Abstract:
A method and apparatus which uses ultrasonic techniques to inspect critical pipe joints and other critical industrial areas that are normally inaccessible. A waveguide including one or more flexible fibers is embedded in concrete or whatever else embeds the piping which includes the critical area. One end of the waveguide is accessible so that an ultrasonic transducer can be used to transmit ultrasonic signals along the waveguide and receive reflected echoes to provide an ultrasonic image of the critical area. In a case where the area to be inspected is submerged, the waveguide takes the form of a flexible fiber bundle which is manipulated until its end is adjacent to the critical area. Some of the fibers in the bundle can be used to illuminate the critical area, and other fibers can transmit optical images for display on a video monitor. In an alternative embodiment, a single optical fiber waveguide is used to transmit illumination, optical signals and ultrasonic signals.

Description:
This application is a File Wrapper Continuation of Ser. No. 08/386,330, filed Feb. 10, 1995 now abandoned, which is a continuation of Ser. No. 08/193,612, filed Feb. 8, 1994 now abandoned, which is a continuation of application Ser. No. 07/832,816, filed Feb. 7, 1992 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to ultrasonic imaging and deals more particularly with the use of ultrasonic techniques for the inspection of areas to which access is restricted. 
     BACKGROUND OF THE INVENTION 
     In a variety of industrial processes, there are areas that are inaccessible and yet at the same time critical to the process. For example, pipes which conduct the flow of process fluids are often embedded in concrete or a similar material such that inspection of critical pipe joints is impossible. If a faulty weld exists or if a critical area should otherwise fail while the pipes are in service, the lack of ability to carry out inspections creates a situation where no warning is given of a possibly dangerous condition. As an example, in a nuclear power plant or other critical facility, if piping which conducts cooling fluid should leak, disastrous consequences can follow. If the piping is capable of being inspected on a regular basis, the problem can be detected early enough to allow corrective action to be taken before there is a complete failure. 
     Similar situations arise as to pipes and fittings that are submerged in storage tanks for petroleum based liquids and other types of liquids. Access to submerged areas is restricted if not precluded altogether, so leaks and other problems can arise without any warning because inspections of the submerged areas are not practical and perhaps not even possible. The same problems are presented as to inspections in hostile environments such as areas exposed to the high levels of radiation or toxic chemicals. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method and apparatus for carrying out ultrasonic inspections and examinations of locations that are normally inaccessible and thus not subject to inspection. By way of example, through the techniques employed by the present invention, a critical pipe weld which is embedded in a concrete slab can be inspected while the piping remains in service. Accordingly, signs of problems in the weld can be detected before they become so great that the weld fails. In addition, submerged components and structures located in hostile environments can be inspected to detect problems before they have developed to the point of complete failure. 
     In accordance with the invention, a waveguide for transmitting ultrasonic signals takes the form of at least one and usually a number of quartz fibers arranged in a bundle. In the case of a pipe weld or other critical part which is embedded in concrete or another material, the waveguide may also be embedded with one end adjacent to the weld that is to be inspected and the other end situated at the surface of the concrete or at another accessible location. A conventional ultrasonic transducer can be permanently or detachably connected to the accessible end of the waveguide and used to transmit ultrasonic signals and receive signals that are reflected back to the waveguide from the critical weld. In this manner, an ultrasonic image can be generated of the critical area and examined to give a warning of any problems that may exist. 
     In the case of a part that is submerged well below the surface of a liquid, the waveguide can be manipulated in the liquid using conventional techniques to position its end adjacent to the submerged part. Then, an ultrasonic transducer system above the liquid can be used to apply signals to the waveguide and receive reflected signals in order to provide an ultrasonic image of the part. The image that is generated can be examined for signs of damage or impending failure. The fibers can include some which transmit ultrasonic signals, others which are used for illumination of the tip end of the waveguide, and still others which transmit optical images. With the use of a video monitor, the operator of the apparatus can actually observe on the monitor how the waveguide tip is positioned relative to the part that is undergoing inspection. In many situations, this can enhance the accuracy of the procedure and the overall effectiveness of the inspection process. 
     It is an important feature of the invention that the ultrasonic waveguide is flexible. This allows it to be manipulated to provide access to areas that are at best difficult to reach with conventional rigid waveguides. The considerable length of the waveguide also provides it with the capability of making relatively remote areas accessible for inspection. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views: 
     FIG. 1 is a fragmentary sectional view illustrating how the apparatus of the present invention can be used to monitor a critical pipe joint that is embedded in concrete; 
     FIG. 2 is a fragmentary sectional view showing one way of coupling a quartz fiber with an ultrasonic transducer in accordance with the invention; 
     FIG. 3 is a fragmentary sectional view similar to FIG. 2, but showing a different way of coupling a fiber to the ultrasonic transducer; 
     FIG. 4 is a diagrammatic view showing how the apparatus of the present invention can be used to inspect a component that is submerged in a tank containing liquid; 
     FIG. 5 is a diagrammatic view depicting the use of a dual element transducer and different waveguides oriented in different directions in accordance with the invention; 
     FIG. 6 is an end elevational view of quartz fibers which are arranged in a bundle having the fibers closely packed together; and 
     FIG. 7 is an end view similar to FIG. 6, but showing the fibers in the bundle arranged in ordered rows. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in more detail and initially to FIG. 1, numeral  10  designates a horizontal pipe which is embedded in a concrete slab  12  having only its upper surface  14  accessible. A vertical pipe  16  is connected with the horizontal pipe  10  by a weld  18 . The pipes  10  and  16  may carry industrial process fluids, and the weld  18  may be at a critical area in which weld failure could lead to the leakage of the process fluid or other adverse consequences. The piping system may be a critical one such as a system which conducts cooling fluid for a nuclear power plant or some other critical facility. Because the pipes  10  and  16  are embedded in the concrete  12 , the weld  18  is not accessible for inspection. The concrete  12  is relatively impervious to ultrasonic signals so that ultrasonic signals applied from the accessible surface  14  cannot be used in a practical manner for reliable inspection of the weld  18 . 
     In accordance with the present invention, a flexible waveguide  20  is embedded in the concrete slab  12  when it is poured or otherwise initially constructed. The waveguide  20  is arranged with its free end  22  located adjacent to and pointed at the weld  18 . The waveguide  20  may have a serpentine shape or any other suitable shape, and its opposite end  24  is located adjacent to the accessible surface  14  or at some other accessible location. A collar  26  located on top of the slab surface  14  provides a port to permit detachable connection of ultrasonic equipment to the accessible end  24  of the waveguide  20  as will be explained in more detail. 
     A conventional ultrasonic pulser-receiver controls an ultrasonic transducer  30 . A tapered transition piece  32  which is preferably of a frusto conical configuration connects with the transducer  30  and may be fitted at its lower or smaller end closely within the collar  26 . This couples the small end of the transition piece  32  with the waveguide  20 . The transducer  30  transmits ultrasonic signals which are applied to the transition piece  32  and from the transition piece to the end  24  of waveguide  20 . The signals are transmitted along the length of the waveguide to its opposite end  22  and then to the area of the weld  18 . Ultrasonic echoes are reflected from the area of the weld back to the end  22  and along the length of the waveguide  20  to end  24 . The reflected signals are transmitted through the transition piece  32  to the transducer  30 . 
     In this manner, the transducer system and waveguide act to provide an ultrasonic image of the weld  18  to permit detection of any problems in the weld that could lead to leakage of fluid or otherwise adversely affect the process. As described, the transducer  30  acts as both a transmitter of ultrasonic signals and as a receiver of the reflected signals. An alternative arrangement would be to provide one transducer acting as a transmitter and a second transducer acting as a receiver, with the transmitted signals traveling along one path defined by the waveguide  20  and the reflected signals traveling along a different path provided by the waveguide. In addition, the transducer equipment can be permanently attached to the waveguide end  24  rather than being detachable in the manner previously described. 
     The flexibility of the waveguide  20  is important, as it allows the waveguide to be bent, curved or formed in virtually any other desired configuration. The surface  14  immediately above the weld  18  may be inaccessible in some applications, and the ability of the waveguide to be shaped as desired thus becomes essential. 
     As shown in FIG. 2, the transition piece  32  may be a solid element constructed of a material that is suitable for the transmission of ultrasonic signals. Alternatively, as shown in FIG. 3, the transition piece  32  may be a hollow element having its interior filled with a liquid  34  that is suitable for the transmission of ultrasonic signals. In either case, the transition element  32  provides a tapered transition between the transducer  30  and the smaller waveguide  24  which, in the case of FIGS. 2 and 3, is formed by a single fiber. The fiber may be constructed of quartz or some other material that has suitable acoustic properties for transmitting ultrasonic signals. 
     FIG. 4 depicts an ultrasonic system for inspecting one or more welds  36  which are used to connect a fitting  38  in extension through one wall of a liquid storage tank  40 . The tank  40  contains liquid  42  which may be a petroleum based liquid, a chemical that is potentially dangerous, or some other type of liquid. The fitting  38  is submerged well below the surface  44  of the liquid  42  where access to it is restricted. The welds  36  are critical to the liquid storage facility, and leakage or other problems that develop at the welds can lead to serious adverse consequences. 
     In accordance with the present invention, a flexible waveguide  46  can be manipulated such that its free end  48  is positioned adjacent to the weld  36  that is to undergo inspection. The waveguide  46  may be flexed in a serpentine shape or any other desired configuration, and its opposite end  50  connects with a transition piece  52  which may be of the type shown in either FIG. 2 or FIG. 3, or some other type if desired. The opposite or large end of the transition piece  52  connects with a conventional ultrasonic transducer  54  which operates to apply ultrasonic signals to the transition piece  52  and to receive reflected signals which are returned to the transition piece by the waveguide  46 . Manipulation of the waveguide  46  as desired is carried out by a conventional manipulating device  56  which functions in a manner known to those skilled in the field of manipulation of long flexible objects such as the waveguide  46 . Again, the flexibility of the waveguide is important because it allows positioning of the waveguide as necessary to reach the critical area. 
     The equipment may also include a conventional video monitor  58 . The waveguide end  50  and the components connected with it are situated at a fixed location above the liquid level in the tank and preferably close to the tank. 
     In operation, the transducer  54  transmits ultrasonic signals which are applied to the transition piece  52  and then to the waveguide which directs the signals toward the weld  36 . The reflected echo signals are received by the tip  48  of the waveguide and transmitted back along the waveguide to the transition piece  52  and the transducer  54  in order to provide an ultrasonic image of the weld area. The ultrasonic image can be examined to detect any flaws or other problems in the weld  36  or at any other critical area that is inaccessible for inspection by conventional techniques. 
     FIG. 5 depicts a dual element system in which a pair of ultrasonic transducers  60  and  62  are used. The transducer  60  is provided with a pair of side by side fibers  64  and  66 . Fiber  64  is used for the transmission of ultra sonic signals toward the area that is to be inspected, as indicated by the directional arrow  64   a . The other fiber  66  is used for the transmission of reflected echo pulses as indicated by the directional arrow  66   a . The tips of the fibers  64  and  66  are turned to the side such that the ultrasonic signals that are transmitted and received by them have a horizontal orientation, as the arrows  64   a  and  66   a  illustrate. This shows one version of a possible multiple element system. 
     The other transducer  62  has a pair of side by side fibers  68  and  70 . Fiber  68  is used for the transmission of ultrasonic signals toward the area that is to be inspected, as indicated by the directional arrow  68   a . The other fiber  70  is used for the receipt of reflected ultrasonic signals, as indicated by the directional arrow  70   a . The tips of the fibers  68  and  70  are directed downwardly so that the ultrasonic signals they transmit and receive have a vertical orientation, as the arrows  68   a  and  70   a  illustrate. 
     By using the dual element transducer shown in FIG. 5, inspections can be carried out at the same time in different directions. In many applications, this can facilitate and expedite the inspection procedure and provide ultrasonic imaging information that is complete as to the entire area that is undergoing inspection. Additional fibers can be provided and directed at different orientations if desired. 
     The waveguides  20  (FIG. 1) and  46  (FIG. 4) can include a single fiber or virtually any number of fibers which are arranged in a fiber bundle which may be of the type shown in FIG.  6 . The individual fibers  72  are packed closely together in the bundle which is depicted in FIG.  6 . In a waveguide which includes a bundle of fibers, the individual fibers are connected together in the same configuration at both ends of the waveguide but may be disconnected between the opposite ends of the waveguide. This provides the necessary flexibility of the waveguide while assuring accuracy because the locations of the ends of the different fibers are known. 
     An alternative arrangement of a multiple fiber bundle which comprises the waveguide is shown in FIG.  7 . Here, the individual fibers  72  are arranged in ordered rows of fibers which may or may not be packed so closely as to touch one another. FIG. 7 depicts the individual fibers spaced apart from each other. 
     In the type of bundle shown in FIG. 6 or the type shown in FIG. 7, the individual fiber  72  may serve different functions. For example, some of the fibers  72  are used for the transmission of ultrasonic signals from the transducer and others may be used for the transmission of reflected signals back toward the transducer (or some of the fibers may perform both functions). Other fibers may be used for illuminating the tip end of the waveguide  46 . These fibers  72  may be optical fibers of the type that are able to transmit light from a suitable light source such as a laser located in the above ground equipment. Other of the fibers  72  in the bundle may be optical fibers used to transmit optical images from the tip end  48  of the waveguide back to the above ground equipment for display on the video monitor  78 . This permits the operator of the equipment to view the area immediately ahead of the waveguide tip  48  in order to enhance his ability to properly manipulate the waveguide so that its tip is positioned properly for inspecting the weld  36 . Thus, an actual optical image of the weld  36  may be displayed on the video monitor  58  in order to assist in the proper positioning of the waveguide, and the ultrasonic image of the weld is separately generated for the purpose of inspecting the integrity of the weld or other component that is undergoing examination. 
     It should be noted that the waveguide may be a probe which moves independently within a larger tube, either axially or rotationally or both. It should also be noted that various types of operations can be carried out along with the inspection. For example, a laser or cutting device can be combined with the waveguide and used to remove unwanted deposits or other material. The ultrasonic imaging equipment provides feedback for use in controlling the removal process. 
     In addition to the specific applications which are illustrated in the drawings, the flexible waveguide system of the present invention has use in a wide variety of industrial applications. By way of example, laser bored holes are known to be relatively irregular, and the system of this invention can be used to provide an image of the hole geometry and determine the extent of the irregularities. Chemical machining of large surfaces such as panels used in aircraft construction is a commonly used process. A flexible quartz waveguide constructed according to the present invention could be used to make ultrasonic measurements of the part without requiring the part to be removed from the chemical bath as is currently required. The quartz is inert to chemical attack and would greatly improve the process efficiency as well as reducing the errors which can lead to ruined panels. Environments which are otherwise hostile because of chemicals, radiation or other dangerous materials can be made accessible through use of the waveguide. 
     The monitoring of interior surfaces of vessels or pipe networks is also made possible. Chemical processes can likewise be monitored because the waveguide is able to withstand chemical attack whereas transducers cannot be directly placed at the site of the chemical reactions because caustic chemicals would quickly destroy them. Measurement of pitting caused by corrosion or other deterioration of airframe structures or critical areas in chemical plants is also made possible by embedding the waveguide in the structure which is to be monitored. The monitoring of various other inaccessible areas such as surfaces which are subject to degradation or unwanted deposits can also be carried out. 
     From the foregoing, it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure. 
     It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. 
     Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.