System and Methods For Non-Destructive Testing of Tubular Systems

Abstract

Method and systems for non-destructive testing of a gas or liquid filled object at atmospheric pressure or high pressure. The method includes the steps of providing an acoustic pulse reflectometry (APR) system (200) having a wideband transmitter (210), a pressure sensor and short mixed wave tube (214) performing at least one calibration parameter, attaching the object to the APR system and performing a measurement to obtain at least one calibration parameter, attaching the object to the APR system and performing a measurement to obtain an object test result and processing the object test result and the at least one calibration parameter to obtain an object impulse response that reflects a status of the object.

Description

FIELD OF THE INVENTION[0001]The present invention relates generally to non-destructive testing (NDT) systems and methods and more particularly to acoustic pulse reflectometry (APR) systems and methods used in tubular objects.BACKGROUND OF THE INVENTION[0002]Acoustic pulse reflectometry is the generic name given to a family of techniques used to measure the acoustic response of a given system. Its application to systems consisting of volumes of air bound by rigid surfaces is known. The term “APR” is derived from the fact that an excitation pulse (or “impulse”) is applied to the system, and the reflections created inside the system are then measured. The pulse need not be “real”, but may be in the form of pseudo-noise or frequency sweeps, see below. Various algorithms are applied to this acoustic response, in order to gain information regarding the system being examined.[0003]Ideally, APR should enable extraction of the theoretical impulse response of the system being measured. In pra...

AI Technical Summary

Benefits of technology

[0032]The present invention provides an elegant solution to the long standing problem of signal overlap, described in the Background. Previous solutions are improved on by the use of a combination of signal processing techniques and a separation algorithm with reduced numerical sensitivity. The present solution, embodied in both systems and methods, uses an APR system with a mixed wave tube and unique calibrations.

[0035]According to the present invention there is provided an APR system for non-destructive testing of a pressurized test object, including a wide band signal transmitter for providing source acoustic pulses, a mixed wave tube for serving as conduit for the source pulses between the transmitter and object, a pressure sensor equidistantly spaced between two opposite ends of the mixed tube and used for sensing impulse responses from the test and calibration objects and means for pressurizing the mixed wave tube, calibration and test objects, thereby enabling non-destructive testing of a pressurized object.

[0036]According to the present invention there is provided an APR system for non-destructive testing of a test object filled with liquid, including a wide band signal transmitter for providing source acoustic pulses, a mixed wave tube for serving as conduit for the source pulses between the transmitter and object, a pressure sensor equidistantly spaced between two opposite ends of the mixed tube and used for sensing impulse responses from the test and calibration objects and means for introducing and removing a liquid into or from the mixed wave tube, calibration and test objects, thereby enabling non-destructive testing of a liquid filled object.

Problems solved by technology

In practice this is impossible, since an ideal pulse has an infinite bandwidth (BW), and therefore cannot be created under laboratory conditions.

From a purely experimental point of view, several technical problems are encountered in this type of setup:1. The acoustic pulse typically has high amplitude, but is very short in duration.

This results in a pulse having rather low energy content.

This makes it difficult to obtain a high signal to noise ratio (SNR) in the reflections measured from the object.2. The excitation pulse and the reflections from the object have finite duration, which can cause them to overlap at the microphone.

This can make them very difficult to separate.3. Reflections from the object eventually travel down to the transducer itself, reflect off it, and return to be measured once again by the microphone.

These secondary reflections can once more interfere with measurements of the response of the object.

Current methods assume that no transverse modes are excited in the tube, a fact that limits the usable bandwidth.

This is somewhat in conflict with the objective of attaining an excitation pulse having the largest possible bandwidth, and some compromise must be reached.

This would probably result in major inaccuracies.

A common problem in APR systems is the presence of background noise, especially when such measurements are carried out in the field, as opposed to ideal laboratory conditions.

Incoherent background noise is reduced considerably this way, though this method prolongs the measurement process to an extent that is unacceptable in certain setups.

Presently, a major drawback in implementing APR is the presence of long tubes (L1 and L2 in FIG. 1) on either side of the measurement microphone.

These cause the instrument to be extremely bulky, even when they are coiled.

They also introduce a large degree of attenuation, which limits the accuracy and the range of the instrument.

On the other hand, propagation through these tubes causes attenuation of high frequencies, thereby reducing the bandwidth of the pulse impinging on the object, and reducing the effective range of the equipment.

Errors in accurately deriving Zi and Hi and various numerical sensitivities in applying the above formula caused this method to give poor results.

In complicated systems where there are valid discontinuities such as changes in cross sections, finding the peaks related only to faults can be difficult and unreliable.

This method is also simplistic, since different sized leaks will have different acoustic patterns, and it may not be feasible to store a large number of such patterns.

Furthermore, acoustic wave propagation properties change with temperature and moisture, so that library measurements may not fit well with field measurements taken under varied conditions.

This method is also sensitive to low frequency noise, when present.

As shown in the latter reference, this method is most useful if separate measurements can be taken from either side of the tube, which is rarely feasible.

Otherwise, application of the bore reconstruction algorithm gives a false indication of a steadily increasing flare, which can be interpreted as a leak if a priori knowledge indicates that such a flare is not in fact present.

Automated detection of such a false flare is not straightforward [Chilekawa], especially when it is located near other discontinuities in the tube.

No prior art APR method and system provide all of these features.

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