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ULTR SONI PULSE E HO ONT T TE HNIOUE

 a)

 b)

PlASTlC INSERT

¡- 8 In -----¡¡- 0.125 In

.25 In

r

40 50 60 ~

0.06 In HOLE '\ I

4 r f\-- 2 In DIAMETER HOlE

31 6

U 60 70 75

FOCAl POINT   l

12

In

I

=_: ¡i i 1:1

FIGURE 18. Block standards for angle beam

transducer verification: la)/nternationallnstitut

of Welding IIIW) block and lb) miniature ang

beam block

A1thoughhe majOlity of contact testing is done with

b1gitudinalwaves propagating normal to the test object

surface,here are many instances when an angled beam is

preferred.The predominant reason for angle beam testing

thedetectionof discontinuities with geometJies and ori

entationsother than parallel to the test surface. Planar

cracksnormal to the test object sUlface, voids with small

reflecti\'eurfaces parallel to the test object surface and dis

continuitiesn welds with uneven top surfaces are examples

ofsituationsthat require angle beam techniques.

Verificatian af Shear Wave Angle

Angledlongitudinal waves, shear waves or surface waves

aregenerated in a test object by mounting the piezoelectJic

elementat an angle in the contact transducer. The correct

anglecanbe determined with Snel ' s law of refraction. Most

 ART 2

NGLE BEAM CONTACT TESTING

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Weld Testi

FIGURE 22. S

outer wal ls in

Ultrasonic

Angle beam t

repeatedly alon

wavesare used b

Figure 22shows

wallsofa tube d

c ra cks in the pa

are indicated on

the e ntir e a re a o

be r otated whi

direction.

T he a ngle be

testing see Fig

a fullskip, maki

t he a ng le b ea m

assistin interpre

r ea ding ultra son

developed for th

top of the card

e xit point of the

DISCONTINUITY

BACK SURFACE

BACK SURFACE

DISCONTINUITY

 b

c

8A CK S UR FA CE

 a

FIGURE 21. Possiblesound beam paths in angle

beam testing

i nd ic at ed i n F ig . 2 1a , t he s ou nd b ea m u nd erg oe s f ou r

s la nted trips to c om plete a r ound trip to a c ra ck loc ated a t

or near the topsurface. When thecrack islocated at ornear

the bottom surface, the sound beam only takestwo trips to

make the round trip Fig.21b).  n Fig. 21c, where the crack

i s l oc at ed n ea r t he m id dl e o f t he p la te , t he s ou nd b ea m

b ou nc es o ff b ot h t he u pp er a nd l ow er s ur fa ce s a nd ma y

retu m t o th e t ran sduc er, i f t he p lat e is no t t oo thi ck.

W he ne ve r pos sible, the pla te s hould be tes te d f rom both

sides to judge the crack location more accurately.

54

54

54

52

52

52

0

8

48 50

48 50

TIME

  microseconds)

TIME

  microseconds)

TIME

  microseconds)

46

46

46

-1

-1

-1

w

o

::l

1-::;

 JO

C...

>

¿

«

w

o

::J

1-::;

  O

C . . .

>

¿

«

 c

w

o

::l

1-::;

 JO

C . . .

>

¿

«

 a

b

FIGURE 20. Angle beam verif icat ion test with

45 degree shear wave transdueer and steel I IW

referenee block: la response at 43 degrees,

lb response at maximum 45 degrees and

le response at 47 degrees

s ig na l o n t he m on it or d is pl ay ma y b e d iff ic ul t t o j ud ge

because ofthe beam spread. Another difficulty in disconti

nuity ranging líes in the uncertainty of where the disconti

nuity may be located relative to the boundary surfaces. As

72

72

7

7

64 66 68

TIME

  microseconds)

64 66 68

TIME

  microseconds)

64 66 68 70 72

TIME

  microseconds)

 8

Q6

Q4

Q2

QO

 Q2

 Q4

 Q6

 Q8

0.8

0 6

 4

 2

QO

 Q2

 ~

 Q6

 Q8

w

o

::l

f-~

::J o

C...

>

¿

«

w

o

::lV;-

1-- =

::JO

C...

>

¿

«

w

o

::lV;

1--,=

::JO

C . . . >

¿

«

¡URE 19. Angle beam verif ieat ion tests with

degree shear wave transdueer and steel I IW

renee block: la response at 53 degrees,

response at maximum 55 degrees and

response at 57 degrees

0 8

 6

0.4

0.2

 

0 2

 0 4

 0 6

 0 8

la}

[b

range estimating, the beam spread ofthe angle beam

d a ls o be taken into a cc ount. T he s ound bea m r adi

f rom the tra ns duce r f ans out or diver ge s. T he e xa ct

on of the discontinuity represented by the reflected

Ic

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;URE 23. Ultrasonic angle beam weld tests

A

10

l

Surface W

W it h a p ro pe

t es t o bj ec t s ur h

T he r e1 r ac te d w

o ft he t es t o bj ec

w av es a re t yp ic

to 1 00 m m 4

S ur fa ce w av

a lo ng t he s ur fa

t he t ec hn iq ue

e l i ns tr um en ta ti

d et ec te d i n a lu

A ng le b ea m c on ta ct t es ti ng c an a ls o b e c on du ct ed u si ng

t wo t ra ns du ce rs i n a p it ch a nd c at ch m od e. T he t ra ns mi tt in g

t ra ns du ce r p it ch es a s ou nd b ea m t ha t s ki ps i n t h e p la te a nd

i s c au gh t b y a r ec ei vi ng t ra ns du ce r s ee F ig . 2 5) .

The distan ce betwee n the two tra nsduce rs can be cali

b ra te d t o m ax im iz e t he r ec ei ve d s ig na l a mp li tu de . A s s h ow n

i n F ig . 2 5b , a pl an ar d is co nt in ui ty p er pe nd ic ul ar t o t he p la te

s urface in the p ath ol the sound b eam d eflects the so und

b ea m a nd p re ve nt s i t l r om r ea ch in g t he r ec ei vi ng t ra ns du c

e l . T he re fo re , a l os s o f s ig na l o n t he m on it or i nd ic at es t he

presence 01 a discontinuity.

Pitch and Catch Contact Testing

~O-

70

60

htJ+-+

~?U I 1

5

6

0

U

7

~~

1

80

6

I I

2

70

5

DISCONTINUITY

6 ~J x

I

I I I

I

4050 I '

I I I j 1

D A SH ED U N E

,¿>\ P O IN T O F I N CI D EN C~

~yj I 2 3 ,;:)...

lb

FIGURE 25. Pitch and catch angle beam testing

FIGURE 24. Direct reading ultrasonic

discontinulty location calculator

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• •• •. •• - •• .• •• •• •• •_••• •.

FIRSTLEG

r  

THIRD LEG •

i

I I I

1 I I

, ,  

1+- FIRSTV ~ SECONDV •..••

PATH PATH

e

b

l

BACKSURFACE

RECEIVER

/1'

/

lb

ne ce nter of the weld is laid out a long this sc alc. The

a l s ca le r ep re se nt s d is ta nc e i n t he t hi ck ne ss d ir ec ti on .

me n thickn ess is in dicated on this scale and the a rc

; the angle of the s ound beam .

a n e xa mp le o f u si ng t he c al cu la to r, a ss um e a d ou bl e

Id w ith an opening of 30 degrees in a 50 mm 2 in.)

) la te . T he w el d i s t o b e t es te d u si ng a 6 0 d eg re e s he ar

t ra ns du ce r. A l in e i s f i rs t d ra wn f ro m t he p oi nt o f i n

~ e a t t he u pp er l ef t c or ne r 0 1 t he c al cu la to r t hr ou gh

O degree mark on the arc, extending to the 50 mm

I

p oi nt r ep re se nt in g t he p la te t hi ck ne ss .

i br at e t he h Ol iz on ta l s we ep o f t he m on it or t o r ep re se nt

t ra ve l d is ta nc e i n t he t es t m at et ia l. T he 1 u lJ sk ip d is

o f t h e s ou nd b ea m i s o bt ai ne d b y d o ub li ng t he 8 6 m m

1 .) i nt er se ct in g p oi nt a t t he b ot to m 0 1 t he p la te a nd

ng the point at 175 mm 6.9 in.) on the upper plate

e . T he 3 0 d eg re e V w el d i s n ex t d ra wn o n t ra ns pa re nt

p os it io ne d o ve r t he m on it or s cr ee n - h er e a t a v al ue

I

m m 5 .5 i n. ). T he d is ta nc e b et we en t he c en tc r o f t he

ucer exit point) a nd the cente r ol t he we Jdmcnt is

1 1e as ur ed , g iv in g 1 16 m m 4 . 6 i n. ). T he t ra ns pa re nt

i s m ov ed b y t he s am e d is ta nc e. T he p os it io n o l t he

t in ui ty i s i n di ca te d a nd c an b e e va lu at ed .