Pulse-echo system and method for detecting discontinuities

Abstract: A pulse-echo system uses ultra-sound signals to detect discontinuities or flaws in a wall. The system comprises a transducer which transmits ultra-sound signals and receives reflected ultra-sound signals, and reflection means (3,5,6) which comprise at least two reflection planes (3,5,6) which create two paths for the ultra-sound signals. The two paths (12,13) meet in the wall such that they are essentially perpendicular to each other. At the location of a discontinuity (4), where the two paths meet, the ultra-sound signals are reflected back along the respective paths to be detected at the transducer (2). The path lengths can be varied by altering the relative positions of the reflection planes. One of the paths (13) for the ultra-sound signals may have a circumferential component within the wall. In this way a wide range of orientations of discontinuities can be detected.

Description: The present invention relates to a pulse-echo system which uses ultra-sound signals to detect discontinuities or flaws. The system includes a transducer for transmitting and receiving pulsed ultra-sound signals which travel to the wall of an article to be inspected for discontinuities. An example of such an article is a pipe wall. The invention also relates to a method for detecting discontinuities in a wall. This kind of pulse-echo system is known from US-A-4,022,055, which describes the use of reflection means to define a pair of transmission paths for ultra-sound waves whereby the path portions situated between the transducer and the reflection means extend essentially parallel to the wall to be inspected. In accordance with US 4,022,055 a first transmission path is directed perpendicularly to a pipe wall to be inspected and the second of the transmission paths is directed at an angle to the said wall so that ultra-sound waves reaching the pipe wall being inspected enter it via this latter path and continue on their course. There is a short lapse of time between entry of ultra-sound waves along these respective paths. Detection of discontinuities takes place by means of the ultra-sound waves of the said second transmission path. The first transmission path serves for propagation of ultra-sound waves which serve to determine the thickness of the pipe wall. A problem with this known apparatus is that with the proposed provision of beaming at the pipe wall at an angle, discontinuities may indeed be detected but only those which extend around the circumference of the pipe wall. Sound waves which enter the pipe wall via the second transmission path tend to continue on axially, and have no circumferential component. Consequently cracks or other discontinuities in the longitudinal direction of the pipe wall, or generally parallel to the direction of continuation of the ultra-sound waves may not be detected by this method. US-A-4,502,330 also discusses a system where two paths of ultra-sound signals are directed towards a wall. The paths do not meet in the wall, and the system is used primarily for detecting wall thickness. An object of the invention is therefore to improve detection of discontinuities and flaws. The pulse-echo system in accordance with the invention comprises a transducer for transmitting and receiving ultra-sound signals, reflecting means comprising at least two reflection planes, said reflection planes defining a first and a second path each of which has a portion which is parallel to said wall between the transducer and reflecting means. The two paths meet in the wall essentially perpendicular to each other. The invention also provides a method for detecting discontinuities and flaws. The method comprises providing two paths for said signals which meet in the wall. The angle at which the two paths meet is essentially a right-angle i.e. the two paths are essentially mutually perpendicular at the point at which they meet in the wall. Surprisingly it has been found that discontinuities beamed at from two directions in this way can usually be detected by the ultra-sound waves of both paths without so much cross-talk occurring from one transmission path to the other transmission path that detection of the discontinuity becomes disturbed. Because the ultra-sound waves are sent into the wall to be inspected in two independent directions, discontinuities with various orientations in the wall being inspected may be detected by analysis of the reflections received back via the first and the second path. In the pulse-echo system and method of the invention, pulsed ultra-sound signals are normally employed. Preferably the first path for the ultra-sound waves defined by the reflection has a portion which is parallel to the longitudinal axis of the wall. Also preferably, and when the wall to be inspected is part of a pipe, the second path defined by the reflection means will have a circumferential portion within the wall. In another preferred embodiment of the invention the pulse-echo system is characterized in that the first and the second reflection planes are able to move in relation to one another. In this way the length of the first path and of the second path can be made equal to one another. This has the advantage that the time lapse between transmission by the transducer of the ultra-sound waves and the receiving back of the reflections via the first and the second path, caused, among other reasons, by the discontinuity, can be made equal so that relative comparison is enabled and the analysis of the test results simplified. The invention will now be illustrated by reference to the accompanying drawing which shows a pipe in which a pulse-echo system embodying the invention is drawn, as a non-limitative example of the invention. The drawing 1 shows a transducer 2 for transmitting and receiving back ultra-sound waves, located in a pipe 1. A first path of ultra-sound waves is defined by the co-operation of the transducer 2 and a reflection plane 3 which converts an axial path component between the transducer 2 and the reflection plane 3 into a path component 12 in the direction of the inner wall of the pipe 1. This path component has a component which is longitudinal to the axis. The ultra-sound waves which reach the wall of pipe 1 via this path 12 enter the wall and continue on in a direction having an axial component to a discontinuity 4 to be detected in the wall of the pipe 1. This discontinuity 4 causes a reflection of the ultra-sound waves arriving via path 12. The reflected ultra-sound waves travel via path 12 in the reverse direction up to transducer 2 which detects the reflections. The transducer 2 is further linked to an oscilloscope which can make the detected reflections visible. A second path of ultra-sound waves is defined by the transducer 2 in co-operation with a reflection plane 5, the ultra-sound waves being directed by an eccentric mirror 6. The eccentric mirror 6 is needed to direct the waves at the reflection plane 5 which is located somewhat off the centre of the transducer 2 so that the ultra-sound waves are directed onto the inner wall of the pipe 1 in a direction which diverges from that of the first path 12. Propagation of ultra-sound signals takes place via reflection plane 5 along path 13 in the direction of the inner wall of the pipe 1. After entering the pipe wall the ultra-sound waves continue to travel along this path 13 in a direction which is essentially perpendicular to that of the ultra-sound waves of path 12 up to the discontinuity 4. Once at discontinuity 4, reflection again occurs, now of the ultra-sound waves of path 13, in the reverse direction. The reflected ultra-sound waves are then detected with transducer 2 and made visible on the oscilloscope. Reflection plane 5 and reflection plane 3 are able to move relative to one another in such a way that the lengths of the transmission paths 12 and 13 can be made equal to each other and also so that the transmission period of the ultra-sound waves from the transducer 2 up to the discontinuity 4 and back is made equal for both paths. Consequently the differing reflections observed with the oscilloscope occur at the same times thus enabling a simple relative comparison and simplified analysis of the test results.

Claims: A pulse-echo system for detecting discontinuities in a wall (1) comprising a transducer (2) for transmitting and receiving ultra-sound signals, reflecting means comprising at least two reflecting planes (3,5,6), said reflecting planes defining a first and a second path (12,13) for said signals, each of said paths including a portion between said transducer (2) and the reflecting means, said portion being parallel to said wall, characterised in that said two paths meet in the wall at a right-angle. A system according to claim 1 wherein at least two said reflecting planes defining said two paths are movable relative to each other to vary at least one of the path lengths. A system according to claim 1 or claim 2 wherein said first path 12 has a portion which is parallel to a longitudinal axis of said wall, within said wall. A system according to any preceding claim wherein the system is adapted to detect discontinuities in the wall of a cylindrical pipe. A system according to claim 4 wherein said second path 13 has a circumferential portion, within said wall. A method of detecting discontinuities in a wall using ultra-sound signals comprising providing a transducer (2) for transmitting and receiving said ultra-sound signals and reflecting means with at least two reflecting planes (3,5,6), said reflecting planes defining two paths (12,13) for said signals, each of said paths including a portion between said transducer (2) and the reflecting means, said portion being parallel to said wall, characterized in that said paths meet in the wall at right angles. A method according to claim 6 wherein the wall is a wall of a cylindrical pipe and one of said paths has a circumferential portion in the wall. A method according to claim 6 or claim 7 wherein one of said paths has a portion which is parallel to a longitudinal axis of said wall. A method according to any of claims 6 to 8 wherein the length of at least one of said two paths is varied to make the lengths of said two paths equal.

Inventors: KETELAAR KEES CORNELIS JACOBUS, KETELAAR, KEES CORNELIS JACOBUS
Applicants: HOOGOVENS TECH SERVICES, HOOGOVENS TECHNICAL SERVICES INSPECTION SYSTEMS BV
Application year: 1991
Main classification: G01N29
IPC codes: G01N29