CN108007971B - Buried metal pipeline corrosion health state assessment method considering interference of power transmission and transformation equipment - Google Patents
Buried metal pipeline corrosion health state assessment method considering interference of power transmission and transformation equipment Download PDFInfo
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Abstract
The invention discloses a corrosion health state of a buried metal pipeline considering the interference of power transmission and transformation equipmentThe state evaluation method is characterized by comprising the following steps: 1) measuring the cathodic protection current density; 2) calculating the alternating current density; the calculation formula is as follows:
wherein: u shapeacIs an alternating current interference voltage with the unit of V; i.e. iacIs the AC current density in units of A/m2(ii) a Rho is the resistivity of the soil and has the unit of omega m; d is the diameter of the breakage point and is m; 3) calculating and collecting relevant influence data of alternating current density and pipeline corrosion rate under different cathodic protection conditions, and fitting to obtain the pipeline corrosion health state influenced by power transmission and transformation equipment; and obtaining a functional relation between the cathodic protection current density and the alternating current density through fitting, and integrating to obtain a pipeline corrosion health state judgment diagram.
Description
Technical Field
The invention relates to the field of health state evaluation of power transmission and transformation equipment and pipelines, in particular to a buried metal pipeline corrosion health state evaluation method considering interference of the power transmission and transformation equipment.
Background
In recent years, with the annual increase of economic growth speed, China gradually accelerates the progress of laying power transmission lines and buried metal pipelines. However, because the preferred selection schemes of the two transmission paths are very similar, the overhead line and the pipeline are close to or cross over in parallel, so that the distance between the overhead line and the pipeline often does not meet the requirements of relevant standards (specifications). Finally, the interference is generated on the adjacent buried metal pipeline, so that the corrosion of the surface of the pipeline is intensified and even the pipeline is punctured.
In order to avoid a series of explosion safety hidden dangers and accident disputes caused by the distance not meeting the national standard requirements, the mutual influence mechanism of the power transmission and transformation facilities and the buried metal pipeline, the corrosion health state assessment technology, the prevention measures and the like need to be developed for further research,
therefore, a method for evaluating the corrosion health status of the buried metal pipeline considering the interference of the power transmission and transformation equipment is needed.
At present, researchers at home and abroad make a great deal of research on the analysis of the corrosion risk of the pipeline. The progress of the corrosion assessment technology of the gas pipeline is gradually transited to multi-dimensional and differentiated analysis from the initial single-factor analysis; analytical techniques have also evolved from qualitative analysis to quantitative analysis to a combination of quantitative and qualitative analysis.
Because the analysis of the corrosion health state of the metal pipeline is started late in China and a certain gap still exists between the equipment configuration and the risk management level and the foreign countries, the method still faces some problems in the aspect of pipeline corrosion health state evaluation.
The method mainly comprises the steps that pipeline operation data basically depend on manual recording, and real and reliable original data are difficult to obtain; the external environment of the pipeline is complex, and influence factors are difficult to determine; the relevant standard regulations are mostly established according to research and analysis and a small amount of actual data, and the applicability and the popularity are also deficient in the aspect of engineering actual application.
In addition, it is known from the literature that there is no complete and systematic research on the evaluation of the corrosion health of gas pipelines under the interference of power transmission and transformation equipment.
Disclosure of Invention
The invention aims to solve the problems in the prior art and provides a buried metal pipeline corrosion health state assessment method considering the interference of power transmission and transformation equipment.
The technical scheme adopted for achieving the purpose of the invention is that the method for evaluating the corrosion health state of the buried metal pipeline considering the interference of the power transmission and transformation equipment is characterized by comprising the following steps of:
1) measuring the cathodic protection current density;
2) calculating the alternating current density;
the calculation formula is as follows:
wherein: u shapeacIs an alternating current interference voltage with the unit of V;
iacis the AC current density in units of A/m2；
Rho is the resistivity of the soil and has the unit of omega m;
d is the diameter of the breakage point and is m;
3) calculating and collecting relevant influence data of alternating current density and pipeline corrosion rate under different cathodic protection conditions, and fitting to obtain the pipeline corrosion health state influenced by power transmission and transformation equipment;
obtaining a functional relation between the cathodic protection current density and the alternating current density through fitting, and integrating to obtain a pipeline corrosion health state judgment diagram;
in the pipeline corrosion health state judgment diagram:
① when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (2), the corrosion rate of the pipeline is 0.01mm/a, and the corrosion health state is in an excellent state;
y＜101x+12 (2)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
② when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (3), the corrosion rate of the pipe is 0.01mm/a to 0.1mm/a,at the moment, the corrosion is in a healthy and good state;
101x+12＜y＜110.1-71.29cos(3.424x)+60.37sin(3.424x) (3)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
③ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the formula (4) is satisfied, the corrosion rate of the pipeline is between 0.1mm/a and 1mm/a, and the pipeline is in a corrosion healthy state;
110.1-71.29cos(3.424x)+60.37sin(3.424x)＜y＜14850sin(2.377x+
1.045)+14680sin(2.387x+4.199) (4)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
④ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (5), the corrosion rate of the pipeline is between 1mm/a and 10mm/a, and the corrosion health state of the pipeline is poor;
14850sin(2.377x+1.045)+14680sin(2.387x+4.199)＜y＜-1448x3+
1237x2+379x+98.2 (5)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
⑤ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the case of the range, the ratio,
if the corrosion rate satisfies the formula (6), the corrosion rate of the pipeline is greater than 10mm/a, and the corrosion state of the pipeline is poor;
y＞-1448x3+1237x2+379x+98.2 (6)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2。
The technical effects of the present invention are undoubted, and the present invention has the following advantages:
the invention provides a corrosion health state evaluation method for a buried metal pipeline considering power transmission and transformation interference, which not only considers the double functions of alternating current density and cathodic protection current density, but also ensures that the evaluation result is more accurate and provides beneficial reference for state evaluation in the future.
Drawings
FIG. 1 is a diagram of an evaluation index system for corrosion health status of a buried metal pipeline;
FIG. 2 is a flow chart of evaluation of the health status of corrosion of pipelines under interference of power transmission and transformation equipment;
FIG. 3 is a diagram illustrating a health status of corrosion of a pipeline.
Detailed Description
The present invention is further illustrated by the following examples, but it should not be construed that the scope of the above-described subject matter is limited to the following examples. Various substitutions and alterations can be made without departing from the technical idea of the invention and the scope of the invention is covered by the present invention according to the common technical knowledge and the conventional means in the field.
Example 1:
referring to a corrosion health status assessment index system diagram of a buried metal pipeline as shown in fig. 1; determining a pipeline corrosion risk criterion and dividing corrosion health state grades under the interference of power transmission and transformation equipment;
considering the limitation caused by the judgment of the density of single alternating current, the density of alternating current and direct current is selected as a measurement parameter, and the corrosion resistance of metal in the pipeline corrosion protection manual is taken as a grade judgment standard.
The total is divided into five states of excellent, good, medium, poor and poor, and specific judgment standards are given as shown in table 1.
TABLE 1
Example 2:
a corrosion health state assessment method for a buried metal pipeline considering interference of power transmission and transformation equipment is characterized by comprising the following steps:
1) measuring the cathodic protection current density;
2) calculating the alternating current density;
the calculation formula is as follows:
wherein: u shapeacIs an alternating current interference voltage with the unit of V;
iacis the AC current density in units of A/m2；
Rho is the resistivity of the soil and has the unit of omega m;
d is the diameter of the breakage point and is m;
3) because the interference mechanism of the power transmission and transformation equipment on the buried metal pipeline is very complex, it is difficult to establish a simple functional relationship to determine the corrosion health state of the pipeline through the direct ratio of the alternating current density and the cathodic protection current density.
For this purpose, an indirect approach is taken.
The pipeline corrosion health state influenced by the power transmission and transformation equipment can be obtained by collecting relevant influence data of alternating current density and pipeline corrosion rate under different cathodic protection conditions and fitting; the corrosion rate and ac density values of the pipes for each cathodic protection current density are shown in table 2.
TABLE 2
Obtaining a functional relation between the cathodic protection current density and the alternating current density through fitting, and integrating to obtain a pipeline corrosion health state judgment diagram shown in FIG. 3;
in the pipeline corrosion health state judgment diagram:
① when the cathodic protection current density is 0.01A/m2～0.8A/m2When it is full ofThe corrosion rate of the pipeline is under 0.01mm/a, and the corrosion health state is in an excellent state at the moment in the formula (2);
y＜101x+12 (2)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
② when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (3), the corrosion rate of the pipeline is between 0.01mm/a and 0.1mm/a, and the pipeline is in a healthy and good corrosion state;
101x+12＜y＜110.1-71.29cos(3.424x)+60.37sin(3.424x) (3)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
③ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the formula (4) is satisfied, the corrosion rate of the pipeline is between 0.1mm/a and 1mm/a, and the pipeline is in a corrosion healthy state;
110.1-71.29cos(3.424x)+60.37sin(3.424x)＜y＜14850sin(2.377x+
1.045)+14680sin(2.387x+4.199) (4)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
④ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (5), the corrosion rate of the pipeline is between 1mm/a and 10mm/a, and the corrosion health state of the pipeline is poor;
14850sin(2.377x+1.045)+14680sin(2.387x+4.199)＜y＜-1448x3+
1237x2+379x+98.2 (5)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
⑤ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the case of the range, the ratio,
if the corrosion rate satisfies the formula (6), the corrosion rate of the pipeline is greater than 10mm/a, and the corrosion state of the pipeline is poor;
y＞-1448x3+1237x2+379x+98.2 (6)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2。
Example 3:
using the methods of example 1 and example 2, the corrosion health status of a gas pipeline in north China was evaluated;
specifically, the method comprises the following steps:
the laying length of a certain gas pipeline in North China reaches 20km, the outer diameter of the pipeline is 219mm, the thickness of the pipeline is 6.4mm, and the burial depth of the pipeline is 2 m. The protective layer is made of 3PE and conforms to the national standard polyethylene anticorrosive coating of buried steel pipelines.
Wherein the resistivity of the 3PE anticorrosive layers is 105 omega m2The relative dielectric constant was 2.3.
The cathodic protection system of the pipeline adopts a cathode protection mode of forced current, and the cathodic protection current density is 0.014A/m2。
The two ends of the pipeline are respectively provided with a separate transmission station, the process equipment of the separate transmission station, the pipeline and the main pipeline are connected by insulating flanges, and no grounding measure is taken along the pipeline.
The pipeline is close to and parallels many alternating current transmission lines, and on-the-spot alternating current interference detection shows that this pipeline alternating current interference is serious, and the maximum voltage is about 40V, and in the measuring period, the alternating current interference voltage reading is relatively stable, and the change is no more than 0.5V, and data measurement result is as shown in table 3 (interference voltage is the average value in the measuring period in the table).
The pipeline is mainly plain along the line, and the soil resistivity is about 80-100 omega-m2It is considered to be a uniform soil layer.
TABLE 3
Taking the pile number 3 as an example to solve the problem, the method comprises the following steps:
1) measuring the cathodic protection current density;
the cathodic protection current density is 0.014A/m2；
2) Calculating the alternating current density;
the AC density value i of the pipeline can be obtained according to the formula (1)acComprises the following steps:
in the formula iacIs the alternating current density of the pipeline, A/m2；UacIs an alternating interference voltage, V; d is the diameter of the damaged point of the coating, m; ρ is the soil resistivity, Ω · m.
3) The cathodic protection current density value is 0.014A/m2Substituting the alternating current density value into the corrosion risk judgment graph to approximately obtain the poor corrosion health state of the pipeline;
y is calculated by substituting in formula (5)1,y2The values of (A) are as follows.
y1＝14850sin(2.377x+1.045)+14680sin(2.387x+4.199)
＝14850sin(2.377×0.014+1.045)+14680sin(4.23)
＝14850×0.88114+14680×(-0.887)
＝63.769(A/m2)
y2＝-1448x3+1237x2+379x+98.2
＝-1448×0.0143+1237×0.0142+379×0.014+98.2
＝103.7444(A/m2)
Finally, comparing the value with the actually calculated alternating current density value to obtain the following result;
63.769A/m2＜86.796A/m2＜103.7444A/m2
therefore, the corrosion health state of the section of buried metal pipeline is poor, and certain protection measures are required to avoid safety accidents caused by aggravation of the corrosion condition.
Claims (1)
1. A corrosion health state assessment method for a buried metal pipeline considering interference of power transmission and transformation equipment is characterized by comprising the following steps:
1) measuring the cathodic protection current density;
2) calculating the alternating current density;
the calculation formula is as follows:
wherein: u shapeacIs an alternating current interference voltage with the unit of V;
iacis the AC current density in units of A/m2；
Rho is the resistivity of the soil and has the unit of omega m;
d is the diameter of the breakage point and is m;
3) calculating and collecting relevant influence data of alternating current density and pipeline corrosion rate under different cathodic protection conditions, and fitting to obtain the pipeline corrosion health state influenced by power transmission and transformation equipment;
obtaining a functional relation between the cathodic protection current density and the alternating current density through fitting, and integrating to obtain a pipeline corrosion health state judgment diagram;
in the pipeline corrosion health state judgment diagram:
① when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (2), the corrosion rate of the pipeline is 0.01mm/a, and the corrosion health state is in an excellent state;
y＜101x+12 (2)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
② when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (3), the corrosion rate of the pipeline is between 0.01mm/a and 0.1mm/a, and the pipeline is in a healthy and good corrosion state;
101x+12＜y＜110.1-71.29cos(3.424x)+60.37sin(3.424x) (3)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
③ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the formula (4) is satisfied, the corrosion rate of the pipeline is between 0.1mm/a and 1mm/a, and the pipeline is in a corrosion healthy state;
110.1-71.29cos(3.424x)+60.37sin(3.424x)＜y＜14850sin(2.377x+1.045)+14680sin(2.387x+4.199) (4)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
④ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the range, if the corrosion rate satisfies the formula (5), the corrosion rate of the pipeline is between 1mm/a and 10mm/a, and the corrosion health state of the pipeline is poor;
14850sin(2.377x+1.045)+14680sin(2.387x+4.199)＜y＜-1448x3+1237x2+379x+98.2 (5)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2；
⑤ when the cathodic protection current density is 0.01A/m2～0.8A/m2In the case of the range, the ratio,
if the corrosion rate satisfies the formula (6), the corrosion rate of the pipeline is greater than 10mm/a, and the corrosion state of the pipeline is poor;
y＞-1448x3+1237x2+379x+98.2 (6)
wherein y is the alternating current density in A/m2；
x is cathodic protection current density and has the unit of A/m2。
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