RU2438120C1 - Method of estimating depth of defect - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: first and second images are taken without changing the direction of illumination at different distances from the radiation source to the inspected article, after which dimensions of the images of the defect on both images are measured and the depth of the defect is calculated using a certain mathematical expression based on the measurements and known geometry of illumination. ^ EFFECT: high accuracy of estimating depth of a defect. ^ 1 dwg

Description

The invention relates to the field of flaw detection and can be used for radiographic inspection of welded joints.

A known method for assessing the depth of a defect by double transmission with a shift of the radiation source during the second transmission by a certain angle with respect to the first transmission. Measuring the shift of the image of the defect on the film relative to the image of the lead mark mounted on the product from the side of the film cassette, and based on the known transmission geometry, calculate the depth of the defect in the metal of the product (see Rumyantsev S.V. Radiation defectoscopy, M., Atomizdat, 1974, pp. 258-260).

The claimed method closest in its technical essence is a method for estimating the depth of a defect by double exposure with a change in the direction of radiation and the installation of two lead marks: from the side of the radiation source and from the side of the film (see OST 108.004.110-87), which is accepted as the prototype of the proposed method. The depth of the defect in this method is estimated based on the measured values of the displacement of the images of the moving mark (from the side of the radiation source) and the defect relative to the image of the fixed mark (from the side of the film cassette).

The problem to which the invention is directed is to increase the capabilities of the method and improve the accuracy of estimating the depth of the defect.

The problem is solved due to the fact that in the method of assessing the depth of the defect, which consists in comparing the images of the defect in two pictures with different different geometry of transmission, the first and second pictures are performed without changing the direction of transmission at a different distance from the radiation source to the controlled product, and then measure the sizes of the defect images in both images and on the basis of the measurements taken and the known transmission geometry conduct a calculated estimate of the depth of the defect .

The invention is illustrated in the drawing.

The drawing shows a diagram for assessing the depth of the defect of the claimed method.

A calculated estimate of the depth h of the occurrence of the defect can be carried out on the basis of geometric relationships for two positions of the radiation source — A ₁ and A ₂ , corresponding to focal lengths f ₁ f ₂ .

Designations in the drawing: l - half-width of the defect; L ₁ , L ₂ - the half-width of the image of the defect for two positions of the radiation source.

Of these triangles ΔA ₁ BC and ΔA ₁ DE ₁ we have the ratio:

Given that BC = l, A ₁ D = f ₁ , A ₁ B = f ₁ -h, DE ₁ = L ₁ , and substituting these relations in (1), we obtain

Similarly, from the triangles ΔA ₂ BC and ΔA ₂ DE ₂ :

From the expression (2) follows

From the expression (3) follows

Equating the expression for l, we have:

,

,

(f ₁ -h) × L ₁ × f ₂ = (f ₂ -h) × L ₂ × f ₁ ,

f ₁ × L ₁ × f ₂ -h × L ₁ × f ₂ = f ₂ × L ₂ × f ₁ -h × L ₂ × f ₁ ,

h × L ₂ × f ₁ -h × L ₁ × f ₂ = f ₂ × L ₂ × f ₁ -f ₁ × L ₁ × f ₂ ,

h × (L ₂ × f ₁ -L ₁ × f ₂ ) = f ₂ × f ₁ × (L ₂ -L ₁ ),

from here

The inventive method was used to assess the depth of defects such as simulated discontinuities (cylindrical holes, rectangular grooves) located at different distances from the surface of the sample.

Sample thickness 70 mm. Actual depth of imitated defects h = 10; 60; 70 mm. Radiation was performed by an MG-420 x-ray apparatus at a voltage on the x-ray tube of U _p.t = 400 kB on a radiographic film of type D5. Focal length: f ₁ = 670 mm, f ₂ = 270 mm.

For example, for a simulated shell with a diameter of ⌀ = 10 mm (size in the transillumination direction of 2 mm) with a focal length f ₁ = 670 mm, the image diameter ⌀ measured in the image ^and _zam. at the actual depth:

h _f1 = 70 mm - ⌀ ^and _replacement 1 = 11.2 mm (L ₁ = ⌀ ^and _{replacement 1/2} / = 5.6 mm);

h _f2 = 60 mm - ⌀ ^and _{replacement 2} = 10.8 mm (L ₁ = ⌀ ^and _{replacement 2/2} = 5.4 mm);

h _f3 = 10 mm - ⌀ ^and _replacement 3 _≅ 10.0 mm (L ₁ = ⌀ ^and _{replacement 3/2} = 5.0 mm);

When f ₂ = 270 mm:

h _f1 = 70 mm - ⌀ ^and _replacement 1 = 14.0 mm (L ₂ = 7.0 mm);

h _f2 = 60 mm - ⌀ ^and _{replacement 2} = 13.0 mm (L ₂ = 6.5 mm);

h _f3 = 10 mm - ⌀ ^and _{replacement 3} = 10.2 mm (L ₂ = 5.1 mm);

In accordance with (4), the calculated values of the depth h _calculation will be:

since the thickness of the sample is 70 mm, take h _calc. 1 = 70 mm;

The above example shows that when the defect is located at a relatively large distance from the radiographic film, the calculated depth is obtained to a certain extent greater than the actual one. This is due to the unaccounted for in the calculations increase in the measured image size of the defect due to the presence of geometric blur. However, for the purpose of determining the direction (side) of sampling of a defective product location, which is usually the task of assessing the depth of a defect, the indicated error is quite acceptable.

To increase the accuracy of estimating the depth of the defect, it is recommended to use radiation sources with the smallest possible focal spot size and to ensure that the maximum value of geometric blur is not exceeded by the difference between the measured dimensions of the defect image at the selected first and second focal lengths.

The inventive method allows an assessment of the depth of defects in cases where the double translucence method with an angular displacement of the radiation source is not applicable, for example, when controlling translucency of hard-to-reach, difficult for the specified displacement of the source structures, incompletely welded seams with narrow edges, etc.

Claims (1)

A method for assessing the depth of a defect, which consists in comparing images of a defect in two images with different different geometry of transmission, characterized in that the first and second images are taken without changing the direction of transmission at a different distance from the radiation source to the controlled product, after which the dimensions of the images of the defect are measured on both images and on the basis of the measurements and the known geometry of the translucent conduct a calculated assessment of the depth of the defect according to the formula

where h is the estimated depth of the defect,
f ₁ and f ₂ - focal lengths at two positions of the radiation source,
L ₁ and L ₂ - the half-width of the image of the defect for two positions of the radiation source.