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Technical Discussions
09:56 Jul-08-2010

aizuddin

NDT Inspector, SGS Malaysia ,
Malaysia,
Joined Jun 2010
7
602 views
minimun thickness and maximum rocking during UT/PAUT inspection
Hi all,
Here I need some information regarding the minimun thickness of PAUT that can up to.What is the minimun thickness(generally) that PAUT/UT can inspect?
For PAUT, I have the probe 7.5Mhz,30 element,0.6 pitch and the footprint size is 28 X 17.6mm. Is is suitable to do PAUT on pipe 3" Schedule 40 (thickness = 5.48mm)?
Also, what is the maximun rocking factor/coupling probe to pipe?Because when running with software ESWedgeGap, the gap is almost 1.02 mm for my probe.
If need any info, please reply to this forum or email me.
Acceptance Criteria ASME CC 181.

Thanks all.
 
 
11:02 Jul-08-2010

Joe Buckley
Engineering, Applications Technology Manager ASNT L-III,
Sonatest Ltd.,
United Kingdom,
Joined Oct 1999
344 Stand of Sonatest Ltd
Re: minimun thickness and maximum rocking during UT/PAUT inspection
In Reply to aizuddin on 09:56 Jul-08-2010 (Opening).

For reliable inspection on 3" pipe you WILL need a shaped wedge.

By using loads of couplant on a flat wedge and holding it carefully you might get a rough idea what's going on, but results will not be consistent enough to be described as a 'test'.

I'm not sure if anyone has ever defined a generic 'maximum gap', i tend to go with what 'feels OK' in practice this probably equates to around 0.2-0.3 mm or so

 
 
11:57 Jul-08-2010

aizuddin

NDT Inspector, SGS Malaysia ,
Malaysia,
Joined Jun 2010
7
Re: minimun thickness and maximum rocking during UT/PAUT inspection
In Reply to Joe Buckley on 11:02 Jul-08-2010 .

Hi Joe,
Thanks for your reply. I just know that in EN 583-2, there is some explaination regarding the coupling gap between probe and test piece.Have anyone familiar and have softcopy of it?
How about the minimun thickness for PAUT?Anyone have experience with this sort of inspection/thickness and what sort of specification must have to do PAUT?
Any specialist here to give some opinion/clarification about the minimun thickness that can cover by PAUT/UT?
Thanks all.

 
 
13:44 Jul-08-2010

Ed Ginzel
R & D, -,
Materials Research Institute,
Canada,
Joined Nov 1998
757 Stand of Materials Research Institute
Re: minimun thickness and maximum rocking during UT/PAUT inspection
In Reply to Joe Buckley on 11:02 Jul-08-2010 .

ASME does not specifically "require" wedges to be adapted to curvatures (I think this is an unfortunate oversight). However, there is good instruction in EN 1714 (6.3.3) that requires the wedges to be shaped if the gap between the test surface and the probe shoe is greater than 0.5mm. ESWedgeGap will provide this dimension for either convex or concave tect surfaces.
As for minimum thickness weld inspections in accordance with CC181...this topic was already discussed on the forum. It does not matter if it is phased-array UT or mono-element, the same problems will be encountered. Stand-off approach to the weld cap will mean high angles are needed. Even with a small aperture probe (e.g. 6mm) the back of beam will be approaching a full skip before the front of beam has reached the half-skip point...interpretation of signals will be a nightmare for the operator. Weld-cap and root reinforcement geometry will add to the difficulties of interpretation.
For standard manual techniques on standard welds, the 8mm limit stated in EN1714 is probably an absolute minimum practical thickness.
If you think you can do 5.5mm wall for CC181 work, keep in mind you will need to demonstrate your ability to detect and size flaws in a 5.5mm thick pipe-weld specifically made for demonstrating your technique...

 
 
20:41 Jul-08-2010

andrew cunningham

NDT Inspector,
Canada,
Joined Jun 2008
233
Re: minimun thickness and maximum rocking during UT/PAUT inspection
In Reply to aizuddin on 09:56 Jul-08-2010 (Opening).

Aizuddin

You cover two topics, 1 rocking of the probe and 2 minimum thickness.
You did not state the material or if it is a welded butt and to what.
1 Rocking of the probe; It is not practical to have concave and convex shoes for every possible diameter pipe. There are two ways to get round this. 1st glue onto the probe a sacrificial wear shoe to the wedge to contour and discard after the job (use low quality super glue as the high quality glues may damage the probe when you knock it off). 2nd use your fingertips as a guide on either side of the probe to ensure the probe is kept on its centreline.
2 The minimum thickness for UT; There has been lines drawn as a safeguard, but one can push the limit at your own risk and reputation. The thinner the material the less likely one is to position the reflector. You must have some reference blocks made from the same material with the maximum acceptable size defect and a minimum rejectable size defect. If the client is happy that you can find and discern between the two and he is happy that the positioning may be out, then you may have the chance to push the envelope.
There is a thickness measured in wave lengths that it is impossible to test with PE and PAUT. A small note to for you to remember is that the thinner the pipe the less the need for accuracy, on a 4mm thick pipe you are never more than 4mm out. A go/no go is more to the point.

Andrew C
www.practical-ndt.com

 
 
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