Patent Description:
In the manufacture of cables with lead sheathing, special attention is to be paid by the operating personnel to the quality of the lead sheath applied to the cable. It is an important aspect of cable manufacturing to inspect the lead sheath for imperfections, contaminations etc., and in particular it is important to monitor and inspect areas where lead sheath sections are spliced.

Traditionally such inspections are performed using imaging of the lead sheath or lead sheath splice by means of a high energy Gamma-Ray or X-ray Source. The imaging resulting from such methods gives not satisfactory images of the lead sheath for interpretation of the quality of the manufactured lead sheath. It is not possible to get an image of the complete circumference of the lead sheath/lead sheath splice due to high reflectivity of the cable core. The prior art techniques are very time consuming and the radiation sources are potentially harmful for the operator, which gives high demands to the safety procedures and equipment in order to reduce risk for radiation injury for the operators.

It is thus a need for improved inspection and testing methods.

Ultrasonic testing (UT) is a family of non-destructive testing techniques based on the propagation of ultrasonic waves in the object or material tested. In most common UT applications, very short ultrasonic pulse-waves with center frequencies ranging from <NUM>-<NUM>, and occasionally up to <NUM>, are transmitted into materials to detect internal flaws or to characterize materials. A common example is ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor pipework corrosion.

Ultrasonic testing is often performed on steel and other metals and alloys, though it can also be used on concrete, wood and composites, albeit with less resolution. It is used in many industries including steel and aluminum construction, metallurgy, manufacturing, aerospace, automotive and other transportation sectors.

<CIT> describes a monitoring device for monitoring lead thickness for use in a process for the production of lead cables. Measuring transducers distributed around the circumference are provided for the wall thickness of the lead jacket, for the cable length generated and the amount of lead associated therewith, which are connected by an evaluation unit to an image signal generator, the image signal generator being connected to a color image transmitter arranged at the work place and controlling it.

The device of <CIT> thus focuses on converting the signals from several sensors into a color image representation, which is provided directly on the lead press during the entire lead cable production process.

<CIT> describes an apparatus and method for detecting defects in longitudinal welds. The welds join the edges of metal strips that form sheath for cables. The defects are identified and located by continuously introducing ultrasonic vibrations into the welded region. The vibrations pass through the cable, with the transmitter on one side and the receiver on the opposite side.

Document <CIT> discloses an ultrasonic pipe testing system.

Document <CIT> discloses an X-ray inspection system for pipes.

Document <CIT> discloses an apparatus and method for inspecting an object using ultrasonic waves in the field of material testing.

Document <CIT> discloses a profiling tool for determining material thickness for inspection sites having complex topography.

Document <CIT> discloses a generator retaining ring scanning robot.

Document <CIT> discloses a defect detecting method for lead sheath pipe for electric wire.

Document <CIT> discloses a method of measuring topography in an interface and use of the method for a high-voltage cable.

Document <CIT> discloses a device and method for performing ultrasound scanning of a substantially cylindrical object.

An object of the invention is to provide an ultrasonic testing apparatus and method for ultrasonic imaging of power cable lead sheath that with confidence can verify the quality of the lead sheath or lead sheath splice and without posing health and safety risks for the operators.

It is a further object of the invention to provide an ultrasonic testing apparatus and method for ultrasonic imaging of power cable lead sheath that gives significantly more information about the quality of the lead sheath or lead sheath splice than prior art. This gives more confidence in determining the quality of said material.

The object of the invention is achieved by means of the features of the patent claims.

A power cable lead sheath inspection assembly is provided according to claim <NUM>.

A method for ultrasonic imaging of power cable lead sheath is provided according to claim <NUM>.

The ultrasonic probe comprises an ultrasonic transducer for generating ultrasonic waves with a desired frequency in order to provide signals that can be processed to give information related to the quality of the lead sheath such as thickness, thickness uniformity, defects, imperfections, contaminations etc. Conventional ultrasonic transducers for (non-destructive testing) commonly consist of either a single active element that both generates and receives high frequency sound waves, or two paired elements, one for transmitting and one for receiving. Phased array probes, on the other hand, typically consist of a transducer assembly with from <NUM> to as many as <NUM> small individual elements that can each be pulsed separately. These may be arranged in a strip (linear array), a ring (annular array), a circular matrix (circular array), or a more complex shape. Unlike conventional flaw detectors, phased array systems can sweep a sound beam through a range of refracted angles or along a linear path, or dynamically focus at a number of different depths, thus increasing both flexibility and capability in inspection setups. Phased-array systems can display ultrasonic data as sectorial or linear images allowing an inspector to see instantly a complete zone of the component and thus interpret data more easily.

The Total Focusing Method (TFM) and/or Adaptive Ultrasonic Imaging Method (ATFM) imaging techniques can be applied to ultrasonic data. The data can for example be recorded from a FMC (Full Matric Capture) acquisition to produce an image in a region of the component. The FMC presents the advantage of maximizing the information available from a given array composed of N elements by sending ultrasonic energy everywhere in the component; this way potential defects can be seen from multiple directions. The FMC acquisition consists in firing each element of the array in turn and recording the information reflected/diffracted in the component on all the elements.

In one embodiment, the ultrasonic probe comprises a rubber membrane and a closed water chamber for transmitting the ultrasound waves from the transducer to the lead sheath and to receive the reflected waves. The reflected waves are registered, and the signals generated in the ultrasonic probe are recorded and processed to provide signals representing the characteristics of the lead sheath.

The ultrasonic probe is configured to emit waves with a wavelength adapted to lead. A suitable frequency of the sound waves is for example in the area <NUM>-<NUM>, and is in one embodiment <NUM>.

In one embodiment, the probe guiding device comprises a guiding control unit configured for controlling the movement of the ultrasonic probe to follow the inspection path. The guiding control unit can control to probe to measure the area of interest, such as the complete circumference of the lead sheath and a predetermined length. To achieve this, the probe guiding apparatus will move the probe according to the individual needs. The measurements can be done with a resolution set by the operator and/or adapted to the specific use, ie. the guiding control unit will control the movement accordingly. A resolution of <NUM> is for example achieved by moving the ultrasonic probe <NUM> between each operation of the probe.

The ultrasonic testing apparatus comprises an ultrasonic control unit connected to the ultrasonic probe for controlling the ultrasound waves emitted from the ultrasonic probe. The ultrasonic control unit may be in communication with the probe guiding device for coordination of the movement of the ultrasonic probe and the emittance of ultrasound waves.

The invention will now be described in more detail by means of example and by reference to the accompanying figures.

<FIG> illustrates an ultrasonic testing apparatus configured to inspect a splice in a cable lead sheath.

<FIG> illustrates an ultrasonic testing apparatus configured to inspect a section of a cable lead sheath.

In the figures an ultrasonic testing apparatus <NUM> for inspection of power cable lead sheath is illustrated in different configurations. Same elements have same reference numbers in the figures. The ultrasonic testing apparatus <NUM> comprise an ultrasonic probe <NUM> for emitting ultrasound waves towards the power cable lead sheath <NUM> and recording ultrasound waves reflected from the power cable lead sheath <NUM>, a probe guiding device <NUM>,<NUM> configured to move the ultrasonic probe along an inspection path, and a processing device <NUM> connected to the ultrasonic probe for receiving signals from the ultrasonic probe and processing the signals to provide an image representing the lead sheath along the inspection path. The signals are transferred through the signal cable <NUM> from the ultrasonic probe <NUM> to the processing device <NUM>.

The ultrasonic probe <NUM> is a configured to measure the lead sheath and comprises an ultrasonic transducer configured to emit waves in the ultrasound range. To transmit the waves to the lead sheath and receive the reflected waves, the ultrasonic probe <NUM> comprises a rubber membrane closing a chamber filled with water, gel or other suitable substance. The ultrasonic probe is in one embodiment configured to emit sound waves with a frequency of <NUM>.

In the example of <FIG> the probe guiding device <NUM> is a rotary probe guiding device which is configured to move the ultrasonic probe along the circumference of the lead sheath <NUM>. The rotary probe guiding device comprises a fixing frame <NUM> which fixes the ultrasonic probe in the desired location around the lead sheath <NUM>. The fixing frame is rotatable arranged in order to allow the ultrasonic probe to be rotated around the lead sheath.

The rotary probe guiding device comprises or is connected to a motor or other driving means that causes the movement of the fixing frame and the ultrasonic probe.

In this example the ultrasonic testing apparatus <NUM> is arranged to inspect a splice <NUM>. The ultrasonic probe <NUM> is then rotated around the complete circumference while it is operated, thus scanning the circumference and providing information regarding the thickness and shape of the splice over the circumference. The signals from the ultrasonic probe <NUM> are transmitted to the processing device <NUM> which processes the signals to provide an image of the cross section of the lead sheath splice.

In the example of <FIG>, the ultrasonic testing apparatus <NUM>' also is configured to inspect a splice <NUM>, but in this embodiment, the probe guiding device <NUM> comprises an elongated fixing frame <NUM> which is arranged in parallel to the power cable during operation. The ultrasonic probe <NUM> can be moved along the fixing frame <NUM>, thus scanning the length of the lead sheath. The ultrasonic probe will then be moved the desired length in order to inspect the area of interest.

The embodiments of <FIG> may be combined to scan the lead sheath in both longitudinal and circumferential direction to map a larger area of the lead sheath.

<FIG> illustrates similar embodiments of an ultrasonic testing apparatus as shown in <FIG>, but the ultrasonic testing apparatus is in these embodiments arranged to inspect a section of the lead sheath without splice.

Claim 1:
A power cable lead sheath inspection assembly, comprising a power cable having a lead sheath (<NUM>) and an ultrasonic testing apparatus (<NUM>) for inspection of power cable lead sheath (<NUM>), comprising
- an ultrasonic probe (<NUM>) for emitting ultrasound waves towards the power cable lead sheath (<NUM>) and recording ultrasound waves reflected from the power cable lead sheath (<NUM>),
- a probe guiding device (<NUM>) configured to move the ultrasonic probe (<NUM>) along an inspection path,
- a processing device (<NUM>) connected to the ultrasonic probe (<NUM>) for receiving signals from the ultrasonic probe (<NUM>) and processing the signals, characterized in that the processing device (<NUM>) provides an image representing the lead sheath (<NUM>) along the inspection path, and in that the power cable lead sheath inspection assembly further comprises:
- an ultrasonic control unit connected to the ultrasonic probe (<NUM>) for controlling the ultrasound waves emitted from the ultrasonic probe (<NUM>), where the ultrasonic control unit is in communication with the probe guiding device (<NUM>) for coordination of the movement of the ultrasonic probe (<NUM>) and the emittance of ultrasound waves.