CN108680607A - Pipeline crack corrosion monitoring process based on multi-communication potential drop - Google Patents
Pipeline crack corrosion monitoring process based on multi-communication potential drop Download PDFInfo
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Abstract
The present invention provides the pipeline crack corrosion detecting method based on multi-communication potential drop, present invention firstly provides multidirectional current methods, it is passed through exciting current from four different directions, obtain four groups of voltage ratios, according to the relationship of electrode direction of check and voltage ratio, maximum voltage ratio is selected to substitute into depth solving formula, solution obtains the depth of crackle.The multidirectional current method of the present invention makes crack position and angle (complementary angle) range of electric current pole line become 67.5 90 degree from 0 90 degree, significantly improves the precision of crack depth solution.
Description
Technical field
The invention belongs to pipeline inspection technology fields, more particularly to the corrosion prison of the pipeline crack based on multi-communication potential drop
Survey method.
Background technology
Corrosive pipeline is one most dangerous in all multi-risk Systems that oil-gas pipeline is faced, the pipe safety of 70%-90%
Accident is caused by corrosive pipeline.
Currently, common Pipeline Corrosion Inspection Techno-logy, including relatively advanced field fingerprint technique (Field Signature
Method, FSM), also only to local corrosion (localized corrosion) and homogeneous corrosion (general corrosion)
Accuracy of detection it is high；Alternating-current field fingerprint technique (the Alternating Current Field Signature of newest proposition
Method, ACFSM), using the measurement data evaluation of corrosion depth of multiple Frequency points, the detection essence of cracking corrosion can be improved
Degree, but this method requires direction of check and the angle in electric current pole line direction to be more than 45 degree, cannot solve angle and be less than 45 degree
Crackle, the line direction of current current excitation electrode is axially parallel with pipeline, can limit the detection range of crack defect.
Therefore, in order to meet actual detection demand, further investigation random crack Corrosion monitoring technology seems extremely necessary.
Invention content
It is an object of the invention to solve the problems of the above-mentioned prior art, the pipe based on multi-communication potential drop is provided
Road cracking corrosion detection method makes direction of check connect with electric current pole by applying the exciting current of different directions to tested pipeline
Angle (complementary angle) range in line direction becomes 67.5-90 degree from 0-90 degree, and the corrosion that can more accurately detect random crack is deep
Degree.
The present invention adopts the following technical scheme that：
Pipeline crack corrosion detecting method based on multi-communication potential drop, step include：
Step 1. welding arrangement several groups in the circumferential direction of test pipeline test electrode.
Step 2. signal generator generates pumping signal and generates exciting current by power amplifier, from four not Tongfangs
To being passed through exciting current successively to input electrode, the frequency of power amplifier is adjustable, and exciting current amplitude is adjustable.
Step 3. measures the voltage of flawless normal pipeline with high-precision lock-in amplifier, obtains normal pipeline test voltage
It is worth and inputs computer, recycles high-precision lock-in amplifier to measure voltage to be measured in test pipeline region to be measured respectively, will survey
It measures result and inputs computer, obtain four groups of different voltage ratios；
Step 4. selects maximum voltage ratio to substitute into following depth solving according to the relationship of direction of check and voltage ratio
Formula, and use computer solving：
Step 5. obtains the depth of pipeline crack according to the result of Computer display.
Further technical solution is that in step 2, the 4 groups of test electrodes arranged in circumferential direction refer to horizontal direction, vertically
Direction, diagonal, wherein input electrode and output electrode are positioned opposite, and line passes through position to be tested.
Further technical solution is, defeated when testing region voltage to be measured using high-precision lock-in amplifier in step 3
The input electrode for entering exciting current is consistent with probe line measurement direction is measured with the line of the output electrode of output drive electric current.
Preferred technical solution is that the frequency of power amplifier selects 59-500Hz, exciting current amplitude to select 2A.
Preferred technical solution is, in step 2, the frequency of power amplifier selects 100Hz.
Beneficial effects of the present invention：
1. present invention firstly provides multidirectional current method, it is passed through exciting current from four different directions, obtains four groups of voltages
Ratio selects maximum voltage ratio to substitute into depth solving formula according to the relationship of electrode direction of check and voltage ratio；This hair
Bright multidirectional current method makes crack position and angle (complementary angle) range of electric current pole line become 67.5-90 degree from 0-90 degree,
Significantly improve crack depth and solving precision.
2. the present invention due to using alternating current potential drop technology principle, so with exciting current is small, measurement sensitivity is high,
The advantages that strong antijamming capability.
3. the method for the present invention and traditional potential drop technology ACFSM are using single with conduit axis parallel excitation electric current ratio
Compared with for, the depth of the method for the present invention quantitative solving random crack defect for the first time show according to emulation and experimental data, electric
When stream flows through crack defect, the direction of crackle can influence the distribution of current field, to change the voltage of measuring electrode.
Description of the drawings
Fig. 1 is skincurrent distribution schematic diagram；
Fig. 2 is the voltage distribution graph at the different-thickness that table one is tested；
Fig. 3 (a), Fig. 3 (b), Fig. 3 (c), Fig. 3 (d), the schematic diagram that Fig. 3 (e) is five kinds of direction of check and electrode connecting line；
Fig. 4 is the ratio depth map of different angle crackle；
Fig. 5 is the multidirectional current measurement schematic diagram of the present invention；
Fig. 6 is the maximum ratio depth map of two kinds of crack defects of emulation testing.
Fig. 7 is the Experimental equipment of the method for the present invention；
Fig. 8 is metal plate probe layout schematic diagram；
Fig. 9 is assay plate back schematic diagram.
Specific implementation mode
To make the object, technical solutions and advantages of the present invention clearer, the technical solution below in the present invention carries out clear
Chu is fully described by, it is clear that described embodiments are some of the embodiments of the present invention, instead of all the embodiments.It is based on
Embodiment in the present invention, those of ordinary skill in the art are obtained every other without creative efforts
Embodiment shall fall within the protection scope of the present invention.
Term is explained：
1.1, Kelvin effect
The ac-excited electric current (AC) of different frequency is passed in the duct, and current distribution follows Kelvin effect.Skin depth δ
Calculation formula：
μ in above formularFor the relative permeability of material；μ0For space permeability；σ is the conductivity of material；F is exciting current
Frequency.Current distribution schematic diagram is as shown in Figure 1.
By formula (1) it is found that when applying high frequency pumping electric current, current convergence is present in pipeline outer wall, with exciting current frequency
The reduction of rate, electric current permeate gradual inward wall, and the current density, J (r) in duct wall meets formula：
Wherein,
I is the current amplitude that angular frequency is ω in formula；R is the outer radius of pipeline；R is radial distance；J0(kr) it is first
Class zero Bessel function, J1(kR) it is first kind first-order bessel function.
According to the relationship between current density and voltage, the expression formula of voltage value U (r) is：
L is the spacing of measuring electrode in formula.
Bessel function in (3) formula is replaced with exwponential function approximation, then voltage value amplitude is represented by：
Contact depth d of the measuring electrode with pipeline outer wall0=R-r ≈ 0.5mm after being passed through exciting current at this time, measure electricity
The voltage magnitude U that pole measures can use formula (5) to indicate：
Pipeline wall thickness is T, and the raw voltage values measured before not eroded are U(d=0), it is actually measured after pipeline puts into production
Voltage value be U(d).When the corrosion default of inner wall of the pipe is extremely shallow (d ≈ 0), meet always with the reduction of frequency：
U(d)/U(d=0)≈1；
If there are the homogeneous corrosion defects that depth is d to measure voltage value U after δ=T-d for bottom(d)It remains unchanged,
U(d)/U(d=0)≈m/U(d=0)(m is constant)；And when defect is crack defect, after δ=T-d, as frequency reduces, defect
Electric current around " layer " can also permeate downwards, U(d)<M, U(d)/U(d=0)<m/U(d=0)。
Therefore the U of crack defect(d)/U(d=0)Value can be by under two kinds of limiting cases (corrosion-free defect, homogeneous corrosion defect)
U(d)/U(d=0)Linear superposition is approximate：
A in formula1,a2,a3For with the relevant constant of measured material characteristic.
1.2, multidirectional electric current
It is 400mm, internal diameter 140mm, the pipeline progress finite element analysis that outer diameter is 160mm, finite element software to length
For COMSOL Multiphysics 5.0.Measured zone is located among pipeline, probe spacing 20mm, and Injection Current amplitude is
2A, depth of defect 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm.
Material parameter is shown in Table 1：
Known to formula (3) when exciting current frequency difference, the voltage's distribiuting at different " thick layers " is different, in order to ensure
Galvanic contact is permeated to " defect layer ", needs to set suitable exciting current, each radial distance voltage (voltage etc. when with direct current
Distribution value) on the basis of, it is passed through voltage's distribiuting when frequency is 2.5KHz and 500Hz, as shown in Figure 2.
It can be seen from the figure that exciting current frequency is excessively high, such as 2.5KHZWhen, electric current can not permeate duct wall completely,
In this case, infiltration electric current can not touch " defect layer " of depth as shallow, and defect information cannot be reflected by measuring signal；It reduces and swashs
Encourage power frequency, skin depth increases, and infiltration electric current can reach " defect layer " of each depth, when such as frequency being 500Hz.
In view of pipeline wall thickness is 10mm, maximum skin depth is 10mm, can be with according to formula (1) and 1 parameter of table
It is 59Hz to calculate corresponding power frequency at this time.
By taking four kinds of Fig. 3 (b), Fig. 3 (e) position defects as an example (For the angle of direction of check and electrode connecting line direction).
Fig. 3 (a) is zero defect pipeline, and the voltage value measured at this time is U (d=0, f=100Hz), as primary voltage：
The defect of the four kinds of positions Fig. 3 (b)-Fig. 3 (e) is measured into voltage value U under different depth(d)With U(d=0)Make ratio, obtains
Arrive that the results are shown in Figure 4.
As shown in Figure 4, when the angle of direction of check and electrode connecting line directionWhen less than 45 °, U(d)/U(d=0)Value with split
The relationship of line depth does not meet formula (6), at this time U(d)/U(d=0)It cannot be used for solving depth of defect；
WhenWhen more than 45 °,It is 90 ° closer, U(d)/U(d=0)Value and the relationship of crack depth more follow the fingers of formula (6)
Number distribution form, by U(d)/U(d=0)The crack depth that calculates afterwards of substitution formula (6) closer to actual grade,It is solved when being 90 °
Precision can reach 97.16%；Emulating data also shows place simultaneously：It is 90 degree closer, U(d)/U(d=0)Value it is bigger.
Therefore, it for the depth solving problem of random crack, utilizesCloser to 90 degree, the higher feature of measurement accuracy is created
New property proposes multidirectional current method.By increasing by three groups of exciting currents so thatRange becomes 67.5-90 degree from 0-90 °, figure
5 be instrumentation plan.
Same defect can obtain one group of characterization signal under same frequency：
Take maximum U(d)/U(d=0)Value substitutes into formula (6) and solves crack depth.
2, the pipeline crack corrosion detecting method based on multi-communication potential drop, step include：
Step 1. welding arrangement several groups in the circumferential direction of test pipeline test electrode.
Step 2. signal generator generates pumping signal and generates exciting current by power amplifier, from four not Tongfangs
To being passed through exciting current successively to input electrode, the frequency of power amplifier is adjustable, and exciting current amplitude is adjustable.
Step 3. measures the voltage of flawless normal pipeline with high-precision lock-in amplifier, obtains normal pipeline test voltage
It is worth and inputs computer, recycles high-precision lock-in amplifier to measure voltage to be measured in test pipeline region to be measured respectively, will survey
It measures result and inputs computer, obtain four groups of different voltage ratios；
Step 4. selects maximum voltage ratio to substitute into following depth solving according to the relationship of direction of check and voltage ratio
Formula, and use computer solving：
Step 5. obtains the depth of pipeline crack according to the result of Computer display.
Further technical solution is that in step 2, the 4 groups of test electrodes arranged in circumferential direction refer to horizontal direction, vertically
Direction, diagonal, wherein input electrode and output electrode are positioned opposite, and line passes through position to be tested.
Further technical solution is, defeated when testing region voltage to be measured using high-precision lock-in amplifier in step 3
The input electrode for entering exciting current is consistent with probe line measurement direction is measured with the line of the output electrode of output drive electric current.
Preferred technical solution is that the frequency of power amplifier selects 59-500Hz, exciting current amplitude to select 2A.
Preferred technical solution is, in step 2, the frequency of power amplifier selects 100Hz.
3. embodiment 1. carries out emulation testing using a flat plate model
First flat plate model is accurately solved.
Tablet long 220mm, wide 220mm, thickness 10mm, measurement probe spacing are 20mm, and Injection Current amplitude is 2A, frequency
Rate is 100HZ, is referred to as shown in Figure 6.
Depth of defect is 2mm, 2.5mm, 3mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, material parameter such as the following table 2：
By taking 0 degree of crack defect and 45 degree of crack defects as an example, the measurement result that the two obtains under above-mentioned simulated conditions is：
The value of 0 degree of defect is taken to do depth fitting, formula is：
The result that 45 degree of defects are calculated with formula (7) is as shown in upper table 2.
Embodiment 2 is tested using 5 blocks of aluminium sheets
Experiment material：The aluminium sheet of 5 pieces of 220mm × 220mm × 10mm, integral experiment device are as Figure 7-8.
Before undressed defect, successively by Iin1、Iin2、Iin3、Iin4Electrode to tablet inject 2A, the alternating current of 100Hz, such as
Shown in Fig. 5, Fig. 8, probe is measured respectively to (P with high-accuracy digital lock-in amplifier SR8501-P2)、(P1-P3)、(P2-P3)、
(P2-P4) between primary voltage U1 (d=0)、U2 (d=0)、U3 (d=0)、U4 (d=0)。
Then, 5 Cracks are depicted respectively in 5 pieces of flat plate bottoms, wherein 1-3 tablets are 0 degree of crack defect, depth point
Not Wei 2mm, 4mm, 6mm, width is 2mm；4-5 tablets are 45 degree of crack defects, depth distribution 3mm, 5mm, such as Fig. 9 institutes
Show.
Then, by Iin1、Iin2、Iin3、Iin4Electrode is shown in as shown in figure 8,2A electric currents, 59- can be injected to tablet successively
500Hz alternating currents, it is preferable to use the alternating currents of 100Hz for this experiment, measure U1(d)、U2(d)、U3(d)、U4(d)。
Voltage will be measured and make ratio with primary voltage, obtained result is as shown in table 3 below：
Note：U10=U1 (d=0),U20=U2 (d=0),U30=U3 (d=0),U40=U4 (d=0)。
By the corresponding maximum U of each depth(d)/U(d=0)Value substitutes into formula (7), as a result as shown in table 4 below.
Therefore, compared with the previous non-detectable situation of random site defect, multidirectional current method can solve random crack
Depth.
The method for solving depth with voltage ratio in formula (7), can eliminate environmental disturbances, improve the anti-of measuring system
Interference performance.
Analysis of conclusion：
For traditional potential drop technology using single with conduit axis parallel excitation electric current, the present invention utilizes electric current and crackle
AngleWhen being 90 degree, measures voltage and primary voltage ratio maximum, ratio and depth of defect function characteristic are best simultaneously
Feature is passed through ac-excited electric current from four direction so thatRange become 67.5-90 degree from 0-90 degree, select maximum
Voltage ratio calculates depth of defect.
The experimental data of emulation testing shows that new computational methods improve the accuracy of detection of random crack, can more have
The detection corrosion condition of effect.
Finally it should be noted that：The above embodiments are merely illustrative of the technical solutions of the present invention, rather than its limitations；Although
Present invention has been described in detail with reference to the aforementioned embodiments, it will be understood by those of ordinary skill in the art that：It still may be used
With technical scheme described in the above embodiments is modified or equivalent replacement of some of the technical features；
And these modifications or replacements, various embodiments of the present invention technical solution that it does not separate the essence of the corresponding technical solution spirit and
Range.
Claims (5)
1. the pipeline crack corrosion detecting method based on multi-communication potential drop, which is characterized in that step includes：
Step 1. welding arrangement several groups in the circumferential direction of test pipeline test electrode；
Step 2. signal generator generates pumping signal and generates exciting current by power amplifier, from four different directions, to
Input electrode is passed through exciting current successively, and the frequency of power amplifier is adjustable, and exciting current amplitude is adjustable；
Step 3. measures the voltage of flawless normal pipeline with high-precision lock-in amplifier, obtains normal pipeline test voltage value simultaneously
Computer is inputted, recycles high-precision lock-in amplifier to measure voltage to be measured in test pipeline region to be measured respectively, is tied measuring
Fruit inputs computer, obtains four groups of different voltage ratios；
Step 4. selects maximum voltage ratio to substitute into following depth solving public according to the relationship of direction of check and voltage ratio
Formula, and use computer solving：
Step 5. obtains the depth of pipeline crack according to the result of Computer display.
2. the pipeline crack corrosion detecting method according to claim 1 based on multi-communication potential drop, which is characterized in that
In step 2, the frequency of power amplifier selects 59-500Hz, exciting current amplitude to select 2A.
3. the pipeline crack corrosion detecting method according to claim 2 based on multi-communication potential drop, which is characterized in that
The frequency of power amplifier selects 100Hz.
4. the pipeline crack corrosion detecting method according to claim 1 based on multi-communication potential drop, which is characterized in that
In step 2, the 4 groups of test electrodes arranged in circumferential direction refer to horizontal direction, vertical direction, diagonal, wherein input electrode
Positioned opposite with output electrode, line passes through position to be tested.
5. the pipeline crack corrosion detecting method according to claim 1 based on multi-communication potential drop, which is characterized in that
In step 3, when testing region voltage to be measured using high-precision lock-in amplifier, input electrode and the output of input stimulus electric current swash
The line for encouraging the output electrode of electric current is consistent with probe line measurement direction is measured.
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