JP2018017517A - Corrosion degree estimation method, corrosion degree estimation device and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a corrosion degree estimation method, a corrosion degree estimation device and a program for facilitating the formulation of maintenance priority of an aged structure by expanding the range in which the possibility of reinforcing bar corrosion can be estimated. SOLUTION: A collation electrode portion in which a steel material embedded in a concrete member and one terminal of a potential measuring unit are electrically connected and a collation electrode and the other terminal of the potential measurement unit are electrically connected is connected to the concrete member. The amount of change, which is the difference between the maximum potential and the minimum potential among the potentials measured at the plurality of measurement points included in the measurement range, and the measurement step S13 in which the potential is measured by pressing against a plurality of measurement points in the measurement range of Is characterized by having corrosion degree estimation steps S18 and S19 based on the potential change amount for estimating whether or not the steel material is corroded based on the calculated potential change amount and the predetermined potential change amount threshold. To do. [Selection diagram] Fig. 2

Description

  The present invention relates to a corrosion degree estimation method, a corrosion degree estimation apparatus, and a program for estimating a corrosion degree of a steel material in concrete.

  In aged reinforced concrete structures, there is a desire to evaluate the quantitative progress of corrosion of steel materials (also referred to as reinforcing bars) in concrete. On the other hand, the self-potential measurement method is known as one of the non-destructive investigation methods to evaluate the possibility of corrosion of the reinforcing bar by measuring the potential of the reinforcing bar surface that changes due to corrosion of the reinforcing bar in the concrete. . The self-potential measurement method is utilized as a method for evaluating whether or not a reinforcing bar of a reinforced concrete structure is in a corrosive environment (see, for example, Patent Documents 1 to 3).

  The natural potential measurement method is defined by JSCE-E601 “Method for measuring natural potential in concrete structures” by the Japan Society of Civil Engineers. In addition, a standard defined as ASTM C876 by ASTM International (former name: American Society for Testing Materials) is also known as an official evaluation standard for a method for measuring a natural potential (see FIG. 7).

JP 2012-181130 A JP 2000-044364 A JP-A-10-212292

  However, in the evaluation standard defined as the above-mentioned ASTM C876, there is a region where the possibility of rebar corrosion is uncertain. Therefore, even if the natural potential is measured using the natural potential method for an aging reinforced concrete structure, there are problems that many measurement points included in an indeterminate region are generated.

  Furthermore, if there is an area where the possibility of rebar corrosion is uncertain, there is a problem that it becomes difficult to formulate maintenance priorities when planning the maintenance of aged reinforced concrete structures.

  The present invention has been made in order to solve the above-described problems, and it is possible to facilitate the creation of maintenance priorities for aged structures by expanding the range in which the possibility of rebar corrosion can be estimated. An object of the present invention is to provide a corrosion degree estimation method, a corrosion degree estimation device, and a program.

In order to achieve the above object, the present invention provides the following means.
The corrosion degree estimation method according to the first aspect of the present invention electrically connects a steel material embedded in a concrete member and one terminal of a potential measuring unit, and includes a reference electrode and the other terminal of the potential measuring unit. A measurement step of measuring the potential by pressing the reference electrode part electrically connected to the plurality of measurement points in the measurement range of the concrete member, and the potential measured at the plurality of measurement points included in the measurement range A potential change amount that calculates a potential change amount that is a difference between the maximum potential and the minimum potential, and estimates whether the steel material is corroded based on the calculated potential change amount and a predetermined potential change amount threshold value. And a corrosion degree estimation step based on.

  The corrosion degree estimation apparatus according to the second aspect of the present invention includes a potential measurement unit, a connection unit that electrically connects a steel material embedded in a concrete member and one terminal of the potential measurement unit, and the potential measurement. A reference electrode unit electrically connected to the other terminal of the unit and pressed against a measurement point in the measurement range of the concrete member, and a maximum of the potentials measured at the plurality of measurement points included in the measurement range A calculation unit that calculates a potential change amount that is a difference between the potential and the minimum potential, and estimates whether the steel material is corroded based on the calculated potential change amount and a predetermined potential change amount threshold; It is characterized by being.

  In the program according to the third aspect of the present invention, one terminal is electrically connected to a steel material embedded in a concrete member, and the other terminal is pressed against a plurality of measurement points in the measurement range of the concrete member. A program for estimating corrosion of the steel material based on a potential measured by a potential measurement unit electrically connected to a unit, an acquisition function for causing a computer to acquire a potential measured by the potential measurement unit, and A potential change amount that is a difference between a maximum potential and a minimum potential among potentials measured at a plurality of measurement points included in a measurement range is calculated, and based on the calculated potential change amount and a predetermined potential change threshold value And a corrosion degree estimation function based on a potential change amount for estimating whether or not the steel material is corroded.

  According to the corrosion degree estimation method according to the first aspect of the present invention, the corrosion degree estimation device according to the second aspect, and the program according to the third aspect, the calculated potential change amount and a predetermined potential change amount threshold value Therefore, it is possible to estimate the degree of corrosion even when the degree of corrosion of the steel cannot be estimated from only the measured potential.

  In the first aspect of the invention, when the value of the measured potential is greater than a first threshold value between the measurement step and the corrosion degree estimation step based on the potential change amount, the steel material is It is estimated that the steel material is not corroded with a predetermined probability, and when the measured potential is equal to or smaller than a second threshold value smaller than the first threshold value, the steel material is estimated to corrode with a predetermined probability. A step of estimating the degree of corrosion based on the potential to be measured, and when the measured potential value is less than or equal to a first threshold and the measured potential is greater than the second threshold, the potential change amount It is desirable that the corrosion of the steel material is estimated in the estimation step based on the above.

  In the second aspect of the invention, when the value of the measured potential is greater than a first threshold value, the calculation unit estimates that the steel material has not corroded with a predetermined probability, and the measurement is performed. When the potential is equal to or less than a second threshold value that is smaller than the first threshold value, the steel material is estimated to corrode with a predetermined probability, and the measured potential value is equal to or less than the first threshold value. And, when the measured potential is larger than the second threshold value, estimating whether the steel material is corroded based on the calculated potential change amount and the predetermined potential change amount threshold value. Is desirable.

  In the second aspect of the invention, when the value of the measured potential is greater than the first threshold value between the acquisition function and the corrosion degree estimation function based on the potential change amount, the steel material is It is estimated that the steel material is not corroded with a predetermined probability, and when the measured potential is equal to or smaller than a second threshold value smaller than the first threshold value, the steel material is estimated to corrode with a predetermined probability. The potential change amount when the measured potential value is less than or equal to a first threshold value and the measured potential is greater than the second threshold value. It is desirable to estimate whether the steel material is corroded by a corrosion degree estimation function based on the above.

  Regarding the range in which the corrosion degree of the steel material can be estimated based on the measured potential, the first threshold value, and the second threshold value, the corrosion degree of the steel material is estimated using the measured potential, and the corrosion degree of the steel material is measured using the measured potential. As for the range in which it is difficult to estimate, it is easier to estimate the corrosion degree of the steel material by estimating the corrosion degree of the steel material using the potential change amount.

  According to the corrosion degree estimation method, the corrosion degree estimation device and the program of the present invention, since it is estimated whether or not the steel material is corroded based on the calculated potential change amount and a predetermined potential change amount threshold, the possibility of rebar corrosion As a result, it is possible to widen the range in which it is possible to estimate the maintenance priority of aging structures.

It is a model diagram explaining one Embodiment of the corrosion degree estimation apparatus by this invention. It is a flowchart explaining the corrosion estimation method of the reinforcing bar by the corrosion degree estimation apparatus of FIG. It is a schematic diagram explaining the example of arrangement | positioning of the measurement point in the measurement range of a reinforced concrete structure, and the electric potential distribution map (equivalent electric potential map) created by a measurement. It is a table | surface explaining the response | compatibility with the condition of a corrosion grade and a reinforcing bar. It is a graph explaining the measurement result by the corrosion degree estimation apparatus of FIG. 1, and a determination result. It is a schematic diagram explaining other embodiment of the corrosion degree estimation apparatus of FIG. It is a table | surface explaining the evaluation criteria prescribed | regulated as ASTMC876.

  A corrosion degree estimation method, a corrosion degree estimation apparatus, and a program according to an embodiment of the present invention will be described with reference to FIGS. In this embodiment, when estimating and evaluating whether or not the reinforcing bar (steel material) 51 of the reinforced concrete structure (concrete member) 50 is corroded using the corrosion degree estimation method, the corrosion degree estimation apparatus, and the program of the present invention. It applies to and explains. Here, examples of the reinforced concrete structure 50 include buildings made of reinforced concrete and structures such as bridges.

  Further, in the present embodiment, description will be made by applying to an example in which a natural potential (potential) is measured using a natural potential measurement method defined as JSCE-E601 “Method for Measuring Natural Potential in Concrete Structures”.

  As shown in FIG. 1, the corrosion degree estimation apparatus 1 according to the present embodiment includes a potentiometer (potential measurement unit) 10, a connection unit 11, a probe (reference electrode unit) 12 used for measuring a natural potential, and a reinforcing bar. An estimation unit (calculation unit) 20 that estimates 51 corrosion is mainly provided.

  The potentiometer 10, the connecting portion 11, and the probe 12 may be any one that can perform the natural potential measuring method defined as JSCE-E601 “Spontaneous Potential Measuring Method in Concrete Structures”, and is a known commercially available device. Can be used. In the description of the present embodiment, the description will be made based on the natural potential measured using canin + of Prosec.

  The potentiometer 10 has a connection portion 11 connected to one terminal and a probe 12 connected to the other terminal. The potentiometer 10 is a natural object of the rebar 51 that is a measurement object located in the measurement range set in the reinforced concrete structure 50. It is used for measuring the potential difference.

  The connection part 11 peels off the concrete on the surface of the reinforced concrete structure 50, and one end is electrically connected to the exposed reinforcing bar 51, and the other end is connected to the terminal of the potentiometer 10. It is what is done. For example, one end is a clip-like end sandwiching the reinforcing bar 51, and the other end is a connector connected to the terminal of the potentiometer 10, and a lead wire capable of conducting an electrical signal between the two ends. Can be given as an example.

  The probe 12 has a reference electrode inside, and is pressed against the concrete surface where the reinforcing bar 51 to be measured is located in the measurement range set in the reinforced concrete structure 50. As the reference electrode, any of a saturated copper sulfate electrode, a saturated calomel electrode, a saturated silver chloride electrode, and a lead electrode specified in JSCE-E601 “Method for Measuring Natural Potential in Concrete Structures” may be used.

  The estimation unit 20 acquires the natural potential measured by the potentiometer 10 and estimates the corrosion of the reinforcing bar 51 as the measurement target. In the present embodiment, description will be made by applying to an example in which the estimation unit 20 is a computer having a CPU (Central Processing Unit), ROM, RAM, input / output interface and the like. The program stored in the storage device such as the ROM described above causes the CPU to function as the calculation unit 21 and the input / output interface or the like to function as the acquisition unit 22.

  The computing unit 21 has a corrosion degree estimation function based on a potential and a corrosion degree estimation function based on a potential change amount, which estimates whether or not the reinforcing bar 51 is corroded based on the natural potential measured by the potentiometer 10. It is realized. Details of the calculation processing by the corrosion degree estimation function based on the potential and the corrosion degree estimation function based on the potential change amount will be described later.

  The acquisition unit 22 realizes an acquisition function for acquiring the measured natural potential from the potentiometer 10. As a specific method for acquiring the natural potential from the potentiometer 10, a known information acquisition method such as a method of acquiring via a wired or wireless communication or a method of acquiring via a portable recording medium is used. However, it is not limited to a specific method.

  In the present embodiment, the potentiometer 10 and the estimation unit 20 are described as applied to an example in which they are housed in separate housings. However, the potentiometer 10 and the estimation unit 20 are housed in one housing. There may be, and the format is not particularly limited.

Next, a method for estimating corrosion of the reinforcing bar 51 in the corrosion degree estimation apparatus 1 having the above-described configuration will be described with reference to FIGS.
First, an operation of confirming whether the reinforcing bars 51 to be measured have electrical continuity with each other is performed (S10). When the electrical continuity is confirmed, water is sprayed onto the concrete surface in the measurement range set in the reinforced concrete structure 50 (S11). In the watering operation, water is sprayed and sprayed before measuring the natural potential so that the concrete surface becomes wet. However, the work is performed so that floating water is not generated on the concrete surface.

  Thereafter, as a preparation for the corrosion degree estimation apparatus 1, a connection between the potentiometer 10 and the connection portion 11 and a connection between the potentiometer 10 and the probe 12 are performed (S12). As shown in FIG. 1, the end portion of the connecting portion 11 is electrically connected to a reinforcing bar 51 to be measured. At this time, when the surface of the reinforcing bar 51 is covered with an insulating material such as rust, the connecting part 11 is attached so as to be electrically connected to the reinforcing bar 51 after the insulating material is removed.

  Then, the potentiometer 10 performs an operation of measuring the natural potential in the measurement range set in the reinforced concrete structure 50 (measurement step: S13). For example, as shown in FIG. 3, the natural potential is measured at a plurality of measurement points 55 so that a potential distribution diagram (equivalent potential diagram) can be drawn along the reinforcing bars 51 arranged in the measurement range. It is preferable that the arrangement position of the reinforcing bar 51 is grasped in advance using a commercially available reinforcing bar probe.

  Further, when measuring the natural potential, water is contained in a sponge or the like disposed at the end of the probe 12 (reference electrode) pressed against the concrete surface, and the probe 12 is pressed against the measurement point 55. When measuring using canin + of Prosec Corp., the self-potential may be measured by pressing the stick-shaped probe 12 at each measurement point 55, or the wheel-shaped probe 12 is rotated on the line where the measurement points 55 are aligned. The self-potential may be measured by pressing it.

  The natural potential measured by the potentiometer 10 is acquired by the acquisition unit 22 to the estimation unit 20. The acquisition of the natural potential may be performed every time the natural potential is measured at the measurement point 55, or the value of the natural potential measured by the potentiometer 10 is stored, and a plurality of natural potentials are collectively collected by the estimation unit 20. May be obtained.

  The estimation unit 20 that has acquired the measured natural potential performs a process of determining whether or not the value of the natural potential measured by the calculation unit 21 is larger than the first threshold (corrosion degree estimation step based on potential: S14). ). As the value of the natural potential used for the determination, the value of the natural potential selected as representing the measurement range among the natural potentials measured at the plurality of measurement points 55 in the measurement range is used. As a representative method for selecting a natural potential, various methods can be used such as using a natural potential occupying a majority of the measured natural potentials, and the method is not particularly limited.

  In this embodiment, the first threshold value is -200 mV according to the evaluation standard of ASTM C 876 and applied to an example in which the second threshold value described later is -350 mV. Values described in the evaluation criteria may be used, and the values are not limited.

  When it is determined that the value of the natural potential measured in the determination of S14 is larger than the first threshold (in the case of YES), the calculation unit 21 corrodes the rebar 51 with a probability of 90% or more within the measurement range. It is estimated that there is not (S15).

  When the value of the natural potential measured in the determination of S14 is determined to be equal to or smaller than the first threshold value (in the case of NO), the calculation unit 21 determines whether the value of the measured natural potential is equal to or smaller than the second threshold value. (Corrosion degree estimation step based on potential: S16). When it is determined that the measured natural potential value is equal to or less than the second threshold value (in the case of YES), the calculation unit 21 estimates that the reinforcing bar 51 is corroded with a probability of 90% or more within the measurement range (S17). .

  When it is determined that the value of the natural potential measured in the determination of S16 is larger than the second threshold value (in the case of NO), the calculation unit 21 performs a process of calculating a potential change amount within the measurement range ( Corrosion degree estimation step based on potential change amount: S18). Specifically, among all the natural potentials measured at the measurement point 55 in the measurement range, the potential change amount is obtained by subtracting the lowest natural potential value from the highest natural potential value. It is done.

  When the potential change amount is obtained, the calculation unit 21 performs a process of determining whether or not the potential change amount is equal to or less than a predetermined potential change amount threshold (corrosion degree estimation step based on the potential change amount: S19). In this embodiment, the description is applied to an example in which the predetermined potential change threshold is 100 mV. However, the predetermined potential change threshold is not limited to 100 mV, and other values may be adopted.

  When it is determined in S19 that the potential change amount is equal to or less than the predetermined potential change amount threshold value (in the case of YES), the calculation unit 21 does not corrode the reinforcing bars 51 with a probability of 90% or more within the measurement range. (S20). On the other hand, when it is determined that the potential change amount is less than the predetermined potential change amount threshold value (in the case of NO), the calculation unit 21 estimates that the rebar 51 is corroded with a probability of 90% or more within the measurement range. (S21). Thus, the estimation of corrosion of the reinforcing bar 51 in the measurement range is completed.

  Note that the first threshold value of −200 mV, the second threshold value of −350 mV, and the potential change amount threshold value of 100 mV indicate that grades I and II in the table shown in FIG. III and IV are defined as values estimated to cause corrosion of the reinforcing bars 51.

  Next, an example in which corrosion of the reinforcing bar 51 is estimated in the corrosion degree estimation apparatus 1 having the above configuration will be described with reference to FIG. FIG. 5 is a diagram showing the estimation results of the corrosion of the reinforcing bars 51 performed on two different reinforced concrete structures 50. The vertical axis indicates the value of the representative natural potential selected in the measurement range, and the horizontal axis indicates the potential change that is the difference between the maximum potential and the minimum potential of the natural potential in the measurement range.

  Moreover, the measurement result of the measurement point 55 in one reinforced concrete structure 50 is shown by a white figure, and the measurement result of the measurement point 55 in the other reinforced concrete structure 50 is shown by a black figure. The shape of the figure used according to the degree of corrosion of the reinforcing bar 51 is divided into three stages. The circle figure has the lightest degree of corrosion and is judged to be no corrosion (sound) according to the estimation of this embodiment. The square figure has a moderate degree of corrosion. The triangular figure has the highest degree of corrosion, and in this embodiment, it is determined to be corrosion.

  A region A having a natural potential larger than −200 mV shown in FIG. 5 corresponds to a region (healthy region) in which the value of the natural potential measured in the determination of S14 is determined to be larger than the first threshold. . On the other hand, the region C in which the natural potential is −350 mV or less corresponds to a region (corrosion region) in which the value of the natural potential measured in the determination in S14 is determined to be equal to or less than the first threshold value.

  In addition, a region where the natural potential is larger than −350 mV and −200 mV or less is divided into a region BA whose potential change is 100 mV or less and a region BC which is larger than 100 mV. The area BA is an area where the reinforcing bar 51 is determined to be a healthy area similarly to the area A, and the area BC is an area where the reinforcing bar 51 is determined to be a corrosion area like the area C.

  According to said structure, about the range which can estimate the corrosion degree of the reinforcing bar 51 based on the measured natural potential, the 1st threshold value, and the 2nd threshold value, whether the reinforcing bar 51 is corroded using the measured natural potential. For the range in which it is difficult to estimate the degree of corrosion of the reinforcing bar 51, it is estimated whether the reinforcing bar 51 is corroded based on the calculated potential change amount and a predetermined potential change amount threshold value. Therefore, even when the corrosion degree of the reinforcing bar 51 cannot be estimated only by the measured natural potential, the corrosion degree can be estimated.

  In other words, it is possible to widen the range in which the possibility of rebar corrosion can be estimated, and it is possible to easily set the maintenance priority of an aged structure. Therefore, the estimation result is used as a quantitative deterioration progress degree of the reinforcing bar corrosion of the reinforced concrete structure 50, and the basis for establishing the maintenance priority and the diagnostic accuracy of the remaining life of the reinforced concrete structure 50 including the building are improved. Can be achieved.

  In addition, since the degree of deterioration of the reinforced concrete structure 50 can be quantified, it becomes possible to identify the reinforced concrete structure 50 that needs to be refurbished for the time being, and it is easy to reduce the required annual investment cost for the reinforced concrete structure 50. Become.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, the description has been made by applying the example in which the connecting part 11 is electrically connected to the reinforcing bar 51 that is exposed to the outside and is exposed to the outside. Other members that are electrically connected to 51 may be used. Specifically, as shown in FIG. 6, a sash frame 56 that is a metal member installed around an opening such as an entrance is often electrically connected to the reinforcing bar 51. You may make it connect the connection part 11 to this sash frame 56 electrically.

  DESCRIPTION OF SYMBOLS 1 ... Corrosion degree estimation apparatus, 10 ... Potentiometer (potential measuring part), 11 ... Connection part, 12 ... Probe (reference electrode part), 20 ... Estimation part (calculation part), 21 ... Calculation part, 50 ... Reinforced concrete structure (Concrete member), 51 ... rebar (steel), S13 ... measurement step, S14 ... corrosion degree estimation step based on potential, S16 ... corrosion degree estimation step based on potential, S18 ... corrosion degree estimation step based on potential change, S19 ... Step of estimating corrosion based on potential change

Claims (7)

The concrete member is electrically connected to the steel material embedded in the concrete member and one terminal of the potential measuring unit, and the reference electrode unit is electrically connected to the other terminal of the potential measuring unit. A measurement step of measuring the potential by pressing against a plurality of measurement points in the range;
A potential change amount that is a difference between a maximum potential and a minimum potential among potentials measured at a plurality of measurement points included in the measurement range is calculated, and the calculated potential change amount and a predetermined potential change amount threshold value are calculated. Corrosion degree estimation step based on potential change amount to estimate whether the steel material is corroded based on,
A method for estimating the degree of corrosion, comprising: Between the measurement step and the corrosion degree estimation step based on the potential change amount,
When the value of the measured potential is larger than the first threshold value, it is estimated that the steel material is not corroded with a predetermined probability, and the measured potential is a second value smaller than the first threshold value. In the case of a threshold value or less, the steel material has a corrosion degree estimation step based on a potential that estimates that the steel material is corroded with a predetermined probability.
When the measured potential value is less than or equal to the first threshold and the measured potential is greater than the second threshold, corrosion of the steel material is estimated in the estimation step based on the potential change amount. The corrosion degree estimation method according to claim 1, wherein:   The predetermined potential change amount estimation value in the corrosion degree estimation step based on the potential change amount, and the first threshold value and the second threshold value in the corrosion degree estimation step based on the potential are over the entire circumference or the entire length of the steel material. It is estimated that the state in which the rust is generated and the state in which the cross-sectional defect is generated in the steel material is corroded, the state in which the skin is formed on the steel material, and the spot-like rust is generated. The corrosion degree estimation method according to claim 2, wherein the value is a value that estimates that the state is not corroded. A potential measurement unit;
A connecting portion for electrically connecting a steel material embedded in a concrete member and one terminal of the potential measuring portion;
A reference electrode unit electrically connected to the other terminal of the potential measuring unit and pressed against a measurement point in the measurement range of the concrete member;
A potential change amount that is a difference between a maximum potential and a minimum potential among potentials measured at a plurality of measurement points included in the measurement range is calculated, and the calculated potential change amount and a predetermined potential change amount threshold value are calculated. A calculation unit for estimating whether the steel material is corroded based on,
Corrosion degree estimation device characterized by that. The computing unit is
When the value of the measured potential is larger than the first threshold value, it is estimated that the steel material is not corroded with a predetermined probability, and the measured potential is a second value smaller than the first threshold value. If the threshold and below, the steel is estimated to corrode with a predetermined probability,
When the measured potential value is less than or equal to the first threshold value and the measured potential is greater than the second threshold value, the calculated potential change amount and the predetermined potential change amount threshold value are used. The corrosion degree estimation apparatus according to claim 4, wherein the steel material is estimated to corrode or not. One terminal is electrically connected to a steel material embedded in a concrete member, and the other terminal is electrically connected to a reference electrode unit pressed against a plurality of measurement points in the measurement range of the concrete member. A program for estimating corrosion of the steel material based on a measured potential,
An acquisition function for causing a computer to acquire the potential measured by the potential measurement unit;
A potential change amount that is a difference between a maximum potential and a minimum potential among potentials measured at a plurality of measurement points included in the measurement range is calculated, and the calculated potential change amount and a predetermined potential change amount threshold value are calculated. Corrosion degree estimation function based on the potential change amount that estimates whether the steel material is corroded based on,
A program characterized by realizing. Between the acquisition function and the corrosion degree estimation function based on the potential change amount,
When the value of the measured potential is larger than the first threshold value, it is estimated that the steel material is not corroded with a predetermined probability, and the measured potential is a second value smaller than the first threshold value. In the case of the threshold and the following, the steel material has a corrosion degree estimation function based on a potential that is estimated to corrode with a predetermined probability,
When the measured potential value is less than or equal to the first threshold value and the measured potential is greater than the second threshold value, the steel material is corroded by the corrosion degree estimation function based on the potential change amount. The program according to claim 6, wherein it is estimated whether or not there is.