Experimental device and experimental method for stress corrosion of submarine pipeline in gas phase hydrogen environment

Abstract

The application discloses an experimental device and experimental method for submarine pipeline stress corrosion in a gaseous hydrogen environment, which comprises a high-pressure kettle body arranged on a support, a flange kettle cover arranged on the high-pressure kettle body, NaCl solution arranged in the high-pressure kettle body, a rod-shaped sample arranged in the NaCl solution, a tension sensor arranged on a rack, an upper stretching rod connected with the tension sensor, a servo motor arranged on the rack, an electric cylinder connected with the servo motor, and a lower stretching rod connected with a piston rod of the electric cylinder. The application has the characteristics that hydrogen-induced material damage and seawater corrosion damage are connected together, and reliable data basis is provided for the selection of materials for manufacturing submarine hydrogen pipelines.

Description

Technical Field

[0001] This invention relates to the field of stress corrosion testing technology for subsea pipelines, and in particular to an experimental apparatus and method for subsea pipeline stress corrosion that is simple in structure, easy to operate, and capable of simulating the stress corrosion of materials in a gaseous hydrogen environment in the deep sea. Background Technology

[0002] With the continuous maturation and improvement of hydrogen energy development and utilization technologies, large-scale centralized hydrogen production and long-distance hydrogen transportation are future trends. Submarine pipeline transportation is the most economical method, and establishing a pure hydrogen high-pressure transportation network is the ultimate goal of building a hydrogen society.

[0003] Currently, my country has established a relatively complete network of subsea hydrogen pipelines. However, due to the long-term exposure of these pipelines to the harsh marine environment, they are subjected to complex operational loads, environmental loads, and unexpected risk loads. This leads to direct contact between chloride-containing seawater and the pipeline steel, causing uniform corrosion, pitting corrosion, and stress corrosion. Because hydrogen has an extremely high diffusion coefficient in pipeline steel, high-pressure hydrogen within the pipeline can penetrate the steel, leading to hydrogen embrittlement. Furthermore, as hydrogen continues to diffuse within the steel, the localized hydrogen concentration on the outer surface of the pipeline steel increases, causing hydrogen-induced damage. These effects exacerbate the localized corrosion process of the pipeline steel by seawater.

[0004] Current experiments on stress corrosion of subsea pipelines mainly include:

[0005] Pre-charged hydrogen stress corrosion test and electrochemical hydrogen-charged stress corrosion test; Pre-charging the subsea pipeline material with hydrogen can saturate some hydrogen inside the material, but due to the hydrogen embrittlement sensitivity of pipeline steel and the high hydrogen diffusion coefficient, the hydrogen inside the material cannot be stored for a long time, which has a significant impact on the error of subsequent experimental test data.

[0006] The stress corrosion experiment of electrochemical hydrogen charging was conducted in a modified Devanathan-Stachurski dual electrolytic cell. By applying a polarization potential at the cathode, hydrogen atoms were electrolyzed from the alkaline or acidic solution in the hydrogen charging cell and adsorbed onto the material surface. Some hydrogen atoms under external stress were studied through adsorption and desorption on the metal surface and diffusion within the matrix.

[0007] However, electrochemical hydrogen charging results in a surface hydrogen concentration that is much higher than the actual gas-phase hydrogen concentration in the pipe, deviating significantly from the actual hydrogen diffusion behavior. Secondly, during the polarization release of hydrogen, the surface charge distribution of the hydrogen detection end changes, deviating from its initial equilibrium potential. This causes the adsorption and dissociation of hydrogen on the surface to deviate from actual behavior, making it difficult to meet the reference standards for practical applications. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide an experimental device and method that is simple in structure, easy to operate, and capable of simulating stress corrosion of materials in a gaseous hydrogen environment in the deep sea for submarine pipelines.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] An experimental apparatus for stress corrosion of subsea pipelines in a gaseous hydrogen environment includes a high-pressure vessel body mounted on a support, a flanged vessel cover mounted on the high-pressure vessel body, a NaCl solution in the high-pressure vessel body, a rod-shaped sample in the NaCl solution, a tensile sensor mounted on a frame, an upper tension rod connected to the tensile sensor, a servo motor mounted on the frame, an electric cylinder connected to the servo motor, and a lower tension rod connected to the piston rod of the electric cylinder. The lower part of the upper tension rod extends into the high-pressure vessel body through the flanged vessel cover, and the upper part of the lower tension rod extends into the high-pressure vessel body through the bottom of the high-pressure vessel body. The lower end of the upper tension rod is fixedly connected to the upper end of the sample via an upper clamp, and the upper end of the lower tension rod is fixedly connected to the lower end of the sample via a lower clamp. A displacement sensor is provided on the lower tension rod. An air inlet hole extending axially along the upper end face of the sample is provided. The flanged vessel cover is provided with a sample vent pipe, a vessel body vent pipe, a vessel body exhaust pipe, and a vessel body safety valve. An auxiliary electrode, a reference electrode, and a working electrode are provided on the left side of the high-pressure vessel body. The right ends of the specific electrodes are all inserted into the NaCl solution. The right end of the working electrode is connected to the middle of the sample via a wire. The left ends of the working electrode, auxiliary electrode, and reference electrode are all connected to the electrochemical workstation. The lower end of the sample vent pipe is connected to a reversing connector, which is connected to a transfer pipe. The transfer pipe is inserted into the upper part of the inlet port. The upper end of the sample vent pipe is connected to the first gas pressure gauge. The upper part of the sample vent pipe is connected to the first inlet valve and the first exhaust valve, respectively. The first exhaust valve is connected to the first mechanical pump. The exhaust pipe of the reactor body is connected to the second mechanical pump via the second exhaust valve. The lower ends of both the reactor body inlet pipe and the reactor body exhaust pipe are located above the NaCl solution surface. The upper end of the reactor body inlet pipe is connected to the second gas pressure gauge. The upper part of the reactor body inlet pipe is connected to the second inlet valve. A heating resistance wire is provided on the outer circumference of the high-pressure reactor body. A thermocouple thermometer is provided in the reactor body wall. Both the heating resistance wire and the thermocouple thermometer are electrically connected to the temperature controller. The servo motor, tension sensor, and electrochemical workstation are all connected to the computer data.

[0011] The gaseous environment of this invention consists of a sample inlet pipe, a transfer pipe, and a sample inlet port. NaCl solution is used to simulate the deep-sea environment of a subsea pipeline. A gas safety valve ensures the safety of the autoclave. The reversing connector facilitates the replacement of the sample and transfer pipe; only the sample and transfer pipe need to be replaced for repeated experiments. This invention simulates the coupled stress corrosion experiment of a subsea hydrogen pipeline under various conditions by simulating the solution environment and the gaseous hydrogen environment within the autoclave.

[0012] Preferably, the autoclave is equipped with an inlet and an outlet at the bottom, with the inlet connected to a metering pump. The metering pump facilitates the quantitative and pressure-controlled filling of liquid into the autoclave.

[0013] Preferably, the upper clamp includes a cylinder and an insert; the insert includes a circular base and a surrounding plate disposed on the circular base; the circular base has a through vertical hole, and the surrounding plate has two left and right corresponding opening slots; the surrounding plate can be inserted into the cylinder and threadedly connected to the lower part of the cylinder, the lower end of the upper tension rod can be inserted into the cylinder and threadedly connected to the upper part of the cylinder, and the adapter pipe passes through the opening slot on the left side of the surrounding plate;

[0014] The lower clamp is cylindrical, with a sample recess corresponding to the through vertical hole on the upper surface of the lower clamp and a connecting groove on the lower surface of the lower clamp. The upper end of the lower tension rod can be inserted into the connecting groove and threadedly connected to the connecting groove. The upper end of the sample is inserted into the through vertical hole and threadedly connected to the through vertical hole. The lower end of the sample is inserted into the sample recess and threadedly connected to the sample recess.

[0015] The structure of the upper and lower clamps makes the connection between the sample and the upper and lower clamps, the connection between the upper clamp and the upper tension rod, and the connection between the lower clamp and the lower tension rod more stable.

[0016] Preferably, the first air inlet valve is connected to the sample air inlet pipe via a first control valve, and the first exhaust valve is connected to the sample air inlet pipe via a second control valve. The arrangement of the first and second control valves makes it easier to precisely control the air pressure during inflation.

[0017] Preferably, the autoclave body and the flange cover are connected by several hard bolts, and a sealing copper ring is provided on the inner side of the connection between each hard bolt and the autoclave body; an upper sealing sleeve is provided at the connection between the upper tension rod and the flange cover, and a lower sealing sleeve is provided at the connection between the lower tension rod and the bottom of the autoclave body. Both the lower end of the upper sealing sleeve and the upper end of the lower sealing sleeve are provided with O-ring grooves, and O-ring sealing rings are provided in the O-ring grooves.

[0018] The sealing method of the present invention is achieved by the cooperation of static sealing and dynamic sealing. The static sealing is composed of multiple hard bolts and a detachable and replaceable sealing copper ring; the dynamic sealing is composed of an upper sealing sleeve, a lower sealing sleeve, an O-ring groove and an O-ring sealing ring coated with vacuum sealing grease located in the O-ring groove, which together achieve the purpose of dynamic sealing.

[0019] Preferably, the heating resistance wire is provided with a 316L stainless steel circumferential reinforcement layer on the outside, and the 316L stainless steel circumferential reinforcement layer is connected to the outer peripheral wall of the autoclave by a number of circumferential reinforcement bolts.

[0020] The 316L stainless steel circumferential reinforcement layer is used to improve the pressure-bearing capacity of the reactor body and can wrap the bundled heating resistance wires to ensure that the NaCl solution in the high-pressure reactor body is heated evenly and reduce heat loss inside the reactor.

[0021] An experimental method for an experimental setup of stress corrosion testing equipment for submarine pipelines in a gaseous hydrogen environment includes the following steps:

[0022] Step 1: Grind, polish, and clean the sample;

[0023] Step 2: Insert the lower end of the adapter into the upper part of the air inlet. Apply vacuum solder paste to the connection between the adapter and the air inlet. Place the sample and the adapter flat into the sintering test tube. Evacuate the sintering test tube. After the vacuum degree of 1.0E-4Pa is reached in the sintering test tube, set the sintering temperature and holding time and perform brazing.

[0024] The sample is made by stretching a single-hole round bar and using vacuum brazing technology. Under the action of high vacuum and high temperature sintering, the brazing filler metal flows through the gap between the pipe and the air inlet under the action of capillary vessels, realizing the welding of dissimilar materials and achieving high shear strength and excellent sealing characteristics. In order to avoid changes in the microstructure of the sample during the heating process, which would affect the mechanical properties of the material and cause experimental errors, the brazing filler metal is selected to be compatible with the sintering temperature below the recrystallization temperature of the sample.

[0025] Remove the brazed sample and the transfer tube from the sintering test tube. Connect the sample to the right end of the working electrode. Connect the sample to the upper clamp and the lower clamp respectively. Connect the upper clamp to the upper tension rod and the lower clamp to the lower tension rod. Connect the transfer tube to the reversing connector.

[0026] Step 2: Use a temperature controller to control the heating resistance wire to heat the autoclave body, maintaining the temperature of the autoclave body within the range of 23℃-27℃; open the second mechanical pump and the second exhaust valve to evacuate the autoclave body.

[0027] After the vacuum extraction is complete, turn off the second mechanical pump and the second exhaust valve, and close the outlet. Open the inlet and use a metering pump to fill the autoclave with a 3.5% sodium chloride solution with a pH of 7.5-7.8, so that the liquid level of the 3.5% sodium chloride solution is higher than the top of the sample, and then close the inlet.

[0028] Step 3: Open the high-purity nitrogen gas source connected to the second inlet valve, set the gas source pressure, open the second inlet valve, and fill the high-pressure vessel with nitrogen. Observe the change in the reading of the second pressure gauge. After the reading stabilizes, close the high-purity nitrogen gas source connected to the second inlet valve and the second inlet valve.

[0029] Step 4, set i = 0;

[0030] Step 4-1: Open the first mechanical pump and the first exhaust valve to evacuate the air inlet of the sample. After the vacuum is completed, close the first mechanical pump and the first exhaust valve.

[0031] Step 4-2: Open the first inlet valve and the high-purity nitrogen gas source connected to the first inlet valve, and fill the sample with 0.5 MPa of nitrogen gas into the inlet hole to increase the value of i by 1; when i < 3, return to step 4-1.

[0032] When i=3, close the first intake valve and the high-purity nitrogen gas source connected to the first intake valve, and proceed to step 5;

[0033] Step 5: Open the high-purity hydrogen gas source connected to the first inlet valve, set the hydrogen pressure, open the first inlet valve, and fill the sample's inlet with hydrogen gas. Observe the change in the reading of the first pressure gauge. After the reading stabilizes, close the high-purity hydrogen gas source and the first inlet valve.

[0034] Step 6: Measure the electrochemical corrosion data of the 3.5% sodium chloride solution using the auxiliary electrode, reference electrode, and working electrode;

[0035] The computer controls the servo motor to drive the electric cylinder, which in turn drives the lower tension rod to stretch the sample downwards. The computer determines the sample's state by using the tension data detected by the tension sensor and the displacement data detected by the displacement sensor. When the sample breaks, the tension data detected by the tension sensor becomes 0, and the computer controls the servo motor to stop working. The computer uses the electrochemical corrosion data, tension data, and displacement data to plot an electrochemical impedance spectroscopy or a tensile stress-strain curve for tensile engineering.

[0036] Preferably, the first inlet valve is connected to the sample vent pipe via a first control valve, and the first exhaust valve is connected to the sample vent pipe via a second control valve; steps 4 and 5 are replaced by the following steps:

[0037] Step 4, set i = 0;

[0038] Step 4-1: Open the first mechanical pump, the first exhaust valve, and the second control valve to evacuate the air inlet of the sample. After the vacuum is completed, close the first mechanical pump, the first exhaust valve, and the second control valve.

[0039] Step 4-2: Open the first inlet valve, the first control valve, and the high-purity nitrogen gas source connected to the first inlet valve. Inject 0.5 MPa of nitrogen gas into the inlet of the sample to increase the value of i by 1. When i < 3, return to step 4-1.

[0040] When i=3, close the first intake valve, the first control valve and the high-purity nitrogen gas source connected to the first intake valve, and proceed to step 5;

[0041] Step 5: Open the high-purity hydrogen gas source connected to the first inlet valve, set the hydrogen pressure, open the first inlet valve and the first control valve, and fill the sample with hydrogen gas into the inlet hole. Observe the change in the reading of the first pressure gauge. After the reading stabilizes, close the high-purity hydrogen gas source, the first inlet valve and the first control valve.

[0042] Therefore, the present invention has the following beneficial effects: it has a simple structure and is easy to operate. It can simulate the gaseous hydrogen environment of materials in the deep sea environment, link hydrogen-induced material damage with seawater corrosion damage, and provide a reliable data basis for the selection of materials for the construction of submarine hydrogen pipelines. Attached Figure Description

[0043] Figure 1 This is a schematic diagram of the structure of the present invention;

[0044] Figure 2 This is a partially enlarged view of the present invention;

[0045] Figure 3 This is a cross-sectional view of the insert of the present invention;

[0046] Figure 4 This is a cross-sectional view of a sample of the present invention;

[0047] Figure 5 This is an electrochemical impedance spectroscopy diagram according to an embodiment of the present invention;

[0048] Figure 6 This invention relates to a tensile stress-strain curve diagram for tensile engineering. Detailed Implementation

[0049] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0050] like Figures 1-4The illustrated embodiment is an experimental apparatus for stress corrosion testing of a subsea pipeline in a gaseous hydrogen environment. It includes a high-pressure vessel 1 mounted on a support, a flanged vessel cover 2 mounted on the high-pressure vessel, a NaCl solution 11 inside the high-pressure vessel, a rod-shaped sample 3 in the NaCl solution, a tensile sensor mounted on a frame, an upper tension rod 13 connected to the tensile sensor, a servo motor mounted on the frame, an electric cylinder connected to the servo motor, and a lower tension rod 14 connected to the piston rod of the electric cylinder. The lower part of the upper tension rod extends through the flanged vessel cover into the high-pressure vessel. The upper part of the lower tension rod passes through the bottom of the autoclave and extends into the autoclave body. The lower end of the upper tension rod is fixedly connected to the upper end of the sample via the upper clamp 4, and the upper end of the lower tension rod is fixedly connected to the lower end of the sample via the lower clamp 5. A displacement sensor is provided on the lower tension rod. An air inlet 31 extending axially along the upper surface of the sample is provided. The flange cover of the autoclave is provided with a sample vent pipe 21, an autoclave inlet pipe 22, an autoclave exhaust pipe 23, and an autoclave safety valve 24. An auxiliary electrode 101, a reference electrode 102, and a working electrode 103 are provided on the left side of the autoclave body. The right ends of both the electrode and the reference electrode are inserted into the NaCl solution. The right end of the working electrode is connected to the middle of the sample via a wire. The left ends of the working electrode, the auxiliary electrode, and the reference electrode are all connected to the electrochemical workstation. The lower end of the sample vent pipe is connected to the reversing connector 201, which is connected to the adapter pipe 202. The adapter pipe is inserted into the upper part of the inlet hole. The upper end of the sample vent pipe is connected to the first gas pressure gauge 211. The upper part of the sample vent pipe is connected to the first inlet valve 212 and the first exhaust valve 213, respectively. The first exhaust valve is connected to the first mechanical pump. The exhaust pipe of the vessel is connected to the second mechanical pump through the second exhaust valve 231. The lower ends of both the vessel inlet pipe and the vessel exhaust pipe are located above the liquid surface of the NaCl solution. The upper end of the vessel inlet pipe is connected to the second gas pressure gauge 221, and the upper part of the vessel inlet pipe is connected to the second inlet valve 222. A heating resistance wire 15 is provided on the outer circumference of the high-pressure vessel, and a thermocouple thermometer 16 is provided in the vessel wall of the high-pressure vessel. Both the heating resistance wire and the thermocouple thermometer are electrically connected to the temperature controller. The servo motor, the tension sensor, and the electrochemical workstation are all connected to the computer data.

[0051] The bottom of the high-pressure vessel is equipped with an inlet 17 and an outlet 18, and the inlet is connected to a metering pump.

[0052] The upper clamp includes a cylinder 41 and an insert 42; the insert includes a circular base 421 and a surrounding plate 422 disposed on the circular base; the circular base has a through vertical hole 423, and the surrounding plate has two left and right corresponding opening slots 424; the surrounding plate can be inserted into the cylinder and threadedly connected to the lower part of the cylinder, and the lower end of the upper tension rod can be inserted into the cylinder and threadedly connected to the upper part of the cylinder; the adapter pipe passes through the opening slot on the left side of the surrounding plate;

[0053] The lower clamp is cylindrical, with a sample recess corresponding to the through vertical hole on the upper surface of the lower clamp and a connecting groove on the lower surface of the lower clamp. The upper end of the lower tension rod can be inserted into the connecting groove and threadedly connected to the connecting groove. The upper end of the sample is inserted into the through vertical hole and threadedly connected to the through vertical hole. The lower end of the sample is inserted into the sample recess and threadedly connected to the sample recess.

[0054] The first air inlet valve is connected to the sample air inlet pipe via the first control valve 2120, and the first exhaust valve is connected to the sample air inlet pipe via the second control valve 2130.

[0055] The autoclave body and the flange cover are connected by five hard bolts 104. Each hard bolt is provided with a sealing copper ring 105 on the inner side of the connection between it and the autoclave body. An upper sealing sleeve 106 is provided at the connection between the upper tension rod and the flange cover, and a lower sealing sleeve 107 is provided at the connection between the lower tension rod and the bottom of the autoclave body. Both the lower end of the upper sealing sleeve and the upper end of the lower sealing sleeve are provided with O-shaped grooves, and O-shaped sealing rings 108 are provided in the O-shaped grooves.

[0056] The heating resistance wire is provided with a 316L stainless steel circumferential reinforcement layer 19, which is connected to the outer peripheral wall of the autoclave by a number of circumferential reinforcement bolts 191.

[0057] An experimental method for an experimental setup of stress corrosion testing equipment for submarine pipelines in a gaseous hydrogen environment includes the following steps:

[0058] Step 1: Grinding, polishing, and cleaning the sample:

[0059] The inner and outer sides of the air inlet of the sample were ground with silicon carbide sandpaper of 240 mesh, 600 mesh, 1000 mesh, 1200 mesh, 1500 mesh and 2000 mesh in sequence. Then, diamond polishing paste was used to polish the two sides until they were smooth and without obvious scratches. After polishing, the sample was placed in anhydrous ethanol and acetone for ultrasonic cleaning and then dried with hot air.

[0060] Step 2: Insert the lower end of the adapter into the upper part of the air inlet, leaving a uniform gap of 0.5mm between the outer wall of the adapter and the circumference of the air inlet. Apply vacuum solder paste into the gap, place the sample and the adapter flat into the sintering test tube, evacuate the sintering test tube, and after the vacuum degree inside the sintering test tube reaches 1.0E-4Pa, set the sintering temperature and holding time, and perform brazing.

[0061] Remove the brazed sample and the transfer tube from the sintering test tube. Connect the sample to the right end of the working electrode. Connect the sample to the upper clamp and the lower clamp respectively. Connect the upper clamp to the upper tension rod and the lower clamp to the lower tension rod. Connect the transfer tube to the reversing connector.

[0062] Step 2: Use a temperature controller to control the heating resistance wire to heat the pressure vessel body, so that the temperature of the pressure vessel body is maintained within 25°C; open the second mechanical pump and the second exhaust valve to evacuate the pressure vessel body.

[0063] The pH value of a 3.5% sodium chloride solution was adjusted using 0.1 mol / L NaOH. Taking pH = 7.5 (25℃) as an example, the dissolved oxygen concentration was controlled by passing high-purity nitrogen gas through the prepared 3.5% sodium chloride solution for different times and at different flow rates. The dissolved oxygen concentration was determined using a dissolved oxygen monitor.

[0064] After the vacuum extraction is complete, turn off the second mechanical pump and the second exhaust valve, and close the outlet. Open the inlet and use a metering pump to fill the autoclave with a 3.5% sodium chloride solution with a pH of 7.5, so that the liquid level of the 3.5% sodium chloride solution is higher than the top of the sample, and then close the inlet.

[0065] Step 3: Open the high-purity nitrogen gas source connected to the second inlet valve, set the gas source pressure by tightening the pressure reducing valve, open the second inlet valve, and fill the high-pressure vessel with nitrogen. Observe the change in the reading of the second pressure gauge. After the reading stabilizes, close the high-purity nitrogen gas source connected to the second inlet valve and the second inlet valve.

[0066] Step 4, set i = 0;

[0067] Step 4-1: Open the first mechanical pump, the first exhaust valve, and the second control valve to evacuate the air inlet of the sample. After the vacuum is completed, close the first mechanical pump, the first exhaust valve, and the second control valve.

[0068] Step 4-2: Open the first inlet valve, the first control valve, and the high-purity nitrogen gas source connected to the first inlet valve. Inject 0.5 MPa of nitrogen gas into the inlet of the sample to increase the value of i by 1. When i < 3, return to step 4-1.

[0069] When i=3, close the first intake valve, the first control valve and the high-purity nitrogen gas source connected to the first intake valve, and proceed to step 5;

[0070] Step 5: Open the high-purity hydrogen gas source connected to the first inlet valve, set the hydrogen pressure, open the first inlet valve and the first control valve, fill the gas inlet of the sample with hydrogen, observe the change in the reading of the first pressure gauge, and after the reading stabilizes, close the high-purity hydrogen gas source, the first inlet valve and the first control valve.

[0071] Step 6: Measure the electrochemical corrosion data of the 3.5% sodium chloride solution using the auxiliary electrode, reference electrode, and working electrode;

[0072] The computer controls the servo motor to drive the electric cylinder, which in turn drives the lower tension rod to stretch the sample downwards. The computer determines the sample's state by using the tension data detected by the tension sensor and the displacement data detected by the displacement sensor. When the sample breaks, the tension data detected by the tension sensor becomes 0, and the computer controls the servo motor to stop working. The computer uses the electrochemical corrosion data, tension data, and displacement data to plot the electrochemical impedance spectroscopy shown in the figure.

[0073] The following are the experimental parameters and results analysis for the two sets of experiments:

[0074] I. Measurement of AC impedance spectroscopy under constant stress

[0075] 1. Test material: X52 low-strength pipeline steel, processed into the shape of the test sample along the rolling direction of the pipeline steel, and ground, polished and brazed according to the above experimental process;

[0076] 2. Test solution: 3.5% sodium chloride solution, with 0.1 mol / L NaOH added until the solution pH = 7.7 ± 0.2 (25℃). The pH value of the solution was determined using a pH meter (PHS-25-2F); dissolved oxygen content 7 mg / L;

[0077] 3. Experimental environment: 6.3 MPa high-purity hydrogen gas, 6.3 MPa high-purity nitrogen gas; experimental temperature: room temperature (25℃); pressure of NaCl solution: 10 MPa;

[0078] 4. Stress setting: The constant tensile stress applied during the experiment was 0.75R. eL (R eL (The yield strength of the original X52 material);

[0079] 5. Electrochemical testing: The open circuit potential was measured under constant tensile stress for 5 hours. After the open circuit potential stabilized, the electrochemical impedance spectroscopy of the system was then measured. The test voltage was 0V (vs. OCP), and the test frequency range was 100KHz-0.01Hz. The perturbation voltage was ±5mV.

[0080] 6. Results Analysis:

[0081] from Figure 5The electrochemical impedance spectroscopy reveals that the impedance spectra of the test sample under both different gaseous environments are characterized by a single half-capacitive half-arc shape. A larger diameter of the capacitive half-arc indicates a higher impedance response and better protection of the sample by the passivation film. Experimental results show that the corrosion resistance of pipeline steel is reduced under gaseous hydrogen and simulated seawater coupling media compared to the gaseous nitrogen coupling medium. This indicates that under stress, hydrogen atoms inside the pipeline steel diffuse to the outer surface of the material, causing hydrogen embrittlement and resulting in surface defects, thus accelerating the corrosion process of the pipeline steel by seawater. These results are consistent with the experimental expectations of this invention.

[0082] II. Slow Strain Rate Tensile Test

[0083] 1. Test material: X52 low-strength pipeline steel, processed into the shape of the test sample along the rolling direction of the pipeline steel, and ground, polished and brazed according to the experimental process described above;

[0084] 2. Test solution: 3.5% sodium chloride solution, with 0.1 mol / L NaOH added until the solution pH = 7.7 ± 0.2 (25℃). The pH value of the solution was determined using a pH meter (PHS-25-2F); dissolved oxygen content 7 mg / L;

[0085] 3. Experimental environment: 6.3 MPa high-purity hydrogen gas, 6.3 MPa high-purity nitrogen gas; experimental temperature: room temperature (25℃); pressure of NaCl solution: 10 MPa;

[0086] 4. Tension setting: The strain-tension rate controlled during the experiment was 5 × 10⁻⁶. -5 s -1 Before the experiment, measure the gauge length at the parallel end of the sample before breakage, and record it as L0. After breakage, measure the gauge length after breakage and record it as L. Then the elongation of the sample is...

[0087] 5. Results Analysis:

[0088] from Figure 6 The tensile stress-strain curve diagram shown in the figure illustrates that:

[0089] In a coupled medium environment simulating seawater with gaseous hydrogen, the fracture elongation of pipeline steel decreased by 4% compared to that simulating seawater with nitrogen. Figure 6 It can also be seen that the tensile strength of pipeline steel materials decreases in a gaseous hydrogen environment.

[0090] The above phenomena indicate that under external stress, hydrogen inside the pipe diffuses from the inside of the inlet to the outside through diffusion, and causes hydrogen embrittlement of the material during its necking stage, resulting in a decrease in the mechanical properties of the material and increasing the risk of material fracture failure. The above results are consistent with the corrosion performance results measured by electrochemical impedance spectroscopy and meet the expected results.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An experimental apparatus for stress corrosion of submarine pipelines in a gaseous hydrogen environment, characterized in that it includes: The apparatus consists of a high-pressure vessel body (1) mounted on a support, a flanged vessel cover (2) mounted on the high-pressure vessel body, a 3.5% NaCl solution (11) with a pH of 7.5-7.8 placed inside the high-pressure vessel body, a rod-shaped sample (3) placed in the NaCl solution, a tension sensor mounted on a frame, an upper tension rod (13) connected to the tension sensor, a servo motor mounted on a frame, an electric cylinder connected to the servo motor, and a lower tension rod (14) connected to the piston rod of the electric cylinder; the lower part of the upper tension rod passes through the flanged vessel cover and extends into the high-pressure vessel body, while the upper part of the lower tension rod passes through the high-pressure vessel body. The bottom of the body extends into the high-pressure vessel body. The lower end of the upper tension rod is fixedly connected to the upper end of the sample via the upper clamp (4), and the upper end of the lower tension rod is fixedly connected to the lower end of the sample via the lower clamp (5). A displacement sensor is provided on the lower tension rod. An air inlet (31) extending along the axial direction of the sample is provided on the upper end face of the sample. The flange of the vessel cover is provided with a sample air inlet pipe (21), a vessel air inlet pipe (22), a vessel exhaust pipe (23), and a vessel safety valve (24). An auxiliary electrode (101), a reference electrode (102), and a working electrode (103) are provided on the left side of the high-pressure vessel body. The working electrode and the auxiliary electrode are provided with a reference electrode (102). The right ends of both the working electrode and the reference electrode are inserted into the NaCl solution. The right end of the working electrode is connected to the middle of the sample via a wire. The left ends of the working electrode, the auxiliary electrode, and the reference electrode are all connected to the electrochemical workstation. The lower end of the sample vent pipe is connected to the reversing connector (201), the reversing connector is connected to the adapter (202), the adapter is inserted into the upper part of the air inlet, the upper end of the sample vent pipe is connected to the first gas pressure gauge (211), the upper part of the sample vent pipe is connected to the first air inlet valve (212) and the first exhaust valve (213) respectively, and the first exhaust valve is connected to the first mechanical pump. The exhaust pipe of the vessel is connected to the second mechanical pump through the second exhaust valve (231). The lower ends of the vessel inlet pipe and the vessel exhaust pipe are both located above the liquid surface of the NaCl solution. The upper end of the vessel inlet pipe is connected to the second gas pressure gauge (221), and the upper part of the vessel inlet pipe is connected to the second inlet valve (222). A heating resistance wire (15) is provided on the outer circumference of the high-pressure vessel. A thermocouple thermometer (16) is provided in the vessel wall of the high-pressure vessel. The heating resistance wire and the thermocouple thermometer are both electrically connected to the temperature controller. The servo motor, the tension sensor and the electrochemical workstation are all connected to the computer data.

2. The experimental apparatus for stress corrosion of subsea pipelines in a gaseous hydrogen environment as described in claim 1, characterized in that, The bottom of the high-pressure vessel is provided with an inlet (17) and an outlet (18), and the inlet is connected to a metering pump.

3. The experimental apparatus for stress corrosion of submarine pipelines in a gaseous hydrogen environment as described in claim 1, characterized in that, The upper clamp includes a cylinder (41) and an insert (42); The insert includes a circular base (421) and a surrounding plate (422) on the circular base; the circular base has a through vertical hole (423), and the surrounding plate has two left and right corresponding opening slots (424); the surrounding plate can be inserted into the cylinder and threadedly connected to the lower part of the cylinder, the lower end of the upper tension rod can be inserted into the cylinder and threadedly connected to the upper part of the cylinder, and the adapter pipe passes through the opening slot on the left side of the surrounding plate; The lower clamp is cylindrical, with a sample recess corresponding to the through vertical hole on the upper surface of the lower clamp and a connecting groove on the lower surface of the lower clamp. The upper end of the lower tension rod can be inserted into the connecting groove and threadedly connected to the connecting groove. The upper end of the sample is inserted into the through vertical hole and threadedly connected to the through vertical hole. The lower end of the sample is inserted into the sample recess and threadedly connected to the sample recess.

4. The experimental apparatus for stress corrosion of submarine pipelines in a gaseous hydrogen environment as described in claim 1, characterized in that, The first intake valve is connected to the sample vent pipe via the first control valve (2120), and the first exhaust valve is connected to the sample vent pipe via the second control valve (2130).

5. The experimental apparatus for stress corrosion of submarine pipelines in a gaseous hydrogen environment as described in claim 1, characterized in that, The pressure vessel body and the flange cover are connected by several hard bolts (104), and a sealing copper ring (105) is provided on the inner side of the connection between each hard bolt and the pressure vessel body; an upper sealing sleeve (106) is provided at the connection between the upper tension rod and the flange cover, and a lower sealing sleeve (107) is provided at the connection between the lower tension rod and the bottom of the pressure vessel body. O-shaped grooves are provided at the lower end of the upper sealing sleeve and the upper end of the lower sealing sleeve, and an O-shaped sealing ring (108) is provided in the O-shaped groove.

6. The experimental apparatus for stress corrosion of subsea pipelines in a gaseous hydrogen environment as described in claim 1, 2, 3, 4, or 5, characterized in that, The heating resistance wire is provided with a 316L stainless steel circumferential reinforcement layer (19) on the outside. The 316L stainless steel circumferential reinforcement layer is connected to the outer peripheral wall of the autoclave by a number of circumferential reinforcement bolts (191).

7. An experimental method for stress corrosion testing of submarine pipelines in a gaseous hydrogen environment based on the experimental apparatus described in claim 2, characterized in that, Includes the following steps: Step 1: Grind, polish, and clean the sample; Step 2: Insert the lower end of the adapter into the upper part of the air inlet. Apply vacuum solder paste to the connection between the adapter and the air inlet. Place the sample and the adapter flat into the sintering test tube. Evacuate the sintering test tube. After the vacuum degree of 1.0E-4Pa is reached in the sintering test tube, set the sintering temperature and holding time and perform brazing. Remove the brazed sample and the transfer tube from the sintering test tube. Connect the sample to the right end of the working electrode. Connect the sample to the upper clamp and the lower clamp respectively. Connect the upper clamp to the upper tension rod and the lower clamp to the lower tension rod. Connect the transfer tube to the reversing connector. Step 2: Use a temperature controller to control the heating resistance wire to heat the autoclave body, maintaining the temperature of the autoclave body within the range of 23℃-27℃; open the second mechanical pump and the second exhaust valve to evacuate the autoclave body. After the vacuum extraction is complete, turn off the second mechanical pump and the second exhaust valve, and close the outlet. Open the inlet and use a metering pump to fill the autoclave with a 3.5% sodium chloride solution with a pH of 7.5-7.8, so that the liquid level of the 3.5% sodium chloride solution is higher than the top of the sample, and then close the inlet. Step 3: Open the high-purity nitrogen gas source connected to the second inlet valve, set the gas source pressure, open the second inlet valve, and fill the high-pressure vessel with nitrogen. Observe the change in the reading of the second pressure gauge. After the reading stabilizes, close the high-purity nitrogen gas source connected to the second inlet valve and the second inlet valve. Step 4, set i = 0; Step 4-1: Open the first mechanical pump and the first exhaust valve to evacuate the air inlet of the sample. After the vacuum is completed, close the first mechanical pump and the first exhaust valve. Step 4-2: Open the first inlet valve and the high-purity nitrogen gas source connected to the first inlet valve, and fill the sample with 0.5 MPa of nitrogen gas into the inlet hole to increase the value of i by 1; when i < 3, return to step 4-1. When i=3, close the first intake valve and the high-purity nitrogen gas source connected to the first intake valve, and proceed to step 5; Step 5: Open the high-purity hydrogen gas source connected to the first inlet valve, set the hydrogen pressure, open the first inlet valve, and fill the sample's inlet with hydrogen gas. Observe the change in the reading of the first pressure gauge. After the reading stabilizes, close the high-purity hydrogen gas source and the first inlet valve. Step 6: Measure the electrochemical corrosion data of the 3.5% sodium chloride solution using the auxiliary electrode, reference electrode, and working electrode; The computer controls the servo motor to drive the electric cylinder, which in turn drives the lower tension rod to stretch the sample downwards. The computer determines the sample's state by using the tension data detected by the tension sensor and the displacement data detected by the displacement sensor. When the sample breaks, the tension data detected by the tension sensor becomes 0, and the computer controls the servo motor to stop working. The computer uses the electrochemical corrosion data, tension data, and displacement data to plot an electrochemical impedance spectroscopy or a tensile stress-strain curve for tensile engineering.

8. The experimental method for the experimental apparatus for stress corrosion of submarine pipelines in a gaseous hydrogen environment as described in claim 7, characterized in that, The first inlet valve is connected to the sample vent pipe via the first control valve, and the first exhaust valve is connected to the sample vent pipe via the second control valve; steps 4 and 5 are replaced by the following steps: Step 4, set i = 0; Step 4-1: Open the first mechanical pump, the first exhaust valve, and the second control valve to evacuate the air inlet of the sample. After the vacuum is completed, close the first mechanical pump, the first exhaust valve, and the second control valve. Step 4-2: Open the first inlet valve, the first control valve, and the high-purity nitrogen gas source connected to the first inlet valve. Inject 0.5 MPa of nitrogen gas into the inlet of the sample to increase the value of i by 1. When i < 3, return to step 4-1. When i=3, close the first intake valve, the first control valve and the high-purity nitrogen gas source connected to the first intake valve, and proceed to step 5; Step 5: Open the high-purity hydrogen gas source connected to the first inlet valve, set the hydrogen pressure, open the first inlet valve and the first control valve, and fill the sample with hydrogen gas into the inlet hole. Observe the change in the reading of the first pressure gauge. After the reading stabilizes, close the high-purity hydrogen gas source, the first inlet valve and the first control valve.

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