Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2002-01-23
2003-07-22
Kwok, Helen (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S598000, C073S622000, C073S624000, C073S644000
Reexamination Certificate
active
06595061
ABSTRACT:
FIELD OF INVENTION
This invention relates to noninvasive testing of the internal conditions of containers such as pipes, especially to a novel ultrasonic method for noninvasive testing purposes.
COPYRIGHT NOTICE
Pursuant to 37 C.F.R. 1.71 (e), Applicants note that a portion of this disclosure contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
BACKGROUND OF THE INVENTION
Detecting inner wall corrosion in containers such as pipes, cylinders, tanks, pressure vessels, etc. has been a longstanding concern in many industries. For example, MIC (microbiologically influenced corrosion) in water systems is of particular concern. Microbes live in water everywhere and are difficult to kill. Corrosion pitting, slimy fluid and rusty nodules are often the products of MIC. Such corrosion and foreign objects cause wall thinning and reduction of flow area that are detrimental to the structural performance of pipes or other containers, and can sometimes lead to disastrous consequences. Chemical, petroleum, water utility, fire and power industries have been battling MIC and other forms of internal container (e.g., pipe) corrosion (e.g., in water and other fluid storage and/or conducting systems) for many years.
Many nondestructive or noninvasive methods have been applied, with varying degrees of success, to locating MIC and assessing its effects. X-ray and gamma ray radiographs provide images that can be used to gauge the presence of MIC, the amount of occlusion and wall thinning. However, drawbacks of these methods include slow inspection speed, high cost and safety/health concern issues.
Ultrasonic thickness gauging is used routinely to measure wall thickness in refinery piping and tanks. Compared to radiography, ultrasound is cheaper and doesn't emit harmful radiation. A single thickness gauge measurement is much faster than radiography, but it only covers a localized area the size of the transducer. Thus, to obtain the thickness information over a large area, the ultrasonic thickness gauge method may not be as fast as radiographic methods. More importantly, a wall thickness reading at a given point depends on good through-thickness echoes so that an accurate time can be measured. Rough corroded internal wall surface and porous MIC nodules make it difficult to get a valid reading. Often the wall thickness reading is greater than nominal. In some cases, no echoes are available because the ultrasonic energy is simply absorbed or scattered. The ultrasonic thickness gauge cannot be used to detect the existence of slimy fluid either.
The present invention provides a new guided wrap wave ultra sound method which is particularly useful in testing dry containers, and which overcomes the limitation of the prior art.
In contrast, the present application relates to a method which uses guided wrap wave ultrasound (GWWU), which is particularly useful in testing dry containers such as pipes, e.g., containers that are not fluid filled.
SUMMARY OF THE INVENTION
A “guided wrap wave ultrasound” (GWWU) method is described for fast and reliable detection of container features such as pitting, loss, thinning, or irregularities of container wall material, container wall corrosion, MIC, etc. The methods herein are also suitable for detecting foreign objects in containers, e.g., objects such as ice or inner wall attachments which are in contact with the inner wall of the container. Inner wall attachments can be deliberate (e.g., structural features of the container) or unintended (e.g., unwanted ice in a pipe or other container).
The methods herein are well-suited to testing containers (e.g., pipes, conduits, tanks, barrels, drums, cylinders, plates and other appropriate structures that will be apparent upon further review of the following) that are not filled with fluids. In particular, containers that are not fluid filled are particularly suitable for testing according to the methods, devices and systems herein (e.g., essentially or putatively empty or dry containers such as dry pipes, empty cylinders, etc.).
In the methods of the invention, a transmitting transducer excites a guided wave in the container wall (the transducer is, e.g., placed circumferentially on the outside of the container). The guided wave travels along the container wall and enters the receiving transducer. The GWWU method measures resulting direct fields and/or wrap waves. Since the direct field and wrap wave interact with the inner and outer surfaces of the pipe wall, the GWWU method is able to reliably detect container features such as corrosion and MIC on the container inner wall (as well as the outer wall), and any foreign objects or structures in intimate contact with the inner or outer walls.
The GWWU measurement can also be used to detect the existence of ice in the container due to frozen condensation water, e.g., if the ice is attached to the container wall, as well being able to detect other materials attached to or contacting the inner container wall.
In addition, a single GWWU measurement covers a significant portion of the circumference of the inner wall. Therefore, as few as two or three GWWU measurement locations can provide essentially 100% inspection coverage of the whole container (e.g., pipe, etc.) circumference. Thus, the inspection speed is faster than any prior method.
The present invention also provides devices, apparatus, integrated systems and kits for practicing the methods of the invention. For example, the invention provides an integrated system and/or device for detecting corrosion and MIC on the inner wall of containers, and foreign objects in contact with the inner wall of the container, using guided wrap wave ultrasound (GWWU).
The system/device includes components for performing the methods herein, such as a transmitting transducer and a receiving transducer configured for placement at circumferential positions of a pipe or other container, a guided wave generator which produces a shaped tone burst pulse at a specified frequency and means for measuring the direct field, thereby providing an indication of existence of corrosion and MIC on the pipe inner wall, and foreign objects in contact with the pipe inner wall. Typically, direct field and/or wrap waves are the received signals resulting from guided wave propagation along the pipe.
The guided wave can be excited at a selected frequency and angle to maximize the direct field for selected container ODs and materials. Other suitable wave characteristics can also be selected or modulated in the methods and systems herein; e.g., the amplitude of a given phase point on the tone bursts can be modulated or selected.
The device, apparatus, kit or system can include a computer or computer readable medium (or multiple associated computers or computer media) having an instruction set for controlling the system e.g., including an instruction set for controlling the system e.g., for controlling the transmitting transducer the guided wave generator, or the like. The computer or computer readable medium can include other relevant instruction sets, e.g., for measuring the direct field and the leakage field, reporting the results of the measurement to a user, recording and analyzing the direct field energy and wrap wave energy, and the like. Kits can include any of the apparatus or integrated systems elements plus containers for storing the apparatus or system elements, instructions in using the apparatus or integrated systems elements, packaging, etc.
A presently preferred method/system is to use an arbitrary function generator (which, e.g., generates a pulse at a user-defined frequency) in combination with a wideband transducer, so that a range of frequencies can be excited and received. This approach typically uses computer software to control and shape the pulse and frequency along with wideband amplifiers and f
Gorman Michael R.
Ziola Steven M.
Digital Wave Corporation
Kwok Helen
Quine Jonathan Alan
Quine Intellectual Property Law Group P.C.
Saint-Surin Jacques
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