A device and method for testing the corrosion fatigue limit of a pipe under corrosion and alternating load

Abstract

The application provides a device and method for testing corrosion fatigue limit of pipe under corrosion and alternating load, which comprises a high-temperature and high-pressure kettle, the high-temperature and high-pressure kettle comprises a kettle body and a kettle cover, the kettle body is externally provided with a heating jacket and a heat preservation layer, the kettle body is provided with gas inlets and outlets, the gas inlets and outlets of the kettle body are connected with a booster pump of a booster system, the bottom of the kettle body is provided with a kettle stabilizer shell, the inside of the kettle stabilizer shell is provided with a wedge, an annular fixer and a kettle rotation stabilizer, the kettle body and the kettle cover are connected through sealing bolts and sealing nuts, the kettle cover is provided with a combined sealing ring, a torque transmission shaft is installed on the kettle cover through a kettle cover sealing combination and a main shaft cap joint, and the torque transmission shaft is sequentially connected with a torque applying shaft and an axial and radial loading assembly. The application finely simulates a high-temperature, high-pressure and high-H2S-CO2 corrosion environment, accurately tests the limit stress of corrosion fatigue fracture of pipe under complex alternating load conditions such as tension, compression, bending and torsion, and provides technical support for pipe quality inspection and optimal design.

Description

TECHNICAL FIELD

[0001] The application provides a high-temperature and high-pressure multiphase flow and complex alternating load working condition pipe corrosion fatigue limit testing device and method, and belongs to the technical field of mining industry, and is used for evaluating the limit stress of metal pipe under the conditions of high-temperature and high-pressure high-H2S-CO2 corrosion environment, tensile-compressive-bending-torsional complex alternating load and long-time service without corrosion fatigue fracture. BACKGROUND

[0002] During the service period of the oil and gas well pipe, the pipe is subjected to high-temperature and high-pressure, high-H2S-CO2 corrosion medium, and tensile-compressive-bending-torsional complex alternating load during downhole production operation. During the long-time service of the pipe, the pipe is prone to fracture under a stress state lower than the yield strength due to the coupling effect of corrosion and fatigue.

[0003] Patent 201410008876.0 proposes a corrosion fatigue life prediction method based on damage evolution. This method only considers tensile load and cannot simulate the tensile, compressive, bending and torsional complex load state of the oil and gas well pipe during the service period. There is a certain gap between the corrosion fatigue data obtained by the test and the field working condition, and the accuracy of the prediction result does not meet the engineering requirements.

[0004] Patent 201510234278.X provides a rotating bending corrosion fatigue test device for simulating the actual working conditions of oil well pipes under oil field conditions. This technology does not consider the tensile, compressive, bending and torsional complex load state of the oil and gas well pipe during the service period.

[0005] Patent 201911150010.6 proposes a method for predicting the fatigue strength of metal materials through tensile testing. This method cannot simulate the tensile, compressive, bending and torsional complex load state of the oil and gas well pipe during the service period. At the same time, due to the significant size effect of small-size samples, the results obtained are not strong in practical engineering reference.

[0006] Patent 202210835317.1 proposes a test device for realizing the coupling effect of corrosion environment and bending fatigue. This device cannot simulate the tensile, compressive, bending and torsional complex load state of the oil and gas well pipe during the service period.

[0007] In summary, the related test devices and methods cannot meet the test requirements of the pipe corrosion fatigue fracture limit stress under the conditions of high-temperature and high-pressure high-H2S-CO2 corrosion environment, tensile-compressive-bending-torsional complex alternating load state, greatly limiting the test means of pipe manufacturers to manufacture high corrosion fatigue limit, and greatly restricting the evaluation method of optimizing the design of oil and gas field pipes. SUMMARY

[0008] The application establishes a pipe corrosion fatigue limit test device under corrosion and alternating load, and forms a test method for evaluating pipe corrosion fatigue fracture limit stress by using the device. The purpose is to accurately test the limit stress of pipe corrosion fatigue fracture under complex alternating load conditions such as tension, compression, bending and torsion in the high-temperature high-pressure high-H2S-CO2 corrosion environment, and to provide technical support for pipe quality inspection and optimization design.

[0009] The problems to be solved by the device of the application are:

[0010] 1. A set of indoor test device for pipe corrosion fatigue limit stress under high-temperature high-pressure H2S-CO2 working condition and complex load condition is provided.

[0011] 2. The extreme working condition can be simulated: the temperature is room temperature to 350 DEG C, the pressure is normal pressure to 150 MPa, and the H2S / CO2 corrosive medium gas-liquid-solid multiphase flow corrosion environment.

[0012] 3. The complex alternating load conditions such as tension, compression, shear and torsion during the service of the pipe can be simulated.

[0013] The specific technical scheme is a pipe corrosion fatigue limit test device under corrosion and alternating load, which comprises a high-temperature high-pressure kettle.

[0014] The high-temperature high-pressure kettle comprises a kettle body and a kettle cover; the kettle body is externally provided with a heating jacket and a heat preservation layer.

[0015] The kettle body is provided with a gas inlet and outlet; the gas inlet and outlet of the kettle body are connected with a booster pump of a booster system.

[0016] The kettle body is internally provided with a kettle stabilizer shell, an internal wedge and an annular fixator, and a kettle rotation stabilizer.

[0017] The kettle body and the kettle cover are connected through sealing bolts and sealing nuts; the kettle cover is provided with a combined sealing ring; the torque transmission shaft is installed on the kettle cover through the sealing combination of the kettle cover and the main shaft cap.

[0018] The torque transmission shaft is sequentially connected with a torque applying shaft and an axial and radial loading assembly.

[0019] The axial and radial loading assembly comprises an axial loading assembly and a radial loading assembly.

[0020] The axial loading assembly comprises, from top to bottom, an upper stabilizer, an upper fixator, an upper sample joint, a radial loading upper cantilever, a corrosion fatigue sample, a radial loading lower cantilever, a lower sample joint, a lower fixator and a lower stabilizer, which are sequentially connected. The axial tensile and compressive stress loading and unloading of the corrosion fatigue sample can be realized.

[0021] The radial loading assembly comprises an upper cantilever stabilizer and a lower cantilever stabilizer; the upper cantilever stabilizer and the lower cantilever stabilizer are respectively connected to the upper end and the lower end of the corrosion fatigue sample;

[0022] The upper cantilever stabilizer is connected to the upper cantilever adapter through an upper cantilever adapter pin;

[0023] The lower cantilever stabilizer is connected to the lower cantilever adapter through a lower cantilever adapter pin;

[0024] The upper cantilever adapter and the lower cantilever adapter are connected to a bending stress loading shaft, and the bending stress loading shaft is provided with a bending stress loading nut;

[0025] The kettle body is provided with a high-temperature and high-pressure kettle temperature and pressure sensor;

[0026] The torque transmission shaft is provided with a load sensor, a first strain sensor, a second strain sensor and a rotary power device; the first strain sensor and the second strain sensor are respectively installed on a strain sensor fixing plate through a first strain sensor upper fixing flange and a second strain sensor upper fixing flange; the strain sensor fixing plate is installed on the kettle cover sealing flange through a strain sensor base and a strain sensor base fixing flange.

[0027] The high-temperature and high-pressure kettle temperature and pressure sensor, the load sensor, the first strain sensor and the second strain sensor are respectively connected to a high-temperature and high-pressure kettle temperature and pressure data processor, a load data processor, a first strain data processor and a second strain data processor;

[0028] The pressurizing system comprises a gas mixing device and a pressurizing pump; the gas mixing device comprises a gas mixing cylinder and a hydraulic cylinder; a matching piston is arranged between the gas mixing cylinder and the hydraulic cylinder;

[0029] The pressurizing pump is connected to the gas mixing cylinder; the gas mixing cylinder is further connected to an H2S gas cylinder, a CO2 gas cylinder, an N2 gas cylinder (312) and a CH4 gas cylinder;

[0030] The hydraulic cylinder is connected to a liquid filling tank, a liquid tank and a hydraulic pump;

[0031] The gas mixing device is installed on a gas mixing device base;

[0032] The hydraulic pump is provided with a hydraulic pump pressure sensor; the pressurizing pump is provided with a pressurizing pump pressure sensor; the hydraulic cylinder is provided with a hydraulic cylinder pressure sensor; and the gas mixing cylinder is provided with a gas mixing cylinder pressure sensor;

[0033] The hydraulic pump pressure sensor, the pressurizing pump pressure sensor, the hydraulic cylinder pressure sensor and the gas mixing cylinder pressure sensor are respectively connected to a hydraulic pump pressure data processor, a pressurizing pump pressure data processor, a hydraulic cylinder pressure data processor and a gas mixing cylinder pressure data processor;

[0034] The high-temperature high-pressure kettle temperature and pressure data processor, the load data processor, the first strain data processor and the second strain data processor, the hydraulic pump pressure data processor, the pressure pump pressure data processor, the hydraulic cylinder pressure data processor and the gas mixing cylinder pressure data processor are connected with the computer controller respectively, and the corrosion fatigue experiment parameters such as temperature, pressure, load and strain in the whole experiment process are dynamically monitored, recorded and curve-drawn.

[0035] The defects overcome by the device of the application are:

[0036] 1. The device solves the problem of the need for a pipe corrosion fatigue limit testing device under extreme working conditions and complex load conditions of a wellbore simulated in a laboratory.

[0037] 2. The device overcomes the problem that the pipe corrosion fatigue strength simulation test is far away from the field working conditions, and cannot finely simulate the extreme working conditions, complex load and dynamic multiphase flow conditions of deep wells, super-deep wells and ten-thousand-meter deep wells.

[0038] 3. The device overcomes the problem of the deficiency of the current testing method and device structure design, which only considers tensile and rotational load, and there is a significant difference between the actual field working conditions and the pipe bearing complex alternating load of tension-compression-bending-torsion.

[0039] The problems to be solved by the method of the application are:

[0040] 1. The method forms a pipe corrosion fatigue strength testing method under extreme working conditions and complex load conditions.

[0041] 2. The method establishes a limit stress determination method for pipe under the conditions of high temperature, high pressure, high H2S-CO2 corrosion environment, tensile-compressive-bending-torsion complex alternating load and no corrosion fatigue fracture of the pipe for a specific period or a long time, and provides a testing method for manufacturing pipe with high corrosion fatigue limit.

[0042] 3. The method dynamically monitors the applied load, sample deformation and corrosion fatigue fracture data, and effectively supports the development of deep well, super-deep well and ten-thousand-meter deep well pipe optimization design technology.

[0043] The specific technical scheme is:

[0044] A pipe corrosion fatigue limit testing method under corrosion and alternating load, which can be divided into six aspects of experiment preparation, sample loading, parameter setting, data monitoring, post-experiment processing and corrosion fatigue limit calculation.

[0045] S1. Experiment preparation:

[0046] S1.1, determine the experimental conditions for carrying out the indoor simulation test of corrosion fatigue limit. The corrosion parameters need to be determined according to the field working conditions, including temperature, pressure, gas composition and partial pressure, liquid and solid phase composition and ion content, pipe grade and steel grade used in the experiment, load type and load size during service, tension-compression-bending-torsion load;

[0047] S1.2, process the corrosion fatigue limit indoor simulation test sample. The pipe used in the experiment is processed into a rod-shaped tensile sample, and the length of the parallel section, the chamfer of the transition section, the outer diameter and the length of the sample, and other dimensions need to meet the installation requirements of the corrosion fatigue limit indoor simulation test device;

[0048] S1.3, prepare the corrosive gas with the corresponding gas content. The gas mixing cylinder is evacuated; connect the required gas with H2S cylinder, CO2 cylinder, N2 cylinder and CH4 cylinder; according to the required content, open the H2S / CO2 / N2 / CH4 cylinder valve in turn to make the gas enter the gas mixing cylinder, and prepare the mixed gas with the corresponding gas component ratio.

[0049] S1.4, prepare the corrosive liquid medium with the corresponding liquid-solid content and ion ratio. According to the liquid and solid phase composition and ion content, prepare the corrosive liquid medium with the corresponding liquid-solid component and content, and continuously pass in the corresponding gas component until saturation.

[0050] S1.5, use the hydraulic cylinder pressure sensor to monitor the hydraulic cylinder pressure, and use the gas mixing cylinder pressure sensor to monitor the gas mixing cylinder pressure.

[0051] S2. Sample loading:

[0052] S2.1, install the radial loading assembly. Assemble the upper cantilever stabilizer inside the radial loading upper cantilever, and fix it by inserting the corrosion fatigue sample upper clamping end close to the parallel section; assemble the lower cantilever stabilizer inside the radial loading upper cantilever, and fix it by inserting the corrosion fatigue sample lower clamping end close to the parallel section; connect the upper cantilever adapter, the lower cantilever adapter and the bending stress loading shaft respectively;

[0053] S2.2, install the axial loading assembly. Assemble the lower sample joint at the lower end of the corrosion fatigue sample; install the lower fixer on the torque applying shaft and connect it with the lower sample joint, put it into the radial loading assembly and fix it with the lower stabilizer; assemble the upper sample joint at the upper end of the corrosion fatigue sample; install the upper fixer on the torque applying shaft and connect it with the upper sample joint, and fix it as a whole on the radial loading assembly using the upper stabilizer;

[0054] S2.3, axial tension or compression load is applied. By adjusting the upper and lower fixers, tension or compression load is applied to the corrosion fatigue sample, and the calculated relationship between the applied load and the deflection can be directly used σ=E·ε, where σ is the tensile / compressive stress, E is the tensile elastic modulus or the compressive elastic modulus, and ε is the tensile / compressive strain.

[0055] S2.4, radial bending load is applied. By tightening the bending stress loading nut, the deflection of the parallel section of the corrosion fatigue sample is increased, and the radial bending load is applied to the corrosion fatigue sample. The relationship between the applied load and the deflection can be calculated using the four-point bending standard formula, or it can be corrected by trial and error.

[0056] S3. Parameter setting:

[0057] S3.1, set the simulation corrosion environment parameters. The prepared corrosive liquid medium is added to the kettle body, the liquid surface needs to immerse the radial loading assembly, the kettle cover and the kettle body are sealed using sealing bolts and sealing nuts; the strain sensor base is fixed on the kettle cover sealing assembly using the strain sensor base fixing flange; the strain sensor fixing plate is fixed on the torque transmission shaft using the strain sensor upper fixing flange and the strain sensor upper fixing flange, and the first strain sensor and the second strain sensor are installed on the strain sensor fixing plate; the load sensor, the rotary power device and the torque transmission shaft are connected in turn.

[0058] S3.2, kettle body temperature and pressure increase. Set the temperature and pressure data processor in the computer controller to the corresponding temperature and pressure of the experiment, control the kettle body heating by the high temperature and pressure kettle temperature and pressure sensor, until the experimental set temperature is reached; control the kettle body pressure increase by the high temperature and pressure kettle temperature and pressure sensor, until the experimental set pressure is reached.

[0059] S4. Data monitoring:

[0060] S4.1, the first strain data processor and the second strain data processor are connected to the first strain sensor and the second strain sensor respectively, and the axial deformation of the corrosion fatigue sample during the experiment is monitored;

[0061] S4.2, the high temperature and pressure kettle temperature and pressure data processor is connected with the high temperature and pressure kettle temperature and pressure sensor, and the temperature and pressure value change of the kettle body during the experiment is monitored;

[0062] S4.3, the load data processor is connected with the load sensor, and the axial tensile load and torque change of the corrosion fatigue sample during the experiment is monitored;

[0063] S4.4, the hydraulic pump pressure data processor, booster pump pressure data processor is connected with hydraulic pump pressure sensor, booster pump pressure sensor respectively, monitor the hydraulic pump, booster pump pressure, the hydraulic cylinder pressure data processor, gas mixing cylinder pressure data processor is connected with hydraulic cylinder pressure sensor and gas mixing cylinder pressure sensor respectively, monitor the internal pressure of hydraulic cylinder and gas mixing cylinder, to guarantee the safety of experiment.

[0064] S5. Post-experiment processing:

[0065] S5.1, take out the corrosion fatigue sample. After reaching the predetermined period of the experiment, cool down, depressurize, open the corrosion fatigue limit test device, and take out the corrosion fatigue sample.

[0066] S5.2, observe the corrosion cracking characteristics. Use macroscopic and microscopic methods to analyze and observe the morphology, composition, and protective properties of the corrosion product film on the surface of the corrosion fatigue sample; observe and judge the crack nucleation, propagation characteristics, and crack size of the parallel section of the corrosion fatigue sample.

[0067] S5.3, sample fatigue strength analysis. If the corrosion fatigue sample breaks, continue to conduct corrosion fatigue limit test experiments under conditions of less than the stress; if the corrosion fatigue sample does not break, conduct room temperature tensile experiments to determine the remaining strength of the pipe after the corrosion fatigue limit test experiment, and continue to conduct corrosion fatigue limit test experiments under conditions of greater than the stress;

[0068] S6. Evaluation of corrosion fatigue limit:

[0069] S6.1, evaluation method of corrosion fatigue limit when the bending stress remains unchanged and the tensile / compressive stress changes.

[0070] Maintain the applied radial bending load unchanged, and design a series of groups of corrosion fatigue limit indoor simulation experiments under different tensile / compressive stress states, measure the corrosion fatigue S-N curve, and evaluate the corrosion fatigue limit stress of the pipe under the bending stress when subjected to tensile / compressive stress.

[0071] S6.2, evaluation method of corrosion fatigue limit when the tensile / compressive stress remains unchanged and the bending stress changes.

[0072] Maintain the applied axial tensile / compressive load unchanged, and design a series of groups of corrosion fatigue limit indoor simulation experiments under different bending stress states, measure the corrosion fatigue S-N curve, and evaluate the corrosion fatigue limit stress of the pipe under the tensile / compressive stress when subjected to bending stress.

[0073] S6.3, evaluation method of corrosion fatigue limit under tensile / compressive / bending / torsional alternating state.

[0074] Adopt factor molecule method or orthogonal experiment method, design different tensile, compression, bending and torque state series group of corrosion fatigue limit indoor simulation experiment respectively, measure corrosion fatigue S-N curve, and evaluate corrosion fatigue limit stress of the pipe in the corrosion environment.

[0075] The method of the present application overcomes the defects:

[0076] 1. The limit stress testing technical scheme of pipe without corrosion fatigue fracture for a specific period or a long time in the high temperature, high pressure and high H2S-CO2 corrosion environment is determined.

[0077] 2. The problem of the current pipe corrosion fatigue limit stress testing method not applicable to the extreme working conditions, complex load and dynamic multiphase flow conditions of deep well, ultra-deep well and ten-thousand-meter deep well is solved.

[0078] 3. The problem of the current corrosion fatigue fracture limit stress testing data being insufficient and difficult to support the pipe design technology of deep well, ultra-deep well and ten-thousand-meter deep well is effectively changed.

[0079] Effects and advantages of the present application:

[0080] 1. The corrosion fatigue indoor experiment device has the corrosion fatigue indoor simulation experiment of the pipe under the combined action of tensile stress-shear stress, or tensile stress-torque, or tensile stress-shear stress-torque load in the gas-liquid-solid multiphase flow corrosion environment of room temperature-350℃, normal pressure-150MPa and H2S / CO2 containing corrosion medium.

[0081] 2. The temperature, pressure, applied load, sample deformation and corrosion fatigue fracture data in the corrosion fatigue experiment process can be dynamically monitored.

[0082] 3. The crack nucleation and propagation characteristics of the pipe under the complex alternating load state of tensile-compression-bending-torsion in the 350℃, 150MPa, H2S / CO2 containing multiphase flow corrosion environment can be tested.

[0083] 4. The corrosion fatigue limit stress of the pipe under the complex alternating load state of tensile-compression-bending-torsion in the 350℃, 150MPa, H2S / CO2 containing multiphase flow corrosion environment can be tested.

[0084] 5. The limit stress value of the pipe without corrosion fatigue fracture for a specific period or a long time in the service environment is measured, which provides a quality inspection means for pipe manufacturers to develop high corrosion fatigue limit pipes, and provides an experimental device and a reliable evaluation method for the pipe optimization design of oil and gas fields. BRIEF DESCRIPTION OF DRAWINGS

[0085] Figure 1 is one of the structural schematic diagrams of the present application;

[0086] Figure 2 is the second structural diagram of the present application

[0087] Figure 3 is the top view of the corrosion fatigue limit test system of the present application

[0088] Figure 4 is the structural diagram of the axial and radial loading assembly of the present application DETAILED DESCRIPTION

[0089] The specific technical solutions of the present application are described in combination with the embodiments.

[0090] As shown in Figure 1 , a corrosion fatigue limit test device for pipe under corrosion and alternating load comprises three parts of a control system 1, a corrosion fatigue limit test system 2 and a pressurization system 3.

[0091] As shown in Figure 1 , the control system 1 comprises a computer controller 101, a high-temperature and high-pressure autoclave temperature and pressure data processor 1A, a load data processor 1B, a first strain data processor 1C-1 and a second strain data processor 1C-2, and a hydraulic pump pressure data processor 1D, a pressurization pump pressure data processor 1E, a hydraulic cylinder pressure data processor 1F and a gas mixing cylinder pressure data processor 1G. The corrosion fatigue test parameters such as temperature, pressure, load and strain can be dynamically monitored and controlled during the whole experiment, and the data can be recorded and the curve can be drawn.

[0092] As shown in Figure 2 and Figure 3 , the corrosion fatigue limit test system 2 comprises a control assembly, a high-temperature and high-pressure autoclave, an auxiliary assembly, an axial loading assembly and a radial loading assembly.

[0093] The control assembly comprises a high-temperature and high-pressure autoclave temperature and pressure sensor 2A, a load sensor 2B, a first strain sensor 2C-1, a second strain sensor 2C-2, a rotary power device 210, a strain sensor upper fixed flange 211, a strain sensor upper fixed flange 212, a strain sensor fixed plate 213, a strain sensor base 214, a strain sensor base fixed flange 215 and an autoclave cover sealing flange 216. The parameters such as temperature, pressure, load and strain during the whole corrosion fatigue experiment can be tested in real time, and the data can be transmitted to the control system.

[0094] The high-temperature and high-pressure autoclave comprises sealing bolts 220, sealing nuts 221, an autoclave cover 222, an autoclave body 223, a heating sleeve 224, an insulation layer 225, an autoclave cover sealing combination 226, a torque transmission shaft 227, a combined sealing ring 228, a main shaft cap 229 and an axial and radial loading assembly 240. The gas-liquid-solid multiphase flow corrosion environment simulation of room temperature to 350℃, normal pressure to 150MPa and H2S / CO2-containing corrosive gas can be realized.

[0095] The auxiliary assembly is composed of a torque application shaft 230, a gas inlet and outlet 231, a kettle body stabilizer shell 232, a wedge 233, a ring-shaped fixer 234, and a kettle body rotation stabilizer 235. It cooperates with the high-temperature and high-pressure kettle and the loading assembly to assist in the safe and stable performance of the corrosion fatigue experiment.

[0096] The axial loading assembly is composed of an upper stabilizer 241, an upper fixer 242, an upper sample joint 243, a radial loading upper cantilever 244, a corrosion fatigue sample 245, a radial loading lower cantilever 246, a lower sample joint 247, a lower fixer 248, and a lower stabilizer 249. It can realize the loading and unloading of axial tensile and compressive stress of the corrosion fatigue sample.

[0097] The radial loading assembly is composed of an upper cantilever stabilizer 250, an upper cantilever adapter 251, an upper cantilever adapter pin 252, a bending stress loading nut 253, a bending stress loading shaft 254, a lower cantilever adapter pin 255, a lower cantilever adapter 256, and a lower cantilever stabilizer 257. It can realize the loading and unloading of bending stress of the corrosion fatigue sample.

[0098] Figure 3 The top view of the corrosion fatigue limit test system 2 shows the top features of the high-temperature and high-pressure kettle of the corrosion fatigue limit test system. It includes:

[0099] The first strain sensor 2C-1 and the second strain sensor 2C-2 can measure the strain of the sample during the corrosion fatigue experiment. The rotary power device 210 can be externally connected to a multi-stage speed reduction control system to provide the required torque for the corrosion fatigue experiment. The strain sensor fixing plate 213 is used to fix the first strain sensor 2C-1 and the second strain sensor 2C-2 to ensure accurate measurement of the strain. The kettle cover sealing flange 216, sealing bolt 220, sealing nut 221, kettle cover 222, and kettle cover sealing combination 226 are used to ensure the ultra-high temperature and ultra-high pressure sealing effect of the high-temperature and high-pressure kettle. The heating jacket 224 and the insulation layer 225 are used for heating and insulation, respectively.

[0100] As Figure 4 , the enlarged view of the axial and radial loading assembly 240 shows the installation of the components of the axial and radial loading assembly. It includes:

[0101] The axial loading assembly is composed of an upper stabilizer 241, an upper fixer 242, an upper sample joint 243, a radial loading upper cantilever 244, a corrosion fatigue sample 245, a radial loading lower cantilever 246, a lower sample joint 247, a lower fixer 248, and a lower stabilizer 249. It can realize the loading and unloading of axial tensile and compressive stress of the corrosion fatigue sample.

[0102] The radial loading assembly is composed of the upper cantilever stabilizer 250, the upper cantilever adapter 251, the upper cantilever adapter pin 252, the bending stress loading nut 253, the bending stress loading shaft 254, the lower cantilever adapter pin 255, the lower cantilever adapter 256, the lower cantilever stabilizer 257. The bending stress loading and unloading of the corrosion fatigue specimen can be realized.

[0103] The pressurization system 3 is composed of the hydraulic pump pressure sensor 3D, the pressurization pump pressure sensor 3E, the hydraulic cylinder pressure sensor 3F and the gas mixing cylinder pressure sensor 3G, H2S gas cylinder 310, CO2 gas cylinder 311, N2 gas cylinder 312, CH4 gas cylinder 313, pressurization pump 314, gas mixing cylinder 320, deployment piston 321, hydraulic cylinder 322, gas mixing device base 323, liquid filling tank 324, liquid tank 325, hydraulic pump 326. The mixing and preparation of H2S / CO2 / N2 / CH4 gas components can be realized, and the internal pressure of the high-temperature and high-pressure kettle can be pressurized and dynamically adjusted according to the required pressure of the corrosion fatigue experiment.

[0104] The connection relationship between the above-mentioned parts is as follows:

[0105] The high-temperature and high-pressure kettle includes a kettle body 223 and a kettle cover 222; the kettle body 223 is externally provided with a heating jacket 224 and a thermal insulation layer 225;

[0106] The kettle body 223 is provided with a gas inlet and outlet 231;

[0107] The bottom of the kettle body 223 is provided with a kettle body stabilizer housing 232, which is internally provided with a wedge 233 and an annular fixator 234, and a kettle body rotation stabilizer 235;

[0108] The kettle body 223 and the kettle cover 222 are connected through sealing bolts 220 and sealing nuts 221; the kettle cover 222 is provided with a combined sealing ring 228; the kettle cover 222 is installed with a torque transmission shaft 227 through a kettle cover sealing combination 226 and a main shaft cap 229;

[0109] The torque transmission shaft 227 is connected with a torque applying shaft 230 and an axial and radial loading assembly 240 in sequence;

[0110] The axial and radial loading assembly 240 includes an axial loading assembly and a radial loading assembly;

[0111] The axial loading assembly, from top to bottom, includes an upper stabilizer 241, an upper fixator 242, an upper specimen adapter 243, a radial loading upper cantilever 244, a corrosion fatigue specimen 245, a radial loading lower cantilever 246, a lower specimen adapter 247, a lower fixator 248 and a lower stabilizer 249 connected in sequence. The axial tensile and compressive stress loading and unloading of the corrosion fatigue specimen can be realized.

[0112] The radial loading assembly comprises an upper cantilever stabilizer 250 and a lower cantilever stabilizer 257, and the upper cantilever stabilizer 250 and the lower cantilever stabilizer 257 are respectively connected to the upper end and the lower end of the corrosion fatigue test sample 245;

[0113] The upper cantilever stabilizer 250 is connected to the upper cantilever adapter 251 through an upper cantilever adapter pin 252.

[0114] The lower cantilever stabilizer 257 is connected to the lower cantilever adapter 256 through a lower cantilever adapter pin 255.

[0115] The upper cantilever adapter 251 and the lower cantilever adapter 256 are connected to a bending stress loading shaft 254, and the bending stress loading shaft 254 is provided with a bending stress loading nut 253.

[0116] The autoclave body 223 is provided with a high-temperature and high-pressure autoclave temperature and pressure sensor 2A.

[0117] The torque transmission shaft 227 is provided with a load sensor 2B, a first strain sensor 2C-1, a second strain sensor 2C-2, and a rotary power device 210, the first strain sensor 2C-1 and the second strain sensor 2C-2 are respectively installed on a strain sensor fixing plate 213 through a first strain sensor upper fixing flange 211 and a second strain sensor upper fixing flange 212, and the strain sensor fixing plate 213 is installed on a autoclave cover sealing flange 216 through a strain sensor base 214 and a strain sensor base fixing flange 215.

[0118] The high-temperature and high-pressure autoclave temperature and pressure sensor 2A, the load sensor 2B, the first strain sensor 2C-1, and the second strain sensor 2C-2 are respectively connected to a high-temperature and high-pressure autoclave temperature and pressure data processor 1A, a load data processor 1B, a first strain data processor 1C-1, and a second strain data processor 1C-2.

[0119] The gas inlet and outlet 231 of the autoclave body 223 is connected to a booster pump 314 of a booster system.

[0120] The booster system comprises a gas mixing device and the booster pump 314, and the gas mixing device comprises a gas mixing cylinder 320 and a hydraulic cylinder 322, and a deployment piston 321 is arranged between the gas mixing cylinder 320 and the hydraulic cylinder 322.

[0121] The booster pump 314 is connected to the gas mixing cylinder 320, and the gas mixing cylinder 320 is further connected to an H2S gas cylinder 310, a CO2 gas cylinder 311, an N2 gas cylinder 312, and a CH4 gas cylinder 313.

[0122] The hydraulic cylinder 322 is connected to a liquid filling tank 324, a liquid tank 325, and a hydraulic pump 326.

[0123] The gas mixing device is installed on a gas mixing device base 323.

[0124] The hydraulic pump 326 is provided with a hydraulic pump pressure sensor 3D; the booster pump 314 is provided with a booster pump pressure sensor 3E; the hydraulic cylinder 322 is provided with a hydraulic cylinder pressure sensor 3F; and the gas mixing cylinder 320 is provided with a gas mixing cylinder pressure sensor 3G;

[0125] The hydraulic pump pressure sensor 3D, the booster pump pressure sensor 3E, the hydraulic cylinder pressure sensor 3F and the gas mixing cylinder pressure sensor 3G are connected with a hydraulic pump pressure data processor 1D, a booster pump pressure data processor 1E, a hydraulic cylinder pressure data processor 1F and a gas mixing cylinder pressure data processor 1G respectively;

[0126] The high-temperature and high-pressure kettle temperature and pressure data processor 1A, the load data processor 1B, the first strain data processor 1C-1 and the second strain data processor 1C-2, the hydraulic pump pressure data processor 1D, the booster pump pressure data processor 1E, the hydraulic cylinder pressure data processor 1F and the gas mixing cylinder pressure data processor 1G are connected with a computer controller 101 respectively, so as to dynamically monitor the monitoring and control of corrosion fatigue experiment parameters such as temperature, pressure, load and strain in the whole experiment process, record data and draw curves.

[0127] The extreme corrosion and alternating load working condition pipe corrosion fatigue limit test method can be divided into six aspects of experiment preparation, sample loading, parameter setting, data monitoring, post-experiment processing and corrosion fatigue limit calculation.

[0128] S1. Experiment preparation:

[0129] S1.1, determine the experimental conditions for carrying out the corrosion fatigue limit indoor simulation test. The corrosion parameters need to be determined according to the field working conditions, including temperature, pressure, gas component and partial pressure, liquid and solid component and ion content, pipe grade and steel grade used in the experiment, load type and tensile-compressive-bending-torsional load size during service;

[0130] S1.2, process the corrosion fatigue limit indoor simulation test sample. The pipe used in the experiment is processed into a rod-shaped tensile sample, and the parallel section length, transition section chamfer, sample outer diameter and length and other dimensions need to meet the installation requirements of the corrosion fatigue limit indoor simulation test device;

[0131] S1.3, prepare the corrosion gas with the corresponding gas content. The gas mixing cylinder 320 is pumped to vacuum; the experimental required gas is connected with the H2S cylinder 310, the CO2 cylinder 311, the N2 cylinder 312 and the CH4 cylinder 313; according to the required content, the H2S / CO2 / N2 / CH4 cylinder valves are opened in turn to make the gas enter the gas mixing cylinder 320, and the mixed gas with the corresponding gas component ratio is prepared.

[0132] S1.4, prepare the corrosive liquid medium with corresponding liquid-solid content and ion ratio. According to the liquid phase and solid phase components and ion content, prepare the corrosive liquid medium with corresponding liquid-solid components and content, and continuously pass in the corresponding gas components until saturation.

[0133] S1.5, monitor the hydraulic cylinder pressure using the hydraulic cylinder pressure sensor 3F and monitor the gas mixing cylinder pressure using the gas mixing cylinder pressure sensor 3G.

[0134] S2. Sample loading:

[0135] S2.1, install the radial loading assembly. Assemble the upper cantilever stabilizer 250 inside the radial loading upper cantilever 244, and fit it into the corrosion fatigue sample 245 upper clamping end near the parallel section and fix it; assemble the lower cantilever stabilizer 257 inside the radial loading upper cantilever 244, and fit it into the corrosion fatigue sample 245 lower clamping end near the parallel section and fix it; connect the upper cantilever adapter 251, the lower cantilever adapter 256 and the bending stress loading shaft 254 respectively;

[0136] S2.2, install the axial loading assembly. Assemble the lower sample joint 247 at the lower end of the corrosion fatigue sample 245; install the lower fixer 248 on the torque applying shaft 230 and connect it with the lower sample joint 247, and put the whole into the radial loading assembly 240 and fix it using the lower stabilizer 249; assemble the upper sample joint 243 at the upper end of the corrosion fatigue sample 245; install the upper fixer 241 on the torque applying shaft 230 and connect it with the upper sample joint 243, and fix the whole on the radial loading assembly 240 using the upper stabilizer 241;

[0137] S2.3, apply axial tensile or compressive load. Apply tensile or compressive load to the corrosion fatigue sample 245 by adjusting the upper fixer 241 and the lower fixer 248, and the calculation relationship between the applied load and the deflection can be directly used as σ=E·ε, where σ is the tensile / compressive stress, E is the tensile elastic modulus or compressive elastic modulus, and ε is the tensile / compressive strain.

[0138] S2.4, apply radial bending load. Increase the deflection of the parallel section of the corrosion fatigue sample 245 by tightening the bending stress loading nut 253, and apply radial bending load to the corrosion fatigue sample 245, and the relationship between the applied load and the deflection can be calculated using the four-point bending standard formula, or can be corrected by trial experiment.

[0139] S3. Parameter setting:

[0140] S3.1, set the simulated corrosion environment parameters. The prepared corrosive liquid medium is added to the kettle body 223, the liquid surface needs to immerse the radial loading assembly 240, the kettle cover 222 is sealed with the kettle body 223 by using the sealing bolt 220 and the sealing nut 221; the strain sensor base 214 is fixed on the kettle cover sealing combination 226 by using the strain sensor base fixing flange 215; the strain sensor fixing plate 213 is fixed on the torque transmission shaft 227 by using the strain sensor upper fixing flange 211 and the strain sensor upper fixing flange 212, and the first strain sensor 2C-1 and the second strain sensor 2C-2 are installed on the strain sensor fixing plate 213; the load sensor 2B, the rotary power device 210 and the torque transmission shaft 227 are connected in sequence.

[0141] S3.2, kettle body temperature and pressure increase. The temperature and pressure data processor 1A in the computer controller 101 is set to the experimental corresponding temperature and pressure, the kettle body 223 is heated by the heating jacket 224 through the high temperature and pressure kettle temperature and pressure sensor 2A until the experimental set temperature is reached; the kettle body 223 is pressurized by the booster pump 314 through the high temperature and pressure kettle temperature and pressure sensor 2A until the experimental set pressure is reached.

[0142] S4. Data monitoring:

[0143] S4.1, the first strain data processor 1C-1 and the second strain data processor 1C-2 are connected with the first strain sensor 2C-1 and the second strain sensor 2C-2 respectively, and the axial deformation amount of the corrosion fatigue specimen 245 during the experiment is monitored;

[0144] S4.2, the high temperature and pressure kettle temperature and pressure data processor 1A is connected with the high temperature and pressure kettle temperature and pressure sensor 2A, and the change amount of the temperature and pressure value in the kettle body 223 during the experiment is monitored;

[0145] S4.3, the load data processor 1B is connected with the load sensor 2B, and the change amount of the axial tensile load and the torque of the corrosion fatigue specimen 245 during the experiment is monitored;

[0146] S4.4, the hydraulic pump pressure data processor 1D and the booster pump pressure data processor 1E are connected with the hydraulic pump pressure sensor 3D and the booster pump pressure sensor 3E respectively, and the pump pressure of the hydraulic pump 326 and the booster pump 314 is monitored, the hydraulic cylinder pressure data processor 1F and the gas mixing cylinder pressure data processor 1G are connected with the hydraulic cylinder pressure sensor 3F and the gas mixing cylinder pressure sensor 3G respectively, and the internal pressure of the hydraulic cylinder 322 and the gas mixing cylinder 320 is monitored to ensure the safety of the experiment.

[0147] S5. Post-experiment processing:

[0148] S5.1, take out the corrosion fatigue sample. After reaching the predetermined period of the experiment, cool down, depressurize, open the corrosion fatigue limit test device, and take out the corrosion fatigue sample 245.

[0149] S5.2, observe the corrosion cracking characteristics. Use macroscopic and microscopic methods to analyze and observe the morphology, composition, and protective properties of the corrosion product film on the surface of the corrosion fatigue sample 245; observe and judge the crack nucleation, propagation characteristics, and crack size of the parallel section of the corrosion fatigue sample 245.

[0150] S5.3, sample fatigue strength analysis. If the corrosion fatigue sample 245 breaks, continue to conduct corrosion fatigue limit test experiments under conditions of less than the stress; if the corrosion fatigue sample 245 does not break, conduct room temperature tensile experiments to determine the remaining strength of the pipe after the corrosion fatigue limit test experiment, and continue to conduct corrosion fatigue limit test experiments under conditions of greater than the stress;

[0151] S6. Evaluation of the corrosion fatigue limit:

[0152] S6.1, evaluation method of corrosion fatigue limit when the bending stress is constant and the tensile / compressive stress changes.

[0153] Maintain the applied radial bending load constant, and design a series of groups of corrosion fatigue limit indoor simulation experiments under different tensile / compressive stress states to measure the corrosion fatigue S-N curve, and evaluate the corrosion fatigue limit stress of the pipe under the bending stress when subjected to tensile / compressive stress.

[0154] S6.2, evaluation method of corrosion fatigue limit when the tensile / compressive stress is constant and the bending stress changes.

[0155] Maintain the applied axial tensile / compressive load constant, and design a series of groups of corrosion fatigue limit indoor simulation experiments under different bending stress states to measure the corrosion fatigue S-N curve, and evaluate the corrosion fatigue limit stress of the pipe under the bending stress when subjected to tensile / compressive stress.

[0156] S6.3, evaluation method of corrosion fatigue limit when the tensile / compressive / bending / torsion alternating state changes.

[0157] Use the factor molecule method or orthogonal experiment method to design a series of groups of corrosion fatigue limit indoor simulation experiments under different tensile, compression, bending, and torsion states, measure the corrosion fatigue S-N curve, and evaluate the corrosion fatigue limit stress of the pipe in the corrosion environment.

Claims

1. A device for testing the corrosion fatigue limit of a pipe material under corrosion and alternating load, characterized in that The high-temperature and high-pressure kettle comprises a kettle body (223) and a kettle cover (222); the kettle body (223) is externally provided with a heating jacket (224) and a heat preservation layer (225); The kettle body (223) is provided with a gas inlet and outlet (231); the gas inlet and outlet (231) of the kettle body (223) is connected with a booster pump (314) of a booster system; The inner bottom of the kettle body (223) is provided with a kettle stabilizer shell (232), and the inside is provided with a wedge (233), an annular fixator (234) and a kettle rotation stabilizer (235); The kettle body (223) and the kettle cover (222) are connected through sealing bolts (220) and sealing nuts (221); the kettle cover (222) is provided with a combined sealing ring (228); the kettle cover (222) is provided with a kettle cover sealing combination (226) and a main shaft cap (229) to install a torque transmission shaft (227); The torque transmission shaft (227) is sequentially connected with a torque applying shaft (230) and an axial and radial loading assembly (240); The axial and radial loading assembly (240) comprises an axial loading assembly and a radial loading assembly; The axial loading assembly comprises, from top to bottom, an upper stabilizer (241), an upper fixator (242), an upper sample joint (243), a radial loading upper cantilever (244), a corrosion fatigue sample (245), a radial loading lower cantilever (246), a lower sample joint (247), a lower fixator (248) and a lower stabilizer (249); axial tensile and compressive stress loading and unloading of the corrosion fatigue sample can be realized; The radial loading assembly comprises an upper cantilever stabilizer (250) and a lower cantilever stabilizer (257); the upper cantilever stabilizer (250) and the lower cantilever stabilizer (257) are respectively connected to the upper and lower ends of the corrosion fatigue sample (245); The upper cantilever stabilizer (250) is connected with an upper cantilever adapter pin (252) through an upper cantilever adapter (251); The lower cantilever stabilizer (257) is connected with a lower cantilever adapter pin (255) through a lower cantilever adapter (256); The upper cantilever adapter (251) and the lower cantilever adapter (256) are connected with a bending stress loading shaft (254), and the bending stress loading shaft (254) is provided with a bending stress loading nut (253). The booster system comprises a gas mixing device and a booster pump (314); the gas mixing device comprises a gas mixing cylinder (320) and a hydraulic cylinder (322); a deployment piston (321) is arranged between the gas mixing cylinder (320) and the hydraulic cylinder (322); 2. The apparatus for testing the corrosion fatigue limit of a pipe material under corrosion and alternating load according to claim 1, wherein The booster pump (314) is connected with the gas mixing cylinder (320); the gas mixing cylinder (320) is further connected with an H2S gas cylinder (310), a CO2 gas cylinder (311), an N2 gas cylinder (312) and a CH4 gas cylinder (313); The hydraulic cylinder (322) is connected with a liquid filling tank (324), a liquid tank (325) and a hydraulic pump (326); The gas mixing device is installed on a gas mixing device base (323). The kettle body (223) is provided with a high-temperature and high-pressure kettle temperature and pressure sensor (2A).

3. The apparatus for testing the corrosion fatigue limit of a pipe material under corrosion and alternating load according to claim 2, wherein ​ The torque transmission shaft (227) is provided with a load sensor (2B), a first strain sensor (2C-1), a second strain sensor (2C-2) and a rotary power device (210), the first strain sensor (2C-1) and the second strain sensor (2C-2) are respectively installed on a strain sensor fixing plate (213) through a first strain sensor upper fixing flange (211) and a second strain sensor upper fixing flange (212), the strain sensor fixing plate (213) is installed on a kettle cover sealing flange (216) through a strain sensor base (214) and a strain sensor base fixing flange (215); The high-temperature and high-pressure kettle temperature and pressure sensor (2A), the load sensor (2B), the first strain sensor (2C-1) and the second strain sensor (2C-2) are respectively connected with a high-temperature and high-pressure kettle temperature and pressure data processor (1A), a load data processor (1B), a first strain data processor (1C-1) and a second strain data processor (1C-2); The hydraulic pump (326) is provided with a hydraulic pump pressure sensor (3D), the booster pump (314) is provided with a booster pump pressure sensor (3E), the hydraulic cylinder (322) is provided with a hydraulic cylinder pressure sensor (3F), and the gas mixing cylinder (320) is provided with a gas mixing cylinder pressure sensor (3G); The hydraulic pump pressure sensor (3D), the booster pump pressure sensor (3E), the hydraulic cylinder pressure sensor (3F) and the gas mixing cylinder pressure sensor (3G) are respectively connected with a hydraulic pump pressure data processor (1D), a booster pump pressure data processor (1E), a hydraulic cylinder pressure data processor (1F) and a gas mixing cylinder pressure data processor (1G); The high-temperature and high-pressure kettle temperature and pressure data processor (1A), the load data processor (1B), the first strain data processor (1C-1) and the second strain data processor (1C-2), the hydraulic pump pressure data processor (1D), the booster pump pressure data processor (1E), the hydraulic cylinder pressure data processor (1F) and the gas mixing cylinder pressure data processor (1G) are respectively connected with a computer controller (101), and the corrosion fatigue test parameters in the whole experiment process are dynamically monitored and controlled, and the data is recorded and the curve is drawn.

4. A pipe corrosion fatigue limit test method under corrosion and alternating load, which is tested by using the pipe corrosion fatigue limit test device under corrosion and alternating load in claim 3, and includes the following steps: S1. Experimental preparation: S1.1, determining the experimental conditions for carrying out the corrosion fatigue limit indoor simulation test; The corrosion parameters need to determine the temperature, pressure, gas component and partial pressure, liquid and solid component and ion content according to the field working condition, the pipe grade and steel grade used in the experiment, the load type and the tensile-compressive-bending-torsional load size during service; S1.2, processing the corrosion fatigue limit indoor simulation test sample; the pipe used in the experiment is processed into a rod-shaped tensile sample; S1.3, prepare the corrosive gas with corresponding gas content; draw the gas mixing cylinder (320) to vacuum; connect the experimental required gas with H2S gas cylinder (310), CO2 gas cylinder (311), N2 gas cylinder (312), CH4 gas cylinder (313); according to the required content, open the H2S / CO2 / N2 / CH4 gas cylinder valve in turn to make the gas into the gas mixing cylinder (320) to prepare the mixed gas with corresponding gas component ratio; S1.4, prepare the corrosive liquid medium with corresponding liquid-solid content and ion ratio; prepare the corrosive liquid medium with corresponding liquid-solid component and content according to the liquid phase and solid phase component and ion content, and continuously pass in the corresponding gas component until saturation; S1.5, use the hydraulic cylinder pressure sensor (3F) to monitor the hydraulic cylinder pressure, and use the gas mixing cylinder pressure sensor (3G) to monitor the gas mixing cylinder pressure; S2. Sample loading: S2.1, install the radial loading assembly; assemble the upper cantilever stabilizer (250) inside the radial loading upper cantilever (244), and fix it by sleeving the upper clamping end of the corrosion fatigue sample (245) to the position close to the parallel section; assemble the lower cantilever stabilizer (257) inside the radial loading lower cantilever (246), and fix it by sleeving the lower clamping end of the corrosion fatigue sample (245) to the position close to the parallel section; connect the upper cantilever adapter (251), the lower cantilever adapter (256) and the bending stress loading shaft (254) respectively; S2.2, install the axial loading assembly; assemble the lower sample joint (247) at the lower end of the corrosion fatigue sample (245); install the lower fixer (248) on the torque applying shaft (230) and connect it with the lower sample joint (247), put the whole into the radial loading assembly (240) and fix it with the lower stabilizer (249); assemble the upper sample joint (243) at the upper end of the corrosion fatigue sample (245); install the upper fixer (241) on the torque applying shaft (230) and connect it with the upper sample joint (243), and fix the whole on the radial loading assembly (240) using the upper stabilizer (241); S2.3, apply axial tensile or compressive load; adjust the upper fixer (241) and the lower fixer (248) to apply tensile or compressive load to the corrosion fatigue sample (245), the calculation relationship between the applied load and the deflection is directly used as σ=E·ε, where σ is the tensile / compressive stress, E is the tensile elastic modulus or compressive elastic modulus, and ε is the tensile / compressive strain; S2.4, apply radial bending load; increase the deflection of the parallel section of the corrosion fatigue sample (245) by tightening the bending stress loading nut (253) to apply radial bending load to the corrosion fatigue sample (245), the relationship between the applied load and the deflection adopts the four-point bending standard calculation formula, or adopts trial experiment for correction; S3. Parameter setting: S3.1, set the simulated corrosion environment parameters; add the prepared corrosive liquid medium into the kettle body (223), the liquid surface needs to immerse the radial loading assembly (240), use the sealing bolt (220) and the sealing nut (221) to seal the kettle cover (222) and the kettle body (223); use the strain sensor base fixing flange (215) to fix the strain sensor base (214) on the kettle cover sealing combination (226); use the first strain sensor upper fixing flange (211) and the second strain sensor upper fixing flange (212) to fix the strain sensor fixing plate (213) on the torque transmission shaft (227), and install the first strain sensor (2C-1) and the second strain sensor (2C-2) on the strain sensor fixing plate (213); connect the load sensor (2B), the rotary power device (210) and the torque transmission shaft (227) in turn; S3.2, kettle body temperature and pressure increase; set the temperature and pressure data processor (1A) in the computer controller (101) to the experimental corresponding temperature and pressure, control the heating jacket (224) to heat the kettle body (223) through the high temperature and high pressure kettle temperature and pressure sensor (2A) until the experimental set temperature is reached; control the kettle body (223) to be pressurized through the high temperature and high pressure kettle temperature and pressure sensor (2A) by the booster pump (314) until the experimental set pressure is reached; S4. Data monitoring: S4.1, connect the first strain data processor (1C-1) and the second strain data processor (1C-2) with the first strain sensor (2C-1) and the second strain sensor (2C-2) respectively, and monitor the axial deformation of the corrosion fatigue sample (245) during the experiment; S4.2, connect the high temperature and high pressure kettle temperature and pressure data processor (1A) with the high temperature and high pressure kettle temperature and pressure sensor (2A), and monitor the change of the temperature and pressure value in the kettle body (223) during the experiment; S4.3, connect the load data processor (1B) with the load sensor (2B), and monitor the change of the axial tensile load and torque of the corrosion fatigue sample (245) during the experiment; S4.4, connect the hydraulic pump pressure data processor (1D) and the booster pump pressure data processor (1E) with the hydraulic pump pressure sensor (3D) and the booster pump pressure sensor (3E) respectively, monitor the pump pressure of the hydraulic pump (326) and the booster pump (314), connect the hydraulic cylinder pressure data processor (1F) and the gas mixing cylinder pressure data processor (1G) with the hydraulic cylinder pressure sensor (3F) and the gas mixing cylinder pressure sensor (3G) respectively, monitor the internal pressure of the hydraulic cylinder (322) and the gas mixing cylinder (320) to ensure the safety of the experiment; S5. Post-experiment processing: S5.1, take out the corrosion fatigue sample; after reaching the predetermined period of the experiment, cool down, depressurize, open the corrosion fatigue limit test device, and take out the corrosion fatigue sample (245); S5.2, observe the corrosion cracking characteristics; use macroscopic and microscopic methods to analyze and observe the surface corrosion product film morphology, composition and protective properties of the corrosion fatigue specimen (245); observe and judge the crack nucleation, propagation characteristics and crack size of the parallel section of the corrosion fatigue specimen (245); S5.3, specimen fatigue strength analysis; if the corrosion fatigue specimen (245) breaks, continue to carry out corrosion fatigue limit test experiments under conditions of less than the stress; if the corrosion fatigue specimen (245) does not break, perform a room temperature tensile test to determine the remaining strength of the pipe after the corrosion fatigue limit test, and continue to carry out corrosion fatigue limit test experiments under conditions of greater than the stress; S6. Evaluation of the corrosion fatigue limit: S6.1, evaluation method for the corrosion fatigue limit when the bending stress is constant and the tensile / compressive stress changes; Maintain the applied radial bending load unchanged, and design a series of groups of corrosion fatigue limit indoor simulation experiments under different tensile / compressive stress states to measure the corrosion fatigue S-N curve and evaluate the corrosion fatigue limit stress of the pipe under the tensile / compressive stress at the bending stress; S6.2, evaluation method for the corrosion fatigue limit when the tensile / compressive stress is constant and the bending stress changes; Maintain the applied axial tensile / compressive load unchanged, and design a series of groups of corrosion fatigue limit indoor simulation experiments under different bending stress states to measure the corrosion fatigue S-N curve and evaluate the corrosion fatigue limit stress of the pipe under the bending stress at the tensile / compressive stress; S6.3, evaluation method for the corrosion fatigue limit when the tensile / compressive / bending / torsion alternating state changes; Use the factor molecule method or orthogonal experiment method to design a series of groups of corrosion fatigue limit indoor simulation experiments under different tensile, compression, bending and torsion states to measure the corrosion fatigue S-N curve and evaluate the corrosion fatigue limit stress of the pipe in the corrosion environment.

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