JPH1019826A - Apparatus for measuring corrosion of metallic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To monitor the rate and mode of local corrosion reliably advantageously in industry by taking out the measurement data of electrochemical noise, analyzing the local corrosion mode and displaying the results of analysis. SOLUTION: Under a state where electrodes 21, 22, 23 of same material as the metallic surface of an object to be measured are exposed to same conditions of corrosion, corrosion current voltage measuring means 24, 26 and 25, 27 measure the electrochemical current noise (b) and electrochemical potential noise (c) between respective electrodes. A data memory means 72 takes in each measurement data of the measured current noise (b) and potential noise (c) and stores them in time series. Corrosion mode determining means 81 and 91-94 takes out the measurement data of the stored current noise (b) or the potential noise (c) and determine the local corrosion mode analytically. Output display means 101, 102 output and display the local corrosion mode thus determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring corrosion of metal materials, and more particularly, to an apparatus for measuring corrosion.
The present invention relates to a corrosion measurement apparatus using an electrochemical noise method that measures local corrosion of a metal material and makes it possible to determine the form of the local corrosion.

[0002]

2. Description of the Related Art In a chemical plant or the like, a metal surface inside a device that comes into contact with a fluid such as cooling water or plant liquid,
In this case, the corrosion of the metal material on the internal metal surfaces of the reactor, the distillation tower, the tank (reservoir), the heat exchanger, and the internal metal surfaces of the metal piping connecting these components to each other, etc. Often a problem. That is, for example, in the internal piping of the heat exchanger, it is known that the portion in contact with the fluid is likely to be corroded because it becomes a so-called heat transfer surface, and it is necessary to prevent such a corrosion obstacle beforehand. The corrosion rate or tendency of the metal surface must be checked.

[0003] In general, as methods for measuring the corrosion of metal materials of this type, as is well known, a weight loss measurement method and a polarization resistance measurement method (DC polarization resistance method, AC polarization resistance method, impedance method) are known. Each with electrical resistance measurement method. Here, the outline and the details of the advantages and disadvantages of each of these measurement methods will be described below.

In the weight loss measurement method (also called a coupon method or an immersion test method), a sample test piece (strip coupon) made of the same material as the surface of a metal to be measured is immersed in a corrosive test fluid. The corrosion is allowed to proceed (the weight of the sample test piece itself decreases with the corrosion), and after a certain period of time (usually about 30 to 90 days), the sample test piece before and after the immersion is removed. It is a means to determine the average corrosion rate (corrosion rate) during the test period from the corrosion weight loss (mass difference).

[0005] In the present weight loss measurement method, (a) the corrosion rate cannot be measured instantaneously (real time), and (b) it takes a relatively long time to obtain the measurement result, and the response may be delayed. (C) Local corrosion cannot be measured.

The polarization resistance measuring method is a means for determining the corrosion rate at the time of measurement from electrochemical polarization resistance, that is, immersing a plurality of sample test pieces in a corrosive test fluid so that they are opposite to each other. In the state where the corrosion has progressed, a weak constant current of DC or AC is applied between the test specimens, and a change in the current or potential caused by the current is measured, thereby instantaneously (in real time) over the entire surface. It is a means to determine the corrosion rate.

The polarization resistance measurement method has disadvantages such as (a) the measurement sensitivity is low, the influence of temperature is large, and measurement at high temperatures cannot be performed, and (b) local corrosion cannot be measured. .

In the electric resistance measurement method, the sample test piece is immersed in a corrosive test fluid to progress corrosion (in accordance with the decrease in the cross-sectional area of the sample test piece itself due to the corrosion, the electric resistance value of the sample test piece is reduced). Is increased), and at the same time, the electric resistance value of the sample test piece is measured at regular intervals, and the average corrosion rate at the corresponding time is obtained from the measured value gradient.

In the present electric resistance measurement method, (a) the corrosion rate cannot be measured instantaneously (real time); (b) the measurement sensitivity is low, the influence of the temperature is large, and the measurement at a high temperature cannot be performed. (C) Local corrosion cannot be measured.

Therefore, as a means for improving these disadvantages, an electrochemical noise method is disclosed in US Pat. No. 5,139,627.
No. has been proposed. This proposal measures the coupling current between the electrodes consisting of two specimens of the same metal surface immersed in a corrosive fluid and the electrochemical current noise, and compares both of them. A means for determining the degree of local corrosion of a metal surface, further measuring electrochemical potential noise generated between two electrodes, and comparing the electrochemical potential noise with the electrochemical current noise. Means for determining the corrosion rate of local corrosion by comparing the resistance / impedance noise output with the output of the degree of local corrosion.

[0011]

However, the electrochemical noise method according to the above proposal only discloses the basic principle as one corrosion measurement method, and is industrially effective and has an appropriate corrosion rate. It does not specifically show the measurement of the absolute value of the corrosion rate or the degree of corrosion, and furthermore, cannot reliably monitor local corrosion.

In view of such circumstances, the present invention uses the electrochemical noise method to monitor the corrosion rate of local corrosion on a metal surface reliably and industrially advantageously, and to evaluate the local corrosion. It is an object of the present invention to provide an apparatus for measuring corrosion of a metal material, which makes it possible to easily determine the form of the corrosion.

[0013]

In order to achieve the above object, according to the first aspect of the present invention, a plurality of electrodes of the same or substantially the same material as a metal surface to be measured for corrosion are used. In a state of being exposed under substantially the same corrosion conditions, the corrosion current voltage measurement means for measuring the electrochemical current noise and the electrochemical potential noise between the respective electrodes, respectively, were measured by the corrosion current voltage measurement means. Incorporating each measurement data of electrochemical current noise and electrochemical potential noise, data storage means for accumulating the measurement data in time series, and electrochemical current noise or time data accumulated in the data storage means in time series The measurement data of the electrochemical potential noise is extracted, and the form of local corrosion is determined from the extracted electrochemical current noise or electrochemical potential noise measurement data. And localized corrosion form determining means for determining by analysis, the a corrosion measurement device for a metallic material, characterized in that it comprises an output display unit for outputting display the localized corrosion pattern determined by the localized corrosion form determining means.

In the corrosion measuring apparatus of the present invention, the electrochemical current noise and the electrochemical potential noise between the respective electrodes exposed to the corrosive conditions are measured by the corrosion current voltage measuring means and then stored in the data storage means. Based on the electrochemical current noise or the electrochemical potential noise accumulated in time series and taken out from the data storage means, the local corrosion form determining means determines the form of the local corrosion, and further, the determined The form of local corrosion is output and displayed by the output display means.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a corrosion measuring device for metallic materials according to the present invention will be described below in detail with reference to FIGS.

FIG. 1 is a block diagram showing an outline of the overall configuration of a corrosion measuring apparatus including this embodiment.
The configuration of the entire corrosion measuring apparatus including the present embodiment, its operation and effects will be described.

In the apparatus configuration shown in FIG. 1, the corrosion measuring apparatus including this embodiment has a corrosion measuring vessel 11 containing a required amount of a corrosive solution 12 therein. Some materials are the same or almost the same as the metal surface to be measured for corrosion (hereinafter simply referred to as the same material)
In this case, the three measurement electrodes, in this case, the first, second, and third electrodes 21, 22, and 23 are immersed in the same or almost the same corrosion condition as the metal surface (hereinafter simply referred to as the same corrosion condition). In this case, exposure is performed under the same or almost the same temperature condition (hereinafter simply referred to as the same temperature condition).

Further, the first electrode 21 and the second electrode 2
Between the two, a current measuring circuit having an internal resistance of almost zero, that is, a so-called zero resistance ammerter 24 is connected, and between the second electrode 22 and the third electrode 23,
An amplifier circuit having a very large input impedance capable of measuring a signal voltage without affecting the electrode side, here a buffer circuit 25 is connected.

Accordingly, in the case of this embodiment, a coupling current (coupling current:
_{Ime an} ) a, and the coupling current a is measured by the non-resistance ammeter 24, and after signal processing described later, is accumulated in the data storage unit 72 of the computer 71 in time series. .

At this time, the electrochemical current noise (I _n )
Regarding b, the fluctuation of the coupling current a is filtered by a filter circuit, particularly a band-pass filter circuit 26, to reduce the current fluctuation in a low frequency region, particularly in a frequency region of about 1 Hz or less, preferably in a frequency region of about 0.01 to 1 Hz. Is measured, and the measured electrochemical current noise b is also time-sequentially stored in the data storage unit 72 of the computer 71 after performing signal processing described later. Here, the electrochemical current noise b can be obtained in the same manner by appropriately calculating the coupling current a taken into the computer 71 and calculating the standard deviation thereof.

On the other hand, with respect to the electrochemical potential noise (V _n ) c, the potential difference (V _mean ) between the second electrode 22 and the third electrode 23 is measured by the buffer circuit 25, and the potential difference of this potential difference is measured. The fluctuation can be obtained by measuring a potential difference fluctuation in a low frequency region, particularly in a frequency region of about 1 Hz or less, preferably in a frequency region of about 0.01 to 1 Hz, by a filter circuit, particularly a band-pass filter circuit 27. The measured electrochemical potential noise c is also subjected to signal processing, which will be described later, and is stored in the data storage unit 72 of the computer 71 in time series. Also in this case, the electrochemical potential noise c can be obtained in the same manner by directly taking the potential difference into the computer 71, subjecting the computer 71 to appropriate arithmetic processing, and calculating the standard deviation.

Next, the details of specific circuit means for data processing until each measurement data signal (each measurement data of current and voltage) is inputted to the computer 61 will be described with reference to FIG.
(A), (b) and FIGS. 3 (a), (b).

FIGS. 2A and 2B show an example in which the data processing circuit is formed by an analog circuit.
In this case, first, the current signal, that is, the coupling current a between the first electrode 21 and the second electrode 22 is measured by a non-resistance ammeter 24 as shown in FIG. At the same time, one of the current signals is an RMS circuit for calculating the square mean of the signal → D for converting the obtained signal to DC.
C circuit → LOG to convert DC converted signal to logarithm
The logarithmic conversion is performed by a converter (hereinafter, referred to as a logarithmic converter) 31 composed of a circuit, and further, an analog / digital converter (hereinafter, referred to as an A / D converter) 3
2 after the digital conversion by the computer 7
1 is input as a coupling current (I _mean ) a, and the other of the current signals is subjected to frequency conversion of about 1 Hz or less by the band-pass filter circuit 26, and is similarly log-converted by the log converter 41, and , After being digitally converted by the A / D converter 42, the computer 71 supplies an electrochemical current noise (I
_n ) Input as b.

Next, the voltage signal, that is, the potential difference between the second electrode 22 and the third electrode 23 is measured by a buffer circuit 25 as shown in FIG. After a frequency component of about 1 Hz or less is extracted by the band-pass filter circuit 27, the log component is again log-converted by the log converter 51, and the digital component is further converted by the A / D converter 52. Is input as the static potential noise (V _n ) c.

On the other hand, FIG. 3A and FIG.
In the figure, an example is shown in which the data processing circuit is configured by a digital circuit corresponding to the analog circuit configuration of (a) and (b).
The same reference numerals indicate the same or corresponding parts, and the same operation can be obtained by the digital circuit configuration.

Further, corrosion measurement data obtained by measuring a metal piece of the same material as the metal surface under the same corrosion conditions, that is,
For example, in FIG. 1, a sample test piece (strip coupon) 61 made of the same metal as the metal surface is used,
After the sample test piece 61 was immersed in the corrosive solution 12 in the corrosion measurement container 11 under the same corrosion conditions for a certain period of time, it was taken out, and the weight loss at that time was measured by the mass measuring device 62. The corrosion degree d obtained from the data is also stored in the data storage unit 72 of the computer 71.

In the computer 71, as shown in FIG. 1, each measurement data stored in the data storage section 72, that is, the coupling current (I _mean ) a and , Electrochemical current noise (I _n ) b and electrochemical potential noise (V _n ) c
Based on the respective measured data of the corrosion rate d and the corrosion rate d, the corresponding corrosion coefficients K ₁ , K ₂ and K ₃ are calculated by the following equations (1), (2) and (3).

Calculation of the first corrosion coefficient K ₁ (calculation step 7)
3)

(Equation 1) Here, C _n is the metal sample test piece 61 in the corrosion solution 12.
Is the degree of corrosion (mm) d when the sample is immersed for a predetermined time.
I _mean is the accumulated amount (ampere) of I _mean corresponding to the time (predetermined time) corresponding to the corrosion degree (d) C _n .

Calculation of the second corrosion coefficient K ₂ (calculation step 7)
4)

(Equation 2) Here, ΔI _n / V _n is the accumulation of the ratio of I _n (electrochemical current noise b) / V _n (electrochemical potential noise c) corresponding to the time (predetermined time) corresponding to the degree of corrosion C _n. Quantity (amps / volt).

Calculation of the third corrosion coefficient K ₃ (calculation step 7)
5)

(Equation 3) Here, .SIGMA.I _n and, the .SIGMA.I _mean and [sigma] v _n, I _n corresponding to the corrosion degree (d) time corresponding to C _n (predetermined time)
(Ampere) of (electrochemical current noise b)
The amount of accumulation (ampere) of I _mean (coupling current a) and the amount of accumulation (volt) of V _n (electrochemical potential noise c).

Next, the calculated respective By using each corrosion coefficients _{K 1, K 2, K 3} , and was measured every certain time period I _mean (coupling current a), I _n (Electrochemical (4), (5), and ( _n ) based on the measured data of the static current noise b) and V _n (electrochemical potential noise c).
The respective corrosion rates (mm
/ Year) is calculated _{C 1, C 2, C 3} .

Calculation of the first corrosion rate C ₁ (calculation step 7)
6)

(Equation 4)

Calculation of the second corrosion rate C ₂ (calculation step 7)
7)

(Equation 5)

Calculation of the third corrosion rate C ₃ (calculation step 7)
8)

(Equation 6)

Further, each of the calculated corrosion rates (mm /
Year) The average corrosion rate C is the value obtained by arithmetically averaging C ₁ , C ₂ , and C ₃
Calculate as ₄ .

Calculation of average corrosion rate C ₄ (calculation process 79)

Equation 7

Here, the transitions of the corrosion rates C ₁ , C ₂ , C ₃ and the average corrosion rate C ₄ obtained as described above are represented by C
It is output and displayed on the screen of the RT 101 and / or as a printout of the printer 102. Similarly, the instantaneous value of the corrosion rate and a transition of a trend value representing the corrosion rate in a time series can be output and displayed.

On the other hand, the output display shows the corrosion rate C ₁ ,
In addition to C ₂ , C ₃ and the average corrosion rate C ₄ , the coupling current (I _mean ) a and the electrochemical current noise (I
_n ) The instantaneous value of each measurement data with b and electrochemical potential noise (V _n ) c, the transition of the trend value expressed in a time series, and the accumulated value thereof are also correlated with each other. Can also be displayed.

Next, FIG. 4 shows an example of signal processing for judging the corrosion mode in this embodiment.

That is, in the present embodiment, as shown in FIG. 4, the degree of corrosion is determined by associating the coupling current (I _mean ) a with the electrochemical current noise (I _n ) b. It is possible to grasp.

In this case, the ratio of I _n (electrochemical current noise b) / I _mean (coupling current a) (I _n / I
_{Using the mean} comparison unit 81), the form of corrosion is divided into the following four forms, and each form is determined. Overall corrosion: 0.001 <I _n / I _mean <0.01 [Form determination of the overall corrosion 82] Mixed corrosion: 0.01 <I _n / I _mean <0.1 Local (partial) corrosion: 0.1 <I _n / I _mean <1.0 [Each form judgment 83 of the mixed and local corrosion] Pitching (porous corrosion): 1.0 <I _n / I _mean [A form judgment 84 of the pitting]

The ratio 81 of I _n / I _mean can be easily grasped by the output display from the instantaneous value and the transition of the trend value representing the instantaneous value in time series. be able to.

Further, in this embodiment, as shown in FIG. 4, the electrochemical current noise (I _n ) b or the electrochemical potential noise (V _n ) stored in the data storage section 72 is stored. C) From the measurement data of c, the noise peak waveform analyzer 91 determines the form of overall corrosion 95 and other forms of local corrosion, for example, the form determination 96 of stress corrosion cracking and the form determination 97 of pitting. It is done as follows. That is, in local corrosion,
This is because a quantitative determination such as a corrosion rate or a degree of corrosion in general corrosion is not sufficient, and it is important to determine a form of the corrosion.

In this case, regarding the local corrosion, in the measurement data of the electrochemical current noise (I _n ) b or the electrochemical potential noise (V _n ) c, a low-frequency noise component in the measurement data signal component is used. Is increased, the peak waveform signal of the low-frequency noise component can be analyzed to determine the form of the local corrosion.

Here, an example of a method of analyzing the form of the local corrosion is as follows. (A) Judgment is made by comparing the ratio of the peak height / peak width of the noise signal. (B) The judgment is made by comparing the peak repetition period of the noise signal. (C) The judgment is made by comparing the number of low frequency peak components of the noise signal.

Here, in the computer 71,
Described case of the embodiment determines the local corrosion in the use of the electrochemical current noise (I _n) b.

First, the peak waveform of the signal of the electrochemical current noise (I _n ) b extracted from the data storage unit 72 is analyzed by the noise peak waveform analysis unit 91, and subsequently,
The magnitude of the ratio of the peak height / peak width of the analyzed signal is compared by a height / width comparison unit 92, and the peak repetition period of the compared signal is compared with the repetition period detection unit 9.
3, and the number of low frequency peak components is compared by the frequency component number detection unit 94, and the respective results are classified into the following three types to determine the corrosion mode. (A) The noise signal in a region where the ratio of peak height / peak width is small and at least one of the peak repetition period and the number of low frequency peak components is small is corroded entirely. (B) A noise signal in a region where the ratio of peak height / peak width is large and at least one of the peak repetition period and the number of low frequency peak components is large is stress corrosion cracking. (C) The noise signal in the intermediate region between (a) and (b) is pitched.

That is, the electrochemical current noise (I _n )
The signal b is divided into the general corrosion 95 and the stress corrosion cracks 96 or the pitting 97 in this way, and the form of the corrosion is determined. Then, the judgment result is output and displayed on the CRT 101 or the printer 102, and the transition of the corrosion form can be easily grasped from the instantaneous value and the transition of the trend value representing the instantaneous value in a time series.

In this case, the judgment criteria were determined by using a standard metal sample specimen which had a known corrosion, stress corrosion cracking or pitting, and large, medium and small judgment criteria for each check item. Should be decided.

[0050]

As described above in detail with the embodiments, according to the present invention, in a corrosion measuring apparatus applied to corrosion measurement of a metal material, a plurality of electrodes of the same material as the metal surface to be corroded are measured. Measure the electrochemical current noise and electrochemical potential noise data between each electrode under the same corrosion conditions, and measure the measured electrochemical current noise and electrochemical potential noise. Time-sequentially accumulated, and the stored electrochemical current noise or electrochemical potential noise measurement data was taken out, the form of local corrosion was analyzed, and the analysis result was output and displayed. There is an excellent feature that the corrosion mode, particularly the corrosion rate of local corrosion and the corrosion mode can be monitored and judged with good reliability and industrially advantageously.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an outline of an overall configuration of a corrosion measuring apparatus including an embodiment of the present invention.

FIGS. 2A and 2B are block diagrams each showing an example in which a processing circuit for each measurement data signal of a current and a voltage in the above device is configured by an analog circuit.

FIGS. 3A and 3B are block diagrams each showing an example of a case where a processing circuit for current and voltage measurement data signals in the above device is configured by a digital circuit.

FIG. 4 is a block diagram illustrating an example of signal processing for determining a corrosion mode in the above device.

[Explanation of symbols]

Reference Signs List 11 Corrosion measurement container 12 Corrosive solution 21, 22, 23 Electrode 24 Non-resistance ammeter 25 Buffer circuit 26, 27 Bandpass filter circuit 31, 41, 51 Logarithmic converter 32, 42, 52 A / D converter 61 Sample test piece ( strip coupons) 62 mass meter 71 computer 72 data storage unit 73 calculating step 76 first first corrosion coefficient K ₁ of the process of calculating 74 the second calculation process of corrosion coefficient K ₂ of the 75 third corrosion coefficient K ₃ corrosion rate C ₁ of the calculation process 77 second calculation process 81 I _n / I _mean comparing unit 82 uniform corrosion of the process of calculating 79 an average corrosion rate C ₄ of the process of calculating 78 the third corrosion rate C ₃ of the corrosion rate C ₂ of 83 Form judgment of mixing and local corrosion 84 Form judgment of pitching 91 Noise peak waveform analysis section 92 Height / width comparison section 93 Repetition period Detector 94 Frequency component number detector 95 Judgment of form of general corrosion 96 Judgment of form of stress corrosion cracking 97 Judgment of form of pitching 101 CRT 102 Printer a Coupling current (I _mean ) b Electrochemical current noise (I _n ) c Electricity Chemical potential noise (V _n ) d Corrosion rate

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenji Morita 1-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu-shi, Fukuoka Inside the Mitsubishi Chemical Corporation Kurosaki Office

Claims (1)

[Claims] 1. A method in which a plurality of electrodes of the same or substantially the same material as a metal surface to be measured for corrosion are exposed to the same or substantially the same corrosion conditions, and the electrochemical current noise and electric current between the electrodes are measured. Corrosion current / voltage measurement means for measuring the chemical potential noise respectively; and taking the respective measurement data of the electrochemical current noise and the electrochemical potential noise measured by the corrosion current / voltage measurement means, and measuring the measured data. Data storage means that accumulates in a series, and retrieves measurement data of electrochemical current noise or electrochemical potential noise accumulated in time series in the data storage means, and extracts the retrieved electrochemical current noise or electrochemical A local corrosion form determining means for analyzing and determining the form of local corrosion from the measured data of the potential noise; And an output display means for outputting and displaying the local corrosion form.