JP2013076627A - Copper pitting corrosion evaluation method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper pitting corrosion evaluation method allowing accurate evaluation of a progress state of pitting corrosion generated in copper being in contact with an aqueous system.SOLUTION: In a pitting corrosion evaluation method of copper, an evaluation electrode including a plurality of anodes 2 composed of copper pieces covered with a corrosion product and a cathode 3 composed of a copper plate whose contact liquid surface is not covered with the corrosion product is immersed in an aqueous system, and a current flowing through a circuit electrically connecting the anodes 2 with the cathode 3 is measured by a zero-shunt ammeter.

Description

  The present invention relates to a method for evaluating corrosion of copper in contact with an aqueous system, particularly pitting corrosion, and more particularly, to the evaluation of copper using an evaluation electrode having an anode covered with a corrosion product and a cathode not covered with the corrosion product. The present invention relates to a pitting corrosion evaluation method.

  As methods for evaluating copper corrosion in water systems, JIS K 0100 describes a method for measuring the corrosion rate from the corrosion weight loss of the test piece, and a method for measuring the corrosion rate of the test electrode by the polarization resistance method. Not what you want. Japanese Patent Laid-Open No. 5-322831 describes a method for monitoring the risk of corrosion by measuring the potential of a test electrode.

  In Japanese Patent Laid-Open No. 2-310452, as a method of evaluating the progress of pitting corrosion occurring in an aqueous metal material, a liquid reservoir communicating with an aqueous medium through a small hole and a liquid in the liquid reservoir are contacted. A test piece provided, and using a monitor device in which the area of the surface of the metal piece in contact with the liquid in the liquid reservoir is larger than the opening area of the small hole, the metal piece and the metal member are electrically connected A method of monitoring local corrosion of a metal member by measuring the current flowing between the two in contact with each other.

JP-A-5-322831 JP-A-2-310452

  The method disclosed in JP-A-5-322831 is a method for monitoring the risk of pitting corrosion by measuring the potential continuously and comparing it with the potential at which pitting corrosion occurs. It is not a method of evaluating the inhibitory effect of water treatment agents on the situation and pitting corrosion.

  The method disclosed in Japanese Patent Laid-Open No. 2-310452 relates to a method for evaluating pitting corrosion of mild steel. When this method was applied to copper, the copper has a low exchange current density due to corrosion and is made of copper, which is a corrosion-resistant material. It was recognized that it was difficult to evaluate the progress of pitting corrosion.

  An object of the present invention is to provide a copper pitting corrosion evaluation method capable of accurately evaluating the progress of pitting corrosion occurring in copper in contact with an aqueous system. Moreover, this invention aims at providing the pitting corrosion evaluation method of copper which can evaluate the inhibitory effect of the water treatment chemical | medical agent with respect to pitting corrosion in the one aspect | mode.

  According to the copper pitting corrosion evaluation method of the present invention, a plurality of anodes made of copper pieces covered with corrosion products and a cathode made of copper pieces whose wetted surfaces are not covered with corrosion products are electrically connected. An evaluation electrode arranged in an insulated state is immersed in an aqueous system, a circuit is formed in which each anode is electrically connected in parallel to the cathode, and a current flowing through each anode is measured. .

  The cathode is made of a copper plate or a copper tube, and a plurality of through holes penetrating in the thickness direction are provided in the cathode, and an anode is inserted into each through hole. It is preferable that an insulating material is interposed between the side peripheral surfaces. Further, the front surface of the cathode and the front end surface of the anode are preferably flush with each other.

  In the present invention, the anode covered with the corrosion product is obtained by immersing the anode not covered with the corrosion product in water and energizing it to generate the corrosion product on the wetted surface of the anode. Is preferred.

  In the present invention, the treatment to be covered with the corrosion product may be performed at different times for each anode.

  It is difficult with the prior art by using an evaluation electrode in which the anode covered with the corrosion product and the cathode simulating a healthy surface not covered with the corrosion product are electrically insulated. It is possible to evaluate the progress of pitting corrosion. In the present invention, a highly reliable evaluation result can be obtained by providing a plurality of anodes in parallel.

  In the present invention, it is possible to evaluate the pitting corrosion that proceeds in the lower part of the corrosion product, and therefore it is possible to accurately evaluate the progress of pitting corrosion occurring in the actual copper piping or the like. It is also possible to evaluate the effect of water treatment chemicals on copper pitting corrosion.

  By subjecting each anode to a treatment for generating corrosion products at different times and measuring the short-circuit current between each anode and cathode, a highly reliable evaluation reflecting the environmental change of the water system becomes possible.

It is a block diagram of the evaluation in embodiment. It is a connection circuit diagram of the evaluation electrode and ammeter in an embodiment. It is a connection circuit diagram of the evaluation electrode and ammeter in an embodiment. It is a block diagram of the evaluation electrode in a comparative example. It is a graph which shows an experimental result. It is a graph which shows an experimental result. It is a graph which shows an experimental result.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

  FIG. 1 shows an example of the evaluation electrode. 1A is a front view of the evaluation electrode, and FIG. 1B is a cross-sectional view taken along the line BB of FIG. The evaluation electrode 1 is arranged in a state where a plurality (three in this embodiment) of anodes 2 and one cathode 3 are electrically insulated by a resin 4, and the coated conductor 5 is connected to the anode 2 and the cathode 3. , 6 are connected.

  The liquid contact surfaces of the anode 2 and the cathode 3 are flush with each other. The anode 2 and the cathode 3 are embedded in the resin 4 except for the liquid contact surface. An epoxy resin or the like can be used as the resin 4, but is not limited to this.

As the anode 2, for example, a copper wire can be used. The area of one wetted surface of the anode 2 is not limited as long as assessing the progression of localized corrosion, desirably 10 mm ² or less, more desirably 1 mm ² or less. The number of anodes 2 provided on the cathode 3 is preferably about 2 to 10, particularly about 3 to 6.

  For example, a copper plate or a copper tube can be used as the cathode 3, but a copper plate is used in this embodiment.

  The cathode 3 is provided with three through-holes, and the anode 2 is inserted into each through-hole. The front end surface of the anode 2 is the front surface of the cathode 3 (if the cathode 3 is a tube, the inner peripheral surface of the tube is the front surface). This is true). Resin is interposed between the side peripheral surface (outer peripheral surface) of the anode 2 and the hole surface (inner peripheral surface) of the through hole, and the two are insulated.

  The area of the liquid contact surface of the cathode 3 is not limited as long as the progress of local corrosion can be evaluated. However, the area of the liquid contact surface of the anode 2 needs to be larger than the area of the liquid contact surface of the anode 2. It is preferably at least 10 times, preferably 100 times or more, and more preferably 1000 times or more with respect to the total area of the surface.

  As a method for generating a corrosion product on the anode 2, a method in which the evaluation electrode 1 is immersed in water, a circuit in which the anode 2 and the cathode 3 are connected to a constant current generator is formed, and a predetermined current is applied for a certain period of time. It is possible to do so. Further, in addition to the evaluation electrode 1, it is possible to immerse the reference electrode and the counter electrode in water, use the anode 2 of the evaluation electrode 1 as a sample electrode, and apply a predetermined current for a certain time using a potentiogalvanostat or the like. is there.

  There are no particular limitations on the current value and the energization time for energizing the anode 2 as long as the anode 2 is covered with the corrosion product. Since the production of the corrosion product is affected by the water quality conditions, the current value, the energization time, etc. are appropriately adjusted according to the water quality.

  The treatment for generating the corrosion products on the plurality of anodes 2 may be performed at different times. Each of the plurality of anodes 2 is subjected to a treatment for generating a corrosion product at an arbitrary period and at a different time, thereby forming a corrosion product according to the state of the aqueous system at the time of performing the treatment. Therefore, assuming that pitting corrosion has occurred in the environment at the time when the processing is performed, it is possible to evaluate how the progress of the pitting corrosion changes thereafter.

  The progress of copper pitting corrosion is performed by electrically immersing the evaluation electrode 1 in the water to be evaluated and electrically connecting the anode 2 covered with the corrosion product and the cathode 3 simulating a healthy surface as shown in FIG. It can be evaluated by forming a connected circuit and measuring the current (short-circuit current) flowing through the circuit as pitting corrosion progresses. At that time, as shown in FIGS. 2 and 3, the anodes 2 are connected in parallel to the cathode 3, and the short-circuit current between the common cathode 3 and the plurality of installed anodes 2 is measured for each anode.

  The surface state of the copper-based member immersed in the aqueous system changes according to the environmental change of the aqueous system regardless of the occurrence of pitting corrosion. Also in the evaluation electrode 1 of the present invention, since the surface state of the cathode 3 changes according to the change in the aqueous environment, it is highly reliable by comparing the short-circuit current value flowing between the cathode 3 and each anode 2. Evaluation can be performed.

  By measuring the currents flowing through the plurality of anodes 2 that have been subjected to the treatment for generating the corrosion products at different times, it is possible to perform a more reliable evaluation reflecting the environmental change of the water system.

  The short-circuit current can be measured using a non-resistance ammeter 10 as shown in FIGS. Since the current value between the anode 2 and the cathode 3 corresponds to the progress rate of pitting corrosion, it is possible to evaluate the progress of pitting corrosion from the behavior of the short circuit current. In FIG. 2, a non-resistance ammeter 10 is arranged between each of the plurality of anodes 2 and cathodes 3 to measure a short circuit current. In FIG. 3, the short-circuit current flowing through each anode 2 is measured at regular intervals while the circuit between the anode 2 and the cathode 3 is switched by the switching circuit 11 using one non-resistance ammeter 10.

  For the circuit in which the anode 2 and the cathode 3 of the evaluation electrode 1 are electrically connected, the state of corrosion of the anode 2 can be evaluated by measuring the polarization resistance of the anode 2 with the circuit being disconnected. Is possible. The polarization resistance can be measured using the anode 2 as a sample electrode by a measuring method described in, for example, JIS K0100 “Industrial Water Corrosion Test Method”.

  It is possible to measure the natural potential of the evaluation electrode 1 in a state where the reference electrode is immersed in the evaluation water system and the anode 2 and the cathode 3 of the evaluation electrode 1 are short-circuited, and the short-circuit current measurement between the anode 2 and the cathode 3 is possible. By considering it together with the results, it becomes possible to consider the cause of the progress of pitting corrosion. It is also possible to measure the natural potential of each anode and to measure the potential difference between the anode 2 and the cathode 3 as long as the evaluation of the progress of pitting corrosion is not hindered.

  Periodically, the anode 2 may be energized, and the anode 2 covered with the corrosion product may be operated to elute copper to restore the anode 2 to an active state of corrosion. In this way, it becomes possible to evaluate with high sensitivity over a long period of time. The energization method can be performed by a method similar to the method of generating the corrosion product on the anode 2, and is preferably performed by appropriately adjusting the energization amount and the energization time.

  The process of energizing the plurality of anodes 2 to restore the anodes 2 to the active state of corrosion may be performed on all the anodes 2 at the same time or may be performed on the plurality of anodes 2 at different times. Each of the plurality of anodes 2 is subjected to a process of restoring the anode 2 to a corrosive active state at a different time after a certain period of time, so that evaluation using the anode 2 that is always highly active is performed over a long period of time. Is possible.

  It is also possible to evaluate the current water treatment effect against pitting corrosion from the short-circuit current change of the evaluation electrode 1 and to perform chemical injection control of the water treatment chemical.

  The immersion mode of the evaluation electrode 1 in the aqueous system is not particularly limited as long as the anode 2 and the cathode 3 are in contact with the aqueous water. The evaluation electrode 1 may be mounted on a pipe, may be mounted in a device such as a refrigerator, or may be mounted so as to be immersed in a tank or a cooling tower pit.

  A water treatment agent is added to the test water in a state where pitting corrosion is progressing, that is, in a state where current is flowing between the anode 2 and the cathode 3 covered with the corrosion products, and then the short-circuit current change or the anode 2 It is possible to evaluate the inhibitory effect on the pitting corrosion of the water treatment agent by changing the polarization resistance.

  In the present invention, copper means pure copper or a copper alloy having a copper content of 60% by weight or more.

  Hereinafter, examples and comparative examples will be described.

[Example 1]
Using the evaluation electrode 1 having the structure shown in FIG. 1 having three anodes, the progress of pitting corrosion was evaluated. Here, a copper specimen having a diameter of 30 mm was used as the anode 2 and a copper wire having a diameter of 0.45 mm and the cathode 3 having three holes having a diameter of 1 mm. Each hole was provided on the circumference having a radius of 7.5 mm from the center of the disk-shaped cathode 3 at an interval of 120 degrees. The surface of the anode 2 and the surface of the cathode 3 were wet-polished with # 400 abrasive paper. As the resin 4, an epoxy resin was used.

  This evaluation electrode 1 was installed in the cooling tower pit and immersed in cooling water. Table 1 shows the average water quality of the cooling water.

  The treatment for making the anode 2 covered with the corrosion product was performed on each anode 2 simultaneously. This treatment was performed by applying a current of 10 μA to the anode 2 for 2 hours using a potentiogalvanostat (potentiostat / galvanostat HA-151A type manufactured by Hokuto Denko). A carbon rod was used as a counter electrode, a saturated KCl silver-silver chloride electrode was used as a reference electrode, the anode 2 of the evaluation electrode 1 was used as a sample electrode, and corrosion products were generated at the anode 2.

  The anode 2 that has been treated so that the anode 2 is covered with the corrosion product immediately passes through the cathode 3 and a non-resistance ammeter (a portable non-resistance ammeter MODELAM-03 manufactured by Toho Giken) 10 as shown in FIG. Connection was made, and the current accompanying the progress of pitting corrosion was measured.

  FIG. 5 shows the change over time in the current between the anode 2 and the cathode 3 as the pitting corrosion progresses. The horizontal axis of the graph of FIG. 5 indicates the elapsed time when the process of completing the process in which each anode 2 is covered with the corrosion product is completed and the short-circuit current measurement with the cathode 3 is started is set to zero. Yes.

[Comparative Example 1]
In Example 1, an evaluation electrode was manufactured in the same manner as in Example 1 except that one hole (diameter 1 mm) was provided in the center of the cathode 3 and only one anode 2 was installed. FIG. 4 is a configuration diagram of this evaluation electrode. Three evaluation electrodes were produced. Each evaluation electrode 1 ′ was subjected to the same corrosion product generation treatment as in Example 1. These three evaluation electrodes 1a, 1b, and 1c were installed in the same cooling tower as in Example 1, and the change with time of pitting corrosion was measured at the same time as in Example 1. The results are shown in FIG.

[Consideration of Example 1 and Comparative Example 1]
From the 35th to the 40th day from the start of evaluation, there was a failure in which the concentration of oxidizing substances in the water system became abnormal. The short-circuit currents flowing through the three anodes 2 (anode I, anode II, and anode III) of the evaluation electrode 1 of Example 1 showed the same change, whereas the three evaluation electrodes 1 (evaluation of the comparative example) The short-circuit currents flowing through the anodes of the electrode 11a, the evaluation electrode 1b, and the evaluation electrode 1c) resulted in large variations. From this result, it was recognized that according to Example 1, it is possible to evaluate pitting corrosion with high accuracy and less variation compared to Comparative Example 1.

[Example 2]
The same evaluation electrode 1 as in Example 1 having three anodes was prepared, installed in the cooling tower pit, and immersed in cooling water. Table 2 shows the average water quality of the cooling water.

  In the present example, the process of making the three anodes 2 covered with the corrosion products was performed in three different times. That is, first, a corrosion product formation process is performed on the first anode A, five days later, a corrosion product formation process is performed on the anode B, and five days later, a corrosion product formation process is performed on the anode C. It was. The treatment for making the anode 2 covered with the corrosion product is the same as in Example 1, using a potentiogalvanostat (potentiostat / galvanostat HA-151A type manufactured by Hokuto Denko). This was performed by applying a current of 10 μA for 2 hours. A carbon rod was used as a counter electrode, a saturated KCl silver-silver chloride electrode was used as a reference electrode, the anode 2 of the evaluation electrode 1 was used as a sample electrode, and corrosion products were generated at the anode 2.

  After the anode 2 was covered with the corrosion product, the anode 2 was immediately connected to the cathode 3 via a non-resistance ammeter (Toho Giken portable non-resistance ammeter MODELAM-03) The electric current with the progress of eating was measured.

  FIG. 7 shows changes with time in the current between the anodes A, B, C and the cathode. The horizontal axis of FIG. 7 shows the elapsed time when the process of completing the anode A covered with the corrosion product is completed and the measurement of the short-circuit current with the cathode is started is zero. The current values corresponding to the anode B and the anode C are recorded from the time point when the measurement of the current between the cathode and the cathode is completed after the treatment to be covered with the corrosion product is completed. The time when the anode B was treated to be in a state of being covered with the corrosion product was the time when the concentration of the water treatment chemical added to the water system was reduced to a maximum of a quarter of the normal level. overlapping.

  A failure occurred in which the concentration of the oxidizing substance in the aqueous system became abnormal after 22 days from the start of the current measurement of the anode A. At this time, the current values of all the anodes A, B, and C showed an upward trend, but there was a difference in the degree of current increase, and the result was that the anode B was at a higher level than the others. This is presumably because the property of the corrosion product formed on the anode B was affected by the decrease in the concentration of the water treatment chemical at the time when the treatment was carried out so as to be covered with the corrosion product.

  From the above results, the corrosion products corresponding to the state of the water system at the time of the treatment are formed by performing the treatment for generating the corrosion products at different times for each of the plurality of anodes 2 (A, B, C). Therefore, it was confirmed that the evaluation reflecting the environmental change of the water system would be possible.

1, 1 'Evaluation electrode 2 Anode 3 Cathode 4 Resin 10 Non-resistance ammeter

Claims (5)

  An evaluation electrode in which a plurality of anodes made of copper pieces covered with corrosion products and a cathode made of copper pieces whose wetted surfaces are not covered with corrosion products are electrically insulated. A copper pitting corrosion evaluation method comprising: dipping in an aqueous system; forming a circuit in which each anode is electrically connected in parallel to the cathode; and measuring a current flowing through each anode. In claim 1, the cathode comprises a copper plate or a copper tube,
The cathode is provided with a plurality of through holes penetrating in the thickness direction,
Anode is inserted in each through hole,
A pitting corrosion evaluation method, wherein an insulating material is interposed between a hole surface of the through hole and a side peripheral surface of the anode.   3. The copper pitting corrosion evaluation method according to claim 2, wherein the front surface of the cathode and the front end surface of the anode are flush with each other.   The anode covered with a corrosion product according to any one of claims 1 to 3, wherein the anode not covered with the corrosion product is energized by immersing the anode in water, and the corrosion product is formed on the wetted surface of the anode. A method for evaluating pitting corrosion of copper, characterized in that   5. The copper pitting corrosion evaluation method according to claim 4, wherein the process of covering the substrate with the corrosion product is performed at different times for each anode.

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