NL2012363C2 - Ultrasonic phased array approach. - Google Patents

Description

Titel: Ultrasonic Phased Array Approach

The present invention relates to a method for inspecting an object such as a metal pipeline or a metal storage tank by means of ultrasonic waves. Such a method is known. The known method comprises the following steps: a. coupling an ultrasonic transducer to a first surface of the object; b. emitting by means of the transducer ultrasonic waves into the object and detecting reflected and/or diffracted waves from the object; c. combining the detected waves and producing based on the combined detected waves a image representing al least a first portion of the inner volume of the object on a screen.

Such types of inspections are carried out because an integrity of an object can be reduced due to degradation, for example corrosion when water is in contact with a metal object. The integrity assessment of installations is difficult for locations that are not directly accessible for inspection (visually or using non-destructive testing) due to an obstacle like a support or foundation. Some locations are difficult to inspect while (local) degradation is likely to occur, like the bottom plates of storage tanks or the location where pipes are in contact with supports, often referred to as CUPS (Corrosion Under Pipe Supports). Such situations exist worldwide in various industries like chemical, oil and gas, power.

Installations are exposed to environmental conditions like rain or moist which is in many cases a cause for corrosion. If the installation is allowed to dry then the impact will be small. However, some locations tend to ‘collect’ moist and will only dry slowly, if at all. Examples are water ingress under a storage tank bottom or between a pipe and a support. Other degradation mechanisms (not specified here) could also occur at inaccessible areas. Local circumstances influence the degradation process but are not considered here, like temperature, materials, design and maintenance. Degradation of an installation can lead to leakage or failure with impact on personal safety, environmental damages, loss of production, downtime and unplanned repairs. To prevent such situations the industries want to evaluate the integrity of installations before failure and take preventive actions. This requires a timely and reliable inspection, also of inaccessible parts.

Making the locations accessible for conventional inspection (like visual inspection or straight beam ultrasonic thickness measurement) is often not a practical/economical option because it requires significant preparations like emptying the tank for measurement of the storage tank bottom from the top side, excavating under the storage tank bottom, entrance into the pipe for measurement of the pipe wall from the inside, or lifting the pipe from the support.

For inaccessible locations the existing inspection solutions are inaccurate, impractical, time consuming, difficult to interpret or require specialized equipment.

Using a single conventional ultrasonic transducer, typically using a shear wave angled beam, will provide only limited results because the signals received by the transducer after reflection on the corrosion will depend strongly on the combination of the impinging beam direction and the shape/orientation of the corrosion. Only part of the reflected signals will be recorded by the transducer. Using multiple transducers, each having a different beam angle, requires more steps during the examination and also an appropriate combination of data during evaluation.

Some ultrasonic methods use a transmission method with two transducers, one on either side of the area under examination, hke CHIME and Multi-Skip. This requires access on both sides of the pipe support and a dedicated manipulator to maintain a fixed distance and orientation while moving the transducers simultaneously in circumferential direction around the pipe. Obviously, this setup is not suitable for the bottom plates of storage tanks.

Radiographic examination is not suitable for storage tank bottom plates because it requires access on both sides and it has typically very limited performance on pipe on supports because of restrictions to properly align the source, area under examination and the film.

The object of the invention is to provide a solution to these problems.

The method according to the invention comprises the following steps: a. coupling a first transmitter phased array ultrasonic transducer (104) to a first surface of the object; b. emitting by means of the transducer an ultrasonic wave into the object under a first angle relative to a normal of the first surface at the position of the transducer so that the wave propagates in the object between the first surface of the object and a second surface of the object while in succession being reflected in the object at the second surface and the first surface respectively multiple times, so called multiple skip (one skip is defined as a wave coming from the first surface, reflecting at the second surface and arriving at the first surface again) and detecting the wave propagating through the object; c. repeating step b. at least one time for another angle than the first angle and/or another transducer position wherein the position of the transducer is varied in a direction from the transducer to a zone of the object to be inspected; d. combining the detected waves and producing based on the combined detected waves a image representing at least a first portion of the inner volume of the object on a screen wherein the first portion of the inner volume corresponds to a position which is offset relative to the normal.

Because by means of the phased array transducer step b can be repeated for multiple different angles on the one hand and wherein the waves propagates through the object by means of multiple internal reflection to locations of the object which can not be directly accessed by means of ultrasonic techniques using direct beams, on the other hand sufficient information can be obtained for creating an image of that location.

This solution is intended for the inspection of inaccessible locations, like bottom plates of storage tanks or pipes in contact with supports, for various industries like chemical, oil and gas, power. For bottom plates of storage tanks only the outer part of the bottom plates can be examined (e.g. 0.5 - 1.5 meters), not the entire tank bottom. For pipe supports various designs are known, from direct contact (generally susceptible to corrosion) to clamped or welded supports.

The examples in this document mention external corrosion of the installation due to water, but also other degradation mechanisms can be inspected like internal corrosion or erosion.

Thus it is possible to carry out the method with one single transducer and optionally a wedge if the same phased array transducer is used for transmitting and receiving. It is however also possible that a separate phased array transducer is used for the detection of the waves.

Thus as an aspect of the invention, a method for inspecting an object, such as a pipe or plate, especially inaccessible parts of a pipe or plate, such as sections of pipes obstructed by supports or clamps, annular and bottom plates of storage tanks, is provided. The method including coupling a transmitter phased array ultrasonic transducer to one of the surfaces of the object to emit shear waves in the object; coupling a receiver phased array ultrasonic transducer to one of the surfaces of the object to detect ultrasonic waves propagating through the object.

The transmitter phased array ultrasonic transducer and the receiver may be separately transducers, which are spaced apart for each other up to 0.5 metre or more, and they may be placed to the same or to opposite surfaces of the object. Alternatively, the transmitter phased array ultrasonic transducer may be the same transducer with the receiver in some circumstances where the ultrasonic waves are reflected back to the transmitter by any discontinuity in the object, such as crack, corrosion, or edge of the object.

The method may further comprise collecting ultrasonic data from the object and analysing the data to detect discontinuities therein. Conducting the phased array ultrasonic inspection may include using ultrasonic testing techniques consisting of electronic scanning, sectorial scanning, dynamic depth focusing, and a combination thereof.

As another aspect of the invention, a phased array ultrasonic testing system is provided for testing the inaccessible components in accordance with the method of the invention. The phased array ultrasonic testing system may include a phased array ultrasonic set, a computer, a scanner with an encoder and one/two phased array transducer^) working in pitch-catch and/or pulse-echo mode. The phased array ultrasonic set and a computer are used for phased array ultrasonic data acquisition to define a plurality of focal laws of ultrasonic beams controlhng the emission/receiving of the ultrasonic beams from the phased array ultrasonic transducers, and analysis. And the scanner with an encoder is to manipulate the transducer(s) into desired positions in order to perform the inspection. Alternatively the transducer is manipulated manually into desired positions while an encoder registers the position of the transducer in order to perform the inspection.

The invention will be further described in the preferred embodiments with reference to the accompanying drawings in which:

Fig. 1 shows a schematic sectional view of an apparatus for phased array ultrasonic inspection of a bottom plate in one tank;

Fig. 2a shows B-scan obtained using the apparatus of Fig. 1 wherein the horizontal axis denotes the position y as shown in Fig. 1 and the vertical axis denotes time t along beam axis (alternatively, the vertical axis denotes depth d);

Fig. 2b shows C-scan obtained using the apparatus of Fig. 1 wherein the horizontal axis denotes the position y and the vertical axis denotes the position x as shown in Fig. 1;

Fig. 2c shows Sectorial scan obtained using the apparatus of Fig. 1 wherein the horizontal axis denotes the position x as shown in Fig. 1 and the vertical axis denotes depth ;

Fig. 2d shows a cross-sectional view of an object wherein one transmitted beam is shown which is internally reflected 5 times (multiple skip);

Fig. 2e shows a hnear scan obtained using the apparatus of Fig. 1 wherein the horizontal axis denotes the position x as shown in Fig. 1 and the vertical axis denotes depth;

Fig. 3a shows a schematic sectional view of an apparatus for phased array ultrasonic inspection of a pipe on a support;

Fig. 3b shows Sectorial scan obtained using the apparatus of Fig. 3a wherein the horizontal axis denotes the position x as shown in Fig. 3a and the vertical axis denotes depth ;

Fig. 4 shows a steep sectorial scan inspection of a first fillet weld;

Fig. 5 shows a less steep sectorial scan inspection of a second fillet weld;

Fig. 6 shows a typical scan plan, 3 skips

Fig. 7 shows a shallow angle to inspect deep into an object like the bottom plate of Fig. 1 or the pipe of Fig. 3a; and

Fig.8 shows a collection of images which may be displayed alone or in combination on a screen. The present invention is related to a phased array ultrasonic test system and method for inspecting various objects, such as, but not limited to, pipes and tanks - especially pipe on supports, annular and bottom plates of tanks.

The present invention can be applied to a wide variety of industrial equipment (including pipes). However, for convenience of description, the invention will be described herein as applied to the phased array ultrasonic inspection of pipe on supports, and annular plates of tanks.

As employed herein, the phrase “pipe on support” corresponds to one section of pipe on top of a support, or concealed by a support.

As employed herein, the phase “inaccessible part” means that one part of an object is not directly accessible, or easily accessible. For example, the pipe on a support cannot be accessible for visual inspection directly without lifting the pipe.

The present invention employs phased array ultrasonic inspection system which can comprise one single phased array transducer or two or more phased array transducers. Each of the transducer is typically made as a series of individual elements. These individual elements can be excited in various sequences that allow the ultrasonic beams generated therefrom to be shaped, angled or focused within the tested object. The phased array transducer and wedge are used to allow multiple angle beam inspection sweeps to be conducted consecutively without the need to use numerous individual wedges which is required in the conventional inspection. Referring now to Fig. 1 there is shown that an apparatus 300 used for inspection of a bottom plate of a tank 302 which is 10 mm thick. The apparatus 300 comprises a first phased array ultrasonic transducer 304 (combining a phased array transducer unit 306 a phased array wedge 312), a scanner 402 and an encoder 404 to record the position of the phased array transducer 304. The phased array ultrasonic transducer 304 is coupled to a receiver-transmitter 307.

When the phased array transducer 304 is excited, it generates a pulse of shear waves in the form of a beam 310 propagating in a direction 0 from the normal. The pulse of shear waves (also referred to as a beam or wave beam) will reflect one or more reflections before being reflected back to the phased array transducer 304 by any discontinuity in the object, such as crack, corrosion, or edge of the bottom plate 302. The apparatus is designed so that it subsequently generates pulsed shear waves with mutually different values for the angle Θ. In this manner a plurality of reflected signals can be received which comprise information about the volume of the bottom plate of the tank.

Thus when the phased array transducer unit 306 is excited, it generates a pulse of compression waves via the coupling wedge 312 of the transducer 304 into the bottom plate 302. This generally generates a pulse of shear waves or beam 310 propagating in a direction 0 from the normal. The shear wave angles Θ (comprising θι, θ2...θη) in the plate generated by the transducer 304 are larger than the shear-compression critical angle, which easily cover the frequently-used angles (45°, 60° and 70°) in Multi Skip technique. When this pulse of shear waves 310 reaches the opposed surface 320 of the plate, it will reflect back as shear waves 312 without any mode conversion. And the pulse of shear waves 312 will reflect from the other surface 322 one or more times as shear wave 324 etc. Thus this implies multiple skips. This is also shown in Fig. 2d for one generated beam. These multiple skips provide the possibility to investigate areas of the plate which would normally not be accessible for conventional ultrasonic inspection methods using direct beams. If there would be corrosion 358 on position 150 this can be derived from the interaction of the waves with the corroded area. The waves would be reflected back towards the transducer and reach the transducer after having reflected at least one time on the surfaces 320 and 322. The reflected signals are received by the transducer 304.

In the method according to Fig. 1 the angles of shear waves (Oi, θ2...θη) will be varied in phased array sectorial scan. The wave paths are indicated by rays, but it will be understood that the transducer 304 will in fact emit a beam of finite width which will diverge slightly.

Each of the detected signals by means of the transducer 304 will be supplied to a computer 200 for processing in combination the received signals to provide an image of the internal of the object on a screen 220. The computer may be provided with special software for processing the detected signals such as commercially available as ISONIC 2010 Portable Ultrasonic Digital Flaw Detector and Recorder which does include both the computer and the software. The image may for example be in the form/format of a well known B-scan, C-scan or Sectorial scan. Thus although a B-scan, C-scan and Sectorial scan are actually not (completely) carried out, the way the information is presented on the screen may be in the format of such a scan. This is convenient for a user who is familiar in the interpretation of such scans. In the Sectorial scan the color indicated the amplitude at a position x on a depth d. In the B-scan the color indicated the amplitude at a position x on a depth corresponding with time t or alternatively in the B-scan the color indicated the amplitude at a position x on a depth d corresponding with time t and taking the beam angle Θ into account. In the C-scan the color indicated the amplitude as seen on a top view of the product at a position (x,y). In Fig. 1 the direction of vector Y is perpendicular to the direction of vector d and vector x.

Fig. 2a and b shows images in the format of a B-scan and C-scan obtained using the apparatus 300 for inspection of a steel plate of thickness 12mm. To represent the effect of defects, 8 flat bottom holes had been machined in the upper surface, as shown in Table 1.

Table 1 Details of defects machined in the test plate

The phased array probe was placed near one edge of the plate, 100 mm from the 8 mm flat bottom holes, and 290 mm from the 16 mm flat bottom holes. In Fig. 2a, Defects No. 1-4 are shown in the upper position from the left to the right, and Defects No. 5-8 are shown in the lower position from the left to the right. In Fig. 2B, Defects No. 1-4 are shown in the lower position from the left to the right, and Defects No. 5-8 are shown in the upper position from the left to the right. It can be evidently observed that all flat bottom holes are detected with correct positions. And the signals from the far end of the plate are disappeared or weakened due to the existence of defects.

Fig. 2C shows an example of an image generated by the computer 200 in the format of a sectorial scan of a defect obtained using the apparatus 300 for inspection of a steel plate.

Fig. 3a shows an apparatus 100 used for inspection of a steel pipe 102 which is 20 mm thick. The pipe rests on a support 120. Thus positions in the pipe above the support are not accessible for conventional methods wherein ultrasonic transducers are used. The apparatus 100 includes a first phased array ultrasonic transducer 104 (combining a phased array transducer unit 106 with a phased array wedge 112) and optionally a second phased array ultrasonic transducer 104’(combining a second phased array transducer unit 106’ with a phased array wedge 112’), separated by a distance of 1000 mm along the pipe 102 from the first phased array transducer 104.The first phased array ultrasonic transducer 104 is connected to a transmitter-receiver 107 and the second phased array ultrasonic transducer 104’is connected to a receiver 107’.The transmitter-receiver 107 and the receiver 107’ are connected to a computer 200. And the apparatus also includes a scanner 202 used to keep the probe distance constant and an encoder 204 to record the position of phased array transducers.

When the phased array ultrasonic transducer unit 106 of the transducer 104 is excited by means of the transmitter-receiver 107, it generates a pulse of compression waves in the coupling wedge 112. This generally generates a pulse of shear waves 116 propagating in a direction Θ from the normal. The shear wave angles Θ (comprising Οι, θ2...θη) in the pipe generated by the transducer 104 are larger than the shear-compression critical angle, which easily cover the frequently-used angles (45°, 60° and 70°) in Multi Skip technique. When this pulse of shear waves 116 reaches the apposed surface of the pipe, it will reflect back as shear waves 118 without any mode conversion. And the pulse of shear waves will reflect from the surfaces one or more times before being received by the second phased array ultrasonic transducer 104’. Thus this implies multiple skips. These multiple skips provide the possibility to investigate areas of the plate which would normally not be accessible by conventional ultrasonic inspection methods. If there would be corrosion on position 150 this can be derived form the interaction of the waves with the corroded area.

Each of the signals detected by means of the second phased array ultrasonic transducer 104’ and the receiver 107’ is submitted to the computer 200. The computer processes this detected signals in combination for creating an image on a screen 220 of the detected object. The computer 200 may be provided with special software for processing the detected signals such as commercially available as ISONIC 2010 Portable Ultrasonic Digital Flaw Detector and Recorder which does include both the computer and the software. The image may for example be in the form of a well known B-scan, C-scan or Sectorial scan. An example if the Sectorial scan is shown in Fig.3b.Thus although a B-scan, C-scan and Sectorial scan are actually not (fully) carried out, the way the information is presented on the screen may be in the format of such a scan. This is convenient for a user who is familiar in the interpretation of such scans.

In Fig 3a the angles of shear waves (θι, 02. ..θη) will be varied in phased array sectorial scan, and kept the same in phased array linear scan. The wave paths are indicated by rays, but it will be understood that the phased array ultrasonic transducer 104 will in fact emit a beam of finite width which will diverge slightly.

It is also possible to receive waves, which are reflected back, for example due to the corrosion, by means of the first phased array ultrasonic transducer 104. Thus the first phased array ultrasonic transducer 104 can also be used in combination with the transmitter-receiver 107 for receiving the reflected waves. The waves which are thus received by means of the transmitter-receiver 107 can also be submitted to the computer 200 for processing these detected signals in combination for creating an image on a screen 220 of the detected object. In that case the receiver 106’ could be deleted.

In Fig. 1 and Fig. 3a, no welds are shown in the pipe 102 and plate 302, but it does not indicate that the present invention cannot test objects with welds. On the contrary, it is shown in experiments that an object with a weld between the transmitter and receiver phased array transducers or in front of the single phased array transducer can be tested by the present invention.

For each of the examples provided and also in general for a method according to the invention the inaccessible part of a pipe or plate is inspected by coupling an ultrasonic transmitter phased array transducer to an accessible surface of the tested object to emit an angled shear wave ultrasound beam propagating in a direction that is inclined from the normal to the surface. The ultrasonic beam reflects on the opposite surface of the object back to the surface where the transducer is positioned, this is referred to as skip. Using multiple skips allows for examination of an area further away and not directly accessible for positioning the transducer itself, like near a pipe support or beyond a tank shell.

Instead of using a conventional transducer with a fixed beam direction, a phased array transducer is used connected to a phased array system. This allows for steering the ultrasonic beam in various beam angles as known to the person skilled in the art. Using various beam angles ensures better coverage of the complete wall thickness and makes the examination less dependent on the shape and orientation of the corrosion because each part of the corrosion surface is hit by ultrasound beams at various angles.

For tank base plate condition assessment only the part 370 in Fig. 1 of the tank base plate (extending outside the tank wall) can be examined with conventional direct beams, for example with 0° beams as used for wall thickness measurement. However, also other parts at the underside of the bottom plate are susceptible to corrosion due to water ingress under the tank, like the area 372 directly under the tank wall 350 or the area 374 located inside of the tank wall.

For tank base plate condition assessment as discussed for Fig 1. the new approach enables using one phased array transducer to evaluate different parts that are not directly accessible: area 372 located directly under the tank wall 350, inspect the fillet welds 354, 356 that connect the tank wall to the tank base plate, and provide imaging into the tank base plate, and detect corrosion 358 for example on location 150. This system is designed to inspect locally and deep into a storage tank base - this is normally carried out with LORUS (Long Range Ultrasonics), using conventional transducers with fixed beam angles. A vertical wall of the tank 350 (shell) is welded to the tank floor plate 302. In the tank base inspection the transducer is positioned on the tank base plate outside the tank shell and the ultrasonic beam is directed into the tank floor plate beyond the vertical tank shell. Suitable angles are selected to inspect the fillet welds (between the shell and base plates) and shallower angles to inspect well inside the tank floor plate. The beam may be swinged to perform four inspections: 1- Straight beam thickness measurement on the outside part of the storage tank bottom plate, using compression waves (θ=0) wherein no multiple skip is used. 2- Steep Sectorial scan inspection of the first fillet weld, using shear waves (Θ is varied between θι and Θ2 wherein a single skip is used. One example for a value of Θ is shown in Fig. 4. 3- Less steep Sectorial scan to inspect the second fillet weld, using shear waves (Θ is varied around Θ3) wherein a single skip is used. One example for a value of Θ is shown in Fig. 5. 4- Shallow angle to inspect deep into the tank base (using shallow angle sectorial or linear scans), using shear waves (Θ is varied between Θ3 and almost 90 degrees) wherein multiple skip is used. Fig. 6 shows a typical scan plan using three skips. Fig. 7 shows the image on the display corrected for the skips (true geometry).

The focus is the ability using one Phased Array transducer to undertake tank base plate condition assessment. The drive here is the look at the water ingress / corrosion directly under the tank wall, inspect the fillet welds and provide imaging into the tank base plate. The method according to the invention has provided excellent results for both the localized weld inspection as well as the long range phased array inspection. For Annular plate inspection it is preferred to use the back wall 360 (far edge, see Fig. 1) of the plate as a reference.

In this inspection shear wave angled beams are used in a pulse echo way. Depending on the situation a plate bulk wave can be used. In certain situations not only the above referred to angled compression wave beams can be used but also creep wave or surface wave (wherein Θ = 90 degrees) could be used. These angled compression wave beams are generated if the shear wave angled beam is at or below the critical angle (Snell’s law), as known to the person skilled in the art.

The above examples for Fig. 1 and Fig. 3a describes the examination while the transducer is in a static (fixed) position wherein Gis varied by means of the phased array transducer and multiple skip is applied. In addition if Θ = 0 degrees a thickness measurement can be carried out and if Θ = 90 degrees an inspection using creep waves could be carried out.

Alternatively the examination is performed while the transducer is moved sideways in the direction of the arrow y in Fig. 1 and in a tangential direction of the pipe in Fig. 3a. (thus compared to the direction of the ultrasonic beam) to scan the object, e.g. moving the transducer along the tank bottom plate or around the pipe. An encoder is used to record the position/movement of the transducer and store this information together with the ultrasonic results. The receiving signals obtained are again submitted to the computer for processing in combination and generating an image as shown in Fig. 8. In that case also multiple skip will be applied as is schematically shown in Fig. 2d.

Also for the examination of the bottom plate as shown in Fig 1 or the pipe on supports as shown in Fig. 3a, more information of the corrosion can be obtained while the transducer is at one position if the ultrasonic beams are entered into the object at different positions at the surface. This can be done by activating other elements of the transducer unit 106 or 306, also known as linear scan in phased array technology. Fig. 2e shows the result of such a linear scan for the embodiment of Fig. 1. In addition even more information of the corrosion can be obtained if the transducer is moved towards or away /from the area under examination, in the direction of the ultrasound beam, typically in axial direction x of a pipe when examining a pipe on a support or in a direction perpendicular to a side wall of a tank when examining a bottom plate of the tank. This direction is indicated with x in Fig. 1 and Fig.3a. Thus the position of the transducer is varied in a direction from the transducer to a zone 358 of the object to be inspected, thus in a direction of the component of the beam along the surface of the object whereon the transducer is positioned. Using an encoder and suitable software known as such allows for a geometric reconstruction of the area under examination, consisting of multiple overlayed Sectorial scans based on various transducer positions, as shown in Fig. 3b.

The results of the various beam angles in the sectorial scan or hnear are combined into one overview for evaluation. For evaluation the measured amplitudes can be shown in the format of a C-scan (a top view), B-scan (a side view) or Sectorial scan (a side view). In each of such scans the color represents an amplitude of the wave received from a certain position or area. Thus, the evaluation is amplitude based. From the B/C scan the dimensions of the corrosion can be determined (length, width, depth). Please note that a B-scan can be obtained by moving the transducer (an actual scan) or by using different elements, at different positions, of the phased array transducer. In the present invention a sectorial scan and/or hnear scan is actually carried out and the results are shown in the format of B-scan and/or C-scan and/or Sectorial scan and/or even a D-scan if desired.

The received signal in the form of an A-scan (Fig. 8; 8.1), the generated format of a B-scan (Fig. 8; 8.2; note the vertical axes denoted t (time) or d (depth)), the generated format of a C-scan (Fig. 8; 8.3) and/or the generated format of a Sectorial or Linear scan (Fig. 8; 8.4) can be generated by the computer 200 and shown as an image on the screen 220 alone or in combination.

For the side view display (B-scan) the measured signals can be displayed uncorrected for the skips (see Fig. 2c) (typical Sectorial-scan display). The software of the computer 200 is capable to correct the signals for the reflections at the objects (skips), so called true geometry (see Fig. 7).

In the corrected or uncorrected side view the depth/height of an indication (corrosion) can be measured using the amplitudes of the signals, e.g. -6 dB method. Some software provides statistical analysis of the data, for example a histogram, that support the evaluation of the depth/height of an indication. This software is known as such and described on page 352 and 373 of the manual ISONIC 2005 / 2010/ STAR, showing the histogram/statistical function, and stating that the histogram represents the occurrence of‘informative parameter (amphtude or distance) represented by colors in the area of polygon; statistical distribution is presented by appropriate graph.

Several phased array possibilities can be used (pitch-catch, electronic scanning, sectorial scanning, dynamic depth focusing) depending on the geometry (thickness of the plate, length to be examined, transducer position) and is taken into account by the measuring and display software.

The ultrasonic examination can be carried out using an ultrasonic testing technique consisting of pulse-echo, pitch-catch, electronic scanning, hnear or sectorial scanning, dynamic depth focusing, and a combination of thereof and a transmitting phased array transducer and a receiving phased array transducer may be used, separated by some distance and or a single phased array transducer can be used. The method can be used in plates, pipes, tanks, vessels, etc. The phased array ultrasonic transducer mentioned may include 1-D, 1.5-D and 2-D arrangements.

Claims (18)

A method of inspecting an object (102), the method comprising the steps of: a. Coupling a first phased array ultrasonic transducer (104) to a first surface of the object; b. emitting an ultrasonic wave through the transducer in the object at a first angle to a normal of the first surface at the position of the transducer so that the wave propagates in the object between the first surface of the object and a second surface of the object while being successively reflected at least once in the object on the second surface and the first surface respectively, so-called multiple skip and detecting the wave propagating through the object; c. repeating step b at least once. for an angle other than the first angle and / or another converter position where the position of the converter is varied in a direction x along the first surface of the converter to an area of the object to be inspected and / or in a direction along the surface perpendicular to the x direction; d. combining the detected waves and creating based on the combined detected waves an image representing at least a first part of the inner volume of the object on a screen with the at least first part of the inner volume corresponding to a position which offset is relative to the normal. The method of claim 1, wherein step c. a plurality of times is repeated for mutually different angles respectively and / or for a plurality of mutually different converter positions respectively. A method according to any one of the preceding claims wherein the converter position is varied in step c. wherein in step d. combining the detected waves to create the image is also based on the positions of the converter taken by an encoder. The method of claim 3, wherein the transducer position is varied in a direction perpendicular to the direction in which transmitted waves propagate through the object. The method of claim 1, 2, 3, or 4, wherein in step d. an image is created in the format of a B-scan, C-scan, D-scan and / or Sectorial scan. A method according to any one of the preceding claims, wherein the wave is detected by means of the first phased array ultrasonic converter. A method according to any one of the preceding claims 1-5, wherein the wave is detected by means of a second phased array ultrasonic converter which is also coupled to a surface of the object at a position other than the first phased array ultrasonic converter. A method according to any one of the preceding claims, wherein the object is a bottom of a tank wherein the first phased array ultrasonic converter is coupled to the first surface of the object outside the tank and wherein the first part of the volume is below an interior space of the tank. A method according to any preceding claim wherein the article is a pipeline that rests on a support with the first part of the volume above the support. The method of claim 9, wherein the first phased array ultrasonic transducer is coupled to the first object at a longitudinal position of the pipeline which is offset from the support. A method according to claim 6 and / or 7 and claim 8 or 9. A method according to any one of the preceding claims wherein a reflection on an end surface connecting the first and second surface is detected and wherein a relatively low intensity of such detected reflection indicates a defect along the path in which the wave moved within the object. A method according to any one of the preceding claims, wherein corrosion is detected in the first part based on reflections of the wave on a corroded area in the first part. A method according to any one of the preceding claims, wherein the emitted beam is a shear wave beam. The method of any one of the preceding claims, wherein the displayed scan is corrected for the reflections on the second and first surface to project the signals at their true positions. A method according to any one of the preceding claims, wherein the depth of the corrosion and / or remaining thickness is determined from the image. A method according to any one of the preceding claims wherein a statistical analysis is performed on the image to determine a distance between indications and the first or second surface. A system provided with at least a phased array converter, a computer and a screen for performing the method according to any one of the preceding claims.