JPH07209238A - Method and apparatus of c/s macrocell corrosion measurement for metal pipe - Google Patents

Abstract

PURPOSE:To measure a C/S macrocell corrosion and the extent thereof quickly and accurately by obtaining the variation width of conduction and comparing a predetermined correlation between the variation width of conduction and the actual measurement of maximum corrosion rate. CONSTITUTION:After turning a conduction switch 10 off, the potential of a buried piping is measured with reference to a reference electrode 6 and stored in a microcomputer 1. The switch 10 is then turned on and a current if fed between a conduction electrode 7 and the piping 3. The potential of the piping 3 is measured with reference to the electrode 6 and the current flowing through a lead 11, the piping 3, the soil 2, the electrode 7 and a lead 12 is measured. The measurements are sent to the microcomputer 14 where the variation width of conduction is calculated based on these three measurements. The maximum C/S corrosion rate of the piping, corresponding to the variation width of conduction, is then determined with reference to a prestored correlation between the variation width of conduction based on the measurements at each part and the maximum C/S macrocell corrosion rate thus predicting the corrosion rate of an existing metal piping 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to C / C for buried metal pipes.
More specifically, it relates to a measuring method and apparatus for S macrocell corrosion, and more specifically, between C / S, that is, concrete (Concret).
The present invention relates to a method and an apparatus for measuring macrocell corrosion that occurs in a metal pipe for a gas such as LPG, which is arranged across or through between e) and soil (Soil).

[0002]

2. Description of the Related Art LP supplied as fuel for households, hospitals, schools, various other facilities, or various factories
For gas such as G, pipe the gas from a gas storage tank such as a cylinder.
Buried in concrete that constitutes various facilities, etc., buried in concrete that constitutes various facilities from soil,
These and are laid in a composite type and laid in various types, and are supplied to burners and other combustors, heating equipment, etc. through these gas pipes.

[0003] Gas pipes such as LPG are usually made of metal such as steel pipes. When the steel pipes are arranged in soil, for example, the surrounding soil is in a homogeneous state. In some cases, the progress of corrosion is slow, and it is therefore unlikely that corrosion pits will occur in a short period of time. Many cases have been reported.

[0004] These corrosions are caused by a concentration cell action, a contact action of different metals, an action of a stray current, an action of bacteria, a combined action of these, and various other causes. Among them, the one caused by stray current causes the most severe corrosion, but the second one is the one caused by the contact between the rebar in the rebar concrete and the pipe such as the gas pipe, which is a kind of contact action of dissimilar metals. Corrosion of underground pipes has been pointed out.

The natural corrosion of the gas pipe is roughly divided into macro cell corrosion and micro cell corrosion. Of these, macro cell corrosion is a macro cell corrosion in which a current flows between different metals or metals of the same kind having different environments due to a battery action. It is generated by a macroscopic battery phenomenon and is generated in the metal on the negative electrode side of this cell.

[0006] Looking at the gas pipe made of iron (steel pipe) which is buried in soil and arranged in the concrete therefrom, the electric potential of the steel pipe in the concrete is the same as that of the steel pipe in neutral soil. Since it is more noble than the electric potential, a battery is formed in the pipe where the steel pipe in the concrete and the steel pipe in the soil are connected, and this causes corrosion of the part buried in the soil that is electric potential base. become.

When the steel pipe is a pipe embedded in the reinforcing bar concrete, not only the contact action with the reinforcing bar in the reinforcing bar concrete but also the concrete itself has strong alkalinity (pH about 12.5). ), Which acts to make the electric potential of the reinforcing bars and steel pipes embedded in it noble.

Therefore, when the gas steel pipe is installed from the soil into the concrete, an electric current flows from the steel pipe in the concrete having a high potential to the steel pipe having a low potential buried in the ground, This current flows from the surface of the steel pipe buried in the ground into the ground, returns to the steel pipe in the concrete through the soil, and the part where the current flows from the surface of the steel pipe buried in the ground into the ground It will cause corrosion.

In this case, if the area of the steel pipe embedded in the concrete is small, the corrosion current is small and the progress of the corrosion is weak, so that the corrosion problem does not occur in a short period of time.
The larger the area of the embedded steel pipe, the larger the corrosion current, and the more severe the progress thereof becomes. If this concrete is a rebar concrete, if the rebar and the gas pipe are in contact with each other, the corrosion current will increase. It would be the same as embedding a large amount of steel pipes inside.

[0010]

As described above, the formation of macrocells in a metal-embedded gas pipe made of iron or the like is important as a factor for its corrosion. Therefore, the formation of these cells must be avoided in advance. However, for this purpose, if the presence or absence of macrocells that cause such corrosion is detected in advance for the piping and the quantitative ratio can also be measured in advance, countermeasures will be taken to prevent corrosion due to this macrocell. Can be prevented.

From this point of view, the inventor of the present invention has carried out actual measurement and actual condition investigations on corrosion of various metal gas buried pipes. In the case of metal piping such as (galvanized carbon steel tube for piping), the value obtained by dividing the change in potential by the applied current, that is, between the change width of the applied current and the measured value of the maximum corrosion rate It was found that there is a high correlation with.

Here, the current change width (mV / mA) is
In the measurement of the pipe-to-ground potential distribution of a metal buried pipe, the potential value (mV) during energization is subtracted from the potential value (mV) of the buried pipe near the side of the building into which the gas pipe is drawn, and the resulting potential The difference is divided by the energization current value (mA) during energization, which is represented by the following formula.

[Equation 4]

FIG. 1 is a diagram showing an example of the relationship between the variation width (mV / mA) of the energization and the actual measurement value of the maximum corrosion rate obtained by actual measurement at various places. The measured value of the corrosion rate is "mm / yr", that is, the corrosion depth per year (yr) is shown in units of millimeters (mm). As shown in FIG. 1, the measured value of the maximum corrosion rate tends to be relatively large as the value of the change width of energization becomes small, and it can be seen that there is a certain strong relative relationship between the two.

The present invention utilizes such a correlation between the change width of energization (mV / mA) and the actual measured value of the maximum corrosion rate, that is, as a reference or standard, the target buried pipe. The present invention provides a corrosion measuring method capable of measuring the presence or absence of C / S macrocell corrosion of metal pipes and the degree thereof by comparing and processing the measured values of the electric potential and the electric current of C, and the comparison and the processing are performed automatically. It is an object of the present invention to provide a corrosion measuring method and apparatus capable of accurately and quickly measuring the presence or absence of C / S macrocell corrosion and the degree thereof by carrying out by, for example, a micro computer.

[0015]

The present invention is a method for measuring C / S macrocell corrosion for a metal buried pipe for gas such as LPG, which is an actual measurement value of a change width of electric current and a maximum corrosion rate of the metal buried pipe. After presetting the correlation with, the potential value of the target metal buried pipe, the potential value during energization and the current value during energization are measured, and the energization change width is calculated based on these measured values, By comparing this calculated value with the correlation between the preset width of change in energization and the actual measurement value of the maximum corrosion rate, the corrosion rate of the metal embedded piping is measured, and the C of the metal embedded piping is characterized. / S provides a corrosion measurement method for macrocell corrosion.

Here, the current change width (mV / mA) is
When measuring the ground potential of a metal buried pipe, the potential value during energization is subtracted from the potential value of the buried pipe near the building where the gas pipe is drawn, and the difference in potential obtained by this is the It is divided by the energizing current value, and is expressed by the following formula.

[Equation 5]

Further, in the above-described corrosion measuring method according to the present invention, the energization change width is calculated based on the measured values of the electric potential of the target metallic buried pipe, the electric potential during energization and the current during energization,
By carrying out a process of comparing the calculated value with the correlation between the temporary energization change width and the actual measured value of the maximum corrosion rate by an automatic processing means such as a micro computer, the calculation and the process are executed accurately and promptly. be able to.

Further, according to the present invention, after the correlation between the variation range of the current flow of the metal buried pipe and the actual measured value of the maximum corrosion rate is set in advance, the potential value of the target metal buried pipe and the potential value at the time of current conduction are set. And measuring the current value during energization, calculating the energization change width based on these measured values, and comparing this calculated value with the correlation between the preset energization change width and the actual measured value of the maximum corrosion rate. According to the present invention, there is provided a corrosion measuring device for C / S macrocell corrosion of a metal buried pipe, characterized in that the corrosion rate of the metal buried pipe is measured.

Here, the current change width (mV / mA) means
In the measurement of the ground potential of a metal buried pipe, the potential value at energization is subtracted from the potential value of the buried pipe, and the difference in potential obtained by this is divided by the energizing current value at energization. , Is expressed by the following formula.

[Equation 6]

In this apparatus, the energization change width is calculated based on the measured values of the electric potential on the building side of the target buried metal pipe, the electric potential during energization and the current during energization, and this calculated value is referred to as the energization change width. By performing the processing that correlates with the correlation with the actual measurement value of the maximum corrosion rate by the automatic processing means, the measurement, calculation, and processing can be performed accurately and quickly.As this automatic processing means, It is preferable to use a micro computer.

When a microcomputer is used for the automatic processing, the mode of the apparatus and its operation are as follows.
A power supply, an electrometer, an ammeter, a current-carrying electrode, a micro computer, etc. are integrally provided, and the target metal buried pipes of the target are buried by the micro computer. Based on the electric potential value and the electric potential value and electric current value at the time of energizing the energizing electrode, the energization change width (mV
/ MA) is calculated by the following formula, and the calculated value is set in advance according to the following formula.
By comparing the correlation between A) and the actual measured value of the maximum corrosion rate, the corrosion rate of C / S macrocell corrosion of the metal buried pipe can be measured automatically, quickly and accurately. it can.

[0022]

Embodiments of the present invention will be described below with reference to the drawings, but it goes without saying that the present invention is not limited to these embodiments. FIG. 2 shows the outline of the C / S macro cell corrosion measuring device according to the present invention. In FIG. 2, 1 is a building (wall) / concrete, 2 is soil, and 3 is a metal gas pipe. As shown in the drawing, the metal pipe 3 is arranged from the concrete of the building 1 to the soil 2.

Reference numeral 4 is an electrometer (voltmeter), 5 is an ammeter, 6 is a reference electrode, 7 is a conducting electrode, 8 is a variable resistor, 9 is a power source, and 10 is a conducting switch. Be wired to. Among these, the energizing electrode 7 is installed in the soil 2, while the electrometer (voltmeter) 4 is connected to the building 3 of the pipe 3 by the wiring 11. In the figure, 12 is a conducting wire to the current-carrying electrode 7, and 13 is a conducting wire for transmitting signals of the measured values of the potential and current.

The values measured by the voltmeter 4 and the ammeter 5 are sent to the microcomputer 14, where the potential of the buried pipe, the potential during energization and the current during energization (potential = m).
Based on V, current = mA), the "current change width (mV / mA)" is calculated according to the above formula, and the corresponding corrosion rate as shown in FIG. 1 is measured. For this reason, a storage function, a calculation function, a comparison function and the like for performing these processes are set in the microcomputer 14 in advance.

Using the C / S macrocell corrosion measuring device for metal pipes having the above-mentioned structure, each required value, that is, the potential of the buried pipe, and the current when the pipe is energized The electric potential and the electric current during energization are measured, the energization change width (mV / mA) is obtained from these, and the corresponding corrosion rate is measured. This process will be described below.

First, based on the measured values obtained at various places as shown in FIG. 1, the "current change width (mV / mA)" and the corresponding maximum corrosion rate of C / S macrocell corrosion of metal pipes Is set in advance, and the set correlation between the two is stored in the microcomputer 14.

Next, this apparatus is set in an existing metal conduit for which the C / S macrocell corrosion rate is required or intended to be measured as shown in FIG.
Is turned off, the potential of the buried pipe is measured with the reference electrode 6 as a reference, and the value is transmitted to the microcomputer 14 as the “buried pipe potential value” and stored therein.

Subsequently, the energizing switch 10 is turned on.
Then, a current is caused to flow between the energizing electrode 7 and the pipe 3, and the potential of the buried pipe 3 is measured with the reference electrode 6 as a reference to obtain the “potential value during energization”, and the conductor 11, the pipe 3, the soil 2, The current flowing between the current-carrying electrode 7 and the conducting wire 12 is measured, and this value is sent to the microcomputer 14 through the conducting wire 13 as the "current value during energization".

In the micro-computer 14, the width of change in energization (mV / mA) based on the measured values of the "buried pipe potential value", "potential value during energization" and "current value during energization".
Then, by comparing this value with the correlation between the above-mentioned energization change width and the maximum corrosion rate of C / S macrocell corrosion stored in advance by the microcomputer 14, the energization change width is calculated. C of the metal pipe corresponding to
The maximum corrosion rate of / S macrocell corrosion is determined, and the rate of C / S macrocell corrosion of the existing metal pipe is predicted.

[0030]

As described above, according to the method and apparatus for measuring C / S macrocell corrosion of metal piping according to the present invention, the presence or absence of C / S macrocell corrosion occurring in the metal buried gas piping is detected in advance. And the rate or extent of its corrosion can be predicted, which
Corrosion due to the C / S macro cell can be prevented in advance.

Further, if this corrosion measuring method and apparatus are carried out by an automatic processing means, the detection, prediction and prevention of the C / S macrocell corrosion can be carried out quickly, accurately and automatically. As the automatic processing means, a micro computer can be preferably used.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an energization change width (mV / mA) obtained from an actual measurement value for a buried metal pipe and an actual measurement value of a maximum corrosion rate.

FIG. 2 is a diagram showing an outline of a C / S macrocell corrosion measuring device according to the present invention.

[Explanation of symbols]

 1 Building (wall) / Concrete 2 Soil 3 Metal gas pipe 4 Electrometer (voltmeter) 5 Ammeter 6 Reference electrode 7 Energizing electrode 8 Variable resistance 9 Power supply 10 Energizing switch 14 Microcomputer

Claims (6)

[Claims] 1. A potential value of a target metal buried pipe, a potential value when power is applied, and a current value when power is applied after presetting a correlation between an energization change width of a metal buried pipe and an actually measured value of a maximum corrosion rate. Measuring the current value, calculating the energization change width based on these measured values, by comparing the calculated value with the correlation between the preset energization change width and the actual measurement value of the maximum corrosion rate, the metal A corrosion measurement method for C / S macrocell corrosion of a metal buried pipe, characterized by measuring the corrosion rate of the buried pipe. Here, the energization change width (mV / mA) is the difference between the potentials obtained by subtracting the potential value during energization from the potential value of the buried pipe in the measurement of the ground potential of the metal buried pipe. , Which is divided by the value of the energizing current during energization, and is represented by the following formula. [Equation 1] 2. An energization change width is calculated based on measured values of a potential of a target buried metal pipe on the building side, an energized potential, and an energized current, and the calculated value is used as the energization change width and maximum corrosion. 2. The method for measuring corrosion of C / S macrocell corrosion of a metal buried gas pipe according to claim 1, wherein the processing that correlates with the correlation with the measured value of the speed is performed by an automatic processing means such as a micro computer. . 3. The potential value of the target metallic buried pipe, the potential value at the time of energization, and the value at the time of energization are set after presetting the correlation between the variation range of the energization of the buried metal pipe and the measured value of the maximum corrosion rate. By measuring the current value, calculating the energization change width based on these measured values, by comparing the calculated value with the correlation between the preset energization change width and the actual measurement value of the maximum corrosion rate, the metal A corrosion measuring device for C / S macrocell corrosion of a metal buried pipe, characterized in that the corrosion rate of the buried pipe is measured. Here, the energization change width (mV /
mA) is the difference between the potentials obtained by subtracting the potential value at the time of energization from the potential value of the buried pipes in the measurement of the pipe-to-ground potential of the metal buried pipe, and the value of the energizing current at the time of energization. The values are divided by the following formula. [Equation 2] 4. An energization change width is calculated based on measured values of a potential of a target buried metal pipe on the building side, an energization potential, and an energization current, and the calculated value is used as the energization change width and maximum corrosion. 4. The corrosion measuring device for C / S macrocell corrosion of a metal buried gas pipe according to claim 3, wherein a process for comparing with a correlation with an actual measured value of speed is performed by an automatic processing means. 5. A corrosion measuring device for C / S macrocell corrosion of a buried metal pipe for a gas such as LPG according to claim 4, wherein the automatic processing means is a micro computer. 6. A micro computer including a power source, an electrometer, an ammeter, a current-carrying electrode, a micro computer, etc.
For the target buried metal pipe, the potential change value (mV / mA) for the target buried metal pipe based on the potential value of the buried pipe measured by those electrometers and ammeters, and the potential value and current value when current is applied to the current-carrying electrode. ) Is calculated by the following formula, and this calculated value is preset by the following formula.
/ MA) and the correlation between the actual measured value of the maximum corrosion rate and the correlation, and the corrosion measurement device for C / S macrocell corrosion of a buried metal pipe. [Equation 3]