Using Emat Transducers - Olympus 38DL PLUS User Manual

DMTA-10004-01EN, Rev. D, November 2016

6. Using EMAT Transducers

This section provides background information regarding EMAT transducers and how
to make basic thickness measurements using the 38DL PLUS and the E110-SB
transducer.
An electromagnetic acoustic transducer (EMAT) uses the magnetostrictive principle
to generate shear wave sound energy in ferrous metals that are externally coated with
high temperature oxide scale. The E110-SB [U8471001] transducer does not work on
nonferrous metal or in cases where the external surface is not coated with oxide scale.
The EMAT transducer uses the external scale to generate shear wave sound energy
and does not require the use of ultrasonic couplant. When the scale is not fully
bonded to the surface of the steel, the shear wave sound energy is not transmitted to
the steel.
The EMAT transducer is an effective way to estimate the remaining thickness of steel
boiler tubes since you do not have to remove the external scale to perform the
measurement. The EMAT transducer creates a nonfocused signal and is designed to
give a good estimate of the remaining (±0.25 mm or ±0.010 in.) wall thickness. Because
of the nonfocused nature of the transducer, it is relatively insensitive to small internal
pits. The minimum thickness measurement capability of the 38DL PLUS and EMAT
transducer is approximately 2.0 mm (0.080 in.) depending on material properties.
NOTE
Remove the external oxide and use a standard single or dual element transducer for a
more accurate thickness measurement of remaining metal. Focused dual element
transducers are also more sensitive to any internal pitting.
Using EMAT Transducers 87