WO2008079100A1

WO2008079100A1 - Method and apparatus for detecting and assessing parameters of discontinuities in the surface layer of metal products

Info

Publication number: WO2008079100A1
Application number: PCT/UA2007/000015
Authority: WO
Inventors: Sergiy A. Malynka; Dmytro V. Goriachkin; Oleksandr V. Kalashov; Volodymyr L. Nayda; Igor V. Goriachkin
Original assignee: Tovarystvo Z Obmezhenoyu Vidpovidalnistyu 'lazerna Magnito-Akustyka'
Current assignee: Tovarystvo Z Obmezhenoyu Vidpovidalnistyu 'lazerna Magnito-Akustyka'
Priority date: 2006-12-25
Filing date: 2007-03-01
Publication date: 2008-07-03
Anticipated expiration: 2009-06-25
Also published as: UA79416C2

Abstract

The invention relates to non-destructive testing of the surface layer condition in metal products, particularly non-ferromagnetic products. It can be used for detecting and assessing the parameters of discontinuities in the surface layer of the rolled sheet and strip, sections, tubes and pipes, forgings, ingots, including continuously cast products at their normal and high temperature up to 1200°C. The essence of the invention is in the following: a surface area of the metal product that contains a discontinuity is irradiated with an ultrasonic Rayleigh wave, the actual amplitude is measured of the Rayleigh wave that interacts with the discontinuity, the ultrasonic wave transformed by the discontinuity is recorded, a decision on the discontinuity parameters is taken according to the actual amplitude of the Rayleigh wave and to the amplitude and polarization of the transformed ultrasonic wave. The apparatus embodying this method is comprised of EMA transducers, amplifiers, an informative parameters measuring unit, a decision-making unit, a pulse laser for exciting Rayleigh waves, a light conduit that forwards the laser radiation into the EMA operating zone of the transducers, a control unit, while it additionally contains a Rayleigh wave receiver. Technical result: upgraded sensitivity, reliability, effectiveness and throughput during quality inspection of metal products, extended fields of application.

Description

METHOD AND APPARATUS FOR DETECTING AND ASSESSING PARAMETERS OF DISCONTINUITIES IN THE SURFACE LAYER OF METAL

PRODUCTS

Field of the Invention

The invention relates to the field of non-destructive testing of the surface layer condition in metal products, in particular to detecting and assessing parameters of discontinuities in the surface layer thereof, especially in non-ferromagnetic articles. The invention can be used for detecting and diagnostics of discontinuities in the surface layer of rolled sheet and strip, tubes and. pipes, forgings, ingots, including continuously cast ingots, at normal or high temperatures up to 1200 ⁰C under commercial-scale production conditions.

Background of the Invention

Known in the art is a method and apparatus for ultrasonic diagnostics of discontinuities in the surface layer, including those in the rolled stock (US, 5894092), that includes exciting in the product of Rayleigh waves, in particular with a laser, measuring the time during which the Rayleigh waves travel from the excitation place to the receiver, recalculating the measured time to the Rayleigh waves velocity. According to this solution the time-to-velocity recalculation is performed for several Rayleigh wave frequencies while the decision concerning the parameters of the detected discontinuities is taken according to the value of the Rayleigh waves velocity.

A disadvantage of the known method and apparatus for its realization, is the impossibility of quantifying the defects on the surface layer area being subjected to diagnostics. Besides, it is also impossible to assess the individual parameters of the defects within a group of defects.

Patent RU 2262689 discloses a method for detecting discontinuities in the surface layer of metal products that allows to detect and assess the parameters of discontinuities. The method includes irradiating with a Rayleigh ultrasonic wave a surface area of the metal product being controlled, recording the ultrasonic wave being transformed by the discontinuity, superposing a magnetic field on that surface area and recording of the magnetic flux scattered by the discontinuity and modulated by the ultrasonic wave.

Based on the known method, a decision on the parameters of the detected discontinuity, namely, on the depth of the discontinuity, for example, of a crack, was made according to the amplitude of the transformed ultrasonic wave, and concerning the opening of the crack - according to the determined depth of the

^; crack and to the amplitude of the determined component of the scattered magnetic flux. Known from the same source of information is an apparatus for realization of the known method that includes electromagnetoacoustic (EMA) transducers, amplifiers, an informative parameters measuring unit, a defectoscope, a decision- making unit, a control unit, a pulsed laser generator for Rayleigh waves excitation, and a light conduit that forwards the laser radiation into the EMA transducers operating zone..

The feasibility of detecting discontinuities in the surface layer of ferromagnetic metal products using the known method and apparatus was based on two factors.

It is known that the amplitude of a transformed wave is duly non-linearly related to the crack depth and is proportional to the Rayleigh wave amplitude [Physical grounds for applying Rayleigh and Lamb ultrasonic waves in technology / IA

Viktorov - Moscow: "Nauka" Publishers, 1966, p.72, In Russian]. It is also known that a static magnetic stray flux of a crack is a function of both its depth and its opening [Nondestructive Testing. In 5 vol. Vol. 3. Electromagnetic Testing:

Practical handbook / V. G. Gerasimov, A. D. Pokrovsky, V. V. Sukhorukov; Edited by V. V. Sukhorukov - Moscow.: "Vysshaya Shkola" Publishers, 1992, p.101-103,

In Russian]. If a crack is crossed by the Rayleigh wave this initiates oscillations of the crack walls that in its turn leads to modulations of its opening and, hence, of the stray flux. Thus, the Rayleigh wave modulates the stray flux of the crack that results in the appearance of a variable component in the latter. Therefore the amplitude of the variable component in the stray flux of a crack is a function of the crack depth and opening and of the Rayleigh wave amplitude.

With due regard of these known dependencies it becomes obvious that the realization of the known method and apparatus is possible when the amplitude value of the Rayleigh wave applied for irradiating the surface area of the metal product being subjected to diagnostics is known and is the same as was used earlier during the setting up of the calibration charts, hence, it has a nominal value.

At any method of exciting the Rayleigh ultrasonic wave its amplitude in the surface layer of the tested object (TO) will depend on the condition of the surface area being used for exciting or introducing the Rayleigh waves, as well as on the condition of the surface area that is being crossed by the Rayleigh wave on its way from the site of its excitation or introduction to the place where the discontinuity is located. Hence, when the diagnostics are performed under the commercial production conditions when the condition of the surface area being tested is generally not determined the amplitude of the Rayleigh wave that interacts with the discontinuity has fortuitous fluctuations, and this indicates the appearance of a noncontrollable error in the assessment of the discontinuity parameters, particularly of the crack depth.

The use of conventional methods and apparatuses also becomes practically impossible for metal product diagnostics carried out in commercial-scale production when impurities that are present on the surface of metal products (such as scale or technological lubricants) impede the excitation of the Rayleigh waves.

It should be also noted that the throughput of such conventional method and apparatus _, is also rather low when the indicatrix orientation of lengthy discontinuities, such as cracks, is to be determined. The above disadvantages preclude an adequately effective use of the Rayleigh wave irradiation of the surface layer of metal products, especially at temperatures exceeding the Curie point of the metal product material, they do not allow to perform diagnostics of nonferromagnetic metal products, reduce the sensitivity and operating rate of the diagnostics, and lower the reliability of the defect parameters evaluation, especially under commercial-scale testing conditions.

SUMMARY OF THE INVENTION The object of the invention is to develop such a method of detecting and assessing the parameters of discontinuities in the surface layer of metal products, particularly non-ferromagnetic products, and an apparatus for realizing the method, wherein due to taking into account the error related to fluctuations ofthe Rayleigh wave amplitude it becomes possible to upgrade the sensitivity and reliability of quality inspection of metal products, particularly of non-ferromagnetic products, to detect and assess the parameters of discontinuities, including cracks, with a high degree of reliability, particularly under commercial-scale production conditions.

The object set is solved by applying a method of detecting and assessing the parameters of discontinuities in the surface layer of metal products that particularly includes irradiating with an ultrasonic Rayleigh wave a surface area of the metal product that is subjected to diagnostics, recording the ultrasonic wave transformed by a discontinuity which becomes the basis for taking a decision on the parameters of the detected discontinuity, while according to the invention, measurement is performed of the Rayley wave actual amplitude applied for discontinuity irradiation, the difference between the measurement result and the nominal amplitude value is evaluated, and the decision is made on the parameters of the detected discontinuity taking into consideration that difference.

The use in the method being proposed of Rayleigh wave amplitude measurement directly on the object to be inspected, and the use of this amplitude together with the amplitude and polarization of the transformed ultrasonic wave while taking a decision on the discontinuity parameters allows to eliminate the error in assessing the discontinuity parameters related to the influence of the conditions under which the Rayleigh wave is being excited and propagated, because the decision is being taken using the actual amplitude value of the Rayleigh wave that interacts with the discontinuity, thus allowing to upgrade the reliability, sensitivity and effectiveness of the diagnostics of metal products, including non-ferromagnetic products, especially under commercial production conditions.

The amplitude of a transformed ultrasonic wave, for example, when the Rayleigh wave is transformed on a crack, has a known functional dependence on the crack depth being simultaneously proportional to the Rayleigh wave amplitude [Physical grounds for applying Rayleigh and Lamb ultrasonic waves in technology / I. A. Viktorov - Moscow: "Nauka" Publishers, 1966, p.72, In Russian]. When a previously developed calibration chart is used the proposed technical solution allows to determine the crack depth according to the amplitude of the Rayleigh wave and of the transformed wave. In such case the transformed volume wave, for example, a cross wave, is polarized perpendicularly to the area of the crack walls, hence the proposed method of polarizing the transformed volume wave simultaneously allows determining the crack orientation.

According to one of the preferred embodyments of the proposed method, preliminary to irradiating with the ultrasonic Rayleigh wave a surface area of the metal product being subjected to inspection, the metal product surface can be cleaned in the place of irradiation, while it is reasonable to perform such cleaning by means of laser irradiation.

The task is also solved^" by the apparatus for detecting and assessing the parameters of discontinuities in the surface layer of metal products, particularly non-ferromagnetic, that contains electromagnetoacoustic transducers, amplifiers, an informative parameters measuring unit connected to a decision-making unit, a control unit, a pulse laser for Rayleigh wave excitation and a light conduit that forwards the laser radiation into the operating zone of the electromagnetoacoustic transducers, containing, according to the invention, at least one Rayleigh wave receiver whose output signal is forwarded to the decision making unit via the informative parameters measuring unit.

In a preferable embodyment of the invention such an apparatus can include at least one unit for moving the laser beam over the metal product surface.

The additional use of a unit for moving the laser beam over the metal product surface allows moving the the Rayleigh wave excitation point, thus changing the direction of irradiating the discontinuity that is beneficial for upgrading the reliability and throughput during the diagnostics of arbitrarily oriented discontinuities.

Besides it is reasonable to use one more laser in the invented apparatus for removing impurities off the metal product surface.

The use of one more laser, for example a solid-state Nd-YAG laser that operates in a pulse free generation mode allows, in case of impurities presence on the surface being diagnosed that interfere with the excitation of the Rayleigh wave, to influence the impurity by the additional laser irradiation before the laser irradiation initiates the excitation of the Rayleigh wave. If impurities are present on the surface area, being irradiated, for example a layer of scale or technological lubricant, the radiation of the additional laser is absorbed by the impurities. In such case the impurity is warmed up. At a certain power and duration of the additional laser radiation the temperature of the impurity reaches its evaporation point and the impurity is evaporated off the surface area being inspected. The laser beam intended for Rayleigh wave excitation falls on the surface area of the metal product that is free of the impurities and excites the Rayleigh wave.

BRIEF DESCRIPTION OF DRAWINGS

The essence of the invention will be further described in more detail with reference to the accompanying drawings in which:

Fig.1 is a block diagram of the apparatus that realizes the method according to the invention; Fig.2 is a block diagram of the preferable variant of the apparatus that additionally contains a unit for moving the laser beam over the metal product surface. Fig.3 is a block diagram of the preferable variant of the apparatus that additionally contains another laser for removing impurities off the metal product surface.

PREFERRED EMBODIMENT OF THE INVENTION

As it is shown in the drawings, the proposed apparatus that provides a most effective realization of the invented method, includes an EMA unit 1 of transducers that provide recording of the signals generated by discontinuities during the interaction with the Rayleigh wave. The output signals of unit 1, via unit 2 of amplifiers that amplify the EMA signals of the transducers, are forwarded into the informative parameters measuring unit 3. The proposed apparatus also includes a decision making unit 4, laser 5 that excites Rayleigh waves in the surface layer of the tested object (TO), light conduit 6 that directs the radiation of laser 5 onto the TO surface, control unit 7 and Rayleigh wave receiver 8 that provides measuring of the actual amplitude of the Rayleigh wave that interacts with the discontinuity.

As EMA transducers can be used, for example, EMA transducers for the cross wave [Instruments for nondestructive testing of materials and articles. Reference manual. In 2 vol. Edited by V.V. Kliuyev. Vol.2 Ultrasonic testing - Moscow: Mashinostroyeniye Publishers, 1976, p.197-199, in Russian].

As amplifier 2 can be used any variable voltage amplifier with a corresponding operating frequency range, for example, within 0.5...3.0 MHz. Unit 3 for measuring informative parameters can be- comprised of a measuring device that allows amplitude measuring of the output signal of the amplifiers. It may consist, for example, of a 12-bit analog-to-digital transducer with a 25 MHz discretization frequency.

The decision-making unit 4 may consist of any electronic computing device, for example, of a computer having an adequate operating rate and memory volume that is able to provide: - storage of the previously set up chart that interrelates the amplitude of the ultrasonic wave transformed, for example, by a crack, with the depth, correspondingly, of the crack taking into regard the nominal value of the amplitude of the Rayleigh wave that correspondingly interacts with the crack;

- calculation of the deviation coefficient of the actual amplitude value of the Rayleigh wave that interacts with a discontinuity, for example, with a crack, that passes via amplifier 2 and informative parameters measuring unit 3 from Rayleigh wave receiver 8 to the corresponding inlet of decision-making unit 4, from its nominal value;

- adjustment of the amplitude value of the wave being currently transformed on the available discontinuity and passing via amplifier 2 and informative parameters measuring unit 3 from the EMA of receiver 1 of the transformed wave to the corresponding inlet of the decision-making unit 4 by using the deviation coefficient of the Rayleigh wave actual amplitude value from its nominal value;

- using the stored chart, to determine according to the adjusted amplitude of the wave currently transformed by the present discontinuity, for example, by a crack, the actual depth, correspondingly, of the crack.

As laser 5 that provides Rayleigh waves excitation in the TO surface layer it is preferably to use a pulse solid state Nd-YAG laser in the modulated Q-factor mode, with pulse energy of 200...400 mJ and duration of 10...15 ns.

Light conduit 6 that directs the laser 5 beam onto the TO surface can be comprised, for example, of a rigid mirror-lens light conduit of an adequate length.

Control unit 7 can consist of an electronic device, such as a controller that is programmable and is able to form signals for controlling the decision-making unit 4 and laser 5 to maintain the sequence of their operation required for the device functioning. As the Rayleigh wave receiver 8 intended for measuring the actual amplitude of the Rayleigh wave that interacts with a discontinuity can be preferably used, for example, an EMA transducer of the Rayleigh wave [Instruments for nondestructive testing of materials and articles. Reference manual. In 2 vol. Edited by V.V. Kliuyev. Vol.2 Ultrasonic testing - Moscow: Mashinostroyeniye Publishers, 1976, p.197-199, In Russian] or [US 5894092], or an optical receiver, for example, an interferometric laser receiver [Chabanov V.E. Laser ultrasonic testing of materials. - Leningrad. : Leningrad University Publishers, 1986, p.148, In Russian].

An apparatus according to the invention operates as follows.

To excite a Rayleigh wave emission, pulses of laser 5 are directed via light conduit 6 onto the TO surface area. An intensive Rayleigh wave is generated during the interaction of the emission pulse of laser 5 that operates in the modulated Q-factor duty with the TO surface. The Rayleigh wave excited in such manner is distributed over the TO surface, and its amplitude is measured by means of receiver 8 whose signal, after being amplified in unit 2 and after measuring the informative parameters in unit 3, is fed to the decision-making unit 4. When the excited Rayleigh wave that is found on the extention way interacts with a discontinuity (for example, a crack) it gets partially transformed to volumetric ultrasonic waves that are recorded by EMA transducers 1 whose output signals, after being amplified by amplifiers 2 and after measuring the informative parameters in unit 3, are fed to the decision-making unit 4 where a decision is taken as to the discontinuity parameters. The control unit 7 provides the necessary operating sequence of laser 5 and of the decision-making unit 4.

In another alternative embodyment of the invention that is illustrated by Fig.2 the apparatus according to the invention additionally contains unit 9 for moving the laser beam over the TO surface. In the process of diagnostics unit 9 effects changing of the Rayleigh wave excitation point so that the Rayleigh wave crosses the TO surface area being inspected, in a direction that differs from the previous one while a decision is being made in unit 4 taking into consideration the direction in which the Rayleigh wave crosses the TO area being inspected. Unit 9 for moving the laser beam over the TO surface can be preferably made as an optical device that provides the necessary range of moving the laser beam over the TO surface, for example, as a mirror galvanometer or acoustooptical deflector.

In another alternative embodyment that is shown in Fig.3 the free-generation emission pulses of an additional laser 10 are directed via light conduit 6 onto the TO surface area that is to be irradiated by laser 5 for exciting a Rayleigh wave. In case the TO surface area contains impurities the latter absorbs the emission of laser 10 and as a result it gets warmed up and evaporated. Onto the thus cleaned TO surface area the emission pulses of laser 5 that operates in the modulated Q- factor mode are directed via the light conduit 6. During the interaction between the emission pulse of laser 5 and the TO surface an intensive Rayleigh wave is generated.

Laser 10 that provides cleaning of the TO surface area can consist of, for example, a pulse solid-state Nd-YAG laser operating in the free generation mode with a pulse energy of 5...15 J and duration of 1...5 ms.

The method and apparatus of this invention have proved their practical effectiveness especially at high temperatures under the commercial scale production conditions because the proposed technical solutions eliminate errors in the assessment of discontinuities parameters, upgrade the reliability and throughput of inspecting the surface layer of metal products, particularly non- ferromagnetic products, for the presence of, in particular, arbitrarily oriented discontinuities.

Claims

CLAIMS:

1. Method for detecting and assessing the parameters of discontinuities in the surface layer of metal products, particularly non-ferromagnetic products, that includes irradiating with an ultrasonic Rayleigh wave a surface area of the metal product being subjected to diagnostics, recording the ultrasonic wave transformed by the discontinuity, decision making on the basis of the said recording on the parameters of the detected discontinuity, wherein the actual amplitude is measured of the Rayleigh wave by which the discontinuity is irradiated, the difference between the measurement result and the nominal value of the Rayleigh wave amplitude is evaluated, and a decision is made on the parameters of the detected discontinuity taking into consideration that difference.

2. Method according to claim 1, wherein preliminary to irradiating with an ultrasonic Rayleigh wave of a surface area of the metal product being subjected to diagnostics the metal product surface in the place of irradiation is cleaned.

3. Method according to claim 2, wherein cleaning is effected by means of a laser beam.

4. Apparatus for detecting and assessing the parameters of discontinuities in the surface layer of metal products, particularly nonferromagnetic products, that includes electromagnetoacoustic transducers, amplifiers, an informative parameters measuring unit connected with the decision-making unit, a control unit, a pulse laser for exciting a Rayleigh wave, and a light conduit that forwards the laser beam into the operating zone of the electromagnetoacoustic transducers, wherein is included at least one Rayleigh waves receiver whose ^' output signal is passed via the amplifier and the informative parameters measuring unit to the decision-making unit.

5. Apparatus according to claim 4, wherein at least one unit for moving the laser beam over the metal product surface is included.

6. Apparatus according to claim 4, wherein one more laser is additionally included for removing impurities off the surface of the metal product.