KR20020092009A - Internal metal pipe inspection apparatus having centralizer - Google Patents

Abstract

PURPOSE: An underground metal pipe inspection apparatus is provided to reduce noise of obtained signal and achieve improved accuracy of inspection, by allowing the axis forming centers of an exciter and a detector to be coaxial with the internal central axis of the pipe. CONSTITUTION: An underground metal pipe inspection apparatus, comprises an amplifier power module(100) having a housing(110) and a battery mounted within the housing; a flexible unit(200) arranged into a predetermined length, at both sides of the amplifier power module, which is bent or stretched in accordance with the bending direction of the pipe; an exciter module(300) having a housing(310) arranged at an end of the flexible unit, and an exciter mounted within the exciter module so as to generate an AC magnetic field; a detector module(400) having a housing(410) arranged at the other end of the flexible unit, a detector for detecting the AC magnetic field generated from the exciter module, and an amplifier for amplifying the signal detected by the detector and transmitting the amplified signal to a computer; and a centralizer(500) arranged outside the exciter module and the detector module, which controls the axis forming centers of the exciter module and the detector module to be coaxial with the internal central axis of the pipe.

Description

INTERNAL METAL PIPE INSPECTION APPARATUS HAVING CENTRALIZER}

The present invention relates to a device for inspecting underground buried metal pipes having a centralizer for inspecting abnormality of metal pipes buried underground, and more particularly, to the inside of a pipe irrespective of the change in the inner diameter of the pipe or the formation of the curvature of the pipe. It is possible to smoothly run, and to provide an inspection device for underground buried metal pipe with a centralizer to make the axis of the exciter and detector at the time of driving coaxial with the central axis inside the tube.

In general, many pipes are buried underground, such as water and sewage pipes, city gas pipes, and petrochemical plant pipes. If such pipes are damaged, they lead to direct disaster.

Therefore, it is essential to understand the pipe condition in terms of maintenance and repair of underground pipes, and various inspection methods have been developed and used. Such inspection methods include magnetic flux leakage inspection, remote field eddy current inspection, visual inspection, and ultrasonic inspection. There are inspections, etc., and it adopts and uses inspection methods that are suitable for pipe use and geometry.

For example, the magnetic flux leakage test method is used for large diameter pipes such as long-distance gas pipes or subsea pipes. For heat exchanger tubes installed in petrochemical plants or factories, eddy current inspection method or solid state imaging device (CCD) is used. ; Charge Coupled Device) Visual inspection using a borescope with camera and light source is used.

In the case of a water supply pipe, the inside of the pipe is mortar-lined, and corrosion products are attached to the pipe wall. Therefore, the ultrasonic test method or the magnetic flux leakage test method, which can be inspected only when the detector contacts the pipe wall, cannot be used. Observable visual inspection methods do not check the corrosion of the pipes on the outer wall of the pipes.

Therefore, a remote field eddy current test is used to check for defects caused by corrosion or mechanical wear in the water supply pipe.

The remote field eddy current inspection method is an electromagnetic non-destructive testing method using the through wall transmission characteristic of the remote field eddy current energy that has been discharged from the exciter after passing through the tube wall, flowing a certain distance along the outer wall, and then flowing back into the tube. As a kind, when a low frequency alternating current passes through an exciter having the same axis as the pipe inside the conductive pipe, a magnetic field is formed.

This magnetic field is generated by the exciter according to the way the pipe shaft flows and overcomes the direct magnetic field and skin effect that rapidly attenuates along the pipe axis by the action of the eddy current generated inside the conductive pipe wall near the exciter. The magnetic field that penetrates the adjacent pipe wall and reaches the outside of the pipe is divided into a remote field that passes through the axial distance of the pipe back into the pipe, which is larger than the rapidly attenuated direct field. The abnormality of the pipe is determined by measuring the signal emitted from the detector coil located inside the pipe near the remote field.

The device used in the remote field eddy current test method is mainly pushed from the back by using the rigidity of the cable.In order to level the injected test device, wires with elastic force are installed at regular intervals, or flexibility is provided. It is formed of a material such as PVC having a structure having a comb-tooth shape having an inner diameter slightly smaller than the outer diameter of the pipe.

In order to apply the remote field eddy current test method to the water supply network inspection, the remote field eddy current signal should be examined.

The alternating magnetic field can be measured by winding a coil or using a hall sensor, etc. The remote field eddy current signal is the magnitude of the induced electromotive force measured by a detector located two to three times the diameter of the exciter. The magnitude of the induced electromotive force is proportional to the dot product of the coil wound and the area vector of the coil enclosed area and the frequency of the magnetic field and the magnetic flux density vector passing vertically through the area.

Therefore, when the center of the coil to be detected is out of the central axis of the pipe or the axis of the coil does not coincide with the central axis of the pipe, the inner product of the coil area vector and the magnetic flux density vector are different. The intensity of induced electromotive force varies.

That is, if there is no defect and the axis forming the detection coil is outside the central axis inside the pipe, the signal does not change much.However, if there is a partially existing defect, the strength of the magnetic field increases as the distance from the defect occurs. By summing up the magnetic field coming in through the missing pipe, it mitigates the change in the magnetic field caused by the defect, so if the detector moves away from the central axis of the pipe and away from the defect, the correct signal cannot be obtained.

Therefore, in the remote field eddy current inspection method, not only the center of the inspection apparatus should be located at the inner center of the pipe, but also the axis forming the center of the inspection apparatus should coincide with the central axis of the pipe in order to reduce the error of the inspection result.

As described above, the pipe inspection apparatus used in the conventional remote field eddy current inspection method will be described with reference to the accompanying drawings.

1 is a view for explaining a pipe inspection device of US Pat. No. 5,567,525 as a prior art, the pipe inspection device having a size corresponding to the inner diameter of the pipe and a plurality of housings moving along the path of the pipe ( 12, 14, and 16, and the plurality of housings 12, 14, and 16 each have a sphere or oval shape to prevent blockage in a bent conduit and to block fluid from entering the interior. It is sealed.

One housing 14 of the plurality of housings 12, 14, and 16 is provided with a detector (not shown) inside, and three centralizers 17 are provided on the outside, so that the pipe inspection device moves the pipe when the pipe is moved. Make sure that the center of the inspection device is aligned with the inner center of the pipe.

The plurality of housings 12, 14, 16 are connected to each other by a cable 18 or a flexible tube 20 so that the pipe inspection apparatus can be freely bent, and the housing 12 and the housing 14 are located inside the tube 20. The electric wire 22 connected between the () is installed.

In addition, the housing 12 located on the rear side is provided with a flexible tube 28 connected to the ground, and the electric wire 26 connected to the housing 12 is provided inside the tube 28.

However, such a conventional pipe inspection device is configured to pass through the curved pipe, and the center of the detector is located in the center of the pipe, but the axis forming the center of the detector is the central axis of the inside of the pipe There is no way to make it coaxial with.

The centering device of the endoscope of US Pat. No. 5,535,331 and the centralizer of the pipe inspecting apparatus of US Pat. No. 5,329,824 are the prior art pipe inspecting apparatus of US Pat. Although it is the same as the method of using the elastic force and the rigid wire, it is difficult to apply to the remote field eddy current inspection method with a relatively high filling rate.

In addition, Korean Patent Application No. 1998-49225, "Mobile robot for internal inspection of pipes," is designed so that two links are operated by springs independent of each other, so that the axis of the moving device can deviate from the axis of the pipe due to the connection structure of the links. I have a problem.

The present invention is to solve the above-mentioned conventional problems, an object of the present invention can run smoothly inside the tube irrespective of the change in the inner diameter of the tube or the curvature forming portion of the tube, and the center of the exciter and detector when running Underground buried metal piping with a centralizer that not only coincides with the internal center of the sensor, but also the axis of the exciter and detector is coaxial with the central axis inside the tube, reducing the noise of the acquired signal and performing accurate detection. To provide a test device for.

The present invention for realizing such an object comprises: an amplifier power supply module for supplying power by forming a housing in the center and mounting a battery therein; A free bend portion formed on each side of the amplifier power module with a predetermined length and freely bent and unrolled according to the bending direction of the tube; An exciter module which forms a housing at one end of both ends of the free bend and mounts an exciter for generating an alternating magnetic field therein; The housing is formed at the other end of the free bend on the opposite side of the exciter module and amplifies the signal detected from the detector by receiving power from a detector and an amplifier power module that detects an alternating magnetic field generated from the exciter of the exciter module. A detector module equipped with an amplifier for transmitting to a computer located above the ground; It is formed on the outside of the exciter module and detector module, respectively, characterized in that it comprises a centralizer for adjusting the axis forming the center of the exciter module and the detector module coaxial with the central axis inside the tube.

The centralizer includes a guide shaft which is formed to extend at a predetermined diameter in the longitudinal direction of the tube at the center of the exciter module and the detector module, respectively; A guide member fitted to the outside of the guide shaft with a slightly larger inner diameter than the outer diameter of the guide shaft and installed to slide freely along the surface; It consists of three or more link members which have hinge points on the outer side of the guide member and the outer side of the guide shaft and are coupled to move the guide member along the inner diameter of the tube to support the guide shaft to coincide with the central axis of the tube. Guide shaft support means; Characterized in that it comprises an elastic means mounted to the guide shaft in the direction for generating an elastic force on the guide member sliding by the guide shaft support means.

The link member of the guide shaft support means includes: a first link having one end coupled to the guide member with a hinge point, and the other end coupled to a rotating shaft of a first roller for crimping and supporting the inner wall of the tube; It consists of a second link that intersects with the first link, forms a link point in the center, one end of which is coupled with a hinge point to the guide shaft, and the other end of which is coupled to a rotational axis of a second roller that compressively supports the inner wall of the tube. It is characterized by.

In addition, the link member of the guide shaft support means couples one end of the third link with the hinge point to the guide member and the other end to the rotating shaft of the first roller, and the one end of the fourth link to the rotating shaft of the first roller. A first set of links for engaging one end and engaging the other end with a hinge point to the guide shaft; One end of the fifth link is coupled to the hinge point of the guide shaft to which the fourth link of the first set of links is coupled and the other end is coupled to the axis of rotation of the second roller, and one end of the sixth link to the axis of rotation of the second roller. And a second link set for coupling the other end to a hinge point of the guide member to which the third link of the first link set is coupled.

1 is a view for explaining a pipe inspection apparatus of US Pat.

Figure 2 is an overall perspective view showing the inspection device of the metal buried underground pipe with a centralizer according to an embodiment of the present invention,

Figure 3 is a front view showing the inspection device of the underground metal buried pipe having a centralizer according to an embodiment of the present invention,

Figure 4 is an overall perspective view showing the inspection device of the underground metal buried pipe having a centralizer according to another embodiment of the present invention,

5 is a view for explaining the centralizer of the inspection apparatus of the underground buried metal pipe having a centralizer shown in FIGS. 2 and 4;

6 is a view showing another embodiment of the link member constituting the guide shaft support means of the centralizer of the inspection device of the underground buried metal pipe having a centralizer shown in FIG.

7 is a view showing another embodiment of the elastic means of the centralizer shown in FIGS. 5 and 6;

8 is a view showing another embodiment of the elastic means of the centralizer shown in Figures 5 and 6,

9 is a view showing a state of use of the inspection device for underground buried metal pipe with a centralizer according to the present invention.

<Description of Symbols for Main Parts of Drawings>

100; Amplifier power supply module 200; Free bend

300; Exciter module 400; Detector module

500; Centralizer 510; Guide shaft

520; Guide member 530; Guide shaft support means

531,540; Link member 550; Elastic means

560, 570; Tension Spring

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention.

2 is an overall perspective view showing the inspection device of the underground buried metal pipe with a centralizer according to an embodiment of the present invention, Figure 3 is a underground buried metal pipe with a centralizer according to an embodiment of the present invention Is a front view showing the inspection apparatus of the.

As shown, the inspection device of the underground buried metal pipe with a centralizer according to the present invention is constantly extended in the longitudinal direction of the pipe 600, the amplifier power module 100 is formed in the center of the amplifier The free bends 200 are formed on both sides of the power supply module 100, respectively, and the exciter module 300 and the detector module 400 are formed at both ends of the free bends 200, respectively. The centralizer 500 is formed outside the exciter module 300 and the detector module 400, respectively.

The amplifier power module 100 is configured to mount a battery (not shown) inside the housing 110 to supply power to an amplifier mounted on the detector module 300 to be described later. It forms a circle corresponding to the internal shape and is divided into two sides to be joined together and integrated.

The free bend 200 is formed while extending from the center of both sides of the housing 110 of the amplifier power module 100 to bend freely along the traveling direction of the tube 600 to facilitate the curved portion of the tube 600. It is. Therefore, the free bend portion 200 may be composed of a universal pipe and a flexible pipe 210 having an external corrugation.

2 shows an example in which the material pipe 210 is applied to the free bend portion 200, and the material pipe 210 of the free bend portion 200 is bent at a portion where the pipe 600 is changed in direction. The wrinkles on the losing side are folded and the other wrinkles are unfolded to switch the traveling direction along the bending direction of the tube 600.

In addition, Figure 4 is a perspective view showing the inspection device of the underground buried metal pipe with a centralizer according to another embodiment of the present invention, the free bending portion 200 is composed of a universal joint 220. Therefore, when the traveling direction of the pipe 600 is switched, the joint part is folded, so that the inspection device for the underground metal buried pipe proceeds to the curved portion of the pipe 600.

Exciter module 300 is coupled to any one of both ends of the free bend portion 200, the exciter (not shown) mounted inside the housing 310 is connected to one side of the inspection device to reach the ground ( 700 (shown in FIG. 9) to form a magnetic field by receiving power through a wire provided therein. The exciter module 300 is equipped with the exciter in the housing 310 so that the axis forming the center of the housing 310 and the axis forming the center of the exciter is aligned, the housing 310 is the inside of the tube 600 It is preferable that it is formed in the same circular shape.

Detector module 400 is coupled to one end of the exciter module 300 of the both ends of the free bent portion 200, and is equipped with a detector and an amplifier (not shown) inside the housing 410 as an exciter module ( The detector detects induced electromotive force generated from 300 and amplifies the detected signal by an amplifier supplied with power from the amplifier power module 100 and transmits the signal to a computer located on the ground through the wire provided in the cable 700.

The detector module 400 also has a detector mounted on the housing 410 such that the axis forming the center of the housing 410 and the axis forming the center of the detector coincide with each other, and the housing 410 has an internal shape of the tube 600. It is preferably formed in the same circle as.

The centralizer 500 adjusts to support the inner surface of the tube 600 such that an axis forming the exciter module 300 and the detector module 400 is coaxial with a central axis inside the tube 600. Thus, this embodiment mounts the centralizer 500 at adjacent positions outside the exciter module 300 and the detector module 400, respectively, and the inner surface of the tube 600 no matter what inner diameter of the tube 600 is. To be held in close contact with

The centralizer 500 is formed by extending the guide shaft 510 having a constant diameter in the longitudinal direction of the tube 600 from the center of each of the housings 310 and 410 of the exciter module 300 and the detector module 400. The guide member 520 having an inner diameter slightly larger than the outer diameter of the guide shaft 510 is fitted to the outside of the guide shaft 510, and the guide member 520 is mounted on the surface of the guide shaft 510. The guide shaft supporting means 530 supporting the guide shaft 510 while sliding along is formed, and the elastic means 550 is mounted on the guide shaft 510 in the direction in which the elastic force is generated in the guide member 520.

The guide shaft support means 530 is composed of three or more link members 531. In FIG. 2 and FIG. 3, an example in which three link members 531 are formed to have the same angle as each other is illustrated. Instead, the guide shaft supporting means 530 may be configured such that four or more link members 531 are formed at the same angle to each other.

One link member 531 constituting the guide shaft support means 530 is described with reference to FIG. 5 as follows.

The link member 531 is composed of a first link 531a and a second link 531b having the same length, and each end of the first link 531a has a hinge point H1 at the guide member 520. The other end is coupled to the axis of rotation of the first roller 531c for crimping and supporting the inner wall of the tube 600, the second link 531b intersects with the first link 531a and the link point L at the center. One end is coupled to the guide shaft 510 with the hinge point (H2) and the other end is coupled to the rotation shaft of the second roller (531d) for crimping and supporting the inner wall surface of the tube (600).

As the elastic means 550, a compression spring is mounted on the guide shaft 510 between the stopper 511 and the guide member 520 formed by extending the stopper 511 having a larger diameter than the other portion at the end of the guide shaft 510. It is.

Accordingly, the first and second links 531a and 531b of the link member 531 are formed by the guide member 520 provided with the elastic force by the compression spring 550 and according to the inner diameter of the tube 600. The two rollers are folded or unfolded according to the height of the rollers 531c and 531d.

That is, the guide member 520 moves along the guide shaft 510 by the compression spring 550 so that the hinge point H1 formed on the guide member 520 is connected to the hinge point H2 formed on the guide shaft 510. The first and second rollers 531c and 531d of the same length are folded to each other by being provided with an elastic force adjacent to each other so that the first and second rollers 531c and 531d compress and support the inner wall of the tube 600. In addition, the inspection device is rolled when moving the inside of the tube.

In addition, since the first and second rollers 531c and 531d have two contacts with the inner wall surface of the tube 600, the excitation module not only prevents the guide shaft 510 of the centralizer 500 from twisting. The axis constituting the center of the 400 and the detector module 500 is made to coincide with the central axis inside the tube 600.

6 is a view showing another embodiment of the link member constituting the guide shaft support means of the centralizer of the inspection device for the underground metal buried pipe having a centralizer shown in FIG. As shown, the link member 540 of the guide shaft supporting means 530 includes a first set of links 541 and a fourth and third links including third and fourth links 541a and 541c of different lengths. And a second set of links 542 including fifth and sixth links 542a and 542c formed the same length as 541c and 541a, respectively.

The first set of links 541 couples one end of the third link 541a with the hinge point H3 to the guide member 520 and the other end to the rotating shaft of the first roller 541b. One end of the fourth link 541c is coupled to the rotating shaft of the first roller 541b, and the other end is coupled to the guide shaft 510 with the hinge point H4.

The second link set 542 couples one end of the fifth link 542a to the hinge point H4 of the guide shaft 510 to which the fourth link 541c of the first link set 541 is coupled, and the other One end is coupled to the rotation axis of the second roller 542b, and one end of the sixth link 542c is coupled to the rotation axis of the second roller 542b, and the other end is the third link of the first set of links 541. 541a is coupled to the hinge point H3 of the guide member 520 to which it is coupled.

Accordingly, the first and second link sets 541 and 542 are folded to each other by the guide members 520 that receive the compressive force from the compression spring 550 to support the inner wall of the pipe 600, and have a centralizer. As the inspection device for the underground buried metal pipe proceeds inside the pipe 600, the first and second rollers 541b and 542b are compressed by rolling the inner wall of the pipe 600.

FIG. 7 is a view showing another embodiment of the elastic means of the centralizer shown in FIGS. 5 and 6, wherein the elastic means is provided between the exciter module 300 and the detector module 400 and the guide member 520. The tension spring 560 is attached to the guide shaft 510.

FIG. 8 shows another embodiment of the elastic means of the centralizer shown in FIGS. 5 and 6, wherein the elastic means of the guide shaft 510 having the tension spring 570 formed by the link member 531. The hinge point H2 and the hinge point H1 of the guide member 520 are connected to each other.

Accordingly, the tension springs 560 and 570 as the elastic means shown in FIGS. 7 and 8 are formed by sliding the guide member 520 in the axial direction so that the hinge points H1 and H2 of the link member 531 are in contact with each other. 531 is expanded to the inner surface of the tube 600, the first and second rollers (531c, 541d) support the inner surface of the tube 600, and the inspection device for underground buried metal piping with a centralizer Rolled along the inner surface of the tube 600 to smoothly slide the inside of the tube 600.

9 is a view showing a state of use of the inspection device of the underground buried metal pipe with a centralizer according to the present invention, a link member constituting the guide shaft support means 530 of the centralizer 500 for convenience of description. As an example of the four-piece 531, the inspection device for the underground buried metal pipe provided with the centralizer is used to move the inside of the pipe 600 by using the rigidity of the cable 700 provided at one side of the device. At this time, it is supported by the guide shaft support means 530 of the centralizer 500 formed on the outside of the exciter module 300 and the detector module 400, the exciter module 300 and the detector module 400 The axis forming the center of the tube 600 is coaxial with the central axis of the inside of the tube 600, and the free bend 200 is bent in the same direction as the traveling direction of the tube 600 to provide the centralizer according to the present embodiment. Inspection of an Underground Metal Pipeline It can be seen that to match with the direction of movement of the value tube 600.

Then, the exciter of the exciter module 300 that receives an alternating current from the ground through the wire provided in the cable 700 forms an alternating magnetic field, and the detector of the detector module 400 located at a predetermined distance is induced therefrom. Measures the electromotive force, which is amplified by the amplifier supplied from the amplifier power supply module 100, and transmits a signal to the computer located on the ground along the wire of the cable 700 to the constant data according to the internal situation of the tube 600 To form.

As described above, in the inspection device of the underground buried metal pipe with a centralizer according to the present invention, the guide member 520 provided with the elastic force by the elastic means 550 moves along the guide shaft 510 while supporting the guide shaft. The first and second rollers 531c and 531d of each link member 531 of the means 530 support the inner wall of the tube 600 so that the inner diameter of the tube 600 is changed or the curvature of the tube 600 is formed. Irrespective of the area, the tube 600 can travel smoothly, and the axis forming the center of the exciter and detector as well as matching the center of the exciter and detector with the inner center of the tube 600 during driving is the tube 600. Make it coaxial with the internal central axis.

As described above, the inspection device of the underground buried metal pipe having a centralizer according to the present invention can smoothly travel inside the pipe regardless of the change in the inner diameter of the pipe or the formation of the curvature of the pipe. Not only does the center coincide with the inner center of the tube, but the axis forming the center of the exciter and detector is coaxial with the center axis inside the tube, thereby reducing the noise of the acquired signal and performing accurate detection.

What has been described above is just one embodiment for carrying out the inspection device for the underground buried metal pipe with a centralizer according to the present invention, the present invention is not limited to the above embodiment, in the claims below As claimed, any person having ordinary skill in the art without departing from the gist of the present invention will have the technical spirit of the present invention to the extent that various modifications can be made.

Claims (7)

In the remote field eddy current inspection device for detecting a decrease in the thickness of the tube inside the tube, An amplifier power module which forms a housing in the center and mounts a battery therein to supply power; A free bend portion formed on each side of the amplifier power module with a predetermined length and freely bent and unrolled according to the bending direction of the tube; An exciter module having a exciter which forms a housing at one end of both ends of the free bend and generates an alternating magnetic field therein; A detector which forms a housing at the other end of the free bend of the opposite side of the exciter module and detects an alternating magnetic field generated from the exciter of the exciter module and is supplied with power from the amplifier power module and detected by the detector. A detector module equipped with an amplifier for amplifying the signal and transmitting the signal to a computer on the ground; Centrally formed on the outside of the exciter module and the detector module, the centralizer comprises a centralizer for adjusting the axis forming the center of the exciter module and the detector module is coaxial with the central axis inside the tube. Inspection device for underground buried metal pipes with risers. The method of claim 1, wherein the centralizer, Guide shafts each extending at a predetermined diameter in a longitudinal direction of the tube from the center of the exciter module and the detector module, respectively; A guide member having an inner diameter that is somewhat larger than an outer diameter of the guide shaft and installed to slide freely along a surface of the guide shaft; Three or more link members having a hinge point on the outer surface of the guide member and the outer surface of the guide shaft are coupled to move the guide member along the inner diameter of the tube to support the guide shaft to coincide with the central axis of the tube. And guide shaft support means made by mounting; Inspection device for underground buried metal pipe with a centralizer, characterized in that the elastic means mounted to the guide shaft in the direction of generating an elastic force in the guide member sliding by the guide shaft support means. 3. The link member of claim 2, wherein the link member of the guide shaft support means has one end coupled to the guide member with a hinge point, and the other end coupled to the rotary shaft of the first roller for crimping and supporting the inner wall of the tube. A link; A second point intersecting the first link and forming a link point at the center thereof, one end of which is coupled with a hinge point to the guide shaft, and the other end of which is coupled to a rotating shaft of a second roller that press-supports the inner wall of the tube; Inspection device for underground buried metal piping with a centralizer, characterized in that consisting of a link. The link member of claim 2, wherein the link member of the guide shaft support means couples one end of the third link with the hinge point to the guide member, and the other end to the rotation shaft of the first roller, and the rotation shaft of the first roller. A first set of links for coupling one end of the fourth link to the other and coupling the other end with the hinge point to the guide shaft; One end of the fifth link is coupled to the hinge point of the guide shaft to which the fourth link of the first link set is coupled, and the other end is coupled to the axis of rotation of the second roller, and one of the sixth links to the axis of rotation of the second roller. And a second link set for coupling one end and the other end to a hinge point of the guide member to which the third link of the first link set is coupled. According to claim 2, The elastic means is provided with a centralizer, characterized in that the compression spring is mounted to the guide shaft between the guide member and the stopper formed to a diameter larger than the outer diameter of the guide shaft extending to the guide shaft Inspection equipment for an underground buried metal pipe. [3] The apparatus of claim 2, wherein the elastic means comprises a tension spring mounted on a guide shaft between the exciter module, the detector module, and the guide member. According to claim 2, wherein the elastic means is a device for inspecting underground buried metal piping with a centralizer, characterized in that the tension spring is mounted by connecting the hinge point of the guide shaft formed with the link member and the guide member.