JPH09297117A - Corrosion measuring device for metallic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To grasp the state of corrosion with high reliability by exposing a metal electrode of the same material as a metal surface to be measured to accumulate current measurement data, exposing a metal sample of the same material to measure the corrosion degree from the corrosion loss, and comparing the current measurement data with the corrosion degree measurement data. SOLUTION: Measuring electrodes 21, 22, 23 of the same material as a metal surface to be measured are dipped in a corrosive solution 12 and exposed to the same corrosive condition. A coupling current (a) is generated between the electrodes 21, 22, and accumulated in the data memory part 72 of a computer 71 in time series. An electrochemical current noise (b) and an electrochemical potential noise (c) are also accumulated in the data memory part 72. Further, a sample test piece 61 of the same material is used, and the corrosion degree (d) obtained by dipping it in the corrosive solution 12 for a fixed time under the same condition and then measuring the corrosion loss is also accumulated in the memory part 72. In the computer 71, corrosion coefficients K1 , K2 , K3 are calculated, and corrosion speeds C1 , C2 , C3 and average corrosion speed C4 are then calculated to easily measure the general corrosion and local corrosion.

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 measuring device by an electrochemical noise method capable of measuring general corrosion and local corrosion of a metal material and grasping the states of the general corrosion and 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).

In this weight loss measuring 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 too late. And (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 the above situation, the present invention enables reliable and industrially advantageous monitoring of corrosion rates of general corrosion and local corrosion of metal surfaces by using the electrochemical noise method. To provide a corrosion measuring device for a metal material.

[0013]

In order to achieve the above object, the invention according to claim 1 according to the present invention is characterized in that a plurality of metal electrodes made of the same or substantially the same material as the metal surface to be measured for corrosion are the same. Alternatively, a metal sample of the same or substantially the same material as the corrosion current measuring means for measuring the coupling current and the electrochemical current noise between the metal electrodes under the condition of being exposed to substantially the same corrosion conditions. Under the same or almost the same corrosion condition, the corrosion degree measuring means for measuring the corrosion degree from the corrosion weight loss of the metal sample, and the coupling current and electrochemical measured by the corrosion current measuring means. Data storage means for taking in and accumulating each current measurement data of current noise in time series, and for taking in and accumulating the corrosion degree measurement data measured by the corrosion degree measuring means Corrosion coefficient calculation means for calculating each corrosion coefficient by mutually comparing each current measurement data and corrosion degree measurement data accumulated in the data storage means, and calculated by each current measurement data and the corrosion coefficient calculation means Corrosion rate calculation means for calculating respective corrosion rates and average corrosion rates from corresponding corresponding corrosion coefficients, and output display means for outputting and displaying the corrosion rates and average corrosion rates calculated by the corrosion rate calculation means in time series. A corrosion measuring device for metallic materials, comprising:

In the corrosion measuring apparatus of the present invention, first, the coupling current and the electrochemical current noise between the metal electrodes exposed to the corrosive condition are stored in the data storage means after being measured by the corrosion current measuring means. Corrosion of metal samples accumulated in time series and exposed under the same corrosion conditions
After being measured by the corrosion degree measuring means, it is accumulated in time series in the data storage means. Next, the corrosion coefficient calculation means calculates each corrosion coefficient by comparing each current measurement data and corrosion degree measurement data with each other, and subsequently,
Corrosion rates and average corrosion rates are calculated from the respective current measurement data and corresponding corrosion coefficients by the corrosion rate calculation means, and the calculated corrosion rates and average corrosion rates are output and displayed in time series by the output display means. Will be done.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a metal material corrosion measuring apparatus 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 according to the present embodiment has a corrosion measuring container 11 in which a required amount of corrosive solution 12 is stored. Is the same or almost the same material 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)
It is the accumulated amount of I _mean (coupling current a) (ampere) and the accumulated amount of V _n (electrochemical potential noise c) (volt).

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)

[Formula 5]

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

[Formula 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)

[Formula 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, by correlating the coupling current (I _mean ) a and the electrochemical current noise (I _n ) b, the degree of corrosion, in other words, the degree of local corrosion can be grasped.

In this case, the form of corrosion is classified into the following four forms according to the ratio of I _n (electrochemical current noise b) / I _mean (coupling current a). General corrosion: 0.001 <I _n / I _mean <0.01 Mixed corrosion: 0.01 <I _n / I _mean <0.1 Local (partial) corrosion: 0.1 <I _n / I _mean <1. 0 Pitching: 1.0 <I _n / I _mean

With respect to the ratio of I _n / I _mean , the transition of the desired form of corrosion can be grasped from the instantaneous value and the transition of the trend value representing it in time series by the output display. In addition to the corrosion rates C ₁ , C ₂ , C ₃ and the average corrosion rate C ₄ , the coupling current (I _mean ) a, the electrochemical current noise (I _n ) is added to the output. The instantaneous value of each measurement data such as b and the electrochemical potential noise (V _n ) c, the transition of the trend value representing it in time series, and the cumulative value thereof are also displayed in association with each other. You can also do it.

Next, a substantial and specific apparatus configuration to which the above-described embodiment example is applied and an experimental example will be described.

FIG. 4 is an explanatory view schematically showing the outline of the apparatus configuration according to this example, and FIG. 5 is a graph showing an example of the same experimental results.

Here, the product tank 101 shown in FIG. 4 is used as a measurement object, and the metal top plate 102 of the product tank 101 is used.
Corresponding corrosion measurement device (electrochemical noise measurement device)
Was attached to measure corrosion of the metal top plate 102 by corrosive gas. Here, in order to prevent the corrosive gas contained in the product from corroding the product tank 101, nitrogen gas is blown into the inside of the product tank 101 to seal the product tank 101 to adjust the corrosion. In FIG. 4, reference numeral 10
3 is an auxiliary equipment of the product tank 101.

That is, with respect to the inside of the product tank 101,
As shown in FIG. 1, the polarization resistance measurement method is applied to dispose three electrodes 21, 22, and 23 of the same metal material as the inner metal surface of the metal top plate 102, and to corrode the inside. After introducing the gas, as described above, the coupling current (I _mean ) a and the electrochemical current noise (I _n ) b
And electrochemical potential noise (V _n) c were measured, respectively. On the other hand, by applying the mass loss measurement method, the sample test piece 61 of the same metal material as the metal surface is exposed to the same corrosion conditions, and after a certain period of time, the weight loss of the corrosion is measured, and the mass measurement is performed. The degree of corrosion d was determined from the data.

Then, the corrosion coefficients K ₁ , K ₂ and K ₃ are calculated by the equations (1), (2) and (3), and the above-mentioned (4), (5) and (6) are obtained. ) And equation (7) to calculate the average corrosion rate (mm / year) C ₄ . The results are shown in the graph of FIG.

As is clear from the graph of FIG. 5, the corrosion rate when the present corrosion measuring means is used is about 0.3 mm / year on average, and here it is easy to measure the corrosion in real time. It is possible. On the other hand, the corrosion rate by the mass loss measurement method is about 0.3 to 0.4 on average.
mm / year, which was almost the same result.

[0047]

As described above in detail with reference to the embodiments, according to the present invention, in the corrosion measuring apparatus applied to the corrosion measurement of the metal material, a plurality of materials having the same or substantially the same material as the metal surface to be measured for corrosion are used. With the metal electrodes exposed to the same or almost the same corrosion condition, the coupling current and the electrochemical current noise between the metal electrodes were measured respectively, and the measured current measurement data were obtained. Accumulated in time series, and in the state where the metal sample of the same or almost the same material as the above is exposed to the same or almost the same corrosion condition, the corrosion degree is measured from the corrosion weight loss of the metal sample,
The corrosion rate measurement data is accumulated, and the respective current measurement data and the corrosion rate measurement data are compared with each other to calculate the respective corrosion coefficients, and then the respective current measurement data and the corresponding corrosion coefficients. Since the respective corrosion rate and average corrosion rate are calculated from, the general corrosion and local corrosion of the metal material can be easily measured, and the state of the general corrosion and local corrosion can be reliably and industrially determined. Also has an excellent feature that it can be grasped advantageously.

[Brief description of 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 an explanatory diagram schematically showing an outline of a corrosion measuring device embodied in the present embodiment.

FIG. 5 is a graph showing an example of the same experimental result.

[Explanation of symbols]

11 Corrosion Measuring 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 ( 62 coupon measuring device 71 computer 72 data storage unit 73 calculation process of _first corrosion coefficient K ₁ 74 calculation process of second corrosion coefficient K ₂ 75 calculation process of third corrosion coefficient K ₃ 76 first Corrosion rate C ₁ calculation process 77 Second corrosion rate C ₂ calculation process 78 Third corrosion rate C ₃ calculation process 79 Average corrosion rate C ₄ calculation process 81 CRT 82 Printer 101 Product tank 102 Product tank 102 Metal top plate 103 Ancillary equipment for product tank a Coupling current (I _mean ) b Electrochemical current noise (I _n ) c Electricity Chemical potential noise (V _n ) d Corrosion degree

 ──────────────────────────────────────────────────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 coupling current and an electric current between each metal electrode under the condition that a plurality of metal electrodes made of the same or almost the same material as the metal surface to be measured for corrosion are exposed to the same or almost the same corrosion condition. Corrosion current measuring means for respectively measuring chemical current noise and a metal sample of the same or almost the same material as the above are exposed under the same or almost the same corrosion condition, and the corrosion weight loss of the metal sample And a corrosion degree measuring means for measuring, while accumulating in time series the current measurement data of each of the coupling current and the electrochemical current noise measured by the corrosion current measuring means and accumulating in time series, the corrosion degree is measured by the means. Data storage means for taking in and accumulating the corrosion degree measurement data, and the current measurement data and the corrosion degree measurement data accumulated in the data storage means are mutually paired. Corrosion coefficient calculation means for calculating each corrosion coefficient by comparison, and each corrosion rate and average corrosion rate are calculated from each current measurement data and each corresponding corrosion coefficient calculated by the corrosion coefficient calculation means. A corrosion measuring device for a metal material, comprising: a corrosion rate calculating means; and an output displaying means for outputting and displaying the corrosion rate and the average corrosion rate calculated by the corrosion rate calculating means in time series.