Method for testing internal stress of field oil and gas pipeline girth joint and pipe replacement method

Abstract

This invention discloses a method for testing the internal stress of welded joints in oil and gas pipelines and a method for replacing pipes. The internal stress testing method includes the following steps: excavating the soil at the welded joint of the oil and gas pipeline, measuring the strain of the pipeline before and during excavation; after the excavation is completed, cutting the pipeline along the first incision on one side of the welded joint, and measuring the strain on the other side of the welded joint after the first incision is made; obtaining the internal stress of the welded joint by measuring all the strains. This invention allows for precise testing of the stress borne by the pipeline during excavation, which is beneficial for selecting the specifications of the new pipeline and for quantitatively analyzing the force exerted on the pipeline by the soil in the replacement area.

Description

Technical Field

[0001] This invention belongs to the field of oil and gas pipeline emergency repair technology, specifically involving a method for testing the internal stress of the ring weld joint of oil and gas pipelines on site and a method for replacing the pipe. Background Technology

[0002] For unsafe circumferential welds in pipelines containing cracks or subjected to deformation, emergency repair work such as shutting down the pipeline and replacing it is often necessary after assessment. Pipe replacement repair requires cutting open the problematic pipeline. Before cutting, the pipeline itself is subject to soil constraint stress; after cutting, the pipeline may deform significantly due to stress release. However, current on-site construction rarely tests the stress on the pipeline and does not consider the additional internal stress generated after the replacement pipeline is reinstalled and buried. If a pipeline of the same specifications is directly replaced at the cut location, the soil constraint and other factors after reinstallation and burial may increase the internal stress of the pipeline. This could cause the actual stress on the replaced pipeline at the circumferential weld to be greater than expected, resulting in a significantly shortened service life and jeopardizing the safe operation of the pipeline. Summary of the Invention

[0003] To address the problems existing in the prior art, the purpose of this invention is to provide a method for testing the internal stress of the welded joint of an oil and gas pipeline in the field and a method for replacing the pipeline. This invention allows for precise testing of the stress borne by the pipeline during pipeline excavation, which is beneficial for selecting the specifications of the new pipeline and also helps in the quantitative analysis of the force exerted on the pipeline by the soil in the pipeline replacement area.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for testing the internal stress of a welded ring joint in an oil and gas pipeline on-site includes the following steps:

[0006] Excavate the soil at the welded joint of the oil and gas pipeline at the site, and measure the strain of the oil and gas pipeline before and during the excavation. After the soil excavation is completed, cut the oil and gas pipeline along the first cut on one side of the welded joint. After the first cut is completed, measure the strain on the other side of the welded joint. Obtain the internal stress of the welded joint of the oil and gas pipeline by measuring all the strains.

[0007] Preferably, the strain is measured using an axial strain gauge and strain rosette installed on the oil and gas pipeline on one side of the ring weld joint, and the tensile load, compressive load, bending moment and torque at the ring weld joint of the oil and gas pipeline on site are calculated based on the measured strain.

[0008] Preferably, the on-site oil and gas pipeline circumferential weld joint internal stress testing method of the present invention further includes the measurement and calibration process of axial strain gauges and strain rosettes. Specifically, after the axial strain gauges and strain rosettes are installed, a steel pipe and circumferential weld joint that are the same as the on-site oil and gas pipeline and are in a free state are used for the measurement and calibration of the strain gauges and strain rosettes.

[0009] Preferably, several measuring points are evenly arranged around the same circumference of the on-site oil and gas pipeline, and each measuring point is equipped with an axial strain gauge and a strain rosette; among them, measuring points are located at the top and bottom of the on-site oil and gas pipeline.

[0010] Preferably, the distance between the circumference of the measuring point and the welded joint of the oil and gas pipeline on site is 30-50 mm.

[0011] Preferably, the strain gauge is a triaxial strain gauge, with an included angle of 45° between adjacent strain gauges in the triaxial strain gauge, and one of the strain gauges is set along the axial direction of the on-site oil and gas pipeline.

[0012] Preferably, the distance between the first cut and the ring weld joint of the on-site oil and gas pipeline is 1000-1500mm.

[0013] Preferably, the internal stress of the welded joint of the oil and gas pipeline in the field is calculated using Origin software and all measured strains.

[0014] This invention also provides a method for replacing pipes in the field at the ring weld joint of an oil and gas pipeline, comprising the following steps:

[0015] Test site for internal stress in the welded joint of oil and gas pipeline rings;

[0016] The specifications and welding method of the new pipeline are determined by combining the working conditions of the on-site oil and gas pipeline ring weld joint and the internal stress of the on-site oil and gas pipeline ring weld joint obtained by testing.

[0017] The selected new pipe is welded into the on-site oil and gas pipeline to complete the replacement of the on-site oil and gas pipeline ring weld joint.

[0018] Preferably, after the on-site stress test of the oil and gas pipeline ring weld joint is completed, the on-site oil and gas pipeline ring weld joint is cut off.

[0019] When cutting off the welded joint of the oil and gas pipeline ring at the site, the distance between the cuts on both sides of the welded joint and the welded joint should be 1000-1500mm.

[0020] The present invention has the following beneficial effects:

[0021] This invention provides a method for testing the internal stress of welded joints in oil and gas pipelines on-site. By measuring the strain before and during excavation, as well as the strain during cutting, the internal stress of the welded joints in oil and gas pipelines on-site can be obtained. By considering these stresses, that is, by taking into account the internal stress of the pipeline itself and the force exerted on the pipeline by the soil in the pipeline replacement area, this invention can provide data support when replacing pipelines, which helps to select pipelines of appropriate specifications and ensure that the replaced pipelines meet the usage requirements after installation. Attached Figure Description

[0022] Figure 1(a) is a schematic diagram of the measuring point cross section and strain measuring point arrangement in the embodiment of the present invention (the unit of dimensions in the figure is mm);

[0023] Figure 1(b) is a schematic diagram of the strain measurement point arrangement end face in Figure 1(a);

[0024] Figure 1(c) shows a schematic diagram of the strain gauge arrangement at each measuring point;

[0025] Figure 2 This is a schematic diagram of the earthwork excavation sequence and measurement process for implementing the present invention (the units of dimensions in the diagram are mm);

[0026] Figure 3(a) is a photograph of a pipe section during on-site testing according to an embodiment of the present invention; Figure 3(b) is another photograph of a pipe section during on-site testing according to an embodiment of the present invention;

[0027] Figure 4 This is a flowchart illustrating the excavation sequence and measurement process for the circumferential weld seam of a pipeline according to an embodiment of the present invention (the units of dimensions in the figure are mm).

[0028] Figure 5(a) is a photograph of the first cut near the circumferential weld of the pipe in an embodiment of the present invention; Figure 5(b) is another photograph of the first cut near the circumferential weld of the pipe in an embodiment of the present invention;

[0029] Figure 6 This is a regression diagram of the measurement point location and axial stress distribution in an embodiment of the present invention.

[0030] Figure 7 This is a regression diagram of the shear stress distribution at the measurement point location in an embodiment of the present invention.

[0031] Figure 8 This is a schematic diagram of the cross-sectional load of the circumferential weld of the pipe section in an embodiment of the present invention (4m upstream excavation);

[0032] In the figure: 1-adjacent weld joint, 2-work area, 3-weld joint to be taken, 4-strain measurement point layout section, 5-buried steel pipe, 6-soil covering around the pipe, 7-first cut position, 8-second cut position, 9-excavation section I, 10-excavation section II, 11-excavation section III, 12-excavation section IV, 13-straight pipe I, 14-straight pipe II, 15-strain gauge, 16-strain element, 17-steel pipe surface. Detailed Implementation

[0033] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. These descriptions are intended to explain the invention and not to limit it.

[0034] This invention utilizes experimental methods and the strain effect of resistive materials to convert the internal deformation of a pipeline circumferential weld into a change in resistance, based on the sensor principle. The strain difference is calculated by measuring the resistance change using strain gauges and strain rosettes. Considering the assembly stress during the welding process, residual stress after welding, soil constraint stress during construction and backfilling, and the working stress during operation, the accurate measurement and calculation of the stress on the pipeline circumferential weld is crucial. Following the previously described measurement steps, axial strain gauges and strain rosettes are first deployed. Based on the principle of superposition of cross-sectional stress caused by axial force and bending moment, the normal stress caused by axial force can be obtained. The axial force and bending moment of the cross-section are then determined using Origin. Similarly, based on the principle of superposition of cross-sectional shear stress caused by torque and shear force, the shear stress caused by torque and the torque borne by the cross-section can be obtained. The torque and shear force of the cross-section are then determined using Origin.

[0035] The objective of this invention is achieved through the following steps:

[0036] Step 1: For oil and gas pipelines with high stress, the on-site team will test the internal stress of the circumferential weld joints. Based on axial strain gauges and the strain rosette resistance change conversion method, the changes in tensile (compressive) loads, bending moments, and torques before and during pipeline excavation will be measured. The strain difference value will be obtained by strain gauge and strain rosette testing and calculation.

[0037] Determine the locations of the pipe body and circumferential weld for on-site strain testing, and determine the axial spacing and circumferential test point distribution. Then, calibrate the strain gauges and strain rosettes using free-state steel pipes and circumferential welds of the same material.

[0038] Step 2: After excavating and cleaning the surface of the steel pipe in a single section, install axial strain gauges and attach strain rosettes at the designed measuring points near the weld to be tested. Each specimen has only one test section with a total of 8 measuring points. After connecting all measuring points and calibrating them using steel pipes and circumferential welds of the same material in a free state, the testing equipment is zeroed and the strain values ​​at each measuring point are recorded as baseline data. In this step, before testing, the pipe body and circumferential weld locations for on-site strain testing are determined, as well as the axial spacing and circumferential test point distribution. Strain gauges and strain rosettes are measured and calibrated using steel pipes and circumferential welds of the same material. After connecting all measuring points and calibrating them using steel pipes and circumferential welds of the same material in a free state, the testing equipment is zeroed and the strain values ​​at each measuring point are recorded as baseline data.

[0039] Step 3: After confirming the data is correct and storing it, excavation is allowed to proceed sequentially along the designed excavation direction and length. After each segment is excavated, the excavator stops operation and completes the collection of strain gauge data. After the data collection is completed, the excavator is allowed to continue excavating along the designed direction and length to complete all designed earthwork excavation conditions. In this step, after confirming the data is correct and storing it, excavation is allowed to proceed sequentially along the designed excavation direction and length. After each segment is excavated, the excavator stops operation and completes the collection of strain gauge data. After the data collection is completed, the excavator is allowed to continue excavating along the designed direction and length, repeating the above steps to complete all designed earthwork excavation conditions.

[0040] Step 4: After the earthwork excavation is completed, the steel pipe is allowed to be cut along the first cut (30mm away from the circumferential weld). After the steel pipe is cut, immediately record the strain values ​​of each measuring point after the constraint of the adjacent pipeline segment is released. After confirming that the data is correct and storing it, immediately remove the strain gauges near the weld and cut the pipe segment along the second cut.

[0041] Step 5: Then prepare for the strain test of the next pipe section. Repeating steps 1-4 can achieve on-site strain testing and recording for all pipe sections.

[0042] Step 6: For cases without earthwork excavation, after completing Step 1, once all measuring points are connected and the testing equipment is properly adjusted, zero the equipment and record the strain values ​​at each measuring point as the baseline data. Next, cut the steel pipe along the first incision. After the pipe is cut, immediately record the strain values ​​at each measuring point after the constraints of adjacent pipe segments are released. Once the data is confirmed to be correct and stored, immediately remove the strain gauges near the weld and cut the pipe segment along the second incision. The measurement work is now complete.

[0043] Step 7: After the field test is completed, first calculate the polar moment of inertia, moment of inertia, and cross-sectional area of ​​the cross section to determine the material and geometric parameters; then calculate the initial strain data based on the test data of the axial strain gauge and the change in resistivity of the strain.

[0044] Polar moment of inertia of cross section:

[0045]

[0046] Moment of inertia of cross section:

[0047]

[0048] Cross-sectional area:

[0049]

[0050] In the formula, D is the outer diameter of the steel pipe and d is the inner diameter of the steel pipe.

[0051] The initial strain value is calculated based on the test point location and the test-related resistance strain difference data.

[0052] The cross-sectional stress can be calculated using measured cross-sectional strain values ​​and methods from mechanics of materials. The calculation formula is as follows:

[0053]

[0054]

[0055]

[0056] Where: ε x ε y and ε 45 ° represents the measured strain values ​​at each measuring point in the axial, circumferential, and 45° directions; τ represents the strain values ​​at each measuring point. x τ y and τ xy These represent the normal stress, circumferential stress, and shear stress of the cross section, respectively; the meanings of the other symbols are the same as before.

[0057] Step 8: Based on the strain data, calculate the normal stress of the pipe circumferential weld section, which is mainly composed of axial force and bending moment. The strain distribution of the section conforms to the plane section assumption. Use Origin to calculate the axial force and bending moment of the section and perform regression fitting of the axial stress distribution.

[0058] Based on the principle of superposition of cross-sectional stresses caused by axial force and bending moment, the normal stress caused by axial force can be obtained as follows:

[0059]

[0060] The axial force borne by the cross section is:

[0061] P = σ p A (8)

[0062] The bending moment borne by the section is:

[0063]

[0064] Step 9: Based on the strain data, calculate that the shear stress of the pipe circumferential weld section is mainly caused by torque and shear force, and the section strain conforms to the trigonometric function distribution. Use Origin to calculate the section torque and shear force, and perform regression fitting of shear stress distribution and torque.

[0065] Based on the principle of superposition of cross-sectional shear stress caused by torque and shear force, the shear stress caused by torque can be obtained as follows:

[0066]

[0067] The torque borne by the cross section is:

[0068]

[0069] Similarly, the maximum shear stress at the vertex of the cross section caused by shear force can be obtained as follows:

[0070]

[0071] The shear force borne by the cross section is:

[0072] F = τ f A (13)

[0073] In summary, the present invention provides a method for testing the internal stress of circumferential welded joints in oil and gas pipelines. Based on the characteristics of the weld joint and the stress characteristics during operation, the method models and analyzes the stress on the circumferential welded joint under different service environments. This provides technical support for replacing problematic pipelines in the field. This achievement has been applied to the later stages of the China-Russia East Route pipeline construction, the Fujian-Guangdong branch line construction, the West Fourth Line, and the West Fifth Line pipeline construction. The assessment of circumferential weld defect tolerance provides theoretical support for unifying circumferential weld defect detection criteria, improving circumferential weld quality, and ensuring pipeline operational safety. Based on the test calculation of axial strain gauges and strain rosette resistance change conversion methods, this invention performs data processing and related calculation methods and test techniques. It uses strain gauges and strain rosettes with axial position spacing distribution and circumferential stress point distribution (main axial stress area). Simultaneously, it measures and calibrates strain gauges and strain rosettes on steel pipes and circumferential welds of the same material in a free state, fitting and calculating the strain difference under different constraint stresses. Simultaneously, based on the calculated cross-sectional moment of inertia, strain difference, and stress state of the pipeline circumferential weld, the initial strain value is calculated. The analysis shows that the normal stress of the cross-section is mainly caused by axial force and bending moment, and the strain distribution of the cross-section conforms to the plane section assumption. Axial force and bending moment are calculated using Origin. The analysis also shows that the shear stress of the cross-section is mainly caused by torque and shear force, and the strain distribution of the cross-section conforms to a trigonometric function distribution. Torque and shear force are calculated using Origin. Regression fitting is performed on the distribution of shear stress and axial stress at the test points to reflect the actual internal stress distribution during the service process of the pipeline circumferential weld, providing a reasonable assessment basis for the service safety of the pipeline circumferential weld.

[0074] Compared with traditional stress testing methods, the on-site stress testing method, testing steps, and calculation method for circumferential welded joints of oil and gas pipelines provided by this invention can more scientifically and accurately measure and calculate the complex internal stresses of pipeline welds, such as residual stress, assembly stress, and soil constraint stress. This plays a crucial role in accurately calculating and predicting the crack initiation toughness and defect tolerance of circumferential welds in in-service pipelines, ensuring the safe operation of the pipelines.

[0075] Example

[0076] Taking the internal stress of the circumferential weld of a certain X80 pipeline in service as an example, based on the test calculation using strain gauges and strain rosette resistance change conversion method, the data processing and related calculation methods and test techniques are carried out, and the steps are as follows:

[0077] Step 1: Selection of measuring point sections and arrangement of measuring points

[0078] To obtain the strain variation law of the weld section before and after the backfill excavation and cutting of the pipe section, strain measurement points were arranged near the location of the weld to be taken in the pipe section, as shown in Figure 1(a). A total of 8 strain measurement points were set at equal intervals in the section, of which measurement point a was located at the top of the pipe, and the numbering of the remaining measurement points increased sequentially in a clockwise direction. Axial strain gauges and triaxial strain rosettes were arranged at each measurement point, and the included angle between adjacent strain gauges was 45°, as shown in Figure 1(b) and Figure 1(c).

[0079] Step 2: After excavating and cleaning the surface of the steel pipe in a single pipe section, install axial strain gauges and attach strain rosettes at the designed measuring points near the weld to be taken. Only one test section is set for each specimen, with a total of 8 measuring points. After the measuring points are connected and calibrated according to the free state of the steel pipe and the circumferential weld of the same material, the testing equipment is adjusted and zeroed in time, and the strain values ​​of each measuring point are recorded as the basic data values, as shown in Figure 3(a) and Figure 3(b).

[0080] Step 3: After confirming the data is correct and storing it, on-site workers are allowed to excavate sequentially along the designed excavation direction and length. After each segment is excavated, the excavator stops operating and collects strain gauge data. After collection, the excavator is allowed to continue excavating along the designed direction and length, repeating the above steps to complete all designed earthwork excavation conditions, such as... Figure 4 As shown.

[0081] Note: For specimen No. 1, which was designed with segmental excavation conditions, in order to avoid damage to the pipe body by the excavator and to reduce the excavation cycle, the mechanical excavation was carried out to 1 / 2 height of the pipe body cross section in each stage, and the soil at the bottom of the pipe was not completely removed.

[0082] Step 4: After the earthwork excavation is completed, the steel pipe is allowed to be cut along the first cut. After the steel pipe is cut, immediately record the strain values ​​of each measuring point after the constraint of the adjacent pipeline segment is released. After confirming that the data is correct and storing it, immediately remove the strain gauges near the weld and cut the pipe segment along the second cut, as shown in Figure 5(a) and Figure 5(b).

[0083] Step 5, Initial strain values ​​and processing methods

[0084] Material and geometric parameter determination

[0085] X80 steel material parameters: Elastic modulus E = 210 GPa; Poisson's ratio μ = 0.3; Shear modulus G = 81 GPa; Density ρ = 7850 kg / m³ 3 ;

[0086] Geometric parameters of the steel pipe: outer diameter D = 1016 mm; inner diameter d = 1000.7 mm;

[0087] Polar moment of inertia of cross section:

[0088]

[0089] Moment of inertia of cross section:

[0090]

[0091] Cross-sectional area:

[0092]

[0093] Initial strain values ​​and treatment methods

[0094] The cross-sectional stress can be calculated using measured cross-sectional strain values ​​and methods from mechanics of materials. The calculation formula is as follows:

[0095]

[0096]

[0097]

[0098] Where: ε x ε y and ε 45° These represent the measured strain values ​​at each measuring point in the axial, circumferential, and 45° directions, respectively; τ x τ y and τ xy These represent the normal stress, circumferential stress, and shear stress of the cross section, respectively; the meanings of the other symbols are the same as before.

[0099] Based on the field strain test results of pipe section 1 and combined with formulas (1)-(3), the axial stress and shear stress of the test section can be calculated as shown in red in Table 1. In addition, considering the influence of the cantilever effect of the pipe section after cutting on the stress of the test section, the axial stress and shear stress of the section after eliminating this influence are shown in Table 1.

[0100] Table 1

[0101]

[0102] Step 6

[0103] Determination of axial force and bending moment at cross section

[0104] The normal stress in the cross-section is mainly caused by axial force and bending moment, and the strain distribution of the cross-section conforms to the plane section assumption. Therefore, Origin is used to determine the axial force and bending moment of the cross-section. The normal stress is plotted along the pipe cross-section and interpolated in the coordinate system. Figure 6 The minimum and maximum stress values ​​of the cross section are -2.2 MPa and 2.9 MPa, respectively, and their locations are 1191 mm and 3182 mm, respectively (the starting point is defined at the 12 o'clock direction, with clockwise rotation as positive).

[0105] Based on the principle of superposition of cross-sectional stresses caused by axial force and bending moment, the normal stress caused by axial force can be obtained as follows:

[0106]

[0107] Therefore, the axial force borne by the cross section can be obtained as follows:

[0108] P = σ p A = -8.48 kN (under pressure)

[0109] Similarly, the maximum tensile stress at the top of the cross section caused by the bending moment can be obtained as follows:

[0110] σ m =2.92 - 0.35 = 2.57 MPa

[0111] Therefore, the bending moment borne by the section can be obtained as:

[0112] (The neutral axis is at an angle of 224.3° to the vertical, with the neutral axis under tension at the lower right and compression at the upper left), results refer to Figure 6 ;

[0113] Determination of cross-sectional torque and shear force

[0114] The analysis shows that the shear stress in the cross-section is mainly caused by torque and shear force, and the cross-section strain follows a trigonometric function distribution. Therefore, Origin is used to determine the torque and shear force of the cross-section. The shear stress is plotted along the pipe cross-section in a coordinate system. Figure 7 The minimum and maximum shear stresses of the cross section are -0.9MPa and 0.5MPa, respectively, and their positions are 0mm and 1596mm, respectively (the starting point is defined at the 12 o'clock direction, with clockwise rotation as positive).

[0115] Based on the principle of superposition of cross-sectional shear stress caused by torque and shear force, the shear stress caused by torque can be obtained as follows:

[0116]

[0117] Therefore, the torque that the cross-section can withstand is:

[0118] (clockwise)

[0119] Similarly, the maximum shear stress at the vertex of the cross section caused by shear force can be obtained as follows:

[0120]

[0121] Therefore, the shear force borne by the cross section can be obtained as follows:

[0122] F = τ f A = -16.96 kN (the direction of action is 90° to the vertical and to the right);

[0123] Finally, based on the above cross-sectional load analysis, the cross-sectional load of the pipe section can be obtained as follows: Figure 8 As shown.

Claims

1. A method for replacing pipes at the circumferential welded joint of an oil and gas pipeline in the field, characterized in that, The process includes the following: The test involves assessing the internal stress of the welded joint of an oil and gas pipeline at the site. Specifically, this includes: excavating the soil at the welded joint and measuring the strain of the pipeline before and during excavation; after excavation, cutting the pipeline along the first incision on one side of the welded joint; measuring the strain on the other side of the welded joint after the first incision is completed; obtaining the internal stress of the welded joint using all measured strains; measuring the strain using an axial strain gauge and strain rosette installed on the pipeline and located on one side of the welded joint; and calculating the tensile load, compressive load, bending moment, and torque at the welded joint based on the measured strains; the distance between the first incision and the welded joint is 1000-1500 mm. Based on the working conditions of the on-site oil and gas pipeline ring weld joint and the internal stress of the on-site oil and gas pipeline ring weld joint obtained by testing, the specifications of the new pipeline and the welding method of the new pipeline are determined. The selected new pipeline is welded into the on-site oil and gas pipeline to complete the replacement of the on-site oil and gas pipeline ring weld joint; The measurement and calibration process of axial strain gauges and strain rosettes is as follows: After the axial strain gauges and strain rosettes are installed, a steel pipe and circumferential weld seam that are the same as those of the on-site oil and gas pipeline and are in a free state are used for the measurement and calibration of the strain gauges and strain rosettes.

2. The method for replacing pipes at the on-site oil and gas pipeline ring weld joint according to claim 1, characterized in that, After the on-site stress test of the ring weld joint of the oil and gas pipeline is completed, the on-site ring weld joint of the oil and gas pipeline will be cut off. When cutting off the welded joint of the oil and gas pipeline ring at the site, the distance between the cuts on both sides of the welded joint and the welded joint is 1000~1500mm.

3. The method for replacing pipes at the on-site oil and gas pipeline ring weld joint according to claim 1, characterized in that, Along the same circumference of the on-site oil and gas pipeline, several measuring points are evenly arranged around the circumference of the on-site oil and gas pipeline. Each measuring point is equipped with an axial strain gauge and a strain rosette. Among them, there are measuring points at the top and bottom of the on-site oil and gas pipeline.

4. The method for replacing pipes at the on-site oil and gas pipeline ring weld joint according to claim 3, characterized in that, The distance between the circumference of the measuring point and the welded joint of the oil and gas pipeline on site is 30~50mm.

5. The method for replacing pipes at the on-site oil and gas pipeline ring weld joint according to claim 1, characterized in that, The strain gauges are triaxial, with an included angle of 45° between adjacent strain gauges. One strain gauge is set along the axial direction of the on-site oil and gas pipeline.

6. The method for replacing pipes in the field at the ring welded joint of an oil and gas pipeline according to claim 1, characterized in that, The internal stress of the welded joint of the oil and gas pipeline in the field was calculated using Origin software and all measured strains.

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