Method for evaluating influence of hydrogen on stress corrosion fracture of pipeline steel in acid environment

Abstract

The invention relates to a method for evaluating the influence of hydrogen on stress corrosion fracture of pipeline steel in an acid environment, which comprises the following steps: (1) respectively carrying out slow strain rate tensile tests in the acid environment and a nitrogen environment, and determining the damage degree of the acid environment on the mechanical property of a pipeline steel sample; (2) carrying out fast and slow scanning anodic polarization curve test, hydrogen permeation curve test and hydrogen filling-slow stretching test on the pipeline steel sample, and determining the damage degree of hydrogen separated out by cathodic reaction on the mechanical property of the pipeline steel sample; and (3) determining the influence degree and contribution rate proportion of hydrogen to the stress corrosion fracture of the pipeline steel in the acid environment. According to the method, the stress corrosion performance of the sulfur-resistant pipeline steel can be accurately and quickly evaluated, the proportion and contribution rate of hydrogen-induced stress corrosion sensitivity in the stress corrosion sensitivity of the pipeline steel in the acid environment are analyzed, and the influence degree of hydrogen on stress corrosion fracture of the pipeline steel in the acid environment is quantitatively represented.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pipeline steel stress corrosion performance detection, and particularly relates to a method for evaluating the influence of hydrogen on stress corrosion fracture of pipeline steel in an acidic environment. BACKGROUND

[0002] Stress corrosion cracking refers to a phenomenon that a metal material subjected to tensile stress produces lagging cracking or lagging fracture in some specific medium due to the synergistic effect of the corrosion medium and the stress, and is one of the most common and most harmful corrosion failure forms. In recent years, with the exploration and development of super-deep, super-high temperature, super-high pressure and super-corrosive harsh environment oil and gas wells, the working conditions of oil and gas wells generally have the characteristics of "high temperature, high pressure, high H2S, high Cl - , high salinity", because of the complex and harsh working conditions and special operation process, the steel for ground transportation pipeline is facing severe challenges, especially in the process of long-distance, high-temperature and high-pressure oil and gas transportation, stress corrosion cracking failure often occurs in the pipeline steel, which seriously affects the normal production and operation of oil and gas fields.

[0003] In the acidic well condition containing sulfur elements, the pipeline steel for transportation needs to withstand the combined action of tension and corrosion and other factors, and finally stress corrosion cracking occurs. Its mechanism mainly includes anodic dissolution type, hydrogen-induced cracking type, and mixed type of anodic dissolution and hydrogen-induced cracking coupling, that is, the fracture of the pipeline steel is usually the result of corrosion alone, hydrogen-induced cracking alone, and the coupling effect of the two.

[0004] At present, the stress corrosion cracking degree of the pipeline steel is generally evaluated by using stress corrosion sensitivity, and the stress corrosion sensitivity of the pipeline steel is composed of three parts, one is caused by anodic dissolution, the second is caused by hydrogen entering the sample, and the third is caused by the coupling effect of hydrogen and anodic dissolution. Under normal circumstances, the stress corrosion sensitivity of the pipeline steel is obtained by using a slow strain rate test in the test, and the test result is the sum of the stress corrosion sensitivity of the above three parts, but the actual contribution degree of a certain part cannot be obtained. Especially, the proportion of hydrogen to stress corrosion sensitivity cannot be evaluated. In order to accurately analyze the proportion of stress corrosion sensitivity caused by single hydrogen atom, the influence of the proportion of stress corrosion sensitivity caused by corrosion needs to be shielded. In order to realize hydrogen charging without additional corrosion of the oil well pipe, the method of electrochemical cathodic hydrogen charging is the most suitable, which not only facilitates the realization in the slow rate tensile equipment, but also has high hydrogen charging efficiency, but how to ensure that the hydrogen charging amount is equal to the hydrogen permeation amount caused by corrosion is a technical difficulty.

[0005] The constant strain method, constant load method, and slow strain rate tensile method (SSRT) are commonly used both domestically and internationally to study the stress corrosion resistance of pipeline steel. However, the constant strain method and constant load method can only provide information on whether a sample fails or not, and cannot quantitatively evaluate the sample's resistance to sulfidation stress corrosion, nor can they provide stress corrosion sensitivity data. They need to be combined with other experimental methods, which leads to a longer test cycle or the need to purchase new equipment, and the test cost is high.

[0006] The slow strain rate tensile method is a commonly used experimental technique for studying the stress corrosion resistance of pipeline steel. It involves stretching the specimen at a slow and constant strain rate on a testing machine until fracture, and then evaluating the stress corrosion susceptibility using the tensile property data. The stress corrosion susceptibility index is defined as: Ψ0 represents the reduction of area, yield strength, or elongation of the sample in nitrogen, as well as the fracture time, while Ψ1 represents the reduction of area, yield strength, or elongation of the sample in the ambient medium, as well as the fracture time, etc. The experiment uses an acidic aqueous solution as the test solution to evaluate the stress corrosion performance of pipeline steel at a constant rate. The obtained stress corrosion sensitivity result is the overall stress corrosion sensitivity and does not provide the specific contribution of any particular component. Summary of the Invention

[0007] This invention provides an evaluation method for the influence of hydrogen on stress corrosion cracking of pipeline steel in acidic environments. It can accurately and quickly evaluate the stress corrosion performance of sulfur-resistant pipeline steel, analyze the proportion and contribution rate of hydrogen-induced stress corrosion sensitivity in the stress corrosion sensitivity of pipeline steel in acidic environments, and quantitatively characterize the degree of influence of hydrogen on stress corrosion cracking of pipeline steel in acidic environments.

[0008] To achieve the above objectives, the present invention employs the following technical solution:

[0009] A method for evaluating the effect of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment includes the following steps:

[0010] (1) Slow strain rate tensile tests were conducted in acidic and nitrogen environments to obtain stress-strain curves of pipeline steel specimens in the two environments, and the degree of damage to the mechanical properties of pipeline steel specimens by acidic environment was determined; and hydrogen permeation curve tests were conducted on pipeline steel specimens in acidic environment, and steady-state hydrogen permeation current density was recorded.

[0011] (2) Perform fast and slow sweep anodic polarization curve tests on pipeline steel samples, and determine the maximum corrosion potential V. s The minimum corrosion potential V is the initial potential of anodic dissolution acting alone. fTo determine the initiation potential of hydrogen-induced cracking alone, the range of cathode hydrogen charging potential was determined, and the influence of anodic dissolution was eliminated while charging with hydrogen. Hydrogen permeation curve tests were performed on pipeline steel samples to obtain simulated curves of cathode hydrogen charging potential and hydrogen permeation current density within the range of cathode hydrogen charging potential. The cathode hydrogen charging potential value corresponding to the steady-state hydrogen permeation current density was obtained, and hydrogen charging-slow tensile tests were performed on pipeline steel samples at this cathode hydrogen charging potential to obtain the corresponding stress-strain curves and determine the degree of damage to the mechanical properties of pipeline steel samples caused by hydrogen evolution from the cathode reaction.

[0012] (3) Based on the degree of damage to the mechanical properties of pipeline steel samples caused by acidic environment, and combined with the degree of damage to the mechanical properties of pipeline steel caused by hydrogen evolution from cathodic reaction, determine the degree of influence and contribution rate of hydrogen on stress corrosion cracking of pipeline steel in acidic environment.

[0013] The acidic environment is a sodium chloride solution containing sulfur with a mass concentration of 3.5% to 5% and a pH value of 2 ≤ 6; wherein the sulfur is gaseous sulfur, solid sulfur, or a mixture of one gaseous sulfur and one solid sulfur, the gaseous sulfur including H2S and SOx, and the solid sulfur including Na2S and CH4N2S.

[0014] The degree of damage to the mechanical properties of pipeline steel samples by the acidic environment is determined by using the tensile properties of the pipeline steel samples in nitrogen as a benchmark, combined with the tensile properties in the acidic environment, to determine the stress corrosion cracking susceptibility in the acidic environment; the specific process is as follows:

[0015] Based on the cross-sectional area of ​​the pipeline steel specimen before and after tensioning, the cross-sectional reduction rate Ψ of the pipeline steel specimen is calculated by formula (1).

[0016]

[0017] In formula (1), S0 is the cross-sectional area of ​​the gauge section before the specimen breaks, and S1 is the cross-sectional area of ​​the gauge section after the specimen breaks.

[0018] Based on the reduction of area Ψ of pipeline steel samples in a nitrogen environment a And the reduction of area Ψ of pipeline steel samples in an acidic environment. b The stress corrosion cracking susceptibility factor of pipeline steel samples in an acidic environment was calculated using formula (2). ;

[0019]

[0020] The combined effect of anodic dissolution and cathodic hydrogen evolution in an acidic environment on stress corrosion cracking of pipeline steel samples.

[0021] The hydrogen permeation curve test was conducted using a Devanathan-Stachurski double-sided electrolytic cell. When measuring the hydrogen permeation curve of the pipeline steel sample in an acidic environment and obtaining the steady-state hydrogen permeation current density, the hydrogen charging side contained the test solution of the acidic environment, and the hydrogen measuring side contained NaOH solution. When using cathode hydrogen charging to conduct the hydrogen permeation test on the pipeline steel sample, the hydrogen charging side contained a NaCl solution with a mass concentration of 3.5% to 5%, and the hydrogen measuring side contained NaOH solution. In the hydrogen permeation curve test, the preload value of the pipeline steel sample under test was 50% to 80% of its yield strength.

[0022] When performing fast and slow sweep anodic polarization curve tests on pipeline steel samples, a NaCl solution with a mass concentration of 3.5%–5% was used. The fast sweep rate was 1000–1200 mV / min, and the slow sweep rate was 5–10 mV / min. The hydrogen-induced cracking onset potential V was determined. f The highest value; the cathode hydrogen charging potential range is V. f ~V f -200mV, the stabilization time of hydrogen permeation current density is over 2000s.

[0023] The simulated curves of cathode hydrogen evolution potential and hydrogen permeation current density within the cathode hydrogen evolution potential range conform to the following relationship: In the formula, a and b are constants, with the value of a ranging from -3.18E-4 to -2.11E-4 and the value of b ranging from 0.01098 to 0.01142; x is the cathode hydrogen charging potential, and y is the hydrogen permeation current density.

[0024] The slow strain rate tensile test specifically involves: first, following a 1×10... -4 Preload the pipeline steel specimen with a strain rate of mm / s to 80% of its yield strength, and then, after stabilization, apply a strain of 5 × 10⁻⁶ mm / s. -6 Loading begins at a strain rate of mm / s.

[0025] The hydrogen-charged-slow tensile test specifically involves performing a hydrogen-charged-slow tensile test on pipeline steel samples exposed to a NaCl solution with a mass concentration of 3.5%–5% at the cathode hydrogen-charged potential corresponding to the steady-state hydrogen permeation current density, obtaining the corresponding stress-strain curves. The preloading method and strain rate are the same as those in the slow strain rate tensile test. By comparing the stress-strain curves under nitrogen, electrochemical cathode hydrogen-charged conditions, and acidic environments, the degree of damage to the mechanical properties of pipeline steel samples caused by hydrogen evolution from the cathode reaction in acidic environments is determined. The specific calculation process is as follows:

[0026] The reduction of area of ​​the pipeline steel sample under cathodic hydrogen charging was calculated according to formula (1). Based on the reduction of area of ​​the pipeline steel sample in nitrogen and formula (2), the stress corrosion cracking susceptibility factor of the pipeline steel sample under cathodic hydrogen charging was calculated. That is, the stress corrosion cracking susceptibility factor of the pipeline steel sample caused by hydrogen permeation into the pipeline steel sample in the acidic environment alone. The influence of hydrogen evolution from the cathodic reaction in an acidic environment on the stress corrosion fracture of pipeline steel samples was calculated using formula (3). H ;

[0027] .

[0028] The test solutions used in the hydrogen permeation curve test, fast and slow sweep anodic polarization curve test, slow strain rate tensile test, and electrochemical cathode hydrogen charging test were all deoxygenated with high-purity nitrogen.

[0029] Compared with the prior art, the beneficial effects of the present invention are:

[0030] 1) This invention uses an electrochemical cathode hydrogen charging method to simulate hydrogen permeation in an acidic environment. By combining electrochemical cathode hydrogen charging with slow strain rate stretching, the stress corrosion cracking (SCC) susceptibility factor caused by hydrogen permeation from cathodic reaction in an acidic environment is obtained. By comparing this susceptibility factor with that of SCC in an acidic environment, the influence and contribution rate of hydrogen evolution from cathodic reaction in an acidic environment on SCC can be quantitatively calculated. This provides a theoretical basis for elucidating the control mechanism of stress corrosion cracking in pipeline steel and improving the SCC resistance of pipeline steel.

[0031] 2) The evaluation method described in this invention has a simple experimental process and accurate measurement results.

[0032] 3) This invention simulates the actual service environment of pipeline steel, firstly calculates the stress corrosion cracking susceptibility factor, and then further analyzes the stress corrosion performance of pipeline steel to elucidate the stress corrosion mechanism, providing a theoretical basis for improving the SCC resistance of pipeline steel.

[0033] 4) By evaluating the impact of hydrogen in acidic environments on stress corrosion cracking of pipeline steel, the stress corrosion performance and service life of pipeline steel under actual service conditions can be predicted, ensuring the safety and stability of oil and gas field exploitation and pipeline transportation processes. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the slow-tension specimen described in an embodiment of the present invention.

[0035] Figure 2 The figures shown are the fast and slow sweep anodic polarization curves of the pipeline steel sample in a 5% NaCl solution in this embodiment of the invention.

[0036] Figure 3 This is the hydrogen permeation curve of the pipeline steel sample in an acidic environment in an embodiment of the present invention.

[0037] Figure 4 This is a simulated curve of the cathode hydrogen charging potential and hydrogen permeation current density of the pipeline steel sample in the embodiment of the present invention.

[0038] Figure 5 These are the stress-strain curves of pipeline steel samples in the embodiments of the present invention under nitrogen, acidic H2S, and cathodic hydrogen charging environments. Detailed Implementation

[0039] The present invention provides a method for evaluating the effect of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment, comprising the following steps:

[0040] (4) Slow strain rate tensile tests were conducted in acidic and nitrogen environments to obtain stress-strain curves of pipeline steel specimens in the two environments, and the degree of damage to the mechanical properties of pipeline steel specimens by acidic environment was determined; and hydrogen permeation curve tests were conducted on pipeline steel specimens in acidic environment, and steady-state hydrogen permeation current density was recorded.

[0041] (5) Perform fast and slow sweep anodic polarization curve tests on pipeline steel samples, and determine the maximum corrosion potential V. s The minimum corrosion potential V is the initial potential of anodic dissolution acting alone. f To determine the initiation potential of hydrogen-induced cracking alone, the range of cathode hydrogen charging potential was determined, and the influence of anodic dissolution was eliminated while charging with hydrogen. Hydrogen permeation curve tests were performed on pipeline steel samples to obtain simulated curves of cathode hydrogen charging potential and hydrogen permeation current density within the range of cathode hydrogen charging potential. The cathode hydrogen charging potential value corresponding to the steady-state hydrogen permeation current density was obtained, and hydrogen charging-slow tensile tests were performed on pipeline steel samples at this cathode hydrogen charging potential to obtain the corresponding stress-strain curves and determine the degree of damage to the mechanical properties of pipeline steel samples caused by hydrogen evolution from the cathode reaction.

[0042] (6) Based on the degree of damage to the mechanical properties of pipeline steel samples caused by acidic environment, and combined with the degree of damage to the mechanical properties of pipeline steel caused by hydrogen evolution from cathodic reaction, determine the degree of influence and contribution rate of hydrogen on stress corrosion cracking of pipeline steel in acidic environment.

[0043] The acidic environment is a sodium chloride solution containing sulfur with a mass concentration of 3.5% to 5% and a pH value of 2 ≤ 6; wherein the sulfur is gaseous sulfur, solid sulfur, or a mixture of one gaseous sulfur and one solid sulfur, the gaseous sulfur including H2S and SOx, and the solid sulfur including Na2S and CH4N2S.

[0044] The degree of damage to the mechanical properties of pipeline steel samples by the acidic environment is determined by using the tensile properties of the pipeline steel samples in nitrogen as a benchmark, combined with the tensile properties in the acidic environment, to determine the stress corrosion cracking susceptibility in the acidic environment; the specific process is as follows:

[0045] Based on the cross-sectional area of ​​the pipeline steel specimen before and after tensioning, the cross-sectional reduction rate Ψ of the pipeline steel specimen is calculated by formula (1).

[0046]

[0047] In formula (1), S0 is the cross-sectional area of ​​the gauge section before the specimen breaks, and S1 is the cross-sectional area of ​​the gauge section after the specimen breaks.

[0048] Based on the reduction of area Ψ of pipeline steel samples in a nitrogen environment a And the reduction of area Ψ of pipeline steel samples in an acidic environment. b The stress corrosion cracking susceptibility factor of pipeline steel samples in an acidic environment was calculated using formula (2). ;

[0049]

[0050] The combined effect of anodic dissolution and cathodic hydrogen evolution in an acidic environment on stress corrosion cracking of pipeline steel samples.

[0051] The hydrogen permeation curve test was conducted using a Devanathan-Stachurski double-sided electrolytic cell. When measuring the hydrogen permeation curve of the pipeline steel sample in an acidic environment and obtaining the steady-state hydrogen permeation current density, the hydrogen charging side contained the test solution of the acidic environment, and the hydrogen measuring side contained NaOH solution. When using cathode hydrogen charging to conduct the hydrogen permeation test on the pipeline steel sample, the hydrogen charging side contained a NaCl solution with a mass concentration of 3.5% to 5%, and the hydrogen measuring side contained NaOH solution. In the hydrogen permeation curve test, the preload value of the pipeline steel sample under test was 50% to 80% of its yield strength.

[0052] When performing fast and slow sweep anodic polarization curve tests on pipeline steel samples, a NaCl solution with a mass concentration of 3.5%–5% was used. The fast sweep rate was 1000–1200 mV / min, and the slow sweep rate was 5–10 mV / min. The hydrogen-induced cracking onset potential V was determined. f The highest value; the cathode hydrogen charging potential range is V. f ~V f -200mV, the stabilization time of hydrogen permeation current density is over 2000s.

[0053] The simulated curves of cathode hydrogen evolution potential and hydrogen permeation current density within the cathode hydrogen evolution potential range conform to the following relationship: In the formula, a and b are constants, with the value of a ranging from -3.18E-4 to -2.11E-4 and the value of b ranging from 0.01098 to 0.01142; x is the cathode hydrogen charging potential, and y is the hydrogen permeation current density.

[0054] The slow strain rate tensile test specifically involves: first, following a 1×10... -4 Preload the pipeline steel specimen with a strain rate of mm / s to 80% of its yield strength, and then, after stabilization, apply a strain of 5 × 10⁻⁶ mm / s. -6 Loading begins at a strain rate of mm / s.

[0055] The hydrogen-charged-slow tensile test specifically involves performing a hydrogen-charged-slow tensile test on pipeline steel samples exposed to a NaCl solution with a mass concentration of 3.5%–5% at the cathode hydrogen-charged potential corresponding to the steady-state hydrogen permeation current density, obtaining the corresponding stress-strain curves. The preloading method and strain rate are the same as those in the slow strain rate tensile test. By comparing the stress-strain curves under nitrogen, electrochemical cathode hydrogen-charged conditions, and acidic environments, the degree of damage to the mechanical properties of pipeline steel samples caused by hydrogen evolution from the cathode reaction in acidic environments is determined. The specific calculation process is as follows:

[0056] The reduction of area of ​​the pipeline steel sample under cathodic hydrogen charging was calculated according to formula (1). Based on the reduction of area of ​​the pipeline steel sample in nitrogen and formula (2), the stress corrosion cracking susceptibility factor of the pipeline steel sample under cathodic hydrogen charging was calculated. That is, the stress corrosion cracking susceptibility factor of the pipeline steel sample caused by hydrogen permeation into the pipeline steel sample in the acidic environment alone. The influence of hydrogen evolution from the cathodic reaction in an acidic environment on the stress corrosion fracture of pipeline steel samples was calculated using formula (3). H ;

[0057] .

[0058] The test solutions used in the hydrogen permeation curve test, fast and slow sweep anodic polarization curve test, slow strain rate tensile test, and electrochemical cathode hydrogen charging test were all deoxygenated with high-purity nitrogen.

[0059] To more intuitively illustrate the present invention, the embodiments of the present invention will be further described in conjunction with the examples. The following examples are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any technical solutions that can be obviously obtained by those skilled in the art within the scope of the technology disclosed in the present invention, including simple variations or equivalent substitutions, are all within the scope of protection of the present invention.

[0060] Example:

[0061] In this embodiment, the evaluation process for the influence of hydrogen in an acidic environment on stress corrosion cracking of pipeline steel is as follows:

[0062] First, slow strain rate tensile testing (SSRT) tests were conducted on pipeline steel specimens using a CORTEST slow strain rate tensile testing machine (USA) in both acidic and nitrogen atmospheres. The specimen dimensions are shown in [reference needed]. Figure 1 Before the test, the pipeline steel sample was prepared using 1000... # After sanding to a bright finish, clean with acetone and anhydrous ethanol respectively, then dry with cold air. After installing the pipeline steel sample, apply a load of 200 kgf to eliminate clearances in the reduction gears, clamps, etc. First, follow a 1×10... -4 The strain rate was rapidly preloaded to 80% of the yield strength of the pipeline steel specimen at a strain rate of mm / s, with a load of 1600±10 kgf. After stabilization, the strain was increased by 5×10 mm / s. -6 Slow tensile tests were conducted at a strain rate of mm / s until the pipeline steel specimen broke. Stress-strain curves and mechanical property parameters of the pipeline steel specimens in acidic and nitrogen environments were recorded. The reduction of area of ​​the pipeline steel specimens in acidic and nitrogen environments was calculated according to formula (1). In this embodiment, the values ​​of the two reductions of area were 8.04% and 73.77%, respectively. The stress corrosion cracking susceptibility factor of the pipeline steel specimen in the acidic environment was calculated according to formula (2). The sensitivity factor is the total effect of anodic dissolution (AD), cathodic reaction hydrogen permeation (i.e. hydrogen embrittlement, HE) in acidic environment, and the combined effect of the two on stress corrosion cracking (SSC) of pipeline steel samples. It is the total stress corrosion cracking sensitivity in acidic environment and characterizes the stress corrosion cracking sensitivity of pipeline steel samples in acidic environment.

[0063] Secondly, in a 5% NaCl solution, the pipeline steel sample was subjected to fast and slow sweep anodic polarization curve testing using an electrochemical workstation. Figure 2 As shown, determine V s The value is -695mV (relative to a saturated calomel electrode SCE, the same below), determine V f The value is -743mV, and the potential range of -743mV to -695mV represents the region of mixed effects of anodic dissolution and hydrogen embrittlement. In this embodiment, the cathode hydrogen charging potential starts at -743mV and reaches a minimum of -943mV.

[0064] Next, hydrogen permeation curves of pipeline steel samples in an acidic environment were tested using a hydrogen permeation testing apparatus (Devanathan-Stachurski double-sided electrolytic cell). The test sample was preloaded to 80% of its yield strength, maintaining an elastic deformation state where dislocations did not multiply or move, resulting in weak hydrogen-dislocation interaction and facilitating hydrogen diffusion. The hydrogen-charging side contained the test solution in an acidic environment (specifically, a 5% NaCl solution with hydrogen sulfide mass concentration), and the hydrogen-measuring side contained a 0.2 mol / L NaOH solution. The steady-state hydrogen permeation current density of the pipeline steel sample was obtained as I = 2.2094 μA / cm². -2 .

[0065] To calculate the impact of hydrogen permeation in an acidic environment on the SCC susceptibility of pipeline steel samples, the pipeline steel samples were charged with hydrogen using an electrochemical cathodic hydrogen charging method. This simulated the hydrogen permeation effect caused by hydrogen evolution from the cathodic reaction in an acidic environment, achieving hydrogen charging while simultaneously eliminating the influence of anodic dissolution. The specific process is as follows:

[0066] a. An electrochemical workstation and hydrogen permeation testing device were used to measure the electrochemical cathodic hydrogen charging and hydrogen permeation curves of pipeline steel samples. The test sample was preloaded to 80% of its yield strength, maintaining an elastic deformation state. Simultaneously, the hydrogen permeation potential density was recorded at different charging potentials. The charging side used a 5% NaCl solution, and the measuring side used a 0.2 mol / L NaOH solution. The precise cathodic hydrogen charging potential range was -743 mV to -943 mV. When the potential was set to -743 mV, hydrogen permeation current was immediately detected until the hydrogen permeation current density stabilized for 2000 s. The hydrogen permeation current density at this point was recorded. The current density was gradually decreased in increments of 10 mV, and the current density corresponding to different charging potentials was recorded (e.g., ...). Figure 3 As shown), until the voltage is reduced to -943mV, simulated curves of hydrogen permeation current density of pipeline steel samples under different cathode hydrogen charging potentials are obtained, as shown. Figure 4 As shown. According to the formula Where a = -2.6485E⁻⁴ and b = 0.0112, when a cathodic hydrogen charging potential of -808 mV is applied to the surface of the pipeline steel sample, a steady-state hydrogen permeation current density equal to that in an acidic environment can be obtained, i.e., I = 2.2094 μA / cm². -2 .

[0067] b. The corrosive medium used in the hydrogen charging-slow tensile test was a 5% NaCl solution. A high-temperature, high-pressure reference electrode was used, and the cathode hydrogen charging potential was set to -808mV. The test was initially performed according to a 1×10⁻⁶... -4 The strain rate was rapidly preloaded to 80% of the yield strength of the pipeline steel specimen at a strain rate of mm / s, with a load of 1600±10 kgf, and then subjected to 5×10 -6The test was conducted at a strain rate of mm / s until the pipeline steel specimen broke, and the stress-strain curve was recorded (e.g., ...). Figure 5 (As shown) and mechanical property parameters. By comparing the stress-strain curves and mechanical property parameters of the nitrogen environment, the cathode hydrogen-filled environment, and the acidic environment, the degree of damage to the mechanical properties of the pipeline steel sample caused by the cathodic reaction in the acidic environment can be calculated.

[0068] c. According to formula (1), the section reduction rate of the pipeline steel sample under cathodic hydrogen charging environment is calculated to be 13.19%. Then, based on the section reduction rate in nitrogen environment and formula (2), the stress corrosion cracking susceptibility factor of the sample in -808mV cathodic hydrogen charging environment is calculated. The value is 82.12%, meaning that hydrogen permeation into the pipeline steel sample from an acidic environment alone causes the stress corrosion cracking susceptibility factor of the pipeline steel sample to be 82.12%.

[0069] d. Calculate the influence of hydrogen evolution from the cathodic reaction in an acidic environment on the stress corrosion fracture of pipeline steel samples using formula (3). H The percentage was 92.16%, indicating the extent to which hydrogen alone in this acidic environment affected the stress corrosion cracking of the pipeline steel sample.

[0070] Therefore, it can be seen that in this embodiment, the stress corrosion cracking process of pipeline steel in acidic environment is jointly controlled by anodic dissolution and hydrogen embrittlement. Among them, the hydrogen embrittlement caused by hydrogen evolution from cathodic reaction penetrating into the pipeline steel sample accounts for 92.16% of the stress corrosion cracking.

[0071] In this embodiment, the pipeline steel sample is X65S sulfur-resistant pipeline steel, and the acidic environment is a NaCl solution with a hydrogen sulfide mass concentration of 5% (pH=3) purged.

[0072] The test data under other acidic environments are shown in the table below:

[0073]

[0074] It can be seen that, under these two acidic environments, a 5% NaCl solution containing sodium sulfide (pH=4) and a 5% NaCl solution containing thiourea (pH=6) will produce different results. Hydrogen penetration contributes significantly to hydrogen-induced cracking, while anodic dissolution contributes very little.

[0075] The stress corrosion susceptibility of pipeline steel samples in an acidic environment, containing a 5% NaCl solution (pH=2) with SO2 concentration, was observed. It is generally believed that pipeline steel will not experience stress corrosion cracking, does not have a tendency for hydrogen-induced cracking, and mainly undergoes anodic dissolution.

[0076] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for evaluating the effect of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment, characterized in that, Includes the following steps: (1) Slow strain rate tensile tests were conducted in acidic and nitrogen environments to obtain stress-strain curves of pipeline steel specimens in the two environments, and the degree of damage to the mechanical properties of pipeline steel specimens by acidic environment was determined; and hydrogen permeation curve tests were conducted on pipeline steel specimens in acidic environment, and steady-state hydrogen permeation current density was recorded. (2) Perform fast and slow sweep anodic polarization curve tests on pipeline steel samples, and determine the maximum corrosion potential V. s The minimum corrosion potential V is the initial potential for anodic dissolution alone. f To determine the initiation potential of hydrogen-induced cracking alone, the range of cathode hydrogen charging potential was determined, and the influence of anodic dissolution was eliminated while charging with hydrogen. Hydrogen permeation curve tests were performed on pipeline steel samples to obtain simulated curves of cathode hydrogen charging potential and hydrogen permeation current density within the range of cathode hydrogen charging potential. The cathode hydrogen charging potential value corresponding to the steady-state hydrogen permeation current density was obtained, and hydrogen charging-slow tensile tests were performed on pipeline steel samples at this cathode hydrogen charging potential to obtain the corresponding stress-strain curves and determine the degree of damage to the mechanical properties of pipeline steel samples caused by hydrogen evolution from the cathode reaction. (3) Based on the degree of damage to the mechanical properties of pipeline steel samples caused by acidic environment, and combined with the degree of damage to the mechanical properties of pipeline steel caused by hydrogen evolution from cathodic reaction, determine the degree of influence and contribution rate of hydrogen on stress corrosion cracking of pipeline steel in acidic environment.

2. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, The acidic environment is a sodium chloride solution containing sulfur with a mass concentration of 3.5% to 5% and a pH value of 2 ≤ 6; wherein the sulfur is gaseous sulfur, solid sulfur, or a mixture of one gaseous sulfur and one solid sulfur, the gaseous sulfur including H2S and SOx, and the solid sulfur including Na2S and CH4N2S.

3. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, The degree of damage to the mechanical properties of pipeline steel samples by the acidic environment is determined by using the tensile properties of the pipeline steel samples in nitrogen as a benchmark, combined with the tensile properties in the acidic environment, to determine the stress corrosion cracking susceptibility in the acidic environment. The specific process is as follows: Based on the cross-sectional area of ​​the pipeline steel specimen before and after tensioning, the cross-sectional reduction rate Ψ of the pipeline steel specimen is calculated by formula (1). ； In formula (1), S0 is the cross-sectional area of ​​the gauge section before the specimen breaks, and S1 is the cross-sectional area of ​​the gauge section after the specimen breaks. Based on the reduction of area Ψ of pipeline steel samples in a nitrogen environment a And the reduction of area Ψ of pipeline steel samples in an acidic environment. b The stress corrosion cracking susceptibility factor of pipeline steel samples in an acidic environment was calculated using formula (2). ; ； The combined effect of anodic dissolution and cathodic hydrogen evolution in an acidic environment on stress corrosion cracking of pipeline steel samples.

4. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, The hydrogen permeation curve test was conducted using a Devanathan-Stachurski double-sided electrolytic cell. When measuring the hydrogen permeation curve of the pipeline steel sample in an acidic environment and obtaining the steady-state hydrogen permeation current density, the hydrogen charging side contained the test solution of the acidic environment, and the hydrogen measuring side contained NaOH solution. When using cathode hydrogen charging to conduct the hydrogen permeation test on the pipeline steel sample, the hydrogen charging side contained a NaCl solution with a mass concentration of 3.5% to 5%, and the hydrogen measuring side contained NaOH solution. In the hydrogen permeation curve test, the preload value of the pipeline steel sample under test was 50% to 80% of its yield strength.

5. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, When performing fast and slow sweep anodic polarization curve tests on pipeline steel samples, a NaCl solution with a mass concentration of 3.5%–5% was used. The fast sweep rate was 1000–1200 mV / min, and the slow sweep rate was 5–10 mV / min. The hydrogen-induced cracking onset potential V was determined. f The highest value; the cathode hydrogen charging potential range is V. f ~V f -200mV, the stabilization time of hydrogen permeation current density is over 2000s.

6. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, The simulated curves of cathode hydrogen evolution potential and hydrogen permeation current density within the cathode hydrogen evolution potential range conform to the following relationship: In the formula, a and b are constants, with the value of a ranging from -3.18E-4 to -2.11E-4 and the value of b ranging from 0.01098 to 0.01142; x is the cathode hydrogen charging potential, and y is the hydrogen permeation current density.

7. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, The slow strain rate tensile test specifically involves: first, following a 1×10... -4 Preload the pipeline steel specimen with a strain rate of mm / s to 80% of its yield strength, and then, after stabilization, apply a strain at a rate of 5 × 10⁻⁶ mm / s. -6 Loading begins at a strain rate of mm / s.

8. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, The hydrogen-charged-slow tensile test specifically involves performing a hydrogen-charged-slow tensile test on pipeline steel samples exposed to a NaCl solution with a mass concentration of 3.5%–5% at the cathode hydrogen-charged potential corresponding to the steady-state hydrogen permeation current density, obtaining the corresponding stress-strain curves. The preloading method and strain rate are the same as those in the slow strain rate tensile test. By comparing the stress-strain curves under nitrogen, electrochemical cathode hydrogen-charged conditions, and acidic environments, the degree of damage to the mechanical properties of pipeline steel samples caused by hydrogen evolution from the cathode reaction in acidic environments is determined. The specific calculation process is as follows: The reduction of area of ​​the pipeline steel sample under cathodic hydrogen charging was calculated according to formula (1). Based on the reduction of area of ​​the pipeline steel sample in nitrogen and formula (2), the stress corrosion cracking susceptibility factor of the pipeline steel sample under cathodic hydrogen charging was calculated. That is, the stress corrosion cracking susceptibility factor of the pipeline steel sample caused by hydrogen permeation into the pipeline steel sample in the acidic environment alone. The influence of hydrogen evolution from the cathodic reaction in an acidic environment on the stress corrosion fracture of pipeline steel samples was calculated using formula (3). H ; 。 9. The method for evaluating the influence of hydrogen on stress corrosion cracking of pipeline steel in an acidic environment according to claim 1, characterized in that, The test solutions used in the hydrogen permeation curve test, fast and slow sweep anodic polarization curve test, slow strain rate tensile test, and electrochemical cathode hydrogen charging test were all deoxygenated with high-purity nitrogen.

Images