1、SSPC-PA 9July 20, 2015Editorial revisions August 8, 20151SSPC: The Society for Protective CoatingsPAINT APPLICATION SPECIFICATION NO. 9Measurement of Dry Coating Thickness Using Ultrasonic Gages1. Scope1.1 This standard describes procedures to measure the thickness of dry, homogeneous coatings appli
2、ed on a variety of surfaces such as concrete, wood, wallboard, plastic, fiber and composite material 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 int
3、ended to replace them.1.2 The procedures for calibration, adjustment, and general use of ultrasonic coating thickness gages are described in ASTM D6132 and the gage manufacturers instructions. This document focuses on the correct method for taking measurements.1.3 Current ultrasound technology may n
4、ot be capable of accurately measuring the DFT of some coatings (see Notes 9.1 and 9.2).2. Description2.1 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 t
5、o project specifications.2.2 DESCRIPTION OF GAGES: Ultrasonic gages 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 9.3).2.3 DEFINITIONS2.3.1 Gage Reading: A single instrument r
6、eading. 2.3.2 Spot Measurement: The average of three or at least three gage readings made within a 15-cm (6-inch) diameter circle.Discussion: 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 discar
7、ded. The average of the acceptable gage readings is the spot measurement.2.3.4 Homogeneous: Of the same or similar 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
8、sand.3. References3.1 The date of the referenced standards in effect at he time of publication of this standard is shown below. Upon mutual agreement, the latest revision of a referenced standard in effect on the date of invitation to bid may be used, provided it does not change the technical requir
9、ements of this SSPC standard. Standards marked with an asterisk (*) are referenced 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 pr
10、evail.3.3 ASTM INTERNATIONAL STANDARDS * D1005-95(2013) Standard Test Method for Measure-ment of Dry-Film Thickness of Organic Coatings Using Micrometers * D4138-07a(2013) Standard Test Methods for Measure-ment of Dry Film Thickness of Protective Coating Systems by Destructive, Cross-Sectioning Mean
11、s * D4414-95(2013) Standard Practice for Measurement of Wet Film Thickness by Notch Gages D6132-13 Standard Test Method for Nonde-structive Measurement of Dry Film Thickness of Applied Organic Coatings Using an Ultrasonic Coating Thickness Gage * D7091-13 Standard Practice for Nondestructive Measure
12、ment of Dry Film Thickness of Nonmagnetic Coatings Applied to Ferrous Metals and Nonmagnetic, Nonconductive Coatings Applied to Non-Ferrous Metals3.4 SSPC STANDARDS* SSPC-PA 2(2015) Procedure for Determining Confor-mance to Dry Coating Thickness RequirementsSSPC-PA 9July 20, 2015Editorial revisions
13、August 8, 201524. Gage RequirementsThe ultrasonic gage shall be capable of measuring the thickness of a coating over a non-metallic substrate. To qualify under this standard, the gage shall have a minimum accuracy within 5 percent. All gages shall be calibrated and adjusted following the manufacture
14、rs instructions and be in accordance with ASTM D 6132.5. Calibration and Verification of Accuracy5.1 ASTM D6132 describes three operational steps necessary to ensure accurate coating thickness measurement: calibration, verification of accuracy and adjustment of coating thickness measuring gages, as
15、well as proper methods for obtaining coating thickness measurements. These steps shall be completed before taking coating thickness measurements to determine conformance to a specified coating thickness range. Verification of accuracy shall be performed in accordance with ASTM D6132.5.2 Gages shall
16、be calibrated by the equipment manufacturer, its authorized agent, or an accredited calibration laboratory. A test certificate 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 req
17、uired. Calibration intervals are usually established based upon experience and the work environment, or when specified. 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 verified
18、according to the procedures described in ASTM D6132. Verification shall be performed, at minimum, at the beginning and end of each work shift. 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
19、 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
20、 verify gage accuracy. If the same gage, reference standard, and method of verification are used throughout a job, the information need be recorded only once. The stated value of the standard and the measured value shall be recorded each time accuracy is verified.5.5 If the gage fails the post-measu
21、rement accuracy verification check, all measurements acquired since the last accuracy verification 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 measur
22、ing accurately, it shall not be used until it is repaired and/or recalibrated (usually by the gage manufacturer).6. Measurement Procedures6.1 Verify that the gage will provide accurate readings of the coating to be measured, using the procedure in Note 9.2.6.2 NUMBER OF READINGS: Repeated gage readi
23、ngs, even at points close together, often differ due to small surface irregularities of the coating and the substrate (see Notes 9.4 and 9.5). 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 lo
24、cation within the 15-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 readings that are not repeated consistently. The average of the acceptable gage readings is the spot mea
25、surement. See Note 9.6 regarding removal of couplant after completing spot measurements.6.3 NUMBER OF MEASUREMENTS: Unless otherwise specified in the procurement documents (project specification), an area measurement is obtained by taking five (5) separate spot measurements (average of the gage read
26、ings, described in Section 6.2) randomly spaced throughout each 10-m2(approximately 100-ft2) area to be measured and representative of the coated surface. The five spot measurements shall be made for each 10-m2(100-ft2) area as follows:6.3.1 For areas of coating not exceeding 30 m2(300 ft2) in area,
27、 each 10-m2(100 ft2) (or increment thereof) area shall be measured.6.3.2 For areas of coating greater than 30 m2(300 ft2) in area and not exceeding 100 m2(1,000 ft2) in area, three 10-m2(100-ft2) (or increment thereof) areas shall be arbitrarily selected by the inspector and measured.6.3.3 For areas
28、 of coating greater than 100 m2(1000 ft2) in area, the first 100 m2(1000 ft2) shall be measured as stated in Section 6.3.2. For each additional 100-m2(1000-ft2) coated area (or increment thereof), arbitrarily select and measure one 10-m2(100-ft2) area.6.4 NONCONFORMING AREAS: If the coating thicknes
29、s for any 10-m2(100-ft2) area is not in compliance with the contract documents, the procedure described here shall be followed to assess the magnitude of the nonconforming thickness. 6.4.1 Determine the spot DFT at 1.5-m (5-ft) intervals in eight equally spaced directions radiating outward from the
30、nonconforming 10-m2(100-ft2) area. 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 ar
31、e acquired in that direction or until no additional measurements SSPC-PA 9July 20, 2015Editorial revisions August 8, 20153are possible. Acceptable spot measurements are defined by the minimum and maximum values in the contract documents. No allowance is made for variant spot measurements, as is the
32、practice when determining the area DFT. An illustration of this procedure is shown in Figure 1.6.4.1.1 On complex structures or in other cases where making spot measurements at 1.5-m (5-ft) intervals is not practical, spot measurements shall be performed on repeating structural units or elements of
33、structural units. This method shall be used when the largest dimension of the unit is less than 3 m (10 ft). Make spot measurements 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. 6.3
34、.2 Non-compliant areas shall be demarcated using removable chalk or other specified marking material and documented. All of the area within 1.5 m (5 ft) of any non-compliant spot measurement shall be designated as non-compliant. For a given measurement direction or unit measurement, any compliant ar
35、ea 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 (see Note 9.7).7. Conformance to Specified Thickness7.1 A minimum and a maximum thickness are normally specified for each layer of coating
36、. If a single thickness value is specified 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 percent (%) of the stated value. 7.2 Table 1 provides four thickness restriction levels. Level 1 is the
37、 most restrictive and does not allow for any deviation of spot or area measurements from the specified minimum and maximum thickness, while Level 4 is the least restrictive. Depending on the coating type and the prevailing service environment, the specifier selects the dry film thickness restriction
38、 level for a given project. If no restriction level is specified, then Level 3 is the default. It is possible to specify a maximum thickness threshold for Level 4 Spot or Area measurements for some generic product types and service environments. 7.3 For the purpose of final acceptance of the total d
39、ry film thickness, the cumulative thickness of all coating layers shall be no less than the cumulative minimum specified thickness and no greater than the cumulative maximum specified thickness.8. Disclaimer8.1 While every precaution is taken to ensure that all information furnished in SSPC standard
40、s 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 specified therein, or of the standard itself.FIGURE 1DETERMINING EXTENT OF NONCONFORMING AREASSSPC-PA 9July 20, 2015Editorial rev
41、isions August 8, 201548.2 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 practices described herein, is responsible for instituting appropriate health and safety practices and for ensurin
42、g compliance with all governmental regulations.9. NotesNotes are not requirements of this standard.9.1 PROBLEM COATINGS: Ultrasonic gages are not recommended for certain coatings, such as mortars, which are heavily filled with aggregate. Similarly, an acrylic floor coating may contain flakes that we
43、re broadcast across the wet coating, creating a non-homogeneous medium whose thickness is difficult to determine accurately with ultrasonic gages. If thickness readings are suspect, they can be verified using destructive means per ASTM D4138 (see Note 9.8).9.2 DETERMINING COATING SUITABILITY FOR DFT
44、 MEASUREMENT USING ULTRASONIC TECHNOLOGY: To determine if it is possible to accurately measure coatings described in Note 9.1 using an ultrasonic gage, apply the coating to a smooth steel panel. Verify the measurement accuracy of an SSPC-PA 2, Type 2 electronic gage for use on ferrous substrates per
45、 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 described in ASTM D7091. Next, verify the measurement accuracy of the ultrasonic gage using the manufacturers
46、 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 combined tolerances of both instruments. If repeatable readings fall outside this tolerance, follow the manufactu
47、rers 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 9.8).9.3 MEASUREMENT RANGE: Ultrasonic thickness gages can measure polymer coating thicknesses from approximately 8
48、m to 7.6 mm (0.3 to 300 mils). The upper limit depends on the acoustical properties of the material being measured and the transducer in the probe.9.4 REPEATABILITY: Ultrasonic gages are sensitive to small irregularities of the coating surface or of the surface directly below the probe center. Repea
49、ted gage readings 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.9.5 VARIATION 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 individual spot measurement is permitted to be below the specified minimum thickness as long as
