JP2532038B2 - Method for flaw detection on inner surface of pipeline - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides information on the presence or absence of inner surface coating damage of a pipe line coated with an inner surface and the position of the damage, outside the pipe or remotely without disassembling the pipe line. The present invention relates to a flaw detection method for a pipe line inner surface coating that can be detected from a position.

[Conventional technology]

The conventional method for detecting the damage to the inner surface of the pipe is to disassemble the pipe and investigate it. As another method, a method of inserting a camera into the pipe and observing the pipe is practical. is there.

[Problems to be solved by the invention]

However, all of these conventional methods are troublesome,
In particular, since it is necessary to scan the entire length and circumference of the tube, the number of steps is enormous, and it is not suitable for constant monitoring. Also,
The method using a camera has a problem that an inlet for inserting the camera is required and the pipe diameter is also limited.

As a method of detecting damage to the inner surface coating without disassembling the pipe, a method of providing one electrode in contact with the liquid in the pipe and detecting the presence or absence of energization between this electrode and the pipe is
No. 58-165649. However, the conductivity between the electrode and the tube is affected by the position and size of the inner surface coating damage, and it is not necessary to simply measure the conductivity between one electrode and the tube as disclosed in the above publication. However, there was a fatal problem that the location of the damage could not be identified.

Since damage to the inner surface coating is a serious problem that leads to corrosive perforation of the pipe wall, it is desirable to detect it within as short a day as possible after the damage has occurred, accurately identify the site, and repair it immediately. For that purpose, it is necessary to perform frequent damage inspections, and there has been a strong demand for a method that can easily detect the entire surface of the duct.

As a result of various studies in view of such a situation, the present inventors have used the principle that the electrical resistance of the liquid in the pipeline in the longitudinal direction of the pipeline is proportional to the pipeline length, and whether the coating is damaged or not. The inventors have found that it is possible to identify the position, and have completed the present invention.

[Means for solving problems]

The gist of the first invention of the present application is, as shown in FIG. 1, at two points A and B which are spaced in the longitudinal direction of a conduit consisting of a conductive tube body 2 having an inner surface coated with an insulating coating 1. Electrodes 4,5 to make contact with the liquid in the conduits but to maintain insulation from the conductive conduit
Is arranged to take a terminal, and the terminal 6 is also taken to the conductive tube 2, and three kinds of terminal pairs which are a combination of three terminals respectively connected to the electrodes 4 and 5 and the conductive tube 2, that is, Between two electrodes (4-5), between one electrode and terminal of conductive tube (4-6), between other electrode and terminal of conductive tube (5
-6), at least two terminal pairs, the resistance is measured, the resistance ratio is measured, or the potential difference is measured while one of the three terminal pairs is energized.
Distance l ₀ between 4,5, the distance l ₁ between the position and the one electrode 4 in line lined injury, the distance l ₂ between the other electrode 5, the obtained resistance values measured , A resistance ratio, a potential difference value, or a proportional relationship with the calculation result thereof, the distances l ₁ and l ₂ are obtained to detect the existing position of the damage on the inner surface of the conduit. is there.

Further, the gist of the second invention of the present application is that, in the method of the first invention, guard electrodes 21, 21 '(FIG. 6a, FIG. 6b
(See the figure) and place each guard electrode 21, 21 'at the same potential as the measuring electrodes 4 and 5 on the side close to it, and in this state, perform measurement in the same manner as in the first aspect of the invention described above. _This is a flaw detection method for a pipe inner surface coating, which is characterized by detecting ₁ and l ₂ and detecting the existing position of the pipe inner surface coating damage.

In addition, the gist of the third invention of the present application is that, as shown in FIG. 6c, guard electrodes 21 and 21 'that come into contact with the liquid in the pipeline are arranged outside the electrodes 4 and 5 for measurement, respectively, and Of which, 2
Measure the resistance between the pair of measuring electrodes 4 and 5 and the terminal 6 of the conductive tube 2 after short-circuiting the two measuring electrodes 4 and 5 and the two guard electrodes 21 and 21 '. A flaw detection method for coating the inner surface of a pipeline is characterized by detecting the presence or absence of damage to the coating on the inner surface of the pipeline and detecting the approximate size.

[Action]

In general, liquids have some conductivity, which is why
The two points A and B on the conduit are electrically connected through the liquid.
Letting R ₀ be the liquid resistance in the pipe between A and B, this resistance R ₀ is a finite value that is related to the specific resistance of the liquid in the pipe and is proportional to the distance l ₀ between A and B. When a predetermined amount of current is applied, a potential difference (E ₀ ) corresponding to the resistance R ₀ occurs between the two. On the other hand, if there is no damage to the pipe inner surface coating 1, the liquid in the pipe and the conductive pipe body 2 are not electrically connected to each other, so that the electrodes 4 and 5 and the terminal 6 connected to the conductive pipe body 2 are not electrically connected. The resistance between them becomes infinite, and no potential is generated at the terminal 6 even when a current is passed between the electrodes 4 and 5. However, as shown in FIG. 1, when there is a damage 7 at the position D on the inner surface of the tube, the electrode 4 and the terminal 6 are electrically connected through the liquid between AD and the tube between DC. Now, assuming that the liquid resistance in the tube between AD is R ₁ , this resistance R ₁ becomes a value proportional to the distance l ₁ between AD, and the resistance between electrode 4 and terminal 6 is this liquid resistance.
It includes R ₁ . Similarly, assuming that the liquid resistance between BDs is R ₂ , this resistance R ₂ has a value proportional to the BD distance l ₂ , and the resistance between the terminal 6 and the electrode 5 has a value including this liquid resistance R ₂ .
When a current is applied between electrodes 4 and 5, there is a potential difference between AD (corresponding to liquid resistance R ₁ ) (E ₁ ) and between DB is liquid resistance R ₂
A potential difference (denoted by E ₂ ) corresponding to the above occurs, and the potential of the liquid at the D position appears at the terminal 6.

Therefore, there are three types of terminal pairs that are combinations of the three terminals of the electrodes 4 and 5 and the terminal 6, that is, between two electrodes (4-5) and between one electrode and the terminal of the conductive tube (4-. 6), between at least two terminal pairs between the other electrode and the terminals of the conductive tube (5-6), measurement of resistance, measurement of resistance ratio,
Or, when the potential difference is measured with one of the three terminal pairs being energized, the distance l ₀ between the two electrodes 4 and 5, the position of the coating damage on the inner surface of the conduit and one electrode 4 Since the distance l ₁ between them, the distance l ₂ between the other electrode 5 and the resistance value, resistance ratio or potential difference value obtained by the above-mentioned measurement, or the calculation result thereof have a predetermined proportional relationship. , The distances l ₁ and l ₂ can be obtained, and thus the position of the damage on the inner surface of the pipe can be detected.

For the resistance measured between the electrode 4 or 5 and the terminal 6, in addition to R ₁ and R ₂ mentioned above, the liquid contact resistance R _S related to the size of the damage 7 is connected in series with R ₁ and R ₂ . Included in form. This liquid contact resistance R _S can be obtained by measuring the resistance between all of the above-mentioned three types of terminal pairs, and from the measured value, the magnitude of damage can be calculated from the calculated liquid contact resistance R _S. You can also know

By the way, when measuring the resistance value, the resistance ratio or the potential difference value between the electrodes 4 and 5 and the terminal 6, the liquid in the conduit is connected to a conductive pipe through a valve or a pump on the extension of the measuring point. In some cases, current may flow from the electrodes 4 and 5 through the fluid in the pipe to the valve or pump, which may disturb the measurement. Therefore, in the second invention of the present application, as shown in the embodiment of FIGS. 6a and 6b, the electrodes 4, 5
The guard electrodes 21, 21 'are placed outside the
It is kept the same as 4,5, which can prevent the measurement disturbance.

Further, in the third invention of the present application, as shown in the embodiment of FIG. 6c, when the guard electrodes 21 and 21 'are arranged, two measuring electrodes 4 and 5 and two guard electrodes 21 and 21' are comrades. After short-circuiting, the measuring electrode pairs 4,5 and the terminal 6 of the conductive tube 2
The resistance between and is being measured. The resistance value r ₃ measured by this is, as described later, Is a value including the liquid contact resistance. Therefore, the presence or absence of damage and the approximate size can be easily determined from the resistance value r ₃ .

The pipe line to which the flaw detection method of the present invention can be applied is such that a metal pipe is coated with an inner surface by an insulator, and this is connected with a flange or a victor type connector, or after welding connection, the inner surface of the welded portion. It is designed so that the metal pipe does not conduct to the liquid in the pipe, such as a pipe with a repaired coating or a pipe with a metal pipe that has a continuous coating on its inner surface. Further, the detection of the perforation of a pipeline made of an insulating non-metal pipe reinforced or shielded with a conductive fiber or a wire can also be a target of the flaw detection method of the present invention. It corresponds to the insulating coating on the inner surface, and conductive fibers or wires for reinforcement or shielding correspond to the conductive tube.

The distance between the electrodes 4 and 5 arranged in the pipe line depends on the pipe diameter and the conductivity of the liquid in the pipe, but approximately 10 joints (about 55 m) can be measured sufficiently. In this case, it is desirable that the tubes located between the electrodes be electrically connected to each other with the joint section interposed therebetween. According to the ordinary piping method, the metal pipes are naturally connected to each other, but if there are mixed insulation points, the insulation points may be temporarily short-circuited for measurement. Alternatively, the metal pipes on both sides of the insulated portion may be measured separately.

The terminal 6 attached to the conductive tube body 2 is a terminal for measuring the in-tube liquid potential of the damaged portion of the inner surface coating and the liquid resistance to the electrode as described above. Generally, the conductive tube used for the conduit is a metal tube and has a much higher conductivity than the liquid in the tube. Therefore, the terminal 6 may be taken from the tube at an arbitrary position on the conduit. From the point of minimizing noise,
It is best taken from a metal tube between the two electrodes.

The liquid to which the flaw detection method of the present invention can be applied is arbitrary as long as it provides electrical conduction in the direction along the pipeline, and includes seawater, fresh water, tap water, pure water, tap water, sewage, an aqueous solution of chemicals, Examples include earth and sand slurry and polar organic liquids. The liquid in the tube may be in a flowing state, a static full state, or a state where there is a continuous liquid film only on the tube wall.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to the embodiments of the drawings.

FIG. 2 shows a first embodiment of the present invention, and 10 is an ohmmeter. In the first embodiment, the resistance between the electrode 4 and the terminal 6, the resistance between the electrode 5 and the terminal 6, and the resistance between the electrodes 4 and 5 are directly measured by the resistance meter 10. Here, if the resistance measurement value between the electrodes 4 and 5 is r ₀ , the resistance measurement value between the electrode 4 and the terminal 6 is r ₁ , and the resistance measurement value between the electrode 5 and the terminal 6 is r _2. Since the resistance of the tube body 2 from the damaged position to the terminal 6 is extremely small as compared with the liquid resistance, these resistance measurement values have the following relationship with the liquid resistance and the liquid contact resistance in the tube. That is, r ₀ = R ₀ = R ₁ + R ₂ r ₁ = R ₁ + R _S r ₂ = R ₂ + R _S Therefore, this liquid contact resistance R _S is Further, since the liquid resistances R ₀ , R ₁ and R ₂ are proportional to the distances l ₀ , l ₁ and l ₂ , Becomes If this is expressed using the resistance measurement value, Is. Therefore, as described above, the resistance between the electrodes 4 and 5 and the terminal 6 is measured, the liquid contact resistance R _S is obtained from the above equation (1), and then the distance l ₁ to the coating damage from the equation (3), l ₂ can be obtained.

Here, since the liquid contact resistance R _S is a value related to the opening size of the coating damage and the dent depth (that is, the coating thickness), it is possible to detect the damage size from this liquid contact resistance. .

In equation (3), if the liquid contact resistance is smaller than the resistance measurement value, Holds approximately. In this case, the measured resistance value r ₀ ,
It is not necessary to measure all of r ₁ and r ₂ , but by measuring two of them, l ₁ and l ₂ can be obtained with l ₀ as a reference.

By the way, this method is a method of measuring the resistance value including the liquid resistance and the liquid contact resistance and obtaining the position of the damage from the resistance value, but as the opening size of the coating damage becomes smaller,
The liquid contact resistance R _S rapidly increases and the liquid resistance falls within the error range. Therefore, if the damage is small, the position detection error increases, and it is hard to say that this method is optimal for identifying the damaged position.

On the other hand, the above method is very useful for detecting the presence or absence of damage and the magnitude of the damage because the measurement result includes the magnitude of the conductivity of the damaged coating portion 7. That is, in this measurement, the resistance between the terminal 6 and the electrode 4 or 5 is infinite (above a specific value).
It is proved that no damage is caused.

FIG. 3 shows a second embodiment of the present invention, in which a power source 11, a resistor 12 and a potentiometer 13 are connected between the electrode 4 and the terminal 6 as shown in FIG. The resistance of is measured by the insulation measurement method. Similarly, the resistance between the terminal 6 and the electrode 5 and the resistance between the electrodes 4 and 5 can be measured. In the case of this embodiment as well, by measuring the resistance between the terminals as in the case of the embodiment of FIG. 2, it is possible to detect the presence or absence of the coating damage, its size and its position. Also in this case, if the liquid contact resistance is significantly larger than the liquid resistance in the pipe, the liquid resistance in the pipe falls within the error range. Therefore, similar to the first embodiment, such resistance measurement is performed. It is hard to say that the method is the most suitable for identifying the damage location.

FIG. 4 shows a third embodiment of the present invention, in which the terminal 6
This is a method of simultaneously measuring the resistance ratio between the electrodes and the electrodes 4 and 5 by the bridge method. In the figure, 14 is a power supply and 15
A variable resistor with a scale
It comprises a split terminal 15b sliding on 15a and a scale 15c for indicating the position of the split terminal 15b. 16 is a galvanometer. In this embodiment, an appropriate potential is applied between the electrodes 4 and 5 by the power source 14,
Adjust the split terminal 15b of the variable resistor 15 by sliding it on the resistor 15a so that the current between the split terminal 15b and the terminal 6 is minimized. To read. Where the total resistance of resistor 15a is
If r ₀ ′ and the resistance component on the electrode 4 side of the split terminal 15b are r ₁ ′ and the resistance component on the opposite side is r ₂ ′, then terminal 6 and split terminal 15b
In the condition that no current flows between Becomes Therefore, from this equation (5) and the above equation (2), Holds approximately. Thus, the resistance ratio of the right and left of the divided terminal 15b in the variable resistor 15 (that is, r ₂ ′ /
The distances l ₁ and l ₂ can be obtained from r ₁ ′), and the presence or absence of coating damage and the existing position can be detected by this. In the this system, with the current through the coating damage (i.e. the current through the wetted resistor R _S) is minimum, since seek resistance ratio, error due wetted resistor R _S is less likely to occur.

In this method, when there are multiple damages between the electrodes 4 and 5, for example, the outermost two damages are short-circuited by the metal tube and measured as if it were one damage, and one of the electrodes is damaged. To the outermost damage on the electrode side l ₁ ′ and the distance l ₂ ′ from the other electrode to the outermost damage on the electrode side are (However, it is simply obtained as l ₀ ′ = l ₁ ′ + l ₂ ′). That is, here l ₀ ′ is an unknown number, and true l ₁ ′ and l ₂ ′ cannot be found on the basis of this. Therefore, in order to identify l ₀ ′, it becomes necessary to add an operation for obtaining the in-tube liquid resistance between the two electrodes under the above-mentioned circumstances.

However, the above method has an advantage that the object can be achieved with a simple instrument as in the first and second embodiments.

FIG. 5 shows a fourth embodiment of the present invention, in which 17 is a power source,
18 is a potentiometer. In this embodiment, the electrodes 17 are connected to the electrodes 4 and 5.
Connect a constant current i ₀ , and connect the terminal 6 with the potentiometer 18.
The potential difference between the electrode and the electrode 4, or between the terminal 6 and the electrode 5, between the electrodes 4 and 5 is measured. Here, the potential difference measured between the electrodes 4 and 5 is E ₀ , and the potential difference measured between the terminal 6 and the electrode 4 is
Let E ₁ be the potential difference measured between terminal 6 and electrode 5, and let E ₂ be: The approximate relationship of is established. Therefore, the potential difference E ₀ , E ₁ ,
The position of the damaged part can be detected by measuring at least two of E ₂ .

If the potentiometer used here has a high input impedance, the effect of liquid contact resistance at the damaged part can be avoided. The input impedance required for the instrument depends on the tube diameter and the conductivity of the liquid in the tube, but any instrument with a resistance of 10 ⁹ to 10 ¹¹ Ω is suitable for most targets. In order to ensure the accuracy of the potential measurement, it is desirable to first correct the natural potential difference based on the material difference between the charging electrodes 4, 5 and the metal tube 2. The self-potential difference ΔE to be corrected is calculated by using E ₁ and E ₂ ^* obtained by the measurement in which the polarities between the two electrodes are opposite. Can be asked. Next, it is sufficient to correct the effect of electrolytic polarization on the two-electrode surface, but the ratio of the polarization voltage to the liquid potential drop in the tube can be minimized by selecting the energizing current, and the correction can be omitted. In addition, energization of electrode i ₀
If not performed from 5, but from another pair of electrodes placed so as to sandwich the electrodes 4 and 5, there will be no polarization at the electrodes 4 and 5.

According to this embodiment, even if there is a plurality of damage, total l ₀ of the distance leading to the second electrode from the outermost damage _{'= l 1' + l 2} ', Therefore, it is possible to accurately identify the section where multiple damages exist.

As described above, as an embodiment of the method of the present invention, two electrodes 4,5
Although different methods of measuring the electrical characteristics between the terminals 6 and 6 have been shown, the present invention is not limited to these methods, and these methods may be combined as appropriate. It goes without saying that various methods such as current measurement can be applied. Further, although all the examples show the method using the DC power supply, the AC method may be used. In addition, it is natural that the instrument and the power source used in the present invention are provided with necessary accuracy, stability and the like.

In the valve or pump in the middle of the pipeline, there is a part where the inner surface is not covered, and when this is conducting to the metal pipe body of the pipeline, or when the ends of the pipeline are extended, the liquid in the pipeline is grounded. As a result, when this is conducted to the metal tube, the measurement may be disturbed. 6a, 6b,
FIG. 6c shows an embodiment provided with means for preventing measurement disturbance in such a case. In the figure, the same parts as those in the embodiment up to FIG. 5 are designated by the same reference numerals. 20, 20 'are bypass-grounded conduits, 21 and 21' are guard electrodes mounted between the grounding point and the measuring electrode 4 or 5, 22 is a power source, 23 is a variable resistor, and 24, 24 'are potentiometers. Is. The mounting positions of the guard electrodes 21, 21 'are not particularly limited,
It may be outside the electrodes 4 and 5 for measurement, but in order to effectively prevent disturbance, it is better to be close to the electrodes 4 and 5.

FIG. 6a shows the resistance r between the two electrodes 4 and 5 as in the embodiment shown in FIG.
_It shows a method of measuring ₀ = R ₀ .

Here, by adjusting the power supply 22 and the variable resistor 23,
By setting the guard electrodes 21 and 21 'to the same potential as the measurement electrodes 4 and 5, no current flows in and out of the electrodes 4 and 5, and measurement disturbance can be avoided.

FIG. 6b is based on the embodiment of FIG. 5 in that a predetermined current is made to flow between the two electrodes 4 and 5 and the potential difference between the electrodes 4 and 5 at that time is measured to determine the damaged position. To do. The setup to avoid measurement disturbance is the same as in Fig. 6a.

FIG. 6c relates to the measurement of R ₁ , R ₂ and R _S in the embodiment of FIG. In this case, the measurement electrodes are not guarded by the configurations shown in Figs. 6a and 6b, so that the electrodes 4,
5 is short-circuited and electrodes 21 and 21 'are short-circuited.
Here, if the potentials of the electrode pairs 21 and 21 'are made to coincide with the potentials of the electrode pairs 4,5, current will not flow in and out of the electrodes 4,5, and disturbance of measurement can be prevented. When the resistance between the short-circuited electrodes 4 and 5 and the terminal 6 is measured in this state, the measured resistance r ₃ is Has become. R ₁ and R ₂ are based on the measurement results by the method shown in Figs. 6a and 6b. Then, R _S is also identified. However, if the damage is small, R _S becomes dominant with respect to r ₃ , and r ₃ ≈ R _S
Can often be regarded as Therefore, the presence or absence of damage and the approximate size can be easily determined simply by measuring the resistance value r ₃ .

Incidentally, in FIG. 6b, the moving terminal 23a of the variable resistor is brought close to the guard electrode 21 'side in advance, and then the power source is turned on.
'When the equal adjustment to the voltage E ₀ of the power supply 17, if there is no damage to the coating, potentiometer 24, 24' 22 voltage E ₀ reaches to zero both at the same time the potentiometer 18 instruction value E is E = E ₀ = E ₀ ′. However, if there is damage, neither of the potentiometers 24, 24 'will be zero, and the indication of the potentiometer 18 will be E =
The value is below E ₀ ′. That is, it is also possible to make a setup in which the presence or absence of damage is first known by such an operation within the range of the potential difference measuring method, and then the damage position is identified.

The guard electrode 21 shown in FIGS. 6a, 6b and 6c or
The potential of 21 'may be adjusted manually, but by using a servo mechanism or a feedback mechanism, the measurement operation can be facilitated.

Up to now, the basic form in which 2 or 4 electrodes are installed on the pipeline has been described in detail, but a large number of electrodes are arranged in series on the pipeline at appropriate intervals, and the number of electrodes can be set to 2 depending on the situation of the pipeline.
It is also a practical aspect of the method of the present invention to sequentially carry out the method of the present invention by the electrode method or the four-electrode method.
In this case, about 10 joints (approx. 55 m) described above for the basic shape is also suitable for the electrode installation interval. When the flaw detection is attempted over the entire length of the pipeline in the above-mentioned manner, the damage existing in the section adjacent to the section under measurement may distort the data, but this may occur over the entire pipeline. It may be corrected by analyzing the series data. It is also effective to change the length of the measurement section instead. For example, if the measurement of a section yields data that is determined to be damaged, to determine whether it is due to damage within that section or due to damage within adjacent sections. There is a method such that the measurement section is widened and the measurement is performed again, or conversely, the measurement is first performed in the wide section and then in the narrow section.

As described above in detail, if the conventional wet pinhole detection technology is simply applied to the inner surface of the conduit, the damage level
Of course, the detection of position, even the detection of the presence or absence of damage,
In many cases, it will be accompanied by an error. Therefore, in detecting the position of damage, it is important to perform measurement and analysis using at least two electrodes and a tube terminal installed on the conduit as basic elements, based on the technical idea of the present invention. is there. In addition, even in the situation where the liquid in the pipeline is grounded on the extension of the pipeline, the presence or absence of damage and the position detection can be accurately detected based on the technical concept of the present invention by four electrodes (). It is essential to avoid misidentification of electrical specifications of the target pipeline by performing measurement and analysis with the inner two electrodes as the measurement electrodes and the outer two electrodes as the guard electrodes) and the tube terminals as basic elements. It will be.

In the present invention, the electrode arranged so as to come into contact with the liquid in the pipeline is not particularly limited in shape, size, mounting position, etc., and is electrically connected to the liquid in the pipeline while maintaining insulation with respect to the tubular body. It is arbitrary as long as it is one, and it is possible to incorporate it into the pipeline with various configurations. The example will be described below. 7 and 8 show an example in which an electrode is incorporated in a gasket that is attached to a flange connection portion, 30 is a gasket, 31 is a metal wire enclosed in the gasket, a conductor such as a metal plate, Reference numeral 32 is an external connection terminal connected to the tip of the conductor 31. A part 31A of the conductor 31 projects from a plurality of locations on the inner peripheral surface of the gasket to form a wetted outcrop. This gasket
By mounting 30 between flanges at the time of piping like a normal gasket, the conductor 31 is insulated from the flange by the gasket, and its liquid contact outcrop 31A is conducted to the liquid in the pipe. Therefore, the conductor 31 can act as an electrode. FIG. 9 shows that a conductor 36 such as a metal wire or a metal plate is arranged on the insulating coating 35 on the end face of the flange 34 at one end of the tube 33 so that a part of the conductor 36 forms a wetted outcrop 36A, and the sealing material is formed. 37 and gasket 38 are fixed with scissors. Further, FIG. 10 shows that an insulating coating 39 similar to the insulating coating on the inner surface of the tube is formed on the end surface of the flange 34 of the tube 33, and a conductor 41 such as a metal wire or a metal plate is provided in the coating 39. The portion is provided so as to be exposed inward to form the liquid contact outcrop 41A. In these structures, the conductors 36 and 41 act as electrodes, and since they are fixed to the flange 34, the mounting is extremely easy. FIG. 11 shows that an insulating member 46 is attached to the center of the seal ring 45 arranged inside the housing 44 of the victoric connector 43 that connects the pipes 42, 42 in the pipe axial direction. A conductor 47 such as a metal wire or a metal plate is arranged so that the inner end thereof is exposed inside the pipe to form a facility outcrop 47A. In this case also, the conductor 47 acts as an electrode. Although the above description shows the case where the electrodes are arranged at the connecting portions of the pipe body, it goes without saying that the electrodes may be arranged at arbitrary positions in the middle of the pipe body. Fig. 12 shows an example of such a case.
A socket 51 is provided at an appropriate position of 50, a conductor 53 serving as an electrode is attached through a sealing material 52 so that its lower end is exposed in the pipe, and an opening of the socket 51 is closed by a cap 54. Incidentally, 55 is an insulating coating. Of course, the electrodes can be arranged in sockets, branch pipes, tee pipes, etc. that are installed to measure temperature, flow velocity, pressure, etc.

In these electrodes, liquid contact with the electrodes may be performed at at least one point in the circumferential direction of the tube, but it is more preferable to arrange the liquid contact points continuously or isotropically in the circumferential direction. It is advantageous that the surface area of the wetted outcrop is large so that electrolytic polarization and wetted resistance can be reduced as long as it does not hinder the flow itself. For the material of the electrode, use one that is not easily attacked by the liquid in the pipe, at least for the contact surface of the liquid. Copper-nickel alloy, stainless steel, etc. are suitable for many liquids such as seawater. In addition, platinum, a platinum-plated material, or the like can be used for special purposes. Conductive resin (resin to which conductivity is added by adding conductive resin and conductive filler etc.)
Alternatively, ceramics (ceramics such as electrically conductive carbon, titanium boride, silicon carbide, titanium carbide, etc. or cermets compounded with fibers and metals) may be used.

When the method of the present invention is applied to a pipeline on the ground, it is only necessary to previously install the electrode group, but in the case of buried piping, piping in the underdrain, etc., wiring is carried out in advance from the pipeline to the ground. Is good. Further, if this wiring is integrated into a manhole, a handhole, etc., it is easy to detect flaws at any time. Furthermore, if the wires are integrated in one place and connected to a permanent device or to a computer for instructing measurement and processing data, it becomes easy to obtain the flaw detection information every moment. When performing remote wiring consolidation in this way,
Depending on the situation, it may be better to install an impedance converter, preamplifier, switch, etc. near the pipeline.

When the inner surface of the pipe is damaged by the method of the present invention,
Ideally, immediate repairs are ideal, but this may be difficult for operational or economic reasons. In consideration of such a situation, the charging electrode group and the wiring group provided for the purpose of flaw detection can be treated so that they can be switched at any time to the external power source type electrolytic protection. In this case, energization will take a long time, so
The electrode material should be more corrosion resistant. Normally, cathodic protection in pipelines is not often used because the effective distance is short, but in the pipelines to which the method of the present invention is applied, the insulation by the inner surface is effective, and especially corrosive liquids with large conductivity are used. Then,
The required anticorrosion effect can be obtained even with electrodes in relatively long intervals.

Hereinafter, the present invention will be described more specifically with reference to actual measurement data.

In a pipe line in which a flanged steel pipe with a nominal diameter of 150 mm and a single pipe length of 5.5 m, whose inner surface is covered with polyethylene with a thickness of 1 to 1.5 mm, is connected with bolts and nuts, two connecting parts that sandwich 10 single pipes A gasket shown in FIG. 7 in which a copper-30% nickel alloy wire having a diameter of mm was enclosed in neoprene rubber was loaded. In addition, the third single pipe from the upstream side has (a) undamaged inner surface coating, (b) 0.3 mm diameter penetration damage in the immediate vicinity of the downstream side, (c) 1 mm diameter damage, (D) The damage can be changed to 4 types with a diameter of 3 mm.

Next, the following measurements and calculations were performed while running tap water in such a way that the water in the pipeline entered and did not contact the outlet side.

The electrical resistance r ₀ between the upstream electrode and the downstream electrode was measured by an insulation measurement method (see FIG. 3).

Measure the electrical resistance r ₁ between the steel pipe body and the upstream electrode.

In Fig. 5, measure the interelectrode potential difference E ₀ with a potentiometer with an input impedance of 10 ⁹ Ω while energizing 0.1 mA between both electrodes.

While continuing to energize between the electrodes, measure the potential difference E ₁ between the steel tube and the upstream electrode. (Including correction of the self-potential difference between the electrode and tube) Calculate.

Estimate the wetted resistance R _S of the damaged part from R _S = r ₁ −R ₁ .

 The above experimental results are shown in Table 1.

Since the actual damage was at a position 16.5 m from the upstream electrode, it is clear from Table 1 that a minute damage can be detected with an error of 1 m or less, and the size of the damage can also be determined by the wetted resistance R _S. It will be.

〔The invention's effect〕

As described above, the present invention has two pipes separated in the longitudinal direction of the pipeline.
Electrodes are arranged at the points so that they come into contact with the liquid in the tube but are insulated from the tube, and terminals are connected to the tube, and the electrical characteristics such as resistance and potential difference between these electrodes and terminals are measured. By doing so, it is possible to correctly detect the damage on the inner surface of the pipeline, regardless of the presence or absence and the existing position, without the need for disassembling the pipeline or inserting a device into the tube as in the conventional case, and it is possible to quickly perform a simple operation. Can detect coating damage. As a result, it is possible to prevent corrosion and piercing accidents in various pipelines, and systematization makes a great contribution to the industry, such as confirmation of no damage leads to omission of unnecessary maintenance.

[Brief description of drawings]

FIG. 1 is a sectional view showing a conduit for explaining the principle of the present invention and electrodes and terminals attached thereto, and FIGS. 2 to 5 are sectional views schematically showing the embodiment of the present invention. Wiring diagrams, FIGS. 6a, 6b, and 6c are schematic side views and wiring diagrams of yet another embodiment, respectively, and FIG. 7 is a gasket provided with electrodes used in the practice of the present invention. FIG. 8 is a side view, FIG. 8 is a cross-sectional view thereof, and FIGS. 9 and 10 are cross-sectional views showing an end portion of a conduit provided with an electrode used for carrying out the present invention.
FIG. 11 is a cross-sectional view showing a victoric connector equipped with an electrode used in the embodiment of the present invention, and FIG. 12 is a cross-sectional view showing a state in which the electrode used in the embodiment of the present invention is mounted in the middle of a pipeline. Is. 1 ... Insulating coating, 2 ... Conductive tube, 3 ... Pipe line 4,5 ... Electrode, 6 ... Terminal, 7 ... Damaged part 10 ... Resistance meter, 11 ... Power supply, 12 ... … Resistance 13 …… Potentiometer, 14 …… Power supply, 15 …… Variable resistor 16 …… Galvanometer, 17 …… Power supply, 18 …… Potentiometer 21,21 ′ …… Guard electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideyuki Takamori 3-8-33 Shiritate, Tsurumi-ku, Yokohama (56) References JP-A-55-66747 (JP, A) JP-A-55-82959 (JP, A) ) Actual development Sho 58-165649 (JP, U)

Claims (6)

(57) [Claims] 1. Two points A, which are spaced from each other in the longitudinal direction of a conduit made of a conductive tube body (2) having an inner surface coated with an insulating coating (1),
Electrodes (4,5) are placed in B so that they are in contact with the liquid in the conduits but keep insulation from the conductive tubes, and terminals are taken from each electrode, and also in the conductive tubes (2). The terminal (6) is taken, and three kinds of terminal pairs which are combinations of three terminals respectively connected to the electrodes (4,5) and the conductive tube body (2), that is, between two electrodes (4-5) Measuring resistance of at least two terminal pairs between one electrode and a terminal of the conductive tube (4-6) and between the other electrode and a terminal of the conductive tube (5-6), Measure the resistance ratio or measure the potential difference with one of the three terminal pairs energized.
Distance l ₀ between the points of the electrodes (4,5), the distance l ₁ between the position and the one electrode of the pipe inner surface coating damage (4), the other electrode (5)
Presence of the coating on the inner surface of the pipeline by calculating the distances l ₁ and l ₂ from the proportional relationship between the distance l ₂ between the and and the resistance value, the resistance ratio or the potential difference value obtained in the above measurement, or the calculation result thereof. A method for detecting flaws on the inner surface of a pipeline, which is characterized by detecting the position. 2. The three terminal pairs (4-5), (4-
6) and (5-6) were measured, and from the measured values r ₀ , r ₁ , r ₂ obtained at each terminal pair, (However, The flaw detection method for coating the inner surface of a pipe line according to claim _1, wherein the distances l ₁ and l ₂ are obtained by a proportional relationship. 3. A variable resistor (1) is attached to the two electrodes (4,5).
Connect both ends of 5), and connect the movable split terminal (15b) of the variable resistor (15) and the terminal (6) connected to the tube body (2) through a galvanometer (16). , The galvanometer (1 with the power supply (14) connected to the two electrodes (4,5).
6) Adjust the variable resistor (15) so that the current passing through it becomes a minimum, and then use the proportional relationship between the ratio of the dividing resistance by the dividing terminals of the variable resistor and the distances l ₁ and l ₂ above. ₁ , l ₂
The flaw detection method for coating the inner surface of a pipe line according to claim 1, wherein 4. The three terminal pairs (4-) in a state where a power source (17) is connected to the two electrodes (4,5) and a constant current is applied.
5), (4-6), and (5-6) were measured for the potential difference, and from the measured values E ₀ , E ₁ , E ₂ obtained at the respective terminal pairs, The flaw detection method for coating the inner surface of a pipe line according to claim _1, wherein the distances l ₁ and l ₂ are obtained by a proportional relationship. 5. Two points A, which are spaced apart in the longitudinal direction of a conduit made of a conductive tube body (2) having an inner surface coated with an insulating coating (1),
In B, the measuring electrodes (4,5) are arranged so as to contact the liquid in the conduits respectively, but to keep the insulation from the conductive tubes, and terminals are taken from the electrodes, and the conductive tubes (2 ) Also has a terminal (6), and further, guard electrodes (21, 21 ') that come into contact with the liquid in the pipeline are arranged outside the two electrodes (4,5), and the guard electrodes (21, 21) are arranged. ′) Is made to match the potential of the measuring electrodes (4,5) on the side close to it, and in this state, a combination of three terminals respectively connected to the electrodes (4,5) and the conductive tube (2). 3 different terminal pairs,
That is, between the two electrodes (4-5), between one electrode and the terminal of the conductive tube (4-6), and between the other electrode and the terminal of the conductive tube (5-6) , For at least two terminal pairs, measuring the resistance, measuring the resistance ratio, or measuring the potential difference with one of the three terminal pairs energized, 2
Distance l ₀ between the points of the electrodes (4,5), the distance l ₁ between the position and the one electrode of the pipe inner surface coating damage (4), the other electrode (5)
Presence of the coating on the inner surface of the pipeline by calculating the distances l ₁ and l ₂ from the proportional relationship between the distance l ₂ between the and and the resistance value, the resistance ratio or the potential difference value obtained in the above measurement, or the calculation result thereof. A method for detecting flaws on the inner surface of a pipeline, which is characterized by detecting the position. 6. Two points A, which are spaced apart in the longitudinal direction of a pipe line made of a conductive pipe body (2) having an inner surface coated with an insulating coating (1),
In B, the measuring electrodes (4,5) are arranged so as to contact the liquid in the conduits respectively, but to keep the insulation from the conductive tubes, and terminals are taken from the electrodes, and the conductive tubes (2 ) Also has a terminal (6), and further, guard electrodes (21, 21 ') that come into contact with the liquid in the pipeline are arranged outside the two electrodes (4,5), respectively. Measuring electrodes (4,5) Comrade, 2
The two guard electrodes (21, 21 ') are short-circuited together, and the resistance between the measuring electrode pair (4,5) and the terminal (6) of the conductive tube (2) is measured to determine the conduit. A flaw detection method for a pipe inner surface coating, which comprises detecting the presence or absence of an inner surface coating damage and an approximate size.