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Technical Discussions
Robert Rock
Robert Rock
03:17 Oct-10-2002
monel 400 clad gauging

Can anyone describe the proper setup for ultrasonically gauging
monel 400 cladding with hy80,100 backing steel,using a .5" 5mhz
transducer with a panametrics epoch 3b? The bondline is defined
well enough to get a good response. My problem is a cannot obtain
readings without an error rate of approx .030 one would think one could get much more accurate than this.The min clad is .125
and the min backing is 1.187



    
 
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Tom Nelligan
Engineering,
retired, USA, Joined Nov 1998, 390

Tom Nelligan

Engineering,
retired,
USA,
Joined Nov 1998
390
06:55 Oct-11-2002
Re: monel 400 clad gauging
: Can anyone describe the proper setup for ultrasonically gauging
: monel 400 cladding with hy80,100 backing steel,using a .5" 5mhz
: transducer with a panametrics epoch 3b? The bondline is defined
: well enough to get a good response. My problem is a cannot obtain
: readings without an error rate of approx .030 one would think one could get much more accurate than this.The min clad is .125
: and the min backing is 1.187

If the error is a constant 0.030" across the full thickness range, that sounds like a zero calibration problem. Are you calibrating velocity and zero on two reference standards of the same Monel material that you're measuring? If so, there is also the possibility that the monel/steel boundary is giving you an echo that is phase inverted with respect to an air-backed reference standard. (I don't have exact impedance numbers for those alloys available to check whether that's likely.) You can check this by going to the RF display mode and observing whether the echo inverts between the reference standard and the actual cladding. If so, you need to compensate. There are a couple ways of doing this depending on the exact echo shape, but what I'd probably do is either work in RF mode with gating on both positive and negative lobes of the echo, or alternate between half wave negative and half wave positive rectification as appropriate for each boundary condition. You will also want to look carefully at how the thickness measurement gate interacts with the echo peak to be sure that you're getting consistent detection.

--Tom Nelligan
GE Panametrics


    
 
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