Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2000-09-27
2003-06-17
Moller, Richard A. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S644000
Reexamination Certificate
active
06578424
ABSTRACT:
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.
FIELD OF INVENTION
This invention relates to noninvasive testing of the internal conditions of fluid-filled containers such as pipes, especially to a novel ultrasonic hand-held variable angle membrane (VAM) scanning head for such testing purposes.
BACKGROUND OF THE INVENTION
Detecting inner wall corrosion in pipes, cylinders, tanks, pressure vessels, and other containers has been a longstanding concern in many industries. MIC (microbiologically influenced corrosion) in water systems is of particular concern. The microbes live in water everywhere and are difficult to kill. Corrosion pitting, slimy fluid and rusty nodules are often the products of MIC. Corrosion and foreign objects in pipes and other containers cause wall thinning and reduction of flow areas that are detrimental to the structural performance of the pipes, and can sometimes lead to disastrous consequences. The chemical, petroleum, water utility and power industries have been battling MIC for many years.
The use of ultrasonic waves for the inspection of pipes uses transducers coupled to the pipe at a correct angle for excitation and detection of various wave modes used for MIC detection. Coupling of the transducers is complicated by the curvature of the pipe or other container under inspection.
Typical approaches in ultrasound detection use solid Lucite® or plastic wedges (or shoes) or fluid filled rubber wheels to couple the ultrasound into the pipe. When using plastic shoes, the shoes are machined so that the transducers are positioned at a correct angle to the pipe surface to create the guided wave mode of interest, while the contact area of the shoes are machined to fit the curvature of the pipe. While this approach works, it requires manufacture of a large number of shoes to cover the various diameters of pipe and other containers in use, since each pipe or other container diameter requires a different radius shoe.
Also, the user either needs transducers for each set of shoes, or has to move the transducers to a new set of shoes if a different pipe size is to be inspected. This takes time, and can result in damaged transducers due to the large amount of handling involved.
The wheel method places the ultrasonic transducer inside a fluid filled wheel. The wheel is then rolled over the surface to be inspected. The fluid couples the sound from the transducer to the rubber wheel and the rubber wheel couples the sound into the part under inspection (e.g., container wall, etc.). For angles other than normal to the part surface (guided wave ultrasonics requires angling the sensor to excite the correct wave modes), angular positioning of the transducer becomes difficult. Also, depending on the size of the transducers, the wheels can be large and difficult to handle.
The present invention overcomes the problems of the prior art by providing compact adjustable hand-held ultrasonic scanning heads for pipes and other containers. These and other features of the invention will be clear upon review of the following.
SUMMARY OF THE INVENTION
As noted, the present application provides compact hand-held ultrasonic scanning heads for pipes and other containers. These hand held scanning heads are on the order of a few inches in length, width and height. For example, in one embodiment, the external dimensions of an exemplar scanning head is about 6 inches long by about 3 inches wide by about 3 inches high. The transducers are mounted on pivot points in a rigid frame, allowing for control of angular positioning of the transducer sensors for guided wave excitation and detection. Coupling is performed through a rubber membrane, which conforms to various diameters of pipe. This design eliminates positioning errors that occur with a fluid filled wheel, and does not require a new set of shoes for each pipe diameter. The compact size allows the head to be used in confined areas encountered in inspections.
Accordingly, a hand-held variable angle membrane (VAM) MIC ultrasonic scanning head is described for fast and repeatable coupling of ultrasound into pipes, tanks, plates, pressure vessels, etc., for the detection of corrosion, MIC and foreign obstructions.
In the methods of the invention, an ultrasonic transmitting transducer is used to couple ultrasound into the pipe or other container to excite guided waves, which propagate away from the transducer along the pipe wall. A receiving transducer is used to detect ultrasound excited by the transmitting transducer after it has traveled along the pipe wall.
The head design incorporates a flexible polymer (e.g., rubber) membrane to contact the pipe surface. The membrane conforms to the pipe diameter, providing a stable, repeatable ultrasonic coupling of the ultrasound into the pipe over any diameter. The ultrasound from the transducer is coupled to the membrane through a fluid filled cavity. The transducer is attached and sealed to one end of a hollow housing, so that only the face of the transducer contacts the coupling fluid. This eliminates having to place the entire transducer in the coupling fluid as is done in a wheel-based method. The rubber membrane is attached and sealed to the other end of the housing. The cavity between the transducer face and the rubber membrane is filled with fluid. The membrane is specially shaped to extend outward beyond the base of the housing so that it can deform to the pipe surface in a fluid-like manner ensuring good coupling to the pipe. Sound is coupled from the transducer to the membrane through the fluid.
Fluid filled housings are mounted on pivot pins in a rigid frame. The frame ensures that the transducers are held a specific selected distance apart, and the pivot pins allow each housing to be rotated a known angle for ultrasound injection into the pipe wall. The frame also allows the operator to easily hold and position the transducers on the pipe to be inspected. The rubber membranes are coupled to the pipe with a suitable couplant, such as a small amount of water or ultrasonic gel.
By incorporating the membrane, any diameter of pipe can be scanned, since the membrane deforms to the pipe diameter. The ability to rotate each housing allows the user to adjust the angle of the ultrasonic transducers for each pipe diameter and thickness for excitation of the correct guided wave mode for the inspection of corrosion and obstructions.
Quick connect electrical connections between the transducers and the system electronics allow for easy replacement or changing of scanning heads.
REFERENCES:
patent: 4407293 (1983-10-01), Suarez, Jr. et al.
patent: 5426980 (1995-06-01), Smith
patent: 5585565 (1996-12-01), Glascock et al.
Gorman Michael R.
Miller William J.
Ziola Steven M.
Digital Wave Corporation
Moller Richard A.
Quine Jonathan Anan
Quine Intellectual Property Law Group P.C.
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