JP5616757B2 - How to determine the renewal order of buried metal water pipes - Google Patents

Description

  The present invention relates to a method for determining the renewal rank of a metal water pipe such as steel embedded in soil, and particularly relates to a method for determining a renewal rank by estimating the service life of a metal water pipe. Is.

  In recent years, with the background that countermeasures against water leakage accidents due to corrosion of metal water pipes have become a major social issue, the lifetime of metal water pipes buried in soil should be determined with a more objective index. Is important.

  However, it is not always easy to evaluate the corrosion of buried metal water pipes, and it is actually difficult to evaluate more simply and more appropriately by various methods proposed so far. For example, in the method for evaluating the corrosion state by measuring the ground resistance of an embedded steel pipe (see Patent Documents 1 and 2), a very large burden is imposed, and the measurement accuracy is not always satisfactory.

  In addition, it has been proposed to perform corrosion diagnosis of steel underground objects by paying attention to the buried soil environment (see Patent Document 3), but the corrosion of the soil environment and buried metal water pipes The relationship is not always clear. This is the same in the evaluation based on ANSI (American Standards Association Standard) about soil corrosiveness generally performed as corrosion evaluation of buried metal water pipes.

  This is because the corrosion phenomenon is not simply determined by the nature of the geology, but depends on various factors such as the history of the corrosive environment, moisture distribution, and the installation structure of the pipeline. Moreover, the soil survey has a problem that a great amount of cost and labor are required because the state of the soil is actually investigated by excavation. In the conventional method, the evaluation of the heterogeneity of the soil environment, which has a significant influence on the corrosion rate, cannot be made, and the validity is lacking.

  From the above situation, the present inventors have conducted extensive research, and as a result, corrosion of metal structures such as steel embedded in the soil can be more easily performed with less expense and labor, and A new evaluation method capable of evaluating non-uniformity has been completed (see Patent Document 4).

  According to this technical means, a metal test specimen is embedded from the surface of the soil in the vicinity of the embedded position of the metal structure in the soil, and is extracted after a predetermined period of time to measure the corrosion rate of the metal test specimen. It evaluates or predicts the corrosion of metal structures.

  This method is excellent in that it can grasp the properties of the soil from the corrosion rate of the metal specimen and can be easily mapped, but the corrosion rate of the metal specimen and the metal structure embedded in the vicinity of this metal specimen. Since the relationship with the corrosion rate of the body is indirect through the soil, it is not possible to estimate the exact life of the metal structure from the corrosion rate of the metal specimen alone. Has not been fully utilized.

Japanese Patent Laid-Open No. 2003-232764 JP 2006-275623 A JP 2003-262580 A JP 2008-298688 A

  The present invention has been made in view of the circumstances as described above, and by a simpler method, with a low cost and labor burden, an accurate metal water pipe service life can be determined only from the corrosion rate of a metal inspection member. It is an object of the present invention to provide a method for determining an update order.

  The present invention is characterized by the following in order to solve the above problems.

1stly, it is the method of determining the renewal | ranking order of a buried metal water pipe by estimating the lifetime of the metal water pipe buried in the soil, Comprising: The burial position of the metal water pipe in the soil beforehand embedding a metallic test elements from the soil surface portion in the vicinity, pull out after a predetermined period of time, measures the amount of weight loss before and after embedding of the metal test element, corrosion from weight loss and embedded period of the metallic test element Calculate the speed, measure the corrosion depth of the metal water pipe embedded in the vicinity of the metal inspection member, calculate the corrosion speed of the metal water pipe from the corrosion depth of the metal water pipe and the burial period , The maximum value of the corrosion rate of the metal water pipe corresponding to the corrosion rate of the metal inspection member is determined from the correspondence between the corrosion rate of the metal inspection member and the corrosion rate of the metal water pipe of the inspection target part. the thickness of the water pipe of the corrosion rate of a metal water pipe Determining the minimum service life of metallic water pipe, which is estimated from the rate of corrosion of the metal test member by dividing a large value, for the thickness of the metal water pipes, and corrosion rate of the metal test element, metal After obtaining the relationship between the service life of the water pipes, embed a metal inspection member from the surface of the soil in the vicinity of the metal water pipe burying position in the soil and pull it out after a predetermined period of time. calculating a corrosion rate of a metal test elements from embedding period and amount of weight loss before and after embedding of the test elements, for the thickness of the metal water pipes the calculation result of the corrosion rate obtained by the said metallic test element, metal and corrosion of the casting test element, by applying the relationship of life of the metal water pipes, I guess life of metallic water pipes in the soil.

Second, in the method for determining the renewal order of buried metal water pipes according to the first invention, a plurality of metal inspection members are embedded, the corrosion rates of the metal inspection members are calculated, and the corrosion rates of these corrosion rates are calculated . The average value is defined as the corrosion rate of the metal inspection member.

Third, in the method for determining the renewal order of buried metal water pipes according to the first or second invention, the corrosion rates at a plurality of locations of the metal water pipes are calculated, and the maximum value of these corrosion rates is made of metal. Corrosion rate of water pipe.

4thly, in the determination method of the update order of the buried metal water pipe of the said 1st to 3rd invention, the metal test | inspection member is a round bar shape, The front-end | tip part is removable and removed. The amount of weight loss before and after embedding the tip is measured to calculate the corrosion rate of the metal inspection member.

Fifth, in the method for determining the renewal order of buried metal water pipes according to the first to fourth inventions, when the calculation result of the corrosion rate of the metal inspection member is less than the criterion value, the metal water pipe Apply the relationship between the corrosion rate of the metal inspection member and the service life of the metal water pipe in the soil to the wall thickness of the metal, and if it exceeds the criterion value, measure the corrosion state of the metal water pipe in the soil .

  Sixth, in the method for determining the renewal rank of the buried metal water pipe of the fifth invention, the determination reference value is 0.02 mm / year.

  According to the present invention as described above, a correspondence relationship between the corrosion rate of the metal inspection member and the corrosion rate of the metal water pipe at the site to be inspected is obtained in advance, and the corrosion rate of the metal inspection member is determined from the correspondence relationship. Obtain the relationship between the service life of the metal water pipe in the soil, and from the corrosion rate of the metal test member, the corrosion rate of the metal test member obtained above and the life of the metal water pipe in the soil Based on the relationship, the service life of the metal water pipes in the soil is estimated, so the order of renewal of the metal water pipes in the soil is determined easily, in a short time and accurately, without incurring costs and labor. It becomes possible to do.

It is a flowchart until it derives | leads-out the relationship of the lifetime of a water pipe from the corrosion rate of an inspection member and a water pipe. It is a perspective schematic diagram illustrated about division of an inspection member. It is an explanatory outline figure of inspection member embedding. It is the plane schematic diagram shown about embedding of the inspection member. It is the schematic shown about embedding of the inspection member. It is the cross-sectional schematic which showed the measurement site | part of the corrosion depth of a water pipe. It is the schematic which showed the measuring apparatus of the corrosion depth of a water pipe. It is the graph which showed the relationship between the corrosion rate of an inspection member, and the corrosion rate of a water pipe. It is the graph which showed the relationship between the corrosion rate of an inspection member, and the corrosion rate of a water pipe. It is the graph which showed the relationship between the corrosion rate of a test | inspection member, and the useful life according to the thickness of a water pipe. It is a flowchart from the corrosion rate measurement of a test | inspection member to the determination of the update order of a water pipe. It is the graph which showed the relationship between the ANSI evaluation score and the corrosion rate of a water pipe.

  The present invention has the features as described above, and an embodiment thereof will be described below.

  In the method of the present invention, first, the corrosion rate of a metal inspection member (hereinafter simply referred to as an inspection member) and the corrosion rate of a metal water pipe (hereinafter simply referred to as a water tube) in the soil at the site to be inspected. The relationship between the corrosion rate of the inspection member and the service life of the water pipe is obtained from the relationship.

Specifically, as shown in the flowchart of FIG. 1, the corrosion rate of the inspection member and the corrosion rate of the water pipe are calculated. Hereinafter, it demonstrates along a flowchart.
<Preparation of inspection member>
The material of the inspection member used in the method of the present invention is preferably steel or cast iron that is often used as a water pipe, and any of those that can be appropriately obtained can be used.

  Both the steel and cast iron are generic names of alloys containing iron as a main component. In the metallurgy, the former is Fe-C binary alloy with a C content of 0.0214 to 2.14 mass%, and the latter is This refers to an Fe-C binary alloy having a C content of 2.14 to 6.67 mass%, which is also used in this specification as its definition.

  Moreover, when it describes with steel etc., it is mainly used as the meaning of steel or cast iron. However, it goes without saying that even if the inspection member and the water pipe are both classified as steel or cast iron, those having completely different degrees of corrosion are not preferable.

  The shape of the inspection member is not particularly limited, but from the viewpoint of insertion and extraction workability, ease of measurement and observation of corrosion, accuracy, etc., for example, a round bar type, a cylindrical type, a conical tip type, etc. A pulling ring, a wire, a rope, or the like may be attached, or the shape or structure of these divided / connected types may be used, and these are preferably used in accordance with the purpose. In the present invention, a split type inspection member 3 having a round bar shape as shown in FIG. 2 and capable of dividing only the tip portion 32 can be suitably used for ease of weight measurement. Alternatively, the material of only the distal end portion 32 may be steel or the like, and the long portion 31 may be connected to a material such as resin or ceramics.

  In the case of using the inspection member 3 that can divide the tip 32, the length of the tip 32 that can be divided is L (the length excluding the extraction ring 30 portion α). Is preferably about L × 0.1.

  It is desirable that the inspection member as described above should be sufficiently taken care of so as not to cause dirt and rust before the embedment test. Therefore, as a pretreatment, surface polishing with abrasive paper or the like and sufficient degreasing treatment with ethanol or the like are effective.

  After performing such pretreatment, the weight of the inspection member before embedding is accurately measured in order to obtain the weight reduction amount after collection of the inspection member. In the case of a split type inspection member, the weight of the split tip is measured in advance.

Between the pretreatment and embedding, it is preferable to store in a dehumidified container with silica gel or the like enclosed so that rust does not occur on the surface of the inspection member.
<Embedded inspection member>
As shown in FIG. 3, the position where the inspection member is embedded in the soil is in the vicinity of the embedded position of the water pipe 2. In this case, the “near” is the depth of the inserted inspection member 3. The depth H of the tip 3A from the soil surface 10 is related to the depth position of the water pipe 2, that is, the depth from the soil surface 10 of the water pipe to the position H ₁ at the lower end, and the upper end from the soil surface 10 of the water pipe. the relationship between the depth of up to the position H _2,
0.8H ₂ ≦ H ≦ 1.2H ₁
As a guide. More preferably, 0.8H ₂ ≦ H ≦ H ₁ .

In addition, as the insertion length H ₀ of the inspection member 3, in relation to the embedded length D ₁ of the water pipe 2 (the length in the depth direction, for example, the outer diameter in the case of metal piping),
0.1D ₁ ≦ H ₀
Is considered.

That is, the insertion length H ₀ of the inspection member 3 may be the entire length from the soil surface 10 to the tip 3A, or, as illustrated in FIG. 2, a ring, a wire, a rope, or the like connected. It may be a part of the entire length of the insert connected to resin or ceramics.

  In addition, the above “neighborhood” means that in the horizontal position of the inserted inspection member 3 with respect to the water pipe 2, in the soil 1, in the backfill soil (reference number omitted) in which the water pipe is backfilled when buried. It is assumed that there is. This is because it is difficult to evaluate the progress of corrosion because the soil quality is different if the soil is outside the backfill soil where the water pipe is buried.

And the inspection member 3 does not contact the water pipe 2, and the mutual distance M is in relation to the width D ₂ of the water pipe ₂ (the length in the horizontal direction, for example, the outer diameter if it is a metal pipe).
0 <M ≦ 0.2D ₂
It is preferably considered to be within the range.

  Regarding the number of test members to be embedded, as described later, the corrosion rate is obtained from the weight reduction amount of the test member, so that only one test member may be embedded. However, collecting as much data as possible from one place, Since it is desired to obtain the average value of these, it is preferable to bury a plurality of them simultaneously.

When embedding a plurality of inspection members, as illustrated in FIG. 4 as the embedding plane position of the water pipe 2, a single row, a plurality of lines are provided on both sides (A) or one side (B) of the water pipe 2 in the pipe length direction. They may be arranged in rows or staggered. Although the distance W of the arrangement of the pipe length direction can be appropriately determined in consideration of the characteristics of the soil 1, 5 times the width D ₂ of the water pipe 2 is a view to measure the average value of corrosion rate: 5D It may be considered to be ₂ or less. In addition, the interval between the inspection members 3 is approximately 0.1D ₂ or more.

In addition, after inserting the inspection member, as illustrated in FIG. 3, measures such as providing an appropriate lid 12 at the upper end of the inspection member 3 in order to prevent water from entering from the soil surface 10. Is desired.
<Test>
The length of the predetermined period of the test from embedment to withdrawal of the inspection member can be determined as appropriate in consideration of the environment of the test site, road traffic, life constraints, etc. From a viewpoint, it is preferable to set it as six months or more, Preferably it is one year or more, According to the objective, it can also use properly for a long term (several years or more) or a short term (semi-year-1 year).
<Recovery / weight measurement of inspection members>
After the test period has elapsed, the inspection member is pulled out and collected.

  Regarding the collection of the inspection members, when there are a plurality of embedded inspection members, these may be collected all at once, but may be collected one by one or several at a time. According to the method in which the interval of the collection period (test period) is appropriately set and the test member is collected in several times, the corrosion state by the soil at the buried place can be grasped in a time series, which is more preferable.

The collected inspection member is subjected to accurate weight measurement using a precision balance or the like after sufficiently removing deposits such as rust.
<Calculation of corrosion rate of inspection member>
As for the corrosion rate of the inspection member, the corrosion rate is calculated from the weight change before and after embedding of the collected inspection member or the tip of the separable inspection member.

  Specifically, the corrosion rate can be calculated from the weight loss before and after the burying test measured by a precision balance and the burying period and the following equation.

  When one inspection member is collected, the corrosion rate calculated for one of them is regarded as the corrosion rate. When a plurality of inspection members are collected, each corrosion rate is calculated, and the average of these results is calculated. The value is the corrosion rate.

Next, the calculation of the corrosion rate of the water pipe embedded in the vicinity of the inspection member will be further described with reference to the flowchart shown in FIG.
<Excavation and exposure of buried water pipe>
The excavation and exposure of the buried water pipe are not particularly limited as long as the excavation time and excavation form are limited as long as the corrosion investigation can be performed by exposing the water pipe buried in the vicinity of the buried position of the inspection member. It is more preferable to perform excavation at a two-stage depth of the water pipe survey section 13 and the inspection member embedding section 14 as shown in FIG. 6 because the inspection member embedding and the water pipe corrosion investigation can be performed simultaneously.
<Water pipe corrosion investigation>
To investigate the corrosion of water pipes, first, use a wire brush, an electric brush, a grinder with a cup brush, a test hammer, etc. for the exposed water pipes to remove surface soil, rust, and water pipe deposits that are a mixture of these. Remove.

  As shown in FIG. 6, the measurement location of the corrosion depth of the corroded portion of the water pipe is as follows. It is preferable to divide into four investigation ranges under the pipe 6-D and measure the corrosion depth of each investigation range.

  Moreover, in the said investigation range, in order to acquire more exact data, it is preferable to measure corrosion depth in as many places as possible.

  Corrosion depth is measured by first judging the state of corrosion visually, and measuring the depth of corrosion at a place where corrosion is observed, using a depth gauge as shown in FIG. 7, an ultrasonic thickness gauge, or the like.

In the measurement of the corrosion depth, a depth gauge 70 as shown in FIG. 7A is used in a place where concentrated corrosion occurs, and in a place where full thickness reduction occurs, FIG. It is preferable to measure accurately by appropriately selecting a measuring method according to the corrosion status of the water pipe, such as using an ultrasonic thickness meter 71 as shown in FIG.
<Calculation of water pipe corrosion rate>
In calculating the corrosion rate of water pipes, data on the maximum corrosion depth among the results obtained in the above corrosion investigation shall be adopted. This is to obtain the safest estimate of water pipe corrosion by determining the corrosion rate based on the most corroded part of the water pipe and determining the shortest service life of the water pipe. is there.

  The corrosion rate of a water pipe can be calculated by dividing the above maximum corrosion depth by the number of years of burial.

The corrosion rate of the inspection member and the corrosion rate of the water pipe calculated by the above steps are preferably collected at as many points as possible to accumulate the data. By using a large number of collected data, it is possible to estimate the service life of a water pipe with higher accuracy in the end.
<Analysis of relationship between corrosion rate of inspection member and corrosion rate of water pipe>
Next, these relationships are analyzed from the data of the corrosion rate of the inspection member and the corrosion rate of the water pipe collected by the above process.

  As a method of analyzing the relationship between the corrosion rate of inspection members and the corrosion rate of water pipes, the vertical axis is the corrosion rate of water pipes (mm / year), and the horizontal axis is the corrosion rate of inspection members (mm / year). Above, we plot a lot of collected data. A graph plotting the data is shown in FIG.

  As can be seen from the graph of FIG. 8, each plotted point tends to converge to the origin 0 and spread from the origin 0 point into a fan shape.

  If a straight line is drawn so as to sandwich the fan-shaped plot between the upper side and the lower side, it can be drawn as shown by a broken line in FIG. Here, this broken line may be assumed that when the corrosion rate of the test member is 0 in principle, the soil environment may not be corrosive at all, and therefore water pipe corrosion will not occur. And the intercept can be zero.

  In this way, both the upper and lower broken lines pass through the origin 0 and show a tendency of rising to the right. The upper broken line is the maximum value estimated from the corrosion rate of the inspection member, and the lower broken line is the inspection. This is considered to correspond to the minimum value estimated from the corrosion rate of the member.

  Next, in order to make it easy to see the slope of the upper broken line in the graph of FIG. 8, the corrosion rate of the test member on the horizontal axis is re-plotted on the coordinates expanded from 0 to a specific corrosion rate range. The expansion of the horizontal axis is not particularly limited as long as the slope of the upper broken line is clearly expressed. In the re-plotted graph shown in FIG. 9, the corrosion rate of the inspection member is increased up to 0.020 mm / year. It is.

From this graph, the correlation between the corrosion rate of the inspection member and the corrosion rate of the water pipe can be read more clearly. In this range, if a straight line is drawn so that each plotted point is buried below, a straight line passing through the origin 0 with an inclination of 12.5 can be applied as shown in the graph. That is, it can be read from this graph that the corrosion rate of the water pipe reaches a maximum of about 12.5 times the corrosion rate of the inspection member.
<Creating the relationship between the corrosion rate of the inspection member and the service life of the water pipe>
Next, the relationship between the corrosion rate of the inspection member and the service life of the water pipe is derived from the relationship between the corrosion rate of the inspection member and the corrosion rate of the water pipe derived from the graphs of FIGS.

  Specifically, it can be obtained by substituting into the following formula. That is, the theoretical corrosion rate of the water pipe is obtained by multiplying the corrosion rate (mm / year) of the inspection member by the slope of the straight line of 12.5 in FIG. 9, and the wall thickness (mm) of the water pipe is calculated as the theoretical water supply. By dividing by the corrosion rate of the pipe, the service life (year) of the water pipe can be obtained.

  As shown in the graph of FIG. 10, the data for each wall thickness of the water pipe is plotted on the coordinate with the vertical axis representing the life of the water pipe (year) and the horizontal axis representing the corrosion rate (mm / year) of the inspection member The thickness curve can be derived by plotting.

  In the case of the graph of FIG. 10, curves of wall thicknesses of 10 mm, 8 mm, and 6 mm are derived, but by substituting the values of the water pipe wall thickness and the corrosion rate of the inspection member into the above formula, It is possible to derive a wall thickness curve.

  By using this graph, the service life of the water pipe can be easily estimated from the measured corrosion rate of the inspection member and the numerical value of the thickness of the water pipe buried in the vicinity thereof.

  For example, from this graph, when the corrosion rate of the inspection member is 0.015 mm / year, the estimated service life of the water pipe is about 50 years with a thickness of 10 mm, about 40 years with a thickness of 8 mm, It turns out that it is about 30 years at 6 mm.

  In the present invention, by previously deriving the relationship between the corrosion rate of the inspection member and the service life of the water pipe in advance, only the corrosion rate of the inspection member is calculated from the actual measurement value and is embedded in the vicinity thereof. It is possible to estimate the useful life of a water pipe without drilling or exposing it.

The estimation and determination of the service life of the water pipe will be described below with reference to the flowchart shown in FIG.
<Setting of inspection route range>
The method of estimating the service life of a water pipe using the method of the present invention can be used without any particular limitation on the location and range, but in a normal inspection, the route to be inspected is set based on information such as the age of burial. It is preferable to perform a quantitative inspection within the range of the lever.

Since the water pipe is a supply pipe over a continuous long distance, it is effective to conduct a systematic inspection in the route range rather than performing random range setting or inspection for each single location. Set the route range.
<Setting of inspection member installation interval>
Next, the installation interval of the inspection member, the burial location, etc. are set. Although this is not particularly limited, the section length and interval are usually set. For example, in the route range to be inspected, the section length is about 1 km, the interval is about 100 m, and the total is 10 locations. Moreover, it is desirable to determine the number of inspection members to be embedded in each embedding location together with the setting.
<Calculation of corrosion rate from preparation of inspection member>
As described above, after setting the route range to be inspected, the length of the inspection section, the interval, and the burial location, the test member is buried in the vicinity of the water pipe buried at the location, the test is performed, and the weight is reduced by collection. The corrosion rate is calculated from the amount. Each step is the same as the above <Preparation of inspection member> to <Calculation of corrosion rate of inspection member>.
<Extraction of the maximum value in the route to be inspected>
Next, the maximum value in the inspection target route is extracted from the calculated data of the corrosion rate of the inspection member.

This is to obtain a safe estimate of water pipe corrosion by calculating the corrosion rate based on the most corroded part of the surveyed route and determining the shortest service life of the surveyed route. is there.
<Judgment>
Next, the maximum value of the extracted corrosion rate of the inspection member is determined.

  In this determination, a determination reference value is set and the determination is equal to or greater than the determination reference value, and the case where the determination reference value is less than the determination reference value is examined for subsequent responses.

  Needless to say, this criterion value must be set with sufficient consideration given to the safety against corrosion of water pipes. It is also possible to set for each.

In the present invention, it is set to 0.02 mm / year in consideration of safety against corrosion. By setting the judgment reference value at 0.02 mm / year, for example, in a water pipe having a thickness of 10 mm, the service life can be calculated as 40 years. This is because it can be renewed according to the criteria for a legal service life of 40 years, and sufficient safety against corrosion can be secured.
<If it is less than the criterion value>
When the corrosion rate of the inspection member is less than the criterion value set above, the service life of the water pipe is estimated from the graph shown in FIG.

Next, the remaining life is calculated by subtracting the buried period of the water pipe from the estimated life of the water pipe in this way, and the renewal order of the water pipe is determined.
<If it is above the criterion value>
If the corrosion rate of the inspection member is equal to or higher than the criterion value set above, there is a high possibility that the corrosion of the water pipe has progressed. From the slope of the straight line of the graph shown in FIG. Calculate the theoretical corrosion rate.

  In this way, after confirming the theoretical corrosion rate of the water pipe, the water pipe is actually excavated and exposed to investigate the water pipe. The water pipe survey is the same as the above <Water pipe corrosion survey>.

  The maximum depth of water pipe corrosion is measured by the above process, and the initial thickness of the water pipe × 0.6 is compared with the maximum depth of corrosion. If the maximum depth of corrosion is equal to or greater than the initial thickness x 0.6, it is determined that there is a need for renewal. If the maximum depth of corrosion is less than the initial thickness x 0.6, water supply The update order is determined from the tube status.

  In the present invention, the above method makes it possible to estimate the service life of the water pipes in the soil easily, in a short time and accurately, without burdening the costs and labor. Judgment can be made.

  In addition, in the estimation method of the lifetime of the water pipe of this invention, a various change is possible without being limited to the method of said each process.

  For example, analysis of collected data can be aggregated using a spreadsheet software on a personal computer, and the slope of a straight line in the graph shown in FIG. 9 is automatically derived by setting a mathematical formula in advance. It is possible.

  Furthermore, the curve on the graph shown in FIG. 10 can also be regarded as a numerical correspondence by the software of the personal computer, and when deriving the service life of the water pipe, the corrosion rate of the inspection member and the wall thickness of the water pipe are used as variables. It is also possible to determine the service life of a water pipe by setting a formula.

  Hereinafter, examples will be shown and described in more detail. Of course, the invention is not limited to the following examples.

Example 1
In the inspection area where the water pipe was actually buried, the test by embedding the inspection member and the measurement of the corrosion depth of the water pipe were carried out.
<Inspection range>
As the inspection range, four routes from the A route to the D route and the embedment place of each inspection member were set.
<Preparation of inspection member>
As the inspection member, a round rod of FCD400 having a diameter of 18φ and a length of 80 cm as shown in FIG. The distal end portion 32 and the long portion 31 were cut out from the same material, and the connecting portion was threaded 33. In addition, Teflon (registered trademark) packing 34 was used for the tip 32 and the threaded portion 33 to prevent the occurrence of rust at the contact portion. In this way, the distal end portion 32 is screwed to the long portion 31 to form one inspection member 3.

This inspection member 3 was previously subjected to surface polishing with # 500 polishing paper and sufficient degreasing with ethanol to remove machine oil adhering to the surface. Next, after measuring the weight of the tip 32 with a precision balance, the silica gel was enclosed and stored in a dehumidified container, and care was taken not to cause rust immediately before embedding.
<Embedment of inspection members and corrosion investigation of water pipes>
The inspection member was buried in a two-stage section shown in FIG. 5, and the corrosion depth of the water pipe 2 was measured simultaneously with the insertion of the inspection member 3.

The insertion depth of the inspection member 3 was the same depth as the lowest part of the water pipe 2, and two or six inspection members were embedded. The specific drilling, burial and survey procedures were as follows.
1. Pavement cutting, pavement demolition, soil excavation work.
2. Water pipe 2 upper sample soil collection: about 30 cm above the water pipe 2 (for ANSI analysis of Comparative Example 1).

    Water pipe 2 horizontal sample soil collection (for ANSI analysis of Comparative Example 1).

Water pipe 2 lower sample soil (natural soil) Collection: Water pipe 2 lower part about 50 cm (for ANSI analysis of Comparative Example 1).
3. Water pipe 2 excavation, exposure completed (water pipe survey section (13)): Corrosion investigation of water pipe.
4). Excavation of inspection member 3 burial place (inspection member burial section (14))
5. Mark both ends of the water pipe 2 embedded (FIG. 5A).
6). Drill a vertical hole with a diameter of 17φ and a depth of 20cm at the position where the inspection member 3 is buried.

Uses an electric drill.
7). The inspection member 3 having a diameter of 18φ was driven into the vertical hole with a hammer and inserted (FIG. 5B).

A drawing wire 36 is connected to the ring portion of the inspection member 3 in consideration of drawing.
8). A vinyl chloride pipe 35 is placed above the inspection member and the soil is refilled.
9. The valve chamber 11 is constructed so that the pipe body 35 made of vinyl chloride is accommodated.
10. A lid 12 is installed to prevent rainwater from entering through the upper opening of the vinyl chloride pipe 35 (FIG. 5C).
11. Restoration work <Water pipe corrosion investigation>
Step 3 above. The corrosion investigation of water pipes will be explained.

  Dirt, rust, and water pipe deposits that were a mixture of these were removed from the surface of the water pipe that was exposed by excavation.

  Next, the depth gauge shown in FIG. 7 (A) is used for a place where concentrated corrosion occurs, and the ultrasonic thickness meter shown in FIG. 7 (B) is used for a place where full thickness reduction occurs. The corrosion depth of the tube was measured.

The measurement location is measured on the top (6-A), side / left (6-B), side / right (6-C), and bottom (6-D) of the cross section of the water pipe shown in FIG. When there was an obstacle, measurement was impossible.
<Test period>
The test was conducted with the test period set between 255 days and 1017 days at the set four burial locations.

Moreover, after the end of the predetermined test period, the embedded inspection member was pulled out, and the tip portion fixed with a screw to the tip of the inspection member was separated and collected.
<Calculation of corrosion rate of inspection member>
The weight of the inspection member tip was measured with a precision balance, and the weight reduction amount of the inspection member tip was determined. The corrosion rate was calculated from the weight loss by the following formula.

Tables 1 to 4 show the results of the corrosion rates at the respective buried sites in the inspection range from the A route to the D route.
<Calculation of water pipe corrosion rate>
Of the results obtained in the water pipe corrosion survey, the data on the maximum corrosion depth was adopted, and the maximum corrosion depth was divided by the number of years of burial to calculate the water pipe corrosion rate.

  Tables 1 to 4 show the maximum corrosion depth and corrosion rate of water pipes by route.

  Of the data summarized in Tables 1 to 4, the corrosion rate of the inspection member and the corrosion rate of the water pipe are plotted in a graph with the vertical axis indicating the corrosion rate of the water pipe and the horizontal axis indicating the corrosion rate of the inspection member. did. The graph is shown in FIG.

  The horizontal axis of the graph of FIG. 8 is enlarged to make 0.02 mm / year the maximum value, and a replotted graph is shown in FIG. From this graph, it can be seen that a straight line having an inclination of 12.5 can be drawn as a boundary line of the plotted data.

  From this slope 12.5, the maximum corrosion rate of the water pipe is assumed to be 12.5 times the corrosion rate of the inspection member. As shown in FIG. 10, the vertical axis represents the service life of the water pipe, and the horizontal axis represents the corrosion of the inspection member. It was set as speed, and the graph of the curve of wall thickness 6mm, 8mm, 10mm of the water pipe was created.

From this graph, the service life of the water pipe can be estimated from only the corrosion rate of the inspection member.
(Comparative Example 1)
3. Investigation procedure of the first embodiment with respect to the embedding location of each inspection member on the four routes from the A route to the D route in the examination range The soil samples on the water pipes collected in (1), next to the pipe, under the pipe, and the natural ground were analyzed to give ANSI evaluation scores, and the maximum score was taken to be the ANSI score of the place. The results are shown in Tables 1 to 4 for each route.

  The ANSI score is an index for determining the corrosiveness of soil using 10 points as a criterion. Therefore, using the data in Tables 1 to 4, the correspondence between the ANSI evaluation score on the horizontal axis (the maximum score including ground) and the corrosion rate of the water pipe on the vertical axis was plotted. The result is shown in the graph of FIG. From the graph of FIG. 12, it was found that there was little correlation between the ANSI evaluation score and the water pipe corrosion rate.

  As shown by the broken line in the graph of FIG. 12, the corrosion rate from the data obtained by actually measuring the water pipe is scattered at 0 to 0.2 mm / year regardless of the ANSI evaluation score. Therefore, it was found that it was difficult to evaluate the corrosion rate on the measured route from the size of the ANSI evaluation score.

  From the above, it can be said that it is difficult to evaluate the corrosion rate of water pipes only with the ANSI evaluation score, and it is difficult even with an approximate analogy.

  From the above results, the relationship between the corrosion rate of the inspection member derived by the method of the present invention and the service life of the water pipe, the water pipe in the soil can be simply, quickly and accurately without burdening the cost and labor. It has become clear that the lifetime of can be estimated.

1: soil 10: soil surface 11: valve chamber 12: lid 13: water pipe survey section 14: inspection member buried section 15: backfill soil 2: metal water pipe 3: metal inspection member 30: extraction ring 31 : Long body 32: Tip portion 33: Screw portion 34: Teflon (registered trademark) packing 35: Vinyl chloride tube 36: Pull-out wire 6-A: On the tube 6-B: Tube side / left 6-C: Tube side / Right 6-D: Under tube 70: Depth gauge 71: Ultrasonic thickness gauge

Claims (6)

A method of determining the renewal order of buried metal water pipes by estimating the useful life of the metal water pipes buried in the soil,
Previously, buried metal test elements from the soil surface portion in the vicinity embedded position of the metal water pipes in the soil, pull out after a predetermined period of time, it measures the amount of weight loss before and after embedding of the metallic test element, by weight from the decrease with embedded period to calculate the corrosion rate of the metallic test element,
Measuring the corrosion depth of the metal water pipes buried in the vicinity of the metallic test element, to calculate the corrosion rate of the metallic water pipe from corrosion depth and burying the period of the metallic water pipe,
The maximum value of the corrosion rate of the metallic water pipe that corresponds to corrosion rate of the metallic test element from the correspondence relationship between the corrosion rate of a metal water pipe of the inspected portion and the corrosion rate of the metallic test element ,
Obtain the minimum metal water pipe lifetime estimated from the corrosion rate of the metal inspection member by dividing the thickness of the metal water pipe by the maximum value of the corrosion rate of the metal water pipe,
For the thickness of the metal water pipes, and corrosion rate of the metallic test member in advance to obtain the relationship between the life of the metallic water pipe,
Thereafter, embedded a metal test elements from the soil surface portion in the vicinity embedded position of the metal water pipes in the soil, pull out after a predetermined period of time, from the embedded period and the amount of weight loss before and after embedding of the metallic test element calculating a corrosion rate of the metallic test element,
The calculation result of the corrosion rate of the metal inspection member is applied to the relationship between the corrosion rate of the metal inspection member and the lifetime of the metal water tube with respect to the thickness of the metal water tube obtained above, and in the soil A method for determining the renewal order of buried metal water pipes, characterized in that the service life of metal water pipes is estimated. As the corrosion rate of the metallic test element, the metallic test element and a plurality of buried, to calculate the corrosion rate of each of the metallic test element, the corrosion rate of the average value of the corrosion rate the metallic test element The method for determining the update order of buried metal water pipes according to claim 1. As the corrosion rate of the metallic water pipe, the claims calculating a corrosion rate of a plurality of locations of the metal water pipes, the maximum of these corrosion rate, characterized in that the corrosion rate of the metallic water pipe A method for determining the renewal order of buried metal water pipes according to 1 or 2. Wherein a metallic test element is rod-shaped, that the tip be calculated has become removable, and by measuring the weight loss before and after embedding of the removable tip corrosion rate of the metallic test element The method for determining the update order of buried metal water pipes according to any one of claims 1 to 3. Calculation result of the corrosion rate of the metallic test member, is less than the determination reference value, for the thickness of the metal water pipes, and corrosion rate of the metallic test element, the life of the metallic water pipe The renewal order of buried metal water pipes according to any one of claims 1 to 4, wherein the relationship is applied and the corrosion state of the metal water pipes in the soil is measured when it is equal to or higher than the criterion value. How to determine. 6. The method for determining the renewal order of buried metal water pipes according to claim 5, wherein the criterion value is 0.02 mm / year.

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