METHOD FOR ASSESSING INCLUSIVE LEVEL IN STEEL TUBES USING HIGH FREQUENCY TRANSDUCER IN THE AUTOMATIC ULTRASOUND INSPECTION

Abstract

The present invention refers to a method for assessing the inclusive level in steel tubes using high frequency transducer (2) in the automatic ultrasound inspection, characterized in that it comprises the steps of: transporting a tube (1) through a bed (10) to an acoustic coupling unit (3); coupling the acoustic coupling unit (3) with the tube (1) through a radial movement (16) of transducer approximation (2) regarding the tube external surface (1); detecting inclusions information in at least one sweep region (11) along the length of the tube (1); sending the inclusions information to a sonic emitting and receiving unit (9); determining an inclusions index for the tube (1) or specific region; continuing the tube transportation (1) in an inspection line; and giving continuity to the inspection cycle with the next tube (1) in the production flow.

Claims

1. A method for assessing the inclusive level in steel tubes using high frequency transducer in the automatic ultrasonic inspection, wherein the steps of: transporting a tube through a bed to an acoustic coupling unit; coupling the acoustic coupling unit with the tube (1) through a radial movement of transducer approximation (2) regarding the tube external surface; detecting inclusions information in at least one sweep region the length of the tube; sending the inclusions information to a sonic emitting and receiving unit; determining an inclusions index to the tube or specific region; continuing the tube transportation in an inspection line; and giving continuity to the inspection cycle with the next tube in the production flow.

2. The method according to claim 1, wherein the speed of the tube transportation through the bed may be set to ensure the stabilization of the acoustic coupling in the ends and along the length of the tube.

3. The method according to claim 1, wherein the detection of inclusions information is performed by outputting a sonic beam by an ultrasonic transducer.

4. The method according to claim 1, wherein the ultrasonic transducer performs the detection of inclusions information operating a nominal frequency preferably of 15 MHz.

5. The method according to claim 1, wherein the sweep region is a specific region or a helical trajectory along the whole length of the tube.

6. The method according to claim 1, wherein the inclusions information is defined by the number of sonic pulses with signals with amplitudes above the monitoring threshold of inclusions.

7. The method according to claim 1, wherein the emitting and receiving unit of sonic pulses determines the inclusions index for the tube based on the amplitudes of the signals of inclusions with amplitudes above the monitoring threshold of the signals of inclusions.

8. The method according to claim 1, wherein the emitting and receiving unit of sonic pulses determines the inclusions index through the relation of the sonic pulses sum with signals above the monitoring threshold of the inclusions indications by summing the total sonic pulses emitted in the tested length.

9. The method according to claim 1, wherein the sum of the sonic pulses with signals above the monitoring threshold (12) of the inclusions indications by summing the total sonic pulses emitted in the tested length is reached through the formula: $\mathrm{FI}\left[\%\right]=100\times {\left[A\times \frac{N_{\mathrm{Ind}.}}{N_{\mathrm{Pulsos}}}\right]}_{\mathrm{FI}\left[\%\right]=100\times \left[A\times \frac{N_{\mathrm{Ind}.}}{N_{\mathrm{Pulsos}}}\right]}$ wherein: FI=Impurity factor (Index of inclusions); N.sub.Pulsos=Total amount of pulses emitted in the volume tested; N.sub.Ind=Amount of signals with amplitudes above the monitoring threshold; and A=Multiplier factor for signals with amplitudes above the monitoring threshold.

10. The method according to claim 1, wherein the sample sensibility is defined using artificial reflectors of type “Flat bottom hole” machined in the internal surface of the tube, which must be machined in reference tube with the same nominal dimensions and acoustic characteristics of the material to be tested.

11. The method according to claim 1, wherein the individual results of the inclusion indices of the tubes are correlated with the processing conditions in the steel manufacturing stage, representing a tool for monitoring the degree of purity of steel and continuous improvement in the steelmaking process.

12. The method according to claim 1, wherein the individual results of the inclusion indices of the tubes correlated with the results of the corrosion tests required by manufacturing and supply standards of the tubes, representing a tool for monitoring and improving the corrosion resistance of the steel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be then more detailed described.

[0022] FIG. 1—according to the invention, FIG. 1 is a diagram of an embodiment of the evaluation system of inclusions during the step of the production flow of automatic autosomal inspection of a steel tube.

DETAILED DESCRIPTION OF THE DRAWINGS

[0023] In FIG. 1, it is shown the system according to the invention in a preferred embodiment, comprising a bed 10 for tube transportation 1 during its step of automatic ultrasonic inspection of manufacturing, an acoustic coupling unit 3, which is filled with a liquid mean of acoustic coupling 4, and has at least one ultrasonic transducer of high frequency 2 arranged immersed in liquid medium of acoustic coupling 4 and an sonic emitting and receiving unit 9, which operates with a determined Frequency of Pulse Repetition. The high frequency ultrasonic transducer 2 has a piezoelectric crystal capable of generating sound waves (mechanical energy) when receiving electric pulses, and the inverse effect, that is, generate electric energy when receiving sound waves, and must operate preferably at 15 MHz, which results in a detectability of inclusions with approximate dimensions starting at 0.20 mm.

[0024] The acoustic coupling liquid medium 4 should preferably be water as a function of the cost benefit ratio, and serves to ensure that the sonic energy propagates from the ultrasonic transducer 2 to the test tube 1. The acoustic coupling is ensured by the positioning of the acoustic coupling unit 3 adjacent to the surface of the tube 1 with constant supply of the liquid medium ensuring a column of the acoustic coupling between the tube 1 and the ultrasonic transducer 2. The system is capable of monitoring the acoustic coupling, ensuring the effectiveness of the evaluation of inclusions.

[0025] The transport bed 10 comprises the rollers 5 which transmit the rotational movement and/or transport the tube 1 during the test. The test sweep 11 is described by the helical conveying of the tube 1, rotational movement 8 of the tube simultaneously with displacement in the axial direction 6, or further by the rotational movement of the tube 1 with displacement in the axial direction 7 of the acoustic coupling unit 3. In both transport configurations, the rotational speeds and axial displacement must be defined and adjusted depending on the desired sweep 11, physical conditions of the tube, such as straightness, surface finish, finish of the ends, etc. these speeds are reduced when the coupling unit is at the ends of the tube to enable stabilization of the acoustic coupling liquid medium 4 of the acoustic coupling unit 3, thus the present invention is adaptable to any automatic ultrasonic tube inspection unit. The adjustment of the axial and rotational velocity of the tube must also be defined as a function of the Pulse Repetition Frequency, so that the distance between two sequential sonic pulses is limited and compatible with the desired pulse density for assessing the presence of inclusions. The distance between two sequential pulses should preferably be limited to a maximum of 2 mm in order to provide a sufficient pulse density for detection of the inclusions.

[0026] The test sweep 11 will be effected along the length of each individually tested tube 1 by relative displacement of the high frequency ultrasonic transducer 2 along the length of the tube 1 with radial movement 16 simultaneous with the displacement of the high frequency transducer. The test sweep 11 will be performed statistically along the length of the tube, considering that the relative axial displacement between the high frequency transducer and the tube at each revolution will be greater than the sonic beam width in the volume tested, but it is representative of the level of individual inclusions of the test tube. If a larger test sweep 11 is intended, either at one or both ends, or along the entire length of the test tube, the advance of each revolution can be suitably defined to be compatible with the dimensions of the sonic beam generated by ultrasonic transducer 2. Alternatively, the number of ultrasonic devices 2 may be conveniently increased in the acoustic coupling unit 3 to ensure an increase in the test sweep 11. In addition, the relative speed of displacement between the test surface of the tube 1 and the ultrasonic transducer 2 can be reduced to ensure an increase in the density of the sonic pulses, i.e. a reduction between two sonic sequential pulses.

[0027] The sonic emitting and receiving unit 9 will emit the electrical pulses at a given pulse repetition frequency up to the high frequency transducer 2 generating the sound waves which will propagate through the acoustic coupling liquid 4, perpendicularly to the external surface of the tube 1, the sound propagation continued through the thickness of the tube 1. The interface signal 14 relating to the sonic beam reflection on the outer surface of the tube and the background echo signal 15 relating to the reflection of the sonic beam on the inner surface of the tube will be represented in the sonic receiving and receiving unit 9. Possible inclusions in the test volume may result in a reflection signal 13 between the interface signals 14 of the bottom echo 15, depending on whether they have acoustic impedance different from the steel being evaluated, and the height of the reflection signal (amplitude) of the inclusions conditioned to the adjustment of the test sensitivity and characteristics of the inclusions, such as orientation, morphology and size.

[0028] The test sensitivity shall be established using “Flat Bottom Hole” type artificial reflectors machined on the inner surface of tube 1, which shall be machined into a reference tube having the same nominal dimensions and acoustic characteristics of the material to be tested. The evaluated volume will be set as a function of the width of the monitoring threshold 12 of inclusion signals, having as large a width as possible, considering its start as close as possible to the signal corresponding to the interface signal 14 (external surface of the tube 1 under inspection) and its termination as close as possible to the signal corresponding to the background echo signal 15 (signal corresponding to the inner surface of the tube 1 under inspection). In addition, the test sensitivity will also be defined by the height of the inclusion threshold monitoring threshold, and should be adjusted preferably between 30% and 50% of the total screen height.

[0029] The presence of general macroinclusions is inherent in the steel fabrication process and only the inclusion reflection signals with amplitudes above the monitoring threshold 12 will be accounted for to determine the impurity factor of the steel. The impurity factor will be defined as a function of the amount of sonic pulses with inclusion reflection signals with amplitudes above the monitoring threshold 12 by the total amount of sonic pulses emitted during the test. A multiplying factor of the occurrences of inclusion reflection signals with amplitudes above the monitoring threshold 12 can be applied to define different weights according to the application and criticality of the product. The impurity factor of the steel shall be calculated by the following formula:

[00001]$\mathrm{FI}\left[\%\right]=100\times {\left[A\times \frac{N_{\mathrm{Ind}.}}{N_{\mathrm{Pulsos}}}\right]}_{\mathrm{FI}\left[\%\right]=100\times \left[A\times \frac{N_{\mathrm{Ind}.}}{N_{\mathrm{Pulsos}}}\right]}$

[0030] wherein:

[0031] FI=Impurity factor (Index of inclusions);

[0032] NPulsos=Total amount of pulses emitted in the volume tested;

[0033] NInd=Amount of signals with amplitudes above the monitoring threshold; and

[0034] A=Multiplier factor for signals with amplitudes above the monitoring threshold.

[0035] The impurity factor can be calculated at each revolution (turn) or fraction of length of the test tube, and/or considering any test sweep 11 along the length tested. In the case of the length fraction of the test tube, for example, the impurity factor can be assigned to the specified regions, for example one or both ends, or in specific regions along the length of the tube.

[0036] After the ultrasonic transducer 2 detects inclusion information during the test sweep 11 of the tube 1, the amplitude values found are sent to the emission and reception unit of the sonic pulses 9, which in turn will determine the impurity factor from the steel to that particular pipe or region. In addition, the Result of Total Impurity Factor can be attributed to the batch of tubes produced in the campaign.

[0037] After evaluation of the inclusions in the tested tube 1, the acoustic coupling unit 3 moves away from the tube 1 and the transport bed 10 will initiate a new test cycle by withdrawing the test tube and feeding the next tube from the inspection line.

[0038] Thus, the method for assessing the inclusive level in steel tubes using high frequency transducer in the automatic ultrasonic inspection of the present invention comprises a first step of transporting the tube through the bed 10 to the acoustic coupling unit. The speed of tube transportation through the bed 10 may be adjusted to ensure the stabilization of the acoustic coupling in the ends and along the length of the tube.

[0039] Next, it is performed a step of coupling the acoustic coupling unit with the tube through a radial movement 16 of transducer approximation regarding the tube external surface.

[0040] After coupling, it is performed a step of detecting inclusions information in at least one sweep region 11 along the length of the tube. The sweep region 11 is defined by the region where the test sweep 11 is performed and may be a specific region or a helical trajectory along the whole length of the tube. But the detection of inclusions information is performed by outputting a sonic beam by the ultrasonic transducer, which performs the detection of inclusions information and may operate a nominal frequency preferably of 15 MHz.

[0041] Next, the inclusions information is sent to the sonic emitting and receiving unit. This inclusions information is defined by the number of sonic pulses with signals with amplitudes above the monitoring threshold of inclusions.

[0042] The method also comprises a step of determining the inclusions index for the tube or specific region based on the amplitudes of the signals of inclusions with amplitudes above the monitoring threshold of the signals of inclusions. The inclusions index is determined by the emitting and receiving unit of sonic pulses.

[0043] Finally, the tube transportation continues in an inspection line and the inspection cycle continues with the next tube in the production flow.

[0044] In addition, the individual results of the pipe inclusion indices are correlated with the processing conditions in the steel manufacturing stage, representing a tool for monitoring the steel purity and continuous improvement in the steelmaking process.

[0045] The individual results of the pipe inclusion indices are also correlated with the corrosion test results required by pipe manufacturing and supply standards, representing a tool for monitoring and improving the corrosion resistance of steel.

[0046] No previously known method was able to provide in a simple and efficient manner the provision of a single tube inclusion index tested during the production and inspection process, not limited to a small sample of the total volume of steel produced, to dispense with the need for sampling and additional laboratory tests.

[0047] Having described a preferred embodiment example, it should be understood that the scope of the present invention encompasses other possible variations, being limited only by the content of the claims only, including possible equivalents thereto.

REFERENCES LIST

[0048] 1—Inspection tube [0049] 2—Ultrasonic transducer [0050] 3—Acoustic coupling unit [0051] 4—Liquid of acoustic coupling [0052] 5—Transport rolls [0053] 6—Displacement of the tube in the axial direction [0054] 7—Displacement of the acoustic coupling unit in the axial direction [0055] 8—Rotational movement of the tube over the transportation bed [0056] 9—Emitting and receiving unit [0057] 10—Bed of tube transportation [0058] 11—Test sweep [0059] 12—Monitoring threshold [0060] 13—Sign of reflection [0061] 14—Interface signal [0062] 15—Background echo signal [0063] 16—Transducer movement in the radial direction of the tube