JPS60190851A - Eddy current flaw detection test of steel pipe - Google Patents

Abstract

PURPOSE:To efficiently and easily perform a flaw detection test with high accuracy, by magnetizing a steel pipe by directly supplying a current thereto from an external power source and scanning the flaw detection testing coil inserted into the steel pipe to perform flaw detection. CONSTITUTION:Electrode terminals 5 are contacted with a steel pipe 1 and a current is supplied to the steel pipe 1 from an external power source 3 to magnetize the same to obtain a magnetic saturation state. A current is blocked according to necessity to bring about a residual magnetization state. A flaw detection testing coil 2 is inserted into the steel pipe 1 held under the magnetic saturation or residual magnetization sate and scanned to perform a flaw detection test. When the steel pipe 1 has a crack or other flaws, change is generated in the eddy current flowed to the coil 2 and the impedance or induced voltage of the coil 2 changes to obtain an electric signal. This signal is guided to a flaw detector 6 and the presence or degree of a flaw part is judged from the amplitude and phase of the signal. By this method, the flaw detection test is efficiently and easily performed with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to eddy current flaw detection of steel pipes, which is carried out to detect cracks and other defects in ferromagnetic steel pipes used in heat exchangers and other applications. Concerning test methods.

Conventionally, in order to perform a flaw detection test by inserting a flaw detection coil into the inner surface of a steel pipe, a magnetizing coil or a permanent magnet is used as a magnetizer, and the magnetizer and flaw detection coil are inserted into the inner surface of the steel pipe as an integrated probe to conduct a tensile scan. The method used was to conduct flaw detection.

However, when using the magnetizing coil as a magnetizer, the maximum current for the magnetizing coil is 1.
．． Only about 5 amperes could be passed, and the magnetization of the steel pipe could not be sufficiently maintained. Furthermore, even when a permanent magnet is used as a magnetizer, the degree of magnetization is extremely weak, and in this case, it is also necessary to manage the attenuation of the magnetomotive force.

Such weak magnetization causes unevenness in the magnetic properties of the steel pipe, and this magnetic unevenness is further amplified by backlash when the flaw detection coil scans inside the pipe under weak magnetization. As a result, large noise due to magnetic unevenness occurs during the flaw detection test, making the flaw detection difficult.Furthermore, since the steel pipe is magnetized and flaw detected at the same time, a special probe that combines a magnetizer and a flaw detection coil is required. The disadvantage was that it was not very efficient and the work efficiency was poor.

The present invention solves the above-mentioned conventional drawbacks, and instead of using a conventional magnetizer, the steel pipe is made into a strong magnetized state.
The object of the present invention is to provide an eddy current flaw detection test method for steel pipes in which flaw detection is performed by inserting only a flaw detection test coil inside the steel pipe.

That is, the first invention provides an eddy current flaw detection testing method for steel pipes, in which the steel pipe is magnetized by directly applying electricity to the steel pipe from an external power source, and flaw detection is performed by scanning a flaw detection test coil inserted inside the steel pipe. That is.

The second invention also provides a method for detecting flaws in a steel pipe by magnetically saturating the steel pipe by energizing a conducting wire penetrating the inside of the steel pipe, and then scanning a flaw detection test coil inserted inside the steel pipe in a state of residual magnetization. The gist is the eddy current testing method.

The specific aspects of the eddy current testing method for steel pipes according to the first invention will be explained in more detail based on the drawings.
) are steel pipes used in heat exchangers, (2)
is a flaw detection test coil that is inserted into the inside of a steel pipe (1) and performs flaw detection by scanning.

(3) is an external power source for magnetizing and saturating the steel pipe (1), and the positive and negative charge transmission lines (
4), and an electrode terminal (5) for contacting the steel pipe (1) is provided at the end of the power transmission line (4). The signal from the flaw detection test coil +21 is sent to the flaw detector (4) through a signal line (6). The flaw detector (A) is composed of an oscillator, an AC bridge, an amplified detector, a phase shifter, an amplified filter, and a recorder, or the configuration of the flaw detector (A) is specifically limited to these. (The structure can be changed as necessary.

In the configuration described in Section 2 above, when performing an eddy current flaw detection test on the steel pipe (1), first the Wl pipe (1) is brought into a magnetized state.

Therefore, the electrode terminal (5) is brought into contact with the mesh width (1), and a current is passed through the steel pipe (1) from the external power source (3). In this case, there are two methods: directly applying electricity by contacting the electrode terminals (5) to appropriate locations on the steel pipe (1) (plot method), and contacting the electrode terminals (5) to both ends of the steel pipe (1). Possibly steel pipe (1)
A method of directly applying current in the axial direction (+Ijl+, 1ffiT
There are two methods for bringing the electrode terminal (5) into contact with the steel @(j) and energizing it.

In this way, the energized steel plate '5' becomes in a state of magnetic saturation where a magnetic field is generated by the current. In this state, the magnetic permeability is low, the magnetization state is very stable, and the magnetization state is very strong. In the steel 'rH], which has been magnetically saturated in this way, residual magnetism remains even if the electrode terminal (5) is removed from the steel pipe (1) and the current is cut off. Even in this state of residual magnetization, the magnetic permeability is the same as in the state of magnetic saturation! j is a small and stable magnetization state, and the magnetic flux density is somewhat small.

In the first invention, when performing an eddy current detection/corrosion test on the steel pipe (1), there are two cases in which the steel pipe (1) is subjected to magnetic saturation (continuous method) and a case in which the steel pipe (1) is subjected to a residual magnetization state. (There is a residual method 9.

Further, the magnitude of the current for magnetization used here is determined as follows. The current value flowing through the entire conductor is 1
Ampere (A), radius r cm from center of conductor
When the strength of the magnetic field around the circumference of Torr (cm 2 ) is n Oersted (Oe), the relational expression JJ=i15·r is obtained, and the magnitude of the magnetic field is directly proportional to the current and inversely proportional to the radius. Therefore, the current I is 5·rH, and the strength of the magnetic field required for magnetic saturation of steel is usually H=
100 oersteds (oe) or more, where the radius of the steel pipe ++, + is r = 1.27 cm (c
m), it becomes 635 (A). That is, when the current is passed up to 635 amperes (A), the steel pipe (1) becomes magnetically saturated. Also, steel pipes (
Since a maximum current of 3000 amperes (A) can be applied to 11, the @tube fil can be easily brought into a state of magnetic saturation.

Further, the type of current may be any of direct current, pulsating current, and impulse current.

A flaw detection test coil (2) is inserted into the steel pipe (1) which is in a state of magnetic saturation or residual magnetization, and the flaw detection test is performed by scanning the coil. The scanning of this flaw detection test coil (2) is as follows:
It is not shown in the figure.It is either movable or self-propelled. When the steel pipe () has cracks or other defects, a change occurs in the eddy current flowing through the flaw detection test coil (2), causing a change in the impedance of the flaw detection test coil (2) or the induced voltage. C electrical signals are obtained. This signal is led to the flaw detector culm through the signal line (6), and the presence and extent of a defect in the steel pipe (1) is determined from the amplitude and phase of the signal. The results may be recorded with a recorder. An eddy current flaw detection test on steel pipes is conducted as shown below.

Next, specific aspects of the eddy current testing method for steel pipes according to the second invention will be explained in detail based on drawings.
Similar to the first invention, (1) is RLi W, and (3) is the external view. (7) is a ring line, and the inside of the steel pipe ('') is 111! It is configured to be powered by an external power source (3). (Current passing method) In the above configuration, after the steel pipe (1) is brought into a state of magnetic saturation by the magnetic field of the energized conductor (7), the current is cut off and the conductor (
7) Remove. The magnitude of the current for achieving this magnetic saturation may be the same as that according to the first invention. Steel pipe (1)
becomes a state of residual magnetization. In this state, as shown in FIG. 3, the steel pipe (1) is subjected to an eddy current flaw detection test using the same method as disclosed in the first invention.

Since the first and second inventions have a diagonal configuration, they significantly exhibit various excellent effects as described below.

a) The steel pipe is magnetized by directly energizing the steel pipe from an external power source, or magnetically saturated by energizing the conductor that runs inside the steel pipe.
Normally, it is possible to easily energize the steel pipe at around 850 amperes (A), and it is possible to energize up to 3,000 amperes (A), making it possible to achieve strong magnetic saturation of the steel pipe. .

b) According to the magnetic method “L” of the first invention and the second invention,
Since the magnetic flux takes a closed magnetic path, the magnetic attenuation is very small, and there is no need for practical remagnetization for about one month after magnetization, allowing flaw detection testing operations to be performed extremely efficiently.

C) Since the magnetization device and the flaw detection test coil are separated, there is no intralayer scanning of the magnetizer as in conventional methods.
There is no occurrence of magnetization unevenness due to backlash caused by the scanning of the magnetizer inside the tube, and as a result, there is no risk of noise caused by magnetic unevenness during the first flaw detection test, and the flaw detection accuracy can be significantly improved. Furthermore, scanning the flaw detection test coil does not require any effort and no special test conditions are required, so the flaw detection operation can be performed extremely easily.

d) The magnetization devices of the first and second inventions can be used by converting conventional magnetization devices for magnetic particle testing as they are, and furthermore, since the magnetization devices are used in the magnetic saturation region, Variations in output power and voltage are extremely small, so there is no risk of deterioration in flaw detection accuracy, and the flaw detection section only uses a conventional flaw detection test coil, eliminating the need for special flaw detectors and special jigs. There is no need to use

[Brief explanation of the drawing]

Figure 1 (J, one of the strengths of the first invention
The cock diagram and FIG. 2 are longitudinal sectional views showing one embodiment of the second invention, and FIG. 3 is a block diagram showing one embodiment of the second invention. (1) is a steel pipe, (2) is a probe/positive test coil, (3) is an external power source, (4) is a power transmission line, (5) is an electrode terminal, (6) is a signal wire, (7) is a core wire, (A) is deep (easy). Patent applicant: Nondestructive Inspection Co., Ltd. Figure 1 Figure 2 Figure 3

Claims (1)

[Claims] 1. Eddy current flaw detection for steel pipes, characterized in that the steel pipe is magnetized by directly applying electricity to the 81 pipe from an external power source, and flaw detection is performed by scanning a flaw detection test coil inserted inside the steel pipe. Test method. 2. The eddy current testing method for steel pipes according to claim 1, wherein the magnetization state is a state of magnetic saturation. 3. The eddy current testing method for steel pipes according to claim 1, wherein the magnetization state is a residual magnetization state. 4. Eddy current flaw detection of steel pipes, which involves magnetically saturating the steel pipe by energizing a conductor that penetrates the inside of the steel pipe, and then performing flaw detection by scanning a test coil inserted into the steel pipe in a state of residual magnetization. Test method.