By W.D. Corbett
Surface profile is defined as the
average peak-to-valley depth
that is created during surface
preparation. It sometimes is
referred to as ?anchor pattern?
or ?tooth.? Surface profile
observed under high magnification resembles lunar craters or a series
of peaks and valleys in the surface
of the steel. These peaks and valleys can
be sharp, or ?angular,? or they may be
Surface profile or anchor pattern is
generated by abrasive blast cleaning and
by some power tool cleaning methods.
The adhesion of the coating system to
the underlying steel surface is greatly
enhanced by generating this ?peak and
valley? pattern in the steel, which effectively
increases the total surface area.
Surface profile is quantified by measuring
the depth of the ?valleys? in relationship
to the top of the ?peaks.? Although
an inadequate surface profile
depth may not properly ?anchor? the
coating system (and disbonding may
occur), an excessive surface profile
depth may cause rogue peaks to protrude
above the coating film. The protrusion
causes pinpoint rusting and
accelerated corrosion. Therefore, accurately
assessing the surface profile depth
for compliance with the governing
specification is paramount to a successful
For the greatest accuracy in measuring
surface profile depths, the steel surface can be examined microscopically
and the surface profile depth measured
in cross-section using a calibrated ocular.
Such a method is impractical in the
shop or field, however. There are three
methods that are more practical and
routinely used on the shop floor and
in the field for quantifying the depth
of the surface profile after surface
preparation. ASTM D4417,1 ?Standard
Test Methods for Field Measurement of
Surface Profile of Blast Cleaned Steel,?
describes three such methods:
- Method A: Visual Surface Profile
- Method B: Surface Profile Depth
- Method C: Replica Tape (NACE
RP0287-912 describes the proper
use of the replica tape as well).
THE VISUAL SURFACE
Method A of the ASTM standard describes
the use of the Visual Surface
Profile Comparator method. For this
method, one visually compares the prepared
steel surface to an electroformed
nickel disc containing known anchor
patterns through a 5-power illuminated
Step 1: Understanding the
Comparator Disc Stencils
Each comparator disc contains five
segments. Each segment of each disc
is stenciled with a code identifying the
surface profile depth, the disc type,
and the year that a master disc was generated
(the discs are electroformed
copies of a master disc; they are not
prepared individually by abrasive blast
cleaning). The first stencil on each segment
indicates the surface profile
depth depicted in mils (e.g., 1, 2, 2.5,
3 mils [25, 50, 64, 76 Ám], etc.). The
second stencil on each segment indicates
the abrasive type (S for Sand, SH
for SHot, and G/S for Grit/Slag) (Figure
Figure 1: Visual surface profile comparator discs.
Your choice of disc will depend on
the abrasive media used to blast-clean
the steel surface.
Step 2: Selecting
Select the comparator
matches the type
of abrasive used to
blast-clean the surface.
Use the S disc
to compare surfaces
silica sand; use the
SH disc to compare
were prepared using
steel shot; and
use the G/S disc to
that were prepared
using grit or
slag abrasives. G/S
can represent a variety
some of which include
copper, coal, and
nickel slags; garnet;
others. Many fabrication shops use an operating mix of
steel shot and steel grit in their centrifugal
blast machines. Because this is a visual
assessment of surface profile depth,
the G/S disc likely is the best candidate
as it depicts angular peaks and valleys.
Step 3: Attaching the Comparator
Disc to the Illuminated Magnifier
Choose the disc that represents the
abrasive used to prepare the surface,
then attach the disc to the viewing head
of the 5X illuminated magnifier (faceup,
centered). The magnifier head is
equipped with a magnetic strip that
holds the disc in place during prepared
Step 4: Examining the Prepared
Turn on the magnifier?s light switch
and place the magnifier with the attached
disc directly onto the abrasive
blast-cleaned steel (Figure 2). The hole
in the center of the disc reveals the prepared surface. Compare
this surface to each of the
five segments and select
the segment that is the closest
match to the surface
profile depth. If the surface
falls between two segments,
do not interpolate
but simply record both segments
as a range (e.g., 2 to
3 mils). Record the type of
disc used and the surface
profile depth (in mils). If
the specification refers to
surface profile depth in
terms of Ám (micrometers
or microns), convert the
surface profile in mils to
Ám by simply multiplying
that amount by 25.4 (e.g.,
3 mils is 76 Ám).
Figure 2: Using the visual surface profile comparator.
THE SURFACE PROFILE
Figure 3: Surface profile depth micrometer, dial display.
Figure 4: Surface profile depth micrometer, digital display.
Method B of the ASTM
standard describes the use
of a surface-profile-depth
micrometer. For this
method, one measures the depth of the
?valleys? using a conical-shaped metal
tip. The surface profile depth appears
on the gauge dial (Figure 3) or on the
digital display (Figure 4), depending on
Step 1: Verification of ?Zero?
Before using the depth micrometer,
verify the zero reading by placing the
micrometer base onto a piece of plate
glass. The gauge should indicate ?0.? If
it does not, adjust the dial gauge or the
digital display until attaining a zero
Step 2: Obtaining Surface
Place the base of the calibrated
gauge onto the abrasive-blast-cleaned
steel and push downward. Do not slide
the gauge as this will dull the protruding
pinpoint and affect gauge accuracy.
Read the scale or digital display and
record the surface profile depth. The gauge reading represents the depth of
the valley in a very small area. Therefore,
it is important to obtain multiple
measurements in a given area and to
obtain measurements in multiple areas.
Record each individual gauge reading in
order to calculate the average and range
of the anchor pattern.
Step 3: Reverification of ?Zero?
After using the depth micrometer,
verify the zero reading again by placing
the micrometer base onto a piece
of plate glass. The gauge should indicate
?0.? If the zero adjustment is off
by a significant amount, it may be
necessary to measure the surface profile
THE REPLICA TAPE METHOD
NACE RP0287-91 and Method C of
ASTM D4417 describe the use of a replica
tape in conjunction with a springloaded
micrometer. This method of surface
profile measurement entails
generating an ?impression? of the anchor
pattern and measuring the impression
using a spring-loaded micrometer.
According to ASTM, this method is the
most repeatable and reproducible of the
three methods that are described in the
The Testex? replica tape itself consists
of a noncompressible 2-mil-thick
polyester film and a compressible layer
of foam, which is attached to the underside
of the film (Figure 5). The film
remains a constant 2 mils, but the
amount of compressible foam varies depending
on the range of the replica
tape. The compressible foam is pressed
into the anchor pattern, effectively creating
a mirror image of the surface profile
in the foam. The peak-to-valley impression
is then measured using a
calibrated spring micrometer.
Figure 5: Replica tape components: (a) replica tape film, (b) burnishing plastic stick, (c) spring-loaded micrometer.
Step 1: Selecting the
Appropriate Replica Tape
Prior to obtaining a surface profile
measurement, select the range of the replica tape to be used. There are four
ranges to choose from, including:
Replica tape typically is selected
based on the specified surface profile
- ?Coarse,? which measures surface
profile depth from 0.8 (20 Ám) to
- ?Paint Grade,? which measures
surface profile depth from 1.3 to 3.3
mils (33 to 84 Ám)
- ?X-Coarse,? which measures surface
profile depth from 1.5 to 4.5
mils (38 to 114 Ám)
- ?X-Coarse Plus,? which measures
surface profile depth from 4.0 to 6.5
mils (102 to 165 Ám).
Step 2: Preparing the Surface
Unlike the previous two methods of
surface profile measurement, the replica
tape method can be adversely affected
by residual abrasive and dust remaining
on the abrasive-blast-cleaned
surface. Therefore, prior to obtaining
a measurement, ensure that the measurement
area is free of dust and abrasive
debris by lightly sweeping the surface
with a clean brush.
Step 3: Preparing
the Replica Tape
Remove a piece of the tape selected
for use from the roll. Carefully remove
the replica tape from the paper backing,
exposing the adhesive on the tape.
Discard the paper backing and the
small black and white protective circle
attached to the paper backing. Ensure
that the protective circle does not remain
attached to the replica tape.
Firmly attach the replica tape to the
surface to be measured, leaving one
corner folded over to create a pull-tab.
Step 4: Burnishing
the Replica Tape
Using the rounded tip of the plastic
stick provided with the micrometer,
burnish the white, 3/8-in. (0.6-cm)-
diameter circle located in the center
of the replica tape until it turns uniformly gray. After verifying that there
are no visible white streaks, use the
pull-tab to lift the replica tape carefully
from the surface.
Step 5: Adjusting the Micrometer
Adjust the micrometer so that the
indicator needle rests on ?0? with the
micrometer anvils closed.
Step 6: Measuring the Replica
Tape and Determining the
Surface Profile Depth
Insert the replica tape containing
the surface profile impression into the
anvils of the micrometer and release
the lever, allowing the top and bottom
anvils to close in the center of the 3/8-
in.-diameter film/foam circle (Figure 6). The micrometer indicates the thickness
of the noncompressible 2-mil film
and the peak/valley impression in the
compressible foam. Determine the surface
profile depth by subtracting the
2-mil film thickness from the micrometer
Figure 6: Measuring surface profile depth using replica tape and micrometer.
To eliminate the need for deducting
the film thickness, set the micrometer
needle on ?8? rather than ?0? in Step
5. This effectively presets the micrometer
to ?2 mils.
Using the X-Coarse Plus Range
of Replica Tape
The X-Coarse Plus replica tape can
be used to measure very deep anchor
patterns?up to ~6.5 mils or more. To
use this tape, confirm that there is sufficient
compressible foam mounted
to the film before trying to obtain a
Prepare the tape as described in
Step 3. Prior to attaching the tape to
the surface, however, set the needle
on the micrometer to ?8? (effectively
?2 mils). Insert the unused piece of replica
tape into the anvils of the micrometer
and release the lever. The micrometer
reading is the maximum
surface profile depth that can be measured
with that piece of replica tape.
Follow steps 4 through 6 above from
this point forward.
Step 7: Recording the
Document the area tested and surface
profile measurement on the tape
itself in the sections labeled ?No.? and
?Reading,? respectively. Always record
the surface profile depth after the 2
mils has been deducted for the polyester
film. Finally, verify that the recorded
surface profile depth falls
within the range of the tape chosen for
measurement. If it does not, then the
reading may be invalid.
Calibration of Surface Profile
It is not necessary to calibrate the
visual surface profile comparator. If the
comparator discs become tarnished,
however, they can be difficult to use.
A soft pencil eraser can be used to remove
the tarnish without disturbing
the electroformed pattern on each
Calibration of the surface profile
depth micrometer was described earlier.
Conduct this ?zero-verification/
adjustment? procedure prior to and
after each period of use.
Although the replica tape itself
needs no calibration, routinely confirm
the micrometer?s level of accuracy by
inserting shims of known thickness
into the instrument and verifying a correct
measurement. Plastic shims used
to calibrate coating thickness gauges
can be used for this purpose. Recognize,
however, that these shims may
not represent an exact thickness.
Documentation of Surface
When documenting the surface profile
measurements, be sure to include
the date of measurement, the method
employed, the area(s) of measurement,
the number of measurements obtained,
and the range and average of
the measurements obtained.
1. ASTM D4417, ?Standard Test Methods for Field
Measurement of Surface Profile of Blast Cleaned Steel?
(West Conshohocken, PA: ASTM).
2. NACE RP0287, ?Field Measurement of Surface
Profile of Abrasive Blast Cleaned Steel Surfaces Using
a Replica Tape (Houston, TX: NACE, 1995).
This article is based on Module 2 from
the KTA-Tator publication, Using Coatings
Inspection Instruments, by W.D. Corbett.
Reprinted with permission.
William D. Corbett is the Technical Services
Administrator for KTA-Tator, Inc. (KTA), 115
Technology Drive, Pittsburgh, PA 15275. Corbett
holds an Associate?s Degree in business
administration from Robert Morris College and has
been employed with KTA since 1979. He is a
SSPC Certified Protective Coatings Specialist
(#344-249-0645) and a NACE International
Certified Coatings Inspector (#5450). Corbett has
written numerous case histories published in The
American Painting Contractor and authored the
KTA Coating Inspection Instrument Use Handbook
(1st and 2nd editions). Corbett was the co-recipient
of the SSPC 1992 Outstanding Publication Award
and co-recipient of the SSPC 2001 Editors Award.
He is a member of NACE, ASTM, and SSPC.