Method for non-destructive testing of walls of components

Abstract

A method for non-destructive testing of walls of components, at least one ultrasonic transducer (1) which is fixed to a surface of the wall is used to emit horizontally polarized transverse waves (3) in a lateral propagation direction and compression waves or vertically polarized transverse waves (6) in a radial propagation direction. The at least one ultrasonic transducer (1) and/or at least one further ultrasonic transducer arranged at a known distance from the at least one ultrasonic transducer (1) on the respective wall of the component (2) is/are used to detect horizontally polarized transverse waves (4) reflected by defects and compression waves or vertically polarized transverse waves (7) after or while running the non-destructive testing of the wall in order to determine the respective wall thickness.

Claims

1. Method for the non-destructive testing of walls of components; fixing at least one ultrasonic transducer to a surface of the wall which transducer is a piezoelectric transducer and is used to emit horizontally polarized transverse waves in a lateral propagation direction substantially parallel to a central longitudinal axis on the surface of the wall being tested and compression waves or vertically polarized transverse waves in a radial propagation direction substantially perpendicular to the central longitudinal axis of the wall being tested in the wall of the component; detecting horizontally polarized transverse waves reflected from defects by the at least one ultrasonic transducer and/or at least one further ultrasonic transducer arranged at a known distance from the at least one ultrasonic transducer on the wall being tested of the component; and determining the thickness of the wall being tested with compression waves or vertically polarized transverse waves after or while detecting the defects by the ultrasonic transducer.

2. The method according to claim 1, detecting amplitude and/or travel time of the horizontally polarized transverse waves reflected by defects and the amplitude and/or the travel time of the compression waves or the vertically polarized transverse waves in order to determine the thickness of the wall being tested.

3. The method according to claim 1 emitting the horizontally polarized transverse waves in the lateral propagation direction and the compression waves or the vertically polarized transverse waves in the radial propagation direction with a frequency in the range of 10 kHz to 1 MHz.

4. The method according to claim 1, wherein the at least one ultrasonic transducer is embedded or laminated in an elastically deformable material on the component.

5. The method according to claim 1, fastening the at least one ultrasonic transducer to the component by means of a sleeve running over the periphery of the wall being tested.

Description

DESCRIPTION OF THE DRAWINGS

(1) The invention shall be explained in more detail by way of example below and in the figures:

(2) FIG. 1 shows a schematic form of a measurement setup suitable for carrying out the method according to the invention, with an explanation of the functionality;

(3) FIG. 2 shows a graph illustrating the dependences of the propagation speed on the frequency, the emitted ultrasonic waves and the wall thickness of the respective component wall;

(4) FIG. 3 shows a graph of the temporal profile of the amplitude of ultrasonic waves emitted using at least one ultrasonic transducer at a frequency of 100 kHz;

(5) FIG. 4 shows a graph of the propagation speed of emitted ultrasonic waves against the frequency, wherein the actual propagation speed (measured values) is contrasted with the theoretical propagation speed (dispersion curve) for steel pipe having an outer diameter of 219.3 mm and a wall thickness of 8 mm;

(6) FIG. 5 shows a graph of the ratio of detected amplitudes of the T(0,1) mode with respect to the L(0,2) mode against the frequency of the ultrasonic waves in a steel pipe as a component.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 1 shows a measurement setup which can be used to carry out the method, with the measurement principle.

(8) In this case, an ultrasonic transducer 1 is fixed to an outer lateral surface of a pipe as a component 2. The ultrasonic transducer 1 is connected to an electrical voltage source (not shown) and is operated with an electrical AC voltage at a predefined frequency, with the result that ultrasonic waves are emitted by said transducer. In addition, in this embodiment, the transducer is connected to an electronic evaluation unit (not shown) which is designed to evaluate ultrasonic waves 3, 4, 6 and 7 detected using the ultrasonic transducer 1, which relates, in particular, to their amplitude and/or travel time.

(9) During the emission of ultrasonic waves, laterally emitted horizontally polarized transverse waves 3 are emitted once and propagate in the wall of the pipe 2, which is indicated with arrows. Said waves can be used for the non-destructive testing of defects, for example cracks. For this purpose, waves 4 which are reflected by a defect and contain damage information can be detected using the ultrasonic transducer 1 at times at which ultrasonic waves are not emitted. The type and position of a defect can be inferred from the travel time and amplitude of the detected ultrasonic waves. This can be carried out by means of the electronic evaluation unit.

(10) As can be gathered from FIG. 1, horizontally polarized transverse waves 3 can be emitted in two opposite directions and ultrasonic waves 4 reflected back from there can be detected.

(11) In this case, the sphere of influence depends on the respective ultrasonic transducer 1 and its opening angle.

(12) The ultrasonic transducer 1 can be used to simultaneously also emit vertically polarized transverse waves 6 and 7 which run along the periphery of the component 2 and reach the ultrasonic transducer 1 again. In interaction with the electronic evaluation unit, the wall thickness of the component 2, in particular, can be determined, with the result that suitable measured values can be obtained in this direction for the purpose of determining a condition of the respective component 2.

(13) As a result of the type of ultrasonic waves, the propagation of which depends significantly on the choice of the frequency and the wall thickness (guided waves), the detected signals contain integral information relating to wall erosion, corrosion and wall thickness on the periphery at the transducer position. The sphere of influence depends in this case on the respective ultrasonic transducer 1, the exciting frequency and the opening angle of the transducer and describes the component section in which the wall thickness influences the measurement result and can therefore be measured.

(14) In order to determine faults in the axial direction of the component wall, horizontally polarized transverse waves 4 reflected by defects, faults or changes in the reception signal can be evaluated. The travel time of the compression waves or vertically polarized transverse waves can be evaluated in the component peripheral direction, and the wall thickness can be determined on the basis of the propagation speed of the L(0,2) wave mode determined using the travel time on the basis of the dispersion curves. This can be gathered from FIG. 2 for different wall thicknesses.

(15) The change in the propagation speed is illustrated in FIG. 2. Minor faults in the peripheral direction can also likewise be determined by means of changes in the reception signal.

(16) For example, the propagation speed of the L(0,2) mode at 300 kHz and for a wall thickness of 6 mm is approximately 4200 m/s and is approximately 4750 m/s for a wall thickness of 5 mm.

(17) Experimental investigations were carried out using an ultrasonic transducer 1 having dimensions of 25 mm×16 mm on the outer lateral surface of a pipe having an outer diameter of 219.3 mm and a wall thickness of 8 mm. Ultrasonic waves were emitted between 75 kHz and 190 kHz in 5 kHz steps, with the result that a frequency dependence becomes discernible.

(18) The ultrasonic waves 6 and 7 propagating in the pipe peripheral direction can be recorded as periodic echo at the ultrasonic transducer 1, which can be gathered from FIG. 3 which shows, by way of example, a time signal at the ultrasonic transducer 1 at an excitation frequency of 100 kHz.

(19) The propagation speed of the wave mode L(0,2) can be determined from the time differences of the vertically polarized transverse waves 6 and 7 running around and can be compared with theoretically determinable dispersion curves, and the wall thickness of the respective component 2 can therefore be determined.

(20) FIG. 4 illustrates superimposition of the measured propagation speed at different frequencies with the theoretical dispersion graph for a steel pipe with an outer diameter of 219.3 mm and a wall thickness of 8 mm.

(21) The ratio of the energy of the emitted wave modes in the transverse and longitudinal directions can be adjusted or adapted to the structure using the dimension of the ultrasonic transducer 1, which may be a piezoelectric transducer element, or the transmission frequency. The decisive factor for this is the wavelength of the emitted ultrasonic waves at the selected excitation frequency (mode tuning) and the underlying wall thickness of the respective component 2. If a multiple of the wavelength of a wave mode is identical to the dimension of the ultrasonic transducer 1 used in the propagation direction of the emitted ultrasonic waves, the energy is minimal. If a multiple of half the wavelength of a wave mode is identical to the dimension of the ultrasonic transducer 1 in the propagation direction, the energy is maximal.

(22) The amplitude ratio can therefore be adjusted using the dimension of the ultrasonic transducer 1 for a particular frequency and wall thickness or by varying the frequency of the emitted ultrasonic waves in the case of a particular aspect ratio of the ultrasonic transducer 1.

(23) FIG. 5 illustrates the amplitude ratio of the T(0,1) mode to the L(0,2) mode in a pipe 2.

(24) This is shown, by way of example, for different frequencies. The amplitude of the horizontally polarized transverse wave 4 of the T(0,1) mode reflected at the edge of the pipe in the axial direction was compared with the amplitude of the vertically polarized transverse waves 7 of the L(0,2) mode emitted in the axial direction in the peripheral direction. For 100 kHz, the amplitude ratio of both waves is 1, at 200 kHz, the considered echo of the T(0,1) wave exhibits only half the amplitude of the L(0,2) mode for the selected geometrical relationship.