Acid gas field conveying elbow cracking risk analysis method and system and medium

Abstract

The invention discloses an acid gas field conveying elbow cracking risk analysis method and system and a medium, and the method comprises the steps: obtaining the basic information of a certain block conveying elbow in combination with the actual working condition of an acid oil and gas field; constructing a finite element analysis model of a crack-containing elbow pipe structure according to the basic information of the conveyed elbow pipe; based on a finite element analysis model, equivalent stress fields and stress intensity factors of a crack-containing elbow structure under different parameter conditions are simulated and calculated, and then a stress intensity factor calculation formula of an elbow crack tip is determined in combination with a linear elastic fracture mechanics theory; a high-temperature and high-pressure kettle is adopted to simulate an acid gas field conveying pipeline field corrosion working condition environment, and a double-cantilever-beam method is adopted to measure the fracture toughness of a bent pipe structure material under the corrosion working condition environment; and based on the stress intensity factor calculation formula and the fracture toughness, carrying out conveying elbow cracking risk analysis. According to the method, the limitations that an existing evaluation method is not high in pertinence to the bent pipe structure, and the related calculation amount is large and complex are overcome.

Description

Technical Field

[0001] The present invention relates to the technical field of integrity evaluation of defective oil and gas transmission pipelines, and in particular to a cracking risk analysis method, system and medium for sour gas field transmission elbows. Background Art

[0002] As one of the most common pipe defects, crack defects are difficult to completely avoid in oil and gas pipelines. Sour gas field pipelines are faced with high H2S, high CO2, and Cl - Pipelines are often laid in hilly and mountainous areas, often in harsh corrosive media environments such as water. Compared to the overall pipeline, pipe bends exhibit geometric discontinuities, which are prone to stress concentration. Furthermore, under soil constraints and temperature loads, they experience significant additional bending loads and even deformation, making them highly susceptible to hydrogen-induced cracking or sulfide stress corrosion cracking. Once microcracks continue to propagate, leading to pipe leakage and failure, they can cause significant safety and environmental issues. Therefore, it is necessary to conduct a cracking risk assessment for cracked pipe bends. Traditionally, the safety of a material or structure has been assessed based on its strength. However, in high-sulfur environments, sulfide stress corrosion cracking (SSC) is generally a low-stress failure, with the stress value far below the tensile strength of steel. Therefore, fracture mechanics analysis methods have been introduced. From a fracture mechanics perspective, the stress intensity factor (SIF) is a key physical quantity reflecting the strength of the stress field at the crack tip. When the SIF exceeds the fracture toughness of the material, the crack will rapidly and unstablely propagate. The SIF has a quantitative relationship with component stress and crack size.

[0003] Standards and specifications such as the US ASME, API, EU SINTAP, and UK R5 have established safety assessment methods for plane defects, volume defects, and crack defects in high-temperature pressure vessels and pressure piping. However, due to the specific stresses on bends, these methods are not particularly targeted for bend locations in sulfur-containing oil and gas pipelines. For example, the mechanical analysis of bends in the standard evaluation algorithms is not clearly explained, and the various parameters and applicable conditions are particularly cumbersome. Current safety assessment and analysis methods for defective oil and gas pipelines primarily rely on failure assessment curves based on residual strength calculations. The calculation process for the key indicator, stress intensity factor, is cumbersome, requiring various parameters in the expression to be referenced in the appendix. Safety assessments are then completed through a series of interpolation calculations. When operating conditions dynamically change during pipeline service and crack defects expand, safety assessments must be repeated through a series of complex calculations, which lacks practicality.

[0004] Therefore, it is necessary to establish a highly applicable, simple and reliable cracking risk analysis method for sour gas field transmission elbows, which can effectively guide on-site staff to quickly and scientifically analyze the safe service capacity of elbows, which is of great significance for improving the service safety and risk management level of pipelines. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the current safety evaluation and analysis methods for defective oil and gas transmission pipelines are mainly based on failure assessment curves calculated based on residual strength. The calculation process of the key indicator stress intensity factor is cumbersome, and various parameters in the expression need to be checked in the appendix table, and the safety assessment can be completed through a series of interpolation calculation methods. When the working conditions of the pipeline change dynamically and crack defects expand during service, it is necessary to conduct a safety assessment again through a series of complex calculation processes, which lacks practicality to a certain extent, and has the limitations of large and complex related calculations. The purpose of the present invention is to provide a method, system and medium for analyzing the cracking risk of sour gas field transmission elbows. The present invention overcomes the limitations of existing assessment methods that are not targeted at elbow structures and have large and complex related calculations. Subsequent related evaluations of the block no longer require the use of finite element modeling analysis, thereby improving the ability and efficiency of pre-identification of safety risks of elbows.

[0006] The present invention is achieved through the following technical solutions:

[0007] In a first aspect, the present invention provides a method for analyzing cracking risk of a sour gas field transmission elbow, the method comprising:

[0008] Combined with the actual working conditions of sour oil and gas fields, basic information of the transmission elbows in a certain block is obtained;

[0009] Based on the basic information of the conveying elbow, a finite element analysis model of the elbow structure with cracks is constructed;

[0010] Based on the finite element analysis model, the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions are simulated and calculated. Then, the stress intensity factor calculation formula at the crack tip of the elbow is determined by combining the linear elastic fracture mechanics theory.

[0011] A high-temperature autoclave was used to simulate the on-site corrosion conditions of sour gas field transmission pipelines, and the double cantilever beam (DCB) method was used to measure the fracture toughness of the elbow structure material under this corrosion condition.

[0012] Based on the stress intensity factor calculation formula and fracture toughness, the cracking risk analysis of the conveying elbow is carried out.

[0013] This method collects basic information about pipe elbows in a specific area of ​​a sour gas field; constructs a finite element analysis model that considers the pipe elbow's geometric parameters, crack size, and service conditions; then, through multiple finite element model calculations and function fitting under different conditions, derives a formula for the stress intensity factor of cracked pipe elbows. Finally, combined with the measured fracture toughness of the material under simulated conditions, it conducts an analysis and assessment of the risk of pipe elbow cracking. This method is highly applicable and improves the ability and efficiency of pre-identifying pipe elbow safety risks. This method can accurately and quickly calculate the stress intensity factor level at the crack tip under service conditions in a specific area, eliminating the need for further finite element modeling and analysis techniques. It also avoids the complex and complex process of existing assessment methods, which require multiple parameters and require a lot of computation.

[0014] Furthermore, the basic information of the conveying elbow includes the material properties, geometric parameters, operating parameters and crack type defect characteristics of the elbow.

[0015] Furthermore, based on the operating temperature and pressure of the elbow, loads and boundary conditions were applied to the finite element analysis model of the cracked elbow structure. One end face of the elbow structure was fixed, internal pressure was applied inside the elbow, and the axial load was given in the form of a uniformly distributed force acting on the other end face of the elbow.

[0016] The relevant parameters of the finite element analysis model of the cracked elbow structure are pipe diameter D0, wall thickness t0, elbow angle B0, temperature T0, internal pressure P0, crack length C0 = 0 mm and crack depth a0 = 0 mm.

[0017] Furthermore, based on the finite element analysis model, the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions were simulated and calculated. Then, combined with the fracture mechanics theory, the calculation formula of the stress intensity factor at the crack tip of the elbow was determined, including:

[0018] According to the theory of linear elastic fracture mechanics, the calculation formula of stress intensity factor is obtained; and considering the crack size, the stress intensity factor function of the crack tip of the elbow is obtained;

[0019] Based on the finite element analysis model, the first dimensionless coefficient, second dimensionless coefficient, third dimensionless coefficient and stress intensity factor of the crack tip of the elbow are obtained by multivariate function fitting.

[0020] Substituting the first dimensionless coefficient, the second dimensionless coefficient, the third dimensionless coefficient and the stress intensity factor into the stress intensity factor function, the calculation formula of the stress intensity factor at the crack tip of the elbow is obtained;

[0021] Among them, the first dimensionless coefficient is a dimensionless coefficient related to the operating internal pressure, pipe diameter, and wall thickness of the elbow; the second dimensionless coefficient is a dimensionless coefficient related to the operating temperature of the elbow; the third dimensionless coefficient is a dimensionless coefficient related to the elbow angle; the stress intensity factor is the crack tip stress intensity factor under different crack depths and crack lengths of the elbow.

[0022] Furthermore, the stress intensity factor calculation formula K at the crack tip of the bent pipe is I for:

[0023]

[0024] in, is the first dimensionless coefficient; P is the operating internal pressure of the elbow, MPa; D is the diameter of the elbow, mm; t is the wall thickness of the elbow, mm; σ0 is the yield strength of the pipe, MPa; f(T) is the second dimensionless coefficient; f(B) is the third dimensionless coefficient; f(a,c) is the stress intensity factor.

[0025] Furthermore, the calculation formula for the axial load is:

[0026] σ L =Eα(T1-T2)

[0027] Where: σ L is the actual axial load applied after the internal pressure is applied to the elbow, MPa; E is the elastic modulus of the material, MPa; α is the linear expansion coefficient of the elbow material, °C -1 ; T1 is the temperature during installation, ℃; T2 is the temperature during operation, ℃.

[0028] Furthermore, the on-site corrosion environmental parameters include H2S / CO2 partial pressure, temperature, Cl ions and total pressure.

[0029] Furthermore, based on the stress intensity factor calculation formula and fracture toughness, the cracking risk analysis of the conveying elbow is carried out, including:

[0030] A nondestructive test is performed on an on-site elbow in a certain area. If a crack defect is detected, the crack size and basic information of the elbow are substituted into the stress intensity factor calculation formula at the elbow crack tip to obtain the calculated result.

[0031] The calculated results are compared with the fracture toughness of the elbow structure material measured under simulated corrosion conditions.

[0032] If the calculated result is less than the fracture toughness, the crack will not continue to grow under the current working conditions, and the crack type defect is acceptable and can continue to serve under enhanced inspection conditions;

[0033] If the calculated result is greater than or equal to the fracture toughness, the crack is likely to expand under the current working conditions, and the elbow needs to be replaced in time.

[0034] In a second aspect, the present invention further provides a sour gas field transmission elbow cracking risk analysis system, which uses the above-mentioned sour gas field transmission elbow cracking risk analysis method; the system comprises:

[0035] The acquisition unit is used to obtain basic information of the transmission elbow in a certain block based on the actual working conditions of the sour oil and gas field;

[0036] A model building unit is used to build a finite element analysis model of the elbow structure containing cracks based on the basic information of the conveying elbow;

[0037] The stress intensity factor calculation formula determination unit is used to simulate and calculate the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions based on the finite element analysis model, and then determine the stress intensity factor calculation formula at the crack tip of the elbow in combination with the linear elastic fracture mechanics theory;

[0038] The fracture toughness test unit is used to simulate the on-site corrosion conditions of sour gas field transmission pipelines using a high-temperature autoclave and measure the fracture toughness of the elbow structure material under this corrosion condition using the double cantilever beam (DCB) method;

[0039] The elbow cracking risk unit is used to analyze the cracking risk of conveying elbows based on the stress intensity factor calculation formula and fracture toughness.

[0040] In a third aspect, the present invention further provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the computer program implements the above-mentioned method for analyzing cracking risk of a sour gas field transmission elbow.

[0041] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0042] 1. The present invention provides a cracking risk analysis method, system, and medium for sour gas field transmission elbows. For sour gas field elbows with crack defects, the special structure and stress state of the elbow are specifically considered. Based on a large amount of basic information collected from on-site elbows, multiple sets of finite element model calculations and relationship function fitting are performed in the early stage to obtain a calculation formula for the stress intensity factor of the cracked elbow. Combined with the fracture toughness value of the elbow material measured under simulated corrosion conditions, an effective cracking risk assessment and analysis is performed. The method has strong applicability and improves the ability and efficiency of pre-identifying safety risks of elbows.

[0043] 2. The present invention provides a cracking risk analysis method, system, and medium for sour gas field transmission elbows. These methods can accurately and quickly calculate the stress intensity factor level at the crack tip under service conditions in a certain block, eliminating the need for finite element modeling and analysis technology. This also avoids the complex, multi-parameter, and computationally intensive processes of existing assessment methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] The drawings described herein are used to provide a further understanding of the embodiments of the present invention, constitute a part of this application, and do not constitute a limitation of the embodiments of the present invention. In the drawings:

[0045] Figure 1 This is a flow chart of a cracking risk analysis method for a sour gas field transmission elbow according to the present invention;

[0046] Figure 2 The stress intensity factor calculation example verification result in Example 2 of the present invention;

[0047] Figure 3 This is a structural block diagram of a cracking risk analysis system for sour gas field transmission elbows according to the present invention. DETAILED DESCRIPTION

[0048] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with examples and drawings. The exemplary embodiments of the present invention and their descriptions are only used to explain the present invention and are not intended to limit the present invention.

[0049] Example 1

[0050] like Figure 1 As shown, the present invention provides a cracking risk analysis method for a sour gas field transmission elbow pipe, which is based on the calculation of the crack tip stress intensity factor; the method comprises:

[0051] Step 1: Based on the actual working conditions of the sour oil and gas field, basic information of the transmission elbow in a certain block is obtained;

[0052] Specifically, the basic information of the conveying elbow includes the material properties, geometric parameters, operating parameters and crack type defect characteristics of the elbow.

[0053] Among them: material properties include yield strength σ, MPa; elastic modulus E, MPa; Poisson's ratio v;

[0054] Geometric parameters include pipe diameter D, mm; wall thickness t, mm; elbow angle θ, °;

[0055] Working parameters include temperature T, °C; internal pressure P, MPa;

[0056] The crack defect characteristic of the elbow is usually a surface defect with a sharp root, generally including surface cracks, buried cracks, and through cracks. The main parameters of the crack size are crack length c, mm; crack depth a, mm.

[0057] Step 2: Based on the basic information of the conveying elbow, a finite element analysis model of the elbow structure with cracks is constructed;

[0058] Considering that for a cracked elbow structure, it is often difficult to obtain an accurate crack tip field stress intensity factor using the calculation method in the standard, the present invention needs to use a finite element simulation method to obtain it;

[0059] Specifically, ANSYS was used to construct a finite element analysis model of a cracked elbow structure. The hexahedral element SOLID186 was selected as the structural unit, the linear strengthening model was used for the material, and the KSCON command was used to control the mesh at the crack tip so that the mesh near the crack expanded outward in a radial manner. Based on the operating temperature and operating pressure of the elbow, loads and boundary conditions were applied to the finite element analysis model of the cracked elbow structure. One end face of the elbow structure was fixed, internal pressure was applied inside the elbow, and the axial load was given in the form of a uniformly distributed force acting on the other end face of the elbow. Among them, the relevant parameters of the finite element analysis model of the cracked elbow structure were pipe diameter D0, wall thickness t0, elbow angle B0, temperature T0, internal pressure P0, crack length C0=0 mm and crack depth a0=0 mm.

[0060] Step 3: Based on the finite element analysis model, simulate and calculate the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions, and then combine the linear elastic fracture mechanics theory to determine the calculation formula of the stress intensity factor at the crack tip of the elbow;

[0061] Step 3: By changing the parameter values ​​in the finite element analysis model, the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions are simulated and calculated. Then, the stress intensity factor calculation formula at the crack tip of the elbow is determined by combining the linear elastic fracture mechanics theory. The specific steps include:

[0062] a. According to the theory of linear elastic fracture mechanics, the calculation formula of stress intensity factor is obtained: The calculation formula of stress intensity factor is:

[0063] Where: K is the desired stress intensity factor, MPa·mm 1 / 2 ; Y is the coefficient, dimensionless; σ is the principal stress of the vertical crack, MPa; a is the crack length, mm;

[0064] According to the theory of linear elastic fracture mechanics, the stress intensity factor is closely related to the size of the crack itself and the mechanical state it is in. The crack size mainly includes the crack length and crack depth. The mechanical state of the elbow position is directly related to the pipe diameter, wall thickness, pressure, temperature, and elbow angle. Therefore, considering these parameters comprehensively, the stress intensity factor function of the elbow crack tip is given (Formula (1)). By inputting the relevant parameters, the stress intensity factor of the elbow crack tip can be calculated. The stress intensity factor function is:

[0065] K I = Y P ·Y T ·Y B ·Kc (1)

[0066] where Y P =f(P,D,t), which is a dimensionless coefficient related to the operating internal pressure P, pipe diameter D, and wall thickness t of the elbow; Y T =f(T), a dimensionless coefficient related to the operating temperature T of the elbow; Y B =f(B), which is a dimensionless coefficient related to the elbow angle; Kc = f(a,c), which is the stress intensity factor at the crack tip under different crack depths a and crack lengths c of the elbow, MPa·mm 1 / 2 .

[0067] b. In the finite element basic model of the elbow structure, the crack size parameter is used as a variable, and other parameters are kept unchanged; the setting range of the crack length c is from c1 to ci (ci≤0.5D) with a step size of 1, and the crack length matrix C=[c1,c2…c i ]; The setting range of crack depth a is from a1 to ai (ai≤0.8t) with a step size of 2, and the crack depth matrix A=[a1,a2…a j ]; Each element in the crack length matrix and each element in the crack depth matrix can be used as a set of command parameters to calculate a stress intensity factor k at the crack tip of the elbow through the finite element model of the elbow structure, thereby establishing the stress intensity factor matrix K of the crack tip of the elbow as follows: Where: k ij The stress intensity factor of the elbow is obtained under the reference command composed of the i-th element in the crack length matrix C and the j-th element in the crack depth matrix A; that is, a crack length c i and a crack depth a j Get a corresponding elbow stress intensity factor k ij ;

[0068] Furthermore, by using multivariate function fitting, the calculation formula of the stress intensity factor of the crack tip of the bent pipe is obtained: Kc=f(a,c);

[0069] c. The temperature parameter is used as a variable in the finite element basic model of the elbow structure, and other parameters are kept unchanged; the equivalent stress field analysis and calculation of the elbow structure are used to obtain the temperature T0, T1, T2…T n (20℃≤T n Additional stress influence factor y of elbow at ≤60℃ T0 ,y T1 ,y T2 …y Tn , the dimensionless coefficient Y related to temperature is obtained by polynomial fitting T =f (T) , which is the second dimensionless coefficient;

[0070] d. In the finite element basic model of the elbow structure, the elbow angle parameter is used as a variable, and other parameters are kept unchanged; the equivalent stress field analysis and calculation of the elbow structure are used to obtain different elbow angles B0, B1, B2...B n (0°<B n Additional stress influence factor y under ≤90°) B0 ,y B1 ,y B2 …y Bn , the dimensionless coefficient Y related to the bend angle is obtained by polynomial fitting B =f (B) , which is the third dimensionless coefficient;

[0071] e. Through the equivalent stress field analysis and calculation of the finite element basic model of the elbow structure, the primary stress σ0 of the elbow is obtained, and the membrane stress σ generated by the internal pressure is set. p =PD / 2t, and then we get the first dimensionless coefficient:

[0072] f. The first dimensionless coefficient Y P , the second dimensionless coefficient Y T , the third dimensionless coefficient Y B , the stress intensity factor Kc is substituted into formula (1), and the calculation formula of the stress intensity factor of the crack tip of the bent pipe is obtained: I for:

[0073]

[0074] in, is the first dimensionless coefficient; P is the operating internal pressure of the elbow, MPa; D is the diameter of the elbow, mm; t is the wall thickness of the elbow, mm; σ0 is the yield strength of the pipe, MPa; f(T) is the second dimensionless coefficient; f(B) is the third dimensionless coefficient; f(a,c) is the stress intensity factor.

[0075] Collect at least 5 sets of basic information of bent pipes as examples, and use formula (2) and finite element model to calculate the stress intensity factor respectively, and obtain the average deviation E of the calculation results of the two methods. E should not be higher than 10%.

[0076] Step 4: Use a high-temperature autoclave to simulate the on-site corrosion environment of the sour gas field transmission pipeline. The on-site corrosion environment parameters can include H2S / CO2 partial pressure, temperature, Cl ion and total pressure. The double cantilever beam (DCB) method is used to measure the fracture toughness K of the elbow structure material under this corrosion environment. ISSC ;

[0077] Step 5: Based on the stress intensity factor calculation formula and fracture toughness, conduct cracking risk analysis of the conveying elbow.

[0078] Step 5 specifically includes:

[0079] A nondestructive test is performed on a pipe elbow in service in a certain area. If a crack defect is detected, the crack size and the basic information of the pipe elbow (material properties, geometric parameters, working condition parameters, etc.) are substituted into the stress intensity factor calculation formula of the pipe elbow crack tip to obtain the calculation result K I ;

[0080] The calculated result K I The fracture toughness K of the elbow structure material measured under simulated corrosion conditions ISSC Make comparisons;

[0081] If the calculation result K I Less than fracture toughness K ISSC , then the crack does not continue to expand under the current working conditions, the crack type defect is acceptable, and the vehicle can continue to serve under enhanced inspection conditions;

[0082] If the calculation result K I Greater than or equal to fracture toughness K ISSC , the crack may expand under the current working conditions, and the elbow needs to be replaced in time.

[0083] As a further implementation, after the internal pressure is applied to the elbow in step 2, the actual axial load applied is mainly generated by the temperature load. The calculation formula of the axial load is:

[0084] σ L =Eα(T1-T2) (3)

[0085] Where: σ L is the actual axial load applied after the internal pressure is applied to the elbow, MPa; E is the elastic modulus of the material, MPa; α is the linear expansion coefficient of the elbow material, °C -1 ; T1 is the temperature during installation, ℃; T2 is the temperature during operation, ℃.

[0086] This method collects basic information about pipe elbows in a specific area of ​​a sour gas field; constructs a finite element analysis model that considers the pipe elbow's structural geometry, crack size, and service conditions; then, through multiple finite element model calculations and function fitting under different conditions, derives a formula for the stress intensity factor of cracked pipe elbows. Finally, combined with the measured fracture toughness of the material under simulated conditions, it conducts an analysis and assessment of the risk of pipe elbow cracking. This method is highly applicable and improves the ability and efficiency of pre-identifying pipe elbow safety risks. This method can accurately and rapidly calculate the stress intensity factor level at the crack tip under service conditions in a specific area, eliminating the need for further finite element modeling and analysis techniques. It also avoids the complex and parameter-intensive processes of existing assessment methods.

[0087] Example 2

[0088] The difference between this embodiment and embodiment 1 is that this embodiment specifically takes a certain acidic oil and gas field as an example and is implemented as follows:

[0089] Step 1: Using a sour oil and gas field as an example, basic information on pipe bends from a typical block was collected, primarily including material properties, geometric parameters, operating parameters, and crack-type defect characteristics. Material properties included yield strength σ (MPa), elastic modulus E (MPa), and Poisson's ratio v; geometric parameters included pipe diameter D (mm), wall thickness t (mm), and bend angle θ (°); and operating parameters included temperature T (°C) and internal pressure P (MPa), as shown in Tables 1 and 2. Considering circumferential cracks, the crack length c was assumed to be equal to the measured crack length, and the crack plane was assumed to be perpendicular to the plane of maximum primary tensile stress.

[0090] Table 1 Basic information of elbows in a sour gas field block

[0091]

[0092] Table 2 Mechanical properties of different elbow materials

[0093]

[0094] Step 2: Use ANSYS to build a finite element analysis model of the cracked elbow structure. The structural unit is selected as the hexahedral unit SOLID186, the material adopts the linear strengthening model, and the KSCON command is used to control the mesh at the crack tip so that the mesh near the crack expands outward in a radial shape. Based on the operating temperature and operating pressure, loads and boundary conditions are applied to the finite element model of the elbow structure. One end face of the elbow structure is fixed, and internal pressure is applied inside the elbow. The axial load is given in the form of a uniformly distributed force acting on the other end face of the elbow. The axial load is mainly generated by the temperature load. The axial load calculation formula is as follows:

[0095] σ L=Eα(T1-T2) (4)

[0096] Where: σ L is the actual applied axial load, MPa; E is the elastic modulus of the material, MPa; α is the linear expansion coefficient of the elbow material, °C -1 ; T1 is the temperature during installation, ℃; T2 is the temperature during operation, ℃.

[0097] In the finite element basic model of the elbow structure, the elbow material is L245NS, the pipe diameter D0 is 325 mm, the wall thickness t0 is 11 mm, the elbow angle B0 is 10°, the temperature T0 is 20°C, the internal pressure P0 is 5 MPa, the crack length c0 = 0 mm, and the crack depth a0 = 0 mm;

[0098] Step 3: Based on the finite element analysis model of the elbow structure, by changing the parameter values, simulate and calculate the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions, and then combine the linear elastic fracture mechanics theory to determine the calculation formula of the stress intensity factor at the crack tip of the elbow; specifically, the following steps are included:

[0099] a. Based on the theory of linear elastic fracture mechanics, it is assumed that the stress intensity factor function at the crack tip of the elbow is:

[0100] K I =Y P ·Y T ·Y B ·Kc (5)

[0101] where Y P =f(P,D,t), which is a dimensionless coefficient related to the operating internal pressure P, pipe diameter D, and wall thickness t of the elbow; Y T =f(T), a dimensionless coefficient related to the operating temperature T of the elbow; Y B =f(B), a dimensionless coefficient related to the bend angle; Kc = f(a,c), the stress intensity factor at the crack tip under different crack depths a and crack lengths c, MPa·mm 1 / 2 ;

[0102] b. In the finite element basic model of the elbow structure, the crack length and crack depth are used as variables, and other parameters are kept constant; the setting range of the crack length c is from 18mm to 30mm in steps of 2mm, and the crack length matrix C = [c1, c2…c i ]=[18,20…30],i=1,2…7; the setting range of crack depth a is from 1mm to 8mm in steps of 1mm, and the crack depth matrix A=[a1,a2…a j]=[1,2…8],j=1,2…8;each element in the crack length matrix and each element in the crack depth matrix can be used as a set of command parameters to calculate a stress intensity factor k at the crack tip of the elbow through the finite element model of the elbow, thereby establishing the stress intensity factor matrix K of the crack tip of the elbow as follows:

[0103]

[0104] Where: k ij The stress intensity factor of the elbow is obtained under the reference command composed of the i-th element in the crack length matrix C and the j-th element in the crack depth matrix A; that is, a crack length c i and a crack depth a j Get a corresponding elbow stress intensity factor k ij ;

[0105] Furthermore, the calculation formula of the stress intensity factor at the crack tip of the elbow is obtained by multivariate function fitting:

[0106] Kc=f(a,c)=1.285a+0.1757c+0.911 (7)

[0107] c. In the finite element basic model of the elbow structure, the temperature parameter is used as a variable, and other parameters are kept unchanged. Through the analysis and calculation of the equivalent stress field of the elbow structure, the additional stress influence factors of the elbow at different temperatures of 20℃, 25℃, 30℃, 35℃, 40℃, and 50℃ are obtained as 1, 1.01, 1.03, 1.04, 1.06, and 1.07. The dimensionless coefficient related to temperature is obtained by polynomial fitting:

[0108] Y T =-8.99×10 -3 ·T 3 +3.88×10 -4 ·T 2 -4.058×10 -6 ·T+1.0569 (8)

[0109] d. In the finite element basic model of the elbow structure, the elbow angle parameter is used as a variable, and other parameters are kept unchanged. Through the analysis and calculation of the equivalent stress field of the elbow structure, the additional stress influence factors of 1.00, 1.00, 1.12, 1.19, 1.23, 1.26, 1.29, 1.31, and 1.32 at different elbow angles of 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, and 90° are obtained through finite element model analysis. The dimensionless coefficient related to the elbow angle is obtained through polynomial fitting:

[0110] Y B=0.0044·B+0.973 (9)

[0111] e. Through the equivalent stress field analysis and calculation of the finite element basic model of the elbow structure, the primary stress σ0 of the elbow is obtained to be 84MPa, and the membrane stress σ generated by the internal pressure is set p =PD / 2t, and then we get the dimensionless coefficient:

[0112]

[0113] f. The dimensionless coefficients Kc and Y T 、Y B 、Y P , that is, substitute equations (7), (8), (9), and (10) into equation (5), and finally obtain the stress intensity factor calculation formula K at the crack tip of the elbow I :

[0114]

[0115] g. Collect the basic information of 5 sets of elbows on site as examples, and use formula (11) and construct finite element model to calculate the stress intensity factor. The error rate of the calculation results is shown in Table 3. The maximum error rate is less than 10%, and the average error rate is 6.34%, indicating that the stress intensity factor K of the elbow crack tip is I The calculation formula has good accuracy.

[0116] Table 3 Verification of calculation results under different working conditions

[0117] name Calculation example 1 Calculation example 2 Calculation example 3 Calculation example 4 Calculation example 5 Operating pressure / MPa 8 8 6 7 6 Operating temperature / ℃ 30 30 30 40 40 Elbow outer diameter / mm 200 88.9 114.3 168.3 219 Bend wall thickness / mm 10 10 10 12 14 Bending angle / ° 20 20 30 30 40 Crack length / mm 20 8 10 8 28 Crack depth / mm 5 3 3 4 6 <![CDATA[Formula calculation result K I / MPa.m 1 / 2 > 10.6420 2.6907 3.0714 5.1725 9.5410 <![CDATA[Calculation results of finite element software / MPa·m 1 / 2 > 11.0379 2.9784 3.2873 5.0194 8.7472 Error rate / % 3.6％ 9.6％ 6.5％ 3.0％ 9.0％

[0118] The stress intensity factor calculation example of the present invention verifies the results as follows Figure 2 shown.

[0119] Step 4: Use a high-temperature autoclave to simulate the harsh corrosion working environment on site, with H2S partial pressure of 0.8MPa, CO2 partial pressure of 1.5MPa, total pressure of 8MPa, temperature of 30°C, and Cl ion concentration of 20000mg / L. After 30 days of testing under this corrosion condition, the actual fracture toughness value K of the elbow material under the service condition is measured using the double cantilever beam (DCB) method. ISSC 27.6MPa.m 1 / 2 ;

[0120] Step 5: Perform crack risk analysis on the elbow with crack defects found during on-site pipeline inspection. After simplifying the crack type defect rules found in the elbow, the crack length is 18 mm, the crack depth is 4 mm, the elbow material is L245NS, the pipe diameter is 219 mm, the wall thickness is 10 mm, the elbow angle is 40°, the operating internal pressure is 6 MPa, and the operating temperature is 50 °C. Substitute the basic parameters into formula (11) to calculate the crack tip stress intensity factor K. I 9.09MPa.m 1 / 2 ;

[0121] Crack tip stress intensity factor K I 9.09MPa.m 1 / 2 Less than the measured fracture toughness value K under service conditions ISSC 27.6MPa.m 1 / 2 , indicating that the risk of crack propagation in the bent pipe under the current service conditions is low, the defect is acceptable, and the pipe can continue to serve under enhanced monitoring and inspection.

[0122] The advantages of the present invention are as follows:

[0123] (1) For crack-defective elbows in sour gas fields, the special structure and stress state of the elbow part are specifically considered. Based on a large amount of basic information collected from on-site elbows, a calculation formula for the stress intensity factor of the cracked elbow is obtained through the early calculation of multiple sets of finite element models and relationship function fitting. Combined with the fracture toughness value of the elbow material measured under simulated corrosion conditions, an effective cracking risk assessment analysis is carried out, which has strong applicability and improves the ability and efficiency of pre-identification of safety risks of elbows.

[0124] (2) The stress intensity factor level at the crack tip of a certain block under service conditions can be calculated accurately and quickly without the need for finite element modeling analysis technology again. At the same time, it also avoids the complex process of many parameters, large amount of calculations and so on in the existing assessment method.

[0125] Example 3

[0126] like Figure 3 As shown, the difference between this embodiment and embodiment 1 is that this embodiment provides a sour gas field transmission elbow cracking risk analysis system, which uses the sour gas field transmission elbow cracking risk analysis method of embodiment 1. The system corresponds one-to-one with the sour gas field transmission elbow cracking risk analysis method of embodiment 1. The system includes:

[0127] The acquisition unit is used to obtain basic information of the transmission elbow in a certain block based on the actual working conditions of the sour oil and gas field;

[0128] A model building unit is used to build a finite element analysis model of the elbow structure containing cracks based on the basic information of the conveying elbow;

[0129] The stress intensity factor calculation formula determination unit is used to simulate and calculate the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions based on the finite element analysis model, and then determine the stress intensity factor calculation formula at the crack tip of the elbow in combination with the linear elastic fracture mechanics theory;

[0130] The fracture toughness test unit is used to simulate the on-site corrosion conditions of sour gas field transmission pipelines using a high-temperature autoclave and measure the fracture toughness of the elbow structure material under this corrosion condition using the double cantilever beam (DCB) method;

[0131] The elbow cracking risk unit is used to analyze the cracking risk of conveying elbows based on the stress intensity factor calculation formula and fracture toughness.

[0132] The execution process of each unit can be performed according to the process steps of the method for analyzing cracking risk of a sour gas field transmission elbow in Example 1, and will not be described in detail in this embodiment.

[0133] At the same time, the present invention also provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the above-mentioned method for analyzing cracking risks of a sour gas field transmission elbow is implemented.

[0134] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0135] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0136] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0137] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0138] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A cracking risk analysis method for a sour gas field transmission elbow, characterized in that: The method includes: Based on the actual working conditions of sour oil and gas fields, basic information on pipeline elbows in a certain block is obtained; Constructing a finite element analysis model of the cracked elbow structure based on the basic information of the pipeline elbow; Based on the finite element analysis model, the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions are simulated and calculated, and then the calculation formula of the stress intensity factor at the crack tip of the elbow is determined by combining the linear elastic fracture mechanics theory; A high-temperature autoclave was used to simulate the on-site corrosion conditions of the sour gas field transmission pipeline, and the double cantilever beam method was used to measure the fracture toughness of the elbow structure material under this corrosion condition. Based on the stress intensity factor calculation formula and the fracture toughness, a cracking risk analysis of the conveying elbow is performed.

2. The method for analyzing cracking risk of an acid gas field transmission elbow according to claim 1, characterized in that: The basic information of the conveying elbow includes the material properties, geometric parameters, working condition parameters and crack type defect characteristics of the elbow.

3. The method for analyzing cracking risk of an acid gas field transmission elbow according to claim 1, characterized in that: Based on the operating temperature and pressure of the elbow, loads and boundary conditions are applied to the finite element analysis model of the cracked elbow structure. One end of the elbow structure is fixed, internal pressure is applied inside the elbow, and the axial load is given in the form of a uniformly distributed force acting on the other end of the elbow. The relevant parameters of the finite element analysis model of the cracked elbow structure are pipe diameter, wall thickness, elbow angle, temperature, internal pressure, crack length and crack depth.

4. The method for analyzing cracking risk of an acid gas field transmission elbow according to claim 1, characterized in that: Based on the finite element analysis model, the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions are simulated and calculated. Then, the calculation formula of the stress intensity factor at the crack tip of the elbow is determined by combining the fracture mechanics theory, including: According to the theory of linear elastic fracture mechanics, the calculation formula of stress intensity factor is obtained; and considering the crack size, the stress intensity factor function of the crack tip of the elbow is obtained; Based on the finite element analysis model, the first dimensionless coefficient, the second dimensionless coefficient, the third dimensionless coefficient and the stress intensity factor of the crack tip of the elbow are obtained respectively by multivariate function fitting; Substituting the first dimensionless coefficient, the second dimensionless coefficient, the third dimensionless coefficient and the stress intensity factor into the stress intensity factor function to obtain a calculation formula for the stress intensity factor of the crack tip of the bent pipe; Among them, the first dimensionless coefficient is a dimensionless coefficient related to the operating internal pressure, pipe diameter, and wall thickness of the elbow; the second dimensionless coefficient is a dimensionless coefficient related to the operating temperature of the elbow; the third dimensionless coefficient is a dimensionless coefficient related to the elbow angle; and the stress intensity factor is the crack tip stress intensity factor under different crack depths and crack lengths of the elbow.

5. The method for analyzing cracking risk of an acid gas field transmission elbow according to claim 4, characterized in that: Calculation formula of stress intensity factor K at crack tip of bent pipe I for: in, is the first dimensionless coefficient; P is the operating internal pressure of the elbow, MPa; D is the diameter of the elbow, mm; t is the wall thickness of the elbow, mm; σ0 is the yield strength of the pipe, MPa; f(T) is the second dimensionless coefficient; f(B) is the third dimensionless coefficient; f(a,c) is the stress intensity factor.

6. The method for analyzing cracking risk of an acid gas field transmission elbow according to claim 3, characterized in that: The calculation formula of the axial load is: s L =Eα(T1-T2) Where: σ L is the actual axial load applied after the internal pressure is applied inside the elbow; E is the elastic modulus of the material; α is the linear expansion coefficient of the elbow material; T1 is the temperature during installation; T2 is the temperature during operation.

7. The method for analyzing cracking risk of an acid gas field transmission elbow according to claim 1, characterized in that: The on-site corrosion working environment parameters include H2S / CO2 partial pressure, temperature, Cl ions and total pressure.

8. The method for analyzing cracking risk of an acid gas field transmission elbow according to claim 1, characterized in that: Based on the stress intensity factor calculation formula and the fracture toughness, a cracking risk analysis of the conveying elbow is performed, including: A nondestructive test is performed on an on-site elbow in a certain area. If a crack defect is detected, the crack size and basic information of the elbow are substituted into the stress intensity factor calculation formula at the elbow crack tip to obtain the calculated result. Comparing the calculated results with the fracture toughness of the elbow structure material measured under simulated corrosion working condition environmental parameters; If the calculated result is less than the fracture toughness, the crack will not continue to grow under the current working conditions, the crack type defect is acceptable, and the vehicle can continue to serve under enhanced inspection conditions; If the calculated result is greater than or equal to the fracture toughness, the crack is likely to expand under the current working conditions, and the elbow needs to be replaced in a timely manner.

9. A cracking risk analysis system for sour gas field transmission elbows, characterized in that: The system uses a sour gas field transmission elbow cracking risk analysis method as described in any one of claims 1 to 8; the system includes: The acquisition unit is used to obtain basic information of the transmission elbow in a certain block based on the actual working conditions of the sour oil and gas field; A model building unit, configured to build a finite element analysis model of the cracked elbow structure based on the basic information of the conveying elbow; A stress intensity factor calculation formula determination unit is used to simulate and calculate the equivalent stress field and stress intensity factor of the cracked elbow structure under different parameter conditions based on the finite element analysis model, and then determine the stress intensity factor calculation formula at the crack tip of the elbow in combination with the linear elastic fracture mechanics theory; The fracture toughness test unit is used to simulate the on-site corrosion conditions of sour gas field transmission pipelines using a high-temperature autoclave and measure the fracture toughness of the elbow structure material under this corrosion condition using the double cantilever beam method; The elbow cracking risk unit is used to perform a cracking risk analysis of the conveying elbow based on the stress intensity factor calculation formula and the fracture toughness.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for analyzing cracking risks of elbow pipes in sour gas fields according to any one of claims 1 to 8 is implemented.

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