Transcript Preparing a Coating Inspection Plan

Complying with
SSPC-PA2, “Measurement of
Dry Coating Thickness with
Magnetic Gages”
William D. Corbett
KTA-Tator, Inc.
Complying with SSPC-PA 2
• Webinar Content
 Overview and Purpose of SSPC-PA 2
 Definitions
 Proper Gage Use
 Acquisition of Measurements
 Frequency of Measurements
 Tolerance of Measurements
 Measuring Coating Thickness on Steel Beams (girders)
 Measuring Coating Thickness on Test Panels
 Potential Changes to SSPC-PA 2 (2011/2012)
Learning Objectives/Outcomes
• Completion of this webinar will enable the participant to:
 Describe the purpose of SSPC-PA 2
 Describe the differences between Type 1 and Type 2 gages
 Describe the processes associated with calibration,
verification of accuracy and adjustment
 Explain Base Metal Reading acquisition
 Describe the differences between measurement acquisition
using manual verses electronic gages
 Describe the frequency and tolerance of measurements
 Describe the measurement acquisition process for steel
beams. laydowns and test panels
Overview and Purpose
of SSPC-PA 2
• Describes the procedures to measure the
thickness of dry, nonmagnetic coatings
applied to magnetic substrates
• Measurements are acquired using
commercially available gages (two “types”)
• Procedures for gage adjustment &
measurement acquisition are described
• Procedure for determining conformance to
specified thickness range over extended areas
is described
Definitions
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Gage Reading
Spot Measurement
Calibration
Verification of Accuracy
Gage Adjustment
Coating Thickness Standard (Test Block)
Shim (Foil)
Dry Film Thickness Reference Standard
Accuracy
Structure
Gage Descriptions
• Gage type is determined by magnetic properties
employed to measure thickness (not the readout mode)
 Type 1 – Pull-off Gages
 Type 2 – Electronic Gages
• Gages not addressed by SSPC-PA 2
 Measurement of coatings on non-ferrous metal surfaces
 Measurement of coatings on non-ferrous surfaces
 To qualify for use, gages must have an accuracy of
+/- 5% or better (0.1 mil or better when < 1 mil DFT)
Gage Types
Type 1 – Pull-off Gages
Type 2 – Electronic Gages
Gage Types, continued
• Type 1 – Pull-off Gages
Permanent magnet
contacts coated
surface
Force required to
detach magnet is
measured
Force interpreted as
the coating thickness
on scale or display
Scale is nonlinear
Gage Types, continued
• Type 2 – Electronic
Gages
 Electronic circuitry
converts reference
signal to coating
thickness
Gage Calibration
• Performed by the gage manufacturer or
qualified laboratory
• Certificate of calibration traceable to a
National Metrology Institute required
• No standard calibration interval
(established based on experience & work
environment)
• One year interval is common
Verification of Type 1 Gage Accuracy
 Performed using reference
standards (traceable test
blocks)
 Beginning and end of each
work shift
 If gage is dropped or readings
are suspect
 Record:
 Serial no. of gage & standard
 Stated & measured thickness
 Use of shims (foils) not
permitted
Verification of Type 1 Gage Accuracy
• Single Point Verification
Select one reference test block representing the
mid-range of the anticipated coating thickness
E.g., 4-6 mils (100-150 µm), select 5 mil (125 µm)
reference standard
• Tw0 Point Verification
Select a reference test block below and above
the median anticipated coating thickness
E.g., 5 mils (125 µm), select 3 mil (75 µm) and 7
mil (175 µm) reference standards
Verification of Type 1 Gage Accuracy
• Most Type 1 gages cannot be “adjusted”
• Adjustments to the helical spring may void
the gage warranty
• Combined tolerance of gage and reference
standard determines gage accuracy
E.g., if gage accuracy is 5% and reference
standard accuracy is 3%, combined tolerance is
~6%, calculated as: √ 52 + 32
On a 10 mil reference standard, the gage
reading can range from 9.4-10.6 mils
Correction for Surface Roughness
• Base Metal Reading
(BMR)
• Effect of surface
roughness on coating
thickness gage
• NOT surface profile
• Measure the prepared,
uncoated substrate;
calculate average BMR
• Deduct BMR from
measured coating
thickness
BMR
Correction for Surface Roughness
Area
BMR
1
30 µm (1.2 mils)
2
25 µm (1.0 mils)
3
18 µm (0.7 mil)
4
13 µm (0.5 mil)
5
20 µm (0.8 mil)
6
8 µm (0.3 mil)
7
25 µm (1.0 mil)
8
28 µm (1.1 mils)
9
23 µm (0.9 mil)
10
13 µm (0.5 mil)
11
18 µm (0.7 mil)
12
25 µm (1.0 mil)
Measuring Base Metal Effect with Type 1
DFT Gage
Average BMR: 21 µm (0.8 mil)
BMR Correction for Multiple
Coat Systems
Measured Primer Thickness:
BMR:
Actual Primer Thickness:
102 µm (4.0 mils)
13 µm (0.5 mils)
89 µm s (3.5 mils)
Measured Primer + Finish Thickness:
BMR:
Actual Total System Thickness:
178 µm (7.0 mils)
13 µm (0.5 mils)
165 µm (6.5 mils)
Correction for Surface Roughness
 What if access to blast cleaned steel is not
available (already coated)?
 Appendix A2.3 addresses smooth surface
adjustment
 Verify gage accuracy on a smooth surface (per
gage manufacturer instructions)
 Deduct “assumed” approximate correction
value from each gage reading (see Table A2)
Correction for Surface Roughness
Table A2
Typical Gage Correction Values Using
ISO 8503 Profile Grades
ISO 8503 Profile
Grade
Correction Value
(µm)
Correction value
(mils)
Fine
10
0.4
Medium
25
1.0
Coarse
40
1.6
Adjustment of Type 2 Gages
• Follow the gage
manufacturers step-bystep procedures for gage
adjustment
• Instructions vary by
gage manufacturer
• Adjustment is typically
performed using plastic
shims (foils) of known
thickness
Verification of Type 2 Gage Accuracy
 Verify accuracy per
manufacturer instructions
 Typically performed using
reference standards or
shims
 Beginning and end of each
work shift
 If gage is dropped or readings
are suspect
 Record:
 Serial no. of gage & standard
 Stated & measured thickness
Verification of Type 2 Gage Accuracy
• Single Point Verification
Same as described for Type 1 gages
Can use reference blocks or shims (per gage
manufacturer)
• Tw0 Point Verification
Same as described for Type 1 gages
Can use reference blocks or shims (per gage
manufacturer)
Verification of Type 2 Gage Accuracy
• If smooth reference
standards are used (A),
user must correct* for
surface roughness
• If shims (foils) are used
(over the prepared steel;
B), no correction is
needed
A
*Via Base Metal Reading (BMR)
B
Adjustment of Type 2 Gages
• Aligning a gage’s
thickness readings to
those of a known
thickness value to
improve gage accuracy on
a specific surface or
within a measuring range
• Corrects for:
– Substrate properties
– Coating
– Ambient conditions and
surface temperature
Acquiring Coating Thickness
Measurements – Type 1 Gages
• Rotate the thumbwheel
forward to set the magnet
(or depress the power
button on the digital
model)
• Retract the thumbwheel
until the magnet breaks
contact (digital version
breaks contact
automatically)
• Read coating thickness
from the gage dial or
display
Acquiring Coating Thickness
Measurements – Type 2 Gages
• Power-up the gage
• Position the probe on the
coated surface until a
measurement is displayed
• Most models have
integral and remote
probes
Type 2 Gage Data Management
• Many Type 2 gages have
“PA 2” Data Management
Systems
• Programmed to collect
correct no. of values,
perform averaging and
indicate conformance
• Features and programs
vary by gage
manufacturer
Measurement Frequency
• Terminology:
Gage Reading: A single reading at one location
Spot Measurement: The average of at least 3
gage readings made within a 1.5” (4 cm)
diameter circle
Area Measurement: The average of 5 spot
measurements made within a 100 square foot
(10 square meter) area
Measurement Frequency
Measurement Frequency
 If the structure is less than 300 square feet, (~28
square meters) each 100 square feet (~10 square
meters) is measured
 If the structure is between 300 and 1000 square
feet (~28 and 100 square meters), arbitrarily select
3 random 100 square foot (~10 square meter) test
areas and measure
Measurement Frequency
 For structures exceeding 1000 square feet (~100
square meters), arbitrarily select 3 random 100
square feet (~10 square meter) testing areas for
the first 1000 square feet (~100 square meters),
and 1 random 100 square foot(~10 square meter)
testing area for each additional 1000 square feet
(100 square meters)
Measurement Frequency
Measurement Frequency Example 1
(US Standard)
Structure Size:
900 square feet
No. of Areas:
No. of Spots:
3 areas
3 Areas x 5 Spots/Area = 15
Spots
Minimum No. of Gage
Readings:
15 Spots x 3 Readings/Spot =
45 Gage Readings
Measurement Frequency Example 2
(US Standard)
Structure Size:
55,000 square feet
No. of Areas:
No. of Spots:
3 + 54 = 57 areas
57 Areas x 5 Spots/Area = 285
Spots
Minimum No. of Gage
Readings:
285 Spots x 3 Readings/Spot =
855 Gage Readings
Measurement Frequency
Example 3 (metric)
Structure Size:
5200 Square Meters
No. of Areas:
No. of Spots:
3 + 51 = 54 areas
54 Areas x 5 Spots/Area = 270
Spots
Minimum No. of Gage
Readings:
270 Spots x 3 Readings/Spot =
810 Gage Readings
Measurement Tolerance
 Individual gage readings obtained and averaged
to generate a spot measurement are unrestricted
(unusually low or high readings that can’t be
repeated are discarded)
 Spot measurements (the average of the gage
readings) must be within 80% of the minimum
thickness and 120% of the maximum thickness
 Area measurements must be within specified
range
Measurement Tolerance
EXAMPLE:
 Target DFT: 4-6 mils (102-152 microns)
 Individual gage readings unrestricted
 Spot measurements must be between 3.2 mils and 7.2 mils
(82 microns and 182 microns)
 Area measurement must be between 4 and 6 mils (102 and
152 microns)
 If spot or area measurements are out of tolerance,
measure each 100 sq. ft (~ 10 sq. meter) area coated during
that work shift to isolate the nonconforming area
(independent of structure size)
Specifying Coating Thickness
Specifications should indicate the range of
coating thickness (e.g., 5-7 mils or 127-178
microns), not as a single value (e.g., 5 mils
or 127 microns)
Nearly impossible for an applicator to
achieve a single thickness value
The Quality Control and Quality Assurance
inspectors should not have to assume a
range
Cumulative Thickness
Measurements
 Nondestructive coating thickness gages:
 Most cannot distinguish coating layers
 Measure the total cumulative thickness
Cumulative Thickness
Measurements
EXAMPLE:
Specification
Primer thickness:
Intermediate Coat Thickness:
Finish Coat Thickness:
3-5 mils (76-127 microns)
4-6 mils (102-152 microns)
2-3 mils (51-76 microns)
Target After:
Primer Application:
Intermediate Application:
Finish Coat Application:
3-5 mils (76-127 microns)
7-11 mils (178-279 microns)
9-14 mils (229-356 microns)
Appendix 3: Measuring Coating
Thickness on Steel Beams (Girders)
 Full Determination
 Sample Determination
 Beams < 20 ft (6 m)
 Beams 20 ft - 60 ft (6 m-18 m)
 Spot measurement tolerance
(80% of minimum and 120%
of maximum) applies
 The average of all spot
measurements (per area)
must conform to specified
range
 Measurement locations on
stiffeners arbitrarily selected
Stiffener
Appendix 3: Measuring Coating
Thickness on Steel Beams (Girders)
 Full Determination
 Divide beam into 5 equal
sections along the length
 Web > 36”: Obtain one spot
measurement in 14 areas,
per section (total of 70 spot
measurements)
 Web < 36”: Obtain one spot
measurement in 12 areas,
per section (total of 60 spot
measurements)
Full Determination
Note: Areas 2, 6, 8 and 12 (Toe) may not be measured
Appendix 3: Measuring Coating
Thickness on Steel Beams (Girders)
 Sample Determination
 Beam length < 20 ft: Obtain 2
spot measurements randomly
distributed in all 12 areas
(total of 24 spot
measurements)
 Beam length 20-60 ft: Obtain
3 spot measurements
randomly distributed in all 12
areas (total of 36 spot
measurements)
Note: If toe areas are not
included, measure in 8 areas
(16 or 24 spot measurements)
Appendix 4: Measuring Coating
Thickness on Laydowns
 Laydown: Group of steel
members laid down to be
painted in one shift by one
applicator
 Full DFT Determination
 Beams (girders)
 Miscellaneous parts
 Sample DFT Determination
 Beams < 20 ft (6 m)
 Beams 20 ft - 60 ft (6 m-18 m)
Appendix 4: Measuring Coating
Thickness on Laydowns
 Full DFT Determination
 Beams: Same procedure
described earlier
 Miscellaneous parts: 1 spot
measurement per “surface”
(minimum of 5 spots)
 Spot measurement
tolerance (80% of minimum
and 120% of maximum)
applies
 The average of all spot
measurements (per area)
must conform to specified
range
Appendix 4: Measuring Coating
Thickness on Laydowns
 Sample DFT Determination
 Beams: Same procedure
described earlier
 Miscellaneous parts: 3 spot
measurements per part
 Spot measurement
tolerance (80% of minimum
and 120% of maximum)
applies
 The average of all spot
measurements (per area)
must conform to specified
range
Appendix 5: Measuring Coating
Thickness on Test Panels
 Minimum panel size:
3” x 6” (7.5 x 15 cm)
 Maximum panel size:
12” x 12” (30 x 30 cm)
 Use Type 2 gage
 Two gage readings from
top, middle and bottom
third
 At least 0.5” from edge and
1” from other readings
 80% min.120% max. applies
to gage readings
Appendix 6: Measuring Thickness of Thin
Coatings on Abrasive Blast Cleaned Test
Panels
• “Thin” is considered 1 mil
(25.4 µm) or less
• Obtain 10 gage readings
from each of three
“zones”
• Calculate the mean and
standard deviation in
each zone
• The mean of all three
zones is the coating
thickness
10 gage readings
10 gage readings
10 gage readings
Potential Changes to SSPC PA 2
• Most recent revision is May 2004 (editorial changes to
Appendix 6 made in 2009)
• Document revisions and updating in progress
• Changes may include:
 Re-title, “Procedure for Determining Conformance to Dry Coating
Thickness Requirements”
 Use in concert with ASTM D 7091*
 Measurement of coatings on ferrous and non-ferrous metal surfaces
 Information on calibration and verification of accuracy removed
(already in ASTM D 7091)
 *Primarily focus on frequency and tolerance of measurements
(instead of gage use)
Summary
• During this webinar, we have:
 Described the purpose of SSPC-PA 2
 Described the differences between Type 1 and Type 2 gages
 Described the processes associated with calibration,
verification of accuracy and adjustment
 Explained Base Metal Reading acquisition
 Described the differences between measurement acquisition
using manual verses electronic gages
 Described the frequency and tolerance of measurements
 Described the measurement acquisition process for steel
beams, laydowns and test panels
Complying with
SSPC-PA2, “Measurement of
Dry Coating Thickness with
Magnetic Gages”
THE END