Abstract:
Disclosed is an improved method of sizing a defect using a phased array system with a single probe orientation requiring only a simple one-pass scan. It is an improvement of the ADDT standard which is adapted to phased array systems with fixed probe orientations. Based on pre-configured parameters obtained from C-scans, the method as presently disclosed provides novel analysis on C-scans and more complete information on defects, including the orientation and sizes in length and depth or thickness of the defects. Phased array systems devised with the presently disclosed method can perform such inspection and complete sizing automatically for longitudinal, transverse and oblique defects in one pass of scan.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure generally relates to a method and a system for inspecting and identifying flaws in test objects using phased array ultrasonic systems and, more particularly, to an improved method of sizing defects in the test objects and to an apparatus with the devised improvement in the phased systems, accordingly. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ultrasonic phased array (later as “PA”) instruments provide a significant advantage for many applications because they display a cross section of the region being inspected, thereby facilitating the visualization of an imperfection, its feature, location and size, typically sought by ultrasonic inspection. Another significant advantage of ultrasonic phased array instruments is that they provide much higher inspection speed and therefore higher productivity in comparison to single element probe systems. 
         [0003]    For inspecting a pipe during production, typically a PA system includes a linear phased array probe installed in parallel with the longitudinal axis of the pipe. The PA probe moves and scans circumferentially around the pipe. The relative circumferential movement is encoded to enable C-Scan production. Sizable imperfections that such PA systems target include longitudinal, transverse and oblique cracks that are located at either the inside diameter (ID) or outside diameter (OD) of the pipe. 
         [0004]    The typical pipe inspection using PA systems uses a widely known standard given by American Petroleum Institute. Specifically related to defect sizing, the widely used and recommended practice is given by  Recommended Practice for Ultrasonic Evaluation of Pipe Imperfections —API Recommended Practice 5UE 2 nd  Edition, June 2005—Addendum 1, APRIL 2009 8.2.2 page 7— Amplitude Distance Differential Technique  (Later as ADDT). According to ADDT, “The ADDT is based on the premise that the radial depth or thickness of an imperfection affects both the amplitude of the received echo signal and the differential time of flight of the transmitted ultrasonic wave as it passes over the imperfection. ADDT relates to the loss of signal amplitude, relative to the time (distance), as the ultrasonic beam is moved over the imperfection. The amount of time (distance) to incur a 50% drop in amplitude of the returned signal is related to the depth or thickness of the imperfection.” A discussion of the ADDT method can be found in reference material ADDT, which is herein incorporated by reference. 
         [0005]    One drawback brought by the method mentioned in the above ADDT is that the process is completely manual, comprising at least six steps to be performed for calibration and six more steps for inspection. More specifically, the existing practice has to re-orient the probe manually after a possible indication is found, to make sure the probe is scanning the pipe perpendicularly to the indication. This will take at least one more pass of scanning. However, using PA system wherein PA probes are usually placed to scan the pipe circumferentially and the probes could be in any orientation relative to the unknown indications. It would be desirable to achieve a method so that, in one pass of scan, the indication can be both found, sized and accurately located without having to re-scan with re-oriented probe. 
         [0006]    Another existing effort is seen in U.S. Pat. No. 7,240,554 which describes a variation of the ADDT measurement method, adding mechanism achieving a semi-automation for the process. It teaches the use of an A-Scan envelope to keep track of the maximums of one pass inspection over the indication that is perpendicular to its length. 
         [0007]    Although both methods stated above permits to size longitudinal, transversal and oblique imperfections manually or semi-automatically, they are rather slow and heavily dependent on user&#39;s interaction or operation. 
         [0008]    Therefore, it is needed and desirable to provide a system capable of providing size information of all directions during a pipe inspection with a one-step calibration and inspection. 
       SUMMARY OF THE INVENTION 
       [0009]    Disclosed is an improved method of sizing a defect using a phased array system with a single probe orientation requiring only a simple one-pass scan. It is an improvement of the ADDT standard which is adapted to phased array systems with fixed probe orientations. Based on pre-configured parameters obtained from C-scans, the method as presently disclosed provides novel analysis on C-scans and more complete information on defects, including the orientation and sizes in length and depth or thickness of the defects. Phased array systems devised with the presently disclosed method can perform such inspection and complete sizing automatically for longitudinal, transverse and oblique defects in one pass of scan. 
         [0010]    The method as presently disclosed uses a known technique for storing and analyzing data, named C-Scan. Each A-Scan maximum amplitude and its related time-of-flight are stored in a two dimensional table referenced to their physical position. 
         [0011]    Two sets of C-Scans are analyzed with two specific gates applied, with the first of which produces the length and orientation of the indication. Using the information of the orientation to identify the angle of a sectioning line, the second C-scan is sectioned to produce a plurality of A-scans at the identified orientation. Analyses on the resulting A-scans provide more accurate differences in time-of-flights which can be used to deduce the exact size of in length and depth or thickness of the indication. 
         [0012]    The imperfection is then sized in length and depth using ADDT according to its orientation. One of the key novel aspects of the present disclosure is that the method takes into account the orientation of the defect and it allows to size both length and depth or thickness of transversal, longitudinal and oblique imperfections from a single probe and scan orientation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic diagram showing the presently disclosed system and method providing improved sizing for defects of different orientations. 
           [0014]      FIGS. 2   a  and  2   b  are schematic diagrams showing resultant C-Scans and measurements therefrom produced, one of which is the orientation of the defect and the gates used to generate the C-Scans, whereas  FIG. 2   c  is an exhibition showing the usage of shorter and longer gates associated with the C-scans. 
           [0015]      FIGS. 3   a ,  3   b  and  3   c  are exhibitions of A-Scans used to provide time of flight measurements needed by the presently disclosed method. 
           [0016]      FIG. 4  is a flow chart showing the calibration steps used by the presently disclosed method for the PA system. 
           [0017]      FIG. 5  is a flow chart showing the operational steps used by the presently disclosed method during an inspection session. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    Referring to  FIG. 1 , a phased array ultrasonic system  10  embodies, besides other conventional components, a PA probe  12  and an acquisition unit  14  and a C-scan generator  16  which is used to produce C-Scans according to the echo signal acquired by acquisition unit  14 . C-scan generator  16  provides two C-scans, namely Gate A C-scan and Gate B C-scan. The two C-scans are then provided to two signal analyzer modules, the length &amp; orientation module  18  and the C-scan slicer module  20 , respectively. Gate A C-Scan is used to obtain indication orientation θ and length L in length &amp; orientation module  18 . Gate B C-Scan is used to obtain a C-scan slice from the orientation θ in C-scan slicer module  20 . The slice is then used by the depth module  26  to find the size in depth D of the Indication. Three measurements, namely the length L, orientation θ and depth D, are then displayed by a display unit  28 . 
         [0019]    It should be noted that, PA inspection on a pipe is herein used in this embodiment as an exemplary case of applying the presently disclosed method and apparatus. The framework and teaching shown in the present disclosure can be readily applied to inspections on other test objects of different shapes and sizes, such as bars, rods, panels, etc; and such application to other types of test objects should all be covered by the scope of the present disclosure. 
         [0020]    Referring now to  FIGS. 2   a ,  2   b  and  2   c , the amplitude of Gate A C-Scan from length and orientation module  18  shows an indication that has length L and orientation angle θ in respect to horizontal axis. This amplitude of C-Scan is obtained with using Gate A shown in  FIG. 2   c  which has a short time of flight range and is positioned at pipe inner diameter (ID) or outer diameter (OD, not shown). Amplitude of Gate B C-Scan from C-scan Slicer module  20  also shows the same Indication. The Gate B C-Scan shown in  FIG. 2   b  has the amplitude that is obtained with Gate B of  FIG. 2   c  that has a longer time of flight range, allowing obtaining a more complete indication data. Gate B is centered to the center of Gate A. Referring to  FIG. 2   b  and  FIG. 3 , a C-Scan sectioning line is positioned at the maximum indication amplitude point P max  and has orientation θ with respect to vertical axis. Half amplitude point P A  and half amplitude point P B  are located on the sectioning line. As can be seen from  FIG. 2 , indication orientation θ is used to find indication length L and depth D (not shown), which represents a novel approach in PA C-Scan analysis. Therefore it can be noted that this method generally applies to those possible defects located near either the inner surface or the outer surface of the pipe. 
         [0021]    Referring to  FIG. 3 , an exhibition of A-scans corresponding to amplitude points P A , P max  and P B  are illustrated. A-Scan at P A  corresponding to C-Scan half amplitude point P A  has a maximum amplitude A half  and time of flight T A . A-Scan at P max  corresponding to C-Scan maximum amplitude point P max  has maximum amplitude A max . A-Scan at P B  corresponding to C-Scan half amplitude point P B  has a maximum amplitude A half  and time of flight T B . 
         [0022]    Continuing referring to previous  FIGS. 1˜3 , reference is now primarily made to  FIG. 4 , a calibration must be done to obtain the factors needed to calculate the depth of an unknown indication according to the presently disclosed invention. According to  FIG. 4 , the calibrations steps include the following. In step  402 , user scan a calibration pipe containing a known indicator using a phased array probe  12  in a way to completely cover the known indication (not shown as it is practice known by those skilled in the art). In step  404 , acquisition unit  14  acquires echo signals then in step  406 , two C-Scans, Gate A C-Scan and Gate B C-Scan are generated and given to length &amp; orientation module  18  and to C-Scan Slicer module  20  respectively. In step  408 , indication length L and orientation θ are measured based on Gate A C-Scan. In step  410 , maximum amplitude A max  of the indication and its position P max  are calculated by C-Scan Slicer module  20  based on the Gate B C-Scan. In step  412 , C-Scan Slicer module  20  determines the sectioning line according to the angle of the orientation θ, and to the maximum amplitude position P max . In step  414 , amplitude values along the sectioning line are analyzed to find half-Amplitude point A half  and half-Amplitude B half  corresponding to each indication side P A  and P B , respectively. In step  416 , A-Scan exhibitions A-Scan at P A  and A-Scan at P B  are analyzed to obtain Time-of-flights T A  and T B  shown in  FIG. 3 , respectively. In step  418 , a calibration factor is then calculated using the following equation 1. In step  420 , calibrated length L c  and depth D c  (not shown) are displayed by display unit  28 . 
         [0000]    
       
         
           
             
               
                 
                   CalibrationFactor 
                   = 
                   
                     
                       D 
                       c 
                     
                     
                       
                         A 
                         max 
                       
                       * 
                       
                         ( 
                         
                           
                             T 
                             B 
                           
                           - 
                           
                             T 
                             A 
                           
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   Eq 
                   . 
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
         [0023]    wherein, D C  is the size of depth of the known indicator, A max  the maximum amplitude along the sectioning line, T A  and T B  the time of flight at half amplitude before and after A max  on the sectioning line. 
         [0024]    Continuing referring to previous  FIGS. 1˜3 , reference is now primarily made to  FIG. 5 , which is an exhibition of the inspection steps for the operation of a phased array system devised according to the present disclosure. According to  FIG. 5 , in step  502 , a test object, such as a pipe, is scanned in a way the same as a conventional PA operation on pipes. The pipe contains an unknown imperfection at an unknown spot. It should be noted that this unknown imperfection should be of the same type as that of the known indication used in the above calibration process. For example, the location of the imperfection, i.e., ID or OD; or the orientation such as longitudinal, transverse or oblique should be similar to that of the known indication. 
         [0025]    Phased array probe  12  is moved circumferentially relative to the pipe, completely covering the indication. In step  504 , acquisition unit  14  acquires echo signals. In step  506 , two C-Scans, Gate A C-Scan and Gate B C-Scan, are generated and provided to length &amp; orientation module  18  and to C-Scan Slicer module  20 , respectively. In step  508 , length L and orientation θ of the indication are calculated from Gate A C-scan. In step  510 , maximum amplitude A max  of the indication and its position P max  are calculated by C-Scan Slicer module  20  from the Gate B C-Scan. In step  512 , C-Scan Slicer module  20  determines the sectioning line according to the orientation θ, and to the maximum amplitude position P max . In step  514 , amplitude values along the sectioning line are analyzed to find half-Amplitude point A half  and half-Amplitude B half  corresponding to each indication side P A  and P B , respectively. In step  516 , A-Scan exhibition at P A  and P B  in  FIG. 3  are analyzed to obtain Time-of-flights T A  and T B  shown in  FIG. 3 , respectively. In step  518 , the indication depth D is calculated using Eq. 2 shown below. In step  520 , calculated length L and depth D (not shown) are displayed by display unit  28 . 
         [0000]        D=A   max *( T   B   −T   A )*CalibrationFactor   Eq. 2
 
         [0026]    wherein, D is the size of depth or thickness of the found indicator, A max  the maximum amplitude along the sectioning line, T A  and T B  are the time of flights at half amplitude before and after A max  respectively on the sectioning line and Calibration Factor is the calibrated factor obtained from Eq. 1 corresponding to the calibration process shown in  FIG. 4 . 
         [0027]    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 ultrasonic systems such as, but not limited to Ultrasonic (UT) single element, multi-element, and array probes. It should also be understood that pipes are herein used as exemplary test object, the usage of which should not limit the scope of the present disclosure. It therefore can be appreciated that the principle and scope of the sizing method herein disclosed can be applied to other type of test objects.