Magnetics Business & Technology - January/February 2022 - 15

FEATURE ARTICLE
or bottom side. When combined with MFL users can switch
between top side, bottom side, and complete plate views to
show the origin of the corrosion. STARS also provides a simple
visual representation of the inspection surface through thick
non-magnetic material up to 10 mm thick.
This system is explained by Matthew Kircough, senior application
specialist, in another blog that is available on the
company's website. While magnetic flux leakage (MFL) is the
most deployed technology for corrosion surveys of storage tank
floors, there is a growing demand to report whether corrosion
originates at the top surface, the product side, or the bottom
surface, the soil side. This is something that cannot be determined
from MFL data alone, he notes. Without the use of technology,
gathering this valuable information is a time consuming,
laborious, error-prone task involving a whole lot of " hands and
knees " time.
STARS (Surface Topology Air Gap Reluctance Sensors) is
Eddyfi Technologies' proprietary, patented technology. STARS
data is collected alongside MFL data during an inspection and
used by the Floormap software to automatically discriminate
between soil side and product side corrosion. The amplitude
of an MFL signal from a top-side defect is different from the
bottom side; STARS in combination with MFL helps reduce this
ambiguity. This relatively new technology has already provided
substantial real-world benefits to most tank owners, but it is
generally not well understood, says Kircough.
As seen in the image above right, the horseshoe shape magnet
bridge is suspended over the plate being inspected. The
Floormap includes two separate Hall-Effect sensor arrays, one
Cross section view of Floormap magnet bridge and sensor positions
for MFL and the other for STARS, each with a resolution of 64
channels across the 300-millimeter width of the bridge. HallEffect
sensors are sensitive to magnetic fields that are perpendicular
to their surface. MFL sensors are located between the
front and rear poles of the magnet to detect magnetic leakage
fields caused by corrosion pitting from either the top or bottom
surface of the plate. STARS sensors are mounted on the
bottom surface of the rear magnet pole and are oriented to
respond to top surface variation only.
STARS works on the principle of air-gap reluctance. When
scanning over areas with no product side corrosion, the gap will
remain mostly constant. The magnetic flux lines will travel vertically,
taking the path of least reluctance between the pole and
plate surface. They travel parallel to the STARS sensor, do not
intersect it, and there is no response from STARS.
For more info and to see the blogs, go to www.eddyfi-ndt.com.
Visualize the magnetic fields in real-time
In-depth analysis of all magnetic field properties
www.MagneticsMag.com
January/February 2022 * Magnetics Business & Technology 15

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Magnetics Business & Technology - January/February 2022

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