complying with sspc-pa2, “measurement of dry coating thickness with magnetic gages” william d....

Complying with SSPC-PA2,

“Measurement of Dry Coating Thickness with

Magnetic Gages”

William D. CorbettKTA-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 2Describe the purpose of SSPC-PA 2 Describe the differences between Type 1 and Type 2 Describe the differences between Type 1 and Type 2

gagesgages Describe the processes associated with calibration, Describe the processes associated with calibration,

verification of accuracy and adjustmentverification of accuracy and adjustment Explain Base Metal Reading acquisitionExplain Base Metal Reading acquisition Describe the differences between measurement Describe the differences between measurement

acquisition using manual verses electronic gagesacquisition using manual verses electronic gages Describe the frequency and tolerance of measurementsDescribe the frequency and tolerance of measurements Describe the measurement acquisition process for steel Describe the measurement acquisition process for steel

beams. laydowns and test panelsbeams. 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• 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 read-out mode)Type 1 – Pull-off GagesType 2 – Electronic Gages

• Gages not addressed by SSPC-PA 2Measurement of coatings on non-ferrous metal surfacesMeasurement 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 GagesPermanent 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 GagesElectronic 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 VerificationSelect a reference test block below and above

the median anticipated coating thicknessE.g., 5 mils (125 µm), select 3 mil (75 µm) and

7 mil (175 µm) reference standards


• 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 accuracyE.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


AreaArea BMRBMR

11 30 µm (1.2 mils)30 µm (1.2 mils)

22 25 µm (1.0 mils)25 µm (1.0 mils)

33 18 µm (0.7 mil)18 µm (0.7 mil)

44 13 µm (0.5 mil)13 µm (0.5 mil)

55 20 µm (0.8 mil)20 µm (0.8 mil)

66 8 µm (0.3 mil)8 µm (0.3 mil)

77 25 µm (1.0 mil)25 µm (1.0 mil)

88 28 µm (1.1 mils)28 µm (1.1 mils)

99 23 µm (0.9 mil)23 µm (0.9 mil)

1010 13 µm (0.5 mil)13 µm (0.5 mil)

1111 18 µm (0.7 mil)18 µm (0.7 mil)

1212 25 µm (1.0 mil)25 µm (1.0 mil)

Measuring Base Metal Effect with Type 1 DFT Gage

Average BMR: 21 µm (0.8 mil)µm (0.8 mil)

BMR Correction for Multiple Coat Systems

Measured Primer Thickness: 102 µm (4.0 mils)BMR: 13 µm (0.5 mils)Actual Primer Thickness: 89 µm s (3.5 mils)

Measured Primer + Finish Thickness: 178 µm (7.0 mils)

BMR: 13 µm (0.5 mils)Actual Total System Thickness: 165 µm (6.5

mils)


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)


Table A2Typical Gage Correction Values Using

ISO 8503 Profile GradesISO 8503

Profile GradeCorrection 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-by-step procedures for gage adjustment

• Instructions vary by gage manufacturer

• Adjustment is typically performed using plastic shims (foils) of known thickness


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 gagesCan use reference blocks or shims (per

gage manufacturer)

• Tw0 Point VerificationSame as described for Type 1 gagesCan use reference blocks or shims (per

gage manufacturer)


• 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

*Via Base Metal Reading (BMR)

A 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

locationSpot 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


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


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)

Structure Size: 900 square feet

No. of Areas: 3 areasNo. of Spots: 3 Areas x 5 Spots/Area =

15 SpotsMinimum No. of Gage Readings: 15 Spots x 3

Readings/Spot = 45 Gage Readings

Measurement Frequency Example 1 (US Standard)

Structure Size: 55,000 square feet

No. of Areas: 3 + 54 = 57 areasNo. of Spots: 57 Areas x 5 Spots/Area =



Measurement Frequency Example 2 (US Standard)

Structure Size: 5200 Square Meters

No. of Areas: 3 + 51 = 54 areasNo. of Spots: 54 Areas x 5 Spots/Area =



Measurement Frequency Example 3 (metric)

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:

SpecificationPrimer thickness: 3-5 mils (76-127 microns)Intermediate Coat Thickness: 4-6 mils (102-152 microns)Finish Coat Thickness: 2-3 mils (51-76 microns)

Target After:Primer Application: 3-5 mils (76-127 microns)Intermediate Application: 7-11 mils (178-279 microns)Finish Coat Application: 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


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


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)


Laydowns Full DFT Determination

Beams: Same procedure described earlier

Miscellaneous parts: 1 spot measurement per “surface” (minimum of 5 spots)




Laydowns Sample DFT Determination

Beams: Same procedure described earlier

Miscellaneous parts: 3 spot measurements per part



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 2Described the purpose of SSPC-PA 2 Described the differences between Type 1 and Type 2 Described the differences between Type 1 and Type 2

gagesgages Described the processes associated with calibration, Described the processes associated with calibration,

verification of accuracy and adjustmentverification of accuracy and adjustment Explained Base Metal Reading acquisitionExplained Base Metal Reading acquisition Described the differences between measurement Described the differences between measurement

acquisition using manual verses electronic gagesacquisition using manual verses electronic gages Described the frequency and tolerance of measurementsDescribed the frequency and tolerance of measurements Described the measurement acquisition process for steel Described the measurement acquisition process for steel

beams, laydowns and test panelsbeams, laydowns and test panels

Complying with SSPC-PA2, “Measurement of Dry Coating Thickness

with Magnetic Gages”

THE ENDTHE END

complying with sspc-pa2, “measurement of dry coating thickness with magnetic gages” william d....

Documents

thickness slide

gages type

gage descriptions gage

gage standard

gage calibration

gage types type

electronic gages gages

gage manufacturer