JPS60154152A - Investigating method of corrosion state of buried pipe - Google Patents

Abstract

PURPOSE:To obtain a method for investigating the corrosion state of an urban buried pipe which is influenced by a stray current from an electric car track effectively without digging by employing a statistical method. CONSTITUTION:Three items, i.e. (1) the number and positions (item 1) of electric cars running in a section, (2) the distance (item 2) between a measurement point and a substation, and (3) the distance (item 3) between the measurement point and track are employed, the current direction of a conduit at the measurement point to the environmental soil ring is regarded as a target variable by digitizing logic II, etc., and discriminants of the inflow (corrosion prevention) and outflow (electrolytic corrosion) of the stray current are generated to investigate the corrosion state of the conduit buried along the electric car track. Then, the buried pipe laid along the railway shown in figure is investigated to obtain the cumulative probability distribution of the investigated sample as shown in the figure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for effectively investigating the state of corrosion of underground pipes in urban areas, which are affected by stray currents, without excavating the pipes.

Stray current is a current that flows in a place other than the normal circuit, and when this type of current flows into a metal object such as a buried pipe, the metal object can be severely eroded at the point where the current flows out again into the soil or water. . Leakage current from train tracks is considered to be one of the sources of this stray current. Trains are often
The track is used as a return path for train current, but because the track's absolute radius with respect to the ground is insufficient, a portion of the current flowing through the rail flows into nearby underground pipes, causing damage to the substation, which is the negative power supply point. It flows out nearby and flows back. However, the locations of inflow and outflow change in complex ways over time, and the extent of this change is not constant. For this reason, it is necessary to periodically investigate the corrosion state of buried pipes to prevent accidents from occurring.

The investigation method used in this case is to measure the pipe-to-ground potential (P/S) using a saturated copper sulfate electrode.

That is, the natural potential of the tube is set to -500 to -600 mV, and if the potential is negative, it is determined that it is on the outflow (electrolytic corrosion) side, and if it is negative, it is determined that it is on the inflow (corrosion protection) side. However, since this potential varies depending on soil resistance, oxygen content, etc., the measurement accuracy is low, and extensive experience and skill are required to judge the corrosion state from the measurement results. Furthermore, since the stray current is greatly affected by the running condition of the train, it is necessary to collect data regarding various conditions, and measurement must be carried out over a long period of time. Furthermore, in order to understand the time-series changes that occur as trains run, it is necessary to carry out simultaneous measurements at 8 to 10 consecutive measurement terminals, as well as 24-hour measurements as necessary. However, there are problems such as the need to measure one point at a time at every 8 to 10 locations and estimate the potential distribution at the same time by correlating them.

The present invention was made in view of the above-mentioned circumstances, and it is an object of the present invention to provide a method that makes it possible to investigate the corrosion state of buried pipes using a statistical method that is simpler than conventional methods. be.

The method for investigating the corrosion state of buried pipes of the present invention measures the corrosion state of pipes buried along train tracks by measuring (i) the number and location of trains running within the investigation section, (a) measurement points and substations; c) Distance between the measurement point and the track are adopted as explanatory variables, and according to quantification theory (III), the direction of the current with respect to the soil ring surrounding the pipe at the measurement point is used as the objective variable, and the stray current is calculated. This method is characterized by creating and investigating discriminants for inflow (corrosion protection) and outflow (electrolytic corrosion).

Hereinafter, one embodiment of the method of the present invention will be described in detail. Figure 1 shows the relationship between the pipeline to be investigated and the train tracks. The buried pipes are asphalt-coated pipes laid along the railway, and the length of the survey section is approximately 13 pipes. In this conduit, 200 to 4
There are 63 measuring terminals installed at 00m intervals. A-F are stations, and the sections between each station are I-■ as shown in the diagram.
And so. T is a substation, located near D station.

When analyzing and examining the corrosion caused by stray current in conduits buried under electric train tracks, the following factors should be considered.

l) Total number of train locations and substation locations within the survey section.
There is a relationship between the potential gradient of the track and the magnitude of the return current, that is, the magnitude of the stray current.

2) Distance between the measurement point and the substation and track The return current from the track enters the buried pipe located at the shortest distance from the track, and is thought to flow underground from the point closest to the substation.

Therefore, during analysis, explanatory variables (hereinafter referred to as items)
1) The number and location of trains running within the section (
Item 7), 2) Distance between measurement point and substation (Item 2), 3) Distance between measurement point and track (Item 3)
I decided to adopt the item.

Regarding item 1, use the train running diagram to check the number of trains in the sections ■ to V, and calculate this as 21
It was divided into t+ turns and classified into 21 categories. Items 2 and 3 were classified into 7.4 categories according to the table below.

On the other hand, the objective variable was the direction of the current flowing from the pipe at the measurement point. That is, insert a globe electrode into a borehole near the terminal, measure the direction of the globe current,
It was divided into two groups: inflow and outflow.

Then, analysis was performed using the following discriminant.

However, Y: Sanzor score atiy azi+asi: Item 1, 2 respectively
．． 3 i category score δ11'+δ21. δ31: Applicable Category 1° Not Applicable Category 0 Next, the globe current data for analysis was collected at 1 minute intervals at 22 measurement points, changing the measurement time as shown in the table below, for a total of 248 samples. And so. In this case, the number of simultaneous measurement points is 3 to 6, and the cumulative measurement time is over 1 hour.

Some of the measured data is shown in the table below.

The analysis results will be explained below. The correlation ratio, which is the ratio between the between-group variance and the total variance, was 0.5761.

In addition, the scores for each item and category are within the range of 0 to 1.9552 for item 1, and for item 2.
, 3, the values are shown in the table below.

The score of each sample is determined by entering the score of each item/category into the above-mentioned discriminant. For example,
As mentioned above, the categories of each item in 7° Le 1 are 1 and 4.3, respectively (the score of category 1 of item 1 is 0D552) Y = (10552-3,71
64+[72=-25892 is stopped. When the scores of each sandal are thus calculated and shown in a cumulative probability distribution diagram, the result is as shown in Fig. 2. The number of data for the inflow group is 133, the average is 1, and the standard deviation is 0.9898, and the number of data for the outflow group is 115, the average is -1,1565, and the standard deviation is 0.
．． 8381, and some of the discrimination points are 1678. Therefore, if the sample score is thicker than the value of this discrimination point, it is determined to be an inflow, and if it is smaller than this value, it is determined to be an outflow. The accuracy rate (minimax accuracy rate) of the discriminant in this case is 88.1% with a probability sigma of 11798.

Therefore, for measurement points other than the measurement points used in the analysis, the inflow and outflow predictions based on the discriminant were compared with the actual measured values for 95 Sansols, and 10 misclassifications were found. However, there was no misjudgment that occurred for more than three consecutive minutes in chronological order.

Therefore, it was confirmed that the accuracy was sufficient for practical use.

Furthermore, when considering the categories of item 1 in order of score size, when the location and number of trains are biased to one side around substation T in central section I, especially toward stations A and B, It was found that the corrosion current is most likely to flow out when it is concentrated. That is, when trains are located on average within a section, they interfere with each other, which is not necessarily a bad situation.

In addition, if you enter the sum of the scores of the corresponding categories in the cross-tabulation table of Item 2 and Item 3, the following table will be obtained.

Here, the score for each category of item 1 is θ~1.
It is a positive value within the range of 95, and the value of the discriminant point is -0,16
78, so the score in the table above is (7) At the measurement points marked with a ◎, there is always no fear of corrosion on the inflow side, regardless of item 1, that is, nofter/of train regression.1. On the other hand, at the measurement points marked *, even if the maximum value of the category of item 1, 1.95, is taken into account, the length of the leakage is always id.

At the remaining measurement points, depending on the train schedule pattern (item l category score 0 to x, 9s), there may be an inflow, but the trend is interpreted as an outflow side. This can be summarized in terms of measurement points as shown in the following equation.

Therefore, a needle electrode was used to investigate paint film damage between measurement points 40 and 41, which were likely to be corroded, and as a result, reactions were observed at six locations. Therefore, taking external conditions into consideration, excavation surveys were conducted at four of the locations.

As a result, pitting corrosion was confirmed in all locations, and repairs were made immediately.

Since the method for measuring the corrosion state of buried pipes according to the present invention is as described above, the measurement time and number of samples required for analysis are extremely small compared to the conventional methods, and the number of personnel and two pieces of equipment required for investigation is significantly reduced. be able to. However, by using appropriate explanatory variables (items), the accuracy of estimating the corrosion state is extremely high, and the method is sufficiently practical.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a buried pipe installed on a railway that was investigated in an embodiment of the present invention, and FIG. 2 is a cumulative probability distribution diagram of the survey sample.

Claims (1)

[Claims] Corrosion status of underground conduit (train track 11CG) is determined by a) the number and location of trains running in the survey section, a) distance between the measurement point and the substation, and c) distance between the measurement point and the track. Corrosion status investigation of buried pipes, which uses distance as an explanatory variable and uses quantification theory type II to create a discriminant formula using the direction of current flowing in and out of the pipe at the measurement point as the objective variable. Method.