CN113376247A - Novel composite excitation multi-extension-direction defect leakage magnetic field detection method - Google Patents

Novel composite excitation multi-extension-direction defect leakage magnetic field detection method Download PDF

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CN113376247A
CN113376247A CN202110822714.0A CN202110822714A CN113376247A CN 113376247 A CN113376247 A CN 113376247A CN 202110822714 A CN202110822714 A CN 202110822714A CN 113376247 A CN113376247 A CN 113376247A
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circumferential
magnetic
coil
axial
current
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韦明辉
涂凤秒
张鹏
刘俊
江丽霞
姜蓬勃
邓霜
蔡卫
许明泽
何怡林
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Southwest Petroleum University
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Abstract

The invention provides a novel composite excitation multi-extension-direction defect leakage magnetic field detection method, and belongs to the field of defect detection. The defect detection method comprises the following steps: the circumferential detector and the axial detector are two parts. The circumferential detector is of a magnetic pole component annular structure and is formed by winding a small-amplitude alternating current coil and a non-saturated direct current coil on a yoke, and a magneto-dependent sensor array is uniformly arranged among 4 separated magnetizers around the pipe wall and is mainly used for detecting axial extension defects. The axial detector is a two-stage coil structure, two exciting coils are connected in series to provide a direct current exciting power supply, a relatively uniform magnetizing field is generated at the center of the coils, a magnetic-sensitive sensor is arranged between the two coils to form an axial magnetic-sensitive detection array, and the axial magnetic-sensitive detection array is mainly used for detecting circumferentially extending defects. Meanwhile, the two magnetizers are spaced by a corresponding distance, so that the mutual interference of magnetic fields is further reduced. The invention realizes the miniaturization of the pipeline magnetic flux leakage nondestructive testing magnetizer, reduces the probability of leakage testing and has better testing effect on the axial direction and the circumferential extension direction.

Description

Novel composite excitation multi-extension-direction defect leakage magnetic field detection method
Technical Field
The invention relates to the field of defect detection, in particular to a method for carrying out axial and circumferential magnetization on a pipeline by using a novel composite excitation magnetizer and sensing magnetic flux leakage information of pipeline defects by using a magnetic sensor.
Background
When long-distance oil and gas transmission is carried out, the oil and gas pipeline generates tiny defects due to corrosion perforation, fatigue fracture, external force damage and the like, and particularly, the welding position of a pipeline ring is always the weakest part of the pipeline. The oil gas leakage is easily caused by the generation of cracks, so that safety accidents are caused. Therefore, the long oil and gas pipeline is necessary to be regularly detected and evaluated. The magnetic flux leakage internal detection technology has low requirement on the operating environment, does not need coupling, and is economical and practical, so the magnetic flux leakage internal detection technology is the most widely and mature technology at present.
Because the volume of the oil and gas pipeline is relatively large, the traditional magnetization method leads the pipeline to reach a local saturation magnetization state, which inevitably leads to higher power consumption and larger volume of the magnetizer. Meanwhile, due to volume limitation, the MFL magnetizer in the current industrial application can only carry out axial or circumferential magnetization, defects in different directions cannot be completely and quickly identified, so that the problems of missing detection and pipeline safety are easily caused; therefore, a novel magnetizer and composite excitation multi-extension-direction defect detection method combining the characteristics and advantages of the circumferential excitation technology and the axial excitation technology is found, and the method has important significance for the problem of missed detection of the oil and gas conveying pipeline.
Disclosure of Invention
When the magnetic leakage detection of the defects is carried out, the MFL magnetizer in the current industrial application can only carry out axial or circumferential magnetization, the defects in different directions cannot be completely and quickly identified, and the leakage detection is easily caused. In order to overcome the defects, the invention provides a composite excitation multi-extension-direction defect detection method.
The invention is realized by the following technical scheme:
a novel composite excitation multi-extension-direction defect leakage magnetic field detection method comprises the following steps:
step A, detecting circumferential defects:
a1, axially magnetizing the oil-gas pipeline by using a secondary coil magnetizing structure;
a2, collecting circumferential defect information by using a magnetic sensor array arranged between secondary coils in combination with the pipeline magnetized in the step A1;
b, detecting axial defects:
b1, a small-amplitude sinusoidal alternating-current excitation magnetization field and a non-saturated direct-current magnetization field (or a permanent magnet magnetization field) are superposed together by using a magnetic pole separation ring-shaped structure magnetizer to establish a variable-strength non-saturated alternating-current and direct-current composite magnetization field, and the oil and gas pipeline is magnetized in the circumferential direction;
b2, collecting axial defect information by using a method of measuring alternating components of the leakage magnetic field to equivalently detect the change rate of the leakage magnetic field along with the excitation intensity;
further, in step a1, wherein the diameter of the secondary coil is 13cm, the number of turns is 200, the current is input to 3A, and the interval between the two coils is set to be about 2-4cm apart in consideration of the strength and width of the magnetization field; the two coils adopt coaxial arrangement, can produce even superimposed magnetic field, and the magnetic induction intensity that arbitrary point secondary coil produced on the axis can be solved by magnetic induction intensity and the magnetic field superposition principle of arbitrary point on the axis of circular telegram coil:
Figure BDA0003172363230000021
in the formula, x is the distance from the center of the coil to any point on the central axis; n is the number of coil turns; the excitation current is I; the radii of the secondary coils are both R; magnetic induction B generated by the coil;
further, in step a2, the magnetic sensor array comprises 120 magnetic sensors, and the magnetic sensors are uniformly distributed among the secondary coils and arranged along the whole periphery of the pipeline;
further, in step B1, the circumferential composite unsaturated magnetizer is mainly composed of an unsaturated dc coil, a small ac coil, a yoke, a working air gap, etc., and the small sinusoidal ac electro-excited magnetization field and the unsaturated dc magnetization field (or the permanent magnetic magnetization field) are superimposed together to establish a variable-strength unsaturated ac/dc composite magnetization field;
further, in step B2, the method measures the alternating component of the leakage magnetic field to equivalently detect the rate of change of the leakage magnetic field with the excitation strength
Further, in step a and step B, the distance between the two detection parts is set to be greater than five times of the radius of the coil, and in order to study the rule of the multi-stage coil magnetization field and the interference to the circumferential magnetization field, the magnetic induction formula taylor series expansion of any point on the axis of the electrified coil can be obtained:
Figure BDA0003172363230000022
when x is 0, namely the central positions of the two coils, the other derivatives of the two coils except the second derivative are all zero, the uniformity of the magnetization field is best, and the central magnetic field intensity is maximum:
Figure BDA0003172363230000031
i.e. about 1.5 times more than a single-stage coil, and the magnetizing field is more uniform. When x is five times R (i.e. coil radius and coil pitch), we can obtain:
Figure BDA0003172363230000032
it is clear that the magnetic field at 5R is more than two orders of magnitude less than the strength of the central magnetic field. Meanwhile, since the principle of the axial detection part is to detect Δ U (i.e., the variation value of the leakage magnetic field voltage), the influence of the axial detection part and the circumferential detection part can be reduced to a certain extent when the distance between the two parts is more than five times the radius of the coil.
The invention has the following beneficial effects:
the invention combines the characteristics and advantages of the circumferential excitation technology and the axial excitation technology, and the composite excitation multi-extension-direction defect detection method is divided into a circumferential magnetization detection part and an axial magnetization detection part. The circumferential magnetization detection is based on a detection method of external excitation change and the change rate of a leakage magnetic field, so that the defects in the axial extension direction are detected, and the volume and the weight of the magnetizer are reduced; the axial magnetization adopts a multi-stage coil structure, can generate a uniform superposed magnetic field, reduces the magnetic field variation of a detection area, enhances the magnetization intensity of a magnetization field, and increases the stability and the uniformity of magnetization time and the magnetization field. The composite excitation multi-extension-direction defect detection method provides a new idea for realizing the miniaturization and the light weight of the magnetizer and reducing the occurrence of missing detection.
Drawings
FIG. 1 schematic view of pipeline defect detection
FIG. 2 is a schematic cross-sectional view of a circumferential magnetizer
FIG. 3 is a schematic front view of an axial magnetizer
Brief description of the drawings:
in fig. 1: 1. pipe 2, circumferential magnetizer 3, axial magnetizer
In fig. 2: 4. circumferential yoke iron 5, magnetic sensor 6, pipeline defect 7, radial yoke iron 8, permanent magnet 9 and steel brush
In fig. 3: 10. secondary coil 11, magnetic sensitive sensor
Detailed Description
The invention will be further described with reference to the accompanying drawings.
The invention designs a composite excitation multi-extension-direction defect magnetic flux leakage detection method which comprises a secondary coil detection part and a circumferential unsaturated magnetizer detection part, wherein a two-stage coil axial magnetizer comprises two solenoid excitation coils which are mutually connected in series and provide a direct current excitation power supply, the same magnetic field is generated by the two same coils, and a more uniform magnetization field is generated at the center position of the coils. And a magnetic-sensing sensor is arranged between the two coils to form an axial magnetic-sensing detection array. The circumferential unsaturated magnetizer is formed by winding a small-amplitude alternating current coil and an unsaturated direct current coil on a yoke. The small-amplitude alternating current coil is uniformly wound on the framework of the yoke iron for 20 turns by using an enameled wire with the diameter of 0.001m, and the unsaturated direct current coil is uniformly wound on the frameworks of the two pole shoes for 200 turns by using the same enameled wire. Meanwhile, the two magnetizers are spaced by a corresponding distance, so that the mutual interference of magnetic fields is further reduced. The method comprises two steps of detecting circumferential and axial defects:
step A, detecting circumferential defects:
a1, axially magnetizing the oil-gas pipeline by using a secondary coil magnetizing structure;
a2, collecting circumferential defect information by using a magnetic sensor array arranged between secondary coils in combination with the pipeline magnetized in the step A1;
b, detecting axial defects:
b1, a small-amplitude sinusoidal alternating-current excitation magnetization field and a non-saturated direct-current magnetization field (or a permanent magnet magnetization field) are superposed together by using a magnetic pole separation ring-shaped structure magnetizer to establish a variable-strength non-saturated alternating-current and direct-current composite magnetization field, and the oil and gas pipeline is magnetized in the circumferential direction;
b2, collecting the information of the leakage magnetic field by using a method for equivalently detecting the change rate of the leakage magnetic field along with the excitation intensity by measuring the alternating component of the leakage magnetic field;
step A1) wherein, the two-stage coil axial magnetizer, two solenoid exciting coils are connected in series to provide a 3A exciting power supply, the same magnetic field is generated by the two same coils, a more uniform magnetizing field is generated at the center position of the coils, the diameter of the two-stage coil is 13cm, the number of turns is 200, current is input, and the interval setting installation range of the two coils is about 2-4 cm; magnetizing the axial direction of the pipeline by an axial magnetizer; an axial magnetizer (3) portion as in fig. 1;
step a2) axially magnetizes the pipeline in step a1, and collects circumferential defect information by 120 magnetic sensor arrays uniformly distributed between the secondary coils, such as the magnetic sensor array (11) in fig. 3;
step B1) the circumferential composite unsaturated magnetizer mainly comprises an unsaturated direct current coil, a small amplitude alternating current coil, a yoke iron, a working air gap and the like, a small amplitude sinusoidal alternating current electric excitation magnetization field and an unsaturated direct current magnetization field (or a permanent magnetic magnetization field) are superposed to establish a variable-strength unsaturated alternating current and direct current composite magnetization field, as shown in figure 2, the circumferential magnetizer comprises a circumferential yoke iron (4), a magnetic sensor (5), a permanent magnet (7), a radial yoke iron (8) and a steel brush (9);
step B2) and after the step B1 carries out circumferential magnetization on the pipeline, the principle of detecting the defect leakage magnetic field by adopting a composite excitation unsaturated magnetization detection method is as follows: the whole excitation loop is formed by a steel plate magnetization field and an air magnetization field together, and when the steel plate to be detected is magnetized, the steel plate and air around the steel plate are also magnetized by the magnetizer; wherein the air magnetization field is equivalent to the magnetic leakage field, and by the magnetic leakage detection rationale, the air still equals the change of excitation field magnetic flux in the yoke with steel sheet magnetic flux change under the condition of changing the excitation:
ΔφY＝ΔφS+ΔφF
in the formula, delta phiYIs the magnetic flux variation of the magnetic yoke; delta phiSIs the amount of change in the magnetic flux inside the steel plate; delta phiFIs the air flux variation;
according to the basic principle of magnetic flux leakage detection, the magnetic resistance at the defect position of the detected steel plate can be obviously increased, the magnetic permeability can be reduced, and the intensity of the magnetization field at the defect position inside the steel plate can be obviously increased. Magnetic flux variation delta phi of steel plate without defectSAt the same variation magnetization delta phiYUnder the condition, the defect rate is obviously higher than that of the steel plate with the defect. Therefore, the amount of change Δ φ in the magnetic flux can be adjusted to the inside of the steel sheetSAmount of change of magnetic flux from yokeYDefining a defect evaluation function Q (·);
Figure BDA0003172363230000051
in general, the actual magnetization is realized by exciting current to realize total magnetic flux in the magnetic yoke, i.e. the total magnetic flux in the magnetic yoke is a function of the exciting current, i.e. phiY＝φY(I) In that respect Therefore, the amount of change Δ φ of magnetic flux in the yokeYCan be expressed as:
Figure BDA0003172363230000061
in the formula, phiY(I) Is a function of the yoke flux with respect to the excitation current I; Δ I is an excitation current variation amount;
amount of change of magnetic flux delta phiYIs a function of the amount of current change Δ I and the current I. If the output voltage of the detection system is recorded as UMFor detecting the intensity B of the leakage magnetic field in the air by a magnetic sensitive element in the systemFFunction of the detected value, i.e. BF＝B(UM). Similarly, the amount of change Δ B in the intensity of the leakage magnetic fieldFCan be expressed as:
Figure BDA0003172363230000062
in the formula of UMIs the leakage magnetic field detection output voltage;
the area of the leakage flux in air is approximately constant, while the leakage field intensity flux B in airFAre variable. In addition, the magnetic flux phi can be obtained by the integral of the magnetic induction intensity B and the area S, namely phi is obtainedF＝∫BFds. Therefore, the amount of change Δ φ in the leakage flux in the air can be calculated approximatelyFComprises the following steps:
ΔφF＝∫ΔBFds＝∫B′(UM)ΔUMds≈B′(UM)ΔUMS
in the formula, S is the equivalent area of the leakage magnetic flux in the air and is a constant;
the evaluation function Q (-) available after finishing is expressed as:
Figure BDA0003172363230000063
apparently in the formula B' (U)M) ,/φ' (I) is constant, and further:
Figure BDA0003172363230000064
combining the above two formulas
Figure BDA0003172363230000065
It is apparent that the sensitivity of the above equation is determined by the leakage field voltage fluctuation and the input excitation current fluctuation, i.e., Δ UMand/Delta I. Delta I is the fluctuation value of input excitation voltage, and delta U is the fluctuation value of leakage magnetic field output voltage which can be detected by a magnetic sensor; namely, a detection method based on external excitation change and leakage magnetic field change rate is utilized to realize the detection of the defects in the axial extension direction.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting the same, and although the present invention is described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: modifications and equivalents may be made to the embodiments of the invention without departing from the spirit and scope of the invention, which is to be covered by the claims.

Claims (5)

1. A novel composite excitation multi-extension-direction defect leakage magnetic field detection method comprises an axial detection part and a circumferential detection part, and comprises the following steps:
step A, detecting circumferential defects:
a1, axially magnetizing the oil-gas pipeline by using a secondary coil magnetizing structure;
a2, collecting circumferential defect information by using a magnetic sensor array arranged between secondary coils in combination with the pipeline magnetized in the step A1;
b, detecting axial defects:
b1, a small-amplitude sinusoidal alternating-current excitation magnetization field and a non-saturated direct-current magnetization field (or a permanent magnet magnetization field) are superposed together by using a magnetic pole separation ring-shaped structure magnetizer to establish a variable-strength non-saturated alternating-current and direct-current composite magnetization field, and the oil and gas pipeline is magnetized in the circumferential direction;
b2, collecting the information of the leakage magnetic field by using a method for equivalently detecting the change rate of the leakage magnetic field along with the excitation intensity by measuring the alternating component of the leakage magnetic field;
2. the method of claim 1, wherein in step a1, the secondary coil structure has a diameter of 13cm and a number of turns of 200, an ac excitation power source is input, the input current has the same magnitude and direction, and the intensity of the magnetization field is controlled by the current input to the coil and the number of turns of the coil. The coils are mutually connected in series and are coaxially arranged, and the mutual influence between the coils can be effectively reduced by the coil radius of which the distance between the two coils is more than five times;
3. the method according to claim 1, wherein in step a2, the magneto-sensitive sensor array comprises 120 magneto-sensitive sensors uniformly distributed between the secondary coils and arranged along the entire periphery of the pipe, the magneto-sensitive elements determining the characteristics of the defect by detection of the leakage magnetic signal;
4. the method as claimed in claim 1, wherein in step B1, the circumferential detector is composed of 4 pairs of symmetrical structures formed by permanent magnets and four quarter yokes, respectively, and 4 magnetic circuits formed by the tube wall and steel brushes, so as to form 4 independent detection areas in the detection area inside the pipeline, and the circumferential composite unsaturated magnetizer is mainly composed of unsaturated direct current coil, small alternating current coil, yoke and working air gap, and the annular structure has certain diameter-changing capability;
5. a method as claimed in claim 1, wherein, to reduce the effect of the two sensing portions to a certain extent, the axial and circumferential sensing portions are spaced more than five coil radii apart.
CN202110822714.0A 2021-07-21 2021-07-21 Novel composite excitation multi-extension-direction defect leakage magnetic field detection method Pending CN113376247A (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114062481A (en) * 2021-12-14 2022-02-18 国家石油天然气管网集团有限公司 Phi 1219 gas transmission pipeline bidirectional excitation ultra-high-definition magnetic flux leakage internal detection system
CN117589862A (en) * 2024-01-18 2024-02-23 湖北工业大学 Magnetic chromatography detection device and method

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114062481A (en) * 2021-12-14 2022-02-18 国家石油天然气管网集团有限公司 Phi 1219 gas transmission pipeline bidirectional excitation ultra-high-definition magnetic flux leakage internal detection system
CN117589862A (en) * 2024-01-18 2024-02-23 湖北工业大学 Magnetic chromatography detection device and method
CN117589862B (en) * 2024-01-18 2024-05-17 湖北工业大学 Magnetic chromatography detection device and method

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