Surface World May 2019 Surface World May 2019 | Page 34

TESTING & MEASUREMENT
Measuring dry fi lm thickness
on blasted substrates
Dry Film Thickness (DFT)
is arguably the single most
important measurement
made during the
inspection of protective
coatings because of its
impact on the integrity
of the coating process,
quality and cost. Dry fi lm
thickness measurements
can be used to evaluate
a coating’s expected life,
the product’s appearance
and performance, and also
ensure compliance with
a host of International
Standards.
When steel surfaces are prepared using an
abrasive blasting process the surface is left
with a profile. Creating the required level of
surface profile increases the surface area and
provides an anchor pattern for the coating
to adhere to, leading to optimised coating
performance and efficient material usage.
Coating thickness gauges are set up during
the manufacturing process using a smooth
metal surface. Smooth metal surfaces are
easier to characterise and reproduce than
a textured or profiled surface. A gauge set
up to measure known thicknesses on a
smooth steel surface will show an error when
used to measure the same thickness on a
profiled surface, such as one achieved by
abrasive blasting.
The Elcometer 456 IPC
The Elcometer 456 Industrial Protective
Coating (IPC) Thickness Gauge provides
a new method for accurately measuring dry
film thickness on shot or grit blasted ferrous
(steel) substrates; such as ships, pipelines
or storage tanks. Designed to significantly
reduce inspection times, the Elcometer 456
IPC is fast and very simple to use on both flat
and curved surfaces, taking over 70 readings
per minute, in either microns or mils.
With its rugged hand-held design which is
ideal for use in the field; the Elcometer 456
IPC gauge features a built-in integral probe
for stable, repeatable readings. Users are
able to store 150,000 readings in up to
2,500 batches and thanks to its easy-to-use
menu structure in multiple languages, the
gauge requires minimal training to get
started.
Working towards
International Standards
ISO 19840 outlines a method for measuring
the DFT on a profiled surface where the
DFT gauge has been adjusted on a smooth
surface. With a measurement range of up
to 1,500µm, the Elcometer 456 IPC gauge
enables the user to measure the DFT on
a blasted surface by simply selecting the
relevant profile from the menu; smooth,
fine, medium or coarse, and placing the
gauge on the coated surface to take a
measurement. The gauge can also be used
in accordance with US Navy NSI 009-32
in the same way, when the measurement
units are set to mils.
A recent 12 month study by the National
Shipbuilding Research Program found that
by using a pre-calibrated Elcometer 456 IPC,
they were able to measure coatings in half
the time of the current dry film thickness
measurement method, whilst still maintaining
accuracy.
Also working in accordance with SSPC-PA2,
the Elcometer IPC gauge takes readings in
groups of three to the nearest 10µm (1 mil).
When the third reading is taken, the average
(mean or xbar) of the three readings is
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MAY 2019
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