Measuring Dry Film Coating Thickness According to SSPC-PA 2

THIS ARTICLE HAS BEEN UPDATED WITH THE REVISED STANDARDS FOR 2015:

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Coating thickness shall be measured in accordance with SSPC: The Society for Protective Coatings Paint Application Standard No. 2 (SSPC-PA 2) is a simple enough statement, yet this common specification requirement is often misinterpreted or regarded as a document that simply states how to measure the dry film thickness (DFT) of coatings, something we already profess to know how to do. Yet the requirements of SSPC-PA 2 regarding gage calibration, verification of gage accuracy and adjustment procedures, the number of measurements to obtain, and the tolerance of the measurements are complex and should be fully understood by the specification writer before invoking PA 2 in a contract.


Step 1: Instrument Calibration
On more than one occasion, I have heard the question, “When did SSPC-PA 2 and dry film thickness measurement become so complicated?” In fact, when you take a close look, measuring DFT isn’t that complex. We have allowed it to become more technologically complex while making the data easier to analyze. We can gather hundreds of gage readings in a relatively short time; batch the measurements; print the data or upload it to a computer for graphing; report the highest, the lowest, the mean, and standard deviation of the collected data; incorporate digital images of the structure or coated area; and even program the gage to produce an audible signal if a spot measurement is outside of the tolerance range. I am no doubt leaving out other bells and whistles, but my point is that while we are able to do a lot with the readings obtained, measuring DFT involves four or five basic steps.

  • Step 2: Verification of Gage Accuracy on Certified Coated Standards or Certified Shims
  • Step 3: Base Metal Reading Acquisition or Gage Adjustment (using certified or measured shims)
  • Step 4: Measurement of Coating Thickness
  • Step 5: Correction for Base Metal Reading (if acquired).

After a brief review of the history of SSPC-PA 2, this article will describe each of the five steps, based on the 2012 edition of SSPC-PA 2. Special attention will be given in the article to how PA 2 addresses the required number of coating thickness measurements; the acceptability of gage readings, spot measurements, and area measurements; nonconforming thickness; measuring DFT on coated edges; and measuring DFT on pipe exteriors.

Some History

SSPC-PA 2 was originally published as a temporary standard 40 years ago in 1973 (73T) as “Measurement of Dry Coating Thickness with Magnetic Gages.” The standard referenced gages like the one shown in Fig. 1, which are now all but obsolete. The standard has been updated on multiple occasions. Until 2012, the most recent technical changes were published in May 2004, with a minor editorial revision in 2009 to one of the appendices (regarding measurements on test panels). The SSPC Committee on Dry Film Thickness Measurement began revising and updating the 2004 version in 2007. The revisions took five years to complete. The latest edition of the standard (“Procedure for Determining Conformance to Dry Coating Thickness Requirements”) is dated May 2012 and was made available to the industry in July 2012.

magnetic gage sspc-pa 2
Fig. 1: One type of magnetic gage referenced in original SSPC-PA 2 for measuring dft Figures courtesy of the author except where otherwise indicated

In nearly the same timeframe, the 2005 version of ASTM D7091, “Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to NonFerrous Metals” was being revised and updated. It, too, was published in 2012. The most current version of the ASTM standard focuses on proper gage use, while SSPC-PA 2 focuses primarily on the frequency of measurements and the acceptability of the acquired measurements. References to the frequency of measurements were removed from the ASTM standard. The two documents are designed to be used together. It is important to note that both documents address the measurement of the DFT of coatings on ferrous and non-ferrous metal substrates. Before 2012, SSPC-PA 2 addressed measurement of coatings only on steel, a ferrous metal. (The sidebar on p. 32 in this article summarizes the key changes made to PA 2 in 2012.)

Summary of Changes to SSPC-PA 2: 2004 Version and 2012 Version

20042012
“Measurement of Dry Coating Thickness with Magnetic Gages”“Procedure for Determining Conformance to Dry Coating Thickness Requirements”
Addressed measurement of coatings on steel onlyAddresses measurement of coatings on ferrous and non-ferrous metal surfaces
No referenced standards sectionASTM D7091 and SSPC Guide 11 included by reference
Definitions section included Calibration; Verification; Adjustment; Coating Thickness Standard; Shim (foil); Dry Film Thickness Reference Standard; Accuracy; Structure.Definitions section includes Gage Reading, Spot Measurement and Area Measurement only. All definitions related to gage calibration, accuracy and adjustment are incorporated by reference in ASTM D7091. Spot measurement definition was expanded.
No. of “Area Measurements” based on the size of the structureNo. of “Area Measurements” based on the size of the area of coated surface
Isolation of nonconforming areas required measurement of each 100 square foot area painted during the work shift.The magnitude of nonconforming thickness assessed by obtaining spot measurements in eight equally spaced directions radiating outward from the nonconforming area
Recommended specifying minimum & maximum thickness range; if no range was specified, thickness value was considered minimum (with no maximum)If a single value is specified and the coating manufacturer does not recommend a range, the minimum and maximum thickness range is established at ±20% of the stated value
Contained a minimum gage accuracy requirement to qualify for useNo minimum gage accuracy requirement to qualify for use
Conformance to Specified Thickness:
Gage Readings: Unrestricted
Spot Measurements: ± 20% of specified range
Area Measurements: Per Specification
Conformance to Specified Thickness:
Five different Coating Thickness Restriction Levels established. If no Restriction Level is specified, default is based on 2004 conformance requirement.
Notes section contained principles of gage operation and various substrate/surface conditions that may affect measurements; overcoating; and correcting for low/high thickness.Notes section includes Overcoating and Correcting for Low/High Thickness only ASTM D7091 describes principles of gage operation and various substrate/surface conditions that may affect measurements.
Contained 6 appendicesContains 8 appendices. Six appendices from 2004 version included. Added two:

  • Method for Measuring DFT of Coating on Edges
  • Method for Measuring DFT of Coated Steel Pipe Exterior

Gage Types

SSPC-PA 2 addresses two types of DFT gages, both of which are supplied by a variety of manufacturers. Magnetic pull-off gages are categorized as Type 1 (Fig. 2).

magnetic dft gage sspc-pa 2
Fig. 2: Example of magnetic DFT gage categorized as Type 1 in SSPC-PA 2

These gages were designed in the 1950s. While their use has declined, they are still readily available and used by some. For these 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 converted to coating thickness, which is displayed on a scale on the gage. The operating principle is simple. Less force is required to remove the magnet from a thick coating, while more force is required to remove the magnet from a thinner one. The scale is not linear, as will be discussed below.

Electronic gages are categorized as Type 2 (Fig. 3). These gages use electronic circuitry to convert a reference signal into coating thickness and are more popular than Type 1 gages. They are typically regarded to be faster, more accurate, and easier to use.

electronic dft gage
Fig. 3: Example of electronic DFT gage categorized as Type 2 in SSPC-PA 2

Gage Calibration, Accuracy Verification, and Adjustment

To help assure the reliability of the coating thickness measurements, ASTM D 7091 describes three operational steps that must be performed before taking the measurements. These steps are (1) gage calibration, (2) verification of gage accuracy and (3) gage adjustment. The steps are incorporated by reference in SSPCPA 2 and are completed before obtaining coating thickness measurements to determine conformance to a specified coating thickness range. The steps to verify the accuracy of the gage are based on the principle that you check the gage by measuring a known thickness before you use the same gage to measure an unknown thickness.Verification of gage accuracy is typically performed using certified coated thickness standards (for Type 1 or Type 2 gages) or certified shims (Type 2 gages). Adjustment of Type 2 gages to compensate for substrate characteristics (described later) is typically performed using certified shims. Measured shims (individually labeled with a stated thickness value) commonly supplied with Type 2 gages can also be used for gage adjustment.

Dry film thickness gages are calibrated by the equipment manufacturer, its authorized agent, or an accredited calibration laboratory (under controlled conditions). A test certificate or other documentation showing traceability to a national metrology institution is required. While there is no standard time interval for re-calibration, an interval can be established based on experience, the work environment, and/or the internal equipment calibration procedures of the company using the gage. A one-year calibration interval is a typical starting point suggested by gage manufacturers.

Verifying Gage Accuracy in accordance with SSPC-PA 2

To guard against measuring with an inaccurate gage, SSPC-PA 2 requires that gage accuracy be verified (at a minimum) at the beginning and end of each work shift according to the procedures described in ASTM D 7091. If a large number of measurements are being obtained, the user may opt to verify gage accuracy during measurement acquisition (for example, hourly). If the gage is dropped or suspected of giving erroneous readings during the work shift, its accuracy should be rechecked.

Verifying the Accuracy of Type 1 Gages

 

The accuracy of Type 1 (magnetic pull-off) gages is verified by placing the gage probe onto a certified coated thickness standard (Figs. 4 and 5). A one-point or two-point accuracy verification procedure can be performed; typically, the two-point verification provides greater accuracy. If a one-point verification procedure is adopted, the coated standard should be selected based on the intended range of use. For example, if the intended use is between 4 and 6 mils, then a five-mil coated standard is appropriate. Using the same example, if a two-point verification procedure is adopted, then a two-mil and an eight-mil set of coated standards (slightly below and above the intended range of use) is appropriate.

type 1 gage
type 1 gage
Fig. 4: (top) and 5 (bottom) Verifying the accuracy of Type 1 gages using certified coated thickness standards

The final step in the process is to obtain a set of base metal readings (BMRs) to compensate for substrate characteristics including (but not limited to) substrate metallurgy, geometry, thickness/thinness, and roughness (Fig. 6). These readings represent the effect of the substrate conditions on the coating thickness measurement device. SSPC-PA 2 states that a minimum of 10 (arbitrarily spaced) locations should be measured (one reading per location) and then averaged. This average BMR is then deducted from subsequent coating thickness measurements to remove any effect of the base metal surface and its conditions.

base metal reading
Fig. 6: Obtaining base metal readings with Type 1 gage

Because Type 1 gages cannot be adjusted, some gage operators believed that a “correction value” could be applied to the coating thickness readings to compensate for the inaccuracy of the gage. For example, if a gage reading was 5.7 mils on a five-mil coated standard, a 0.7-mil “correction value” could be deducted (by the gage operator) from subsequent coating thickness measurements. However, because Type 1 gages are non-linear, one cannot assume a linear (mil-for-mil) correction value across the full range of the gage. While the gage may be out of tolerance by 0.7 mils at 5 mils, it may be out of tolerance by more or less than 0.7 mils at a different thickness. Accordingly, SSPC-PA 2 states that the practice of using a linear correction value is not appropriate.

However, Note 6 in the standard states, “A correction curve can be prepared by plotting the actual gage readings against the stated values on the (coated) test blocks (standards). Subsequent coating thickness measurements can be “corrected” by plotting the measurements along the correction curve. The correction curve may or may not cover the full range of the gage, but should cover the intended range of use. The Base Metal Readings (BMR) described in 6.1 may also need to be plotted on the correction curve.”

This requirement makes Type 1 gages very difficult to use. While some gage operators may simply subtract a fixed amount (for example, 0.5 mils) from any reading, such a practice is not in compliance with SSPC-PA 2.

Verifying the Accuracy of Type 2 Gages

 

The accuracy of Type 2 (electronic) gages can be verified by placing the gage probe onto a certified coated thickness standard (described for Type 1 gages) or certified shims (Figs. 7 and8). The certified shim should be placed onto a smooth, uncoated metal surface to remove any effect of the surface roughness during this process. A one-point or two-point accuracy verification procedure can be performed (as described earlier for Type 1 gages).

type 2 gage
Fig. 7: Verifying accuracy of Type 2 gage on a certified coated standard
type 2 gage shim
Fig. 8: Verifying accuracy of Type 2 gage using a certified shim

Adjusting Type 2 Gages

The final step in the process is to adjust the gage on the surface to which the coating will be applied. Adjustment is accomplished by placing a certified or measured shim (or shims) onto the prepared, uncoated metal surface and adjusting the gage (when feasible) to compensate for substrate characteristics including (but not limited to) substrate metallurgy, geometry, thickness/thinness, and roughness (Fig. 9). The gage reading is adjusted to match the thickness of the shim, which effectively removes any influence from the underlying surface.

type 2 gage shim
Fig. 9: Adjusting Type 2 gage using a measured shim on the surface to which the coating will be applied

This step sounds reasonably straightforward but poses several hidden challenges. First, once the surface is coated (for example, with a primer), an uncoated surface may no longer be available for subsequent gage adjustments, so the user may want to have a similar uncoated surface prepared and reserved for future gage adjustments on a given project. Naturally, this surface must be representative of the metallurgy, geometry, thickness/thinness, and roughness of the actual surface, which can be a challenging requirement.

Second, some Type 2 gages cannot be adjusted. In such cases, the user will need to obtain BMRs from the prepared, uncoated substrate (described earlier for Type 1 gages). While many Type 2 (electronic) gages have a “zero-set” function, the gages should never be adjusted to zero unless the surface is smooth.

Required Number of Coating Thickness Measurements

The section of SSPC-PA 2, “Required Number of Measurements for Conformance to a Thickness Specification,” causes many users confusion, which can result in either under- or over-inspection. Arguably the most critical section in the document, Section 8, describes how many areas to check, the size of the areas, the number of measurements to obtain in each area, and the steps to take if spot or area measurements do not conform to the specification.

SSPC-PA 2 contains three definitions that are critical to understanding this next area of discussion.

  • Gage Reading: A single instrument reading.
  • Spot Measurement: The average of at least three gage readings made within a 4-cm (≈1.5-inch) diameter circle. Acquisition of more than three gage readings within a spot is permitted. Any unusually high or low gage readings that are not repeated consistently are discarded. The average of the acceptable gage readings is the spot measurement.
  • Area Measurement: The average of five spot measurements obtained over each 10 m2(≈100 ft2) of coated surface, or increment (portion) thereof.

An area is defined as approximately 100 square feet. Within each area, five randomly spaced spots are selected. Each spot consists of a 1.5-inch diameter circle. A minimum of three gage readings is obtained in each spot, culminating in a minimum of 15 gage readings within an area. Unusually high or low gage readings that cannot be repeated consistently are discarded. The average of the three acceptable gage readings is the spot measurement; the average of five spot measurements is the area measurement. Figure 10, from Appendix 1 in SSPC-PA 2, depicts an approximate 100-square-foot area containing gage readings and spot measurements.

Fig. 10: Approximate 100-square-foot area containing gage readings and spot measurements, as depicted in Appendix 1 of SSPC-PA 2. Courtesy of SSPC

The number of areas that must be measured for coating thickness varies, depending on the size of the coated area. There are three categories of coated area: less than 300 square feet; 300 to 1,000 square feet; and greater than 1,000 square feet. For areas containing less than 300 square feet of coated surface, every 100-square-foot area must be measured for coating thickness. For areas of coating 300 to 1,000 square feet, three random areas are selected and measured. For areas of coating exceeding 1,000 square feet, three random areas are selected from the first 1,000 square feet, along with one additional area for each additional 1,000 square feet.

Because areas of coating often exceed 1,000 square feet, our example will be based on this third tier (>1,000 square feet). Let’s assume that the total coated area (perhaps the area coated during a work shift, although SSPC-PA 2 does not equate coated area with work shift) is 12,500 square feet. A total of 15 areas must be measured (three in the first 1,000 square feet and one additional area in each of the 12 remaining 1,000-square-foot areas or portions thereof). This culminates in a total of 75 spot measurements (15 x 5) and a minimum of 225 gage readings (15 x 5 x 3). If spot measurement variances result in area measurements that do not meet the specification, then additional spot measurements are acquired (radiating outward in eight directions from the nonconforming area) to determine the magnitude of the non-conforming thickness. This process is described later in this article.

Acceptability of Gage Readings, Spot Measurements, and Area Measurements

While individual gage readings that are unusually high or low (and cannot be repeated consistently) can be discarded, there are limitations on the thickness values representing the spot measurements (the average of three gage readings). A minimum thickness and a maximum thickness are normally specified for each layer of coating. However, if a single thickness value is specified and the coating manufacturer does not provide a recommended range of thickness, then the minimum thickness and maximum thickness for each coating layer are established by SSPC-PA 2 at ±20% of the stated value. For example, if the specification requires 3 mils’ DFT and the coating manufacturer does not provide any additional information regarding a recommended thickness range, then, by default, the specified range is established as 2.4–3.6 mils. Because the coating may not perform at the lower thickness, it is important for the specifier to indicate an acceptable range for each coating layer. To assist the specifier, the 2012 edition of SSPC-PA 2 incorporates a Restriction Level Table (Fig. 11). The Table enables the specifier to select from five different restriction levels related to spot and area measurements.

coating thickness
Fig. 11: Coating Thickness Restriction Levels (as shown in Table 1 of SSPC-PA 2, Section 9)
Courtesy of SSPC

Level 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. Depending on the coating type and the prevailing service environment, the specifier can select the DFT restriction level for a given project. The specifier may also invoke a maximum thickness threshold for Level 5 Spot or Area Measurements for a generic product type and/or service environment that will not tolerate an unlimited thickness. If no Restriction Level is specified, then the default is Level 3, which is based on the 2004 version of SSPC-PA 2 (what many users of the standard have become accustomed to).

For the purpose of final acceptance of the total DFT, the cumulative thickness of all coating layers in each area must be no less than the cumulative minimum specified thickness and no greater than the cumulative maximum specified thickness.

For example, assume that the specification requires a four- to six-mil application of primer. The actual minimum and maximum spot and area thickness requirements are shown in Fig. 12 for each of the five restriction levels.

coating thickness
Fig. 12: Coating Thickness Restriction Levels Based on a Four-to-Six-Mil Requirement
Derived using the 2012 edition of SSPC-PA 2, “
Table 1, Coating Thickness Restriction Levels”

Determining the Magnitude of Nonconforming Thickness

Another change in the 2012 version of the standard is the procedure for identifying nonconforming areas (Fig. 13). In the 2004 edition, if spot or area measurements were out of conformance, each 100-square-foot area coated during the work shift had to be measured, and nonconforming areas had to be demarcated. On a larger structure with multiple applicators, the measurement and documentation process could be extensive, so the approach was changed in the 2012 revision. If a nonconforming area is identified, spot measurements are made at five-foot intervals in eight equally spaced directions radiating outward from the nonconforming area, as shown in Fig. 13.

nonconforming areas
Fig. 13: Depiction of procedure for identifying nonconforming areas, as described in the 2012 edition of SSPC-PA 2.
Courtesy of SSPC

If there is no place to measure in a given direction, then no measurement in that direction is necessary. Spot measurements are obtained in each direction (up to the maximum surface area coated during the work shift) until two consecutive conforming spot measurements are acquired in that direction, or until no additional measurements can be made. Acceptable spot measurements are defined by the minimum and maximum values in the contract documents. No allowance is made for variant spot measurements (for example, ±20%), which is consistent with the practice followed when determining the area DFT.

On complex structures or in other cases where making spot measurements at five-foot intervals is not practical, spot measurements are taken on repeating structural units or elements of structural units. This method is used when the largest dimension of the unit is less than 10 feet. Spot measurements are obtained on repeating structural units or elements of structural units until two consecutive units in each direction are conforming or until there are no more units to test.

Non-compliant areas are demarcated using removable chalk (or another specified marking material) and documented. All of the area within five feet of any non-compliant spot measurement is considered non-compliant. For a given measurement direction or unit measurement, any compliant area or unit preceding a non-compliant area or unit is designated as suspect, and, as such, is subject to re-inspection after corrective measures are taken.

Appendices to the Standard

There are eight appendices in the 2012 version of SSPC-PA 2. Two of the eight appendices were added in 2012 (the remaining were in the 2004 edition) and are highlighted below. The appendices to SSPC-PA 2 are not mandatory but may be invoked by contract documents.

Appendix 6: Method for Measuring the Dry Film Thickness of Coatings on Edges

For decades, the industry was cautioned about taking coating thickness measurements within one inch of an edge, let alone on an edge. However, several Type 2 (electronic) gage manufacturers offer a variety of probe configurations, some of which are less affected by proximity to edges and are designed to better measure the thickness of coatings on edges (Fig. 14). Obviously, the gage operator should consult the gage manufacturer’s instructions before measuring coating thickness on edges.

Fig. 14: One of a variety of Type 2 gage probe configurations designed to better measure DFT of coatings on edges

Before measuring coating thickness on edges, the user should verify the gage and probe for accuracy by placing a thin, flexible shim (certified or measured) onto the prepared, uncoated edge. Adjustments to the gage may or may not be required. This procedure also verifies that the probe configuration will accommodate the edge configuration before acquiring coating thickness data.

Once verification of accuracy and adjustments are made, a minimum of three gage readings are taken within 1.5 linear inches of coated edge. The average of the gage readings is considered a spot measurement. The number of spot measurements along the edge will vary, depending on the total length of the coated edge.

Appendix 7: Method for Measuring Dry Film Thickness on Coated Steel Pipe Exterior

Appendix 7 was added to accommodate pipe coaters that need to determine coating thickness conformance on non-flat (or non-plate) areas, including smaller pipe sections on a cart or rack and longer pipe spools.

Pipe sections loaded onto a cart or rack can be considered a complete unit (Fig. 15). The total number of spot and area measurements is based on the total square footage of pipe on the cart or rack. The square footage is calculated as shown on p. 35.

Fig. 15: (top and bottom): Appendix 7 of the 2012 edition of SSPC-PA 2 describes a method for measuring DFT on non-flat steel, such as pipe sections that can be loaded on racks or carts. Photos courtesy of Turner Industries Group, L.L.C.

Some carts may have several small pipe sections, and the total coated surface may exceed 100 square feet. In this case, a Pipe DFT Frequency Factor shown below may be invoked.

  • Pipe DFT Frequency Factor 2 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 2
  • Pipe DFT Frequency Factor 3 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 3
  • Pipe DFT Frequency Factor 4 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 4
  • Pipe DFT Frequency Factor 5 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 5
  • Pipe DFT Frequency Factor 6 = (length of each pipe x circumference) x number of pipe sections on cart or rack = (number of spot measurements) x 6

Based on the example above, if “Pipe DFT Frequency Factor 4” was invoked, 20 spot measurements would be taken (5 spots x Frequency Factor 4)

Pipe spools that are not loaded onto a rack or cart are typically measured individually (Fig. 16). The number and locations of spot measurements are based on Appendix 7’s Table A7 (Fig. 17). Three sets of four circumferential spot measurements should be obtained on pipe spools less than 10 feet in length.

Fig. 16: DFT of pipe spools not loaded on cart or rack are typically measured individually.
Fig. 17: Number and Locations of Spot Measurements—Pipe Spools (Table A7 from 2012 edition of SSPC-PA 2, Appendix 7)
Courtesy of SSPC

Conclusion

SSPC-PA 2 has undergone significant changes in an attempt to make it more complete; more in concert with ASTM D7091; easier to use in the shop and field; and more flexible in providing the specifier with options for coating thickness restrictions based on the type of structure, the coatings to be applied, and the service environment. SSPC-PA 2 and ASTM D7091 are both undergoing additional technical and editorial changes to bring them into even greater alignment with one another.

Get the Latest Standards on Dry Film Thickness of CoatingsThe 2012 edition of SSPC-PA 2, “Procedure for Determining Conformance to Dry Coating Thickness Requirements,” is available from the SSPC: The Society for Protective Coatings through sspc.org, under the “Standards” tab at the top of the home page.The 2012 edition of ASTM D7091, “Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to NonFerrous Metals,” is available from ASTM International through astm.org under the “Standards” at the top of the navigation bar on the site.

Change is never easy…. Communicating the new requirements of this standard to the industry is challenging but essential. One conduit is through training and education. For example, SSPC offers a short course, “Using SSPC-PA 2 Effectively,” that was recently updated to reflect changes made to the standard. Free webinars are available through SSPC/JPCL for those who cannot participate in instructor-led training. Updates to SSPC and other industry-provided inspector training and certification courses (and the associated instructor education) will be critical to fully understanding and effectively communicating the requirements of this highly regarded industry standard.

The Journal Of Protective Coatings & Linings ©2013 Technology Publishing Company

BCorbett3William D. Corbett is the Vice President and Professional Services Group Manager for KTA-Tator, Inc. He holds an A.D. in Business Administration from Robert Morris University and has been employed by KTA for over 33 years. Mr. Corbett is an SSPC Certified Protective Coatings Specialist, an SSPC Level 3 Certified Protective Coatings Inspector, an SSPC Level 2 Certified Bridge Coatings Inspector and a NACE International Level 3 Certified Coatings Inspector. He was the co-recipient of the SSPC 1992 Outstanding Publication Award, co-recipient of the 2001 JPCL Editor’s Award, received SSPC’s Coatings Education Award in 2006, and the SSPC 2011 John D. Keane Award of Merit. He is the author of the first, second and third editions of the KTA publication, Using Coatings Inspection Instruments. He also authored Chapter 8 of the SSPC Inspection of Coatings and Linings Handbook and co-authored Chapter 6, “Inspection” of the Steel Structures Painting Manual, Volume 1, Good Painting Practice. Mr. Corbett is a member of the ASTM International and SSPC: The Society for Protective Coatings, where he is Chair of the Education Committee and the Dry Film Thickness Committee.

14 comments

  1. Pingback: The Protective Coating Users Handbook | WWW.INFOPAGESHUB.COM

  2. Jim Gardner

    Thank you. …I truly appreciate the concise information regarding SSPC PA2 and. ASTM D 7091 their uses and how to apply them correctly. I feel empowered and have gained valuable knowledge. Thank You again
    Jim Gardner
    NACE level II Certified

  3. BRUCE AHLGREN

    I would like to purchase a book regarding painting standards on thickness of painting.Please email me back with price and where to purchase standards on paint thickness.Thx Bruce

  4. Haarik

    Recently I had problem while calibrating. I calibrated the DFT gauge by keeping the zero plate & shim on a wooden surface. Then I calibrated by keeping the same on a metal surface, which resulted in a 0.5mm deduction in DFT. Will the surface on which we keep the calibrating tools affect the reading? If so which is the correct surface for calibrating?
    Thank you.

    • Jason Weslager

      Haarik,

      You are not calibrating the coating thickness gage, but rather verifying accuracy, then adjusting. I am assuming you are using an electronic gage:

      1. You do not need to zero the gage.
      2. Place the gage probe on a certified coated standard and adjust the gage as necessary. This will determine whether the gage is operating correctly
      3. Place a measured shim (comes with the gage) onto the prepared, uncoated metal surface to be coated; Adjust the gage reading to match the thickness of the shim.
      4. Measure the coating thickness.
      5. There should be no “correction” for the gage, as any effect of the base metal has been eliminated.

      Bill Corbett, KTA

    • Jason Weslager

      Don,
      The standard is independent of the substrate type, as long as the substrate is a ferrous or non-ferrous metal. However it will be important to place a measured shim onto the prepared, uncoated pipe and adjust the gage to match the shim thickness to remove any effect of the base metal.

      Bill Corbett, KTA

  5. Don berry

    Thank you. Just to clarify; with the substrate profile being like hills and valleys its completely ok to just mill it and hopefully your getting a reading on the peak, sort of speaking cause most of the mills will be in the “valleys”. So if your reading is within the spec your fine. Correct?

  6. Lorenzo Castañeda

    La informacion contenida ayuda a la comprension facil, gracias al autor por la EXPLICACIÓN.

    English: The contained information helps for easy understanding. Thanks to the author for the explanation.

  7. i need to setup a factory procedure to measure dft of a generator unit (only outside surface) of approx 300 sqft totally – according to sspc p a 2.
    this shall make totally 15 spot measurements necessary.
    i plan to arrange 3 spot measurements taken randomly on sides (3 x 4) and 2 spot measurements each on the top and bottom surfaces.
    this is totally 16 spot measurements.
    and multiple guage readings for specific ‘critical areas’ such as hidden faces, stiffeners, corners etc for confirmation.
    in the dft report sheet, the spot measurements taken on each side only shall be noted and not the single guage readings taken on ‘critical areas’.
    pls suggest your comments. will it comply with sspc p a 2?

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