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Address:No. 6, No. 18 Zhongtai science and Technology Park, No. A02, Huayuan Road, Garden Road, Baohe Economic Development Zone, Hefei

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Finite Element Analysis of Marine Cock Valve Body

Marine cock valve is one of the closing tools of the internal blowout prevention system in drilling. It covers both upper and lower marine cock valves. The main body of the upper marine cock valve is installed between the end joint and the upper end of the square drill pipe, and the lower marine cock valve body is installed between the square drill pipe and the drill string. Its main use is to close the through hole in the drill string when tap, tap, straw or riser are punctured or broken in case of blowout. Marine cock valves play an important role in avoiding blowout in drill string. In practical application, some marine cock valves bear inferior office load and cause ineffective disconnection, which not only directly affects the normal work of drilling, but also causes the shutdown and abandonment of oil wells, and even injuries and deaths of those who hold positions.



Marine cock valve body is the main part of marine cock valve. It is generally a group structure. Rotary torsion device is installed at the side wall opening. Marine cock body < br/>


1 valve body



The problem of disconnection of marine cock valve body has been besieging and disturbing producers and users. In view of this problem, this paper carries out research and discussion, carries out mechanics theory analysis on marine stopper valve body under different office load, studies and discusses the stress concentration problem of body, uses ANSYS software, establishes finite element plate type of valve body, and considers it appropriate to use bilinear follow-up consolidation plate type criterion to make the body in tension. The strength of the body under various loads, such as torsion, internal pressure and so on, is carefully analyzed, and the non-linear finite element analysis is carried out. The distribution law of structural stress is summarized and summarized, so as to further optimize the preset inventive conditions. Find out the main causes of stress concentration in valve body, and put forward improvement proposals.



2. Finite element plate type of marine cock valve body < br/>


2.1 Principles in Modeling Valve Ontology



(1) The force pattern of the body is similar to that of the actual structure, but it can be simplified or neglected if it has no great influence on the key parts of the study. (2) For the lower cock, the inner part of the screw is constrained and the outer part of the screw is loaded. A clear meshing of the screw will take up a large number of meshes. Because the main consideration is the strength of other parts of the marine cock valve, the equivalent treatment of the local force applied to the outer part of the screw is two. Local screw fasteners are simplified to conical surfaces. (3) The rotation and torsion holes of the body are preserved partly because they are the focus of analysis. Chamfer, middle groove and arc transition section are omitted. (4) In order to facilitate very accurate analysis and calculation, according to the unique symmetrical structure of the valve, the ontology is dissected, half of which is dissected, and constraints are imposed on the dissection surface.



2.2 Establishment of Finite Element Plate Shape



Free mesh method is suitable to distinguish solid plate shape. In order to obtain better calculation precision, this study considers that it is appropriate to use 10-node element with higher precision for space southeast and northwest body. Smart element size is suitable for mesh density restriction, and Smart element size restriction is suitable for mesh density restriction. Form. Set the size level to 6. The finite element mesh shape of the lower cock is obtained by distinguishing the meshes clearly, as shown in Figure 2. The number of nodes is 10963 and the number of elements is 6614.



2. Solid element mesh plate shape of lower cock body < br/>.


3. Finite Element Analysis under Tensile Load



For the strength analysis and calculation of preset structure, the preset criterion is whether the calculated stress in the dangerous part of the high stress zone is less than the allowable stress to confirm whether the preset structure satisfies the preset requirement. This is appropriate if the material is in the elastic stage at the beginning and end. However, in the structural strength analysis and calculation, the calculated stress obtained by the linear elastic method exceeds the elastic limit and enters the normative stage, so the linear elastic strength calculation method can not satisfy the requirements of the analysis and calculation. At this time, the material should carry out stress analysis and strength presupposition according to the calculation method of elastic norm law, and increase the accuracy and precision of the final calculation results.



The main body material of marine cock valve is low carbon boron steel 40CrMnMo, material flexibility limit 640 MPa, breaking limit 750 MPa, shear deformation modulus 1652.5 MPa, when the load reached the flexural limit, the proportional relationship between stress and strain no longer maintained and entered a non-linear stage. It is considered appropriate to use the classical bilinear follow-up consolidation (BKIN) criterion. As shown in Figure 3, the criterion contains the Bauschinger effect because of the use of the follow-up consolidation flexion criterion. This option is applied to the small strain problem of isotropic materials, which initially follows the Von Mises flexure criterion, and covers most metals, because it covers most metals. This is considered appropriate to use this material to consolidate the plate shape. The tension on the body is simplified to load uniformly on the right section. The variation of tensile load is 2250-4516 kN (referring to the maximum load of hooks of different drilling rigs). The stress cloud and stress variation curve obtained are different < br/>.


5. The variation of maximum equivalent stress with tensile load < br/>.


From 4 and 5, it can be seen that with the increase of the tensile load, the range of partial stress concentration gradually expands, but the stress in the inner wall of the hole and the upper and lower outlines parallel to the X direction are mainly stretched, the stress in other directions of the inner wall of the hole is smaller, and the stress in other parts of the body is far lower than the stress extreme value of the inner wall of the hole. Because of the process requirements, the main body has two different diameter stepped holes. When bearing the tension load, the stress concentration on the inner wall of the holes is more serious. When the tension load of the valve body reaches a certain number, the maximum equivalent stress is close to the flexure, but with the increase of the load, the maximum stress rise curve is not fast. It is considered that the stress analyzed by using the double-linear follow-up consolidation criterion is more than the allowable stress calculated by linear elasticity, so the special characteristics of the problem material can be considered. The structural strength can be calculated accurately so as to make full use of the material.



4. Finite element analysis of body under internal pressure < br/>.


When blowout occurs in drill string, the pressure of fluid is very long. There are certain standards for the internal blowout prevention pressure of marine cock valves in different countries. Different marine cock valves have different requirements. According to investigation and research, according to the national standards, the pressure values between 70 MPa and 130 MPa are taken for analysis. The stress cloud at the chamfer height of 0 is shown in Figure 6. The stress extreme variation curve of the chamfer height at the intersection line at 130MPa is shown in Figure 7. The stress variation curve at the intersection line at 70MPa is shown in figure 8.



The stress distribution near the hole is < br/> when the internal pressure is 130MPa and the chamfer is 0.


The maximum stress curve < br/> when the chamfer height at the intersection line varies at 7 130 MPa


Stress variation curve at intersection line < br/> at 8 70MPa


It can be seen from 6 and 8 that when the valve body is subjected to internal pressure load, the stress extreme value concentrates on the intersection line between the twist hole and the through hole of the body, and mainly in the area near the simplest side of XOY. The chamfer at the intersection line is necessary. It is more appropriate to take the height of chamfer at the intersection line (1-1.5 mm) from 7 analysis.



5. Finite Element Analysis of Body under Torque Load



When the valve body is subjected to torsion, in order to ensure the convergence of iteration, the upper finite element plate is further simplified. In order to give the torsion easily, the symmetrical structure can not be taken again, and the group analysis is carried out. The way of simplifying the torsion into force is added to the key points of the body end. As shown in 9, the number of distinct nodes is 8075 and the number of units is 4657. In order to give the torque easily, the symmetrical structure can not be taken again, and the group analysis can be carried out. The way of simplifying the torque into force is added to the key points of the body end surface. Through investigation and research data, the volume of torque is (28400-31600) kN. When the torque is 30800N/m, the hole stress is partially amplified, as shown in Figure 10.



Element grid plate shape < br /> when 9 valve body is twisted


Stress distribution near the hole under torsion < br />


It can be seen from 10 that when the valve body is subjected to torque load, the area of duck egg circle on the inner wall of the hole is within the range of stress concentration, and the area of stress concentration is 45-deg with the simplest surface of YOZ; therefore, there are four areas of stress concentration in the inner wall, 90-deg with each other, and stress distribution varies with the torque. The range of extreme value varies by half. As shown in Table 1.



Among the above mentioned loads, tensile load has a greater impact on the strength of the body, followed by internal pressure, and torsional overload has the smallest impact on the strength of the body.



6. Summarize
.


(1) After the finite element analysis of the marine cock valve body, stress concentration is a major factor of the validity of the valve body. Tensile load has a greater impact on the strength of the body, followed by internal pressure, and torsional overload has the smallest impact on the strength of the body. (2) Stress concentration in the inner wall of the hole is more serious when the tension load is borne. With the increase of tension load, the range of partial stress concentration gradually expands, but the stress in the inner wall of the hole and the upper and lower profiles parallel to the X direction are mainly stretched. The stress in other directions of the inner wall of the hole is smaller, and the stress in other parts of the body is far lower than the stress extremum of the inner wall of the hole. When the tension load of the valve body reaches a certain number, the maximum equivalent stress is close to the flexure, but with the increase of the load, the maximum stress rise curve is not fast. (3) When the valve body is subjected to internal pressure load, the stress extreme value concentrates on the intersection line between the rotary and torsional holes and the through holes of the body, and the chamfer height at the intersection line is (1-1).5) mm is more suitable. (4) When the valve body is subjected to torque load, the circle area of duck eggs on the inner wall of the orifice is within the range of stress concentration, and the area of stress concentration is 45-deg with the simplest surface of YOZ; so there are four small areas of stress concentration in the inner wall, 90-deg with each other; the range of stress extreme value varies with the variation of torque. Half.





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Contact:Miss Cheng
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Address:No. 6, No. 18 Zhongtai science and Technology Park, No. A02, Huayuan Road, Garden Road, Baohe Economic Development Zone, Hefei
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