Method for the non-destructive inspection of a test object of great material thickness by means of ultrasound, the use of a test probe for carrying out the method, an ultrasonic test probe, a control unit for an ultrasonic test probe and a device for the non-destructive inspection of a test object of great material thickness by means of ultrasound

1. Method for the non-destructive inspection of a test object ( 10 ) with a great material thickness by means of ultrasound comprising the following method steps:

a. providing an ultrasonic test probe ( 20 ) with an ultrasonic transducer ( 22 ) divided into a plurality of individually activatable transducer segments ( 24 ), wherein the transducer segments ( 24 ) are concentric circles or rings, or sections thereof, characterized in that the transducer segments ( 24 ) are dimensioned in such a way that the diameter Dm of the circular active surface Fm of the ultrasonic transducer ( 22 ) formed by a group i (i=1, 2, 3, . . . ) of transducer segments ( 24 ) is substantially proportional to the square root of i,

b. selecting a first group j (j=1, 2, 3, . . . ) of transducer segments ( 24 ) in such a way that a parallel activation of these transducer segments ( 24 ) results in a circular active surface Fj of the ultrasonic transducer ( 22 ), and

c. carrying out an ultrasound inspection of the test object ( 10 ) with the first group j (j=1, 2, 3, . . . ) of transducer segments ( 24 ), wherein they are being activated in parallel;

characterized in that a predetermined criterion K has to be satisfied when the method is being carried out which is dependent upon the ultrasonic field that is generated by the active surface Fj of the ultrasonic transducer ( 22 ), comprising the following further method steps:

selecting the first group j (j=1, 2, 3, . . . ) of transducer segments that are activated in parallel in such a way that the ultrasonic field generated by the active surface Fj of the ultrasonic transducer ( 22 ) satisfies the criterion K;

wherein the criterion K is satisfied if:

dj≧ 0.7× Nj

applies, with dj being the minimum distance of the sector Rj to be inspected from the coupling location ( 14 ) of the ultrasound into the test object along the sound path in the test object ( 10 ) and Nj being the near-field length of the active surface Fj of the ultrasonic transducer ( 22 ) formed by the first group j (j=1, 2, 3, . . . ) of transducer segments ( 24 ).

2. Method according to claim 1 , characterized by the following further method steps:

a. selecting a sector Rj to be inspected of the test object ( 10 ),

b. selecting the first group j (j=1, 2, 3, . . . ) of transducer segments that are activated in parallel in such a way that the ultrasonic field in the sector Rj generated by the active surface Fj of the ultrasonic transducer ( 22 ) satisfies the criterion K.

3. Method according to claim 2 , characterized by the following further method steps:

a. presetting a material thickness S to be inspected of the test object ( 10 ),

b. dividing the material thickness S to be inspected of the test object ( 10 ) into a plurality of sectors Ri (i=1, 2, 3, . . . ) disposed one behind the other in the ultrasound propagation direction in the test object ( 10 ),

c. selecting the sector Rj to be inspected from amongst the sectors Ri.

4. Method according to claim 1 , characterized in that the ultrasound inspection is carried out in accordance with the DGS method.

5. Method according to claim 4 , characterized in that the specific DGS diagram ( 34 j ) for the ultrasonic transducer ( 22 ) having the circular active surface Fj formed by the selected group j of transducer segments ( 24 ) is computed from the general DGS diagram ( 34 ).

6. Method according to claim 1 , characterized in that the ultrasound inspection is carried out in accordance with the DAC method.

7. Method according to claim 1 , characterized in that the method is carried out for different sectors Rj,k.

8. Method according to claim 7 , characterized in that the sectors Rj,k have substantially the same extent in the sound propagation direction.

9. Method according to claim 7 , characterized in that electronic screens are used for acquiring different sectors Ri,j of the test object ( 10 ).

10. Method according to claim 7 , characterized in that the first and second ultrasound inspections are carried out from the same coupling location ( 14 ).

11. Method according to claim 1 , characterized in that the transducer segments ( 24 ) of the ultrasonic transducer ( 22 ) of the provided ultrasonic test probe ( 20 ) are dimensioned in such a way that the diameter Dm of the circular active surface Fm of the ultrasonic transducer ( 22 ) formed by a selected group i of transducer segments ( 24 ) is substantially proportional to the square root of i.

12. Method according to claim 1 , characterized in that the transducer segments ( 24 ) have substantially the same surface f.

13. Ultrasonic test probe ( 20 ) according to claim 1 , characterized in that the transducer segments ( 24 ) have substantially the same surface f.

14. Control unit ( 30 ) for an ultrasonic test probe ( 20 ) for the non-destructive inspection of a test object ( 10 ) with a great material thickness by means of ultrasound, wherein the ultrasonic test probe ( 20 ) comprises an ultrasonic transducer ( 22 ) divided into a plurality of individually activatable transducer segments ( 24 ), wherein the transducer segments ( 24 ) are concentric circles or rings, or sections thereof, characterized in that the control unit ( 30 ) is configured to activate in parallel a first group j (j=1, 2, 3, . . . ) of transducer segments ( 24 ) in such a manner that the result is a circular active surface Fj of the ultrasonic transducer ( 22 ), characterized in that the transducer segments ( 24 ) are dimensioned in such a way that the diameter Dm of the circular active surface Fm of the ultrasonic transducer ( 22 ) formed by a group i (i=1, 2, 3, . . . ) of transducer segments ( 24 ) is substantially proportional to the square root of i;

characterized in that the control unit:

a. is configured for executing an ultrasonic inspection method during whose execution a predetermined criterion K has to be satisfied which is dependent upon the ultrasonic field that is generated by the active surface Fj of the ultrasonic transducer ( 22 ), and

b. is configured to select a first group j (j=1, 2, 3, . . . ) of transducer segments ( 24 ) whose parallel activation results in a circular active surface Fj of the ultrasonic transducer ( 22 ), wherein the ultrasonic field generated by the active surface Fj of the ultrasonic transducer ( 22 ) satisfies the criterion K;

wherein the criterion K is satisfied if:

dj≧ 0.7× Nj

applies, with dj being the minimum distance of the sector Rj to be inspected from the coupling location ( 14 ) of the ultrasound into the test object along the sound path in the test object ( 10 ) and Nj being the near-field length of the active surface Fj of the ultrasonic transducer ( 22 ) formed by the first group j (j=1, 2, 3, . . . ) of transducer segments ( 24 ).

15. Device ( 1 ) for the non-destructive inspection of a test object ( 10 ) by means of ultrasound, characterized in that the device ( 1 ) comprises the following:

a. an ultrasonic test probe ( 20 ) with an ultrasonic transducer ( 22 ) divided into a plurality of individually activatable transducer segments ( 24 ), wherein the transducer segments ( 24 ) are concentric circles or rings, or sections thereof, and

b. a control unit ( 30 ) according to claim 14 .