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09:54 Aug-17-2012
Ultrasound velocity in high temperature steel.

hi everyone!
I got some confuse with ultrasound velocity vs temperature.
Base on this link
http://www.ndt-ed.org/EducationResources/HighSchool/Sound/tempandspeed.htm
i understand that high temperature make velocity of sound increase.
but base on this link
http://www.springerlink.com/content/2678k3624v732646/
it is said that temperature increase then velocity of ultrasound decrease.
SO that, there is conflict for this relative between ultrasound velocity and temperature.
Everyone can explain this????

10:24 Aug-17-2012
Re: Ultrasound velocity in high temperature steel.

The first link is referring to the speed of sound (audible sound not Ultrasound) in air which increases as temperature increases.

The second link is referring to Ultrasound in which the speed of sound decreases as temperature increases.

14:57 Aug-17-2012
Re: Ultrasound velocity in high temperature steel.

But audible sound and ultrasound are same physical principle (moving in a material). It does not make sense when said that audible sound is difference with ultrasound when move in a material. I need more clarification.

16:31 Aug-17-2012
Re: Ultrasound velocity in high temperature steel.

Kevin, the acoustic velocity in any medium is a result of a combination of parameters. The amount of change in velocity with change in temperature is given as dV/dT (m/s/C°).
The dV/dT depends not only on the material but on the temperature. In the CRC Handbook for Chemistry and Physics, dV/dT for dry air is given as 0.59. The same book indicates for water a dV/dT of 2.5 (m/s/C°). But when we plot the actual values for water, this "approximation" only applies up to about 60°C (see http://www.nikhef.nl/~h73/kn1c/praktikum/phywe/LEP/Experim/1_5_12.pdf). At about 70°C the velocity in water actually starts to drop again. For other liquids the dV/dT value given is negative (e.g. ethanol is -4m/s/C°). Metals and plastics will almost always have a negative dV/dT (I am not aware of any that are positive but others may have more information on solids).

17:34 Aug-17-2012
Re: Ultrasound velocity in high temperature steel.

You are comparing speed of sound in gas with speed of sound in solid. Completely different parameters apply. for example Young's Modulus and Poisson's Ratio apply to solids, viscosity and compressibility apply to fluids.

18:05 Aug-17-2012
Re: Ultrasound velocity in high temperature steel.

I’m sorry that I have to dumb it down to my level.
Heat your calibration block to the required temperature, place high temperature couplant on the probe and place on the block. Calibrate the flaw detector and record the velocity. Commit this velocity to the flaw detector’s memory so you never have to bother again, unless you want to put in a range of temperatures.
Secondly, when measuring hot metal use the “echo to echo” function. This will alleviate any expansion to the transducer shoe.

ac

13:46 Aug-18-2012
Re: Ultrasound velocity in high temperature steel.

Thanks everyone,
Properly my comparison is wrong because there are some parameter to determine the velocity in a medium.
The best way to calibrate the UT device when measure the thickness of high temp steel is heating up the step block and calibrate the device then record the velocity of ultrasound, not thinking to much!!!!

Cheer mates.

05:49 Aug-19-2012
Re: Ultrasound velocity in high temperature steel.

Hi,

Heating up a calibration block is totally in-accurate, out of procedure and old school. The calibration block will never get hot enough as the process on the inside of the pipe. The transducer will also heat up, causing your zero offset / delay to drift and possibly overheat which destroys the bonding agents used within the probe.

Anyone I've witnessed using the hot cal block technique has been removed from his duties with all thickness measurements required to be re-performed using the techniques and procedures as agreed to in the contract.

ASME provides a "rule of thumb" correction calculation for carbon steel of 1% over thick per 55 degrees above calibration temperature ( see ASME V Article 23 SE-797 Paragraph 8.5 ). There are other more complicated versions of correction factors / methods but this one is the simplest to quote here.

Unfortunately any thickness measurement locations can only to be trusted +/- 1 mm due to the huge misunderstandings between technicians as to how to do any reading properly (when to do echo-echo, temperature corrections, dual probe placement on small bore piping etc).

Read the code and the contract, do what you're told not what you think is right!

Regards,

David Hermanutz

12:53 Aug-19-2012
Re: Ultrasound velocity in high temperature steel.

I agree with the previous post that it is difficult to calibrate properly because of temperature variations. However, using an EMAT will reduce a lot of error an uncertainty, especially on small diameter pipes. We sell a handheld instrument with a built in thermacouple and Automatic temperature compensation especially designed for HT measurements. Here is the link http://www.innerspec.com/node/25.

18:40 Aug-19-2012
Re: Ultrasound velocity in high temperature steel.

Hi David,

You are right, temperature compensation is just a small correction under field conditions:
When we take a temperature coefficient of 1*10E-4/K as a rough estimate, we have 1%/100 °C. Measuring e.g. a 20 mm thick pipeline wall, we will get a correction of 0.2 mm only! Therefore, it does not make much difference when the "real" temperature coefficient is 0.8 or 1.2*10E-4/K. In any case the correction is quite small compared to other uncertainities in ultrasound measurement at high temperatures.

Regards,
Gerhard

17:08 Apr-11-2015
Re: Ultrasound velocity in high temperature steel.

Is this formula is utilizing for unknown alloy velocity that is 5920x actuall thickness/indicated thickness ?