Method for determining boiler tube cold side cracking and article for accomplishing the same

Disclosed herein is a scanning device for performing ultrasonic nondestructive testing of a tube, comprising a housing; the housing having bottom surface that is concavely curved with cavities to accommodate a waveguide assembly and an encoder assembly; where the waveguide assembly comprises a waveguide and a probe that are in communication with one another; the waveguide having at least one surface that is contoured to match an outer surface of the tube; where the waveguide facilitates the transmission of ultrasonic signals into the tube generated by the probe; and where the encoder assembly comprises a spring loaded wheel that contacts the tube; and where the encoder assembly provides a signal indicative of a location of the probe relative to a position on the tube as the scanning device is moved in a direction of a longitudinal axis of the tube.

FIELD OF THE INVENTION

This disclosure relates to a method for determining boiler tube cracking. In particular, this disclosure further relates to a method for determining boiler tube cold side cracking and an article for determining the same.

BACKGROUND

Boiler tube failures are a major cause of forced shutdowns in fossil fuel power plants. As a result of various operational conditions such as heat, pressure, and wear over time, boiler tubes eventually begin to fail by developing circumferential and axial cracks, as well as experience wall thinning (through both erosion and corrosion). When a boiler tube begins to leak, for example, steam escaping through the leak is lost to the boiler environment. Unless the leak is discovered and repaired, the leak may continue to grow until the tube eventually ruptures, thereby forcing the utility operating the boiler to shut it down immediately. These failures prove to be quite expensive for utilities and, as such, early boiler tube leak detection methods are highly desirable.

In boiler systems, tubes may be interconnected by welding material to form a waterwall. As a result of the construction of the tubes to form a waterwall, commercially available scanners are unable to complete a circumferential scan of the tubes. In addition, waterwall tubes are accessible from the hot side of the tubes during a shutdown. The hot side of the tubes is that side that is in direct contact with a flame and the hot gases in the boiler, while the cold side is disposed opposite to the hot side and contacts insulation. Cracking generally occurs at attachment welds at the “cold side” of the tube which is insulated and not easily accessible without insulation removal. Accordingly, it would be desirable to provide an improved scanning device for applications such as boiler tube inspection.

SUMMARY

Disclosed herein is a scanning device for performing ultrasonic nondestructive testing of a tube, comprising a housing; the housing having bottom surface that is concavely curved with cavities to accommodate a waveguide assembly and an encoder assembly; where the waveguide assembly comprises a waveguide and a probe that are in communication with one another; the waveguide having at least one surface that is contoured to match an outer surface of the tube; where the waveguide facilitates the transmission of ultrasonic signals into the tube generated by the probe; and where the encoder assembly comprises a spring loaded wheel that contacts the tube; and where the encoder assembly provides a signal indicative of a location of the probe relative to a position on the tube as the scanning device is moved in a direction of a longitudinal axis of the tube.

Disclosed herein too is a method comprising disposing upon a tube a scanning device comprising a housing; the housing having bottom surface that is concavely curved with cavities to accommodate a waveguide assembly and an encoder assembly; where the waveguide assembly comprises a waveguide and a probe that are in communication with one another; the waveguide having at least one surface that is contoured to match an outer surface of the tube; where the waveguide facilitates the transmission of ultrasonic signals into the tube generated by the probe; and where the encoder assembly comprises a spring loaded wheel that contacts the tube; and where the encoder assembly provides a signal indicative of a location of the probe relative to a position on the tube as the scanning device is moved in a direction of a longitudinal axis of the tube; contacting a surface of the tube with the waveguide; introducing ultrasonic signals into the tube at an incident angle of 20 degrees to 40 degrees with respect to the probe centerline; and where the ultrasonic signals travel through the wall thickness in the circumferential direction; retrieving the ultrasonic signals through the waveguide when the ultrasonic signals contact a crack in the tube; and analyzing the ultrasonic signals to determine the location of cracks in the tube.

DETAILED DESCRIPTION

Disclosed herein is a portable scanning device for nondestructive testing of tubes. The tubes are part of a waterwall and are generally used in boilers and furnaces. The scanning device is compact and easily adaptable for use with tubes having different diameters, and is particularly useful for scanning waterwall tubes in steam generators (boilers). In one embodiment, the portable scanning device is used to determine cracks that occur at attachment welds located on the cold side of the waterwall tube, particularly those cracks that occur at attachment welds, which is generally insulated and therefore not easily accessible without insulation removal.

As defined herein the term “tube” includes an enclosed channel through which fluids can be transported. The closed channel can have any desired geometrical shape (when measured perpendicular to an axial direction of the conduit) and may have a circular, oval, square, or rectangular cross-sectional area. The axial direction is also referred to herein as the longitudinal direction and is measured along the length direction of the conduit.

Disclosed herein too is a method that permits crack detection on the “cold side” of waterwall tubing when the portable scanning device contacts the “hot side” of the waterwall tubing. In one embodiment, the method permits axial crack detection on the cold side of water wall tubing, when the scanning device contacts the hot side of the waterwall tubing. The method comprises introducing sound waves into a waveguide that is machined to contact a portion of the tubes outside surface. The sound waves are in the ultrasonic frequency range (hereinafter referred to as “ultrasonic signals”). The ultrasonic signals exit the waveguide material and are refracted into the tube at multiple angles based on Snell's law. The ultrasonic signal is a phased array signal and is introduced into the tube wall in a manner that facilitates the detection of corrosion fatigue and cracking initiated on either surface of the tube wall.

The scanning device is configured to enable quick change out of probes and ultrasonic (UT) waveguides (also sometimes termed a wedge), such that multiple inspections of tubes having different diameters are expeditiously facilitated. The configuration of the scanning device also allows for smooth operation, thereby eliminating or minimizing chatter or skew, as will be described further herein.

The portable scanning device comprises a housing which contains a waveguide assembly for transmitting to and receiving ultrasonic signals from a waterwall tube, a magnet and screw assembly for adjusting the magnetic strength for holding the scanning device to the waterwall tube, and an encoder assembly for measuring the distance traversed (by the scanning device) along the tube and correlating this distance with any detected cracks. Also contained in the housing are associated supporting and operating mechanisms for the waveguide assembly, the magnet and screw assembly and the encoder assembly.

Turning now toFIGS. 1A and 1B, a portable scanning device100for performing nondestructive testing of tubes will now be described in accordance with exemplary embodiments. TheFIGS. 1A and 1Bare isometric views of an exemplary portable scanning device100. TheFIG. 1Ais an isometric side view, while theFIG. 1Bis an isometric bottom view. The portable scanning device100includes a housing102having a top surface104and a bottom surface110. The bottom surface110is opposed to the top surface104. The portable scanning device100also has opposing sidewalls106and108extending downward from two edges of the top surface.

In one embodiment, the housing102does not have a handle to permit one to hold the scanning device. The top surface104and sidewalls106,108are designed so that the housing102can be held and manipulated by hand without having a discrete handle. The shape of the housing102enables testing personnel to manually guide the scanning device100on a tube to be tested for cracks. It is generally desirable for the housing102to be light weight so that it can be transported and manipulated manually by hand. It is also desirable for the housing to be manufactured from a material that can withstand moderately high temperatures of up to about 110° F., if indeed it turns out to be desirable to make measurements in a slightly elevated temperature environment. The housing102can be manufactured from a metal, a ceramic, or a polymer. When the housing102is manufactured from a polymer or from a ceramic, it is desirable for the polymer or the ceramic to be impact toughened so that the scanning device does not undergo cracking or chipping if it is dropped. In an exemplary embodiment, the housing102is manufactured from a polymer. Exemplary polymers are wood, a thermoplastic polymer or a thermosetting resin.

Exemplary thermosetting polymers are polyurethanes, natural rubber, synthetic rubber, epoxies, phenolics, polyesters, polyamides, silicones, or the like, or a combination comprising at least one of the foregoing thermosetting resins. Blends of thermoset resins as well as blends of thermoplastic resins with thermosets can be utilized.

FIG. 2is a depiction of the bottom surface110of the housing102. As can be seen fromFIGS. 1A and 1B, the bottom surface110is a concave curved surface for smooth motion across the outer surface of the waterwall tubes. The curvature of the bottom surface110is concave to accommodate the convex curvature of the tube outer surface. The housing102has openings115(SeeFIGS. 1B and 2) at its bottom surface110to accommodate the magnet and screw assemblies120A,120B and120C, an opening171to accommodate the waveguide assembly140(SeeFIG. 2.) and an opening159to accommodate the encoder assembly160(SeeFIGS. 1B and 2.). The view of the bottom surface in theFIG. 2(and the cross-sectional side view in theFIG. 3D) depicts three magnet and screw assemblies120A,120B and120C, each of which are depicted in a dotted ellipse. The first magnet and screw assembly120A is located proximate to the first end114, while the second magnet and screw assembly120B is located farther away from the first end114. The first magnet and screw assembly120A and the second magnet and screw assembly120B are located on opposite sides of the waveguide assembly140. The third magnet and screw assembly120C lies proximate to the second end116of the housing102. Located between the second magnet and screw assembly120B and the third magnet and screw assembly120C is a cavity159that houses the encoder assembly160(which is detailed later with respect to theFIG. 3D).

Each magnet and screw assembly comprises a cylindrically shaped magnet122(122A,122B and122C corresponding to assemblies120A,120B and120C respectively) and a screw124(124A,124B and124C corresponding to assemblies120A,120B and120C respectively), which is adjustably threaded to a nut132(132A,132B and132C corresponding to assemblies120A,120B and120C respectively) contained in a space in the housing102. The space for the nut has a geometrical shape that corresponds to the outer surface of the nut132. The nut132therefore cannot rotate in the space that holds it in position. Each magnet122has a hole at its geometrical center through which passes the screw124. The screw124then passes through the housing and is threaded by the nut132. By rotating the screws124A,124B and124C in the nuts132A,132B and132C respectively, the position of the respective magnets122A,122B and122C relative to the bottom surface110of the housing102can be adjusted. The magnets122A,122B and/or122C can thus be moved closer to or further away from the tubes of the waterwall in the radial direction (where the radial distance is measured from the center of the tubes). By moving the magnets closer to or further away from the tubes, the attractive force exerted by the magnet on the tube can be changed to provide the desired force to hold the scanning device100onto the tube200(seeFIG. 3A), while at the same time allowing the scanning device100to easily slide along the tube. The magnets also allow the user to keep the probe attached to the tube to allow the user to reposition without losing the encoder position reference.

Referring to theFIGS. 1B, 2 and 3D, disposed upon the bottom surface110of the housing102are at least two strips of soft absorbent material—a first strip126A and a second strip1126B that can absorb and discharge a liquid (hereinafter a couplant). The first strip of absorbent material126A and the second strip of absorbent material126B are bonded to the bottom surface110of the housing102. The first strip of absorbent material126A and the second layer of absorbent material126B partially cover the first magnet122A and the second magnet122B respectively. Each layer of absorbent material126A and126B includes an opening127(SeeFIG. 1B.) to permit access to the screws124A and124B respectively for adjustment.

In addition to absorbing and desorbing the couplant, the first strip of absorbent material126A and the second strip of absorbent material126B also act as seals to capture or to retain a film of couplant between the first strip126A and the second strip126B respectively, while the scanning device100is moved over the surface of a tube. The film of couplant lies between the waveguide142and the tubes that are being inspected for cracks and facilitates coupling of ultrasonic signals between the waveguide142and the tube. The couplant is supplied to the region between the waveguide142and the tube through a couplant tube128(SeeFIG. 1A.) and through a couplant manifold130(SeeFIG. 3B.). The couplant manifold130is in fluid communication with a plurality of ports186in the bottom surface via tubes180,182and184contained or formed in the housing102. The ports186are disposed in the housing102at the bottom surface110and lie on either side of the waveguide142of the waveguide assembly140. While the figure shows two rows of ports186, it is to be noted that a single row may be sufficient.

A couplant is continuously discharged from the ports186on the bottom surface110of the housing102when the scanning device100is being operated. The tubes180,182and184of the manifold130are molded as part of the housing102during the manufacturing of the housing102by additive manufacturing, which is discussed below.

The couplant tube128has a first end connected to a couplant supply source (e.g., pressurized container or pump—not shown here) and a second end connected to a couplant manifold130disposed at the second end116of the housing102. The couplant tube128receives couplant from the supply source (not shown) and delivers the couplant to the couplant manifold130(e.g., via a barbed fitting), which in turn, delivers the couplant directly to a plurality of ports186located at the bottom surface110of the housing102. The couplant forms a layer (referred to herein as a “film”) between the waveguide142and the tube to be examined and between the first and second strips of absorbent material126A and126B. It is through this couplant film that the ultrasonic signals are directed to the tube from the waveguide142. The couplant material may be water, an organic solvent or a gel. In an exemplary embodiment, the couplant is water.

The soft absorbent material can comprise a fibrous material or a porous material that is capable of absorbing and desorbing a liquid. The fibrous material may be a weave or a non-woven fibrous strip (e.g., felt) that comprises a polymer. The porous material may also be a polymeric foam. The polymeric foam has an average pore size of 1 to 1,000 micrometers. Exemplary polymeric foams comprise cellulose, polyurethanes, polyacrylates, or the like. In an exemplary embodiment, the soft absorbent material is felt. An adhesive may be used to bond the strip of soft absorbent material126A and126B onto the bottom surface110of the housing102.

Details of the waveguide assembly140and the encoder assembly160will now be provided with reference toFIGS. 3A-3D, which are sectional views obtained from theFIG. 1A. TheFIG. 3Adepicts a section taken at A-A in theFIG. 1A, while the Figure BB depicts a section taken at B-B in theFIG. 1A. TheFIG. 3Cis an end view of the scanning device100showing a section C-C, which is depicted in theFIG. 3D. TheFIG. 3Dis another exemplary embodiment, of an end view of the housing102taken with the waveguide assembly140and the encoder assembly160assembled in the housing102of the scanning device100.

FIG. 3Ais a depiction of section A-A (from theFIG. 1A) and displays the waveguide assembly140disposed between the first and the second magnet and screw assemblies120A and120B is the waveguide assembly140. The waveguide assembly140facilitates the transmitting and receiving of ultrasonic signals into a waterwall tube and from the waterwall tube respectively. The waveguide assembly140comprises a waveguide142in contact with a probe150. The probe150is an ultrasonic transducer that transmits and receives a phased array of ultrasonic waves (referred to herein as “signals”). In one embodiment, the surface141of the waveguide142that contacts the tube is concave so that it can contact the convex outer surface of the tube. The contact surface141of the waveguide142is contoured or curved to contact the tube surface as closely as possible. The lower side surface153of the waveguide142proximate to the probe150is tapered away from the housing102to minimize reflection of the ultrasonic signals back towards the probe and to prevent interference of the ultrasonic signals. The side surfaces153and155of the waveguide142are also textured to minimize reflection of the ultrasonic signals from these surfaces back to the probe150. In one embodiment, the side surfaces153and155of the waveguide142are serrated (e.g., have a saw tooth shape) to minimize reflection of the ultrasonic signals back to the probe150.

The arcuate length of the waveguide142is much larger than a side of the cross-sectional area of the probe. This increased arcuate length of the waveguide142provides strength and stability to the waveguide assembly140in the housing102. The couplant facilitates contact between the concave surface of the waveguide142and the outer convex surface of the tube200so that ultrasonic signals may be introduced into the tube200and signals may be received from the tube200.

The waveguide assembly140(which comprises the waveguide142, the probe150and the cable152) can be removed through the upper surface104of the waveguide by removing a slidable holder131that is located in the housing102. The slidable holder131is manufactured from a polymer and contains a groove191that houses a screw144. The screw has at its bottom a spring loaded ball145. The spring loaded ball145snap fits into a notch contained in the upper surface (the surface opposed to the surface141that contacts the tube200) of the waveguide142. The screw144is adjustably threaded to a nut146and facilitates radially moving the waveguide142in the housing102. The waveguide142may be moved closer to or farther away from the tube200(that is being examined) by rotating the nut146.

The slidable holder131can be inserted into the housing102(by sliding) and removed from the housing by virtue of grooves187and189. When in position, the slidable holder131is supported by a block157that is an integral part of the housing102.

In order to insert the waveguide assembly142into the housing102, the slidable holder131is first removed by sliding it out of the housing along grooves187and189. The waveguide assembly140comprising the waveguide142, the probe150and the cable152is then inserted into the housing102through a cavity in the upper surface104. The slidable holder131is then slid back into the housing102, wherein the spring loaded ball145snaps into a slot in the waveguide142thus holding the waveguide assembly140in position.

When it is desired to remove the waveguide assembly142from the housing102, the waveguide140is extracted from the spring loaded ball145by pulling the waveguide140away from the slidable holder131. The slidable holder131is then slid out of the housing via grooves187and189. The waveguide assembly142is then removed from the housing102via an opening in the upper surface of the housing102.

The waveguide142comprises an optically transparent piece of plastic. The optically transparent piece of plastic comprises a polyester, a polymethylmethacrylate, a polycarbonate, a polystyrene, a crosslinked styrene copolymer, a polyetherimide, or the like, or a combination comprising at least one of the foregoing pieces of plastic. In one embodiment, the waveguide is machined from REXOLITE® (a crosslinked styrene copolymer) or from LUCITE® (a polymethylmethacrylate), which have suitable acoustic properties.

The waveguide has a slot151that accommodates the probe150. In one embodiment, the portion of the waveguide142between the probe150and the tube200guides the ultrasonic signals towards the tube.

As detailed above, it is desirable to use a waveguide142whose concave surface is contoured to match the outer convex surface of the waterwall tubes200. It may thus be desirable to replace a waveguide142used for one set of tubes with another waveguide for another set of tubes, whose radii are different from those of the previous set of tubes. The waveguide may thus be easily replaced by removing it from the spring loaded ball145and snapping a new waveguide (having a different contoured surface) into position in its place using the spring loaded ball145. While replacing an existing waveguide142with a new waveguide142, the probe150is first removed from the existing waveguide142. A couplant is added to the slot151of the new waveguide142, prior to pressure fitting the probe150into the new waveguide142. The new waveguide142is then snapped into position (using the spring loaded ball145) in the housing102.

Advantageously, a surface147of the waveguide142is contoured or curved to the outer circumference of the tube200, thus allowing a portion of the tube200circumference to be scanned. For example, if the tube200has a 2.5-inch diameter, the waveguide142selected for use with the scanning device100will have about a 1.25 inch contoured radius. This is particularly advantageous where tube200is part of a waterwall, as depicted in theFIG. 2A. In a waterwall, tubes200are coupled in side-by-side fashion by welded webs (membranes)202. In one embodiment, the contour of the waveguide142allows a probe150to scan substantially the entire portion of the tube200from the web202on one side of the tube200to web202on the other side of the tube200.

The probe150is in operative communication with the waveguide142. A slot151in the upper surface of the waveguide142accommodates the probe150and holds the probe at a fixed known orientation and angle of incidence to the outer surface of the tube200. The slot151may be molded during the manufacturing of the waveguide142or alternatively may be machined into the waveguide142. The probe150can be attached and detached from the waveguide142. As noted above it is pressure fit into the waveguide142. Some couplant may be used in the slot151to facilitate proper signal transmission between the probe150and the waveguide142.

The detachability of the probe150provides for quick change out of the various waveguide142sizes that may be required for the varying sizes of tubes under inspection. The probe150transmits sound waves in the ultrasound frequency range through the waveguide142into the tube200. The transmitted sound is in a phase array signal which transmits ultrasonic signals at varying angles.

The probe150generally has a square cross-sectional area, but may have other geometrical cross-sectional areas (e.g., circular, triangular, polygonal, and the like) as well. The position of the probe150in the waveguide142is fixed in a predetermined orientation and angle so that ultrasonic signals may be introduced into the hot side of a tube wall and travel circumferentially in the cold side of a tube wall. As can be seen in theFIG. 3A, the probe150is located at an incident angle of 20 to 40 degrees with respect to two lines—a first line that passes through the center of the cross-sectional area of the probe150and a line that passes through the center of the tube200(that is being examined) and the point at which the ultrasonic signals contact the surface of the tube200. This angle between the first line and the second line is termed the angle of incidence. By adjusting the angle of incidence to be between 20 to 40 degrees, the sound waves obey Snell's law and are refracted into the tube200and travel in the circumferential direction as shown in theFIG. 4. The probe150is disposed off-center in the waveguide142to get the signal as close to the membrane202of the waterwall as possible (SeeFIG. 3A.).

The probe150includes a cable152extending therefrom (SeeFIG. 1A.). The cable152is operative to transmit electrical signals between the probe150and an ultrasonic puller and receiver (not shown) and a computing device (also not shown) (e.g., a general purpose computer, signal processor or analyzer) having memory to record the electrical signals received from the probe150. The computing device processes the received information and has a display screen to allow an operator to view a visual indication of the electrical signals received from the probe150. Using various applications, the data acquired and recorded from the inspection may be converted in graphical form and displayed by the computing device. The graphical form of the data may illustrate qualitative and quantitative results of the inspections via the ultrasonic probe150. For example, the results may include defects in the tube wall under inspection, as well as the extent of the defects (such as size, range, and depth). The scanning device in theFIG. 2Cis depicted being disposed upon a waterwall tube comprising a plurality of tubes200that are held together by a membrane202that is welded to the respective tubes200.

In one embodiment, the probe150comprises a phased array of ultrasonic transmitters and sensors. The phased array utilizes a linear or two-dimensional array of ultrasonic transducers that are sequentially pulsed in sequence. Through superposition of individual wavelets, phased arrays provide the capability of steering the angle of the beam. Thus, the beam angle may be set by adjusting the timing of the individual pulses. By having the ability to sweep through multiple angles, an increase in detectability can be realized.

The scanning device100also comprises an encoder assembly160that is housed in the cavity159of the housing102(SeeFIG. 2.) and is operative to provide a reference point for a physical location on the pipe200at which the inspection is initiated, as well as a means for tracking and recording the responses from the probe150with respect to the ongoing inspection. The encoder assembly160may be located at any place on the bottom surface110of the scanning device100. In an exemplary embodiment the encoder assembly160is located on the side of the second magnet and screw assembly120B that is opposed to the side that faces the waveguide assembly140.

In theFIG. 3D, the encoder assembly160includes an encoder163in communication with a wheel162that rests on the tube200and rotates as the scanning device100is moved relative to the tube200. The encoder assembly160is held in place by a bracket167that is part of the housing102. The wheel162and the encoder163are mounted on a shaft (not shown) that is suspended at the opposite end of a cantilever beam166that pivots on a shaft165housed on the bracket167. The wheel162is spring loaded with a spring164that forces the wheel162towards the tube to contact the surface of the tube200. The spring164may be a cantilever spring, which has one end contacting the bracket167, while the other end contacts the shaft on which the wheel162is mounted. Other forms of springs (e.g., leaf springs, coil springs, and the like) may also be used. The spring164prevents the scanning device100from being moved over the tubes200without the wheel162being rotated and thus not recording the movement. A sensor within the encoder163detects rotation of the wheel, which indicates the relative position of the probe150as it moves along the tube200. The encoder163provides electrical signals indicative of this position to the computer device via cable166, thus allowing the computer device to correlate probe150readings with specific locations on tube200.

The scanning device100also comprises a plurality of hardened wear pins190(SeeFIGS. 1A and 2.) that are disposed on the bottom surface110proximate to the first end and second end of the scanning device to prevent damage to the waveguide. The hardened wear pins190can be manufactured from carbides. In one embodiment, at least a pair of carbide wear pins are disposed at the on the bottom surface110at the first end114and another pair of carbide wear pins are disposed on the bottom surface110at the second end116.

During operation of the scanning device100, the waveguide142contacts the tube200via a couplant, as described hereinafter. In an exemplary embodiment, the waveguide142may be arranged to scan in a direction generally parallel to longitudinal axis of the tube200. The longitudinal axis of the tube200is perpendicular to the plane of the paper in theFIG. 3A. The scanning device100is moved along the surface of the tube200(on the hot side of the waterwall) along the longitudinal axis of the tube. The scanning device100is moved along the surface of the tube200as close as possible to the membrane202(SeeFIG. 3A.) to obtain a scan of at least a quadrant (90 degrees) of the tube that lies on the opposite side of the membrane but on the same side of the tube as the side on which the scan is conducted. With reference to theFIG. 4, the ultrasound signal is introduced into the wall of the tube200at a predetermined angle, which is determined by the geometry and characteristics of the tube, i.e., the radius, the material, the wall thickness, and the like.

The ultrasonic signals210are refracted through the waveguide142and travel through the tube wall past the membrane202in the circumferential direction. Due to Snell's law, the angle of the signal may refract about 10 degrees additionally when passing into the tube wall. The ultrasonic signals210travel through the tube wall in the circumferential direction as shown in theFIG. 4and are represented by numeral220. Electronic sweeping of the beam assists in getting sound past the membrane and allows for improved direction by interacting with the cracking more perpendicularly. When a section of the tube200contains no crack, the beam travels through the tube wall and produces a background spectrum (that does not contain any peaks) on the computer screen. When the signal encounters a crack in the tube wall, the sound is reflected back along the path it travels and is received by the waveguide142and the probe150and is provided to a computer via the cable152. A computer screen displays a spectrum containing higher amplitude peaks (that can be distinguished from the background spectrum) from which the location and approximate size of the crack can be detected. Cracks can be detected by this method. In one embodiment in order to completely scan the cold side of the tube200for cracks, the scanning device100is rotated 180 degrees and is then traversed along the tube200(again on the hot side) in the opposite direction from the direction in which it was previously traversed on the other side of the tube200. It is to be noted that by using ultrasonic signals or signals having a greater intensity, the entire cold side of the tube200can be scanned for cracks in a single scan along one side of the tube200.

The method for determining crack location in the tube200will now be detailed with reference to theFIG. 3A. In order to determine the crack location in the quadrant500of the tube200, the scanning device is moved along the quadrant300of the tube. The ultrasonic signals (signals) traverse counterclockwise past the membrane202of the tube200, and if any cracks are present in the quadrant500, the signals are reflected back and displayed on the computer screen. In order to determine the crack location in the quadrant600of the same tube200, the scanning device is moved along the quadrant400of the tube. The ultrasonic signals traverse clockwise past the membrane202of the tube200, and if any cracks are present in the quadrant600, the signals are reflected back and are displayed on the computer screen. A two-dimensional or three-dimensional view of the scanned portion of the tube may be displayed on the computer screen.

In one embodiment, in one method of manufacturing the scanning device100, the housing102is first printed by a method that comprises additive manufacturing. The additive manufacturing is also termed 3-D manufacturing. The housing102is manufactured such that it contains cavities for housing the magnet and screw assemblies120A,120B and120C. The housing102also contains cavities that house the waveguide assembly140and the encoder assembly160. The tubes180,182and184for transporting the couplant are also integrally contained in the housing102. In other words the tubes180,182and184are formed in the housing and are not inserted separately into the housing.

The magnet and screw assemblies120A,120B and120C are then affixed to the housing102. The strips of soft absorbent material126A and126B (e.g., felt) are then bonded to the housing102. The waveguide assembly140and the encoder assembly160are then affixed to the housing102. The carbide wear pins may then be disposed in the third magnet and screw assembly120C and in the curved bottom surface of the housing102respectively. The position of the magnet and screw assemblies and the waveguide assembly can be adjusted by turning the nut on the screw for each of these assemblies. The conduits and electrical supply are then connected to the housing102in their respective positions that are detailed above.

The scanning device and the method disclosed herein have a number of advantages. The scanning device is printed using additive manufacturing techniques (also known as 3-dimensional printing or rapid prototyping), which makes them lightweight, compact, ergonomic and comfortable. The scanning device is printed with specific curvatures that match the outer diameter of the waterwall tubes. The scanning device has an encoder that has a spring loaded wheel to prevent slippage while being displaced along the outer surface of the waterwall tubes thus allowing for determining accurate axial position on tube. The scanning device has self-contained water channels and passages for couplant delivery to the probe. It has felt inserts, which help with tube wetting and containment of couplant. It also has carbide wear pins to limit probe waveguide wear.

The term and/or is used herein to mean both “and” as well as “or”. For example, “A and/or B” is construed to mean A, B or A and B.

The transition term “comprising” is inclusive of the transition terms “consisting essentially of” and “consisting of” and can be interchanged for “comprising”.

While this disclosure describes exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the disclosed embodiments. In addition, many modifications can be made to adapt a particular situation or material to the teachings of this disclosure without departing from the essential scope thereof. Therefore, it is intended that this disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure.