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Industrial processing and chemical plants work at high
temperatures and pressures, with often aggressive media and
stainless steel is often the material of choice for these applications.
If the ferrite content of the steel steel is too low, then welding of
stainless material may crack at elevated temperature or with high
stress or vibration. Alternatively, if the ferrite content is too high, the
weld may be weaker and corrode.
To address the need to measure the amount of ferrite in a sample
the Welding Research Council introduced the Ferrite Number (FN)
as standardised value which related to the ferrite content of an
equivalently magnetic weld metal.
The volume percentage of ferrite can be estimated as about 70% of
the FN but the relationship depends upon the type and origin of the
stainless steel used and the measurement technique (see section
on Ferrite %)
The Diverse Ferrite meter MF300Fe+
measures the Ferrite number (FN) of
austenitic and duplex stainless steel weld
material. It has a choice of probes: e.g. see
image for P10 probe that is sensitive to ferrite content in a 10 mm
area to a depth of approximately 1 mm. The instrument is
calibrated using the secondary ferrite number standards prepared
by the National Institute of Standards and Technologies (NIST) in
USA. Sixteen standards are used ranging from 0.5 to 111.9 FN
giving an instrument with a measurement range from 0 to 115 FN.
Transfer standards are supplied with the instrument allowing
performance to be verified at any time.
Introduction
