CA1169541A - Ultrasonic flaw detector having a transducer with an involute-like transmitting surface - Google Patents

Abstract

ULTRASONIC INSPECTION

Abstract An ultrasonic flaw detector for detecting irregularities in an object, such as a pipe having a segment of annular cross-section. The detector includes a transducer with an involute transmitting surface for sending ultrasonic signals into the object at equal non-radial angles of incidence. The detector further includes transmission apparatus for maintaining a constant physical relationship between the transducer and the pipe and interpretive apparatus for correlat-ing reflections of ultrasonic signals within the object with irregularities.

Description

3l~LG~5~1 Description Technical Field .. . ..
This invention relates to an ultrasonic flaw detecting deviGe for determinin~ abnormalities within a pipe or similar structure. Nondestructive ultrasonic testing of objects such as pipes is well known. With such testing an ultrasonic beam oE energy is sent into an ohject by a transducer and detection o~ reflections or echoes off internal structure within the object permits determination of characteristics of that internal structure.
More particularlyr if a piezoelectric crystal ; is pulsed with an electrical energy signal, that electric pulse causes an ultrasonic signal to be e~itted. It is also known that if the ultrasonic sic3nal reflects off an object within its path and returns to the piezoelectric crystal, that crystal responds by producing an electric si~nal. It is possible, therefore, to send ultrasonic signals into a test object whose internal structure is of interest and to develop information from cry~tal output signals which result from the reflections ofE the internal structure of the object.
BacXground Art Ultrasonic techniques for examining the in-ternal structure of a pipe or other cylindrical objects are known. Wben the object of interest is a pipe and the area of interest within the pipe i5 a longitudinally extending weld area, it has been more effective in studying the internal struc-ture of the pipe weld area to send the ultrasonic signals into the pipe transverse to the weld area rather than along its length.
One example of a proposed mechanism for de-termining the internal structure o~ a pipe or cylindrical object is the patent No. 3,924,453 to Clark et al. The angles of incidence of the ultrasonic beams into the pipe in the Clark device : ~ , :

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are une~ual. If this technique of ultrasonic flaw detection is utilized, the correlatlon of flaw severity to reflected signal strength becomes diEficult due to the non-monotonic variations in the strength o the received echo as a function of distance.
Patent No. 3,693,~15 to Whittington proposes another orm of ultrasonic Elaw detection for use with a cylindrical obiect. The Whittington patent teaches the use of an array of u:ltrasonic transducers which must be positioned about the pipe in a circular or cylindrical arrangement. Means must be provided for sequentially pulsing the transducers which make up this array in order that ùltrasonic beams of the proper phase arrive at a given point in the pipe structure and then enter that struature to be reflected by flaws or irregularities within the pipe.
Patent No. 3,916,675 to Perdljon propos~s still another method for ultrasonically testing the internal structure of a cylindrical device.
The Perdijon device, utilizes a complex deElector means which receives parallel ultrasonic beams from an ultrasound transducer and reflects these beams into the pipe structure. As can be seen by the complexity of the Perdijon proposal much care must be taken in designing the deflector means in order that the angle of incidence of the deflected beam strikes the pipe in the proper angle. The complex design reguired for the proper reflector shape must be repeated for pipes of different sizes and shapes and the complexity ;s significantly increased if any variation in detection capability is to be achieved.
Disclosure of Invention The present invention comprises an ultrasonic flaw detector for scannina an annular section of an object whose internal structure is of interes~.

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The use of a novel ultrason1c transducer design causes ultrasonic energy to enter the section and completely scan that section for flaws and irregu-larities. When a flaw exists within the section ultrasound ener~y is reflected from that flaw and returns along its incident path to the transducer where the reflected ultrasound energy is converted to electrical energy. Increased scanning reliability is achieved by causing the ultrasound energy to initiall~ impinge the annular section of interest along a waveform whose angles of incidence with - that section are substantially equal. Equal angles of beam incidence result in equal angles of bea~
refraction when the ultrasound enters the object oE interest. If the angles of refraction are equal and the transducer dimensions properl~ determined, the ultrasonic beam will completely scan the in-terior o the annular section and no flaws wi:ll ~e missed.
Equal angles of incidence can be achieved by the utilization of an ultrasonic transducer device whose shape coincides or substantially coincides with that of an involute. An involute is a curve traced by the end of a taut strin~ which when wound or unwound upon a fixed cuxve creates a certain configuration. In theory, the ultrasonic transducer surface could comprise a series of planar involutes of infinitesimal width which when summed together would create a surface involute.
Engineering considerations, however, have dictated that instead of an actual involute being utilized, a portion of a circle is used in creating the transducer.
In designing the actual transducer surface three points are chosen on a theoretical involute and a circle is traced through those three points.
The transducer which is actually constructed comprises a section of a cylinder-the radius of which coincides with the radius of the circle which appraxima~es a real involute.

5 ~1 It can be shown ~rom geometrical considerations that if an ultrasonic beam's angles of incidence are to impinge upon an angular cross-sectlon such as that of a pipe the involute must be generated from a generating curve or evolute which coincides with a circle. It can also be shown that the center of the circular evolu~e which generates the involute must coincide with the axis of the pipe to be scanned.
With the present invention the exact shape and size of the evolute, i.e., the generating curve is determined based on considerations of the pipe dimension to be studied. In determining the evolute's radius it is of primary importance to determine at what angle oE incidence the ultrasonic beam lS is to be projected into the pipe. The two constraints oE pipe radius and beam angle o~ incidence deine a constant radius evolute Eor generating a theo~etical transducer surface oE the proper involute shape.
From the theoretical transducer surface a quasi-involute which coincides with a portion of a circleis chosen and frorn that circle a cylindrical trans-ducer surface is constructed.
A transducer surface in this configuration causes ultrasonic waves to impinge upon a pipe's surface with equal or substantially equal angles of incidence. When refracted within the pipe structure these waves tend to travel in paths which neither concentrate nor diffuse beam energy.
Equal angles of incidence also provide more uniform energy transferral to the pipe. It is known that varying the angle of incidence of the ultrasonic energy varies the amount of energy trans-mitted to the pipe. If the waveform incident- on the pipe varies along its length in angle of inci-dence, the transmitted waveform therefore var;esin the amount of energy transmitted through the pipe. This non-uniform energy distribution will , S ~L

provide non-uniform echo signals from pipe flaws which produce peaks and valleys in signal amplitude.
The constant energy content of rays coming from an involute transducer provides a signal response which minimizes the peaks and valleys.
The transducer surface, once constructed, must be maintained in a proper geometric relatiorlship with the pipe structure in order that the proper angles of incidence are maintained. To achieve this proper correlation between the transducer surface and the pipe surface a wedge structure which transmits ultrasonic beams is placed between the pipe and the transducer. To achieve the proper correlation the wedge structure is designed to contain two important surfaces. One sur~ace coacts with the pipe structure and the other sur~ace coacts with the ultrasonic transducer surEace. The same quasi-involute used to construct the tran~ducer can be used to create one wedge surEace. For the other surface it is only necessary that the outside diameter of the pipe be known in order that the second surface of the wedge structure coi~cides with that diameter.
In addition to the constraints placed upon the shape of the transducer surface, a requirement exists with regard to a dimension of the transducer structure Xn the embodiment of the transducer surface which comprises a segment of a cylinder, this dimension refers to the circumferential extent or size of the segment of the cylinder or the number of pi radians that segment intersec-ts.
To understand this constraint one must examine the propa~ation of ultrasonic beams within -tne pipe structure. Once the ultrasonic beam enters the pipe it is re~racted at the outer surface tthe angle of refraction of course depends upon the refractive index of the wedge and pipe material) and then travels to the inside surface of the pipe.

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The angle oE incidence on this surface is such that there is substantially total internal re-flection.
The ultrasonic beam of substantially undiminished energy is then transmitted again to the outside sur~ace and again substantially totally internally reflectedO Internal reflection continues for a number of reflections until the beam is gradually attenuated.
It can be seen that to be certain a flaw within the pipe struc-ture is detected, the multiple reflections must cause the ultrasonic beam to sweep the entire section oE interest within the pipe.
If the quasi-involute surface is of an insufficient circumferential extentl it is conceivable that there will exist se~ments within the pipe structure which the ultrasonic beam never intersects. For this reason there is a minimum transducer dimsnsion which insures the pipe to be examined is adequately swept by the reflected beams within that pipe structure. It also should be noted that any climension beyond this minimum is excess and serves no useful function. Since the cos~ of fabricating the ultra-sonic transducer surEace increases as the size of the transducer increases, the minimum dimension should not be greatly exceeded.
If areas other than that in direct contact with the ul~rasonic transducer are of interest the plexiglass wedge and transducer surface can be moved circumferentially about the pipe structure in order that other areas of the pipe structure are tested. Thus it is seen that the present inven-tion does not require the design of an ultrasonic transducer SUL Eace which completely surrounds the pipe structure nor is a complex deflecting device necessary.
Accordingly one ob~ect of the present invention is to provide a flaw scanning device and ~ethod which completely scans an area of interest in an ~:~6~

annular object.- These and other objects, features and advantages of this invention hecome more apparent from the detailed description that follows when considered in connection with the accompanying drawings.
Brief Description oE the Drawin~s Figure 1 i5 a perspective view oE an ultrasonic ~law detector scanning a pipe section for flaw~;
Fic3ure 2 is a cross-sectional view of an ultrasonic flaw detector in contact with a section of a pipe;
Figure 3 is a diagrammatic sectional view showing two flaw detectors in difEerent positions about the circum~erence of a pipe to be inspected;
Figure ~ shows a 1aw detector whose circum-ferential length i5 adequate to scan ~he pipe shown in that figure;
Figure S shows an end elevational view with parts broken away and removed, oE a flaw det~ctor assembly that maintains its detector in close relation to a pipe to be scanned;
Figure 6 shows a lower plan view from the pipe of the flaw detector assembly of Fig. 5;
Figure 7 shows a schematic electrical diagram of the electronics for controlling the sending and receiving of ultrasonic signals.
Best Mode for Carrying Out the Invention Figure 1 shows the ultrasonic flaw detector assembly of the present invention positioned along a pipe 10. The pipe 10 has a center axis 11 and a longitudinal weld 14. It can be seen that the weld 14 forms a substantially straight line along a length of the pipe. The pipe has inside and outside surfaces lS, 17 whose spacing determine the thickness of the pipe to be scanned.

A detector mounting assembly or structure 16 is shown in Figure 1 resting atop the pipe 10.
This mounting structure is drawn along the pipe length in a direction indicated by -the arrow A
by ally suitable means, not shown. Alternatively the pipe 10 is moved relatlve to the detector mounttng structure 16 since relative motion is to be achieved.
The detector mounting structure 16 is an outriyger arrangement which includes a cross-member - 26 which carries a pair of end pieces 32. Each end piece 32 includes a pair of outrigger arms 28, only three of which are visible in Fi~ure 1.
Each outrigger arm 28J carries an outrigger roller 30.
lS A rotatable mounting ro~ 34 extends between the two end pieces 32. r~wo detector mount ar~s 18 are mounted to ~his rod 34.
~ s relative motion oE the pipe and detector occurs the outrigger crosspiece 26 maintains ~he four outrigger arms 28 in rigid relatlonship, one with the other. The detector mounting arms 18 on the contrar~ are rotatably mounted with the rod 34 and are arranged to rotate as the detector mounting structure encounters small variations in the pipe's surface. ~s the detector mounting structure 16 is drawn along the pipe in the direction indicated by arrow A~ the outrigger rollers 30 are maintained in symmetric relationship to each other relative to the weld area 14. Thus, the assembly 16 is intended to be opera~ed such that a plane located by the center axis 11 of the pipe and the weld area will bisect the rod 34.
Two ultrasonic transducer de~ecting de~ices 20 ar~e mounted to the detector mount arms 18~
As the ultrasonic detecting devices ~0-move alony - the pipe 10 signals are sent from an electronic signal module 24 by means of two diagrammatically illustrated electrical interconnects 22 and 23.

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An electronic signal processor contained within the module sends sign~ls to the ultrasorlic transducer detecting devices 20 causing them to send ultrasonic ; sound waves ;nto the pipe to scan for flaws and ; 5 defects as the detecting mounting structure moves along the pipe. The electronic signal module 24 also interprets reflected siqnals from wi-thin the -pipe structure when those signals rebound or echo of variations in density within the pipe structure.
As will be seen with reference to Figure 7, suitable means are connected to the electronic signal module to suitably mark the pipe at locations in which defects or flaws are found.
To ensure ultrasonic coupling between the transducer devices 20 an~ the pipe 10 a liquid coupling medium is provided by two hoses 21. These hoses typically provide a layer of water which is forced between the devices 20 and the pipe 10 to couple them for ultrasound transmittal.
By using two opposi~ely positioned transducers, each transducer can be tested by sending it a pulse from the other transducer. In this way proper coupling between pipe and transducer is assured.
Also certain flaws may be difficult to detect for one transducer but due to the difference in orientation to the second transducer they will appear on that second device.
j Figure 2 is a schematic diagram of an ultrasonic flaw detector 50 with its mechanical mounting structure removed. The flaw detector 50 has an ultrasonic transducer 51 having a surface 52. The detector 50 also includes a sound transmitting wedge 54 which coacts with the surface 52, a transducer housing 56, and an electrical interconnection 58 attached to the transducer 51.
The wedge 54 is shown in direct contact with - an outside surface 62 of a pipe 60. The wedge must be transmissive to sound and can be constructed from a synthetic acrylate resin such as that sold commercially under the trademark Lucite. Since the wedge 54 is in direct contact with the outside surface 62 of the pipe, the wedge obviously has one surface with a radius of curvature correspondin~
to the pipe outside surface's radius of curvature.
In operation, the signal module shown in sc~emat:ic ~orm in Figure 1 sencls an electrical signal along an electrical interconnect 58 to the transducer Sl. The transducer is comprised of a material which upon receiving an electrical signal produces an ultrasonic sound energy wave over its surface 52. When the ultxasonic txansducer receives an electrical signal from the electrical signal modulet ultrasonic energy beams are transmitted through the wedge 54 unt.il they imp;.n~e upon the p.ipe 50. It is accura~e to speak o.E the ultrasonic energy as a volume o~ energy, but, E~r illustration purposqs, the beam ~ill be considered in a plane o~ cross-section re~erre~ to as a number o.~ individual beam elements whose paths Eollow substantially straighk lines.
Upon entering the pipe 60 the ultrasonic beams are refracted away from normal to the p.ipe surEace and travel through the pipe searching for 1aws or other irregularities in the pipe. If a ~law or irregularity is found, ultrasonic energy beam energy is reflected off that flaw and retraces its incident path to the ultrasonic transducer surface 52.
Ult.rasonic beams travel from the transducer surface 52 along straight line paths and strilce the outside surEace 62 of the pipe. Typical incident beam elements indicated by ~he dashed lines 70, 72, 74 travel from the transducer 51 ancl strike the pipe 60 at exterior locations 76, 77, 78 along the pipe's outer surEace 62.

ll ` When typical beam elements 70, 72, 74 strike . the pipe surface they form angles of incidence A', A " and A' ". Upon entering the pipe structure the individual ultrasonic beams are refracted away from the normal to the sur~ace o~ the pipe along reEracted beam paths 80, B2, 84 to form re~raction angles S', S'l and S'''. These refracted beams travel through the pipe stxucture searching for flaws and irregularities until they reach internal points 86, ~7, 88 located upon inside surface 64 of the pipe 60. If this refracted angle of incidence on the inside surface is greater than a critical angle (the definition of a critical angle is known within the art) there occurs substantially total internal reflection and the beams are sent from the inside toward the outside sur~ace. The critical angle is dependen~ upon the index oE refraction oE the pipe and of the composition contained within the pipe. In the configuration shown in Figure 1 the intexnal composition is air. The ultrasonic beams continue to bounce from the inside and outside surfaces oE the pipe until gradually there occurs an attenuation which causes the beam strength to diminish.
As best seen in Fig. 2 the ultrasound producing transducer surface 5? comprises substantially an involute. A generating curve or evolute shown as a circle S9 is located coaxial with the pipe and has a diameter less than the pipe's inside surface 64. The transducer surface 52 is constructed such that for any point on its surEace there exists .
an imaginary line to that point which intersects the evolute 59 at a point and in a direction tangent to that evolute. Choosing a point 53 in the mid-region of transducer surface 52 it is possible to trace a path 72 to the surface 52 that intersects the evolute 59 at a point 92. The path 72 intersects the evolute 89 in a direction that is perpendicular ~: "

to a radius ~6 to the point 92 of intersection.
Similarl~ it can be seen that for other points 55 and 57 on the transducer surface 52 there exists perpendicular paths 70 and 74 that intersect evolute 59 at points 90 and 94 and with directions tangential to the evolute 59. -One method oE tracing an involute comprises the technique oE unwinding a string with a pencil or other marker at its end from around the generating curve or evolute. Thus, referring to Figure 2 a ~aut string with a pencil or marker tied to its end could be wound around evolute 5~. As the string is unwound it will coinci~e with the paths 70, 72 and 74 and ~he pencil would trace out the involu~e cross-sec~ional shape oE the surEace 52.
The si~e of angles oE incidence A', A ", and A''' hetween the pipe 60 and the ultrasonic beams will depend upon the size oE the generating circle or evolute 59~ ~s the radius 95 oE the evolute approaches the radius o~ the pipe'~ inside surEace 64 those angles oE incidence will increase. As the radius 95 of the evolute becomes smaller angles o~ incidence A', A'', and A''' will also becom2 smaller. As the size of the evolute 59 approaches the limit of a point centered at the pipe axis the angles of incidence shrink to zero and the typical rays 70, 72, and 74 become radial to the pipe's outside sur~ace 62.
It can be shown that regardless of the size of the evolute 59, as long as it comprises a circle, the angles of incidence A', A'' and A''' must be equal. In fact, any parts of an ultrasonic beam emitted by a transducer having a transducer surface generated ~y a circular evolute, will strike the annular cross-section of a pipe at equal angles along the outside surface of that pipe.

The proof oE.this propos;tion is straightforward.
It requires the showing of congr~ency bet~een two triangles shown in Figure 2. One triangle contains vertices de~ine~ by the center 99 of the evolute, S the point of tangency 90 to the evolute oE a typical ray 70, and the point the ray 70 intercepts the pipe's outside sur~ace 7G. The second triangle contains vertices de~ined hy the center 99 of the evolute, a second point 92 of tangency to the evolute and a second point 77 oE interception of that tangency with the pipe's outside sur~ace 62.
By hypothesis the angles between the typical rays 70 and 72 and typical evolute radii 95 and 96 are right angles. Since radii 95 and 96 are radi.i to the same circle those sides o the two trianc~les are e~ual in .l.ength. Also the distarlce from t:he center o~ the evolute 99 to the two points oE
interception 77 and 76 are equal since they a~e merel~ the outside radius Oe the pipe 60. Th~refo.re the two above de~ined triangles have two equal sides and one equal angle and therefore must be congruentO Since this is true the ang}e A'' defined by typical ray 72 and the normal to the pipe at the poin-t 77 typical ray 72 intercepts the pipe must equal the angle A' defined by a second typical ray 70 ana the normal at the point 76 that ray 70 strikes the outer surface 62 of the pipe 64.
This completes the proof that an involute will send typical beam rays to impinye upon the pipe .
. 30 with equal non-normal angles or lncidence.
By utilizing equal angles of incidence Al, A'' and A''' a detector made according to the present invention completely scans the pipe 60. It is instruc-tive to examine the three typical beam paths 70, 72, 74 as they enter the pipe 60. These typical beams enter the pipe at points 76, 77, 78 which are equally,spaced about the outside surface 62 of the pipe 60. That is, the circumferential distance between the lower point 76 an~l the midpoint 77 is ap-proximately equal to the circumferential distance from the midpoint 77 to the uppermost point 78.
Upon entering the pipe the ultrasonic beam is reEracted due to the diEferent indexes oE refraction of the pipe ~0 and the wedge 54. Upon refraction typical beam paths 70, 72, 74 are bent to ~orm equal angles of refractiQn S', S'' and Sl'l, respectively.
In traversing the pipe 30 the typical beams follow paths 80, 82, 84 and strike the inside surface 54 at nearly equally spaced points 86, 87, 88. Thus, the circumferen~ial distance between the lower posi-tion 86 and the mid-position 87 is approximately equal to the circumEerential distance between the mid-position 87 to ~he uppermost position 88. Thus, these typical beams tencl to maintaiJl their ~epar~ion without diverging or converging as th~y travel throughout the pipe 60.
If proper angles of incidence are chosen ~he ~o beam paths 80, ~2, 8~ will strike the inslde surE~ce 64 at anyles sufficiently large to result in nearly total internal reflection. As seen in Fi~ures 3 and 4, if these angles of incidence are properly chosen the beam will enter the pipe and be reflected o~E the inside and outside pipe wall a number of ; times before they are attenuated. In one embodiment oE the invention, incident angles of from 33 degrees to 45 degrees prove effective to achieve the required performance with an angle of incidence of approximately 35 degrees producing the best results. As noted previously it is possible to selectively choose the desired angle of incidence by changing the radius ol the evolute or generating curve, The preceding geometrical proof and discussions of performance all relate to a transducer surEace with a cross-section coincident with an involute.
While engineering considerations do not preclude the pos.sibility of the construction of an involu~e . ~

transducer surface they do suggest the use of a transducer su~Eace which approximates an involute.
In practice tllree points such as the three points 53, 55, 57 chosen in Figure 2 are chosen on a real involute. Using these three points it is possible to construc~ a circle passing throuyh these points whic~ closely approximates the real involute.
The circle in turn is the cross-sectional representation of a cylinder. The actual transducer ~omprises a segment of a cylinder whose cross-section coincides with a segment of that circle, three points of whic~ coincide with an optimum involute shape.
Although this quasi-involute or circle cannot produc2 exac~ly equal angles ~f incidence, the results approximate e~ual an~l~s to the degree of accurac~
requirecl to ade~uately scan a weld area for flaws or irregularities.
Figures ~ and 4 show how ultrasonic scanning performance can vary depencling on the physical dirnensions of the transducer surf~ce. The ultrasonic flaw detector 110 shown on the right in Figure 3 - is a schematic representation of a flaw detector constructed using the design described in Fiyure 2.
It comprises a transducer housing 112, a signal cable llI, a wedge 122 and a transducer 115 having a surface 116. The ~ucite wedge 122 coacts with a Fipe 160 having inside I64 and outside 162 surfaces.
As shown in the figure, the size of the transducer surface 116 is small relative to the width ~f the pipe segment. The width of the ultrasonic beam propagating from the transducer is indicated by the two boundary ultrasound beams 118 and 120.
An ultrasound beam 124 emi~ted from the surface 116 travels to a location 121 on the outside-surLace 162 of the pipe 160 where it is refracted. The beam 124 then travels throug-h the pipe 160 to a location 126 on the inside surface where nearly total internal reflection occurs. Similar internal reflections occur at locations 12~, 130 along the pipe's cross-section. To illustrate these multiple reflections that can occur, the ultrasonic beam 124 as pictured is internally reflected five times S before the bea~ strilces a flaw 100 and similarly rebounds five times before re-entering the Lucite wedge .
The transducer 115 is constructed of a piezo-electric crystal. This crystal exhibits the property that when it receives physical energy in the form of sound waves, it conver-ts-that energy to an electrical signal. Thus, when the wave retraces its incident path and strlkes the transducer 115 an electrical signal is sent to a cable 111 which transmlts that signal to a suitable electronic signal moclule tnot shown in Figure 3~. Throu~h electronic diagnostic techniques known within th~
art (and to be described) it is possible to deduc~
the existence and locatiQn of the ~law 100 within the pipe 160 through interpretation of the reflected signals.
As seen Erom the repreSentatiQn of the flaw detector 150 when moved to the left of Fig. 3, a narrow beam transducer surface may inadequately 2S scan the entire pipe structure. The flaw detector 150 comprises a transducer housing 152, signal cable ISl, Lucite wedge 153 and transducer 155 having a surface 156. The sur~ace 156 produces an ultrasonic heam 167 with outermost boundaries 166, 168 defining a relatively narrow beam. The beam 167 enters the pipe at a location 161 on the outside surface 152 and is refracted. When the beam strikes the inside surEace 164 total tor nearly total) internal reflection occurs and the beam CQntinues its travel along the pipe's interior.
Due to the narrow width of the beam 167, however, the beam never strikes the flaw 100. Instead the beam continues along its path until it is totally attenuated.

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It is appaxen~ from ~his discussion that in one position the detector 110 receives reflected signal~ from the flaw 100 and that in the second position the detector 150 receives no reElected signal from the flaw. rrhus, an ultrasonic signal with width dimensions which are relatively too narrow Eor the pipe 160 may rniss à Elaw or irreg~llarity in the pipe's internal s~ructure.
As shown in Figure 4 it is possi~le to construct an ultrasonic flaw detector 180 according to the present invention with a transducer 182 large enougl to completely scan the pipe 160. ~t should be noted that the pipe 160 shown in Figure 4. has the same inside 162 ancl outside 16~ su.rface as the pipe shown in Figure 3. The detector 180 compris~s a transducer housing 184l cabling 186, a Lucite wedge 138 and an ultrasonic transducer 189 having a surface 190. Three typical ultrasonic beams segmen~s 191~ 192, 193 are schemRti.call.y shown emerging ~rom the t.ransducer surEAce 190. If the ultrasonic beam is shortened to produce only one such beam 192 of width appro~imately equal to the beam width o~ Figure 3, the ~law 100 might be missed as the beam inadequately scanned the pipe.
With the.transducer wiclth increased to produce a beam de~ined by the two outside limits 191, 193 shown in Figure 4, any change in densit~ dùe to the existence of a flaw, regardless of its location within the pipe, will be detected. As seen in Figure 4 either o~ two representative beam segments 191 or 193 will strike tne flaw 100 producing a.
reflection which will return to the ultrasonic transducer and be interpreted by the electronic signal module. (Not shown in Figure 4).
. The two representative beam paths 191, 193 show the requisite conditions for adequate beam scanning for a given pipe dimension. If there exists one beam path 193 which is first reflected ~6~S ~l 1~
fror~l the outside surface 162 at a point 194 within the boundary 191 of the incident ultrasonic energy then con~plete ultrasonic scanning will occur.
Thus~ in Figure 4 either oE the representative paths 191 or 193 will strike the flaw 100. Due to the non-converging and non-diverging nature o the beams, they will comple~ely scan the pipe 160 in the vicinity of the detector 180 and will continue to scan as they travel in a circumEerential direction about the pipe.
For pipe of a given outside and inside diameter it is possible to determine optimum transducer widths. It is apparent tha~ as pipe thickness increases transducer width also must increase.
For wall thickness o three-eights inch it has been deter~ined khat a transducer surEace width oE two inches scans the pipe for Elaws. For other pipe thicknesses it is desirable to select tr~nsducer dimensions selected to scan as completely as desired Eor flaws or other iLregul~rities within the pipe s~ucture. Since due to engineering considerations an arc of a circle is used instead of a true involute, the circumferential extent o the arc is the dimension which is varied to match the thickness of the pipe to be scanned.
Shown in Figures 5 and 6 is one method of mounting an ultrasonic tran~ducer according to the present invention. Figuce 5 is an end view of the detecting mounting structure shown in less detail in Figure 1.
An end piece 202 is provided which has two circumferentially extending outrigger arms 20~.
The outrigger arm 20~ (on the left) has been partially sectione~ to indicate how roller bores 20& carries a roller 208 for contact with the pipe 210. The r~ller 208 comprises a rodlike cross-member 212 whi~h extends into the bores 206 found in the out-rigger arm 204. By means of two bearings 21~ the 5 ~

roller 208 rotates about the rodlike cross-member.
The outrigger arm 20~ .is representcltive o~ the other three outrigger arms which are not shown in Fi~ure 5.
1'he outrigger arm 204 to the right in Figure 5 has been brokerl away to show an ultrasonic detector mounting arrangement. 216. This cletector mounting arrangeme~t is adius~ably mounted to a detecto~
mounting arm 218. The detector mounting arm 218 comprises a slotted arm which serves as a mount - for two detector mounting brackets 220, only one . - of which is shown. A crosspiece not shown in Figure 5 maintains the two detector mounting brackets 220 a fixed d.istance apart longitudinally of the pipe. ~ach mounting bracket has an attachecl threaded stud 222 which extends through the slot .in the detector mounting arm 218.
The position oE the bracket 220 rel~tive to the arm 218 can be a~jus~ed by ~lns~rewing a threaded knob 22~ which coacts w.ith the threaded knob 222.
The knob further acts against a tightening washer 226 which creates a friction joint with the slotted arm 218. When the knob 224 is loosenea the ~riction joint between the arm 218 and the tightening washer 25. 226 is lost and the bracket 220 may be moved along the detecting mount arm 218 circumferentially of the pipe to be inspected. When the proper adjustment is achieved the knob 224 is retightened and the frictional joint ree$tablished~ The adjusting . 30 capability of t'ne bracket 220 allows the ultrasonic testing device embodied by the present invention to be adjustably mounted upon pipes of different diameters.
The detector mounting bracket 220 c~rries a pivot 228. An intermediate mounting bracket 230 is pivotally mounted by the pivot 228. This pivot arrangement allows the intermediate bracket 230 to rotate about an axis 232 of the pivot 228 t5.~

; tFi9ure 6). The ultrasonic detector is mounted to rotate witll the intermediate bracket 230 about the axis 232 as a part o~ a gimbal arrangement to mount the ultrasonic detector.
A support member ~34 i5 rotatably moullted to the intermediate bracket 230. Two shoe support : members 236 are attachecl to the support member 234.
Each shoe support member 236 comprises a U-shaped member with inner portion 238 and outer portion 240.
These portions serve to main-tain a number of sliding shoes 242 in fixed relationship to the shoe support member 236. These sliding shoes 242 rest upon . the pipe and as the detector mounting structure 200 is drawn along the len~th of the pipe ~hese shoes slide along the pipe and maintain the detector mount in the proper relationship to the pipe.
Eacll suppor~ member 234 is rotatably mounted on i~s int~rmediate bracket 230 ~or rota~ion about an axis 244 perpendicular to the axis 232. This 2D ro~ational axis is the second axis of the gimbal arrangement for the shoe support members 236.
- Thus, the member are free to rotate about two axes to allow the supporting shoes 242 to contact the pipe regardless of variations in the pipe.
The ultrasonic flaw detector is mounted within a detector mount 250. The detector mount 250 i5 rigidly attached to the shoe support member 236.
A transducer housing structure 252 is adjustably mounted within the detector mount 250. The position of the transducer housing.structure 252 relative to the detector mount 250 can be adjusted until the mount's relationship to the pipe is optimum for sending ultrasound waves with equal an~:les : of incidence into the pipe.
A first pair of screws 254 coact with two slots 25~ within the detector mount 250. These screws 254 are screwed into the transducer housing structure and can be loosened and their position acljusted by slicling the~ along the two slots.
Once this adjustment has been made for a particular pipe these screws are tightened and the transducer housing structure remains Eixed relative to the detector mount.
A Lucite wedge 260 is interposec~ between the transducer, which is mounted to tlle ~ransclucer housing, and the pipe. Since the shape of the Lucite wedge like the transducer depends on the ~0 pipe to b2 scanned, means are provided for removing - the wedge and replacing it with a wedge of different shape. The Lucite wedge 260 is attached to the transducer housing structure 252 by means of two countersunk screws 262.
15When pipes oE different dimansions are to be scanned a new transducer is mounted within the housing 252 by any suitahle means to maintain the ho~lsing and the transducer in constan~ physical relation t~ one another. The irst pair oE screws 254 are then adjusted to maintain the transducer surEace (not shown in ~igure 5) in proper relation to the pipe 210. When this is done, a proper Lucite wedge with a radius curvature the same as the pipe under study is attached to the housing 252 by the countersunk screws 262.
Figure 6 shows the mounting arrangement 216 as seen from the surface of -the pipe. There are five sliding shoes 242 on either side of the transducer housing structure 252. Although the countersunk Lucite mounting screws canno-t be seen from th-is view, the Lucite wedge 260 can be seen attached to the transducer housing structure. Located near the sides Qf the Lucite wedge 260 are water spouts 264 throu~h which water is sprayed. This water serves to ultrasonically couple the Lucite wedge 260 to the pipe 210. Typically a gap oE between .010 to .035 inches is maintained between the wedge and the pipe wall. Water is forced through the '~ ,S~

` 22 spou~s to fill this yap to couple the wed~e to the wall. The water may contain additives, such as aerosol which act as wett;ng agents.
An ultrasonic transducer surface 266 corresponding to those which have been described in detail, is shown in phantom in Figure 6. ~hile the description o~ Figure ~ characterized the sue~ace as an involute, : or as a ~uasi-involute, the view from the pip2 is one o~ a rectangular transducer. The longer f the two sides are actually involute or quasi-involute in shape. The shorter of the two sides are lines :
in both this view and in any other possible view oE the transducer surface. In one embodiment used for testin~, a pipe whose inside and outside surfaces form a 2 inch cross-section, the dimension of this rectangular transducer is 1~ x 2-1/4 inches.
~ As the detector mounting structure 216 kravels ~ alonc3 the pipe, the transducer mountecl within th~
detector mount 250 emits ultrasonic signals which scan the pipe for irregularities witllin the weld structure. The timing o these emitted signals is controlled by the electronic signal module 24 of Figure 1. A block diagram illustrating a typical circuit 300 which might be used Eor controlling the sending and receiving of signals by the ultrasonic transducer is shown in Figure 7. The circuit 300 is electrically connected to two transducers 302, 304 by means of electrical interconnects 306, 308.
These two transducers correspond to the two transducers arranged on either side o the pipe as shown in Figure 1.
The transaucers are activated by an acti~ation signal which is sent from a pulser circuit 310.
The pulser circuit 310 is located within the electronlc signal module and connected to each o ~he two transducers. The electrical energy sent from the pulser is converted to ultrasonic energy by the transduoers.

s a:~

As the emitted signal rebounds off flaws or irregularities within the pipe structure the returning or reflected signals impinge upon the transducer and are reconverted to electrical signals. These return signals return along cabling 306, 308 to a receiver unit 312~ These returned electrical signals are processed by the receiver and sent to a gating circuit 31~ or 316 wh:ich sends a signal by means of electrical interconnection to a recording device which records the existence oE the flaw or defect within the pipe. The system shown in Figure 7 includes a redundant recording system which includes both a strip chart recorder 3~0 and a paint marker 322 Eor marking the pipe surEace lS with a paint spot at the site of -the Elaw.
The signal sent from the pulser 310 to ~he transduceL~s 302, 304 is an electronic pulse which resembles a voltage spike ollowed by a damped volta~e sine wave. The dclmped portion of the signal is due to ringing within the circuit.
Due to the positioning oE the two transducers it is necessary that the pulsers alternate their activating signal to insure the signal from one ~for example 302) does not adversely affect the ~5 receiving of the ultrasonic energy by the other 304. If for example both transducers were simultaneously activated by the pulser unit the transducers would not know whether they were receiving a reflected signal from a flaw or defec~ within the weld struct~e or whether they were merely receiving a transmitt~d wave from the other of the two transducers~ To properly sequence the transducer activation, a pulser unit contains a sequencing device which is controlled by a triggering device. The trigger device acts as a clock or time reference within the pulser uni. and the sequencer alternately activates the two transducers to produce the ultrasonic sound waves of the present invention.

s'~

2~
Pulsers such as the one mention~ed above are known within the art. One commercially available device is a Krautkramer-Branson, Inc. unit which includes a Model TGl triggering unit and a Model PSI sequencer. This unit uses two SD4 transmitter devices which are powered by a NE2 power supply module. It is the NE2 or an equivalent power supply which provides energy for the remaining elements of the electronic signal module to be described.
As noted in Figure 7 both transducers are electrically connected to a receiver unit 312.
The two primary functions of the receiver 312 are to ampliEy and shape the signals from the transducers 302 and 304. The typical reflection signal from a flaw within the weld area causes the transducer to produce an envelope of RF signals oE fairly small voltage. In order for the su~sequent recorc}ing apparatus to respond to these signals they must be signiEicantly ampli~ied. Since the recording devices 320 and 322 most conveniently respond to pulses or spikes, the amplified RF envelope must also be shaped to achieve a single pulse of approxi-mately 5 microseconds.
Circuitry for achieving this requisite pulse is known within the art. A Krautkramer-Branson, Inc. Model ANS 11 and ANS 1, for example, operate as amplifiers in one typical receiving unit. A
TAl distance amplitude correction unit should also be included to automatically correct for changes in reflected beam amplitude due to naturally occurring attenuation within the pipe. This TAl unit automati-cally corrects for this attentuation and therefore provides a uniform signal for the gating circuitry 314, 316.
The gating circuitry 314, 316 receives signals from the reflected ultrasound energy regardless of whether the flaws producing these signals are inside the weld area. In the disclosed embodiment, ~l~

3l essentially only flaws within the weld area are of interest to the user. The gates 314, 316 serve to block out signals coming from flaws or irregulari-ties outside of the weld area. This capability is achieved through a knowledge of how long it takes the pulse to reach the weld area and to return to the transducer.
Considering Figure 3, for examp:Le, the weld area may be a range indicated by two boundaries 178, 17~ surrounding the defect 100 as shown in that igure. Utilizing knowledge of how rapidly the ultrasonic beam travels through the pipe, it is possible to program the gating circuitry 314, 316 of Figure 7 to allow signals to activate the lS recording means only after an initial delay during which time any reElected signals must be coming ~rom outside the weld area. If, for example, the gating circuitry allowed earlier signals to ac~ivate ~he recording apparatus, irregularities to the right of the boundary area 179 in Figure 3 will be detected. ~hese irregularities are of littla interest to the user in this application and therefore are not allowed to control the recording devices 320 or 322. In a like manner irregularities to the left of the leftmost weld boundary 178 are of little interest. The gating circuitry therefore is operative to activate the recording circuitry for only a short period of time during which the reflected signals will be coming from within the weld area.
A gating circuit with the above mentioned capa-bilities is a Model No. BLl produced by Krautkramer-Branson, Inc. This circuitry is adjustable to allow for inspection of pipes of varying diameters and differing transducer placements relative to the pipe weld structure. As an illustration, in one embodiment the BLl gating circuits are closed and allow no signals to reach the recording device ~, .

s~

for a period of 50 microseconds. These circuits then open and allow reflected signals to activate the recording device for a period of 20 microseconds.
During this 20 microsecond open period the reflected signals would have been scanning the weld area and are of interest to the user. The BLl then closes and disregards any returning signals which would be coming from areas beyond the weld structure and therefore of no interest.
During the period in which the gates 314, 316 send received signals to a recording device, they also operate to shape and lengthen the pulse sent by the receiver. In a typical example the 5 micro-second pulse sent by the receiver may be lengthened to a 30 millisecond pulse which is operative to control the recording devices.
The circuitry of Figure 7 can be used ta activate a series of different recording devices all of which indicate the presence of a flaw in the weld area. As shown in Figure 7 apparatus 320 may be provided ~or recording permanently upon a strip chart recorder the presence of a flaw within the weld structure. It is also possible to connect the gating circuitry to a paint marking device 322 which automatically produces a spot of paint on the pipe in the area of the weld flaw. A cathode ray tube mounted upon a viewing device might also be used to produce a representation indicative of a flaw in a workpiece.
As examples of devices known within the art to produce these results, one could choose a TOl model by Krautkramer-Branson, Inc. to activate the painting device, an RVl model by the same manu-facturer to activate the strip chart recorder, and a PSl sequencer again by the same manufacturer could be used as an oscilloscope CRT device for providing directly readable signal indicating the presence of a flaw.

~7 While the present invention has been described with particularity, it should be understood that various modifications and alterations may be made therein without departing from the spirit and the scope of the invention set forth in the appended claims.

Claims (40)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An ultrasonic flaw detector for detecting irregulari-ties in an object, the object having at least a segment of an annular cross-section, such as a pipe, said detector comprising:
(a) a transducer for sending a wave of ultrasonic energy into such object; said transducer being configured to have a cross-section which approximates an involute with a circular generating curve such that when a center of the generating curve substantially coincides with a center axis of the object, at any given point in a plane of transverse object cross-section the energy impinges such object at a non-radial angle of incidence substan-tially equal to the angle of incidence of every other point in the plane;
(b) transmission means including a first surface coacting with said transducer to insure said transducer maintains a substantially constant physical relationship with said object while transmitting said energy to the object; and (c) interpretive means to correlate reflections of said ultrasonic signals with irregularities in the structure of said object.

2. The ultrasonic flaw detector of claim 1 wherein the transducer comprises a detecting-transmitting piezo-electric crystal.

3. The ultrasonic flaw detector of claim 2 wherein the transmission means comprises a Lucite wedge with a second surface coacting with said object.

4. The ultrasonic flaw detector of claim 1 wherein said surface is a portion of a cylinder and wherein said cross-section comprises an arc of a circle three points of which coincide with an actual involute.

5. An ultrasonic flaw detector for detecting irregulari-ties in an object with an annular cross-section, said detector comprising:
(a) a transducer including a signal emitting surface for sending a wave of ultrasonic energy to said object;
said transducer emitting surface configured such that at any point in a plane of transverse object cross-section the wave impinges said object at non-radial angles of incidence substantially equal to the angles of incidence of every other point in the plane, said transducer having a sufficient length to insure an over-lap of incident energy from one portion of the emitting surface with energy reflected from an internal surface of such object and originating from a different portion of said signal emitting surface;
(b) a transmission means coacting with both said emitting surface and said object for transmitting ultra-sonic signals to said object, said transmission means orienting said surface with respect to said object to insure that total internal reflection of said waves occurs when said wave reaches an inside surface of said object; and (c) means attached to said transducer for corre-lating reflections of said ultrasonic signals with the structure of said object.

6. The ultrasonic flaw detector of claim 5 wherein a cross-section of said surface coincides with an involute characterized by a circular evolute whose center coincides with the axis of the annular cross-section to be inspected.

7. The ultrasonic flaw detector of claim 6 wherein the transmission means comprises a Lucite wedge with a first wedge surface coacting with said cylindrical object and a second wedge surface coacting with said involute.

8. The ultrasonic flaw detector of claim 5 wherein said surface comprises a segment of a cylinder; a cross-section of said cylinder comprising a segment of a circle, three points of which coincide with three points on an involute whose generating curve comprises a circular evolute.

9. The flaw detector of claim 5 wherein a cross-section of said surface approximates a segment of a circle and wherein the arc length of said segment is of sufficient extent to insure an overlap of incident energy with energy reflected from an interior surface of said object originating from a different portion of said surface.

10. The flaw detector of claim 5 wherein said transmis-sion means directs ultrasonic signals to said object at equal angles of incidence of between 33° and 45°.

11. A method for scanning a workpiece having an annular section such as a pipe or a pipe weld area comprising the steps of:
(a) positioning an ultrasonic transducer surface next to said workpiece, the transducer being shaped such that a plane cross-section parallel to the annular section intercepts said transducer at three points along an involute having a circular generating curve;
(b) pulsing said transducer with an electrical signal thereby producing an ultrasonic waveform whose individual components travel to said workpiece along different straight line paths; said components impinging upon said object at substantially equal non-radial angles of incidence; and (c) correlating reflections of said waveform from said object with irregularities within said object's structure.

12. The method of claim 11 which further comprises the step of interposing a transmission means between said transducer and said object to maintain the desired spatial relation between said transducer and said object without significantly attenuating said waveform.

13. The method of claim 12 wherein said transmission means comprises a Lucite wedge and said ultrasonic trans-ducer comprises a piezoelectric crystal.

14. The method of claim 13 wherein said ultrasonic transducer surface comprises a four-edge figure; two of said edges comprising involutes and two of said edges comprising straight lines.

15. A method for scanning a pipe weld area for weld defects and structural irregularities comprising the steps of:
(a) fabricating an ultrasonic transducer surface with a cross-section whose shape corresponds with a circle; at least three points of said circle coinciding with three points on an involute; said involute generated by a circular generating evolute whose center coincides with the center axis of said pipe;
(b) placing said surface in close relation to said pipe and causing relaltive pipe and surface movement;
(c) pulsing said ultrasonic transducer surface with repetitive electronic signals thereby causing ultra-sonic energy beams to be transmitted toward said pipe;

(d) coupling said surface to said pipe with a translucent media; said media operative to maintain said surface and said pipe in a substantially constant physical relationship thereby insuring said beams enter said pipe with substantially equal angles of incidence;
and (e) interpreting electrical signals from said ultrasonic transducer produced by ultrasonic beam re-flections within said pipe which have reflected off a density variation within said pipe indicative of a structural irregularity.

16. An ultrasonic flaw detector for detecting irregu-larities in an object having at least a segment of an annular cross-section comprising:
(a) a transducer including a signal emitting sur-face which approximates a segment of a cylinder; a cross-section of said cylinder intercepting three points on a circle which coincides with three points on an involute whose generating curve comprises a circular evolute;
(b) transmission means coacting with said surface and transmitting ultrasonic signals to said object; and (c) electronic means attached to said transducer for correlating reflections of said ultrasonic signals with the structure of said object.

17. The flaw detector of claim 16 wherein the transmis-sion means defines two surfaces; a first surface coacting with said transducer and a second surface coacting with said object; and where said first and second surfaces include cross-sections which approximate circles.

18. The flaw detector of claim 17 wherein the transmis-sion means defines a path for supplying a fluid for ultrasonically coupling said second surface and said object.

19. An ultrasonic flaw detector for detecting flaws in a weld area of a pipe comprising:
(a) a transducer including a signal emitting surface with a cross-section approximating an involute with a circular generating curve;
(b) pulse generating means for energizing said transducer and thereby transmitting ultrasonic energy to said pipe;
(c) transmission means including a first surface with approximately involute cross-section coacting with the transducer and a second cylindrical surface coupled to the pipe; said transmission means comprising an ul-trasonic transmissive material attached to said transducer to maintain the transducer in relation to said pipe;
and (d) electronic circuitry coupled to said transducer for correlating reflections of ultrasonic energy with flaws in the weld area.

20. The flaw detector of claim 19 wherein the trans-mission means defines a path for providing an ultrasonic coupling fluid between the cylindrical surface and the pipe.

21. A method for scanning a workpiece having an outer surface including at least a segment which is generally cylindrical and defines an axis, such as a pipe or pipe weld area, said method comprising the steps of:
(a) positioning proximate the workpiece an ultra-sonic transducer having an emitting surface shaped such that a plane perpendicular to the axis intercepts the emitting surface along an involute having a circular generating curve coincident with said axis;
(b) pulsing said transducer with an electrical signal for providing an ultrasonic waveform, which wave-form impinges upon the exterior surface of the workpiece at substantially equal incident angles nonradially with respect to the workpiece, and (c) correlating reflections of said waveform from said object with irregularities within said object struc-ture.

22. The method of claim 21, further comprising the step of interposing a transmission means between the transducer and the workpiece to maintain a desired spatial relation between the transducer and the workpiece without significantly attenuating the waveform during its passage to the workpiece.

23. The method of claim 22, wherein said interposing step comprises interposing a transmission means compri-sing a Lucite wedge, and in which said positioning step comprises positioning an ultrasonic transducer including a plezoelectric crystal.

24. The method of claim 23, wherein said positioning step further comprises positioning an ultrasonic trans-ducer having a surface defining a four-edged figure, two of said edges defining involutes and two of said edges defining straight lines.

25. A method for scanning a workpiece having a generally cylindrical outer surface defining an axis, such as a pipe or a pipeweld area, said method comprising the steps:

(a) positioning an ultrasonic transducer proximate the workpiece, said transducer defining a cross-section perpendicular to said axis corresponding with part of a circle, at least three points of said circle coinciding with three points on an involute, said involute being defined as generated by a circular generating evolute concentric with said axis;
(b) causing relative pipe and transducer movement;
(c) pulsing said transducer with repetitive elec-trical signals for causing ultrasonic energy to be trans-mitted toward the workpiece;
(d) coupling the emitting surface of the transducer to the workpiece with a coupling medium, to maintain the emitting surface and the workpiece in a substantially constant physical relationship for maintaining the ultra-sonic energy incident on the outer surface of the work-piece at substantially equal angles of incidence, and (e) interpreting electrical signals from the ultra-sonic transducer produced in response to ultrasonic energy reflections within the workpiece which have re-flected from a density variation within the workpiece indicative of an internal structural irregularity.

26. The method of claim 25 wherein the transducer is oriented to direct ultrasonic energy into the cylindrical outer surface of the workpiece at an angle of between 45° and 33°.

27. An apparatus for detecting flaws in a workpiece defining at least a segment of a generally cylindrical outer surface having an axis, said apparatus comprising:
(a) an ultrasonic transducer having a generally concave emitting region at least approximately defined by a set of lines substantially parallel to said axis, a cross-section of said emitting region having three points in common with an involute generated by a circular evolute;
(b) structure for holding said transducer proximate the workpiece during operation with normals defined by said transducer's emitting region extending into the workpiece without intersecting said axis and at substan-tially equal incident angles;
(c) circuitry for electrically pulsing the trans-ducer for propagating ultrasonic energy to the workpiece along said normals; and (d) interpretive circuitry responsive to ultrasonic echoes from within the workpiece to indicate the existence of a workpiece flaw.

28. An ultrasonic inspection apparatus for detecting flaws in a workpiece having an outer surface including at least a segment which is generally cylindrical and has an axis, said apparatus comprising:
(a) an ultrasonic transducer having a generally concave curved emitting surface defined by a set of lines parallel to said axis;
(b) mounting structure for holding the transducer proximate the workpiece during operation with normals defined by the emitting surface extending into the work-piece without intersecting said axis but which intersect the outer surface of said workpiece with substantially equal angles of incidence of between 33° and 45°.

29. A method for scanning a workpiece having a generally annular shape having a center axis, such as a pipe or pipeweld area, said method comprising the steps of:
(a) positioning an ultrasonic transducer proximate the workpiece, said transducer having a generally concave emitting surface at least approximately defined by a set of lines substantially parallel to the axis;

(b) causing relative workpiece and transducer movements;
(c) coupling the emitting surface of the transducer to the workpiece with a coupling medium;
(d) maintaining the emitting surface and the work-piece oriented in a desired scanning relationship;
(e) pulsing said transducer with repetitive signals for causing ultrasonic energy to be transmitted toward an outer surface of the workpiece at substantially equal angles of incidence, said angles of incidence and the arc length of said concave surface about the workpiece being such that at least some of the energy entering said outer surface overlaps energy which has reflected from an inner surface of said workpiece thereby avoiding gaps in scanning coverage; and (f) interpreting electrical signals from the ultra-sonic transducer produced in response to ultrasonic energy reflections within the workpiece which have re-flected from a density variation within the workpiece indicative of an internal structural irregularity.

30. The method of claim 29 wherein the equal angles of incidence are between 33° and 45° with respect to a normal to the workpiece outer surface.

31. The method of claim 29 wherein a plane perpendicular to said axis intersects said emitting surface along an arc of the circle, at least three points of said arc coinciding with three points on an involute defined by a circular generating evolute concentric with the axis.

32. The method of claim 31 where the radius of the evolute is adjusted to insure ultrasonic energy enters said object at between 33° and 45° to insure total in-ternal reflection of said energy at said inner surface.

33. An ultrasonic flaw detector for detecting irregu-larities in an object having at least a segment of an annular cross-section such as a pipe, said detector comprising:
(a) a transducer for sending a wave of ultrasonic energy into such object; said transducer defining an energy emitting surface which approximates a segment of a cylinder having a cross-section with three points coincident with an involute having a circular evolute;
(b) transmission means for ultrasonically coupling said energy emitting surface by relatively positioning said object and said emitting surface in an orientation when in use that energy from the surface enters said object at substantially equal nonradial angles along an incident waveform and is reflected from an internal surface of said object to ultrasonically scan said object;
and (c) means to correlate reflections of said ultra-sonic signals with irregularities in the structure of said object.

34. The ultrasonic flaw detector of claim 33 wherein said surface has a radius of curvature and arc length sufficient to cause ultrasonic energy reflected from said internal surface to overlap energy impinging said object to assure no gaps in scanning coverage exist.

35. The ultrasonic flaw detector of claim 33 wherein a cross-section of said surface approximates an involute corresponding to a generating circular evolute with a center substantially coincident with a center axis of said annular object.

36. The ultrasonic flaw detector of claim 33 wherein the transducer comprises a detecting-transmitting piezo-electric crystal and said transmission means comprises a Lucite wedge.

37. An ultrasonic flaw detector for detecting irregulari-ties in an object with an annular cross-section, said detector comprising:
(a) a transducer including an emitting surface for transmitting ultrasonic energy incident to said object, said emitting surface configured such that at any point in a plane of transverse object cross-section the ultrasonic energy impinges said object at a non-radial angle of incidence substantially equal to the angles of incidence of the remainder of ultrasonic energy incident upon the object;
(b) a transmission means coacting with both the emitting surface and the object for transmitting ultra-sonic signals to said object, said transmitting means maintaining a constant orientation of said emitting surface relative to said object to provide for internal reflection of ultrasonic energy when said energy reaches an inside surface of said object, (c) the arc length of said emitting surface being of sufficient extent to insure an overlap of energy incident upon said object relative to energy reflected from said interior surface of said object and impinging upon the outer surface of the object from within the object, and (d) means coupled to said transducer for correla-ting reflections of said ultrasonic signals with the structure of said object.

38. An ultrasonic flaw detector for detecting irregu-larities in an object having at least a segment of annular cross-section, such as a pipe, said detector comprising:

(a) a transducer for sending a wave of ultrasonic energy into said object, said transducer defining an energy emitting surface approximating a segment of a cylinder, said transducer having a curved energy emit-ting surface with a radius of curvature and arc length selected to cause ultrasonic energy entering the work-piece from the transducer to be reflected from an inter-nal surface of the object back to the outer surface of the object at a location overlapping other ultrasonic energy impinging upon the outer surface of said object from the transducer;
(b) transmission means for ultrasonically coupling said energy emitting surface by relatively positioning said object and said emitting surface in an orientation such that energy from the surface enters the object at substantially equal nonradial angles along an incident waveform and is reflected from an internal surface of said object, and (c) means to correlate reflections of said ultra-sonic signals with irregularities in the structure of said object.

39. An ultrasonic inspection apparatus for detecting flaws in a workpiece having inner and outer generally cylindrically shaped surfaces, said apparatus comprising:
(a) an ultrasonic transducer having a generally concave curve emitting surface of at least a specified arc length;
(b) means for holding the transducer proximate the workpiece during operation to direct ultrasonic energy toward said outer surface at substantially equal angles of incidence;
(c) said angles of incidence falling within a range to cause ultrasonic energy to be substantially totally reflected from said inner surface to scan the entire workpiece volume of interest with ultrasonic energy.

40. An ultrasonic inspection apparatus for detecting flaws in a workpiece having an outer surface including at least a segment which is generally cylindrical and has an axis, said apparatus comprising:
(a) an ultrasonic transducer having a generally concave curved emitting surface defined by a set of lines parallel to said axis said surface having a cross-section which coincides with at least three points on an involute generated from a circular evolute;
(b) mounting structure for holding the transducer proximate the workpiece during operation with normals defined by the emitting surface extending into the work-piece without intersecting said axis at substantially equal angles of incidence to said outer surface, and (c) said angles of incidence chosen such that when ultrasonic energy from the transducer enters the workpiece and strikes an inner wall of said workpiece nearly total internal reflection occurs.