Method for constructing pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model and use of the same

Abstract

To provide a method for constructing a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model, and use of the same.SOLUTION: Using a cathodic hydrogen charging method and a wet hydrogen sulfide environment method, hydrogen is charged into sample materials under different reaction conditions and plural first hydrogen charge samples and second hydrogen charge samples are acquired. After that, the contents of hydrogen in the first and second hydrogen charge samples are determined. Variables in two methods based on the obtained hydrogen contents are curve-fitted and a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model is obtained on the basis of the result of fitting.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the field of corrosion electrochemistry, and more particularly to a method for constructing a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model and its use. [Background technology]

[0002] As important non-renewable energy, oil and natural gas are important for the development and use of people's lives. The advantages of pipeline transportation, such as safety, efficiency, and convenience, make it the main type of long-distance energy transportation. As the main carrier of pipeline transportation, the safety evaluation of pipeline steel has become a hot topic. H2S is a common gas in the oil and gas transportation process. Although it is generally not strongly corrosive, it is easy to dissolve in water to form an acidic solution, which will cause corrosion of the pipeline. Corrosion and protection in wet hydrogen sulfide environments are considered to be safety factors that must be considered for petrochemical industry equipment.

[0003] The wet hydrogen sulfide environment defined in the NACE MR0175-2015 "Oilfield Machinery Sulfide Stress Cracking Resistant Metallic Materials" standard by the American Society of Corrosion Engineers is as follows: (1) Acid gas system: gas total pressure ≥ 0.4 MPa, H2S partial pressure ≥ 0.0003 MPa; (2) Acid multiphase system: when there is a two-phase or three-phase medium (oil, water, gas) in the treated crude oil, the conditions are: gas phase total pressure ≥ 1.8 MPa and H2S partial pressure ≥ 0.0003 MPa; gas phase pressure ≤ 1.8 MPa and H2S partial pressure ≥ 0.07 MPa; or gas phase H2S content exceeds 15%. At present, the experimental method for evaluating hydrogen damage is to perform the test under the simulated wet hydrogen sulfide environment recommended in the standard, that is, immerse the sample in NACE-A solution (5% NaCl and 0.5% CH3COOH aqueous solution) at 24±3℃, pass H2S gas with a partial pressure of 100KPa, charge with hydrogen for 4 days, and perform the test under this environment. However, the wet hydrogen sulfide environments in the actual use of pipeline steel are different, and the procedure of the above test method is complicated, the operation requirements are high, and the H2S gas used is extremely toxic, which poses great risks to the safety of the tester and the environmental safety, and is inconvenient for research. Summary of the Invention

[0004] In view of the deficiencies of the prior art, the objective of the present invention is to provide a method for constructing an equivalent wet hydrogen sulfide environment hydrogen charging model for pipeline steel and its use, thereby solving the problems of complicated steps, high operational requirements and low safety in the conventional hydrogen damage evaluation method for pipeline steel.

[0005] In order to achieve the above object, in one aspect of the present invention, a method for constructing an equivalent wet hydrogen sulfide environment hydrogen charging model of a pipeline steel is provided, the method including the following steps: S1: Each test sample is charged with hydrogen under different reaction conditions using the cathodic hydrogen charging method and the wet hydrogen sulfide environment method, respectively, to obtain a plurality of first hydrogen-charged samples and a second hydrogen-charged sample. S2: Measure the hydrogen content of each of the first hydrogen-charged sample and the second hydrogen-charged sample. S3: Curve fitting the variables in the two methods based on the hydrogen content obtained in step S2, and obtain a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model based on the fitting results.

[0006] Preferably, in step S1, the method of obtaining the test samples is to take multiple samples from pipeline steel, ensure that the thickness direction of each sample is parallel to the diameter direction of the pipeline steel when taking the samples, and then ultrasonically clean the samples in acetone and anhydrous ethanol to obtain the test samples.

[0007] Preferably, in step S1, the test sample is pretreated before hydrogen charging, specifically by connecting a conductor to one side of the test sample and polishing the other side, and then sealing the entire sample so that only the polished surface and the wire connector are exposed.

[0008] Preferably, in step S1, the cathodic hydrogen charging method specifically involves placing the test sample as a cathode in an electrolyte solution and performing cathodic hydrogen charging for a predetermined hydrogen charging time and current density.

[0009] Preferably, in step S1, the humid hydrogen sulfide environment method specifically involves placing a test sample in a test solution in a sealed environment, and introducing hydrogen sulfide gas into the test solution for a predetermined hydrogen charging time and hydrogen sulfide concentration, thereby achieving hydrogen charging in a humid hydrogen sulfide environment.

[0010] Preferably, in step S2, the hydrogen content is measured by an electrochemical method. Specifically, the change in anode current of a non-hydrogen-charged sample is measured and used as a background current curve, and then the change in anode current of each of the first and second hydrogen-charged samples under equivalent conditions is measured, and an interpolation operation is performed between the change in anode current and the area of ​​the background current curve to obtain the hydrogen content of each of the first and second hydrogen-charged samples.

[0011] Preferably, in step S3, curve fitting is performed by the least squares method.

[0012] Preferably, in step S3, the pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model is specifically:

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[0013] In another aspect of the present invention, there is provided a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model constructed by the above method. Specifically, the model comprises:

number

[0014] In another aspect of the present invention, there is provided a method for evaluating hydrogen damage of a pipeline steel using the pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model, the method comprising the steps of: (a): Using the pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model, based on the hydrogen sulfide concentration of the target wet hydrogen sulfide environment, determine the hydrogen charging time and current density of the cathodic hydrogen charging method equivalent to the target wet hydrogen sulfide environment; (b) based on the parameters determined in step (a), hydrogen charging the test pipeline steel by cathodic hydrogen charging method to obtain an equivalent hydrogen-charged pipeline steel; (c) Evaluate hydrogen damage to the equivalent hydrogen-charged pipeline steel, and define the hydrogen damage as the intended hydrogen damage of the pipeline steel in a wet hydrogen sulfide environment.

[0015] The technical means of the present invention have the following beneficial effects compared with the prior art: 1. The method for constructing a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model provided in the present invention has the advantages of simple operation, small volume of the devices and equipment used, and low cost, which can greatly reduce the cost of testing on pipeline steel hydrogen charging and is favorable for studying the mechanism of hydrogen damage to pipeline steel under engineering and laboratory conditions. The obtained model can greatly improve the testing efficiency of evaluating pipeline steel hydrogen damage, and there is no need to use highly toxic gases such as hydrogen sulfide in the subsequent pipeline steel hydrogen damage evaluation test, which can ensure the safety of testers and equipment and do not harm the environment. 2. In particular, in the present invention, the measurement method for the hydrogen content of the first hydrogen-charged sample and the second hydrogen-charged sample is optimized, which further simplifies the model building process while ensuring the measurement accuracy, and reduces the associated testing costs. 3. The present invention provides a method for evaluating hydrogen damage of pipeline steel using the constructed model. This method achieves efficient research and safe and rapid evaluation of hydrogen damage of pipeline steel by equating the cathodic hydrogen charging method to the hydrogen charging behavior of pipeline steel in a wet hydrogen sulfide environment, and has the advantages of simple operation, safety, reliability, high test efficiency, etc., compared with the prior art method that does not require the use of hydrogen sulfide gas and requires the simulation of a wet hydrogen sulfide environment. [Brief description of the drawings]

[0016] [Figure 1] 1 is a flowchart showing the construction of a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model provided in an embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic diagram of a test sample provided in an embodiment of the present invention. [Diagram 3] FIG. 1 is a schematic diagram of a process for a cathodic hydrogen charging method provided in an embodiment of the present invention. [Figure 4] FIG. 1 is a schematic diagram of a wet hydrogen sulfide environment method provided in an embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram of hydrogen concentration measurement by an electrochemical method provided in an embodiment of the present invention. [Figure 6] 1 is a fitting curve surface of hydrogen charging concentration in a cathodic hydrogen charging method provided in an embodiment of the present invention. [Figure 7] 1 is a fitting curve surface of hydrogen charge concentration for a humid hydrogen sulfide environment method provided in an embodiment of the present invention.

[0017] In all drawings, the same reference numbers refer to the same elements or structures. 1 - negative electrode, 2 - positive electrode, 3 - sample, 4 - platinum electrode, 5 - working electrode, 6 - reference electrode, 7 - auxiliary electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] In order to clarify the objectives, technical means and advantages of the present invention, the present invention will be described in more detail below with reference to the drawings and examples. Note that the specific examples described in this specification are only used to interpret the present invention and are not intended to limit the present invention.

[0019] According to one aspect of the present invention, a method for constructing an equivalent wet hydrogen sulfide environment hydrogen charging model of a pipeline steel is provided, as shown in Fig. 1. The method includes the following steps S1 to S3. S1: A sample is taken from the pipeline steel used for the test, and processed to obtain a plurality of test specimens, and then each test specimen is hydrogen-charged under different reaction conditions by a cathodic hydrogen charging method and a wet hydrogen sulfide environment method, to obtain a plurality of first and second hydrogen-charged samples, where different hydrogen charging times and current densities are used in the cathodic hydrogen charging method, and different hydrogen charging times and hydrogen sulfide concentrations are used in the wet hydrogen sulfide environment method. S2: The hydrogen content of each of the first hydrogen-charged sample and the second hydrogen-charged sample is measured, preferably by an electrochemical method. S3: Based on the hydrogen content obtained in step S2, perform curve fitting for the variables in the two methods respectively, and obtain the pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model based on the fitting results.

[0020] Furthermore, in step S1, the method of obtaining the test samples is as follows: That is, a plurality of samples are taken from the pipeline steel used for the test. When taking the samples, ensure that the thickness direction of each sample is parallel to the diameter direction of the pipeline steel. Then, the samples are ultrasonically cleaned in acetone and absolute ethanol to obtain the test samples. In addition, the test samples are pre-treated in advance before hydrogen charging. Specifically, one side in the thickness direction of the test sample (i.e., the surface perpendicular to the thickness direction) is connected to a conductor via a conductive paste, and the other side is polished with sandpaper, and then polished with a polishing paste until the surface is free of scratches, and then the entire test sample is sealed with epoxy resin so that only the polished surface and the wire connector area are exposed.

[0021] Furthermore, in step S1, the wet hydrogen sulfide environment method is specifically as follows: the test solution is deoxygenated, and the test sample is placed in the test solution in a sealed environment, and hydrogen sulfide gas is introduced into the test solution for a predetermined hydrogen charging time and hydrogen sulfide concentration, thereby hydrogen charging the test sample in wet hydrogen sulfide. The test solution is preferably a NACE-A solution, i.e., a mass fraction of 5% NaCl and 0.5% CH3COOH aqueous solution, and the purity of the introduced H2S gas is 99.5% or more.

[0022] Specifically, the cathodic hydrogen charging method is as follows: the test sample is placed in an electrolyte solution as the cathode, and cathodic hydrogen charging is performed for a predetermined hydrogen charging time and current density, with a platinum electrode connected to the positive electrode of a galvanostat and the test sample connected to the negative electrode.

[0023] Furthermore, in step S2, the hydrogen content is measured by an electrochemical method. Specifically, the change in anode current of a sample that is not hydrogen-charged is measured, and this is used as the background current curve. Thereafter, the change in anode current of the first hydrogen-charged sample and the second hydrogen-charged sample under equivalent conditions is measured, and an interpolation calculation is performed on this and the area of ​​the background current curve to obtain the hydrogen content of each of the first hydrogen-charged sample and the second hydrogen-charged sample. Here, the formula for calculating the hydrogen concentration C is

number

[0024] Furthermore, in step S3, curve fitting is performed by the least squares method. Here, the fitting result obtained by the cathodic hydrogen charging method is

number

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[0025] The two fitting results can be combined to obtain a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model. Specifically,

number

[0026] In another aspect of the present invention, there is provided a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model constructed by the above method. The model specifically includes:

number

number

[0027] In another aspect of the present invention, there is provided a method for evaluating hydrogen damage of a pipeline steel using the pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model, which specifically includes the following steps (a) to (c): (a) Using a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model, the hydrogen charging time and current density of the cathodic hydrogen charging method equivalent to the target wet hydrogen sulfide environment are determined based on the hydrogen sulfide concentration of the target wet hydrogen sulfide environment. (b) Based on the parameters determined in step (a), hydrogen is charged to the test pipeline steel by cathodic hydrogen charging, which is equivalent to hydrogen charging in a wet hydrogen sulfide environment, to obtain an equivalent hydrogen-charged pipeline steel. (c) Evaluate hydrogen damage to the equivalent hydrogen-charged pipeline steel, and correspond the evaluation result to hydrogen damage in the intended wet hydrogen sulfide environment of the pipeline steel, i.e., the evaluation result is the hydrogen damage in the intended wet hydrogen sulfide environment of the pipeline steel.

[0028] Since pipeline steels are subject to hydrogen damage such as hydrogen-induced cracking (HIC) and sulfide stress corrosion cracking (SSCC) in a wet hydrogen sulfide environment, the safety evaluation of pipeline steels is very important. Currently, simulating a wet hydrogen sulfide environment for testing is not only complicated and expensive, but also has a very high safety risk to testers and the environment due to the hydrogen sulfide gas used. The method provided by the present invention can equate the method of cathodic hydrogen charging to the hydrogen charging behavior of pipeline steels in a wet hydrogen sulfide environment, thereby realizing efficient research and safe and rapid evaluation of hydrogen damage to pipeline steels. Since there is no need to use highly toxic gases such as hydrogen sulfide, the safety of testers and equipment can be ensured, and there is no harm to the environment, which is advantageous for studying the hydrogen damage mechanism of pipeline steels under engineering and laboratory conditions.

[0029] The technical solutions provided by the present invention are further illustrated below through specific examples.

[0030] Step 1: Take a thin section sample from the pipeline steel to be used for the test, and process it to obtain the test sample. In the specific implementation, first select the material and select X65 pipeline steel base material. The mechanical properties of the material are shown in the table below.

[0031] Table 1: Mechanical properties of pipeline steel base material [Table 1]

[0032] When taking samples, it should be ensured that the thickness direction is parallel to the diameter direction of the pipe. The size of the thin section sample is 10 x 10 x 2 mm. After taking, they were ultrasonically cleaned in acetone and absolute ethanol for 15 min, respectively.

[0033] Then, a conductor was connected to one side of the thin specimen in the thickness direction via conductive paste, and the other side was polished with sandpaper up to 2000#, and then polished with a polishing paste with a grain size of 2.5 μm until the surface was free of scratches. The entire thin specimen was then sealed with epoxy resin so that only the polished surface and the wire connector were exposed, thereby obtaining the test specimen shown in Figure 2.

[0034] Step 2: Hydrogen charging was performed under different reaction conditions for each test sample using the cathodic hydrogen charging method to obtain multiple first hydrogen charging samples. The test sample was connected to the negative electrode of a galvanostat and placed in an acidic solution to perform cathodic hydrogen charging. The time gradient and current density gradient were controlled respectively during the test. As shown in Figure 3, for samples of different sizes and materials, the solution used during the cathodic hydrogen charging process can be changed. For the X65 flake sample used in this experiment, the solution used was a mixture of 0.5 mol / L sulfuric acid and 1 g / L thiourea. The positive electrode 2 of the galvanostat was connected to a platinum electrode 4, and the negative electrode 1 was connected to a sample 3. The test environment was temperature: 24 ± 3 °C, pressure: 0.1 MPa.

[0035] Under the above test conditions, (1)t1=2h,i=10, 20, 40, 80mA / cm 2 ; (2)t1=4h,i=10, 20, 40, 80mA / cm 2 Cathodic hydrogen charging was performed using the parameters given below.

[0036] Step 3: Hydrogen charging was performed under different reaction conditions for each test sample using the wet hydrogen sulfide environment method to obtain a second hydrogen-charged sample. The controlled variables in the test were time and hydrogen sulfide concentration, respectively. The wet hydrogen sulfide environment hydrogen charging was performed in accordance with the standard NACE MR0175-2015 using NACE-A solution, i.e., a mass fraction of 5% NaCl and 0.5% CH3COOH aqueous solution, and the purity of the H2S gas introduced was 99.5% or higher. The test environment was kept consistent with that of the cathodic hydrogen charging.

[0037] A corrosion-resistant sealed container is required for hydrogen charging in a wet hydrogen sulfide environment. The container includes an inlet, an exhaust port, a liquid supply port, and a liquid drain port. Before introducing H2S gas into the solution, nitrogen gas with a purity of 99.5% was introduced into the solution to remove oxygen gas. The flow rate of nitrogen gas was 100 mL / min, and the maintenance time was 1 hour.

[0038] After introducing H2S gas, the H2S concentration in the solution was measured by the iodometric titration method in NACE TM0177-2016. (1) C H2S= 1500mg / L,t2=1, 2, 3, 4, 6, 8 days; (2) C H2S= 2000mg / L, t2=1, 2, 3, 4, 6, 8 days; (3) C H2S= 2500mg / L,t2=1, 2, 3, 4, 6, 8 days Hydrogen charging in a wet hydrogen sulfide environment was carried out using three groups of parameters.

[0039] The wet hydrogen sulfide environment method is shown in Figure 4.

[0040] Step 4: The hydrogen contents of the first and second hydrogen-charged samples were measured by electrochemical methods. As shown in Figure 5, the solution used to measure hydrogen concentration by electrochemical method is 0.2mol / L sodium hydroxide solution, the working electrode 5 is connected to the sample 3, the reference electrode 6 is connected to the saturated calomel electrode, and the auxiliary electrode is connected to the platinum electrode 4. The electrochemical tester provides an anode potential of +0.3V, and the change in the anode current I within 30 minutes is recorded in real time. Immediately after the hydrogen charging is completed, the sample should be immediately transferred to the sodium hydroxide solution. The test environment is kept consistent with the cathodic hydrogen charging, the humid hydrogen sulfide environment hydrogen charging.

[0041] It is necessary to measure the change in the anodic current under the equivalent conditions of a non-hydrogen-charged sample. The data is used as the background current curve, and the hydrogen concentration at the given parameters of the material is calculated based on the interpolation of the area between the current curves before and after hydrogen charging. The formula is:

number

[0042] The calculated hydrogen concentration (unit: 10 -6 mol / cm 3 ) are shown in the table below.

[0043] Table 2: Hydrogen content of the first hydrogen charge sample [Table 2]

[0044] Table 3: Hydrogen content of the second hydrogen charge sample [Table 3]

[0045] Step 5: The above variables were surface-fitted using the least squares method on the obtained results, and the time or current density required for cathodic hydrogen charging equivalent to a specified humid hydrogen sulfide environment was calculated using the fitting formula.

[0046] each

number

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[0047] The hydrogen charge concentration fitting curves for the cathodic hydrogen charging method and the humid hydrogen sulfide environment method are shown in Figure 6 and Figure 7, respectively.

[0048] Final formula:

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[0049] Step 6: Determine the relevant parameters of the cathode hydrogen charging equivalent to the target wet hydrogen sulfide environment according to the above formula.

[0050] In this example, the target wet hydrogen sulfide environment is as follows: the hydrogen sulfide concentration in the solution is 1800 mg / L, the hydrogen charging time is 4 days, and it is desired to obtain a similar hydrogen charging effect after 4 hours of cathodic hydrogen charging. As a result of substituting the above into equation (11) and calculating, the current density is 33.6 mA / cm 2 should be selected.

[0051] As can be understood by those skilled in the art, the above description is only a preferred embodiment of the present invention, and does not limit the present invention, and any modifications, equivalent replacements and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model, comprising the following steps S1 to S3: S1: A plurality of first and second hydrogen-charged samples are obtained by charging each test sample with hydrogen under different reaction conditions using a cathodic hydrogen charging method and a wet hydrogen sulfide environment method, and the cathodic hydrogen charging method is specifically to place the test sample as a cathode in an electrolyte solution and perform cathodic hydrogen charging for a predetermined hydrogen charging time and current density; S2: Measure the hydrogen content of each of the first hydrogen-charged sample and the second hydrogen-charged sample by electrochemical method, specifically, measure the change in anode current of the non-hydrogen-charged sample and use it as a background current curve, then measure the change in anode current of each of the first hydrogen-charged sample and the second hydrogen-charged sample under equivalent conditions, and perform an interpolation calculation on the area of ​​the background current curve to obtain the hydrogen content of each of the first hydrogen-charged sample and the second hydrogen-charged sample; S3: Curve fitting the variables in the two methods according to the hydrogen content obtained in step S2, and obtain a pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model according to the fitting result. The pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model is specifically: [0010] and In the formula, C Ｈ１ is the hydrogen concentration of the first hydrogen-charged sample obtained by the cathodic hydrogen charging method, and A １ , B １ , C １ are the corresponding term coefficients of the fitting surface in the cathodic hydrogen charging method, and t １ is the hydrogen charging time in the cathodic hydrogen charging method, i is the current density in the cathodic hydrogen charging method, and C Ｈ２ is the hydrogen concentration of the second hydrogen-charged sample obtained by the wet hydrogen sulfide environment method, and A ２ , B ２ , C ２ are the corresponding term coefficients of the fitting surface in the wet hydrogen sulfide environment method, and t ２ is the hydrogen charging time in the wet hydrogen sulfide environment method, and C Ｈ２Ｓ is the hydrogen sulfide concentration of the solution in the wet hydrogen sulfide environment method.

2. 2. The method according to claim 1, characterized in that in step S1, the method of obtaining the test sample is to take a plurality of samples from a pipeline steel, ensure that the thickness direction of each of the samples is parallel to the diameter direction of the pipeline steel when taking the samples, and then ultrasonically clean the samples in acetone and absolute ethanol to obtain the test samples.

3. 2. The method according to claim 1, characterized in that in step S1, before hydrogen charging, the test sample is pretreated, specifically by connecting a conductor to one side of the test sample and polishing the other side, and then sealing the entire sample so that only the polished surface and the wire connector are exposed.

4. The method according to claim 1, characterized in that in step S1, the humid hydrogen sulfide environment method specifically comprises placing a test sample in a test solution in a sealed environment and introducing hydrogen sulfide gas into the test solution at a predetermined hydrogen charging time and hydrogen sulfide concentration, thereby achieving hydrogen charging in a humid hydrogen sulfide environment.

5. 2. The method according to claim 1, wherein in step S3, curve fitting is performed by a least squares method.

6. A method for assessing hydrogen damage in pipeline steel by the method according to any one of claims 1 to 5, comprising the steps of: (a): Using the pipeline steel equivalent wet hydrogen sulfide environment hydrogen charging model, determine the hydrogen charging time and current density of the equivalent cathodic hydrogen charging method based on the hydrogen sulfide concentration of the target wet hydrogen sulfide environment; (b) based on the parameters determined in step (a), hydrogen-charging the test pipeline steel by cathodic hydrogen charging to obtain an equivalent hydrogen-charged pipeline steel; (c) evaluating hydrogen damage on the equivalent hydrogen-charged pipeline steel, and determining the evaluation result as hydrogen damage of the pipeline steel in its intended wet hydrogen sulfide environment.

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