CN105738837A - Method for calculating magnetic induction intensity of natural leakage magnetic field of non defective steel pipeline - Google Patents

Abstract

The invention provides a method for calculating the magnetic induction intensity of a natural leakage magnetic field of a non defective steel pipeline, and belongs to the technical field of petroleum and natural gas pipeline detection. The calculating method includes five steps of: firstly collecting pipeline basic data; secondly measuring a geomagnetic field of the environment where the pipeline is; thirdly calculating the magnetization intensity of the pipeline by using a stress magnetization model and obtaining the magnetization intensity of any position on the pipeline; fourthly calculating natural leakage magnetic field three components of the pipeline by using a natural leakage magnetic field model, and obtaining the three component values of the magnetic induction intensity of the natural leakage magnetic field of the non defective steel pipeline; and fifthly calculating a total amount of the magnetic induction intensity of the natural leakage magnetic field of the pipeline based on the determination of the natural leakage magnetic field three components. The calculating method of the invention is simple and practical, accurately calculates the total amount and the three components of the magnetic induction intensity of the natural leakage magnetic field of the non defective steel pipeline, provides theoretical supports for the quantitative judgment of the pipeline magnetic abnormality, and improves the reliability of defect identification.

Description

A kind of computational methods of non-defective steel pipe natural leak magnetic field magnetic induction

Technical field

Patent of the present invention relates to oil and gas pipeline non-destructive testing technical field, particularly the computational methods of a kind of non-defective pipeline natural leak magnetic field magnetic induction for steel pipe Magnetic testi.

Background technology

At present, along with the continuous propelling of oil and gas pipe-line construction, China's land pipelines total kilometrage is more than 120,000 kilometers.The development ensureing China's pipe safety Effec-tive Function and national economy is significant by the detection of pipeline location, trend and defective locations.

Conventional pipeline non-destructive testing method has ray detection, ultrasound detection, Magnetic testing, Magnetic Flux Leakage Inspecting etc..These detection techniques are all a kind of passive detection technology, it is necessary to pipeline carries out forced signal (ray, ultrasound wave, magnetic) and processes, inconvenient operation.Such as Magnetic Flux Leakage Inspecting technology, not only need pipeline is magnetized, pipeline and surrounding are caused electromagnetic pollution, and easily blocks in the duct, affect the properly functioning of pipeline.

Steel pipe issues magnetisation in the combined effect of external force and geomagnetic field, produce from stray field, thus causing that the magnetic induction of Near Pipelines changes, and defect of pipeline place from stray field will be distorted from stray field relative to non-defective pipeline place, and yet suffer from after pipeline external force disappears from stray field, this phenomenon is referred to as the Metal magnetic memory of pipeline.According to Metal magnetic memory principle, occur in that some defect inspection methods based on pipeline magnetic exception in recent years.These detection methods can only judge the position that pipeline magnetic is abnormal qualitatively, causes that the reliability to defect of pipeline identification is not high.But, for the quantitative criterion that magnetic anomaly judges, then need natural leak magnetic field magnetic induction produced by non-defective steel pipe is carried out quantitative Analysis and analysis.

Therefore, present stage is badly in need of the computational methods of a kind of non-defective steel pipe natural leak magnetic field magnetic induction, and the rational judgment for realizing steel pipe magnetic anomaly lays the foundation, and then improves the reliability of defect of pipeline identification.

Summary of the invention

It is an object of the invention to provide the computational methods of a kind of non-defect of pipeline natural leak magnetic field magnetic induction, thus obtaining the value of the natural leak magnetic field magnetic induction of non-defective pipeline overhead surface optional position under unlike material, caliber, wall thickness, buried depth and operating pressure.And then effectively grasp the non-defective pipeline distribution characteristics from stray field, for quantitative analysis non-defective pipeline, the impact of pipeline magnetic detection technique is laid the foundation.The core of method is in that to determine the non-defective pipeline intensity of magnetization by stress magnetization model, and on the basis that the intensity of magnetization is known, by calculating the natural leak magnetic field magnetic induction three-component of non-defective pipeline and the value of total amount from leakage magnetic field model.

This defect of pipeline includes herein below from the computational methods of stray field:

(1) collection of non-defective pipeline foundation data, mainly includes the material of non-defective pipeline, the yield strength of non-defective pipeline, the trend of non-defective pipeline, the external diameter of non-defective pipeline, the wall thickness of non-defective pipeline, the operating pressure of non-defective pipeline and the buried depth of non-defective pipeline and length.

(2) adopt Magnetic Sensor that non-defective pipeline institute earth's magnetic field three-component in the environment is measured, obtain in horizontal plane, being perpendicular to the geomagnetic field component G that pipeline is axial_x；Geomagnetic field component G along pipeline axial direction_y；It is perpendicular to ground level geomagnetic field component G upwards_z。

(3) intensity of magnetization of pipeline is calculated, setting up rectangular coordinate system in space as shown in Figure 1, x-axis axis with pipeline in horizontal plane is vertical, and y-axis axis with pipeline in horizontal plane is parallel, z-axis is perpendicular to horizontal plane straight up, and initial point is at the center of pipeline., there are the magnetized intensity of magnetization three component M in space coordinates by non-defective place pipeline can be obtained in the survey result according to (1) non-defective pipeline basic document and the three-component measurement result in earth's magnetic field, (2) non-defective pipeline location_x, M_yAnd M_z.Based on ferromagnetic material stress magnetization model, the intensity of magnetization at defect of pipeline place being calculated, its specific formula for calculation is as follows:

$M_y=(1350a+0.001{\mathrm{bM}}_s\frac{PD}{{\mathrm{\δ\σ}}_s})G_y---\left(2\right)$

In formula: M_xThe intensity of magnetization in a certain micro unit x-axis direction, A/m on pipeline；

M_yThe intensity of magnetization in a certain micro unit y-axis direction, A/m on pipeline；

M_zThe intensity of magnetization in a certain micro unit z-axis direction, A/m on pipeline；

M_sThe saturation magnetization of pipeline, A/m, generally take 1.6 × 10⁶A/m；

The operating pressure of P pipeline, Pa；

The external diameter of D pipeline, m；

The wall thickness of δ pipeline, m；

σ_sThe yield strength of pipeline, MPa；

The angle of line and x-axis between pipeline upper stress point and pipeline section center；

α, b, the correction constant relevant with material character, generally 1 is all taken for mild steel.

(4) the pipeline intensity three component M in space coordinates are being obtained_x, M_yAnd M_zAfter, the natural leak magnetic field magnetic induction of pipeline overhead surface any point is calculated.As shown in Figure 1, the coordinate at pipeline overhead surface any point P place is (x_p,y_p,z_p).Then the magnetic induction component at P point place is obtained by from leakage magnetic field model, shown in equation below:

In formula, B_xThe pipeline natural leak magnetic field magnetic induction component in x-axis direction, A/m；

B_yThe pipeline natural leak magnetic field magnetic induction component in y-axis direction, A/m；

B_zThe pipeline natural leak magnetic field magnetic induction component in z-axis direction, A/m.

u₀Permeability of vacuum, generally takes 4 Π × 10^-7；

x_pThe coordinate in x direction, any point P place；

y_pThe coordinate in y direction, any point P place；

z_pThe coordinate in z direction, any point P place；

The half of the length of L pipeline, m；

On r pipeline, any point is to the distance of P point, m, can be calculated by formula (12).

According to above summary of the invention, the natural leak magnetic field magnetic induction three-component B of any point above non-defective pipeline can be tried to achieve in simultaneous formula (6)～(11)_x, B_y, B_zValue.

(5) after obtaining magnetic induction component, can obtaining the magnetic induction total amount B from stray field, its computing formula is as follows.

$B=\sqrt{{B_x}^2+{B_y}^2+{B_z}^2}---\left(8\right)$

Accompanying drawing explanation

Accompanying drawing 1 non-defective pipeline is from leakage magnetic field model schematic diagram.

Accompanying drawing 2 non-defective pipeline from stray field three-component along the scattergram of x-axis.

Accompanying drawing 3 non-defective pipeline from stray field three-component along the scattergram of y-axis.

Accompanying drawing 4 natural leak magnetic field magnetic induction total amount is along the scattergram of x-axis.

Accompanying drawing 5 natural leak magnetic field magnetic induction total amount is along the scattergram of y-axis.

Detailed description of the invention

Advantages and features of the invention below in conjunction with accompanying drawing and calculated examples, detailed description of the invention are described in detail, so that can be easier to be it is understood by those skilled in the art that thus protection scope of the present invention is made apparent clear and definite defining.

A kind of non-defective pipeline comprises the following steps from the computational methods of stray field:

Step one, pipeline foundation collection of data, mainly include the length of the material of pipeline, caliber, wall thickness, operating pressure, the buried depth of pipeline, pipeline and the saturation magnetization of pipeline.When tubing specification is known, inquire about following table, it is determined that the yield strength of tubing.

The yield strength value of table 1 primary line steel

Step 2, the measurement in earth's magnetic field, adopt Magnetic Sensor to the earth's magnetic field three-component measurement in pipeline environment, obtain in horizontal plane, being perpendicular to the geomagnetic field component G that pipeline is axial_x；Geomagnetic field component G along pipeline axial direction_y；It is perpendicular to ground level geomagnetic field component G upwards_z。

Step 3, the collection result according to step one pipeline foundation data: outer diameter tube D, pipeline wall thickness δ, conduit running pressure P, pipeline yield strength σ_s, the saturation magnetization M of pipeline_s；The measurement result in step 2 earth's magnetic field: by geomagnetic field component G axial for pipeline_x；Geomagnetic field component G along pipeline axial direction_y；It is perpendicular to ground level geomagnetic field component G upwards_z, and the yield strength σ of pipeline_s, bring stress magnetization model into, the intensity of magnetization at non-defect of pipeline place be calculated, it is possible to obtain the intensity of magnetization of optional position, M on pipeline_x, M_yAnd M_z.Specific formula for calculation is as follows:

$M_y=(300a+0.001{\mathrm{bM}}_s\frac{PD}{{\mathrm{\δ\σ}}_s})G_y---\left(2\right)$

Step 4, obtain pipeline x, y, z tri-direction intensity of magnetization component after, be 2L according to the length of pipeline, height to earth up is h₁The coordinate at pipeline overhead surface any point P place is (x_p,y_p,z_p) its height overhead is h₂.By can obtain the value of three components of magnetic induction at P point place, B from leakage magnetic field model_x, B_y, B_z, it specifically calculates such as formula (4)～(7):

Step 5, is obtaining magnetic induction component B_x, B_y, B_zAfter, the magnetic induction total amount B from stray field can be obtained, its specific formula for calculation is as follows.

$B=\sqrt{{B_x}^2+{B_y}^2+{B_z}^2}---\left(8\right)$

Therefore, the calculating to non-defective pipeline natural leak magnetic field magnetic induction can be realized according to above five steps.

Below for the process that calculates in detail of an example, embodiment is described in detail

The first step, the basic document of gathering line, including material, caliber, wall thickness, height to earth up and operating pressure and saturation magnetization.The pipeline section choosing pipeline is calculated, and its pipe parameter is as shown in table 1.

Table 1 pipe parameter

Second step, adopts Magnetic Sensor to the earth's magnetic field three-component measurement in pipeline environment, obtains being perpendicular to the geomagnetic field component G that pipeline is axial in horizontal plane_x=12A/m；Geomagnetic field component G along pipeline axial direction_y=20A/m；It is perpendicular to ground level geomagnetic field component G upwards_z=31A/m.

3rd step, the earth's magnetic field three-component that the pipe parameter obtain the collection of the basic data of step one pipeline and the geomagnetic field measuring of step 2 obtain brings formula (1), (2) and (3) into, obtains following result

$M_y=(300a+0.001{\mathrm{bM}}_s\frac{PD}{{\mathrm{\δ\σ}}_s})G_y=21887A/m---\left(2\right)$

4th step, on the basis that stress solves, by model parameter；Step one, two and three the data obtained substitute into formula (4), (5), (6) and (7).And adopt computer to solve, obtain working as z_pDuring=2m, from stray field three-component along the distribution of x-axis as shown in Figure 2, from stray field three-component along the distribution of y-axis as shown in Figure 3.

5th step, is obtaining magnetic induction component B_x, B_y, B_zAfter, bring formula (8) into, the magnetic induction total amount B from stray field can be obtained, obtain working as z_pDuring=2m, natural leak magnetic field magnetic induction total amount along x-axis distribution as shown in Figure 4, the sensing of natural leak magnetic field magnetic always measure by force along y-axis distribution as shown in Figure 5.

Above-described embodiment only for technology design and the feature of the present invention are described, its object is to allow person skilled in the art will appreciate that present disclosure and to implement according to this, can not limit the scope of the invention with this.All equivalences made according to spirit of the invention change or modify, and all should be encompassed within protection scope of the present invention.

Claims (3)

1. the computational methods of a non-defective steel pipe natural leak magnetic field magnetic induction, it is characterised in that the computational methods of this non-defective steel pipe natural leak magnetic field magnetic induction mainly comprise the steps that

Step one, pipeline foundation collection of data, mainly include the material of pipeline, caliber, wall thickness, operating pressure, the buried depth of pipeline, the length of pipeline and the yield strength of tubing and saturation magnetization.

Step 2, the measurement in earth's magnetic field, adopt Magnetic Sensor to the earth's magnetic field three-component measurement in pipeline local environment, obtain in horizontal plane, being perpendicular to the geomagnetic field component that pipeline is axial；Along the geomagnetic field component of pipeline axial direction be perpendicular to ground level geomagnetic field component upwards.

Step 3, the collection result according to step one pipeline foundation data: outer diameter tube, pipeline wall thickness, conduit running pressure, pipeline yield strength, the saturation magnetization of pipeline；The measurement result in step 2 earth's magnetic field: by geomagnetic field component axial for pipeline；Geomagnetic field component along pipeline axial direction；It is perpendicular to ground level geomagnetic field component upwards and the yield strength of pipeline, brings stress magnetization model into, based on stress magnetization model, the non-defective pipeline intensity of magnetization is calculated, it is possible to obtain the intensity of magnetization of optional position on pipeline.

Step 4, after the intensity of magnetization component obtaining pipeline three direction, according to the parameter such as the length of pipeline, pipeline height to earth up, adopts from leakage magnetic field model, can the natural leak magnetic field magnetic induction three-component at any point place, ground be calculated.

Step 5, after obtaining non-defective pipeline natural leak magnetic field magnetic induction three-component, can be calculated from the magnetic induction total amount of stray field.

2. the computational methods of the non-defective pipeline intensity of magnetization as claimed in claim 1, it is characterised in that in step 3, adopt stress magnetization model that the non-defective pipeline intensity of magnetization is calculated, and its concrete formula is as follows:

In formula: M_xThe intensity of magnetization in a certain micro unit x-axis direction, A/m on pipeline；

M_yThe intensity of magnetization in a certain micro unit y-axis direction, A/m on pipeline；

M_zThe intensity of magnetization in a certain micro unit z-axis direction, A/m on pipeline；

M_sThe saturation magnetization of pipeline, A/m, generally take 1.6 × 10⁶A/m；

The operating pressure of P pipeline, Pa；

The external diameter of D pipeline, m；

The wall thickness of δ pipeline, m；

σ_sThe yield strength of pipeline, MPa；

The angle of line and x-axis between pipeline upper stress point and pipeline section center；

α, b, the correction constant relevant with material character, generally 1 is all taken for mild steel.

3. the non-defective pipeline natural leak three-component computational methods of magnetic field magnetic induction as claimed in claim 1, it is characterized in that, in step 4, adopting and from leakage magnetic field model, non-defective pipeline natural leak magnetic field magnetic induction three-component is calculated, its specific formula for calculation is as follows:

In formula, B_xThe pipeline natural leak magnetic field magnetic induction component in x-axis direction, A/m；

B_yThe pipeline natural leak magnetic field magnetic induction component in y-axis direction, A/m；

B_zThe pipeline natural leak magnetic field magnetic induction component in z-axis direction, A/m.

u₀Permeability of vacuum, generally takes 4 Π × 10^-7；

x_pThe coordinate in x direction, any point P place；

y_pThe coordinate in y direction, any point P place；

z_pThe coordinate in z direction, any point P place；

The half of the length of L pipeline, m；

On r pipeline, any point is to the distance of P point, m, can be calculated by formula (12).

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