JPH06288958A - Method for detecting corroded part of cast-iron pipe buried in ground - Google Patents

Abstract

PURPOSE:To obtain a corrosion detecting method by which the corrosion of a buried cast-iron pipe can be easily detected from the ground surface and, at the same time, the future progress of corrosion can be predicted. CONSTITUTION:The corrosion of a buried cast-iron pipe 2 is discriminated from the ground potential value of the pipe 2 and the difference between the ground and corrosion potential values of the pipe 2 by measuring the ground potential value by bringing the terminal 4 of a ground potential measuring instrument 3 into contact with the pipe 2 and moving a copper-copper sulfate electrode 6 along the pipe and, at the same time, measuring the corrosion potential value from the ground surface with a corrosion potential measuring instrument 8. In addition, the degree of corrosion and future progress of corrosion are predicted from the magnitudes of the values.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a corroded portion of a cast iron pipe (for example, gas or water pipe) buried in the ground.

[0002]

2. Description of the Related Art Cast iron pipes buried in the ground are routinely corroded by various causes, and eventually internal fluid leaks out. Proper treatment is the most important issue in maintaining and managing soil-embedded cast iron pipes.

As a conventional method for detecting a corroded portion of a cast iron pipe, there are the following methods.

A. A method of excavating the buried part to expose the cast iron pipe and visually detecting it.

B. A method of excavating a part of the buried pipeline, cutting the cast iron pipe, and inserting a sensor using a TV camera, electromagnetic waves, overcurrent, etc. into the pipe.

[0006]

However, the above conventional example has the following drawbacks.

A. The method of excavating the burial site is not realistic because it requires a huge amount of cost if it is carried out along a long pipeline, and it causes problems such as traffic obstacles.

B. In the case of the method of inserting the sensor into the pipe, it is practically difficult to carry out the inspection with the live pipe, so that gas and water must be stopped once and the device becomes large-scale. Further, if no severely corroded portion is detected in the pipe, it is impossible to predict future corrosion progress.

The object of the present invention is to detect the corrosion from the ground and to detect the degree of this corrosion numerically and to calculate the progress of the corrosion in the future without the need to excavate the buried pipe. It is to propose a predictable new method for detecting corrosion points in soil-embedded cast iron pipes.

[0010]

Means for Solving the Problems A method for detecting a corrosion portion of a soil-embedded cast iron pipe according to the present invention is as follows.

The terminal is attached to the buried cast iron pipe and the copper-copper-sulfate electrode is moved along the pipe axis on the ground surface to measure the pipe-to-ground potential which is the potential difference between the terminal and this electrode. At the same place as the copper sulfate electrode, insert a cast iron probe and a reference electrode near the buried cast iron pipe to measure the corrosion potential of the cast iron, measure the value of the pipe-to-ground potential, the pipe-to-ground potential and the corrosion of the cast iron. A method for detecting a corroded portion of a soil-embedded cast iron pipe that determines that there is corrosion based on both values of the potential difference.

Depending on the conditions, the corrosion potential measurement location may be set at a coarser interval than the pipe-to-ground potential measurement location.

[0013]

[Operation] First, when the detection section is determined in the pipeline, a small diameter vertical hole is bored at this end, and the terminal of the ground potential measuring instrument is inserted into this vertical hole to connect this terminal to the cast iron pipe. Contact the surface in an electrically conductive state. Next, a copper-sulfate-copper-sulphate electrode for measuring the ground potential is moved along the conduit on the ground surface, and the ground potential (P / S) of the cast iron pipe is measured at regular intervals.

Next, a cast iron probe of a corrosion potential measuring instrument and a vertical hole for inserting a copper-copper-sulfate electrode as a reference electrode, for example, are drilled near the location measured by the copper-copper-sulfate electrode to near the pipe line. A probe and a reference electrode are inserted into the vertical hole to measure the corrosion potential (Ecorr) of cast iron. This measurement point may be performed at the same interval as the ground potential measurement point, or may be performed at a rough interval such as every other one or every two. However, although it takes time and labor, it is preferable that the intervals are the same.

After measuring the ground potential (P / S) and the corrosion potential (Ecorr) as described above, the progress of corrosion is predicted by the P / S and (P / S-Ecorr).

[0016]

Embodiments of the present invention will be described with reference to FIG.
Reference numeral 1 is soil, 2 is a gray cast iron pipe buried in the soil 1, 3 is a ground potential measuring instrument, 4 is a terminal as a terminal of the ground potential measuring instrument 3, and this terminal 4 is a bowl from the ground. Insert it into the vertical hole 5
The surface of the cast iron pipe 3 is contacted in an electrically conductive state. Next, the copper sulfate copper electrode 6 which is one terminal of the ground potential measuring device 3 is moved along the pipeline of the cast iron pipe 3 to the points A, B, C ...
The ground potential (P / S) of the cast iron pipe 2 at each point is measured.

Next, a vertical hole 7 is bored up to the vicinity of the cast iron pipe 2 near the location where the ground potential (P / S) is measured, and the corrosion potential (Ecor) is passed through the vertical hole 7.
r) Inserting the cast iron probe 9 as the electrode of the measuring instrument 8 and the copper sulfate copper sulfate electrode 10 as the reference electrode, the corrosion potential of the cast iron (Eco
rr) is measured.

In this way, P / S and Ecorr are measured, and the progress of corrosion is predicted from the magnitudes of P / S and (P / S-Ecorr). Further, by calculating the degree of progress of corrosion in the future from the magnitude of these values, the life or the time of coping is predicted.

FIG. 2 shows the relationship between relative corrosion depth and P / S. Although there is a positive correlation between the two, the relative corrosion depth increases as the P / S becomes higher overall.
Since there is considerable variation, it is difficult to predict the relative corrosion depth from the P / S value alone. However, P
A plot in which / S is nobler than -550 mV and P / S-Ecorr is 140 mV or more (a plot belonging to a region surrounded by a diagonal line in FIG. 2) corresponds to a portion corroded by 60% or more of the pipe thickness.

FIG. 3 shows the relative corrosion depth and P / S-Ecor.
It shows the relationship with r. In FIG. 3, a plot belonging to a region surrounded by a diagonal line shows that P / S-Ecorr is 140 mV or more and P / S is nobler than -550 mV, and the relative corrosion depth is 0.6 or more. In Fig. 2, the number in the plot within the shaded area is P / S.
-The value of Ecorr.

From the above, P / S and P / S-Ecorr
From the values of both, it is understood that it is possible to detect the corroded portion of the soil-embedded cast iron pipe.

[0022]

INDUSTRIAL APPLICABILITY As described above, the present invention measures the ground potential of a cast iron pipe and the corrosion potential of cast iron, and when the cast iron pipe corrodes, graphitization always occurs, and P / S becomes noble than Ecorr. Corrosion is detected using the corrosion phenomenon peculiar to pipes, so all detection work can be performed from the ground. As a result, the following effects are achieved.

A. The work efficiency is good, and a large-scale device for excavating the soil and inserting the sensor into the pipe is not required, and the measurement cost is much lower than the conventional example.

B. The detection work can be performed with the live tube.

C. Since the progress of corrosion can be known from the magnitudes of the values of P / S and P / S-Ecorr, it is possible to predict the life and future repair time.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a corrosion point detecting method according to the present invention.

FIG. 2 is an explanatory diagram showing the relationship between relative corrosion depth and P / S.

FIG. 3 is an explanatory diagram showing a relationship between relative corrosion depth and P / S-Ecorr.

[Explanation of symbols]

 1 Soil 2 Cast iron pipe 3 Ground potential measuring device 4 Terminals 5, 7 Vertical hole 6, 10 Copper copper sulfate electrode 8 Corrosion potential measuring device 9 Cast iron probe

Claims (3)

[Claims] 1. A terminal is attached to an embedded cast iron pipe, and a copper-copper-sulfate electrode is moved along the pipe axis on the ground surface to measure a pipe-to-ground potential which is a potential difference between the terminal and this electrode. At the same place as the copper sulfate electrode, measure the corrosion potential of the cast iron by inserting the cast iron probe and the reference electrode in the vicinity of the buried cast iron pipe, the value of the pipe ground potential and the pipe ground potential and cast iron. Corrosion location detection method for soil-embedded cast iron pipes that determines that there is corrosion based on both of the values of the difference in corrosion potential. 2. The method for detecting a corrosion point of a soil-embedded cast iron pipe according to claim 1, wherein the corrosion potential of the cast iron pipe is measured by making a vertical hole at a corrosion potential measurement point and inserting a cast iron probe and a reference electrode into the vertical hole. . 3. The method for detecting a corrosion location of a soil-embedded cast iron pipe according to claim 1, wherein the corrosion potential measurement location is set at a coarser interval than the pipe-to-ground potential measurement location.