Abstract:
Disclosed is an improved ultrasonic probe for Internal Rotating Inspection System (called IRIS) for inspecting tube-like structures from the inside of the tubes. The improved design deploys a rotor with rotor blades and a slotted stator located close to the emitting face of the transducer, to direct the flow of water such that air bubbles are carried away from a zone immediately in front of the transducer emitting face. Inspection accuracy and efficiency is significantly improved when air bubbles are effectively removed.

Description:
FIELD OF THE INVENTION 
     The present invention relates to non-destructive testing and inspection devices (NDT/NDI) and more particularly to an ultrasonic internal rotating inspection probe assembly that self-eliminates air bubbles in front of the probe sensor. 
     BACKGROUND OF THE INVENTION 
     Internal Rotating Inspection System (called IRIS) ultrasonic probes are used to inspect tubes from the inside of the tubes. They measure the thickness and possible defects of the tube wall around the circumference by performing helical scanning as the probe is pulled along the tube&#39;s axial direction. An IRIS probe is typically comprised of the following four parts: a) a cable, which brings a coaxial cable for ultrasound measurement signals and pressurized water flow; b) a centering device, which is a mechanically spring-loaded device that centers the probe assembly within the tube to be tested; c) a turbine, which uses the water flow/pressure to propel a rotating 45° mirror that deflects the ultrasonic signal to the tube wall when the tube interior wall is inspected; and d) an ultrasonic transducer that is called an “immersion focalized” transducer that focuses its ultrasonic beam at a small distance in front of its emitting zone. The tube being inspected has to be flooded with water in order for the ultrasonic signals to travel to the tube wall and back again. 
     IRIS ultrasonic probes as disclosed in U.S. Pat. Nos. 4,008,603 and 4,212,207 are today a common practice for the inspection of in-service tubes such as heat exchanger tubing. These IRIS probes exhibit a significant sensitivity to air bubbles, as the ultrasound waves employed by the device cannot travel through the air. The problem with the current design is that the air bubbles constantly get trapped in front of the ultrasonic transducer, causing an inevitable loss of signal. Eliminating the air bubbles typically requires the operator to shake the probe until the signal is retrieved, which requires not only time of the operator, but experience of the operator in recognizing the presence of the air bubbles. As this is an issue frequently impeding the inspection accuracy and efficiency, it causes significant downtime of the system. 
     To describe the problem more specifically, reference is made to  FIG. 1  showing the existing design of the conventional IRIS probes. The current design of IRIS probes employs an assembly called the “turbine” as it uses pressurized water to propel a reflective mirror P 10  which is mounted on a rotor P 6 . All components are held into a turbine housing P 22 . The water flow is pushed from the back of the turbine, forced in a thin layer around the ultrasonic transducer P 18 , and then is deflected by angled slots on a stator P 16 . The water flow is finally forced into “circumferential jet holes” P 12  and exits the mirror hole P 8 . 
     As can been seen in  FIG. 1 , as the water flows in a peripheral layer around stator P 16 , there is no significant water flow near the immediate front of the transducer ultrasonic coupling face P 20 . When small air bubbles are present in front face P 20 , whether coming through the water source or being forced from through the mirror hole P 8 , they tend to be trapped in front of the transducer ultrasonic coupling face P 20 , reducing or significantly blocking the ultrasonic waves. 
     SUMMARY OF THE INVENTION 
     The invention disclosed herein solves the problems related to the Internal Rotating Inspection System (IRIS) ultrasonic probes, transducers and sensors used in NDT/NDI devices where the existing IRIS probes present the aforementioned drawbacks, such as inaccuracy, loss of signals and undesirable operation down time caused by air bubbles trapped in front of transducers. 
     Note that the terms “probe”, “transducer”, and “sensor” used herein may be used interchangeably. 
     Accordingly, it is a general object of the present disclosure to provide an Internal Rotating Inspection System (IRIS) ultrasonic probe with the capability of self-eliminating undesirable air bubbles to achieve higher inspection accuracy and efficiency. 
     The increase of water flow for an equivalent pressure of water is a desired condition as it contributes to further elimination of air bubbles and helps further to locally flood the tube under test at the region of the minor hole of the iris. 
     It is further an object of the present disclosure to provide an improved design of the IRIS probe to achieve less water flow resistance than the conventional IRIS turbine design, therefore resulting in a significant increase of water flow for an equivalent pressure. This in turn further alleviates air-bubble problem through the whole probe and testing area. 
     It is further an object of the present disclosure to improve the design of the IRIS probe in a manner to help better flood the tube being tested, especially in the region of the mirror hole of the IRIS. 
     It also can be understood that the presently disclosed probe provides the advantages of better removal of air bubbles in front of the transducers and through-out the probe system and improved water flow with lower resistance. 
     It can also be understood that the presently disclosed method and probe provide the advantages of higher inspection accuracy, higher operational efficiency less overall operation cost and longer service life. 
     In addition, it can be appreciated by those skilled in the art that the novel design according to the present disclosure can be employed without any significant increase in manufacturing and operational cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view of a typical prior art IRIS probe turbine, which has the bubble retention problem. 
         FIG. 1A  is an exploded view of the preferred embodiment of the IRIS probe that self-eliminates air bubbles. 
         FIG. 1B  is another exploded view of the preferred embodiment of the IRIS probe that self-eliminates air bubbles, to show all components from a different angle than  FIG. 1A . 
         FIG. 2A  is cross-sectional view of the preferred embodiment according to the present invention, showing how the new assembly design directs the water flow, flushing air bubbles away from the front of the ultrasonic transducer. 
         FIG. 2B  is another cross-sectional view of the preferred embodiment of the self-eliminating air bubble ultrasonic probe turbine, in order to show the water flow inside the rotor blades. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The preferred embodiment of the present invention proposes a modified IRIS probe turbine that self-eliminates the air bubbles. 
     The present invention is an improvement to the existing IRIS probe turbine design formed to self-eliminate air bubbles. In the preferred embodiment of the present invention, this is achieved by a modification of the way the water is directed in order to generate the rotation force required to spin the rotor and force the water to flow in front of the ultrasonic transducer. 
     Referring now to both  FIG. 1A  and  FIG. 1B , in a preferred embodiment of the present invention, an IRIS probe preferably is comprised of a turbine base  6 , turbine housing  4 , an ultrasonic transducer  18 , a stator  12 , a rotor  2  with angled blades  10 , two bearings  20 , a spacer ring  22 , a simple retaining clip  24 , a spring pin  26 , a rotating acoustically reflective mirror  28  and a simple screw  30 . Except for base  6  and transducer  18 , all the parts listed here together form an assembly that is normally not disassembled during field operation of the probe. 
     It should be noted that the assembling manner of all the parts of the herein disclosed probe is exemplary. Variations in assembling manner and use of retaining parts are within the scope of this disclosure when they are employed to achieve the same functionality as described herein. 
     Continuing with  FIGS. 1A and 1B , turbine base  6  is normally assembled on the probe centering device (see background art) transducer  18  is held in place into turbine housing  4  between stator  12  and turbine base  6 . The turbine assembly, including housing  4  and rotor  2  are preferably mounted or dismounted on the base  6  in order to change transducer  18 . 
     During an IRIS inspection using the presently disclosed probe, water with predetermined pressure enters from a hose embedded in a co-axial cable (see background art) which is connected to base  6 . Water then travels ‘up’ from base  6  to mirror  28 . 
     Similar to existing methods used in existing IRIS probes, transducer  18  employs piezoelectric material to convert electric pulse to ultrasonic energy, emits and receives ultrasonic pulse energy and converts ultrasonic energy to electric signals. 
     In the preferred embodiment of the present invention shown in  FIGS. 1A and 1B , stator  12  is a separate part that is preferably “press-fitted” within housing  4  in order to fix its position. Stator  12  includes several angled slots  14  that are used to direct the water flow. 
     It should be noted in  FIG. 2B  that stator  12  also includes a recessed face  13  that prevents the transducer from moving and to come into contact with rotor  2 , which is undesirable. 
     Further continuing with  FIGS. 1A and 1B , according to the present invention, rotor  2  is a mobile part that rotates on its axis when the pressured water flowing through turbine blades  10  exerts force upon it. Rotor  2  is centered and allowed to rotate within the inner circumference of bearings  20 . Bearings  20  are kept fixed in axial position as they are mounted onto rotor  2  co-axially and confined by spacer ring  22 . Part of spacer ring  22  is then held by a synchronization spring pin  26  that is locked into an internal groove at the end of the housing  4 . Rotor  2  itself is blocked from moving in the axial position to have direct contact with bearings  20  on the stator side. On the mirror  28  side, simple retaining clip  24  that is fixed on the rotor  2  blocks axial movement of rotor  2  as it is also in contact with the bearings  20 . 
     In the preferred embodiment of the present invention, rotor  2  holds reflective mirror  28  that directs the ultrasonic waves out through the mirror hole  8  and further to the wall of the tube being tested. The test response signal travels this path in the opposite direction. Mirror  28  is simply mounted into rotor  2  preferably with screw  30 . 
     It should be noted that rotor  2  rotates when adequate water flow pressure is applied to angled blades  10 . 
     Reference is now made to  FIGS. 2A and 1A . As can be seen in the preferred embodiment of the present invention, the water flow is also forced to form a thin layer around ultrasonic transducer  18 , similar to the conventional IRIS probe design. As depicted in  FIG. 2B , the water flow is also directed by the stator  12  via angled slots  14 . 
     One important aspect of the novelty herein disclosed, is that these angled slots  14  create a water path flowing to the center of stator  12 . As a result, the water flows, passing directly in front of the transducer ultrasonic coupling face  16  (also see  FIG. 1B ). The transducer ultrasonic coupling face  16  is used to either emit or receive ultrasonic test signals. Allowing water to pass directly in front of face  16  is not presented nor allowed by prior art designs, as the water flow had to pass around the stator rather than within the inner circumferential region where face  16  is located (also see  FIG. 1 ). 
     As seen in  FIG. 1 , the space in prior art design between stator rotor P 6  and transducer face P 20  presents a ‘dead’ water flow zone with undesirable water flow that traps air bubbles. Another important aspect of the novelties presented in the preferred embodiment of the present disclosure is that stator  12  and rotor blades  10  are mounted to be very close to emitting face  16  of the transducer  18  in  FIG. 2A , therefore eliminating the ‘dead water flow zone’ as shown in existing design within stator P 6  in  FIG. 1 . 
     Continuing with  FIG. 2A  and  FIG. 2B , in the preferred embodiment of the present invention, the water flow is directed to apply pressure on rotor blades  10  with desirable impact angle to create a spinning motion to rotor  2  on its axis. While most of the water flow is used to propel the rotor  2  as it flows through the blades  10 , a lesser part of the water flow is forced to travel in front of transducer ultrasonic coupling face  16 . Both parts of water flow continue travel upward through rotor  2 , exiting rotor  2  through its center channel  9  and later through mirror hole  8 . The travel of the water flow carries away any air bubble that could have been trapped in front of the transducer ultrasonic coupling face  16 . 
     With the preferred embodiment of the current invention, the design of rotor blades  10  offers less resistance to water flow than the original “circumferential jet holes” design (see prior art and  FIG. 1 ), as the blade design offers a much larger “free” section for the water flow than that of the jet holes design. 
     Important aspects of the present invention involve the design of the rotor  2 , especially its blades  10  and stator  12  with its slots  14  that direct the flow of water in a way that the air bubbles are carried away through the rotor hole  9 . The other parts of the presently disclosed IRIS probe design remain similar to that of existing designs. The minimum but significant change helps easy adoption of this novel design while providing the significant advantages as follows: 1) it eliminates air bubbles and the problems associated with it; 2) it presents less resistance to water flow than the conventional IRIS turbine design (see prior art &amp;  FIG. 1 ), resulting in a significant increase of water flow for an equivalent pressure. The increase of water flow is a desirable condition as it contributes to further eliminate air bubbles throughout the whole system; and 3) it helps further to locally flood the tube under test in the region near mirror hole  8  where water exits. This feature is particularly useful when inspecting horizontal tubing, which tends to accumulate local air “pockets” around mirror hole  8  that block the transmission of ultrasonic waves. Having more water flow helps to move these air pockets away from the mirror hole  8 , resulting in fewer losses of measuring data. 
     Alternate Embodiments 
     The following design variations from the preferred embodiment should be recognized by those skilled in the art to be within the scope of the present disclosure. The description of the following alternative embodiments focuses on the portion of the embodiments varied from the preferred embodiment, and should be construed to complement to the preferred embodiment. 
     One alternative embodiment herein disclosed is to build stator  12  in  FIGS. 1A-2B , as part of the turbine housing  4  instead of being machined separately as shown in the preferred embodiment. 
     Another alternative design is to have rotor blades  14  assembled rather than machined. 
     Yet another alternative design is to make the shape of rotor blades  10  curved instead of being flat. 
     Further alternatively, designs can use any number of predetermined rotor blades  10  and stator slots  14 . 
     Yet further, different stator slot and/or rotor blade angles can be employed by alternative designs in order to achieve various rotor speeds. 
     Although the present invention has been described in relation to particular exemplary embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention not be limited by the specific disclosure. For example, the scope of the present disclosure may be applied to a wide range of probes such as, but not limited to Ultrasonic (UT) single element, multi-element, and array probes.