A structural design and calibration method for oilfield pipe metal crimping fittings

Abstract

The present invention discloses a structural design and verification method for a metal crimped pipe fitting for oilfield pipes, comprising the following steps: 1) determining key parameters of the pipe fitting, including geometric parameters, material parameters, and operating condition parameters of the pipe fitting; 2) determining common failure modes of the metal crimped pipe fitting, including shear failure between an inner core and an outer sleeve, and interlayer peeling between an inner tooth and a plastic layer; 3) based on the failure mode in step 2) and the pipe fitting parameters in step 1), combined with failure formulas of mechanical theory, respectively proposing numerical models for theoretical calculation and verification; the present invention proposes numerical models for theoretical calculation and verification for the two failure modes of shear failure between the inner core and the outer sleeve and interlayer peeling between the inner tooth and the plastic layer, respectively, which are of great value not only for the development of new pipe fittings, but also for the safety verification of existing pipe fittings.

Description

Technical Field

[0001] The invention relates to the field of oilfield pipeline connection structure design, and in particular to an oilfield pipe crimping pipe fitting structure design and calibration method. Background Art

[0002] Currently, in the oilfield pipe industry, the primary connection method for composite pipes is metal crimping. The design of these fittings relies primarily on experience combined with practical testing, requiring extensive blasting tests. Since crimping fittings are disposable, each test requires significant labor and material costs. Currently, this field lacks a mature and reliable theoretical basis for design and a method for verifying tooth profile load-bearing capacity.

[0003] In the oilfield pipe industry, the high-pressure operation of pipelines, coupled with the transportation of high temperatures and corrosive media, places higher demands on the long-term service life of the pipeline system. The majority of accidents in the oilfield pipeline industry are caused by joint failures, and leaks in oilfield pipelines are accompanied by explosive or toxic gases and fluids. Therefore, joint design is key to the entire pipeline system. Currently, the design of crimp joints in this field mainly has the following problems:

[0004] 1) Pipe fitting structural design is experience-oriented and lacks sufficient theoretical support. The development process of new pipe fittings requires a large number of joint verification tests, and existing pipe fittings also lack safety verification methods.

[0005] 2) The failure modes of pipe fittings are mainly shear failure between the inner core and outer sleeve of the metal pipe fittings and interlayer delamination between the inner teeth and the plastic layer. There is a lack of verification formulas for these two failure modes. Summary of the Invention

[0006] In response to the problems existing in the prior art, the present invention provides a rationally designed oilfield pipe metal crimping fitting structure design and calibration method to solve many pain points in the field of oilfield metal pipe crimping fittings.

[0007] The technical solutions of the present invention are as follows:

[0008] A structural design and verification method for oilfield pipe metal crimping fittings includes the following steps:

[0009] 1) Determine the key parameters of pipe fittings, including geometric parameters, material parameters and working condition parameters of pipe fittings;

[0010] 2) Identify common failure modes of metal crimp fittings, including shear failure between the inner core and outer sleeve, and delamination between the inner teeth and the plastic layer;

[0011] 3) According to the failure mode in step 2) and the pipe parameters in step 1), combined with the failure formula of mechanical theory, numerical models for theoretical calculation and verification are proposed respectively.

[0012] Furthermore, for the failure mode of shear failure between the inner core and the outer sleeve, the following theoretical calculation and verification numerical model is proposed:

[0013] 3.1) Calculate the three-dimensional stress components:

[0014] According to the three-dimensional stress state analysis, the stress of a unit body in the pipe is mainly divided into: axial stress σ x , hoop stress σ θ , radial stress σ r For a metal pipe under uniform internal pressure, the hoop stress and radial stress at a distance r from the center axis are as follows (1)-(2):

[0015]

[0016]

[0017] Where: r1 is the center distance of the inner core tooth pitch, r2 is the center distance of the outer sleeve tooth pitch, r3 is the center distance of the interface between the inner core and the outer sleeve, r4 is the inner radius of the inner core, and Pn is the nominal pressure of the pipe fitting; substituting r=r3, the hoop stress and radial stress at the interface between the inner core and the outer sleeve can be obtained;

[0018] At the same time, the axial stress component under the internal pressure can be obtained as shown in formula (3):

[0019]

[0020] 3.2) Calculate the equivalent Mises stress:

[0021] According to the third strength theory, the three stress components obtained in step 3.1) are integrated into the equivalent Mises stress σ e As a discriminant indicator, as shown in formula (4):

[0022]

[0023] 3.3) Failure identification and verification:

[0024] The equivalent stress calculated in step 3.2) is equal to the interface strength σ of the inner and outer sleeves of the pipe fitting. L For comparison, as shown in formula (5):

[0025]

[0026] Wherein: μ is the safety factor, which is obtained by multiplying the two coefficients of the in-situ working condition and the type of the connected composite pipe. The in-situ working condition is divided into two types: cyclic working condition and stable working condition. The composite pipe type is divided into two types: bonded type and non-bonded type.

[0027] Furthermore, a numerical model for theoretical calculation and verification is proposed for the failure mode of interlayer peeling between the inner teeth and the plastic layer.

[0028] 3.4): Calculate the axial force that a single tooth can provide:

[0029] The axial force provided by the tooth profile is divided into two categories: friction force F1 and reaction force F2. The specific calculation formulas are shown in equations (6)-(7):

[0030]

[0031] F2=2πr1H1σ y (7)

[0032] Where: f is the friction coefficient between the pipe fitting and the pipe, H1 is the inner core tooth depth, L1 is the inner core tooth bottom width, L2 is the inner core tooth top width, σ y is the yield strength of the material;

[0033] Similarly, the friction force F3 and reaction force F4 corresponding to the outer sleeve teeth can be obtained, as shown in equations (8) and (9):

[0034]

[0035] F4=2πr2H2σ y (9)

[0036] Among them: L3 is the lower width of the outer sleeve teeth, L4 is the upper width of the outer sleeve teeth;

[0037] 3.5) Calculate the maximum axial force required under limit conditions:

[0038] The ultimate working condition of the connection between pipes and fittings is generally the burst test, which requires a pressure of more than 3 times the nominal pressure. Under this condition, the maximum axial force F5 required to be provided by the tooth profile of the pipe fitting can be obtained by formula (10):

[0039]

[0040] 3.6) Tooth profile bearing capacity verification:

[0041] Combined with the results of steps 3.4) and 3.5), the tooth structure bearing capacity is checked, as shown in formula (11):

[0042]

[0043] Where n1 is the minimum number of teeth required for the inner core, n2 is the minimum number of teeth required for the outer sleeve, and μ is the safety factor. The safety factor is obtained by multiplying the two coefficients of the in-situ working condition and the connected composite pipe type. The in-situ working condition is divided into cyclic working condition and stable working condition. The composite pipe type is divided into bonded type and non-bonded type.

[0044] The beneficial effects of the present invention are as follows:

[0045] 1) Combined with the common failure modes of metal crimping fittings and the failure formula of mechanical theory, a theoretical reference basis is provided for the key design of metal fittings (such as tooth shape, number of teeth, effective length of fittings, inner and outer sleeve dimensions, and material selection).

[0046] 2) For the two failure modes of shear failure between the inner core and the outer sleeve, and interlayer peeling between the inner teeth and the plastic layer, theoretical calculation and verification numerical models are proposed respectively. These models are not only valuable for the development of new pipe fittings, but also for the safety verification of existing pipe fittings.

[0047] 3) After the key parameters of the pipe fittings are determined, only one set of pressure verification tests is required. This saves a lot of blasting tests for the development of new pipe fittings, saving manpower and material resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 is a cross-sectional view of the pipe fitting of the present invention;

[0049] Figure 2 A cross-sectional view of the tooth shape of the present invention;

[0050] In the figure: 1-inner core, 2-outer sleeve. DETAILED DESCRIPTION

[0051] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0052] like Figure 1-2 As shown, a structural design and verification method for oilfield pipe metal crimping fittings is provided, and the specific steps are as follows:

[0053] 1. A method for designing and verifying the structure of a metal crimped oilfield pipe fitting, comprising the following steps:

[0054] 1) Determine the key parameters of the pipe fittings, including the geometric parameters, material parameters and working condition parameters of the pipe fittings, as shown in Table 1;

[0055] Table 1

[0056]

[0057] 2) Identify common failure modes of metal crimp fittings, including shear failure between the inner core and outer sleeve, and delamination between the inner teeth and the plastic layer;

[0058] 2.1) The inner core and outer sleeve of the pipe fall off: At present, the metal joints of the buckle type in the oil field are mainly composed of two parts: the inner core and the outer sleeve. The main structure is shown in the figure Figure 1As shown, 1 is the inner core and 2 is the outer sleeve. Both the inner core and the outer sleeve are toothed. Initially, there's enough space between them to allow the pipe to fit in. The pipe is clamped by crimping, achieving an interference fit between the pipe and the fitting. Because metal materials are inherently strong, the connection between the inner core and the outer sleeve is prone to failure. This is typically achieved by threading, welding, or, in the case of high-pressure fittings, by combining both. Therefore, strength verification of this connection is paramount.

[0059] 2.2) Delamination between the inner teeth and the plastic layer: The connection between the pipe fitting and the pipe mainly relies on the interference fit between the middle tooth shape and the pipe. The upper and lower teeth are firmly embedded in the composite pipe to provide sufficient axial force to the pipe. Therefore, the design of the tooth shape and the load-bearing capacity verification are crucial for a crimping pipe fitting.

[0060] 3) Based on the failure mode in step 2) and the pipe parameters in step 1), combined with the failure formula of mechanical theory, a numerical model for theoretical calculation and verification is proposed respectively;

[0061] For the failure mode of shear failure between the inner core and the outer sleeve, the following theoretical calculation and verification numerical model is proposed:

[0062] 3.1) Calculate the three-dimensional stress components:

[0063] According to the three-dimensional stress state analysis, the stress of a unit body in the pipe is mainly divided into: axial stress σ x , hoop stress σ θ , radial stress σ r For a metal pipe under uniform internal pressure, the hoop stress and radial stress at a distance r from the center axis are as follows (1)-(2):

[0064]

[0065]

[0066] Where: r1 is the center distance of the inner core tooth pitch, r2 is the center distance of the outer sleeve tooth pitch, r3 is the center distance of the interface between the inner core and the outer sleeve, r4 is the inner radius of the inner core, and Pn is the nominal pressure of the pipe fitting; substituting r=r3, the hoop stress and radial stress at the interface between the inner core and the outer sleeve can be obtained;

[0067] At the same time, the axial stress component under the internal pressure can be obtained as shown in formula (3):

[0068]

[0069] 3.2) Calculate the equivalent Mises stress:

[0070] According to the third strength theory, the three stress components obtained in step 3.1) are integrated into the equivalent Mises stress σ e As a discriminant indicator, as shown in formula (4):

[0071]

[0072] 3.3) Failure identification and verification:

[0073] The equivalent stress calculated in step 3.2) is equal to the interface strength σ of the inner and outer sleeves of the pipe fitting. L For comparison, as shown in formula (5):

[0074]

[0075] Where: μ is the safety factor, which is related to the designed in-situ operating conditions and the type of composite pipe connected, and is obtained by multiplying two factors. In-situ operating conditions are divided into cyclic conditions and stable conditions. The safety factor for cyclic conditions is smaller. Composite pipes are available in two types: bonded and non-bonded. Non-bonded pipes are generally used for water injection pipelines in oil fields. Due to the higher pressure, the safety factor is smaller. The specific results can be seen in Table 2:

[0076] For the failure mode of interlayer peeling between the inner teeth and the plastic layer, a numerical model for theoretical calculation and verification is proposed;

[0077] 3.4): Calculate the axial force that a single tooth can provide:

[0078] The axial force provided by the tooth profile is divided into two categories: friction force F1 and reaction force F2. The specific calculation formulas are shown in equations (6)-(7):

[0079]

[0080] F2=2πr1H1σ y (7)

[0081] Where: f is the friction coefficient between the pipe fitting and the pipe, H1 is the inner core tooth depth, L1 is the inner core tooth bottom width, L2 is the inner core tooth top width, σ y is the yield strength of the material;

[0082] Similarly, the friction force F3 and reaction force F4 corresponding to the outer sleeve teeth can be obtained, as shown in equations (8) and (9):

[0083]

[0084] F4=2πr2H2σ y (9)

[0085] Among them: L3 is the lower width of the outer sleeve teeth, L4 is the upper width of the outer sleeve teeth;

[0086] 3.5) Calculate the maximum axial force required under limit conditions:

[0087] The ultimate working condition of the connection between pipes and fittings is generally the burst test, which requires a pressure of more than 3 times the nominal pressure. Under this condition, the maximum axial force F5 required to be provided by the tooth profile of the pipe fitting can be obtained by formula (10):

[0088]

[0089] 3.6) Tooth profile bearing capacity verification:

[0090] Combined with the results of steps 3.4) and 3.5), the tooth structure bearing capacity is checked, as shown in formula (11):

[0091]

[0092] Where n1 is the minimum number of teeth required for the inner core, n2 is the minimum number of teeth required for the outer sleeve, and μ is the safety factor. The safety factor μ is related to the design in-situ operating conditions and the type of composite pipe to be connected, and is obtained by multiplying the two factors. In-situ operating conditions are divided into cyclic conditions and stable conditions. The safety factor for cyclic conditions is smaller. Composite pipes are available in two types: bonded and non-bonded. Non-bonded pipes are generally used for water injection pipelines in oil fields. Due to the higher pressure, the safety factor is smaller. The specific results can be seen in Table 2:

[0093] Table 2

[0094]

Claims

1. A structural design and calibration method for oilfield pipe metal crimping fittings, characterized in that: The steps include: 1) Determine the key parameters of pipe fittings, including geometric parameters, material parameters and working condition parameters of pipe fittings; 2) Identify common failure modes of metal crimp fittings, including shear failure between the inner core and outer sleeve, and delamination between the inner teeth and the plastic layer; 3) For the failure mode of shear failure between the inner core and the outer sleeve, the following theoretical calculation and verification numerical model is proposed: 3.1) Calculate the three-dimensional stress components: According to the three-dimensional stress state analysis, the stress of a unit body in the pipe is mainly divided into: axial stress σ x , hoop stress σ θ , radial stress σ r For a metal pipe under uniform internal pressure, the hoop stress and radial stress at a distance r from the center axis are as follows (1)-(2): Where: r3 is the distance from the center of the interface between the inner core and the outer sleeve, r4 is the inner radius of the inner core, and Pn is the nominal pressure of the pipe fitting. Substituting r=r3, the hoop stress and radial stress at the interface between the inner core and the outer sleeve can be obtained. At the same time, the axial stress under the internal pressure can be obtained as shown in formula (3): 3.2) Calculate the equivalent Mises stress: According to the third strength theory, the three stresses obtained in step 3.1) are integrated into the equivalent Mises stress σ e As a discriminant indicator, as shown in formula (4): 3.3) Failure identification and verification: The equivalent stress calculated in step 3.2) is equal to the interface strength σ of the inner and outer sleeves of the pipe fitting. L For comparison, as shown in formula (5): Wherein: μ is the safety factor, which is obtained by multiplying the two coefficients of the in-situ working condition and the type of the connected composite pipe. The in-situ working condition is divided into two types: cyclic working condition and stable working condition. The composite pipe type is divided into two types: bonded type and non-bonded type.

2. A structural design and calibration method for oilfield pipe metal crimping fittings, characterized in that: The steps include: 1) Determine the key parameters of pipe fittings, including geometric parameters, material parameters and working condition parameters of pipe fittings; 2) Identify common failure modes of metal crimp fittings, including shear failure between the inner core and outer sleeve, and delamination between the inner teeth and the plastic layer; 3) For the failure mode of interlayer peeling between the inner teeth and the plastic layer, a numerical model for theoretical calculation and verification is proposed; 3.1): Calculate the axial force that a single tooth can provide: The axial force provided by the tooth profile is divided into two categories: friction force F1 and reaction force F2. The specific calculation formulas are shown in equations (6)-(7): Where: f is the friction coefficient between the pipe fitting and the pipe, H1 is the inner core tooth depth, L1 is the inner core tooth bottom width, L2 is the inner core tooth top width, σ y is the material yield strength; r1 is the distance between the inner core teeth and the center; r3 is the distance between the inner core and the outer sleeve interface from the center; r4 is the inner radius of the inner core; Pn is the nominal pressure of the fitting; Similarly, the friction force F3 and reaction force F4 corresponding to the outer sleeve teeth can be obtained, as shown in equations (8)-(9): F4=2πr2H2σ y (9) Where: L3 is the lower width of the outer sleeve teeth, L4 is the upper width of the outer sleeve teeth; r2 is the distance between the outer sleeve teeth and the center; 3.2) Calculate the maximum axial force required under limit conditions: The ultimate working condition of the connection between pipes and fittings is generally the burst test, which requires a pressure of more than 3 times the nominal pressure. Under this condition, the maximum axial force F5 required to be provided by the tooth profile of the pipe fitting can be obtained by formula (10): 3.3) Tooth profile bearing capacity verification: Combined with the results of steps 3.1) and 3.3), the tooth structure bearing capacity is checked, as shown in formula (11): Where n1 is the minimum number of teeth required for the inner core, n2 is the minimum number of teeth required for the outer sleeve, and μ is the safety factor. The safety factor is obtained by multiplying the two coefficients of the in-situ working condition and the connected composite pipe type. The in-situ working condition is divided into cyclic working condition and stable working condition. The composite pipe type is divided into bonded type and non-bonded type.

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