CN106501318A - A kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method - Google Patents
A kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method Download PDFInfo
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- CN106501318A CN106501318A CN201610974741.9A CN201610974741A CN106501318A CN 106501318 A CN106501318 A CN 106501318A CN 201610974741 A CN201610974741 A CN 201610974741A CN 106501318 A CN106501318 A CN 106501318A
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- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
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Abstract
A kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method, belongs to technical field of nondestructive testing.In tested metallic conduit（3）Region two ends to be measured are installed by exciting current electrode（1）, measuring electrode is installed in region to be measured（2）, by exciting current electrode（1）To tested pipeline（3）Apply the ac-excited electric current of different frequency, due to the presence of Kelvin effect, when exciting current frequency is higher, skincurrent（4）Exist only in the shallow-layer of metallic conduit outer wall, with the reduction of frequency, skincurrent（4）Will be present in whole metal pipe-wall；Defect（5）Presence can affect skincurrent（4）Distribution, that is to say and have impact on measuring electrode（2）Between voltage amplitude, the depth information of defect can be obtained by the differential derivation to voltage.This technology need not measure primary voltage, reference voltage and original wall thickness etc., the impact that can effectively overcome system drifting, original wall thickness measurement error to cause measurement.
Description
Technical field
Present invention is mainly used for the depth of defect of measurement metallic conduit, specifically, is related to a kind of to tested pipeline applying
The series of voltage value that obtains of measurement is carried out differential derivation by the ac-excited electric current of different frequency, using derivative extreme point come
The method for solving depth of defect.The alternating current potential drop method of traditional field fingerprinting based on unidirectional current potential drop method and single-frequency is all
Need accurately measurement to obtain the original wall thickness information of tested pipeline, wall thickness loss amount is solved according to magnitude of voltage then, be that is to say
The absolute thickness of direct measurement tested pipeline is unable on both technological essences, opposite wall can only be solved according to original wall thickness value
Thick amount etc., therefore the measurement error of original wall thickness can the final depth of defect testing result of cumulative effect.In addition traditional field refers to
The alternating current potential drop method of stricture of vagina method and single-frequency needs to measure primary voltage and reference voltage etc., and the drift of system can be to measurement
Cause very big adverse effect.And the present invention no longer needs to measure primary voltage and reference voltage, that is to say that system drifting will not
Again detection is adversely affected, while original wall thickness of the present invention also without measurement tested pipeline, it is to avoid original wall thickness
The impact of measurement error.
Background technology
The various defects that the metallic conduit generally existing of petrochemical industry is produced because of factors such as corrosion at present, are to ensure that safety is needed
Real-time detection is carried out to defect, will especially detect the depth information of defect.One of which Corrosion monitoring technology is to be based on
The field fingerprinting of unidirectional current potential drop method, its operation principle are as follows：
1st, be spaced a distance on tested pipeline axial direction two electrodes of installation, for applying exciting current, then in excitation electricity
Measuring electrode is installed in stream inner side, then installs one piece of reference plate on the outside of pipeline, and reference plate has carried out good protection and processed, will not
Corrode, reference plate ampere wires are electrically connected with tested pipeline, reference electrode is installed on reference plate.Corrosion can cause by
The resistance increase of the equivalent resistance between measuring electrode on test tube road, on the premise of the torrent electric current of identical amplitude is applied, surveys
Measure interelectrode voltage to rise, that is to say that the situation of change of voltage between measuring electrode just represents the change of tested pipeline wall thickness
Change situation；
2nd, after fingerprinting system installation on the scene, the tested voltage on the reference voltage and pipeline for obtaining is measured for the first time
Record as primary voltage, be designated as respectivelyV i （t 0 ）WithV ref （t 0 ）；As time goes on, tested pipeline there occurs
Corrosion, the tested voltage now measured on the reference voltage and pipeline for obtaining are designated as respectivelyV i （t x ）WithV ref （t x ）, then profit
Corrosion depth is calculated with below equation：
FC i (t x ）=((V i (t x )/V i (t 0 ))/Vref(t x )/V ref (t 0 )-1)×1000 （1）
In formula：
V i （t 0 ）,V i （t x ）Original moment and the tested voltage at corrosion moment；
V ref （t 0 ）,V ref （t x ）Original moment and the reference voltage at corrosion moment；
D(t x )=WT(t 0 )-WT(t 0 )×1000/(FC i (t x )+1000) （2）
In formula：D(t x ) defect depth；WT(t 0 ) tested pipeline original wall thickness；
By formula（1）As can be seen that field fingerprinting needs introducing reference voltage to be calculated, and need to carry out with primary voltage
Relatively；Field fingerprinting belongs to long-term on-line monitoring equipment again, in practical engineering application, circuit system meeting under long-term work state
The various drifting problems of generation, including baseline drift and null offset etc., that is to say tested voltage and reference voltage all while increase
Or reduce identical amplitude.By mathematical knowledge it is known that in a division arithmetic, molecule and denominator increase or reduce simultaneously
Same numerical value, final ratio will change, and therefore drift can cause very big mistake to the testing result of field fingerprinting
Difference.By formula（2）Understand, field fingerprinting calculates the formula of depth of defect and also needs to the original wall that accurately measurement obtains tested pipeline
Thickness, the measurement error of original wall thickness also can be adversely affected to the calculating of depth of defect；
Current alternating current potential drop method simply using the high frequency pumping electric current of single-frequency, can only typically detect metallic conduit outer wall
Defect, but there is the inwall in metallic conduit, and alternating current potential drop technology in the overwhelming majority such as corrosion default of metallic conduit
Be also required to measure reference voltage, testing result is obtained compared with reference voltage by voltage will be measured, therefore traditional alternating current
Potential drop method equally also can be affected by drifting about；
This patent is directed to a kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method, it is no longer necessary to measure
Reference voltage, it is not necessary to measure primary voltage, it is not necessary to measure the original wall thickness of tested pipeline, can effectively eliminate and be
The impact to measuring such as system drift, original wall thickness measurement error.
Content of the invention
The present invention is primarily directed to the field fingerprinting based on unidirectional current potential drop method traditional at present and traditional single-frequency
Alternating current potential drop method is easily disturbed this present situation by system drifting, it is proposed that a kind of metal based on frequency-changing AC fall-of-potential method
Defect inspection technology, is specifically a series of ac-excited electric current for applying different frequencies to tested pipeline, using becoming
Distribution of the skin effect control electric current in tested pipeline, measurement obtain the contact potential series corresponding to the exciting current of different frequency, right
The contact potential series carries out differential derivation, finally solves the depth of corrosion default using the extreme value of derivative curve；
Two electrodes are installed at tested pipeline two ends, for applying ac-excited electric current, then in current excitation electrode medial area
Measuring electrode is installed in domain, and axially upper two adjacent measuring electrodes constitute a pair of measuring electrodes pair, for measuring voltage.Due to swashing
Electric current is encouraged for exchange, therefore the CURRENT DISTRIBUTION on pipeline can be affected by Kelvin effect, i.e., when the frequency of exciting current is higher,
By integrated distribution in a shallow-layer near metallic conduit outer wall, this electric current is referred to as becoming skin electricity to electric current on tested pipeline
Stream, the skin depth of skincurrentδBy formula（3）Determine：
δ=1/(πμ r μ 0 σf)½ （3）
In formulaμ r It is the relative permeability of tested pipeline material,μ 0 It is the pcrmeability of air,σIt is the conductance of tested pipeline material
Rate,fIt is the frequency of exciting current.By this formula it is recognised that with the reduction of exciting current frequency, skincurrent becomes
Skin depth will increase, i.e., electric current gradually will be permeated to metal pipe internal wall, and this will result in the depth that electric current flows through regional metal block
Degree increases, and that is to say that electric current flows through the equivalent resistance in region and reduces, in the presence of the exciting current of identical amplitude, measuring electrode
Between voltage will be gradually reduced, after the skin depth of skincurrent and the wall thickness of tested pipeline are consistent, skincurrent will
Full of in whole tube wall, with the further reduction of exciting current frequency, skin depth is limited to pipeline wall thickness no longer to be reduced, because
Voltage between this measuring electrode will keep constant.If carrying out differential derivation to the series of voltage value that measurement is obtained, it will
First it is gradually lowered to one, final negative curve again equal to 0, this curve there will be an extreme point；
If tested pipeline existing defects, the trommel of tested pipeline is equivalent to, now applies frequency from height to tested pipeline
A series of low exciting currents are arrived, with the reduction of exciting current frequency, skin depth gradually increases, and now measures for obtaining
Series voltage value will be tended towards stability in advance, this is because skincurrent will can be managed full of whole in advance in upper frequency point
Wall.Voltage derivative curve now, for the voltage derivative curve of the metallic conduit for not occurring to corrode, it will reach in advance
Be worth point to 0, its extreme point can also change, therefore depth of defect can be solved using the extreme point of voltage derivative curve；
Concrete scheme step is as follows：
（1）Two electrodes are arranged on tested pipeline axial direction, for applying ac-excited electric current；
（2）In two current excitation electrode disposed inboard measuring electrodes, axially upper two adjacent a pair of measurements of electrodes composition are electric
Extremely right；
（3）Apply frequency ac-excited electric current from high to low to tested pipeline, measure and record each Frequency point corresponding
Voltage between measuring electrode pair, by this series of voltage be named asV f ；
（4）The series of voltage that measurement is obtainedV f Differential derivation is carried out, extreme point is calculatedE；
（5）The defect that tested pipeline can be calculated using equation belowd：
d=-0.029E+1.462
Beneficial effects of the present invention：To a series of ac-excited electric current that tested pipeline applies different frequencies, measurement is obtained
Series of voltage carries out differential derivation, and from mathematical knowledge, constant term does not affect the result of differential derivation, that is to say if being
System circuit there occurs drift so that all magnitudes of voltage for obtaining of measurements also will not all while increase or reduce identical amplitude
Affect final solving result.Therefore the present invention can eliminate impact of the system drifting to detecting, improve long-term on-line monitoring
The reliability of equipment.Additionally, the present invention need not measure original wall thickness, the unfavorable shadow that original wall thickness measurement error is caused is eliminated
Ring.
Description of the drawings
Field fingerprinting schematic diagrams of the Fig. 1 based on unidirectional current potential drop method
The alternating current potential drop technical schematic diagram of the traditional measurement outer wall defects based on single driving frequency of Fig. 2
Distribution situation of the skincurrent under Fig. 3 different frequency exciting currents on tested pipeline
The voltage value sequence of different depth defect under Fig. 4 variable frequency excitations
The differential derivative and its extreme point of the voltage value sequence of Fig. 5 different depth defects.
Specific embodiment
Details are as follows for one embodiment of the present of invention：
The present invention is a kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method, and specific implementation step is as follows：
（1）Choose an endwall thick for 10mm, caliber is 219mm, length for 1000mm ordinary carbon steel pipeline as measurand,
In pipe ends outer wall welded and installed current excitation electrode, heart outer wall welded and installed five is to measuring electrode, measurement electricity in the duct
Die opening is 40mm；
（2）In the defect that the corresponding inner-walls of duct difference working depth of measuring electrode is 1mm, 2mm, 3mm, 4mm and 5mm, defect
Area be 40mm × 40mm；
（3）According to the material behavior of tested pipeline, the frequency of exciting current is adjusted, according to the computing formula of skincurrent so that
The skin depth of skincurrent arranges altogether 100 Frequency points from 0.1mm to 10mm with 0.1mm as waiting increment incremented by successively, i.e.,；
（4）5 pair measuring electrodes magnitude of voltage under the exciting current of different frequency is measured successively；
（5）The derivative extreme value of every group voltage is calculated respectivelyE, and calculated according to the formula for finally calculating depth of defect
Depth of defect is as shown in the table：
.
Claims (2)
1. a kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method, arranges two on metallic conduit axial direction
Electrode, for applying exciting current；In current excitation electrode disposed inboard measuring electrode, the upper two adjacent measuring electrodes in axial direction
Constitute a pair of measuring electrodes pair；Then according to following steps solve depth of defect：
（1）Apply frequency ac-excited electric current from high to low to tested pipeline, measure and record each Frequency point pair successively
Voltage between the measuring electrode pair that answers, by this series of voltage be named asV f ；
（2）The series of voltage that measurement is obtainedV f Differential derivation is carried out, extreme point is calculatedE；
（3）The defect that tested pipeline can be calculated using equation belowd：
d=-0.029E+1.462..
2., according to Kelvin effect formula, the frequency of the torrent electric current of applying will make appropriate tune according to the material behavior of metallic conduit
Whole.
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| CN201610974741.9A CN106501318A (en) | 2016-11-07 | 2016-11-07 | A kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method |
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| CN201610974741.9A CN106501318A (en) | 2016-11-07 | 2016-11-07 | A kind of metallic conduit defect detecting technique based on frequency-changing AC fall-of-potential method |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107643321A (en) * | 2017-09-05 | 2018-01-30 | 四川大学 | Multifrequency alternating-current field fingerprint technique metal pipeline corrosion detecting technology based on phase identification |
| CN108680607A (en) * | 2018-08-30 | 2018-10-19 | 四川大学 | Pipeline crack corrosion monitoring process based on multi-communication potential drop |
| CN110470726A (en) * | 2019-08-14 | 2019-11-19 | 中国特种设备检测研究院 | Steel pipe defect inspection method and device based on multifrequency electromagnetism |
| CN115301516A (en) * | 2022-08-09 | 2022-11-08 | 南京工程学院 | Method and device for detecting and repairing metal coating damage by electric pulse |
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| US3721896A (en) * | 1971-12-23 | 1973-03-20 | Nippon Kokan Kk | Improved phase sensitive eddy current defect detector utilizing frequency doubling of detected signal prior to phase detection |
| CN103472098A (en) * | 2013-04-16 | 2013-12-25 | 四川大学 | Method for measuring residual thickness of metal pipeline or metal pressure container after local corrosion |
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| US3721896A (en) * | 1971-12-23 | 1973-03-20 | Nippon Kokan Kk | Improved phase sensitive eddy current defect detector utilizing frequency doubling of detected signal prior to phase detection |
| CN103472098A (en) * | 2013-04-16 | 2013-12-25 | 四川大学 | Method for measuring residual thickness of metal pipeline or metal pressure container after local corrosion |
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107643321A (en) * | 2017-09-05 | 2018-01-30 | 四川大学 | Multifrequency alternating-current field fingerprint technique metal pipeline corrosion detecting technology based on phase identification |
| CN108680607A (en) * | 2018-08-30 | 2018-10-19 | 四川大学 | Pipeline crack corrosion monitoring process based on multi-communication potential drop |
| CN110470726A (en) * | 2019-08-14 | 2019-11-19 | 中国特种设备检测研究院 | Steel pipe defect inspection method and device based on multifrequency electromagnetism |
| CN110470726B (en) * | 2019-08-14 | 2023-03-07 | 中国特种设备检测研究院 | Steel pipeline defect detection method and device based on multi-frequency electromagnetism |
| CN115301516A (en) * | 2022-08-09 | 2022-11-08 | 南京工程学院 | Method and device for detecting and repairing metal coating damage by electric pulse |
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Application publication date: 20170315 |