Olympus nortec 600 - Figure 5-134 the List of All Parameters; Inspecting Heat Exchanger Tubing Using Dual Frequency - NORTEC 600 D Model

DMTA-10040-01EN, Rev. E, February 2018
Using the Instrument 215
Figure 5‑134 The list of all parameters
5.3.3 Inspecting Heat Exchanger Tubing Using Dual Frequency —
NORTEC 600D Model
The procedure in this section uses the dual frequency function to remove the heat
exchanger’s tube-support signal in order to obtain cleaner readings of possible flaws
at support locations. You can use this procedure on any type of heat exchanger tubing
as long as it is non-ferromagnetic. Although this procedure has been prepared using a
differential bobbin probe, other types of tube probe coils can also easily be used; for
example, differential pancake coils for air conditioner tubing. Several tips for absolute
measurements have been provided at the end of this section.
The frequency calculation for the prime frequency should follow the ASME standard
or be based on obtaining at least a 90° phase lag between the thru-wall hole and the
20 % outside flat-bottom holes. The following formula is also recommended:
Prime frequency = 5 × resistivity / (wall thickness)
2
where
• Resistivity is in micro-ohm centimeters (µΩ-cm);
• Wall thickness is in millimeters (mm); and
• Frequency is in kilohertz (kHz).