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Technical Discussions
D Wallace
USA, Joined Nov 2019, 2

D Wallace

Joined Nov 2019
10:44 Nov-09-2019
UT testing for Weld Overlay / Clad thickness

We need to determine the thickness of a heavy barrel nozzle, Base metal is a CR-Mo carbon steel, with internal Stainless steel overlay (Electroslag overlay) for corrosion resistance.
So far our readings are showing much higher than the design nominal.
But there are isolated areas with a lower amplitude reflector before the backwall. I'm not qualified or calibrated to determine if these are flaws

For equipment I'm using a flaw detector with A Scan, a 5 mhz dual probe. CS and SS step wedges. We do not have a welded/Overlay cal block, but would that alone be the answer to our problem?

Can this job be done with this equipment or no? Should I mention the reflectors at least? They could be flaws..

If i find a few spots where a reflector appears before the suspect backwall, could I use the time of flight function and use the two peak values to calculate both the base metal and the internal SS overlay thickness?

Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 856

Michel Couture

NDT Inspector,
Joined Sep 2006
17:52 Nov-11-2019
Re: UT testing for Weld Overlay / Clad thickness
In Reply to D Wallace at 10:44 Nov-09-2019 (Opening).

One of the rules for UT inspection is to calibrate using a bloc that has properties similar to what your are inspecting. Basically, you don't compare apples to oranges. So yes, you should use a CR-Mo carbon steel block with a SS overlay. Your problem will be to fabrication a block having an overlay with the same thickness as what you have on your barrel nozzle.

As for your reflector, if you know the exact thickness of the CR-Mo carbon steel of your nozzle, you should be able to determine the location of the reflector. It should tell you if it is located in the carbon steel, at the CS/SS interface or in the stainless steel.


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