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Hi-Spec Systems
we are specialised in the design, development and manufacture of Phased Array and Time-of-Flight Diffraction (ToFD) ultrasonic inspection systems.
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Technical Discussions
William Friedman
William Friedman
06:21 Oct-11-2000
Effect of temperature on attenuation in UT wedges

Recently I had an experience where the amplitude calibration
of a 10 MHz transducer changed. The problem seems to be
due to a change in temperature of the acrylic wedge used to launch
a 70 degree shear wave. Experiments with longitudinal waves in a
5 cm thick piece of the material shows the effect can be
demonstrated by a temperature change of perhaps 5 to 10 C when
the reflecting end of the plastic is placed on a hot plate. The
relection can drop from the calibrated 80% of screen height to
60%. Is anyone aware of the temperature sensitivity of attenuation
in this material? The ASNT handbook only mentions that acrylic
has more attenuation than metals. No temperature effect is
described.

William Friedman


 
 Reply 
 
Michael Trinidad
Consultant,
LMATS Pty Ltd , Australia, Joined Jan 2003, 138

Michael Trinidad

Consultant,
LMATS Pty Ltd ,
Australia,
Joined Jan 2003
138
06:50 Oct-11-2000
Re: Effect of temperature on attenuation in UT wedges
If you are performing this experiment with the piezoelectrical crystal attached to the wedges, could the phenonemon your are seeing be the crystal degradation as it nears it's curie point?

If the refraction is temperature depedent could it be proven by refracting light through a prism at different temperatures and measuring the changes?

Kindest Regards

Michael Trinidad




 
 Reply 
 
P. Palanichamy
R & D, SCIENTIFIC OFFICER
INDIRA GANDHI CENTRE FOR ATOMIC RESEACH, India, Joined Jul 2000, 10

P. Palanichamy

R & D, SCIENTIFIC OFFICER
INDIRA GANDHI CENTRE FOR ATOMIC RESEACH,
India,
Joined Jul 2000
10
07:48 Oct-11-2000
Re: Effect of temperature on attenuation in UT wedges
REPLY: Dear Mr. Freidman,

Not only attenuation increases but at the same time velocity of the wave decreases. This is a general fact valid for any material. Depeding on the temperature of operation and the accuracy with which testing has to be done, it is left to the individual to take into consideration this temperature effect on attenuation and velocity.
We have observed similar drop in amplitude of the wave when we tested 10mm wall thickness carbon steel pipe filled with hot water. We have calibrated the drop in amlitude of the wave with rise in temperature and incorporated this effect during sizing of the of the flaw.

Yours truely,

P.Palanichamy
-------------



 
 Reply 
 
David Davies
Level III , QA Engineer , Ops. Supervisor
Vetco Saudi Arabia Ltd, Saudi Arabia, Joined Sep 2000, 3

David Davies

Level III , QA Engineer , Ops. Supervisor
Vetco Saudi Arabia Ltd,
Saudi Arabia,
Joined Sep 2000
3
07:58 Oct-11-2000
Re: Effect of temperature on attenuation in UT wedges
: REPLY: Dear Mr. Freidman,

: Not only attenuation increases but at the same time velocity of the wave decreases. This is a general fact valid for any material. Depeding on the temperature of operation and the accuracy with which testing has to be done, it is left to the individual to take into consideration this temperature effect on attenuation and velocity.
: We have observed similar drop in amplitude of the wave when we tested 10mm wall thickness carbon steel pipe filled with hot water. We have calibrated the drop in amlitude of the wave with rise in temperature and incorporated this effect during sizing of the of the flaw.

: Yours truely,

: P.Palanichamy
: -------------




 
 Reply 
 
David Davies
Level III , QA Engineer , Ops. Supervisor
Vetco Saudi Arabia Ltd, Saudi Arabia, Joined Sep 2000, 3

David Davies

Level III , QA Engineer , Ops. Supervisor
Vetco Saudi Arabia Ltd,
Saudi Arabia,
Joined Sep 2000
3
08:08 Oct-11-2000
Re: Effect of temperature on attenuation in UT wedges
Dear Mr Friedman
I se you are using a 70 degree angle, a tricky beast at the best of times, have you repeated this result with a lesser angle? Is the amplitude change due to angle changes caused by velocity change causing the beam to be off axis to the reflector? what kind of reflector are you using? is the couplant efficiency changing with temperature? you have not said at what kind of temperature the effect is noted.
If high enough temperature then the curie point effect noted by Michael Trinidad may be a possibility, does the effect stabilise after a time or is it instantaneous?
More information is really neede as there are many factors that could affect the amplitude.
Maybe if you cemented a zero degree probe with perspex stand off and increased the temperature of the plate gradually you may be able to isolate the effect.

Dave Davies


 
 Reply 
 
William Friedman
R & D,
Lockheed Martin, USA, Joined Nov 1998, 6

William Friedman

R & D,
Lockheed Martin,
USA,
Joined Nov 1998
6
03:31 Oct-11-2000
Re: Effect of temperature on attenuation in UT wedges
: Dear Mr Friedman
: I se you are using a 70 degree angle, a tricky beast at the best of times, have you repeated this result with a lesser angle? Is the amplitude change due to angle changes caused by velocity change causing the beam to be off axis to the reflector? what kind of reflector are you using? is the couplant efficiency changing with temperature? you have not said at what kind of temperature the effect is noted.
: If high enough temperature then the curie point effect noted by Michael Trinidad may be a possibility, does the effect stabilise after a time or is it instantaneous?
: More information is really neede as there are many factors that could affect the amplitude.
: Maybe if you cemented a zero degree probe with perspex stand off and increased the temperature of the plate gradually you may be able to isolate the effect.

: Dave Davies

The effect with 70 degree shear waves was large enough that the calibration based on amplitude of reflection from a side
drilled hole could not be repeated after the system was calibrated on a previous day.

We did the experiment with L waves by contacting the wedge on its side and looked at reflections from the flat
flat surface on the opposite side. A change in attenuation large enough to affect calibration was seen with only
the lower surface of the wedge being heated. The transducer and couplant temperature did not change.
This same effect is not seen if the transducer contacts a metal block. The concern is that
temperature changes that can occur in the course of a normal inspection can affect the
accuracy of amplitude based methods.

William Friedman


 
 Reply 
 
William Friedman
R & D,
Lockheed Martin, USA, Joined Nov 1998, 6

William Friedman

R & D,
Lockheed Martin,
USA,
Joined Nov 1998
6
04:25 Oct-12-2000
Re: Effect of temperature on attenuation in UT wedges
: REPLY: Dear Mr. Freidman,

:
: "We have observed similar drop in amplitude of the wave when we tested 10mm wall thickness carbon steel pipe filled with hot water."

: Yours truely,

: P.Palanichamy
: -------------

Do you think the change in amplitude was controlled by attenuation in the steel or in the material used to couple the sound into the steel. Our experience suggests that the attenuation occurs in the wedge. It was particularly noticable in our case because the round trip acoustic path length in the acrylic was about 5 cm. It is not as noticeable in smaller transducers with shorter paths in the wedge.

William Friedman


 
 Reply 
 
Rainer Meier
R & D
retired from intelligeNDT Systems & Services, Germany, Joined Nov 1998, 15

Rainer Meier

R & D
retired from intelligeNDT Systems & Services,
Germany,
Joined Nov 1998
15
06:15 Oct-12-2000
Re: Effect of temperature on attenuation in UT wedges
and appr. 1 dB loss of amplitude.

acrylic (Roehm):
10 centigrade rise of temperature causes an amplitude loss of appr. 0,065 dB for
each mm sound pass in the acrylic wedge and the sound speed in the acrylic is
decreased by 30 meter per sec.
Therefore the angle of incidence will change from 70° shearwave to nearly 72°.

Rainer


 
 Reply 
 
P. Palanichamy
R & D, SCIENTIFIC OFFICER
INDIRA GANDHI CENTRE FOR ATOMIC RESEACH, India, Joined Jul 2000, 10

P. Palanichamy

R & D, SCIENTIFIC OFFICER
INDIRA GANDHI CENTRE FOR ATOMIC RESEACH,
India,
Joined Jul 2000
10
06:46 Oct-13-2000
Re: Effect of temperature on attenuation in UT wedges
: : REPLY: Dear Mr. Freidman,

: :
: : "We have observed similar drop in amplitude of the wave when we tested 10mm wall thickness carbon steel pipe filled with hot water."

: : Yours truely,

: : P.Palanichamy
: : -------------

: Do you think the change in amplitude was controlled by attenuation in the steel or in the material used to couple the sound into the steel. Our experience suggests that the attenuation occurs in the wedge. It was particularly noticable in our case because the round trip acoustic path length in the acrylic was about 5 cm. It is not as noticeable in smaller transducers with shorter paths in the wedge.

: William Friedman

REPLY: At 17:29 12.10.00 +0530, you wrote:
Dear Dr. William,
*Do you think the change in amplitude was controlled by attenuation in the
steel*----certainly yes and that too to be more clear "rise in material tempertaure
reduces the echo height-increases in atttenuation of the wave.
*or in the material used to couple the sound into the steel*---yes in this case too.---I will discuss more about this later.----Could you give your full address and then I can send you an article of my
colleague who worked in this line.

P. Palanichamy
--------------




 
 Reply 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 178

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
178
07:14 Oct-16-2000
Re: Effect of temperature on attenuation in UT wedges
rameters of the wedge by local heating will have big effect on the distortion of the beam.

Heating up the wedge by contact to a hot surface generates a temperature distribution within the plastic wedge. And because plastics are not good heat conductors, the temperature gradient within the wedge may become big.
Because attenuation and velocity change with temperature, then this two parameters change within the wedge with time and location.
The result is a transverse wave sound beam in the metal changing in shape and direction. In most cases the beam angle increases with temperature and the beam width increases, the beam symmetry may be lost.

An echo amplitude from a given reflector therefore decreases with temperature because the beam angle changes. A secondary effect is the distortion caused by the change in beam shape which causes a changing distance-amplitude curve.

Because when heating the wedge during testing, the temperature distribution in the wedge will never be uniform, it makes no senseto calculate a temperature dependent beam angle with a known temperature dependent coefficient for velocity and attenuation of the plastics material.

To avoid these effects in practice the metal reference block used for calibration should have the same temperature as the test object, and the contact time of the transducer to the object should be short. Together with breaks where the probe is off the object this helps to keep the wedge at an approximately constant temperature.

Kind regards

Udo Schlengermann

++++++++


: Recently I had an experience where the amplitude calibration
: of a 10 MHz transducer changed. The problem seems to be
: due to a change in temperature of the acrylic wedge used to launch
: a 70 degree shear wave. Experiments with longitudinal waves in a
: 5 cm thick piece of the material shows the effect can be
: demonstrated by a temperature change of perhaps 5 to 10 C when
: the reflecting end of the plastic is placed on a hot plate. The
: relectioncan drop from the calibrated 80% of screen height to
: 60%. Is anyone aware of the temperature sensitivity of attenuation
: in this material? The ASNT handbook only mentions that acrylic
: has more attenuation than metals. No temperature effect is
: described.

: William Friedman




 
 Reply 
 
F. Brochin
F. Brochin
08:43 May-28-2001
Effect of temperature on attenuation in Brass
Does anybody have an idea (experience or theory) of the temperature dependence of the attenuation in yellow brass (70 % Cu) ? The echo measurement I have performed in brass exhibit a strong decrease of sensitivity with temperature up to 150 C. The peak shift on the signal curve show only a slow decrease of the velocity which can not account for the sensitivity decrease. I have no idea about the attenuation but for metals, it should theoretically hardly change with temperature. Is there another factor that should be taken into account ?


 
 Reply 
 

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