Abstract:
Disclosed is an ultrasonic IRIS inspection system and a method of providing automatically compensated concentric B-scans by means of curve-fitting the unadjusted tube boundaries from inspection data, and from the curve fitted theoretical circle, using non-linear regression analysis to determine an adjusted center. The off-center distance between the adjust center and the misaligned center is then used to produce concentric inspection result by compensating the unadjusted inspection result with the off-center distance.

Description:
FIELD OF THE INVENTION 
     This invention relates to non-destructive testing and inspection systems (NDT/NDI), particularly to conducting internal rotating inspection system (IRIS) ultrasonic inspection of tubular test objects using a corrected display compensating for changes in probe centering. 
     BACKGROUND OF THE INVENTION 
     An internal rotating inspection system (IRIS) is an immersion ultrasonic non-destructive testing (NDT) system used to measure the wall thickness or inspect the wall conditions of tubular materials, in particular for, but not limited to, heat exchanger tubing and boilers. IRIS technology is often used to confirm and provide sizing of outside diameter (OD) or internal diameter (ID) defects, such as multiple pit clusters. 
     An IRIS C-scan view is a succession of IRIS B-scans representing one probe turn. The B-scan is alternatively represented in a cylindrical view, which puts more into evidence the importance of probe centering. While the IRIS probes detect OD and ID pitting relatively easily by means of the B-scan view, the screening of the multiple defects in a C-scan view is a tedious process, and can lead to missing defects as errors are inevitable. 
     The C-scan view offers a color-coded display of the local ID value or the OD value. However in practice, the centering of the IRIS probe is virtually never perfect, and, more than often, significantly off-centered. This has the effect of shifting the whole color spectrum of ID or OD C-scan views, and hiding the defects that may be pushed outside the effective color range for detection. 
     While OD pits can be easily represented in a C-scan view by means of a “wall thickness” C-scan, ID pits cannot use such compensation; therefore the identification of ID pits in a C-scan view is very much dependent on probe centering. 
     Moreover, IRIS probe centering dynamically changes several times, in random moments, during the inspection. As a result, a simple ID defect analysis cannot be done. Standard practice is to find the deepest defect, yet an analyst must select each and every defect, measure or estimate its depth, take notes, and find the deepest one. This is a tedious process as many as several hundred defects can be found in tubes. 
     Some existing probe-centering methods inside a tubular testing material are used in existing practice. U.S. Pat. No. 5,329,824 discloses a probe-centering method of using multiple bendable support legs that are pivotally connected at different points to an inspection device inside a tube. U.S. Pat. No. 4,597,294 discloses a probe positioning system inside a tube using an oscilloscope, cam lock assemblies, and a predetermined axial extent from a magnetic tape recorder. However these solutions to centering a probe are mechanical, and do not have the precision offered by software working directly with the IRIS probe. 
     Considering the background information above, a solution that automatically centers an IRIS probe for C-scans would be of great economic value. It would be possible to obtain the same inspection and analysis results with existing IRIS equipment and software, but more intuitively and in a much faster way. An analyst could instantly locate the deepest defects and speed up the analysis, once the color palette has been properly adjusted. This would allow huge time savings while increasing the probability of detection, and also add further confidence in the IRIS technology or system being sold by a manufacturer. 
     SUMMARY OF THE INVENTION 
     It is a general object of the present disclosure to provide an IRIS inspection system that automatically compensates for the centering change by means of a signal processor that would eliminate the need for probe centering in an IRIS turbine featuring a rotatable motor. 
     It is a further a general object of the present disclosure to automatically recognize an OD, ID, or both tube diameters from a single B-scan in order to detect its center, and artificially displace the whole B-scan data in order to realign the center to where it should be. 
     It is a further a general object of the present disclosure to apply the automatic B-scan data center correction in continuous mode, and independently from each B-scan data, in order to enable the construction of fully corrected ID and OD C-scan views. 
    
    
     
       BRIEF DESCRIPTION OF THE OF THE DRAWINGS 
         FIG. 1  is a schematic view of the IRIS inspection system with non-concentric correction according to the present disclosure. 
         FIGS. 2 a , 2 b , 2 c , and 2 d    illustrate an IRIS probe head inside a tubular material in a perfectly centered condition, with their associated B-scan and concentric B-scan views. 
         FIGS. 3 a , 3 b , 3 c , and 3 d    illustrate an IRIS probe inside a tubular material in a non-centered condition, with their associated B-scan and concentric B-scan views. 
         FIGS. 4 a  and 4 b    illustrate an IRIS probe head inside a tubular material in a non-centered condition being corrected by the present disclosure. 
         FIG. 5  is a flow chart of the components involved in compensating the measurement distances from an off-centered IRIS probe during an NDT/NDI test. 
         FIG. 6  is a flow chart of the steps involved in compensating the measurement distances from an off-centered IRIS probe during an NDT/NDI test. 
         FIGS. 7 a  and 7 b    are detailed schematic views of the off-center calculator. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , the apparatus of the present disclosure is comprised of a signal processor  20 , which is further comprised of: an ultrasonic data processing module  14 , an off-center calculator  16 , and a center adjuster  100 . Signal processor  20  is connected to a data acquisition unit  12 , which has data connections to center adjuster  100  and to a probe  10 , and is also connected to a display unit  18 . 
     During a B-scan, probe  10  sends echo signals to data acquisition unit  12 , which feeds data to signal processor  20 , which further provides center location and correction from data processing module  14  and center adjuster  100 . 
     Ultrasonic data processing module  14  determines the distance from the center location of a test object to a normal concentric B-scan reference center. If the center location is not aligned, off-center calculator  16  calculates a horizontal distance and a vertical distance from the normal concentric B-scan reference center. Center adjuster  100  then adjusts the horizontal distance and vertical distance values from the misaligned data center, so that the misaligned data center is aligned with the normal concentric B-scan reference center. 
     Continuing with  FIG. 1 , the adjusted distances from center adjuster  100  are sent to display unit  18 , which obtains data from the corrected, centered view of the B-scan in order to build a fully corrected C-scan. This process is described in more detail in the following drawings and their descriptions. 
     Referring to  FIG. 2 a   , a probe assembly for an existing typical IRIS inspection is herein introduced for illustration purposes, exhibiting the concept of the “center” of a B-scan when it is aligned with the physical center of a tubular test object  101 . Tubular test object  101  is connected by a cable  106 , which provides an electrical connection, and fills the tubular test object with pressurized water. The pressurized water exits through a turbine rotatable mirror assembly  201 . It&#39;s a common practice that an IRIS turbine  102  includes an immersion ultrasonic focalized transducer  220  that sends ultrasonic waves towards a turbine mirror  221 . Ideally, the IRIS probe head inside tubular test object  101  is in a perfectly centered condition. The associated B-scan and concentric B-scan views associated with this perfectly centered condition are later directed by turbine mirror  221  to the surface of tubular test object  101 . The ultrasonic wave is then reflected by the tubular test object&#39;s internal and external surfaces, returns into turbine mirror  221 , and is received by immersion ultrasonic focalized transducer  220 . 
     Referring to  FIG. 2 b   , the resulting ultrasonic signals received from both the internal (ID) and external (OD) echoes of the surfaces are displayed in the Cartesian form of a B-scan view  210 , featuring the time of flight measurement from an ID echo  230  and an OD echo  231 , plotted against one complete turn (360°). For clarity, the positions around a full mirror rotation are represented as letters A, B, C, and D, referring to arbitrary references 90° apart.  FIG. 2 b    shows the B-scan results in an ideal situation under which there is no non-concentric problem between the B-scan center and the physical ID or OD centers. 
     Referring to  FIG. 2 c   , B-scan view  210  is also commonly represented in a polar pattern (a concentric B-scan  211 ). While it includes the same information as B-scan  210  under an ideal situation, the polar plot allows easier interpretation of the inspection results and easier visualization of eventual centering problems. 
     Referring to  FIG. 2 d   , IRIS probe turbine  102  is considered perfectly centered when it is equally positioned inside tubular test object  101  through equal positioning of the centering arms  104  within turbine rotatable mirror assembly  201 . When this occurs, B-scan view  210  displays ID echo  230  and OD echo  231  as straight lines in B-scan view  210 , and results in a perfectly aligned pattern in concentric B-scan  211 . 
     Referring to  FIGS. 3 a  and 3 b   , IRIS turbine  102  is considered in a non-centered condition when it has a center of rotation  301  that is not perfectly aligned with a tubular probe center  320  of tubular test object  101 . This condition is very common and could result from various causes during the inspection process. 
     Referring to  FIG. 3 b   , the Cartesian form of a B-scan view from a non-centered condition produces a waved ID echo  330  and a waved OD echo  331 , because the time of flight to a defect-free internal surface of tubular test object  101  is not constant across positions A, B, C, and D. 
     Referring to  FIG. 3 c   , a concentric B-scan  310  from a non-centered condition also exhibits a misaligned data center  302  against a nominal reference center  303 . Ultrasonic data processing module  14  (in  FIG. 1 ) uses software pattern recognition in the misaligned concentric B-scan view to generate surface signals and their angle positions, and to locate the center of an ID echo  340  and also the center of an OD echo  341 , which are the unadjusted inner and outer echoes, respectively. The center of ID echo  340  and alternatively, the center of OD echo  341  (in case ID echo  340  cannot be correlated) is used as a base to obtain adjustments of misaligned data center  302 . How off-center calculator  16  uses the software pattern recognition from ultrasonic data processing module  14  is described in more details in  FIGS. 5 and 6 . 
     Referring to  FIG. 3 d   , off-center calculator  16  compares the distance from an adjusted reference center  303   a  to misaligned data center  302 , and calculates a horizontal distance  312  and a vertical distance  313  between the two centers. Off-center calculator  16  is described in more detail in  FIGS. 7 a    and  7   b.    
     Referring to  FIG. 4 a   , center adjuster  100  adjusts horizontal distance  312  and vertical distance  313  from misaligned data center  302 , in order to obtain the view of adjusted reference center  303   a.    
     Referring to  FIG. 4 b   , center adjuster  100  returns successive corrected B-scan data  401  with adjusted reference center  303   a  to display unit  18  in order to build a fully corrected C-scan, allowing easier and more rapid depth analysis of internal defects through color identification. 
     Reference is now made to  FIG. 5 , which shows the components of the present disclosure executing the process involved for returning successive corrected B-scan data  401  with adjusted reference center  303   a  to display unit  18 . Ultrasonic data processing module  14  is further comprised of an internal surface (ID) signal and angle generator  14   a  and an external surface (OD) signal and angle generator  14   b . Off-center calculator  16  is further comprised of an internal filter  506 , an external filter  508 , an internal calculator  510 , and an external calculator  512 . Center adjuster  100  is further comprised of a signal selector  514  and a signal compensator  516 . 
     Reference is now made to  FIG. 6 , which along with  FIG. 5  show a flowchart of the steps involved for compensating horizontal distance  312  and vertical distance  313  from misaligned data center  302 , and obtaining adjusted reference center  303   a , using ID echo  340  and OD echo  341 , which are misaligned or unadjusted data. First, an analyst enters a nominal circular shape of the diameter of tubular test object  101  for the internal diameter in step  602 , and for the external diameter in step  604 . Along with the tubular test object&#39;s internal surface signals and angle positions  24   a  and external surface signals and angle positions  24   b  (from internal surface signal and angle generator  14   a  and external surface signal and angle generator  14   b  in  FIG. 5 ), these nominal circles are sent to off-center calculator  16 . 
     Continuing with  FIGS. 5 and 6 , off-center calculator  16  first filters the signals from internal surface signal and angle generator  14   a  and an external surface signal and angle generator  14   b . The purpose of the filters ( 506  and  508 ) is to remove signal data that is too high or too low for the nominal circles. More specifically, the filters determine all the radial boundary positions between misaligned data center  302  and adjusted reference center  303   a  that can be connected with a straight line, and that do not intersect with the border of tubular test object  101 . Internal filter  506  filters internal surface signals and angle positions  24   a  in step  606 , and external filter  508  filters external surface signals and angle positions  24   b  in step  608 . The filtered signals are the data over which the nominal circles from step  602  and step  604  are fitted. 
     Referring to  FIG. 7 a   , a part boundary computed from a B-scan is shown. The radial position of the part boundary relative to an assumed reference center  303   a ( j ) can be calculated by Eq. 1 as follows:
 
 R (φ j   ;r   0 ,φ 0 )=√{square root over ( r   2 (φ j )+ r   0   2 −2 r (φ j )* r   0 *cos(φ j −φ 0 ))}  Eq. 1
 
where R(φ j ;r 0 ,φ 0 ) is the radial position of the part boundary relative to assumed reference center  303   a ( j ), the φ j , j=1 . . . J, are the J boundary position sample angles with respect to misaligned data center  302 , r 0  is the distance between misaligned data center  302  and assumed reference center  303   a ( j ), φ 0  is the offset angle of assumed reference center  303   a ( j ) with respect to misaligned data center  302 , and r(φ j ) is the radial position of the part boundary relative to misaligned data center  302 .
 
     Referring to  FIG. 7 b   , adjusted reference center  303   a  defined with respect to misaligned data center  302  through parameters r 0  and φ 0  is optimized so that a circle of nominal radius R 0  best fits the filtered data. Then horizontal distance  312  and vertical distance  313  shown in  FIG. 4 a    can be computed in order to obtain corrected centering data for center adjuster  100 . 
     Referring back to  FIGS. 5 and 6  and along with  FIG. 7 b   , with adjusted reference center  303   a  and nominal radius R 0  defined, off-center calculator  16  then fits a theoretical circle over the filtered internal surface signals and angle positions  24   a  and external surface signals and angle positions  24   b  in order to obtain ID echo  340  and OD echo  341 . In step  610 , internal calculator  510  fits the circle over the internal signals and their angle positions of tubular test object  101 ; and in step  612  external calculator  610  fits the circle over the external signals. 
     Referring to  FIG. 7 b   , a theoretical circle over the part boundary from a B-scan is shown. The method of obtaining the optimal position of adjusted reference center  303   a , which thereafter becomes the adjusted reference center relative to misaligned data center  302 , consists of adjusting the theoretical circle or radius R 0  over the filtered signals from step  610  for the internal signals and step  612  for the external signals with respect to an objective function. This can be performed by many mathematical methods, including non-linear regression analysis. One of the often used non-linear regression analysis is called “non-linear least squares” method. Using “non-linear least squares,” an objective function S(r 0 , φ 0 ) can be generated in Eq. 2 that sums the residual distances for all J boundary sample angles φ j , j=1 . . . J, from the circle of nominal radius R 0  and the observed boundary position from assumed reference center  303   a  (as calculated by Eq. 1): 
                     S   ⁡     (       r   0     ,     ϕ   0       )       =       ∑     j   =   1     J     ⁢       [       R   ⁡     (         ϕ   j     ;     r   0       ,     ϕ   0       )       -     R   0       ]     2               Eq   .           ⁢   2               
where S(r 0 , φ 0 ) is an objective function to be minimized with respect to parameters r 0  and φ 0 , φ j  are the boundary sample angles with respect to the misaligned center  302 , r 0  is the distance between misaligned data center  302  and assumed reference center  303   a ( j ), φ 0  is the offset angle of assumed reference center  303   a  relative to misaligned data center  302 , and R 0  is the nominal radius of the part, either the part inner radius or the part outer radius. The non-linear least-squares method iteratively changes the parameters (r 0 , φ 0 ), starting from an initial guess, until the objective function S(r 0 , φ 0 ) computed by Eq. 2 is minimal. Once the minimum value of S(r 0 , φ 0 ) is reached, the assumed reference center is deemed the adjusted reference center  303   a  with optimal parameters (r 0 , φ 0 ). In other words, the adjusted reference center  303   a  is a special case of assumed reference center  303   a ( j ) such that the sum of the squared differences between the part boundary position as observed from the assumed reference center and the circle of nominal radius R 0  whose origin is placed at the assumed reference center is minimal.
 
     With the filtered radial position from Eq. 1, and the optimally adjusted reference center from Eq. 2, horizontal distance  312  and vertical distance  313  can now be calculated by off-center calculator  16  and sent to center adjuster  100 . 
     Returning to  FIGS. 5 and 6 , center adjuster  100  evaluates the optimal radial position of the part boundary relative to adjusted reference center  303   a , and implements it for centering the IRIS probe. In step  614 , signal selector  514  compares the fittings from step  610  and step  612 , and selects the lowest residual distance value, either from the internal or external signals. From the selected fit, the resulting offset radius and offset angle of the current scan are transformed from a polar to a Cartesian coordinate system, where horizontal distance  312  and vertical distance  313  are applied. 
     In step  616 , signal compensator  516  transforms the surface signals and their angle positions of tubular test object  101  from a polar to a Cartesian coordinate system. Center adjuster  100  then compensates the X and Y coordinates of the output by the resulting offsets from step  614 . In step  618 , display unit  18  displays the compensated data as corrected B-scan data  401  shown in  FIG. 4   b.    
     While this invention has been described with reference to an exemplary embodiment, it will be understood that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. The embodiment described herein and the claims described hereof are not to be read restrictively unless there is clear and convincing evidence manifesting a certain exclusion, restriction, or disclaimer.