DMTA-10040-01EN, Rev. E, February 2018
Chapter 5
256
5.4.3
RFT Pitting and Wear — NORTEC 600D Model
This remote-field testing (RFT) application uses a differential configuration to identify
small localized defects such as pitting and wear in ferromagnetic tubing.
Remote-field testing (RFT) probes can successfully inspect ferromagnetic tubing such
as carbon steel or ferritic stainless steel. Their high sensitivity enables detection and
measurement of volumetric defects caused by erosion, corrosion, wear, and baffle
cuts.
RFT is a thru-wall transmission technique. The remote-field probe is a low-frequency
variant of the exciter (driver)-pickup eddy current probe, which is characterized by an
exciter-to-pickup distance of at least 2.5 to 3 times the tube OD. This distance is
essential and critical for the pickup coils to be able to sense the “remote” magnetic
field rather than the “direct” field.
The basic probe is made of one exciter coil and two pickup coils (see Figure 5-189 on
page 257). There are two magnetic fields present: the
direct field
in the vicinity of the
exciter coil is rapidly attenuated with distance, while the
indirect field
is diffused
outward through the tube wall. The indirect field then propagates along the tube axis,
before being rediffused back through the tube wall. The zone in which the indirect
field is dominant is called the remote field. This zone is present at a distance greater
than two tube diameters.
All remote-field probes have their pickup coils set to 2.5 to 3 times the tube OD to
ensure that only the indirect field is sensed (“picked up”) by the coils. All Olympus
RFT probes have a set of circumferential pickup coils that can be operated
simultaneously in absolute and differential mode.
Содержание nortec 600
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