Pipeline steel stress corrosion cracking critical stress intensity factor testing system and method

Abstract

The present application relates to the field of corrosion evaluation test, in particular to a pipeline steel stress corrosion cracking critical stress intensity factor test system and method, the present application includes corrosion environment device and double cantilever beam corrosion test device, in the test process, the corrosion solution is updated in real time through the corrosion environment device, the stability of the corrosion solution can be maintained in the long period experiment process, the crack propagation is monitored in real time through the double cantilever beam corrosion test device, and the K ISSC The crack is completely stopped under the condition of expansion, which overcomes the defects of the existing detection technology in the long period experiment, and ensures the accuracy of the test result.

Description

Technical Field

[0001] This invention belongs to the field of corrosion evaluation testing, specifically relating to a system and method for testing the critical stress intensity factor of stress corrosion cracking in pipeline steel. Background Technology

[0002] With the depletion of non-acidic oil and gas reservoirs, oil companies are forced to develop acidic reservoirs to meet the growing energy demands of the market. Acidic oil and gas media are rich in H2S and moisture. H2S can significantly increase the hydrogen absorption capacity of materials, thereby promoting hydrogen embrittlement and triggering various forms of material failure. Some early studies indicated that when the yield strength is below 550 MPa, steel is almost immune to cracking caused by hydrogen embrittlement. Therefore, the problem of sulfide stress cracking (SSC) in pipeline steel has long been neglected by academia and industry. However, over the past 30 years, premature failures of gathering and transporting oil and gas pipelines caused by SSC have occurred repeatedly, indicating that SSC has consistently been one of the important failure mechanisms for oil and gas gathering and transport pipelines. The SSC problem of pipeline steel used for oil and gas gathering and transport is increasingly attracting attention.

[0003] Stress intensity factor K It is the mechanical driving force for crack propagation. The stress intensity factor at the tip of the largest potential crack in a pipe operating in an acidic environment. K Below the SSC threshold ( K ISSC When [the method is implemented], it can effectively prevent crack propagation and achieve SSC failure control for pipeline steel. Current standards specify [the method for] determining [the specific steps]. K ISSC Standard test methods include NACE™ 0177, ISO 15156, and GB / T 4157, all of which recommend the double cantilever beam (DCB) test immersed in solution. Under constant displacement loading conditions, the stress intensity factor of the specimen... K It will continue to decrease as the crack expands, when K Down to K ISSC The crack will stop propagating due to insufficient driving force, thus the crack length can be calculated based on the applied displacement and the final crack length. K ISSC Due to the low strength of pipeline steel, crack propagation in DCB specimens can take weeks or even months to stop in standard environments, rendering current standard testing methods ineffective for pipeline steel. K ISSC The measurement process has the following shortcomings: (1) Lack of crack propagation monitoring. To ensure... K ISSCThe test was conducted under the condition that the crack had completely stopped propagating. Therefore, the crack propagation process must be monitored in real time during the test. (2) Long-term tests lead to an increase in the pH value of the solution, which affects the accuracy of the test results. Due to the limited volume of the test solution, the pH value of the solution increases with the amount of Fe in the environment. 2+ As Fe accumulates during the experiment, the pH value of the solution will change due to the accumulation of Fe. 2+ The hydrolysis reaction causes the temperature to rise continuously. For pipeline steel, extending the experimental period leads to more severe Fe... 2+ The accumulation of Fe. 2+ The accumulation of [something] and an increase in pH will inhibit hydrogen production, thereby reducing the hydrogen concentration in the steel, leading to [something]. K ISSC The measured value is higher than the actual SSC threshold value.

[0004] Regarding the determination of the critical stress intensity factor for stress corrosion cracking, Chinese patent CN100494972C, "Evaluation Method of Critical Stress Intensity and Sensitivity Factor for Stress Corrosion Cracking of Oil Well Tubes," focuses on oil well tubing. By establishing an analytical function of DCB specimen compliance and crack length, it can quantitatively track the crack propagation during the pre-cracking process of DCB specimens requiring pre-existing fatigue cracks. Based on the compliance closed-loop curve under wedge loading, the initial effective crack length is calculated, and an initial loading stress intensity factor is established. K i The method describes a method for determining corrosion, but it does not consider the influence of stress corrosion conditions on the test results. Chinese Patent CN 111157383 A, "A Material Stress Corrosion Testing System and Method for Precisely Controlling Corrosion Conditions," uses a temperature control component to control the temperature of the corrosive solution and a component measurement and alarm component to measure and alarm the composition of the corrosive solution to ensure the stability of the corrosion effect during the experiment and improve the accuracy of the experimental results. However, it does not consider how to replace the corrosive solution in long-term experiments, nor does it consider the monitoring of crack propagation.

[0005] Therefore, the challenge lies in maintaining the stability of the corrosive solution and monitoring crack propagation in real time during long-term experiments, overcoming the shortcomings of existing detection technologies, and ultimately obtaining accurate and reliable results. K ISSC Failure control of pipeline steel used in acidic conditions is extremely important. Summary of the Invention

[0006] The purpose of this invention is to propose a test system and method for the critical stress intensity factor of pipeline steel stress corrosion cracking, so as to solve the problems of unstable properties of corrosion solution and inability to monitor crack propagation in real time.

[0007] To achieve the above objectives, the present invention proposes the following technical solution: A pipeline steel stress corrosion cracking critical stress intensity factor testing system, including a corrosion environment device and a double cantilever beam corrosion testing device; The corrosive environment device includes a corrosive solution unit, a gas-liquid mixing unit, and a gas unit; the corrosive solution unit is equipped with an inlet and an outlet; the gas-liquid mixing unit is equipped with an inlet, an outlet, and an outlet; the gas unit is equipped with an outlet; the outlet of the corrosive solution unit is connected to the inlet of the gas-liquid mixing unit through a liquid guide pipe; the inlet of the gas-liquid mixing unit is connected to the outlet of the gas unit through a gas guide pipe. The double cantilever beam corrosion testing device includes a corrosion testing unit, a crack monitoring unit, and a liquid treatment unit. The corrosion testing unit is equipped with a liquid inlet, a lead wire outlet, and a liquid outlet. The liquid treatment unit is equipped with a liquid inlet and a liquid outlet. The liquid outlet of the corrosion testing unit is connected to the liquid inlet of the liquid treatment unit through a liquid guide pipe. The corrosion testing unit contains a sample, and a wire is spot-welded onto the sample. The wire is connected to the crack monitoring unit through the lead wire outlet. The liquid outlet on the gas-liquid mixing unit is connected to the liquid inlet on the corrosion testing unit via a liquid guide pipe; The sample has a pre-existing crack. The crack monitoring unit is equipped with a DC source and a micro-voltage measurement unit. Two wires are spot-welded to the sample to connect to the DC source to form a DC circuit. Wires are spot-welded to both ends of the pre-existing crack to connect to the micro-voltage measurement unit to form a measurement circuit. Two wires are led out from opposite sides of the crack opening to connect to the micro-voltage measurement unit to form another measurement circuit. Furthermore, a wedge is provided in the pre-crack of the specimen, with the tail end of the wedge flush with the end of the specimen.

[0008] Preferably, a first constant flow pump is provided on the liquid guide pipe between the corrosion solution unit and the gas-liquid mixing unit; a second constant flow pump is provided on the liquid guide pipe between the gas-liquid mixing unit and the corrosion testing unit; and a third constant flow pump is provided on the liquid guide pipe between the corrosion testing unit and the liquid processing unit.

[0009] Preferably, the liquid treatment unit is provided with an air outlet, which is connected to the waste gas absorption tower through an air guide pipe.

[0010] Preferably, a gas flow controller is provided on the gas guide pipe between the gas-liquid mixing unit and the gas unit.

[0011] Preferably, the crack monitoring unit further includes a recording device connected to the micro-voltage measurement unit.

[0012] The test method for the critical stress intensity factor of pipeline steel under stress corrosion cracking includes the following steps: S1. Prepare a cantilever beam stress corrosion test specimen and pre-induce fatigue cracks on the specimen; press the wedge into the narrow groove of the specimen so that the exposed part of the wedge is flush with the end of the specimen. S2. Two wires are spot-welded onto the sample to connect to a DC source to form a DC circuit. Wires are spot-welded to both ends of the pre-crack on the sample to connect to a micro-voltage measurement unit to form a measurement circuit. Two wires are led out from opposite sides of the crack opening on the sample to connect to a micro-voltage measurement unit to form another measurement circuit. The sample is placed inside the corrosion testing unit, and the wires on the sample are led out from the lead-out port on the top cover of the corrosion testing unit. S3. Install and connect the corrosion environment device and the double cantilever beam corrosion test device; seal the outlet of the corrosion solution unit; seal the inlet, outlet, and outlet of the gas-liquid mixing unit; seal the inlet, lead wire, and outlet of the corrosion test unit; seal the inlet and outlet of the corrosion solution treatment unit on the top cover. S4. Continuously add the prepared corrosion solution from the injection port. After the solution reaches three-fifths of the volume of the corrosion solution unit, turn on the first constant flow pump to allow the corrosion solution to enter the gas-liquid mixing unit. Operate the gas flow rate controller to allow the hydrogen sulfide gas in the gas unit to enter the gas-liquid mixing unit to obtain the gas-liquid mixed medium. S5. Turn on the second constant flow pump and adjust the flow rates of the second and first constant flow pumps to allow the gas-liquid mixture to enter the corrosion test unit. After the ratio between the volume of the gas-liquid mixture and the surface area of ​​the sample reaches 3 ml / cm², turn on the third constant flow pump and adjust the flow rates of the third, first, and second constant flow pumps to maintain the volume of the gas-liquid mixture in the corrosion test unit unchanged. S6. Open both measurement circuits and the DC circuit; S7. After detecting that the crack has stopped propagating, shut down the two measurement circuits and the DC circuit, stop liquid injection, and shut down the first constant flow pump, the second constant flow pump and the gas unit. S8. After all the gas-liquid mixture in the corrosion testing unit has been pumped into the liquid handling unit by the third constant flow pump, the third constant flow pump is turned off, the top cover of the corrosion testing unit is opened, the sample is taken out, the wedge is removed, the sample is opened and the cracked surface is exposed, and the calculation is performed. K ISSC .

[0013] Preferably, when performing a single multi-sample test, all samples undergo the same S1 and S2 treatments.

[0014] Preferably, when testing multiple samples, the samples are connected in series to share a DC circuit.

[0015] The advantages of this invention are: By setting up a corrosion solution unit with an injection port, the corrosion solution was updated in real time during the experiment, maintaining the stability of the corrosion solution during long-term experiments. By connecting the sample to the micro-voltage measurement unit to form a measurement circuit, and adding a recording device, crack propagation can be monitored in real time during the test, ensuring that the KISSC is measured under the condition that the crack has completely stopped propagating, thus ensuring the accuracy of the test results. By connecting samples in series in a DC circuit, multiple sets of samples can be tested in a single test, reducing testing time and cost. Attached Figure Description

[0016] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 Schematic diagram of a test system for critical stress intensity factor of stress corrosion cracking in pipeline steel; Figure 2 This is a schematic diagram of a crack propagation monitoring device.

[0017] In the diagram: 1 is the corrosion solution unit; 2 is the gas-liquid mixing unit; 3-1 is the first constant flow pump, 3-2 is the second constant flow pump, and 3-3 is the third constant flow pump; 4 is the corrosion testing unit; 5 is the liquid treatment unit; 6 is the waste gas absorption tower; 7 is the crack monitoring unit; 8 is the sample; 9 is the gas unit; 10 is the DC source; 11 is the micro voltage measurement unit; 12 is the recording device; and 13 is the gas flow controller. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0019] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0020] Example 1: The pipeline steel stress corrosion cracking critical stress intensity factor testing system includes a corrosion environment device 100 and a double cantilever beam corrosion testing device 200.

[0021] The corrosion environment device 100 includes a corrosion solution unit 1, a gas-liquid mixing unit 2, and a gas unit 9; the corrosion solution unit 1 is used to update the corrosion solution in real time, and the gas unit 9 is used to provide hydrogen sulfide gas required for corrosion tests.

[0022] The corrosion solution unit 1 is provided with an injection port and an outlet; the gas-liquid mixing unit 2 is provided with a liquid inlet, an air inlet, and a liquid outlet; the gas unit 9 is provided with an air outlet. The outlet of the corrosion solution unit 1 is connected to the inlet of the gas-liquid mixing unit 2 through a liquid guide pipe; a first constant flow pump 3-1 is provided on the liquid guide pipe between the corrosion solution unit 1 and the gas-liquid mixing unit 2 to keep the corrosion solution flowing continuously; the inlet of the gas-liquid mixing unit 2 is connected to the outlet of the gas unit 9 through a gas guide pipe, and a gas flow controller 13 is provided on the gas guide pipe. The double cantilever beam corrosion testing device 200 includes a corrosion testing unit 4, a crack monitoring unit 7, and a liquid handling unit 5; The corrosion testing unit 4 is equipped with an inlet, a lead wire outlet, and an outlet; the liquid handling unit 5 is equipped with an inlet and an outlet; a third constant flow pump 3-3 is installed on the liquid guide pipe between the corrosion testing unit 4 and the liquid handling unit 5 to maintain the continuous flow of the corrosion liquid.

[0023] The outlet of the corrosion testing unit 4 is connected to the inlet of the liquid treatment unit 5 through a liquid guide pipe. A third constant flow pump 3-3 is installed on the liquid guide pipe between the corrosion testing unit 4 and the liquid treatment unit 5.

[0024] The liquid treatment unit 5 is connected to the waste gas absorption tower 6 through the gas outlet.

[0025] The corrosion testing unit 4 contains a sample 8 with pre-existing cracks. The pre-existing cracks are filled by wedges, and the tail of the wedges is flush with the end of the sample 8. The wedges are responsible for providing pre-stress. Sample 8 is connected to crack monitoring unit 7, which includes a DC source 10, a micro-voltage measurement unit 11, and a recording device 12. Two wires are spot-welded to sample 8 to connect to the DC source 10 to form a DC circuit. Wires are spot-welded to both ends of the pre-existing crack on sample 8 to connect to the micro-voltage measurement unit 11 to form a measurement circuit. Two wires are led out from opposite sides of the crack opening on sample 8 to connect to the micro-voltage measurement unit 11 to form another measurement circuit. The micro-voltage measurement unit 11 is connected to the recording device 12, which records data from the micro-voltage measurement unit 11. The two measurement circuits measure voltages at two locations, and the crack propagation is determined by the change in the voltage difference, thus achieving real-time monitoring of crack activity.

[0026] Platinum wire or stainless steel wire should be used for the conductor.

[0027] The outlet of the gas-liquid mixing unit 2 is connected to the inlet of the corrosion testing unit 4 through a liquid guide pipe. A second constant flow pump 3-2 is installed on the liquid guide pipe between the gas-liquid mixing unit 2 and the corrosion testing unit 4 to keep the corrosion liquid flowing continuously.

[0028] Example 2: Test method for critical stress intensity factor of pipeline steel in the event of stress corrosion cracking: S1. Prepare cantilever beam stress corrosion specimen 8 and pre-fabricate fatigue cracks; select a wedge of appropriate thickness, press the wedge into the pre-fabricated crack of specimen 8, and make the tail of the wedge flush with the end of the specimen. S2. Two wires are spot-welded to the sample 8 and connected to the DC source 10 to form a DC circuit. Two wires are spot-welded to the two ends of the pre-crack of the sample 8 and connected to the micro voltage measurement unit 11 to form a measurement circuit. Two wires are led out from the opposite side of the crack opening of the sample 8 and connected to the micro voltage measurement unit 11 to form another measurement circuit. The micro voltage measurement unit 11 is connected to the recording device 12. The recording device 12 is used to record the data from the micro voltage measurement unit 11. The sample 8 is placed inside the corrosion test unit 4, and the wires on the sample 8 are led out from the lead-out port on the top cover of the corrosion test unit 4.

[0029] S3. When conducting a single multi-sample test, steps S1 and S2 must be repeated for all samples. When testing multiple samples, a DC power source can be shared in series, but each sample needs to have its own measurement circuit for separate recording.

[0030] S4. Install and connect the corrosion environment device 100 and the double cantilever beam corrosion testing device 200, seal the outlet of the corrosion solution unit 1; seal the inlet, outlet and outlet of the gas-liquid mixing unit 2; seal the inlet, lead wire and outlet of the corrosion testing unit 4; seal the inlet and outlet of the corrosion liquid treatment unit 5 on the top cover.

[0031] S5. Continuously inject freshly prepared corrosion solution into the injection port of corrosion solution unit 1. After the solution reaches three-fifths of the corrosion solution unit 1, turn on the first constant flow pump 3-1 to allow the corrosion solution to enter the gas-liquid mixing unit 2. Operate the gas flow controller 13 to allow the hydrogen sulfide gas in the gas unit 9 to enter the gas-liquid mixing unit 2 to obtain a gas-liquid mixed medium that meets the test requirements.

[0032] S6. Turn on the second constant flow pump 3-2, and adjust the flow rates of the second constant flow pump 3-2 and the first constant flow pump 3-1 to allow the gas-liquid mixture to enter the corrosion test unit 4. After the ratio between the volume of the gas-liquid mixture and the surface area of ​​the sample 8 reaches 3 ml / cm², turn on the third constant flow pump 3-3 and adjust the flow rates of the third constant flow pump 3-3, the first constant flow pump 3-1 and the second constant flow pump 3-2 to maintain the volume of the gas-liquid mixture in the corrosion test unit 4 unchanged.

[0033] S7. Open the measurement circuit and DC circuit, and monitor the crack propagation of the sample by recording the data from the recording device 12.

[0034] S8. After detecting that the crack has stopped propagating, shut down the measurement circuit and the DC circuit, stop the liquid injection, and shut down the first constant flow pump 3-1, the second constant flow pump 3-2 and the gas unit 9.

[0035] S9. After all the gas-liquid mixture in the corrosion test unit 4 has been pumped into the liquid treatment unit 5 by the third constant flow pump 3-3, the third constant flow pump 3-3 is turned off, the top cover of the corrosion test unit 4 is opened, the sample 8 is taken out, the wedge is removed, the cracked surface of the sample 8 is exposed, and the calculation is performed. K ISSC .

[0036] As is known from common technical knowledge, this invention can be implemented through other embodiments that do not depart from its spirit or essential characteristics. Therefore, the disclosed embodiments described above are merely illustrative in all respects and are not the only ones. All modifications within the scope of this invention or its equivalents are included in this invention.

Claims

1. A system for testing the critical stress intensity factor of pipeline steel under stress corrosion cracking, characterized in that, Includes a corrosion environment device (100) and a double cantilever beam corrosion testing device (200). The corrosive environment device (100) includes a corrosive solution unit (1), a gas-liquid mixing unit (2), and a gas unit (9); the corrosive solution unit (1) is provided with an inlet and an outlet; the gas-liquid mixing unit (2) is provided with an inlet, an outlet, and an outlet; the gas unit (9) is provided with an outlet; the outlet of the corrosive solution unit (1) is connected to the inlet of the gas-liquid mixing unit (2) through a liquid guide pipe; the inlet of the gas-liquid mixing unit (2) is connected to the outlet of the gas unit (9) through a gas guide pipe; The double cantilever beam corrosion testing device (200) includes a corrosion testing unit (4), a crack monitoring unit (7), and a liquid treatment unit (5); the corrosion testing unit (4) is provided with an inlet, a lead wire outlet, and an outlet; the liquid treatment unit (5) is provided with an inlet and an outlet; the outlet of the corrosion testing unit (4) and the inlet of the liquid treatment unit (5) are connected by a liquid guide pipe; a sample (8) is provided inside the corrosion testing unit (4); a wire is spot-welded on the sample (8); the wire is connected to the crack monitoring unit (7) through the lead wire outlet. The liquid outlet on the gas-liquid mixing unit (2) is connected to the liquid inlet on the corrosion testing unit (4) through a liquid guide pipe; The sample (8) is provided with a pre-made crack. The crack monitoring unit (7) is provided with a DC source (10) and a micro voltage measurement unit (11). The sample (8) is spot-welded with two wires to connect to the DC source (10) to form a DC circuit. The two ends of the pre-made crack of the sample (8) are spot-welded with wires to connect to the micro voltage measurement unit (11) to form a measurement circuit. Two wires are led out from opposite sides of the crack opening of the sample (8) to connect to the micro voltage measurement unit (11) to form another measurement circuit. Furthermore, a wedge is provided in the pre-crack of the specimen (8), and the tail end of the wedge is flush with the end of the specimen (8).

2. The pipeline steel stress corrosion cracking critical stress intensity factor testing system as described in claim 1, characterized in that, A first constant flow pump (3-1) is installed on the liquid guide pipe between the corrosion solution unit (1) and the gas-liquid mixing unit (2); a second constant flow pump (3-2) is installed on the liquid guide pipe between the gas-liquid mixing unit (2) and the corrosion test unit (4); and a third constant flow pump (3-3) is installed on the liquid guide pipe between the corrosion test unit (4) and the liquid treatment unit (5).

3. The pipeline steel stress corrosion cracking critical stress intensity factor testing system as described in claim 1, characterized in that, The liquid treatment unit (5) is provided with an air outlet, which is connected to the waste gas absorption tower (6) through a gas guide pipe.

4. The pipeline steel stress corrosion cracking critical stress intensity factor testing system as described in claim 1, characterized in that, A gas flow controller (13) is installed on the gas guide pipe between the gas-liquid mixing unit (2) and the gas unit (9).

5. The pipeline steel stress corrosion cracking critical stress intensity factor testing system as described in claim 1, characterized in that, The crack monitoring unit (7) also includes a recording device (12), which is connected to the micro voltage measurement unit (11).

6. A method for testing the critical stress intensity factor for stress corrosion cracking in pipeline steel, characterized in that, The pipeline steel stress corrosion cracking critical stress intensity factor testing system based on any one of claims 1-5 includes the following steps: S1. Prepare a cantilever beam stress corrosion specimen (8) and pre-fabricate fatigue cracks on the specimen (8); press the wedge into the narrow groove of the specimen (8) so that the exposed part of the wedge is flush with the end of the specimen. S2. Two wires are spot-welded on the sample (8) to connect to the DC source (10) to form a DC circuit. Two wires are spot-welded to the two ends of the pre-crack of the sample (8) to connect to the micro voltage measurement unit (11) to form a measurement circuit. Two wires are led out from the opposite side of the crack opening of the sample (8) to connect to the micro voltage measurement unit (11) to form another measurement circuit. The sample (8) is placed inside the corrosion test unit (4), and the wires on the sample (8) are led out from the lead-out port on the top cover of the corrosion test unit (4); S3. Install and connect the corrosion environment device (100) and the double cantilever beam corrosion test device (200), seal the outlet of the corrosion solution unit (1); seal the inlet, outlet and outlet of the gas-liquid mixing unit (2); seal the inlet, lead wire and outlet of the corrosion test unit (4); seal the inlet and outlet of the liquid treatment unit (5) on the top cover. S4. Continuously add the prepared corrosion solution from the injection port. After the solution reaches three-fifths of the volume of the corrosion solution unit (1), turn on the first constant flow pump (3-1) to allow the corrosion solution to enter the gas-liquid mixing unit (2). Operate the gas flow rate controller to allow the hydrogen sulfide gas in the gas unit (9) to enter the gas-liquid mixing unit (2) to obtain the gas-liquid mixed medium. S5. Turn on the second constant flow pump (3-2), adjust the flow rate of the second constant flow pump (3-2) and the first constant flow pump (3-1) to allow the gas-liquid mixture to enter the corrosion test unit (4). After the ratio between the volume of the gas-liquid mixture and the surface area of ​​the sample (8) reaches 3 ml / cm², turn on the third constant flow pump (3-3) and adjust the flow rates of the third constant flow pump (3-3), the first constant flow pump (3-1) and the second constant flow pump (3-2) to maintain the volume of the gas-liquid mixture in the corrosion test unit (4) unchanged. S6. Open both measurement circuits and the DC circuit; S7. After the crack stops propagating, shut down the two measurement circuits and the DC circuit, stop the liquid injection, and shut down the first constant flow pump (3-1), the second constant flow pump (3-2) and the gas unit (9). After all the gas-liquid mixture in the corrosion test unit (4) is pumped into the liquid treatment unit (5) by the third constant flow pump (3-3), the third constant flow pump (3-3) is turned off, the top cover of the corrosion test unit (4) is opened, the sample (8) is taken out, the wedge is removed, the sample (8) is opened and the crack surface is exposed, and the calculation is performed. K ISSC .

7. The method for testing the critical stress intensity factor for stress corrosion cracking of pipeline steel as described in claim 6, characterized in that, When performing a single multi-sample test, all samples undergo the same S1 and S2 treatments.

8. The method for testing the critical stress intensity factor for stress corrosion cracking of pipeline steel as described in claim 7, characterized in that, When testing multiple samples, the multiple samples (8) are connected in series to share a DC circuit.

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