RU2556336C1 - Measurement of contact layer depth at ultrasound flaw detection - Google Patents

Abstract

FIELD: instrumentation.

SUBSTANCE: beam of ultrasound oscillations is irradiated to piezoelectric transducer prism. Longitudinal oscillations reflected from object contact surface by extra piezo-plate. This method allows measurement of time-shift of reflected oscillations is measured to define thereof the layer depth.

EFFECT: possibility to measure contact layer depth to add to validity of ultrasound control.

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Description

The invention relates to the field of acoustic non-destructive testing methods and can be used to increase the reliability of ultrasonic testing of various products.

Acoustic contact between the piezoelectric transducer and the control object is provided with a thin layer of contact liquid. In the process of moving the piezoelectric transducers through the controlled product, especially at significant scanning speeds (for example, when monitoring the rails with a flaw detector car), the piezoelectric transducer may detach from the surface of the controlled product due to a change in the thickness of the contact liquid layer between the working surface of the piezoelectric transducer and the controlled product.

To monitor the quality of the acoustic contact during the scanning process, various methods are used based on the analysis of bottom signals, signals from the structural elements of piezoelectric transducers, low-frequency oscillations emitted by an additional device (ed. Certificate No. 574668, bull. Image No. 36, 1977 ), as well as taking into account the magnitude of the average level of structural interference (ed. certificate. No. 1753405, bull. Inventory No. 28, 1992).

A known method of controlling the quality of acoustic contact during ultrasonic inspection, in which two piezoelectric plates are used - the primary and secondary. Ultrasonic vibrations emitted by the main plate of the transducer, mirrored from the working surface of the prism of the inclined transducer, take an additional plate. Moreover, the quality of the acoustic contact is judged by the phase value of the received oscillations (US Pat. RU 2141653).

None of the above methods addressed the issue of measuring the thickness of the liquid contact layer, which, in turn, affects both the accuracy of measuring the coordinates of defects [1] and the sensitivity of the control [1], [2].

From the literature [1] it is known about calculating the time delay of ultrasonic waves in the contact layer of a liquid, as well as about an experimental study on measuring the delay time in contact layers, during which two identical transducers with a dip angle of 24 ° were mounted on a steel sample with a pre-polished surface . The time delay in the layer was determined by the difference between the measured values obtained by installing one of the transducers on the sample, with gaskets of known thickness and without them, while ensuring the immobility of the second transducer. The main disadvantage of this method of measurement is the impossibility of its use when moving the transducers relative to the object of control directly in the process of ultrasonic inspection.

The problem solved by the present invention is the development of a method to improve the reliability of ultrasonic testing of various products.

The problem is solved due to the fact that in the proposed method, as well as in the known [1], a beam of ultrasonic vibrations is emitted into the prism of an inclined ultrasonic transducer. But, in contrast to the known method [1], in which two statically located transducers are used and past vibrations are recorded, in the proposed method, vibrations reflected from the contact surface of the controlled article are recorded using an additional plate on the prism of the piezoelectric transducer. Thus, the proposed method can be applied when moving the transducer relative to the control object in the process of ultrasonic inspection.

In FIG. 1 and FIG. 2 (enlarged) presents a diagram of the implementation of the proposed method. This method is based on measuring the temporal displacement of the signal, which is directly proportional to the thickness of the liquid contact layer 1 between the working surface 2 of the prism 3 of the piezoelectric transducer and the surface 4 of the controlled product. Using the main piezoelectric plate 5 mounted on the prism 3 of the piezoelectric transducer at an angle β to the working surface 2 and excited by a flaw detector (not shown in Fig. 1 and Fig. 2), a beam of pulsed ultrasonic vibrations is emitted, which penetrate through the layer 1 of contact liquid into the controlled product , and part of the vibrations reflected from the surface 4 of the product is recorded using an additional plate 6.

Depending on the change in the thickness of the contact layer 1 between the working surface 2 of the converter and the surface 4 of the controlled product, the temporal displacement of the signals received by the additional plate 6 will be different, directly proportional to the thickness of the contact layer 1 between the working surface 2 of the prism 3 of the converter and the surface 4 of the controlled products.

In the case of a negligible thickness H of the contact fluid layer 1, the temporal shift Δt of the signal is also negligible. This displacement is determined and subsequent measurements of the time displacement are carried out relative to it. The temporary displacement of the signal occurs due to the wave propagating the distance AB from the contact surface 2 of the prism 3 to the surface 4 of the controlled product and vice versa BD at the corresponding angle α minus the reduction in the propagation of the DC distance in the prism 2 of the piezoelectric transducer.

where: N is the thickness of the layer of contacting liquid;

Δt is the temporary displacement;

C ₁ is the wave propagation velocity in the contact fluid;

C ₂ - the propagation velocity of a longitudinal wave in the prism of the transducer;

β is the angle of the prism;

α is the angle of entry into the contact fluid.

Based on this, determine the thickness of the contact layer:

So, for example, for a plexiglass prism (C ₂ = 2.67 mm / μs) with an angle β = 40 ° and water as a contact liquid (C ₁ = 1.59 mm / μs) with a signal bias of 0.2 μs the thickness of the contact layer is 0.18 mm.

Taking into account the known influence of the thickness of the contact liquid layer on the sensitivity of ultrasonic testing and on the accuracy of measuring the coordinates of the reflectors, it is possible to make appropriate corrections to the measurement results during ultrasonic testing, which will increase the reliability of the control results.

Bibliography

1. Weinstock II, Lerner B.C. The effect of delay in contact layers on the accuracy of measuring the propagation time of ultrasound. The journal Defectoscopy, 1982, No. 11, p. 68-72.

2. Mogilner L.Yu., Sakhranov A.V., Urman N.S. The passage of a limited ultrasonic beam through a flat layer of contacting liquid with an inclined incidence and a pulsed radiation mode. The journal Defectoscopy, 1986, No. 1, pp. 70-80.

Claims (1)

A method for measuring the thickness of the liquid contact layer during ultrasonic inspection, which consists in emitting a beam of ultrasonic vibrations into the prism of the piezoelectric transducer, receiving longitudinal vibrations reflected from the contact surface of the test object by an additional piezoelectric plate, characterized in that the temporal displacement of the reflected vibrations is measured and judged by its value layer thickness.

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