Presented by: David Beamish

DeFelsko Corporation

Update to SSPC-PA 9Paint Application Specification

Measurement of Dry Coating Thickness Using Ultrasonic Gages

September 2015

“The New PA 9”Content

Background of SSPC-PA 9 Overview and Scope of SSPC-PA 9 (2015) Purpose of ASTM D6132-13 Gage Descriptions Calibration & Verification of Accuracy Measurement Procedures Frequency and Number of Measurements Conformance to Specified Thickness Content of the two Appendices

Overview The document focuses on the correct method for taking

measurements

Includes criteria for determining:– Number and location of measurements– Whether or not the DFT conforms to project specifications

Applies to ultrasonic devices specifically designed to measure coating thicknesses

Procedures described in SSPC-PA 9 are intended to supplement manufacturers’ operating instructions

There is only 1 previous version which was published 2008.

Current version dated July 20, 2015

Background of SSPC-PA 9

SSPC-PA 9 extends the functionality of ASTM D6132

ASTM D6132-13 describes“how” to use the gage

SSPC-PA 9 (2015) focuses on acceptability of acquired measurements by describing “where” and “how often”

Background of SSPC-PA 9

Describes procedures to measure the thickness of dry, homogeneous coatings applied on a variety of surfaces

Homogeneous: Refers to a coating of uniform composition throughout that does not contain large, solid particles such as sand.

Ultrasonic gages are not recommended for coatings such as mortars which are heavily filled with aggregate.

Scope of SSPC-PA 9

Describes procedures to measure the thickness of dry, homogeneous coatings applied on a variety of surfaces

Thickness readings can be verified using destructive means –ASTM D4138

Scope of SSPC-PA 9

Measurements are acquired using purpose-built ultrasonic coating thickness gages

Procedures for gage calibration, verification of accuracy and adjustment are described

Procedure for determining conformance to specified thickness range over extended areas is described

Standard is not intended to prescribe a frequency of measurement for a coating failure investigation

Standard contains two non-mandatory appendices

Scope of SSPC-PA 9

Gage Description Must be capable of measuring coatings

over non-metallic substrates

Gages shall be calibrated and verified according to the manufacturer’s instructions and ASTM D6132

Ultrasonic thickness gages measure polymer coating thicknesses from ~0.3 to 300 mils. The upper limit depends on the acoustical properties of the material being measured and the transducer in the probe.

Gage Description

Ultrasonic vibrations reflect off coating interfaces

Three Steps

1. Calibration and verification of gage accuracy (section 5)

2. Measurement procedures (section 6)

3. Conformance to specified thickness (section 7)

Calibration and Verification Shall be performed in accordance with ASTM D6132

Step 1 of 3

ASTM D6132 ASTM D6132 describes 3 operational steps to ensure

accurate measurement:

1. Calibration

2. Verification of Accuracy

3. Adjustment

These steps must be completed before coating thickness data acquisition.

Gage Calibration “Calibration of coating thickness gages is performed by

the equipment manufacturer, their authorized agent, or by an accredited calibration laboratory in a controlled environment using a documented process.”

Certificate of Calibration traceable to a National Metrology Institute can be issued

No standard time interval for re-calibration, (established based on experience & work environment) but 1-year is typical

Gage Verification An accuracy check performed by

the user on known reference standards comprising of at least one thickness value close to the expected coating thickness.

The process is intended to guard against measuring with an inaccurate gage.

Gage Verification Shall be performed, at a minimum, at the beginning and

end of each work shift

If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy shall be rechecked

Gage Verification Record the:

– Serial number of the gage

– The reference standard used

– The state thickness of the reference standard as well as the measured thickness value obtained

– The method used to verify gage accuracy

Three Steps

1. Calibration and verification of gage accuracy (section 5)

2. Measurement procedures (section 6)

3. Conformance to specified thickness (section 7)

Measurement ProcedureStep 2 of 3

Gage Reading: A single instrument reading.

Spot Measurement: The average of at least 3 gage readings made within a 6” diameter circle.

Any unusually high or low gage readings that are not repeated consistently are discarded.

Area Measurement: The average of 5 separate spot measurements over each 100 ft2 of coated surface.

Area Measurement Average of 5 separate spot measurements over each 100

ft2 of coated surface

1. For areas not exceeding 300 ft2, each 100 ft2 is measured

2. For areas 300 - 1000 ft2 , three 100 ft2 areas are selected and measured

3. For areas greater than 1,000 ft2, the first 1,000 ft2 has three 100 ft2 area measurements selected. For each additional 1000 ft2, one area measurement is selected

Area Measurement for 100 ft2

Measurement Frequency

Size of Coated Area: 900 square feet

No. of Areas: 3No. of Spots: 15 (3 Areas x 5 Spots/Area)

Minimum No. of Gage Readings:45 (15 Spots x 3

Readings/Spot)

Measurement Frequency Example

Size of Coated Area: 55,000 square feet

No. of Areas: 57 (3 + 54)No. of Spots: 285 (57 Areas x 5 Spots/Area)

Minimum No. of Gage Readings:855 (285 Spots x 3

Readings/Spot)

Measurement Frequency Example

Nonconforming Area If the coating thickness for a 100 ft2 area is not in

compliance:

Determine the spot DFT at 5 ft. intervals in 8 equally spaced directions radiating outward from the nonconforming 100 ft2 area up to the limit of area coated during the work shift

Acquire spot measurements in each direction until 2 consecutive conforming spot measurements are acquired in that direction or until no additional measurements are possible

5 ftNO

OK

OK

STOP

OK

OK

STOP

OK

OKSTOP

OKSTOP 5 ft5 ftOK

STOP

OK

OK

Dashed line indicates boundary of area painted during work shift

Suspect area preceding a nonconforming spot must be re-measured after corrections are made

OK

NO

STOP

OK

OK

(Limit of area coated during work shift)

5 ft

5 ft

5 ft

5 ft

5 ft

5 ft

5 ft

STOPOK

5 ft

5 ft

5 ft

5 ft

Dashed line indicates boundary of area painted during work shift

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(Limit of area coated during work shift)

STOP

(Limit of area coated during work shift)

Initial Nonconforming

100 ft2 Area

Three Steps

1. Calibration and verification of gage accuracy (section 5)

2. Measurement procedures (section 6)

3. Conformance to specified thickness (section 7)

Conformance to Specified Coating Thickness

Specifications normally indicate a min/max range of coating thickness for each layer (e.g., 5-7 mils)

When only a single thickness value is specified by manufacturer:

range is established at +20% of the stated thickness value.

E.g., if the stated thickness value is 7 mils, then the minimum and maximum thickness shall be 5.6 to 8.4 mils.

Step 3 of 3

Table 1Coating Thickness Restriction

LevelsThickness

Gage Reading

SpotReading

Area Measurement

Level 1Minimum Unrestricted As specified As specifiedMaximum Unrestricted As specified As specified

Level 2Minimum Unrestricted As specified As specifiedMaximum Unrestricted 120% of maximum As specified

Level 3Minimum Unrestricted 80% of minimum As specifiedMaximum Unrestricted 120% of maximum As specified

Level 4Minimum Unrestricted 80% of minimum As specifiedMaximum Unrestricted 150% of maximum As specified

Level 5Minimum Unrestricted 80% of minimum As specifiedMaximum Unrestricted Unrestricted Unrestricted

Note: If unspecified, Level 3 is the default

Measurement ToleranceEXAMPLE 1:

Target DFT: 4 - 6 mils

Coating Thickness Restriction Level 3 (default)

Individual gage readings unrestricted

Spot measurements must be between 3.2 mils and 7.2 mils

Area measurement must be between 4 and 6 mils

If spot or area measurements are out of tolerance, the magnitude of the nonconforming thickness must be determined and demarcated.

Measurement ToleranceEXAMPLE 2:

Target DFT: 4 - 6 mils

Coating Thickness Restriction Level 2

Individual gage readings unrestricted

Spot measurements must be between 4 mils and 7.2 mils

Area measurement must be between 4 and 6 mils

If spot or area measurements are out of tolerance, the magnitude of the nonconforming thickness must be determined and demarcated.

SSPC-PA 9 Appendices

1. Numerical Example of Average Thickness Measurement

2. Gage Adjustment

Appendix 2 – Gage Adjustment Principle of Operation

- thickness = time of travel

Measurement Accuracy- default sound velocity value produces good measurement accuracy on most polymer coatings

Reference Sample- to verify accuracy or to improve measurement accuracy

Reference Sample Measurement Methods- micrometer, destructive, steel coupon

Tolerance- may increase

Update to SSPC-PA 9Paint Application Specification

Measurement of Dry Coating Thickness Using Ultrasonic Gages

September 2015

Any Questions

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