CN113495053A - Method and device for determining annual corrosion depth of pipeline related to polarization effect - Google Patents

Method and device for determining annual corrosion depth of pipeline related to polarization effect Download PDF

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CN113495053A
CN113495053A CN202110691823.3A CN202110691823A CN113495053A CN 113495053 A CN113495053 A CN 113495053A CN 202110691823 A CN202110691823 A CN 202110691823A CN 113495053 A CN113495053 A CN 113495053A
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pipeline
leakage current
grounding electrode
current
fitting
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曹方圆
白锋
赵录兴
何堃
何宁辉
沙伟燕
黄流建
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
Electric Power Research Institute of State Grid Ningxia Electric Power Co Ltd
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State Grid Corp of China SGCC
China Electric Power Research Institute Co Ltd CEPRI
Electric Power Research Institute of State Grid Ningxia Electric Power Co Ltd
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    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
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Abstract

The invention discloses a method for determining annual corrosion depth of a pipeline related to polarization effect, which comprises the following steps: acquiring the leakage current of the pipeline according to the grounding electrode current related to the polarization effect of the pipeline; acquiring a multivariate nonlinear fitting coefficient among the earth electrode current, the soil resistivity, the approach distance and the pipeline leakage current density; acquiring the total corrosion amount of a damaged point in the operating life cycle of the grounding electrode according to the maximum leakage current density generated on the pipeline when the grounding electrode flows through the rated current and the maximum leakage current density generated on the pipeline by unbalanced current of the grounding electrode under the bipolar operating condition; and acquiring the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current according to the total corrosion amount. The method solves the problem that the annual corrosion depth of the pipeline is calculated inaccurately because the leakage current distribution generated on the adjacent buried metal pipeline by the direct current grounding electrode current is not considered in the prior art.

Description

Method and device for determining annual corrosion depth of pipeline related to polarization effect
Technical Field
The application relates to the field of calculation of leakage current of a direct current grounding electrode pair buried metal pipeline in soil, in particular to a pipeline annual corrosion depth determination method and a pipeline annual corrosion depth determination device, which relate to a polarization effect.
Background
When a single-pole earth loop of a direct current transmission system operates, thousands of amperes of current return through the earth, possibly causing corrosive effects on nearby buried metal pipes, as shown in fig. 3. The annual corrosion depth of the pipeline is an important index for measuring the intensity of external interference on the pipeline, and after the direct current transmission project and the buried metal pipeline system are put into operation, the annual corrosion depth of the pipeline can be measured by burying a test piece in soil; before the direct current transmission project or the buried metal pipeline system is put into operation, the annual corrosion depth of the pipeline is estimated mainly through simulation calculation.
When current leaks through metal, the buried metal pipeline can generate the phenomenon of 'electrode polarization' that the potential of a metal electrode deviates from the potential of a balance electrode. When the high-voltage direct-current grounding electrode is adjacent to a buried metal pipeline, the potential difference caused by the polarization effect is comparable to a limit value under certain conditions, so that the estimation on the influence of the pipeline corrosion by a prediction result obtained by using a theoretical model and a calculation method without considering the polarization effect is inaccurate. Therefore, a theoretical model and a corresponding calculation method for considering the influence of the high-voltage direct-current grounding electrode with the electrode polarization effect on the buried metal pipeline are needed to obtain the leakage current distribution of the high-voltage direct-current grounding electrode on the buried metal pipeline so as to properly evaluate the annual corrosion influence of the grounding electrode current on the buried metal pipeline.
The direct current transmission engineering grounding electrode has unique current characteristics: 1) the current amplitude varies greatly. When a single-pole earth loop of the direct-current transmission system operates, the earth current of the earth electrode can reach thousands of amperes; when the direct current system is in bipolar operation, the unbalanced current flowing through the grounding electrode is less than 1% of the rated current, and the current direction is not fixed; 2) the duration of large current is short, and the duration of small current is long. Based on the consideration of the influence on the surrounding environment, the operation scheduling of the direct current engineering also clearly stipulates that the long-time operation of the monopole earth loop is not allowed (the operation mode needs to be changed into other operation modes within 2-3 hours after the monopole fault), and the probability and the operation time of the monopole earth loop are greatly reduced. Therefore, the rated ground current is used as a calculation condition for analysis and evaluation, which obviously does not conform to the actual engineering and is not beneficial to the design and construction of the engineering. In order to evaluate the corrosion influence of the high-voltage direct-current grounding electrode on the buried oil and gas pipeline more practically, an equivalent current which takes into account the current characteristics of the high-voltage direct-current grounding electrode under different operating conditions needs to be provided.
Disclosure of Invention
In order to solve the above problems, the present application provides a method for determining an annual corrosion depth of a pipe involving a polarization effect, comprising:
acquiring the leakage current of the pipeline according to the grounding electrode current related to the polarization effect of the pipeline;
acquiring a multivariate nonlinear fitting coefficient among the earth electrode current, the soil resistivity, the approach distance and the pipeline leakage current density;
acquiring the total corrosion amount of a damaged point in the operating life cycle of the grounding electrode according to the maximum leakage current density generated on the pipeline when the grounding electrode flows through the rated current and the maximum leakage current density generated on the pipeline by unbalanced current of the grounding electrode under the bipolar operating condition;
and acquiring the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current according to the total corrosion amount.
Preferably, the obtaining of the pipe leakage current according to the earth electrode current related to the pipe polarization effect comprises:
segmenting the pipeline, and acquiring leakage current of any section of pipeline anticorrosive coating and damaged part after segmentation;
and calculating the leakage current of the pipeline according to the leakage current of the anticorrosive coating and the damaged part.
Preferably, obtaining a multivariate nonlinear fitting coefficient between the grounding distance, the soil resistivity, the ground electrode current and the pipeline leakage current density comprises:
the fitting function form of the distance between the pipeline and the center of the grounding electrode relative to the leakage current density of the pipeline is f ═ axbWherein x represents the distance between the pipeline and the center of the grounding electrode, and a and b are fitting coefficients;
the fitting function form of the soil resistivity relative to the pipeline leakage current density is f ═ a + blnx, wherein x represents the soil resistivity, and a and b are fitting coefficients;
the fitting function form of the earth electrode current relative to the pipeline leakage current density is f ═ a + bx, wherein x represents the earth electrode current, and a and b are fitting coefficients;
according to the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the current of the grounding electrode, and the fitting function form of the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the current of the grounding electrode relative to the leakage current density of the pipeline respectively, obtaining the multi-nonlinear fitting relation between the distance between the pipeline and the center of the grounding electrode, the soil resistivity, the current of the grounding electrode and the leakage current density of the pipeline as
Figure BDA0003127081850000021
Wherein J is the maximum leakage current density (A/m) at the damaged point of the pipeline2) I is grounding current (A) of a grounding electrode; d is the distance (km) from the pipeline to the grounding electrode; rhosIs a soil resistivity parameter (omega. m); a is0～a6Fitting coefficients are to be found.
Preferably, the obtaining the total corrosion amount of the damaged point in the operating life cycle of the grounding electrode according to the maximum leakage current density generated on the pipeline when the rated current flows through the grounding electrode and the maximum leakage current density generated on the pipeline by the unbalanced current of the grounding electrode under the bipolar operating condition comprises:
setting the maximum leakage current density generated on the pipeline as J when the ground electrode flows through the rated currentp-N；
Under the working condition of bipolar operation of the grounding electrode, the maximum leakage current density generated on the pipeline by unbalanced current is Jp-0Calculating the total corrosion amount of the damaged point in the operating life cycle of the grounding electrode according to the Faraday's law of electrolysis,
Figure BDA0003127081850000031
m is the corrosion mass (g) of the pipeline metal at the damaged point; m is the molar mass (g/mol) of the metal to be corroded; n is the amount of change (dimensionless) in the valence of the metal after corrosion has occurred; f is the faraday electrolytic constant (F-96484.56C/mol); q is the total leakage current capacity (C); sdIs the area of a breakage point (m)2)；t0Total duration, t, of bipolar symmetrical operation in the life of the DC grounding electrode1Constructing an initial monopole earth loop operation duration time for the direct current grounding electrode; t is t2The duration of the forced shutdown and planned shutdown of the single pole in the life cycle of the direct current grounding pole; t is t0、t1、t2The unit is year; t is0Is the number of seconds corresponding to one year, namely (T)0＝3.1536×107)。
Preferably, according to the total corrosion amount, acquiring the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current, including:
according to the total corrosion amount of the damaged point of the pipeline, the annual corrosion depth of the pipeline is calculated, the formula is,
Figure BDA0003127081850000032
m is the corrosion mass (g) of the pipeline metal at the damaged point; rhometalIs the density (g/m) of the metal3)；sdIs the area of a breakage point (m)2) (ii) a T is the total years of the life.
The present application also provides a device for determining annual corrosion depth of a pipe, involving polarization effect, comprising:
the leakage current acquisition module is used for acquiring the pipeline leakage current according to the grounding electrode current related to the pipeline polarization effect;
the fitting coefficient acquisition module is used for acquiring a multi-element nonlinear fitting coefficient between the earth electrode current, the soil resistivity, the approach distance and the pipeline leakage current density;
the total corrosion amount obtaining module is used for obtaining the total corrosion amount of the damaged point in the service life cycle of the grounding electrode according to the maximum leakage current density generated on the pipeline when the grounding electrode flows through the rated current and the maximum leakage current density generated on the pipeline by unbalanced current under the bipolar operation working condition of the grounding electrode;
and the annual corrosion depth acquisition module is used for acquiring the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current according to the total corrosion amount.
Preferably, the leakage current obtaining module includes:
the leakage current acquisition submodule is used for segmenting the pipeline and acquiring leakage current of any section of pipeline anticorrosive coating and a damaged part after segmentation;
and the leakage current calculation submodule is used for calculating the leakage current of the pipeline according to the leakage current of the anticorrosive coating and the damaged part.
Preferably, the fitting coefficient obtaining module includes:
the first fitting system determines the subunits, and the fitting function of the distance between the pipeline and the center of the grounding electrode relative to the leakage current density of the pipeline is in the form of f ═ axbWherein x represents the distance between the pipeline and the center of the grounding electrode, and a and b are fitting coefficients;
the second fitting system determines a subunit, and the fitting function form of the soil resistivity relative to the pipeline leakage current density is f ═ a + blnx, wherein x represents the soil resistivity, and a and b are fitting coefficients;
a third fitting system determines a subunit, wherein the fitting function form of the earth electrode current relative to the pipeline leakage current density is f ═ a + bx, wherein x represents the earth electrode current, and a and b are fitting coefficients;
determining a subunit by the fitting coefficient to be solved, and acquiring a multi-nonlinear fitting relation among the distance between the pipeline and the center of the grounding electrode, the soil resistivity, the grounding electrode current and the pipeline leakage current density according to the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the grounding electrode current and a fitting function form of the grounding electrode current and the pipeline leakage current density respectively
Figure BDA0003127081850000041
Wherein J is the maximum leakage current density (A/m) at the damaged point of the pipeline2) I is grounding current (A) of a grounding electrode; d is the distance (km) from the pipeline to the grounding electrode; rhosIs a soil resistivity parameter (omega. m); a is0～a6Fitting coefficients are to be found.
The method and the device for determining the annual corrosion depth of the pipeline, which relate to the polarization effect, are used for solving the problem that the annual corrosion depth of the pipeline is not accurately calculated because the leakage current distribution generated on the adjacent buried metal pipeline by direct current grounding pole current is not considered in the prior art.
Drawings
FIG. 1 is a schematic flow chart of a method for determining annual corrosion depth of a pipeline involving polarization effect according to an embodiment of the present application;
FIG. 2 is a diagram of a model of a circuit between metal and soil of a pipeline according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram illustrating the influence of grounding electrode current on corrosion of a pipeline according to an embodiment of the present application;
FIG. 4 is a schematic diagram of a pipeline annual corrosion depth determination structure related to polarization effect according to an embodiment of the present application.
Detailed Description
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. This application is capable of implementation in many different ways than those herein set forth and of similar import by those skilled in the art without departing from the spirit of this application and is therefore not limited to the specific implementations disclosed below.
Fig. 1 is a schematic flow chart of a method for determining an annual corrosion depth of a pipeline related to polarization effect according to an embodiment of the present application, which is described in detail below with reference to fig. 1.
And step S101, acquiring the pipeline leakage current according to the grounding electrode current related to the pipeline polarization effect.
Firstly, segmenting a pipeline, and acquiring leakage current of an anticorrosive coating and a damaged part of any section of pipeline after segmentation; and then calculating the leakage current of the pipeline according to the leakage current of the anticorrosive coating and the damaged part.
The method for calculating the leakage current density of the pipeline without considering the polarization effect (without considering the damage of the pipeline) is mature in the engineering, and the coating is inevitably damaged to become the coating defect in the processes of transportation, welding, laying and the like of the pipeline. After the pipeline is segmented, for a small segment of damaged pipeline, the damaged points of the pipeline are considered to be uniformly distributed on the segmented pipeline, and then the circuit model between the metal and the soil of the segment of pipeline is shown in fig. 2.
In FIG. 2, r1I1 is the resistance of the anticorrosive coating at the undamaged part of the segmented pipeline, and the current flowing out/in from the anticorrosive coating; r is2The polarization resistance of the broken part of the pipeline after segmentation, v is the equivalent voltage source of the broken part, the polarization resistance and the equivalent voltage source can be obtained from a polarization curve, I2Current flowing out/in from the breakage; i is the total current flowing out/in the segmented pipe. Therefore, equivalent ground resistance and voltage to ground of the damaged pipeline can be obtained, the total leakage current of each section of pipeline can be obtained by combining circuit models of other protective measures on the pipeline, the leakage current of the anti-corrosion layer and the damaged part of the pipeline can be further solved, and iteration is carried out according to the polarization curve until convergence.
And S102, acquiring a multi-element nonlinear fitting coefficient among the earth electrode current, the soil resistivity, the approach distance and the pipeline leakage current density.
The leakage current density generated by the direct current grounding electrode grounding current at the damaged point of the buried metal pipeline is not only related to the magnitude of the grounding electrode current, but also related to the resistivity of soil, the approach distance, the type of the pipeline anti-corrosion layer and the polarization characteristic of the metal surface of the damaged point. Therefore, the leakage current density at the pipe breakage point should be a multi-component function that includes both the ground current and other influencing parameters, and that is also non-linear in view of the non-linear polarization characteristics of the metal surface.
The fitting function form of the distance between the pipeline and the center of the grounding electrode relative to the leakage current density of the pipeline is f ═ axbWherein x represents the distance between the pipeline and the center of the grounding electrode, and a and b are fitting coefficients;
the fitting function form of the soil resistivity relative to the pipeline leakage current density is f ═ a + blnx, wherein x represents the soil resistivity, and a and b are fitting coefficients;
the fitting function form of the earth electrode current relative to the pipeline leakage current density is f ═ a + bx, wherein x represents the earth electrode current, and a and b are fitting coefficients;
according to the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the current of the grounding electrode, and the fitting function form of the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the current of the grounding electrode relative to the leakage current density of the pipeline respectively, obtaining the multi-nonlinear fitting relation between the distance between the pipeline and the center of the grounding electrode, the soil resistivity, the current of the grounding electrode and the leakage current density of the pipeline as
Figure BDA0003127081850000061
Wherein J is the maximum leakage current density (A/m) at the damaged point of the pipeline2) I is grounding current (A) of a grounding electrode; d is the distance (km) from the pipeline to the grounding electrode; rhosIs a soil resistivity parameter (omega. m); a is0～a6Fitting coefficients are to be found.
For 3PE corrosion protection layer (resistivity 10)5Ω·m2) Pipeline, final fitting coefficients are as follows:
Figure BDA0003127081850000062
for FBE corrosion protection (resistivity 3X 10)4Ω·m2) Pipeline, final fitting coefficients are as follows:
Figure BDA0003127081850000063
and step S13, acquiring the total corrosion amount of the damaged point in the service life cycle of the grounding electrode according to the maximum leakage current density generated on the pipeline when the rated current flows through the grounding electrode and the maximum leakage current density generated on the pipeline by the unbalanced current of the grounding electrode under the bipolar operation working condition.
Setting the maximum leakage current density generated on the pipeline as J when the ground electrode flows through the rated currentp-N；
Under the working condition of bipolar operation of the grounding electrode, the maximum leakage current density generated on the pipeline by unbalanced current is Jp-0Calculating the total corrosion amount of the damaged point in the operating life cycle of the grounding electrode according to the Faraday's law of electrolysis,
Figure BDA0003127081850000071
m is the corrosion mass (g) of the pipeline metal at the damaged point; m is the molar mass (g/mol) of the metal to be corroded; n is the amount of change (dimensionless) in the valence of the metal after corrosion has occurred; f is the faraday electrolytic constant (F-96484.56C/mol); q is the total leakage current capacity (C); sdIs the area of a breakage point (m)2)；t0Total duration, t, of bipolar symmetrical operation in the life of the DC grounding electrode1Constructing an initial monopole earth loop operation duration time for the direct current grounding electrode; t is t2The duration of the forced shutdown and planned shutdown of the single pole in the life cycle of the direct current grounding pole; t is t0、t1、t2The unit is year; t is0Is the number of seconds corresponding to one year, namely (T)0＝3.1536×107)。
And step S104, acquiring the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current according to the total corrosion amount.
For a set of determined engineering parameters (including the distance between the grounding electrode and the pipeline, the soil resistivity and the type of the pipeline anticorrosive coating), the leakage current density of the pipeline under the action of the grounding electrode current can be obtained through the step S102, the total corrosion amount (within the service life of 60 years) of the damaged point of the pipeline can be obtained through the step S103 by combining the running time of the direct current grounding electrode under different running conditions and the corresponding current, and the annual corrosion depth of the pipeline is further calculated, wherein the formula is as follows:
Figure BDA0003127081850000072
m is the corrosion mass (g) of the pipeline metal at the damaged point; rhometalIs the density (g/m) of the metal3)；sdIs the area of a breakage point (m)2) (ii) a T is the total years of the life.
The specific application examples are as follows:
in the first step, according to the inventive content step S102, the maximum leakage current density on the pipe is obtained. The engineering parameters in this example are as follows: the direct current grounding electrode is rated with the grounding current of 5000A (the grounding current of the grounding electrode is 1 percent of the rated current and is 50A when the bipolar unbalance operation is carried out), the soil resistivity is 100 omega.m, the distance from the center of the grounding electrode to the pipeline is 10km, and the type of the pipeline anticorrosive coating is a 3-layer PE anticorrosive coating. According to the empirical formula between the direct current grounding electrode current and the leakage current density of the pipeline, for the 3PE anti-corrosion layer type pipeline, the condition that the nearest distance between the grounding electrode and the pipeline does not exceed 10km is applicable to the formula,
Figure BDA0003127081850000081
when the grounding electrode current is 5000A, the maximum leakage current density of the pipeline is 5.8292A/m2When the ground current is 50A, the maximum leakage current density of the pipeline is 0.0366A/m2。
In the second step, according to the inventive content step S103, the total corrosion amount (within 60 years of life) at the damaged point of the pipeline is obtained. In this embodiment, the area s of the damaged point of the pipelinedIs 1 x 10-4m2(ii) a Total duration t of bipolar symmetrical operation in the life of the DC grounding electrode0In 29.55 years, the operation duration t of the monopole earth loop at the initial stage of the construction of the direct current grounding electrode10.0034 years; duration t of monopole forced outage and planned outage in life of direct current grounding electrode2For 0.45 years, the total corrosion at the point of pipe failure was 3.4086g, as derived from the equation in step S103.
m＝9151.8[Jp-0t0+Jp-N(t1+t2)]sd
And thirdly, according to the step 4 of the invention content, the annual corrosion depth of the pipeline is calculated. In this example, the density ρ of the pipe metalmetalTake 7.86X 106g/m3The annual depth of corrosion of the pipe was found to be 0.0723mm/a by substituting the following formula.
Figure BDA0003127081850000082
Therefore, the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current is rapidly and accurately obtained by adopting the method.
Based on the same inventive concept, the present application also provides a pipe annual corrosion depth determination apparatus 400 related to polarization effect, as shown in fig. 4, comprising:
a leakage current obtaining module 410, configured to obtain a pipeline leakage current according to a ground electrode current related to a pipeline polarization effect;
the fitting coefficient obtaining module 420 is configured to obtain a multivariate nonlinear fitting coefficient between a ground electrode current, a soil resistivity, a proximity distance, and a pipeline leakage current density;
the total corrosion amount obtaining module 430 is configured to obtain a total corrosion amount of the damaged point in an operation life cycle of the ground electrode according to a maximum leakage current density generated on the pipeline when the ground electrode flows through a rated current, and a maximum leakage current density generated on the pipeline by an unbalanced current of the ground electrode under a bipolar operation condition;
and an annual corrosion depth obtaining module 440, configured to obtain an annual corrosion depth of the pipeline under the influence of the dc ground electrode current according to the total corrosion amount.
The method and the device for determining the annual corrosion depth of the pipeline related to the polarization effect have the advantages that: (1) a calculation method for considering the influence of the direct current grounding electrode of the polarization effect on the buried metal pipeline is established, so that the calculation result of the leakage current density of the pipeline is more accurate; (2) an empirical formula between the grounding electrode current and the pipeline leakage current is formed through fitting, so that the method is simple and easy to use, and the calculation efficiency is greatly improved; (3) the method for calculating the annual corrosion depth of the pipeline under the influence of the direct-current grounding electrode current can accurately, quickly and efficiently evaluate the corrosion influence of the direct-current grounding electrode on the pipeline.
Finally, it should be noted that: although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention.

Claims (8)

1. A method for determining the annual corrosion depth of a pipeline involving polarization effects, comprising:
acquiring the leakage current of the pipeline according to the grounding electrode current related to the polarization effect of the pipeline;
acquiring a multivariate nonlinear fitting coefficient among the earth electrode current, the soil resistivity, the approach distance and the pipeline leakage current density;
acquiring the total corrosion amount of a damaged point in the operating life cycle of the grounding electrode according to the maximum leakage current density generated on the pipeline when the grounding electrode flows through the rated current and the maximum leakage current density generated on the pipeline by unbalanced current of the grounding electrode under the bipolar operating condition;
and acquiring the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current according to the total corrosion amount.
2. The method of claim 1, wherein obtaining the pipe leakage current from a ground current related to pipe polarization effects comprises:
segmenting the pipeline, and acquiring leakage current of any section of pipeline anticorrosive coating and damaged part after segmentation;
and calculating the leakage current of the pipeline according to the leakage current of the anticorrosive coating and the damaged part.
3. The method of claim 1, wherein obtaining a multivariate nonlinear fit coefficient between ground distance, soil resistivity, ground electrode current, and pipe leakage current density comprises:
the fitting function form of the distance between the pipeline and the center of the grounding electrode relative to the leakage current density of the pipeline is f ═ axbWherein x represents the distance between the pipeline and the center of the grounding electrode, and a and b are fitting coefficients;
the fitting function form of the soil resistivity relative to the pipeline leakage current density is f ═ a + blnx, wherein x represents the soil resistivity, and a and b are fitting coefficients;
the fitting function form of the earth electrode current relative to the pipeline leakage current density is f ═ a + bx, wherein x represents the earth electrode current, and a and b are fitting coefficients;
according to the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the current of the grounding electrode, and the fitting function form of the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the current of the grounding electrode relative to the leakage current density of the pipeline respectively, obtaining the multi-nonlinear fitting relation between the distance between the pipeline and the center of the grounding electrode, the soil resistivity, the current of the grounding electrode and the leakage current density of the pipeline as
Figure FDA0003127081840000011
Wherein J is the maximum leakage current at the damaged point of the pipelineFlow Density (A/m)2) I is grounding current (A) of a grounding electrode; d is the distance (km) from the pipeline to the grounding electrode; rhosIs a soil resistivity parameter (omega. m); a is0～a6Fitting coefficients are to be found.
4. The method of claim 1, wherein obtaining the total amount of corrosion at the damage point during the operational life cycle of the earth electrode based on the maximum leakage current density at the pipe resulting from the earth electrode flowing at the rated current and the maximum leakage current density at the pipe resulting from the unbalanced current at the bipolar operating condition of the earth electrode comprises:
setting the maximum leakage current density generated on the pipeline as J when the ground electrode flows through the rated currentp-N；
Under the working condition of bipolar operation of the grounding electrode, the maximum leakage current density generated on the pipeline by unbalanced current is Jp-0Calculating the total corrosion amount of the damaged point in the operating life cycle of the grounding electrode according to the Faraday's law of electrolysis,
Figure FDA0003127081840000021
m is the corrosion mass (g) of the pipeline metal at the damaged point; m is the molar mass (g/mol) of the metal to be corroded; n is the amount of change (dimensionless) in the valence of the metal after corrosion has occurred; f is the faraday electrolytic constant (F-96484.56C/mol); q is the total leakage current capacity (C); sdIs the area of a breakage point (m)2)；t0Total duration, t, of bipolar symmetrical operation in the life of the DC grounding electrode1Constructing an initial monopole earth loop operation duration time for the direct current grounding electrode; t is t2The duration of the forced shutdown and planned shutdown of the single pole in the life cycle of the direct current grounding pole; t is t0、t1、t2The unit is year; t is0Is the number of seconds corresponding to one year, namely (T)0＝3.1536×107)。
5. The method of claim 1, wherein obtaining an annual depth of corrosion of the pipe under the influence of the dc earth current from the total amount of corrosion comprises:
according to the total corrosion amount of the damaged point of the pipeline, the annual corrosion depth of the pipeline is calculated, the formula is,
Figure FDA0003127081840000022
m is the corrosion mass (g) of the pipeline metal at the damaged point; rhometalIs the density (g/m) of the metal3)；sdIs the area of a breakage point (m)2) (ii) a T is the total years of the life.
6. An apparatus for determining the annual corrosion depth of a pipe involving polarization effects, comprising:
the leakage current acquisition module is used for acquiring the pipeline leakage current according to the grounding electrode current related to the pipeline polarization effect;
the fitting coefficient acquisition module is used for acquiring a multi-element nonlinear fitting coefficient between the earth electrode current, the soil resistivity, the approach distance and the pipeline leakage current density;
the total corrosion amount obtaining module is used for obtaining the total corrosion amount of the damaged point in the service life cycle of the grounding electrode according to the maximum leakage current density generated on the pipeline when the grounding electrode flows through the rated current and the maximum leakage current density generated on the pipeline by unbalanced current under the bipolar operation working condition of the grounding electrode;
and the annual corrosion depth acquisition module is used for acquiring the annual corrosion depth of the pipeline under the influence of the direct current grounding electrode current according to the total corrosion amount.
7. The apparatus of claim 6, wherein the leakage current obtaining module comprises:
the leakage current acquisition submodule is used for segmenting the pipeline and acquiring leakage current of any section of pipeline anticorrosive coating and a damaged part after segmentation;
and the leakage current calculation submodule is used for calculating the leakage current of the pipeline according to the leakage current of the anticorrosive coating and the damaged part.
8. The apparatus of claim 6, wherein the fitting coefficient obtaining module comprises:
the first fitting system determines the subunits, and the fitting function of the distance between the pipeline and the center of the grounding electrode relative to the leakage current density of the pipeline is in the form of f ═ axbWherein x represents the distance between the pipeline and the center of the grounding electrode, and a and b are fitting coefficients;
the second fitting system determines a subunit, and the fitting function form of the soil resistivity relative to the pipeline leakage current density is f ═ a + blnx, wherein x represents the soil resistivity, and a and b are fitting coefficients;
a third fitting system determines a subunit, wherein the fitting function form of the earth electrode current relative to the pipeline leakage current density is f ═ a + bx, wherein x represents the earth electrode current, and a and b are fitting coefficients;
determining a subunit by the fitting coefficient to be solved, and acquiring a multi-nonlinear fitting relation among the distance between the pipeline and the center of the grounding electrode, the soil resistivity, the grounding electrode current and the pipeline leakage current density according to the distance between the pipeline and the center of the grounding electrode, the soil resistivity and the grounding electrode current and a fitting function form of the grounding electrode current and the pipeline leakage current density respectively
Figure FDA0003127081840000031
Wherein J is the maximum leakage current density (A/m) at the damaged point of the pipeline2) I is grounding current (A) of a grounding electrode; d is the distance (km) from the pipeline to the grounding electrode; rhosIs a soil resistivity parameter (omega. m); a is0～a6Fitting coefficients are to be found.
CN202110691823.3A 2021-06-22 2021-06-22 Method and device for determining annual corrosion depth of pipeline related to polarization effect Pending CN113495053A (en)

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