Measuring and testing – Vibration – By mechanical waves
Reexamination Certificate
2002-07-25
2004-11-09
Kwok, Helen C. (Department: 2856)
Measuring and testing
Vibration
By mechanical waves
C073S622000
Reexamination Certificate
active
06813950
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to the non-destructive testing of tubes and pipes. In particular, it relates to the detection of longitudinal, transverse and oblique defects in tube walls using a phased array ultrasonic system.
BACKGROUND OF THE INVENTION
A new paradigm was defined in the field of non-destructive testing (NDT) with the introduction of phased array (PA) multi-element ultrasonic technology to upgrade the performance of conventional ultrasonic single-element probe systems. A general description of how phased array technology can be adapted to NDT systems is given in U.S. Pat. No. 5,563,346 with recent examples of applications for the inspection of spherically-bounded materials and turbine blades described in U.S. Pat. Nos. 6,279,397 and 6,082,198 respectively.
Another application is that of the inspection of tubes during production. Here, the “virtual rotation” of ultrasonic beams emitted by PA probes means that the probes themselves do not have to move as a tube being inspected passes through an inspection station. For a non-rotating tube, it is necessary to place PA probes at positions that cover the entire circumference of the tube.
Further advantages result when inspecting tubes or similar pieces (e.g., pipes, rods) using a PA ultrasonic NDT inspection system compared to conventional ultrasonic single-element probe systems. Little maintenance is required because such systems are robust with a relatively simple mechanical design, and what maintenance that is required is straightforward and structured for easy and quick implementation. Further, PA technology permits stationary, multi-element probes to thoroughly inspect a moving tube during manufacture with greater flexibility than conventional designs permit.
Such computer-controlled systems can be reliably and rapidly adapted to meet the requirements of various types and sizes of tubes by simply selecting electronically the software that corresponds to a new tube diameter and wall thickness to be inspected. The parameters affected would include the identification of specific piezoelectric elements in each probe for the formation of each beam, the number of beams per probe and the beam angle of incidence with respect to the outer surface of the tube. Further, the focus point of the PA ultrasonic beams can be adjusted electronically to be closer to the suspected location of defects in the tube walls for a given configuration. This is not possible with single-element probes.
PA technology has the important capability of readily detecting a wide range of defects having longitudinal, transverse and oblique orientations. This occurs because PA probes can electronically scan a much wider inspection zone than single-element probes are able to do. Previous work with single-element ultrasonic probes to broaden the inspection zone of such single-element probes is described in U.S. Pat. Nos. 4,718,277, 5,228,343, 5,473,943 and 5,485,751. It involves grouping single-element probes in clusters wherein the centerlines of the elements of such probes are angled relative to one another such that the beams they emit intersect at a predetermined position in the tube or pipe under inspection. Such single-element probe clusters, however, lack flexibility and the capacity to effect comprehensive inspections for oblique defects precisely because the ultrasonic beams are directed along the only a few discrete angles with respect to the inspected region.
Phased array prior art at R/D Tech Inc. in Québec City, Canada has been based upon a series of phased array probes that entirely encircle a tube, the multiple elements in each probe being angled as if lying on a conic surface with an included conic apex angle of, for example, 135 degrees. In such applications the inspected tube, while passing longitudinally through the ring of piezoelectric elements along the conic axis of the conic array of probes, has its surface analyzed for defects that are principally transverse or perpendicular to the longitudinal axis of the tube. In such systems each individual phased array beam emitted by a given probe enters the tube wall at a separate entry point. Thus a given portion of the tube wall is not inspected from multiple bearing angles originating from a single probe.
The objects of the invention are, therefore, to improve the way in which tubes are inspected during manufacture by being able to detect defects in a nearly continuous range of multiple orientations (e.g. longitudinal, transverse and oblique) in the wall of a tube; and by allowing the same system, with only minor adjustments (if any), to inspect a range of tube diameters and wall thickness for a given tube material and manufacturing process, or in tubes of differing materials and involving differing manufacturing processes.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.
SUMMARY OF THE INVENTION
According to the invention in one aspect, a method of non-destructive testing for defects in the wall of tubes or pipes to be inspected is based upon a phased array (PA) ultrasonic probe system. The inspected tube may be rotated continuously while it is moving past an inspection station or the inspection station may be moved with respect to the tube. At the inspection station a plurality of PA beams from each of one or more probes are directed into an entry zone in the form of a spot on the outer surface of the tube wall. The position of the entry zone is fixed with respect to the probes. Said beams arrive at the entry zone with a fixed angle of incidence but from a range of bearing angles along conically oriented paths. Thus, the beams enter an inspection volume within the wall of the tube below the entry zone at a constant inspection angle. Defects within the inspection volume are detected by sensing reflected ultrasonic pulses created by such defects. Sensing may be effected by a circularly deployed array of dual-purpose emitter/receptor piezoelectric elements operating in either a pulse/echo or pitch/catch mode, or by dedicated emitters and receptors.
The invention is directed to a PA ultrasonic probe system that will detect reflecting longitudinal, transverse and oblique defects in the entire three-dimensional volume of the wall of a tube while the tube is moving with both longitudinal and rotational motion with respect to an inspection station. This can also be achieved, for example, by having the tube only rotate and the inspection system moving longitudinally with respect to the tube. By “reflecting defects” is meant defects that reflect sound waves either back to the source of such waves or laterally to other sensors.
As a preferred arrangement, a constant inspection angle (i.e., the angle of refraction of the beams in the tube wall) is pre-selected such that it meets the requirements of the inspection. These requirements depend principally on the tube material and the method of tube manufacture and establish an inspection angle that is most likely to detect anticipated defects. Since the inspection angle is constant, it follows that the angle of incidence at the entry zone for the ultrasonic beams emitted by the PA probes will also be predefined and constant.
The conically oriented PA beams are preferably generated by an arc of ultrasonic emitter/receptor elements mounted on a common, conic support surface, each of the elements having an emission face that is positioned to lie on the surface of an imaginary cone in space having a conic axis that is substantially normal to the longitudinal axis of the tube and which passes through the entry zone. The arc is preferably a circular arc. A set of elements occupying a sector portion, or all, of the circle con
Butin Laurent
Dubé Noël
Glascock David
Pasquer Vincent
Eilberg William H.
Kwok Helen C.
R/D Tech Inc.
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