JP2007107882A - Corrosion estimation method for buried pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To estimate the amount of corrosion of a buried pipeline without performing any on-site survey on the burying environment as to burying points of the pipeline. <P>SOLUTION: Corrosion depths in outer surfaces of cast iron pipes and environmental factors of burying places are measured as to the plurality of burying points with the iron pipes buried therein. The result of the measurement is applied to known ground information to prepare a calculation expression for a corrosiveness evaluation coefficient on the burying environment of a place whose ground information is known. From the calculation expression for the evaluation coefficient and from the burying period of the iron pipes, a corrosion depth estimation expression is prepared capable of calculating the corrosion depth of the outer surfaces of the iron pipes buried in this place. From known ground information on an object place and from information on the burying period of the iron pipes in this place, corrosion depths are estimated of outer surfaces of the iron pipes buried in this place by using the estimation expression. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for predicting corrosion of buried pipes in soil.

  As a water pipe, a cast iron pipe is used in a state of being buried in the soil. When a considerable number of years have passed since the burial, corrosion occurs on the surface portion of the cast iron pipe that is in contact with the soil, and the thickness of the cast iron pipe decreases. If corrosion progresses to some extent and the thickness of the cast iron pipe decreases, the pipe must be replaced with a new pipe.

  When investigating the degree of corrosion, that is, the reduction in wall thickness of cast iron pipes buried in the soil, it is practical to measure the wall thickness by cutting the pipe line over the entire length, which is a lot of work. is not. For this reason, conventionally, various corrosion prediction methods have been used so that the degree of corrosion can be predicted without cutting the pipe over the entire length.

  In order to predict the degree of corrosion of the cast iron pipe buried in the soil, it is necessary to evaluate the corrosiveness of the buried environment, that is, the buried soil to the cast iron pipe. For this reason, conventionally, for example, the soil corrosivity of buried pipes has been qualitatively compared with soil environment factors such as soil and groundwater in the light of the US ANSI standard and the German DIN standard soil corrosion evaluation method. I was judging. However, this soil corrosivity evaluation method is only for evaluating the corrosiveness of the soil, and the amount of corrosion of the buried pipe cannot be predicted quantitatively.

  As a method for quantitatively predicting the amount of corrosion of the buried pipe, Patent Document 1 discloses that the soil is excavated to partially expose the pipe along the length direction, and the pipe constituting the pipe is corroded. Collecting information and information on the embedded environment such as soil, and analyzing the data to create a corrosion depth prediction formula, etc., and predict the amount of corrosion of the pipe in the entire pipeline in the area Is described. However, it is necessary to obtain the corrosion information and the embedded environment information. Especially, since the number of items of the embedded environment information is as large as about 10, the information collection requires a great deal of cost and time.

As a corrosion prediction method that simplifies the method described in Patent Document 1 described above, Patent Document 2 classifies the embedded environment factors existing in the target region (for example, the whole country of Japan) into a plurality of types in advance, and Prepare the corrosion amount prediction formula using multiple factors in advance, obtain the buried environment information of the place where the pipe to be actually investigated is buried, and then use the above prediction formula to corrode It is described to predict the amount. However, in this case, there is an advantage that it is not necessary to measure the corrosion amount of some pipes or create a prediction formula for each buried place, but collecting information on the buried environment such as soil is not possible. is necessary. In addition, when obtaining the buried environment information of a survey point, it may be necessary to increase the number of survey points because a corrosive place or a weak place cannot be identified.
JP-A-1-250841 JP 2000-148178 A

  As described above, in the conventional methods, it is necessary to collect information on the buried environment such as the soil of the survey point, and there is a problem that a great deal of cost and time are required for that purpose.

  In view of the above, the present invention aims to solve such problems and to predict the amount of corrosion of a buried pipeline without investigating the actual buried environment of the buried portion of the pipeline. To do.

In order to achieve this object, the buried pipe corrosion prediction method of the present invention comprises:
Measure the corrosion depth of the cast iron pipe outer surface and the environmental factors of the buried site for multiple buried parts where the cast iron pipe is buried,
Applying the measurement results to known ground information, create a calculation formula for the corrosivity evaluation coefficient of the buried environment where the ground information is known,
Create a corrosion depth prediction formula that can calculate the corrosion depth of the outer surface of the cast iron pipe buried at the location from the calculation formula of this corrosive evaluation coefficient and the cast iron pipe burial period,
Predicting the corrosion depth of the outer surface of the cast iron pipe embedded at the location from the known ground information about the target location and the information on the burial period of the cast iron pipe at that location, using the corrosion depth prediction formula It is.

  Therefore, according to the present invention, a calculation formula for the corrosivity evaluation coefficient of the buried environment in a place where the ground information is known is prepared, and the corrosion depth using the calculation formula of the corrosivity evaluation coefficient and the burial period of the cast iron pipe is used. By creating a prediction formula, without investigating the burial environment such as the soil where the cast iron pipe is buried, just obtaining the ground information of that place, if the burial period of the cast iron pipe is known, The corrosion depth can be predicted quantitatively.

According to the buried pipe corrosion prediction method of the present invention, the corrosion depth prediction formula is preferably the following formula.
η = k × t ^0.4
Where η is the corrosion depth (mm) of the cast iron pipe, k is the corrosive evaluation coefficient of the embedded environment, and t is the years of embedment (years).

  According to the buried pipe corrosion prediction method of the present invention, it is preferable that the calculation formula for the corrosiveness evaluation coefficient of the buried environment is a combination of the topographic classification, surface geological classification, and soil classification as ground information. In addition, it is preferable to consider whether the location is close to the coastline as ground information.

Further, according to the buried pipe corrosion prediction method of the present invention, it is preferable that the calculation formula of the corrosive evaluation coefficient k of the buried environment is the following formula.
_{k = exp (-0.909 + 0.000σ 11} + 0.049σ 12 + 0.000σ 21 + 0.031σ 22 + 0.265σ 23 + 0.000σ 31 + 0.119σ 32 + 0.274σ 33 + 0.362σ 34 + 0.403σ 35 + 0.613σ ₃₆ + 0.000σ ₄₁ + 0.126σ ₄₂ + 0.268σ ₄₃ )
However,
σ ₁₁ = 1 [when the place is inland] or 0 [others]
σ ₁₂ = 1 [when the location is a coastal area] or 0 [other cases]
σ ₂₁ = 1 [if the topography is a plateau / terrace] or 0 [others]
σ ₂₂ = 1 [when topography is mountainous, lowland, etc.] or 0 [other cases]
σ ₂₃ = 1 [if the terrain is a hilly or modified land] or 0 [others]
σ ₃₁ = 1 [when surface geology is metamorphic rock and plutonic rock] or 0 [other cases]
σ ₃₂ = 1 [surface geology is sedimentary rock 1 (unconsolidated sand, gravel, silt, etc.) or sedimentary rock 5 (consolidated biological rock / chart, quartzite, limestone, etc.) or sedimentary rock 6 (alternate layers of sedimentary rock) ] Or 0 [In other cases]
σ ₃₃ = 1 [surface geology is volcanic rock 1 (sediment such as volcanic ash and pyroclastic flow, shirasu, etc.) or volcanic rock 2 (volcanic ash or loam) or volcanic rock 3 (whiteish volcanic rocks, rhyolites, tuffs, etc.) or volcanic rock 4 (If it is dark volcanic rocks, basalts, etc.)] or 0 [other cases]
σ ₃₄ = 1 [surface geology is sedimentary rock 2 (such as unconsolidated clay) or sedimentary rock 3 (such as consolidated sandstone, conglomerate)] or 0 [other cases]
σ ₃₅ = 1 [when surface geology is not displayed] or 0 [other cases]
σ ₃₆ = 1 [when the surface geology is sedimentary rock 4 (consolidated mudstone, shale, etc.)] or 0 [other cases]
σ ₄₁ = 1 [when the soil is immature soil, red / red-yellow soil, urban area, dry area] or 0 [other cases]
σ ₄₂ = 1 [when the soil is black soil, brown forest soil, podzol soil, glai soil, wetland, etc.] or 0 [other cases]
σ ₄₃ = 1 [when the soil is tan brown forest soil, lowland soil, peat soil, peat zone] or 0 [other cases]
It is.

  Further, according to the method for predicting corrosion of buried pipes according to the present invention, data obtained by dividing an arbitrary region into a mesh shape is created, and information on the corrosiveness evaluation coefficient of the buried environment for each mesh area is created in each mesh data. It is preferable to have

Other buried pipe corrosion prediction methods of the present invention,
Measure the corrosion depth of the cast iron pipe outer surface and the environmental factors of the buried site for multiple buried parts where the cast iron pipe is buried,
Applying the measurement results to known ground information, create a calculation formula for the corrosivity evaluation coefficient of the buried environment where the ground information is known,
Data is created by dividing an arbitrary area into a mesh shape, and the data of each mesh is given information on the corrosiveness evaluation coefficient of the embedded environment calculated by the above formula for the area in the mesh. .

  If it does in this way, the evaluation map which evaluated quantitatively the corrosivity of the embedding environment of a cast iron pipe can be created.

  As described above, according to the present invention, even if the buried environment such as the soil where the cast iron pipe is buried is not investigated, it is only necessary to obtain the ground information of the place if the buried period of the cast iron pipe is known. The corrosion depth can be predicted quantitatively.

In the present invention, first, a prediction formula for the corrosion depth is created. This is performed by the same method as described in Patent Document 2 described above.
That is, for example, excavation surveys of buried pipes are conducted in various regions throughout Japan, and the corrosion depth of the cast iron pipe surface is measured and the soil around the pipes as the buried environment is analyzed. The larger the number of surveys, the better. For example, it is possible to obtain data by conducting surveys at thousands of locations across Japan. Table 1 shows the outline. In Table 1, what is referred to as “investigation data” corresponds to the data, which is divided into tube information and buried environment information. Typical attributes of tube information include corrosion depth and burial period. The attribute of the buried environment information includes an analysis value of soil, and specifically includes the specific resistance shown in Table 1 and many other items.

  Next, the existing ground information of Japan is used. As this ground information, for example, national land numerical information issued by the Geographical Survey Institute of the Ministry of Land, Infrastructure, Transport and Tourism can be used. This includes information on topography, surface geology, soil, etc. in a standard 1 km mesh. Then, the ground information is integrated and organized into several types as shown in Table 1 based on attribute names and the like.

  That is, in Table 1, what is referred to as “ground information 1” corresponds to the topographic, surface geology, and soil information of the national land numerical information issued by the Geographical Survey Institute. However, in the national land numerical information published by the Geospatial Information Authority of Japan, there are 50 types of topographic information, 85 types of surface geological information, and 60 types of soil information. In Table 1, for simplicity, from the name of the attribute, For example, 6 types of topographic information, 13 types of surface geological information, and 14 types of soil information are used. Details thereof will be described later. The attributes of the topographic information include mountains, hills, and plateaus. Attributes of surface geological information include sedimentary rocks and volcanic rocks. Examples of soil classification include gly soil, urban areas, and the like.

次に、上記した数千箇所の調査位置について、それぞれの位置に該当する国土数値情報の標準１ｋｍメッシュを割り出し、そのメッシュにおける地形、表層地質、土壌の属性を調べる。

Next, for the above-described thousands of survey positions, a standard 1 km mesh of national land numerical information corresponding to each position is determined, and the topography, surface geology, and soil attributes in the mesh are examined.

  In addition, since the corrosion of cast iron pipes is generally fast at locations close to the sea, as shown in Table 1 as “Ground information 2”, the attributes of the coastal area are set for the standard 1 km mesh including the range of 1 km from the coastline. In addition, the inland attribute is given to other meshes.

And using the prediction model described in the above-mentioned patent documents 1 and 2 etc., the multiple regression analysis is performed from the survey data of Table 1 and the ground information 1 and 2, and a corrosion depth prediction formula is created.
The following shows an example of a corrosion depth prediction formula that is specifically created.

η = k × t ^0.4
Where η is the corrosion depth (mm) of the cast iron pipe, k is the corrosive evaluation coefficient of the embedded environment, and t is the years of embedment (years).

According to the result of the multiple regression analysis described above, the corrosiveness evaluation coefficient k of the embedded environment can be obtained by the following equation.
_{k = exp (-0.909 + 0.000σ 11} + 0.049σ 12 + 0.000σ 21 + 0.031σ 22 + 0.265σ 23 + 0.000σ 31 + 0.119σ 32 + 0.274σ 33 + 0.362σ 34 + 0.403σ 35 + 0.613σ ₃₆ + 0.000σ ₄₁ + 0.126σ ₄₂ + 0.268σ ₄₃ )
However,
σ ₁₁ = 1 [when the place is inland] or 0 [others]
σ ₁₂ = 1 [when the location is a coastal area] or 0 [other cases]
σ ₂₁ = 1 [if the topography is a plateau / terrace] or 0 [others]
σ ₂₂ = 1 [when topography is mountainous, lowland, etc.] or 0 [other cases]
σ ₂₃ = 1 [if the terrain is a hilly or modified land] or 0 [others]
σ ₃₁ = 1 [when surface geology is metamorphic rock and plutonic rock] or 0 [other cases]
σ ₃₂ = 1 [surface geology is sedimentary rock 1 (unconsolidated sand, gravel, silt, etc.) or sedimentary rock 5 (consolidated biological rock / chart, quartzite, limestone, etc.) or sedimentary rock 6 (alternate layers of sedimentary rock) ] Or 0 [In other cases]
σ ₃₃ = 1 [surface geology is volcanic rock 1 (sediment such as volcanic ash and pyroclastic flow, shirasu, etc.) or volcanic rock 2 (volcanic ash or loam) or volcanic rock 3 (whiteish volcanic rocks, rhyolites, tuffs, etc.) or volcanic rock 4 (If it is dark volcanic rocks, basalts, etc.)] or 0 [other cases]
σ ₃₄ = 1 [surface geology is sedimentary rock 2 (such as unconsolidated clay) or sedimentary rock 3 (such as consolidated sandstone, conglomerate)] or 0 [other cases]
σ ₃₅ = 1 [when surface geology is not displayed] or 0 [other cases]
σ ₃₆ = 1 [when the surface geology is sedimentary rock 4 (consolidated mudstone, shale, etc.)] or 0 [other cases]
σ ₄₁ = 1 [when the soil is immature soil, red / red-yellow soil, urban area, dry area] or 0 [other cases]
σ ₄₂ = 1 [when the soil is black soil, brown forest soil, podzol soil, glai soil, wetland, etc.] or 0 [other cases]
σ ₄₃ = 1 [when the soil is tan brown forest soil, lowland soil, peat soil, peat zone] or 0 [other cases]
It is.

  Using the above prediction formula, without investigating the buried environment such as the soil where the cast iron pipe is buried, just obtaining the ground information of that place, if you know the buried period of the cast iron pipe, The corrosion depth can be predicted quantitatively.

  Specifically, using the national land numerical information issued by the Geographical Survey Institute of the Ministry of Land, Infrastructure, Transport and Tourism as described above, it is known about the mesh only by examining which part of the standard 1 km mesh the buried location corresponds to Based on the ground information, the corrosion depth can be predicted with reference to the burial period of the cast iron pipe.

  Using the prediction formula created as described above and the ground information published as described above (standard 1 km mesh), the corrosivity of the cast iron pipe burial environment throughout the country is quantitatively evaluated. Created a map. An example of the evaluation map is shown in FIG. In FIG. 1, thick lines represent administrative divisions such as municipalities, and vertical and horizontal lines form a mesh. The value of the corrosiveness evaluation coefficient k of the embedded environment is calculated for each mesh, and in FIG. 1, the color density of the mesh is changed according to the value of the corrosiveness evaluation coefficient k. In FIG. 1, the darker the mesh color, the stronger the corrosiveness.

  Thus, since the value of k is set for every mesh, if the years of burying the pipeline at the location of the mesh are known, the corrosion depth can be predicted by the above equation.

  FIG. 2 shows an evaluation map created for Hyogo Prefecture. This evaluation map is originally a k value displayed in a chromatic color, but here it is displayed in an achromatic color for patent application. For this reason, both the weakly corrosive part and the strong part are displayed darkly, while the corrosive strength is displayed lightly in the middle part.

  Next, the accuracy of the corrosion prediction method of the present invention was verified. First, the survey points were selected with reference to the above evaluation map. That is, as shown in FIG. 3, the meshes having the same corrosive strength are gathered and divided into five regions A to E, and the survey points are set to three points in each region. Based on this, 15 sites with different years of burial were investigated, and the relationship between the measured value and the predicted value of the corrosion depth was as shown in FIG. 4, and the correlation between the two was high.

  For this reason, it turned out that the corrosion prediction method of the present invention has high accuracy. Further, according to the corrosion prediction method of the present invention, it was possible to confirm the corrosiveness of the target area from the strong corrosive area to the weak area with the minimum number of survey points.

  In addition, although the evaluation map shown in FIG.1 and FIG.2 represents the magnitude of the value of the corrosivity evaluation coefficient k of the embedded environment for every mesh as mentioned above, such an evaluation map was mentioned above. It can also be utilized when implementing the methods described in Patent Document 1 and Patent Document 2. In other words, when implementing these methods, it is necessary to obtain information about the buried environment as described above. However, if an evaluation map such as the one shown in the figure is used, the number of survey points when obtaining information about the buried environment is obtained. Can be efficiently reduced, and a reliable basis for selecting survey points can be provided.

It is a figure which shows an example of the evaluation map about the corrosivity of the embedding environment of a cast iron pipe based on this invention. It is a figure which shows the example of the evaluation map about Hyogo Prefecture. It is a figure which shows the example of a division | segmentation of the diagnosis object area for selection of the corrosion depth of a cast iron pipe based on this invention. It is a graph which shows the relationship between the predicted value of the corrosion depth of the cast iron pipe based on this invention, and its measured value.

Claims (7)

Measure the corrosion depth of the cast iron pipe outer surface and the environmental factors of the buried site for multiple buried parts where the cast iron pipe is buried,
Applying the measurement results to known ground information, create a calculation formula for the corrosivity evaluation coefficient of the buried environment where the ground information is known,
Create a corrosion depth prediction formula that can calculate the corrosion depth of the outer surface of the cast iron pipe buried at the location from the calculation formula of this corrosive evaluation coefficient and the cast iron pipe burial period,
Predict the corrosion depth of the outer surface of the cast iron pipe buried at the location from the known ground information about the target location and the information of the burial period of the cast iron pipe at the location using the corrosion depth prediction formula A method for predicting corrosion of buried pipes. The corrosion prediction method for buried pipes according to claim 1, wherein the corrosion depth prediction formula is the following formula.
η = k × ^{t 0.4}
Where η is the corrosion depth (mm) of the cast iron pipe, k is the corrosive evaluation coefficient of the embedded environment, and t is the years of embedment (years).   The method for predicting the corrosion of buried pipes according to claim 1 or 2, wherein the calculation formula for the corrosiveness evaluation coefficient of the buried environment is a combination of topographic classification, surface geological classification and soil classification as ground information. .   4. The buried pipe corrosion prediction method according to claim 3, wherein the calculation formula of the corrosiveness evaluation coefficient of the buried environment takes into account whether or not the place is near the coastline as ground information. 5. The method for predicting corrosion of a buried pipe according to claim 4, wherein the formula for calculating the corrosivity evaluation coefficient k of the buried environment is the following formula.
_{k = exp (-0.909 + 0.000σ 11} + 0.049σ 12 + 0.000σ 21 + 0.031σ 22 + 0.265σ 23 + 0.000σ 31 + 0.119σ 32 + 0.274σ 33 + 0.362σ 34 + 0.403σ 35 + 0.613σ ₃₆ + 0.000σ ₄₁ + 0.126σ ₄₂ + 0.268σ ₄₃ )
However,
σ ₁₁ = 1 [when the place is inland] or 0 [others]
σ ₁₂ = 1 [when the location is a coastal area] or 0 [other cases]
σ ₂₁ = 1 [if the topography is a plateau / terrace] or 0 [others]
σ ₂₂ = 1 [when topography is mountainous, lowland, etc.] or 0 [other cases]
σ ₂₃ = 1 [if the terrain is a hilly or modified land] or 0 [others]
σ ₃₁ = 1 [when surface geology is metamorphic rock and plutonic rock] or 0 [other cases]
σ ₃₂ = 1 [surface geology is sedimentary rock 1 (unconsolidated sand, gravel, silt, etc.) or sedimentary rock 5 (consolidated biological rock / chart, quartzite, limestone, etc.) or sedimentary rock 6 (alternate layers of sedimentary rock) ] Or 0 [In other cases]
σ ₃₃ = 1 [surface geology is volcanic rock 1 (sediment such as volcanic ash and pyroclastic flow, shirasu, etc.) or volcanic rock 2 (volcanic ash or loam) or volcanic rock 3 (whiteish volcanic rocks, rhyolites, tuffs, etc.) or volcanic rock 4 (If it is dark volcanic rocks, basalts, etc.)] or 0 [other cases]
σ ₃₄ = 1 [surface geology is sedimentary rock 2 (such as unconsolidated clay) or sedimentary rock 3 (such as consolidated sandstone, conglomerate)] or 0 [other cases]
σ ₃₅ = 1 [when surface geology is not displayed] or 0 [other cases]
σ ₃₆ = 1 [when the surface geology is sedimentary rock 4 (consolidated mudstone, shale, etc.)] or 0 [other cases]
σ ₄₁ = 1 [when the soil is immature soil, red / red-yellow soil, urban area, dry area] or 0 [other cases]
σ ₄₂ = 1 [when the soil is black soil, brown forest soil, podzol soil, glai soil, wetland, etc.] or 0 [other cases]
σ ₄₃ = 1 [when the soil is tan brown forest soil, lowland soil, peat soil, peat zone] or 0 [other cases]
It is.   6. The data according to any one of claims 1 to 5, wherein data obtained by dividing an arbitrary region into a mesh shape is created, and the data of each mesh is provided with information on a corrosiveness evaluation coefficient of a buried environment for an area in the mesh. The method for predicting corrosion of buried pipes according to any one of the above. Measure the corrosion depth of the cast iron pipe outer surface and the environmental factors of the buried site for multiple buried parts where the cast iron pipe is buried,
Applying the measurement results to known ground information, create a calculation formula for the corrosivity evaluation coefficient of the buried environment where the ground information is known,
Create data by dividing an arbitrary area into a mesh shape, and make each mesh data have information on the corrosiveness evaluation coefficient of the embedded environment calculated by the above formula for the area in the mesh. Corrosion prediction method for buried pipes.

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