JP2007017433A - Numerical analysis method of corrosive environment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a numerical analysis method capable of accurately reflecting the state of the scene and precisely estimating the corroded state of a conductor. <P>SOLUTION: The numerical analysis method of a corrosive environment generated in the conductor 3 in a medium by a leaked current comprises a reference model analysis process for constructing and analyzing a reference model where current flows from a leaked current source 1 to an inflow object 2 via a medium while the conductor 3 is removed; a region potential distribution extraction process for obtaining a potential distribution at a region where the conductor 3 is present from the obtained potential distribution; and an object-to-be-analyzed analysis process for determining that the conductor 3 comprises a plurality of analysis segments and determining the analysis polarization characteristics of the segments, based on the potential distribution of the region and the material polarization characteristics of the conductor 3, performing an analysis in which only the conductor 3 is present in the field and a macro cell is formed by the segments, and obtaining the polarization potential distribution of the conductor 3 and the outflow/inflow distribution of current from the conductor to the medium. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a numerical analysis method for performing an electrochemical analysis of a target object existing in a field where current flows from a current source to a target object through a medium.

The description of the present technology will be described with respect to corrosion of a conductive buried pipe as an example.
Corrosion targeted by the present application includes electrolytic corrosion due to leakage current shown in FIGS. 1 (a) and 1 (b) and corrosion due to interference shown in (c), as shown in FIG.
In the former example, in the DC electric railway 100, a part of the current flowing through the rail 101 flows out into the ground 102, so that the corrosion generated in the conductive buried pipe 103 buried in the vicinity thereof is a problem. In this example, a leakage current flows as shown by arrows in FIGS.
The latter example is an example of corrosion that occurs when a portion of the anticorrosive current flows into another adjacent conductive buried tube 103 when the external power supply device 105 performs an electric corrosion protection on the buried tube 104 and occurs in the current outflow portion. There is an example called a so-called interference problem. In this case, an anticorrosion current flows as indicated by an arrow in (c). In these figures, the corrosion site is indicated by A.

  In these examples, the current outflow source is the rail portion 101a located far from the substation 106 in the former case or the rail 101 itself, and in the latter case is the counter electrode 105a. On the other hand, the inflow object is the rail portion 101b close to the substation 106 in the former case, and the buried pipe 104 (conductor) to be protected against corrosion in the latter case. In the former case, the object to be examined as referred to in this application corresponds to the conductive buried tube 103, and in the latter case, the conductive buried tube 103 in a non-corrosive state corresponds to this.

  Now, since corrosion occurs at a site where the current flows into the medium, for example, into the soil, it is necessary to specify this position. In addition, the inflow part of an electric current will be in a corrosion prevention state.

As a technical technique related to the estimation of this type of corrosion site, estimation from on-site actual measurement, a method using simulation, and the like have been proposed.
1 Method of Estimating from On-Site Measurements In Patent Document 1, the potential of a buried metal structure is measured, and the anticorrosion state of the buried structure is determined based on the ground potential of the object that may cause electrical corrosion. An electric corrosion countermeasure system for judging has been proposed.

2 Method of Using Simulation In Patent Document 2, the inventors of the present application regard the potential distribution as a Laplace field according to the Laplace equation, so that the object to be interfered has a predetermined potential state with respect to the object to be protected. We have proposed a method for solving the interference problem by taking certain boundary conditions into consideration.

JP 2004-176103 A Japanese Patent Laid-Open No. 11-160271

However, each conventional technique has the following problems.
1 Problems of the technique described in Patent Document 1 In the technique described in this document, it is possible to grasp in real time, but the site where the corrosion state can be estimated is limited only to the point where the potential measurement is performed. It is difficult to grasp where measurement is not possible.

2. Problems of the technique described in Patent Document 2 In the technique described in this document, when a large-scale model is handled, giving a constant potential difference state at all positions is a good representative of the current situation. In addition, when there are a plurality of types of buried pipes, since there are a plurality of parameters as shift values of polarization characteristics, convergence tends to be unstable in the simulation calculation.

  An object of the present invention is to obtain an analysis method that can accurately reflect the state of the site and accurately estimate the state of the object to be examined. The analysis target is the one applicable to both the above-described leakage current and interference.

In order to achieve the above object, according to the present invention, the characteristic configuration of the numerical analysis method of the corrosive environment in which the examination target exists in the field where the current flows from the current outflow source to the inflow target through the medium,
A reference model for constructing a reference model in which the examination object is removed and current flows from the current outflow source to the inflow object through the medium, and the analysis is performed by regarding the reference model as a Laplace field according to a Laplace equation The model analysis process;
A region potential distribution extraction step for obtaining a potential distribution in a region where the object to be examined exists from the potential distribution in the reference model obtained in the reference model analysis step;
Based on the potential distribution obtained by the region potential distribution extraction step and the material polarization characteristics of the examination object, an analysis is performed assuming that only the examination object exists in the field, and the polarization potential distribution of the examination object And a target object analyzing step for obtaining a current inflow / outflow distribution from the target object to the medium.

In this method, first, an analysis based on a reference model is performed to obtain a potential distribution of the entire field to be analyzed. The potential distribution obtained here is a potential distribution that can represent a potential gradient in the corrosive environment under consideration. That is, a field where a potential gradient is generated in a state orthogonal to the equipotential line is handled.
In this model, since the current outflow source and the inflow target are specified, the potential distribution can be obtained based on the positional relationship, and the amount of current that is estimated to normally flow is appropriately used. be able to. The amount of current can also be estimated from the voltage between the current outflow source and the inflow object and the resistance between them.

  Now, based on the potential distribution in the field obtained in this way, the potential distribution of the region where the object to be examined that actually does not exist in the analysis of the reference model is extracted in the region potential distribution extraction step (obtained). ).

In the examination object analysis step, only the examination object is targeted, and the potential distribution of the region in the reference model and its material polarization characteristics (for example, measured values of material polarization characteristics) are used. Then, by treating the object to be examined as a conductor in which an inflow and outflow of current occurs, the polarization potential distribution of the object to be examined and the current inflow / outflow distribution from the object to be examined to the medium can be obtained. it can. At this time, the analysis of the examination object can be performed by executing the analysis on the assumption that this constitutes a macro cell in the field.
As a result, it is possible to satisfactorily analyze the field where the current outflow source, the inflow target, and the examination target exist in the medium in a state suitable for the current situation regardless of the existence of the examination target.
Therefore, the above-described corrosion due to leakage current and corrosion due to interference can be analyzed.

When the above analysis is performed, since the boundary condition in the analysis at the position where the target object exists is set, the material polarization characteristics of each part of the target object (each part corresponds to a segment described later) Necessary. This material polarization characteristic is determined by, for example, the position of each part of the buried pipe and the relationship between the buried pipe and the surrounding soil, and in fact, each part has a different material because the environmental conditions at each position are different. Take polarization characteristics.
However, if the material polarization characteristics of each part (segment) are measured for each analysis, the operation becomes complicated and is not practical. That is, when the material polarization characteristics are to be measured, it is necessary to sequentially measure the relationship between the potential and the current density for each segment while changing the potential side, for example, but such work is complicated. In this work, when the analysis target is a buried pipe buried in the soil, specifically, a probe (a test piece made of the same material as the buried pipe that is the object of investigation) is inserted into the soil, and the buried pipe This is an operation to measure the polarization characteristics of only the probe after it is short-circuited with the tube and blended with the soil, then separated from the buried tube.

Therefore, in order to set the material polarization characteristics of the examination object, the predetermined material polarization characteristics may be shifted in the potential axis direction for each part so as to match the natural potential of each part of the examination object. preferable. The work to obtain this natural potential is, when the analysis target is an embedded pipe embedded in soil, specifically, after performing the process excluding the above-mentioned polarization characteristic measurement, only the natural potential of the probe is measured, This is an operation to shift a predetermined material polarization characteristic in the potential axis direction so as to coincide with the natural potential. Moreover, in the field, it can also be shifted using the natural potential of the actual buried pipe.
Here, the predetermined material polarization characteristic is a material polarization characteristic as a reference prepared in advance. For this kind of reference material polarization characteristics, for example, empirical values are adopted, or material polarization characteristics are measured once in advance at each site, and converted into a reference natural potential and averaged (actual values are measured). And by shifting the polarization characteristics in the direction of the potential axis so that the natural potential becomes the reference natural potential, and averaging the current density for each potential for the material polarization characteristics after the shift) Can do.

On the other hand, the natural potential of each part is measured in advance on site before analysis for each part.
In the analysis, as the material polarization characteristic of each part, the above-mentioned predetermined material polarization characteristic is shifted in the potential axis direction for each part so as to coincide with the natural potential of each part of the object to be examined. Use polarization characteristics. That is, instead of measuring the material polarization characteristics in the field, only the measurement of the natural potential is performed, and the material polarization characteristics of each part are obtained by using this natural potential and the predetermined material polarization characteristics obtained in advance. The analysis object analysis process is analyzed using the analysis polarization characteristics reflecting the potential distribution obtained by the potential distribution extraction process as a boundary condition. As a result, as the field work, only the natural potential measurement at each position is performed, and by using the numerical analysis method of the corrosive environment according to the present application, the polarization potential distribution of the object to be examined and the object to be examined can be easily obtained. The distribution of current flowing into and out of the medium can be obtained.

Now, in adopting the above method, in the examination object analysis step,
Considering the examination object as a continuum consisting of a plurality of analysis segments electrically connected, and based on the potential distribution obtained by the region potential distribution extraction step, corresponding to the position of the analysis segment, The analysis polarization characteristics of each analysis segment can be set, and the polarization potential distribution of the examination object and the current inflow / outflow distribution from the examination object to the medium can be obtained.

  In the examination object analysis step in the present application, the identification of the behavior of the examination object becomes a problem. As previously indicated, in this application, the potential distribution of the region obtained in the region potential distribution extraction step is used. On the other hand, since the material constituting the object to be examined is known in advance, this is the polarization characteristic that can be taken in relation to the medium (for example, soil) in the vicinity thereof (in this application, this polarization characteristic is called the material polarization characteristic). Can be found or measured.

  Therefore, in order to obtain the current distribution of the object to be examined in the field to be analyzed, for example, the object is divided into analysis segments, and the polarization characteristics of each analysis segment are determined according to the potential distribution separately obtained at the position of the analysis segment. (In this application, this polarization characteristic is referred to as analytical polarization characteristic). For example, for each analysis segment, a polarization characteristic that is shifted to the potential axis method by the potential difference according to the potential distribution of the required region (soil) is adopted for the material polarization characteristics.

Then, the shifted analysis polarization characteristic is given to each analysis segment. As a result, each analysis segment behaves as if the natural potential (potential when the current is zero with no current flowing in and out) differs from each other, and the macrocell analysis can be performed with these as short circuits. In this way, the polarization potential distribution of the examination object and the current inflow / outflow distribution from the examination object to the medium are obtained.
In deriving this type of current distribution, etc., the current source and inflow target are removed and only the object to be examined is included, and only this object to be examined is in the field, contrary to the above reference model. By solving the Laplace field in a certain state, it is possible to obtain the current distribution of the object to be studied that forms a nonlinear boundary. This method is generally called macrocell corrosion analysis. By doing in this way, the current outflow site where corrosion becomes a problem can be specified by identifying the current distribution in the object to be examined.

As described above, the numerical analysis method for the corrosive environment according to the present application includes the reference model analysis step, the region potential distribution extraction step, and the examination object analysis step.
Then, the corrosive environment is analyzed using a solver that can solve the Laplace field according to the Laplace equation. As this solver, as a boundary condition, the polarization given to each element with respect to each element constituting the boundary is analyzed. A solver that can obtain a Laplace solution that satisfies the characteristic conditions is used.
In the analysis, first, in the reference model analysis step, the potential distribution in the region is obtained assuming that there is no object to be examined. Next, the potential distribution extracted in the region potential distribution extraction step is used, and further, the object to be examined is considered to be composed of a plurality of analysis segments, and the analysis polarization characteristics of each analysis segment are determined.
Thereafter, the macro cell analysis is performed assuming that the object to be studied is composed of a plurality of analysis segments, each of which forms a kind of boundary that should satisfy the analysis polarization characteristic condition. By doing in this way, the polarization potential distribution of the object to be examined and the current inflow / outflow distribution from the object to be examined to the medium can be obtained.

  Now, in order to use the potential distribution obtained in the region potential distribution extraction step for setting the analytical polarization characteristics, for example, the boundary element method is used to discretize by the number of boundary elements, etc. Alternatively, the electric potential obtained as a discretized distribution value may be converted into a function, and this function may be used to determine the analytical polarization characteristic.

  In this case, based on the potential distribution obtained by the region potential distribution extraction step, in order to set the analysis polarization characteristics of each analysis segment corresponding to the position of the analysis segment, the material polarization of the examination object For the characteristics, the potential distribution is set as a function based on the position of each analysis segment obtained by the region potential distribution extraction step, and the material polarization characteristics are shifted in the potential axis direction.

  Without using the discretized potential distribution, by setting the potential distribution based on a function having a certain relationship, the region division state of the part of the object to be examined in the reference model used in the reference model analysis process, and When there is a difference between the division state of the examination object in the examination object analysis process (the number of divisions in the reference model used in the reference model analysis process and the division number of analysis segments used in the examination object analysis process vary widely) (If any) can also be analyzed appropriately.

Embodiments of the present application will be described below with reference to the drawings.
The present application relates to a numerical analysis method that can be applied to a specific corrosive environment.

1 Numerical analysis method of corrosive environment (simulation)
In the explanation of this numerical analysis method, a current is passed from a counter electrode (corresponding to a train) as a current outflow source to a flat plate (corresponding to a substation) as an inflow target, and the current is examined in the field. An explanation will be given by taking an example of an electrolytic corrosion problem that flows through a buried pipe and generates corrosion.

  The present application proposes a unique numerical analysis method, and was verified by a model experiment to confirm the reliability of the numerical analysis method. Therefore, in describing the numerical analysis method, first, a corrosive environment to which the present technique is applied will be described, and a numerical analysis technique according to the present application and the result thereof will be described.

1-1 Corrosion environment to be analyzed (target of model experiment)
The object of analysis was the corrosive environment shown in FIG.
A platinum counter electrode (current outflow source 1 corresponding to a train) and an upper part of the water tank (on the upper side of the figure) below the water tank 4 (long side 1500 mm, short side 700 mm, depth 120 mm) shown in FIG. A stainless steel plate (inflow object 2 corresponding to a substation) is installed in the location), and the water tank 4 is filled with an aqueous solution of sodium sulfate (specific resistance 2520 Ω · cm), and direct current flows from the platinum counter electrode 1 to the stainless steel plate 2. (30 mA) was energized. Then, in this place, a steel round bar (corresponding to a buried pipe) at a position of 7 cm in depth, parallel to the short side of the water tank, on the back side of the platinum counter electrode 1 (the back side in the direction of the paper and on the bottom side of the water tank) The object 3) to be examined was immersed.

  In this field, the platinum counter electrode is a current outflow source 1 that causes galvanic corrosion, the stainless steel plate is an inflow object 2 into which current that causes galvanic corrosion flows, and the steel round bar is a tube that receives galvanic corrosion. Therefore, this steel round bar is the object to be examined 3 referred to in the present application, and the identification of the current outflow portion in the object to be examined is an analysis target.

  The steel round bar used in the experiment is composed of 12 test pieces having a length of 5 cm (Φ1 cm). Lead wires (not shown) for measuring the current are output from each test piece 30 and the current distribution is measured. The configuration is measurable. By adopting this configuration, each current flowing through the test piece 30 is determined.

1-2 Numerical analysis method In the numerical analysis of the field used in the present application, the potential distribution of the field to be analyzed is regarded as a Laplace field according to the Laplace equation, and a numerical analysis model corresponding to this field is constructed, and linear and nonlinear as in the past. Simulation analysis is performed by applying a solver that can solve the Laplace field under various boundary conditions to the constructed numerical analysis model.
However, in the present application, in the field to be analyzed, analysis of the field excluding the examination object 3 is executed once, and then the potential distribution in the arrangement area of the examination object obtained in this analysis is used. Further, a numerical analysis is further performed on the Laplace field in which only the examination object 3 exists in the field, and an inflow / outflow distribution of current from the examination object 3 to the medium is obtained.

  In order to solve the Laplace field numerically under this kind of linear / nonlinear boundary condition, the boundary element method can be applied as a numerical analysis method, but solvers that can use such a method are known. In this example, a program having a function equivalent to “Corrosion analysis system 3D-Café” (manufactured by Mizuho Information & Research Institute) was used as a solver. This solver is a solver that can analyze the corrosive environment as a Laplace field according to Laplace's equation. Regarding the setting of the boundary condition, the constant current condition, the constant potential condition, or the polarization of the element is defined for each element that forms the boundary. Analysis can be performed by selectively giving any one of the polarization characteristic conditions with the characteristic as a condition.

Hereinafter, the case of applying the numerical analysis procedure to the analysis target will be described in the order of steps.
FIG. 3 shows the flow of this numerical analysis.
(B) Standard model analysis process For each field to be analyzed, a numerical analysis model in which the platinum counter electrode (current outflow source 1) and the stainless steel plate (inflow target 2) are in the sodium sulfate aqueous solution (medium 5) , 2, and 5 and the specific resistance of the medium 5 are represented (step 1). In this numerical analysis model, it is assumed that the examination object 3 is not included in the model, and the medium 5 is uniformly distributed. However, even if the specific resistance distribution is not uniform, analysis can be performed by setting boundary conditions. This model is referred to as a reference model in the present application. FIG. 4 shows the configuration of this reference model corresponding to FIG.
In this reference model, the potential distribution in the field is obtained under the condition that a predetermined current flows from the current outflow source 1 through the medium 5 to the inflow target 2 (step 2). As the amount of current, 30 mA is applied. The potential distribution thus obtained is shown in FIG. A potential distribution (a potential distribution due to a voltage drop (IR drop) due to a current flowing in an aqueous solution having resistance) that satisfies the Laplace equation from the current source 1 toward the target 2 is generated. It can be seen that is formed.

(B) Region potential distribution extraction step From the potential distribution in the reference model obtained in the reference model analysis step, the potential distribution in the region where the object 3 is present is obtained (step 3). FIG. 6 shows the positional relationship of the examination object 3 in the water tank 4. This figure shows that this examination object 3 is divided into 60 analysis segments 300 from the left side of the figure.
FIG. 7 shows the potential distribution obtained as 60 discrete values at the position of the object 3 to be examined from the potential distribution obtained in the reference model analysis step, and a function obtained by functionalizing this distribution. . As shown in the figure, a potential peak exists at a position near a distance of 0.07 m where the counter electrode 1 which is a current outflow source exists, and as the distance increases, the potential decreases (voltage drop due to current and solution resistance, that is, It is reduced by the drop due to IRdrop).

(C) Study object analysis step Based on the potential distribution obtained by the region potential distribution extraction step and the material polarization characteristics of the study object 3, the current distribution flowing through the study object 3 is obtained (step 4). An example of this material polarization characteristic is shown in FIG. 8 as a solid line polarization curve (actual measurement value of the polarization characteristic of steel in this solution). This polarization curve is bifurcated into two on the right side of the figure. This is because the current density is expressed in logarithmic coordinates. When the potential is higher than the natural potential, the upper branch line shows the potential and the outflow current. The relationship with the density is expressed. When the potential is lower than the natural potential, the relationship between the potential and the inflow current density is expressed with the lower branch line.
In this examination object analysis step, the examination object 3 is regarded as a continuum composed of the analysis segments 300, and each of the analysis objects 300 corresponds to the position of the analysis segment 300 based on the potential distribution obtained by the region potential distribution extraction process. A potential difference is given to the analysis segment, and the analysis polarization characteristics of each analysis segment 300 are set based on the potential difference. After that, all of them are electrically connected to perform macrocell analysis, and the current from the object to be examined 3 to the medium is analyzed. Find outflow distribution. Here, the analytical polarization characteristic is a polarization characteristic that also takes into consideration the mutual potential difference between the analysis segments when each exists independently in the field to be analyzed.

FIG. 9 shows a processing flow in this examination object analysis process.
In this analysis step, the polarization characteristics (material polarization characteristics) of the analysis segment 300 constituting the examination object 3, the potential distribution of the area where the examination object 3 exists (area potential distribution), and the examination object 3 are The position and electrical connection relationship of each analysis segment 300 to be configured are captured (steps 4-1a, 4-1b, 4-1c).

Then, using these captured data, the polarization characteristics of each analysis segment 300 are obtained as analysis polarization characteristics (step 4-2). Specifically, this analytical polarization characteristic is based on the potential distribution at the position of each analysis segment obtained by the region potential distribution extraction step with respect to the material polarization characteristic as shown by the solid line in FIG. It can be obtained by shifting the material polarization characteristics only in the potential axis direction. In FIG. 8, this analytical polarization characteristic is indicated by a broken line, and the shift amount is indicated by s. Note that the analysis segment on the upstream side shifts to the high potential side with respect to the direction of the current flowing in the solution because the potential obtained in the region potential extraction step is higher than the analysis segment on the downstream side. Regardless of the analysis segment, the current distribution results are the same. The only problem here is the potential difference between the analysis segments. Here, although the same polarization characteristics are shifted, the polarization characteristics individually measured in the vicinity of this segment may be shifted (in the example described later with reference to FIGS. 15 to 22, the position of each segment is Analyzes taking into account potential).
Although the analytic polarization characteristics shown in the figure are single, in the actual analysis, the analytic polarization characteristics are set by the number of analysis segments 300 (60).

  In this shift operation, an actual value obtained as a discretized potential value as shown by each point in FIG. 7 may be used, or as shown by a continuous line in FIG. It is also possible to set the potential distribution in the region as a function based on the obtained position of each analysis segment 300 to shift the material polarization characteristics.

  As described above, the polarization characteristic of each analysis segment 300 that integrally forms the examination object 3 is obtained in a shifted state. Then, with respect to the Laplace field in which only the examination object 3 is in the field, numerical analysis is executed with the examination object 3 as a boundary. At this time, the shifted polarization characteristic (analysis polarization characteristic) of each analysis segment 300 becomes a non-linear boundary condition at that portion at the position of each analysis segment 300. Thereafter, in the analysis, substantially all the object 3 to be examined is treated as being electrically short-circuited, and the current distribution is obtained by analyzing the current inflow and outflow amounts at this boundary (step). 4-4). In this macrocell analysis, a solver for a Laplace field that can handle nonlinear boundary conditions is used, assuming that only the object to be examined 3 is in the field that was previously analyzed (structure in FIG. 6). (This solver is the same as that used in the previous reference model analysis step.) In other words, the analysis conditions are different, and this analysis is performed in a Laplace field having boundaries consisting of analysis segments in which the current outflow source and the inflow target are removed, the analysis segments are divided, and the analysis polarization characteristics are fixed. (This analysis is called macrocell analysis for the object under consideration). In this way, the current distribution in the examination object 3 can be obtained, and the result is output (step 4-5).

1-3 Effectiveness of Numerical Analysis According to the Present Application In the corrosive environment of the model experiment shown in 1-1, the measured value of the current distribution in the steel round bar that is the object to be examined 3 is indicated by a circle in FIG. The result of numerical analysis according to the numerical analysis method is indicated by ◇ in the figure (current inflow is expressed as negative and outflow as positive). This analysis result is displayed as an average value for every five adjacent points in FIG. Both results are in good agreement. Therefore, it can be seen that the numerical analysis method according to the present application is effective.

The above is the description regarding the numerical analysis method of the corrosive environment according to the present application, and further, the analysis in a complicated corrosive environment will be described.
The processing flow of this analysis is shown in FIG. Further, FIG. 12 shows a processing state corresponding to this processing flow.

2-1 Corrosive environment subject to analysis FIG. 13 shows the state of a model experiment targeted for analysis. For the example shown in FIG. 2, a steel round bar 13 having a more complicated shape was used.
As shown in FIG. 13 (a), 2190 Ω · cm sodium sulfate aqueous solution is filled in the water tank 14 (long side 1500 mm, short side 700 mm, depth 120 mm), and the object 3 to be examined is made of relatively complex steel. A round bar 13 was used. This steel round bar 13 is obtained by electrically shorting 34 test pieces 30 (length 5 cm, diameter Φ1 cm).
The current outflow source 1 in this example was disposed immediately above the test piece 10 shown in FIG. The inflow object 2 is assumed to be at the right end of the figure. Furthermore, the amount of current flowing through the field was 30 mA.
FIG. 13B shows the current distribution in the steel round bar 13 generated in this corrosive environment (current inflow is expressed as negative and outflow is expressed as positive).

2-2 Numerical Calculation The numerical calculation was performed according to the following procedure shown in FIG.
2-2-1 Preconditions The conditions such as the position of the examination object (step 11), the polarization characteristics of the examination object 3, and the specific resistance of the medium (aqueous solution) around the examination object 3 are obtained in advance (step 12). .

2-2-2 Numerical analysis (simulation)
Based on the conditions found in the model experiment, a numerical analysis model is constructed.
At this time, in the present application, since the numerical analysis method described above is used, a model (reference model described above) excluding the examination object 3 is prepared. The state of this model is shown in FIG.
Then, as shown in FIG. 12B, the specific resistance of the medium forming the field is set to the specific resistance measured in the measurement process (step 14).
After completing the above preparation, as described above in the numerical analysis, the position of the current outflow source 1 and the position of the inflow target 2 are obtained through the reference model analysis step, the region potential distribution extraction step, and the examination target analysis step. Further, a potential distribution satisfying these conditions is obtained for the current amount, and an inflow / outflow distribution of the current from the examination object 3 to the medium is obtained (steps 15 to 17).

  In this analysis, as described above, derivation of the potential distribution using the reference model (step 15), extraction of the potential distribution in the region where the examination object 3 exists, and the examination object 3 based on the extraction. Are determined (step 16), and current distribution is derived using the analysis polarization characteristics set in each analysis segment 300 (step 17). The derivation state of the potential distribution is schematically shown in FIG. 12C, and the derivation state of the current distribution is schematically shown in FIG.

  FIG. 14B specifically shows the potential distribution in the field thus obtained analytically, and FIG. 14C specifically shows the analysis of the potential. It is the current distribution of each analysis segment 300 which was calculated | required automatically. In FIG. 3C, the horizontal axis represents each analysis segment number, and the vertical axis represents the amount of current.

2-2-3 Comparison Result The result of FIG. 13B, which is a model experiment result, and the result of FIG. 14C, which is a numerical analysis result, are in good agreement.

An example was shown in which the material polarization characteristics of the object to be examined were single, and the analysis was advanced. However, if the material polarization characteristics change depending on the position and environment, the material polarization characteristics at that position are measured and used. Will be. However, in an actual buried corrosive environment, the natural potential differs depending on the position of each part of the object to be examined (for example, in the case of an buried pipe, the position of each part of the buried pipe), and the material polarization characteristics of each part are naturally Different. On the other hand, as described above, it is easy to measure the natural potential, but it is complicated to measure the material polarization characteristics for each part.
Therefore, hereinafter, an example in which only the natural potential of each part is measured and applied to the analysis of the present application using the result will be described.
With respect to this example, FIG. 15 shows the state of a model experiment of an embedded corrosive environment in which a pipe is embedded by simulating FIG.
In the figure, the 15 positions where the material polarization characteristics were actually measured are indicated by ◯ marks. As representative examples, FIGS. 16 and 17 show measured values of material polarization characteristics at points A and B, respectively. Table 1 below shows a list of natural potentials at 15 points. The left column shows each measurement point (A to O: corresponding to each part described so far), and the right column shows the natural potential at each point. In this example, the inflow object 2 was fixed at the position ▲, and the position of the current outflow source 1 was appropriately moved about 10 locations along the broken line to measure the outflow current.

  In this analysis, the polarization characteristics (corresponding to the predetermined material polarization characteristics) of the metal forming the buried pipe are assumed as shown in FIG. 18, and the material polarization characteristics shown in FIG. The material polarization characteristics were set by shifting in the direction of the potential axis for each part (point) so as to coincide with each other. As a representative example, the result of shifting the material polarization characteristics of FIG. 18 so as to coincide with the natural potential (−747 mV) at the point A is shown in FIG. 19, and the polarization characteristics of FIG. 18 are similarly converted to the natural potential (−493 mV) at the point B. FIG. 20 shows the result of shifting so as to coincide with. In the actual analysis using these material polarization characteristics, the current density values of all the material polarization characteristics were corrected to 1/200 as an example in consideration of the effect of coating.

The numerical calculation was performed in the same procedure as 2-2-1 and 2-2-2 shown in FIG. In this analysis, the material polarization characteristics considering the natural potential described above were used, and the above-described current density was also corrected. If there is a point that cannot be measured in the vicinity of a point where the self-potential can be measured, refer to the distance from the point where the self-potential can be measured. Was estimated and set. The results obtained using the analysis method of the present application were compared with the actual measurement values (the probe was inserted into the soil, short-circuited with the tube, and the current flowing between the probe and the tube was measured).
As a comparison result, FIG. 21 shows a graph in which the measured value of the outflow current is plotted on the horizontal axis, and the analysis result obtained by using the material polarization characteristics of FIG. . Note that the comparison between the actual measurement value and the analysis result was performed at nine points A, B, C, E, F, G, H, I, and M shown in FIG. The distribution of the plots goes up to the right, showing that the measured values and the analysis results are qualitatively consistent. For reference, FIG. 22 shows the result of performing the same analysis using all the material polarization characteristics actually measured at 15 positions. It can be seen that the tendency is almost the same as FIG.

[Another embodiment]
(A) In the above embodiment, electric corrosion is a problem, but interference problems other than electric corrosion can also be handled.
(B) In the above embodiment, the material polarization characteristics obtained in advance are used as the material polarization characteristics, or the material polarization characteristics in consideration of the natural potential are used for each part. The material polarization characteristic at an impossible position can be determined by performing position-dependent interpolation or extrapolation.
In this way, assuming that the shape of the polarization characteristic changes when the positions are different, an analysis using the polarization characteristic measured in a finite place becomes possible.
Further, the polarization characteristics may be given as a relationship diagram between current density and potential as shown in FIG. 8, or may be stored as an electrochemical relationship number table or the like and given as the relationship number table. .
(C) In the above-described embodiment, an example in which the current distribution is obtained for the object to be examined has been described. However, the polarization potential distribution in the object may be obtained.
When the current distribution is converted into the polarization potential distribution of the steel pipe, the polarization potential is obtained by converting the current into the potential using the material polarization characteristics (not the analysis polarization characteristics).

  An analysis method that accurately reflects the state of the site and can accurately estimate the corrosion state of the object subject to electrical corrosion investigation was obtained.

Explanatory diagram of the cause of the occurrence of electrolytic corrosion subject to analysis according to the present application Diagram showing the configuration of the electric erosion field in the experimental example The figure which shows the general | schematic flow of the numerical analysis method which concerns on this application Diagram showing the configuration of the reference model Diagram showing potential distribution in solution obtained by reference model analysis process Diagram showing the division structure of the object to be examined Figure showing the analysis result of potential distribution in the solution of the target Diagram showing material polarization characteristics and analytical polarization characteristics of the object under study The figure which shows the flow of the examination object analysis process which relates to this application Diagram showing measured values and numerical analysis results Diagram showing the analysis flow of another model experiment example Explanatory diagram of execution procedure for analysis of another model experiment example The figure which shows the actual value of composition of the electric corrosion field of another model experiment example, and current distribution The figure which shows the analysis result of the experiment example shown in FIG. The figure which shows the state of the model experiment of buried corrosive environment The figure which shows the actual value of the material polarization characteristic of point A The figure which shows the actual measurement value of the material polarization characteristic of B point Diagram showing assumed material polarization characteristics The figure which shows the material polarization characteristic of A point calculated | required by shifting from the material polarization characteristic of FIG. The figure which shows the material polarization characteristic of the B point calculated | required by shifting from the material polarization characteristic of FIG. The figure which shows the relationship between the measured value of the outflow current at the time of using the material polarization characteristic of each point calculated | required by shifting from the material polarization characteristic of FIG. 18, and an analysis result Diagram showing the relationship between the measured value of the outflow current and the analysis result when the measured material polarization characteristics at each point are used

Explanation of symbols

1: Current outflow source 2: Inflow target 3: Investigation target

Claims (7)

A numerical analysis method for a corrosive environment in which a target object is present in a field where current flows from a current source to a target object through a medium,
A reference model for constructing a reference model in which the examination object is removed and current flows from the current outflow source to the inflow object through the medium, and the analysis is performed by regarding the reference model as a Laplace field according to a Laplace equation The model analysis process;
A region potential distribution extraction step for obtaining a potential distribution in a region where the object to be examined exists from the potential distribution in the reference model obtained in the reference model analysis step;
Based on the potential distribution obtained by the region potential distribution extraction step and the material polarization characteristics of the examination object, an analysis is performed assuming that only the examination object exists in the field, and the polarization potential distribution of the examination object And a numerical analysis method for a corrosive environment, comprising: a target object analysis step for obtaining an inflow / outflow distribution of current from the target object to the medium.   2. To set the material polarization characteristics of the examination object, the predetermined material polarization characteristics are shifted in the potential axis direction for each part so as to coincide with the natural potential of each part of the examination object. The numerical analysis method of the corrosive environment described. In the examination object analysis step,
The examination object is regarded as a continuum consisting of a plurality of electrically connected analysis segments, and based on the potential distribution obtained by the region potential distribution extraction step, each of the analysis objects corresponding to the position of the analysis segment. The numerical analysis method of a corrosive environment according to claim 1 or 2, wherein an analytical polarization characteristic of an analysis segment is set, and a polarization potential distribution of the examination object and a current inflow / outflow distribution from the examination object to a medium are obtained. Based on the potential distribution obtained by the region potential distribution extraction step, in order to set the analysis polarization characteristics of each analysis segment corresponding to the position of the analysis segment,
The material polarization property is shifted in the direction of the potential axis based on the potential distribution at the position of each analysis segment obtained by the region potential distribution extraction step with respect to the material polarization property of the object to be examined. Numerical analysis method for corrosive environment. Based on the potential distribution obtained by the region potential distribution extraction step, in order to set the analysis polarization characteristics of each analysis segment corresponding to the position of the analysis segment,
A potential distribution in the region is set as a function based on the position of each analysis segment obtained by the region potential distribution extraction step with respect to the material polarization property of the examination object, and the material polarization property is set in the potential axis direction. The numerical analysis method of the corrosive environment according to claim 3 to be shifted.   The current outflow source is a leakage current source, the inflow target is an inflow target into which the leakage current flows, and the examination target is a conductor in the field. The numerical analysis method of the corrosive environment described.   The current source is a counter electrode for anticorrosion, the inflow target is an anticorrosion target that is a target for anticorrosion, and the examination target is a conductor in the field. A numerical analysis method for a corrosive environment according to claim 1.

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