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Technical Discussions
ASHWANI KUMAR
Engineering,
MIDHANI, Hyderabad, India, Joined Jun 2015, 95

ASHWANI KUMAR

Engineering,
MIDHANI, Hyderabad,
India,
Joined Jun 2015
95
10:45 Sep-16-2016
DGS Vs DAC in UT

Dear sir,

I would like to kow , what will be the maximum difference in dB (for 80% of FSH) between DGS & DAC for 1.2 mm defect size?

Regards

ashwani kumar

    
 
 Reply 
 
francois
francois
11:54 Sep-17-2016
Re: DGS Vs DAC in UT
In Reply to ASHWANI KUMAR at 10:45 Sep-16-2016 (Opening).

Same result

    
 
 Reply 
 
ashwani kumar
Engineering,
MIDHANI, Hyderabad, India, Joined Jun 2015, 95

ashwani kumar

Engineering,
MIDHANI, Hyderabad,
India,
Joined Jun 2015
95
12:18 Sep-17-2016
Re: DGS Vs DAC in UT
In Reply to francois at 11:54 Sep-17-2016 .

Dear sir,

If DGS & DAC gives the same result, why to make many FBHs for the differet frade and sizes?

ashwani kumar

    
 
 Reply 
 
Sankar
Sankar
17:19 Sep-19-2016
Re: DGS Vs DAC in UT
In Reply to ashwani kumar at 12:18 Sep-17-2016 .


Dear Sir,
May be DGS theoretical and DAC practical. For DGS, we need absolute values of attenuation, correction for roughness and curvature. DAC blocks eliminate this.

    
 
 Reply 
 
Marcelo
Engineering,
Brazil, Joined Sep 2015, 5

Marcelo

Engineering,
Brazil,
Joined Sep 2015
5
00:16 Sep-20-2016
Re: DGS Vs DAC in UT
In Reply to ASHWANI KUMAR at 10:45 Sep-16-2016 (Opening).

Kumar,

Could you be more specific? What did you really mean? FBH to SDH?

    
 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
12:26 Sep-20-2016
Re: DGS Vs DAC in UT
In Reply to Marcelo at 00:16 Sep-20-2016 .

DGS (Distance-Gain-Size) is probe-specific as a means of setting sensitivity from a series of either the same dıameter flat-bottomed holes (FBH) at different soundpath distances OR using different diameter flat-bottomed holes at the same soundpath. Its an equivalent area defect sizing method,

A DAC (Distance Amplitude Correction) implies insonificatıion of equal diameter side-drilled holes (SDH) and is a threshold method of determining whether to investigate further a reflector or whether to ignore it. It is NOT a defect sizing method

Hope thşs helps

    
 
 Reply 
 
Daniel Braun
Daniel Braun
14:50 Sep-20-2016
Re: DGS Vs DAC in UT
In Reply to ashwani kumar at 12:18 Sep-17-2016 .

Depending of the inspection specs DAC may be created using a number of equal reference reflectors of various types (FBH, NOTCHES, SDH, VDH etc) based on the signals from the equal reference reflectors situated at various MTDs (Material Travel Distances) from the probe

DGS is based on the equivalent reflector diameter (ERD)i.e. it relates to the FBHs only. So in case the DAC was prepared with the use of FBHs the results should be matching with DGS

DGS line is created based on the specific probe data, attenuation in the material, etc and the selected ERD. For creating DGS it is still necessary to receive a reference echo and settle it to the standard level but one time only. Usually the reference reflector is the back wall surface OR the cylindrical concave surface in the V1 or V2 block (the appropriate correction factor should be used in that case); the attenuation in the reference block influences the shape of the DGS line, it should be keyed in at the calibration stage as well. To use DGS it is necessary to provide the sufficient (high) repeatability of the parameters for the various probes of the same type, in past it was possible for the original Krautkramer probes only; actually DGS term comes from Krautkramer. SOme references are here:

http://www.ndt.net/article/v05n09/berke/berke.pdf

http://www.sonotronndt.com/article.asp?ArtID=4

http://www.sonotronndt.com/pdf/OM_utPod/ISONIC_utPod_OM.pdf - pages 37-39

http://www.sonotronndt.com/pdf/om2005.pdf - pages 71-82

    
 
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