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You are on page 1of 11

May 1, 2012

1

SSPC: THE SOCIETY FOR PROTECTIVE COATINGS

COATING APPLICATION STANDARD NO. 2

PROCEDURE FOR DETERMINING CONFORMANCE TO

DRY COATING THICKNESS REQUIREMENTS

1.6 This standard is not intended to be used for measure-

ment of thermal spray coatings. The thickness measurement

procedures for these coatings are described in SSPC-CS

23.00

2

.

2. Referenced Standards

2.1 The latest issue, revision, or amendment of the refer-

enced standards in effect on the date of invitation to bid shall

govern unless otherwise specifed. Standards marked with an

asterisk (*) are referenced only in the Notes, which are not

requirements of this standard.

2.2 If there is a confict between the requirements of any

of the cited reference standards and this standard, the require-

ments of this standard shall prevail.

2.3 ASTM International Standard

3

D 7091 Standard Practice for Nondestructive Measure-

ment of Dry Film Thickness of Nonmagnetic

Coatings Applied to Ferrous Metals and

Nonmagnetic, Nonconductive Coatings Applied

to Non-Ferrous Metals (mandatory document)

2.4 SSPC: The Society for Protective Coatings

Standard:

* PA Guide 11 Protecting Edges, Crevices, and Irreg-

ular Steel Surfaces by Stripe Coating

3. DEFINITIONS

3.1 Gage Reading: A single instrument reading.

3.2 Spot Measurement: The average of three, or at least

three gage readings made within a 1.5-inch (approximately

4-centimeter [~4-cm]) diameter circle. Acquisition of more than

three gage readings within a spot is permitted. Any unusually

2

CS 23.00/AWS C2.23M/NACE No. 12, Specifcation for the Applica-

tion of Thermal Spray Coatings (Metallizing) of Aluminum, Zinc, and

Their Alloys and Composites for the Corrosion Protection of Steel is

available online at <http://www.sspc.org/marketplace>

3

ASTM International, 100 Barr Harbor Drive, West Conshohocken,

PA 19428-2959. For referenced ASTM standards, visit the ASTM

website, www.astm.org, or contact ASTM Customer Service at

service@astm.org. For Annual Book of ASTM Standards volume

information, refer to the standard’s Document Summary page on the

ASTM website.

1. Scope

1.1 This standard describes a procedure for determining

shop or feld conformance to a specifed coating dry flm thick-

ness (DFT) range on ferrous and non-ferrous metal substrates

using nondestructive coating thickness gages (magnetic and

electronic) described in ASTM D 7091.

1.2 The procedures for adjustment and measurement

acquisition for two types of gages: “magnetic pull-off” (Type 1)

and “electronic” (Type 2) are described in ASTM D 7091.

1.3 This standard defnes a procedure to determine

whether dry coatings conform to the minimum and the

maximum thickness specifed. See Note 11.1 for an example

of a possible modifcation when measuring dry flm thickness

on overcoated surfaces.

1.4 This document is not intended to prescribe a

frequency of coating thickness measurement for a coating

failure investigation

1.

1.5 This document contains the following non-mandatory

appendices:

Appendix 1 - Numerical Example of Average Thickness

Measurement

Appendix 2 - Methods for Measuring Dry Film Thickness

on Steel Beams (Girders)

Appendix 3 - Methods for Measuring Dry Film Thickness

for a Laydown of Beams, Structural Steel, and Miscellaneous

Parts after Shop Coating

Appendix 4 - Method for Measuring Dry Film Thickness

on Coated Steel Test Panels

Appendix 5 - Method for Measuring Dry Film Thickness

of Thin Coatings on Coated Steel Test Panels that Have Been

Abrasive Blast Cleaned

Appendix 6 – Method for Measuring the Dry Film Thick-

ness of Coatings on Edges

Appendix 7 – Method for Measuring Dry Film Thickness

on Coated Steel Pipe Exterior

Appendix 8 – Examples of the Adjustment of Type 2

Gages Using Shims

1

The number and location of measurements during a coating failure

investigation may be more or less frequent than described by this

standard.

SSPC-PA 2

May 1, 2012

2

high or low gage readings that are not repeated consistently

are discarded. The average of the acceptable gage readings is

the spot measurement.

3.3 Area Measurement: The average of fve spot

measurements obtained over each 100 ft

2

(~10 m

2

) of coated

surface.

4. Description of Gages

4.1 Gage Types: The gage type is determined by the

operating principal employed in measuring the thickness and

is not determined by the mode of data readout, i.e. digital or

analog.

4.1.1 Type 1 – Magnetic Pull-Off Gages: In magnetic

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 or display on the

gage. Less force is required to remove the magnet from a thick

coating. The scale is nonlinear.

4.1.2 Type 2 – Electronic Gages: An electronic gage

uses electronic circuitry to convert a reference signal into

coating thickness.

5. Calibration and Verifcation of Accuracy

5.1 ASTM D 7091 describes three operational steps

necessary to ensure accurate coating thickness measurement:

calibration, verifcation and adjustment of coating thickness

measuring gages, as well as proper methods for obtaining

coating thickness measurements on both ferrous and non-

ferrous metal substrates. These steps shall be completed

before taking coating thickness measurements to determine

conformance to a specifed coating thickness range.

5.2 Gages shall be calibrated by the manufacturer or

a qualifed laboratory. A Certifcate of Calibration or other

documentation showing traceability to a national metrology

institution is required. There is no standard time interval for

re-calibration, nor is one absolutely required. Calibration inter-

vals are usually established based upon experience and the

work environment. A one-year calibration interval is a typical

starting point suggested by gage manufacturers.

5.3 To guard against measuring with an inaccurate gage,

gage accuracy shall be verifed at a minimum of the begin-

ning and end of each work shift according to the procedures

described in ASTM D 7091. The user is advised to verify gage

accuracy during measurement acquisition (e.g., hourly) when

a large number of measurements are being obtained. If the

gage is dropped or suspected of giving erroneous readings

during the work shift, its accuracy shall be rechecked.

5.4 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, refer-

ence standard, and method of verifcation are used throughout

a job, they need to be recorded only once. The stated value of

the standard and the measured value must be recorded each

time accuracy is verifed.

5.5 If the gage fails the post-measurement accuracy

verifcation check, all measurements acquired since the

last accuracy verifcation check are suspect. In the event of

physical damage, wear, or high usage, or after an established

calibration interval, the gage shall be rechecked for accuracy

of measurement. If the gage is not measuring accurately, it

shall not be used until it is repaired and/or recalibrated (usually

by the gage manufacturer).

5.6 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; therefore adjustment of the gage is not recom-

mended. 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.

4

6. Measurement Procedure - Type 1 Gages

6.1 Type 1 gage accuracy is verifed using smooth test

blocks. In order to compensate for any effect of the substrate

itself and surface roughness, obtain measurements from the

bare, prepared substrate at a minimum of ten (10) locations

(arbitrarily spaced) and calculate the average value. This value

represents the effect of the substrate/surface roughness on a

coating thickness gage. This average value is the base metal

reading (BMR). The gage shall not be adjusted to read zero on

the prepared, bare substrate.

6.2 Measure the DFT of the dry coating at the number of

spots specifed in Section 8.

6.3 Subtract the BMR from the gage reading to obtain the

thickness of the coating.

7. MEASUREMENT PROCEDURE - TYPE 2 GAGES

7.1 The manufacturers of Type 2 (electronic) gages

prescribe different methods of adjustment to measure dry flm

thickness over abrasive blast cleaned surfaces. Adjust the

gage according to the manufacturers instructions using one of

the methods described in ASTM D 7091 or Appendix 8 of this

standard.

4

A correction curve can be prepared by plotting the actual gage

readings against the stated values on the calibration test blocks.

Subsequent coating thickness measurements can be “corrected” by

plotting the measurements along the correction curve. The correc-

tion 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.

SSPC-PA 2

May 1, 2012

3

7.2 Measure the DFT of the dry coating at the number of

spots specifed in Section 8.

8. Required Number of Measurements for

Conformance to a Thickness Specifcation

8.1 Number of Measurements: Repeated gage read-

ings, even at points close together, often differ due to small

surface irregularities of the coating and the substrate. There-

fore, a minimum of three (3) gage readings shall be made for

each spot measurement of the coating. For each new gage

reading, move the probe to a new location within the 1.5 inch

(4-cm) diameter circle defning the spot. Discard any unusually

high or low gage readings that are not repeated consistently.

The average of the acceptable gage readings is the spot

measurement.

8.2 Unless otherwise specifed in the procurement docu-

ments (project specifcation), an area measurement is obtained

by taking fve (5) separate spot measurements (average of the

gage readings described in 8.1) randomly spaced throughout

each 100 ft

2

(~10-m

2

) area to be measured and representative

of the coated surface. The fve spot measurements shall be

made for each 100 ft

2

(~10-m

2

) of area as follows:

8.2.1 For areas of coating not exceeding 300 ft

2

(~30 m

2

)

arbitrarily select and measure each 100 ft

2

(~10-m

2

) area.

8.2.2 For areas of coating greater than 300 ft

2

(~30 m

2

)

and not exceeding 1,000 ft

2

(~100 m

2

), arbitrarily select and

measure three 100 ft

2

(~10-m

2

) areas.

8.2.3 For areas of coating exceeding 1,000 ft

2

(~100 m

2

),

arbitrarily select and measure the frst 100 m

2

(~1,000 ft

2

) as

stated in Section 8.2.2. For each additional 1,000 ft

2

(~100

m

2

) coated area (or increment thereof), arbitrarily select and

measure one additional 100 ft

2

(~10-m

2

) area.

8.2.4 If the coating thickness for any 100 ft

2

(~10-m

2

)

area is not in compliance with the contract documents, the

procedure described below shall be followed to assess the

magnitude of the nonconforming thickness.

8.2.4.1 Determine the spot DFT at 5-ft (1.5-m) intervals

in eight equally spaced directions radiating outward from the

nonconforming 100 ft

2

(~10-m

2

) area as shown in Figure 1.

If there is no place to measure in a given direction, then

no measurement in that direction is necessary. Acquire spot

measurements 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. Accept-

able spot measurements are defned by the minimum and

maximum values in the contract documents. No allowance is

made for variant spot measurements as is the practice when

determining the area DFT.

8.2.4.1.1 On complex structures or in other cases where

making multiple spot measurements at 5-ft (1.5-m) intervals is

not practical, single spot measurements shall be performed on

repeating structural units or elements of structural units. This

method shall be used when the largest dimension of the unit

is less than 10 ft (3 m). Make single spot measurements on

repeating structural units or elements of structural units until

spot measurements on two consecutive units in each direction

are conforming or until there are no more units to test.

8.2.4.2 Non-compliant areas shall be demarcated using

removable chalk or other specifed marking material and docu-

mented. All of the area within 5 ft (1.5 m) of any non-compliant

spot measurement shall be designated as non-compliant.

For a given measurement direction or unit measurement,

any compliant area or unit preceding a non-compliant area or

unit shall be designated as suspect, and as such is subject to

re-inspection after corrective measures are performed.

8.2.5 Appendices 2 through 7 provide specifers with

optional alternatives for defning the area size as well as the

number and frequency of spot measurements to include in

project specifcations as appropriate for the size and shape of

the item or structure to be coated.

9. Conformance to Specifed Thickness

9.1 A minimum and a maximum thickness are normally

specifed for each layer of coating. If a single thickness value

is specifed and the coating manufacturer does not provide

a recommended range of thickness, then the minimum and

maximum thickness for each coating layer shall be +/- 20% of

the stated value.

9.2 Table 1 provides fve thickness restriction levels. Level

1 is the most restrictive and does not allow for any deviation

of spot or area measurements from the specifed minimum

and maximum thickness, while Level 5 is the least restrictive.

Depending on the coating type and the prevailing service envi-

ronment, the specifer selects the dry flm thickness restriction

level for a given project. If no restriction level is specifed, then

Level 3 is the default. It is possible to specify a maximum thick-

ness threshold for Level 5 Spot or Area measurements for

some generic product types and service environments.

9.3 For the purpose of fnal acceptance of the total dry

flm thickness, the cumulative thickness of all coating layers

NONCONFORMING

AREA

FIGURE 1

RADIATING SPOT MEASUREMENTS TO DETERMINE

EXTENT OF NONCONFORMING AREA

SSPC-PA 2

May 1, 2012

4

shall be no less than the cumulative minimum specifed thick-

ness and no greater than the cumulative maximum specifed

thickness.

10. Disclaimer

10.1 While every precaution is taken to ensure that all

information furnished in SSPC standards and specifcations is

as accurate, complete, and useful as possible, SSPC cannot

assume responsibility nor incur any obligation resulting from

the use of any materials, coatings or methods specifed therein,

or of the specifcation or standard itself.

10.2 This standard does not attempt to address prob-

lems concerning safety associated with its use. The user of

this standard, as well as the user of all products or practices

described herein, is responsible for instituting appropriate

health and safety practices and for ensuring compliance with

all governmental regulations.

11. Notes

Notes are not requirements of this standard.

11.1 Overcoating: Maintenance painting often involves

application of a new coating over an existing coating system.

It can be very diffcult to accurately measure the DFT of this

newly applied coating using non-destructive methods. First,

access to the profle is not available, compromising the accu-

racy of the BMR or the adjustment of a Type 2 gage. Second,

unevenness in the DFT of the existing coating necessitates

careful mapping of the “before and after” DFT readings. This

unevenness also adds to the statistical variation in trying to

establish a base DFT reading to be subtracted from the fnal

DFT.

A paint inspection gage (sometimes called a Tooke or PIG

gage) will give accurate DFT measurements, but it requires

that an incision be made through the coating (overcoat only

or total system), so each measurement site will require repair.

A practical approach to monitoring DFT (when overcoating)

is to compute the DFT using wet flm thickness (WFT) read-

ings, the percent volume solids of the coating being applied,

and any thinner addition as shown below.

DFT = Measured WFT x % Volume Solids,

or

DFT = Measured WFT x % volume

solids ÷ (100% + % thinner added)

If the DFT of the existing coating is not too uneven or

eroded, the average DFT of the existing coating can be

measured per this standard to establish a base DFT. This base

DFT can then be subtracted from the total DFT to isolate the

thickness of the overcoat(s).

11.2 Correcting for Low or High Thickness: The speci-

fer should specifcally state the methodology to correct the

applied dry flm for low or high thickness. If this information

is not contained in the specifcation, then the manufacturer’s

instructions should be followed.

APPENDIX 1 - Numerical Example of Average

Thickness Measurement

Appendix 1 is not a mandatory part of this standard.

The following numerical example is presented as an illus-

tration of Section 8. Metric values are calculated equivalents

from U.S. Customary measurements (reference Journal of

Protective Coatings and Linings, Vol. 4, No 5, May 1987). The

example is based on a Level 3 Restriction (default).

TABLE 1

COATING THICKNESS RESTRICTION LEVELS

Thickness Gage Reading

Spot

Measurement

Area Measurement

Level 1

Minimum Unrestricted As specifed As specifed

Maximum Unrestricted As specifed As specifed

Level 2

Minimum Unrestricted As specifed As specifed

Maximum Unrestricted 120% of maximum As specifed

Level 3

Minimum Unrestricted 80% of minimum As specifed

Maximum Unrestricted 120% of maximum As specifed

Level 4

Minimum Unrestricted 80% of minimum As specifed

Maximum Unrestricted 150% of maximum As specifed

Level 5

Minimum Unrestricted 80% of minimum As specifed

Maximum Unrestricted Unrestricted Unrestricted

SSPC-PA 2

May 1, 2012

5

Suppose this structure is 300 ft

2

(~30 m

2

) in area. Mentally

divide the surface into three equal parts, each being about 100

ft

2

(~10 m

2

).

Part A - 100 ft

2

(~10 m

2

)

Part B - 100 ft

2

(~10 m

2

)

Part C - 100 ft

2

(~10 m

2

)

First, measure the coating thickness on Part A. This

involves at least 15 gage readings with a Type 1 or Type 2

device (see Figure A1). Assume the specifcation calls for

2.5 mils (~64 micrometers [µm]) minimum thickness. The

coating thickness for area A is then the average of the fve

spot measurements made on area A, namely 2.6 mils (65.4

µm).

Spot 1 2.5 mils 64 µm

Spot 2 3.0 76

Spot 3 2.1 53

Spot 4 3.0 76

Spot 5 2.3 58

Average 2.6 mils 65.4 µm

Considering the U.S. Customary Measurements:

The average, 2.6 mils, exceeds the specifed minimum of 2.5

mils and thus satisfes the specifcation. Next, determine if

the lowest spot measurement, 2.1 mils, is within 80% of the

specifed minimum thickness. Eighty percent of 2.5 mils is 2.0

mils (0.80 x 2.5 = 2.0). Although 2.1 mils is below the specifed

minimum, it is still within 80 percent of it, so the specifcation is

satisfed. There are individual gage readings of 1.5 mils at Spot

5 and 1.8 mils at Spot 3, both of which are clearly less than

2.0 mils. This is allowed because only the average of the three

readings (i.e. the spot measurement) must be greater than or

equal to 2.0 mils.

Considering Equivalent Metric Measurements: The

average, 65.4 µm, exceeds the specifed minimum of 64 µm

and thus satisfes the specifcation. Next, determine if the

lowest spot measurement, 53 µm, is within 80% of the speci-

fed minimum thickness. Eighty percent of 64 µm is 51 µm (0.80

x 64 = 51). Although 53 µm is below the specifed minimum, it

is still within 80% of it so the specifcation is satisfed. There

are individual gage readings of 38 µm (1.5 mils) at spot 5 and

46 µm (1.8 mils) at spot 3, both of which are clearly less than

51 µm. This is allowed because only the average of the three

readings (i.e., the spot measurement) must be greater than or

equal to 51 µm.

Since the structure used in this example is 300 ft

2

(approximately 30 m

2

), the procedure used to measure the flm

thickness of part A must be applied to both part B and part C.

The measured thickness of part B must exceed the (64 µm)

specifed minimum, as must the thickness of part C.

FIGURE A1

PART “A” OF STRUCTURE

(AREA 100 FT

2

[APPROXIMATELY 10 M

2

])

10 ft

10 ft Part “B”

Spot 1

2.6

3.0

2.0

Avg. 2.5

1.5 inch

1.8

2.2

2.3

Avg. 2.1

Spot 3

3.6

2.6

2.7

Avg. 3.0

Spot 2

Spot 4

2.6

3.2

3.1

Avg. 3.0

Spot 5 1.5

2.8

2.6

Avg. 2.3

GAGE READINGS

SSPC-PA 2

May 1, 2012

6

To monitor the thickness of this entire 300-ft

2

(approxi-

mately 30-m

2

), structure, at least 45 individual gage readings

must be taken, from which 15 spot measurements are calcu-

lated. The fve spot measurements from each 100 ft

2

(10-m

2

)

part of the structure are used to calculate the thickness of that

part.

APPENDIX 2 - Methods for Measuring Dry Film

Thickness on Steel Beams (Girders)

Appendix 2 is not a mandatory part of this standard, but it

provides two sample protocols for measuring DFT on beams

and girders.

A2.1 A challenge for the painter in coating steel beams or

girders is providing the same uniform thickness over high and

low vertical surfaces as over horizontal surfaces. On a beam,

there are proportionately more edges that tend to have low dry

flm thickness (DFT) and inside corners that tend to have high

DFT compared to the center of the fat surfaces. Each painter

usually develops a pattern of work for a specifc task. Hence,

the DFT on the underside of the top fange, for example, may

be consistently on the high side or the low side of the target

DFT. This type of error is easy to detect and correct. Random

errors pose a more diffcult problem. Gross errors where the

paint is obviously too thin or too thick must be corrected and

are beyond the scope of this standard.

The number of spot measurements in these protocols

may far exceed the “5 spot measurement per 100 ft

2

(10 m

2

)”

required in the standard. The full DFT determination, described

in Section A3.2, provides a very thorough inspection of the

beam. The sample DFT determination, described in Section

A3.4, allows for fewer spot measurements. The user does not

have to require a full DFT determination for every beam in the

structure. For example, the requirement may be for a full DFT

determination on one beam out of ten, or a sample DFT deter-

mination on one beam out of fve, or a combination of full and

sample DFT determinations. Note that for existing structures,

the top side of the top fange (Surface 1) may not be accessible

for measuring coating thickness.

A beam has twelve different surfaces as shown in Figure

A2. Any one of these surfaces may have a DFT outside the

specifed range, and hence, shall be measured. If the thick-

ness of the fange is less than 1 inch (25 mm), the contracting

parties may choose not to measure the DFT on the toe, i.e.,

surfaces 2, 6, 8, and 12 of Figure A2. As an informal initial

survey, the inspector may want to check for uniformity of DFT

across each surface. Is the DFT of the fange near the fllet the

same as near the toe? Is the DFT uniform across the web? The

inspector must be sure to use a gage that is not susceptible

to edge effects. Follow the gage manufacturer’s instructions

when measuring the edges.

A2.2 Full DFT Determination of a Beam: Divide the

beam or girder into fve equal sections along its length. Identify

the 12 surfaces of the beam as shown in Figure A2 for each

section. For tall beams where the height of the beam is 36

inches (91 cm) or more, divide the web in half along the length

of the beam. For the full DFT determination, each half of the

web is considered a separate surface. Take one spot measure-

ment (as defned in Section 8.1) on surface 1 in each of the fve

sections. The location of the surface 1 measurement within a

section is arbitrarily chosen by the inspector in each of the fve

sections. The average of these fve spot measurements is the

FIGURE A2

THE SURFACES OF A STEEL BEAM

(36 in [91 cm] in height)

1

8

9

7

Less than 36 inches (91 cm) in height

12 Spots

5

2

10

6

4

3

11

Top Flange

12

Fillet

Bottom Flange

Web

Toe

36 inches (91 cm) in height or greater

14 Spots

1

5

2

10b

bbb

10t

8 6

4b

9

4t

7

3

11

12

SSPC-PA 2

May 1, 2012

7

DFT of surface 1. Repeat for the other 11 surfaces (7 surfaces

if the toe is not measured; 14 surfaces for tall beams). The data

can be reported in a format shown in Table A2.

A2.3 If Coating Thickness Restriction Level 3 is invoked

by the specifcation (or if no Restriction Level is invoked by

the specifcation), then no single spot measurement can be

less than 80% of the specifed minimum DFT, and no single

spot measurement can be more than 120% of the specifed

maximum DFT. The average value for each surface must

conform to the specifed DFT. (There will be only eight average

values if the DFT of the toe is not measured; there may be as

many as 14 average values for beams greater than 36 inches

in height.)

A2.4 SAMPLE DFT DETERMINATION OF A BEAM: In

lieu of a full DFT determination of each beam, the job speci-

fcation may require only a sample DFT determination for

selected beams less than 60 ft (18 m) long. For a sample DFT

determination, the web of beams less than 36 inches (91 cm)

in height is not split.

A2.4.1 Beams less than 6 m (20 ft) in length: For beams

less than 20 ft (6 m) in length, take two spot measurements,

randomly distributed, on each of the 12 surfaces (8 surfaces if

the toe is not measured) of the beam as defned in Figure A2.

Each spot measurement must conform to the specifed DFT.

A2.4.2 Beams 20 ft (6 m) up to 60 ft (18 m) in length:

For beams 20 ft (6 m) up to 60 ft (18 m) in length, take three

spot measurements, randomly distributed, on each of the 12

surfaces (8 surfaces if the toe is not measured) of the beam as

defned in Figure A2. Each spot measurement must conform to

the specifed DFT.

A2.5 NON-CONFORMANCE: If any spot measurement

falls outside the specifed range, additional measurements

may be made to defne the non-conforming area.

TABLE A2.1 – NUMBER OF SPOT MEASUREMENTS NEEDED

ON EACH SURFACE OF A BEAM FOR A FULL OR A SAMPLE DFT DETERMINATION

Number of Spot Measurements per Surface

Length of Beam Full DFT Determination* Sample DFT Determination

less than 20 ft (6 m) 5 2

from 20 to 60 ft (6 to 18 m) 5 3

over 60 ft (18 m) 5 NA

* For beams 36 inches (91 cm) or more, the top half and the bottom half of the web are treated as separate surfaces in a full DFT determination.

TABLE A2

DATASHEET FOR RECORDING SPOT MEASUREMENTS AND

AVERAGE DFT VALUES FOR THE 12 SURFACES OF A BEAM OR GIRDER

Spot Measurements of DFT on Beam # _______________

Surface Section 1 Section 2 Section 3 Section 4 Section 5 Average

1

2

3

4t

4b

5

6

7

8

9

10t

10b

11

12

t = top half of web (for beams equal to or greater than 36 in [91 cm] in height)

b = bottom half of web (for beams equal to or greater than 36 in [91 cm] in height)

SSPC-PA 2

May 1, 2012

8

A2.6 RESTRICTED ACCESS: If the beam is situated

such that one or more of the surfaces are not accessible, take

measurements on each accessible surface in accordance with

Section A2.2 or Section A2.4 through A2.4.2, as specifed.

A2.7 ATTACHMENTS: Stiffeners and other attachments

to a beam shall be arbitrarily measured.

APPENDIX 3 - Methods for Measuring Dry Film

Thickness for a Laydown of Beams, Structural Steel,

and Miscellaneous Parts After Shop Coating

Appendix 3 is not a mandatory part of this standard, but

it provides two sample protocols for measuring DFT for a

laydown.

A3.1 GENERAL: A “laydown” is a group of steel members

laid down to be painted in one shift by one painter. For inspec-

tion of a laydown, frst make a visual survey to detect areas

with obvious defects, such as poor coverage, and correct as

necessary. As an informal initial survey, the inspector may

want to check for uniformity of DFT across each surface.

A3.2 FULL DFT DETERMINATION

A3.2.1 Beam (Girder): Follow the procedure described in

Section A2.2.

A3.2.2 Miscellaneous Parts: Take 1 spot measurement

(as defned in Section 8.1) on each surface of the part. If the

part has fewer than 5 surfaces, take multiple spot measure-

ments on the larger surfaces to bring the total to 5. If the total

area of the part is over 100 ft

2

(10 m

2

), take 5 spot measure-

ments randomly distributed over the part for each 100 ft

2

(10

m

2

), or fraction thereof.

A3.3 If Coating Thickness Restriction Level 3 is invoked

by the specifcation (or if no Restriction Level is invoked by

the specifcation), then no single spot measurement can be

less than 80% of the specifed minimum DFT, and no single

spot measurement can be more than 120% of the specifed

maximum DFT. The average value of the spot measurements

on each surface must conform to the specifed DFT. If there is

only a single spot measurement on a surface, it must conform

to the specifed DFT.

A3.4 SAMPLE DFT DETERMINATION: In lieu of a full

DFT determination of each painted piece as described in

Section A2.2, the job specifcation may require only a sample

DFT determination for selected pieces.

A3.4.1 Beams less than 20 ft (6 m): Follow the procedure

described in Section A2.4.1.

A3.4.2 Beams greater than 20 ft (6 m): up to 60 ft (18 m)

in length: Follow the procedure described in Section A2.4.2.

A3.4.3 Miscellaneous parts: For a miscellaneous part,

take three spot measurements, randomly distributed on the

part. Each spot measurement must conform to the specifed

DFT.

A3.5 NON-CONFORMANCE: If any spot measurement

falls outside the specifed range, additional measurements

may be made to defne the non-conforming area.

A3.6 RESTRICTED ACCESS: If a beam or miscellaneous

part is situated such that one or more of the surfaces are not

accessible, take measurements on each accessible surface in

accordance with Section A2.2 or Section A2.4, as specifed.

A3.7 NUMBER OF BEAMS OR PARTS TO MEASURE:

In a laydown, the number of beams or parts to receive a full

DFT determination and the number to have a sample DFT

determination can be specifed. For example, do a full DFT

determination on a piece painted near the beginning of the

shift, near the middle of the shift, and near the end of the shift

in accordance with Section A3.2; and perform a sample DFT

determination on every third piece in accordance with Section

A3.4.

A3.8 ATTACHMENTS: Stiffeners and other attachments

to a beam shall be arbitrarily measured.

APPENDIX 4 - Method for Measuring Dry Film Thick-

ness on Coated Steel Test Panels

Appendix 4 is not a mandatory part of this standard, but it

provides a sample protocol for measuring DFT on coated steel

test panels.

A4.1 PANEL SIZE: The test panel shall have a minimum

area of 18 in

2

(116 cm

2

) and a maximum area of 144 in

2

(930 cm

2

); e.g., minimum 3 x 6 inch (7.5 x 15 cm) and maximum

12 x 12 inch (30 x 30 cm).

A4.2 PROCEDURE: Use a Type 2 electronic gage. Take

two spot readings from the top third, the middle third, and the

bottom third of the test panel. Readings shall be taken at least

½ inch (12 mm) from any edge and 1 inch (25 mm) from any

other spot reading. Discard any unusually high or low gage

reading that cannot be repeated consistently. The DFT of the

test panel is the average of the six acceptable spot readings.

A4.3 MINIMUM THICKNESS: The average of the accept-

able spot readings shall be no less than the specifed minimum

thickness. No single spot reading shall be less than 80% of the

specifed minimum.

A4.4 MAXIMUM THICKNESS: The average of the

acceptable spot readings shall be no more than the specifed

maximum thickness. No single spot reading shall be more than

120% of the specifed maximum.

A4.5 REJECTION: If a spot reading is less than 80% of

the specifed minimum DFT or exceeds 120% of the speci-

fed maximum DFT, additional measurements may be made

to reevaluate the DFT on the area of the test panel near the

SSPC-PA 2

May 1, 2012

9

low or high spot reading. If the additional measurements indi-

cate the DFT in the disputed area of the panel to be below

the minimum or above the maximum allowable DFT, the panel

shall be rejected.

APPENDIX 5 - Method for Measuring Dry Film Thick-

ness of Thin Coatings on Coated Steel Test Panels

that have been Abrasive Blast Cleaned

Appendix 5 is not a mandatory part of this standard, but

it provides a sample protocol for measuring DFT of thin coat-

ings on coated steel test panels that had been abrasive blast

cleaned.

A5.1 For the purposes of this standard, a coating is

defned as thin if the dry flm thickness (DFT) is on the order of

1 mil (25 µm) or less. Because the DFT is the same order as

the statistical fuctuations of a DFT gage on bare blast cleaned

steel, many gage readings must be taken to get a meaningful

average.

A5.2 PANEL SIZE: The test panel shall have a minimum

area of 18 in

2

(116 cm

2

) and a maximum area of 144 in

2

(930 cm

2

); e.g., minimum 3 x 6 inch (7.5 x 15 cm) and maximum

12 x 12 inch (30 x 30 cm).

A5.3 PROCEDURE: Use a properly adjusted Type 2

electronic gage. Take ten gage readings randomly distributed

in the top third of the panel. Compute the mean (average)

and standard deviation of these ten readings. Similarly, take

ten readings from the middle third and ten readings from the

bottom third of the test panel and compute their means and

standard deviations. Readings shall be taken at least ½ inch

(12 mm) from any edge and 1 inch (25 mm) from any other

gage reading. Discard any unusually high or low gage reading,

i.e., a reading that is more than three standard deviations from

the mean. The DFT of the test panel is the average of the three

means.

A5.4 MINIMUM THICKNESS: The average of the means

shall be no less than the specifed minimum thickness. No

single mean shall be less than 80% of the specifed minimum.

A5.5 MAXIMUM THICKNESS: The average of the means

shall be no more than the specifed maximum thickness.

No single mean shall be more than 120% of the specifed

maximum.

APPENDIX 6 - Method for Measuring fhe Dry Film

Thickness of Coatings on Edges

Appendix 6 is not a mandatory part of this standard, but it

provides a sample protocol for measuring DFT of coatings on

edges.

A6.1 Type 2 gage manufacturers offer a variety of probe

confgurations, some of which are less affected by proximity

to edges and are designed to better measure the thickness of

coatings on edges. The user should consult the gage manu-

facturer’s instructions before measuring coating thickness on

edges. SSPC-PA Guide 11 describes the use of coatings with

edge retention properties and references a method (MIL-PRF-

23236D) for assessing edge retention properties of coatings.

A6.2 Prior to measurement of coating on edges, the gage

and probe should be verifed for accuracy by placing a thin,

fexible shim onto the prepared, uncoated edge. Adjustments

to the gage may or may not be required. This procedure also

verifes that the probe confguration will accommodate the

edge confguration prior to coating thickness data acquisition.

A6.3 Obtain a minimum of three gage readings within 1.5

linear inches (~4 linear cm) of coated edge. The average of

the gage readings is considered a spot reading. The number of

spot readings 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 is not a mandatory part of this standard, but it

provides a sample protocol for measuring DFT of the exterior

of coated pipe.

A7.1 Pipe sections that are loaded onto a cart or rack

are considered a complete unit, as opposed to a single joint

of pipe. 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 can be calculated using the formula below:

Area = (length of each pipe x circumference) x number of pipe

sections on cart or rack

A7.2 Some carts may have several small items that could

exceed the number of spot DFT readings required based on

TABLE A7

NUMBER AND LOCATIONS OF SPOT MEASUREMENTS – PIPE SPOOLS

Pipe Diameter Circumferential Spot Measurements Interval Spacing

Up to 12 in (30 cm) 4 evenly spaced 10 feet (3 meters) apart

14 to 24 inches (36-60 cm) 6 evenly spaced 10 feet (3 meters) apart

Greater than 24 inches (60 cm) 8 evenly spaced 10 feet (3 meters) apart

SSPC-PA 2

May 1, 2012

10

total square footage. In this case, the Owner/Contractor may

select a Pipe DFT frequency Level shown below:

A7.2.1 Pipe DFT Level 1 Area = (length of each pipe x

circumference) x no. of pipe sections on cart or rack = (number

of spot measurements) x 2

A7.2.2 Pipe DFT Level 2 Area = (length of each pipe x

circumference) x no. of pipe sections on cart or rack = (number

of spot measurements) x 3

A7.2.3 Pipe DFT Level 3 Area = (length of each pipe x

circumference) x no. of pipe sections on cart or rack = (number

of spot measurements) x 4

A7.2.4 Pipe DFT Level 4 Area = (length of each pipe x

circumference) x no. of pipe sections on cart or rack = (number

of spot measurements) x 5

A7.2.5 Pipe DFT Level 5 Area = (length of each pipe x

circumference) x no. of pipe sections on cart or rack = (number

of spot measurements) x 6

A7.3 Pipe spools that are not loaded onto a rack or cart

are measured individually. The number and locations of spot

measurements are based on Table A7. Three sets of four

circumferential spot measurements should be obtained on

pipe spools less than 10 feet (3 meters) in length.

A7.4 A challenge for the painter in coating fabricated pipe

spools is providing a uniform thickness throughout the entire

surface. On a fabricated pipe spool, valves, fanges, and

elbows tend to have low or high DFTs when compared to the

straight run section. Painters may develop a pattern of work for

a specifc task. Hence, the DFT on the fange and valves may

be consistently on the high side or the low side of the target

DFT. This type of error is easy to detect and correct. Random

errors pose a more diffcult problem. Gross errors where the

paint is obviously too thin or too thick must be corrected and

are beyond the scope of this standard.

The number of spot measurements in this protocol may far

exceed the “5 spot measurement per 100 ft

2

(10 m

2

)” required

in the standard. The full DFT determination, described in Table

A7, provides a very thorough inspection of a joint of pipe. The

DFT determination, described in Section A7.1, may allow for

fewer spot measurements. The user does not have to require a

full DFT determination for every joint of pipe. For example, the

requirement may be for a full DFT determination on one pipe

out of ten, or a sample DFT determination on one pipe out of

fve, or a combination of full and sample DFT determinations.

APPENDIX 8 - Examples of the Adjustment of Type 2

Gages Using Shims

Appendix 8 does not form a mandatory part of this stan-

dard, but it provides examples of how to adjust Type 2 gages

using shims on roughened (e.g., abrasive blast cleaned)

surfaces.

This example describes a method of adjustment to

improve the effectiveness of a Type 2 (electronic) gage on a

blast cleaned or otherwise roughened surface. Blast cleaning

is used throughout this example, but these methods are appli-

cable to other types of surface preparation. A less uniform

surface, such as partially rusted hand tool cleaned steel, may

require more gage readings to achieve a satisfactory level of

statistical signifcance. Since gage operation differs among

manufacturers, follow the manufacturer’s instructions for

adjustment of a particular gage.

A Type 2 gage needs to be adjusted to account for the

profle of the substrate in order to read the coating thickness

directly. Type 2 gages equipped with double pole probes

may provide greater measuring precision on rough surfaces

compared to single pole probes.

A portion of the substrate, after blast cleaning but prior

to coating, can be used to adjust the gage. Alternatively, an

uncoated test panel, blast cleaned at the time the structure

was blast cleaned and having a profle representative of the

structure can be used to adjust the gage provided the test

panel is of material with similar magnetic properties and geom-

etry as the substrate to be measured. If this is not available

then a correction value can be applied to a smooth surface

adjustment as described in A8.3.

Three adjustment techniques can be used depending

on the capability and features of the gage to be used for the

inspection. Note that due to the statistical variation produced

TABLE A8

TYPICAL GAGE CORRECTION VALUES USING ISO 8503 PROFILE GRADES

(SOURCE: ISO 19840)

1

ISO 8503 Profle Grade Correction Value (mil) Correction Value (µm)

Fine 0.4 10

Medium 1.0 25

Coarse 1.6 40

1

International Organization for Standardization (ISO), Case Postale 56, Geneva CH-1211, Switzerland. ISO standards

are available online from the American National Standards Institute (ANSI), 1819 L Street, NW, Suite 600, Washington,

DC 20036 or at <http://www.ansi.org>

SSPC-PA 2

May 1, 2012

11

by a roughened surface, individual readings taken using these

three methods may not perfectly agree.

The frst two examples describe adjustment and verifca-

tion to one or more shims. When shims are used, resultant

gage measurements are less accurate and must be recalcu-

lated. For example, if the accuracy of a properly calibrated

gage is ± 2% and the thickness of a shim is accurate to within

± 3%, the combined tolerance of the gage and the shim will be

± 4% as given by the sum of squares formula:

√2

2

+ 3

2

= 3.6055 ≈ 4%

For the gage to be in agreement with the shim, the

average thickness measured by the gage must be within ±4%

of the shim’s thickness. If the average thickness measured on

a 250-µm (10-mil) shim is between 9.6 mils (240 µm) and 10.4

mils (260 µm), the gage is properly adjusted. The minimum

240 is 250 minus 4% of 250 (9.6 is 10 minus 4% of 10); the

maximum of 260 is 250 plus 4% of 250 (10.4 is 10 plus 4% of

10). [4% of 250 is 10; 4% of 10 is 0.4.]

A8.1 SINGLE POINT ADJUSTMENT: This example uses

a single shim value 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 4.0

mil (100 µm) then a shim of approximately 4.0 mil (100 µm) or

slightly greater should be used to adjust the gage. The shim is

placed on an area of the substrate that has been blast cleaned

to the required standards, or on a blasted test coupon with a

similar surface profle.

The average of 10 readings on the shim is suffcient to

allow for the statistical variation in the blast profle.

A8.2 TWO POINT ADJUSTMENT: This example uses

two shim values, one above and one below the expected flm

thickness to be measured. It should be noted that not all flm

thickness gages can be adjusted in this manner.

Assuming that the coating thickness to be measured is

4.0 mil (100 µm) then shims of 10.0 mil (250 µm) and 2.0 mil

(50 µm) are appropriate for setting the upper and lower values

on the scale of the gage.

As protective coatings are normally applied to blast

cleaned metal surfaces, a statistical approach is required to

obtain a typical value for the adjustment. Ten readings on a

shim are suffcient to establish a reliable average value for that

shim on the roughened surface. Following the manufacturer’s

instructions, the gage is adjusted so that the actual shim thick-

ness is then used to set the gage.

This procedure should be repeated for both the upper and

lower shim values.

The average of 10 readings on an intermediate shim,

approximately 4.0 mil (100 µm) thick in the case described

above, will confrm that the gage has been adjusted correctly.

It is acceptable for the average reading to be within ± 4% of the

shim thickness.

This method ensures that the gage reads the thickness of

the coating over the peaks of the profle.

A8.3 SMOOTH SURFACE ADJUSTMENT: 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. Adjust the gage on a smooth surface

according to the manufacturer’s instructions. Alternatively,

it may be possible to adjust some Type 2 gages through the

coating already applied to an abrasive blast cleaned substrate

(may be necessary if no uncoated substrate exists). This

procedure should be performed according to the manufac-

turer’s instructions.

Readings taken on the blast-cleaned substrate will be

higher than the true value by an amount dependant on the

surface profle and the gage probe design. For most appli-

cations a correction value of 1.0 mil (25 µm) is generally

applicable. Note that this value is not related to the actual

surface profle measurement. This correction value must be

subtracted from each gage reading to correct for the effect

of the profle. The resulting corrected reading represents the

thickness of the coating over the peaks.

For fne profles the correction value may be as low as 0.4

mil (10 µm) but for coarse profles it could be as high as 1.6

mil (40 µm). Table A8 gives approximate correction values to

be used when a blast-cleaned surface is not available to adjust

the gage.

The use of coated standards to adjust gages means that

a correction value must be applied to readings, as the coated

standards make use of smooth substrate surfaces.

Copyright ©

SSPC standards, guides, and technical reports are copyrighted

world-wide by SSPC: The Society for Protective Coatings. Any

photocopying, re-selling, or redistribution of these standards,

guides, and technical reports by printed, electronic, or any other

means is strictly prohibited without the express written consent

of SSPC: The Society of Protective Coatings and a formal

licensing agreement.

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