CN107941900B - Non-contact detection method for defects of steel bent pipe - Google Patents
Non-contact detection method for defects of steel bent pipe Download PDFInfo
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Abstract
The invention provides a non-contact detection method for defects of a steel bent pipe, and belongs to the field of nondestructive detection of pressure pipelines. The calculation method comprises six steps: collecting basic data of a bent pipe; step two, calculating a self-leakage magnetic field of the bent pipe in a non-defective state by adopting a self-leakage magnetic field model of the bent pipe in a non-defective state; measuring the magnetic induction intensity gradient of the actual pipeline self-leakage magnetic field; step four, data normalization; step five, calculating a similarity coefficient; and step six, dividing the defect grade of the bent pipe. The detection method provided by the invention is simple to operate and strong in practicability, is suitable for detecting the defects of the hot-bending elbow in a factory and the cold-bending elbow in a construction site, and can realize the defect detection of the in-service elbow, thereby improving the reliable guarantee for the safe operation of the elbow.
Description
Technical Field
The invention relates to the field of nondestructive testing of pressure pipelines, in particular to a nondestructive testing method for detecting defects of a hot bend and a cold bend.
Background
The pipeline is used as a main transportation mode of an oil-gas medium, and plays an increasingly important role in national economic development and social stability. The bent pipe is used as a key component of the oil and gas conveying pipeline and often bears more complex stress and harsh working conditions, the failure risk of the bent pipe is increased accordingly, and the failure of the bent pipe is particularly obvious in a pipeline system. Therefore, the defect detection and failure control of the bent pipe have important significance for guaranteeing the safe and efficient operation of the pipeline.
In the field of petrochemical industry, elbows are usually manufactured by two processes, one is hot bending in a factory, and the other is cold bending in a construction site. However, at present, no technical standard related to quality detection of the hot bend pipe exists in China, and defects generated in the manufacturing process are difficult to find. For the manufacture of the cold bent pipe, the 'steel pipeline cold bent pipe manufacture and acceptance standard' is issued in China, the specification makes provisions for the size, the shape, the manufacture environment requirement and the like of the bent pipe, but does not make provisions for the bent pipe base metal defect, the mechanical damage defect, the material defect, the residual thermal stress and the like. In addition, the elbow (buried) is easy to fail due to corrosion, erosion, pipe-making defects and other reasons during service, so that the online detection of the elbow defects is also important.
The steel bent pipe is magnetized under the combined action of the earth magnetic field and the stress, a self-leakage magnetic field is formed near the bent pipe, when the bent pipe has parent metal defects, mechanical damage defects, material defects, residual thermal stress and the like, the self-leakage magnetic field above the bent pipe is distorted, and non-contact detection of the defects can be realized by collecting the distortion characteristics of the magnetic field. The calculation method proposed by the current patent or research paper can well calculate and identify the defects of the self-leakage magnetic field of the straight pipe, but a theoretical method for effectively calculating the self-leakage magnetic field of the bent pipe does not exist.
Therefore, a defect detection method for steel bent pipes is urgently needed in the present stage, so as to realize the defect detection of the hot-bending pipes in factories, the cold bent pipes in construction sites and the in-service bent pipes (buried pipes), thereby ensuring the safety of the bent pipes.
Disclosure of Invention
The invention provides a non-contact detection method for defects of a steel bent pipe. The method comprises the steps of firstly calculating the self-leakage magnetic field of a non-defective bent pipe through a theoretical model, and thus obtaining the magnetic induction intensity three-component and three-component gradient of the self-leakage magnetic field of the bent pipe under the conditions of different materials, pipe diameters, wall thicknesses, lifting heights, operating pressures, curvature radiuses, bent pipe angles and the like. And then acquiring the three-component gradient of the self-leakage magnetic field above the actual bent pipe by using a three-component magnetic gradiometer. And finally, carrying out correlation analysis on the three-component gradient of the self-leakage magnetic field acquired by the three-component magnetic gradiometer and the three-component gradient data of the self-leakage magnetic field acquired by the theoretical calculation method, and determining the defect condition of the bent pipe through a correlation coefficient. The method can effectively represent the self-leakage magnetic field of the defect-free bent pipe, and obtain the distribution characteristics and the change rule of the self-leakage magnetic field, so that the evaluation of the defect condition of the pipeline is realized by analyzing the correlation degree of actual detection data and theoretical data. The method is characterized by establishing a model of the self-leakage magnetic field of the defect-free bent pipe, collecting the self-leakage magnetic field above the actual bent pipe and analyzing the correlation between a theoretical calculation result and the actually collected detection signal. The method is not only suitable for detecting the hot bending of a factory and the cold bent pipe on a construction site, but also can realize the defect detection of the in-service bent pipe.
A non-contact detection method for defects of a steel bent pipe mainly comprises the following steps:
(1) collecting basic data of the bent pipe, wherein the basic data comprises the material, Poisson ratio, elastic modulus, yield strength, trend, outer diameter, wall thickness, stress state, curvature radius, bent pipe angle, manufacturing process of the bent pipe and magnetic characteristic parameters of the bent pipe material.
(2) Defect freeAnd (4) calculating the self-leakage magnetic field of the bent pipe. Drawing a geometric model of the elbow according to the collected sizes of the elbow, and then establishing a rectangular coordinate system by taking the curvature radius center of the elbow as the center of a coordinate circle, wherein the direction perpendicular to the inlet straight pipe section of the elbow is taken as an x axis, the direction perpendicular to the inlet straight pipe section of the elbow is taken as a y axis, and the direction perpendicular to the plane of the elbow is taken as a z axis. And obtaining a trajectory equation and main coordinate values of the bent pipe based on the established model. And finally, substituting the collected bent pipe data and coordinate data into a non-defective bent pipe self-leakage magnetic field calculation model, as shown in formulas (1) to (4), so as to obtain the magnetic induction intensity three components of the self-leakage magnetic field at any point P above the non-defective bent pipe in an ideal state. Based on the calculation result of the magnetic induction intensity of the self-leakage magnetic field of the defect-free bent pipe, the height above the axis of the bent pipe is taken as h according to the distance l (generally 0.5m) between two probes of the three-component magnetometers(generally, it may take 0.5m) and a height hsThe magnetic induction intensity value of the self-leakage magnetic field at the + l (generally 1.0m) position can be obtained according to the formulas (5) to (7), and the gradient of the three components of the magnetic induction intensity of the self-leakage magnetic field along the height direction (z-axis direction) can be obtained and respectively marked as Gx1，Gy1，Gz1。
In the formula: mxThe magnetization intensity of a certain infinitesimal body on the bent pipe in the x-axis direction, A/m;
Mythe magnetization intensity of a certain infinitesimal body on the bent pipe in the y-axis direction, A/m;
Mzthe magnetization intensity of a certain infinitesimal body on the bent pipe in the z-axis direction, A/m;
Bxthe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the x-axis direction, T;
Bythe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the y-axis direction, T;
Bzthe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the z-axis direction, T.
u0Vacuum magnetic permeability, typically 4 n × 10-7；
D-bend radius, m;
delta-wall thickness of bend, m
P(xp，yp，zp) -calculating the three-dimensional coordinate m of point P at any point above the bend;
r is the distance m from any point on the elbow body to the calculation point P;
d is the outside diameter of the bent pipe, m;
δ — wall thickness of bend, m;
theta is the included angle between the connecting line between the upper infinitesimal point of the bent pipe and the center of the section of the bent pipe and the z axis, rad;
r-radius of curvature of the bend;
Gx1the component of the magnetic induction intensity gradient of the self-leakage magnetic field of the defect-free bent pipe along the x-axis direction, T/m;
Gy1the magnetic induction intensity of the self-leakage magnetic field of the non-defective bent pipe is along the component of the y-axis direction, T/m;
Gz1the magnetic induction intensity of the non-defective bent pipe grid unit at the point P is along the component of the z-axis direction, T/m;
h is the vertical height m of the probe of the detection instrument from the top of the pipeline;
l-vertical height between probes of the detecting instrument, m.
(3) And measuring the magnetic induction strong gradient of the actual self-leakage magnetic field of the pipeline. Three-component magnetic gradiometer is adopted to measure the magnetic induction intensity gradient three-component value of the self-leakage magnetic field of the pipeline along the upper part of the bent pipe track to form three groups of data Gx2，Gy2，Gz2. The measured path is consistent with the path calculated theoretically during measurement.
(4) And (6) normalizing the data. In order to eliminate the influence of non-defect related parameters such as pipe diameter and wall thickness, the judgment standard of defects is unified, the self-leakage magnetic field obtained by theoretical calculation and the self-leakage magnetic field data (6 groups of data) obtained by actual measurement are normalized, and the calculation is shown as a formula (8).
In the formula: g-one-dimensional array, T/m, where G may be takenx1，Gy1，Gz1，Gx2，Gy2，Gz2；
G-normalized result of one-dimensional array G, which is Gx1，gy1，gz1，gx2，gy2，gz2；
Gmin-the minimum of the one-dimensional array, T/m;
G max-maximum of one-dimensional array, T/m.
(5) And (3) analyzing the similarity of three components of the magnetic induction gradient of the self-leakage magnetic field. And (3) obtaining a similarity coefficient three-component and a maximum quantity by calculating the similarity between the three-component of the magnetic induction gradient of the self-leakage magnetic field of the bent pipe obtained by measurement and the three-component of the magnetic induction gradient of the self-leakage magnetic field of the non-defective bent pipe obtained by calculation, and evaluating the defect condition of the bent pipe according to the maximum quantity of the similarity coefficient, as shown in formulas (9) to (12).
S＝max(Sx,Sy,Sz) (12)
In the formula: sxThe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the x-axis direction;
Sythe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the y-axis direction;
Szthe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the z-axis direction;
s-maximum similarity coefficient of magnetic induction gradient of self-leakage magnetic field of the bent pipe.
(6) And classifying the defect condition of the bent pipe. And classifying the defect condition of the bent pipe based on the minimum similarity coefficient. The defect conditions are classified into five grades, which respectively represent the severity of the defects as none, mild, moderate, high and high. As shown in fig. 4.
Drawings
FIG. 1 is a flow chart of an implementation of the detection method;
FIG. 2 is a schematic plan view of the elbow;
FIG. 3 is a schematic cross-sectional view of an elbow;
FIG. 4 is a table of defect level classifications;
FIG. 5 illustrates the calculation and normalization results of the self-leakage magnetic field of the bent pipe;
FIG. 6 shows normalized data of the self-leakage magnetic field of the hot bend and the cold bend corresponding to the example bend.
Detailed Description
The following detailed description is given with reference to the accompanying drawings and examples in order to make the advantages and features of the present invention more readily understandable by those skilled in the art, and to thereby clearly define the scope of the present invention.
A non-contact detection method for defects of a steel bent pipe mainly comprises five steps, as shown in the attached figure 1, the specific steps are as follows:
step one, collecting basic data of the bent pipe. The basic data comprises the material, Poisson ratio, elastic modulus, yield strength, trend, outer diameter, wall thickness, stress state, curvature radius, bent pipe angle, manufacturing process of the bent pipe and magnetic characteristic parameters of the bent pipe material.
And step two, calculating the self-leakage magnetic field of the bent pipe in the defect-free state. And substituting the collected bent pipe data and the coordinate data into the self-leakage magnetic field calculation model of the bent pipe in the defect-free state, so as to obtain the three components of the self-leakage magnetic field magnetic induction intensity of the bent pipe at any point P above the bent pipe in the defect-free state, as shown in formulas (1) to (4). The geometric parameters in the model are shown in fig. 2 and fig. 3. Based on the calculation result of the magnetic induction intensity of the self-leakage magnetic field of the defect-free bent pipe, the height above the axis of the bent pipe is taken as h according to the distance l (generally 0.5m) between two probes of the three-component magnetometers(generally, it may take 0.5m) and a height hsThe magnetic induction intensity value of the self-leakage magnetic field at the + l (generally 1.0m) position can be obtained according to the formulas (5) to (7), and the gradient of the three components of the magnetic induction intensity of the self-leakage magnetic field along the height direction (z-axis direction) can be obtained and respectively marked as Gx1，Gy1，Gz1。
In the formula: mxThe magnetization intensity of a certain infinitesimal body on the bent pipe in the x-axis direction, A/m;
Mythe magnetization intensity of a certain infinitesimal body on the bent pipe in the y-axis direction, A/m;
Mzthe magnetization intensity of a certain infinitesimal body on the bent pipe in the z-axis direction, A/m;
Bxthe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the x-axis direction, T;
Bythe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the y-axis direction, T;
Bzthe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the z-axis direction, T.
u0Vacuum magnetic permeability, generally taken as 4Π×10-7；
D-bend radius, m;
delta-wall thickness of bend, m
P(xp，yp，zp) -calculating the three-dimensional coordinate m of point P at any point above the bend;
r is the distance m from any point on the elbow body to the calculation point P;
d is the outside diameter of the bent pipe, m;
δ — wall thickness of bend, m;
theta is the included angle between the connecting line between the upper infinitesimal point of the bent pipe and the center of the section of the bent pipe and the z axis, rad;
r is the curvature radius of the bent pipe.
Gx1The component of the magnetic induction intensity gradient of the self-leakage magnetic field of the defect-free bent pipe along the x-axis direction, T/m;
Gy1the magnetic induction intensity of the self-leakage magnetic field of the non-defective bent pipe is along the component of the y-axis direction, T/m;
Gz1the magnetic induction intensity of the non-defective bent pipe grid unit at the point P is along the component of the z-axis direction, T/m;
h is the vertical height m of the probe of the detection instrument from the top of the pipeline;
l-vertical height between probes of the detecting instrument, m.
And step three, measuring the magnetic induction intensity gradient of the actual pipeline self-leakage magnetic field. Three-component magnetic gradiometer is adopted to measure the magnetic induction intensity gradient three-component value of the self-leakage magnetic field of the pipeline along the upper part of the bent pipe track to form three groups of data G2x，G2y，G2z. When measuringThe measured path is kept consistent with the theoretically calculated path.
And step four, normalizing the data. And (3) carrying out normalization processing on the self-leakage magnetic field obtained by theoretical calculation and the three-component data (6 groups in total) of the magnetic induction intensity of the self-leakage magnetic field obtained by actual measurement, wherein the calculation is shown as a formula (8).
In the formula: g-one-dimensional array, T/m, where G may be takenx1，Gy1，Gz1，Gx2，Gy2，Gz2；
G-normalized result of one-dimensional array G, which is Gx1，gy1，gz1，gx2，gy2，gz2；
Gmin-the minimum of the one-dimensional array, T/m;
Gmax-maximum of one-dimensional array, T/m.
And step five, calculating a similarity coefficient. And (3) calculating the similarity between the three components of the magnetic induction intensity gradient of the self-leakage magnetic field of the bent pipe obtained by measurement and the three components of the magnetic induction intensity of the self-leakage magnetic field of the non-defective bent pipe obtained by calculation by adopting an Euclidean formula, and obtaining three components of similarity coefficients and the maximum quantity, wherein the three components and the maximum quantity are shown in formulas (9) to (12).
S＝max(Sx,Sy,Sz) (12)
In the formula: sxThe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the x-axis direction;
Sythe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the y-axis direction;
Szthe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the z-axis direction;
s-maximum similarity coefficient of magnetic induction gradient of self-leakage magnetic field of the bent pipe.
And step six, dividing the defect grade of the bent pipe. And classifying the defect condition of the bent pipe based on the minimum similarity coefficient. The defect conditions are classified into five grades, which respectively represent the severity of the defects as none, mild, moderate, high and high. As shown in fig. 4.
The application principle of the invention is further explained below with reference to examples:
firstly, collecting basic data of the elbow according to the method in the first step to obtain main basic data of the elbow as shown in table 1.
Table 1 main basis data for the example elbow
| Material of | Yield strength | Pipe diameter | Wall thickness | Radius of curvature | Angle of the bent pipe | Stress state | Manufacturing process |
| Q345 | 345MPa | 219mm | 9.5mm | 1.5D | 90° | Without internal pressure | Hot stewing |
And step two, calculating the self-leakage magnetic field of the bent pipe in the defect-free state according to the calculation method in the step two. Three component values of the magnetic induction intensity of the self-leakage magnetic field under the defect-free state of the elbow of the embodiment can be obtained, and the three component values of the magnetic induction intensity of the self-leakage magnetic field at the position where the height from the ground is 0.5m and 1.0m are taken as reference values; then, according to the third step, the distance between the two probes is taken as 0.5m, and the gradient value of the self-leakage magnetic field along the direction of the elbow axis is calculated and obtained as shown in the attached figure 5 (G)1x，G1y，G1z)。
Thirdly, according to the measuring method in the third step, three-component magnetic gradiometer is adopted to measure the magnetic induction intensity gradient three-component value of the self-leakage magnetic field of the pipeline along the upper part of the bent pipe track to form three groups of data G2x，G2y，G2z. The path at the time of measurement is kept consistent with the path theoretically calculated.
And fourthly, normalizing the data obtained by theoretical calculation and actual measurement according to formulas (8) to (11). The theoretical calculation data is normalized as shown in fig. 5. Fig. 6 shows three-component data of a self-leakage magnetic field obtained by actual detection of two bent pipes (a hot bent pipe and a cold bent pipe) with different defect conditions.
And fifthly, according to the normalized data, calculating the similarity according to formulas (8) to (11) to obtain that the maximum similarity coefficient of the hot bend is 0.02, and the maximum similarity coefficient of the cold bend is 0.72.
And sixthly, grading the defect condition of the bent pipe according to the attached figure 4 on the basis of the fifth step. The hot-bending bend has a first-grade defect grade and basically has no defects; the cold bending bent pipe has four-stage defect grade and is higher.
Claims (3)
1. A non-contact detection method for defects of a steel bent pipe is characterized by mainly comprising the following six steps:
collecting basic data of a bent pipe;
step two, calculating a self-leakage magnetic field of the bent pipe in a non-defective state, substituting the collected bent pipe basic data and coordinate data into a self-leakage magnetic field calculation model of the bent pipe in the non-defective state, and obtaining a self-leakage magnetic field magnetic induction intensity three-component and a gradient three-component of any point above the bent pipe in the non-defective state, wherein the self-leakage magnetic field magnetic induction intensity three-component and the gradient three-component are shown in formulas (1) to (7):
in the formula: mxThe magnetization intensity of the micro element body on the bent pipe in the x-axis direction is A/m;
Mythe magnetization intensity of the micro element body on the bent pipe in the y-axis direction is A/m;
Mzthe magnetization intensity of the micro element body on the bent pipe in the z-axis direction is A/m;
Bxthe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the x-axis direction, T;
Bythe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the y-axis direction, T;
Bzthe component of the magnetic induction intensity of the self-leakage magnetic field of the bent pipe in the z-axis direction, T;
μ0vacuum magnetic permeability, taking 4 π × 10-7；
D-bend radius, m;
delta-wall thickness of bend, m
P(xp，yp，zp) -calculating the three-dimensional coordinate m of point P at random above the bend;
r is the distance m from any point on the bent pipe to the calculation point P;
theta is the included angle between the connecting line between the upper micro element body of the bent pipe and the center of the section of the bent pipe and the z axis, rad;
r-radius of curvature of the bend;
Gx1the component of the magnetic induction intensity gradient of the self-leakage magnetic field of the defect-free bent pipe along the x-axis direction, T/m;
Gy1the component of the magnetic induction intensity gradient of the self-leakage magnetic field of the defect-free bent pipe along the y-axis direction, T/m;
Gz1the component of the magnetic induction intensity gradient of the self-leakage magnetic field of the defect-free bent pipe along the z-axis direction, T/m;
h-calculating the vertical height m of the point P from the top of the pipeline;
l-vertical height between two probes of the detection instrument, m;
measuring the magnetic induction gradient of the self-leakage magnetic field of the actual pipeline, and measuring three-component values of the magnetic induction gradient of the self-leakage magnetic field of the pipeline along the upper part of the bent pipe track by using a three-component magnetic gradiometer to form three groups of data Gx2、Gy2、Gz2During measurement, the measurement path is consistent with the path calculated theoretically;
step four, data normalization, namely, the self-leakage magnetic field obtained by theoretical calculation and the magnetic induction intensity gradient three-component data G of the self-leakage magnetic field obtained by actual measurementx1、Gy1、Gz1、Gx2、Gy2、Gz2Normalization processing is carried out, and calculation is shown as formula (8),
in the formula: g-one-dimensional array, T/m, taking Gx1、Gy1、Gz1、Gx2、Gy2、Gz2One of them;
g-normalized result of one-dimensional array G, which is Gx1、gy1、gz1、gx2、gy2、gz2；
Gmin-the minimum of the one-dimensional array, T/m;
Gmax-the maximum value of the one-dimensional array, T/m;
step five, calculating a similarity coefficient, calculating the similarity coefficient between the three components of the magnetic induction intensity gradient of the self-leakage magnetic field of the bent pipe obtained by actual measurement and the three components of the magnetic induction intensity gradient of the self-leakage magnetic field of the non-defective bent pipe obtained by calculation, and obtaining the three components and the maximum quantity of the similarity coefficient, as shown in formulas (9) to (12):
S＝max(Sx,Sy,Sz) (12)
in the formula: sxThe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the x-axis direction;
Sythe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the y-axis direction;
Szthe component of the magnetic induction gradient similarity coefficient of the self-leakage magnetic field of the bent pipe along the z-axis direction;
s is the maximum similarity coefficient of the magnetic induction intensity gradient of the self-leakage magnetic field of the bent pipe;
and step six, dividing the defect grade of the bent pipe.
2. The method of claim 1, wherein the bend datum comprises a material of the bend, a Poisson's ratio, an elastic modulus, a yield strength, a strike, an outer diameter, a wall thickness, a stress state, a radius of curvature, a bend angle, a manufacturing process, and a magnetic property parameter of the bend material.
3. The non-contact detection method for the defects of the steel bent pipe according to claim 1, wherein the sixth step is specifically: and classifying the defect conditions of the bent pipe based on the maximum similarity coefficient, wherein the defect conditions are classified into five grades and respectively represent that the severity of the defects is none, mild, moderate, high and high.
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