CN116297128A - Ground metal pipeline and buried metal pipeline rust degree detection method - Google Patents

Abstract

The application provides a method for detecting the corrosion degree of above-ground metal pipelines and buried metal pipelines. The method for detecting the corrosion degree of above-ground pipelines includes: setting power supply electrodes and measuring electrode circuits on the inner or outer walls of the pipelines, and measuring the measuring points of the measuring electrodes on the inner or outer walls of the pipelines. The potential of the non-corroded layer; based on the potential distribution of the inner or outer wall of the pipeline, use the measuring circuit to measure the inner or outer wall of the pipeline to measure the resistance of the corrosion layer; measure the resistance of the corrosion layer based on the measurement electrode on the inner or outer wall of the pipeline to measure the thickness of the corrosion layer of the pipeline; The corrosion detection method of the buried metal pipeline includes: setting the power supply electrode and the measurement electrode circuit on the inner wall of the pipeline, respectively taking the pipeline center as the origin, the pipeline axial direction as the z axis, and the pipeline radial direction as the r axis to construct a pipeline transmission line stratum model, constructing The equivalent longitudinal conductance of the fluid in the pipeline, the inner wall of the non-corroded pipeline and the corrosion layer on the inner wall of the pipeline is determined, the transmission line equation of the pipeline is determined, and the resistance and thickness of the corrosion layer on the outer wall of the pipeline are calculated.

Description

A method for detecting the corrosion degree of above-ground metal pipelines and buried metal pipelines

technical field

The present application relates to the technical field of pipeline detection and maintenance, in particular to a method for detecting the corrosion degree of above-ground metal pipelines and buried metal pipelines.

Background technique

Water resources are an important factor affecting human living standards, social stability, and economic development. Urban water supply systems, as the infrastructure for human transportation and utilization of water resources, are a symbol of urban development status and capacity, and a basic factor to ensure urban development. However, due to the influence of various complex factors on urban underground pipelines, it is inevitable that various defects will appear in the pipelines during the operation period. A large number of buried oil transportation and water supply pipelines are in a damaged working state, which can easily cause leakage of oil transportation and water supply pipe networks. Among them, the most common and serious problem is the phenomenon of corrosion. As the service time of the pipeline increases, the corrosion will continue to increase, and even cause the pipeline to perforate and rupture, resulting in safety accidents.

At present, domestic and foreign pipeline corrosion detection methods mainly include ultrasonic wave, magnetic flux leakage, eddy current and transient electromagnetic, etc., but a common problem of these detection technologies is that the detection accuracy of pipeline corrosion is not high and most of them are localized, and it is difficult to realize the rust layer. Direct measurement and estimation of electrical resistance or corrosion layer thickness. Generally, inspection and maintenance are only carried out after pipeline safety accidents, resulting in waste of resources and economic losses, and may even cause personal injury, building collapse, and environmental pollution.

Contents of the invention

In view of this, the purpose of this application is to propose a method for detecting the corrosion degree of above-ground metal pipelines and buried metal pipelines that overcomes the above-mentioned problems.

Based on the above purpose, the first aspect of the present application provides a method for detecting the corrosion degree of above-ground metal pipelines, including:

A power supply electrode and a measuring electrode circuit are respectively arranged on the inner or outer wall of the pipeline to measure the potential of the non-corroded layer at the measurement point of the measuring electrode on the inner or outer wall of the pipeline;

Based on the potential distribution of the inner or outer wall of the pipeline, using a measurement circuit to measure the resistance of the corrosion layer at the measuring point of the measuring electrode on the inner or outer wall of the pipeline;

Measuring the resistance of the point corrosion layer based on the measuring electrode on the inner or outer wall of the pipeline, and measuring the thickness of the corrosion layer of the pipeline;

Wherein the measuring electrode circuit comprises a measuring electrode, a first measuring circuit and a second measuring circuit, the first measuring circuit and the second measuring circuit are connected in series with the measuring electrodes respectively, the first measuring circuit and the second measuring circuit The measuring circuits are connected in parallel, the first measuring circuit includes a first potentiometer and a first ammeter connected in series, and the second measuring circuit includes a second potentiometer and a second ammeter connected in series.

Optionally, the calculation formula for measuring the electric potential of the pipeline wall is:

I ₁ R _r +I ₁ (R _V1 +R _I1 )＝U

I ₂ R _r +I ₂ (R _V2 +R _I2 )＝U

Among them, R _r is the resistance of the corrosion layer at the measurement point of the measuring electrode, I ₁ is the reading of the first ammeter, R _V1 is the resistance of the first potentiometer, R _I1 is the resistance of the first ammeter, I ₂ is the reading of the second ammeter; R _V2 is The resistance of the second point potential difference meter, R _I2 is the resistance of the second ammeter, and U is the potential of the non-corroded layer pipeline wall.

Optionally, the calculation formula for measuring the thickness of the corrosion layer of the pipeline is:

Among them, δ is the thickness of the corrosion layer, S is the contact area between the measuring electrode and the pipeline, and _ρr is the resistivity of the corrosion layer of the pipeline.

The second aspect of the present application provides a method for detecting the corrosion degree of buried metal pipelines, including:

The inner wall of the pipeline is provided with a power supply electrode and a measuring electrode circuit to measure the measured potential of the non-rust layer at the measuring point of the measuring electrode on the inner wall of the pipeline; wherein the measuring electrode circuit includes a measuring electrode, a first measuring circuit and a second measuring circuit, and The first measurement circuit and the second measurement circuit are respectively connected in series with the measurement electrodes, the first measurement circuit and the second measurement circuit are connected in parallel, and the first measurement circuit includes a first potentiometer connected in series and a first an ammeter, the second measuring circuit comprising a second potentiometer and a second ammeter connected in series;

Taking the center of the pipeline as the origin, the axial direction of the pipeline as the z-axis, and the radial direction of the pipeline as the r-axis to construct a pipeline transmission line stratum model;

Based on the formation model of the pipeline transmission line and the fluid in the pipeline and the current in the pipeline flowing along the axis of the pipeline, the equivalent longitudinal conductance of the fluid in the pipeline, the inner wall of the non-corroded pipeline and the rusted layer on the inner wall of the pipeline is constructed;

determining the pipeline transmission line equation based on the equivalent longitudinal conductance;

Calculate the transmission line equation of the pipeline to determine the calculated potential of the non-corroded layer of the pipeline wall;

Calculate the partial derivative of the potential of the pipeline transmission line stratum model to the stratum parameter through the potential Jacobi matrix;

determining an inversion objective function through the measured potential and the calculated potential;

Using the pipeline transmission line equation and the partial derivative of the potential to the formation parameters, through the inversion of the objective function inversion iterative approximation, to calculate the resistance of the corrosion layer on the outer wall of the pipeline;

The thickness of the corrosion layer on the outer wall of the pipeline is calculated according to the resistance of the corrosion layer on the outer wall of the pipeline.

Optionally, based on the pipeline transmission bottom line model and the fluid in the pipeline and the current in the pipeline flowing along the axis of the pipeline, the calculation formula for the equivalent longitudinal conductance of the fluid in the pipeline, the non-corroded pipeline wall and the rusted layer in the pipeline is constructed for:

S=S _f +S _C +S _r ,

in,

R is the total equivalent longitudinal resistance of axial unit length;

为沿轴向供水管道内流体单位长度的电阻；

is the resistance per unit length of the fluid in the water supply pipe along the axial direction;

_ρf is the resistivity of the fluid in the pipeline;

a ₁ is the inner radius of the corrosion layer of the pipeline;

_Rc is the resistance per unit length of the non-corroded water supply pipeline along the axial direction;

R _r =ρ _r /[2πa ₂ (a ₃ -a ₂ )] is the resistance per unit length of the corrosion layer in the water supply pipeline along the axial direction, σ _r =1/ρ _r ;

a ₂ is the radius of the inner wall of the non-corroded pipeline, and a ₃ is the radius of the outer wall of the non-corroded pipeline;

σ _r is the electrical conductivity of the pipeline corrosion layer.

Optionally, based on the equivalent longitudinal conductance, the formula for determining the pipeline transmission line equation is:

Among them, U is the potential distribution of the non-corroded water supply pipe wall;

I is the current in the wall of the non-corroded water supply pipe;

T为地层横向电阻，α为地层α系数。

T is the lateral resistance of the formation, and α is the α coefficient of the formation.

Optionally, calculating the partial derivative of the potential of the pipeline transmission line formation model with respect to the formation parameters through the potential Jacobi matrix, including:

dividing the pipeline transmission line stratigraphic model into units along the pipeline;

Determine the form of the Jacobi matrix based on the stratum model of the pipeline transmission line divided by the unit;

Determining the position of the stratum model of the pipeline transmission line where the measuring electrode is located;

Based on the Jacobi matrix form and the position of the pipeline transmission line formation model where the measurement electrode is located, the partial derivative of the potential of the transmission line formation model with respect to formation parameters is determined.

Optionally, the form of the Jacobi matrix is:

ΔU=GΔm,

Among them, ΔU is the potential increment, and Δm is the perturbation increment of the formation model parameters of the pipeline transmission line;

为单元划分的传输线地层模型电阻向量；

The resistance vector of the transmission line formation model divided into cells;

为单元划分的传输线地层模型电势。

Transmission line formation model potentials partitioned for cells.

Optionally, using the pipeline transmission line equation and the partial derivative of the potential with respect to the formation parameters, the resistance of the outer corrosion layer of the pipeline is calculated by inverting an iterative approximation through an inversion objective function;

The calculation formula of the inversion objective function is:

F(m)＝||UU ^obs ||

Among them, U ^obs is the measured non-corroded pipeline wall potential;

U is the potential of the non-corroded pipe wall.

Optionally, the inversion iterative approximate formula is:

d _k ＝-(G _k ^T G _k +β _k I) ^-1 G _k ^T f ^k

where d _k is the formation parameter increment obtained in the kth iteration;

G _k ^T G _k is the partial derivative matrix product of the pipeline transmission line equation;

I is an n-order identity matrix, and β _k is a positive real constant.

It can be seen from the above that the application provides a method for detecting the corrosion degree of the above-ground pipeline, which can directly measure and calculate the thickness of the corrosion layer on the inner wall of the pipeline and the outer wall of the pipeline through the power supply electrode and the measuring electrode circuit, and a method for detecting the corrosion degree of the buried pipeline. , by establishing a pipeline transmission line stratum model, a calculation method for the lateral resistance of the transmission line stratum model, the equivalent transverse resistance of the corroded pipeline and the fluid in the pipeline is proposed, and the calculation of the potential distribution of the non-corroded pipeline wall is realized by means of the pipeline transmission line equation, and the pipeline is inverted based on the pipeline wall field potential The resistance and thickness of the corrosion layer on the outer wall can be used to measure and evaluate the remaining thickness of the corroded pipeline wall, grasp the current status of the pipeline in a timely and accurate manner, make a scientific safety evaluation of the pipeline through the current status of the pipeline and give relevant maintenance suggestions, and reduce the cost of the pipeline. Risk of failure and avoid unnecessary economic losses.

Description of drawings

In order to more clearly illustrate the technical solutions in the present application or related technologies, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or related technologies. Obviously, the accompanying drawings in the following description are only for this application Embodiments, for those of ordinary skill in the art, other drawings can also be obtained based on these drawings without any creative effort.

Fig. 1 is a flow chart of a method for detecting the corrosion degree of an above-ground metal pipeline according to an embodiment of the present application;

Fig. 2 is a schematic diagram of the above-ground metal pipeline and power supply detection mode of the embodiment of the present application;

Fig. 3 is a flow chart of a method for detecting corrosion of buried metal pipelines according to an embodiment of the present application;

Fig. 4 is the schematic diagram of the corroded pipeline of the embodiment of the present application;

Fig. 5 is a schematic diagram of a stratum model of a metal pipeline transmission line according to an embodiment of the present application.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present application clearer, the present application will be further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

It should be noted that, unless otherwise defined, the technical terms or scientific terms used in the embodiments of the present application shall have the usual meanings understood by those skilled in the art to which the present application belongs. "First", "second" and similar words used in the embodiments of the present application do not indicate any order, quantity or importance, but are only used to distinguish different components. "Comprising" or "comprising" and similar words mean that the elements or items appearing before the word include the elements or items listed after the word and their equivalents, without excluding other elements or items. Words such as "connected" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "Down", "Left", "Right" and so on are only used to indicate the relative positional relationship. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

In the process of measuring the corrosion resistance of the above-ground pipeline, when the power supply electrode is in good contact with the pipeline wall, the potential distribution of the pipeline wall is determined. The point difference is a constant. It should be noted that the above ground pipeline does not simply refer to the pipeline existing on the ground, but only refers to the rusty metal pipeline that can contact the inner wall and outer wall of the pipeline through the power supply electrode and the measurement electrode. According to this feature, with reference to Fig. 1 and Fig. 2, the first aspect of the present application provides a method for detecting the corrosion degree of above-ground metal pipelines, including:

S101. Install a power supply electrode and a measuring electrode circuit on the inner wall or the outer wall of the pipeline respectively, and measure the potential of the non-corroded layer at the measuring point of the measuring electrode on the inner wall or the outer wall of the pipeline.

The measurement method shown in Figure 2 realizes the inner wall of the above-ground metal pipeline, the power supply electrode A is used to provide current, and the measurement electrode circuit is used to measure the resistance of the corrosion layer in the pipeline, wherein the measurement electrode circuit includes measurement electrode B, the first measurement circuit and the second measurement circuit, the first measurement circuit and the second measurement circuit are respectively connected in series with the measurement electrode B, while the first measurement circuit and the second measurement circuit are connected in parallel, and the first measurement circuit includes the first potentiometer and the second measurement circuit connected in series An ammeter, the second measuring circuit includes a second potentiometer and a second ammeter connected in series, it should be noted that the internal resistances of the first potentiometer _V1 and the second potentiometer _V2 are different.

S102. Based on the potential distribution of the inner wall or the outer wall of the pipeline, use the measuring circuit to measure the resistance of the corrosion layer at the measuring electrode on the inner wall or the outer wall of the pipeline.

Combined with Figure 2, turn on the power supply of the power supply electrode A, first close the switch k to the position of 1, measure with the first measuring circuit, record the readings V ₁ and I ₁ of the first potentiometer and the first ammeter, then the first potential The differential meter and ammeter readings meet

I ₁ R _r +I ₁ (R _V1 +R _I1 )=U, (1)

Wherein, R _V1 and R _I1 are the internal resistances of the first potentiometer and the first ammeter respectively, and U is the potential of the non-corroded metal pipe wall.

Keep the power-on state of the power supply electrode A unchanged, and then close the switch k to the position of 2. The first measurement circuit measures and records the readings V ₂ and I ₂ of the second potentiometer and the second ammeter. Due to the first potential The resistance of the difference meter and the second potentiometer is large, which has almost no influence on the potential distribution of the pipeline, so the readings of the second potentiometer and the second ammeter satisfy

I ₂ R _r +I ₂ (R _V2 +R _I2 )=U, (2)

Wherein R _V2 and R _I2 are internal resistances of the second potentiometer and the second ammeter respectively.

Use the above measurement data to solve the potential U and resistance R _r in the above equations (1)-(2), the value is the accurate potential of the non-corroded pipeline wall at the measurement point B of the measurement electrode and the resistance of the rust layer after eliminating the influence of the electrode measurement environment .

It can be seen from the above measurement method that the above embodiment is only for the accurate potential of the non-corroded pipeline wall at the measuring point B of the measuring electrode after eliminating the influence of the electrode measurement environment on the corrosion layer on the inner wall of the pipeline and the resistance of the corrosion layer on the inner wall of the pipeline, then the power supply motor in Fig. 2 A and measuring electrode B are arranged on the outer wall of the pipeline, and similarly, the measurement of the resistance and potential of the corrosion layer on the outer wall of the pipeline can be realized.

S103. Measure the resistance of the point corrosion layer based on the measurement electrode on the inner or outer wall of the pipeline, and measure the thickness of the corrosion layer on the pipeline.

Where δ is the thickness of the corrosion layer, S is the contact area between the measuring electrode and the pipeline wall, and _ρr is the resistivity of the corrosion layer of the pipeline.

Of course, the above is for above-ground pipelines. However, many oil pipelines and urban water supply pipelines are deeply buried underground. It is impossible to measure the resistance of the corrosion layer on the outer wall of the pipeline by contacting the above-mentioned measuring electrodes with the outer wall of the pipeline. If you want to measure the pipeline If the resistance of the outer wall is low, then it is necessary to dig out the ground to expose the buried pipeline. If this is done, the workload will become very large, and the cost will be very high. Then the only way is to set the power supply electrode and the measurement electrode circuit on the inner wall of the pipeline. Indirect realization, at this time, the equivalent total lateral resistance of the formation can be successfully measured through casing resistivity logging, but the resistance of the corrosion layer on the outer wall of the pipeline cannot be obtained specifically, which constitutes an underdetermined problem. Based on this, the application In the second aspect, with reference to Fig. 3, Fig. 4 and Fig. 5, a method for detecting the corrosion degree of buried metal pipelines is provided, including:

S201. Install a power supply electrode and a measuring electrode circuit on the inner wall of the pipeline, and measure the measured potential of the non-corroded layer at the measurement point of the measuring electrode on the inner wall of the pipeline. It can be understood that setting the power supply electrode and the measurement electrode circuit on the inner wall of the pipeline can be realized in any way. It can be carried by a special robot to carry the power supply electrode and the measurement electrode circuit and pasted on the inner wall of the pipeline, or by replacing the robot and being able to work with the robot. For other methods that play the same role, as long as the power supply electrode and the measurement electrode circuit can be arranged on the inner wall of the pipeline and they are in good contact with the inner wall of the pipeline, it is not specified how to arrange the power supply electrode and the measurement electrode circuit on the inner wall of the pipeline. limit.

It can be understood that, here, the power supply electrode circuit and the measurement electrode circuit arranged on the inner wall of the buried metal pipeline are the same as those of the aboveground metal pipeline.

S202. Taking the center of the pipeline as the origin, the axial direction of the pipeline as the z-axis, and the radial direction of the pipeline as the r-axis, construct a stratum model of the pipeline transmission line.

S203. Based on the stratum model of the pipeline transmission line and the flow of the fluid in the pipeline and the current in the pipeline along the axial direction of the pipeline, construct the equivalent longitudinal conductance of the fluid in the pipeline, the inner wall of the non-corroded pipeline, and the rusted layer on the inner wall of the pipeline.

Further, the equivalent bus conductance is

S=S _f +S _C +S _r , (4)

in

R is the total equivalent longitudinal (axial) resistance of axial unit length;

为沿轴向供水管道内流体单位长度的电阻；

is the resistance per unit length of the fluid in the water supply pipe along the axial direction;

_ρf is the resistivity of the fluid in the pipeline;

a ₁ is the inner radius of the corrosion layer of the pipeline;

_Rc is the resistance per unit length of the non-corroded water supply pipeline along the axial direction;

R _r =ρ _r /[2πa ₂ (a ₃ -a ₂ )] is the resistance per unit length of the corrosion layer in the water supply pipeline along the axial direction, σ _r =1/ρ _r ;

a ₂ is the radius of the inner wall of the non-corroded pipeline, and a ₃ is the radius of the outer wall of the non-corroded pipeline;

σ _r is the electrical conductivity of the pipeline corrosion layer.

S204. Determine the pipeline transmission line equation based on the equivalent longitudinal conductance.

Furthermore, the pipeline transmission line equation can be written as

T为地层横向电阻(管道单位长度对应的地层电阻)，如图5所示，则在轴向(z轴)第i层中单位长度管道所对应的横向电阻为Equations (5a) and (5b) are called the underground pipeline transmission line equations, U is the potential distribution of the non-corroded water supply pipeline wall, I is the current in the non-corroded water supply pipeline wall,

T is the horizontal resistance of the formation (the formation resistance corresponding to the unit length of the pipeline), as shown in Figure 5, then the horizontal resistance corresponding to the unit length pipeline in the i-th layer in the axial direction (z axis) is

Among them, r is the radial radius of the formation, and R _str is the equivalent lateral resistance of the formation.

S205. Calculate the transmission line equation of the pipeline, and determine the calculated potential of the non-corroded layer on the inner wall of the pipeline.

Then the solution of the pipeline transmission line equation in the i-th stratum in the axial direction is

Among them, A _i and _Bi are undetermined coefficients, which can be determined by using the interface current and potential continuity boundary conditions, ξ _i =T _i α _i , d _i (i=1,2...n) is the z of the i-th layer interface in the axial direction coordinate.

If the outer formation is assumed to be a uniform infinite formation and the fluid in the well is a uniform fluid, then equation (5) has an analytical solution

d _i (i=1,2...n) is the z-coordinate of the i-th layer interface in the axial direction of the pipeline transmission line formation model, T _i is the lateral resistance of the i-th layer, ξ _i =T _i α _i , and α _i is the i-th layer formation α coefficient, u ₀ is the potential of the pipeline wall at z=0, R _r is the lateral resistance of the corrosion layer on the outer wall of the pipeline, and R _Str is the lateral resistance of the formation.

Equations (7a) and (7b) are the solution U obtained by equations (1) and (2), which is the measured potential value of the non-corroded pipeline wall at the measurement electrode measurement point after eliminating the influence of the electrode measurement environment.

S206. Calculate the partial derivative of the potential of the pipeline transmission line stratum model with respect to the stratum parameters through the potential Jacobi matrix.

N_z为总参数个数，第p个观测数据为U_p(电势)，则有U_p＝U_p(m)，p＝1,2…M_q，M_q为观测数据个数，设模型初值为

在m⁰点将U_p展开成Taylor级数并取一级近似有Further, the stratum model of the pipeline transmission line is divided into units along the pipeline, and the model parameter of each small unit is set as Changshu, and the model parameter (resistance) vector is

N _z is the total number of parameters, the pth observation data is U _p (potential), then U _p = U _p (m), p = 1,2...M _q , M _q is the number of observation data, let the model The initial value is

Expanding U _p into Taylor series at point m ⁰ and taking the first order approximation gives

Further, based on the stratum model of the pipeline transmission line divided into units, the Jacobi matrix form is determined, then the matrix form is

ΔU=GΔm (8b)

ΔU is the potential increment, Δm is the surrounding increment of the formation parameters of the pipeline transmission line formation model, and G is the partial derivative of the potential with respect to the formation parameters, also known as the potential gradient. but

Further, determine the position of the stratum model of the pipeline transmission line where the measurement electrode is located, because in the above description, the point measurement method of the measurement electrode is used in this application, and it can be known from the assumption of the pipeline transmission line equation that the measured value measured by this method should be the measurement value of the measurement electrode Lateral resistance at the measurement point. Assuming that the location of the measuring electrode is the i-th layer of the formation, and the potential calculated by equation (5a)(5b) is U _i , then the initial lateral resistance of the pipeline transmission line formation model is

和/>

那么想要确定电势对地层参数偏导数，设/>

由(8c)式得本测量方式的G(电势对地层参数偏导数)为Through the above description, there are two unknown parameters, namely

and />

Then if you want to determine the partial derivative of potential with respect to formation parameters, set />

From the formula (8c), the G (partial derivative of potential to formation parameters) of this measurement method is

in

If the outer formation is assumed to be a uniform infinite formation, and the fluid in the well is a uniform fluid, then

In the formula, the subscript i represents the i-th stratum, and G ₁ and G ₂ are the derivatives of the i-th stratum potential to the lateral resistance of the outer wall of the pipeline and the lateral resistance of the stratum, respectively.

S207. Determine the inversion objective function through the measured potential and the calculated potential.

Let the inversion objective function be

F(m)＝||UU ^obs || (10)

Among them, U ^obs is the measured potential, that is, the potential of the non-corroded pipeline wall measured by the power supply electrode and the measuring electrode circuit, that is, the potential measured by the measurement mode in Figure 1 and obtained by solving equations (1) and (2), U is Compute the electric potential, that is, the potential of the non-corroded pipe wall calculated from the pipe transmission line equation.

S208. Using the pipeline transmission line equation and the partial derivative of the potential to the formation parameters, and inverting the iterative approximation through the inversion objective function, calculating the resistance of the corrosion layer on the outer wall of the pipeline.

Let f(m)=UU ^obs , if m ^k is the k-th inversion iterative approximation of m, so that the objective function is minimized, the iterative residual vector (in the form of formula (8b)) is

d _k = -(G _k ^T G _k ) ^-1 G _k ^T f ^k (11a)

m ^k+1 ＝m ^k +λ ^k d _k (11b)

λ ^k is the step size calculated for the kth iteration. In formula (5), sometimes the matrix G _k ^T G _k is singular or nearly singular. In order to improve the calculation speed and stability, the positive definite diagonal matrix is added to G _k ^T G _k , so that the matrix becomes the condition A symmetric positive definite matrix with better numbers (Marquardt method), the inversion iteration formula is modified as

d _k ＝-(G _k ^T G _k +β _k I) ^-1 G _k ^T f ^k (11c)

Among them, I is the unit matrix of order n, and β _k is a positive real constant, which is properly selected through trial calculation according to the calculation accuracy requirements.

After appropriate iterations, the resistance of the rust layer on the outside of the metal pipe can be calculated

S209. Calculate the thickness of the corrosion layer on the outer wall of the pipeline according to the resistance of the corrosion layer on the outer wall of the pipeline. Here, by iteratively calculating the resistance of the corrosion layer outside the pipeline, then, the thickness δ of the corrosion layer outside the pipeline can be calculated through the above-mentioned formula for calculating the thickness of the corrosion layer when the resistance of the corrosion layer is known, that is, formula (3).

Those of ordinary skill in the art should understand that: the discussion of any of the above embodiments is exemplary only, and is not intended to imply that the scope of the application (including claims) is limited to these examples; under the thinking of the application, the above embodiments or Combinations of technical features in different embodiments are also possible, steps may be implemented in any order, and there are many other variations of the different aspects of the embodiments of the application as described above, which are not provided in details for the sake of brevity.

In addition, to simplify illustration and discussion, and so as not to obscure the embodiments of the present application, well-known power sources or connections to integrated circuit (IC) chips and other components may or may not be shown in the provided figures. ground connection. Furthermore, devices may be shown in block diagram form in order to avoid obscuring the embodiments of the present application, and this also takes into account the fact that details regarding the implementation of these block diagram devices are highly dependent on the implementation of the embodiments of the present application to be implemented. platform (ie, the details should be well within the purview of those skilled in the art). Where specific details (eg, circuits) have been set forth to describe exemplary embodiments of the present application, it will be apparent to those skilled in the art that other embodiments may be implemented without or with variations from these specific details. Implement the embodiment of the present application below. Accordingly, these descriptions should be regarded as illustrative rather than restrictive.

Although the application has been described in conjunction with specific embodiments thereof, many alternatives, modifications and variations of those embodiments will be apparent to those of ordinary skill in the art from the foregoing description.

The embodiments of the present application are intended to embrace all such alternatives, modifications and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent replacements, improvements, etc. within the spirit and principles of the embodiments of the present application shall be included within the protection scope of the present application.

Claims (10)

1. The method for detecting the rust degree of the overground metal pipeline is characterized by comprising the following steps of:

measuring the potential of a non-rusted layer of a measuring point of a measuring electrode on the inner wall or the outer wall of the pipeline by respectively arranging a power supply electrode and a measuring electrode circuit on the inner wall or the outer wall of the pipeline;

measuring the resistance of the rust layer of the measuring point of the electrode measuring electrode of the inner wall or the outer wall of the pipeline by using a measuring circuit based on the potential distribution of the inner wall or the outer wall of the pipeline;

measuring the thickness of the pipeline corrosion layer based on the resistance of the corrosion layer of the measuring point of the measuring electrode of the inner wall or the outer wall of the pipeline;

the measuring electrode circuit comprises a measuring electrode, a first measuring circuit and a second measuring circuit, the first measuring circuit and the second measuring circuit are respectively connected with the measuring electrode in series, the first measuring circuit and the second measuring circuit are connected in parallel, the first measuring circuit comprises a first potentiometer and a first ammeter which are connected in series, and the second measuring circuit comprises a second potentiometer and a second ammeter which are connected in series.

2. The method of claim 1, wherein the calculation formula for measuring the electrical potential of the conduit wall is:

I ₁ R _r +I ₁ (R _V1 +R _I1 )＝U

I ₂ R _r +I ₂ (R _V2 +R _I2 )＝U

wherein R is _r To measure the resistance of the rust layer of the electrode measuring point, I ₁ First ammeter reading, R _V1 R is the resistance of the first potentiometer _I1 Resistance of the first ammeter, I ₂ Reading for a second ammeter; r is R _V2 Resistance of second point level difference meter, R _I2 And U is the potential of the pipeline wall of the non-rusting layer for the resistance of the second ammeter.

3. The method of claim 2, wherein the calculation formula for measuring the thickness of the pipe rust layer is:

wherein delta is the thickness of the rust layer, S is the contact area between the measuring electrode and the pipeline, and ρ is _r Is the resistivity of the rust layer of the pipeline.

4. The method for detecting the rust degree of the buried metal pipeline is characterized by comprising the following steps of:

measuring the measured potential of a non-rust layer at a measuring point of a measuring electrode on the inner wall of the pipeline by arranging a power supply electrode and a measuring electrode circuit on the inner wall of the pipeline; the measuring electrode circuit comprises a measuring electrode, a first measuring circuit and a second measuring circuit, wherein the first measuring circuit and the second measuring circuit are respectively connected with the measuring electrode in series, the first measuring circuit and the second measuring circuit are connected in parallel, the first measuring circuit comprises a first potential difference meter and a first ammeter which are connected in series, and the second measuring circuit comprises a second potential difference meter and a second ammeter which are connected in series;

respectively taking the center of the pipeline as an origin, taking the axial direction of the pipeline as a z axis, and constructing a pipeline transmission line stratum model by taking the radial direction of the pipeline as an r axis;

based on the pipeline transmission line stratum model, the fluid in the pipeline and the current in the pipeline flowing along the axial direction of the pipeline, constructing equivalent longitudinal conductance of the fluid in the pipeline, the non-rusted pipeline inner wall and the rusted layer on the pipeline inner wall;

determining the pipeline transmission line equation based on the equivalent longitudinal conductance;

calculating the pipeline transmission line equation, and determining the calculated potential of the non-rusted layer on the inner wall of the pipeline;

calculating the partial derivative of the potential of the pipeline transmission line stratum model to stratum parameters through a potential Jacobi matrix;

determining an inversion objective function from the measured potential and the calculated potential;

calculating the resistance of the rusted layer on the outer wall of the pipeline by inverting iterative approximation through an inversion objective function by utilizing the pipeline transmission line equation and the partial derivative of the potential to the stratum parameter;

and determining the thickness of the pipeline outer wall corrosion layer according to the resistance of the pipeline outer wall corrosion layer.

5. The method of claim 4, wherein the calculation formula for constructing equivalent longitudinal conductance of the fluid in the pipeline, the non-rusted pipeline wall and the rusted layer in the pipeline based on the pipeline transmission bottom line model, the fluid in the pipeline and the current in the pipeline flowing along the axis direction of the pipeline is as follows:

S＝S _f +S _C +S _r ，

wherein,,

r is the total equivalent longitudinal resistance of the axial unit length;

a resistance per unit length of fluid in the axial water supply pipe;

ρ _f is the resistivity of the fluid in the pipeline;

a ₁ is the inner radius of the pipeline rust layer;

R _c a resistance per unit length of the water supply pipe which is non-rusted along the axial direction;

R _r ＝ρ _r /[2πa ₂ (a ₃ -a ₂ )]for the resistance per unit length of the rust layer in the water supply pipe in the axial direction, sigma _r ＝1/ρ _r ；

a ₂ Is the radius of the inner wall of a non-rusted pipeline, a ₃ Is the radius of the outer wall of the non-rusted pipeline;

σ _r is the conductivity of the rust layer of the pipeline.

6. The method of claim 5, wherein the determining the conduit transfer line equation based on the equivalent longitudinal conductance is calculated as:

wherein U is the potential distribution of the wall of the non-rust water supply pipeline;

i is the current in the non-rusting water supply pipe wall;

t is the formation transverse resistance, and alpha is the formation alpha coefficient.

7. The method of claim 6, wherein calculating the partial derivatives of the electrical potentials of the piped-line formation model to the formation parameters by an electrical potential Jacobi matrix comprises:

performing unit division on the pipeline transmission line stratum model along the pipeline;

determining the Jacobi matrix form based on the unit-divided pipeline transmission line stratum model;

determining the position of the pipeline transmission line stratum model where the measuring electrode is positioned;

and determining partial derivatives of electric potential of the transmission line stratum model to stratum parameters based on the Jacobi matrix form and the position of the pipeline transmission line stratum model where the measuring electrode is positioned.

8. The method of claim 7, wherein the Jacobi matrix is in the form of:

ΔU＝GΔm，

wherein DeltaU is an electric potential increment, deltam is a pipeline transmission line stratum model parameter perturbation increment;

a transmission line stratum model resistance vector divided for the unit;

transmission line formation model potentials for cell divisions.

9. The method of claim 8, wherein the pipeline outer rust layer resistance is calculated by inverting an iterative approximation by inverting an objective function using the pipeline transmission line equation and the partial derivative of the potential to formation parameters;

the calculation formula of the inversion objective function is as follows:

F(m)＝||U-U ^obs ||

wherein U is ^obs For the measured non-rusting pipe wall potential;

u is the non-rusting pipe wall potential.

10. The method of claim 9, wherein the inversion iteration approximation formula is:

wherein d is _k The stratum parameter increment obtained for the kth iteration;

G _k ^T G _k a partial derivative matrix product of a pipeline transmission line equation;

i is an n-order identity matrix, beta _k Is a positive real constant.

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