JP2010190658A - Method for measuring/evaluating corrosion risk of cathodically-protected pipeline and measuring/evaluating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately perform effect evaluation on alternating-current induction to prevent excessive countermeasures from being taken against alternating-current induction while appropriately determining the current range of a probe current to perform measurement with resolution allowing a sufficient collation with a cathodic protection standard, when finding probe current densities (probe DC current density I<SB>DC</SB>and probe AC current density I<SB>AC</SB>) to collate them with the protection standard. <P>SOLUTION: The probe current is measured by a probe current measuring means 10 which includes a low-pass filter 12 of a cut-off frequency larger than a commercial frequency and smaller than twice the commercial frequency and which has a current range set according to a difference between an acceptable maximum value and an acceptable minimum value of a probe current found from the cathodic protection standard. As to the measurement of the probe current within a unit measurement time period, an arithmetic processing means 20 determines whether or not all the measurement values are within the current range to judge the cathodic protection to be unsuccessful in cases where all the measured values are not within the current range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a corrosion risk measurement evaluation method and measurement evaluation apparatus for a cathodic protection pipeline.

As a method of measuring and evaluating the corrosion risk of a cathodic protection pipeline, an evaluation method based on the measured value of the probe current density is known. This is because a probe simulating a coating defect is installed in the electrolyte in which a pipeline with a coating (plastic coating with high resistivity) is laid. The probe and the pipeline are connected by a conductive wire, the current (probe current) flowing between the probe and the pipeline is measured, and the probe current density (probe DC current density I _DC , probe AC current density I _AC ) is measured from the measured value. Corrosion risk is evaluated by ^{comparing the} measured time average values (I _DC ^ave , I _AC ^ave ) with the cathodic protection standard using the probe current density as an index.

The probe current density (probe DC current density I _DC , probe AC current density I _AC ) is calculated from the following formulas (1) and (2) from 200 probe current measurement values measured for 20 msec at a sampling interval of 0.1 msec. ). Here, A is the area of the probe, and I (n) is the nth sampled probe current measurement value.

As described in Non-Patent Document 1 below, the cathodic protection standard using the probe current density as an index is the reference region of the conditions I and II shown in Table 1 below, or the probe inflow DC current density I illustrated in FIG. _DC ^ave (A / m ² ) and probe AC current density I _AC ^ave (A / m ² ) can be defined by regions I and II of a two-dimensional coordinate diagram (see FIG. 1) having coordinate axes. The hatched portions (regions I and II) in FIG. 1 are ranges that pass the cathodic protection standards, and the other portions (regions III, IV, and V) are ranges that fail the cathodic protection standards. In the illustrated area III, there is a concern about corrosion due to the shortage of the DC current density I _DC flowing into the probe. In the illustrated area IV, the probe AC current density I _AC is excessive and there is a concern about AC stray current corrosion. This is a reject area where the inflow direct current density _IDC is excessive and overcorrosion is a concern. Here, the polarity of I _DC, the DC current is a positive orientation flowing from the electrolyte to the probe. Hereinafter, when the cathodic protection standard is simply used, the reference region shown in Table 1 or FIG. 1 is indicated.

Yuji Hosokawa, Fumio Hatakeyama, Yasuhiro Nakamura “Examination of Cathodic Protection Control Standards for Soil Buried Pipelines Using Probe Current Density”, Materials and Environment, Society for Corrosion Protection, 2002, Vol. 51, No. 5, p221 226

The unit measurement time for obtaining one value of the probe current density is set to a time corresponding to one cycle of the commercial frequency in order to evaluate the influence of the AC induction, and when the commercial frequency is 50 Hz, that one cycle. Is set to 20 msec. The probe DC current density I _DC is obtained as an average value of the measurement time obtained by dividing the measurement value sampled in this unit measurement time by the probe area, and the probe AC current density I _AC is sampled in the unit measurement time. The effective value of the value obtained by dividing the calculated value obtained by the measured value and the probe DC current density _IDC by the probe area is obtained.

However, the probe AC current density I _AC obtained in this way is the same as the probe frequency, even if it includes a harmonic (for example, 100 Hz) that is an integral multiple of the commercial frequency (for example, 50 Hz). Since it will be added to _AC , while evaluating the effect of commercial frequency, we are actually evaluating including harmonics that are integer multiples of commercial frequency, which has little effect on AC induction. Although it was intended for safety, there was a problem that it would take excessive AC induction measures.

  In addition, in order to place a measuring instrument for measuring the probe current in a terminal box where installation space is limited, the measuring instrument must be compact. Considering this, the current range of the probe current and the resolution of the A / D converter must be in a reciprocal relationship. If the current range is increased, the resolution of the A / D converter is decreased, and the current range is decreased. Then, the resolution of the AD converter can be increased.

On the other hand, in order to measure the probe current, considering that the change in the probe current is instantaneously increased, the current range is increased so that all the changes can be accommodated. Alternatively, where there are many causes of AC stray current generation, the current range must be increased, thereby reducing the resolution of the measured value. For example, when the probe area is 10 cm ² , the probe inflow DC current is passed. There is a problem that the minimum value of 0.1 mA cannot be accurately measured.

This invention makes it an example of a subject to cope with such a problem. That is, when obtaining the probe current density (probe DC current density I _DC and probe AC current density I _AC ) and checking against the cathodic protection standard, it is possible to accurately evaluate the influence of AC induction and take excessive AC induction measures. It is an object of the present invention to avoid such a problem, to appropriately determine the current range of the probe current, and to have a resolution that can be accurately checked against the cathodic protection standard.

  In order to achieve such an object, a corrosion risk measurement evaluation method and measurement evaluation apparatus for a cathodic protection pipeline according to the present invention include at least the configurations according to the following independent claims.

  [Claim 1] A cathodic protection pipeline for obtaining a probe current density from a probe current measured within a unit measurement time corresponding to one cycle of a commercial frequency, and checking the probe current density with a cathodic protection standard using the probe current density as an index. A corrosion risk measurement and evaluation method, comprising: a low-pass filter having a cutoff frequency greater than the commercial frequency and less than twice the commercial frequency, wherein the probe current passes a maximum value obtained from the cathodic protection standard; A method for measuring and evaluating corrosion risk of a cathodic protection pipeline, characterized in that measurement is performed by probe current measuring means having a current range set according to a difference from a minimum acceptable value.

  [Claim 5] A cathodic protection pipeline for obtaining a probe current density from a probe current measured within a unit measurement time corresponding to one cycle of a commercial frequency, and checking the probe current density with a cathodic protection standard using the probe current density as an index. The corrosion risk measurement and evaluation apparatus includes a probe current measuring means for measuring a probe current and an operation processing means for calculating the measured probe current. The probe current measuring means has a commercial frequency of 2 which is larger than the commercial frequency. A low-pass filter having a cutoff frequency smaller than twice, and having a current range set by a difference between a passing maximum value and a passing minimum value of the probe current obtained from the cathodic protection standard, Are all measured values of probe current within the unit measurement time within the current range? A missing value presence / absence determining means for determining whether or not, a probe current density calculating means for obtaining a probe DC current density and a probe AC current density from a probe current measurement value for each unit measurement time, and the missing value presence / absence determining means When it is determined that all the measured values are within the current range, the probe DC current density output from the probe current density calculating means and the measurement time average value of the probe AC current density are compared with the cathodic protection standard. Cathode anticorrosion evaluation is performed, and when the missing value presence / absence determination means determines that all the measured values are not within the current range, the cathode anticorrosion evaluation means rejects the cathodic protection evaluation. A corrosion risk measurement and evaluation device for cathodic protection pipelines.

Since the present invention has such a feature, when the probe current density (probe DC current density I _DC and probe AC current density I _AC ) is obtained and checked against the cathodic protection standard, the influence evaluation of AC induction is accurately evaluated. To avoid taking excessive AC induction measures. In addition, it is possible to appropriately determine the current range of the probe current, and to perform measurement with a resolution that enables accurate comparison with the cathodic protection standard.

It is explanatory drawing explaining the cathodic protection standard which uses a probe current density as a parameter | index. It is explanatory drawing explaining the corrosion risk measurement evaluation apparatus and measurement evaluation method of a cathodic protection pipeline concerning an embodiment of the present invention. It is explanatory drawing explaining the acceptable maximum value and the acceptable minimum value of the probe current calculated | required from a cathodic protection standard. It is explanatory drawing which shows the frequency characteristic of the analog low pass filter which has a Butterworth characteristic. It is explanatory drawing explaining the data sampling means of the arithmetic processing means in embodiment of this invention. It is explanatory drawing explaining the waveform preservation | save of the arithmetic processing means in embodiment of this invention. It is explanatory drawing which showed the specific processing flow of the arithmetic processing means in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 is an explanatory diagram for explaining a corrosion risk measurement evaluation apparatus and measurement evaluation method for a cathodic protection pipeline according to an embodiment of the present invention.

  Pipeline 1 to be measured and evaluated is coated (high resistivity plastic coating) 1 a and is embedded in an electrolyte such as soil, and is connected to pipeline 1. The cathodic protection is performed by the anticorrosion current output from the anode 2A. In measurement evaluation, a probe 3 simulating a coating defect portion is installed in the electrolyte near the pipeline 1, and this probe 3 is connected to the pipeline 1 by a conducting wire 3 a via a probe current measuring means 10. ing. A corrosion risk measurement and evaluation apparatus for a cathodic protection pipeline according to an embodiment of the present invention includes, as main components, the above-described probe current measurement unit 10 and an arithmetic processing unit 20 that performs arithmetic processing on the measured probe current. The corrosion risk of the pipeline 1 due to the DC stray current or AC stray current inside is measured and evaluated.

  The probe current measuring means 10 is a means for measuring the probe current flowing between the probe 3 and the pipeline 1, and includes an ammeter 11, a low-pass filter 12, and an AD converter 13, and is actually a pipe. It is compact enough to be accommodated in a terminal box TB provided at predetermined distances (for example, 250 m) along the line 1.

  The ammeter 11 has a current range set by the difference between the acceptable maximum value and the acceptable minimum value of the probe current obtained from the cathodic protection standard. In order to evaluate whether or not the probe current density obtained from the measured probe current passes the cathodic protection standard, it is not necessary to measure in detail even a large fluctuation of the probe current that does not fall within the cathodic protection standard range. Considering that the current range × resolution is limited due to the compactness required of the probe current measuring means 10, it is effective to increase the resolution in the current range by minimizing the current range.

FIG. 3 is an explanatory diagram for explaining the acceptable maximum value and the acceptable minimum value of the probe current obtained from the cathodic protection standard. Here, a case where the probe area A = 10 cm ² will be described. At the illustrated point P1, when the probe inflow DC current is 40 mA, which is the maximum value of the cathodic protection standard, the probe AC current passes the cathodic protection standard up to 70 mA. Since the amplitude of the sine wave with the probe AC current of 70 mA is 70 × (2) ^1/2 ≈99.0, the acceptable maximum value of the probe current is 40 + 99.0 = 139 mA. On the other hand, at the point P2 shown in the figure, when the probe inflow direct current is 0.1 mA, which is the minimum value of the cathodic protection standard, the probe alternating current passes the cathodic protection standard up to 2.5 mA. Since the amplitude of the sine wave with the probe alternating current of 2.5 mA is 2.5 × (2) ^1/2 ≈3.5, the minimum acceptable value of the probe current is 0.1−3.5 = −3. 4 mA.

The current range of the ammeter 11 only needs to include the probe current acceptable maximum value of 139 mA to the probe current acceptable minimum value of -3.4 mA. For example, when the current range is ± 200 mA and the resolution of the AD converter 13 is 12 bits, the current per step is 0.098 mA (400/2 ¹² ), and the required minimum current of the probe inflow DC current is 0. It becomes possible to measure 1 mA with high accuracy.

  The low-pass filter 12 has a cutoff frequency fc that is larger than the commercial frequency and smaller than twice the commercial frequency. As a result, the n-th harmonic of the commercial frequency can be removed from the measured probe current. As the low-pass filter 12, an analog low-pass filter having Butterworth characteristics is preferably used. An analog low-pass filter having Butterworth characteristics exhibits frequency characteristics as shown in FIG. According to this, the passband ripple having a frequency lower than the cut-off frequency fc can be minimized, and the noise level can be lowered. The cut-off frequency fc is set to a value higher than the commercial frequency (50 Hz or 60 Hz) but smaller than twice the commercial frequency. Considering the case where the commercial frequency is shared by both 50 Hz and 60 Hz, it is preferable to set the cutoff frequency fc to a value slightly higher than 60 Hz.

The A-D converter 13 converts the analog data of the probe current measured by the ammeter 11 into digital and outputs it to the arithmetic processing means 20. An optimum A-D converter resolution is selected for the current range set as described above. By narrowing the current range to the minimum necessary, the resolution of the A-D converter 13 can be increased. As described above, when the resolution of the AD converter 13 is 12 bits with a current range of ± 200 mA, the current per step is 0.098 mA (400/2 ¹² ), and the minimum required current 0 of the probe inflow DC current is 0. .1 mA can be accurately measured.

  The arithmetic processing unit 20 samples and calculates the probe current measured by the probe current measuring unit 10. Connected to the arithmetic processing means 20 are a data storage means 21 for storing sampled data or results of arithmetic processing and a monitor means 22 for monitoring and displaying the sampled data or arithmetic processing results. The main functional configuration of the arithmetic processing unit 20 includes a data sampling unit 20A, a waveform storage unit 20B, a missing value presence / absence determination unit 20C, a probe current density calculation unit 20D, and a cathodic protection evaluation unit 20E described below. I have. Each processing means can be formed by a set processing program, or each processing means may be formed by a part of a series of processing programs.

  FIG. 5 is an explanatory diagram for explaining the data sampling means 20 </ b> A in the arithmetic processing means 20. The data sampling means 20A continuously samples the data output from the probe current measuring means 10 at a set sampling interval every unit measurement time. Here, the unit measurement time is set to a time corresponding to one cycle of the commercial frequency, and when the commercial frequency is 50 Hz, the unit measurement time is set to 20 msec. Further, when the unit measurement time is 20 msec, one cycle (about 16.7 msec) of the commercial frequency 60 Hz can be included, so that the apparatus can be shared between 50 Hz and 60 Hz. The sampling interval is set so that sufficient data can be obtained within the unit measurement time, and can be set to 0.1 msec, for example. When the sampling interval is 0.1 msec, 200 measurement values can be obtained in a unit measurement time of 20 msec.

  FIG. 6 is an explanatory diagram for explaining the waveform storage 20 </ b> B in the arithmetic processing means 20. The waveform storage unit 20B stores the measurement value (sampling data) sampled by the data sampling unit 20A in the data storage unit 21 as a measurement value waveform along the time series for each unit measurement time. As described above, since the current range of the ammeter 11 is set in accordance with the cathodic protection standard, if a probe current exceeding the current range is measured, no data can be obtained at that point, and there is no data. Missing values will occur.

FIG. 6A shows an example of a measured value waveform when there is no missing value within the unit measurement time. At that time, a continuous waveform can be stored in the data storage means 21 as shown. On the other hand, FIG. 6B shows a measurement value waveform example when there is a missing value within the unit measurement time. At that time, a discontinuous waveform is stored in the data storage means 21 as shown in the figure. If there is no missing value within the unit measurement time as shown in FIG. 5A, the probe current density (probe direct current density I _DC , probe alternating current density I _AC ) is determined according to all the measured values within the unit measurement time. However, when there is a missing value within the unit measurement time as shown in FIG. 5B, the probe current density cannot be obtained.

This waveform storage means 20B is a discontinuous waveform with missing values when the measured values are temporarily saved every unit measurement time and the missing value presence / absence judging means 20C determines that there is a missing value, as will be described later. Is stored when the probe current density calculating means 20D updates I _AC (50 Hz) ^max as described later.

  The missing value presence / absence determining means 20C in the arithmetic processing means 20 determines whether or not all the measured values of the probe current within the unit measurement time are within the current range. In other words, the case where the measurement value sampled at 0.1 msec exceeds the current range is determined as a missing value, and whether or not the missing value exists, that is, the data acquisition rate within the unit time is 100%. It is determined whether or not there is. At the same time as the above-described determination, the missing value presence / absence determination unit 20C obtains the data acquisition rate = {number of acquired data / (unit measurement time / sampling time)} × 100 and stores the obtained value in the data storage unit 21. The level of abnormality can be determined to some extent by the data acquisition rate.

The probe current density calculation unit 20D in the calculation processing unit 20 calculates the above-described equation (2) from the measured value of the probe current for each unit measurement time when the above-described missing value presence / absence determination unit 20C determines that “there is no missing value”. The probe DC current density I _DC and the probe AC current density I _AC are obtained by 1) and (2). The probe DC current density I _DC and the probe AC current density I _AC obtained every unit measurement time are stored in the data storage means 21, and after the measurement time is finished, the probe DC current density I _DC and the probe AC current density I _AC are averaged over the measurement time. The values I _DC ^ave and I _AC ^ave are calculated.

Further, the probe current density calculation means 20D determines that the unit is used when all measurement values within the unit measurement time are within the current range, that is, when the missing value presence / absence determination means 20C determines that there is no missing value. It is determined whether or not the measurement value of the measurement time corresponds to a sine wave having a commercial frequency (50 Hz or 60 Hz), and the probe alternating current density I _AC ( Commercial frequency) (eg, I _AC (50 Hz)). By obtaining this probe AC current density I _AC (commercial frequency), it is possible to further accurately evaluate the influence of AC induction. In the following description, the case where the commercial frequency is 50 Hz will be described as an example, but the present invention is not limited to this.

Whether or not the measurement value of the unit measurement time corresponds to a sine wave having a commercial frequency (50 Hz) can be determined as corresponding when both of the following (i) and (ii) are satisfied. (I) The time difference between the maximum value and the minimum time of appearance of the measured value measured within the unit measurement time (20 msec) is 10 msec. (Ii) In the measurement value measured within the unit measurement time (20 msec), (maximum value) −I _DC = I _DC − (minimum value). Here, when (i) and (ii) are both established, I _AC (50 Hz) = I _AC, and otherwise, I _AC (50 Hz) = 0 and I _AC (50 Hz) is stored as data. Save in means 21. Then, when the measurement time is completed, and calculates the measured time average value I _AC (50Hz) ^ave of I _AC (50Hz).

When the cathodic protection evaluation unit 20E in the arithmetic processing unit 20 determines that the missing value presence / absence determination unit 20C determines that all measured values are within the current range, that is, determines that there is no missing value. , probe flows direct current density I _DC measurement time average value I _DC ^ave and the measured time average value I _AC (50Hz) ^ave the cathodic protection of the probe AC current density I _AC (50 Hz) output from the probe current density calculating means 20D Cathodic protection evaluation is performed by checking the reference, and when the missing value presence / absence discriminating means 20C determines that all measured values are not within the current range, that is, when it is determined that “missing value exists”, cathodic protection evaluation Is rejected.

In other words, the cathodic protection evaluation unit 20E performs different processing depending on whether there is a missing value and when there is no missing value. In particular, if there are missing values, the probe current density (probe DC current density I _DC , probe AC current density I _AC ) cannot be obtained, but the current range of the ammeter 11 is set according to the cathodic protection standard. Therefore, if there is a missing value, it can be judged as abnormal, so this case is evaluated as rejected, the measured value waveform is saved with the highest priority, and the saved measured value waveform Is displayed on the monitor means 22 to visually determine whether or not the failure is recognized. Even if there is a missing value, it is possible to grasp whether or not it is a sine wave at a commercial frequency as shown in FIG. If it can be determined that it is a sine wave of commercial frequency, it can be said that the influence of alternating current induction is extremely high, so a preferential countermeasure for reducing alternating current induction is presented.

  FIG. 7 is an explanatory diagram showing a specific processing flow of the arithmetic processing means 20. Based on this processing flow, the corrosion risk measurement and evaluation method for the cathodic protection pipeline will be described more specifically.

  When the arithmetic processing unit 20 starts the arithmetic processing, the data sampling unit 20A outputs the measured value of the probe current that has passed through the low-pass filter 12 output from the probe current measuring unit 10 at a set sampling interval (0.1 msec). Sampling is performed (S10). The measured value data for each sampling is temporarily stored in the predetermined memory area of the data storage unit 21 as time series data corresponding to the sampling time as needed (S11), and sampling is continued until the unit measurement time (20 msec) elapses ( S12: “NO” → S10).

  When the unit measurement time elapses, the arithmetic processing unit 20 collects temporarily stored sampling data within the unit measurement time, and proceeds to the next arithmetic processing step (S12: “YES” → S13). At the same time, the sampling of data and the temporary storage of the measured value data at the next unit measurement time are continued, and sampling is performed every continuous unit measurement time (S12: “YES” → S10). Thus, the sampling interval (0.1 msec) set without interruption is measured within the measurement time. As a result, it is possible to perform measurement without missing the high-speed phenomenon of AC induction caused by the passage of a high-speed AC electric railway (for example, Shinkansen) vehicle. The temporarily stored measurement value data is stored in correspondence with the sampling time of each data. The sampling time of the n-th measurement value data from the start of sampling (the sampling start time is the first) is calculated as sampling start time + sampling interval (for example, 0.1 msec) × (n−1) and is associated with the measurement value data.

  When the missing value presence / absence discriminating means 20C acquires provisionally stored data within the unit measurement time (S13), the presence / absence of missing values is discriminated (S14). As mentioned above, the missing value is determined as “missing missing value” when there is any missing value as the measured value data for each sampling interval exceeds the current range. If there is no data, it is determined that there is no missing value. When determining the presence or absence of missing values, data acquisition rate = {number of acquired data / (unit measurement time / sampling time)} × 100 is calculated. If the data acquisition rate is not 100%, it can be determined that “there is a missing value”, and if the data acquisition rate is 100%, it can be determined that there is no missing value.

  When the missing value presence / absence determining means 20C determines that “missing value exists” (S14: “missing missing value”), the cathodic protection evaluation means 20E causes the waveform storage means 20B to function to detect the missing value. The generated measurement value waveform within the unit measurement time is stored in the data storage unit 21 and the start time of the unit measurement time is stored in the data storage unit 21 as the occurrence time of missing measurement occurrence (S20). In this case, the cathodic protection evaluation means 20E outputs a failure evaluation (S21), displays the stored waveform in which the missing value is generated on the monitor means 22 (S22), and ends the process.

On the other hand, when the missing value presence / absence discriminating means 20C discriminates that “there is no missing value” (S14: “no missing value”), the probe current density calculating means 20D obtains the measured value within the acquired unit measurement time. by substituting the data into the formula (1) described above to calculate the probe DC current density I _DC, stores the I _DC of each calculated unit measurement time data storage means 21 (S30). Further, the probe current density calculation means 20D calculates the probe AC current density I _AC by substituting the acquired measured value data within the unit measurement time and the calculated probe DC current density I _DC into the above-described equation (2). and it stores the calculated unit measurement every time of the I _AC in the data storage unit 21 (S31).

Further, the probe current density calculating unit 20D determines whether or not the waveform based on the measured value data within the obtained unit measurement time corresponds to a sine wave of a commercial frequency (for example, 50 Hz) (S32). As described above, this determination is based on whether or not both (i) and (ii) are satisfied ((i) the occurrence time of the maximum value and the minimum value of the measurement value measured within the unit measurement time (20 msec)). The time difference is 10 msec. (Ii) In the measurement value measured within the unit measurement time (20 msec), (maximum value) −I _DC = I _DC − (minimum value) can be determined. When the waveform based on the measured value data within the acquired unit measurement time corresponds to a sine wave of commercial frequency, I _AC (50 Hz) = I _AC is set (S33), and the waveform based on the acquired measured value data within the unit measurement time. Is not a sine wave of commercial frequency, I _AC (50 Hz) = 0 is set (S 34), and this I _AC (50 Hz) is stored in the data storage means 21 (S 35).

When _IAC (50 Hz) is stored in the data storage means 21, _IAC (50 Hz) ^max is updated (S36). This respect I _AC required for each unit measurement time (50 Hz), initially with ^{_{I AC (50Hz) max = I}} AC (50Hz), the next unit measurement time I _AC (50 Hz) I _AC (50 Hz ) compared to the ^max to update the I _AC (50Hz) ^max in the case of the _{I AC (50Hz)> I AC} (50Hz) max. When I _AC (50 Hz) ^max is updated (S36: “Updated”), the measured value waveform at the unit measurement time at that time is stored, and the appearance time (measurement start time of the unit measurement time) is stored. Save (S37). It is desirable to store the measured waveform so that the top three waveforms of I _AC (50 Hz) ^max can be stored.

After the missing value presence / absence discriminating means 20C obtains temporarily stored data within one unit measurement time (S13), I _AC (50 Hz) is stored (S35), and I _AC (50 Hz) ^max is updated. The process up to (S36) is performed as a process within the next unit measurement time. If the measurement time has not ended (S38: "NO"), the process again proceeds to the data sampling process by the data sampling means 20A. (S12).

Then, the process for each unit measurement time is performed until the end of the measurement time, and when the measurement time ends (S38: “YES”), the probe current density calculation unit 20D performs I _DC and I _AC (50 Hz) for each unit measurement time. ), The measurement time average values I _DC ^ave and I _AC (50 Hz) ^ave are calculated (S40). At this point, I _DC per unit measurement _{time, I AC, I AC (50Hz} ), I AC (50Hz) max within the measurement time, (3 higher) the measured value waveform and its appearance time is stored (S30, S31, S35, S37).

Thereafter, the cathodic protection evaluation means 20E compares I _DC ^ave and I _AC (50 Hz) ^ave with the cathodic protection standards as processing when the missing value presence / absence judging means 20C judges that “there is no missing value” ( S41), whether or not I _DC ^ave and I _AC (50 Hz) ^ave obtained within the measurement time pass the cathodic protection standard is evaluated (S42). When the cathodic protection standards are not accepted (S42: “failed”), the stored I _DC and I _AC (50 Hz) time-dependent graphs, measured value waveforms and their appearance times are displayed on the monitor means 22 ( S43). If the cathodic protection standards are passed (S42: “Pass”), the process is terminated.

  According to the corrosion risk measurement and evaluation method and measurement evaluation apparatus for the cathodic protection pipeline according to the embodiment of the present invention having the characteristics as described above, the following effects can be obtained.

  For one thing, measurement of the probe current is performed without interruption every unit measurement time. Therefore, when evaluating the AC corrosion risk, the AC induction generated in the pipeline 1 due to the passage of a high-speed AC electric railway (for example: Shinkansen) vehicle is used. It is possible to evaluate without missing the impact.

The probe current is measured by passing through a low-pass filter 12 having a cutoff frequency fc that is larger than the commercial frequency and smaller than twice the commercial frequency, and the measured waveform of the measured probe current is a sine wave of the commercial frequency. The AC corrosion risk is evaluated based on the I _AC (commercial frequency) that is determined after being identified, so the AC corrosion risk can be evaluated except for an increase in I _AC due to n-fold harmonics of the commercial frequency. Excessive measures can be avoided.

  The probe current is measured by the probe current measurement means that has a current range that is set by the difference between the maximum and minimum acceptable probe current values obtained from the cathodic protection standards. The probe current can be measured with a combination of optimal resolutions of the AD converter. According to this, it is possible to measure the probe current measurement value whether or not to pass the cathodic protection standard with an appropriate resolution and evaluate the pass / fail with high accuracy, and the probe current measurement value exceeds the current range. When a missing value occurs, it can be grasped and an abnormality of the measured value can be immediately grasped.

  If the measured value of the probe current does not fall within the current range set based on the cathodic protection standard, introduce the concept of the missing value, and detect the cathodic protection by the presence of this missing value or the data acquisition rate. Since the evaluation is performed, if a missing value occurs, the cathodic protection evaluation can be immediately rejected without waiting for the end of the measurement time.

  If a missing value occurs, the measured value waveform at that time is saved with the highest priority, and the measured value waveform is displayed on the monitor. The cause is due to the AC induction phenomenon at the commercial frequency that generates the AC corrosion risk. Whether it is a thing or not can be immediately recognized visually.

1: Pipeline, 2: External power supply, 2A: Anode, 3: Probe
10: probe current measuring means, 11: ammeter, 12: low-pass filter,
13: AD converter,
20: Calculation processing means, 20A: Data sampling means, 20B: Waveform storage means, 20C: Missing value presence / absence determination means, 20D: Probe current density calculation means, 20E: Cathodic protection evaluation means,
21: Data storage means, 22: Monitor means

Claims (9)

Corrosion risk measurement evaluation of a cathodic protection pipeline that obtains the probe current density from the probe current measured within a unit measurement time corresponding to one cycle of the commercial frequency, and compares the probe current density with the cathodic protection standard using the probe current density as an index. A method,
The probe current includes a low-pass filter having a cutoff frequency that is larger than the commercial frequency and smaller than twice the commercial frequency, and is set by a difference between the accepted maximum value and the accepted minimum value of the probe current obtained from the cathodic protection standard. A corrosion risk measurement and evaluation method for a cathodic protection pipeline, characterized in that the measurement is performed by a probe current measuring means having a current range.   The method for measuring and evaluating corrosion risk of a cathodic protection pipeline according to claim 1, wherein the low-pass filter is an analog low-pass filter having Butterworth characteristics. In the measurement of the probe current within the unit measurement time, it is determined whether all measured values are within the current range,
3. The cathodic protection according to claim 1, wherein when all measured values are not within the current range, the cathodic protection evaluation is rejected and a waveform of the measured values of the unit measuring time is stored. Pipeline corrosion risk measurement and evaluation method. The unit measurement time is continuously measured within the measurement time,
When all the measurement values within the unit measurement time are within the current range, the probe direct current density and the probe alternating current density are determined for each unit measurement time,
Determine whether the measurement value of the unit measurement time corresponds to a sine wave of commercial frequency,
The average value within the measurement time of the probe DC current density and the average value within the measurement time of the probe AC current density when the measurement value of the unit measurement time corresponds to a sine wave of a commercial frequency,
4. The corrosion risk of the cathodic protection pipeline according to claim 3, wherein the average value within the measurement time of the probe DC current density and the average value within the measurement time of the probe AC current density are checked against the cathodic protection standard. Measurement evaluation method. Corrosion risk measurement evaluation of a cathodic protection pipeline that obtains the probe current density from the probe current measured within a unit measurement time corresponding to one cycle of the commercial frequency, and compares the probe current density with the cathodic protection standard using the probe current density as an index. A device,
A probe current measuring means for measuring the probe current and an arithmetic processing means for calculating the measured probe current are provided.
The probe current measuring means includes a low-pass filter having a cutoff frequency that is larger than the commercial frequency and smaller than twice the commercial frequency, and depending on the difference between the accepted maximum value and the accepted minimum value of the probe current obtained from the cathodic protection standard. Has a set current range,
The arithmetic processing means includes:
A missing value presence / absence determining means for determining whether or not all measured values of the probe current within the unit measurement time are within the current range;
Probe current density calculating means for obtaining a probe DC current density and a probe AC current density from the measured value of the probe current for each unit measurement time;
When the missing value presence / absence determining means determines that all the measured values are within the current range, the measurement time average of the probe DC current density and the probe AC current density output from the probe current density calculating means The value is checked against the cathodic protection standard and the cathodic protection evaluation is performed. When the missing value presence / absence determining means determines that all the measured values are not within the current range, the cathodic protection evaluation is rejected. Cathodic protection evaluation means, and a corrosion risk measurement and evaluation device for a cathode protection pipeline.   The waveform storage means for storing the waveform of the measurement value of the unit measurement time when at least the missing value presence / absence determination means determines that all the measurement values are not within the current range. Item 6. A corrosion risk measurement and evaluation device for a cathodic protection pipeline according to Item 5. The probe current measuring means continuously measures the unit measurement time within the measurement time,
The probe current density calculation means includes
When all the measurement values within the unit measurement time are within the current range, the probe direct current density and the probe alternating current density are determined for each unit measurement time,
Determine whether the measurement value of the unit measurement time corresponds to a sine wave of commercial frequency,
The average value within the measurement time of the probe AC current density when the average value during the measurement time of the probe DC current density and the measurement value during the unit measurement time correspond to a sine wave of a commercial frequency is obtained. 5. A corrosion risk measurement and evaluation apparatus for a cathodic protection pipeline described in 5 or 6.   8. The corrosion risk measurement and evaluation device for a cathodic protection pipeline according to claim 5, wherein the low-pass filter is an analog low-pass filter having Butterworth characteristics.   9. The corrosion protection of the cathodic protection pipeline according to claim 5, wherein the probe current measuring means includes an AD converter having a current range of ± 200 mA and a resolution of 12 bits or more. Risk measurement and evaluation device.

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