RU2392609C1 - Method for estimate of defect size in transmission direction - Google Patents

Abstract

FIELD: measurement equipment. ^ SUBSTANCE: usage for estimate of defect size in the transmission direction. One compares images of reference and actual defects radiographed on the same picture. Onto the controlled weld joint one sets a reference imitator with a wedge-shaped extended groove with a depth (ödim.d.) equal to the maximum allowable actual defect depth. After the picture has been taken one measures the defect images width, measures and compares the contrast of the image of the actual defect detected (öDr.d.) and contrast of the image of the wedge-shaped reference groove (öDim.d.) on the length of its image where the measured groove width is equal to the width of the actual defect image; then one estimates the defect size in the transmission direction (öds.d.) according to the following expression öds.d.=[(öDr.d.)/(öDim.d.)]ödim.d. ^ EFFECT: improved reliability and precision of the defect size estimate in the transmission direction. ^ 2 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 size of a defect in the direction of transmission, based on a visual comparison of the optical image densities of the grooves of the reference simulator (reference defects) and the detected (real) defects of the controlled weld (see Rumyantsev S.V. Radiation defectoscopy. M .: Atomizdat 1974, pp. 262-263).

Closest to the technical nature of the claimed method is a method for assessing the size of a defect in the direction of transmission, which issued a patent of the Russian Federation for invention No. 2243541 (published December 27, 2004, bulletin No. 36), which is adopted as a prototype. The specified method is based on the installation on a controlled welded joint of a simulator-standard with grooves of different widths, but the same depth, equal to the maximum permissible depth of a real defect, and after taking a picture of measurements and comparing the optical densities or contrasts of the images of the revealed real defect and the reference groove closest to a real defect in the width of the image in the picture.

The task to which the invention is directed is to reduce the complexity of the method, increase the reliability and accuracy of estimating the size of the defect in the direction of transmission.

The problem is solved due to the fact that in the method for assessing the size of a defect in the transillumination direction, which consists in comparing images of reference and real defects radiographed onto a single image, a reference simulator with a wedge-shaped extended groove with a depth equal to the maximum permissible depth of a real defect is installed on a controlled welded joint and after the image is taken, measurements are taken of the width of the images of defects, measurements and comparison of the contrast of the image of the detected real defect and the contrast of CONTROL wedge grooves on the reference length of its image, wherein the groove width is metered by the real defect image width.

The invention is illustrated by a figure and a graph. Figure 1 shows a reference simulator with a wedge-shaped groove with a recommended length l ^wedge _kan = 40-60 mm and a width of disclosure at the base of the wedge b ^{wedge (main)} _kan = 6-12 mm. The specified longer and with a larger opening size groove is used in the control of thick-walled products (d≥40-80 mm). The depth of the groove Δd ^wedge _kan = d _et equal to the maximum allowable size of the defect in the direction of transmission d ^ave. . The condition d _et = Δd ^wedge _kan ≤d must be fulfilled ^. .

Figure 2 presents the experimentally obtained: the dependence of the contrast ΔD of the image of the rectangular groove on the width of the groove b = b ^pr _channel (curve 1) and the dependence of the contrast ΔD of the image of the wedge-shaped groove on its measured width b = b ^wedge _channel at a given distance from the top of the wedge, reflecting a change in ΔD along the length of the groove image (curve 2) at the same background optical density D _f = 2.4 at the locations of the images of rectangular and wedge-shaped grooves (the value of D _{f was} measured on opposite sides of the image defect and averaged). Translucent steel thickness d = 40 mm, voltage on the x-ray tube U _r.t. = 400 kV, Structurix-D5 radiographic film, “source-product” distance ƒ = 800 mm, the depth of the rectangular and wedge-shaped grooves radiographed per image is the same and is Δd = 2 mm. The dashed line in figure 2 shows the boundary of the region of unreliable estimates of _Δd real defects (lack of penetration) corresponding to the condition b _and <K, where b _and is the width of the image of the defect, K is the required sensitivity of control.

With the image width of a real defect (lack of penetration) b _and <K, an estimate of its size _Δd no picture taken.

As can be seen from the graph of figure 2, when Δd ^pr _kan = Δd ^wedge _kan and D _f = const the difference in the dependencies ΔD ^pr _kan = ƒ (b) and ΔD ^wedge _kan = ƒ (b) is insignificant. Accordingly, in practical work, this difference can be neglected and used to evaluate the size of the defect in the direction of transmission instead of a simulator with a set of rectangular grooves of different widths, a simulator with a wedge-shaped groove.

The inventive method was evaluated in the direction of transmission of defects of the type of simulated imperfections located on the surface of a steel sample with a thickness of d = 40 mm from the side of the radiation source. Translucence was carried out by an MG-420 x-ray apparatus at a voltage on the x-ray tube U _r.t. = 400 kV from a focal length of 800 mm onto a radiographic film of type D5. A transmission pattern from the simulated defect simulator installed standard-tapered groove depth Δd ^wedge _kan = 2 mm. The sensitivity of the control according to the wire standard according to GOST 7512-82 was K = ⌀ _min. ^Et. = 0.5 mm. The obtained photographs were measured using a Helling-301 digital densitometer. The contrasts ΔD were determined in accordance with the expression ΔD = DD _f , where D is the optical density in the center of the image of the reference or real defect, D _f = (D _f1 + D _f2 ) / 2 is the optical density of the background, measured and averaged on both opposite sides of the image (near the edge of the image of the defect).

The measurement results are as follows:

for simulated lack of penetration 1 with a width of b ⁿ ₁ = 2 mm - ΔD ⁿ ₁ = 2.51- (2.44 + 2.43) / 2 = 0.075;

for simulated lack of penetration 2 with a width of b ⁿ ₂ = 5 mm - ΔD ⁿ ₂ = 2.55- (2.45 + 2.44) / 2 = 0.105;

for a wedge-shaped reference groove in a place where the width of its image b ^wedge _kan = 2 mm

ΔD ^wedge _2mm = 2.43- (2.36 + 2.35) / 2 = 0.075;

for a wedge-shaped reference groove in a place where the width of its image b ^wedge _kan = 5 mm

ΔD ^wedge _5mm = 2.46- (2.37 + 2.35) 72 = 0.100.

Since the background optical density in the regions where the images of the compared reference and real defects are located on the image is almost the same: D _f ≅2.4, we can assume Δd ~ ΔD and

Δd _s.d. = [(ΔD _R.D. ) / (ΔD _E.D. )] Δd _E.D.

Accordingly, we obtain the following calculated values of the simulated lack of penetration depth: Δd ⁿ ₁ = 2.0 mm; Δd ⁿ ₂ = 2.1 mm, which practically (with an acceptable small error δ = 5%) coincide with the actual depth of simulated defects Δd ⁿ _{1; 2} = 2.0 mm.

Etalon with a wedge groove in comparison with a sipe standard set of rectangular grooves of different widths, rather than several discrete allows ΔD contrast values at certain widths grooves b = b ^forth _CAD receiving continuous spectrum ΔD = ƒ (b) values. In addition, ΔD measurements are simplified. The use of one groove instead of a whole set of grooves prevents the distortion of images of reference defects compared with real ones, which is observed when installing a standard with several rectangular grooves, for example, when radiographing ring welded joints of small diameter pipelines. All this increases the reliability and accuracy and reduces the complexity of evaluating the size of defects in the direction of transmission.

The claimed method is applicable for the transmission of controlled products not only on radiographic film, but also on other radiation defectors, for example, phosphorus storage plates used in digital radiography, where the size of a defect in the direction of transmission can be estimated by comparing the measured degree of darkening (level gray) or contrast (the difference between the measured value of the defect darkening level and the background) of images of reference and real defects on a computer screen.

Since the contrast ΔD depends on the optical density of the background D _f when evaluating the size Δd _s.d. comparing ΔD _s.d. and ΔD _et.d. the condition of equality of the value of D _f in the regions where the compared images of reference and real defects should be located should be satisfied, which is ensured by the corresponding equality of the transmitted thicknesses: equality of the height of the weld and the thickness of the reference simulator, the use of compensating linings and overlays. Inability to fulfill the conditions of ΔD _f.r.d. = ΔD _ph. instead of comparing the contrasts ΔD = ƒ (ΔD _f ), a comparison is made of values independent of the background optical density - the given contrasts ΔD / γ _D ≠ ƒ (ΔD _f ), where γ _D is the contrast coefficient of the radiographic film at an optical density of D = D _f (similar taking into account the dependence of the degree of darkening of the image of the defect on the background value should also be carried out when using phosphorus storage plates).

Claims (1)

A method for assessing the size of a defect in the transillumination direction, which consists in comparing images of reference and real defects radiographed onto a single image, characterized in that a reference simulator with a wedge-shaped extended groove with a depth (Δd _et.d. ) equal to the maximum allowable depth of the real the defect and after the image is taken, measure the width of the images of the defects, measure and compare the image contrast of the identified real defect (ΔD _s.d. ) and the image contrast of the wedge oval reference groove (ΔD _et.d. ) along the length of its image, where the measured width of the groove is equal to the width of the image of the real defect, after which the size of the defect is measured in the direction of transmission (Δd _s.d. ) according to the following expression: Δd _s.d. = [(ΔD _s.d. ) / (ΔD _s.d. )] Δd _s.d. .

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