CO2 stress corrosion test system and method for non-adhesive flexible pipe

Abstract

The invention discloses a CO2 stress corrosion test system and method for a non-adhesive flexible pipe, and relates to the technical field of ocean engineering and oil and gas equipment tests. The system comprises a base and a supporting frame, an axial loading device, an internal pressure and torsion loading device, a follow-up bending moment balancing device and an end follow-up sealing device are arranged on the base, and a movable lifting environment chamber device is arranged on the supporting frame. The follow-up bending moment balancing device and the end follow-up sealing device form a flexible boundary constraint system, and the movable lifting environment chamber device is used for locally forming a high-temperature and high-pressure COcorrosion environment on the outer wall of the flexible pipe, can move in the axial direction of the flexible pipe and synchronously ascends and descends along with bending displacement in the alternating bending loading process. Therefore, the position of a corrosion area is kept stable under the dynamic load condition, and through the collaborative design of multi-load coupling loading, a local movable corrosion environment and multi-source online monitoring, true simulation and quantitative evaluation of the COstress corrosion behavior of the non-adhesive flexible pipe under the actual service working condition are achieved.

Description

Technical Field

[0001] This invention relates to the field of marine engineering and oil and gas equipment testing technology, specifically to a non-bonded flexible tube CO2 stress corrosion testing system and method. Background Technology

[0002] As offshore oil and gas resource development moves towards deep / ultra-deep water, non-bonded flexible pipes are widely used in wellhead connection and transportation systems due to their superior mechanical properties and ease of transportation and installation. Non-bonded flexible pipes typically consist of a multi-layered structure including a skeleton layer, inner sheath layer, pressure-resistant armor layer, tensile armor layer, and outer sheath layer. In actual service, in addition to bearing the internal pressure caused by the transported medium, the flexible pipe is also affected by platform movement and sea state loads, resulting in complex working conditions such as alternating bending, torsion, and axial tension / compression, exhibiting a multi-load, multi-field coupled stress state.

[0003] When the outer sheath ruptures or partially fails, seawater may enter the annulus of the flexible pipe, forming a high-temperature, high-pressure, CO2-rich corrosive environment together with the infiltrated CO2. In this environment, the metal armor layer of the flexible pipe is prone to corrosion damage, and under alternating loads and stress concentration, it can induce or accelerate stress corrosion cracking (CO2-SCC), leading to interlayer damage, load-bearing capacity degradation, media leakage, and even structural failure. This significantly shortens the service life of the flexible pipe, thereby threatening the safety and reliability of the marine oil and gas transportation system.

[0004] Existing research on CO2-SCC largely focuses on small-sized material specimens. The testing equipment typically employs fixed corrosion chambers and applies single or limited loads, making it difficult to accurately reflect the service behavior of full-size unbonded flexible tube structures under multi-load coupling and dynamic loading conditions. Especially under the combined effects of internal pressure and alternating bending, the end clamping and sealing areas often introduce additional bending moments or constraint effects, leading to the following problems:

[0005] (1) The risk of seal failure increases, making it difficult to maintain stable operation of the test over a long period of time;

[0006] (2) The boundary conditions deviate from the actual service boundary of the flexible tube, the true stress state of the specimen is distorted, and the validity and comparability of the test results are affected;

[0007] (3) Additional bending moment may be transmitted to the axial / torsional load actuator, causing loading deviation or equipment malfunction.

[0008] Furthermore, fixed corrosion chambers typically make it difficult to conduct local comparative evaluations of different axial pipe sections on the same sample; they also make it difficult to flexibly change the contact area / contact method of the sample to conduct variable control tests while maintaining a consistent volume of corrosive medium, resulting in insufficient test repeatability and poor comparability of results.

[0009] The challenges in addressing these issues and deficiencies are as follows: the system needs to achieve long-term stable operation in a high-temperature, high-pressure, CO2-rich corrosive environment; it must be able to apply dynamic loads such as alternating bending and torsion under internal pressure while maintaining reliable sealing and accurate stress boundaries; in addition, the environmental chamber must be able to be flexibly arranged along the axis of the flexible pipe without compromising sealing and loading stability, in order to meet the needs of local corrosion comparison and variable control tests for different pipe sections, while simultaneously ensuring the continuity and reliability of temperature and pressure regulation, as well as the acquisition and transmission of multi-source monitoring signals. Summary of the Invention

[0010] The purpose of this invention is to address the above-mentioned shortcomings by proposing a test system and method that can effectively simulate the CO2-SCC behavior of unbonded flexible tubes under actual service conditions, and to achieve controllable testing under multi-field coupled loading conditions in high temperature, high pressure, and CO2-rich environments.

[0011] The present invention specifically adopts the following technical solution:

[0012] A non-bonded flexible tube CO2 stress corrosion testing system includes a base and a support frame. The base is equipped with an axial loading device, an internal pressure and torsional loading device, a follow-up bending moment balancing device, and an end follow-up sealing device. The support frame is equipped with a movable and lifting environmental chamber device. The axial loading device, internal pressure and torsional loading device, follow-up bending moment balancing device, movable and lifting environmental chamber device, and end follow-up sealing device are arranged sequentially from left to right.

[0013] The base is equipped with a bottom slide rail along its axis. The axial loading device is fixed on the base. The bottom of the internal pressure and torsional loading device, the following bending moment balancing device and the end following sealing device are all connected to the base plate. The base plate is equipped with a slider, which is movablely connected to the base through the cooperation of the slider and the bottom slide rail.

[0014] The support frame is equipped with a top slide rail. The movable and retractable environmental chamber device includes a movable and retractable environmental chamber body and a movable and retractable environmental chamber base. The movable and retractable environmental chamber base cooperates with the top slide rail to realize the free sliding of the movable and retractable environmental chamber device. The movable and retractable environmental chamber body is connected to a CO2 gas injection pipe, a corrosive electrolyte liquid injection pipe and an environmental chamber exhaust gas / liquid discharge pipe.

[0015] The movable lifting environmental chamber is equipped with alternating bending loading devices on both sides, and the alternating bending loading devices are movably connected to the bottom slide rail;

[0016] The bottom connecting plate connected to the following bending moment balancing device is provided with a longitudinal slide rail, and the bottom of the following bending moment balancing device is provided with a slider. The slider is embedded in the longitudinal slide rail to realize the longitudinal movement of the following bending moment balancing device.

[0017] Preferably, limit blocks are provided on the bottom slide rail between the axial loading device and the internal pressure and torsional loading device, between the follow-up bending moment balancing device and the alternating bending loading device, and between the alternating bending loading device and the end follow-up sealing device, and an end limit block is provided at the right end of the bottom slide rail.

[0018] Preferably, the axial loading device includes an axial loading actuator and an axial force sensor. The axial loading actuator applies tensile or compressive loads through the axial force sensor, flange joint, and thrust axial internal pressure and torsional loading device. The internal pressure and torsional loading device includes an outer sleeve, inside which a torsional loading actuator is installed. A coaxial torsional shaft is connected to the torsional loading actuator, and a rotary pressure supply joint is connected to the torsional loading actuator. The rotary pressure supply joint cooperates with the air / liquid inlet to maintain the connectivity and sealing of the medium inside the specimen during the application of torsional load.

[0019] Preferably, the follow-up moment balancing device and the end follow-up sealing device form a follow-up sealing and moment balancing structure for the non-bonded flexible tube. The follow-up moment balancing device includes an outer spherical structure composed of an upper outer spherical seal and a lower outer spherical seal. A sealing joint is provided inside the outer spherical structure. An inner spherical structure is wrapped around the outer spherical structure. The inner spherical structure is formed by an upper fixed outer spherical groove and a lower fixed outer spherical groove to form a spherical pair. A spherical lateral limiting block and a spherical bottom limiting pin are provided on the groove of the inner spherical structure. The base of the follow-up moment balancing device is connected to the lower fixed outer spherical groove.

[0020] Preferably, the alternating bending loading device includes an upper limiting roller pressure head, a lower limiting roller pressure head, a servo hydraulic cylinder, and an alternating bending device telescopic shaft. The upper limiting roller pressure head and the lower limiting roller pressure head form a constraint space that allows the flexible tube to move axially and is laterally limited. The pressing amount / roller displacement sensor is set inside the upper limiting roller pressure head, the force sensor is set inside the lower limiting roller pressure head, and the stroke displacement sensor is set inside the telescopic shaft.

[0021] Preferably, the movable and retractable environmental chamber is equipped with two insulating sealing rings, forming a cavity within the chamber. The cavity houses reaction chamber 1, reaction chamber 2, reaction chamber 3, a heating chamber, and a cooling chamber.

[0022] Preferably, the internal pressure and torsion loading device is equipped with an internal gas / liquid inlet pipe and an internal gas / liquid outlet pipe.

[0023] A CO2 stress corrosion test method for non-bonded flexible pipes, using the system described above, includes the following steps:

[0024] S1: The non-bonded flexible tube specimen is clamped in the test system, so that one end of the non-bonded flexible tube specimen is sealed to the following bending moment balancing device, and the other end passes through the alternating bending loading device and the movable lifting environmental chamber device in sequence, and is sealed to the end following sealing device.

[0025] S2: Remove the outer sheath layer of the non-bonded flexible tube specimen in the target test section, and move the movable lifting environmental chamber device along the axis of the non-bonded flexible tube specimen to form a locally sealed high temperature and high pressure corrosion environment space between the movable lifting environmental chamber device and the outer wall of the target test section.

[0026] S3: Introduce CO2 and electrolyte media into the corrosive environment space of the movable and liftable environmental chamber device, and regulate the temperature and pressure of the corrosive environment space to the preset test conditions;

[0027] S4: Apply one or more of the following loads to the specimen through the load control subsystem: internal pressure, tension, compression, torsion and alternating bending load; during the application of alternating bending load, control the movable lifting environmental chamber device to move up and down and adjust its position according to the fluctuation of alternating bending displacement, and realize independent or combined loading of load in the follow-up state at the end of the specimen;

[0028] S5: During the test, strain, displacement, bending curvature, leakage, internal pressure, acoustic emission signals and / or crack propagation related monitoring signals are collected synchronously along the axial direction of the specimen. The collected signals are then correlated with load parameters and environmental parameters to obtain the monitoring results of stress corrosion cracking process of the specimen under CO2 corrosion environment.

[0029] S6: After the set test time or failure criterion is reached, the alternating bending / torsional / axial loads are unloaded in sequence and the internal pressure is released. Then, the environmental chamber is cooled and depressurized, CO2 and corrosive media are recovered, the sample is disassembled, and the crack morphology, corrosion products and failure mode of the target test section are analyzed.

[0030] The present invention has the following beneficial effects:

[0031] This invention provides a test system and method that can effectively simulate the CO2-SCC behavior of unbonded flexible tubes under actual service conditions. It enables controllable testing under multi-field coupled loading conditions in a high-temperature, high-pressure, CO2-rich environment, improving the authenticity, repeatability, and comparability of test results. This provides a reliable experimental basis and technical support for the safety evaluation and life prediction of unbonded flexible tube structures.

[0032] The follow-up moment balancing device and the end follow-up sealing device constitute a flexible boundary constraint system. When the flexible tube is subjected to internal pressure and alternating bending load, the end of the specimen is allowed to generate angular displacement and axial micro-slippage to offset the additional bending moment generated during alternating bending loading and suppress the transmission of bending moment to the axial loading and torsional load devices, ensuring reliable sealing and real stress state.

[0033] The mobile lifting environmental chamber device is used to locally create a high-temperature, high-pressure CO2 corrosion environment on the outer wall of a flexible tube. It can move axially along the flexible tube and rise and fall synchronously with the bending displacement during alternating bending loading, thus maintaining the stability of the corrosion zone under dynamic load conditions. The environmental chamber contains multiple reaction chambers of the same volume but with different contact methods, used to conduct parallel comparative corrosion tests at different circumferential positions and with different contact interfaces under the same medium volume conditions. Attached Figure Description

[0034] Figure 1 Flowchart of CO2 stress corrosion test method for non-bonded flexible tubes;

[0035] Figure 2 This is a schematic diagram of a CO2 stress corrosion testing system for non-bonded flexible tubes.

[0036] Figure 3 Schematic diagram of the axial loading device, internal pressure and torsional loading device and follow-up bending moment balancing device;

[0037] Figure 4 This is a schematic diagram of an alternating bending loading device and a movable, retractable environmental chamber.

[0038] Among them, 1 is the base, 2 is the support frame, 3 is the axial loading device, 4 is the internal pressure and torsional loading device, 5 is the follow-up bending moment balancing device, 6 is the end follow-up sealing device, 7 is the movable telescopic environmental chamber body, 8 is the movable telescopic environmental chamber base, 9 is the CO2 gas injection pipe, 10 is the corrosive electrolyte liquid injection pipe, 11 is the environmental chamber exhaust gas / liquid discharge pipe, 12 is the alternating bending loading device, 13 is the limiting block, 14 is the end limiting block, 15 is the axial loading actuator, 16 is the axial force sensor, 17 is the flange joint, 18 is the outer sleeve, 19 is the torsional loading actuator, and 20 is the... 21 is a coaxial torsion shaft; 22 is a rotary pressure supply joint; 23 is an air / liquid inlet; 24 is an upper outer spherical seal; 25 is a sealing joint; 26 is an upper fixed outer spherical groove; 27 is a lower fixed outer spherical groove; 28 is a spherical lateral limiting block; 29 is a spherical bottom limiting pin; 30 is the base of the follow-up bending moment balancing device; 31 is an upper limiting roller pressure head; 32 is a lower limiting roller pressure head; 33 is a servo hydraulic cylinder; 34 is the telescopic shaft of the alternating bending device; 35 is a pressing amount / roller displacement sensor; 36 is a force sensor; 37 is a stroke displacement sensor; 38 is reaction chamber 1; 39 is reaction chamber 2; 40 is reaction chamber 3; 41 is a heating chamber; 42 is a cooling chamber; 43 is a leak prevention monitoring sensor; 44 is an acoustic emission (AE) sensor.

[0039] 45 is the gas / liquid inlet pipe inside the tube, 46 is the gas / liquid outlet pipe inside the tube, and 47 is the non-bonded flexible tube specimen. Detailed Implementation

[0040] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and specific examples:

[0041] Combination Figures 1-4 A non-bonded flexible tube CO2 stress corrosion testing system includes a base 1 and a support frame 2. The base is equipped with an axial loading device 3, an internal pressure and torsional loading device 4, a follow-up bending moment balancing device 5, and an end follow-up sealing device 6. The support frame 2 is equipped with a movable lifting environmental chamber device. The axial loading device 3, the internal pressure and torsional loading device 4, the follow-up bending moment balancing device 5, the movable lifting environmental chamber device, and the end follow-up sealing device 6 are arranged sequentially from left to right.

[0042] The base 1 is provided with a bottom slide rail along its axis. The axial loading device 3 is fixed on the base. The bottom of the internal pressure and torsion loading device 4, the following bending moment balancing device 5 and the end following sealing device 6 are all connected to the base plate. The base plate is provided with a slider. The slider and the bottom slide rail cooperate to achieve a movable connection with the base.

[0043] The support frame 2 is equipped with a top slide rail. The movable and retractable environmental chamber device includes a movable and retractable environmental chamber body 7 and a movable and retractable environmental chamber base 8. The movable and retractable environmental chamber base 8 cooperates with the top slide rail to realize the free sliding of the movable and retractable environmental chamber device. The movable and retractable environmental chamber body 7 is connected to a CO2 gas injection pipe 9, a corrosive electrolyte liquid injection pipe 10 and an environmental chamber exhaust gas / liquid discharge pipe 11.

[0044] The movable lifting environmental chamber device is equipped with alternating bending loading devices 12 on both sides, and the alternating bending loading devices are movably connected to the bottom slide rail;

[0045] The bottom connecting plate connected to the following bending moment balancing device 5 is provided with a longitudinal slide rail, and the bottom of the following bending moment balancing device 5 is provided with a slider. The slider is embedded in the longitudinal slide rail to realize the longitudinal movement of the following bending moment balancing device.

[0046] Limiting blocks 13 are provided on the bottom slide rail between the axial loading device 3 and the internal pressure and torsional loading device 4, between the following bending moment balancing device 5 and the alternating bending loading device 12, and between the alternating bending loading device 12 and the end following sealing device 6. An end limiting block 14 is provided at the right end of the bottom slide rail.

[0047] The axial loading device 3 includes an axial loading actuator 15 and an axial force sensor 16. The axial loading actuator 15 applies tensile or compressive loads through the axial force sensor 16, flange joint 17, and thrust axial internal pressure and torsion loading device 4. The internal pressure and torsion loading device 4 includes an outer sleeve 18, and a torsion loading actuator 19 is provided inside the outer sleeve 18. A coaxial torsion shaft 20 is connected to the torsion loading actuator 19. A rotary pressure supply joint 21 is connected to the torsion loading actuator 19. The rotary pressure supply joint 21 cooperates with the air / liquid inlet 22 to maintain the connectivity and sealing of the medium inside the specimen during the application of torsion load.

[0048] The following moment balancing device 5 and the end following sealing device 6 form a following sealing and moment balancing structure for the non-bonded flexible tube. The following moment balancing device 5 includes an outer spherical structure composed of an upper outer spherical seal 23 and a lower outer spherical seal 24. A sealing joint 25 is provided inside the outer spherical structure. An inner spherical structure is wrapped on the outer spherical structure. The inner spherical structure is formed by an upper fixed outer spherical groove 26 and a lower fixed outer spherical groove 27 to form a spherical pair. A spherical lateral limiting block 28 and a spherical bottom limiting pin 29 are provided on the groove of the inner spherical structure. The following moment balancing device base 30 is connected to the lower fixed outer spherical groove.

[0049] The alternating bending loading device 12 includes an upper limiting roller pressure head 31, a lower limiting roller pressure head 32, a servo hydraulic cylinder 33, and an alternating bending device telescopic shaft 34. The upper limiting roller pressure head 31 and the lower limiting roller pressure head 32 form a constraint space that allows the flexible tube to move axially and is laterally limited. The pressing amount / roller displacement sensor 35 is installed in the upper limiting roller pressure head, the force sensor 36 is installed in the lower limiting roller pressure head, and the stroke displacement sensor 37 is installed in the telescopic shaft.

[0050] The movable and retractable environmental chamber is equipped with two isolation sealing rings, forming a cavity within the chamber. Reaction chamber 1 (38), Reaction chamber 2 (39), Reaction chamber 3 (40), Heating chamber (41), and Cooling chamber (42) are housed within this cavity. Temperature sensors monitor the temperature of each chamber, while leak detection sensors (43) are positioned within the cavity to monitor changes in the cavity environment. Acoustic emission (AE) sensors (44) are axially arranged outside the isolation sealing rings on both sides of the cavity to monitor stress corrosion cracking signals in the flexible tubing within each reaction chamber.

[0051] The internal pressure and torsion loading device 4 is equipped with an internal gas / liquid input pipe and an internal gas / liquid discharge pipe.

[0052] A CO2 stress corrosion test method for non-bonded flexible pipes, using the system described above, includes the following steps:

[0053] S1: The non-bonded flexible tube specimen 47 is clamped in the test system, so that one end of the non-bonded flexible tube specimen is sealed to the following bending moment balancing device 5, and the other end passes through the alternating bending loading device 12 and the movable lifting environmental chamber device in sequence, and is sealed to the end following sealing device 6.

[0054] S2: Remove the outer sheath layer of the non-bonded flexible tube specimen in the target test section, and move the movable lifting environmental chamber device along the axis of the non-bonded flexible tube specimen to form a locally sealed high temperature and high pressure corrosion environment space between the movable lifting environmental chamber device and the outer wall of the target test section.

[0055] S3: Introduce CO2 and electrolyte media into the corrosive environment space of the movable and liftable environmental chamber device, and regulate the temperature and pressure of the corrosive environment space to the preset test conditions;

[0056] S4: Apply one or more of the following loads to the specimen through the load control subsystem: internal pressure, tension, compression, torsion and alternating bending load; during the application of alternating bending load, control the movable lifting environmental chamber device to move up and down and adjust its position according to the fluctuation of alternating bending displacement, and realize independent or combined loading of load in the follow-up state at the end of the specimen;

[0057] S5: During the test, strain, displacement, bending curvature, leakage, internal pressure, acoustic emission signals and / or crack propagation related monitoring signals are collected synchronously along the axial direction of the specimen. The collected signals are then correlated with load parameters and environmental parameters to obtain the monitoring results of stress corrosion cracking process of the specimen under CO2 corrosion environment.

[0058] S6: After the set test time or failure criterion is reached, the alternating bending / torsional / axial loads are unloaded in sequence and the internal pressure is released. Then, the environmental chamber is cooled and depressurized, CO2 and corrosive media are recovered, the sample is disassembled, and the crack morphology, corrosion products and failure mode of the target test section are analyzed.

[0059] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A CO2 stress corrosion testing system for non-bonded flexible pipes, characterized in that, It includes a base and a support frame. The base is equipped with an axial loading device, an internal pressure and torsional loading device, a follow-up bending moment balancing device and an end follow-up sealing device. The support frame is equipped with a movable and lifting environmental chamber device. The axial loading device, internal pressure and torsional loading device, follow-up bending moment balancing device, movable and lifting environmental chamber device and end follow-up sealing device are arranged in order from left to right. The base is equipped with a bottom slide rail along its axis. The axial loading device is fixed on the base. The bottom of the internal pressure and torsional loading device, the following bending moment balancing device and the end following sealing device are all connected to the base plate. The base plate is equipped with a slider, which is movablely connected to the base through the cooperation of the slider and the bottom slide rail. The support frame is equipped with a top slide rail. The movable and retractable environmental chamber device includes a movable and retractable environmental chamber body and a movable and retractable environmental chamber base. The movable and retractable environmental chamber base cooperates with the top slide rail to realize the free sliding of the movable and retractable environmental chamber device. The movable and retractable environmental chamber body is connected to a CO2 gas injection pipe, a corrosive electrolyte liquid injection pipe and an environmental chamber exhaust gas / liquid discharge pipe. The movable lifting environmental chamber is equipped with alternating bending loading devices on both sides, and the alternating bending loading devices are movably connected to the bottom slide rail; The bottom connecting plate connected to the following bending moment balancing device is provided with a longitudinal slide rail, and the bottom of the following bending moment balancing device is provided with a slider. The slider is embedded in the longitudinal slide rail to realize the longitudinal movement of the following bending moment balancing device.

2. The CO2 stress corrosion testing system for non-bonded flexible pipes as described in claim 1, characterized in that, Limiting blocks are provided on the bottom slide rail between the axial loading device and the internal pressure and torsional loading device, between the follow-up bending moment balancing device and the alternating bending loading device, and between the alternating bending loading device and the end follow-up sealing device. An end limiting block is provided at the right end of the bottom slide rail.

3. The CO2 stress corrosion testing system for non-bonded flexible pipes as described in claim 1, characterized in that, The axial loading device includes an axial loading actuator and an axial force sensor. The axial loading actuator applies tensile or compressive loads through the axial force sensor, flange joint, and thrust axial internal pressure and torsional loading device. The internal pressure and torsional loading device includes an outer sleeve, inside which is a torsional loading actuator. The torsional loading actuator is connected to a coaxial torsional shaft, and a rotary pressure supply joint is connected to the torsional loading actuator. The rotary pressure supply joint cooperates with the air / liquid inlet to maintain the connectivity and sealing of the medium inside the specimen during the application of torsional load.

4. The CO2 stress corrosion testing system for non-bonded flexible pipes as described in claim 1, characterized in that, The follow-up moment balancing device and the end follow-up sealing device form a follow-up sealing and moment balancing structure for the non-bonded flexible tube. The follow-up moment balancing device includes an outer spherical structure composed of an upper outer spherical seal and a lower outer spherical seal. A sealing joint is set inside the outer spherical structure. An inner spherical structure is wrapped on the outer spherical structure. The inner spherical structure is composed of an upper fixed outer spherical groove and a lower fixed outer spherical groove, forming a spherical pair with the outer spherical structure. The groove of the inner spherical structure is provided with a spherical lateral limiting block and a spherical bottom limiting pin. The base of the follow-up moment balancing device is connected to the lower fixed outer spherical groove.

5. The CO2 stress corrosion testing system for non-bonded flexible pipes as described in claim 1, characterized in that, The alternating bending loading device includes an upper limiting roller pressure head, a lower limiting roller pressure head, a servo hydraulic cylinder, and an alternating bending device telescopic shaft. The upper limiting roller pressure head and the lower limiting roller pressure head form a constraint space that allows the flexible tube to move axially and is laterally limited. The pressing amount / roller displacement sensor is set inside the upper limiting roller pressure head, the force sensor is set inside the lower limiting roller pressure head, and the stroke displacement sensor is set inside the telescopic shaft.

6. The CO2 stress corrosion testing system for non-bonded flexible pipes as described in claim 1, characterized in that, The movable and retractable environmental chamber is equipped with two isolation sealing rings, forming a cavity inside the chamber. The cavity contains reaction chamber No. 1, reaction chamber No. 2, reaction chamber No. 3, heating chamber, and cooling chamber.

7. The CO2 stress corrosion testing system for non-bonded flexible pipes as described in claim 1, characterized in that, The internal pressure and torsional loading device is equipped with an internal gas / liquid inlet pipe and an internal gas / liquid outlet pipe.

8. A method for CO2 stress corrosion testing of non-bonded flexible pipes, employing the system described in any one of claims 1-7, characterized in that, Includes the following steps: S1: The non-bonded flexible tube specimen is clamped in the test system, so that one end of the non-bonded flexible tube specimen is sealed to the following bending moment balancing device, and the other end passes through the alternating bending loading device and the movable lifting environmental chamber device in sequence, and is sealed to the end following sealing device. S2: Remove the outer sheath layer of the non-bonded flexible tube specimen in the target test section, and move the movable lifting environmental chamber device along the axis of the non-bonded flexible tube specimen to form a locally sealed high temperature and high pressure corrosion environment space between the movable lifting environmental chamber device and the outer wall of the target test section. S3: Introduce CO2 and electrolyte media into the corrosive environment space of the movable and liftable environmental chamber device, and regulate the temperature and pressure of the corrosive environment space to the preset test conditions; S4: Apply one or more of the following loads to the specimen through the load control subsystem: internal pressure, tension, compression, torsion and alternating bending load; during the application of alternating bending load, control the movable lifting environmental chamber device to move up and down and adjust its position according to the fluctuation of alternating bending displacement, and realize independent or combined loading of load in the follow-up state at the end of the specimen; S5: During the test, strain, displacement, bending curvature, leakage, internal pressure, acoustic emission signals and / or crack propagation related monitoring signals are collected synchronously along the axial direction of the specimen. The collected signals are then correlated with load parameters and environmental parameters to obtain the monitoring results of stress corrosion cracking process of the specimen under CO2 corrosion environment. S6: After the set test time or failure criterion is reached, the alternating bending / torsional / axial loads are unloaded in sequence and the internal pressure is released. Then, the environmental chamber is cooled and depressurized, CO2 and corrosive media are recovered, the sample is disassembled, and the crack morphology, corrosion products and failure mode of the target test section are analyzed.

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