead connector, the application of the load is divided into two steps: applying a displacement load to the driving piston under the pre-tightening working condition, and the lower end of the Christmas tree squeezes the sealing ring to complete the pre-tightening; applying a working pressure load to the inner wall of the underwater wellhead connector in contact with the oil and gas medium under the operating working condition.

[0103] Based on the finite element method established according to the present invention, the relationship between the contact stress and the pre-tightening force under different contact widths is analyzed, as Figure 8As shown. When the contact width is constant, the contact stress of the metal sealing ring 3 increases with the increase of the pre-tightening force, showing a proportional relationship; when the pre-tightening force is constant, with the increase of the contact width, the contact load decreases rapidly, which is not conducive to sealing. The trend of the finite element calculation result curve is consistent with that of the theoretical calculation result curve. The smaller the contact width, the greater the relative error between the finite element calculation result and the theoretical calculation result. The maximum relative error between the finite element analysis result and the theoretical calculation is 3.6%. When the pre-tightening force is in the given range of 892.5 - 1785 kN, the pre-tightening contact stress of the metal sealing ring 3 is greater than 179.3 MPa, and the metal sealing ring 3 can meet the initial sealing requirements and ensure sealing.

[0104] Based on the finite element method established in the present invention, the relationship between the contact stress and the contact width under different pre-tightening forces is calculated respectively as Figure 9 . With the increase of the contact width, the contact stress decreases, and the contact stress is inversely proportional to the contact width; under the condition of the same contact width, the greater the pre-tightening force, the greater the corresponding contact stress. The trends of the calculation curves of the two methods are consistent. When the contact width is between 1.5 and 6 mm, the pre-tightening contact stress is greater than the pre-tightening sealing specific pressure, and the maximum relative error is 4.9%.

[0105] At the same time, the expressions of the pre-tightening contact stress and the operating contact stress can be expressed as follows:

[0106] Pre-tightening contact stress q0:

[0107]

[0108] Operating contact stress q:

[0109]

[0110] It can be seen from Equations 27 and 28 that, with other parameters unchanged, the pre-tightening contact stress q0 and the operating contact stress q decrease exponentially with the increase of the contact width b, which is not conducive to sealing. For the pre-tightening contact stress, increasing the contact width requires a larger pre-tightening force, which makes the size of the hydraulic cavity of the wellhead connector or the locking pressure larger. However, if the contact width is too small, the adaptability of the metal sealing ring 3 to manufacturing defects and roughness will be reduced. When installing the metal sealing ring 3, the relative movement of the sealing pair is likely to cause abrasion of the sealing surface. Therefore, the contact width of the sealing surface has a great influence on the pre-tightening contact stress and the operating contact stress. When the pre-tightening force is in the given range of 892.5 - 1785 kN, effective sealing can be achieved when the contact width is between 1.5 and 6 mm.

[0111] Based on the finite element method established in the present invention, the relationship between the contact stress and the radial compression amount under different widths is calculated respectively as Figure 10When the contact width is constant, the contact stress of the metal sealing ring 3 increases with the increase of the radial compression amount, showing a proportional relationship. When the radial compression amount is constant, with the increase of the contact width, the operating contact stress decreases rapidly, which is not conducive to sealing. The finite element analysis results are consistent with the theoretical calculation results, and the maximum error is 4%.

[0112] The radial pre-compression amount Δ is directly related to the contact stress of the underwater wellhead connector body 5. A reasonable radial compression amount can adapt to a large pressure fluctuation. The pre-tightening force derived above is proportional to the radial compression amount. Within the range of the pre-tightening force calculated above, it is more appropriate to take the radial pre-compression amount Δ as 0.1045 - 0.2089 mm.

[0113] Based on the finite element method established by the present invention, the influence of the working pressure on the contact stress under different widths is calculated respectively as follows Figure 11 The greater the pre-tightening force, the greater the corresponding operating contact stress. Selecting a larger pre-tightening force is beneficial to sealing.

[0114] The following conclusions can be drawn through the above analysis

[0115] 1. The metal seal of the underwater wellhead connector belongs to a plane contact problem. The outer edge of its sealing surface contacts the sealing groove and there is a small initial sealing angle, which makes the metal sealing ring 3 have good resilience after pre-tightening. It should be avoided that the bottom of the sealing surface of the metal sealing ring 3 contacts the sealing groove or the sealing surface is in full contact.

[0116] 2. The commonly used two-dimensional axisymmetric analysis method at present separately extracts the metal sealing ring 3 and the wellhead 9 and the production tree body 2 in contact with it for simplified analysis. This simplified method ignores the influence of the contact action between components and does not conform to the actual contact force of the wellhead connector. Using 1 / 12 of the circumferential direction of the overall structure to establish a three-dimensional model of the overall wellhead connector for contact analysis can more realistically simulate the load transfer between components, making the contact stress transmitted to the sealing surface of the metal sealing ring more accurate.

[0117] 3. The sealing performance of the wellhead connector is analyzed by the finite element method. Effective sealing can be achieved when the pre-tightening force is 892.5 - 1785 kN and the radial compression amount is 0.1045 - 0.2089 mm. The contact stress of the metal sealing ring increases with the increase of the pre-tightening force and the radial compression amount, and decreases with the increase of the contact width. The operating contact stress q has a linear relationship with the working pressure p of the oil and gas medium. With the increase of the working pressure, the operating contact stress first decreases and then increases linearly. There is an inflection point in the change of the operating contact stress q with the internal pressure p, that is At this time, the corresponding value of the operating contact stress is the smallest, and this inflection point should be particularly concerned about when designing the metal sealing ring.

[0118] Through mechanical analysis of the underwater wellhead connector, the present invention derives the theoretical relationships between the contact stress of the metal sealing ring under preloading and operating conditions, the structural parameters, and the working pressure. On this basis, a design method for the metal sealing structure of the underwater wellhead connector is established, including sealing design criteria and strength design criteria, to ensure the sealing performance during long-term use in high-temperature and high-pressure, deep and shallow water, and corrosive environments.

[0119] The present invention is described with reference to the flowcharts and / or block diagrams of methods, apparatuses (systems), and computer program products according to specific embodiments. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing devices to generate a machine, such that the instructions executed by the processor of the computer or other programmable data processing devices produce a means for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0120] These computer program instructions can also be stored in a computer-readable memory capable of guiding the computer or other programmable data processing devices to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction means that realizes the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0121] These computer program instructions can also be loaded onto the computer or other programmable data processing devices, such that a series of operation steps are executed on the computer or other programmable devices to generate a computer-implemented process, and thus the instructions executed on the computer or other programmable devices provide steps for realizing the functions specified in Figure 1 one process or multiple processes and / or blocks Figure 1 one block or multiple blocks.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A design method for the metal sealing structure of an underwater wellhead connector, characterized in that, It includes the following steps: S1: Under the pre-tightening condition, perform mechanical analysis on the driving piston (6), locking block (4), Christmas tree body (2), and metal sealing ring (3); S2: Under the operating condition, perform mechanical analysis on the wellhead connector body (5) and metal sealing ring (3); S3: According to steps S1 and S2, obtain the theoretical relationship between the operating contact stress of the metal sealing ring (3) and the structural parameters, radial compression amount, and working pressure; S4: According to step S3, establish the sealing design criterion for the metal sealing ring (3); S5: According to step S3, establish the strength design criterion for the metal sealing ring (3); S6: Establish a finite element simulation model for the sealing performance of the subsea wellhead connector; S7: According to the finite element simulation model for the sealing performance of the subsea wellhead connector, analyze the sealing performance of the metal sealing ring (3); S8: According to steps S4, S5, and S7, accurately obtain the contact stress on the sealing surface of the metal sealing ring (3).

2. The design method of the metal sealing structure of the underwater wellhead connector according to claim 1, characterized in that, In step S4, the calculation formula for the sealing design criterion of the metal sealing ring (3) is as follows: Wherein, q0 is the pre-tightening contact stress; q is the operating contact stress; E R is the elastic modulus of the metal sealing ring, F R is the cross-sectional area of the metal sealing ring; b is the contact width; Δ is the radial compression of the metal sealing ring; W0 is the axial pre-tightening force; D1 is the inner diameter of the metal sealing ring; δ is the angle between the sealing surface of the metal sealing ring and the vertical direction; f3 is the friction angle between the Christmas tree body and the metal sealing ring; s p is the area under the action of internal pressure; h is the height at the inner diameter of the sealing ring; L1 is the length of the extended part of the wellhead connector; s1 is the cross-sectional area of the extended part of the wellhead connector; E1 is the elastic modulus of the extended part of the wellhead connector;, y p is the sealing specific pressure of the metal sealing ring; p is the internal pressure.

3. The design method of the metal sealing structure of the underwater wellhead connector according to claim 2, characterized in that In step S5, the calculation formula for the strength design criterion of the metal sealing ring (3) is as follows: In the formula, σ1 is the first principal stress; σ2 is the second principal stress; σ3 is the third principal stress; σ s is the yield strength of the metal sealing ring material.

4. The design method of the metal sealing structure of the underwater wellhead connector according to claim 3, characterized in that, In step S7, the analysis of the sealing performance of the metal sealing ring (3) includes: Analyze the influence of different pre-tightening forces on the radial compression amount, analyze the relationship between the contact stress and pre-tightening force under different contact widths, analyze the relationship between the contact stress and contact width under different pre-tightening forces, analyze the relationship between the contact stress and the radial compression amount under different widths, and analyze the influence of the working pressure on the contact stress under different widths.

5. A design device for a metal sealing structure of an underwater wellhead connector, characterized in that, It includes: The first processing unit is used to perform mechanical analysis on the driving piston (6), locking block (4), Christmas tree body (2), and metal sealing ring (3) under the pre-tightening condition; The second processing unit is used to perform mechanical analysis on the wellhead connector body (5) and metal sealing ring (3) under the operating condition; The third processing unit is used to obtain the theoretical relationship between the operating contact stress of the metal sealing ring (3) and the structural parameters, radial compression amount, and working pressure according to the first processing unit and the second processing unit; The fourth processing unit is used to establish the sealing design criterion for the metal sealing ring (3) according to the third processing unit; The fifth processing unit is used to establish the strength design criterion for the metal sealing ring (3) according to the third processing unit; The sixth processing unit is used to establish a finite element simulation model for the sealing performance of the subsea wellhead connector; The seventh processing unit is used to analyze the sealing performance of the metal sealing ring (3) according to the finite element simulation model for the sealing performance of the subsea wellhead connector; The eighth processing unit is used to accurately obtain the contact stress on the sealing surface of the metal sealing ring (3) according to the fourth processing unit, the fifth processing unit, and the seventh processing unit.

6. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it realizes the steps of the design method of the metal sealing structure of the subsea wellhead connector described in any one of claims 1-4.

7. A computer device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it realizes the steps of the design method of the metal sealing structure of the subsea wellhead connector described in any one of claims 1-4.

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