CN105241952B - A kind of channel bend defect inspection method and detection means based on far-field eddy - Google Patents

Abstract

A detection method and detection device for pipeline elbow defects based on far-field eddy currents. It mainly solves technical problems such as blind areas or poor probe passability when the existing eddy current testing is used for pipe elbows. The key points of the technical solution are: adopting a far-field eddy current sensor composed of two identical excitation units and a receiving unit, and the two excitation units are respectively located on both sides of the receiving unit, and both the excitation unit and the receiving unit are located along the circumference of the cross-section of the pipe elbow to be tested. The receiving unit is located in the far-field area where the indirect coupling magnetic field signal is measured; when the far-field eddy current sensor is applied with harmonic excitation, the double excitation is used to narrow the far-field area and increase the measured signal amplitude; the sensor is along the circumference of the pipe elbow To scan, measure the phase difference of the signal received by the receiving unit relative to the excitation signal, so as to obtain the change characteristics of the phase difference, that is, to obtain the corrosion and crack defect information at the pipe elbow. It mainly adopts the principle of far-field eddy current and is applied to the defect detection of pipe elbows.

Description

A method and device for detecting defects of pipe elbows based on far-field eddy currents

technical field

The invention relates to an electromagnetic non-destructive testing method, in particular to a method and a special device for detecting corrosion or crack defects at pipe elbows based on far-field eddy currents.

Background technique

Pipes are widely used in many industries such as oil and gas, chemical industry, electric power and heating, and pipe elbows are an indispensable part of pipeline piping systems. Most pipe elbows are affected by high temperature, high pressure and complex external environment during work, and the inside of the outer curved surface of the pipe elbow is always eroded by the medium during use, resulting in erosion corrosion and thinning of the pipe wall. In addition, under high temperature and high pressure, the pipe elbow wall is prone to cracks. The above defects are easy to expand rapidly under high pressure, causing cracks in the pipe wall at the pipe elbow, which in turn leads to leakage accidents. The condition of the pipeline elbow directly affects the safe and smooth operation of the entire pipeline system, so it is necessary to research and develop a pipeline elbow detection device.

At present, the detection methods of pipeline elbows include ultrasonic testing, radiographic testing, conventional eddy current testing, pulsed eddy current testing, etc. Ultrasonic testing requires a coupling agent, and the working temperature should not be too high; radioactive testing requires a radioactive source, which is polluted during the actual testing process and is harmful to the human body; conventional eddy current testing is easily affected by the skin effect, and the detection tends to detect defects on the surface of the specimen; Pulsed eddy current testing belongs to the fixed-point detection of placement. When it is used for the detection of pipeline elbows with complex structures, there are certain blind spots, and the sensitivity to local defects is not enough. Most of the existing far-field eddy current testing devices use the internal penetration detection, and the internal penetration detection has a disadvantage: it is difficult to pass through the elbow that may have accumulations.

For example, Sun Yushi, Qu Minxing, and Si Jiatun of Nanjing Aeronautical Institute invented and applied for a patent on July 7, 1990. "Efficient and practical probe for far-field eddy current nondestructive testing" (patent application number 90105697.9, publication number CN1058097) published Three far-field eddy current probe improvement technologies, including setting a magnetic circuit for the exciting coil, setting a magnetic circuit for the receiving coil, and setting a compensation coil between the exciting and receiving coils. Through these improvements, high signal amplitude and low excitation power are obtained. The axial length of the probe is small and so on. These improvements have reduced the difficulty of the application of far-field eddy currents and reduced the length of the probe to a certain extent, but it is still difficult to pass through the elbow of the pipeline. Another example is "a metal defect eddy current detection device and its probe" (application number 201210416556.X, publication number CN102879462) invented by Chen Peihua, Huang Pingjie, Li Guohou, and Zhou Zekui of Zhejiang University and applied for a patent on October 27, 2012. An eddy current detection device for metal defects based on frequency mixing technology and its probe structure. The device combines conventional eddy current and low-frequency far-field eddy current technologies to detect defects in plate-shaped or tubular metal materials, but the above-mentioned tubular shape combined with its probe structure It can only be a straight pipe and can only be placed on the pipe axis. When placed on the circumference, it is equivalent to only applying conventional eddy current testing. Therefore, in the special position of the pipe elbow, the surface of the measured part is complex, and this device is difficult to handle smoothly. detection. Another example is the U.S. patent "Far-field eddy current sensor connected by flexible unit" (patent application number US19970941057, publication number US6087830), which can pass through clean pipe elbows inside, but accumulations are easy to occur at pipe elbows used in industry, thus It is difficult for the far-field eddy current sensor to pass through smoothly, which increases the difficulty of detection.

To sum up, the existing detection methods have certain limitations for the detection of the special position of the pipe elbow.

Contents of the invention

The purpose of the present invention is to overcome various deficiencies in the prior art, and to provide a method that utilizes double excitation to narrow the far-field area, increase the amplitude of the measured signal, fully reflect the advantages of far-field eddy current detection, and solve the problem of internal penetration. A far-field eddy current-based pipeline elbow defect detection method and detection device for the difficult problem of detecting pipeline elbows with conventional far-field eddy current sensors.

The technical solution adopted by the present invention to solve the technical problem is: adopt a far-field eddy current sensor composed of two identical excitation units and a receiving unit, and the two excitation units are respectively located on both sides of the receiving unit, and both the excitation unit and the receiving unit are located along the The cross-section of the detection pipe elbow is set circumferentially, and the receiving unit is located in the far-field area where the indirect coupling magnetic field signal is measured; when the far-field eddy current sensor is applied with harmonic excitation, the double excitation is used to narrow the far-field area and increase the amplitude of the measured signal The sensor scans along the circumference of the pipe elbow to measure the phase difference between the signal received by the receiving unit and the excitation signal, so as to obtain the change characteristics of the phase difference, that is, to obtain the corrosion and crack defect information at the pipe elbow.

The far-field eddy current sensor is sequentially connected with the harmonic signal excitation circuit, signal processing circuit, A/D conversion circuit and computer, the harmonic signal excitation circuit provides harmonic excitation to the far-field eddy current sensor, and the far-field eddy current sensor is arranged on the pipeline The outer surface of the elbow is excited to induce eddy current and receive the indirect coupling magnetic field signal in the far field area of the eddy current, convert it into a voltage signal, and send it to the signal processing circuit. The signal processing circuit amplifies, filters, and compares the received signal , sent to the A/D conversion circuit, the A/D conversion circuit converts the analog signal into a digital signal and sends it to the computer, and the computer processes the data to obtain the corrosion and crack defect information of the pipe elbow under test.

Further, the far-field eddy current sensor is arranged on the cross section of the pipe elbow 1; the excitation unit includes an excitation coil 3, and the receiving unit includes a receiving coil 4, the axis of the excitation coil 3 is arranged along the circumference of the pipe elbow 1, and the receiving unit includes The axis of the coil 4 is arranged radially along the pipeline elbow; the receiving coil 4 is located in the far-field area where the indirect coupling magnetic field signal is measured; a harmonic excitation is applied to the excitation coil 3 of the sensor, and the changing excitation field induces distributed alternating magnetic field, the receiving coil 4 in the receiving unit is located in the far field area to measure the indirect coupling magnetic field signal, the change of the phase difference between the measured signal and the excitation signal indicates the existence of corrosion or crack defects, by observing and analyzing the phase The change characteristics of the difference can realize the detection of the defect of the pipe elbow 1 .

The detection method includes the following steps: Step 1: Install a far-field eddy current sensor in the circumferential direction of the pipe elbow for scanning; Step 2: Apply low-frequency harmonic excitation to the excitation unit of the far-field eddy current sensor; To scan, measure the phase difference between the signal received in the receiving coil in the receiving unit and the excitation signal; Step 4: By observing and analyzing the change characteristics of the phase difference, the corrosion and crack defects at the pipe elbow can be judged .

The pipe elbow detection device of the present invention consists of a far-field eddy current sensor 2 composed of two identical excitation units and a receiving unit, and the two excitation units are respectively located on both sides of the receiving unit. The excitation unit includes an excitation coil 3, the receiving unit includes a receiving coil 4, the axis of the excitation coil 3 is arranged along the circumference of the pipe elbow 1, the axis of the receiving coil 4 is arranged radially along the pipe elbow, and the receiving coil 4 is located in the measuring indirect The far-field region where magnetic field signals are coupled.

The far-field eddy current sensor 2 includes a housing 13, an end cover 11, an excitation coil 3, a receiving coil 4 and a socket; the housing 13 is a "︹" type structure provided with an inner cavity, and two ends are provided with openings, and the end cover 11 is mounted on the open openings at both ends of the shell 13; the exciting coil 3 is fixed on the inner wall of the inner cavity of the shell 13, the receiving coil 4 is fixed on the lower part of the inner cavity of the shell 13, the exciting coil 3 and the receiving coil 4 The lead wires are connected to the socket respectively. The two exciting coils 3 can be arranged symmetrically on both sides of the receiving coil 4 .

The far-field eddy current sensor 2 is connected with a low-frequency harmonic excitation circuit 5 , a signal processing circuit 6 , an A/D conversion circuit 7 and a computer 8 in sequence.

The excitation unit includes an excitation coil 3 and a shielding unit 12, and the excitation coil 3 is installed in the shielding unit 12; the excitation coil 3 is a rectangular coil; the receiving coil 4 is a cylindrical coil.

The present invention narrows the far-field region by using double excitations, increases the measured signal amplitude, fully embodies the advantages of far-field eddy current detection, and solves the difficult problem that the inner through-type far-field eddy current sensor is difficult to detect the pipe elbow. It also has the following advantages: (1) The thickness of the pipe wall is approximately proportional to the phase of the detection signal, which is easy to distinguish defects; (2) It is not affected by the skin effect and is not greatly affected by the lift-off effect; (3) It has the same sensitivity to internal and external defects of the pipe wall; (4) Inheriting the advantages of conventional eddy current non-contact and fast, while adopting scanning mode to greatly reduce detection blind spots.

Description of drawings

Fig. 1 is a schematic cross-sectional structure diagram of a pipe elbow detection device of the present invention

Fig. 2 is a schematic diagram of the structure of the pipeline elbow detection device in use according to the present invention;

Fig. 3 is a schematic diagram of the detection principle of the present invention;

Fig. 4 is the sample diagram that the present invention detects;

Fig. 5 is a schematic diagram of the cross-sectional structure of A-A of Fig. 4;

Fig. 6 is a curve diagram of the amplitude signal detected by the far-field eddy current sensor using an excitation coil and a receiving coil;

Fig. 7 is a graph of the phase difference detected by the far-field eddy current sensor using an exciting coil and a receiving coil;

Fig. 8 is a Poynting vector diagram detected by a far-field eddy current sensor using an exciting coil and a receiving coil;

Fig. 9 is a graph of the amplitude signal detected by the far-field eddy current sensor using double excitation coils;

Fig. 10 is a graph of the phase difference detected by the far-field eddy current sensor using double excitation coils;

Figure 11 is the Poynting vector diagram obtained from the detection of the far-field eddy current sensor using dual excitation coils;

Fig. 12 is a phase diagram corresponding to different defects measured by the device of the present invention when the axis of the detection coil is the center line of the defect.

In the figure: pipeline elbow-1, far-field eddy current sensor-2, excitation coil-3, receiving coil-4, harmonic signal excitation circuit-5, signal processing circuit-6, A/D conversion circuit-7, computer- 8. Aviation socket-9, handle-10, end cover-11, shielding unit-12, shell-13.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments.

The existing general far-field eddy current sensor only uses one exciting coil and one receiving coil. When one exciting coil is used to detect a pipe with an outer diameter of 80 mm, the obtained amplitude signal curve, phase difference curve and Poynting vector diagram are respectively As shown in Figures 6, 7, and 8, the amplitude has an inflection point, the phase has a 90° change, and the energy has penetrated the tube wall twice, indicating that the far-field eddy current phenomenon has occurred. However, the far-field region is located in the region where the amplitude and phase are basically unchanged and the energy is penetrated twice. It can be seen from the figure that when one excitation coil is used, the arc length distance from the far-field region to the axis of the excitation coil is 100mm to 120mm. The three important characteristic signals of "amplitude signal curve, phase difference curve and Poynting vector" of the far-field eddy current phenomenon collected by it have little change compared with the excitation signal, and are easily interfered by noise signals, so it is difficult to use them for judgment. Objects are tested for such defects as corrosion or cracks. Because the amplitude signal is very weak, the requirements for the subsequent signal processing circuit are higher. In addition, the distance between the excitation coil and the far field area is larger, which increases the size of the sensor and thus increases the cost.

The present invention adopts a far-field eddy current sensor composed of two identical excitation units and a receiving unit, and the two excitation units are respectively located on both sides of the receiving unit, and both the excitation unit and the receiving unit are arranged circumferentially along the cross-section of the pipe elbow to be detected, and The receiving unit is located in the far-field area where the indirect coupled magnetic field signal is measured; when the far-field eddy current sensor is applied with harmonic excitation, the double excitation is used to narrow the far-field area to increase the measured signal amplitude; the sensor scans along the circumference of the pipe elbow, and measures The phase difference of the signal received by the receiving unit relative to the excitation signal is taken to obtain the change characteristics of the phase difference, that is, to obtain the corrosion and crack defect information at the pipe elbow.

It can be seen from this that the detection method of the present invention belongs to far-field eddy current detection, and is a non-destructive detection technology based on the far-field eddy current effect. Therefore, whether the far-field eddy current detection technology can be used to detect regular curved surface metal materials depends on whether A far-field eddy current phenomenon occurs. The far-field eddy current phenomenon has three important features: the amplitude inflection point, the 90° phase change, and the two penetration test pieces of energy. The present invention collects the "amplitude signal curve, phase difference curve and Poynting "Vector" three important characteristic signals relative to the change of the excitation signal to judge whether there are such defects as corrosion or cracks in the measured object.

The present invention adopts the dual excitation method, thereby obtains the amplitude signal curve, the phase difference curve and the Poynting vector diagram as shown in Figures 9, 10, and 11 respectively. Similarly, it can be seen that the far-field eddy current phenomenon has occurred, and a relatively When the coil is excited, the amplitude signal in the far field area increases, and the far field area is located at 35mm to 45mm, and the far field area can be shortened. When optimizing the far-field eddy current sensor, the signal amplitude and the distance of the far-field area are often considered.

Embodiment 1, referring to Fig. 1-3, the shielding unit 12 is made of silicon steel sheet. The handle 10 is connected to the end cover 11 by a hexagonal screw, and the end cover 11 is connected to the housing 13 by a cross recessed pan head screw. The excitation coil 3 is fixed at both ends of the bottom of the casing, the receiving coil 4 is fixed at the center of the bottom of the casing cavity, the shielding unit 12 is covered above the excitation coil 3 , and the leads of the excitation coil 3 and the receiving coil 4 are connected to the aviation socket 9 . The far-field eddy current sensor is arranged on the cross section of the pipeline elbow 1; the excitation unit includes an excitation coil 3, and the receiving unit includes a receiving coil 4, the axis of the excitation coil 3 is arranged along the circumference of the pipeline elbow 1, and the axis of the receiving coil 4 It is arranged radially along the pipe elbow; the receiving coil 4 is located in the far-field area where the indirect coupling magnetic field signal is measured; a harmonic excitation is applied to the sensor excitation coil 3, and the changing excitation field causes the circumferential distribution along the cross-section of the pipe elbow 1 Alternating magnetic field, the receiving coil 4 in the receiving unit is located in the far field area to measure the indirect coupling magnetic field signal, the circumferential moving sensor scans the pipe elbow, and the change of the phase difference between the measured signal and the excitation signal indicates corrosion or crack defects The detection of the defect of the pipe elbow 1 is realized by observing and analyzing the change characteristics of the phase difference.

The detection method includes the following steps: Step 1: Install a far-field eddy current sensor in the circumferential direction of the pipe elbow for scanning; Step 2: Apply low-frequency harmonic excitation to the excitation unit of the far-field eddy current sensor; To scan, measure the phase difference between the signal received in the receiving coil in the receiving unit and the excitation signal; Step 4: By observing and analyzing the change characteristics of the phase difference, the corrosion and crack defects at the pipe elbow can be judged .

The far-field eddy current sensor of the present invention adopts an external setting method and uses double excitation to narrow the far-field area to increase the measured signal amplitude, thereby solving the problem that the inner through-type far-field eddy current sensor is difficult to detect the pipe elbow .

Embodiment 2, referring to Fig. 3, the far-field eddy current sensor of the present invention is connected with harmonic signal excitation circuit, signal processing circuit, A/D conversion circuit and computer successively, and harmonic signal excitation circuit provides harmonic wave to far-field eddy current sensor Excitation, the far-field eddy current sensor is set on the outer surface of the pipe elbow to induce the generation of eddy current and receive the indirect coupling magnetic field signal in the eddy current far-field area, convert it into a voltage signal, and send it to the signal processing circuit, the signal processing circuit is responsible for receiving After the signal is amplified, filtered and compared, it is sent to the A/D conversion circuit. The A/D conversion circuit converts the analog signal into a digital signal and sends it to the computer. The computer processes the received data to obtain the measured pipe elbow. Corrosion and crack type defect information. Referring to Fig. 1 to Fig. 5, all the other are the same as embodiment 1.

Embodiment 3, referring to Fig. 1 to Fig. 5, the pipe elbow detection device of the present invention consists of a far-field eddy current sensor 2 composed of two identical excitation units and a receiving unit, and the two excitation units are respectively located on both sides of the receiving unit. The excitation unit includes an excitation coil 3, the receiving unit includes a receiving coil 4, the axis of the excitation coil 3 is arranged along the circumference of the pipe elbow 1, the axis of the receiving coil 4 is arranged radially along the pipe elbow, and the receiving coil 4 is located in the measuring indirect The far-field region where magnetic field signals are coupled. The far-field eddy current sensor 2 includes a housing 13, an end cover 11, an excitation coil 3, a receiving coil 4 and a socket, and the socket can adopt the structural form of an aviation socket 9, or other structural forms; the housing 13 is provided with an internal The "︹" type structure of the cavity, and openings are provided at both ends, and the end cover 11 is fitted on the openings at both ends of the housing 13; the exciting coil 3 is fixed on the inner wall of the inner cavity of the housing 13, and the receiving coil 4 is fixed Installed in the lower part of the waist in the inner cavity of the housing 13, the lead wires of the exciting coil 3 and the receiving coil 4 are connected to the socket respectively. The excitation coil 3 is also fixed at both ends of the bottom of the casing, and the receiving coil 4 is fixed at the center of the bottom of the casing cavity. The two excitation coils 3 are preferably arranged symmetrically on both sides of the receiving coil 4; however, when the currents of the two excitation units are different, that is, the two excitations are different, the symmetrical arrangement may not be adopted.

Figure 4-5 is a schematic diagram of the sample tested by the device of the present invention. The pipe elbow has a rotation angle of 90°, an outer diameter of 80mm, a wall thickness of 2mm, and the depth of the defect is 0.25mm, 0.5mm, 0.75mm, and 1mm in sequence. , 1.25mm, 1.5mm, 1.75mm.

As shown in FIG. 12 , when the present invention is measuring and the axis of the detection coil is the center line of the defect, the measured phase diagrams correspond to different defects in sequence. The relationship between the phase difference and the depth of the defect is approximately linear, which shows that the device can effectively detect the defects of the pipe elbow.

In the present invention, after applying harmonic excitation to the far-field eddy current sensor, by observing and analyzing the change characteristics of the phase difference of the signal received in the sensor receiving coil relative to the excitation signal, the corrosion and crack defect information at the pipe elbow is obtained.

Embodiment 4, referring to FIG. 1 to FIG. 5 , the excitation unit includes an excitation coil 3 and a shielding unit 12 , the excitation coil 3 is installed in the shielding unit 12 , that is, the shielding unit 12 is covered above the excitation coil 3 .

The excitation coil 3 can be made of silicon steel sheets with high magnetic permeability to cover the shielding unit 12, which not only shields and weakens the direct coupling magnetic field, but also plays the role of gathering the excitation magnetic field; The unit is used as an excitation to effectively narrow the far field area, reduce the size of the sensor, and increase the signal amplitude obtained by the receiving coil to facilitate signal acquisition.

Embodiment 5, referring to FIG. 1 to FIG. 5 , the exciting coil 3 is a rectangular coil; the receiving coil 4 is a cylindrical coil.

Embodiment 6, referring to Fig. 1 to Fig. 5, the housing 13 is provided with a handle 10, the hand 10 and the housing 13 can be connected to each other by hexagonal screws, etc. to connect.

Embodiment 7, referring to Fig. 1 to Fig. 5, described far-field eddy current sensor 2 is connected with low-frequency harmonic excitation circuit 5, signal processing circuit 6, A/D conversion circuit 7 and computer 8 successively, harmonic signal excitation circuit 5 Provide harmonic excitation to the far-field eddy current sensor 2. The far-field eddy current sensor 2 is set on the outer surface of the pipe elbow 1 to induce eddy currents and receive the indirect coupling magnetic field signals in the eddy current far-field area. After converting them into voltage signals, they are sent to The signal processing circuit 6, after the signal processing circuit 6 amplifies, filters and compares the received signal, sends it to the A/D conversion circuit 7, and the A/D conversion circuit 7 converts the analog signal into a digital signal and sends it to the computer 8, and the computer 8 A portable computer can be used to realize functions such as signal acquisition control, signal display and data storage through the computer 8, process the received data, distinguish signal characteristics, and obtain defect information of the pipe elbow 1 under test.

The present invention narrows the far-field area by using double excitation, improves the measured signal amplitude, fully embodies the advantages of far-field eddy current detection, and solves the difficult problem that the inner through-type far-field eddy current sensor is difficult to detect the pipe elbow. At the same time, it also It can be used for the inspection of straight pipes.

Claims (9)

1. a kind of channel bend defect inspection method based on far-field eddy, it is characterized in that：Using single including two identical excitations The far-field eddy sensor that member and a receiving unit are formed, and two exciting units are located at receiving unit both sides respectively, excitation is single Member and receiving unit are circumferentially disposed along detected channel bend cross section, and receiving unit is positioned at measurement INDIRECT COUPLING magnetic field letter Number far-field region；After far-field eddy sensor applies harmonic excitation, furthered far-field region using double excitation, improve measured signal Amplitude；Sensor measures the phase difference for the signal relative excitation signal that receiving unit receives along channel bend scanning direction, from And obtain the variation characteristic that arrives of phase difference, that is, obtain corrosion and crack defect information at channel bend.

2. the channel bend defect inspection method based on far-field eddy according to claim 1, it is characterized in that：Far-field eddy passes Sensor is connected with harmonic signal exciting circuit, signal processing circuit, A/D change-over circuits and computer successively, and harmonic signal swashs Encourage circuit and provide harmonic excitation to far-field eddy sensor, far-field eddy sensor is arranged on channel bend outer surface, with excitation The INDIRECT COUPLING magnetic field signal for producing and being vortexed and receive vortex far-field region is induced, after being translated into voltage signal, sends letter to Number process circuit, signal processing circuit is amplified to the signal of reception, filters, relatively after, send A/D change-over circuits, A/D to Change-over circuit converts analog signals into data signal and sent in computer, and computer is handled data, be tested so as to obtain The corrosion of channel bend and crack defect information.

3. the channel bend defect inspection method based on far-field eddy according to claim 1, it is characterized in that：The far field whirlpool Flow sensor is arranged on channel bend（1）On cross section；The exciting unit includes excitation coil（3）, the receiving unit bag Include receiving coil（4）, excitation coil（3）Axis is along channel bend（1）It is circumferentially disposed, receiving coil（4）Axis is along channel bend It is radially arranged；Receiving coil（4）Positioned at the far-field region of measurement INDIRECT COUPLING magnetic field signal；To sensor excitation coil（3）In Apply a harmonic excitation, the exciting field of change triggers along channel bend（1）The circumferentially distributed alternating magnetic field in cross section, receive single Receiving coil in member（4）Positioned at far-field region measure INDIRECT COUPLING magnetic field signal, measured signal relative to pumping signal phase The change of potential difference shows corrosion or the presence of crack defect, by observing and analyzing the variation characteristic of phase difference so as to realizing pair Channel bend（1）The detection of defect situation.

4. the channel bend defect inspection method based on far-field eddy according to claim 1, it is characterized in that：Including following step Suddenly：Step 1：In the circumferentially disposed far-field eddy sensor of channel bend, to be scanned；Step 2：Sensed to far-field eddy The exciting unit of device applies low-frequency harmonics excitation；Step 3：Along channel bend circumferential scanning, the reception line in receiving unit is measured The phase difference of the signal relative excitation signal received in circle；Step 4：By observing and analyzing the variation characteristic of phase difference, i.e., The corrosion at channel bend and crack defect situation can be differentiated.

5. a kind of channel bend detection means, it is characterized in that：By being formed including two identical exciting units and a receiving unit Far-field eddy sensor（2）, and two exciting units are located at receiving unit both sides respectively, the exciting unit includes excitation coil （3）, the receiving unit includes receiving coil（4）, excitation coil（3）Axis is along channel bend（1）It is circumferentially disposed, receiving coil （4）Axis is radially arranged along channel bend, and receiving coil（4）Positioned at the far-field region of measurement INDIRECT COUPLING magnetic field signal.

6. channel bend detection means according to claim 5, it is characterized in that：The far-field eddy sensor（2）Including shell Body（13）, end cap（11）, excitation coil（3）, receiving coil（4）And socket；Housing（13）To be provided with " ︹ " type knot of inner chamber Structure, and both ends set open, end cap（11）Cooperation is arranged on housing（13）In the opening at both ends；Excitation coil（3）It is packed in shell Body（13）On the inwall of inner chamber both sides, receiving coil（4）It is packed in housing（13）Inner chamber Zhong Yao bottoms, excitation coil（3）With connect Take-up circle（4）Lead be connected respectively with socket.

7. according to the channel bend detection means of claim 5 or 6, it is characterized in that：Two excitation coils（3）It is symmetricly set on and connects Take-up circle（4）Both sides.

8. channel bend detection means according to claim 5, it is characterized in that：The far-field eddy sensor（2）Successively with Low-frequency harmonics exciting circuit（5）, signal processing circuit（6）, A/D change-over circuits（7）And computer（8）It is connected.

9. according to the channel bend detection means of claim 5 or 6, it is characterized in that：Exciting unit includes excitation coil（3）With Screen unit（12）, excitation coil（3）Installed in screen unit（12）It is interior；The excitation coil（3）Using square coil；Receive Coil (4) uses cylindrical coil.