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Technical Discussions
Aniss Ziani
, Advanced NDT inspector
ISQ, Algeria, Joined Nov 2014, 32

Aniss Ziani

, Advanced NDT inspector
Joined Nov 2014
07:36 Nov-19-2015
PAUT+TOFD on welds of unequal thickness
zoom image

Dear experts,

We have been requested to perform a TOFD+PAUT inspection on gas pipeline welds of unequal thickness. The thickness are ranging from 9 to 17 mm on large diameter pipes (20 to 48 inch). The weld configuration will certainly looks like the one i have attached.

Could some of you share your experience regarding this specific application especially with regards to TOFD. I suppose that offset scans in both sides of the welds must to be done in order to avoid the blind zone which will be caused by the thinnest thickness. What about the transmitter ? Is that it must be positioned on the thinnest thickness ?

Looking forward to read your valuable feedback. Many thanks.

Kind regards,


United Kingdom, Joined Jun 2012, 14


United Kingdom,
Joined Jun 2012
08:57 Nov-19-2015
Re: PAUT+TOFD on welds of unequal thickness
In Reply to Aniss Ziani at 07:36 Nov-19-2015 (Opening).

Yes, on TOFD transmit on the thin plate - so you do not hit the chamfer-as the loss of energy reflected from the angled plate reduces your signals/Waves or even causes you to lose them. With < 12mm and certainly 9mm, you should focus lower than 2/3 and accept that the PA has to cover the dead zones . If you plot to cover the thicker plate HAZ with your PCS the extra plate will not matter as the area of interest is of relatively equal thickness as the wave has pitched on the flat inner surface.Like ALL AUT PA TOFD ,you need a selection of test plates with reflectors in various points around the weld to prove it out to your client.


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