CN103267723B - Metallic conduit based on field fingerprinting, container pitting corrosion detection method - Google Patents

Abstract

The present invention relates to metallic conduit or the high precision test of container pitting corrosion (hole shape corrosion), detection method based on field fingerprinting (Field Signature Method, FSM) etch pit higher precision little to petrochemical industry oil and gas pipes or container particularly to a kind of improvement.This patent propose technical scheme be main and auxiliary voltage method, specifically random corrosion is cheated region corresponding to measurement electrode to as main electrode, corresponding voltage is as principal voltage；Remaining electrode is to as auxiliary electrode, and corresponding voltage is as auxiliary voltage；Corrosion database is set up by calculating steady high voltage system；By measured and process revised main and auxiliary voltage change and mate with data base, area and the degree of depth of little etch pit in this main electrode corresponding region i.e. can be obtained.Use the present invention that metallic conduit or container pitting corrosion are detected, accuracy of detection can be increased substantially.

Description

Metallic conduit based on field fingerprinting, container pitting corrosion detection method

Technical field

The present invention relates to metallic conduit or the high-precision detecting method of container inner wall pitting corrosion, specifically, relate to a kind of base In the detection method of field fingerprinting etch pit little to petrochemical industry oil and gas pipes or container higher precision, solve biography innovatively The system FSM method unsolvable problem of medium and small etch pit, belongs to field of measuring technique.

Background technology

Petrochemical industry commonly used resistance probe method and the corrosion condition of polarization sonde method on-line checking pipeline at present, but this A little methods can only carry out homogeneous corrosion detection, and pitting corrosion great to hazardness is without power of test, high accuracy and the hole of high reliability Erosion detection method and technology be petroleum chemical industry safe operation in the urgent need to one of technology.Field fingerprinting (Field Signature Method, FSM) due to good reliability, high-low temperature resistant, the life-span is long, be the most widely used in oil and gas pipes, Important container and the Corrosion monitoring of structure.

For ease of understanding technical scheme, first brief introduction FSM principle, development course and the measurement of existing corrosion parameter, Computational methods:

FSM is a kind of glitch-free Pipeline Corrosion Inspection Techno-logy, and its measuring electrode and all corollary equipments are all installed Outside at detected object (such as storage tank, pipeline etc.), contactless with the fluid in detected region.After corrosive pipeline, This corrosion region (being covered by pair of electrodes) is thinning causes resistance to increase, and under the effect of constant-current source I, measures and analytical measurement electrode Between change in voltage obtain the situation of pipeline corrosion.In order to eliminate the impact of temperature and curent change, a pair reference must be increased Electrode, generally places one and is close to pipeline external and and the homogenous metal plate of pipe-line wrapping.Fig. 1 show pipeline external pelivimetry electricity Pole and reference electrode schematic diagram, after installing, then superscribe a layer insulating (such as polyester vinyl) and pipeline one on pipeline Play embedment underground or seabed, without excavating buried layer during measurement.

FSM was proposed in a patent first by Norway scholar H.Hannestad nineteen eighty-three.The method and technology tool Having reliability the highest, safety is good and the king-sized advantage of temperature adaptation scope.The essence of FSM is the potentiometry of matrixing, Will one group measure electrode matrix install (typically welding) outside detected metal object, for detecting the corruption within object Erosion situation.Its ultimate principle is the change of test metallic object resistance.Due to the minimum generally tens u Ω of resistance between electrode, i.e. Making applying tens of peace electric current, voltage across poles also only has tens uV, and the change in voltage caused when corroding 0.1mm only has 0.1uV number Magnitude.Being limited by components and parts at that time and measurement instrument industry level, this technology is not applied.

1989, CorrOcean company of Norway, on the basis of buying above patent, developed practical FSM and produces Product.Correlation technique is made substantial amounts of research and contribution by a lot of scholars.The most representational have:

1991, Norway R.Strommen et al. proposed the model of the FSM of improvement, by increasing by a reference plate, reduced Temperature and the impact of exciting current change, it is proposed that field fingerprint FC concept and algorithm, make pair of electrodes all cover Zonal corrosion amount accuracy of detection be improved, so that FSM is on the Corrosion monitoring of submarine pipeline and seabed important component Obtained applying widely.Being limited by computing technique at that time, FSM limitation in principle is not the most realized, hole The calculating of erosion still based on empirical equation, such as, when all FC change, uses the safety coefficient of 3-5 times to provide pitting corrosion Amount, makes pitting corrosion amount not have precision definitiveness.

2008, British scholar D.M Farrell and A.Daaland et al. was on the basis of simulation calculation, it is understood that When electric current is through pitting corrosion region, and uniform current will be disturbed, and cause the precise decreasing of system.Due to pitting corrosion size, the degree of depth With the randomness of position, make the distribution of current field there is no definitiveness, accuracy of detection be 10-15%WT (during wall thickness 10mm, error 1- 1.5mm)。

G.Sposito, Peter Cawley of Britain Imperial College Imperial College in 2010 et al. recognizes Cause potential change problem the most linearly because corrosion causes electric current to be redistributed, and potential probes layout carried out Optimize.Under conditions of pitting corrosion position priori, it is proposed that the corresponding corrosion area of use pair of electrodes voltage is the most auxiliary Detect the Change and Development situation of corrosion with potential diagram (Potential Drop Mapping), the potential probes spacing be given is Excellent solution does not has universality.

(4 on one wire, 2 exterior points to four-point method for the N.Bowler of American I owa State University in 2009 Applying electric current, point surveys voltages in 2, is FSM special case) carry out theory analysis, give pair of electrodes voltage and thickness approximation Computational methods, it is proposed that the principle of four-point probe layout when measuring metallic plate.Four-point method can measure pitting corrosion, but needs pointwise to move Dynamic detection, is unsuitable to apply to the occasion detected in real time, such as seabed and buried pipeline.

But up to now, there is undecidable decision problem for the detection of little etch pit in FSM method.

The definition of little etch pit is: the region that the area of etch pit covers less than counter electrode.Due to pitting corrosion must be by Without to having, have shallow to deep, therefore little etch pit must be to exist.When little etch pit occurring between a pair measurement electrode, pole Between bulk resistor can increase, meanwhile, the distribution of electric current also can change, thus causes voltage across poles to change, but one Little etch pit has two factors to affect the area changing hole and the degree of depth of voltage, it may be assumed that

ΔV_i,j；i,j+1=f (S, D)

S area, the D degree of depth.

Measure electrode due to correspondence and can only export a voltage change, thus above-mentioned relation formula is solves, the least corruption more The area of pit and the degree of depth have multiple probability, only cannot determine with a voltage change that the area of little etch pit is with deep Degree, the least etch pit not can recognize that problem (Fig. 3).

Conventional processing method is one variable of elimination artificially, and area S is considered as a fixed value, will etch pit Size is defined as one and measures electrode to corresponding border circular areas or rectangular area, the diameter in this region or the length of side etc. In measure electrode pair anode-cathode distance (Fig. 4), with voltage measurement amount all measurements electrode to and reference electrode in corrosion-free hole Time (t₀Moment) and (t when having etch pit_xMoment) voltage, according to the resistance chain model shown in Fig. 2, arbitrary to measuring electrode institute The local corrosion degree represented is judged by fingerprint (FC value):

${\mathrm{FC}}_{i,j;i,j+1}\left(t_x\right)=(\frac{\frac{V_{i,j;i,j+1}\left(t_x\right)}{V_{i,j;i,j+1}\left(t_0\right)}}{\frac{V_{ref}\left(t_x\right)}{V_{ref}\left(t_0\right)}}-1)\×1000$

In formula: V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；

V_ref(t₀), V_ref(t_x) normal electrode is at t₀And t_xThe voltage in moment；

According to FC value, wall thickness WT (Wall Thickness) computing formula can be obtained:

${\mathrm{WT}}_{i,j;i,j+1}\left(t_0\right)=\frac{{\mathrm{WT}}_{i,j;i,j+1}\left(t_0\right)\×1000}{{\mathrm{FC}}_{i,j;i,j+1}\left(t_x\right)+1000}$

In formula: WT_i,j；i,j+1(t_x) it is current tested area thickness, WT_i,j；i,j+1(t₀) it is tested region original thickness.

Said method can not reflect the actual state of etch pit, the little corrosion gone out according to this equations truly, exactly Hole depth error will reach ± 15～25%WT (WT is wall thickness, and when wall thickness is 10mm, precision is ± 1.5～2.5mm, Minimum measurable etch pit area is 1.5WT).

Summary of the invention

The present invention is directed to current FSM method and wait deficiency to pitting corrosion accuracy of detection is low, it is provided that one can accurately differentiate pitting corrosion, special It not the measuring method of little etch pit, thus develop and improve FSM method.

The technical scheme is that

A kind of metallic conduit, receptacle hole shape corrosion detecting method, based on field fingerprinting principle, at metallic conduit or container Outer wall is arranged and is measured electrode matrix, and described measurement electrode matrix has i row electrode, in axis side at the circumferencial direction of pipeline or container To there being j row electrode, arbitrarily axially on two adjacent electrodes constitute one and measure electrode pair；One reference plate, this reference are set The material of plate is identical with the material of tested pipeline or container；A pair reference electrode it is provided with, as reference mark on described reference plate Collimator electrode；The measurement electrode of region, definition random corrosion hole is to as main electrode, and corresponding voltage is as principal voltage；Other Electrode is to as auxiliary electrode, and corresponding voltage is as auxiliary voltage；Measure the most as follows and solve area and the degree of depth of etch pit:

(1), measured zone corresponding for main electrode is sub-divided into a × b community；Using 1/5～the 1/3 of electrode spacing as Pitting corrosion diameter initial value, the maximum of electrode spacing is pitting corrosion diameter stop value, and step-length is 0.5～1mm, with 1/20～1/15 wall Thick as pitting corrosion degree of depth initial value, 7/10～8/10 wall thickness is pitting corrosion degree of depth stop value, and step-length is 0.5～1mm, utilizes steady electricity Flow field method, i.e. t when calculating corrosion-free hole, each community one by one₀Moment and i.e. t when having etch pit_xThe principal voltage in moment, auxiliary voltage, Obtain the changing value of main and auxiliary voltage, set up the corrosion database of main and auxiliary voltage method；

(2), input constant current drive electric current from reference plate to metallic conduit or container, make this exciting current flow through reference electrode With measurement electrode matrix, the intensity of this exciting current is identical with current intensity when using steady high voltage system method to calculate；

(3), with voltage measurement amount all measurements electrode to and reference electrode at t₀Moment and t_xThe voltage in moment；

(4), it is calculated as follows principal voltage t_xThe fingerprint in moment

In formula:

V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；

V_ref(t₀), V_ref(t_x) reference electrode is at t₀And t_xThe voltage in moment；

The solution formula of the fingerprint of auxiliary voltage is identical with the solution formula of the fingerprint of principal voltage；

(5), revised principal voltage is obtained as the following formula:

V’_i,j；i,j+1(t_x)=(FC_i,j；i,j+1(t_x)/1000+1)×V_ref(t_x)×V_i,j；i,j+1(t₀)/V_ref(t₀) (2)

In formula: V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) main electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；Auxiliary Voltage solution formula

Identical with principal voltage solution formula, and solve auxiliary voltage；

(6), revised principal voltage changing value is obtained as the following formula:

ΔV’_i,j；i,j+1(t_x)=V '_i,j；i,j+1(t_x)-V_i,j；i,j+1(t₀) (3)

Auxiliary voltage change solution formula is identical with principal voltage changing value solution formula, and solves auxiliary voltage change；

(7), revised main and auxiliary voltage change is mated with corrosion database, the most revised main and auxiliary change in voltage Area and the degree of depth of etch pit when value differs minimum with the main and auxiliary voltage change in data base are and solve value.

As preferably, described measured zone is subdivided into 3 × 3 totally 9 communities, i.e. a=b=3.

As preferably, described voltameter uses high-resolution accurate voltage measurement module.

Beneficial effects of the present invention: the present invention is not in the case of changing original FSM method probe layout, by main and auxiliary electricity Platen press with the area of the little etch pit of rapid solving and the degree of depth, and can be greatly improved certainty of measurement, makes measurement result more Reflect the actual state that hole is corroded truly, exactly, judge that accident potential provides reliable basis for people.

Accompanying drawing explanation

Fig. 1 FSM method principle schematic

Fig. 2 FSM equivalent resistance network model and main and auxiliary V diagram

Fig. 3 little etch pit undecidable decision problem schematic diagram

The contour shape schematic diagram (this method thinks that the area S of pitting corrosion is fixing) of the pitting corrosion that Fig. 4 traditional F SM method is thought

Equivalent resistance network model figure after Fig. 5 FSM segmentation

Detailed description of the invention

In order to enable accurately to differentiate area and the degree of depth of little etch pit, the present invention proposes a kind of main and auxiliary voltage method, i.e. definition and appoints Meaning electrode corresponding to position, etch pit place is to as main electrode, and corresponding voltage is as principal voltage V_i,j；i,j+1；By remaining axle To electrode to as auxiliary electrode, corresponding voltage is as auxiliary voltage, the most auxiliary voltage V_{i-1,j；i-1,j+1}, V_{i+1,j；i+1,j+1}..., V_{i,j+n；i,j+n+1}；Utilize steady high voltage system method to set up corrosion database, according to the related request of steady high voltage system method to quilt simultaneously Test tube road or container apply constant current drive electric current, measure and process and obtain revised main and auxiliary voltage change, by coupling Main and auxiliary voltage change, thus high accuracy and the area having the pitting corrosion deterministically obtained in this main electrode corresponding region And the degree of depth.Its principle is as follows:

Equivalent resistance chain model in Fig. 2 is carried out ab uniform subdivision according to measurement requirement, is i.e. subdivided into ai × bj son Resistance (Fig. 5), then resistance can be subdivided into ab sub-resistance, calculates the FC ratio array of segmentation resistor network, by under Row formula draws:

$\begin{array}{c}\frac{{\mathrm{FC}}_{i,j;i,j+1}\left(t_x\right)}{{\mathrm{FC}}_{i,j;i,j+1}\left(t_0\right)}=\frac{\frac{I_{\left(n\right)(n+1)}R}{IR}-1}{\frac{I_{(m-1)\left(m\right)}(R+R^{\′})}{IR}-1}\\ =\frac{I_{\left(n\right)(n+1)}R-IR}{I_{(m-1)\left(m\right)}(R+R^{\′})-IR}\end{array}$

Wherein I be do not corrode before the electric current that often flows through on row resistance chain, R is initial resistance value, and R' is the resistance value changed, I_(m-1)mFor flowing through the electric current of the resistance that resistance changes, I_n(n+1)For flowing through the electricity of the resistance that other resistance does not changes Stream, FC_i,j；i,j+1(t_x) it is the FC value of the resistance that resistance changes, FC_i,j；i,j+1(t₀) it is the resistance that do not changes of resistance FC value.

Obtain the expression formula of any time voltage across poles according to FC ratio array, following equation obtain:

$V_{i,j;i,j+1}\left(t_x\right)=\underset{x=1}{\overset{ab}{\mathrm{\Σ}}}\frac{{\mathrm{FC}}_{i,j;i,j+1}\left(t_x\right)}{{\mathrm{FC}}_{i,j;i,j+1}\left(t_0\right)}\×{\mathrm{\ΔV}}_{FC0}+V_{i,j;i,j+1}\left(t_0\right)$

ΔV_{F C}For the voltage at the resistance two ends that resistance changes, V_i,j；i,j+1(t_x) it is t_xThe principal voltage in moment, V_i,j；i,j+1(t₀) it is t₀The principal voltage in moment, after ab represents the segmentation of former resistor network, the sub-resistance number that a resistance is corresponding. The computing formula of other n auxiliary voltage is the most similar.Calculate principal voltage V after a sub-resistance individually changes_i,j；i,j+1 And n auxiliary voltage V (1)_{i-1,j；i-1,j+1}(1), V_{i+1,j；i+1,j+1}(1) ..., V_{i,j+n；i,j+n+1}, then calculate several sub-resistance (1) Principal voltage V after simultaneously changing_i,j；i,j+1(n) and n auxiliary voltage V_{i-1,j；i-1,j+1}(n), V_{i+1,j；i+1,j+1}(n) ..., V_{i,j+n；i,j+n+1}(n).Show according to result of calculation: when the principal voltage of two kinds of situations is equal, auxiliary voltage is unequal, it may be assumed that

V_i,j；i,j+1(1)=V_i,j；i,j+1(n)

V_{i-1,j；i-1,j+1}(1)≠V_{i-1,j；i-1,j+1}(n)

V_{i+1,j；i+1,j+1}(1)≠V_{i+1,j；i+1,j+1}(n)

V_{i,j+n；i,j+n+1}(1)≠V_{i,j+n；i,j+n+1}(n)

Above formula illustrates that different holes is possible consistent on the impact of principal voltage the most theoretically, but the impact on auxiliary voltage is Inconsistent.According to above-mentioned theory, i.e. may utilize main and auxiliary voltage integrated and judge area S and degree of depth D of little etch pit.

Concrete grammar is:

According to the material of tested pipeline, cast, diameter, thickness, electrode matrix is measured in design.Pipeline circumferencial direction with I row, is arranged with j row in the axial direction；Add a reference plate, and arrange a pair ginseng at it along sense of current mid line region Examine electrode.The horizontal and vertical distance of all electrodes is 3～5 times of wall thickness (WT)；

Apply constant current drive electric current from reference plate, then gather and preserve measurement electrode group voltage matrix and reference plate voltage At corrosion-free hole (t₀Moment) and (t when having etch pit_xMoment) voltage, obtain fingerprint FC value:

${\mathrm{FC}}_{i,j;i,j+1}\left(t_x\right)=(\frac{\frac{V_{i,j;i,j+1}\left(t_x\right)}{V_{i,j;i,j+1}\left(t_0\right)}}{\frac{V_{ref}\left(t_x\right)}{V_{ref}\left(t_0\right)}}-1)\×1000$

In formula: V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；

V_ref(t₀), V_ref(t_x) reference electrode is at t₀And t_xThe voltage in moment；

According to FC value, it is calculated as follows and obtains revising principal voltage changing value:

V’_i,j；i,j+1(t_x)=(FC_i,j；i,j+1(t_x)/1000+1)×V_ref(t_x)×V_i,j；i,j+1(t₀)/V_ref(t₀)

In formula: V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；V_ref (t₀), V_ref(t_x) reference electrode is at t₀And t_xThe voltage in moment.Revise the auxiliary voltage derivation of equation and solve public affairs with revising principal voltage Formula is similar, and solves the auxiliary voltage of correction；

It is calculated principal voltage changing value according to the following formula:

ΔV’_i,j；i,j+1(t_x)=V '_i,j；i,j+1(t_x)-V_i,j；i,j+1(t₀)

Auxiliary voltage change solution formula is identical with principal voltage changing value solution formula, and solves auxiliary voltage change； Utilize steady

Constant current field method calculates and sets up corrosion database by experimental verification, and the data of calculating include:

For i=1to i (circumferencial direction of pipeline has i row electrode)

For j=1to j (axis direction at pipeline has j row)

For q=1to ab (there is a × b GongabGe community principal voltage corresponding region)

For Φ=1/5～1/3d to d, step 0.5～1mm (Φ-pitting corrosion diameter, d-electrode spacing.)

For D=1/20～1/15WT to 7/10-8/10WT, step 0.5～1mm (D-pitting corrosion degree of depth.Petrochemical industry Pipeline needs the minimum pitting corrosion degree of depth of detection to be 1/20～1/15WT.)

Goto " calculates V_i,j；1,j+1(t_x) module "

NextΦ

Next D

Next q

Next j

Next i

Reality is measured and revised main and auxiliary voltage mates with data base, can draw the area of etch pit with The degree of depth.Coupling uses pattern match principle, if the main and auxiliary voltage change of data base is Δ V_i,j；i,j+1(m), auxiliary voltage change For Δ V_{i-1,j；i-1,j+1}(m),ΔV_{i+1,j；i+1,j+1}(m),…,ΔV_{i,j+n；i,j+n+1}M (), measuring gained principal voltage changing value is Δ V_i,j；i,j+1It is Δ V with auxiliary voltage change_{i-1,j；i-1,j+1},ΔV_{i+1,j；i+1,j+1},…,ΔV_{i,j+n；i,j+n+1}, then have:

Δ₁=Δ V_i,j；i,j+1(m)-ΔV_i,j；i,j+1

Δ₂=Δ V_{i-1,j；i-1,j+1}(m)-ΔV_{i-1,j；i-1,j+1}

Δ₃=Δ V_{i+1,j；i+1,j+1}(m)-ΔV_{i+1,j；i+1,j+1}

Δ_n=Δ V_{i,j+n；i,j+n+1}(m)-ΔV_{i,j+n；i,j+n+1}

${\mathrm{\μ}}_m=\sqrt{{{\mathrm{\Δ}}_1}^2+{{\mathrm{\Δ}}_2}^2+{{\mathrm{\Δ}}_3}^2+\mathrm{...}+{{\mathrm{\Δ}}_n}^2}$

At a series of μ_mIn, minimum μ_mCorresponding etch pit is i.e. to solve for result.The most revised main and auxiliary voltage becomes Area and the degree of depth of etch pit when change value differs minimum with the main and auxiliary voltage change in data base are and solve value.

The present invention is illustrated below with an example.

Pressing array of measure electrodes on certain way cloth at tested metallic conduit outer wall, the spacing of electrode typically takes the 3 of wall thickness ～4 times.Wall thickness WT=10mm in this example, measures spacing d=30mm of electrode.

Tested metallic conduit is applied DC constant current power supply, and the electric current that this example applies is 2A, adopts through repeatedly accurate voltage Sample, then obtain measuring electrode matrix and reference electrode to the (t when corrosion-free hole after data process₀Moment) voltage Value.

Carry out steady high voltage system calculating according to measuring electrode and tested pipeline parameter, set up corrosion database (partly):

D₂=1.8mm, Φ₃=30mm, D₃=0.8mm (Φ is diameter, and D is the degree of depth).

Carrying out repeatedly accurate voltage sampling again, then data process and show that measurement electrode matrix and reference electrode are to there being corruption (t during pit_xMoment) voltage.

The voltameter measuring electrode group voltage matrix and reference electrode pair is utilized to calculate FC value:

${\mathrm{FC}}_{i,j;i,j+1}\left(t_x\right)=(\frac{\frac{V_{i,j;i,j+1}\left(t_x\right)}{V_{i,j;i,j+1}\left(t_0\right)}}{\frac{V_{ref}\left(t_x\right)}{V_{ref}\left(t_0\right)}}-1)\×1000$

In formula: V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；

V_ref(t₀), V_ref(t_x) reference electrode is at t₀And t_xThe voltage in moment；

Reduce according to FC value, be calculated as follows and obtain revising voltage:

V’_i,j；i,j+1(t_x)=(FC_i,j；i,j+1(t_x)/1000+1)×V_ref(t_x)×V_i,j；i,j+1(t₀)/V_ref(t₀)

In formula: V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；V_ref (t₀), V_ref(t_x) reference electrode is at t₀And t_xThe voltage in moment.Auxiliary voltage solution formula is similar to principal voltage solution formula, And solve auxiliary voltage；

Obtain principal voltage changing value again:

ΔV’_i,j；i,j+1(t_x)=V '_i,j；i,j+1(t_x)-V_i,j；i,j+1(t₀)

Auxiliary voltage change solution formula is similar to principal voltage changing value solution formula, and solves auxiliary voltage change；

Thus obtain the main and auxiliary voltage change in three holes:

Reality is measured and revised main and auxiliary voltage mates with data base, can draw the area of etch pit with The degree of depth.Coupling uses pattern match principle, if the main and auxiliary voltage change of data base is Δ V_i,j；i,j+1(m), auxiliary voltage change For Δ V_{i-1,j；i-1,j+1}(m),ΔV_{i+1,j；i+1,j+1}(m),…,ΔV_{i,j+n；i,j+n+1}M (), measuring gained principal voltage changing value is Δ V_i,j；i,j+1With auxiliary

Voltage change is Δ V_{i-1,j；i-1,j+1},ΔV_{i+1,j；i+1,j+1},…,ΔV_{i,j+n；i,j+n+1}, then have:

Δ₁=Δ V_i,j；i,j+1(m)-ΔV_i,j；i,j+1

Δ₂=Δ V_{i-1,j；i-1,j+1}(m)-ΔV_{i-1,j；i-1,j+1}

Δ₃=Δ V_{i+1,j；i+1,j+1}(m)-ΔV_{i+1,j；i+1,j+1}

Δ_n=Δ V_{i,j+n；i,j+n+1}(m)-ΔV_{i,j+n；i,j+n+1}

${\mathrm{\μ}}_m=\sqrt{{{\mathrm{\Δ}}_1}^2+{{\mathrm{\Δ}}_2}^2+{{\mathrm{\Δ}}_3}^2+\mathrm{...}+{{\mathrm{\Δ}}_n}^2}$

At a series of μ_mIn, minimum μ_mCorresponding etch pit is i.e. to solve for result.The most revised main and auxiliary voltage becomes Area and the degree of depth of etch pit when change value differs minimum with the main and auxiliary voltage change in data base are and solve value.

Through overmatching, the matching result in three holes is as follows:

Depth capacity error σ in hole is obtained by coupling_max=± 1%WT (WT is wall thickness), far below conventional field fingerprinting The error of ± 15～25%WT.

Claims (3)

1. metallic conduit, a receptacle hole shape corrosion detecting method, based on field fingerprinting principle, outside metallic conduit or container Measurement electrode matrix put by wall cloth, and described measurement electrode matrix has i row electrode, at axis direction at the circumferencial direction of pipeline or container Have j row electrode, arbitrarily axially on two adjacent electrodes constitute one and measure electrode pair；One reference plate, this reference plate are set Material identical with the material of tested pipeline or container；A pair reference electrode it is provided with, as reference standard on described reference plate Electrode；The measurement electrode of region, definition random corrosion hole is to as main electrode, and corresponding voltage is as principal voltage；Other electricity Extremely to as auxiliary electrode, corresponding voltage is as auxiliary voltage；Measure the most as follows and solve area and the degree of depth of etch pit:

(1), measured zone corresponding for main electrode is sub-divided into a × b community；Using 1/5～the 1/3 of electrode spacing as pitting corrosion Diameter initial value, the maximum of electrode spacing is pitting corrosion diameter stop value, and step-length is 0.5～1mm, makees with 1/20～1/15 wall thickness For pitting corrosion degree of depth initial value, 7/10～8/10 wall thickness is pitting corrosion degree of depth stop value, and step-length is 0.5～1mm, utilizes steady high voltage system Method, i.e. t when calculating corrosion-free hole, each community one by one₀Moment and i.e. t when having etch pit_xThe principal voltage in moment, auxiliary voltage, obtain The changing value of main and auxiliary voltage, sets up the corrosion database of main and auxiliary voltage method；

(2), input constant current drive electric current from reference plate to metallic conduit or container, make this exciting current flow through reference electrode and survey Amount electrode matrix, the intensity of this exciting current is identical with current intensity when using steady high voltage system method to calculate；

(3), with voltage measurement amount all measurements electrode to and reference electrode at t₀Moment and t_xThe voltage in moment；

(4), it is calculated as follows principal voltage t_xThe fingerprint in moment

(unit: ppt, Part per thousand) (1)

In formula:

V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；

V_ref(t₀), V_ref(t_x) reference electrode is at t₀And t_xThe voltage in moment；

The solution formula of the fingerprint of auxiliary voltage is identical with the solution formula of the fingerprint of principal voltage；

(5), revised principal voltage is obtained as the following formula:

V’_i,j；i,j+1(t_x)=(FC_i,j；i,j+1(t_x)/1000+1)×V_ref(t_x)×V_i,j；i,j+1(t₀)/V_ref(t₀) (2)

In formula: V_i,j；i,j+1(t₀), V_i,j；i,j+1(t_x) main electrode is to (i, j；I, j+1) at t₀And t_xThe voltage in moment；

V_ref(t₀), V_ref(t_x) reference electrode is at t₀And t_xThe voltage in moment；Auxiliary voltage solution formula and principal voltage solve public affairs Formula is identical, and solves auxiliary voltage；

(6), revised principal voltage changing value is obtained as the following formula:

ΔV’_i,j；i,j+1(t_x)=V '_i,j；i,j+1(t_x)-V_i,j；i,j+1(t₀) (3)

Auxiliary voltage change solution formula is identical with principal voltage changing value solution formula, and solves auxiliary voltage change；

(7), revised main and auxiliary voltage change is mated with corrosion database, the most revised main and auxiliary voltage change with Area and the degree of depth of etch pit when the main and auxiliary voltage change in data base differs minimum are and solve value.

Metallic conduit the most according to claim 1, receptacle hole shape corrosion detecting method, it is characterised in that described measurement zone Territory is subdivided into 3 × 3 totally 9 communities, i.e. a=b=3.

Metallic conduit the most according to claim 1, receptacle hole shape corrosion detecting method, it is characterised in that described voltameter Use high-resolution accurate voltage measurement module.