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- since 1996 -
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Technical Discussions
IceClampers
IceClampers
03:29 Feb-13-2001
UT readings on hot pipe.

When taking readings on hot pipe the readings are usually higher than if th pipe was cold. Is this due to the pipe being hot or the heat transfered from the hot pipe increasing the temperature of the transducer. What is the theory behind the fact that the readings do increase. Appreciate any help on this.

Thanks


    
 
 Reply 
 
Jeff Garner
Jeff Garner
01:57 Feb-15-2001
Re: UT readings on hot pipe.
Sound velocity is slower in hot material, making your readings higher if you don't calibrate on a hot calibration block.
.



    
 
 Reply 
 
Dave Wilkes
Dave Wilkes
08:25 Feb-15-2001
Re: UT readings on hot pipe.
Can anyone but any real figures on this problem.

For example what is the actual increase in the
reading obtained when testing a 10 mm wall pipe,
per 10 degree C. increase above ambient ?



    
 
 Reply 
 
David Hermanutz
Consultant,
Hbndt.com, China, Joined Jul 2012, 85

David Hermanutz

Consultant,
Hbndt.com,
China,
Joined Jul 2012
85
03:44 Feb-15-2001
Re: UT readings on hot pipe.
: Can anyone but any real figures on this problem.
.
: For example what is the actual increase in the
: reading obtained when testing a 10 mm wall pipe,
: per 10 degree C. increase above ambient ?
.
The Australian Standards go into a lot of depth concerning this topic, I should be able to have a read of the subject over the weekend and give you the detailed answer that is required on monday



    
 
 Reply 
 
Paul Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
04:16 Feb-15-2001
Re: UT readings on hot pipe.
Do a search of the NDT JOURNAL Archives and you will find some previous discussions on the topic. One reference indicated work by Chandrasekaran and Salma showing the acoustic velocity decreases 0.64 meters per second for each 1 degree C temperature rise. Also, you must consider the temperature effect on the probe. The calibration of a probe, especially a delay line probe, can change with temperature.
Paul


: When taking readings on hot pipe the readings are usually higher than if th pipe was cold. Is this due to the pipe being hot or the heat transfered from the hot pipe increasing the temperature of the transducer. What is the theory behind the fact that the readings do increase. Appreciate any help on this.
.
: Thanks
.



    
 
 Reply 
 
OH - EISI
OH - EISI
05:43 Feb-18-2001
Re: UT readings on hot pipe.
Not having any facts to back this up and the fact that I have 0 hrs of actual UT experience, here's my theory. Obviously, the difference in thickness readings is due to the change in velocity of the mat'l. The reason I believe that velocity changes with temperature is that temperature effects the rigidity/density of the mat'l. Rigidity/Density is one of the main factors for sound velocity (sound travel in steel is much faster than water.) So, imagine taking a piece of steel plate and applying heat to it. As the temperature of the plate rises, the molecules become excited and vibrate at a higher rate. When a certain temperature is reached, you can see the effects of this. The atoms become so excited and vibrate at such a high rate of speed that it actually breaks the solid bond and the steel plate begins to melt into a liquid form. So as heat is applied, the steel plate becomes less and less rigid, making the sound velocity slower and slower. That's why it is very important that you calibrate to not only thesame mat'l but also the same temp.

Any corrections or comments about this theory is greatly appreciated.


: When taking readings on hot pipe the readings are usually higher than if th pipe was cold. Is this due to the pipe being hot or the heat transfered from the hot pipe increasing the temperature of the transducer. What is the theory behind the fact that the readings do increase. Appreciate any help on this.
.
: Thanks
.



    
 
 Reply 
 
S.V.Swamy
Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex , India, Joined Feb 2001, 787

S.V.Swamy

Engineering, - Material Testing Inspection & Quality Control
Retired from Nuclear Fuel Complex ,
India,
Joined Feb 2001
787
04:38 Feb-20-2001
Re: UT readings on hot pipe.
: Not having any facts to back this up and the fact that I have 0 hrs of actual UT experience, here's my theory. Obviously, the difference in thickness readings is due to the change in velocity of the mat'l. The reason I believe that velocity changes with temperature is that temperature effects the rigidity/density of the mat'l. Rigidity/Density is one of the main factors for sound velocity (sound travel in steel is much faster than water.) So, imagine taking a piece of steel plate and applying heat to it. As the temperature of the plate rises, the molecules become excited and vibrate at a higher rate. When a certain temperature is reached, you can see the effects of this. The atoms become so excited and vibrate at such a high rate of speed that it actually breaks the solid bond and the steel plate begins to melt into a liquid form. So as heat is applied, the steel plate becomes less and less rigid, making the sound velocity slower and slower. That's why it is very important that you calibrate to not only the same mat'l but also the same temp.
.
: Any corrections or comments about this theory is greatly appreciated.
.
.
:
: : When taking readings on hot pipe the readings are usually higher than if th pipe was cold. Is this due to the pipe being hot or the heat transfered from the hot pipe increasing the temperature of the transducer. What is the theory behind the fact that the readings do increase. Appreciate any help on this.
: .
: : Thanks
: .
Yes, your theory is correct, since velocity changes due to change in the elastic properties of the material. However, the exact rate of change is rather difficult to predict from theory and it is better to determine empirically.
.



    
 
 Reply 
 
IceClampers
IceClampers
03:30 Feb-20-2001
Re: UT readings on hot pipe.
Thanks to everyone for your input. Is there any way to calculate how much of an increase there is based on temperature. UltraPipe put out by Krautkramer enables you to input the temperature of the inspected pipe so it can correct for this problem. Just wondering if anyone knows what this calculation is?

Thanks




    
 
 Reply 
 
V K Dilip
Consultant
Industrial Support Services, Saudi Arabia, Joined Jan 2001, 8

V K Dilip

Consultant
Industrial Support Services,
Saudi Arabia,
Joined Jan 2001
8
06:49 Feb-21-2001
Re: UT readings on hot pipe.
: Thanks to everyone for your input. Is there any way to calculate how much of an increase there is based on temperature. UltraPipe put out by Krautkramer enables you to input the temperature of the inspected pipe so it can correct for this problem. Just wondering if anyone knows what this calculation is?
.
: Thanks
.Reply:
Please refer to ASTM E 797. This gives guidelines on how to check thicknees at high temp. This found in ASTM Volume 03.03



    
 
 Reply 
 
Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
05:39 Feb-21-2001
Re: UT readings on hot pipe.
: Thanks to everyone for your input. Is there any way to calculate how much of an increase there is based on temperature. UltraPipe put out by Krautkramer enables you to input the temperature of the inspected pipe so it can correct for this problem. Just wondering if anyone knows what this calculation is?

Remember that the exact change in sound velocity with temperature depends on which alloy you're working on --for example, velocity in 304 stainless drops about twice as fact with temperature as in AISI 1018. It depends on the specific elastic constants of the alloy and how they vary with temperature. Plus, velocity chnages are not necessarily linear with temperature.

As several other people have pointed out, for optimum accuracy you should always calibrate the velocity setting of your instrument on a reference standard of the actual material you're working with, at the same temperature as you're testing. Of course this may not always be possible, but in critical applications where maximum accuracy is required, it's the safest way to go.

--Tom Nelligan


    
 
 Reply 
 
N.Kuppusamy
Consultant
Ubited Testing Co. Pte Ltd, Singapore, Joined Jun 2003, 1

N.Kuppusamy

Consultant
Ubited Testing Co. Pte Ltd,
Singapore,
Joined Jun 2003
1
05:36 Aug-04-2001
Re: UT readings on hot pipe.
: Sound velocity is slower in hot material, making your readings higher if you don't calibrate on a hot calibration block.

: For steel, an increase of 55°C above any reference temperature will result in 1% increase in thickness reading.
.



    
 
 Reply 
 

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