JPH03220451A - Remote field vortex sensor - Google Patents

Abstract

PURPOSE:To output a sensor signal ensuring the obtaining of a phase data stabilized against a gradual corrosion and a local corrosion by making the number of turns of a front receiving coil provided on the side of a exciting coil larger than that of a rear receiving coil. CONSTITUTION:A front receiving coil FCn near an exciting coil MC is not only so higher in signal level as compared with a rear receiving coil RCn further than the coil MC but also so greater in the number of winding circuits to obtain a differential signal vector III with a level thereof enough for a phase detection and hence, a stable phase data is obtained. Then, a gradual corrosion part covers both the coils FCn and RCn in a wide range and signal vectors of the both vary likewise. A vector VI is a gradual corrosion part difference vector owing to a differential connection, where the VI contains the gradual corrosion part, which is detected with a phase difference from the III. A local corrosion part contains the coil FCn alone in a narrow range. A vector V is a signal vector owing to a differential connection of the local corrosion part, which is detected by a phase difference between the V and III.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a remote field eddy current sensor, and is particularly applicable to the remote field eddy current method for detecting defects in metal materials such as oil country tubular goods, pipelines, and heat exchangers. Regarding remote field eddy current sensors that can be used.

[Prior Art and Problems to be Solved by the Invention] Conventionally, in order to diagnose the metal material using remote field eddy current when the metal material is a conduit, it is necessary to provide a remote field eddy current sensor consisting of an excitation coil and a receiving coil. A test metal material, for example, is inserted into a conduit, and an excitation signal is applied to an excitation coil.

The electromagnetic waves generated by the excitation coil can be indirectly propagated through the wall thickness of the test tube or directly propagated when the test tube is viewed as a waveguide, but direct propagation is completely attenuated by the frequency characteristics of the test tube. do. Therefore, the diagnostic data that can be used is indirectly propagated waves through the pipe. Changes in the amplitude and phase of the received signal due to remote field eddy currents near the receiving coil are called the skin effect, and the amplitude of the received signal decreases exponentially with the thickness of the pipe. The phase difference between the excitation signal and the received signal is a value that is approximately proportional to the pipe wall thickness under electrical theoretical conditions based on the magnetic permeability and electrical conductivity of the pipe material and the frequency of the excitation signal, so the phase difference is used for diagnosis. Usually, the receiving coil is installed behind the excitation coil and arranged in a star shape along the inner wall of the conduit, and has an absolute value type with several receiving coils, and a front group receiving coil arranged in a star shape. There is a differential type that includes a coil and a rear group receiving coil installed behind it.

In the absolute value type, each of the groups has the same number of turns, and a plurality of receiving coils are connected in series or in parallel, and are connected to a measuring instrument by a necessary pair of lead wires that output a sensor signal.

In the differential type, the reception coils in the front and rear groups have the same number of turns, and the required number of coils from the front and rear groups are connected in series or parallel, and the difference between the front and rear coils is It is designed to be connected dynamically and provide the necessary pairs of lead wires to connect to the measuring instrument.

Since the absolute value type remote field eddy current sensor with the above configuration can obtain a relatively high level sensor signal, stable diagnosis can be performed and it is suitable for detecting gradual corrosion part FW of the pipe under test. The detection sensitivity for FS is low, and there are drawbacks such as the inability to detect local corrosion when the FS becomes small.

On the other hand, the differential 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 is advantageous in that it has high sensitivity for S, it has a disadvantage in that it is difficult to obtain a differential signal for the gradual corrosion part FW.

Furthermore, since the differential signal is small, it is difficult to stably perform phase detection.

For both differential and absolute value types, measurements are not only made based on the level strength of the sensor signal, but also the depth and extent of corrosion are calculated from the phase delay characteristics of the obtained sensor signal, which improves the stability of phase detection. is important.

[Purpose of the Invention] The present invention has been made in view of the above-mentioned difficulties, and by making the number of turns of the front receiving coil provided on the excitation coil side larger than the number of turns of the rear receiving coil, both gradual corrosion and localized corrosion can be prevented. An object of the present invention is to provide a remote field eddy current sensor that can output a sensor signal from which stable phase data can be obtained.

[Means for Solving the Problems] In order to achieve the above object, a remote field eddy current sensor according to the present invention includes an excitation coil that generates a remote field eddy current in a metal material under test, and an excitation coil that is provided at a predetermined distance from the excitation coil. a first receiving coil that receives the remote field eddy current; and a first receiving coil that has a smaller number of turns than the first receiving coil and is disposed at a distance from the excitation coil that is longer than the predetermined interval and receives the remote field eddy current. and a second receiving coil.

[Embodiment] 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 excitation coil. A front reception coil FCn (n is 1 to 6) is provided behind the excitation coil MC at a predetermined distance (at least twice the tube diameter). The front receiving coils FC1 to FCs are 60' apart from each other with respect to the test tube 1.
Provided at intervals. Therefore, the front receiving coil FC, is 1
FC2 is arranged in the 2 o'clock direction, FC2 is arranged in the 10 o'clock direction, and the respective front receiving coils FC0 to FC are arranged in the 2 o'clock direction.
, are connected in series, and leader lines FL0 and FL2 are drawn out,
It is connected to terminals 2c and 2a of the differential coil 2. Also, the rear receiving coil RCn (n is 1 to 6) is replaced with the front receiving coil F.
C to FC, installed further back. Each of the rear receiving coils RC, ~RC, is configured with a coil having a smaller number of turns than the front receiving coils FC1~FC1, and is disposed in the same direction as the front receiving coils FC1~FC. Therefore,
The rear receiving coil RC□ is arranged in the 12 o'clock direction.

The rear receiving coils RC1 to RC are connected in series and connected to terminals 2c and 2b of the differential coil 2 by lead wires RL1 and RL2.

Note that one end of the front receiving coil FCn and one end of the rear receiving coil RCn are connected, and the front receiving coil FCn, the rear receiving coil FCn,
Pull out each other end of RCn.

If the front receiving coil FCn and the rear receiving coil RCn are wired so that they are mutually differentially wound, the differential coil can be omitted.

[Operation of the invention] When the remote field eddy current sensor with the above configuration is placed in a healthy part, as shown in FIG. are signal vectors generated by the rear receiving coil RCn, and since they are close to each other, they have almost the same phase U. (2) is a differential vector due to differential connection. Since m=rn and the directions are the same, the phase is θ. When phase detection is performed on this signal vector ■ using the reference signal ■, phase data θ for the healthy portion is obtained. Conventionally, l-11 = I [I is small, so phase detection became unstable and stable phase data could not be obtained, but in the remote field eddy current sensor according to the present invention, the front receiving coil FCn near the excitation coil MC is excited. Not only is the signal level higher than that of the rear receiving coil RCn, which is farther away from the coil MC, but the number of windings per coil is greater, so the signal level is further added as the number of windings increases, so it is large enough for phase detection. A differential signal vector (■) is obtained, and stable phase data is obtained.

FIG. 3 shows the signal vector change for a large gradual corrosion part FW. The signal vector I is the front receiving coil F.
A signal vector of the healthy portion due to Cn, ■ is a signal vector of the healthy portion due to the rear receiving coil RCn, and ■ is a difference vector of the healthy portion due to the differential connection. Since the gradual corrosion part FW has a large width, both the front receiving coil and the rear receiving coil are included in the corrosion part, and both signal vectors change in the same way. (2) is a gradual corrosion part signal vector due to the front reception coil FCn, (2) is a gradual corrosion part signal vector due to the rear reception coil RCn, and (2) is a gradual corrosion part difference vector due to the differential connection. Here, (2) includes the gradual corrosion part FW, and the gradual corrosion part FW can be detected based on the phase difference with (2).

4 is a signal vector of a healthy portion of the front receiving coil FCn, .largecircle. is a signal vector of a healthy portion of the rear receiving coil RCn, and .largecircle. is a healthy portion difference vector due to differential connection. The local corrosion part FS has a small spread, so the front receiving coil FC
Considering the case where only n is included in the corroded part9 and only the signal vector ■ changes, ■ is the signal vector in the locally corroded part of the front receiving coil FCn, and ■ is the signal vector due to the differential connection of the locally corroded part FS. be. The local corrosion part FS can be detected by the phase difference between (1) and (2).

Excitation coil MC and front and rear receiving coils FCn and RCn
Fig. 5 shows the reception level according to the distance from the station.

The horizontal axis is the distance difference (MC-FCn or RCn), and 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 reception level, the number of turns must be further increased to compensate for the decrease in the reception level, so as is clear from this characteristic diagram, the number of turns should be increased. If a large number of front reception coils FCn are provided in the front, the signal level increased near the excitation coil MC and the signal level increased due to the increase in the number of windings are added, and a stable signal level can be obtained.

Note that the front and rear receiving coils FCn in the above embodiment
, RCn is not limited to six coils.

Further, the receiving coils can be connected in parallel, and the number of connected coils can be arbitrarily configured. It goes without saying that the connection of the front and rear receiving coils FCn and RCn is not limited to the above embodiment, and similar effects can be obtained as long as a circuit configuration capable of performing differential calculations is obtained.

[Effect of the invention] A remote field eddy current sensor according to the invention.

an excitation coil that generates a remote field eddy current in a test metal material; a first receiving coil that receives the remote field eddy current that is provided at a predetermined distance from the excitation coil; and a first receiving coil that has a smaller number of turns than the first receiving coil. and a second receiving coil for receiving the remote field eddy current, which is disposed at a distance from the excitation coil that is longer than the predetermined interval, so that it is effective against both gradual corrosion and localized corrosion. This has the effect of outputting a sensor signal that provides more stable phase data than conventional methods.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram of a remote field eddy current sensor according to the present invention, Fig. 2 is a signal vector diagram in a healthy pipe related to Fig. 1, and Fig. 3 is a signal vector change diagram due to gradual corrosion related to Fig. 1. , FIG. 4 is a diagram of signal vector changes in local corrosion related to FIG. 1, and FIG. 5 is a characteristic diagram showing the signal level with respect to the distance between the excitation coil and the receiving coil. 1... Test tube (metallic material) 2... Differential coil MC... Exciting coil

Claims (1)

[Claims] an excitation coil that generates a remote field eddy current in a test metal material; a first receiving coil that is provided at a predetermined distance from the excitation coil and receives the remote field eddy current; the number of turns is smaller than that of the first receiving coil; A remote field eddy current sensor further comprising: a second receiving coil that is disposed at a distance from the excitation coil that is longer than the predetermined interval and receives the remote field eddy current.