Presentation on theme: "William D. Corbett, KTA-Tator, Inc. Chair – SSPC Committee C.3.2 on"— Presentation transcript:
1“The New PA 2” Procedure for Determining Conformance to Dry Coating Thickness Requirements William D. Corbett, KTA-Tator, Inc.Chair – SSPC Committee C.3.2 onDry Film Thickness MeasurementThis one-hour webinar describes the content of the 2012 version of SSPC’s standard for coating thickness, known as Paint Application Standard No. 2, or SSPC PA2.
2“The New PA 2” Webinar Content Background of SSPC PA 2 Overview and Purpose of SSPC-PA 2 (2012)Purpose of ASTM DDefinitionsGage DescriptionsCalibration & Verification of AccuracyMeasurement ProceduresFrequency and Number of MeasurementsConformance to Specified ThicknessContent of Eight AppendicesThe webinar includes a variety topics relating SSPC’s Paint Application Standard No. 2, including:The background of the standard and reasoning for the change in title and contentThe purpose of SSPC’s dry coating thickness standardThe purpose of ASTM’s standard practice for coating thickness measurementA few basic definitions listed in the standardGage descriptions, including calibration, verification of accuracyThe measurement acquisition processThe number of gage, spot and area measurements to obtainHow far out of specification the measurements are permitted to be, or the tolerance of the acquired measurements, andThe content of 8 appendices to the standard
3Learning Objectives/Outcomes Completion of this webinar will enable the participant to:Describe the purpose and content of SSPC-PA 2Describe the differences between Type 1 and Type 2 gagesDescribe the processes associated with calibration and verification of accuracyExplain Base Metal Reading acquisitionDescribe the frequency and tolerance of measurementsDescribe the procedure for determining the magnitude of a non-conforming areaDescribe the basic content of eight appendices to the standardThere are seven learning outcomes or objectives for this webinar. Completing this webinar will enable you to:Describe the basic purpose and content of SSPC’s standard on measurement of dry coating thicknessDescribe the differences between Type 1 magnetic pull-off and Type 2 electronic gagesDescribe the procedures and frequency for gage calibration and verification of gage accuracyExplain base metal reading and describe when and how to obtain it, and it’s significance relating to true coating thicknessDescribe the number of coating thickness measurements to obtain and how far out of tolerance the measurements can be and still conform to the specification;6. Describe the procedure for determining the magnitude of a non-conforming area; and7. Describe basic content and purpose of the eight appendices to the standard
4Background of SSPC-PA 2Originally published in SSPC Volume 2 in 1973(T)Most recent update was 2004Editorial revision to an Appendix in 2009SSPC committee work on revisions initiated in 2007Current version dated May 1, 2012SSPC-PA2 was originally published as a temporary standard in 1973, nearly 40 years ago. At that time, the standard referenced gages like the one shown on the slide, which is now obsolete. The standard has been updated on multiple occasions – the most recent published version was May An editorial revision to one of the appendices was made in The SSPC Committee on dry film thickness measurement began revising and updating the 2004 version in The latest edition is dated May 2012 and became available in July 2012.
5Background of SSPC-PA 2Update to ASTM D concurrent with revisions to SSPC-PA 2ASTM D focuses on gage useSSPC-PA 2 (2012) focuses on acceptability of acquired measurementsBoth address ferrous and non-ferrous metal surfacesIn nearly the same timeframe, the 2005 version of ASTM D7091 on coating thickness measurement was also being revised and updated. It too was published in The most current version of the ASTM standard focuses on proper gage use, while SSPC-PA2 focuses primarily on the acceptability of the measurements. References to frequency of measurements were removed from the ASTM standard. These two documents now complement one another and are designed to be used in conjunction with one another. It is also important to note that both documents address the measurement of coating thickness on both ferrous and non-ferrous metal substrates. Prior to 2012, SSPC-PA 2 only addressed measurement of coatings on steel.
6Scope of SSPC-PA 2Describes a procedure for determining shop/field conformance to a specified DFT range on ferrous and non-ferrous metalsMeasurements are acquired using commercially available gages (two “types”)Procedures for gage calibration and verification of accuracy are describedProcedure for determining conformance to specified thickness range over extended areas is describedSSPC’s Paint Application Standard No. 2, or PA 2 is one of the most commonly specified standards for measurement of coating thickness.The standard describes procedures for measuring the thickness of non-magnetic coatings applied to ferrous and non-ferrous metal substrates. According to the standard, coating thickness measurements are obtained using two types of commercially-available gages produced by a variety of gage manufacturers across the US and overseas. Many of these gages are depicted in this webinar; however there is no intent to show favoritism of one gage over another.SSPC PA2 describes the procedures for gage calibration, verification of gage accuracy using traceable standards, gage adjustment and measurement acquisition. Finally, the standard provides a procedure for determining whether a coating or coating system conforms to the specified thickness range over extended areas of a structure.
7Scope of SSPC-PA 2Standard is not intended to prescribe a frequency of measurement for a coating failure investigationStandard contains 8 non-mandatory appendices (described later)Standard is not intended to be used for measurement of thermal spray coatings (procedure described in SSPC-CS 23.00)It is important to note that this is a quality inspection standard and is not intended to prescribe a frequency of measurement during a coating failure investigation, as the number and location of measurements may vary widely from that prescribed by this standard. Also the standard contain 8 appendices that are non-mandatory unless they are invoked by a contract document. Finally, PA 2 is not intended to be used for measuring the thickness of thermal spray coatings or metallizing. The procedure for measuring the thickness of metalized coatings is described in SSPC-CS 23.
8Definitions in SSPC-PA 2 Gage Reading: A single instrument readingSpot Measurement: The average of three or at least three gage readings made within a1 ½” diameter circleArea Measurement: The average of five spot measurements over each 100 square feet of coated surfaceThere are three terms listed in the Definitions section of PA 2. These includeGage Reading, which is a single instrument readingSpot measurement, which is the average of three or at least three gage readings made within a 1 ½” or 4 cm diameter circleArea Measurement, which is the average of 5 spot measurements over each 100 square feet of coated surface
9Gage DescriptionsGage type is determined by magnetic properties employed to measure thickness (not the read-out mode)Type 1 – Magnetic Pull-off GagesType 2 – Electronic GagesThe gage type is determined by the specific magnetic properties employed in measuring the thickness and is not determined by the mode of data readout, for example digital or analog.Type 1 gages are considered magnetic pull-off and Type 2 gages are considered electronicThe standard does not include gages that measure coating thickness on non-ferrous surfaces like concrete. Coating thickness measurement on these surfaces is described in SSPC-PA9 and ASTM D6132.
10Gage Types Type 2 – Electronic Gages Type 1 – Magnetic Pull-off Gages A variety of Type 1 magnetic pull-off gages are shown to the left, while several manufacturers of Type 2 electronic gages are shown on the right.
11Gage Types, continued Type 1 – Magnetic Pull-off Gages Permanent magnet contacts coated surfaceForce required to detach magnet is measuredForce interpreted as the coating thickness on scale or displayScale is nonlinearFor pull-off gages, a permanent magnet is brought into direct contact with the coated surface. The force necessary to pull the magnet from the surface is measured and interpreted as the coating thickness value on a scale. Less force is required to remove the magnet from a thick coating.Type 1 gages have nonlinear scales and any adjusting feature is linear in nature. Any adjustment of these gages will limit the DFT range for which the gage will provide accurate readings, and is not recommended. Furthermore, the application of a single “correction value” representing the full range of the gage to compensate for a gage that is not measuring accurately is not appropriate, since the correction will also be non-linear.
12Gage Types, continued Type 2 – Electronic Gages Electronic circuitry converts reference signal to coating thicknessA Type 2 electronic gage uses electronic circuitry to convert a reference signal into coating thickness. In general, Type 2 gages are typically more accurate that Type 1 gages, and data acquisition is typically faster. Also, most Type 2 gages can store readings and provide statistical analysis of the data, and once the data is generated and stored, it can be uploaded into a computer software program or downloaded to a printer.
13Calibration & Verification of Accuracy ASTM D7091 describes 3 operational steps to ensure accurate measurement:CalibrationVerification of AccuracyAdjustmentSteps are required to be completed before coating thickness data acquisition to determine conformance to a specificationThe ASTM D7091 standard practice describes three steps associated with assuring accurate measurement processes, including gage calibration, verification of accuracy and adjustment. Each of these steps must be completed before coating thickness measurements are acquired to determine conformance to a coating specification
14Gage CalibrationPerformed by the gage manufacturer or qualified laboratoryCertificate of calibration traceable to a National Metrology Institute requiredNo standard calibration interval (established based on experience & work environment)One year interval is commonCoating thickness gages must be calibrated by the manufacturer or a qualified lab. A Certificate of Calibration or other documentation showing traceability to a national metrology institute is required. There is no standard time interval for re-calibration, nor is one absolutely required. Calibration intervals are usually established based upon experience and the work environment. A one-year calibration interval is a typical starting point suggested by gage manufacturers.
15Verification of Type 1 Gage Accuracy Performed as described in ASTM D7091Beginning and end of each work shift (minimum)During (e.g., hourly), if:Obtaining a large no. of readingsGage is dropped or readings are suspectRecord:Serial no. of gage & standardStated & measured thicknessMethod used to verify accuracyTo verify the accuracy of Type 1 gages, measure the thickness of a series of reference standards covering the expected range of coating thickness. To prevent acquiring measurements with an inaccurate gage, the gage is checked at least at the beginning and the end of each work shift with one or more of the reference standards. If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy must be rechecked.When documenting gage adjustment processes, record the serial number of the gage, the reference standard used, the stated thickness of the reference standard as well as the measured thickness value obtained, and the method used to verify gage accuracy. If the same gage, reference standard, and method of verification are used throughout a job, they only need to be recorded once. The stated value of the standard and the measured value must be recorded each time accuracy is verified.Shims of plastic or of non-magnetic metals which are acceptable for verifying the accuracy of Type 2 electronic gages are not to be used for verifying the accuracy of the Type 1 gages.
16Verification of Type 1 Gage Accuracy Most Type 1 gages cannot be “adjusted”Adjustments to the helical spring may void the gage warrantyCombined 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: √On a 10 mil reference standard, the gage reading can range from milsMost Type 1 gages cannot and should not be adjusted. Any adjustments made to the helical or wound spring within the first year can void the warranty on the gage.The gage can be verified for accuracy using a reference standard. The combined tolerance of the gage and reference standard is used to verify gage accuracy. For example if the accuracy of the gage is 5% and the accuracy of the reference standard is 3%, the combined tolerance of approximately 6%, as calculated by using the square root of the sum of both accuracies, squared. On a 10 mil reference standard, the gage reading can range from mils and still be considered accurate. If it is outside of this range the gage should be tagged and taken out of service until it is repaired.
17Correction for Surface Roughness Base Metal Reading (BMR)Effect of surface roughness on coating thickness gageNOT surface profileMeasure the prepared, uncoated substrate; calculate average BMRDeduct BMR from measured coating thicknessThe specified dry film thickness of each coating layer is measured from the tops of the peaks of the surface profile. This is depicted by the thick yellow bar on the slide. However, most coating thickness gages must reach down into the surface roughness to satisfy the magnetic properties of the gage. This is depicted by the thin yellow line part way down into the profile on the slide. As a result, the effect of the surface profile on the thickness gage must be measured and subtracted from the coating thickness measurement. This is known as a base metal reading or BMR, which is depicted by the gap between the thick yellow bar and thin yellow line on the illustration.Once the Type 1 thickness gage is verified for accuracy, the next step is to measure and record the Base Metal Reading or BMR. This is accomplished by placing the gage magnet on the prepared, uncoated substrate and obtaining a measurement. The BMR will vary widely, ranging from 0.1 mil to over 1 mil. Therefore, the user should take a minimum of 10 measurements of the base metal and calculate the average. The average BMR is subtracted from the thickness of each coat, in order to assess the thickness of the coating film above the peaks of the surface profile.The BMR is the effect of surface roughness on a coating thickness gage – it is not surface profile. There is no correlation between surface profile depth and the effect of this roughness on a coating thickness gage). It is the BMR and not the surface profile that is deducted from the coating thickness. Also, the gage is never adjusted to zero on the uncoated surface.BMR
18Correction for Surface Roughness AreaBMR130 µm (1.2 mils)225 µm (1.0 mils)318 µm (0.7 mil)413 µm (0.5 mil)520 µm (0.8 mil)68 µm (0.3 mil)725 µm (1.0 mil)828 µm (1.1 mils)923 µm (0.9 mil)10Measuring Base Metal Effect with Type 1 DFT GageA base metal reading is calculated by randomly measuring a number of locations on the structure, then averaging all of the values. In this example, 10 base metal measurements were acquired ranging from 0.3 to 1.2 mils for an average of 0.8 mil.Average BMR: 21 µm (0.8 mil)
19BMR Correction for Multiple Coat Systems Measured Primer Thickness: µm (4.0 mils)BMR: µm (0.5 mils)Actual Primer Thickness: µm (3.5 mils)Measured Primer + Finish Thickness: 178 µm (7.0 mils)Actual Total System Thickness: µm (6.5 mils)Coating thickness measurements are corrected for the base metal reading independent of which layer or layers is being measured. For example, if the measured primer thickness is 4 mils and the base metal reading was 0.5 mil, the actual primer thickness above the peaks of the surface profile is 3.5 mils.Continuing with the example depicted on the slide, if the measured primer & finish coat thickness is 7 mils, the base metal reading remains 0.5 mil, so the actual system thickness above the peaks of the surface profile is 6.5 mils.
20Correction for Surface Roughness What if access to blast cleaned steel is not available (already coated)?Appendix A8.3 addresses smooth surface adjustmentVerify gage accuracy on a smooth surface (per gage manufacturer instructions)Deduct “assumed” approximate correction value from each gage reading (see Table A8)If access to the bare blast cleaned substrate is not available because the coating already covers it, a smooth surface can be used to adjust the gage. The procedure for this is described in Appendix A8.3 of the standard.First, verify the accuracy of the gage on a smooth reference standard.Subsequent measurements of coating thickness taken on the blast cleaned substrate will be higher than the true value by an amount dependant on the surface profile and the gage probe design. Therefore an assumed correction value to compensate for the base metal effect must be subtracted from each gage reading to correct for the effect of the surface roughness. The resulting corrected reading represents the thickness of the coating over the peaks.Table A8 in the appendix to the standard provides some guidance on the assumed amount to be deducted, depending on the coarseness of the surface profile.
21Correction for Surface Roughness Table A8 Typical Gage Correction Values Using ISO 8503 Profile GradesISO 8503 Profile GradeCorrection Value (µm)Correction value (mils)Fine100.4Medium251.0Coarse401.6Table A8 illustrates typical gage correction values that can be applied to coating thickness measurements when the true effect of the base metal cannot be measured. For fine profiles, for example 1-2 mils, a correction factor of 0.4 mil may be appropriate.For medium profiles, for example mils, a correction factor of 1 mil may be appropriate.For coarse profiles, for example 4-5 mils, a correction factor of 1.6 mils may be appropriate.
22Verification of Type 2 Gage Accuracy Verify accuracy per manufacturer instructions (use traceable standards)Performed as described in ASTM D7091Beginning and end of each work shift (minimum)During (e.g., hourly), if:Obtaining a large no. of readingsGage is dropped or readings are suspectRecord:Serial no. of gage & standardStated & measured thicknessAs we described previously, you should always verify the accuracy of the gage according to the manufacturer’s instructions.To prevent acquiring measurements with an inaccurate gage, the gage is checked at least at the beginning and the end of each work shift with one or more of the shims or reference standards. If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy must be rechecked.
23Verification of Type 2 Gage Accuracy Single Point VerificationSelect one reference test block representing the mid-range of the anticipated coating thicknessE.g., 4-6 mils ( µm), select 5 mil (125 µm) reference standardTw0 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 standardsWhen verifying the accuracy of Type 2 gages, the user can employ a single point or two-point process.For single point verification, a single reference test block is selected which is at or close to the thickness to be measured. The thickness range over which this adjustment achieves the required accuracy will vary with gage design.Assuming that the coating thickness to be measured is 4-6 mils, a reference standard of approximately 5 mils should be used verify gage accuracy. For two point verification, two reference standards are selected - one above and one below the expected film thickness to be measured.Assuming that the coating thickness to be measured is 5 mils, then reference standards of 3 mils and 7 mils are appropriate for establishing a range of accuracy.This same approach can be applied to Type 1 gages, except that plastic shims or foils cannot be used.
24Adjustment 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 rangeCorrects for:Surface RoughnessSubstrate PropertiesCurvatureEtc.The final step in verifying gage accuracy is to align the Type 2 gage to a known value to improve gage accuracy on the specific type and design of surface or within a specific measurement range. Some refer to this step as gage optimization.In this case, the gage is adjusted to match the shim or foil thickness by placing a shim or foil of known thickness directly onto the prepared, uncoated structure or part under the same conditions of air and surface temperatures that the coating will be measured under. This also compensates for curvature of the component or structure, the alloy of the steel, proximity to edges or other surface conditions.
25Adjustment of Type 2 Gages Addressed in Appendix 8Follow the gage manufacturers step-by-step procedures for gage adjustmentInstructions vary by gage manufacturerAdjustment is typically performed using plastic shims (foils) of known thicknessAppendix 8 in the new PA2 standard discusses Type 2 gage adjustment. The step-by-step procedures for verifying gage accuracy vary widely between gage manufacturers. It is beyond the scope of this webinar to describe each; however the user should carefully follow the manufacturers instructions when verifying gage accuracy and when making adjustments to the gage. Most Type 2 gages can be verified for accuracy using reference standards or plastic shims. Use of plastic shims is more economical, as most gage manufacturers supply a set of shims with their gage. If needed, calibrated shims are available from many gage manufacturers.
26Measurement Frequency This is where we leave ASTM D7091 and focus solely on SSPC-PA 2, which describes the frequency of coating thickness measurements.The figure shown on the slide was extracted from SSPC PA 2. It illustrates three gage readings taken in each of 5 spots in an area of approximately 100 square feet. The average of the three gage readings in each of the 5 spots has been calculated.
27Measurement Frequency For areas of coating not exceeding 300 square feet, (~30 square meters) each 100 square feet (~10 square meters) is measuredFor areas of coating exceeding 300 square feet and not exceeding 1000 square feet, arbitrarily select 3 random 100 square foot (~10 square meter) areas and measureThe number of areas that are measured is based on the size of the coated areas. This is different than the 2004 version, which based the frequency on the size of the structure as opposed to the size of the area coated.For areas of coating not exceeding 300 square feet, each 100 square foot area is measured. As a result, the maximum number of areas to be measured will be 3.For areas of coating greater than 300 square feet but not exceeding 1000 square feet, three 100 square foot areas are arbitrarily selected and measured.
28Measurement Frequency For areas of coating exceeding 1000 square feet (~100 square meters), arbitrarily select square feet (~10 square meter) areas for the first 1000 square feet (~100 square meters), and 1 additional 100 square foot(~10 square meter) area for each additional 1000 square feet (100 square meters), or increment thereofFor areas of coating exceeding 1000 square feet, three 100 square foot areas are measured in the first 1000 square. For each additional 1000 square feet or portion thereof, one additional 100 square foot area is arbitrarily selected and measured.Other size areas or number of measurements may be specified by the owner in the job specifications.
29Measurement Frequency The figure on this slide illustrates the frequency of coating thickness measurements on large, flat coated steel plates. This figure is not in the standard. The top third of the figure indicates the measurement frequency based on a coated area less than or equal to 300 square feet. The middle third of the figure indicates the measurement frequency based on a coated area greater than 300 square feet and less than or equal to 1000 square feet. The bottom third of the figure indicates the measurement frequency based on a coated area that is greater than 1000 square feet.
30Measurement Frequency Example 1 (US Standard) Size of Coated Area: 900 square feetNo. of Areas: 3 areasNo. of Spots: 3 Areas x 5 Spots/Area = SpotsMinimum No. of GageReadings: 15 Spots x 3 Readings/Spot = Gage ReadingsIn Example 1, the coated area is approximately 900 square feet. As a result, three 100 square foot areas are arbitrarily selected and measured. This culminates in the acquisition of a minimum of 45 gage readings acquired from 15 spots.
31Measurement Frequency Example 2 (US Standard) Size of Coated Area : 55,000 square feetNo. of Areas: = 57 areasNo. of Spots: 57 Areas x 5 Spots/Area = SpotsMinimum No. of GageReadings: Spots x 3 Readings/Spot = Gage ReadingsIn Example 2, the coated area is approximately square feet. As a result, three 100 square foot areas are arbitrarily selected and measured in the first 1000 square feet, then one additional 100 square foot area is arbitrarily selected and measured in each additional 1000 square foot area, for a total of 57 areas . This culminates in the acquisition of a minimum of 855 gage readings acquired from 285 spots.
32SSPC-PA 2 Measurement Specifications Built Into Type 2 Gages Many manufacturers have programmed the measurement frequencies into the software supplied with the gages. This is illustrated on the slide. Measurement specifications is selected from the menu, which reveals four submenu choices – one of which is SSPC-PA 2.
33SSPC-PA 2 Measurement Specifications Built Into Type 2 Gages Continuing with the illustration, once SSPC-PA 2 is selected from the submenu, the number of readings per spot and the number of spots per coated area can be selected. The upper and lower limits for the thickness of the coating in each area can also be entered, in this case 8 to 12 mils.
34Conformance to Specified Coating Thickness Specifications normally indicate the range of coating thickness (e.g., 5-7 mils), not as a single value (e.g., 5 mils)When a single thickness value is specified and no range is indicated by manufacturer:Range established at +/-20% of stated thickness valueE.g., 7 mils is milsProperly prepared coating specifications will provide the contractor with a coating thickness range for each coating layer, since it is essentially impossible to apply a coating to achieve a single thickness value. That is, if 6 mils is the target thickness, the specifier should allow a range of 5 to 7 mils If a coating thickness range is not specified and no range is indicated by the coating manufacturer, then SSPC-PA 2 establishes the range as plus-minus 20% of the stated value. For example, if the specifier and manufacturer require 7 mils thickness, 5.6 mils to 8.4 mils becomes the acceptable range for the coated area.
35Table 1 Coating Thickness Restriction Levels Gage ReadingSpotReadingArea MeasurementLevel 1MinimumUnrestrictedAs specifiedMaximumLevel 2120% of maximumLevel 380% of minimumLevel 4150% of maximumLevel 5The 2012 version of PA 2 contains a table of coating thickness restriction levels for gage, spot and area measurements. Five levels are includedLevel 1 is the most restrictive and does not allow for any deviation of spot or area measurements from the specified minimum and maximum thickness, while Level 5 is the least restrictive, allowing unrestricted maximum thickness of the gage, spot and area measurements. Depending on the coating type and the prevailing service environment, the specifier can select the dry film thickness restriction level for a given project. For example, a maintenance coating project may invoke Level 4, which allows the coating to be 50% higher than the maximum specified thickness, provided the area measurement falls within specification. If no restriction level is specified, then Level 3 is the default. Note that Level 3 allows the spot measurements to be lighter or heavier than specified by 20%, and the average of the 5 spots, the area measurement, must be within specification. This spot measurement tolerance was in the 2004 version of the standard.Note: If unspecified, Level 3 is the default
36Measurement Tolerance EXAMPLE 1:Target DFT: 4-6 milsCoating Thickness Restriction Level 3 (default)Individual gage readings unrestrictedSpot measurements must be between 3.2 mils and 7.2 milsArea measurement must be between 4 and 6 milsIf spot or area measurements are out of tolerance, the magnitude of the nonconforming thickness must be determined and demarcated.In this example the specified coating thickness is 4 to 6 mils. The individual gage reading that are obtained are unrestricted. The average of the gage readings – the spot measurements can range between 3.2 and 7.2 mils, which is 80% of 4 mils and 120% of 6 mils. The average of the five spot measurements – the area measurement must be between 4 and 6 mils.If spot or area measurements are outside of the allowable tolerance, the magnitude of the non-conforming area must be determined and the area demarcated. This will be explained later.
37Measurement Tolerance EXAMPLE 2:Target DFT: 4-6 milsCoating Thickness Restriction Level 2Individual gage readings unrestrictedSpot measurements must be between 4 mils and 7.2 milsArea measurement must be between 4 and 6 milsIf spot or area measurements are out of tolerance, the magnitude of the nonconforming thickness must be determined and demarcated.In this example the specified coating thickness is 4 to 6 mils. The individual gage reading that are obtained are unrestricted. The average of the gage readings – the spot measurements can range between 4 and 7.2 mils since Level 2 only allows 20% error on the maximum thickness and not the minimum. The average of the five spot measurements – the area measurement must be between 4 and 6 mils.
38SSPC-PA 2 Measurement Specifications Built Into Type 2 Gages Many manufacturers have programmed the measurement tolerances into the software supplied with the gages. This is illustrated on the slide. Once the number of gage readings, spot measurements and areas are entered as shown in the upper left, and the minimum and maximum thicknesses are populated, as shown in the upper right, the gage can calculate 80% of the minimum and 120% of the maximum thickness, or 6.4 to 14.4 mils in this example, which is also shown in the upper right. Audible and visual indicators alert the user when spot or area measurements are outside of the established tolerances.Audible and/or visual indicators if spot readings are out of tolerance
39Determining the Magnitude of a Nonconforming Area Obtain spot measurements at 5 foot intervals in 8 equally spaced directions radiating out from the nonconforming area up to the limit of area coated during the work shiftEach spot must conform to requirementsWhen 2 consecutive spots conform to requirements, measuring can stopArea within 5 feet of any nonconforming measurement is suspect and must be re-inspected after correctionRepeating structural units or parts – 1 spot measurement on each unitRepeat until spot readings on 2 consecutive units conformOne of the most significant changes to SSPC-PA 2 was the procedure used to determine the magnitude of a non-conforming area. In 2004, when an area did not conform, the standard required that each 100 square foot area coated during the shift be measured to determine how bad the problem was. If 8000 square feet were coated during a shift, then 80 areas, comprised of 400 spot measurements and 1200 gage readings would have to be acquired, analyzed and the defective areas demarcated for potential rework, which could severely impede production and the project schedule.Recognizing this problem, the committee put forth a considerable effort to create a better approach that would still properly address deficient or excessive film builds. When a defective area is discovered, additional spot measurements at 5 foot intervals are made in 8 directions radiating outward from the nonconforming area, up to the limit of the area coated during the work shift. Each spot must conform the specified thickness, not the allowable spot tolerance. When 2 consecutive spots conform, measuring can stop in that direction. Any area within 5 feet of a nonconforming measurement is considered suspect and must be re-inspected after corrective measures have occurred.For repeating structural units or parts, one spot measurement is made on each unit and the process repeated until the spot readings on 2 consecutive units conform to the specification.
40Initial Nonconforming 100 ft2 Area Dashed line indicates boundary of area painted during work shiftOKOKSTOPSTOPOKSTOPOKNO5 ft5 ft5 ftSuspect area preceding a nonconforming spot must be re-measured after corrections are madeOKOK5 ft5 ft5 ftDashed line indicates boundary of area painted during work shiftDashed line indicates boundary of area painted during work shiftOKSTOP5 ftSTOPOKNO5 ftInitial Nonconforming 100 ft2 Area5 ft(Limit of area coated during work shift)OKSTOPThis slide was developed by SSPC to illustrate the procedure used to determine the magnitude of nonconforming thickness. The initial nonconforming area is shown, which triggered a more thorough inspection of the surrounding coated area. Additional spot measurements were obtained in eight directions radiating outward from the defective area. Each arrow represents approximately 5 linear feet. Once two consecutive spots conformed to the specification, measurement acquisition stopped as shown in the 12:00, 2:00, 8:00, 9:00 and 10:00 positions. Note that only one spot measurement was acquired at the remaining 3 positions, 3:00, 4:00 and 6:00, since the boundary was established by the area coated during the work shift.5 ft5 ft5 ftOK(Limit of area coated during work shift)5 ftOK(Limit of area coated during work shift)STOPSTOPDashed line indicates boundary of area painted during work shiftMegaRust 2008
41SSPC-PA 2 AppendicesNumerical Example of Average Thickness MeasurementMethods for Measuring DFT on Steel Beams (Girders)Methods for Measuring DFT for a Laydown of Beams, Structural Steel & Misc. Parts after Shop CleaningMethod for Measuring DFT on Coated Steel Test PanelsThere are eight appendices to the SSPC PA2 standard. None of the appendices are mandatory unless they are invoked by the contract documents for a project. They include (read). Note that we will be focusing on Appendices 2-7, since the basic content of Appendices 1 and 8 have already been described.
42SSPC-PA 2 Appendices, cont. Method for Measuring the DFT of Thin Coatings on Coated Steel Test Panels that Have Been Abrasive Blast CleanedMethod for Measuring the DFT of Coatings on EdgesMethod for Measuring the DFT of Coated Steel Pipe ExteriorExamples of the Adjustment of Type 2 Gages Using ShimsNew
43Appendix 2: Measuring Coating Thickness on Steel Beams (Girders) Full DeterminationSample DeterminationBeams < 20 ft (<6 m)Beams 20 ft - 60 ft (6 m-18 m)Beams > 60 ft (> 18 m)Coating Thickness Restriction Level 3 (default)The average of all spot measurements (per area) must conform to specified rangeMeasurement locations on stiffeners arbitrarily selectedAppendix 2 of the standard provides a frequency for measuring coating thickness on steel beams or girders. A full determination and sample determination are described. The sample determination is based on two lengths of steel beams – those that are less than 20 feet and those that range from 20 feet up to 60 feet.The tolerance of each of the spot measurements is the default restriction level, which is 80% of the minimum specified thickness and 120% of the maximum specified thickness. Similarly, the average of all of the spot measurements must conform to the specified thickness range.The measurement locations on stiffeners are arbitrarily selected.Stiffener
44Appendix 2: Measuring Coating Thickness on Steel Beams (Girders) Full DeterminationDivide beam into 5 equal sections along the lengthWeb > 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)For a full determination, the total length of the beam is divided into five equal sections. For example, a beam that is 75 feet long is divided into five 15 foot sections.For steel beams fabricated with a web that is greater than or equal to 36” in height, one spot measurement is acquired in each of 14 locations per section, for a total of 70 spot measurements. Each spot measurement is the average of at least three gage readings.For steel beams fabricated with a web that is less than 36” in height, one spot measurement is acquired in each of 12 locations per section, for a total of 60 spot measurements. Again, each spot measurement is the average of at least three gage readings.
45Full DeterminationThe figure in the slide illustrates the locations of the spot measurements for a full determination based on two web sizes. Note that for the larger beam, two spot measurements are taken on either side of the web verses just one spot measurement on either side of the smaller beam. The flange edges or toe may not be measured depending on the thickness of the flange, and the top of the top flange may not be accessible or may not be required to be fully coated in the shop.Note: Areas 2, 6, 8 and 12 (Toe) may not be measured.The top of the top flange may not be accessible
46Appendix 2: Measuring Coating Thickness on Steel Beams (Girders) Sample DeterminationBeam length < 20 ft: Obtain 2 spot measurements randomly distributed in all 12 areas (total of 24 spot measurements)Beam length ft: Obtain 3 spot measurements randomly distributed in all 12 areas (total of 36 spot measurements)When performing a sample determination, the number of spot measurements is based on the beam length. For beam lengths less than 20 feet, two spot measurements randomly distributed in all twelve areas, or a total of 24 spot measurements are acquired. The 12 locations were illustrated in the previous figure. For beam lengths between 20 and 60 feet, three spot measurements randomly distributed in all twelve areas, or a total of 36 spot measurements are acquired. Again, each spot measurement is the average of at least three gage readings, and the edges of the flanges may not be included, reducing the overall number of spot measurements.Note: If toe areas are not included, measure in 8 areas (16 or 24 spot measurements)
47Appendix 3: Measuring Coating Thickness on Laydown of Beams Laydown: Group of steel members laid down to be painted in one shift by one applicatorFull DFT DeterminationBeams (girders)Miscellaneous partsSample DFT DeterminationBeams < 20 ft (6 m)Beams 20 ft - 60 ft (6 m-18 m)Appendix 3 of SSPC PA2 describes a process for measuring coating thickness on laydowns in a shop. A laydown is considered a group of steel members laid down to be coated in one shift by a single applicator. A full dry film thickness determination or sample dry film thickness determination can be performed on beams.
48Appendix 3: Measuring Coating Thickness on Laydown of Beams Full DFT DeterminationBeams: Same procedure described earlierMiscellaneous parts: 1 spot measurement per “surface” (minimum of 5 spots)Spot measurement tolerance Level 3 (80% of minimum and 120% of maximum) is the defaultThe average of all spot measurements (per area) must conform to specified rangeFor a full dry film thickness determination on steel beams, the number of spot measurements is dependent on beam length as described previously.For miscellaneous parts, one spot measurement is obtained on each surface of the part. If the part has fewer than five surfaces, multiple spot measurements are acquired on the larger surfaces to bring the total to five. If the total area of the part is over 100 square feet, 5 spot measurements are taken which are randomly distributed over the part for each 100 square feet or portion thereof.If Coating Thickness Restriction level 3 is invoked (or is the default), then no single spot measurement can be less than 80% of the specified minimum dry film thickness and no single spot measurement can be more than 120% of the specified maximum dry film thickness. The average value of the spot measurements on each surface must conform to the specified dry film thickness. If there is only a single spot measurement on a surface, it must conform to the specified dry film thickness.
49Appendix 3: Measuring Coating Thickness on Laydown of Beams Sample DFT DeterminationBeams: Same procedure described earlierMiscellaneous parts: 3 spot measurements per partSpot measurement tolerance Level 3 (80% of minimum and 120% of maximum) is the defaultThe average of all spot measurements (per area) must conform to specified rangeFor a sample dry film thickness determination on steel beams, the number of spot measurements is dependent on beam length as described previously.For miscellaneous parts, three spot measurements randomly distributed on the part are obtained. Each spot measurement must conform to the specified dry film thickness.
50Appendix 4: Measuring Coating Thickness on Test Panels Minimum panel size: ” x 6” (7.5 x 15 cm)Maximum panel size: ” x 12” (30 x 30 cm)Use Type 2 gageTwo gage readings from top, middle and bottom thirdAt least 0.5” from edge and 1” from other readings80% min. & 120% max. applies to gage readings1234Appendix 4 in SSPC PA2 describes a procedure for measuring coating thickness on test panels. The frequency of measurements is based on a minimum panel size of 3” x 6” and a maximum size of 12” x 12”. Using a properly adjusted Type 2 electronic gage, two gage readings are obtained from the top, middle and bottom thirds of each coated panel. Each gage reading should be ½” from any panel edge and at least 1” from any other gage reading.Each gage reading must be within 80% of the minimum specified coating thickness and within 120% of the maximum coating thickness. The average of the six gage readings must fall within the specified thickness range.56
51Appendix 5: Measuring Thickness of Thin Coatings on Abrasive Blast Cleaned Test Panels “Thin” is considered 1 mil (25.4 µm) or lessObtain 10 gage readings from each of three “zones”Calculate the mean and standard deviation in each zoneThe mean of all three zones is the coating thickness10 gage readings10 gage readingsThe procedure described in Appendix 5 for measuring thin-film coatings of 1 mil or less applied to blast cleaned steel is more rigorous.Using a properly adjusted Type 2 electronic gage, ten gage readings are randomly acquired from the top third of the panel. The average and standard deviation of the ten readings are computed. Similarly, ten readings from the middle third and ten readings from the bottom third of the test panel are obtained and the average and standard deviation are computed for these areas. If test panels smaller than 4” x 9” are used, the measurements are taken at least one-half inch from any edge. For test panels that are 4” x 9 inches and larger, readings are taken at least one-half inch from any edge and at least one inch from any other gage reading. Any unusually high or low gage reading can be discarded. The dry film thickness of the coating on the test panel is the average of the three zones.10 gage readings
52Appendix 6: Measuring Thickness on Edges Gage probe configurations less affected by edge proximityConsult gage manufacturerSSPC Guide 11 (discusses edge retentive coatings)Verify probe will measure using shim placed on edgeMinimum 3 readings within 1.5 linear inches along edge (“spot”)Number of “spots” will varyTraditionally we have been taught to stay at least 1” away from all edges when measuring coating thickness. However, coating build on edges, known as edge retentiveness is a concern particularly in immersion environments. And many gage manufacturers now produce micro probes for measuring coating thickness on small parts, as these probes are less affected by proximity to edges.Appendix 6, which was added to SSPC-PA 2 this year describes a procedure for measuring coating thickness on edges and SSPC Guide 11 discusses edge retentive coatings. Before measuring coating thickness on edges, you should consult with the gage manufacturer to make certain of the application, then verify the accuracy of the probe on an edge using a known thickness, such as a shim. If the probe operates correctly and edge measurements are possible, Appendix 6 suggests a minimum of three gage readings along 1.5 linear inches, which is equivalent to a spot measurement. The number of spots will vary depending on the total length of the edge.
53Appendix 7: Measuring Thickness on Coated Steel Pipe Exterior Pipe sections on cart or rack considered a complete unitArea = (length of each pipe x circumference) x no. of pipe sections on cartAlternative: Pipe DFT Level 1 Area through Level 5 AreaEg., Level 2 Area is (length of each pipe x circumference) x no. of pipe sections on cart = (no. of spot measurements) x 3Appendix 7, which was also added to SSPC-PA 2 this year describes a procedure for measuring coating thickness on the exterior of pipe. Pipe sections on a cart or a rack are considered a complete unit. To determine the total area, multiply the length of each pipe by the circumference, then multiply that by the number of pipe sections on the cart.Alternatively, five pipe DFT Area Levels are pre-defined and can be implemented. For example, if Level 2 area is invoked, multiply the length of each pipe by the circumference, then multiply that by the number of pipe sections on the cart. This will equal the number of spot measurements, which is then multiplied by 3.
54Appendix 7: Measuring Thickness on Coated Steel Pipe Exterior Pipe spools measured individuallyTable A7 describes frequencyPipe spools < 10 ft: 3 sets of circumferential spot measurementsPipe spools are measured individually. Table A7 describes the frequency and location of the spot measurements and is dependent on the diameter of the pipe.For pipe diameters up to 12 inches, 4 evenly spaced circumferential spot measurements are taken at 10 foot intervals; for example 12:00, 3:00, 6:00 and 9:00.For pipe diameters ranging from 14 to 24 inches, 6 evenly spaced circumferential spot measurements are taken at 10 foot intervals; for example 12:00, 2:00, 4:00, 6:00, 8:00 and 10:00. For pipe diameters greater than 24 inches, 2 additional spot measurements, for a total of 8 spots are taken at 10 foot intervals.For pipe spools less than 10 feet in length, 3 sets of spot measurements are obtained. The number spots is dependent upon the pipe diameter.Table A7Pipe DiameterCircumferential Spot MeasurementsInterval SpacingUp to 12 inch (30 cm)4 evenly spaced10 ft (3 m) apart14-24 inches (36-60 cm)6 evenly spaced> 24 inches (60 cm)8 evenly spaced
55Summary Background of SSPC-PA 2 Overview and Purpose of SSPC-PA 2 (2012)Purpose of ASTM DDefinitionsGage DescriptionsCalibration & Verification of AccuracyMeasurement ProceduresFrequency and Number of MeasurementsConformance to Specified ThicknessContent of Eight AppendicesIn summary, we have described:The background of the standard and reasoning for the change in title and contentThe purpose of SSPC’s dry coating thickness standardThe purpose of ASTM’s standard practice for coating thickness measurementA few basic definitions listed in the standardGage descriptions, including calibration, verification of accuracyThe measurement acquisition processThe number of gage, spot and area measurements to obtainHow far out of specification the measurements are permitted to be, or the tolerance of the acquired measurements, andThe content of 8 appendices to the standard
56Complying with SSPC-PA 2, Procedure for Determining Conformance to Dry Coating Thickness RequirementsTHE ENDThank you for attending his one-hour webinar on complying with the newest version SSPC Paint Application Standard No. 2. I’ll turn the presentation back over to Josiah for questions.