GB2201777A

GB2201777A - Testing structures by inducing and detecting vibrations

Info

Publication number: GB2201777A
Application number: GB08801584A
Authority: GB
Inventors: Nobuo Imamoto; Yasuhiro Yamashita; Koichi Sakuno
Original assignee: Mitsui Engineering and Shipbuilding Co Ltd; Power Reactor and Nuclear Fuel Development Corp
Current assignee: Mitsui Engineering and Shipbuilding Co Ltd; Power Reactor and Nuclear Fuel Development Corp
Priority date: 1987-01-28
Filing date: 1988-01-25
Publication date: 1988-09-07
Anticipated expiration: 2008-01-25
Also published as: FR2610110A1; GB2201777B; DE3802138C2; DE3802138A1; JPH0511895B2; JPS63186122A; FR2610110B1; GB8801584D0

Description

1 Y I- 1 2 2 v @ 17 g 71 1.

1 STRUCTURAL DEFECT DETECTING SYSTEM The present invention relates to a system for detecting structural defects and, more particularly, a detecting system for finding a defect or fault in various constructions particularly in such as chemical plants, nuclear power plants and so forth.

Constructions in for example chemical plants in which a corrosive fluid is handled and nuclear power plants in which safety is of a particular importance include such ones of which it is necessary to periodically operate inspections for detecting generation of any structural abnormality. Methods today employed for such inspections comprise measuring the natural frequency of constructions, the object for inspection, and include the impact hammering test method according to which a hammering is applied to-a construction to be inspected by a hammer equipped with a force detector and the natural frequency of the construction is determined.

However, where it is undesirable to subject the 20. construction either to'the danger of impairing or to the aPplicat,;, on of an excessive degree of vibration, the impact hammering test method is not employable. Also, this test method cannot be relied on for the inspection'of 4 4 constructions in nuclear power plants where possible radiation effects prevent man from approaching the constructions.

For the inspection of structural abnormality, it is also proposed to make use of a piezoelectric vibration exciter. However, the frequency region possibly utilized by this vibration exciter is limited only to a high-frequency band, and in addition, the vibration exciting capacity of the exciter is relatively limited. Thus, this proposed method is not put for a practical use.

The present invention has been made to obviate the above-indicated problems in the prior art, and it is a primary object of the invention to provide a structural defect detecting system by which constructions can be inspected for any possible structural abnormality without damaging the constructions, the object for inspection, or imparting any unnecessary or excessive vibration to the constructions.

Another object of the invention is to provide a structural defect detecting system by which the inspection for finding a structural abnormality can be effectively made of not only constructions in chemical plants and nuclear power plants but also substantially all other constructions such as ships and boats, bridges and so forth.

1 1 1 r A still another object of the invention is to provide a structural defect detecting system the operation of which can be remote-controlled.

The present invention attains the above objects by providing a structural defect detecting system which comprises a vibration exciter and a vibration sensor to be detachably attached in a spaced arrangement to a constructi.on to be inspected, by which the vibratory waves generated responsive to vibration excited by the vibration exciter, propagated through the construction and detected by the vibration sensor are analyzed to detect a defect or fault in the construction and which is characterized in that for the vibration exciter a piezoelectric accelerometer is utilized.

Thus, the present invention is characterized in that it makes use of a piezoelectric accelerometer not for its original or normal utility as a vibrometer or vibration sensor but for a vibration exciter.

The piezoelectric accelerometer for use for the present invention should preferably be such a one which has a wide range of the useful frequency band (1 Hz to 10 KHz) and, in addition, does not impart any unnecessary or excessive vibration to a construction to be inspected. One example of useful piezoelectric accelerometers is the high-sensitivity accelerometer, type 213 E, commercially available at ENDEVCO Corporation (U. S. A.).

1 1 r f The piezoelectric accelerometer is connected to a vibration signal generator through a pulser driver so that vibration can be excited by pulsed signals generated by the vibration signal generator, which should preferably be of a capacity of generating 20 to 10,000 pulsed signals per second.

For the vibration sensor, which is for sensing vibratory waves propagated through a construction to be inspected, use is made of a piezoelectric accelerometer as is the case with the above-mentioned vibration exciter.

Upon sensing vibratory waves, the vibration sensor issues signals, which are sent to and amplified by a charge amplifier and then supplied to a data recorder and/or an FFT analyzer (fast Fourier transform analyzer), to which the pulsed signals generated by the vibration signal generator, too, are supplied.

The charge amplifier is of a same channel number as the vibration sensor to be detachably attached to the construction to be inspected. The data recorder is of a channel number equal to an aggregate of the channel number of the vibration exciter and that of the vibration sensor to be detachably attached to the construction, the object for inspection.

1 IR IL t - 5 The FFT analyzer is for use for analysis of the waveform of signals sent from the vibration sensor. While the inspection of a possible structural abnormality in a construction is made with reference to or based on the waveform analyzed by the FFT analyzer, the result of the waveform analysis is stored in or by a controller such as a microcomputer and is also processed for a diagrammatic processing by a plotter.

The system according to the present invention also incorporates a selector which has a function to perform a selection between an on-line side and an off-line side and also a function to selectively take data of any optional two channels.

The above and other structural features, Is operational features and results of the present invention will become more apparent from considering the below given detailed description of the preferred embodiment of the invention illustrated in the accompanying drawings, in which:

Fig. 1 shows a system diagram of a structural defect detecting system embodying the present invention; and Fig. 2 is a view, showing a preferred spaced arrangement of a vibration exciter and a vibration sensor.

r In Fig. 1, the reference numeral 3 denotes a construction, the object for the intended inspection of a structural abnormality, to which two vibration exciter 41 and 42 and six vibration sensors 51, 521 53, 54, 5s and 56 are removably attached.

The vibration exciters and vibration sensors are disposed in a particular spaced arrangement. As shown in Fig. 2, a vibration exciter 4 and a vibration sensor 5 are disposed on opposing sides of a point or a region 3a on the construction 3 in which there is expected to have taken place a reduction of the plate thickness of the construction material due for example to corrosion or the generation of a crack or a like fault. It has been ascertained that the vibration exciter 4 and the vibration sensor 5 should preferably be spaced from each other by a distance up to and including 5 m. For each of the vibration exciters 41 and 42, use is made of a piezoelectric accelerometer having a frequency band within a range of 1 Hz to 10 KHz and not tending to apply any unnecessary or excessive vibration to the construction 3. A piezoelectric accelerometer having a same function as the one for the vibration exciters is used also for each of the vibration sensors 51, 521 53, 54, 55 and 5 r,.

ti Z 1 f f 7 - Also in Fig. 1, a vibration signal generator is shown by the reference numeral 1, which generates 20 to 10,000 pulsed signals per second. Signals generated by this signal generator 1 are put into a pulser driver 2 through a cable 13. The pulser driver 2 comprises two charge amplifiers 2a and 2b, of which the one shown at 2a is connected to the vibration exciter 41 through a cable 141. while the other 2b is connected to the vibration exciter 42 by a cable 142.

Indicated at 6 is a 6-channel amplifier, to the input side of which the vibration sensors 51, 529 53# 54p 55 and 5e are connected through cables 151, 152, 153, 1549 155 and 156, respectively.

The numeral 7 represents an 8-channel data recorder, to which the signals amplified through the amplifier 6 are inputted through cables 161, 162, 163 164, 16s and 166. Pulse signals generated by the vibration signal generator 1 are also inputted to the data recorder 7 through a cable 17 branched from the cable 13.

The numeral 8 shows a selector, which has a function,to selectively take the data of optional 2 channels and a function to effect a selection between an on-line side and an off-line side. That is to say, this se^lector 8 comprises a first selector member 8a which operates the 1 selection between the on-line side and the off-line side and to which the output side of the data recorder 7 is connected through cables 18t, 182P 1839 184, 18s and 186. Cables 191, 1921 1939 194v 195 and 196 branched from cables 161, 162, 163, 1649 16s and 16s respectively and a cable 20 branched from the cable 13, too, are connected to the first selector member 8a. -The selector 8 also comprises a second selector member 8b, which selectively takes data through optional 2 channels and to which an FFT analyzer 9 is connected through a cable 21.

Shown at 11 in Fig. 1 is a controller having a built-in interface. This controller 11 is connected to the FFT analyzer 9 by a cable 22, to a plotter 12 by a cable 23 and also to an FD driver 25 by a cable 24. The FFT analyzer is connected also to the plotter 12 by a cable 26.

The above described structural defect detecting system according to the invention operates as described below. Herein, to avoid complexity in description, it is provided that in connection with the vibration exciter 4 and the vibration sensor 5, the exciter indicated at 41 and the sensor indicated at 51 alone are operated. It also is assumed that the first selector member 8a is constantly connected to the on-line side.

1 Under the above conditions, the system is operated, and then pulsed signals are generated by the vibration signal generator 1, which are amplified by the pulser driver 2 and then transmitted to the vibration exciter 41 to cause this member 41 to excite. The vibration of the exciter 41 is propagated through the construction 3 and sensed by the vibration sensor 51.

The vibratory signals sensed by the sensor 51 are amplified through the amplifier 6, inputted to the FFT analyzer 9, put for a waveform analysis by this analyzer 9 and then stored in the controller 11. Also, the data put for the waveform analysis by the analyzer 9 are subjected to a diagrammatic processing by the plotter 12.

Same as the vibratory signals sensed by the vibration sensor 51, the pulsed signals generated by the vibration signal generator 1 themselves, too, are processed for a waveform analysis by the FFT analyzer, then stored in the controller 9 and, at the same time, processed for a diagrammatic processing by the plotter 12.

It may well be devised to once store the data initially obtained as above by recording them on the data recorder 7 in a condition in which the connection of the first selector member 8a is switched to the off-line side and, at the time when fresh data are collected after the f f 1 1 1 10 lapse of a certain period of time, put the data for the analysis. In this case, after the lapse of the certain period of time, the system may be operated for a second time under same conditions as those under which an initial or a first inspection was made, to collect data on the signals generated by the vibration signal generator 1 and data on the vibratory signals sensed by the vibration sensor 5 and carry out a comparative examination of the newly collected data and the initially collected and previously stored data. Thus, it is feasible to determine any change in the natural frequency or the response characteristic to vibration, of the construction, to thereby effectively detect any defect or fault possibly to be generated in the construction.

Although the above description of the preferred embodiment of-the invention is limited, in its reference,. only to the instance in which the vibration exciter 41 and the vibation sensor 51 alone are operated, it will be readily understood that the two vibration exiters 41 and 42 and the six vibration sensors 51, 52, 53, 54, Ss and 5s can be suitably selectively combined and put for operation to accurately locate a point or points of a defect or fault in the construction.

t C.

1 1 1 r

Claims

1. A structural defect detecting system which comprises a vibration exciter and a vibration sensor to be detachably attached in a spaced arrangement to a construction to be inspected, by which the vibratory waves generated responsive to vibration excited by the vibration exciter, propagated through the construction and detected by the vibration sensor are analyzed to detect a defect or fault in the construction and which is characterized in that for the vibration exciter a piezoelectric accelerometer is utilized.

2. The system as claimed in claim 1, characterized in that said vibration exciter has a vibration signal generator connected thereto through a pulser driver.

3. A structural defect detecting system substantially as hereinbefore described with reference to and as shown in the accompanying drawings.

4. Any novel integer or step, or combination of integers or steps, hereinbefore described and/or as shown in the accompanying drawings, irrespective of whether the present claim is within the scope of, or relates to the same or a different invention from that of, the preceding claims.

Published 1988 at The Patent OVloe, State House, WN1 High Holborn, London WCIR 4TP. Further copies may be obtained ft= The Patent OffLoe, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex technIques ltd, St Mary Cray, Kant. Con. 1/87.