JPS61198055A - Insertion type probe for eddy current examination - Google Patents

Abstract

PURPOSE:To detect a minute defect in the pipe axial direction of a inner surface of a metallic pipe by placing zigzag plural flat detecting coils extending over the whole area in the peripheral direction, on the surface of excitation winding which has been wound to the surface of a cylindrical high permeability magnetic core material. CONSTITUTION:An excitation winding 4 is wound uniformly to a high permeability magnetic core material 1 such as a cylindrical amorphous core, etc., and many flat detecting coils 5 are placed zigzag on its surface so as to cover the whole. Subsequently, it is formed as one body with a holding body 2 of nylon, etc. and a molding material 6, and an eddy current examination insertion type probe for inspecting a pipe surface defect of a metallic pipe is formed. In this state, it is inserted into the pipe, a high frequency current is made to flow to the excitation winding 4, and a defect signal is obtained by detecting and processing a generated eddy current by the detecting coil 5. Accordingly, by selecting correctly a diameter of the detecting coil 5 and its number, a defect in every direction of the pipe surface can be detected with a high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an eddy current insertion type probe for detecting defects on the inner surface of a metal tube such as a heat transfer tube.

(Prior Art) A conventional interpolation type probe consists of two circular coils 22a and 22b as a pair as shown in FIG. 4, and is often used in the circuit shown in FIG.

With such a configuration, an internal probe is inserted into the inner surface of a tube, and when the probe is pulled out, defects on the inner surface of the tube are detected. At this time, if there is a defect on the inner surface of the tube and it is below the detection coil 22a (or 22b), the detection coil 2
Since the impedance of 2a changes, the bridge circuit shown in FIG. 3 becomes unbalanced, and defects are detected by amplifying, synchronously detecting, and discriminating the wave height of the unbalanced voltage.

However, when testing the inner surface of a tube using this method, there is a drawback in that defects extending in the axial direction (hereinafter referred to as "linear defects") can only be detected at their leading and trailing ends. This is because the impedances of the detection coils 22a and 22b change in the same way due to defects, and there is almost no difference between them, so that defects are virtually not detected. Moreover, in reality, many of the linear defects that occur on the inner surface of the tube gradually increase in depth and then become shallower, so that the detection coils 2a and 2b are
The difference in impedance is small and often goes undetected. As shown in Fig. 6, the excitation winding 4 and the detection coil 22
A system (mutual induction system) in which a and 22b are provided is also used, but the drawbacks described above are the same.

Furthermore, in order to compensate for this drawback, one detection coil 22
Defects have also been detected by combining a with a dummy coil that cancels the stationary component and amplifying and detecting the difference in output. However, with this method, it is difficult to eliminate the effects of changes in pipe inner diameter, changes in pipe material, temperature fluctuations, etc., and even if large linear defects can be detected, it is difficult to detect minute linear defects. It is difficult.

Furthermore, in this method, as the inner diameter of the subject increases, the diameter of the circular coil also increases. Therefore, there is a drawback that as the inner diameter of the object becomes larger, the defect detection ability decreases.

In order to solve the above-mentioned drawbacks, an interpolation type rotary probe has already been developed and used.

For example, P, Neumaier, Br1tish
Journal of NDT (Sept.
1983) p, 6000 small probes on 235
They report on a device that can rotate at RPN+ and perform flaw detection at a maximum test speed of 1.2 m/min. According to this method, it is possible to detect linear defects, but a precise rotation mechanism is required, and the test speed is reduced because the entire inner surface of the tube is scanned. Since the probe coil generally has a large lift-off fluctuation tV, it is necessary to make the probe closely follow the inner surface of the tube. Moreover, not only is the probe complicated and expensive, but also the probe must be supplied with power for the rotating motor.

(Problems to be Solved by the Invention) The present invention has been made in view of the above-mentioned problems. The purpose is to detect with precision.

(Means for Solving the Problems) The interpolated probe coil according to the present invention has an excitation winding wound circumferentially around a cylindrical high-permeability magnetic core material, and extends over the entire circumferential direction on the surface of the excitation winding. This is an interpolation type probe coil characterized in that flat detection coils are arranged in a staggered manner and the coils are covered with a holder. The present invention will be described in more detail with reference to FIG. 1, which is one embodiment.

An excitation winding 4 is uniformly wound around a high permeability magnetic core material 1 such as a cylindrical amorphous core or ferrite core. A large number of flat detection coils (hereinafter referred to as "pancake coils") 5 are arranged in a staggered manner so as to cover the entire tube. Since the effective detection area of this Pankey-1 coil is approximately 70% of its diameter, each coil wraps approximately 15% of its diameter on both sides of the coil. Here, the size of the defect to be detected determines the diameter of the pancake coils, and the inner diameter of the tube to be tested determines their number.

This is inserted and held from both sides by a cylindrical holding body 2 made of a non-magnetic material such as nylon or Bakelite. In order to protect the excitation winding 4 and the pancake coil 5, they are hardened with a molding material 6 so as to be flush with the cylindrical holder 2. Lead wire 8 of excitation winding 4 and pancake coil 5
is taken out through a through hole 7 provided in the center of the cylindrical holder 2 and connected to an external cable 10 by a connector 9. FIG. 3 shows an embodiment of an electric circuit used in an interpolation type probe for eddy current flaw detection according to the present invention. It is oscillator 1
1, power amplifier 12, preamplifier 13, buffer amplifier 14, differential amplifier 15, phase shifter 16, synchronous detection circuit 17
, a pulse height discrimination circuit 18.

[Effect]

The high frequency sine wave generated by the oscillator 11 is transmitted to the power amplifier 12.
This turns into a high-frequency sinusoidal current, which is supplied to the excitation winding 4. As a result, the magnetic circuit has a cylindrical magnetic core material 1, a magnetic core material 1
It is formed by a gear between the inner surface of the test object and the test object 20. At this time, since a high permeability magnetic core with good high frequency characteristics, such as an amorphous core, is used, a strong magnetic flux is generated along the inner surface of the tube in the tube axis direction. As a result, a strong induced current flows in the circumferential direction of the inner surface of the subject 2o in the opposite direction to the current flowing through the excitation winding 4. If there is a defect on the inner surface of the test object 20, the flow of the induced current is disturbed, and the magnitude, direction, and orientation of the induced current become non-uniform in position, so that a voltage is induced in the pancake coil 5. Ru. At this time, it will be understood that by using the magnetic core material as described above, a much larger voltage is induced for the same defect than when no magnetic core material is used. This output is then amplified by a preamplifier 13, further passed through a buffer amplifier 14, and differentially amplified by a differential amplifier 15 with respect to a similar signal from an adjacent pancake coil. This output is synchronously detected with respect to the signal of the oscillator 11 by a synchronous detection circuit 17. At this time, the phase of the reference signal is adjusted by the phase shifter 16 so that noise such as backlash can be suppressed and defects can be detected with as high an S/N ratio as possible. The synchronously detected signal is subjected to wave height discrimination by a wave height discrimination circuit 17, and a defective signal is extracted.

In the above, if the defect is a defect that has a component only in the circumferential direction of the pipe opening, the flow of the induced current will not be disturbed, and therefore, in principle, the defect will not be detected. However, this cannot happen with actual natural defects, and they always have an axial component.

Also, most defects are axial, so in practice this pancake coil can detect defects in any direction.

〔Effect of the invention〕

With a relatively simple configuration, minute surface defects in all directions on the inner surface of a tube can be detected at high speed.

Furthermore, since a high permeability magnetic core is used, defects can be detected with a good S/N ratio. The flaw detection sensitivity can be controlled by the diameter of the pancake coil, and the sensitivity does not deteriorate even if the inner diameter of the object becomes larger, unlike with normal interpolation probes.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional front view showing one embodiment of the present invention, and FIG.
The figures are a sectional view taken along line A-A in FIG. 1, FIG. 3 is an explanatory diagram showing the electrical operation of the present invention, FIG. 4 is an explanatory diagram of the prior art, and FIG. 5 is an explanatory diagram of a self-induction type Brifuji circuit. FIG. 6 is an explanatory diagram of a mutual induction type bridge circuit. The symbols in the figure are as follows. 1 is a high permeability magnetic core cylinder,
2 is a non-conductive/non-magnetic holding body, 4 is an excitation winding, 5 is a detection coil (pancake coil), 6 is a molding material, 7
is a hole drilled in the center of the holder, 8 is a lead wire, 9 is a connector, 10 is a cable, 11 is a sine wave oscillator, 12 is a power amplifier, 13 is a preamplifier, 14 is a buffer amplifier,
■5 is a differential amplifier, 17 is a synchronous detection circuit, 1B is a pulse height discrimination circuit, 20 is a subject, 21 is a detection coil holder, 22
a and 22b are detection coils, and 27 and 28 are variable resistors of the bridge circuit. Applicant Nippon Steel Corporation Patent Attorney Minoru Aoyagi Figure 4 Figure 5m Figure 6

Claims (1)

[Claims] A plurality of flat detection coils are arranged in a staggered manner over the entire circumferential direction on the surface of an excitation winding wound on the surface of a cylindrical high permeability magnetic core material, and the outside is covered with a holder. An interpolation type probe for eddy current flaw detection.