Method for fabricating an electrode for measuring pitting potential, an electrode for measuring pitting potential, and a method for measuring pitting potential.

Abstract

This invention provides a method for manufacturing a pitting potential measuring electrode that has a uniform surface area, a pitting potential measuring electrode, and a method for measuring pitting potential using this electrode. [Solution] This electrode 80 for measuring pitting potential and its manufacturing method involves sandwiching a test metal plate 30 between two heat-laminated films 34, each having an opening 36 of a predetermined size on one side, and then pouching the two films to seal the test metal plate 30 within an insulating pouch covering 34a. This allows for the easy manufacture of an electrode 80 for measuring pitting potential in which a predetermined area is exposed as a measuring surface 31a, while the remaining portion is insulated and waterproofed by the pouch covering 34a. In particular, by forming the opening 36 using a punching die, an electrode 80 for measuring pitting potential with a measuring surface 31a of the same area can be manufactured very easily and quickly.

Description

[Technical Field]

[0001] This invention involves applying an electric potential to a test metal plate in a test solution to induce pitting corrosion. This invention relates to pitting potential measurement for evaluating the corrosion resistance of test metals, and more particularly to a method for manufacturing a pitting potential measurement electrode used in this measurement, the pitting potential measurement electrode itself, and a method for measuring pitting potential using this pitting potential measurement electrode. [Background technology]

[0002] Stainless steel is a general term for steel containing 11% or more chromium and is recognized as a highly corrosion-resistant metal that is resistant to rust. This high corrosion resistance is due to the formation of a highly protective film called a passive film on the surface of stainless steel. This passive film is an oxide (hydroxide) containing iron and chromium, and its thickness is extremely thin, 1-3 nm, and it is formed when chromium is oxidized by oxygen in the atmosphere. Furthermore, even if the passive film is damaged by scratches or other means and the underlying metal is temporarily exposed, it is immediately repaired when exposed to air or water, maintaining corrosion resistance. However, in the case of stainless steel piping, for example, corrosion may occur depending on the usage environment and the quality of the water flowing through the pipe. Such corrosion of stainless steel piping is caused by the fact that even if the above-mentioned passive film is damaged, it does not recover, and an anode reaction occurs, causing iron to dissolve. In addition, when the pH of the water is in the neutral range, a cathode reaction in which oxygen accepts electrons proceeds simultaneously in areas where the passive film is normal, forming a corrosion cell, and localized corrosion known as local corrosion progresses.

[0003] Furthermore, the passive film is known to be subjected to chemical destruction not only by physical damage such as scratches, but also by halogen elements in water. Halogen elements are also known to inhibit the formation of the passive film, particularly chloride ions (Cl), which are abundant in the environment. -) is often a problem. Furthermore, it is known that the aforementioned localized corrosion risks occur when the natural immersion potential is nobler (exceeds) than the critical potential for localized corrosion. There are various forms of localized corrosion, but one of these, called pitting corrosion, is a phenomenon in which small holes occur locally, causing deep erosion and eventually penetrating the metal part, leading to leaks in pipes, etc. Therefore, when evaluating the risk of pitting corrosion in stainless steel materials, it is important to know the value of the pitting potential that corresponds to the critical potential for localized corrosion mentioned above.

[0004] The method for measuring the pitting potential involves first preparing a measuring electrode using a plate of the test metal. Next, the measuring electrode is immersed in a test solution, and the potential of the measuring electrode is swept (increased) at a predetermined rate. When the current density flowing through the measuring electrode exceeds a predetermined potential, that potential is defined as the pitting potential of the test metal. Herein, [Patent Document 1] discloses an invention relating to a pitting potential measuring device that can measure under special conditions.

[0005] Furthermore, when the test metal is stainless steel, the measurement conditions for pitting potential are specified by the Japanese Industrial Standard JIS G 0577, which lists "crevice corrosion prevention electrodes" and "coated electrodes using insulating materials such as resin" as usable measuring electrodes. However, "crevice corrosion prevention electrodes" have a complex structure, incurring considerable costs for manufacturing measuring electrodes, and require "adjusting the amount of distilled water or deionized water seeping out of the crevice corrosion prevention electrode to 2-6 mL / h" during pitting potential measurement, making them difficult to handle. In this respect, "coated electrodes using insulating materials such as resin" have an exposed portion of 1 cm on the test metal plate. 2 The specifications stipulate that the electrodes should be covered or embedded with an insulating material such as epoxy resin, polyvinyl chloride resin, or silicone resin. This eliminates the need for water flow during measurement, and the structure is simpler and easier to handle compared to "crevice corrosion prevention electrodes." [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 07-092131 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, although the structure of the "coated electrode using an insulating material such as resin" is simple, the measurement part (exposed part) is 1 cm 2 Applying insulating resin to the test metal plate by hand in this manner is not easy, and the quality of the result will vary depending on the skill level of the worker. In particular, variations in the area of ​​the measurement area are a major factor that reduces the reliability of the measurement results.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for manufacturing a pitting potential measuring electrode that can be easily manufactured with a uniform measurement area, the pitting potential measuring electrode itself, and a method for measuring pitting potential using the pitting potential measuring electrode. [Means for solving the problem]

[0009] The present invention (1) Procedure for connecting the wire 32 to the test metal plate 30, A procedure for forming an opening 36 in one side of an insulating thermal laminate film 34, The procedure involves positioning the opening 36 on the measuring surface 31 of the test metal plate 30, and sandwiching the test metal plate 30 between a heat-laminated film 34 with the opening 36 formed therein and a heat-laminated film 34 without the opening 36 formed therein. The above problem is solved by providing a method for manufacturing a pitting potential measuring electrode 80, which includes the steps of: thermally pressing a heat-laminated film 34 onto the test metal plate 30 while the test metal plate 30 is sandwiched between the plates to pouch the test metal plate 30, sealing the test metal plate 30 within the pouch covering 34a formed by the heat-laminated film 34, and bringing the opening 36 into close contact with the measuring surface 31. (2) The above problem is solved by providing a method for manufacturing the electrode 80 for measuring pitting potential described in (1) above, characterized in that the opening 36 of the thermal laminate film 34 is formed by punching. (3) Punching with a circular die with a diameter of φ11.5 mm to create a 1 cm² area. 2 The above problem is solved by providing a method for manufacturing the pitting potential measuring electrode 80 described in (2) above, characterized in that the opening 36 is formed in the thermal laminate film 34. (4) The wire 32 connected to the test metal plate 30, An insulating pouch covering 34a containing the aforementioned test metal plate 30, An opening 36 is formed in the pouch covering 34a and partially exposes the measuring surface 31, The above problem is solved by providing a pitting potential measuring electrode 80 having a waterproof coating 38 applied to the gap between the pouch coating 34a and the conductor 32. (5) The area of ​​the opening 36 of the pouch covering 34a is 1 cm 2 The above problem is solved by providing the electrode 80 for measuring pitting potential described in (4) above, characterized in that it is the above. (6) A procedure for manufacturing a pitting potential measuring electrode 80 by the method for manufacturing a pitting potential measuring electrode 80 described in any of (1) to (3) above, The procedure involves immersing the pitting potential measuring electrode 80 and counter electrode 22 in a test solution maintained at a predetermined liquid temperature, and immersing the reference electrode 20 in a predetermined solution, A procedure for sweeping the potential of the pitting potential measuring electrode 80 at a preset speed and measuring the current density flowing through the pitting potential measuring electrode 80, The above problem is solved by providing a pitting potential measurement method that includes a procedure for obtaining the pitting potential based on the potential when the current density exceeds a predetermined value. [Effects of the Invention]

[0010] The electrode 80 for measuring the pitting potential according to the present invention and its manufacturing method sandwich a test metal plate 30 with two thermally laminated films 34 each having an opening 36 of a predetermined size on one side, and thermocompression bond them to form a pouch, thereby enclosing the test metal plate 30 in an insulating pouch coating 34a. Thereby, the electrode 80 for measuring the pitting potential corresponding to "a coated electrode using an insulator such as resin" can be easily and inexpensively manufactured. In particular, by forming the opening 36 using a punching die, the electrode 80 for measuring the pitting potential having a measurement surface 31a of the same area can be manufactured more simply and in a shorter time than before.

Brief Description of Drawings

[0011] [Figure 1] It is a flowchart of the manufacturing method of the electrode for measuring the pitting potential according to the present invention. [Figure 2] It is a diagram for explaining the manufacturing method of the electrode for measuring the pitting potential according to the present invention. [Figure 3] It is a schematic configuration diagram showing a pitting potential measuring device. [Figure 4] It is a graph showing the verification result of the electrode for measuring the pitting potential according to the present invention. [Figure 5] It is a graph showing the verification result of the electrode for measuring the pitting potential according to the present invention. [Figure 6] It is an anodic polarization curve showing the verification result of the electrode for measuring the pitting potential according to the present invention.

Embodiments for Carrying Out the Invention

[0012] The manufacturing method of the electrode 80 for measuring the pitting potential according to the present invention, the electrode 80 for measuring the pitting potential, and the method for measuring the pitting potential using the electrode 80 for measuring the pitting potential will be described based on the drawings. Here, FIG. 1 is a flowchart of the manufacturing method of the electrode 80 for measuring the pitting potential. Further, FIG. 2 is a diagram for explaining the manufacturing method of the electrode 80 for measuring the pitting potential.

[0013] In the method for manufacturing the electrode 80 for measuring pitting potential according to the present invention, first, a test metal plate 30 of the metal to be measured is obtained. The thickness of this test metal plate 30 is not particularly limited as long as it is a thickness that can be pouched with a general thermal laminate film 34, but it is preferably about 0.1 mm to 0.6 mm. There are also no particular limitations on the length and width dimensions, but it is preferably about 20 mm x 30 mm to 50 mm x 50 mm (test metal plate acquisition step S102).

[0014] Next, as shown in Figure 2(a), a conductor 32 is connected to one side of the test metal plate 30 by soldering, spot welding, or the like (conductor connection step S104). It is preferable to make the connection on the back side, as far away as possible, so that the heat generated during connection does not affect the measuring surface 31, as described in JIS G 0577. In this configuration, the conductor 32 is not located on the measuring surface 31, maintaining its smoothness, and simultaneously ensuring that the opening 36, described later, makes close contact with the measuring surface 31. There are no particular limitations on the conductor 32 used; well-known conductive copper or stainless steel wires can be used. This establishes electrical conductivity between the test metal plate 30 and the conductor 32. It is preferable that the diameter of the conductor 32 be approximately 0.5 mm to 2 mm, as a thicker wire would increase the gap S between it and the heat-laminated film 34.

[0015] Next, an insulating heat-laminated film 34 is prepared. This heat-laminated film 34 can be a well-known type, for example, one with a base layer and a thermoplastic resin layer as its basic structure, with a layer thickness of, for example, 100 μm to 150 μm, using highly insulating PET (polyethylene terephthalate) or PP (polypropylene) as the base layer, and EVA (ethylene vinyl acetate copolymer) as the thermoplastic resin layer. Here, a plate-shaped object (in this case, a test metal plate 30) is sandwiched between two heat-laminated films 34 larger than the object, with the thermoplastic resin layers facing inward (towards the object). By heat-pressing these films together, the thermoplastic resin layers are melted and hardened, sealing the object within the heat-laminated films 34. This process is generally called pouching. This pouch coating 34a is basically waterproof. Generally, heat-laminated films 34 for pouches come in pairs, with one side joined together and the thermoplastic resin layers facing inward. Then, as shown in Figure 2(b), an opening 36 is formed on one side of the heat-laminated film 34 (opening formation step S106). The formation of this opening 36 is preferably done by punching with a die to minimize variations in the opening area. In particular, when the test metal plate 30 is stainless steel, the area of ​​the measuring surface 31a exposed from the opening 36 should be 1 cm². 2 This is required. Here, a typical thermal laminating film 34 undergoes almost no dimensional change before and after lamination. Therefore, the area is 1 cm². 2 When obtaining a circular measuring surface 31a, it is preferable that the diameter of the opening 36 formed in the heat-laminated film 34 be approximately φ11.5 mm. In this case, it is particularly preferable to form the opening 36 using a circular die with an inner diameter of approximately φ11.5 mm. When using a heat-laminated film 34 that undergoes dimensional changes before and after lamination, it is necessary to form the opening 36 in the heat-laminated film 34 with a value that takes into account the dimensional changes of the heat-laminated film 34.

[0016] Next, the test metal plate 30 is sandwiched between the heat-laminated film 34 on the measuring surface 31 side where the opening 36 is formed and the heat-laminated film 34 on the back side where the opening is not formed. At this time, the opening 36 is positioned at a predetermined location on the measuring surface 31 of the test metal plate 30, usually as shown in Figure 2(c), near the center of the test metal plate 30 and away from the conductor 32 (test metal plate placement step S108).

[0017] Next, both heat-laminated films 34 are heated and pressed together in this state to perform heat-compression bonding. As a result, the thermoplastic resin layer of the heat-laminated film 34 melts and fuses to the test metal plate 30. In addition, the thermoplastic resin layers of the front and back heat-laminated films 34 fuse together in the margins. Then, as these cool and harden, the test metal plate 30 is pouched. As a result, as shown in Figure 2(d), the test metal plate 30 is sealed by the pouch covering 34a formed by the front and back heat-laminated films 34 and enclosed within the pouch covering 34a (heat-compression bonding process S120). At this time, the opening 36 is in close contact with the measuring surface 31 of the test metal plate 30, and the measuring surface 31a is exposed from the opening 36 after hardening, while the periphery of the opening 36 is fused to the test metal plate 30 to provide a waterproof function.

[0018] Next, as shown in Figure 2(e), the excess portion of the pouch covering 34a is removed. Note that in the thicker portion of the conductor 32, the heat-laminated films 34 may not be able to adhere completely to each other, and a gap S may be created between the pouch covering 34a and the conductor 32 after curing. In this case, this gap S is filled with a well-known waterproof covering 38, such as applying epoxy resin, polyvinyl chloride resin, silicone resin, or other waterproof resin, or applying waterproof tape (waterproofing step S122). As a result, as shown in Figure 2(f), the electrode 80 for measuring pitting potential according to the present invention is completed.

[0019] Next, we will verify the electrode 80 for measuring pitting potential according to the present invention and explain the method for measuring pitting potential according to the present invention. Here, Figure 3 is a schematic diagram showing the pitting potential measuring device 100. [Examples]

[0020] First, a shim plate made of SUS304 (18Cr-8Ni) stainless steel, which had been cold-rolled to a thickness of 0.1 mm, was cut to a size of approximately 30 mm x 40 mm to form a test metal plate 30 (test metal plate acquisition process S102). Next, a φ2 mm copper wire was soldered to one of the short edges of the test metal plate 30 as a conductor wire 32 (conductor wire connection process S104). Next, a pair of thermal laminate films 34 for pouches, using PET as the base layer, were prepared, and an opening 36 was formed in one of the thermal laminate films 34 using a φ11.5 mm punch (punching punch) (opening formation process S106). Next, the test metal plate 30 was sandwiched between the heat-laminating film 34 for the pouch, with the opening 36 positioned on the measuring surface 31 of the test metal plate 30 (test metal plate placement step S108), and then pouched using a predetermined laminator (heat-sealing machine for pouches) (heat-sealing step S120). As a result, the test metal plate 30 was sealed in a pouch covering 34a with the heat-laminating films 34 on both sides welded together. Next, the excess portion of the pouch covering 34a was cut off. Next, if the conductor 32 was exposed, a heat-shrinkable insulating tube or the like was placed over it and heat-shrinked to provide insulation and waterproofing. Next, a waterproof resin was applied to the gap S at the connection between the conductor 32 and the pouch covering 34a, and cured to create a waterproof covering 38 (waterproofing step S122). As a result, the electrode 80 for measuring pitting potential according to the present invention was completed.

[0021] [Verification Experiment 1] Next, a pitting potential measuring instrument 100 was prepared, and approximately 400 mL of NaCl aqueous solution was poured into a glass test container 10 with an effective liquid volume of 500 mL for the pitting potential measuring instrument 100. The chloride ion concentration of the test solution was varied within the range of 0.0005 mol / L to 1.0 mol / L during the measurement. Next, the test container 10 was immersed in a constant temperature water bath 14 to maintain the temperature of the test solution at 30°C ± 1°C.

[0022] Next, a counter electrode 22 made of a mesh-like platinum electrode, a reference electrode 20 which is a saturated KCl silver-silver chloride electrode (RE-1CP manufactured by BAS Inc.), a ventilation tube 12a, and an exhaust tube 12b were installed on the lid 10a of the test container 10. Next, the measurement surface 31a (exposed from the opening 36) of the pitting potential measurement electrode 80 of [Example 1] according to the present invention was dry-polished with #600 sandpaper. Next, the polished pitting potential measurement electrode 80 was set on the lid 10a as a working electrode. Next, this lid 10a was placed on the test container 10 and fixed in a sealed state. As a result, the measurement surface 31a of the pitting potential measurement electrode 80, the counter electrode 22, and the reference electrode 20 were immersed in the test solution in the test container 10. In this example, since the measurement time is relatively short, the reference electrode 20 and the pitting potential measurement electrode 80 were immersed in the same test container 10. However, when the measurement time is long, in order to prevent adverse effects on the reference electrode 20 by the test solution, it is preferable to perform the measurement by immersing the reference electrode 20 in a separate container.

[0023] Next, the lead wire 32 of the pitting potential measurement electrode 80, the counter electrode 22, and the terminal electrode of the reference electrode 20 were respectively connected to predetermined terminals of a potentiostat 24 (HZ-7000 series HAG1232m manufactured by Hokuto Denko Corporation). Next, nitrogen gas was supplied to the ventilation tube 12a at a flow rate of about 100 mL / min, and the test solution was bubbled for 30 minutes. The supplied nitrogen gas was discharged from the exhaust tube 12b together with the air in the tank, thereby deaerating the inside of the test container 10 and the test solution. Next, the ventilation tube 12a and the exhaust tube 12b were closed, and the test container 10 was sealed.

[0024] Next, the potentiostat 24 was activated. As a result, the potential sweep device 26 in the potentiostat 24 swept the potential of the pitting potential measurement electrode 80 nobly from the natural potential at a rate of 20 mV / min with respect to the reference electrode 20. Further, the potentiostat 24 acquired the current density flowing through the pitting potential measurement electrode 80 at that time, and the recording unit 28 recorded the potential and the current density at that time. The measurement was terminated when the current density of the pitting potential measurement electrode 80 exceeded 1000 μA / cm 2 And when the current density of the pitting potential measurement electrode 80 reached 100 μA / cm 2The potential at which this occurred was defined as the pitting potential of the sample. Measurements were performed until five pitting potential data points were obtained for each condition. [Comparative Example 1]

[0025] A circular SUS304 steel plate with a thickness of 2 mm and a diameter of 24.5 mm, with a surface finish of BA (Balanced Atomic), was used as the test metal plate. It was then set in an existing sample holder for pitting potential measurement (VM-1, manufactured by EC Frontier Co., Ltd.) to serve as the electrode for pitting potential measurement. The pitting potential was then measured under the same measurement conditions as in Verification Experiment 1. The test metal plate was dry-polished with #600 grit sandpaper on the measurement surface, as in Example 1, and then immediately set in the sample holder for pitting potential measurement for measurement.

[0026] These measurement results are shown in Figure 4. Here, the horizontal axis of Figure 4 represents the chloride ion concentration (mol / L) of the test solution, and the vertical axis represents the pitting potential (V vs. Ag / AgCl). From Figure 4, it can be seen that [Example 1] (pouch sample) and [Comparative Example 1] (existing holder sample) showed similar trends in the behavior of pitting potential with respect to chloride ion concentration.

[0027] Furthermore, when an approximation formula was taken between the two, the electrode 80 for measuring pitting potential (pouch sample) was, y = -0.11ln(x) + 0.27 Correlation function R 2 = 0.91, The existing holder sample in [Comparative Example 1] is y = -0.12ln(x) + 0.13 Correlation function R 2 = 0.86, The correlation function is R 2 Both showed high values ​​of 0.9. Furthermore, the slopes of both were almost the same, at 0.11 and 0.12. From these results, it can be seen that the electrode 80 for measuring pitting potential according to the present invention can replace existing sample holders for measuring pitting potential and can be used for measuring pitting potential. It should be noted that the pitting potential values ​​of [Example 1] (pouch sample) were generally about 10mV to 100mV higher than the pitting potential values ​​of [Comparative Example 1] (existing holder sample), but this difference is thought to be due to differences in the material and surface finish of the samples. [Comparative Example 2]

[0028] An electrode for measuring pitting potential (existing holder sample) was prepared using the same method as in [Comparative Example 1], except that the surface finish was in state 2B.

[0029] [Verification Experiment 2] Then, the pitting potential was measured using the electrode 80 (pouch sample) for measuring pitting potential from [Example 1] and the existing holder sample from [Comparative Example 2], with the chloride ion concentrations of the test solution set to 1 mol / L and 0.5 mol / L, respectively, and all other conditions being the same as in Verification Experiment 1.

[0030] The graph of these results is shown in Figure 5. From Figure 5, it can be seen that there was no significant difference between the pitting potential values ​​of [Example 1] (pouch sample) and [Comparative Example 2] (existing holder sample) at chloride ion concentrations of 1 mol / L and 0.5 mol / L, and almost equivalent results were obtained. Therefore, it can be seen that the electrode 80 for measuring pitting potential according to the present invention can replace existing sample holders for measuring pitting potential and can be used for measuring pitting potential. [Examples]

[0031] An electrode 80 for measuring pitting potential was prepared in the same manner as in [Example 1], except that the measuring surface 31a was wet-polished with #600 sandpaper and then passedivated by immersion in 30 wt% nitric acid at 50°C ± 1°C for 1 hour.

[0032] [Verification Experiment 3] Then, the pitting potential was measured using the pitting potential measuring electrodes 80 from [Example 1] and [Example 2], with the chloride ion concentration of the test solution set to 1 mol / L, and under the same conditions as in Verification Experiment 1.

[0033] The potential and current density graphs (anodic polarization curves) of these samples are shown in Figures 6(a) and (b). Here, Figure 6(a) is the anodic polarization curve of [Example 1] without passivation treatment, and Figure 6(b) is the anodic polarization curve of [Example 2] with passivation treatment. Figure 6(c) is the anodic polarization curve of SUS304 as described in Japanese Industrial Standard JIS G 0577, using SCE (calomel electrode) as the reference electrode 20.

[0034] As shown in Figures 6(a) and (b), the pitting potentials measured with the electrode 80 (pouch sample) for measuring pitting potential according to the present invention were 0.347V, 0.351V, 0.353V, 0.351V, and 0.338V, respectively, without passivation treatment (Example 1), with a maximum value of 0.353V and an average value of 0.348V. With passivation treatment (Example 2), the values ​​were 0.331V, 0.346V, 0.360V, 0.349V, and 0.358V, respectively, with a maximum value of 0.360V and an average value of 0.349V. Furthermore, the conversion value of the reference electrode 20 from a saturated KCl silver chloride electrode to an SCE (calomel electrode) is given as -0.0473V according to the Japanese Industrial Standard JIS G 0577. Therefore, the maximum value after conversion using the calomel electrode without passivation treatment (Example 1) was 0.306V and the average value was 0.301V, while the maximum value with passivation treatment (Example 2) was 0.313V and the average value was 0.302V. Here, the maximum value of the pitting potential of SUS304 described in the Japanese Industrial Standard JIS G 0577 is 0.321V and the average is 0.290V, which is almost equivalent to the results obtained using the electrode 80 for measuring pitting potential according to the present invention. From this, it can be seen that pitting potential can be adequately measured even when using the electrode 80 (pouch sample) for measuring pitting potential according to the present invention.

[0035] Thus, the measurement results of pitting potential using the electrode 80 for measuring pitting potential according to the present invention were almost equivalent to those obtained with existing sample holders for measuring pitting potential. Furthermore, the values ​​were almost equivalent to those of pitting potentials described in Japanese Industrial Standard JIS G 0577. Therefore, it can be seen that the electrode 80 for measuring pitting potential according to the present invention is fully usable for measuring pitting potential.

[0036] Furthermore, the electrode 80 for measuring pitting potential and its manufacturing method according to the present invention involve sandwiching a test metal plate 30 between two heat-laminated films 34, each having an opening 36 of a predetermined size on one side, and then sealing the test metal plate 30 within an insulating pouch covering 34a by heat-pressing them together. This allows for the easy manufacture of a pitting potential measuring electrode 80 equivalent to the "coated electrode using an insulating material such as resin" described in Japanese Industrial Standard JIS G 0577, in which a portion of the test metal plate 30 is exposed through the opening 36 as a measuring surface 31a of a predetermined area, while the remaining portion is insulated and waterproofed by the pouch covering 34a. In particular, by forming the opening 36 using a punching die, a pitting potential measuring electrode 80 with a measuring surface 31a of the same area can be manufactured much more easily and quickly than conventional methods, regardless of the operator's skill level. Moreover, the pitting potential measuring method according to the present invention, by using the above-described pitting potential measuring electrode 80, significantly reduces the time and effort required to manufacture the measuring electrode, allowing for easy measurement.

[0037] Furthermore, since the electrode 80 for measuring pitting potential and the method for manufacturing the same according to the present invention can be manufactured using commercially available thermal laminating film 34 for pouches and a commercially available laminator, the introduction cost and material costs can be kept extremely low.

[0038] Furthermore, the content, procedures, and sequence of the method for manufacturing the electrode for measuring pitting potential shown in this example are merely examples, and necessary procedures may be added as appropriate, or the invention may be modified without departing from the spirit of the present invention. Also, the configuration, shape, material, dimensions, etc. of each part of the electrode 80 for measuring pitting potential shown in this example are merely examples, and the present invention is not limited to this example, and can be modified without departing from the spirit of the present invention. [Explanation of Symbols]

[0039] 20 Reference electrodes 22 Opposite Poles 30 Test metal plates 31, 31a Measuring surface 32 Conductor 34 Thermal laminating film 34a Pouch coating 36 Aperture 38 Waterproof coating 80 Electrodes for measuring pitting potential

Claims

1. The procedure for connecting the wires to the test metal plate, A procedure for forming an opening in one side of an insulating thermal laminate film, The procedure involves positioning the opening on the measuring surface of the test metal plate and sandwiching the test metal plate between a heat-laminated film with the opening formed therein and a heat-laminated film without the opening formed therein, A method for manufacturing an electrode for measuring pitting potential, comprising the steps of: thermally sealing the test metal plate with a thermal laminate film while the test metal plate is sandwiched between the thermal laminate film to pouch the test metal plate, sealing the test metal plate within the pouch covering formed by the thermal laminate film, and bringing the opening into close contact with the measuring surface.

2. A method for manufacturing an electrode for measuring pitting potential according to claim 1, characterized in that an opening in a thermal laminate film is formed by punching.

3. The area is 1 cm² due to punching with a circular die with a diameter of φ11.5 mm. ２ The method for manufacturing an electrode for measuring pitting potential according to claim 2, characterized in that the opening is formed in a thermal laminate film.

4. A wire connected to a test metal plate, An insulating pouch covering containing the aforementioned test metal plate, An opening formed in the pouch covering that partially exposes the measuring surface, An electrode for measuring pitting potential, comprising a waterproof coating applied to the gap between the pouch coating and the conductor.

5. The opening area of ​​the pouch covering is 1 cm². ２ The electrode for measuring pitting potential according to claim 4, characterized in that it is the same as the one described in claim 4.

6. A procedure for manufacturing a pitting potential measuring electrode according to the method for manufacturing a pitting potential measuring electrode described in any one of claims 1 to 3, The procedure involves immersing the electrode and counter electrode for measuring pitting potential in a test solution maintained at a predetermined liquid temperature, and immersing the reference electrode in a predetermined solution. A procedure for sweeping the potential of the electrode for measuring pitting potential at a preset speed and measuring the current density flowing through the electrode for measuring pitting potential, A method for measuring pitting potential, comprising the steps of obtaining pitting potential based on the potential when the current density exceeds a predetermined value.

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