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- since 1996 -
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Technical Discussions
Pakorn Ng.
Pakorn Ng.
10:27 Nov-05-2019
The use of radiography for thickness measurement

Basically it is only possible to determine a wall thickness change in penetration
direction from a density variation of a radiographic film?

I would like to predict the thickness profiles of pipes were determined by using
radiograph density measurement.

Best Regards,
Pakorn Ng.

 
 Reply 
 
Laurie
Australia, Joined Feb 2019, 39

Laurie

Australia,
Joined Feb 2019
39
00:26 Nov-06-2019
Re: The use of radiography for thickness measurement
In Reply to Pakorn Ng. at 10:27 Nov-05-2019 (Opening).

Several ways but since you don’t say what application you have in mind, thinning/root concavity/root penetration, I can suggest a step wedge beside the weld can easily allow you to measure 1mm of penetration, thinning or root concavity by measurement and comparison of density.
AS 2452.1 has other methods and of course if your radiographic exposure is precise you can use density directly after calculating a density/thickness curve.

 
 Reply 
 
Clayton Budinger
Clayton Budinger
11:15 Nov-09-2019
Re: The use of radiography for thickness measurement
In Reply to Laurie at 00:26 Nov-06-2019 .

Use large film. and a 1 inch steel ball (bearing)
Tie/tape the steel ball on the test piece for every shot and take measurements on the 1 inch ball and then the ratio of the measured line you draw on the pipe wall. Right next to the ball,
same direction. Maybe u could use a shim for density? Sorry that's all I can think of!

 
 Reply 
 
Pakorn Ng.
Pakorn Ng.
05:16 Nov-10-2019
Re: The use of radiography for thickness measurement
In Reply to Laurie at 00:26 Nov-06-2019 .

Thank you very much, I try to find out general corrosion with mornitoring technique. I use The double wall radiography technique (DWT) substitute for tangential radiography technique (TRT) because the pipe NPS 36" that can't penetrated maximum thickness to the
pipe-wall thickness while using the tangential radiographic projection technique. That
makes the determination of wall thickness difficult. For the DWT, I make demonstration to find reference step wedge of density as same Pipe NPS 36" by exposure time, energy, radioactivity which the experimental result is Corrosion measurements based on DWT are more sophisticated and use effective attenuation coefficients to calculate wall thickness changes from density differences shown on the film.

 
 Reply 
 
Laurie
Australia, Joined Feb 2019, 39

Laurie

Australia,
Joined Feb 2019
39
00:48 Nov-11-2019
Re: The use of radiography for thickness measurement
In Reply to Pakorn Ng. at 05:16 Nov-10-2019 .

That should work fine but I’d recommend for such a large pipe you also put on the pipe 2 or 3 step wedges as a check that the density difference between the smallest step and pipe is the same as the steps on your wedge at the expected thickness on your reference radiograph. The steps on the wedge need to be the same.
If you rely completely on the density variations of the step wedge alone on your reference radiograph you have no way of correcting any unintended inevitable small variations in exposure or variations in thickness due to increasing thickness as you depart from the centre of the pipe.

 
 Reply 
 
Dr. Uwe Zscherpel
Director,
BAM Berlin, Germany, Joined Jan 2010, 85

Dr. Uwe Zscherpel

Director,
BAM Berlin,
Germany,
Joined Jan 2010
85
11:41 Nov-11-2019
Re: The use of radiography for thickness measurement
In Reply to Laurie at 00:48 Nov-11-2019 .

Please look on ISO 20769-1 and ISO 20769-2 for any wall thickness measurement using radiographic testing.
Best regards
Uwe Z.

 
 Reply 
 

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