JP2008032421A - Numerical analyzing method of corrosive or corrosion-proof environment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a numerical analyzing method capable of accurately reflecting the state of the spot to precisely estimate the corrosion state of a conductor. <P>SOLUTION: In the numerical analyzing method of a corrosive or corrosion-proof environment for regarding the corrosion-proof state of an electric corrosion-proof place, where the current flowing out of a current outflow source flows in an inspection target, as a continuous body, which is composed of a plurality of the analyzing segments electrically connected to the inspection target to analyze the same, as a setting method of the material polarization characteristics of the analyzing segments on the surface of the inspection target, a weight coefficient is used with respect to the respective analyzing segments on the basis of the polarization characteristics of the actually measured material measured at each of the measuring positions on the surface of the inspection target to interpolate the potential value to a constant current value from a part of or all of the polarization characteristics of the actually measured material and the led-out polarization characteristics of the interpolated material are set as the polarization characteristics of the material in the respective analyzing segments. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention provides a corrosion or anti-corrosion environment in which a target object is present in a field where current flows from the current source to the target object through the medium, or current flows from the current source to the target object via the medium. The present invention relates to a numerical analysis method for a corrosion or anticorrosion environment in which the corrosion or anticorrosion environment is analyzed by regarding the object to be examined as a continuous body composed of a plurality of analysis segments electrically connected.

Such a numerical analysis method of corrosion or anticorrosion environment is applied to so-called corrosion problems such as electric corrosion and interference, and general corrosion prevention problems.
For example, in the case of electrolytic corrosion, corrosion due to leakage current or interference occurs in an environment as shown in FIGS. 1A and 1B, and interference occurs in an environment as shown in FIG. appear.
More specifically, in the case of the example shown in FIGS. 1A and 1B, in the DC electric railway 100, a part of the current flowing through the rail 101 flows out into the ground 102 and is buried in the vicinity thereof. Corrosion generated in the conductive buried pipe 103 is a problem, and a leakage current flows as shown by arrows in FIGS.
In the case of the example shown in FIG. 1 (c), when the anticorrosion is applied to the buried pipe 104 by the external power supply device 105, a part of the anticorrosive current flows into the other conductive buried pipe 103 in the vicinity, and at the current outflow portion. The corrosion that occurs is a problem. In this case, an anticorrosion current flows as shown by an arrow in FIG. 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.

  Since corrosion occurs at a site where an electric current flows into a medium, for example, soil, it is necessary to specify this position. In addition, the inflow part of an electric current will be in a corrosion prevention state. In other words, it is necessary to obtain the current inflow / outflow distribution from the object to be examined to the medium (“soil” in the above example).

As a technique related to estimation of this type of corrosion site, an analysis using numerical analysis is proposed in Patent Document 1.
This proposal is due to the inventors of the present application, considering the potential distribution as a Laplace field, and taking into account the boundary condition that the interfered object is in a predetermined potential state with respect to the protected object, Analyzes interference problems.

Japanese Patent Laid-Open No. 11-160271

However, Patent Document 1 has the following problems.
In the analysis described in this document, when dealing with a large-scale model, a potential difference of a constant value is given at all positions, but it is difficult to say that this state can well represent a corrosion or anticorrosion environment. When there is a buried pipe, since there are a plurality of parameters as the shift value of the polarization characteristic, there is a case where the convergence does not occur in the analysis.

Therefore, the inventors set nonlinear boundary conditions that can represent the situation in the field (specifically, each analysis segment when the object to be examined is regarded as a continuum consisting of a plurality of electrically connected analysis segments). The material polarization characteristics that can represent the actual situation in the field) are proposed and analyzed.
By performing the analysis by setting the boundary conditions in this way, it is possible to obtain an analysis result that can better represent the actual situation in the field, and to estimate the position of the corrosion occurrence site and the like.

  Now, when adopting such a numerical analysis method of corrosion or anticorrosion environment, the object to be examined existing in the field to be analyzed is regarded as a continuum consisting of multiple analysis segments, and the material polarization characteristics are set in each analysis segment. There is a need to. Therefore, when this analysis method is employed, it is necessary that the material polarization characteristics be determined for all analysis segments.

  In general, the material polarization property is a property related to the interface between the object to be examined and the medium (for example, soil) in contact with the object to be examined. Therefore, the surrounding environment (for example, moisture content, specific resistance, pH, contained ions, etc.) ) Will change even if the material is the same. That is, if the environment differs depending on the position, the material polarization characteristics at that position also change. And this material polarization characteristic needs to be obtained primarily by on-site measurement.

  In order to measure this material polarization characteristic, this work is performed when the analysis target is a buried pipe buried in soil, specifically, a probe (a test piece made of the same material as the buried pipe to be examined). ) Is inserted into the soil, short-circuited with the buried pipe and blended with the soil, then separated from the buried pipe, and the polarization characteristics of only the probe are measured.

However, the place where the material polarization characteristic can be measured in the field is limited, for example, in the case of a buried pipe, which is only a measurement position called a protector provided on the road at regular intervals.
As described above, for the above analysis, it is necessary to set material polarization characteristics for all analysis segments (that is, it is necessary to set over the entire object to be examined). In this case, it is difficult to actually measure the material polarization characteristics at the positions between the protectors, so the material polarization characteristics at the nearest measurable positions will be used as they are. Then, there was a problem that the reliability of the analysis result decreased.

  An object of the present invention is to obtain a numerical analysis method capable of accurately estimating the state of an object to be examined, particularly when only the material polarization characteristics of a specific part of the object to be examined are known. The object is to obtain a numerical analysis method of corrosion or anticorrosion environment that can accurately estimate the material polarization characteristics of each part and obtain a highly reliable numerical analysis result as an analysis result.

In order to achieve the above object, the first characteristic configuration of the numerical analysis method of the corrosion or anticorrosion environment in which the object to be examined exists in the field where the current flows from the current source to the inflow object through the medium is as follows:
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;
The object to be examined is regarded as a continuum consisting of a plurality of electrically connected analysis segments, and in order to set the material polarization characteristics of each analysis segment, the material polarization characteristics from the analysis segment with unknown material polarization characteristics are set. A weighting factor is defined as a function of the distance to the analysis segment whose characteristics are known, and the current value for a constant potential value is interpolated from some or all known material polarization characteristics using the weighting coefficient. A material polarization property interpolation step for setting the interpolated material polarization property as the material polarization property of each analysis segment in which the material polarization property is unknown,
Using the potential distribution obtained by the region potential distribution extraction step and the material polarization characteristic set by the material polarization property interpolation step, an analysis is performed assuming that only the object to be examined exists in the field, and the examination And a subject analysis step for obtaining a polarization potential distribution of the subject and a current inflow / outflow distribution from the subject to be examined to the medium.

This method is a method that can be adopted when dealing with the corrosion problems such as electric corrosion and interference described above.
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 distribution that can represent a potential gradient in the environment to be analyzed. That is, a field where a potential gradient is generated in a state orthogonal to the equipotential line is handled.
In this reference model, the current outflow source and the inflow target are specified, so the potential distribution can be obtained based on the positional relationship, and the current amount that is estimated to normally flow is used as appropriate. can do. 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 in which the object to be examined that actually does not exist in the analysis of the reference model is extracted (obtained) in the region potential distribution extraction step. .

  In the examination object analysis step, only the examination object is targeted, and the potential distribution of the region in the reference model and the material polarization characteristics of each analysis segment constituting the examination object 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. . 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.

  Now, if it is going to perform the examination object analysis process as mentioned above, it will be necessary to set the polarization characteristic for materials of each analysis segment which constitutes the examination object as a boundary condition at this process. Therefore, for analysis segments with known material polarization characteristics, the known material polarization characteristics are analyzed. For analysis segments with unknown material polarization characteristics, the analysis segments with known material polarization characteristics are obtained in the material polarization characteristics interpolation step. The interpolated material polarization properties, weighted with a function of the distance, are used. The relative relationship of the material polarization characteristics between analysis segments in a specific positional relationship can be determined in relation to the distance between the two segments.

In this way, by setting rational material polarization characteristics for all analysis segments, the analysis of the field where the current outflow source, the inflow target, and the study target exist in the medium is performed. Furthermore, it is possible to perform well in a state suitable for the current situation regardless of the presence of an analysis segment whose material polarization characteristics are unknown.
Therefore, the above-described corrosion due to leakage current and corrosion due to interference can be analyzed.

In order to achieve the above object, the second characteristic configuration of the numerical analysis method of the corrosion or anticorrosion environment where current flows from the current source to the object to be examined through the medium is as follows:
The object to be examined is regarded as a continuum consisting of a plurality of electrically connected analysis segments, and in order to set the material polarization characteristics of each analysis segment, the material polarization characteristics from the analysis segment with unknown material polarization characteristics are set. A weighting factor is defined as a function of the distance to the analysis segment whose characteristics are known, and the current value for a constant potential value is interpolated from some or all known material polarization characteristics using the weighting coefficient. A material polarization property interpolation step for setting the interpolated material polarization property as the material polarization property of each analysis segment in which the material polarization property is unknown,
Using the material polarization characteristic set by the material polarization characteristic interpolation step, the model including the current outflow source and the object to be examined is regarded as a Laplace field according to a Laplace equation, and an analysis is performed. The purpose is to obtain the polarization potential distribution and the current inflow / outflow distribution from the object to be examined to the medium.

This method is a method that can be adopted when dealing with general corrosion or corrosion prevention problems.
In terms of analysis method, the analysis field is regarded as a Laplace field that satisfies the Laplace equation, but current inflow from the current source to the object to be examined is expected, and further, In this case, the present application can be adopted only when the material polarization characteristics of each part (analysis segment in numerical analysis) can be known only at the specific part.
Also in this case, as the solver used for the analysis, a solver that can solve the Laplace field by taking into account the material polarization characteristic that is a nonlinear boundary condition as the boundary condition is used. In addition, the examination object to be set as the boundary condition is divided into a plurality of analysis segments, and the material polarization characteristics need to be set for all analysis segments.

  As in the case of the first feature configuration described above, if there is an analysis segment whose material polarization characteristics are known and an unknown analysis segment for each analysis segment, the material of the unknown analysis segment In the material polarization characteristic interpolation step, the polarization characteristic is obtained by weighting based on the function of distance from the material polarization characteristic of a known analysis segment, and the result is used for the analysis.

  As a result, numerical analysis of the general corrosion or anticorrosion environment where current flows from the current source to the target object through the medium, even in a situation where the material polarization characteristics of only a part of the target object can be known. It came to be able to do well.

In the numerical analysis method of the corrosion or anticorrosion environment having the first characteristic configuration or the second characteristic configuration described above, the weighting factor is determined as a function inversely proportional to the distance, Interpolation is preferably performed.
The material polarization characteristics at different positions are considered to be inversely proportional to the separation distance, and the relationship between the material polarization characteristics can be defined by a rational and simplest relational expression.

Embodiments of the present application will be described below with reference to the drawings.
As an embodiment of the present application, a first embodiment and a second embodiment are shown.
In the first embodiment, there are “current outflow source”, “inflow target”, and “review target” in the field to be analyzed, and current flows into and out of the test target, This is an embodiment when electric corrosion or interference is a problem.
In the second embodiment, there is a “current outflow source” and “subject to be examined” in the field to be analyzed, and general corrosion or corrosion prevention in which current flows from the current outflow source to the subject to be studied becomes a problem. It is an embodiment.
Regarding both of these embodiments, a model experiment using a water tank or an on-site experiment using a buried pipe model using a buried pipe is performed, and a numerical analysis model that can represent those experiments is constructed, and the usefulness of the numerical analysis method according to the present application Was examined.

1 First Embodiment Since the numerical analysis method used in this embodiment is unique, first, the numerical analysis method will be described first, and then only in a part of the object to be examined. The numerical analysis when the material polarization characteristics are not known will be described.

1-1 Model Experiment FIG. 2A shows the state of the environment in which the model experiment was performed.
In the upper part of the water tank 4 (long side 1500 mm, short side 700 mm, depth 120 mm), a platinum counter electrode (current outflow source 1) on the upper part (the part located on the surface side in the figure), and a stainless steel plate (inflow target 2 ), An experimental tank filled with an aqueous solution (medium 5) of sodium sulfate (specific resistance 2520 Ω · cm) in the water tank 4 was prepared, and a direct current (30 mA) was passed from the platinum counter electrode to the stainless steel plate. .

  In this place, it was assumed that a steel rod-like body (examination object 3) was immersed in the bottom part of the water tank (the back side in the direction of the paper surface).

  In this case, 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 rod-like body is a buried pipe that receives galvanic corrosion. Therefore, this steel rod-shaped body is the examination object 3 referred to in the present application, and the identification of the current outflow portion in the examination object 3 is an analysis target.

The steel rod-like body 3 is configured by electrically connecting 34 test pieces 30 having a length of 5 cm (Φ1 cm), and lead wires (not shown) for measuring current from each test piece 30 are provided. The current distribution can be measured.
FIG. 2B shows the current distribution of each test piece 30 in the steel rod-shaped body 3 generated in this environment (current inflow is expressed as minus and outflow is expressed as plus).

1-2 Numerical analysis In numerical analysis, 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 a Laplace field is obtained under linear and nonlinear boundary conditions. Use a solver that can solve
However, in this embodiment, since there are “current outflow source”, “consideration object”, and “inflow object” in the field for the field to be analyzed, an analysis method unique to this embodiment is taken. This analysis method is a method newly proposed by the inventors when using the above solver.

  In order to numerically solve the Laplace field under this kind of linear / nonlinear boundary condition, the boundary element method can be applied as a numerical analysis method, but such a solver itself is 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 a corrosive or anticorrosive environment as a Laplace field according to Laplace's equation. Regarding the setting of the boundary conditions, the `` constant current condition '' and `` constant potential condition '' Alternatively, the analysis can be performed by selectively giving one of the “polarization characteristic conditions in which the polarization characteristic of the analysis segment is specified”.

  In performing the numerical analysis, the field analysis excluding the examination object 3 is executed once, and then the examination object is obtained by using the potential distribution in the arrangement region of the examination object 3 obtained by this analysis. Numerical analysis is further performed on the Laplace field in which only 3 exists in the field, and the inflow / outflow distribution of current between the object 3 to be examined and the medium 5 existing around is obtained.

Hereinafter, the case of applying the numerical analysis procedure to the analysis target will be described in the order of steps.
However, in the description of 1-2, the material polarization characteristics used for each analysis segment are treated as known and the same.

FIG. 3 shows a flow of numerical analysis in this case.
(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, 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. FIGS. 4A and 4B show 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). For example, 30 mA is applied as the amount of current. The potential distribution thus obtained is shown in FIGS. 4C and 5B.
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. ) 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). In this step, the potential of each part of the examination object 3 indicated by a broken line in FIG. 4C is extracted.

(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. 6 as a solid line polarization curve (actual measurement value of the polarization characteristic of steel in this solution). This polarization curve is bifurcated on the right side of the figure because the current density is expressed as a logarithmic graph. In the state where the potential is higher than the natural potential, the potential and the outflow current at the upper branch line. 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 the numerical analysis, the examination object 3 is regarded as a continuum composed of a plurality of analysis segments 300 as shown in FIG. 5A, and based on the potential distribution obtained by the region potential distribution extraction step. Then, a potential difference is applied to each analysis segment 300 corresponding to the position of the analysis segment 300, and the analysis polarization characteristics of each analysis segment 300 are set based on the potential difference, and then all of them are electrically connected to perform macrocell analysis. The flow of current into and out of the object 3 to be examined is obtained.

  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.

The processing flow in this examination object analysis process is shown in FIG.
In this analysis process, the material polarization characteristics of the analysis segment 300 constituting the examination object 3, the region potential distribution of the area where the examination object 3 exists, and the positions of the analysis segments 300 constituting the examination object 3. And the electrical connection relationship is taken in (steps 4-1a, 4-1b, 4-1c).

  Then, using these captured data, the analytical polarization characteristics of each analysis segment 300 are obtained as analytical polarization characteristics (step 4-2). Specifically, this analytical polarization characteristic is based on the potential distribution at the position of each analytical segment 300 obtained by the region potential distribution extraction step with respect to the material polarization characteristic as shown by the solid line in FIG. The material polarization characteristics are shifted in the direction of the potential axis by the amount.

  In FIG. 6, this analytical polarization characteristic is indicated by a broken line, and the shift amount is indicated by s. Note that the analysis segment 300 on the upstream side has a higher potential determined in the region potential extraction step than the analysis segment 300 on the downstream side with respect to the direction of the current flowing in the solution, and therefore shifts to the high potential side. . Regardless of the analysis segment 300, the current distribution results are the same.

  The only problem here is the potential difference between the analysis segments. In this description, the same material polarization characteristics are shifted for easy understanding. Although the analytic polarization characteristics shown in the figure are single, in the actual analysis, as many analytic polarization characteristics as the number of analysis segments 300 are set.

  As described above, the analysis polarization characteristics of each analysis segment 300 that integrally forms the examination object 3 are obtained in a shifted state. Then, with respect to the Laplace field in which only the object to be examined 3 is in the field, numerical analysis is performed with the object to be examined 3 as a boundary. At this time, the shifted analysis polarization characteristic of each analysis segment 300 becomes a non-linear boundary condition at the position of each analysis segment 300. Thereafter, in the analysis, the object 3 to be examined is substantially treated as being electrically short-circuited, and the current inflow / outflow amount at this boundary is analyzed to obtain a current inflow / outflow distribution. (Step 4-4).

In this macrocell analysis, a solver for a Laplace field that can handle a nonlinear boundary condition is used assuming that only the object 3 to be examined is in the field to be analyzed first (this solver is used for the previous analysis). It is the same as that used in the reference model analysis process.)
That is, the analysis conditions are different, and the Laplace field having the boundary composed of the analysis segment 300 in which the current outflow source and the inflow target object are excluded, the analysis segment is formed, and the analysis polarization characteristics are fixed, is analyzed. (This analysis is called macrocell analysis for the object under consideration). In this manner, the current input / output flow distribution in the examination object 3 can be obtained, and the result is output (step 4-5).
In this way, when the current inflow / outflow distribution of the object to be examined is obtained, the polarization potential distribution in the object to be examined is converted from current to potential using material polarization characteristics (not analytical polarization characteristics). Can be obtained.

1-3 Effectiveness of numerical analysis Measured values of the current inflow / outflow distribution between the steel rod-shaped object 3 and the medium 5 in the corrosion or anticorrosion environment of the model experiment shown in 1-1 Is shown in FIG. 2 (b) (inflow of current is expressed as minus and outflow is expressed as plus). On the other hand, the result obtained by numerical analysis is shown in FIG. The results are qualitatively consistent. Therefore, it can be seen that this numerical analysis method is effective.

1-4 Analysis Method when Material Polarization Characteristic is Known Only at Part of Examination Object In the above description, the material polarization characteristic of examination object 3 is known, and all analysis segments 300 The case where the analysis is performed as the same is described.
However, as described above, making the material polarization characteristics the same for the entire examination object 3 has room for improvement in the accuracy of analysis. Furthermore, there are few situations in which the material polarization characteristics are known in all parts of the object 3 to be examined. Therefore, the material polarization characteristic of the unknown part is estimated from the known material polarization characteristic, and for the unknown part, this estimated material polarization characteristic is used in the examination object analysis step.

1-4-1. Basic Method for Interpolating Material Polarization Characteristics A basic method for interpolation will be described with reference to FIGS.
As shown in FIG. 8, it is assumed that the material polarization characteristics can be measured at the points A and B on the object 3 to be examined, and the measurement at the point C in FIG. A case will be described in which the material polarization characteristics at a point are obtained from known material polarization characteristics at points A and B.

  When the measurement points (two points) of the material polarization characteristics are arranged as shown in FIG. 8, assuming that the material polarization characteristics at the point A are f1 and the material polarization characteristics at the point B are f2, the current density q and the potential E Are expressed as q = f1 (E) for point A and q = f2 (E) for point B. At this time, the material polarization characteristics at points other than the points A and B where measurement is impossible (for example, the point C shown in FIG. 9) are closer to the point f1 as the point A is closer, and closer to the point f2 as the point B is closer. It is estimated that it becomes a locus.

Therefore, a weighting factor corresponding to the distance L to the measurement point is given by w (L) as a function of the distance. That is, when a certain current density q is given, the interpolation material polarization characteristic of the current density q at the point C is assumed to follow the following equation.
q = (w (L1) × f1 (E) + w (L2) × f2 (E)) / (w (L1) + w (L2))
Here, L1 and L2 are the distance between point C and point A, and the distance between point C and point B, respectively.

When the number of measurement points is n, q = Σw (Ln) × fn (E) / Σ (w (Ln)) (Here, the integration Σ is executed for the number of measurement points).
In this case, the known material polarization characteristics may be interpolated by using a part of the known material polarization characteristics without using all of them. Actually, when the interpolation material polarization characteristics are obtained, the interpolation material polarization characteristics can be obtained by averaging the current density q at each potential E while changing the potential E.

Assuming that the relational expression w for obtaining the weighting factor is a function inversely proportional to the distance, the weighting factor is expressed as q = Σ (fn (E) / Ln) / Σ (1 / Ln) (where, Integration Σ is executed for the number of measurement points).
However, when Ln = 0, the polarization characteristic q = fn (E) measured as an exception process is used.

  The material polarization characteristics obtained in this way (the known material polarization characteristics for the measurable points and the interpolated material polarization characteristics for the unmeasurable points) are used as the material polarization characteristics at the points of each analysis segment 300. The numerical analysis described in (1) can be performed.

1-4-2 Measurement and Interpolation of Material Polarization Characteristics in Embedded Pipe Model FIG. 10 shows the structure of an embedded pipe model in which a pipe is embedded by simulating FIG. In the figure, the positions of 15 points at which the material polarization characteristics were actually measured are indicated by ◯ marks.

  FIG. 11 shows the actually measured material polarization characteristics at point A, and FIG. 12 shows the actually measured material polarization characteristics at point B, respectively. By following the above interpolation method, an interpolated material polarization characteristic obtained by averaging the measurement results of FIGS. 11 and 12 was obtained as shown in FIG. 13 at an intermediate point between the points A and B.

  In the above buried pipe model, the material polarization characteristics were measured at a total of 15 points shown in FIG. 10, and using these results, the material polarization characteristics at points where measurement was impossible were interpolated with a function inversely proportional to the distance. In the numerical analysis model, the number of analysis segments 300 constituting the examination object 3 is 2023.

1-4-3 Numerical Analysis Using Interpolated Material Polarization Characteristics Material polarization characteristics obtained as described above (based on whether measurement is possible or not, the material polarization characteristics actually measured for the measurable part, measurement not possible) The material polarization characteristics obtained by interpolation with respect to the part (1) were used for each analysis segment 300 according to the position in the analysis object analysis step. In use, correction was made in consideration of the influence of coating (current density was set to 1/200). As a material polarization characteristic to be compared, a theoretical value as shown in FIG. 14 (current density change 10 μA / cm ^{2 with} respect to potential change 35 mV) is corrected in consideration of the effect of coating (current density is 1/200). Numerical analysis using the material polarization characteristics.

  FIG. 15 shows a comparison between an actual measurement value (actual measurement value in an embedded pipe model) and an analysis result when a numerical analysis is performed using theoretical values, and FIG. 16 shows an actual measurement of material polarization characteristics at a measurable point. This is a comparison between the measured value (measured value in the buried pipe model) and the analysis result when the value is analyzed using the interpolated material polarization characteristics at a point where measurement is impossible. From the comparison between FIG. 15 and FIG. 16, it can be seen that a better analysis result can be obtained by interpolating the material polarization characteristics. In FIG. 17, points where measured values were measured as comparison targets are indicated by ◯.

2 Second Embodiment In this embodiment, there are a “current outflow source” and a “subject to be examined” in the field to be analyzed, and general corrosion or anticorrosion in which current flows from the current outflow source to the subject to be examined. This is an embodiment when there is a problem.
When performing the numerical analysis of this embodiment, the analysis is performed using a solver that can solve the Laplace field under linear and nonlinear boundary conditions, as in the previous embodiment.
In the analysis, it is assumed that a constant current flows from the current source to the object to be examined. In order to set the boundary condition on the target object side, it is necessary to segment this target object into analysis segments and set the material polarization characteristics of each of these segments. From the material polarization characteristics of the known part, the interpolation material polarization characteristics are obtained by interpolation according to the method adopted in 1-4-1 of the first embodiment, and for the unknown part, by using the interpolation material polarization characteristics, Analysis can be performed.

Hereinafter, the target model will be described more specifically.
2-1 Buried pipe model A pair of metal buried pipes (hereinafter simply referred to as metal pipes) having an outer diameter of 700 mm and a length of 9 m are buried in parallel, and the pair of metal pipes are positioned at an intermediate position in their separating direction. An embedded pipe model in which a current-carrying electrode having an outer diameter of 125 mm and a length of 5 m was installed perpendicularly to the metal-tube burying direction and the current-carrying current was supplied from the current-carrying electrode to protect the metal pipe was analyzed.
In this buried pipe model, the energizing electrode was installed perpendicularly to the burying direction of the metal tube, and the longitudinal intermediate portion of the energizing electrode was arranged at the position of the metal pipe. That is, assuming that the longitudinal direction of the energization electrode is the embedment depth direction, the longitudinal direction half of the energization electrode is extended to the shallow side and the deep side, respectively, as viewed from the embedment depth of the metal tube.

  Using one end of the metal tube as a reference point, the material polarization characteristics were measured at measurement points at distances from the reference point of 0.5 m, 1 m, 2 m, 3 m, 4 m, and 6 m. The measurement results are shown in FIG. The sign of the current density is negative for the current inflow direction and positive for the current outflow direction.

2-2 Numerical analysis Using these measurement results, the material polarization characteristics of a total of 39 analysis segments defined in the metal tube were measured from each position by the method described in 1-4-1. It was obtained by weighting and interpolating with a function inversely proportional to the distance to. Using the obtained interpolation material polarization characteristics, using the solver described above, a constant current (specifically 2A) is supplied from the energizing electrode (current outflow source) to the metal tube (subject to be examined). Numerical analysis was performed as a flow.

  In FIG. 19, the measured value at the time of energization of 2A at each measurement point is indicated by □, and the numerical analysis result (described as the analysis result on the drawing) is indicated by ●. Further, FIG. 20 shows a comparison between the numerical analysis result of the potential and the actual measurement value with respect to the distance from the reference point. The measured values and the numerical analysis results almost coincided. In this method, the material polarization characteristics are made different for each analysis segment, and numerical analysis that matches the situation at the site is performed. However, when analysis is performed with averaged material polarization characteristics (averaged over all analysis segments). When the material polarization characteristics are used), the error from the actual value becomes large. The reason for this is that while the analysis result changes on the averaged material polarization characteristic, the actual measurement value at each measurement position does not exist on the averaged material polarization characteristic.

  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 configuration of model experiment The figure which shows the general | schematic flow of the numerical analysis method used by 1st embodiment. Explanatory drawing of the analysis procedure in the first embodiment The figure which shows the analysis model and analysis result of 1st embodiment Explanatory diagram of material polarization characteristics and analytical polarization characteristics of the object to be studied Diagram showing the flow of the object analysis process Explanatory diagram for obtaining interpolated material polarization characteristics Explanatory diagram for obtaining interpolated material polarization characteristics Diagram showing the distribution of measurable points Actual value of material polarization characteristics at point A Measured value of material polarization characteristics at point B The figure which shows the material polarization characteristic of C point calculated | required by interpolation Diagram showing theoretical values of material polarization characteristics Diagram showing the relationship between actual measurement values and numerical analysis results when theoretical values are used The figure which shows the relation between the actual measurement value and the numerical analysis result when the interpolation method is used The figure which shows distribution of the comparison point of the result which is shown in FIG. 15 and FIG. The figure which shows the measurement result of the material polarization characteristic in 2nd embodiment The figure which shows the comparison of the measured value and numerical analysis result in 2nd embodiment The figure which shows the comparison of the measured value and numerical analysis result in 2nd embodiment

Explanation of symbols

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

Claims (3)

A numerical analysis method for a corrosion or anti-corrosion 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 in which the examination object is removed and a reference model is constructed in which a 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;
The object to be examined is regarded as a continuum consisting of a plurality of electrically connected analysis segments, and in order to set the material polarization characteristics of each analysis segment, the material polarization characteristics from the analysis segment with unknown material polarization characteristics are set. A weighting factor is defined as a function of the distance to the analysis segment whose characteristics are known, and the current value for a constant potential value is interpolated from some or all known material polarization characteristics using the weighting coefficient. A material polarization property interpolation step for setting the interpolated material polarization property as the material polarization property of each analysis segment in which the material polarization property is unknown,
Using the potential distribution obtained by the region potential distribution extraction step and the material polarization characteristic set by the material polarization property interpolation step, an analysis is performed assuming that only the object to be examined exists in the field, and the examination A numerical analysis method for a corrosion or anticorrosion environment, comprising: a polarization potential distribution of a target object and a target object analysis step for obtaining a current inflow / outflow distribution from the target object to the medium. A numerical analysis method for a corrosion or anticorrosion environment in which current flows from a current source to a target object through a medium,
The object to be examined is regarded as a continuum consisting of a plurality of electrically connected analysis segments, and in order to set the material polarization characteristics of each analysis segment, the material polarization characteristics from the analysis segment with unknown material polarization characteristics are set. A weighting factor is defined as a function of the distance to the analysis segment whose characteristics are known, and the current value for a constant potential value is interpolated from some or all known material polarization characteristics using the weighting coefficient. Executing the material polarization property interpolation step for setting the interpolated material polarization property as the material polarization property of each analysis segment in which the material polarization property is unknown,
Using the material polarization characteristic set by the material polarization characteristic interpolation step, the model including the current outflow source and the object to be examined is regarded as a Laplace field according to a Laplace equation, and an analysis is performed. A numerical analysis method of a corrosion or anticorrosion environment for obtaining a polarization potential distribution and an inflow / outflow distribution of current from the object to be examined to a medium.   The numerical analysis method for a corrosion or anticorrosion environment according to claim 1 or 2, wherein the weighting coefficient is determined by the function of the distance, the weighting coefficient is determined as a function inversely proportional to the distance, and the interpolation is performed.

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