GB1600643A - Method of dynamically discriminating between flaws and indications of faults with ultrasonic testing - Google Patents

Description

(54) METHOD OF DYNAMICALLY DISCRIMINATING BETWEEN FLAWS AND INDICATIONS OF FAULTS WITH ULTRA-SONIC TESTING (71) We, MANNESMANN AKTIENGESELLSCHAFT, a joint stock company organised under the laws of Germany, of Mannesmannufer 2, 4 Dusseldorf 1, Germany, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The invention relates to a method for dynamically discriminating between true flaws and false indications of faults during ultrasonic testing particularly of tubes.

During ultra-sonic testing, employing for example, testing installations using the immersion technique and with relative movement between test head and flaws, flaws in the element being tested can be falsely simulated or indicated by, for example, air bubbles, scale, etc. in the coupling medium. No method is known at present which distinguishes these false fault indications from natural flaws.

We have sought to provide a method for dynamically differentiating between true flaws and false indications or faults, so as to be able to mask out the detected false indications of faults.

Accordingly the present invention provides a method of dynamically distinguishing between false indications of faults and true flaws in an object moving uniformly relative to a test head during ultrasonic testing by a pulse-echo technique, wherein the time between transmitted pulse and a suspected flaw-echo is measured in each testing cycle and the difference between the said times in at least two successive test cycles is compared with a preselected time difference so as to confirm the flaw echo as a true flaw echo or a false flaw echo.

The invention will now be further described giving for example, with reference to the accompanying drawings in which Figure 1 shows a cross-section of a tube being tested; Figure 2 shows ultrasonic images represented in amplitude/time form of a test of the tube of Figure 1.

In principle, indications or readings of actual flaws and false indications of faults caused by scale, etc., are distinguished by substantial differences in the relative speed between test head and the point of indication or reading.

Whereas particles of scale or air bubbles within the immersion tank move at a speed of from 1 to 10 mm/sec., the relative speed of a genuine flaw in the test element depends upon the tube diameter and the number of revolutions within the unit of time: V=7rxDxU D=diameter of the tube U=number of revolutions per second.

With revolutions of from 200 to 1,000 rpm, and tube diameters of from 20 to 200 mm, values of from 200 to 10,000 mm/sec.

are produced as relative speeds between testing head and true flaws.

The relative speed of the true flaw is clearly distinguished from the relative speed of the false fault indications.

The relative speed between testing head and false fault indication or true flaw reading cannot be directly measured, but it is calculated indirectly by means of a transit time measurement by ultra-sonic testing.

In Figure 1 of the drawing, tube 1 has a flaw 2 and is exposed to ultra-sonic waves from a testing head 3. The path of the ultra sonic main beam from the testing head 3 to the flaw 2 and back is indicated by line 5. In this testing operation, the ultra-sonic images shown in Figure 2 for two successive test cycles are produced as an amplitude/time.

The starting of the ultra-sound is initiated by transmission pulse 6. By way of the point of sound entry 4 into the test element 1, which is indicated as an entry echo 7, the ultra-sound reaches flaw 2, which is visible as a flaw amplitude 8 in the cathode ray display.

The sound transit time t1 of the first test cycle is the measurement between transmitted pulse 6 and flaw amplitude 8.

In the succeeding test cycle, a time measurement t2 is made between transmitted pulse 6 and flaw echo 8a, and by the rotation of the tube 1 in the direction towards the testing head 3, the time t2, which is smaller than the time t1 of the preceding testing cycle, is measured depending upon the aforesaid influences, the pulse sequence frequency in the testing and - the sound-entry angle of the ultrasound.

The difference between the times t1 and t2, produces a time differentiation, which is used as a standard for confirming the true flaws in the object being tested or for indicating false fault due to air bubbles in the water or suspended particles of scale.

If the time difference of the sound transit times measured in two successive testing cycles is taken as an absolute value, the effect of the movement of the flaw to or from the testing head is compensated for.

The dynamic suppression of faults in accordance with the invention can be used in conjuction with already proposed statistical suppression with the aid of two discriminator thresholds with a monitor, also with flaw amplitudes in the range of the response threshold of the monitor.

WHAT WE CLAIM IS:- 1. A method of dynamically distinguisving between false indications of faults and true flaws in an object moving uniformly relative to a test head during ultra-sonic testing by a pulse-echo technique wherein the time between transmitted pulse and a suspected flaw echo is measured in each testing cycle and the difference between the said times in at least two successive test cycles is compared with a preselected time difference so as to confirm the flaw echo as a true flaw echo or a false flaw echo.

2. A method as claimed in claim 1, wherein the difference between the times of at least two successive test cycles is considered as absolute value and thus the dependence on the direction of the relative speed between the flaw and testing head is eliminated.

3. A method as claimed in claim 1 substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. The sound transit time t1 of the first test cycle is the measurement between transmitted pulse 6 and flaw amplitude 8. In the succeeding test cycle, a time measurement t2 is made between transmitted pulse 6 and flaw echo 8a, and by the rotation of the tube 1 in the direction towards the testing head 3, the time t2, which is smaller than the time t1 of the preceding testing cycle, is measured depending upon the aforesaid influences, the pulse sequence frequency in the testing and - the sound-entry angle of the ultrasound. The difference between the times t1 and t2, produces a time differentiation, which is used as a standard for confirming the true flaws in the object being tested or for indicating false fault due to air bubbles in the water or suspended particles of scale. If the time difference of the sound transit times measured in two successive testing cycles is taken as an absolute value, the effect of the movement of the flaw to or from the testing head is compensated for. The dynamic suppression of faults in accordance with the invention can be used in conjuction with already proposed statistical suppression with the aid of two discriminator thresholds with a monitor, also with flaw amplitudes in the range of the response threshold of the monitor. WHAT WE CLAIM IS:-

1. A method of dynamically distinguisving between false indications of faults and true flaws in an object moving uniformly relative to a test head during ultra-sonic testing by a pulse-echo technique wherein the time between transmitted pulse and a suspected flaw echo is measured in each testing cycle and the difference between the said times in at least two successive test cycles is compared with a preselected time difference so as to confirm the flaw echo as a true flaw echo or a false flaw echo.

2. A method as claimed in claim 1, wherein the difference between the times of at least two successive test cycles is considered as absolute value and thus the dependence on the direction of the relative speed between the flaw and testing head is eliminated.

3. A method as claimed in claim 1 substantially as herein described with reference to the accompanying drawings.