RU1810809C - Method of determining crack width in ferromagnetic article - Google Patents

Abstract

The invention relates to the field of non-destructive testing by magnetic methods and can be used to determine the size of defects such as narrow surface and internal cracks, it can be used for inspection of ferromagnetic products of pipes, rails, etc. The aim of the invention is to increase accuracy by eliminating errors caused by a change in the path of the transducer. The method involves magnetizing the product with the field Ho, removing the topography of the tangential component of the induction of the magnetic field scattered over the defect with an arbitrary sensor path, then the value Ho is subtracted from the obtained topography values and the area under the obtained curve of the tangential component of the scattering field over the defect is found after which the obtained value of the area is divided by fi H0 / 2 for the surface crack and by fi H0 for the internal crack, while / is the magnetic permeability of the product material, determined EMA from the known characteristics of magnetizing the test material. 5 ill. ate oo o 00 o o

Description

The invention relates to the field of non-destructive testing by magnetic methods and can be used to determine the parameters of defects such as narrow surface and internal cracks, it can be used for inspection of ferromagnetic products, for example, pipes, rails, etc.

The aim of the invention is to increase the accuracy of determining geometric

type surface defect parameters

narrow crack and narrow elongated internal defect.

Figure 1 shows a cross section of a narrow surface defect in a ferromagnetic half-space and a circulation loop of the magnetic induction vector.

Figure 2 shows a cross section of a narrow internal defect in a ferro: magnetic half-space and the circulation loop of the magnetic induction vector.

But Fig. 3 shows a cross section of a real surface crack and its linear approximation.

Figure 4 shows a block diagram of an installation that implements this method.

Figure 5 shows the experimental dependence of the tangential component of the defect field on the X coordinate for the first ME path a) and second b).

The invention is based on the following physical laws. From the laws of magnetostatics it is known that the circulation of the vector of the magnetic field strength in a closed loop, which does not cover the conduction currents, is zero:

Ј НеаТ 0 (4)

S

Draw a contour relative to the crack; located in the ferromagnetic half-space as shown in Fig. 1. Then the curvilinear integral (4) will consist of the following components:

  F D A- #Hedl / Hedl- / Hedl + J Hedl + SE A F

E +7 Hedl 0 (5)

 D

The segments of the contours F, A, and D.E are so far from the center of the crack that the field is uniform there, and the stress vector is relative to their perpendicular. Then:

F e

/ Not di Oh and J Hedl Oh

AD

The stress vector along the line AD passing through the middle of a narrow crack, whose depth is much greater than its width, is constant in direction and equal in magnitude to Ho in the metal and / Н0 inside the crack, where / I is the permeability of the material of the test object. With this in mind, the linear integral on the segment A.D will be equal to: o in / Hedl jH0dl + JH0dl + / rH0 I BC I

AA C

Whereas IADI IBCI b

where b is the width of the crack in its middle part, we can take

IABI + ICDI IADI Expression (5) in this case will take the form:

F about jHedl-jHodl - // Hob 0

EA

For a magnetically sensitive element oriented along the X axis (see FIG. 1):

Fd

/ Hxdx- / H0dx - / "Hob 0

EA

Since | EF | IADI, then / (Hx - H0) dx

E

 H0b Hence the width of a narrow crack in its middle

parts

/ (Hx-Ho) dx

Yeo

 --- -4t- (6)

/ GNO I But v; and when approximating the cross section of a crack in the form of a triangle (see Fig. 3), its opening on the surface will be twice as large as b, i.e.

2 s

Bn

TRo

(7)

The value of S / (Hx - H0) dx is the area

concluded between the curve of the tangential Q component of the magnetic field strength Hx of the defect and the horizontal line corresponding to the magnitude of the magnetizing field Ho, measured using a magnetically sensitive element that has traveled from point E to F. Points E and F (see Fig. 1) are removed at a distance where the scattering field from the crack is practically absent.

From the theorem on the circulation of the magnetic-stress vector it follows that the path is passed. ME between E and F can be anything, for example, E-a-F (see figure 1). The final result will be the same regardless of the shape of the ME trajectory, therefore, the proposed method does not need to ensure the accuracy of determining the position of Me in space, unlike the prototype method, for the implementation of which it is necessary

n to withstand the path of movement of the magnetically sensitive element (ME) strictly parallel to the surface of the monitored product, and this path should be parallel to the magnetizing field

c But also perpendicular to the longitudinal axis of the defect. Similar considerations can be made for an internal narrow defect (see Fig. 2). The width in this sluna is calculated from (6).

An example of a specific implementation The proposed method for determining the width of the opening of a narrow crack was implemented in an experimental setup, a block diagram of which is shown in Fig. 4.

The installation contains a generator 1 (GZ-33), connected to the device 2 by an output, exciting the Hall sensor 3 and issuing a constant voltage proportional to the magnitude of the magnetic field, which was supplied to the two-coordinate recorder 4

0

5

with a time scan, the movement of the Hall sensor along sample 5 is synchronized with the movement of the pen of the recorder in one of the coordinates. In sample 5, a crack was grown with an opening width of 0.045 + 0.05 mm and a depth of 5.8 mm. The Hall sensor was located above sample 5. The sample was magnetized at the poles of an electromagnet 6 until induction B0 1.94 T or c H0

P - J5438 A / cm. Topography Paul TanRO

the genetic component Hx over the defect obtained in this apparatus is experimentally shown in Fig. 5 (a). The area enclosed between this Hx curve and the straight line corresponding to the magnitude of the magnetization field H0 was calculated by numerical method. 5, this area is shaded. The calculated area in the coordinate system where the ordinates are plotted (A / cm) and the abscissa (m) is 36.5 A.

Further, the obtained value of this area H of spares, equal to 36.5 A, was divided by °

 A / cm and the desired defect width was obtained, equal to 0.0473 mm, which differs from the average value of the width of a real crack by only 5%. Next, the field topography was taken for another trajectory of the Hall sensor, which was also chosen randomly, Fig. 5 (b). In this case, the measured area was 33.9 A. Hence, the calculated crack width was 0.0439 mm, which is 2.4% different from the actual value. When applying the prototype method, using the maximum topography values taken when the sensor moved along the first and second path. And with an unknown arbitrary distance of the ME to the product, the width cannot be determined at all, if the values YI and Ya (3) in the prototype method can be determined with an accuracy of 20%, which is confirmed in practice, and then HX1 and Hx2 will also be known no more than 20%, then from (2), for the sake of simplicity T - the total error of the prototype method can be 40% , which, of course, is unacceptable for testing day control of critical details. Thus, the conducted experimental verification showed that the proposed method in comparison with the prototype method provides a more stable and accurate determination of the width of a narrow crack, the method of increasing the measurement accuracy reaches a value of ID-20 times

Based on the foregoing, the following advantages of the proposed method can be distinguished in comparison with the prototype:

1. The final result determined by the proposed method is not affected by the instability of the position of Me in space, since the curvilinear integral over the closed loop is equal to zero (in the absence of conduction currents through

0 of it), in the prototype it is necessary to precisely determine the coordinates of the sensor, since the values of the measured magnetic fields depend on them, according to which, based on formulas (3), which relate the dimensions of the defect to the values of 5 scattered magnetic fields, The geometric parameters of the defects are determined. This advantage is especially important in the practical application of the method, since under conditions

It is most difficult to have a perfect trajectory of the sensor in actual production.

2. In the proposed method, the signal received from the ME is integrated, which increases 5 the noise immunity of the measurements.

3. No complex computational operations are required, which increases the speed of determining the width value and allows the method to be implemented using simple 0 electronic devices.

4. The measurement of the width of the proposed method can be performed with non-magnetic and magnetic coatings applied to the surface of the product.

5 thicknesses, which in principle cannot be carried out using the prototype method, since the field rapidly decreases with increasing distance between the sensor and the product, and individual values of the field can be measured

0 only with a big error.

5. In the proposed method, the ME sizes do not affect the accuracy of defect size determination, since subsequent measurement of the area limited

5 of the distribution curve of the tangential component means that, in other words, the integral is taken anyway, which makes the result independent of the physical dimensions of the most magnetically sensitive

0 element, while in the prototype method the ME should be as small as possible, otherwise, it will not be able to accurately measure the value of the voltage at a specific point, due to the significant heterogeneity of the distribution of the magnetic field strength of the scattering nor over the defect, i.e. in a small space, commensurate with the size of the defect, usually lying within a few microns.

Claims (1)

The claims A method for determining the width of a crack in a ferromagnetic product, the method being that the product is magnetized by a constant magnetic field with a strength Ho. measure the tangential component of the scattering field over the defect and use it to determine the width of the defect, characterized in that, in order to improve accuracy, record the curve 0 the distribution of the tangential component of the loaded magnetic field scattering in the direction perpendicular to the direction of the crack, measure the area S bounded by this curve and the straight line corresponding to the value of the magnetizing field, and the width b of the crack opening is determined from the ratio b S // Н0, where is the magnetic permeability of the product material. Fi2.3 Fig. 21 2 5 xfcM) 1 2 3 x (cm; ajв FI2.5