1、SSPC-PA 9February 1, 20081SSPC: The Society for Protective CoatingsPainT aPPLiCaTiOn SPECiFiCaTiOn nO. 9Measurement of Dry Coating Thickness on Cementitious Substrates Using Ultrasonic Gages1. Scope1.1 This standard describes procedures to measure the thickness of dry, homogeneous coatings applied o
2、n cementi-tious surfaces using commercially available ultrasonic coating thickness gages. These procedures are intended to supplement manufacturers operating instructions for the manual operation of the gages and are not intended to replace them.1.2 The procedures for calibration, adjustment, and ge
3、neral use of using ultrasonic coating thickness gages are described in ASTM D 6132 and the gage manufacturers instructions. This document focuses on the correct method for taking measurements.1.3 Current ultrasound technology may not be capable of accurately measuring the DFT of some coatings (see N
4、otes 8.1 and 8.2). 2. Description 2.1 The procedures described in this standard include criteria for determining the number of measurements, location of measurements, and whether the dry film thickness (DFT) of the coating conforms to project specifications. 2.2 Description of Gages: Ultrasonic gage
5、s use a transducer in the probe to send pulses into the coating and measure the time taken by that pulse to return to the probe tip to calculate coating thickness (see Note 8.3).2.3 DEFiniTiOnS2.3.1 Gage Reading: A single reading at one point.2.3.2 Spot Measurement: The average of at least three gag
6、e readings made within a 15 cm (6 inch) diameter circle.2.3.3 Structure: A unit composed of one or more connected concrete members. It is possible for a single concrete shape (beam, pipe, channel, etc.) to be considered a structure if it is painted in a shop.2.3.4 Homogeneous: of the same or similar
7、 in composition or structure. In this standard, the term “homogeneous coating” refers to a coating of uniform composition throughout that does not contain large, solid particles such as sand.2.3.5 Calibration: The controlled and documented process of measuring traceable calibration standards and ver
8、ifying that the results are within the stated accuracy of the gage. Cali-brations are typically performed by the gage manufacturer or by a qualified laboratory in a controlled environment using a documented process. The standards used in the calibration are such that the combined uncertainties of th
9、e resultant measure-ment are less than the stated accuracy of the gage.2.3.6 Verification: An accuracy check performed by the user using known reference standards.2.3.7 adjustment: The act of aligning the gages thick-ness readings to match those of a known sample in order to improve the accuracy of
10、the gage on a specific surface or in a specific portion of its measurement range.3. References3.1 The latest issue, revision, or amendment of the refer-enced standards in effect on the date of invitation to bid shall govern, unless otherwise specified. Standards marked with an asterisk (*) are refer
11、enced only in the Notes, which are not requirements of this standard.3.2 If there is a conflict between the requirements of any of the cited referenced standards and this standard, the requirements of this standard shall prevail.3.3 aSTM inTERnaTiOnaL STanDaRDS1* D 4138 Standard Test Methods for Mea
12、surement of Dry Film Thickness of Protective Coating Systems by Destructive, Cross-Sectioning MeansD 6132 Standard Test Method for Nondestructive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Gage1 ASTM International, 100 Barr Harbor Drive, West Conshohock-en, PA
13、19428-2959. Standards are available online from http:/www.astm.org.SSPC-PA 9February 1, 20082* D 7091 Standard Practice for Nondestructive Measurement of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals* SSPC-P
14、a 2 Measurement of Dry Coating Thickness with Magnetic Gages4. Gage RequirementsThe ultrasonic gage shall be capable of measuring the thickness of a coating over a cementitious substrate. To qualify under this standard, the gage shall have a minimum accu-racy within 10%. All gages shall be calibrate
15、d and adjusted following the manufacturers instructions and be in accordance with ASTM D 6132. 5. Measurement Procedures 5.1 Verify that the gage will provide accurate readings over the coating to be measured, using the procedure in Note 8.2. 5.2 SPOT MEaSUREMEnT: Repeated gage readings, even at poi
16、nts close together, usually differ due to surface irregularities of the coating and the substrate (see Notes 8.4 and 8.5). Therefore, 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 15
17、 cm (6 inch) diameter circle defining the spot. Each gage reading shall be at least 5 cm (2 inches) from the other gage readings. Discard any single unusually high or low gage reading that cannot be repeated consistently. Take the average of the acceptable gage readings as the spot measure-ment (see
18、 Note 8.6).5.3 nUMBER OF MEaSUREMEnTS: Make five (5) separate spot measurements (average of the gage readings, see Section 5.2) spaced arbitrarily over each 10 m2(108 ft2) area to be measured unless otherwise specified. The five spot measurements shall be made for each 10 m2(108 ft2) of area as foll
19、ows:5.3.1 For structures not exceeding 30 m2(323 ft2) in area, each 10 m2(108 ft2) (or increment thereof) area shall be measured.5.3.2 For structures not exceeding 100 m2(1,076 ft2) in area, three 10 m2(108 ft2) (or increment thereof) areas shall be arbitrarily selected by the inspector and measured
20、.5.3.3 For structures exceeding 100 m2(1,076 ft2) in area, the first 100 m2(1,076 ft2) shall be measured as stated in Section 5.3.2 and for each additional 100 m2(1,076 ft2) of area (or increment thereof), one 10 m2(108 ft2) area shall be arbitrarily selected by the inspector and measured.5.3.4 If t
21、he dry film thickness for any 10 m2(108 ft2) area or increment thereof (see Sections 5.3.1, 5.3.2 and 5.3.3) is not in compliance with the requirements of Section 6, additional measurements shall be made to isolate the non-conforming area, and each 10 m2(108 ft2) area painted during that work shift
22、shall be measured. 5.4 SPECiFYinG THiCKnESS: Both a maximum and a minimum thickness are customarily specified for the coating. If a maximum thickness value is not specified, (as in Restric-tion Level 4 of Table 1) the specified thickness shall be the minimum and there shall be no maximum. Table 1Res
23、triction Levels Coating Thickness on ConcreteThicknessSpotReadingarea ReadingLevel 1Minimum As specified As specifiedMaximum As specified As specifiedLevel 2Minimum As specified As specifiedMaximum 125% of maximum As specifiedLevel 3Minimum 75% of minimum As specifiedMaximum 125% of maximum As speci
24、fiedLevel 4Minimum 75% of minimum As specifiedMaximum Unrestricted UnrestrictedSSPC-PA 9February 1, 200836. COnFORManCE TO SPECiFiED THiCK-nESS6.1 Thickness Restriction Levels: Table 1 provides four thickness restriction levels. Level 1 is the most restrictive and does not allow for any deviation of
25、 spot or area measurements from the specified minimum and maximum thickness, while Level 4 is the least restrictive. The owner shall specify the dry film thickness restriction level for a given project. There is no restriction on individual gauge readings provided that the spot readings and the aver
26、age for the area conform to the require-ments given in Table 1. 6.2 Minimum Thickness: The average of the spot measurements for each 10 m2(108 ft2) area shall not be less than the specified minimum thickness in Table 1. No single spot measurement in any area shall be less than the speci-fied minimum
27、 thickness in Table 1. If the average of the spot measurements for a given area meets or exceeds the specified minimum thickness, but one or more spot measurements is less than the specified minimum thickness, additional measure-ments shall be made to define the non-conforming area (see Appendix 1 a
28、nd Note 8.7).6.3 Maximum Thickness: The average of the spot measure-ments for each 10 m2(108 ft2) area shall not be more than the specified maximum thickness stated in Table 1. Although no single spot measurement in any 10 m2(108 ft2) area shall be more than 125% of the specified maximum thickness s
29、tated in Table 1, it is permissible for any single gage reading to over-run by a greater amount. If the average of the spot measurements for a given 10 m2(108 ft2) area meets or falls below the speci-fied maximum thickness, but one or more spot measurements is more than the specified maximum thickne
30、ss, additional measurements shall be made as specified to define the non-conforming area (see Appendix 1).7. Disclaimer7.1 While every precaution is taken to ensure that all information furnished in SSPC standards is as accurate, complete and useful as possible, SSPC cannot assume responsibility nor
31、 incur any obligation resulting from the use of any materials, coatings or methods specified therein, or of the standard itself.7.2 This standard does not attempt to address problems concerning safety associated with its use. The user of this standard, as well as the user of all products or practice
32、s described herein, is responsible for instituting appropriate health and safety practices and for ensuring compliance with all governmental regulations.8. notesNotes are not requirements of this standard.8.1 PROBLEM COaTinGS: Ultrasonic gages are not recommended for certain coatings, such as mortar
33、s, that are heavily filled with aggregate. Similarly, an acrylic floor coating may contain flakes that were broadcast across the wet coating, creating a non-homogeneous medium whose thickness is diffi-cult to determine accurately with ultrasonic gages. If thickness readings are suspect, they can be
34、verified using destructive means per ASTM D 4138 (see Note 8.8). 8.2 DETERMininG COaTinG SUiTaBiLiTY FOR DFT MEaSUREMEnT USinG ULTRaSOniC TECHnOLOGY: To determine if it is possible to accurately measure coatings described in Note 8.1 using an ultrasonic gage, apply the coating to a smooth steel pane
35、l. Verify the measurement accuracy of an SSPC-PA 2, Type 2 electronic gage for use on ferrous substrates per manufacturers instructions. Measure the coating DFT on the steel test panel using the Type 2 electronic gage, and record the results. The procedures for measurement using magnetic gages are d
36、escribed in ASTM D 7091. Next, verify the measurement accuracy of the ultrasonic gage using the manufacturers instructions, and measure the DFT on the same test panel. Compare the results of the Type 2 electronic gage with readings taken by the ultrasonic gage. The readings should be within the comb
37、ined tolerances of both instruments. If repeatable readings fall outside this tolerance, follow the manufacturers instructions to perform an adjustment to the ultrasonic gage. If repeatable measurements still cannot be obtained, alternative methods of determining DFT should be used (see Note 8.8). 8
38、.3 MEaSUREMEnT RanGE: Ultrasonic thickness gages can measure polymer coating thicknesses from approximately 8 m to 15 mm (0.3 to 600 mils). The upper limit depends on the acoustical properties of the material being measured and the transducer in the probe.8.4 REPEaTaBiLiTY: Ultrasonic gages are sens
39、itive to small irregularities of the coating surface or of the concrete surface directly below the probe center. Repeated gage read-ings on a rough surface, even at points very close together, frequently differ considerably, particularly for thin films over a rough surface with a high profile.8.5 Va
40、RiaTiOn in THiCKnESS (75% of MiniMUM): In any measurement there is a level of uncertainty. Two individuals using the same ultrasonic gage will not necessarily record the exact same number for a given spot measurement using the same 15 cm (6 inch) diameter circle. To allow for this variation, an indi
41、vidual spot measurement is permitted to be below the specified minimum thickness as long as other spots in the 10 m2(108 ft2) area are high enough to make the average thick-ness meet or exceed the specified minimum thickness. SSPC-PA 9February 1, 200848.6 COUPLanT: It is recommended that the couplan
42、t be removed from the coating after making a spot measurement, especially if an additional coat is to be applied.8.7 CORRECTinG LOW THiCKnESS: Non-conforming areas should be corrected as specified.8.8 DESTRUCTiVE TESTinG: A paint inspection gage (sometimes called a Tooke or PIG gage) can give DFT me
43、asure-ments, but it cuts through the coating, so each measurement site must be repaired. The procedures for measurement using destructive gages are described in ASTM D 4138. The job specification should stipulate the number and location of areas to be tested by destructive means.aPPEnDiX 1 - numeric
44、al Example of average Thickness MeasurementAppendix 1 does not form a mandatory part of this stan-dard.The following numerical example is presented as an illustration of Section 5. Suppose this structure is 30 m2(323 ft2) in area. The owner requires Restriction Level 4, 75% minimum, no maximum. Ment
45、ally divide the surface into three equal parts, each being about 10 m2(108 ft2).Part A - 10 m2(108 ft2)Part B - 10 m2(108 ft2)Part C - 10 m2(108 ft2)First, measure the coating thickness on Part A. This involves at least 15 readings of the thickness gage (see Figure A1). Assume the specification requ
46、ires 640 m (25 mils) minimum thickness. The average thickness for area A is then the average of the five spot measurements made on area A, namely 660 m (26 mils).Spot 1 640 m 25 milsSpot 2 770 30Spot 3 540 21Spot 4 770 30Spot 5 580 23Avg. 660 m 26 milsConsidering the U.S. Customary Measurements: The
47、 average, 26 mils, exceeds the specified minimum of 25 mils and thus satisfies the specification. Next, determine if the lowest spot measurement, 21 mils, is within 75% of the speci-fied minimum thickness. Seventy-five percent of 25 mils is 19 mils (0.75 x 25 = 19). Although 21 mils is below the spe
48、cified minimum, it is still within 75 percent of it, so the specification is satisfied.There are individual gage readings of 15 mils at spot 5 and 18 mils at spot 3, both of which are clearly less than 19 mils. This is allowed because only the average of the three readings (i.e. the spot measurement
49、) must be greater than or equal to 19 mils. Because the owner required Level 4, no maximum DFT was specified.Considering Metric Measurements: The average, 660 m, exceeds the specified minimum of 640 m and thus satisfies the specification. Next, determine if the lowest spot measurement, 540 m, is within 75% of the specified minimum thickness. Seventy-five percent of 640 m is 480 m (0.75 x 640 = 480). Although 540 m is below the specified minimum, it is still within 75% of it, so the specification is satisfied. There are individual gage readings of 380 m at spot 5 and 460
