JPH0331792B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a monitoring and control system for corrosion and corrosion protection of metals, and in particular to monitoring the corrosion rate and environment of metal structures, equipment, piping, containers, etc. exposed to corrosive media. The present invention relates to a corrosion/corrosion protection monitoring system and its device that prevent corrosion by controlling environmental factors based on the results of measuring and calculating factors.

[Background of the Invention] It is impossible for devices, structures, equipment, etc. made of metal materials to maintain permanent stability in their respective usage environments, and eventually oxides, which are in a thermodynamically stable state, Or it becomes hydroxide. This is a corrosion phenomenon, and corrosion prevention means reducing the rate at which it turns into oxides or hydroxides.

Corrosion prevention measures for metal materials include (1) selection of corrosion-resistant materials, (2) anti-corrosion design, (3) anti-corrosion coating, (4) water quality adjustment, (5) use of corrosion inhibitors, and (6) cathodic protection. being considered.

However, in most cases, actual corrosion problems are accelerated by environmental changes caused by non-uniformity of materials or inappropriate structures, discontinuities in operation, or other accidental causes, which cannot be predicted at the design stage. There are many. Therefore, continuous measurement of the corrosion rate of metal materials in various actual environments is extremely important for maintenance of equipment, structures, equipment, piping, containers, etc., and for prevention of corrosion problems. . For this reason, various methods for measuring the corrosion rate have been proposed in the past, and for example, in Japan, the Corrosion Prevention Association has reported the results of a survey on "corrosion monitoring using electrochemical measurements."

Traditional corrosion rate measurement methods can be classified into linear methods and indirect methods. Direct methods include (a) measurement of weight loss, (b) measurement of thickness change, (c) analysis of eluted metal ions, (d) measurement of amount of hydrogen generated, (e) measurement of oxygen consumption, (f) Measurement of electrical resistance change using a metal probe, (g) Measurement of electrochemical polarization resistance, etc. Also, as an indirect method, (h)
These include corrosion inhibitor concentration analysis, (i) PH measurement, (j) radioactive tracer analysis, and (k) redox potential measurement.

Among these measurement methods, methods (a) and (b) are basic methods for measuring the amount of corrosion, and although they determine the average corrosion rate over a certain period of time, continuous measurement of the corrosion rate is difficult. Method (c) allows continuous measurement of changes in metal ion concentration, but if the eluted ions change to oxides or hydroxides, there is a problem with sampling, and the corrosion rate cannot be determined directly. is not possible. Methods (d) and (e) are effective for hydrogen-evolving or oxygen-consuming corrosion, but are not common and require special detection probes. In method (f), a measuring device is commercially available as an electrical resistance probe method, but since the change in resistance of the sample is converted into a corrosion rate, there is a risk of overestimating the progress of local corrosion. However, method (g) forms the basis of the electrochemical method for measuring corrosion rate, which has recently become almost an established technology, and allows for continuous measurement. Then (h), (i), (j) and (k)
The method described above is only an indirect method, and it is impossible to determine the corrosion rate from these measured values, and it is only possible to qualitatively infer whether corrosion has occurred.

As described above, among the various corrosion rate measurement methods that have been proposed for corrosion monitoring, the direct measurement methods (a) to (f) cannot be used to directly and continuously measure the corrosion rate. On the other hand, indirect methods (h) to (k) do not provide qualitative The disadvantages of this method are that it only determines whether corrosion has occurred or not, and that it is not possible to measure the corrosion rate continuously.

As mentioned above, it is possible to continuously measure the corrosion rate using method (g), but it is not possible to clarify the correlation between corrosion behavior and various environmental factors with only such continuous measurement of the corrosion rate. First, at present, no attempt has been made to monitor and control corrosion and anticorrosion.

[Purpose of the invention]

In view of these problems of the prior art, the purpose of the present invention is to continuously measure the corrosion rate of metal materials under various environments, further continuously measure various corrosion environment factors, and calculate the correlation between them. The object of the present invention is to provide a corrosion protection monitoring and control system that maintains corrosion protection by controlling the above-mentioned corrosion factors based on this.

[Summary of the invention]

The corrosion/corrosion protection monitoring and control system of the present invention is a monitoring and control system for corrosion and corrosion protection of metal materials exposed to a corrosive medium having conductivity, and the corrosion rate is determined from the polarization resistance of the metal material in the corrosive medium. A device that continuously measures, a device that continuously measures various corrosive environmental factors of a corrosive medium, and the time between these continuously measured values of corrosion rate and the measured values of the various corrosive environmental factors mentioned above. A calculation device that identifies which of the various environmental factors the corrosion rate is caused by by a change in the corrosion rate by calculating the correlation between the changes in the corrosion rate; and an environmental factor control device that changes the environmental factor identified as the cause of the variation in the corrosion rate to a corrosion-protective side based on the correlation calculation.

[Embodiments of the invention]

FIG. 1 shows the basic configuration of an embodiment of the corrosion protection monitoring and control system of the present invention, in which 1 is a corrosive medium such as water or waste liquid, and 2 is a metal material to be protected against corrosion that is exposed to the corrosive medium. , 3 are measuring elements for detecting various environmental factors such as the pH of the corrosive medium, μS/cm, temperature, dissolved oxygen, inhibitor concentration, etc. 4 is a device that measures the polarization resistance of the metal material 2 in the corrosive medium 1 and continuously measures the corrosion rate from this polarization resistance; 5 is an environmental factor measuring element 3;
6 is a device that continuously measures various environmental factors as described above from the detection signals of , and 6 is a calculation that calculates the correlation between the corrosion rate measured by the corrosion rate measuring device 4 and the environmental factor measured by the environmental factor measuring device 5. It is a device.
This arithmetic device 6 is attached with a device 8 for displaying the correlation between corrosion rate and environmental factors, a device 9 for recording the data, and a device 10 for storing the data. Further, an environment control device 7 is directly connected to the arithmetic device 6. This environment control device 7 is a computing device 6
Based on the calculation results, the operation section that changes the various environmental factors described above is controlled.

Note that the corrosion rate measuring device 4 uses a known AC impedance method to measure the corrosion rate from polarization resistance. The measurement principle is shown in FIG. When two identical metal samples are placed in a solution, which is a corrosive environment, as shown in FIG. 5A, the electrical equivalent circuit of the corrosion system is expressed as shown in FIG. The basic equation for corrosion rate in this case is equation (1).

i _cprr = K/Rc... (1) where, i _cprr = corrosion rate (mm/y), K = constant (mm/y・Ω・cm ² ) Rc = polarization resistance (Ω・cm ² ) Rs= Solution resistance (Ω・cm ² ) Cd = interfacial capacitance. When a low frequency AC voltage V _l and a high frequency AC voltage V _h are applied between the above two metal samples, the impedance of this electrical equivalent circuit is: impedance at low frequency Z _l = 2Rc + Rs, impedance at high frequency
Z _h =Rs, and by measuring both of these, the polarization resistance Rc can be found. Therefore, in order to determine the corrosion rate, it is sufficient to know the proportionality constant K. proportionality constant K
Although there are various methods for determining, in the examples of the present invention, it was determined from a polarization curve showing the relationship between potential and current density. Figure 8 shows the relationship between polarization resistance and corrosion rate. As is clear from this figure, there is a nearly linear relationship between polarization resistance and corrosion rate. Therefore, the value of the proportionality constant K is found to be 270 mm/y·Ω·cm ² in the case of stainless steel.

In the corrosion protection monitoring and control system having the above configuration, the reference value of the corrosion rate of the metal sample 2 exposed to the corrosive medium 1 is stored in the arithmetic unit 6, and the detection signal of the environmental factor measuring element 3 is determined based on the environmental factor The measuring device 5 continuously measures environmental factors, and the corrosion rate measuring device 4 continuously measures the corrosion rate. The calculation device 6 continuously monitors these relationships and calculates the correlation. That is, the computing device 6
Continuously compare the temporal variation of the continuously measured corrosion rate with the temporal variation of various environmental factors, and determine which environmental factor the temporal variation of the corrosion rate is closest to, i.e. By calculating which environmental factor's temporal variation has the most correlation with the corrosion rate variation, we can determine the environmental factor most closely related to the corrosion rate variation, that is, the corrosion rate variation. Find out the environmental factors that appear to be the cause. The relationship between temporal fluctuations in corrosion rate and temporal fluctuations in various environmental factors is shown in Figures 3 and 5.
As shown in Figure 6, the corrosion rate varies depending on the environmental factors. Therefore, by monitoring the relationship between the temporal fluctuations of the corrosion rate and the temporal fluctuations of each environmental factor, it is possible to determine which environment the corrosion rate fluctuations are caused by. It is possible to find out whether the corrosion rate is influenced by variations in the corrosion rate, that is, which environmental factors are causing the variation in the corrosion rate. Calculating the correlation between various environmental factors and corrosion rate means performing the calculations as described above.

When the corrosion rate fluctuates above the standard value, the environmental factor identified as the cause of the corrosion rate by the above correlation calculation is corrected by controlling the environmental factor operating section through the operation of the environmental factor control device 7 based on the calculation device 6. By doing so, the corrosion rate is controlled below the standard value and the corrosion prevention effect is maintained.

FIG. 2 shows an example corresponding to the basic example shown in FIG. 1, and its basic configuration is the same as that in FIG.
Continuously measure the corrosion rate of the arithmetic unit 6. When it is found by the correlation calculation in the arithmetic unit 6 that the fluctuation in the corrosion rate is caused by a decrease in the inhibitor concentration, and the corrosion rate exceeds the reference value, the arithmetic unit 6 An example is shown in which an alarm device 11 directly connected to the vehicle issues an alarm and an inhibitor injection device 12 injects an inhibitor.

The system of this example contains 500 ppm of Cl ^- .
In 20% Na ₂ SO ₄ solution at pH 3-0 and temperature 105℃
Figure 3 shows the operation when monitoring and controlling the corrosion protection of SUS 304. In this case, from the above correlation calculation,
It has been found that the increase in the corrosion rate of SUS 304 is caused by a decrease in inhibitor concentration, and when the corrosion rate of SUS 304 increases over time and reaches a value of approximately 1 mm/y, an alarm is issued by the alarm device 11. At the same time as is displayed, Na ₂ HPO ₄ is injected into the corrosive medium 1 as an inhibitor from the inhibitor injection device 12. Then, the corrosion rate gradually decreases and is controlled to enter the corrosion-resistant region.

FIG. 4 shows an embodiment corresponding to still another example of the basic embodiment of the present invention shown in FIG.
This figure shows an example in which the present invention is implemented as a corrosion protection monitoring and control system for a waste liquid storage tank 13 made of SUS 304 that stores an ion exchange resin regenerated waste liquid 18 containing Na ₂ SO ₄ as a main component. In FIG. 4, the corrosion rate of the tank 13 is measured by a corrosion rate measuring device 4 connected to a metal sample 2, and the values of environmental factors determined by an environmental factor measuring device 5 are input into a calculation device 6. The correlation between the corrosion rate and environmental factors is calculated and monitored by the corrosion rate display device 8.
Furthermore, the computing device 6 includes an air bubbling device 1.
4. A PH adjustment device 15 and a start/stop device 16 for a waste liquid stirring pump 17 are connected.

The operation of the corrosion protection monitoring control according to the embodiment shown in FIG. 4 is shown in FIGS. 5 and 6. In Figure 5,
The decrease in dissolved oxygen in waste liquid and the increase in corrosion rate are closely related, and correlation calculations show that the former is the cause of the latter. The corrosion rate is a reference value of approximately 1 stored in the calculation device 6.
mm/y, the air bubbling device 14 and the waste liquid stirring pump 17 are operated to increase the dissolved oxygen concentration, thereby controlling the corrosion rate to decrease. In this way, the corrosion protection of the tank 13 is monitored and controlled. In FIG. 6, when H ₂ SO ₄ is injected into the waste liquid and the pH decreases, the corrosion rate increases. The temporal fluctuations in the pH of the waste liquid and the temporal fluctuations in the corrosion rate are closely related, and correlation calculations reveal that the former is the cause of the latter. When the pH value increases to approximately 1 mm/y, the PH adjustment device 15 is activated to inject NaOH into the waste liquid 18 according to a command from the arithmetic unit 6 shown in FIG. This results in
Control is performed to increase the pH and reduce the corrosion rate, and monitoring and control of corrosion protection is carried out.

〔Effect of the invention〕

According to the present invention, the correlation between the measured value of the corrosion rate and the measured value of various corrosive environmental factors is calculated, and the environmental factor considered to be the cause of the variation in the corrosion rate among the corrosive environmental factors is calculated. The control of the fluctuations in the environmental factors facilitates the management of environmental factor manipulation and enables accurate continuous monitoring and control of the corrosion protection of metal articles exposed to conductive corrosive media.

[Brief explanation of drawings]

Fig. 1 is a basic system diagram of an embodiment of the corrosion protection monitoring and control system of the present invention, and Fig. 2 corresponds to one example of Fig. 1, and is a system diagram of an embodiment in which inhibitor injection is used as an environmental factor manipulation means. , Figure 3 is a curve showing the change in corrosion rate and inhibitor concentration over time, Figure 4 corresponds to yet another example of Figure 1, and is implemented as a corrosion protection monitoring and control system for an ion exchange resin regenerated waste liquid storage tank. Fig. 5 is a curve showing the change in corrosion rate and dissolved oxygen concentration over time, Fig. 6 is a curve showing the change in corrosion rate and pH over time, and Fig. 7 a and b shows corrosion from polarization resistance. FIG. 8, which is an explanatory diagram of the AC impedance method for measuring velocity, is a diagram showing the relationship between polarization resistance and corrosion rate. DESCRIPTION OF SYMBOLS 1...Corrosion medium, 2...Metal material, 3...Environmental factor measuring element, 4...Corrosion rate measuring device, 5...
Environmental factor measuring device, 6... Arithmetic device, 7... Environmental control device, 8... Data display device, 9... Data recording device, 10... Data storage device, 11... Alarm device, 12... Inhibitor injection Device, 13...
Tank, 14... Air bubbling device, 15...
PH adjustment device, 16...Pump start/stop device, 17
... Stirring pump, 18 ... Used ion exchange resin regeneration waste liquid, 19 ... Sacrificial anode, 20 ... Display device, 21 ... Lining.

Claims (1)

[Scope of Claims] 1. A monitoring and control system for the corrosion and corrosion protection of metallic materials exposed to a corrosive medium having conductivity, which continuously measures the corrosion rate from the polarization resistance of the metallic material in the corrosive medium. a device for continuously measuring various corrosive environmental factors of a corrosive medium;
By calculating the correlation of temporal fluctuations between these continuously measured values of corrosion rate and the measured values of the various corrosive environmental factors described above, it is possible to determine which environment among the various environmental factors the fluctuations in corrosion rate are caused by. an arithmetic device that identifies whether the corrosion rate is caused by a change in a factor; and a calculation device that determines whether the corrosion rate is caused by a change in the corrosion rate; A corrosion/corrosion protection monitoring and control system consisting of an environmental factor control device that changes. 2. Corrosion/corrosion prevention monitoring and control according to claim 1, characterized in that a metal article exposed to a corrosive medium is used as an electrode, and the corrosion rate is continuously measured from the polarization resistance value with a counter electrode sample. system. 3. The corrosion/corrosion protection monitoring and control system according to claim 1, wherein the environmental factor control device includes means for injecting a corrosion inhibitor into the corrosive medium. 4. The corrosion/corrosion protection monitoring and control system according to claim 1, wherein the environmental factor control device includes a corrosive medium stirring means. 5. The corrosion/corrosion protection monitoring and control system according to claim 1, wherein the environmental factor control device includes means for changing the dissolved oxygen concentration of the corrosive medium.