Defect detection device enabling easy removal of magnetic impurities

A defect detection device enables easy removal of magnetic impurities. The defect detection device has a structure capable of effectively removing magnetic impurities adhered to a magnetic flux leakage detection device for nondestructive inspection of a small-diameter heat transfer tube or a partially saturated eddy current detection system. With the defect detection device, it is possible to minimize adhesion of magnetic impurities that deteriorate the performance of a leakage magnetic flux detection device for nondestructive inspection of a small-diameter tube of ferromagnetic metal material or a partially saturated eddy current detection system. Further, there is an advantage in that it is possible to remove the adhered magnetic impurities from the defect detection device easily.

CROSS REFERENCE TO RELATED APPLICATION

The present application claims priority to Korean Patent Application No. 10-2016-0136268, filed Oct. 20, 2016, the entire contents of which are incorporated herein for all purposes by this reference.

BACKGROUND

1. Field of the Invention

The present invention generally relates to a defect detection device which enables easy removal of magnetic impurities. More particularly, the present invention relates to a defect detection device having a structure capable of effectively removing magnetic impurities adhered to a magnetic flux leakage detection device for nondestructive inspection of a small-diameter heat transfer tube or a partially saturated eddy current detection system.

2. Description of the Related Art

A heat transfer tube is used to transfer heat energy by allowing high and low temperature mediums to flow within a thin metal walled tube. At this time, cracks, corrosion defects, or abrasion may occur in the metal wall of the heat transfer tube due to high temperature, high pressure, impurities, and a flow and a chemical reaction of the medium.

Since such heat transfer tubes are generally small-sized and bundled, it is difficult to inspect such heat transfer tubes from the outside with a defect detection device. Therefore, the heat transfer tube is generally inspected by inserting the defect detection device into the heat transfer tube.

On the other hand, the heat transfer tube can be used until the next inspection period when a certain thickness of the heat transfer tube remains such that corrosion and abrasion of the heat transfer tube are maintained below a certain allowable value. However, in a case of fatigue cracks in the heat transfer tube, maintenance or replacement should be performed.

Therefore, it is necessary to quantitatively evaluate corrosions, abrasions, and fatigue cracks of the heat transfer tube for accurate determination thereof.

As a conventional technique for solving this problem, a nondestructive testing method of the heat transfer tube using a bobbin type coil, annular array magnetic sensors, or cylindrical array magnetic sensors has been developed.

On the other hand, when a material of the heat transfer tube is a ferromagnetic substance, a method of detecting and evaluating the defects by magnetizing a measurement region of the heat transfer tube which is to be measured and measuring a distribution of the leakage magnetic flux generated around the defects is generally used.

As another method, in a case of applying an eddy current detection to inspect the heat transfer tube of the ferromagnetic substance material, the heat transfer tube has a high permeability and thus it is difficult for the eddy current to penetrate into inside of the test piece, whereby the eddy current detection should be performed after partially self-saturating the heat transfer tube.

Alternatively, a remote field eddy current detection is performed such that two or more coils may be coaxially arranged to be separated a distance two or more times larger than a coil diameter.

FIG. 1is a view showing a nondestructive inspection method using a conventional partially saturated eddy current detection system.

Referring toFIG. 1, an outer diameter of the defect detection device20is smaller than an inner diameter of the tube10so as to be inserted into the test piece10which is a tube of small diameter.

Magnets40a,40b, and40cfor magnetizing the test piece10by applying a magnetic field thereto are built within the defect detection device20. An eddy current detecting coil30for applying an alternating current to a magnetized area is provided at a central portion of each magnetic pole of the magnets.

When the test piece10is magnetized by the magnets40a,40b, and40c, a leakage magnetic flux is generated around the defect. Measuring such leakage magnetic flux using the defect detection device20makes it possible to evaluate whether there is a defect and the magnitude thereof. On the other hand, when an AC current is applied to the coil30in a partially saturated state, a partially saturated eddy current detection can be applied.

However, according to the conventional technology described above, when the defects of the test piece10are inspected, there is a problem in which magnetic impurities adhere to the defect detection device20. In this case, because the test piece10cannot be sufficiently magnetized, there are disadvantages that the defect detection capability and the quantitative evaluation performance are deteriorated.

Further, in a case of the remote field eddy current detection, since an interval between two or more coils must be wide, the length of the sensor itself becomes long and therefore there is disadvantageously a limitation in inspecting a bending tube.

Further, there are disadvantages that a capability of detecting defects in an axial direction is deteriorated in a case of the leakage magnetic flux detection, and a capability of detecting defects in an arc direction is deteriorated in a case of the remote field eddy current detection or the partially saturated eddy current detection.

SUMMARY

The inventors of the present invention have completed the present invention by developing a structure that can easily remove magnetic impurities adhered to a partially saturated defect detection device having the magnets.

It is therefore an aspect of the present invention to provide a defect detection device which enables minimizing adhesion of the magnetic impurities or enables easy removal of the magnetic impurities even if the impurities are adhered thereto.

It is another aspect of the present invention to provide a defect detection device which enables easy removal of the magnetic impurities even when a measured object is stored without inspecting defects thereof.

A further aspect of the present invention is to provide a defect detection device enabling easy removal of magnetic impurities that may be adhered to a bending tube, because a length of the sensor unit is shorter compared with a remote field eddy current inspection method used for inspection of a heat transfer tube of a ferromagnetic material.

It is still another aspect of the present invention to provide a defect detection device that is capable of simultaneously carrying out the leakage magnetic flux detection method that makes it easy to detect a circular defect and the partially saturated eddy current detection method that makes it easy to detect defects in an axial direction.

The aspects of the present invention are not limited to the above-mentioned aspects, and other aspects not mentioned can be clearly understood by those skilled in the art from the following description.

In order to accomplish the above aspect, the present invention provides a defect detection device enabling easy removal of magnetic impurities, the defect detection device comprising: a main body of cylindrical shape housing a magnet for magnetizing a measured object and having internal threads formed in opposite ends thereof; a sensor unit provided with a plurality of magnetic sensors along an outer surface of the main body; a coil wound around an outer surface of the sensor unit; a protective casing surrounding the main body provided with the sensor unit and the coil; a first support and a second support that are hollow and are coupled to opposite ends of the protective casing respectively; a first fixture and a second fixture respectively passing through the first support and the second support and engaged with the internal threads formed in the opposite ends of the main body; and a magnetic impurity removal cap that is hollow and is coupled to one end of the protective casing in a state in that the first support and the first fixture have been removed.

According to an exemplary embodiment, to remove magnetic impurities, the first support and the first fixture are removed, the magnetic impurity removal cap is coupled to the end of the protective casing, and then the magnet is pulled out of the main body using a ferromagnetic material having a magnetic force larger than that of the magnet, whereby the magnetic impurities adhered to the protective casing are attracted to the magnetic impurity removal cap and removed from the protective casing.

According to an embodiment, the magnetic impurity removal cap may be provided with stepped portions of which outer diameters are increasing from a leading portion that is coupled to the protective casing.

According to an embodiment, the defect detection device further includes a fitting engaged with internal threads formed in one end of the second fixture and connecting a transfer pipe for protecting wiring connected to the coil and the sensor unit with the second fixture.

According to an embodiment, the portion of each of the first support and the second support that is coupled to the protective casing may be formed of a flexible elastic body so as to maintain a gap with an inner wall of the measured object.

According to an embodiment, the first support and the second support may be secured to none of the protective casing, the first fixture, and the second fixture and are therefore rotatable.

According to an embodiment, the main body may have a magnet housing portion for housing the magnet therein and a wiring passage portion.

According to an embodiment, the main body may be formed of a non-metallic material or a non-magnetic material.

According to an embodiment, the magnet may be formed in a cylindrical shape.

According to an embodiment, the protective casing may be made of or coated with a material having a property chemically opposite to that of the magnetic impurities

According to an embodiment, the magnetic impurity removal cap may be formed of a non-metallic material or a non-magnetic material.

According to an embodiment, the defect detection device further includes a storage casing having a space to house the defect detection device therein and formed of a non-magnetic material, and the storage casing may be provided with a core of a ferromagnetic material and a coil of a removable element at a portion corresponding to a position of the sensor unit.

According to an embodiment, the portion of the storage casing in which the core and the coil are provided may have a stepped shape with an outer diameter smaller than that of a portion made of the non-magnetic material.

According to an embodiment, an impedance or a phase difference of the coil wound around the outer surface of the sensor unit may be output.

According to an embodiment, an alternating magnetic field distribution locally distorted may be output by the sensor unit provided with the plurality of magnetic sensors.

The present invention has superior advantages as follows.

First, according to a defect detection device enabling easy removal of magnetic impurities of the present invention, it is possible to minimize adhesion of magnetic impurities that deteriorate the performance of a leakage magnetic flux detection device for nondestructive inspection of a small-diameter tube of ferromagnetic metal material or a partially saturated eddy current detection system.

Further, according to a defect detection device enabling easy removal of magnetic impurities of the present invention, there is an advantage in that it is possible to remove the adhered magnetic impurities from the defect detection device easily.

Further, according to a defect detection device enabling easy removal of magnetic impurities of the present invention, there is an advantage in that the magnetic impurities may be easily removed even when a measured object is stored without detecting the defects thereof.

Further, according to a defect detection device enabling easy removal of magnetic impurities of the present invention, there is an advantage in that it is easy to inspect the heat transfer tube that is bended since the device is short compared with a probe for used in a remote field eddy current detection.

Further, according to a defect detection device enabling easy removal of magnetic impurities of the present invention, there is an advantage in that arc defect detection may be easily performed compared with partially saturated eddy current detection.

Further, according to a defect detection device enabling easy removal of magnetic impurities of the present invention, there is an advantage in that axial defect detection may be easily performed compared with magnetic flux leakage detection.

DETAILED DESCRIPTION

The terms used in the present invention are general terms that are widely used at present. However, in some cases, some terms are selected by applicant. In this case, meanings of the terms should be understood considering the terms written in the detailed description part of the invention, not name of simple terms.

Hereinafter, the technical structure of the present invention will be described in detail with reference to exemplary embodiments shown in the accompanying drawings.

However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals designate like elements throughout the specification.

FIG. 2is an exploded view of a defect detection device which enables easy removal of magnetic impurities according to an embodiment of the present invention;FIG. 3is an assembled perspective view of a defect detection device which enables easy removal of magnetic impurities according to an embodiment of the present invention; andFIG. 4is a view assembled with a magnetic impurity removal cap of a defect detection device which enables easy removal of magnetic impurities according to an embodiment of the present invention.

Referring toFIG. 2, a defect detection device100enabling easy removal of magnetic impurities according to an embodiment of the present invention includes a cylindrical main body110, a sensor unit120, a coil130, a protective casing140, a first support150, a second support160, a first fixture170, a second fixture180, and a magnetic impurity removal cap190.

The main body110is configured to secure a magnet for magnetizing a measured object such as a small diameter tube with the sensor unit120for detecting a leakage magnetic flux or an eddy current generated in the measured object due to the presence of a defect and a coil130for inducing an alternating current in the measured object.

The main body110has a magnet housing portion for housing the magnet therein and a wiring passage portion, and is preferably formed in a cylindrical shape to facilitate inserting into a measured object such as a small diameter tube.

The main body110has one end on a side of the first support150penetrating to enable the magnet to be inserted or removed, and is formed with internal threads to be engaged with the first fixture170and the second fixture180respectively at opposite ends.

The main body110is preferably made of a non-metallic material or a non-magnetic material so as to minimize adhesion of magnetic impurities to the protective casing.

It is preferable that the magnets are provided in a cylindrical shape so as to generate a uniform magnetic field.

It is preferable to use the magnets having a high magnetic force, a residual magnetic flux density high sufficient to facilitate magnetization and demagnetization, and a small coercive force.

When the defect detection device provided with the magnets having the magnetic characteristics described above is used, an object to be measured can be magnetized before carrying out the nondestructive inspection thereof, and then demagnetized after completing the inspection.

The sensor unit120is provided around an outer surface of the main body110, and may include a plurality of magnetic sensors.

The sensor unit120may be selected from various types of magnetic sensors, and may be configured such that the plurality of magnetic sensors is arranged in a columnar shape or in a cylindrical shape.

The coil130is wound in a way to surround the sensor unit120along an outer surface of the sensor unit120.

The defect detection device100enabling easy removal of magnetic impurities according to an embodiment of the present invention includes a power supply unit for applying an current to the coil130, a data collecting unit for collecting data output from the sensor unit120, a data processing unit quantitatively quantifying the magnetic flux density distribution of each magnetic sensor according to an intensity of the input current based on the data collected from the data collecting unit, and the like.

The defect detection device100enabling easy removal of magnetic impurities according to an embodiment of the present invention is provided with the protective casing140.

The protective casing140surrounds the main body110, the sensor unit120, and the coil130, to protect them in a form of cylindrical tube.

It is preferable that the protective casing140is made of or coated with a material having a property chemically opposite to that of magnetic impurities in order to minimize adhesion of magnetic impurities and facilitate removal of the adhered magnetic impurities.

For example, when the magnetic impurities are chemically hydrophilic, a surface of the protective casing140may be chemically treated with a hydrophobic material or coated with a hydrophobic material. The surface of the protective casing140may be coated with a material such as fluorine that makes it difficult for the impurities to adhere to the surface thereof.

The first support150and the second support160are coupled to opposite ends of the protective casing140respectively, and serve to maintain a gap between the measured object and the magnetic sensor array. Such a gap is called lift-off.

The first support150and the second support160are provided to be hollow, and the portion coupled to the protective casing140is preferably formed with a flexible elastic body so as to maintain a gap with an inner wall of the measured object.

The first support150and the second support160are secured to none of the protective casing140, the first fixture170, and the second fixture180, and are therefore rotatable.

The first fixture170and the second fixture180pass through the first support150and the second support160which are both hollow, and then are engaged with internal threads foamed in opposite ends of the main body110, respectively.

That is, the first fixture170and the second fixture180serve to secure the protective casing140so as to maintain a predetermined gap therebetween.

The second fixture180may be formed to have a through-hole through which a wiring passes.

The second fixture180is threaded at opposite ends and engaged with the main body110and a fitting181which will be described later.

The defect detection device100enabling easy removal of magnetic impurities according to an embodiment of the present invention further includes a fitting181connecting a transfer pipe182to the second fixture180.

The fitting181is connected to the second fixture180to allow the transfer pipe182to be connected to second fixture for protecting the wiring connecting a power supply and a signal output of the sensor unit120and the coil130to be connected to the second fixture180.

The defect detection device100enabling easy removal magnetic impurities according to an embodiment of the present invention further includes a magnetic impurity removal cap190that is capable of removing magnetic impurities adhered to the protective casing140.

The magnetic impurity removal cap190is provided to be hollow to allow it to be coupled to one end of the protective casing140, in a state in that the first support150and the first fixture170have been removed from the protective casing140.

Preferably, the magnetic impurity removal cap190may be provided with stepped portions of which outer diameters are increasing from a leading portion that is coupled to the protective casing140, and formed of a non-metallic material or a non-magnetic material.

Referring toFIG. 4, it is noted that the first support150and the first fixture170have been removed and the magnetic impurity removal cap190is coupled to one end of the protective casing140.

The leading portion of the magnetic impurity removal cap190coupled to the protective casing140is machined to be tapered, and then step-shaped with large steps.

At this time, the magnet is pulled out of the main body using a ferromagnetic body191having a magnetic force larger than that of the magnet provided in the magnet receiving portion.

That is, as the magnet is pulled out of the protective casing140by the ferromagnetic body191, the magnetic impurities adhered to the protective casing140are magnetically attracted along the tapered portion of the magnetic impurity removal cap190, and then collected at the stepped portion.

As a result, the magnetic impurities collected in the stepped portion of the magnetic impurity removal cap190can be easily removed only by removing the magnetic impurity removal cap190from the protective casing140and then gently shaking the magnetic impurity removal cap190.

As described above, according to the defect detection device100enabling easy removal of magnetic impurities according to the present invention, there is an advantage in that it is easy to remove magnetic impurities adhered to the protective casing140.

Meanwhile, according to the defect detection device100enabling easy removal of magnetic impurities of the present invention, when the object to be measured is magnetized by the magnet to make permeability constant, and then an alternating current is applied to the coil wound around an outer surface of the sensor unit, an impedance or a phase difference of the coil current due to a presence of the defect can be measured.

According to the defect detection device100enabling easy removal of magnetic impurities of the present invention, a leakage magnetic flux caused due to the presence of defects in an arc direction is induced by a magnet for magnetizing a measured object, whereby a flux leakage distribution can be measured by the sensor unit that is provided with a plurality of magnetic sensors.

An alternating magnetic field distribution in which a current of the measured object induced by the coil is locally distorted due to a presence of axial defects is measured by the sensor unit provided with the same plurality of magnetic sensors, whereby the axial defects and arc defects may be easily detected.

Another embodiment of the present invention further includes a storage casing200capable of storing the defect detection device100according to the embodiment of the present invention.

FIG. 5is a view showing a storage casing of a defect detection device enabling easy removal of magnetic impurities according to an embodiment of the present invention.

Referring toFIG. 5, the storage casing200has a space for housing the defect detection device100therein.

The storage casing200is preferably made of a non-metallic material or a non-magnetic material in order to minimize adhesion of magnetic impurities. The storage casing200may be cylindrical in order to easily house the defect detection device100.

It is preferable that the storage casing200is formed to have a thickness sufficient to cause the magnetic force to be insignificant in order to minimize adhesion of magnetic impurities during storage of the defect detection device100.

At this time, the storage casing200is provided with a core210of a ferromagnetic material and a coil220of a removable element at a portion corresponding to a position of the sensor unit120of the defect detection device100.

A portion of the storage casing200in which the core210and the coil220are provided has a stepped shape with an outer diameter smaller than that of a portion made of the non-magnetic material.

That is, in the process of extracting the defect detection device100from the storage casing200, the magnetic impurities adhered to a concave portion (a portion in which the core210and the coil220are formed) of the storage casing200do not come up to the portion of the storage casing200made of the non-magnetic material and remains at the concave portion.

As a result, the magnetic impurities collected in the concave portion of the storage casing200where the core210and the coil220are formed may be easily removed only by shaking the storage casing200gently, in a state where the detect detection device has been pulled out.

As described above, according to another embodiment of the present invention, even when the defect detection device100is being stored, there is an advantage in that the adhered magnetic impurities can be easily removed.