KR200303105Y1 - Magnetic Based Eddy Current Probe - Google Patents

Abstract

The present invention relates to a transducer of an eddy current inspection device for inspecting a defect of a magnetic tube, the coil fixing body having a winding portion of the coil winding; A plurality of internal permanent magnets arranged to be opposite to each other in the longitudinal direction in the coil fixing body; A plurality of outer permanent magnets disposed on both ends of the coil fixing body and spaced apart from the permanent magnets to be opposite to each other; and an outer cover covering the outer edges of the coil fixing body, the inner permanent magnet, and the outer permanent magnet.

Description

Magnetically Based Eddy Current Probe

The present invention relates to an eddy current sensor. Specifically, an eddy current sensor used to detect a defect that may occur in a heat exchanger magnetic tube and to measure the magnitude of the detected defect using a magnetic deflection method is used. It relates to the configured eddy current transducer.

Eddy current refers to a circular current generated in a conductor by an alternating magnetic field of the coil when an alternating current is applied to a conductor. The non-destructive test, which is used to measure the pipe corrosion state of condenser or heat exchanger using such eddy current, is called Eddy Current Test, and the device used for such test is eddy current probe. .

In general, the eddy current inspection method inserts an alternating coil (probe) into a tube, which causes a weak magnetic field in the opposite direction to the tube due to the magnetic field of the coil, and the two magnetic fields interact to cause a change in the impedance of the coil. . The eddy current test is to take this impedance value and use it as test data. The condition of each part of the tube is inspected by inserting the transducer into the tube and withdrawing it gradually.

By the way, in the case of heat exchanger tube which is usually made of non-magnetic material, nondestructive inspection is possible by applying the existing eddy current test method, but some high temperature and high pressure heat exchanger tube is made of magnetic material such as carbon steel or ferritic stainless steel. Due to the tube tube rate change, the existing eddy current test cannot be applied.

The present invention is to solve this problem, improve the reliability of the nondestructive testing and defect size of the magnetic tube, extend the life of the probe to shorten the cost and inspection air required for inspection, and clearly indicate the defect signal The purpose is to facilitate the analysis of the signal analyzer, and also to enable the inspection using magnetic eddy current inspection equipment for magnetic tube inspection.

1 shows the structure of the self-deflection eddy current probe of the present invention,

2 shows the concept of magnetic saturation used in a self-deflection eddy current transducer,

3 shows a fault signal detected by the differential and absolute schemes, and

4 is a configuration diagram of a self-deflection eddy current inspection system.

Explanation of symbols on the main parts of the drawing

10: Eddy current transducer 11: Shear plug

12: Rear Plug 13: Probe Jacket

14: Fixing bolt 15: Permanent magnet

16: carbon steel disc 17: copper ring

18: coil fixture 19: coil

40: computer 41: frequency generator

42: communication cable 43: magnetic tube

In order to achieve this purpose, the present invention provides a transducer with a modified structure of the probe to perform the same inspection as non-magnetic tube inspection by minimizing the change in magnetic permeability by minimizing the magnetic permeability of the magnetic tube to be examined.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

Magnetic deflection technique is a technique that magnetizes an inspection tube by installing an eddy current coil in a transducer body with a permanent magnet or an electromagnet embedded therein. This technique can be fully saturated or partially saturated depending on the material, thickness, and degree of magnetization of the tube. An important factor affecting the eddy current penetration depth in the magnetic material is the material permeability. In general, a change in impedance of a coil caused by a change in permeability shields a defect signal generated in a tube. As a result, it is impossible to detect defects in the tube unless the change in permeability is minimized. The relative magnetic permeability of the nonmagnetic material is almost 1, but the relative magnetic permeability of the magnetic material is usually in the range of 10 to 200 and varies depending on the material composition, cold working and thermal history. If the relative permeability of the material is reduced to around 1 unit, the test can be similar to the general eddy current test. Therefore, in order to make the relative magnetic permeability near 1, it is necessary to use a permanent magnet with strong magnetization.

1 shows the structure of the self-deflection eddy current probe of the present invention. As shown in FIG. 1, the eddy current transducer 10 is designed with two coils 19 so that the differential and absolute tests (see FIG. 3) can be simultaneously applied. The coil fixing body 18 is fixed to the winding machine to prevent the coil from being moved to wind the coil, and made of acetol to facilitate mechanical processing. The transducer front end plugs 11 and rear end plugs 12 are made of lightweight and rigid aluminum, and the outer sheath 13 of the transducers is made of stainless steel so that the coils are not damaged by the scale in the test tube when the transducer is pulled out and inserted. do. The transducer shell 13 is processed to a thin thickness to improve the filling rate, that is, the ratio of the cross section of the transducer to the tube, which affects the size of the signal.

The permanent magnet (15), which plays an important role in the self-deflection eddy current probe, uses rare earth magnets, and each of the two coils in front and rear of the coil coil fixing body (18) in a ring form, and the transducer coil fixing body (18). 4 are arranged so as to be opposite poles to each other. Since the permeability varies depending on the material of the specimen, the arrangement of a plurality of rings as described above allows a specimen having a low permeability to be manufactured by reducing the number of permanent magnets. The central fixing bolt 14 in the center is designed to secure the entire transducer component from the front end plug 14 to the rear end plug 12 at once. The inner permanent magnet and the outer permanent magnet are separated by the carbon steel disk 16. And, both sides of the coil body is provided with a copper ring 17 is a high conductor to shield the high frequency interference. This shield is used to tune the electric field so that the full flow signal is concentrated only at the tube wall.

Fig. 2 illustrates the concept of magnetic saturation used in the self-deflection eddy current probe. As shown in Fig. 2, when the magnetizing force is increased, the initial magnetic flux density rapidly increases to the knee point A, and then gradually increases and saturates. Reach point B. When the saturation point (B) is reached, the magnetic flux density no longer increases even if the magnetization power is increased, and since the magnetic permeability is maintained near the saturation point (B) by the permanent magnet, the magnetic permeability hardly changes. Tubes can be eddy current tested like nonmagnetic materials.

3 shows a defect signal detected by the differential type and the absolute type. As shown in FIG. 3, the differential signal 31 is a defect signal detected when two coils are electrically connected in series, and the absolute signal 32 is detected by connecting only one coil of two coils. It is a fault signal. Differential type is used for defect inspection with local small volume such as point and crack. Absolute type is gradually changed because it is easy to use when thickness thinning occurs in the longitudinal direction of the tube and overall characteristics of material properties. Used for defect detection. Therefore, both methods must be used to improve the accuracy of the soundness diagnosis of the material.

4 is a configuration diagram of a self-deflection eddy current inspection system. As shown in Fig. 4, the signal acquisition and analysis computer 40 stores the acquired signal for use by the analyst in analyzing the signal. The frequency generator 41 transmits several frequencies to the transducer with a constant current. The communication cable 42 is a transmission cable for current and signal between equipments, and a local area network is mainly used.

Using the magnetic deflection eddy current probe 10 of the present invention, the tester is inserted into the magnetic tube 43, the signal is gradually taken out and the signal is acquired and stored in the computer 40 for signal acquisition and analysis. Analyze the presence and size of defects.

According to the present invention, the nondestructive testing reliability of the magnetic tube and the accuracy of the defect size can be improved, the life of the probe can be extended, and the signal analyzer can be clearly indicated to facilitate the analysis of the signal analyzer as well as the magnetic material. It makes it possible to use common eddy current inspection equipment for tube inspection.

Claims (8)

In the eddy current inspection device for inspecting the defect of the magnetic tube, A coil fixing body having a winding part in which coils are wound; A plurality of internal permanent magnets arranged to be opposite to each other in the longitudinal direction in the coil fixing body; A plurality of external permanent magnets disposed at both ends of the coil fixing body so as to be spaced apart from the permanent magnet so as to be opposite to each other; A magnetic deflection eddy current probe comprising an outer sheath covering the outer edges of the coil fixture, the inner permanent magnet and the outer permanent magnet. The method of claim 1, wherein the coil fixing body A self-deflection eddy current probe characterized by winding two coils in series to perform absolute and differential methods. The method of claim 2, wherein the inner and outer permanent magnets are The self-deflection eddy current probe, characterized in that the ring shape detachable to maintain a constant permeability according to the type of test object. The method of claim 3, wherein the inner and outer permanent magnets are Magnetically deflected eddy current probe, characterized in that the rare earth series strong magnetic force. The method of claim 4, wherein the envelope is Magnetic deflection eddy current transducer, characterized in that the stainless steel. The method according to any one of claims 1 to 5, Self-deflecting eddy current transducer, characterized in that the high conductor ring is provided on both sides of the wound coil. The method of claim 6, wherein the high conductor ring Magnetic deflection eddy current transducer, characterized in that the copper ring. The method of claim 7, wherein Magnetic deflection eddy current probe further comprises a carbon steel disk between the inner and outer permanent magnets.