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Re: UT versus RT weld inspection on butt welds

Posted by: Dent McIntyre Profile (PID_125), E-mail: mcintyrj@pgg.mcdermott.com, on March 02, 2000 at 13:59 :

In Reply to: UT versus RT weld inspection on butt welds posted by : Michael Trinidad on March 02, 2000 at 13:06:

: An ispection requires a 100% UT inspection of an 80-90mm butt weld in steel plate followed by a re-test of the same weld by 10% RT.

: The re-test by 10% RT is because the clients do not 'as always happens' trust the little green squiggly lines on the UT set or the operators.

: The only gamma source available in this country is IR192 so RT of this joint is stretching the capabilities and there are other problems, backing strip, access etc. The weld will be FCAW with multiple passes which I believe will have a common decfect of lack of inter-run fusion which RT on this thickness will be unlikely to fix.

: My suggestions to the clients in this case has been to scrap the RT and to ensure confidence in the UT operator's ability, have them perform a practcal test.

: My question is I know of codes that prefer the use of UT on thicker weldments instead of RT but does anyone recall of any papers related to the probability of detection of defects RT versus UT?

: I need as much ammunition as I can find.

:
: Kindest Regards

:
: Michael Trinidad


This is a favorite topic of mine.
You are obviously aware that RT and UT are not interchangeable. They are sensitive to different types of flaws by the laws of physics.
We are in the nuclear business here and our customers demand 100% RT and UT on all welds in that thickness range.
Given your big picture and all the details, if I were your customer I would also insist on RT. The major reason is the FCAW process is prone to rounded indications like slag and porosity.
I have seen some huge pores in FCAW with RT that UT hardly sees. The second reason is the backing strip will likely cause UT some heartache.
UT may find some of these but likely would not reject them. I have many experiences (30+ years)in this area and have learned the hard way.

Regarding RT of this thickness with Iridium 192. I was stationed in China for several years and there they were absolutely against Cobalt.
We had some work that was 110 mm thick so I told them that we needed to buy a Cobalt source.(My knowledge and experience at that time said it could not be done with Iridium.) No way was that going to happen.
so they shot it with Iridium and showed me that they could in fact do it. (Showed 2-2T) I still did not believe it so I watched the whole process closely. Nothing special was done it just took a long exposure.
Maybe Chinese Iridium has more punch???

Dent McIntyre
NDE Manager
B & W Canada




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