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- since 1996 -
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Technical Discussions
Mark
NDT Inspector,
RAE Engineering and Inspection Ltd, Canada, Joined Mar 2016, 13

Mark

NDT Inspector,
RAE Engineering and Inspection Ltd,
Canada,
Joined Mar 2016
13
00:12 Mar-30-2016
sound speed on 304 stainless steel

Hi All ,

I have a reference said 304 ss sound velosity is 5.920mm/um, which is higher than carbon steel of 5.89mm/um, I used carbon steel cal block to calibrate the UT set, and then to measure the 304 ss cal block, ended up the measuered value is slightly higher than the value on the 304 ss block. that means the the sound velosity in 304 ss is lower than carbon steel, I am confusing, or the reference 304 ss sound value is wrong?

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 227

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
227
11:46 Mar-30-2016
Re: sound speed on 304 stainless steel
In Reply to Mark at 00:12 Mar-30-2016 (Opening).

Mark,

Material velocities will vary a little bit, but longitudinal waves in 304 stainless should be a little slower than carbon steel, by about 200 m/s or so.

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1286

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1286
18:32 Mar-30-2016
Re: sound speed on 304 stainless steel
In Reply to Mark at 00:12 Mar-30-2016 (Opening).

Mark, acoustic velocities are not absolutes. Variations can occur due to alloy, heat treatment and rolling processes. We did a study in a single alloy of steel from different mills and found the compression velocity varied from 5802m/s to 6073m/s and the velocity also varied with the direction measured (anisotropic). The "official" velocity for the ISO Calibration block 1 (the IIW block) is 5920m/s +/-30m/s so your version of carbon steel is already at the lower end of the range assumed for the IIW block used for calibrations. Variations in some of the constituents of 304SS can vary by over 1% and then there is also the rolling condition of your samples,
In general, 304 SS might be considered to have a lower velocity than most carbon steels. Throughout the literature I have found published values for 304SS to be 5640m/s to 5888m/s. If it is important, you might want to check the chemistry of the sample you were "told" was 304SS and confirm the accuracy of your measurements.

 
 Reply 
 
Laurent
Consultant,
France, Joined Mar 2016, 16

Laurent

Consultant,
France,
Joined Mar 2016
16
19:10 Mar-30-2016
Re: sound speed on 304 stainless steel
In Reply to Ed Ginzel at 18:32 Mar-30-2016 .

Hi Mark

On site method could be:
- calibrate your longitudinal probe on your carbon steel block using real speed of this one.
- use your probe on a known thickness of the mateial to be controlled and adjust using beam speed your relevant pulse echos to the signal travel time of the known thickness. As it you will have the real speed of the material.
Method particularly appreciate on exotic steel

 
 Reply 
 
massimo carminati
Consultant, AUT specialist
IMG Ultrasuoni Srl, Italy, Joined Apr 2007, 691

massimo carminati

Consultant, AUT specialist
IMG Ultrasuoni Srl,
Italy,
Joined Apr 2007
691
19:34 Mar-30-2016
Re: sound speed on 304 stainless steel
In Reply to Mark at 00:12 Mar-30-2016 (Opening).

Hello Mark,

If you want to do a precise measurement you should first measure the speed of sound of the V1 block you are normally using. To do this use the 100 mm and get measurement from first backwall echo and second backwall echo. You should adjust probe delay and velocity unless you measure 100 and 200; use wizard calibration tools of your set, if you prefere. Fix your probe delay and go to a known thickness of the "unknown" material and adjust only the velocity unless you read the exact thickness on the 2 multiple echoes. That will be the correct Speed of sound. For 304 steel you should get values from 5750 and 5850 m/s.

 
 Reply 
 
Mark
NDT Inspector,
RAE Engineering and Inspection Ltd, Canada, Joined Mar 2016, 13

Mark

NDT Inspector,
RAE Engineering and Inspection Ltd,
Canada,
Joined Mar 2016
13
22:18 Mar-30-2016
Re: sound speed on 304 stainless steel
In Reply to massimo carminati at 19:34 Mar-30-2016 .

Yes, I did check the sound speed based on the known thickness using my Olympus XT, probe:2.25HZ, 0.375" Diameter

1018 steel cal block sound speed 5954 m/s
304 stainless steel sound speed: 5794 m/s

the 304 ss speed is lower than carbon steel.

Then another questiones happened, if I need to check the pipe thickness made of 316L steel, but I only have 304 SS cal block, what I should do? is that ok just found the referece sound velocity of 5745m/s and do the thickness conversion with the sound speed difference.

Thank you all for the positive input.

 
 Reply 
 

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