JP2898681B2 - Remote field eddy current sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a remote field eddy current sensor, and is particularly applicable to a remote field eddy current method for detecting defects in metal materials such as oil country tubular goods, pipelines, and heat exchangers. The present invention relates to a remote field eddy current sensor.

[Problems to be Solved by the Related Art and the Invention] In order to diagnose a metal material using a remote field eddy current when the conventional metal material is a pipe, a remote field eddy current sensor including an excitation coil and a reception coil is provided. It is inserted into a test metal material, for example, a pipe, and an excitation signal is applied to the excitation coil.

The electromagnetic wave generated by the exciting coil may be indirect propagation through the thickness of the test path or direct propagation when the test pipe is regarded as a waveguide, but the direct propagation is completely attenuated by the frequency characteristics of the test pipe. I do. For this reason, the diagnostic data that can be used is an indirectly propagated wave through a pipeline. The change of the amplitude and phase of the received signal due to the remote field eddy current near the receiving coil is called a so-called skin effect, but the amplitude of the received signal decreases exponentially due to the thickness of the conduit. The phase difference between the excitation signal and the reception signal is substantially proportional to the tube wall thickness with respect to the magnetic permeability of the tube, the electrical conductivity, and the electrical theoretical condition based on the frequency of the excitation signal, so the phase difference is used for diagnosis. That is normal.

The receiving coil is provided at the rear of the exciting coil, is arranged in a star shape along the inner wall of the pipeline, and has an absolute value type having several receiving coils, and the receiving coil of the front group arranged in a star shape and the rear thereof. And a differential type provided with a receiving coil of the rear group.

In the absolute value type, each group in the group has the same number of turns, and the plurality of receiving coils are connected in series or in parallel so as to be connected to the measuring instrument with the necessary pairs of leads for outputting sensor signals.

In the differential type, the receiving coils of the front group and the rear group all have the same number of turns.The required number of coils are connected in series or in parallel from the front group and the rear group, and the difference between the front coil and the rear coil is changed. A necessary pair of lead wires are provided by connecting the motion and connected to the measuring instrument.

The absolute value type remote field eddy current sensor with the above configuration can obtain a relatively high level sensor signal and can perform stable diagnosis, and is suitable for detecting the gradually corroded portion FW of the test pipe. There are disadvantages such as low detection sensitivity for FS and the inability to detect if the local corrosion FS is small.

On the other hand, the differential type remote field eddy current sensor detects corrosion based on the level difference between the sensor signals of the front group receiving coil and the rear group receiving coil.
Although it has high sensitivity and is advantageous for FS, there is a disadvantage that it is difficult to obtain a differential signal for the gradually corroded portion FW, which is disadvantageous. Further, there is a problem that the phase detection cannot be performed stably because the differential signal is small.

The stability of phase detection is important because both the differential type and the absolute value type calculate the depth and width of corrosion based on the phase delay characteristics of the obtained sensor signal as well as the level of the sensor signal. It is.

[Object of the Invention] The present invention has been made in view of the above-described difficulties, and has a structure in which the number of turns of the front receiving coil provided on the exciting coil side is made larger than the number of turns of the rear receiving coil, so that both gradual corrosion and local corrosion are achieved. It is an object of the present invention to provide a remote field eddy current sensor capable of outputting a sensor signal capable of obtaining stable phase data.

Means for Solving the Problems In order to achieve the above object, a remote field eddy current sensor according to the present invention is provided with an exciting coil for generating a remote field eddy current in a test metal material and a predetermined distance from the exciting coil. A first receiving coil for receiving the remote field eddy current; a first receiving coil having a smaller number of turns than the first receiving coil, and a distance from the excitation coil being longer than the predetermined interval to receive the remote field eddy current; And a second receiving coil.

Hereinafter, an embodiment of the remote field eddy current sensor according to the present invention will be described in detail with reference to the drawings.

In FIG. 1, MC is an exciting coil. Excitation coil
A front receiving coil Cn (n is 1 to 6) is provided at a position separated by a predetermined interval (at least twice the pipe diameter) behind the MC. The front receiving coils FC _{1 to} FC ₆ are provided at intervals of 60 ° with respect to the test tube 1.
Therefore, the front receiving coil FC ₁ is in the direction of 12:00, FC ₂ is 2
The time FC ₃ is arranged in the direction of 10 o'clock, the respective front receiving coils FC _{1 to} FC ₆ are connected in series, the lead lines FL ₁ and FL ₂ are drawn, and the terminals 2 c and 2 a of the differential coil 2 are connected. Connected. Also,
Rear receiving coil RCn front receiving coil FC ₁ to (n is 1-6)
~ Provided behind FC ₆ . Each rear receiving coil RC ₁
To RC ₆ is a coil winding number is less than the front receiving coil FC ₁ ~FC _6, and the laying direction is forward receiving coils FC ₁ ~FC ₆
In the same direction. Therefore, the rear receiving coils RC ₁ is disposed in the direction ‥‥ 12 o'clock.

Rear receiving coil RC ₁ to RC ₆ are connected in series lead line R
L ₁ and RL ₂ are connected to the terminals 2 c and 2 b of the differential coil 2.

Note that one end of the front receiving coil FCn and the rear receiving coil R
One end of Cn is connected, the other ends of the front and rear receiving coils FCn and RCn are pulled out, and the front receiving coil FCn and the rear receiving coil RCn are wired so as to form a differential winding. Can be omitted.

[Operation of the Invention] When the remote field eddy current sensor having the above configuration is placed in a sound part, as shown in FIG. 2, I is a signal vector by the front receiving coil FCn (hereinafter, I, II... It is a signal vector by the receiving coil RCn, and has almost the same phase θ due to proximity. III is a differential vector by differential connection. Since III = I-II and the direction is the same, the phase is θ. When this signal vector III is subjected to phase detection with the reference signal XI, phase data θ for a healthy part is obtained. Conventionally, when I-II = III, III is small, so that phase detection becomes unstable and stable phase data cannot be obtained. However, in the remote field eddy current sensor according to the present invention, the front receiving coil FCn close to the exciting coil MC has the exciting coil MC. Not only the signal level is higher than the rear receiving coil RCn, which is farther away, but also because the number of windings is large, the signal level is added as much as the number of windings is large, so the difference is large enough for phase detection. The motion signal vector III is obtained, and a stable phase data is obtained.

FIG. 3 shows a signal vector change for a large gradual corrosion portion FW. The signal vector I is the forward receiving coil FC
n is the signal vector of the sound part due to n, II is the rear receiving coil RCn
Is a signal vector of a healthy part, and III is a difference vector of a healthy part due to differential connection. Since the progressively corroded portion FW has a large area, both the front receiving coil and the rear receiving coil are included in the corroded portion, and both signal vectors change similarly. IV is a progressively corroded portion signal vector due to the front receiving coil FCn, V is a progressively corroded portion signal vector due to the rear receiving coil RCn, and VI is a progressively corroded difference vector due to differential connection. Here, VI contains progressively corroded portions FW, and III
The progressively corroded portion FW can be detected based on the phase difference.

In FIG. 4, I is the signal vector of the sound part of the front receiving coil FCn, II is the signal vector of the sound part of the rear receiving coil RCn, I
II is a sound part difference vector by differential connection. Considering the case where only the front receiving coil FCn is included in the corroded portion because the locally corroded portion FS has a small spread, and only the signal vector I changes, IV is the signal vector in the locally corroded portion of the front receiving coil FCn, V Is a signal vector due to the differential connection of the local corrosion portion FS. The local corrosion portion FS can be detected by the phase difference between V and III.

FIG. 5 shows reception levels depending on the distance between the exciting coil MC and the front and rear receiving coils FCn and RCn. The horizontal axis indicates the distance difference (MC
−FCn or RCn), the vertical axis is the signal level. If the receiving coil with a large number of turns is used as the rear receiving coil RCn to obtain the required receiving level, the number of turns must be further increased to cover the decrease in the receiving level. If a large number of front receiving coils FCn are provided in front, a signal level increased near the exciting coil MC and a signal level increased due to an increase in the number of windings are added to obtain a stable signal level.

Note that the front and rear receiving coils FC in the above embodiment are used.
The number of coils of n and RCn is not limited to six. Further, the connection form of the receiving coils can be parallel, and the number of connected coils can be arbitrarily configured. The connection between the front and rear receiving coils FCn and RCn is not limited to the above embodiment, and it goes without saying that a similar effect can be obtained as long as a circuit configuration capable of performing differential operation is obtained.

[Effects of the Invention] A remote field eddy current sensor according to the present invention includes an excitation coil that generates a remote field eddy current in a test metal material, and a first field that receives the remote field eddy current provided at a predetermined distance from the excitation coil. A receiving coil, and a second receiving coil configured to receive the remote field eddy current, the number of turns being smaller than that of the first receiving coil, and the distance from the exciting coil being longer than the predetermined interval. Therefore, there is an effect that a sensor signal capable of obtaining more stable phase data can be output as compared with the related art for both gradual corrosion and local corrosion.

[Brief description of the drawings]

FIG. 1 is a block diagram of a remote field eddy current sensor according to the present invention, FIG. 2 is a signal vector diagram in a sound pipe according to FIG. 1, and FIG. 3 is a signal vector change diagram due to gradual corrosion according to FIG. FIG. 4 is a diagram showing a signal vector change in the local corrosion shown in FIG. 1, and FIG. 5 is a characteristic diagram showing a signal level with respect to a distance between an exciting coil and a receiving coil. 1. Test tube (metal material) 2. Differential coil MC Excitation coil FCn Front receiving coil (first receiving coil) RCn Rear receiving coil (second receiving coil)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-35261 (JP, A) JP-A-61-134658 (JP, A) JP-B-48-18277 (JP, B1) (58) Field (Int.Cl. ⁶ , DB name) G01N 27/72-27/90

Claims (1)

(57) [Claims] 1. An exciting coil for generating a remote field eddy current in a metal material under test, a first receiving coil provided at a predetermined distance from the exciting coil to receive the remote field eddy current, and the first receiving coil A remote coil having a smaller number of turns and a second receiving coil disposed at a distance from the exciting coil longer than the predetermined interval and receiving the remote field eddy current.