CN110470723B - Buried metal pipeline direct current interference determination method for damage of protective layer - Google Patents
Buried metal pipeline direct current interference determination method for damage of protective layer Download PDFInfo
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Abstract
The invention discloses a method for determining direct current interference of a buried metal pipeline with a damaged protective layer, which comprises the following steps: determining a virtual boundary and a nonlinear boundary according to the obtained characteristic parameters of the grounding electrode and the buried metal pipeline to be analyzed; determining a potential profile of the virtual boundary and a simplified current profile of the non-linear boundary; calculating potential distribution on the soil side on the nonlinear boundary in the soil area; determining a simplified polarization potential on the non-linear boundary; determining the potential distribution of the metal side on the nonlinear boundary according to the simplified polarization potential and the potential distribution of the soil side; calculating a process current distribution on the non-linear boundary at a metal region; determining a target polarization potential on the nonlinear boundary when a difference between the process current profile and the simplified current profile is not greater than a predetermined convergence threshold. The direct current interference of the buried metal pipeline determined by the method is high in precision and efficiency.
Description
Technical Field
The invention belongs to the field of direct current interference analysis of buried metal pipelines, and particularly relates to a method for determining direct current interference of a buried metal pipeline with a damaged protective layer.
Background
In recent years, with the construction of west-east power transmission and west-east gas transmission projects, the situation that a direct current grounding electrode is adjacent to a buried oil and gas pipeline is inevitable.
When direct current flows into the ground on the grounding electrode of the direct current transmission system, a direct current field is formed in soil near the electrode site, and the ground potential is increased along with the direct current field. The stray dc current will flow through the pipes near the ground electrode and will corrode electrically in the area out of the pipes.
The problems of corrosion influence and danger influence of the direct current grounding electrode on adjacent buried oil and gas pipelines are increasingly prominent, and some of the direct current grounding electrodes threaten the national energy transmission safety. At present, the method for determining the direct current interference of the grounding electrode to the buried oil and gas pipeline has low precision and low calculation efficiency.
Disclosure of Invention
The method and the device aim to solve the problems of low precision and low efficiency when the direct current interference of the buried metal pipeline with the locally damaged protective layer is calculated in the prior art.
The invention provides a method for determining direct current interference of a buried metal pipeline with a damaged protective layer, which comprises the following steps:
step S100: determining a virtual boundary according to the obtained characteristic parameters of the grounding electrode and the buried metal pipeline to be analyzed, wherein the virtual boundary comprises a metal area occupied by the buried metal pipeline and a soil area between the virtual boundary and the metal area; and are combined
Determining a nonlinear boundary, wherein one side of the nonlinear boundary close to the metal area is a metal side, and one side of the nonlinear boundary close to the soil area is a soil side;
step S200: determining the potential distribution of the virtual boundary and the simplified current distribution of the nonlinear boundary based on an analog charge method without considering the polarization process of the metal area with the damaged protective layer;
step S300: calculating the potential distribution of the soil side on the nonlinear boundary in the soil area by taking the potential distribution of the virtual boundary as an initial value;
step S400: determining a simplified polarization potential on the nonlinear boundary according to a predetermined polarization curve and a simplified current distribution of the nonlinear boundary;
step S500: determining the potential distribution of the metal side on the nonlinear boundary according to the simplified polarization potential and the potential distribution of the soil side;
step S600: calculating the process current distribution on the nonlinear boundary in a metal area by taking the potential distribution of the metal side on the nonlinear boundary as an initial value;
step S700: when the difference between the process current profile and the simplified current profile is not greater than a predetermined convergence threshold,
and determining a target polarization potential on the nonlinear boundary according to a predetermined polarization curve and the process current distribution, wherein the target polarization potential is direct current interference of the buried metal pipeline with the damaged protective layer.
Specifically, the method further comprises:
step S800: when the difference between the process current profile and the simplified current profile is greater than a predetermined convergence threshold,
updating the simplified current distribution according to a preset correction rule, and
steps S400 to S700 are repeated.
In the method, the problem of an infinite area is converted into the problem of a finite element area by setting the virtual boundary, so that the calculated amount is reduced; the pipe-to-ground potential distribution is calculated by a finite element method, the problem of local damage of an anticorrosive coating of the pipeline is considered, and the calculation accuracy and the calculation efficiency of direct current interference of the buried metal pipeline are improved.
Drawings
A more complete understanding of exemplary embodiments of the present invention may be had by reference to the following drawings in which:
fig. 1 is a schematic flow chart of a method for determining dc interference of a buried metal pipeline with a partially damaged protective layer according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the steps of calculating the DC interference of the ground electrode to the buried pipeline by using a hybrid simulation charge method and a finite element method according to an embodiment of the present invention;
FIG. 3 is a diagram of simulated charge distribution when calculating the charge distribution of the ground and the pipe according to an embodiment of the present invention;
fig. 4 is a polarization curve of X80 pipeline steel measured in a simulated soil solution with a conductivity of 100 Ω · m and Ph =8 in yet another embodiment of the invention;
FIG. 5 is a schematic diagram of a non-linear boundary configuration of a pipe local breakage within a virtual boundary according to an embodiment of the present invention
FIG. 6 is a schematic diagram of the spatial distribution relationship between the pipes and the grounding electrode according to another embodiment of the present invention;
fig. 7 is a plot of the polarization potential distribution determined on the pipe.
Detailed Description
The exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein, which are provided for complete and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the drawings are not intended to limit the present invention. In the drawings, the same units/elements are denoted by the same reference numerals.
Unless otherwise defined, terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Further, it will be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense.
At present, the calculation of the direct current interference of the grounding electrode is mainly based on a moment method, and the principle of the moment method leads the local damage characteristic of a metal conductor protective layer to be incapable of being considered. Therefore, at present, electrochemical polarization processes of metal surfaces are often neglected when considering the influence of the grounding electrode on buried metal pipelines. This can cause inaccuracies in the calculated ground potential and leakage current density.
The finite element method has advantages in dealing with local breakage problems. However, because the current field coverage of the grounding electrode is large, when the direct current interference problem of the buried pipeline is calculated by adopting a finite element method, the subdivision difficulty is large, and the calculation amount is overlarge.
According to the method for determining the direct current interference of the buried metal pipeline with the locally damaged protective layer, which is provided by the invention, the simulated charge method and the finite element method are combined, the subdivision difficulty of the finite element calculation method in a large-range area is reduced, the calculation amount of the finite element is reduced, and the direct current interference of the metal pipeline with the locally damaged protective layer can be accurately calculated.
It should be understood that in the following, "pipeline", "buried pipeline", "metal pipeline", "buried metal pipeline" have the same meaning.
It should be understood that "current density", "leakage current density", "current distribution", "current density distribution" have the same meaning in the following.
The method provided by the invention has the advantages that the virtual boundary is arranged in the adjacent area of the metal pipeline, so that the current field is converted from the problem of an infinite area to the problem of a finite area; whereas the finite area problem is calculated by a finite element method.
As shown in fig. 1, a method for determining direct current interference of a buried metal pipeline with a damaged protective layer according to an embodiment of the present invention includes:
step S100: determining a virtual boundary according to the obtained characteristic parameters of the grounding electrode and the buried metal pipeline to be analyzed, wherein the virtual boundary comprises a metal area occupied by the buried metal pipeline and a soil area between the virtual boundary and the metal area; and are combined
Determining a non-linear boundary, wherein one side of the non-linear boundary close to the metal area is a metal side, and one side of the non-linear boundary close to the soil area is a soil side;
it should be understood that the buried metal pipe is included within the virtual boundary and the earth electrode is not included;
the non-linear boundary is located on a portion of the buried metal pipeline between the metal region and the soil region where the protective layer is damaged.
Step S200: determining potential distribution of the virtual boundary and simplified current distribution of the nonlinear boundary based on an analog charge method without considering a polarization process of a metal region with a damaged protective layer;
step S300: calculating the potential distribution of the soil side on the nonlinear boundary in the soil area by taking the potential distribution of the virtual boundary as an initial value;
step S400: determining a simplified polarization potential on the nonlinear boundary according to a predetermined polarization curve and a simplified current distribution of the nonlinear boundary;
step S500: determining the potential distribution of the metal side on the nonlinear boundary according to the simplified polarization potential and the potential distribution of the soil side;
step S600: calculating the process current distribution on the nonlinear boundary in a metal area by taking the potential distribution on the metal side on the nonlinear boundary as an initial value;
step S700: when the difference between the process current profile and the simplified current profile is not greater than a predetermined convergence threshold,
and determining a target polarization potential on the nonlinear boundary according to a predetermined polarization curve and the process current distribution, wherein the target polarization potential is direct current interference of the buried metal pipeline with the damaged protective layer.
Further, the method further comprises:
step S800: when the difference between the process current profile and the simplified current profile is greater than a predetermined convergence threshold,
updating the simplified current distribution according to a preset correction rule, and
steps S400 to S700 are repeated.
Specifically, the preset modification rule includes:
taking an average of the process current profile and the simplified current profile as an updated simplified current profile;
the process current profile is taken as an updated, updated simplified current profile.
Further, the method, in the step S200, determining the potential distribution of the virtual boundary based on an analog charge method without considering a polarization process of the metal region with the damaged protective layer, includes:
setting m analog charges on the grounding electrode, wherein the analog charge values are respectively marked as Q i Wherein i is more than or equal to 1 and less than or equal to m; correspondingly, m matching points are arranged on the outer side of the grounding electrode; the m analog charges and the potentials at the m matching points are
Setting n analog charges on the buried metal pipeline, and recording the analog charge value as Q j J is more than or equal to 1 and less than or equal to m; correspondingly, there are n matching points on the outside of the pipeline; the n analog charges and the potentials at the n matching points are
In combination with the formula:
solving the following equation, determiningCharge distribution Q of analog charges provided on earth and buried metal pipelines 0 And Q 1 ；
Wherein Q is 0 A column vector of charge values that are analog charges disposed on a ground electrode;
Q 1 a column vector of charge values for analog charges disposed on a buried metal pipeline;
[P st ]Is a matrix of potential coefficients, P st For the elements in row s and column t of the matrix, is determined by:
wherein, the first and the second end of the pipe are connected with each other,
respectively is the bit vector of the s-th analog charge and the t-th matching point, s is more than or equal to 1 and less than or equal to (m + n), and t is more than or equal to 1 and less than or equal to (m + n);
ε is a dielectric constant;
will be said virtualSimulating boundary dispersion as y analysis points, solving the following equation, and determining the potential distribution on the virtual boundary
Q is a column vector formed by the charge values of analog charges arranged on the grounding electrode and on the pipeline;
[P ab ]potential coefficient matrix of virtual boundary, P ab For the elements in row a and column b in the matrix, this is given by:
wherein the content of the first and second substances,
respectively representing the bit vectors of the a-th simulation charge and the b-th analysis point, wherein a is more than or equal to 1 and less than or equal to (m + n), and b is more than or equal to 1 and less than or equal to y.
Further, in the step S200, the determining the simplified current distribution of the non-linear boundary based on the analog charge method without considering the polarization process of the metal region with the damaged protective layer includes:
discretizing the nonlinear boundary into k analysis points, and determining the simplified current distribution of the nonlinear boundary according to the following formula:
wherein, sigma is the soil conductivity;
wherein the content of the first and second substances,
respectively representing the g-th simulated charge and the position vector of the h-th analysis point, wherein g is more than or equal to 1 and less than or equal to (m + n), and h is more than or equal to 1 and less than or equal to k;
q is a column vector consisting of the charge values of the analog charges placed on the ground and on the pipe.
Further, the step S300 includes:
and calculating the potential distribution of the soil side on the nonlinear boundary by using the potential distribution of the virtual boundary as an initial value and adopting a finite element method in a soil area:
the soil region omega D Satisfies the following equation:
(x,y,z)∈Ω D
the potential distribution of the virtual boundary is a first type of boundary condition in the current field of the soil region:
further, the step S600 includes:
and calculating the process current distribution on the nonlinear boundary by a finite element method in a metal area by taking the potential distribution of the metal side on the nonlinear boundary as an initial value:
the metal conductor region omega pipe The potential of the current field of (a) satisfies the laplace equation, i.e.:
the boundary inside the conductor and with a complete protective layer meets a second type of boundary condition in the current field of the metal conductor region:
at the non-linear boundary, the following boundary conditions are satisfied:
wherein the content of the first and second substances,
is the current distribution on the non-linear boundary.
The characteristic parameters of the grounding electrode and the buried metal pipeline to be analyzed comprise:
the structure parameters and the position parameters of the grounding electrode, the structure parameters and the position parameters of the pipeline, and the size and the position parameters of the protective layers damaged at multiple positions.
Further, the air conditioner is provided with a fan,
the analog charges on the grounding electrode are arranged on the axis of the guide rod of the grounding electrode, the corresponding matching points are positioned on the outer circumference of the guide rod of the grounding electrode, and the distance between every two adjacent analog charges is greater than the distance between the analog charges and the corresponding matching points;
the analog charges on the pipeline are arranged on a central axis extending along the length of the pipeline in the pipeline, corresponding matching points are located on the outer circumference of the pipeline, and the distance between every two adjacent analog charges is larger than the distance between the analog charges and the corresponding matching points.
Further, in step S700, the difference between the process current distribution and the simplified current distribution is a mean square error, and the preset convergence threshold is 1e-5.
Further, in the step S100, the virtual boundary is determined to be a cylindrical surface which takes the central axis of the buried metal pipeline as the central axis, has a radius of 5m, and has the same length as the buried metal pipeline.
In conclusion, according to the method, a current field distribution calculation model without considering the polarization process is established according to the characteristic parameters of the direct current grounding electrode and the metal pipeline, and the current field distribution calculation model is converted into a simulated charge method according to the electrostatic analog principle to perform initial current distribution calculation; calculating potential distribution on the virtual boundary according to the geometric parameters of the virtual boundary and the charge distribution obtained by simulating charge calculation; and establishing a finite element model of the soil area and the metal area according to a current continuity theorem, and selecting the pipeline leakage current density calculated by a charge simulation method as the initial current density of the nonlinear boundary. Calculating potential distribution of the soil side of the nonlinear boundary through a finite element model of the soil area, calculating current distribution of the pipeline side of the nonlinear boundary through a finite element model of the metal area, obtaining current density of the nonlinear boundary by combining an actually-measured polarization curve, correcting an initial value of the current density of the nonlinear boundary according to a calculation result, and repeating the calculation steps of the finite element model until the result is converged.
Specifically, in the step of calculating the electric field distribution by using the analog charge method, the interference of the grounding electrode on the buried pipeline is converted into the electrostatic field problem from the current field problem by using an electrostatic analog method without considering the electrochemical polarization process.
Specifically, analog charges are respectively arranged on the grounding electrode and the pipeline, potential equation sets of the analog charges are respectively written in series in combination with potential conditions of the surface of the grounding electrode and charge conservation conditions on the pipeline, and the equation sets are solved, so that analog charge distribution on the grounding electrode and the pipeline can be obtained.
Since the normal current density of the earth boundary is 0, the earth boundary is replaced by setting the mirror charge.
Specifically, the known condition of a normal current density at the earth boundary of 0 is represented by setting another set of analog charges on the other side of the earth boundary that are symmetric (mirrored on both sides along the earth) to the analog charges on the earth and the pipe.
As shown in fig. 3, m analog charges are provided inside the ground electrode, and n analog charges are provided inside the pipe. Each matching point is located outside the grounding electrode or the pipeline, is located on the grounding electrode or the pipeline and is not in the soil.
The steps of separately listing the analog charge potential equation (1) on the ground electrode and the analog charge potential equation set (2) on the pipeline are not repeated.
Since the analog charge arranged on the pipe satisfies the current continuity theorem, the net charge as a whole is 0.
The electric charge values of the analog charges on the grounding electrode and the pipeline and the electric potential value on the pipeline can be obtained by combining the equations.
It should be understood that because the ground electrode has current injected by the dc transmission system, the analog charge placed on the ground electrode does not satisfy the current continuity theorem.
When the virtual boundary of the adjacent area of the pipeline is determined, a closed virtual boundary is selected in the adjacent area of the buried pipeline, and the solid area in the virtual boundary is used as a target area of subsequent finite element analysis. This target area is completely comprised of buried metal pipes and does not include an earth ground.
It should be understood that the solid areas within the virtual boundary include soil areas and pipe areas. Whereas the air region within the duct does not belong to the target region.
Solving an equation according to the simulated charge distribution on the ground electrode and the pipeline obtained in the first step, and obtaining the potential distribution on the virtual boundary.
It should be understood that the virtual boundary can be discretized into the number of analysis points of any scale according to the requirements of the subsequent finite element analysis, and the potential distribution on the virtual boundary can be obtained by using an equation.
It should be understood that the potential distribution on the virtual boundary comes from the effect of the analog charge on the ground and on the pipe, respectively.
In the above, the condition that the local shield layer is in a damaged state is not considered. In the following steps, a condition that the local protective layer is in a damaged state is introduced. That is, in the "buried metal pipeline" in the following, at least in a partial region, the protective layer thereof is in a damaged state.
It should be noted that, in the buried pipeline, the metal surface area corresponding to the damaged protective layer is in direct contact with the soil; the electrochemical polarization process occurring in the metal surface region causes the interface conditions of the damaged region of the protective layer on the pipe and the soil region to be different from the interface conditions of the intact regions of the other protective layers on the pipe and the soil region.
Specifically, for the electrochemical polarization process between any soil environment and the metal layer of the buried pipeline in direct contact with the soil environment, the polarization curve of polarization potential-current density on the interface between the metal area and the soil area as shown in fig. 5 can be determined through laboratory tests or engineering field tests
It should be understood that the current density J is a vector whose direction is the normal direction of the boundary.
The soil area to be subjected to finite element analysis is provided with an inner boundary and an outer boundary, wherein the outer boundary is a virtual boundary determined in the second step; the inboard boundary is adjacent the pipe and includes the portion of the outer wall of the pipe where the armor is intact, the portion where the armor is broken and the soil is in direct contact with the metal surface.
The metal conductor area to be subjected to finite element analysis is provided with an inner boundary and an outer boundary, wherein the inner boundary is the outer side of the inner wall adjacent to air; the outer boundary is adjacent to the soil and includes a portion of the outer wall of the pipe where the protective coating is intact, and a portion of the metal surface of the outer wall of the pipe where the protective coating is damaged and in direct contact with the soil.
As shown in fig. 4, the relationship between the metallic surface region and the soil region corresponding to the damaged protective layer is via a non-linear polarization boundary. It should be understood that fig. 4 illustrates the case where all of the protective layers of the metal pipes are broken in order to strengthen the non-linear boundary.
And respectively establishing a finite element model of the soil area and the metal area according to the current continuity theorem so as to solve the potential and the current density at each point.
The soil region is a constant current field with zero divergence of current density. A virtual boundary gamma drawn in the current field of the soil region D As a first type of boundary condition, there are
Wherein f is D (x, y, z) is the potential value of each point on the virtual boundary, e.g. the potential distribution on the virtual boundary obtained in the second step
The metal conductor region is a constant current field, and the divergence of the current density is zero.
In the current field of the metallic conductor region, the boundary gamma inside the conductor and with intact protective layer in Satisfy a second type of boundary condition, i.e.
Where n denotes the normal component of the boundary; boundary Γ inside conductor and intact in protection layer in The amount of change in potential in its normal component direction is zero.
3) The metal surface gamma corresponding to the damaged protective layer M Belonging to non-linear boundaries, satisfying non-linear boundary conditions, i.e.
Where n denotes the normal component of the boundary;
and sigma is the soil conductivity.
In the finite element calculation, the leakage current density on the nonlinear boundary is determined according to the determined simulated charge distribution and is used as the initial current density of the nonlinear boundary.
From the initial current density determined above, the polarization potential on the partially broken pipe is determined by iteration of:
step 1): calculating the potential distribution of the non-linear boundary on the soil side according to the finite element model of the soil area,
specifically, from the potential on the virtual boundary, the potential distribution of the nonlinear boundary on the soil side is determined;
step 2) determining a polarization potential (namely, a potential difference of a nonlinear boundary at a soil side and a pipeline side) corresponding to the initial current density by methods of table look-up, internal fitting, external fitting and the like according to the initial current density and a polarization curve determined by a test;
the polarization potential is added with the potential distribution of the soil side, so that the potential distribution of the nonlinear boundary on the pipeline side (namely the metal side) can be determined;
step 3) taking the potential distribution of the nonlinear boundary at the pipeline side (namely the metal side) as an initial value, and determining the process current density of the nonlinear boundary at the pipeline side according to a finite element model of the metal conductor region;
step 4) determining whether the absolute value of the difference between the process current density determined in the current round and the process current density determined in the previous round of the loop satisfies a preset iteration error?
If so, determining the polarization potential corresponding to the intermediate current density determined in the current round as the polarization potential on the nonlinear interface, namely the direct current interference of the local damaged area, according to the polarization curve determined in the test;
if not, taking the average value of the process current density determined in the current round and the process current density determined in the previous round as the updated initial current density, and repeating the steps 2) -4).
In the above steps, the accuracy of the current density of the nonlinear boundary is improved by continuously correcting the current density of the nonlinear boundary, so that the accuracy of the polarization potential on the nonlinear interface obtained by solving is ensured.
As shown in fig. 2, the method for calculating the dc interference suffered by the buried metal pipeline of the present invention comprises:
a. analog charge distribution calculation
Under the condition of not considering the polarization process, the interference of the grounding electrode on the buried pipeline is converted into the electrostatic field problem from the current field problem through an electrostatic analogy method, and the specific simulation charge configuration is shown in figure 3.
In the grounding electrode, analog charges are arranged in the grounding electrode and the pipeline, so that the analog charges do not exist in the calculation field; writing a simulation charge potential equation set by combining the potential condition of the surface of the grounding electrode and the charge conservation condition on the pipeline, and finally obtaining the simulation charge distribution of the grounding electrode and the pipeline; the potential distribution of the virtual boundary and the initial leakage current density distribution of the metal region at the damaged guard layer can be solved in combination with the simulated charge distribution.
Specifically, in the analog charge configuration, as shown in fig. 3, the analog charge of the ground electrode is placed inside the ground electrode, preferably, on the central axis of the guide bar; the matching points on the ground electrode are located on the outer circumference of the ground electrode.
Specifically, in an analog charge configuration, as shown in fig. 3, the analog charge of the pipe is placed inside the pipe, preferably, on the pipe center axis; the mating point on the pipe is located on the outside circumference of the pipe conductor.
It should be understood that the ground electrode is spatially perpendicular to the pipe and spatially separated by a certain distance.
The cross section of the guide rod is circular, and the central axis of the guide rod is a closed circle; the pipeline central line refers to the central axis of a cylinder formed by the inner radius of the pipeline and is a straight line.
The pipe is usually a thin-walled part, and analog charges are arranged on the central axis of the pipe wall, so that electrostatic field calculation cannot be basically carried out; and the field inside the pipeline is an irrelevant field, so that the analog charge of the pipeline can be arranged on the central axis of the pipeline.
b. Pipe neighborhood virtual boundary determination
The cylindrical surface at a distance of 5m from the central axis of the buried pipeline is set as a virtual boundary to ensure that the boundary can completely contain the metal pipeline.
c. Processing of non-linear boundaries in a limited area
In the area of local damage of the protective layer, the finite element area can be divided into a soil area and a metal area, and the two areas are connected through a nonlinear boundary (namely a polarization boundary). A specific boundary arrangement diagram is shown in fig. 5.
Respectively writing a finite element equation set for the soil area and the metal area, namely
During finite element calculation, the calculation result of the soil area is used as the calculation condition of the metal area; the calculation of the metal area, in turn, serves as the calculation condition for the soil area.
d. Initial value determination and iterative solution
And calculating the initial value of the current density on the pipeline at the damaged position according to the simulated charge distribution.
Solving the potential distribution of the nonlinear boundary through a finite element equation system of the soil area; then obtaining the potential boundary condition of the metal area of the pipeline through a polarization curve; and then carrying out finite element calculation on the metal area to obtain the current density of the metal area.
And correcting the current density of the metal area through multiple iterations until the difference between the current density result of the current iteration and the current density result of the previous iteration is less than a certain small amount after a certain iteration, then iteratively converging and terminating the iteration.
Applying the above method to the graphA long distance buried metal pipeline 200 adjacent to the dc earth 100 shown in figure 6 is subjected to dc interference calculations. The potential of the grounding electrode is 600V, and the material is phi 70 round steel; the cross-sectional diameter of the guide rod of the grounding electrode is d e =10cm; polar ring external diameter D of grounding electrode e =200m, buried depth of grounding electrode h e =1.5m; the inner diameter of the pipeline is 0.59m, the outer diameter is 0.61m, and the wall thickness is 2cm; the total length of the pipeline is 200km and the buried depth of the pipeline is h p =1m; the distance between the grounding pole and the pipeline is D =10km, and the soil conductivity is 100 omega · m; the pipeline anticorrosive coating damage is uniformly distributed on the pipeline edge line, the damage rate is 1 percent (by area), and the area of a single damage point is 4cm 2 。
The calculation result of the polarization potentials along the pipeline after final iterative convergence and assignment is shown in fig. 7, and the polarization potentials in fig. 6 indicate the polarization potentials of the damaged areas.
It should be noted that, in fig. 6, the dc grounding electrode is located in the middle of the long-distance buried metal pipeline.
It should be understood that the non-damaged regions are absent of polarization potential; only a far ground potential is present. The far ground potential is very small across the pipe and can be taken as the pipe potential calculated in the analog charge method.
The invention has been described above by reference to a few embodiments. However, other embodiments of the invention than the ones disclosed above are equally possible within the scope of these appended patent claims, as these are known to those skilled in the art.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [ device, component, etc ]" are to be interpreted openly as referring to at least one instance of said device, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.
Claims (9)
1. A method for determining direct current interference of a buried metal pipeline with a damaged protective layer is characterized by comprising the following steps:
step S100: determining a virtual boundary according to the obtained characteristic parameters of the grounding electrode and the buried metal pipeline to be analyzed, wherein the virtual boundary comprises a metal area occupied by the buried metal pipeline and a soil area between the virtual boundary and the metal area; and are combined
Determining a nonlinear boundary, wherein one side of the nonlinear boundary close to the metal area is a metal side, and one side of the nonlinear boundary close to the soil area is a soil side;
step S200: determining the potential distribution of the virtual boundary and the simplified current distribution of the nonlinear boundary based on an analog charge method without considering the polarization process of the metal area with the damaged protective layer;
step S300: calculating the potential distribution of the soil side on the nonlinear boundary in the soil area by taking the potential distribution of the virtual boundary as an initial value;
step S400: determining a simplified polarization potential on the nonlinear boundary according to a predetermined polarization curve and a simplified current distribution of the nonlinear boundary;
step S500: determining the potential distribution of the metal side on the nonlinear boundary according to the simplified polarization potential and the potential distribution of the soil side;
step S600: calculating the process current distribution on the nonlinear boundary in a metal area by taking the potential distribution on the metal side on the nonlinear boundary as an initial value;
step S700: when the difference between the process current profile and the simplified current profile is not greater than a predetermined convergence threshold,
determining a target polarization potential on the nonlinear boundary according to a predetermined polarization curve and the process current distribution, wherein the target polarization potential is direct current interference of the buried metal pipeline with the damaged protective layer;
step S800: when the difference between the process current profile and the simplified current profile is greater than a predetermined convergence threshold,
updating the simplified current distribution according to a preset correction rule, and
steps S400 to S700 are repeated.
2. The method of claim 1,
in step S200, the determining the potential distribution of the virtual boundary based on the analog charge method without considering the polarization process of the metal region with the damaged protective layer includes:
setting m analog charges on the grounding electrode, wherein the analog charge values are respectively marked as Q i Wherein i is more than or equal to 1 and less than or equal to m; correspondingly, m matching points are arranged on the outer side of the grounding electrode;
setting n analog charges on the buried metal pipeline, and recording the analog charge value as Q j J is more than or equal to 1 and less than or equal to n; correspondingly, there are n matching points on the outside of the pipeline;
in combination with the formula:
solving the following equation, determining the charge distribution Q of the simulated charge disposed on the ground electrode and on the buried metal pipeline 0 And Q 1 ；
Wherein Q is 0 A column vector of charge values that are analog charges disposed on a ground electrode;
Q 1 a column vector of charge values for analog charges disposed on a buried metal pipeline;
[P st ]Is a matrix of potential coefficients, P st For the elements in row s and column t of the matrix, is determined by:
wherein the content of the first and second substances,
respectively representing the bit vector of the s-th analog charge and the t-th matching point, wherein s is more than or equal to 1 and less than or equal to (m + n), and t is more than or equal to 1 and less than or equal to (m + n);
ε is a dielectric constant;
discretizing the virtual boundary into y analysis points, solving the following equation, and determining the potential distribution on the virtual boundary
Q is a column vector formed by the charge values of analog charges arranged on the grounding electrode and on the pipeline;
[P ab ]a potential coefficient matrix, P, being a virtual boundary ab For the elements in row a and column b in the matrix, this is given by:
wherein the content of the first and second substances,
respectively representing the bit vectors of the a-th simulation charge and the b-th analysis point, wherein a is more than or equal to 1 and less than or equal to (m + n), and b is more than or equal to 1 and less than or equal to y.
3. The method of claim 2, wherein the step S200 of determining the simplified current distribution of the non-linear boundary based on the analog charge method without considering the polarization process of the metal region with the damaged protective layer comprises:
discretizing the nonlinear boundary into k analysis points, and determining the simplified current distribution of the nonlinear boundary according to the following formula:
wherein, sigma is the soil conductivity;
wherein, the first and the second end of the pipe are connected with each other,
respectively representing the g-th simulated charge and the position vector of the h-th analysis point, wherein g is more than or equal to 1 and less than or equal to (m + n), and h is more than or equal to 1 and less than or equal to k;
q is a column vector consisting of the charge values of the analog charges placed on the ground and on the pipe.
4. The method according to claim 1, wherein the step S300 comprises:
and calculating the potential distribution of the soil side on the nonlinear boundary by using the potential distribution of the virtual boundary as an initial value and adopting a finite element method in a soil area:
the soil region omega D Satisfies the following formula:
the potential distribution of the virtual boundary is a first type of boundary condition in the current field of the soil region:
5. the method according to claim 4, wherein the step S600 comprises:
and calculating the process current distribution on the nonlinear boundary by a finite element method in a metal area by taking the potential distribution on the metal side on the nonlinear boundary as an initial value:
metal conductor region omega pipe Satisfies the laplace equation, i.e.:
the boundary inside the conductor and with a complete protective layer meets a second type of boundary condition in the current field of the metal conductor region:
at the non-linear boundary, the following boundary conditions are satisfied:
wherein, the first and the second end of the pipe are connected with each other,
is the current distribution on the non-linear boundary.
6. The method of claim 1,
the characteristic parameters of the grounding electrode and the buried metal pipeline to be analyzed comprise:
the structure parameters and the position parameters of the grounding electrode, the structure parameters and the position parameters of the pipeline, and the size and the position parameters of the protective layers damaged at multiple positions.
7. The method of claim 2,
the analog charges on the grounding electrode are arranged on the axis of the guide rod of the grounding electrode, the corresponding matching points are positioned on the outer circumference of the guide rod of the grounding electrode, and the distance between every two adjacent analog charges is greater than the distance between the analog charges and the corresponding matching points;
the analog charges on the pipeline are arranged on a central axis extending along the length of the pipeline in the pipeline, the corresponding matching points are located on the outer circumference of the pipeline, and the distance between every two adjacent analog charges is larger than the distance between the analog charges and the corresponding matching points.
8. The method of claim 1,
in step S700, the difference between the process current distribution and the simplified current distribution is a mean square error, and the preset convergence threshold is 1e-5.
9. The method of claim 1,
in the step S100, the virtual boundary is determined as a cylindrical surface which takes the central axis of the buried metal pipeline as the central axis, has a radius of 5m, and has the same length as the buried metal pipeline.
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| CN114152662A (en) * | 2020-09-08 | 2022-03-08 | 中国石油天然气集团有限公司 | Method, device and medium for determining safe distance between buried pipeline and alternating current grounding body |
| CN112287589B (en) * | 2020-11-10 | 2022-08-16 | 厦门华润燃气有限公司 | Finite element positioning method for buried steel pipeline anticorrosive coating damage point |
| CN113007612A (en) * | 2021-03-02 | 2021-06-22 | 中铁第四勘察设计院集团有限公司 | Railway water supply pipe network leakage detection system and method based on time domain reflection technology |
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