JPS63153460A - Fault locating method for coating of inside surface of conduit - Google Patents

Abstract

PURPOSE:To exactly detect the damage of the coating in a conduit by providing an electrode brought into contact with an in-conduit liquid and insulated from a conduit body, on two points separated in the longitudinal direction of the conduit, and also, providing a terminal on the conduit body, and measuring an electric characteristic between these electrodes and the terminal. CONSTITUTION:In two points A, B being at an interval in the longitudinal direction of the conduit consisting of an electric conductive conduit body 2 in which an insulating coating 1 is performed to the inside surface, electrodes 4, 5 are placed so as to bring into contact with a liquid in the conduit but so as to keep the insulation to the electric conductive conduit body 2, respectively. On the other hand, a terminal 6 is provided on a suitable position C, as well, of the electric conductive conduit body 2. In this state, electric characteristics (electric resistance, potential difference) between the electrodes 4, 5 of the two points and the terminal 6 connected to the conduit body 2 are measured. Based on this measured value, whether a damage exists in the covering 1 of the inside surface of the conduit line or not and its location are detected correctly.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention detects whether or not there is damage to the inner surface coating of a pipe line that has been coated on the inner surface and its location without dismantling the pipe line.

The present invention relates to a method for detecting flaws on the inner surface of a pipe that can be detected from outside the pipe or from a remote location.

[Conventional technology]

The conventional method for detecting damage to the inner surface coating of pipes is to dismantle and investigate the pipes; other methods include:
A method of inserting a camera into the tube and observing it is now ready for practical use.

[Problem that the invention seeks to solve]

However, all of these conventional methods are time-consuming.

In particular, since it is necessary to scan the entire length and circumference of the pipe, it is extremely time-consuming and is not suitable for constant monitoring. Also,
The method using a camera requires an entrance for inserting the camera, and there are also restrictions on the tube diameter.

As a way to detect damage to the inner coating without dismantling the pipe, a single electrode is provided that comes into contact with the liquid inside the pipe.

A method of detecting the presence or absence of electricity between the electrode and the tube body is disclosed in Japanese Utility Model Application Publication No. 58-165649. However, the electrical conductivity between the electrode and the tube body is affected by the position and size of the inner coating damage, and it is not possible to simply measure the electrical conductivity between one electrode and the tube body as disclosed in the above publication. However, there was a fatal problem in that the location of the damage could not be identified.

Since damage to the inner surface coating is a serious problem that leads to corrosion and perforation of the pipe wall, it is desirable to discover the damage as soon as possible after it occurs, accurately identify the two parts, and repair it as soon as possible. For this purpose, it is necessary to conduct damage inspections frequently, and there is a strong need for a method that can easily inspect the entire pipeline.

The present inventors conducted various studies in view of the above situation, and as a result,
Discovered that it is possible to identify the presence or absence of damage to the coating and its location by utilizing the principle that the electrical resistance of the liquid in the pipe in the longitudinal direction of the pipe is proportional to the length of the pipe 2) Completed the present invention This is what I came to do.

[Means for solving problems]

The gist of the first invention of the present application is, as shown in FIG. , the electrodes 4 and 5 are arranged so as to contact the liquid in the pipe line but maintain insulation from the conductive pipe body 2, and the terminal 6 is also placed at an appropriate position C of the conductive pipe body 2. The electrical characteristics between the point electrodes 4, 5 and the terminal 6 connected to the tube body 2 are measured, and the presence or absence and location of pipe inner surface coating loss (jJ) is detected from the obtained electrical characteristics. The main feature lies in the flaw detection method for inner surface coating of pipes.

Furthermore, the gist of the second invention of the present application is, ``In the method of the second invention, furthermore, guard electrodes that are in contact with the liquid in the pipe are arranged on the outside of the two electrodes, and each guard electrode is arranged close to the guard electrode. Match the potential of the side measurement electrode,
In this state, measure the electrical characteristics between the two electrodes and the terminal connected to the tube body to detect the presence or absence and location of damage to the inner surface coating of the tube! There is a flaw detection method for inner surface coating of pipes using l\ image.

[Effect]

Because liquids generally have some conductivity.

Two points A and B on the pipe are electrically connected through the liquid. If the resistance of the liquid in the tube between A and B is R6, this resistance R is related to the specific resistance of the liquid in the tube, and the distance between A and B is 7! o
Furthermore, when a predetermined amount of current is passed between the electrodes 4.5, there is a potential difference (
E o ) occurs. On the other hand, if the inner surface coating 1 of the pipe is not damaged, it will not be electrically connected to the conductive pipe 2 above the liquid in the pipe, and therefore the electrodes 4 and 5 and the terminal 6 connected to the conductive pipe 2 will not be electrically connected. The resistance between the electrodes 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 Figure 2, if there is damage 7 at a position on the inner surface of the tube, the electrode 4 and the terminal 6 will be electrically connected through the liquid between AD and the tube between DC. Now, if the tube-internal fluid resistance between AD is R1, then this resistance R1 is the distance between AD #ff +
The resistance between the electrode 4 and the terminal 6 includes this liquid resistance R3. Similarly, if the liquid resistance between BD is R2, this resistance R2 is the distance between BD mf p 2
The resistance between the terminal 6 and the electrode 5 has a value that includes this liquid resistance R2. The resistance measured between the electrode 4 or 5 and the terminal 6 includes damage 7 in addition to the above R1 and R2.
The wetted resistance R8 is related to the magnitude of .

T? , , R, are included in series. Furthermore, when a current is passed between electrodes 4° and 5, there is a liquid resistance R3 between AD.
There is a potential difference (E, point) depending on the liquid resistance R between DB and
A potential difference (assumed to be 82) corresponding to 2L is generated, and the potential of the liquid at the D position appears at the terminal 6. Therefore, electrode 4.
5 and the terminal 6, and the above R, ,
By determining at least two values of P and R2 or their ratio, it is possible to detect the presence or absence and location of 18.1g on the inner surface of the pipe. Also, the potential difference E is used instead of the resistance. , E, and R2 or their ratio can also detect the presence or absence and location of an I-slip. Note that it is also possible to know the extent of damage by determining the above-mentioned liquid contact resistance R3.

By the way, when measuring the electrical characteristics between the electrodes 4, 5 and the terminal 6 mentioned above, the liquid in the pipe is conducted to the conductive pipe via a valve, pump, etc. located on the extension of the measurement point. In that case, a current flows from the electrode 4.5 through the fluid in the pipe to the valve or pump, which may cause disturbances in measurement. ), as shown in the embodiment of FIG. 6c, the electrode 4
, 5 are arranged outside the guard electrodes 21.21', and keep the potential thereof the same as that of the electrodes 4.5.

This makes it possible to prevent disturbances in measurement.

The pipe line to which the flaw detection method of the present invention can be applied is a metal pipe body coated with an insulating material on the inner surface, which is connected with a flange or a rick-type connector, or by welding, and then the welded part is connected. These pipes are designed so that the metal pipe does not conduct to the liquid inside the pipe, such as a pipe whose inner surface has been repaired, or a pipe whose inner surface is continuously coated after laying a metal pipe. Furthermore, detection of perforations in conduits made of insulating non-metallic pipes reinforced or shielded with conductive fibers or wires can also be applied to the flaw detection method of the present invention. It corresponds to an insulating coating on the inner surface, and corresponds to conductive fibers, wires, or conductive tubes for reinforcing or shielding.

Although the distance between the electrodes 4 and 5 arranged in the pipe depends on the pipe diameter and the conductivity of the liquid in the pipe, it is sufficient to measure the distance approximately before and after the IO joint (approximately 65 m). In this case, it is desirable that the tubes located between the electrodes be electrically connected to each other across the joint portion. According to a normal piping method, the metal tubes will naturally conduct to each other, but in the unlikely event that there are insulated locations, it is sufficient to temporarily short-circuit the insulated locations and perform the measurement. Moreover, instead of this, the metal tubes on both sides of the insulating location may be targeted and the measurements may be performed separately.

The terminal 6 attached to the conductive tube 2 is a terminal for measuring the internal potential of the damaged portion of the inner surface coating and the liquid resistance up to the electrode, as described above. Generally, conductive pipes used for pipes are metal pipes, and their conductivity is much higher than that of the liquid inside the pipe. Well, from the point of view of minimizing noise,
It is best to take it from the metal tube between the two electrodes.

The flaw detection method of the present invention can be applied to any liquid that provides electrical continuity in the direction along the pipe.

Seawater, freshwater, tap water, pure water, gray water, sewage, aqueous drug solutions.

Examples include earth and sand slurry and polar organic liquids. The liquid in the pipe may be in a flowing state, in a static state full of water, or in a state in which there is a continuous liquid film only on the pipe wall.

〔Example〕

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

FIG. 2 shows a first embodiment of the present invention, and 10 is a resistance meter. 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 4.5 are each directly measured using a resistance meter 10.

Here, the measured resistance between electrodes 4.5 is r. .

If the resistance measurement value between electrode 4 and terminal 6 is rl + the resistance measurement value between electrode 5 and terminal 6 is r2, then the resistance of tube body 2 from the damage position to terminal 6 is compared to the liquid resistance. Because they are so small, these resistance measurements have the following relationship to the liquid resistance in the tube (both anti- and tangential): That is.

T o = Ro = R+ +R2r, =R,
+R.

r2 = R2 → R3 Therefore, this liquid contact resistance R,, is.

Moreover, the liquid resistance R6, R,, R2 is the distance ρ. ,l,.

Because it is proportional to 12.

z、　　jl! , β2 becomes. This can be expressed using resistance measurements.

A, i', 7!2.

Therefore, as mentioned above, measure the resistance between each electrode 4, 5 and terminal 6, and calculate the wetted resistance R3 from the above formula (1).
Next, the distance C1°12 to the covered injury can be determined from equation (3).

Here, since the liquid contact resistance R5 is a value related to the opening size and the depth of the dent (ie, the coating thickness) of the coating damage, it is also possible to detect the magnitude of the damage from this liquid contact resistance.

In addition, in equation (3) of item 1, if the wetted resistance is small compared to the measured resistance value.

(l o f I If 2 approximately holds true. In this case, the measured resistance value rQ+rl+
It is not necessary to measure all of r2, but by measuring two of them, 7! with 10 as the standard! ,.

12 can be found.

By the way, in this method, the resistance value including the liquid resistance and the wetted resistance is measured, and the position of the damage is determined from the resistance value. However, as the opening size of the coating damage becomes smaller, the wetted resistance R5 becomes smaller. The resistance increases rapidly, and the liquid resistance falls within the error range. Therefore, when the damage is small, the error in detecting two positions increases, and this method cannot be said to be optimal for identifying the damage position.

On the other hand, the above method is extremely useful for detecting the presence or absence and magnitude of damage, since the measurement results include the magnitude of the electrical conductivity of the damaged coating portion 7. That is, in this measurement, if the resistance between the terminal 6 and the electrode 4 or 5 is infinite (more than a specific value), no tJQ (g is proven).

FIG. 3 shows a second embodiment of the present invention, in which a power supply 11. Resistance 12. A potentiometer 13 is connected as shown, and the resistance between the electrode 4 and the terminal 6 is measured by an insulation measurement method. Similarly, it is also possible to measure the resistance between the terminal 6 and the electrode 5 and the resistance between the electrodes 4 and 5. In the case of this embodiment as well, by measuring the resistance between each terminal as in the case of the second embodiment, it is possible to detect the presence or absence, size, and position of damage to the coating. In this case as well, if the wetted resistance is significantly larger than the liquid resistance in the tube, the liquid resistance in the tube will fall within the error range, so similar to the first embodiment, such resistance measurement It is difficult to say that this method is optimal for identifying damage locations.

FIG. 4 shows a third embodiment of the present invention, in which the ratio of resistance between the terminal 6 and each electrode 4, 5 is simultaneously measured by a bridge method. 14 is a power supply, 15 is a variable resistor with a ruler, and a resistor 15a
, a divided terminal 15b that slides on the resistor, and a ruler 15C that indicates the position of the divided terminal 15b. , 16
is a galvanometer. In this embodiment, the electrodes 4,
Apply an appropriate potential between terminals 1 and 5 of divided terminal 1 of variable resistor 15.
5b on the resistor 15a to adjust the current between the divided terminal 25b and the terminal 6 to be minimum, and read the resistance on the left and right from the position of the divided terminal 15b at that time.

Here, the overall resistance of the resistor 15a is r. The resistance component on the electrode 4 side from the 7-divided terminal 15b is r1, and the resistance component of 21 to 1 is r2'.

R7 Because it is.

1! oA, 412 approximately holds true. This makes it possible to detect the presence or absence of coating damage and its location. In this method, errors due to the liquid contact resistance R, . are unlikely to occur.

In addition, in this method, if there are multiple damages between the two electrodes, for example, the two outermost damages are short-circuited with a metal tube, and the damage is measured as if it were a single point. the distance l,' from the other electrode to the outermost damage on that electrode side, and the distance I22 from the other electrode to the outermost damage on that electrode side.
′ relationship.

1, ' n, ' 12 ' (however, ρ.l, [, l + β2'). That is, here, 10' is an unknown quantity, and the true /,',A2' cannot be determined based on this. Therefore, in order to identify +'O', it is necessary to add an operation to determine the intra-tube liquid resistance between the two electrodes under the above situation.

However, the above method, like the first embodiment and the second embodiment,
It has the advantage that the purpose can be achieved with a simple instrument.

FIG. 5 shows a fourth embodiment of the present invention, in which 17 is a power source and 18 is a potentiometer. In this embodiment, a voltage #17 is connected to the electrode 4°5 and a constant current i is applied. Through the potentiometer 1
At step 8, the potential difference between terminal 6 and electrode 1, between end 7-6 and electrode 5, between electrodes 4 and 5, etc. is measured. Here 7 electrodes 4
．． The potential difference measured between 5 and E. 2. If the potential difference measured between the terminal 6 and the electrode 4 is El, and the potential difference measured between the terminal 6 and the electrode 5 is E2, then between these.

Eo E+ E2 7! +1 1! , β2 holds true. Therefore, the above potential difference E. .

By measuring at least two of E+ and E2, the position of the damaged part can be detected.

If the potentiometer used here has a high input impedance, the influence of the wetted resistance of the damaged part can be avoided.

The input impedance required for a meter varies depending on the pipe diameter, the conductivity of the liquid in the pipe, etc., but a meter of 109 to 10 Ω is suitable for most applications. In order to ensure accuracy in potential measurement, it is desirable to first correct the natural potential difference based on the material difference between the inserted electrodes 4 and 5 and the metal tube body 2.

The natural potential difference ΔE to be corrected can be determined using, for example, E obtained by measuring two electrodes with opposite polarity, and E2'. Next, although it would be sufficient to correct the influence of electrolytic polarization on the two electrode surfaces, it is also possible to omit the correction by minimizing the ratio of one polarization voltage to the potential drop in the tube liquid by selecting the applied current. Also, the current i. Electrode 4
, 5, but instead from another pair of electrodes placed between the electrodes 485, there will be no polarization at the electrodes 4.5.

According to this embodiment, even if there are multiple ID scratches, the total distance from the outermost damage to the two electrodes, ρ I,=,2. ′
+p2'?

Since it can be easily identified as po' ρ0, the area where a plurality of damages exist can be accurately identified.

As described above, two electrodes 4.
Although different methods of measuring the electrical characteristics between terminal 5 and terminal 6 have been shown, the present invention is not limited to these methods.
These methods may be combined as appropriate, and it is needless to say that various other methods such as potential difference regulation and current measurement are also applicable. Furthermore, although all of the embodiments have shown systems using a DC power source, an AC system may also be used. Note that it is a matter of course that the instruments and power supply used in the present invention have the necessary accuracy, stability, etc.

If there is a part of a valve or pump in the middle of a pipe that is not coated on the inside and it is connected to the metal pipe body of the pipe, or if the liquid in the pipe is connected to the ground at both ends of the pipe. As a result, if this is electrically connected to a metal tube, measurement may be disturbed. FIGS. 6a, 6b, and 6cpJ show an embodiment equipped with means for preventing measurement disturbances in such cases. In the drawings, parts that are the same as those in the embodiments up to FIG. 5 are designated by the same reference numerals. 20. 20' is a pipeline to be bypass grounded, 2
1.21' is a guard electrode installed between the ground point and the measurement electrode 4 or 5, and 22 is a power supply.

23 is a variable resistor, and 24.24' is a potentiometer.

The mounting position of the guard electrodes 21, 21' is not particularly limited.

It may be located outside the measurement electrodes 4.5, but it is better to be closer to the electrodes 4 and 5 in order to efficiently prevent disturbances.

FIG. 6a shows a method of measuring the resistance r0=R0 between two electrodes 4.5, similar to the embodiment shown in FIG.

Here, by adjusting the voltage tX22 and the variable resistor 23, the guard electrodes 21 21' are set to ff,
, 5, the current will not flow outside the electrodes 4.5, and disturbances in measurement can be avoided.

FIG. 6b shows the gap between the two electrodes 4 and 5 according to the embodiment shown in FIG.
4. A predetermined current is passed through the electrodes 4, 5 and the terminal 6.
The purpose is to measure the potential difference between them and find the loss (p position).The steps to avoid disturbances in measurement are the same as in the case of Fig. 6a.

FIG. 6C shows R+ and R2 in the embodiment of FIG.

This relates to the measurement of R3. In this case, Fig. 6a.

Since the measurement electrodes are not guarded by the arrangement shown in FIG. 6b, the electrodes 4.5 and 21.about.21' are short-circuited. If the potential of the electrode pair 21.degree. 21' is made to match the potential of the electrode pair 4.5, no current will flow in or out of the electrode 4.5. The resistance r measured by this configuration is R1+R2. R, 42Hj Based on the measurement results by the method shown in Figures 6a and 6b.

El　　　　　　　　　　E2 E, E.

This also identifies R3. but.

If the damage becomes large, R3 becomes dominant over +R3 and can often be regarded as +R3''R3.Therefore, by measuring the resistance value r3, the presence or absence of damage and its approximate size can be easily determined. be able to.

In addition, in Fig. 6b, there is a movable terminal 23 of the variable resistor.
a to the guard' electrode 21' side in advance.

Next, the voltage E0' of the power source 22 is changed to the voltage E of the power source 17. If the coating is undamaged, the potentiometer 2
4.24' both reach zero, and at the same time the indicated value E of the potentiometer 18 becomes.

E""Eo -Eo'. However, if there is damage, two potentiometers 24, 24
' are not zero, and the value indicated by the potentiometer 18 is less than E - Eo '. That is, such operations within the scope of the potentiometric measurement technique result in increased losses (
It is also possible to identify the damage position after knowing the presence or absence of g.

Guard electrode 21 in FIGS. 6a, 6b, and 6c
Alternatively, the potential adjustment of 21' may be done manually,
The measurement operation can be facilitated by using a configuration using a servo mechanism or a feed hack mechanism.

Up to now, we have described in detail the basic form in which two or four electrodes are installed on the pipe, but it is possible to install a large number of electrodes in series at appropriate intervals on the pipe, depending on the situation of the pipe. te2
Of course, it is also a practical embodiment of the method of the present invention to sequentially carry out the method of the present invention using the electrode method or the four-electrode method.

The electrode installation spacing in this case is also 10 as described above for the basic type.
Around the joint (approximately 55rn) is appropriate. When attempting to conduct a search8 over the entire length of a pipe in the manner described above, damage present in the section adjacent to the section being measured may distort the data; This can be corrected by analyzing series data over . Alternatively, it is also effective to change the length of the measurement section. For example, when measuring 3L in a certain section, data is obtained that indicates that there is an injury.

To determine whether the error is due to damage in that section or an error due to tel (g) in an adjacent section, you can widen the measurement section and measure again, or conversely, first measure in a wide section. There are methods such as conducting measurements in a narrow area after that.

As detailed above, if the conventional wet pinhole detection technology is simply applied to the inner surface coating of pipes, it will not be possible to detect even one position of damage, and in many cases, it will not be possible to detect even the presence or absence of damage. This will involve errors. Therefore, in order to detect the position of damage, it is crucial to perform measurement and analysis using at least two electrodes installed on the pipe and the pipe terminal as basic elements based on the technical concept of the present invention. be. Furthermore, even in a situation where the liquid in the pipeline is grounded on the extension of the pipeline, two-position detection of the presence or absence of damage without error is possible based on the technical idea of the present invention.

4 electrodes placed on the pipe (the inner two electrodes are the measurement electrodes.

Measurement and analysis should be performed with the outer two electrodes as guard electrodes and the tube terminal as the basic elements.From this, it is essential to avoid misidentification of the electrical specifications of the target tube.

In the present invention, the electrodes arranged so as to be in contact with the liquid in the pipe are not particularly limited in terms of shape, dimensions, mounting position, etc. ! It is possible to incorporate it into the conduit in two different configurations. An example will be explained below. Figures 7 and 8 show an example in which the electrode is incorporated into a gasket attached to the flange connection part, and the electrode is attached to the flange connection part.
3 is a gasket, 31 is a conductor such as a metal wire or a metal plate sealed therein, and 32 is an external connection terminal connected to the tip of the conductor 31. A portion 31A of the conductor 3I protrudes from a plurality of locations on the inner peripheral surface of the gasket to form a wetted outcrop. By installing this gasket 30 between flanges during piping in the same way as ordinary gaskets 1~, the conductor 31 is insulated from the flange by the gasket, and its wetted outcrop 31△ is conducted to the liquid in the pipe. Therefore, two or two λq electric bodies 31 can act as electrodes. In FIG.

A conductor 36 such as a metal plate is arranged so that a part thereof forms a wetted outcrop 36A, and a sealing material 37 and a gasket 38 are placed.
It is fixed with scissors. In addition, Fig. 10 shows the pipe body 3.
An insulating coating 39 similar to the insulating coating on the inner surface of the tube is formed on the end face of the flange 34 of No. It is provided so as to form a liquid contact outcrop 41A. In these structures, the conductors 36, 41 act as electrodes, and since they are fixed to the flange 34, installation is extremely easy.

FIG. 1I shows an insulating member 4 at the center in the axial direction of a seal ring 45 disposed within the housing 44 of the Victorique type connector 43 that interconnects the tubes 4, 2, 42.
6 is attached thereto, and a conductor 47 such as a metal wire or a metal plate is arranged therein so that its inner end is exposed inside the tube to form a liquid exposure tube 47A. In this case as well, the conductor 47
acts as an electrode. In all of the above cases, the electrodes are disposed at the connecting portion of the tube, but it goes without saying that the electrodes may be disposed at any arbitrary position in the middle of the tube. 12th
1ffl shows an example of that case.

A socket 51 is provided at an appropriate position in a tube body 50, a conductor 53 serving as an electrode is attached via a sealing material 52 so that its lower end is exposed inside the tube, and the opening of the socket 51 is closed with a cap 54. . Note that 55 is an insulating coating. Of course, sockets and branch pipes are installed to measure /IA degree, flow rate, pressure, etc.

Electrodes can also be placed in a tee tube or the like.

Regarding these electrodes, it is sufficient that the electrodes are brought into contact with liquid at at least one point in the circumferential direction of the tube, but it is more preferable that one point of contact with liquid is arranged continuously or equidistantly in the circumferential direction.

As long as the surface area of the liquid contacting outcrop does not impede the flow itself, it is advantageous that the surface area of the liquid contacting outcrop is larger because it can reduce electrolytic polarization and liquid contact resistance. The material of the electrode should be 2 at least for the wetted outcrop.

Use a material that is not easily attacked by the liquid inside the pipe. Copper-2-Nokel alloys, stainless steel, etc. are suitable for saltwater ponds and many liquids. Furthermore, platinum, platinum plating material, etc. can also be used for special purposes. Conductive resins (resins that are made conductive by adding conductive resin and conductive fillers) and ceramics (carbon, titanium boride, silicon carbide, titanium carbide that are themselves conductive) Molded objects, fibers and metals such as !: composites, knots, etc.)
You may also use

When applying the method of the present invention to above-ground pipes, it is sufficient to simply install the electrode group in advance;

In the case of underground piping, it is best to run the wiring from the pipe to the ground level in advance. Furthermore, if this wiring is consolidated into manalls, handballs, etc., flaw detection can be easily performed at any time. Furthermore, the wiring can be consolidated in one place.

If it is connected to permanently installed equipment or to a computer that instructs measurements and processes data, it becomes easy to obtain instant flaw detection information. When performing remote wiring aggregation in this way, it may be better to install impedance converters, standby amplifiers, switching devices, etc. near the conduits depending on the situation.

When damage is observed to the tube inner coating by the method of the present invention.

Ideally, immediate repairs should be carried out, but this may be difficult due to operational or economic reasons. In consideration of such circumstances, it is also possible to take measures such that the inserted electrode group and wiring group provided for the purpose of flaw detection can be switched to externally powered cathodic protection at any time. In this case, the current will be turned on for a long time, so 2.
It is better for the electrode material to be more corrosion resistant.

Normally, cathodic protection inside pipes is not frequently used because the effective distance is short, but insulation with inner coating is effective for pipes targeted by the method of the present invention, especially for corrosive corrosion with high conductivity. In the case of liquids, the necessary anticorrosion effect can be obtained even with relatively long electrodes.

The present invention will be explained in more detail below using actual measurement data.

Two flanged steel pipes with a nominal diameter of 15 (1 m, single pipe length 5.5 rn) whose inner surfaces are coated with polyethylene with a thickness of 1 to 1.5 fi are connected with bolts and nuts, and 110 single pipes are sandwiched between them. A gasket shown in Fig. 7, which is a 0.5+U diameter copper-30% nickel alloy wire encapsulated in neoprene rubber, was inserted into the connection part.In addition, the third single pipe from the 2 upstream side has an inner surface coated with fa). (b) There is penetrating damage with a diameter of 0.31 m immediately on the downstream side. (C) There is damage with a diameter of 1 m.

FDL damage can now be replaced with 4 types of 311 diameter ones.

Next, the following measurements and calculations were performed while running tap water through this pipe in such a way that the water inside the pipe did not touch people or the ground on the outlet side.

■Electrical resistance r between the upstream electrode and the downstream electrode. was measured using the insulation measurement method (see Figure 3).

■Measure the electrical resistance r1 between the steel pipe body and the upstream electrode.

■ In Figure 5, while applying a current of 0.1 mA between the two electrodes, the potential difference E between the electrodes was measured using a potentiometer with an input impedance of 109Ω. Measure.

■Measure the potential difference E1 between the steel pipe body and the upstream electrode while continuing to apply electricity between the electrodes. (Including correction of natural potential difference between electrode and tube body) ■ Calculate El x, = 55X□.

E.

■ El L -r 6 X, R5-r 1 Rl
E.

Estimate the wetted resistance R5 of the damaged part.

The above experimental results are shown in Table 1.

Table 1 The actual damage was located 16.5 m from the upstream electrode, so as is clear from Table 1, minute damage can be detected with an error of less than 1 m, and the damage can be determined by the wetted resistance Rs. This means that the size can also be determined.

〔Effect of the invention〕

As described above, one aspect of the present invention is to arrange electrodes at two points separated in the longitudinal direction of a pipe so as to contact the liquid in the pipe but to be insulated from the pipe body, and to connect a terminal to the pipe body.

Damage to the inner surface coating of the conduit can be detected by measuring electrical characteristics such as the resistance 2 potential difference between these electrodes and terminals.

It is possible to accurately detect the presence and location of the pipe, and there is no need to disassemble the pipe or insert equipment into the pipe, as is the case with conventional methods, and early damage to the sheathing can be discovered with a simple operation. As a result, it will be possible to prevent corrosion and perforation accidents in various pipelines, and systemization will make it possible to confirm that there is no damage and eliminate unnecessary maintenance, making a significant contribution to industry.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing a conduit, electrodes and terminals attached thereto for explaining the present invention in detail, and FIGS. 2 to 5 are a cross-sectional view of the conduit and schematically showing an embodiment of the present invention, respectively Wiring diagrams, Figures 6a, 6b, and 6c respectively schematically show a side view of a conduit and a wiring diagram of further embodiments, and Figure 7 shows a gasket with electrodes used in carrying out the present invention. 5 is a side view of 5. FIG. 8 is a sectional view thereof, FIGS. 9 and 10 are sectional views each showing the end of a conduit equipped with electrodes used in carrying out the present invention, and FIG. FIG. 12 is a cross-sectional view showing a state in which the electrode used in carrying out the present invention is installed in the middle of a conduit. 1- Insulating coating 2- Conductive tube 3- Conduit 4.5
- Electrode 6 - Terminal 7 - Damaged part 1 o - = = Resistance meter 11 - Power supply I2 - Resistor 13 - Potentiometer 14
Power supply 15-variable resistor 16-galvanometer 17-power supply 18-potentiometer 21. 21'-guard electrode agent Patent attorney Kyo Matsu 31B D +sb (1st) 5]5c5,. Figure 5 Fang 6a Fig. 7 Fig. 48 Fig. f 97 Fig. 10 Fig. Fang]] Fig. 12 Fig.

Claims (6)

[Claims] (1) Two points spaced apart in the longitudinal direction of a conduit consisting of a conductive tube with an insulating coating on its inner surface, each in contact with the liquid in the conduit but maintained insulated from the conductive tube. By placing electrodes on the conductive pipe and also connecting terminals to the conductive pipe, measure the electrical characteristics between the two electrodes and the terminal connected to the pipe to determine whether or not there is damage to the inner surface coating of the pipe and where it exists. A flaw detection method for inner surface coating of pipes, characterized by detecting flaws. (2) The inner surface of the pipe according to claim 1, characterized in that the electrical resistance between each of the two electrodes and the terminal is measured, and the location of damage to the inner surface coating of the pipe is determined from the resistance value. Method of testing coatings. (3) Connect a variable resistor in parallel with the two electrodes to form a bridge circuit, connect a power source to the two electrodes, and detect the movable split terminal of the variable resistor and the terminal connected to the tube body. A variable resistor is connected through a current meter, and the variable resistor is adjusted so that the current passing through this galvanometer is minimal. At that time, the location of damage to the inner surface coating of the pipe is determined from the ratio of the divided resistances by the dividing terminal of the variable resistor. 2. A flaw detection method for a pipe inner surface coating according to claim 1, which comprises detecting. (4) Connect a power source between the two electrodes to flow a constant current,
The pipe line according to claim 1, characterized in that a potential difference between the two electrodes and a terminal connected to the pipe body at that time is measured, and the location of damage to the pipe inner surface coating is detected from the potential difference. Inner coating flaw detection method. (5) Two points spaced apart in the longitudinal direction of the conduit consisting of a conductive tube with an insulating coating on its inner surface, each in contact with the liquid in the conduit but maintained insulated from the conductive tube. A measurement electrode is placed on the conductive pipe, and a terminal is also provided on the conductive pipe body. Furthermore, guard electrodes that contact the liquid in the pipe are placed on the outside of the two electrodes, and each guard electrode is placed on the side near it. Match the potential of the measurement electrode, and in this state perform the step 2 above.
1. A flaw detection method for inner surface coating of a pipe, comprising: measuring electrical characteristics between a point electrode and a terminal connected to a pipe body, and detecting the presence or absence and location of damage to the inner surface coating of the pipe. (6) Among the electrodes, two measurement electrodes and two guard electrodes are short-circuited together, and the resistance between the measurement electrode pair and the terminal connected to the tube is measured and the resistance is measured on the inner surface of the tube. 6. A flaw detection method for a pipe inner surface coating according to claim 5, wherein damage to the coating is detected.