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Technical Discussions
Rigzang Tashi
Engineering,
Punatsangchhu-I Hydroelectric Project Authority, Bhutan, Joined Aug 2015, 12

Rigzang Tashi

Engineering,
Punatsangchhu-I Hydroelectric Project Authority,
Bhutan,
Joined Aug 2015
12
07:28 Dec-22-2015
Criteria to draw DAC

I would like to ask what is the thickness criteria to draw Distance Amplitude Curve (DAC) before carrying out Ultrasonic testing of single V welded butt joint in high pressure steel liners?

The thickness of steel liners plate ranges from 28 to 40mm and the pipe diameter ranges from 4m to 6m.


 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 834

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
834
21:16 Dec-22-2015
Re: Criteria to draw DAC
In Reply to Rigzang Tashi at 07:28 Dec-22-2015 (Opening).

Non-Piping - With a single 38 mm (or 1.5 inches) thick block you can cover thickness range from 25 mm to 50 mm.
For piping, Thickness T shall be +/- 25 % of the thickness to be inspected.
Reference ASME V, Article 4

 
 Reply 
 
Rigzang Tashi
Rigzang Tashi
11:03 Dec-23-2015
Re: Criteria to draw DAC
In Reply to Anmol Birring at 21:16 Dec-22-2015 .

Sir Anmol,

Is it necessary to make DAC before carrying out testing for thickness more than 50mm? Is there any thickness criteria of plates to be joined by weld besides the block size used to draw DAC for various thickness?

 
 Reply 
 
Shankar Arumugam
Other, NDE Engineer
India, Joined Oct 2013, 39

Shankar Arumugam

Other, NDE Engineer
India,
Joined Oct 2013
39
12:58 Dec-23-2015
Re: Criteria to draw DAC
In Reply to Rigzang Tashi at 07:28 Dec-22-2015 (Opening).

As your job diameter ranges from 4m to 6m, flat calibration block may be used. Calibration block, thickness range covers +/- 25 %.

As your thickness ranges from 28 mm to 40 mm, if you made a calibration block with 36 mm thickness, it could be used for weld thickness ranges from 27 mm to 45 mm.

1
 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1307

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1307
15:08 Dec-23-2015
Re: Criteria to draw DAC
In Reply to Rigzang Tashi at 07:28 Dec-22-2015 (Opening).

Rigzang, the replies so far assume that you are required to inspect the welds in accordance with ASME Boiler and Pressure Vessel Code; however, that may not be the case. It would be useful if you provided details of the applicable code. You then asked if it necessary to make DAC before carrying out testing for thickness more than 50mm. If ASME Sec. V is applicable to the project, then, unlike some codes, there is no lower or upper limit to the applicable thickness that is tested. The range you identified (28-40mm) is a very common range for UT weld examinations and would normally require some form of correction for attenuation, regardless of the applicable Code.

1
 
 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
06:22 Dec-24-2015
Re: Criteria to draw DAC
In Reply to Rigzang Tashi at 07:28 Dec-22-2015 (Opening).

Rigzang,

regardless of the thickness you are inspecting, you have to make sure that the calibration block you are using allows you to collect all necessary peak amplitude values with all the probes you intend to use, up to 2,25 times the plate thickness as I imagine you will do a half skip and full skip inspection. If you merely stick with the minimum size of the cal block design provided by ASME V Article 4, you might end up with not have enough length for doing this when you use a lower thickness block to calibrate for a higher thickness.

1
 
 Reply 
 

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