JP3862122B2 - Metal corrosion monitoring method and metal corrosion prevention method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a metal corrosion monitoring method and a metal corrosion prevention method. More specifically, the present invention measures the potential change of the metal and the oxidative change of the water due to the adherence of microorganism-based dirt in a system in which the metal is in contact with water. The present invention relates to a metal corrosion monitoring method and a metal corrosion prevention method capable of predicting the property and promptly estimating factors causing corrosion and taking appropriate measures.
[0002]
[Prior art]
In general, in a fresh water environment such as a cooling water system, a corrosion-resistant metal such as stainless steel is passivated and is known as a corrosion-resistant material. However, when the oxidizing property of water is increased due to the presence of an excessive oxidizing agent, the potential becomes noble due to environmental changes such as adhesion of microorganism-based dirt to the surface, and local areas such as crevice corrosion, pitting corrosion, stress corrosion cracking, etc. Corrosion may occur (Nakahara Masahiro, Materials and Environment, Vol. 41, No. 1, p. 56, 1992). Thus, the potential increase of the metal material indicates that the risk of corrosion is increasing, and it is important to manage the potential so that the potential does not increase.
Conventionally, as a method of monitoring corrosion of a metal, a method of monitoring the natural potential of the metal in a system in which the metal and water are in contact is known (Japanese Patent Laid-Open No. Hei 5-98476). However, it is difficult to quickly estimate the cause of the potential rise and take appropriate measures quickly even though the conventional corrosion potential measurement alone can predict the danger of corrosion due to the potential rise. Met.
[0003]
[Problems to be solved by the invention]
The present invention predicts the risk of corrosion of metal pipes and the like in a system in which metal is in contact with water, and also promptly estimates the factors that cause corrosion and can take appropriate measures. The object is to provide a method and a method for preventing metal corrosion.
[0004]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have measured the change in the potential of the metal due to the adhesion of microorganisms in a system in which the metal is in contact with water. Based on this knowledge, we have found that it is possible to predict the risk of corrosion, and further, by measuring changes in water oxidizability and comparing the two, it is possible to accurately and quickly estimate the cause of corrosion. The invention has been completed.
That is, the present invention
(1) Metal corrosion characterized in that, in a system in which a metal is in contact with water, a change in the potential of the metal due to adhesion of dirt mainly due to microorganisms is measured over time, and on the other hand, an oxidative change in water is measured over time. Monitoring method,
(2) The change in the potential of the metal due to adhesion of dirt mainly from microorganisms is obtained from the change in potential of the metal in contact with water, and the change in oxidation of water is obtained from the change in potential of the electrode that measures redox properties. Metal corrosion monitoring method,
(3) The same material with which the change in the potential of the metal due to the adhesion of dirt mainly from microorganisms is obtained from the change in the potential of the metal in contact with water, and the oxidative change of water is in contact with water and the contact surface with water is not contaminated. The method for monitoring metal corrosion according to item (1), which is obtained by measuring the potential of the metal of
(4) In the method described in (1) , when there is only a tendency for the potential of the metal to increase due to adhesion of microorganism-based dirt, control is performed to increase the dose of a drug that inhibits microorganism-based dirt adhesion. , When the oxidization of water is increased with the increase in the potential of the metal due to adhesion of microorganism-based dirt, a metal corrosion prevention method for performing control to reduce the dosage , and
(5) The method for preventing metal corrosion according to ( 4 ) , wherein the chemical is a water treatment chemical containing an oxidizing substance .
Is to provide.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to a metal material that comes into contact with aqueous water (hereinafter referred to as test water) to be monitored, by measuring changes in the potential of the metal due to contamination mainly by microorganisms and changes in the oxidizing properties of water. In addition to monitoring the corrosion of the material, the cause of corrosion is estimated and appropriate measures are taken. The metal material to which the method of the present invention is applied is not particularly limited, but is low alloy steel, stainless steel, nickel, nickel alloy, titanium, titanium alloy, copper, copper alloy, chromium, chromium alloy, molybdenum, molybdenum alloy, tungsten, tungsten It can be particularly suitably applied to corrosion resistant alloys such as alloys. These corrosion-resistant alloys exhibit a small corrosion rate due to the passive film formed on the surface in a normal freshwater environment.
The change in the potential of the metal due to the adhesion of microorganism-based dirt is the time difference between the reference electrode (reference electrode) immersed in the same test water and a metal piece that is in contact with the test water and electrically insulated from the surroundings. It is possible to monitor by measuring at the same time. A lead wire is connected to the metal piece for potential measurement, and the potential is measured through the lead wire. The potential measurement method is not particularly limited, and examples thereof include a potentiometer, a digital multimeter, a tester, and a computer measurement using a voltage input A / D conversion device. In addition, all potential measurements can be performed using a computer.
The method of contacting the metal piece for potential measurement with the test water is that the metal piece for potential measurement is electrically insulated from the surrounding piping, etc., and the connection part between the lead wire used for potential measurement and the metal piece for potential measurement is There is no particular limitation as long as it is not in direct contact with the test water. For example, a test piece-like metal piece with an electrode attached to a test piece is immersed in the test water, or in an electrically insulated metal tube. The method of passing water can be mentioned.
[0006]
There is no particular limitation on the method for measuring the oxidative change of water, for example, a method of measuring the potential change of an electrode for measuring redox properties such as a redox electrode, or contamination on the contact surface with test water. A method of measuring the potential of a metal piece that is not present can be mentioned. The method of measuring the potential of a metal piece that is not contaminated on the contact surface with the test water is based on the phenomenon that the potential of the metal piece that comes into contact with water increases due to increased water oxidation. . The potential measurement method is not particularly limited, and examples thereof include a potentiometer, a digital multimeter, a tester, and a computer measurement using a voltage input A / D conversion device. When using an electrode for measuring oxidation-reduction properties, measure the potential difference between the electrode terminals, and when measuring the potential of a metal piece with no dirt on the contact surface with the test water, refer to The potential difference between the electrodes is measured.
The electrode dipping method for measuring oxidation-reduction properties is not particularly limited as long as the electrode is electrically insulated from surrounding piping and is in contact with test water. The method of contacting the test water with the metal piece for potential measurement, which is not contaminated with the contact surface with the test water, is because the metal piece for potential measurement is electrically insulated from the surrounding piping, etc. There is no particular limitation as long as the connecting part of the lead wire to be used and the metal piece for measuring the potential is not in direct contact with the test water, and an electrode-like one having the lead wire attached to the test piece-like metal piece is immersed in the test water. Examples thereof include a method and a method of passing test water through an electrically insulated metal tube.
[0007]
In observing the corrosion behavior of the metal material, it is preferable that the conditions for measuring the potential change of the metal due to the adhesion of dirt mainly composed of microorganisms coincide with the conditions for measuring the potential change due to the oxidation change of water. In other words, the measurement of the potential change due to the oxidative change of water is the same material and the same shape as the metal piece for measuring the potential change of the metal due to the adhesion of microorganism-based dirt, and the dirt does not adhere to the surface in contact with the test water. It is preferable to use what was made. In addition, the environmental conditions such as the flow rate and temperature of the water at the contact surface between the test water and the metal piece are also the conditions for measuring the potential change of the metal due to the adhesion of dirt mainly by microorganisms and the conditions for measuring the potential change due to the oxidative change of water It is preferable to adjust so that it becomes the same.
There are no particular restrictions on the method of preventing dirt from adhering to the surface of the metal piece that comes into contact with the test water. For example, the method of filtering the dirt component of the test water that comes into contact with the metal piece with a filter, brushing the surface of the metal piece, ultrasonic cleaning For example, a method of cleaning periodically may be used. The frequency of cleaning is not particularly limited as long as it can maintain a state in which dirt does not adhere to the surface of the metal piece.
Measures the potential change of metal due to the adhesion of dirt mainly by microorganisms kept in a state where dirt can be attached. The potential of the metal piece rises due to the adhesion of dirt mainly by microorganisms. It rises by strengthening. At this time, it is possible to quickly determine whether the cause of the potential increase is due to the adhesion of dirt mainly due to microorganisms or due to the increased oxidation of water by measuring the change in the oxidation of water. .
By using this monitoring result, it is possible to control the amount of water treatment agent containing an oxidizing substance, particularly a biofouling control agent that suppresses microbial contamination. For example, if the oxidation potential of water does not change and the potential of the metal piece kept in a state where dirt can be attached tends to increase, by controlling to increase the dosage, It is possible to suppress the adhesion of dirt. In addition, by measuring the oxidative change of water and determining that there is concern about corrosion due to excessive oxidization, excessive control of drugs containing oxidizing substances can be achieved by controlling to reduce the dose. It becomes possible to prevent the risk of corrosion due to the addition.
[0008]
FIG. 1 is an explanatory view showing an embodiment of the method of the present invention. In this embodiment, an electrode in which a conductive wire is attached to a corrosion-resistant metal test piece is used as the metal, and the dirt mainly composed of microorganisms is removed by a filter to prevent the adhesion of dirt. The test water is passed through two lines A and B. Line A is a line that allows dirt to adhere to metal, and line B is a line that prevents dirt from adhering to metal. The test water enters from the water pipe 1, branches and is led to both the A and B lines, and is adjusted through the constant flow valve 2 so that the flow rates of both the A and B lines are constant. Line A includes a column 5 into which a metal electrode 3a and a reference electrode 4 are inserted, and line B includes a column 5 into which a metal electrode 3b and a reference electrode 4 are inserted. Both lines of metal electrodes, reference electrodes, and columns have the same shape and structure. The line B further includes a filter 6 and removes dirt by filtration to prevent the dirt from adhering to the metal electrode. The potential change of the electrodes 3a and 3b with respect to the reference electrode is measured by the potential measuring device 7, and the presence / absence of the risk of corrosion and the cause are estimated from the potentials of the electrodes 3a and 3b. For example, if the potentials of the electrodes 3a and 3b both maintain a constant value and change stably, it is determined that there is no risk of corrosion. When the potential increase is recognized only in the electrode 3a, it is judged that the actual machine tends to adhere dirt mainly composed of microorganisms, and the risk of corrosion of the metal material tends to increase. When the potentials of the electrodes 3a and 3b are both increased, it is judged that the risk of corrosion due to the increase in oxidization in the system tends to increase. For example, when a water treatment chemical containing an oxidizing substance is used There is a risk of excessive addition, and it is necessary to adjust the dosage.
[0009]
FIG. 2 is an explanatory diagram showing another embodiment of the method of the present invention. In this embodiment, a metal tube having a conductive wire attached thereto is used, and test water is passed through the tube, and the dirt in the tube is periodically removed by a cleaning device, thereby removing dirt mainly composed of microorganisms. In addition to preventing adhesion, the amount of the water treatment chemical injected into the cold water tower is controlled based on the monitoring result of potential measurement. The test water is passed through two lines A and B. Line A is a line on which dirt can adhere to the metal, and line B is a line that prevents dirt from adhering to the metal. The test water enters from the water pipe 1, branches and is led to both the A and B lines, and is adjusted through the constant flow valve 2 so that the flow rates of both the A and B lines are constant. The metal tube 8a and the reference electrode 4 are installed in the line A, and the metal tube 8b and the reference electrode 4 are installed in the line B. Both lines of the metal tube and the reference electrode have the same shape. The line B further includes a cleaning tool 9 for periodically cleaning the inside of the tube with a brush or the like so that dirt is not attached to the metal tube 8b. The potential change of the metal tubes 8a and 8b with respect to the reference electrode is measured by the potential measuring device 7, and the presence / absence of the risk of corrosion and the cause are estimated from the potentials of the metal tubes 8a and 8b. For example, if the potentials of the metal tubes 8a and 8b both maintain a constant value and change stably, it is determined that there is no risk of corrosion. When the potential increase is recognized only in the metal tube 8a, it is judged that the actual machine tends to adhere dirt mainly composed of microorganisms, and the risk of corrosion of the corrosion-resistant metal material tends to increase. When the potentials of the metal tubes 8a and 8b are both increased, it is determined that the risk of corrosion due to an increase in oxidization in the system tends to increase. For example, a water treatment chemical containing an oxidizing substance is used. If it is, there is a risk of excessive addition, and it is necessary to adjust the dosage. The monitoring result by the potential measuring device is input to the control device 10, and the chemical injection pump 11 is controlled to appropriately control the chemical injection amount of the water treatment chemical from the chemical liquid tank 12 to the cold water tower 13.
[0010]
FIG. 3 is an explanatory diagram showing another embodiment of the method of the present invention. In this embodiment, a potential change due to adhesion of dirt mainly composed of microorganisms is obtained using an electrode having a lead wire attached to a corrosion-resistant metal test piece as a metal, and an oxidative change of water is obtained using an electrode for measuring oxidation-reduction properties. The test water is passed through two lines A and B. Line A is a line on which dirt can adhere to a metal, and line B is a line provided with a redox electrode. The test water enters from the water pipe 1, branches and is led to both the A and B lines, and is adjusted through the constant flow valve 2 so that the flow rates of both the A and B lines are constant. Line A includes a column 5 into which a corrosion-resistant metal electrode 3a and a reference electrode 4 are inserted, and line B includes a column 5 into which a redox electrode 14 is inserted. Both lines of columns have approximately the same shape and structure. The line B further includes a filter 6 and removes dirt by filtration to prevent the dirt from adhering to the redox electrode. The potential change of the electrode 3a and the redox electrode 14 with reference to the reference electrode is measured by the potential measuring device 7, and the presence or absence of the risk of corrosion and the cause are estimated from the potentials of the electrode 3a and the electrode 14. For example, it is determined that there is no risk of corrosion when the potentials of the electrode 3a and the electrode 14 both maintain a constant value and change stably. When an increase in potential is observed only in the electrode 3a, it is determined that the actual machine tends to adhere dirt mainly composed of microorganisms, and the risk of corrosion of the corrosion-resistant metal material tends to increase. When the potentials of the electrode 3a and the electrode 14 are both increased, it is determined that the risk of corrosion due to the increase in oxidization in the system tends to increase. For example, a water treatment chemical containing an oxidizing substance is used. In some cases, there is a risk of excessive addition, and the dosage should be adjusted.
According to the method of the present invention, the prediction of corrosion and the estimation of the cause of corrosion can be quickly performed from the change in potential of metal and the change in water oxidization due to adhesion of microorganism-based dirt. Can be evaluated comprehensively. In addition, based on the obtained monitoring results, it is possible to control the chemical injection amount of the water treatment chemical containing the oxidizing substance, and to perform proper chemical injection management.
[0011]
【The invention's effect】
According to the method of the present invention, the effect of the corrosion before the occurrence of corrosion can be estimated by promptly estimating the cause of corrosion and the cause of corrosion from the potential change of the metal and the oxidation change of water due to the adhesion of dirt mainly by microorganisms. It is possible to take general anti-corrosion measures. Moreover, based on the monitoring result, it becomes possible to control the chemical injection amount of the water treatment chemical containing the oxidizing substance and to maintain and manage an appropriate water treatment status.
[Brief description of the drawings]
FIG. 1 is an explanatory view showing an embodiment of the method of the present invention.
FIG. 2 is an explanatory view showing another embodiment of the method of the present invention.
FIG. 3 is an explanatory view showing another embodiment of the method of the present invention.
[Explanation of symbols]
1 Water supply pipe 2 Constant flow valve 3a Metal electrode (dirt can be attached)
3b Metal electrode (no contamination)
4 Reference electrode 5 Column 6 Filter 7 Potential measuring device 8a Metal tube (dirt can be attached)
8b Metal tube (no dirt)
DESCRIPTION OF SYMBOLS 9 Cleaning instrument 10 Control apparatus 11 Chemical injection pump 12 Chemical solution tank 13 Cold water tower 14 Redox electrode

Claims (5)

A metal corrosion monitoring method characterized in that, in a system in which a metal is in contact with water, a change in potential of the metal due to adhesion of dirt mainly composed of microorganisms is measured over time, and on the other hand, an oxidative change in water is measured over time .   The metal corrosion monitoring method according to claim 1, wherein a change in the potential of the metal due to adhesion of dirt mainly due to microorganisms is obtained from a change in the potential of the metal in contact with water, and a change in oxidation of water is obtained from a change in potential of the electrode for measuring redox properties.   The change in the potential of the metal due to the adhesion of dirt mainly from microorganisms is obtained from the change in the potential of the metal in contact with water. The metal corrosion monitoring method according to claim 1, which is obtained by measuring a potential. 2. The method according to claim 1, wherein when there is only a tendency of increasing the potential of the metal due to adhesion of microorganism-based dirt, control is performed to increase the dose of a drug that inhibits adhesion of microorganism-based dirt, A method for preventing metal corrosion , wherein when the oxidizability of water increases as the potential of the metal increases due to adhesion, the amount of the chemical injection is controlled to decrease . The method for preventing metal corrosion according to claim 4, wherein the chemical is a water treatment chemical containing an oxidizing substance.

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