JPH02157642A - Gel electrode for electrochemical measurement for evaluating deterioration degree of metallic material - Google Patents

Abstract

PURPOSE:To rapidly and exactly evaluate the deterioration degree of a metallic material by measuring the current and impedance between a 1st electrode which is brought into contact with an electrolyte gel and a 2nd electrode which is brought into contact with a metal to be measured and determining and evaluating the deterioration degree of the metal to be measured. CONSTITUTION:An outside cylinder 27 is so set as to bring its open end into contact with the material 31 to be measured and the positive electrode 32 is brought into contact with the metallic material 31. The negative electrode 29 and the positive electrode 32 are, therefore, electrically connected via the electrolyte gel 30 and the metallic material 31. Further, the reference electrode 28, the negative electrode 29 and the positive electrode 32 are all connected to a potentiostat. A voltage is impressed between the two electrodes and the density of the current flowing from the positive electrode 32 to the negative electrode 29 via the material 31 and the electrolyte gel 30 is measured and the peak current density is extrapolated to the basic curve based on the previously obtd. dynamic data. The deterioration of the metallic material to be measured by the secular change is determined and evaluated in this way.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention aims to evaluate the degree of deterioration of the toughness and creep property of metal materials used as, for example, thermal power boilers, heat exchange tubes for chemical blunts, or steam turbine components. The present invention relates to a means for evaluating the degree of deterioration of metal materials that quantitatively evaluates them non-destructively using an electrochemical method, and particularly relates to gel electrodes for electrochemical measurements that enable measurement of all postures in the field.

(Prior art) As is well known, for example, heater tubes of boilers for thermal power generation,
Metal materials used as heat exchange tubes in chemical plants are
It is known that material deterioration occurs over time due to long-term use under high temperature and high pressure, and it is an important issue to accurately detect the degree of deterioration and predict the remaining life.

This material deterioration phenomenon of metallic materials is caused by changes in the microscopic metal structure,
In other words, carbide agglomeration, dispersion and coarsening.

This is said to be due to the concentration of impurities or the formation of intermetallic compounds mainly occurring at grain boundaries.

Here, conventional methods for detecting and determining material deterioration of the metal materials include evaluation methods based on mechanical measurements based on material tests, such as creep rupture tests and Charpy impact tests, and evaluation methods using optical microscopy and electronic Metallographic evaluation methods such as using a microscope or performing microscopic X-ray analysis are used.

However, in the case of mechanical measurement, although highly reliable data can be obtained, it is necessary to cut out the test piece from the actual metal member for measurement, which poses the problem of making the measurement work difficult. are doing. Therefore, as a means of non-destructively evaluating the degree of deterioration of metal materials, a replica transfer method is being considered in which the structure or precipitates are transferred metallographically to a thin film and then observed and analyzed in the laboratory. .

Furthermore, it is known that if microscopic metallographic changes in a metal material progress further, microcracks and voids will occur along the grain boundaries due to the synergy with stress, and this will become the bud of material failure. Accurately detecting the progress of microscopic metallographic changes is also an important research topic.

In response to the above-mentioned current situation, various physical detection methods such as electrical resistance method, eddy current method, hardness measurement method, and various tissue analysis methods applying replica transfer method have been proposed, but the former has a total n1 value. The latter has the problem that it tends to vary and lacks the ability to detect local abnormalities, and while the latter has an excellent ability to detect local microstructural changes, it has the problem that quantitative analysis is difficult and less rapid. have.

(Issue 8 to be solved by the invention) As described above, with the conventional means for evaluating the degree of deterioration of metal materials,
For various aspects such as measurement work, analysis work and accuracy,
The problem is that it is not satisfactory.

Therefore, this invention was made in consideration of the above circumstances, and it is possible to quickly, easily and accurately evaluate the degree of deterioration of metal materials, and it also makes it possible to maintain n1 constant in all postures at the site, resulting in a total work efficiency of 1. The purpose of the present invention is to provide a gel electrode for electrochemical measurement for extremely good evaluation of the degree of deterioration of metal materials with improved performance.

(Means for Solving the Problems) That is, the gel electrode for electrochemical measurement for evaluating the degree of deterioration of metal materials according to the present invention uses an electrolyte gel obtained by adding a water-absorbing material to an electrolyte solution to form a gel on a metal to be measured. A DC voltage is applied between the first electrode that is in contact with the electrolyte gel and the second electrode that is in contact with the metal to be measured, and the voltage between the first electrode and the second electrode is The current flowing through the electrode and the impedance between the first and second electrodes are measured, and the current density value or impedance is compared with the mechanical properties tested in advance, such as the impact value in the Charpy impact test and the rupture time in the creep rupture test. The standard curve obtained from the correlation is used to quantitatively evaluate the degree of deterioration of the metal to be measured.

(Function) According to the above configuration, the precipitation state of carbides and intermetallic compounds (for example, sigma phase) due to changes in the microstructure of the metal material is electrochemically measured, and the mechanical properties of the metal material tested in advance are determined. Since the degree of deterioration of metal materials such as toughness and creep resistance is quantitatively evaluated in a non-destructive manner based on the correlation with various properties, it is possible to quickly, easily and accurately evaluate the degree of deterioration of metal materials. can. Since the electrolyte gel, which is made by adding a water-absorbing material to the electrolyte solution and is made into a gel, is brought into contact with the metal to be measured, it is possible to measure all postures at the site, and the measurement work efficiency can be improved.

(Example) Before explaining an example of the present invention, the principle of evaluating the degree of deterioration of metal materials used in the present invention will be explained below.
I will briefly explain this. For example, stainless steel pipes used in boiler heaters of thermal power plants, etc.
Because they are used under harsh conditions, such as being exposed to combustion gas at high temperatures and pressures, they are known as components that are often replaced before they reach their designed service life.

Conventionally, when measuring the degree of deterioration of stainless steel pipes, external appearance observation, structure observation, creep test, etc. are performed as mentioned above, but various aspects such as measurement work, analysis work, and accuracy are performed. , has the problem of being unsatisfactory.

Therefore, as a result of examining the correlation between the above conventional test results and electrochemical measurement methods, the inventors of the present invention found that the anode activity peak current density Np that appears in anode polarization measurement in a 1N potassium hydroxide solution. It was revealed that there is a good correlation with changes in metallographic and material mechanical properties. This detection mechanism detects the anode reaction current that occurs when carbides and sigma phases (intermetallic compounds) that appear in the microstructure due to long-term use dissolve in potassium hydroxide solution. A patent application has already been filed for a method for evaluating the degree of deterioration using the present invention by the same inventor and applicant (Patent application No.
No. 8).

That is, in FIG. 2, reference numeral 11 denotes a glass electrolytic cell, in which an alkaline electrolyte solution 12 is sealed. A metal sample (austenitic stainless steel) 14 supported by a holder 13 and an electrode 15 facing the metal sample 14 are immersed in this electrolyte solution 12 .

The metal sample 14 and the electrode 15 are each connected to a potentiometer stat 1B so that voltage values can be measured and voltages can be applied. Further, one end of the probe 17 is immersed in the electrolyte solution 12, and the other end is immersed in the electrolyte solution 19 in the water tank 18. Further, in the electrolyte 19, agar salt bridge 20
One end is immersed, and the other end is immersed in a KCL saturated solution 22 in a water tank 21. A KCL reference electrode 23 connected to the potentiometer cI stat 1B is immersed in this KCL saturated solution 22, so that the current flowing between the metal sample 14 and the electrode 15 is measured.

In addition, the above Botenshi! ! A function generator (potential programmer) 24 is connected to the stat IB, and a plotter 2B is connected to the function generator 24 via an AC/DC (alternating current/direct current) converter 25.

In the measuring device as described above, first, the electrolyte solution 12
High-purity nitrogen gas is sent inside and bubbled for about 30 minutes to sufficiently deoxidize, and then the natural potential (usually about -0.5V) generated between the metal sample 14 and the electrode 15 is measured. . Thereafter, the potential between the metal sample 14 and the electrode 15 is gradually increased from the above-mentioned natural potential (and the density of the current flowing between the metal sample 414 and the electrode 15 is also gradually increased).

As shown in FIG. 3, this current density reaches its maximum peak when the potential between the metal sample 14 and the electrode 15 is 0.1-0.2 V. This means that carbides and intermetallic compounds precipitated in the structure of heat-resistant materials are o, 1 to 0.2 V.
This is due to the fact that the anode current generated when a dissolution reaction occurs selectively at a potential of , increases in proportion to the distribution amount of these precipitates.

Note that FIG. 3 shows the results of anode polarization measurements of the actual material and the artificially aged material (New), which was heat-treated at a predetermined temperature for a certain period of time. That is, the sample symbol (I!3
-10) is a sample that has been used for 100,000 hours at 609°C.6. Sample symbol (N4-3) is used at 620℃ for 3 hours.
It can be seen that the samples were used for 5,000 hours, and the longer the usage time, the higher the peak current density.

And the anode active maximum peak current density lp is:
The creep damage rate obtained from the results of a creep rupture test on test pieces cut from the same specimen material,
It has been proven that there is a correspondence relationship. That is, FIG. 4 is a reference curve showing the correlation between the peak current density 1p and the creep damage rate.

For this reason, the anode activity maximum peak current density obtained by measurement! By extrapolating p to a reference curve created from data obtained from creep rupture tests on multiple materials, it is possible to quickly and easily determine the progress of creep damage due to aging in a target metal sample. Moreover, accurate quantitative evaluation can be performed.

Furthermore, it has been demonstrated that the above-mentioned maximum peak current density of anode activity 1p corresponds to the impact value obtained from the results of Charpy impact test on test pieces cut from the same test material. (The above patent application
9708), by extrapolating the measured peak current density Ip to a reference curve created from data obtained from Charpy impact tests on many materials, It is possible to quantitatively evaluate the progress of toughness.

Therefore, by measuring the anode active maximum peak current density Ip, the degree of deterioration can be determined non-destructively and quickly on site without cutting out a metal sample from an actual machine and conducting a destructive test.

By the way, in the above-mentioned means of measuring the maximum peak current density of anode activity 1p, a strongly alkaline electrolyte solution is used!
However, handling strong alkaline solutions in the limited work environment of the site is extremely dangerous.

Therefore, as a result of various studies, the inventors of the present invention mixed a highly water-absorbing polymeric material such as sodium polyacrylate into a strong alkaline solution to form a gel, and added this electrolyte gel to the electrolyte solution 12. I thought of using it instead. That is, for example, 1N potassium hydroxide solution 5
017 and 1 g of sodium polyacrylate to form a gel, this electrolyte gel was placed in the electrolytic cell 11 instead of the electrolyte solution 12, and the anode active maximum peak current density 1p was adjusted in the same manner as above. It was measured.

As a result, as shown in Figure 5, the polarization curves of applied voltage and current density for both the new material (New) and the sample symbol (N4-3) matched well with those shown in Figure 3. It was demonstrated that even when an electrolyte gel obtained by gelling the electrolyte solution 12 was used, the measured value of the current density did not change significantly and the reproducibility was good.

Therefore, one embodiment of the present invention will be described below.

In FIG. 1, an outer cylinder 27 is made of, for example, an acrylic resin material and has a cylindrical shape with an open end. This outer cylinder 27 has a reference electrode 28 and a negative electrode 29 inside.
are inserted together, and filled with an electrolyte gel 30 made by adding a water-absorbing material to an alkaline solution and turning it into a gel.

This outer cylinder 27 has its open end connected to the metal material 3 to be measured.
1. Furthermore, a positive electrode 32 is brought into contact with this metal material 31 . Therefore, the negative electrode 29 and the positive electrode 32 are electrically connected via the electrolyte gel 30 and the metal material 31. Further, the reference electrode 2B, the negative electrode 29 and the positive electrode 32 are all connected to the potentiostat 16.

Then, a voltage is applied between the negative electrode 29 and the positive electrode 32, and the current density flowing from the positive electrode 32 to the negative electrode 29 via the metal material 31 and the electrolyte gel 30 is measured. By extrapolating to a reference curve created from mechanical data obtained by testing many materials, it is possible to quantitatively evaluate the degree of deterioration due to aging of the target metal sample.

According to the above configuration, by bringing the electrolyte gel 30 and the positive electrode 32 into contact with the metal material 31 to be measured, it is possible to measure a peak current density of 1 p, making it convenient to handle on site. At the same time, measurements can be taken in all postures.

Here, electrolyte gel is agar agar in electrolyte solution.

It is produced by adding gelatin and a super absorbent polymer as a gelling material, and these three types of gelling materials are used depending on the liquid properties of the electrolytic solution selected depending on the material of the sample to be measured.

Therefore, an experimental example will be described in which the deterioration degree planning of turbine members was performed using agar gel using agar as a gel material. Usually, Cr-Mo-V steel used for turbine shafts undergoes tempering embrittlement after long-term use. This phenomenon is said to be due to the fact that impurities such as phosphorus and arsenic contained in trace amounts in the material segregate at the grain boundaries, resulting in a decrease in the bonding strength of the grain boundaries. Until now, as a method for evaluating the degree of embrittlement, the brittle transition temperature (FATT) obtained by the Charpy impact test has been used.
A method was used to evaluate the degree of embrittlement progression based on changes in .

Next, FIG. 6 shows a turbine member 3f with a different history using picric acid and sodium dodecylbenzenesulfonate solution as an electrolyte solution! J.C., G.

This shows the results of measuring the impedance of the sample surface of E using the AC impedance method. Symbols C and G in Figure 6
It was expected that the use temperature would be higher in the order of C, H, and embrittlement would progress, but the respective curves shifted to the lower resistance side in the order of C, G, and H.

In contrast, Figure 7 shows the results when similar impedance measurements were performed using an electrolyte gel made by doubling the concentration of the above picric acid and sodium dodecylbenzenesulfonate solution and gelling it with agar. . Although the overall impedance has increased compared to FIG. 6, it can be seen that the resistance changes of each sample C8G and H show the same tendency as in FIG. 6.

Here, when we consider the correlation between the impedance measurement results and mechanical properties, we find that - As shown in Figure 8, the brittle transition temperature (
FATT) and admittance, which is the reciprocal of impedance, are represented by one line at each frequency f, and it is possible to estimate changes in mechanical characteristics by measuring impedance. Note that the evaluation of the degree of deterioration of metal by impedance measurement is described in Japanese Patent Application No. 63-143570.

Next, detection of geometric changes in metal materials will be described. When impedance measurements are performed on cold rolled high tensile strength FT4 (HT50) and unprocessed new material (New) with the same chemical structure in a sulfuric acid solution electrolyte of 0.72 normality gelled with agar. , a change in impedance as shown in FIG. 9 is observed. This shows that by using electrolyte gel, geometric changes in the material such as plastic deformation, such as deformation and cracks, can be detected.

(Effects of the Invention) Therefore, as detailed above, according to the present invention, it is possible to quickly, easily, and accurately evaluate the degree of deterioration of metal materials, and it is also possible to measure all postures at the site, improving measurement work efficiency. It is possible to provide a gel electrode for electrochemical measurement for extremely good evaluation of the degree of deterioration of metal materials with improved performance.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an embodiment of a gel electrode for electrochemical measurement for evaluating the degree of deterioration of metal materials according to the present invention;
Figure 2 is a configuration diagram for explaining the measurement principle for evaluating the degree of deterioration used in this invention, and Figure 3 shows the relationship between the potential between the sample and the electrode and the current flowing therein in the same measurement principle. Figure 4 is a characteristic curve diagram showing the correlation between peak current density and creep damage rate. Figure 5 is a diagram showing the potential between the sample and electrode when electrolyte gel is used instead of electrolyte solution. A characteristic curve diagram showing the relationship with the current flowing there,
Figure 6 is a characteristic diagram showing the results of measuring the impedance of the sample surface using an electrolyte solution, Figure 7 is a characteristic diagram showing the results of measuring the impedance of the sample surface using electrolyte gel, and Figure 8 is the characteristic diagram showing the results of measuring the impedance of the sample surface using electrolyte gel. FIG. 9 is a characteristic diagram showing the correlation between impedance measurement results and mechanical properties. FIG. 9 is a characteristic diagram for explaining that geometric changes in materials can be measured using electrolyte gel. 11... Electrolytic cell, 12... Electrolyte solution, 13...
Holder 14...metal sample, 15...electrode, 16.
... Potentiostat, 17... Probe, 1B
...water tank, 19...electrolyte, 20...agar salt bridge,
21... Water tank, 22... KCL saturated solution, 23, K
CL reference electrode, 24...Function generator, 25...A
C/DC converter, 2B... Plotter, 27... Outer cylinder, 28... Reference electrode, 29... Negative electrode, 30...
- Electrolyte gel, 31... Metal material, 32... Positive electrode.

Claims (1)

[Claims] An electrolyte gel made by adding a water-absorbing material to an electrolyte solution to form a gel is brought into contact with a metal to be measured, and between a first electrode that is in contact with the electrolyte gel and a second electrode that is in contact with the metal to be measured. A DC voltage is applied to connect the first electrode and the second electrode.
A standard curve obtained by measuring the current flowing between the electrodes and the impedance between the first and second electrodes, and the correlation between this current density value or impedance and the mechanical properties of the metal material tested in advance. A gel electrode for electrochemical measurement for evaluating the degree of deterioration of metal materials, characterized in that the degree of deterioration of the metal to be measured is quantitatively evaluated using the gel electrode.