CN114720255A - Method for measuring most negative cathodic protection potential of steel - Google Patents
Method for measuring most negative cathodic protection potential of steel Download PDFInfo
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- CN114720255A CN114720255A CN202210210102.0A CN202210210102A CN114720255A CN 114720255 A CN114720255 A CN 114720255A CN 202210210102 A CN202210210102 A CN 202210210102A CN 114720255 A CN114720255 A CN 114720255A
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Abstract
The invention relates to a method for measuring the most negative cathodic protection potential of steel, which comprises the following steps: (1) preparing a test solution; (2) electrochemical test: measuring self-corrosion and inflection point potential; (3) slow strain rate stress corrosion test: researching the hydrogen embrittlement sensitivity of the sample in the test solution under different cathode polarization potentials, and calculating the hydrogen embrittlement coefficient; (4) TDS testing: taking a fracture part of the sample after the test in the step (3), measuring the hydrogen content in the sample after the test at different polarization potentials, and calculating the hydrogen permeation rate of the sample corresponding to different potentials in the stress corrosion test process in the step (3); (5) analyzing the fracture morphology; (6) and (3) data analysis: and (5) according to the results of the steps (3) and (4), drawing a hydrogen embrittlement coefficient-polarization potential and hydrogen permeation rate-polarization potential curve by combining the fracture morphology of the step (5), thereby determining the most negative cathodic protection potential of the sample.
Description
Technical Field
The invention relates to a method for determining the most negative cathodic protection potential of high-strength steel, belonging to the technical field of material corrosion resistance research.
Background
With the development of marine industry and the continuous deepening of marine resource development in China, the development and application of the high-strength steel in marine engineering are more and more extensive, and the corrosion resistance of the high-strength steel is concerned while the strength of the high-strength steel is continuously improved.
In the marine environment, cathodic protection is usually adopted to inhibit corrosion of steel, firstly, a reasonable cathodic protection potential interval is determined in cathodic protection, anodic dissolution cannot be effectively inhibited when the potential is over positive, and steel is over-protected when the potential is over negative, so that hydrogen is generated on the surface of a material, and the hydrogen is adsorbed on the surface of a substrate and permeates into metal, and hydrogen embrittlement cracking is more likely to occur. Anodic dissolution is often accompanied with surface corrosion, anode slime generation and other phenomena, and can be directly observed or judged through material quality change before and after experiments, for example, in patent document CN 107782662A, namely cathodic protection test probe, device and method for evaluating cathodic protection effect of metal in seawater, anodic corrosion of material is analyzed by using a weight loss method, and the protection degree is obtained through corrosion rate, so that the most positive cathode protection potential is determined, but the 'over-protection' caused by the over-negative potential by the method cannot be judged, at present, no test method standard for evaluating the cathodic protection of metal in seawater exists, and no relevant patent is provided for the most negative cathode protection potential determination method.
Disclosure of Invention
The invention aims to provide a method for comprehensively and accurately measuring the most negative cathodic protection potential of steel, which provides more support for determining the cathodic protection potential.
The technical scheme adopted by the invention for solving the problems is as follows: a method for measuring the most negative cathodic protection potential of steel is characterized by comprising the following steps: the method comprises the following steps: (1) preparing a test solution; (2) electrochemical test: taking a steel sample, embedding the steel sample on a motor to perform a polarization curve test, and measuring self-corrosion and inflection point potential of the steel sample; (3) slow strain rate stress corrosion test: researching the hydrogen embrittlement sensitivity of the steel sample in the test solution under different cathode polarization potentials by using a slow strain rate test, and calculating a hydrogen embrittlement coefficient; (4) TDS testing: after the test in the step (3) is finished, taking a fracture part of the sample, measuring the hydrogen content in the sample after the test at different polarization potentials, and calculating the hydrogen permeation rate of the sample corresponding to different potentials in the stress corrosion test process in the step (3); (5) fracture morphology analysis: taking the fracture sample in the step (3), and observing the fracture morphology; (6) and (3) data analysis: and (5) according to the results of the steps (3) and (4) and the fracture morphology of the step (5), drawing a hydrogen embrittlement coefficient-polarization potential and hydrogen permeation rate-polarization potential curve, and determining the most negative cathodic protection potential of the sample.
The test solution in the steps (1) and (3) is an artificial seawater solution, and the artificial seawater solution takes sodium chloride, magnesium chloride, sodium sulfate and calcium chloride as main solutes; or directly using seawater as a test solution, wherein the pH value of the test solution is 7-10.
Generally, step (5) refers to the morphological analysis of the fracture of the sample by means of a scanning electron microscope.
Specifically, in step (2), the polarization curve of the sample was measured using an electrochemical workstation, wherein the sample had a size of 10mm x 3mm, was sealed with epoxy, and the potential sweep was within ± 0.5V of the open circuit potential.
Specifically, in the step (3), a tensile sample with the diameter of 5mm is selected as a working electrode, a three-electrode system is formed by the working electrode, a reference electrode and an auxiliary electrode, a slow strain rate stress corrosion test is carried out in a test solution until a test sample is broken, the test time t is recorded, and the reduction of area and the hydrogen embrittlement coefficient F of the test sample are calculatedH＝(φ0-φ)/φ0In the formula of0The reduction of area in the blank test is shown, and phi is the reduction of area at different cathode polarization potentials.
Specifically, in the step (4), the TDS test sample is taken from the fracture part of the fracture sample in the step (3), the TDS hydrogen diffusion test is started within 0.5h after the SSRT test in the step (3) is finished, and the temperature is increased to 600-800 ℃ at the speed of 200 ℃/h to obtain the hydrogen content ppm.
Specifically, after the hydrogen content is obtained in the step (4), the hydrogen permeation rate in the stress corrosion test at different potentials is calculated according to the test time t in the step (3), and the hydrogen permeation rate is equal to the hydrogen content in the sample/the test time t.
Specifically, in the step (6), the hydrogen embrittlement factor F is generally setHThe hydrogen embrittlement coefficient F is obtained according to the drawn hydrogen embrittlement coefficient-potential two-dimensional curveHPotential E at 25%1(ii) a Drawing to obtain a hydrogen permeation rate-potential two-dimensional curve according to the hydrogen permeation rate calculated in the step (4), wherein the potential E corresponding to the inflection point of the curve2Combining the result of the interruption mouth shape analysis in the step (5), and taking E1And E2The higher the median value, i.e. the lower the absolute value, is the most negative cathodic protection potential.
Compared with the prior art, the invention has the characteristics or advantages that:
the invention has the beneficial effects that:
aiming at the problem that steel, particularly high-strength steel with high alloy content is easy to corrode in the marine environment, a method for determining the most negative cathodic protection potential is designed for the purpose of cathodic protection, the primary problem of cathodic protection all the time is solved, the reasonable setting of the protection potential can substantially inhibit the steel from oxygen absorption corrosion and prevent hydrogen embrittlement cracking caused by hydrogen evolution reaction, and the problem that the steel is easy to corrode in the marine environment is solved from the source.
The method utilizes a polarization curve test, and provides a basis for selection of a cathode polarization potential in a subsequent test according to an inflection point (from oxygen activation polarization control to hydrogen evolution activation control) on a cathode polarization curve in a Tafer diagram of a sample in the artificial seawater.
The concept of hydrogen permeation rate is innovatively used in the application, the difficulty degree of hydrogen permeation into a sample under different cathode potentials in a stress corrosion test is quantified, and the hydrogen brittleness sensitivity of the material is more intuitively reflected.
In the application, an electrochemical workstation is combined with a stress corrosion test, and a three-electrode system (working electrode, auxiliary electrode and reference electrode) is used to accurately reduce the corrosion state of a sample in a marine environment under different cathode polarization potentials, so that not only is a method for determining the cathode protection potential described in detail, but also a set of complete cathode protection device is presented, and the method has double meanings.
The application provides a new direction for the research and development of high-strength steel, in particular marine steel.
Drawings
FIG. 1 is a schematic diagram of a slow strain rate stress corrosion test in step (3) of an embodiment of the present invention;
in the figure, 1, tie bar 2, clamp 3, auxiliary electrode 4, deformation sensor 5, reference electrode 6, steel sample.
Detailed Description
The present invention is described in further detail below with reference to examples, which are intended to be illustrative and not to be construed as limiting the invention.
The method for determining the cathodic protection potential of the high-strength steel in the marine environment comprises the following steps:
(1) preparing an artificial seawater solution: preparing artificial seawater solution with sodium chloride, magnesium chloride, sodium sulfate and calcium chloride as main solutes, and adjusting the pH of the solution to be alkalescent (pH 7.0-8.0).
(2) Electrochemical test: performing a polarization curve test on the inlaid sample by using an electrochemical workstation, wherein the sample size is 10 x 3mm, the sample is sealed by using epoxy resin, and the potential scanning range is +/-0.5V of open-circuit potential; in the test, a three-electrode system is used, a platinum sheet is used as an auxiliary electrode, a calomel electrode is used as a reference electrode, a sample is used as a working electrode, the open-circuit potential is firstly measured, the Tafel test technology is selected, and the potential range of the next test is determined through the inflection point of a cathode polarization curve.
(3) Slow strain rate stress corrosion test: selecting phi 5mmStretching a sample, as shown in figure 1, installing the sample on a clamp through a reaction kettle in a through kettle manner, ensuring that the scale distance part of the sample is completely immersed in the solution, connecting a three-electrode system by using an electrochemical workstation, setting a polarization potential and a stretching rate to start an experiment, accurately recording the test time t after the sample is broken, and calculating the reduction of area and the hydrogen embrittlement coefficient F of the sampleH＝(φ0-φ)/φ0，φ0The reduction of area in the blank test is shown, and phi is the reduction of area at different cathode polarization potentials.
(4) TDS testing: within half an hour after the stress corrosion test is finished, the fracture part of the sample is taken, the sample is heated to 600-800 ℃ at the speed of 100-200 ℃/h by using TDS equipment, the hydrogen content of the sample at different potentials is accurately measured under a high vacuum state to be 0.01ppm, and the hydrogen permeation rate under the test of the step (3) is calculated.
(5) Fracture morphology analysis: and (4) taking another part of fracture sample tested in the step (3) for SEM electron microscope analysis, and observing the fracture morphology.
(6) And (3) data analysis: according to the experimental results of (3) and (4), hydrogen permeation rate-polarization potential and hydrogen embrittlement coefficient-polarization potential curves are drawn, wherein the hydrogen embrittlement coefficient FHPotential E at 25%1Inflection point potential E of hydrogen permeation rate-potential two-dimensional curve2Combining the fracture morphology analysis result to ensure that the fracture is mainly ductile fracture at the most negative cathodic protection potential without a great deal of cleavage and along the crystal structure, and taking E1And E2The smaller of the absolute values is used as the most negative cathodic protection potential.
In addition to the above embodiments, the present invention also includes other embodiments, and any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of the claims of the present invention.
Claims (8)
1. A method for measuring the most negative cathodic protection potential of steel is characterized by comprising the following steps: the method comprises the following steps: (1) preparing a test solution; (2) electrochemical test: taking a steel sample, embedding the steel sample on a motor to perform a polarization curve test, and measuring self-corrosion and inflection point potential of the steel sample; (3) slow strain rate stress corrosion test: researching the hydrogen embrittlement sensitivity of the steel sample under different cathode polarization potentials in a test solution by using a slow strain rate test, and calculating a hydrogen embrittlement coefficient; (4) TDS testing: after the test in the step (3) is finished, taking a fracture part of the test sample, measuring the hydrogen content in the test sample after the test at different polarization potentials, and calculating the hydrogen permeation rate of the test sample corresponding to different potentials in the stress corrosion test process in the step (3); (5) fracture morphology analysis: taking the fracture sample in the step (3), and observing the fracture morphology; (6) and (3) data analysis: and (5) according to the results of the steps (3) and (4), drawing a hydrogen embrittlement coefficient-polarization potential and hydrogen permeation rate-polarization potential curve by combining the fracture morphology of the step (5), thereby determining the most negative cathodic protection potential of the sample.
2. The method of claim 1, wherein: the test solution in the steps (1) and (3) is an artificial seawater solution, and the artificial seawater solution takes sodium chloride, magnesium chloride, sodium sulfate and calcium chloride as main solutes; or directly using seawater as a test solution, wherein the pH value of the test solution is 7-10.
3. The method of claim 1, wherein: and (5) carrying out morphology analysis on the fracture of the sample by using a scanning electron microscope.
4. The method of claim 1, wherein: in step (2), the polarization curve of the sample is measured using an electrochemical workstation, wherein the sample has a size of 10mm x 3mm, is sealed with epoxy, and has a potential sweep range of the open circuit potential ± 0.5V.
5. The method of claim 1, wherein: in the step (3), a phi 5mm tensile sample is selected as a working electrode, a three-electrode system is formed by the working electrode, a reference electrode and an auxiliary electrode, a slow strain rate stress corrosion test is carried out in a test solution until a sample is broken, the test time t is recorded, and the reduction of area and the hydrogen embrittlement coefficient F of the sample are calculatedH＝(φ0-φ)/φ0In the formula of0The reduction of area in the blank test was used,phi is the reduction of area under different cathodic polarization potentials.
6. The method of claim 1, wherein: in the step (4), the TDS test sample is taken from the fracture part of the fracture sample in the step (3), a TDS hydrogen diffusion test is started within 0.5h after the SSRT test in the step (3) is finished, and the temperature is increased to 600-800 ℃ at the speed of 200 ℃/h to obtain the hydrogen content ppm.
7. The method of claim 1, wherein: and (4) after the hydrogen content is obtained in the step (4), calculating the hydrogen permeation rate in the stress corrosion test under different potentials according to the test time t in the step (3), wherein the hydrogen permeation rate is the hydrogen content in the sample/the test time t.
8. The method of claim 1, wherein: in step (6), the hydrogen embrittlement coefficient F is generally adjustedHThe hydrogen embrittlement coefficient F is obtained according to the drawn hydrogen embrittlement coefficient-potential two-dimensional curve by regarding the content of less than or equal to 25 percent as a safety areaHPotential E at 25%1(ii) a Drawing to obtain a hydrogen permeation rate-potential two-dimensional curve according to the hydrogen permeation rate calculated in the step (4), wherein the potential E corresponding to the inflection point of the curve2Combining the result of the interruption of the mouth shape analysis in the step (5), and taking E1And E2The higher the median value, i.e. the lower the absolute value, is the most negative cathodic protection potential.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115165984A (en) * | 2022-07-15 | 2022-10-11 | 中国科学院海洋研究所 | Marine environment hydrogen permeation monitoring sensor with plane working surface and monitoring method |
| CN115931538A (en) * | 2022-12-07 | 2023-04-07 | 中国石油大学(华东) | Method for measuring influence degree of hydrogen on metal stress corrosion cracking in acidic environment |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115165984A (en) * | 2022-07-15 | 2022-10-11 | 中国科学院海洋研究所 | Marine environment hydrogen permeation monitoring sensor with plane working surface and monitoring method |
| CN115165984B (en) * | 2022-07-15 | 2023-06-06 | 中国科学院海洋研究所 | Ocean environment hydrogen permeation monitoring sensor with working face being plane and monitoring method |
| CN115931538A (en) * | 2022-12-07 | 2023-04-07 | 中国石油大学(华东) | Method for measuring influence degree of hydrogen on metal stress corrosion cracking in acidic environment |
| CN115931538B (en) * | 2022-12-07 | 2023-08-22 | 中国石油大学(华东) | Method for measuring influence degree of hydrogen in acidic environment on metal stress corrosion cracking |
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