Phased array inspection of cylindrical objects

A first array (A) of ultrasonic transducers transmits ultrasonic shear waves circumferentially around an examined cylindrical object (110). A second array (B) transmits ultrasonic shear waves axially along the examined object. Triggering pulses from a triggering amplifier (22) are switched by a multiplexer (24) to each individual transducer of the first and second arrays. As one of the transducers assumes the role of a transmitting transducer and transmits an ultrasonic wave, the other transducers of the first and second arrays assume a receiving mode to receive reflected ultrasonic components. A wave travel timer (26) measures the duration for an ultrasonic wave to be transmitted from the transmitting transducer to a defect and for a reflected component to propagate from the defect to the receiving transducer. A microprocessor (20) tri-angulates or otherwise computes the location and orientation of a reflective defect from the measured travel time, the spatial relationship of the transmitting and receiving transducers, and the direction of propagation of the transmitted ultrasonic wave.

BACKGROUND OF THE INVENTION 
The present invention relates to the art of acoustical defect detection. 
The present invention finds particular application in the ultrasonic 
inspection of cylindrical objects such as metal pipe and tubing, and will 
be described with particular reference thereto. It is to be appreciated, 
however, that the invention has other applications including acoustical 
examination of sheet materials, polygonal members, rods, and the like. 
Heretofore, ultrasonic transducers have been utilized in a pulse-echo mode 
to locate flaws and defects in an examined object. In the pulse-echo mode, 
an ultrasonic transducer is first caused to transmit an ultrasonic wave 
and then waits to receive an echo from a defect. The angle of incidence 
and angle of reflection relative to the surface of the defect must be 
equal. Thus, a transmitting transducer can only receive an echo from a 
defect surface which is substantially normal to the direction of 
ultrasonic wave transmission. Defect surfaces which are more than 
5.degree. off-normal to the direction of propagation reflect the 
ultrasonic wave, but do not return a sufficiently large component to the 
transmitting transducer for the defect to be detected. 
Ultrasonic transducers have been used in a pulse-echo mode to generate 
ultrasonic shear waves traveling peripherally around the examined object, 
and to detect echoes reflected peripherally back to the transducer. 
Axially oriented ultrasonic transducers have been used to generate axial 
shear waves and detect axial echoes. Similarly, ultrasonic transducers 
have been oriented perpendicular to the examined surface and operated in a 
pulse-echo mode. Further, others have oscillated or rocked the transducers 
to examine the object from a multiplicity of angles. 
A three dimensional defect commonly has at least some surface portion which 
is normal to one of the pulse-echo operated transducers and is readily 
detected. However, a two dimensional defect, such as a crack, can only be 
detected by pulse-echo transducers which are oriented substantially 
perpendicular to the surface of the crack. Thus, peripherally oriented 
pulse-echo transducers and axially oriented pulse-echo transducers are 
only able to detect cracks which are substantially parallel or 
perpendicular to the axis. 
It has been suggested to have ultrasonic transducers propagate ultrasonic 
waves around the examined object in a spiral at various angles, eg., 
45.degree.. However, because the direction of propagation must be within 
5.degree. of normal to a crack to be assured of detection, a wide range of 
wave propagation directions would be required for assuring that cracks 
would not go undetected. 
The present invention contemplates an arrangement which overcomes the above 
referenced problems and others, and provides an ultrasonic inspection 
system which detects defects and cracks oriented at a wide variety of 
orientations in an examined object. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, there is provided a method of 
ultrasonically locating defects in an examined object with first and 
second transducer arrays. The first transducer array is disposed for 
transmitting and receiving ultrasonic waves propagating in a first 
direction, and the second array disposed for transmitting and receiving 
ultrasonic waves propagating in a second direction. The transducers in the 
first transducer array are actuated individually or in small groups to 
transmit an ultrasonic wave. The transducers in both arrays are operated 
in a receive mode to receive ultrasonic echoes. The travel time between 
transmission of the wave and receipt of an echo is measured. From the wave 
transmission direction, travel time, and the spatial relationship of the 
transmitting and receiving transducers, the location of a reflective 
defect is tri-angulated or otherwise determined. This process is repeated 
with each transducer in the first and second arrays operated in its 
transmission mode. 
In accordance with another aspect of the invention, an ultrasonic defect 
detection apparatus is provided. A first transducer array, including a 
plurality of first transducers, is disposed for transmitting ultrasonic 
shear waves along the examined object in a first direction. A second 
transducer array including a plurality of second transducers is disposed 
to transmit ultrasonic shear waves along the object in a second direction. 
A multiplexing means selectively switches triggering pulses to each 
transducer of the first and second ultrasonic transducer arrays. After 
each transmission, the first and second ultrasonic transducer arrays 
assume a receiving mode. An ultrasonic wave travel time measuring means 
measures the time between transmission of the ultrasonic wave and receipt 
of an echo. A defect location determining means determines the location of 
a reflective defect from the wave transmission direction, the determined 
travel time, and the spatial relationship of the transmitting and 
receiving transducers. 
A primary advantage of the present invention is the detection of two 
dimensional defects and cracks having substantially any orientation. 
Another advantage of the invention resides in the capability to examine an 
object for defects relatively quickly and accurately. 
Still another advantage of the invention is found in the accurate location 
and determination of defect dimensions. 
Still other advantages and benefits of the present invention will become 
apparent to those of ordinary skill in the art upon reading and 
understanding the following detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference to the drawings wherein the showings are for purposes of 
illustrating preferred and alternative embodiments of the invention only 
and not for purposes of limiting same, each transducer of a first 
transducer array A in FIG. 1 is oriented so as to transmit ultrasonic 
waves propagating along an examined object in a first direction. Each 
transducer of a second transducer array B is oriented to generate 
ultrasonic waves propagating in a second direction. 
In the preferred embodiment, the first and second directions are orthogonal 
to the circumferential direction. The use of orthogonal propagation 
directions simplifies the algorithm for determining the position at which 
a flaw is located, but is not required. An electronic circuit C 
selectively actuates or triggers transducers of the first and second 
arrays to generate ultrasonic waves propagating in the first and second 
directions, causes the transducers of the first and second arrays to 
assume an echo receiving mode, and determines the size, location, 
orientation, and other physical characteristics of cracks and defects. 
In the preferred embodiment, the examined object comprises a cylindrical 
steel pipe or tube 10. The transducers of the first ultrasonic array A are 
disposed to propagate ultrasonic waves through a coupling medium in a 
collar 12 to the examined object. The transducers of the first array are 
oriented such that shear waves are propagated circumferentially around the 
examined object. The transducers of the second array are oriented to 
transmit ultrasonic waves through the coupling medium to propagate 
ultrasonic shear waves axially along the examined object. In the preferred 
embodiment, the first and second transducer arrays are disposed 
circumferentially or peripherally around the entirety of the object. 
Alternately, the first and second arrays may extend only partially around 
the examined object, and the examined object may be rotated to bring all 
portions thereof into association with the transducer arrays. As the 
object 10 is relatively moved axially through the first and second arrays, 
A, B, a position encoder 14 produces electronic signals indicative of the 
location of the arrays relative to an arbitrary point or origin of the 
object. 
A microprocessor 20 periodically enables or actuates a triggering means 22 
causing it to produce an ultrasonic transducer trigger pulse. A 
multiplexing means 24 switches the triggering pulse to a selected 
ultrasonic transducer of the first and second arrays. The microprocessor 
controls the multiplexing means such that the multiplexing means 
selectively switches trigger pulses serially to each of the transducers in 
the first and second arrays. An ultrasonic wave travel timer 26 measures 
the time interval between transmission of an ultrasonic wave and receipt 
of an ultrasonic echo. Although illustrated as a separate component 
connected with the triggering means and with the transducers of the first 
and second arrays, the wave travel timing means may comprise an integral 
part of the microprocessor 20. Optionally, one or more transducers 28 may 
be disposed a preselected distance from one of the axial transducers to 
measure the velocity of the ultrasonic shear waves in the examined object. 
The microprocessor is programmed to calculate the location of each defect 
which produces a received ultrasonic echo and display the defect location 
on a display means 30. In this manner, the microprocessor functions as a 
location determining means which determines defect locations from the 
spatial relationship of the transmitting and receiving transducers, the 
direction of transmission of the ultrasonic wave, and the travel time. In 
addition, the microprocessor determines and displays other characteristics 
of each defect, such as the orientation of the reflecting surface, the 
reflectivity of the defect, and the like. 
The location of the flaws is calculated using a form of triangulation. It 
is to be appreciated that the transmitting transducer, the defect, and the 
receiving transducer define the three corners of a triangle. The spatial 
relationship of the transducers determines the length of one side of the 
triangle, ie., the distance between the transmitting and receiving 
transducers. The direction of propagation determines the angle between the 
sides of the triangle which meet at the transmitting transducer. The wave 
travel time in conjunction with a premeasured propagation speed provides 
an indication of the sum of the length of the other two sides of the 
triangle. From this data, the location and angular orientation of a defect 
relative to the transmitting transducer may be calculated. 
With reference to FIG. 2A, one or another preselected number of the 
transducers in the first and second arrays A, B is triggered to generate 
an ultrasonic shear wave. As illustrated, one of the axial transducers 40 
generates an ultrasonic shear wave 42 propagating axially along the 
examined object. Upon encountering a crack 44 or other defect, the 
ultrasonic wave is reflected or echoes and produces a reflected component 
46. The transmitting ultrasonic shear wave 42 strikes the crack 44 at a 
point of intersection 48 at an angle 50, known as the angle of incidence. 
The reflected component 46 is reflected from the crack at an angle 52, 
known as the angle of reflection. 
The angle of incidence and the angle of reflection are measured relative to 
a tangent to the point of intersection. In such an interaction, the angle 
of reflection is equal to the angle of incidence. Thus, the angular 
orientation of the crack 44 determines the direction in which the 
reflected component propagates. The reflected component intersects another 
of the transducers, eg., a transducer 54 of the second array B in the 
illustration of FIG. 2A. From this information, the point at which the 
ultrasonic wave struck the crack and the angular orientation of the crack 
relative to the axial direction are readily determined. 
Specifically, it is to be appreciated that a right triangle is defined 
between the generating transducer 40, the point of intersection 48 with 
the crack, and the receiving transducer 54. The travel time between 
transmission of the ultrasonic wave and receipt of the echo component is 
readily measurable. Further, the velocity of the shear wave is readily 
determinable by experimental measurement or the like. 
These experimental relationships can be described mathematically as 
follows: 
EQU d.sub.42 +d.sub.46 =V.sub.s t (1) 
EQU (d.sub.46).sup.2 =(d.sub.42).sup.2 +(d.sub.t).sup.2 (2) 
where d.sub.42 is the distance between the transmitting transducer and the 
crack, d.sub.46 is the distance between the crack and the receiving 
transducer, V.sub.s is the velocity of the shear wave, t is the elapsed 
time between transmission and receipt, and d.sub.t is the distance between 
the transmitting and receiving transducers. These equations are readily 
solvable in terms of the distance in the axial direction between the 
transmitting transducer 40 and the crack: 
##EQU1## 
Similarly, the equal angles of incidence reflection are readily 
determinable from the quadratic equations: 
EQU tan 2.theta.=d.sub.t /d.sub.42 (4) 
EQU 2.phi.+2.theta.=180.degree. (5) 
where .theta. is the angle between the surface normal and each of 
ultrasonic wave 42 and reflected component 46, and .phi. is each of the 
equal angles between the surface tangent and each of the ultrasonic wave 
42 and the reflected component 46. These equations are readily solvable 
for the angle .phi. between the defect surface and the direction of 
propagation and the angle .theta. between the surface normal and the 
direction of propagation: 
##EQU2## 
Further, from the intensity of the reflected component, ie., the relative 
magnitude of the transmitted wave 42 and the reflected component 46, the 
reflectivity and other physical properties of the defect are determinable. 
In FIG. 2B, like components to the components of FIG. 2A are identified by 
the like reference numerals with a primed (') suffix. A transmitting 
transducer 40' transmits an ultrasonic wave 42' which interacts with a 
defect 44'. The orientation of the defect surface is such that a reflected 
component 46' is produced. In the situation of FIG. 2B, the reflected 
component propagates in a circumferential direction and is received by a 
receiving transducer 54'. Analogously, the distance in the axial direction 
from the transmitting transducer to the defect, and the angle of the 
defect surface relative to the axial direction may both be calculated from 
the spatial relationship of the transmitting and receiving transducers, 
the direction of wave propagation, and the wave travel time. 
In the showings of FIG. 2C, like components to the components of FIGS. 2A 
and 2B are identified by like numerals with a double primed (") suffix. A 
transmitting transducer 40" of the circumferential array A generates a 
circumferential ultrasonc wave 42" which interacts with a crack 44". A 
reflected component 46" reflects from the crack such that an angle of 
incidence 56" equals an angle of reflection 52". This echo direction 
results in a receiving transducer 54" receiving the reflected component 
and transforming it into an electrical signal. Analogously, the distance 
of the crack circumferentially from the transmitting transducer and its 
angular orientation relative to the circumference are readily calculated 
from the spatial relationship of the transmitting and receiving 
transducers, and the ultrasonic shear wave travel time. 
With reference to FIG. 3, a hard wired circuit is illustrated for 
controlling the ultrasonic transducers and for determining the location of 
defects. The first array A is oriented to generate ultrasonic shear waves 
which propagate circumferentially around a workpiece 110 and the second 
array B is oriented to generate shear waves axially. A position encoder 
114 determines the relative position between the workpiece and the 
transducer arrays, and a clock 116 periodically generates clocking pulses. 
A Schmidt trigger or other triggering means 122 converts the clock pulses 
into firing pulses of the appropriate amplitude and duration for causing 
one of the ultrasonic transducers to generate an ultrasonic shear wave. A 
multi-plexing means 124 selectively switches the trigger pulses from the 
trigger means serially to each individual transducer of the first and 
second arrays. Each clocking pulse steps the multiplexer such that the 
trigger pulses are switched serially to each transducer. 
An ultrasonic wave travel time measuring means 126 measures the travel time 
between transmission of an ultrasonic wave and receipt of an ultrasonic 
reflected component. A location determining means 120 determines the 
location of a defect for display on a display means 130. In the embodiment 
of FIG. 3, the location determining means includes an ultrasonic shear 
wave velocity determining means 132 which determines the velocity of the 
shear waves along the measured object. As illustrated, the shear wave 
velocity measuring means measures the travel time over a preselected, 
known spatial distance. A multiplying means 134 multiplies the wave travel 
time by the shear wave velocity to determine the total distance traveled 
by the wave, ie., d.sub.42 +d.sub.46. A transducer identifying means 136 
is operatively connected with each of the transducers in the first and 
second arrays to determine which transducer was triggered and which 
transducer received the reflected component. A transducer spatial 
relationship determining means 138, such as a look-up table, determines 
the spatial relationship between the transmitting and echo receiving 
transducer. 
From the spatial relationship of the transmitting and receiving transducers 
and the wave travel distance, a relative location means 140 determines the 
distance along the transmission axis between the transmitting transducer 
and the defect as well as the angle of the defect surface relative to the 
transmission axis. From the spatial relationship of the transmitting and 
receiving transducers and the actual wave travel distance, a unique defect 
location and angle is dictated. An angle look-up table 142 and a relative 
location look-up table 144 are preprogrammed with the relationships 
between transducer spatial relationships and wave travel distance. 
Alternately, the relative location means may be a processor preprogrammed 
for implementing equations (3) and (6) set forth above, and analogous 
equations for the other transmitting and receiving transducer 
combinations. 
A coordinate origin adjustment means 150 defines a unique coordinate 
position on the workpiece relative to a preselected origin point on the 
work-piece. The origin means 150 includes a position encoder 114 for 
determining the axial and circumferential position of the examined object 
110 relative to the first and second transducer arrays A and B. 
Specifically, the origin adjustment means compensates for the relative 
position of the first and second arrays and the examined object, and 
compensates for the position of the transmitting transducer in the array. 
An amplitude detecting means 160 determines the relative amplitude between 
the transmitted and received pulses. The display means 130 produces a 
visual display which indicates the location of each defect, the relative 
reflectivity of the defect surface, the angular orientations of the defect 
surfaces, and the like. 
The invention has been described with reference to the preferred and 
alternate embodiments. Obviously, modifications and alterations will occur 
to others upon reading and understanding this specification. It is 
intended to include all such modifications and alterations insofar as they 
come within the scope of the appended claims or the equivalents thereof.