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Technical Discussions
XiangYan
XiangYan
06:41 Dec-02-2008
equivalent wedge delay calculation in DGS curves

According to EN583-2, when plotting the DGS curves for angle beam transducer, there is an equivalent wedge delay that added to the steel path, which is:
equivalent wedge delay=wedge path*Cwedge/Csteel.

I am not sure of the derivation of this formula, but if I use the equal phase method, I got:
equivalent wedge delay=wedge path*Csteel/Cwedge.

Does anyone look into this problem? I don't know which answer is correct.

Thanks!
Xiang Yan


 
 Reply 
 
Gerhard Splitt
R & D,
Private, Germany, Joined Nov 1998, 38

Gerhard Splitt

R & D,
Private,
Germany,
Joined Nov 1998
38
08:00 Dec-02-2008
Re: equivalent wedge delay calculation in DGS curves
----------- Start Original Message -----------
: According to EN583-2, when plotting the DGS curves for angle beam transducer, there is an equivalent wedge delay that added to the steel path, which is:
: equivalent wedge delay=wedge path*Cwedge/Csteel.
: I am not sure of the derivation of this formula, but if I use the equal phase method, I got:
: equivalent wedge delay=wedge path*Csteel/Cwedge.
: Does anyone look into this problem? I don't know which answer is correct.
: Thanks!
: Xiang Yan
------------ End Original Message ------------

Hi Xiang,
the first formula, equivalent wedge delay=wedge path*Cwedge/Csteel, is the correct one. We are looking for the near field equivalent of the wedge length. As the sound velocity v stands in the denominator of the Near field length calculation N=D^2*f/4v, the near field length in the plastic wedge is bigger than in steel, meaning that the near field equivalent part of the wedge in steel is shorter than the mechanical length of the wedge.
The other formula, equivalent wedge delay=wedge path*Csteel/Cwedge, is for calculation of the steel equivalent time of flight of the wedge.


 
 Reply 
 
Udo Schlengermann
Consultant, -
Standards Consulting, Germany, Joined Nov 1998, 183

Udo Schlengermann

Consultant, -
Standards Consulting,
Germany,
Joined Nov 1998
183
08:56 Dec-03-2008
Re: equivalent wedge delay calculation in DGS curves
reply:

European Standard EN 583-2:2001 (Ultrasonic testing - Part 2: Sensitivity and range setting) in Annex D gives information on the principles how to use the general DGS diagram:
Distance D in the general DGS diagram is normalised by the nearfield length of the probe used. But nearfield length is material dependent. It is direct proportional to frequency and inverse proportional to sound velocity of the material.
If the sound has to travel through different materials, the sound path fragments in all the materials involved have to be normalized by their individual nearfield length, or equivalent sound path fragments have to be summed up and divided by a single reference nearfield length (reference material = material to be tested), e.g. for mild steel and transverse waves.
This is described in equations D.1 and D.2 of EN 583-2:
The equivalent sound path, sdelay, in a delay block (wedge) is given by ldelay * (vdelay/vref), where ldelay is the real delay length and vdelay and vref are the respective sound velocities.

Best regards

Udo Schlengermann
Convener of CEN/TC138/WG2 (in charge of EN 583-*)


----------- Start Original Message -----------
: : According to EN583-2, when plotting the DGS curves for angle beam transducer, there is an equivalent wedge delay that added to the steel path, which is:
: : equivalent wedge delay=wedge path*Cwedge/Csteel.
: : I am not sure of the derivation of this formula, but if I use the equal phase method, I got:
: : equivalent wedge delay=wedge path*Csteel/Cwedge.
: : Does anyone look into this problem? I don't know which answer is correct.
: : Thanks!
: : Xiang Yan
: Hi Xiang,
: the first formula, equivalent wedge delay=wedge path*Cwedge/Csteel, is the correct one. We are looking for the near field equivalent of the wedge length. As the sound velocity v stands in the denominator of the Near field length calculation N=D^2*f/4v, the near field length in the plastic wedge is bigger than in steel, meaning that the near field equivalent part of the wedge in steel is shorter than the mechanical length of the wedge.
: The other formula, equivalent wedge delay=wedge path*Csteel/Cwedge, is for calculation of the steel equivalent time of flight of the wedge.
------------ End Original Message ------------




 
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