Method for testing and evaluating a steel in a multiphase corrosion environment containing carbon dioxide

Abstract

This invention relates to the field of metal corrosion testing and evaluation technology in oil and gas fields, specifically to a method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment. The method involves placing both electrochemical and weight-loss samples of steel in the same container filled with simulated formation aqueous solution. Corrosion simulation experiments are conducted based on the relative positions of the electrochemical and weight-loss samples with the simulated formation aqueous solution. The electrochemical and weight-loss samples are removed at different time points during the corrosion simulation experiments for further testing. An electrochemical behavior correction factor α is obtained based on the electrochemical test results, a localized corrosion severity correction factor β is obtained based on the three-dimensional surface morphology test results, and a corrosion product film correction factor γ is obtained based on the corrosion product film characterization results. The corrosion rate V is calculated by multiplying the initial average corrosion rate V0 by α, β, and γ. This invention enables a comprehensive determination of corrosion rate and corrosion mechanism under multiphase environments.

Description

Technical Field

[0001] This invention relates to the field of metal corrosion testing and evaluation technology in oil and gas fields, specifically to a method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment; and more particularly to a multiphase corrosion evaluation method based on weight loss testing, electrochemical behavior, local corrosion morphology, and corrosion product film characteristics, which can be used for corrosion behavior analysis and corrosion risk assessment in the gas phase zone, gas-liquid interface zone, and fully immersed zone during oil and gas extraction and transportation. Background Technology

[0002] During oil and gas extraction and transportation, pipelines often contain a gas phase zone (containing acidic gases such as CO2), a gas-liquid interface zone (semi-immersed zone), and a bottom liquid accumulation zone (fully immersed zone), forming a complex corrosive environment with multiple phases coexisting. Due to differences in medium composition, wetting state, and mass transfer conditions, the corrosion mechanisms and rates of steel vary significantly across these different phase zones. For example, the gas-liquid interface often experiences more severe localized corrosion due to the thin liquid film effect and localized CO2 concentration; while the fully immersed zone is dominated by uniform corrosion or pitting corrosion.

[0003] Traditional corrosion testing methods, such as electrochemical testing or weight loss sample testing alone, often only target a single-phase environment (such as a fully immersed zone), and cannot simultaneously simulate and compare the corrosion behavior of three typical regions, leading to inaccurate test results. Therefore, they cannot comprehensively reflect the true corrosion risk of pipelines in multiphase environments, and are also difficult to provide an accurate basis for selecting protective measures.

[0004] Current technology urgently needs a method that can simultaneously test, evaluate, and determine the corrosion behavior of different phases, and quantify corrosion rate, localized corrosion risk, and the protective effect of corrosion product films, thereby providing a scientific basis for pipeline material selection, life prediction, and protective measures. Summary of the Invention

[0005] The present invention aims to solve the problem that the existing technology cannot simultaneously simulate and evaluate the corrosion behavior of steel in the gas phase region, gas-liquid interface region and full immersion region in a CO2 environment, and proposes a test and evaluation method for steel in a carbon dioxide multiphase corrosion environment.

[0006] The technical solution of this invention is as follows: A method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment, the method is as follows: Electrochemical and weight loss samples of steel were placed in the same container filled with simulated formation aqueous solution. Based on the relative positions of the electrochemical and weight loss samples with the simulated formation aqueous solution, three different phase regions—gas phase, semi-immersion zone, and fully immersion zone—were simulated, and corrosion simulation tests were carried out. Electrochemical and weightless samples were taken out at different time points in the corrosion simulation test for testing. Based on the electrochemical test results, the electrochemical behavior correction factor α was obtained, the local corrosion severity correction factor β was obtained based on the three-dimensional surface morphology test results, and the corrosion product film correction factor γ was obtained based on the corrosion product film characterization results. The corrosion rate V is calculated by multiplying the initial average corrosion rate V0 by α, β, and γ.

[0007] After completing the weight loss test on the weightless sample and obtaining the initial average corrosion rate V0 at each time point in each phase region (gas phase region, semi-immersion region and full immersion region), this method does not directly use the initial average corrosion rate V0 as the final evaluation result. Instead, it introduces an electrochemical behavior correction factor α, a local corrosion severity correction factor β, and a corrosion product film correction factor γ to jointly correct the initial average corrosion rate V0, so as to obtain a corrosion rate V that is closer to the actual failure risk of the material.

[0008] The weight loss method can only reflect the average mass loss of the material throughout the entire corrosion simulation test, but it cannot distinguish between uniform corrosion and localized corrosion, nor can it reflect the dynamic processes such as corrosion product film formation, rupture, and corrosion activation. Therefore, this method introduces multiple correction factors with different physical meanings to progressively correct the initial average corrosion rate V0: the electrochemical behavior correction factor α is used to reflect the degree of corrosion activation on the material surface and changes in interfacial charge transfer capacity; the localized corrosion severity correction factor β is used to reflect the non-uniformity of corrosion distribution in space and the risk of localized penetration; and the corrosion product film correction factor γ is used to reflect the ability of the corrosion product film to inhibit subsequent corrosion processes.

[0009] There is a clear correlation between the electrochemical behavior correction factor α, the localized corrosion severity correction factor β, and the corrosion product film correction factor γ: when the corrosion product film cracks or locally peels off, it usually leads to a corrosion current density I0. corr Increase, charge transfer resistance R ct This decreases, thereby increasing the electrochemical behavior correction factor α; simultaneously, local film defect regions are prone to forming pitting corrosion sources, increasing the maximum pitting depth d. max This increases and leads to an increase in the localized corrosion severity correction factor β. Conversely, when continuous and dense FeCO3 is formed, the corrosion current density I... corr Reduce charge transfer resistance R ct As the corrosion rate increases, the tendency for local pitting corrosion decreases. Therefore, the electrochemical behavior correction factor α and the local corrosion severity correction factor β decrease, and the corrosion product film correction factor γ reduces the corrosion rate.

[0010] Among them, the electrochemical behavior correction factor α is based on the corrosion current density I. corr and the change in charge transfer resistance ΔR ctget: The initial charge transfer resistance of the electrochemical sample before corrosion is R. ct初 The corrosion simulation experiment was conducted with the final charge transfer resistance R at each time point as the result. ct终 The change in charge transfer resistance ΔR ct =(R ct初 -R ct终 ) / R ct初 ; I corr ≥5×10 -5 A / cm 2 And 0.45 ≤ ΔR ct When the value is less than 1, the electrochemical behavior correction factor α = α1. At this point, the corrosion product film on the surface of the electrochemical sample breaks down or partially detaches, the interfacial charge transfer resistance decreases significantly, the corrosion reaction is strongly activated, and local pitting corrosion develops rapidly. The initial average corrosion rate V0 obtained by the weight loss method will seriously underestimate the actual risk of local penetration, so it needs to be amplified and corrected to the maximum extent. Therefore, the electrochemical behavior correction factor α = α1 is taken as the maximum value. 1×10 -5 A / cm 2 ≤I corr <5×10 -5 A / cm 2 And 0.25 ≤ ΔR ct When <0.45, the electrochemical behavior correction factor α=α2. At this time, the corrosion behavior fluctuates greatly, and local activation and corrosion product film repair occur alternately. There is a certain deviation between the weight loss method results and the electrochemical behavior, but the degree of deviation is not as great as that of the fully activated state. Therefore, the electrochemical behavior correction factor α=α2 adopts a correction value slightly higher than that of the stable state. I corr <1×10 -5 A / cm 2 And 0 < ΔR ct When <0.25, the electrochemical behavior correction factor α=α3=1; at this time, the corrosion state is relatively uniform and stable, and the electrochemical test results are in good agreement with the initial average corrosion rate V0 obtained by the weight loss method. No additional amplification or reduction is required. The electrochemical behavior correction factor α=α3=1.0 is taken as the baseline value. The remaining cases indicate a transitional stage where corrosion activation and corrosion product film formation coexist, with some fluctuations in corrosion behavior. The electrochemical behavior correction factor α = α4 is taken. At this time, a stable and dense corrosion product film (such as FeCO3) gradually forms on the surface of the electrochemical sample, and the interfacial charge transfer is significantly inhibited. The actual corrosion rate is lower than the initial average corrosion rate V0. Therefore, the weight loss results need to be reduced. The electrochemical behavior correction factor α = α4 is taken as the minimum value and α4 > 0. That is, α1>α2>α3>α4>0, preferably α1=1.5, α2=1.2, and α4=0.7.

[0011] The local corrosion severity correction factor β is obtained based on the three-dimensional surface morphology measurement results of the weightless sample after rust removal. Define pitting factor PF=d max / d avg ;d avg =△m / (ρ×A)×10 4 ; In the formula: d max The maximum pitting depth is expressed in μm; d avg The average corrosion depth is expressed in μm; Δm is the mass loss in g; and ρ is the steel density in g / cm³. 3 A represents the exposed area, in cm². 2 ; Average corrosion depth d avg The mass loss obtained by the weight loss method is the result of homogenizing the mass loss of the entire exposed area. However, in CO2 multiphase environments, obvious local pitting corrosion usually exists in the semi-immersed zone and the gas phase zone, with a maximum pitting depth d. max It may be much higher than the average corrosion depth d avg Therefore, if only the average corrosion rate d is used... avg When assessing material failure risk, the danger of localized penetration failure is easily underestimated. The purpose of introducing a localized corrosion severity correction factor β in this method is to correct for the average corrosion depth d obtained using the weight loss method. avg The smoothing effect underestimates the risk of localized pitting corrosion.

[0012] The rules for determining the value of the localized corrosion severity correction factor β are as follows: When the pitting corrosion factor PF < the first threshold, the corrosion is uniform overall, and the local risk is negligible. The local corrosion severity correction factor β = β1 = 1.0, which is related to the average corrosion depth d. avg No need for significant magnification; When the first threshold ≤ pitting factor PF ≤ second threshold, obvious localized corrosion has occurred but is not yet extremely severe. A moderate correction factor is used, and the localized corrosion severity correction factor β = β2 > β1 is taken for the average corrosion depth d. avg Appropriately enlarge it; When the pitting factor PF > the second threshold, the maximum pitting depth d max Far exceeding the average corrosion depth d avg Local penetration has become the dominant failure mechanism, so the largest correction factor must be used. The local corrosion severity correction factor β=β3>β2>β1 should be taken to fully reflect the actual engineering risks. Preferably, the first threshold is 2 and the second threshold is 5; Preferably, when the pitting factor PF < 2, β = β1 = 1.0; when 2 ≤ pitting factor PF ≤ 5, β = β2 = 1.3; when the pitting factor PF > 5, β = β3 = 1.8.

[0013] The selection of the first and second thresholds is based on the statistical results of a large number of experimental data and field failure cases conducted by the inventors in CO2 multiphase corrosion environments: when PF < 2, the corrosion morphology is mainly uniform thinning, and the local risk can be ignored; when 2 ≤ pitting factor PF ≤ 5, the pits develop significantly but have not yet formed penetrating damage; when PF > 5, the risk of local penetration increases sharply. The statistics of actual failure cases show that about 80% of CO2 corrosion perforation accidents occur in this range. Therefore, 2 and 5 are set as the grading thresholds to distinguish the severity of local corrosion, respectively.

[0014] The corrosion product film correction factor γ was obtained based on scanning electron microscopy and X-ray diffraction analysis. The compactness parameter Cd of the corrosion product film was obtained by scanning electron microscopy and used to characterize the structural integrity of the corrosion product film; the degree of FeCO3 formation parameter F in the corrosion product film was obtained by X-ray diffraction analysis. The corrosion product film correction factor γ = 1.0 - 0.5 × Cd × F; When a highly dense corrosion product film and a stable FeCO3 phase simultaneously form on the surface of the weightless sample, the corrosion product film can significantly inhibit the diffusion of the corrosive medium and the interfacial charge transfer, thereby significantly reducing the corrosion rate. Therefore, 0.5 is taken as the maximum reduction factor to characterize the significant inhibitory effect of the stable corrosion product film on the corrosion process.

[0015] The scoring criteria for the density parameter Cd of the corrosion product film are as follows: If no cracks or pores are observed in any of the scanning electron microscope fields of view, then the corrosion product film is continuous and intact, and the value range of the corrosion product film density parameter Cd is 0.8≤Cd≤1; preferably, Cd=1.0. If a crack with a width of less than 1 μm and a length of less than 10 μm or a micropore with a diameter of less than 0.5 μm appears in any field of view but does not affect the overall continuity, the value range of the corrosion product film compactness parameter Cd is 0.5 ≤ Cd < 0.8; preferably, Cd = 0.6. If a crack with a width greater than 1 μm or a porous structure with a porosity greater than 30% appears in any field of view, the value range of the corrosion product film compactness parameter Cd is 0 < Cd < 0.5; preferably, Cd = 0.2.

[0016] The FeCO3 formation degree parameter F in the corrosion product film was obtained based on X-ray diffraction test results. XRD analysis was performed on the weightless sample with the corrosion product film covering its surface. ①If the maximum peak intensity of the FeCO3 characteristic peak is greater than or equal to 50% of the intensity of the strongest diffraction peak of the weightless sample, then F = F1; ②If 20% of the intensity of the strongest diffraction peak of the weightless sample is less than 50% of the maximum peak intensity of the characteristic peak of FeCO3, then F = F2. ③If the maximum peak intensity of the FeCO3 characteristic peak is less than 20% of the strongest diffraction peak intensity of the weightless sample, then F = F3; And it satisfies 1 > F1 > F2 > F3 > 0; preferably, F1 = 1.0, F2 = 0.6, F3 = 0.2.

[0017] Furthermore, considering the varying sensitivities of different phase regions to localized corrosion and electrochemical fluctuations, a phase region weighting coefficient θ is introduced. This coefficient includes weighting coefficients for the fully immersed region, the semi-immersed region, and the gas phase. In the semi-immersed region, due to the thin liquid film at the gas-liquid interface, localized corrosion and CO2 concentration are more pronounced, resulting in a higher actual corrosion risk compared to the weight loss method. In the gas phase, due to the unstable thickness of the condensate film, the weight loss method has a relatively large measurement error; therefore, a higher weighting coefficient is used for conservative correction. Thus, the weighting coefficient for the fully immersed region < the weighting coefficient for the semi-immersed region < the weighting coefficient for the gas phase, with the weighting coefficient for the fully immersed region = 1.00 and the weighting coefficient for the gas phase ≤ 1.15. The final corrected corrosion rate V... 修正 =V×θ.

[0018] Preferably, the weighting coefficient θ of the semi-immersion zone 半 =1.10; Gas phase weighting coefficient θ 气 =1.15.

[0019] The specific processes for the three different phase regions of the simulated gas phase region, the semi-immersion region, and the fully immersion region are as follows: In the simulated gas phase region, the electrochemical sample and the weightless sample are not in contact with the simulated formation aqueous solution at all; in the simulated semi-immersion region, 50% of the electrochemical sample and the weightless sample are immersed in the simulated formation aqueous solution; in the simulated fully immersion region, the electrochemical sample and the weightless sample are completely immersed in the simulated formation aqueous solution.

[0020] The preset temperature gradient for the corrosion simulation test is 25~150 ℃, and the preset experimental period is 24~720 h.

[0021] The simulated formation aqueous solution is a chloride-containing mineralized aqueous solution with a total mineralization of 3000~150000 mg / L, Cl - The concentration is 3000~50000 mg / L, and CO2 is continuously introduced to keep the simulated formation aqueous solution saturated.

[0022] The technical effects of this invention are as follows: This invention features three coexisting regions. The initial average corrosion rate V0 of each phase region is obtained by weight loss testing. Innovatively, the initial average corrosion rate V0 is corrected by electrochemical behavior correction factor α, local corrosion severity correction factor β, and corrosion product film correction factor γ, thereby achieving a comprehensive determination of corrosion rate and corrosion mechanism in a multiphase environment. Attached Figure Description

[0023] Figure 1 3D laser scanning images of the weight loss samples after rust removal at 40℃-168h, 60℃-168h, and 60℃-336h.

[0024] Figure 2 The polarization curve is shown after 168 hours at 40℃.

[0025] Figure 3 The impedance curve is shown after 168 hours at 40℃.

[0026] Figure 4 The figure shows the polarization curves after 168 hours at 60℃.

[0027] Figure 5 The impedance curve is shown after 168 hours at 60℃. Detailed Implementation

[0028] A method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment is described in detail below.

[0029] Step 1: Sample preparation: N80 steel (19mm × 15mm × 3mm) was polished sequentially with 1000-grit sandpaper to remove the surface oxide layer. It was then immersed in acetone for ultrasonic degreasing for 10 minutes, followed by dehydration in anhydrous ethanol for 5 minutes. After drying with cold air, it was weighed using an analytical balance with an accuracy of 0.1 mg and the initial mass was recorded. A portion of the sample was sealed and cured with epoxy resin AB glue (mass ratio 3:1), exposing 2.6cm. 2 The working area is left to stand at room temperature for 24 hours until fully cured, and used as an electrochemical sample for subsequent electrochemical testing; the remaining plates are used as weight loss samples for weight loss testing and morphology and product analysis; two parallel weight loss samples are provided for each phase region.

[0030] Step 2: Prepare a simulated formation aqueous solution. Taking a 1L volumetric flask as an example: NaHCO3 requires 126.97mg, Na2SO4 requires 1308.91mg, MgCl2 requires 506.55mg, NaCl requires 37560.81mg, and CaCl2 requires 3512.84mg. After stirring and dissolving, high-purity nitrogen gas is introduced for 10 minutes to remove dissolved oxygen, and then CO2 (99.9%) is introduced for 30 minutes until saturation is achieved, thus preparing a simulated formation aqueous solution. Take a 500mL wide-mouth bottle and fill it with 250mL of the above simulated formation aqueous solution. Based on the relative positions of the electrochemical and weight-loss samples with the simulated formation aqueous solution, three different phase regions were simulated: a gas phase region, a semi-immersed region, and a fully immersed region. In the simulated gas phase region, the electrochemical and weight-loss samples were not in contact with the simulated formation aqueous solution at all, and were located approximately 2 cm above the surface of the simulated formation aqueous solution. In the simulated semi-immersed region, 50% of the electrochemical and weight-loss samples were immersed in the simulated formation aqueous solution. In the simulated fully immersed region, both the electrochemical and weight-loss samples were completely immersed in the simulated formation aqueous solution. Electrochemical and weight-loss samples were simultaneously placed in each phase region.

[0031] Step 3: Conduct corrosion simulation tests: Set the temperature of the constant temperature chamber to 40℃, 60℃, and 70℃, and take out electrochemical samples and weight loss samples at each temperature for 72h, 168h, and 336h for testing. The removed electrochemical sample was rinsed with deionized water and transferred to a three-electrode electrolytic cell. The electrolyte was a simulated formation aqueous solution. The three electrodes were as follows: the working electrode was the electrochemical sample before rust removal, the reference electrode was a saturated calomel electrode (SCE), and the auxiliary electrode was a platinum electrode. The open-circuit potential was monitored until it stabilized, and then electrochemical impedance spectroscopy was performed at a frequency range of 10 Hz. 5 ~10 -2 The perturbation voltage was 10mV at Hz; then, potentiodynamic polarization testing was performed, with a scan range of -0.4V to +0.6V relative open circuit potential and a scan rate of 1mV / s. The corrosion current density I was calculated using the Tafel extrapolation method. corr The annual corrosion rate (mm / year) was calculated; the EIS data were fitted using an equivalent circuit to extract the final charge transfer resistance R. ct终 ; The removed weightless samples were treated with an acidic rust remover, which was prepared by mixing 500 mL of concentrated hydrochloric acid, 500 mL of deionized water, and 3.5 g of hexamethylenetetramine. The weightless samples were immersed in the rust remover for approximately 1 minute, then rinsed with deionized water, dehydrated with anhydrous ethanol, dried with cold air, and weighed using an analytical balance with an accuracy of 0.1 mg. The initial average corrosion rate V0 was calculated, and the average value of two parallel weightless samples was taken. The weightless sample before rust removal (336 hours prior) was examined using scanning electron microscopy to obtain the morphology of the corrosion products. Energy dispersive spectroscopy (EDS) was performed to determine the elemental composition, and X-ray diffraction (XRD) was used to identify the phase composition. The same weightless sample after rust removal was then scanned using 3D laser confocal microscopy to obtain its three-dimensional morphology and the depth characteristics of the corrosion pits.

[0032] Step 4: Calculate the electrochemical behavior correction factor α, the local corrosion severity correction factor β, and the corrosion product film correction factor γ.

[0033] (1) Calculate the electrochemical behavior correction factor α: I corr ≥5×10 -5 A / cm 2 And 0.45 ≤ ΔR ct When <1, the electrochemical behavior correction factor α = α1 = 1.5; 1×10 -5 A / cm 2 ≤I corr <5×10 -5 A / cm 2 And 0.25 ≤ ΔR ct When <0.45, the electrochemical behavior correction factor α=α2=1.2; I corr <1×10 -5 A / cm 2 And 0 < ΔR ct When <0.25, the electrochemical behavior correction factor α=α3=1.0; Otherwise, the electrochemical behavior correction factor α = α4 = 0.7.

[0034] (2) Calculate the local corrosion severity correction factor β: Define pitting factor PF=d max / d avg ;d avg =△m / (ρ×A)×10 4 ; When the pitting corrosion factor PF < the first threshold, the corrosion is uniform overall, and the local risk is negligible. The local corrosion severity correction factor β = β1 = 1.0, which is related to the average corrosion depth d. avg No need for significant magnification; When the first threshold ≤ pitting factor PF ≤ second threshold, obvious localized corrosion has occurred but is not yet extremely severe. A moderate correction factor is used, and the localized corrosion severity correction factor β = β2 > β1 is taken for the average corrosion depth d. avg Appropriately enlarge it; When the pitting factor PF > the second threshold, the maximum pitting depth d max Far exceeding the average corrosion depth davg Local penetration has become the dominant failure mechanism, so the largest correction factor must be used. The local corrosion severity correction factor β=β3>β2>β1 should be taken to fully reflect the actual engineering risks. Preferably, the first threshold is 2 and the second threshold is 5; Preferably, when the pitting factor PF < 2, β = β1 = 1.0; when 2 ≤ pitting factor PF ≤ 5, β = β2 = 1.3; when the pitting factor PF > 5, β = β3 = 1.8.

[0035] (3) Calculate the corrosion product film correction factor γ: If no cracks or pores are observed in any of the scanning electron microscope fields of view, the corrosion product film is continuous and intact, and Cd = 1.0; if a crack with a width of less than 1 μm and a length of less than 10 μm or a micropore with a diameter of less than 0.5 μm appears in any field of view but does not affect the overall continuity, Cd = 0.6; if a crack with a width of more than 1 μm or a porous structure with a porosity of more than 30% appears in any field of view, Cd = 0.2. XRD analysis was performed on the weight loss sample with a corrosion product film on its surface: ①If the maximum peak intensity of the FeCO3 characteristic peak is greater than or equal to 50% of the intensity of the strongest diffraction peak of the weightless sample, then F = F1 = 1.0; ②If 20% of the intensity of the strongest diffraction peak of the weightless sample is less than 50% of the maximum peak intensity of the characteristic peak of FeCO3, then F = F2 = 0.6. ③If the maximum peak intensity of the FeCO3 characteristic peak is less than 20% of the strongest diffraction peak intensity of the weightless sample, then F = F3 = 0.2; The corrosion product film correction factor γ = 1.0 - 0.5 × Cd × F.

[0036] Step 5: Calculate the corrosion rate V = V0 × α × β × γ.

[0037] Furthermore, it also includes step 6: introducing the phase region weighting coefficient θ, and taking the full immersion region weighting coefficient θ. 全 =1.00, semi-immersion zone weighting coefficient θ 半 =1.10, weighting coefficient θ of the gas phase region 气 =1.15; then calculate the corrected corrosion rate V. 修正 =V×θ.

[0038] Specific application case 1: The test material is N80 oil casing steel, and the working area of ​​the electrochemical sample is 2.6 cm². 2 The dimensions of the weightless sample were 19 mm × 15 mm × 3 mm, and the exposed area A was 5.7 cm². 2The test medium was a saturated CO2-simulated formation aqueous solution. Electrochemical and weight loss samples were arranged in the fully immersed, semi-immersed, and gas phase zones, respectively. The corrosion simulation test was conducted at a constant temperature of 40℃ for 7 days. After the corrosion simulation test, weight loss, electrochemical, scanning electron microscopy (SEM), X-ray diffraction (XRD), and 3D laser scanning tests were performed. The initial charge transfer resistance R of the electrochemical sample before corrosion was measured. ct初 =1844Ω. 3D laser scan image as shown. Figure 1 The polarization curves of the electrochemical test are as follows: Figure 2 As shown in Figure 3, the impedance curve is also shown.

[0039] In the fully immersed zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.2326 mm / a. Electrochemical test results ( Figure 2 , 3 As shown in the figure, the corrosion current density I corr It is 6.86 μA / cm 2 The final charge transfer resistance is R. ct终 The resistance is 964.4 Ω, and the change in charge transfer resistance ΔR ct It is 0.47, but I corr <5×10 -5 A / cm 2 The condition for α1 is not met. Therefore, α = α4 = 0.7. (3D laser scan image) Figure 1 The pitting corrosion factor PF < 2 indicates that localized corrosion is not significant, therefore β = β1 = 1.0; SEM observation shows that the corrosion product film is intact and dense, therefore Cd = 1.0; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is taken as 0.2, and the corrosion product film correction factor γ = 0.90 is calculated. The full immersion zone weighting coefficient θ... 全 =1.00, calculate the corrosion rate V 修正 =0.1465 mm / a.

[0040] In the semi-immersion zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.4488 mm / a. Electrochemical test results ( Figure 2 , 3 As shown in the figure, the corrosion current density I corr It is 11.14 μA / cm 2 The final charge transfer resistance is R. ct终 The resistance is 1779Ω, and the change in charge transfer resistance is ΔR. ct It is 0.035. Because ΔR ct <0.25, the condition for α2 is not met. Therefore, α = α4 = 0.7. 3D laser scan image ( Figure 1The result shows 2≤PF≤5, indicating significant localized corrosion; therefore, β=β2=1.3. SEM observation revealed localized cracks in the corrosion product film with a width less than 1μm and a length less than 10μm, thus Cd=0.6. XRD data showed that the FeCO3 formation degree parameter F in the corrosion product film was set to 0.2, and the corrosion product film correction factor γ=0.94 was calculated. The weighting coefficient θ of the semi-immersion zone... 半 =1.10, calculate the corrected corrosion rate V 修正 =0.4223 mm / a.

[0041] In the gas phase, the initial average corrosion rate V0, measured by the weight loss method, was 1.2675 mm / a. Electrochemical test results ( Figure 2 , 3 As shown in the figure, the corrosion current density I corr 16.29 μA / cm 2 Final state charge transfer resistance R ct终 The resistance is 289.1 Ω, and the change in charge transfer resistance ΔR ct It is 0.47, but I corr <5×10 -5 A / cm 2 The condition for α1 is not met. Therefore, α = α4 = 0.7. (3D laser scan image) Figure 1 The result shows PF > 5, indicating severe localized corrosion; therefore, β = β3 = 1.8. SEM observation revealed a porous corrosion product film, thus Cd = 0.2. XRD results show that the FeCO3 formation degree parameter F in the corrosion product film is set to 0.2, and the calculated corrosion product film correction factor γ = 0.98. The weighting coefficient θ for the vapor phase region... 气 =1.15, calculate the corrected corrosion rate V 修正 =1.800 mm / a.

[0042] The results show that the corrected corrosion rate V in the vapor phase region at 40℃ 修正 The value is the highest, significantly higher than that of the fully immersed and semi-immersed areas. Therefore, this method can effectively identify the actual failure risk caused by localized corrosion.

[0043] In specific application case 2, the test conditions are the same as in specific application case 1, except that the test temperature is 60℃.

[0044] In the fully immersed zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.2085 mm / a. Electrochemical test results ( Figure 4 , 5 As shown in the figure, the corrosion current density I corr It is 4.29 μA / cm 2 Final state charge transfer resistance Rct终 The resistance is 889.7 Ω, and the change in charge transfer resistance ΔR ct It is 0.52, but I corr <5×10 -5 A / cm 2 The condition for α1 is not met. Therefore, α = α4 = 0.7. (3D laser scan image) Figure 1 The pitting corrosion factor PF < 2, therefore β = 1.0; SEM observation revealed that the corrosion product film was intact and dense, therefore Cd = 1.0; XRD data showed that the FeCO3 formation degree parameter F in the corrosion product film was taken as 0.2, and the corrosion product film correction factor γ = 0.90 was calculated. The full immersion zone weighting coefficient θ... 全 =1.00, calculate the corrosion rate V 修正 =0.1314 mm / a.

[0045] In the semi-immersion zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.5544 mm / a. Electrochemical test results ( Figure 4 , 5 As shown in the figure, the corrosion current density I corr It is 9.43 μA / cm 2 Final state charge transfer resistance R ct终 The change in charge transfer resistance is ΔR, which is 1321 Ω. ct It is 0.28, but I corr <1×10 -5 A / cm 2 The condition for α2 is not met, therefore α = α4 = 0.7. (3D laser scan image) Figure 1 The results show that 2 ≤ PF ≤ 5, therefore β = 1.3. SEM observation revealed localized damage to the corrosion product film, with Cd = 0.6; XRD data showed that the FeCO3 formation degree parameter F in the corrosion product film was taken as 0.2, and the corrosion product film correction factor γ = 0.94 was calculated; the semi-immersion zone weighting coefficient θ 半 =1.10, calculate the corrected corrosion rate V 修正 =0.5216 mm / a.

[0046] In the gas phase, the initial average corrosion rate V0, measured by the weight loss method, was 3.1247 mm / a. Electrochemical test results ( Figure 4 , 5 As shown in the figure, the corrosion current density I corr 39.43 μA / cm 2 Final state charge transfer resistance R ct终 The resistance is 398.1 Ω, and the change in charge transfer resistance ΔR ct It is 0.78, but I corr <5×10-5 A / cm 2 The condition for α1 is not met. Therefore, α = α4 = 0.7. (3D laser scan image) Figure 1 The results show PF > 5, therefore β = 1.8. SEM observation revealed a porous corrosion product film, therefore Cd = 0.2; XRD data showed that the FeCO3 formation degree parameter F in the corrosion product film was set to 0.2, resulting in a corrosion product film correction factor γ = 0.98; the gas phase weighting coefficient θ... 气 =1.15, calculate the corrected corrosion rate V 修正 =4.4371 mm / a.

[0047] The results show that the corrosion risk in the gas phase region increases further at 60℃, and the evaluation method of this invention can more accurately reflect the corrosion differences between different phase regions.

[0048] In specific application case 3, the test conditions are the same as in specific application case 1, except that the test temperature is 70℃ and the corrosion period is 3 days.

[0049] In the fully immersed zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.6408 mm / a. Electrochemical testing results showed a corrosion current density I... corr It is 12.86 μA / cm 2 Final state charge transfer resistance R ct终 The change in charge transfer resistance is ΔR, which is 1212 Ω. ct The value is 0.34, satisfying the condition for α2. Therefore, α = α2 = 1.2. The 3D laser scanning image shows that the pitting factor PF < 2, therefore β = 1.0; SEM observation reveals localized formation of the corrosion product film, therefore Cd = 0.6; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the corrosion product film correction factor γ = 0.82 is calculated. The full immersion zone weighting coefficient θ... 全 =1.00, calculate the corrosion rate V 修正 =0.6305 mm / a.

[0050] In the semi-immersion zone, the initial average corrosion rate V0, measured by the weight loss method, was 1.3056 mm / a. Electrochemical testing results showed a corrosion current density I... corr It is 9.43 μA / cm 2 Final state charge transfer resistance R ct终 The resistance is 592.6 Ω, and the change in charge transfer resistance ΔR ct It is 0.68, but I corr <5×10 -5 A / cm 2The condition for α1 is not met. Therefore, α = α4 = 0.7. The 3D laser scan image shows 2 ≤ PF ≤ 5, therefore β = 1.3. SEM observation revealed local cracking of the corrosion product film, Cd = 0.6; XRD data showed that the FeCO3 formation degree parameter F in the corrosion product film was 0.6, and the corrosion product film correction factor γ = 0.82 was calculated. The semi-immersion zone weighting coefficient θ... 半 =1.10, calculate the corrected corrosion rate V 修正 =1.072mm / a.

[0051] In the gas phase, the initial average corrosion rate V0, measured by the weight loss method, was 2.1707 mm / a. Electrochemical testing results showed a corrosion current density I... corr It is 86.57 μA / cm 2 Greater than 50 μA / cm 2 Final state charge transfer resistance R ct终 The resistance is 440.3 Ω, and the change in charge transfer resistance ΔR ct The value is 0.76, satisfying the condition for α1, therefore α = α1 = 1.5. The 3D laser scanning image shows PF > 5, therefore β = 1.8. SEM observation reveals that the corrosion product film is loose and porous, therefore Cd = 0.2; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the calculated corrosion product film correction factor γ = 0.94. The weighting coefficient θ for the vapor phase region... 气 =1.15, calculate the corrected corrosion rate V 修正 =6.3290 mm / a.

[0052] The results show that the corrosion activity is high in the early stage of corrosion at 70℃, and the present invention can accurately identify the early high-risk corrosion area.

[0053] In specific application case 4, the test conditions are the same as in specific application case 3, except that the corrosion period is 7 days.

[0054] In the fully immersed zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.2454 mm / a. Electrochemical testing results showed that the corrosion current density I... corr It is 127.71 μA / cm 2 Final state charge transfer resistance R ct终 The resistance is 939.5 Ω, and the change in charge transfer resistance ΔR ctThe value is 0.49, satisfying the condition for α1, therefore α = α1 = 1.5. The 3D laser scanning image shows PF > 5, therefore β = 1.8. SEM observation reveals localized formation of the corrosion product film, therefore Cd = 0.6; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the corrosion product film correction factor γ = 0.82 is calculated, with the full immersion area weighting coefficient θ... 全 =1.00, calculate the corrosion rate V 修正 =0.5438 mm / a.

[0055] In the semi-immersion zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.7260 mm / a. Electrochemical test results showed that the corrosion current density I... corr 102.85 μA / cm 2 Final state charge transfer resistance R ct终 The change in charge transfer resistance is ΔR, which is 983.3 Ω. ct The value is 0.47, satisfying the condition for α1, therefore α = α1 = 1.5. The 3D laser scan image shows PF > 5, therefore β = 1.8. SEM observation reveals localized cracking of the corrosion product film, therefore Cd = 0.6; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the calculated corrosion product film correction factor γ = 0.82. The semi-immersion zone weighting coefficient θ... 半 =1.10, calculate the corrected corrosion rate V 修正 =1.7697 mm / a.

[0056] In the gas phase, the initial average corrosion rate V0, measured by the weight loss method, was 0.7938 mm / a. Electrochemical testing results showed that the corrosion current density I... corr It is 973.67 μA / cm 2 Final state charge transfer resistance R ct终 The change in charge transfer resistance is ΔR, which is 995 Ω. ct The value is 0.46, satisfying the condition for α1, therefore α = α1 = 1.5. The 3D laser scanning image shows PF > 5, therefore β = 1.8. SEM observation reveals that the corrosion product film is loose and porous, therefore Cd = 0.2; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the calculated corrosion product film correction factor γ = 0.94. The weighting coefficient θ for the vapor phase region... 气 =1.15, calculate the corrected corrosion rate V 修正 =2.3210 mm / a.

[0057] The results show that after 7 days of corrosion at 70℃, all phase regions exhibited strong corrosion activity, and the evaluation model of this invention can effectively reflect the risk of local corrosion.

[0058] In specific application case 5, the test conditions are the same as in specific application case 3, except that the corrosion period is 14 days.

[0059] In the fully immersed zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.2424 mm / a. Electrochemical test results showed that the corrosion current density I... corr 46.28 μA / cm 2 Final state charge transfer resistance R ct终 The change in charge transfer resistance is ΔR, which is 850.5 Ω. ct It is 0.54, but I corr <5×10 -5 A / cm 2 The condition for α1 is not met. Therefore, α = α4 = 0.7. The 3D laser scan image shows PF < 2, therefore β = 1.0. SEM observation reveals local cracking of the corrosion product film, therefore Cd = 0.6; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the corrosion product film correction factor γ = 0.82 is calculated. The full immersion zone weighting coefficient θ 全 =1.00, calculate the corrosion rate V 修正 =0.1391mm / a.

[0060] In the semi-immersion zone, the initial average corrosion rate V0, measured by the weight loss method, was 0.6814 mm / a. Electrochemical test results showed that the corrosion current density I... corr 168.85 μA / cm 2 Final state charge transfer resistance R ct终 The resistance is 726.6 Ω, and the change in charge transfer resistance ΔR ct The value is 0.61, satisfying the condition for α1, therefore α = α1 = 1.5. The 3D laser scan image shows PF > 5, therefore β = 1.8. SEM observation reveals localized cracking of the corrosion product film, therefore Cd = 0.6; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the calculated corrosion product film correction factor γ = 0.82. The semi-immersion zone weighting coefficient θ... 半 =1.10, calculate the corrected corrosion rate V 修正 =1.6602 mm / a.

[0061] In the gas phase, the initial average corrosion rate V0, measured by the weight loss method, was 1.3178 mm / a. Electrochemical testing results showed that the corrosion current density I... corr 392.55 μA / cm 2 Final state charge transfer resistance R ct终 The resistance is 576.8 Ω, and the change in charge transfer resistance ΔR ctThe value is 0.69, satisfying the condition for α1, therefore α = α1 = 1.5. The 3D laser scanning image shows PF > 5, therefore β = 1.8. SEM observation reveals that the corrosion product film is loose and porous, with Cd = 0.2; XRD data shows that the FeCO3 formation degree parameter F in the corrosion product film is 0.6, and the calculated corrosion product film correction factor γ = 0.94. The weighting coefficient θ for the vapor phase region... 气 =1.15, calculate the corrected corrosion rate V 修正 =3.8520 mm / a.

[0062] The results show that with prolonged corrosion time, a protective FeCO3 corrosion product film gradually forms in some areas, but the semi-immersed zone and the gas phase zone still maintain a high corrosion risk. This invention can simultaneously reflect the protective effect of the corrosion product film and the risk of localized corrosion failure, achieving a comprehensive evaluation of the multiphase CO2 corrosion environment.

[0063] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural modifications made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment, characterized in that, The method is as follows: Electrochemical and weight loss samples of steel were placed in the same container filled with simulated formation aqueous solution. Based on the relative positions of the electrochemical and weight loss samples with the simulated formation aqueous solution, three different phase regions—gas phase, semi-immersion zone, and fully immersion zone—were simulated, and corrosion simulation tests were carried out. Electrochemical and weightless samples were taken out at different time points in the corrosion simulation test for testing. Based on the electrochemical test results, the electrochemical behavior correction factor α was obtained, the local corrosion severity correction factor β was obtained based on the three-dimensional surface morphology test results, and the corrosion product film correction factor γ was obtained based on the corrosion product film characterization results. The corrosion rate V is calculated by multiplying the initial average corrosion rate V0 by α, β, and γ.

2. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 1, characterized in that, Also included is a phase region weight factor θ, which modifies the corrosion rate V 修正 = V x θ; the phase region weight factor θ includes a full immersion region weight factor, a semi-immersion region weight factor, and a gas phase region weight factor; wherein the full immersion region weight factor < the semi-immersion region weight factor < the gas phase region weight factor, and the full immersion region weight factor = 1.00, and the gas phase region weight factor ≤ 1.

15.

3. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 1 or 2, characterized in that, The electrochemical behavior correction factor a is based on the corrosion current density I corr and the charge transfer resistance variation AR ct is obtained; The rules for determining the value of the electrochemical behavior correction factor α are as follows: ①I corr ≥ 5×10 -5 A / cm 2 And 0.45 ≤ ΔR ct When <1, the electrochemical behavior correction factor α = α1; ②1×10 -5 A / cm 2 ≤ I corr <5×10 -5 A / cm 2 And 0.25≤ΔR ct When <0.45, the electrochemical behavior correction factor α=α2; ③I corr <1×10 -5 A / cm 2 And 0 < ΔR ct When <0.25, the electrochemical behavior correction factor α=α3=1; ④ Otherwise, the electrochemical behavior correction factor α = α4; And it satisfies α1>α2>α3>α4>0.

4. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 1 or 2, characterized in that, The localized corrosion severity correction factor β is obtained based on the three-dimensional surface morphology measurement results of the weightless sample after rust removal; Define pitting factor PF=d max / d avg ;d avg =△m / (ρ×A)×10 4 ; In the formula: d max The maximum pitting depth is expressed in μm; d avg The average corrosion depth is expressed in μm; Δm is the mass loss in g; and ρ is the steel density in g / cm³. 3 A represents the exposed area, in cm². 2 ; The rules for determining the value of the localized corrosion severity correction factor β are as follows: ① When the pitting corrosion factor PF < the first threshold, the local corrosion severity correction factor β = β1; ② When the first threshold ≤ pitting factor PF ≤ the second threshold, the local corrosion severity correction factor β = β2; ③ When the pitting corrosion factor PF > the second threshold, the local corrosion severity correction factor β = β3; And it satisfies β1<β2<β3.

5. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 1 or 2, characterized in that, The corrosion product film correction factor γ was obtained based on scanning electron microscopy and X-ray diffraction analysis. The compactness parameter Cd of the corrosion product film was obtained by scanning electron microscopy; the degree of FeCO3 formation in the corrosion product film, F, was obtained by X-ray diffraction analysis. The corrosion product film correction factor γ = 1.0 - 0.5 × Cd × F.

6. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 5, characterized in that, The scoring criteria for the density parameter Cd of the corrosion product film are as follows: ① If no cracks or holes are seen in any of the scanning electron microscope fields of view, then the corrosion product film is continuous and intact, and the value range of the corrosion product film density parameter Cd is 0.8≤Cd≤1. ② If a crack with a width of less than 1 μm and a length of less than 10 μm or a micropore with a diameter of less than 0.5 μm appears in any field of view but does not affect the overall continuity, then the value range of the compactness parameter Cd of the corrosion product film is 0.5≤Cd<0.

8. ③ If a crack with a width greater than 1 μm or a porous structure with a porosity greater than 30% appears in any field of view, the value range of the compactness parameter Cd of the corrosion product film is 0 < Cd < 0.

5.

7. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 5, characterized in that, The FeCO3 formation degree parameter F in the corrosion product film was obtained from the X-ray diffraction test results. XRD analysis was performed on the weightless sample with the corrosion product film covering its surface: ①If the maximum peak intensity of the FeCO3 characteristic peak is greater than or equal to 50% of the intensity of the strongest diffraction peak of the weightless sample, then F = F1; ②If 20% of the intensity of the strongest diffraction peak of the weightless sample is less than 50% of the maximum peak intensity of the characteristic peak of FeCO3, then F = F2. ③If the maximum peak intensity of the FeCO3 characteristic peak is less than 20% of the strongest diffraction peak intensity of the weightless sample, then F = F3; And it satisfies 1 > F1 > F2 > F3 > 0.

8. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 1, characterized in that, The specific processes for the three different phase regions of the simulated gas phase region, the semi-immersion region, and the fully immersion region are as follows: In the simulated gas phase region, the electrochemical sample and the weightless sample are not in contact with the simulated formation aqueous solution at all; in the simulated semi-immersion region, 50% of the electrochemical sample and the weightless sample are immersed in the simulated formation aqueous solution; in the simulated fully immersion region, the electrochemical sample and the weightless sample are completely immersed in the simulated formation aqueous solution.

9. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 1, characterized in that, The preset temperature gradient for the corrosion simulation test is 25~150 ℃, and the preset experimental period is 24~720 h.

10. The method for testing and evaluating steel in a carbon dioxide-containing multiphase corrosion environment according to claim 1, characterized in that, The simulated formation aqueous solution is a chloride-containing mineralized aqueous solution with a total mineralization of 3000~150000 mg / L, Cl - The concentration is 3000~50000 mg / L, and CO2 is continuously introduced to keep the simulated formation aqueous solution saturated.

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