Eddy Current Testing Parte 1.2
-
Upload
jorge-luis-olivar-quintero -
Category
Documents
-
view
283 -
download
0
Transcript of Eddy Current Testing Parte 1.2
-
7/27/2019 Eddy Current Testing Parte 1.2
1/4
S Yl-1BOL
A
r
1
t
w
D
B
e
f
fgo
fg
f r
H
p
o
< >
1l
3
w
- i x -
NOMEN
CLATU RE
QUANTITY
C r o s s - S e c t io n a l a r e a
Radius
Leng t h
T h i c k n e s s
Width
Diamete r
Magne t i c
f l u x
d e n s i t y
C a p a c i t a n c e
T e s t
f
r equency
Optimum
tube t e s t i n g f r equency
C h a r a c t e r i s t i c
o r L i m i t
f r equency
Res onan t
f r e q u e n c y
Magne t i c field
i n t e n s i t y
M a g n e t i z i n g
f o r c e )
C u r r e n t
C u r r e n t d e n s i t y
S e l f
I n d u c t a n c e
Number of
t u r n s
W
i n d i n g s )
C h a r a c t e r i s t i c
P a r a m e t e r
R e s i s t a n c e
R e s i s t i v e l o a d
E l e c t r i c
p o t e n t i a l
Depth be low t h e s u r f a c e
I n d u c t i v e
R e a c t a n c e
C a p a c i t i v e
Reac tance
mp ed
ance
S t a n d a r d
Depth
of
P e n e t r a t i o n
P e r m e a b i l i t y
R e s i s t i v i t y
C o n d u c t i v i t y
Magne t i c f l u x
ill F a c t o r
Phase Lag
Angul a r
f r equency
Angle be t ween
Z R
. .;
2
met re
m e t r e
me t r e
metr e
met re
S I UN T
m e t r e
2
w
e b e r / m e t e r
fa
r ads
he r t z
he
rt
z
he
rt
z
o r
t e s l a
he r t z
a m p e r e s / m e t e r o r
l e n z e
amperes
2
amperes / mete r
henry
d i me n s i o n l e s s
d i me n s i o n l e s s
ohm
ohm
v o l t
met re
ohm
ohm
ohm
met re
henry /
me t e r
m i c r o h m c e n t i m e t r ~
s i emens / mete r
weber
d i m e n s i o n l e s s
r a d i a n s
r a d i a n s
/ second
degr ees
-
7/27/2019 Eddy Current Testing Parte 1.2
2/4
1 1
CHAPTER 1 - I NTRODUCTION
EDDY CURRENT
TESTING
Eddy c u r r e n t t e s t i n g
ET)
is
a
n o n d e s t r u c t i v e t e s t t e c h n i q u e
based
on
i n d u c i n g
e l ~ c t r i c l
c u r r e n t s in
t h e
m a t e r i a
l
b e i n g
i n s p e c t e d and o b s e r v i n g t h e i n t e r a c t i o n
between
t h o s e
c u r r e n t s and t h e m a t e r i a l . Eddy c u r r e n t s a r e g e n e r a t e d by
e l e c t r o m a g n e t i c c o i l s
in th e test p r o b e , and
moni to r ed
s i m u l t a n e o u s l y by
measur ing
probe
electrical impedance .
S i n c e it s
an
e l e c t i o m a g n e t i c i n d u c t i o n p r o c e s s , d i r e c t
electrical c o n t a c t w i t h t h e
s ampl e
i s
not
r e qu i r e d ; however ,
t h e sample m a t e r i a l
has
to
be c o n d u c t i v e .
Eddy c u r r e n t
t e s t i n g is
a v e r s a t i l e t e c hn ique . It s main ly
used f o r
t h i n
m a t e r i a l s ; in t h i c k m a t e r i a l s ,
p e n e t r a t i o n
c o n s t r a i n t s l i m i t
t h e
i n s p e c t e d volume to
t h i n s u r f a c e
l a y e r s . In a d d i t i o n to f l aw
i n s p e c t i o n , ET can
be used
t o
i n d i r e c t l y
meas
ure
m e c h a n i c a l
and
m e t a l l u r g i c a l
c h a r a c t e r i s t i c s which c o r r e l a t e w i t h e l e c t r i c a l
and magne t ic
p r o p e r t i e s . Also , g e o me t r i c e f f e c t s such as t h i c k n e s s ,
c u r v a t u r e and
p r o b e - t o - m a t e r i a l s p a c i n g i n f l u e n c e eddy
c u r r e n t f low and can b e measured .
The l a r g e number o f p 9 t e n t i a l l y s i g n i f i c a n t v a r i a b l e s in ET
i s bo th
a
s t r e n g t h and
a
weakness o f ~ h e
t e c h n i q u e s i n c e
e f f e c t s
o f
o t h e r w i s e trivial
p a r a me t e r s
can
mask
impor t an t
i n f o r m a t i o n
o r
be m i s i n t e r p r e t e d .
V i r t u a l l y
e v e r y t h i n g
t h a t
a f f e c t s eddy
c u r r e n t f low o r o
t h e r w i
s e
i n f l ue nc e s probe
impedance
has
to
be
t aken i n t o
accoun t
t o o b t a i n r e l i a b l e
r e s u l t s .
Thus , c r e d i b l e
eddy
c u r r e n t t e s t i n g r e q u i r e s a
h i g h
level of operator
tra1n1ng and awareness.
1 . 2
PURPOSE
OF
THIS M NU L
The
purpose o f
t h i s
manual
is
to promote the deve l opmen t and
use
o f eddy c u r r e
n t
t e s t i n g
by
pr ov id ing
a s c i e n t i f i c a l l y
sound
t r a i n i n g
and
r e f e r e n c e
manual . The
s e l e c t i o n
of
m a t e r i a l
pr e s e n t e d
i s based on t h e
premise t h a t a sound
u n d e r s t a n d i n g of ba s i c
p r i n c i p i e s
i s e s s e n t i a l
t o
o b t a i n i n g
v a l i d
da t a and i n t e r p r e t i n g it c o r r e c t l y .
A
non
-
r i g o r o u s
approach has
been
used
to p r e s e n t
complex
p h y s i c a l
phenomena
in
a
document
o r i e n t e d t owards
a p p l i c a t i o n
o f eddy c u r r e n t
t e c h n i q u e s ,
e s p e c i a l l y
f o r
d e f e c
t
d e t e c t i o n
and
d i a g n o s i s .
The p r e s e n t a t i o n moves from t h e o r y ( i n c l u d i n g
a
rev iew of
b a s i c
e l e c t r i c a l
c o n c e p t s
)
t o t e s t
methods
an
d
s i g n a
a n a l y s i s .
S i m p l i f i e d d e r i v a t i o n s of pr obe r e sponse to test
p a r a me t e r s a r e p r e s e n t e d
to deve lop
a
b a s i c u n d e r s t a n d i n g of
eddy c u r r e n t t e s t p r i n c i p l e s . Thus , eddy c u r
r e n t
s i g n a l s a r e
. ~
-
7/27/2019 Eddy Current Testing Parte 1.2
3/4
1 .3
-2 -
c o n s i s t e n t l y i l l u s t r a t e d on impedance plane diagrams
( the
d i s p l ay used
in
modero eddy cu r ren t t e s t i n s t ru men t s ) and to
a i d ex p lan a t io n ,
t he
paramete r "eddy cu r ren t
phase ,
lag" i s
i n t roduced .
Since
probes
p lay a key r ole in
eddy
cu r ren t t e s t i n g ,
t e chn ica l
as p ec t s
of
probe
d es ig n a re
i n t r oduc e d
wi th
p e r t i n e n t e l e c t r i c a l impedan ce
ca l cu l a t i o n s .
While knowledge
o f b as i c e l e c t r i c a l c i r c u i t s i s requ i red fo r a complete
unde r s t a nd i ng
of eddy cu r ren t t e s t p r in c ip i e s , a good
t e ch n i ca l
base fo r
i n s p ec t i o n can still be obta ined if
s e c t i o n s
of t h i s
manual
r
eq u i r i n g
such a background a re
sk i ppe d .
From an ap p l i ca t i o n s p o i n t
of
view, the mat e r i a l in t h i s
manual prov ides an i n s p ec t o r wi th the necessa ry background to
decide :
1)
what
probe(s )
to use ,
2) what t e s t f requencies a re s u i t a b l e ,
3)
what ca l i b r a
t i o n d e fec t s or s tandards
a re
requ i red
for
s i g n a
c a l i b r a t i o n and / or s imu la t io n ,
4) what t e s t s a re req u i red
to
d i f f e r e n t i a t e between
s i g n i f i c a n t
s i g n a l s
and f a l s e
i n d i c a t i o n s .
5) how
to
es t ma te
depth
of r e a l
d e fec t s
.
To
supplement theory , p r a c t i c a
examples
a re
presen ted to
develop prof ic iency in per forming
i n s p ec t i o n s , and
to
i l l u s t r a t e how bas ic p r i n c i p i e s a re app l ied to d iagnose r ea l
s i g n a l s .
A
number
of
l ab o ra t o ry
demons t ra t ions ,
p r a c t i c a
t e s t s and
mu l t ip l e choice q u es t io n s a re i nc luded in Volume 2 , "Eddy
C
u r r e n t
Course Supplement" . They a re d iv ided
i n to
groups
co
r r esponding to th e ch ap te r s in t h i s manual . The
demonst ra t ions a re i n t ended fo r use in eddy cu r ren t cour ses
to he lp c la
r
i f y
some
o f
t he more
d i f f i c u l t
concep t s . The
p r a c t i c a t e s t s a re to give s t u d en t s prac t i ce in us ing
equipment
and per forming t y p i ca l t e s t s . The mu l t ip l e
choice
ques t ions a re i n t ended to check s tu d en t s unders t and ing
of
the course mat e r i a l and prepare fo r c e r t i f i c a t i o n exams.
H STORICAL
PERSPECTIVE
E l e c t r om a gne t i c t e s t i n g the i n t e r ac t i o n
of
magnet ic f i e ld s
wi th c i r c u l a t i n g e l e c t r i c a l cu r r e n t s had its o r i g i n in
1831 when M.
Faraday
di scovered e l ec t ro mag n e t i c i n d u c t io n .
He
induced cu r ren t
f low in a
secondary c o i l
by
swi tch ing
a
ba t t e ry
on and o f f , D.E. Hughes pe rformed
the
f i r s t re corded
eddy
cu r ren t
t e s t
in 1879 . e
was
ab le to
d i s t i n g u i s h
between d i f f e r e n t
metals
by no t i ng a change in ex c i t a t i o n
f requency
r e s u l t i n g from e f f ec t s of t e s t
mat e r i a l r e s i s t i v i
ty
and magnet ic p ermeab i l i t y .
-
7/27/2019 Eddy Current Testing Parte 1.2
4/4
-3 -
THER
MUST
E
DEFECTS
IN
THB SE TUBES SOMEWHERE
I
S W SQU
IGGLES ON
THE
EDDY
CURRENt SCREEN
/
F i g .
l . l: M i s i n t e r p r e t e d
S i g n a l s
Initially t he
ex t r eme
s e n s i t i v i t y
to
many m a t e r i a l
p r o p e r t i e s and c o n d i t i o n s made
ET
difficult and u n r e l i a b l e .
F i g u r e
1 . 1
illustrates
t h i s
p o i n t .
It t o o k
u n t i l
926 b e f o r e
t h e first eddy c u r r e n t i n s t r u m e n t
was
d e v e lo p e d
to measure
samp le
t h i c k n e s s .
By t he
end
of ~ o r l War
II
f u r t h e r
r e s e a r c h and improved
e l e c t r o n i c s
made i n d u s t r i a l
i n s p e c t i o n
p o s s i b l e ,
and many
p r a c t i c a
i n s t ru me n t s
were d e v e l o p e d .
A
majo r
b re a k th ro u g h
came
in t h e
1 9 5 0 ' s
when F o r s t e r
d e v e lo p e d
i n s t ru me n t s
wi th
impedance
p l a n e s i g n a l d i s p l a y s . These made
it
p o s s i b l e
to
d i s c r i m i n a t e
be t w een d i f f e r e n t
p a ra me t e r s ,
though t h e p r o c e d u r e
was
still e m p i r i c a l .
D ur t ng
t h e
1 9 6 0 ' s
p r o g r e s s in t h e o r e t i c a l and p r a c t i c a u se s
of
edd
y
c u r r e n t
t e s t i n g advanced t h e t e c h n o l o g y f rom an e m p i r i c a l a r t
t o
an
a c c e p t e d e n g i n e e r i n g d i s c i p l i n e .
~