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Technical Discussions
Tomás Gómez-Acebo
Tomás Gómez-Acebo
07:21 Sep-28-1999
Phase shift in measurement of oxide layer thickness

Dear colleages, I have recently joined your discussion forum.
I would appreciate comments or suggestions about this topic.
When measuring with a 25 MHz probe the magnetite layer formed into the tubes of steam boilers (about .2 to 1 mm thick), there is a phase shift between the two echos in the RF signal: the first echo from the steel-oxide interface, and the second from the final oxide interface. How can this be interpreted?
Additionally, is there any way to distinguish between the two sub-layers of the oxide? Both have very similar chemical composition but slightly different porosity and microstructure: the inner (in contact with the steel) is layered, and the outer has columnar magnetite grains.
In the time-domain signal it is impossible to see anything that suggests the interface between the sub-layers, but what about the frequency-domain, or something else?
Best regards
Tomas Gomez-Acebo


 
 Reply 
 
Paul A. Meyer
R & D,
GE Inspection Technologies, USA, Joined Nov 1998, 47

Paul A. Meyer

R & D,
GE Inspection Technologies,
USA,
Joined Nov 1998
47
00:46 Sep-28-1999
Re: Phase shift in measurement of oxide layer thickness
final oxide interface. How can this be interpreted?
: Additionally, is there any way to distinguish between the two sub-layers of the oxide? Both have very similar chemical composition but slightly different porosity and microstructure: the inner (in contact with the steel) is layered, and the outer has columnar magnetite grains.
: In the time-domain signal it is impossible to see anything that suggests the interface between the sub-layers, but what about the frequency-domain, or something else?
: Best regards
: Tomas Gomez-Acebo




 
 Reply 
 

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