1、Designation: G 12 07Standard Test Method forNondestructive Measurement of Film Thickness of PipelineCoatings on Steel1This standard is issued under the fixed designation G 12; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the yea
2、r of last revision. A number in parentheses indicates the year of last reapproval. A superscriptepsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the nondestructive measure-ment of the thickness of a dry, nonmagnetic coating applie
3、d tothe external surface of steel pipe. The method is recommendedfor coating thicknesses up to 6 mm (0.240 in.) and for anydiameter pipe, but not smaller than 10 mm (0.5 in.). It does notapply to excessively soft films.1.2 The values stated in SI units to three significant deci-mals are to be regard
4、ed as the standard. The values given inparentheses are for information only.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determi
5、ne the applica-bility of regulatory limitations prior to use.2. Summary of Test Method2.1 The coating thickness is determined by an instrumentthat measures thickness by nondestructive techniques, based onvariations in magnetic flux or magnetic attraction between itsdetection unit and the magnetic ba
6、se material.3. Significance and Use3.1 Measurements of film thickness are an essential part ofmost ASTM test methods related to coatings on steel pipe.Adequate thickness is important for a coating to fulfill itsfunction of preventing or mitigating corrosion of steel pipe-lines.3.2 The accuracy of th
7、e thickness measurements may beinfluenced by the deformability of the coating. This testmethod is not applicable to coatings that would be readilydeformable under the force exerted by the probe of themeasuring instrument.4. Apparatus4.1 The apparatus shall be a nondestructive-type thicknessgage capa
8、ble of being standardized over its range of intendeduse. It shall be designed so that variations in magnetic flux ormagnetic attraction between its detection unit and the steel basecan be calibrated to indicate the thickness of the coatingmaterial.4.2 It shall be suitable for measuring thicknesses o
9、f dry,nonmagnetic coatings on either a flat or a circular base.5. Standardization of Instruments5.1 The instrument shall be standardized in accordance withthe manufacturers instructions before use by employing suit-able thickness standards. The standardization shall be checkedat frequent intervals d
10、uring use.5.2 Nonmagnetic standards of uniform thickness are avail-able in either of two types, foil or coated substrate, as suppliedor recommended by the manufacturer of the instrument.5.2.1 Foils (Shims)The thickness of the foil should be asclose as possible to the expected thickness of the coatin
11、g to bemeasured. The foil should be placed on a smooth, clean,low-carbon, steel plate, making certain that there is intimatecontact between the foil and the substrate. It is recommendedthat single foils of proper thickness be used and that foils bereplaced frequently, since they are subject to inden
12、tation. Foilsare advantageous for standardizing on curved surfaces and areoften more readily available than coated standards.NOTE 1For some instruments there is an effective depth of penetra-tion of the field created by the instrument probe. This is the critical depthof thickness at which the instru
13、ment will no longer be affected byincreases of substrate thickness. Since it depends on the instrument andsubstrate, it should be determined experimentally.5.2.2 Coated Substrate Standards2These standards con-sist of nonmagnetic coatings of known thickness permanentlybonded to a low-carbon steel (10
14、10 grade) substrate, 8 mm(0.30 in.) thick. The thickness standard should be as close aspossible to the expected thickness of the coating to bemeasured.NOTE 2If the curvature of the coating to be measured is sufficient topreclude standardization on a flat surface, the standardization should bedone wi
15、th a standard foil on a substrate with the same curvature as thecoating to be measured.1This test method is under the jurisdiction of ASTM Committee D01 on Paintand Related Coatings, Materials, and Applications and is the direct responsibility ofSubcommittee D01.48 on Durability of Pipeline Coating
16、and Linings.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 1969. Last previous edition approved in 1998 as published G 12 83 (1998)which was withdrawn March 2007 and reinstated in July 2007.2Coated substrate standards may be obtained from the U. S. Department ofCom
17、merce, National Bureau of Standards, Standard Materials Unit, Washington,DC 20234.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.6. Procedure6.1 Operate each instrument in accordance with the manu-facturers instructions.6.2 Take a m
18、inimum of twelve readings per piece of pipe asfollows: Take three equally spaced readings along the topsurface; rotate the pipe 90 three times, taking three equallyspaced readings after each rotation. Record the average,minimum, and maximum of the twelve readings as the coatingthickness.NOTE 3Instru
19、ments with two contact poles shall be positioned on thecoating surface with the poles in the same plane.NOTE 4The anchor pattern of the steel pipe substrate must beconsidered for its effect on the accuracy of the measurements if the anchorpattern is greater than 25 % of the coating thickness.NOTE 5F
20、oreign materials such as dirt and grease shall be removed bysuitable cleaning without removing any coating materials.NOTE 6Measuring instruments and methods may depend on thetechnique of the operator. For example, the pressure applied to a probe andthe rate of applying a balancing force to a magnet
21、will vary from oneindividual to another. Often such differences can be reduced or eliminatedeither by having the gage calibrated by the same operator who will makethe measurement or by using constant-pressure probes. Probes must bepositioned perpendicular to the surface of the specimen at the point
22、ofmeasurement. Some magnetic instruments of the magnetic-attraction typerequire the pole piece to be in a vertical position. If a magnetic instrumentis to be used in a horizontal or upside-down position, its calibration forthat position should be verified.NOTE 7Instruments using magnetic attraction
23、are sensitive to thespeed with which the magnet is removed from the specimen. The magnetmust be removed so that thickness measurements are not affected by speedof removal.7. Report7.1 The report shall include the following:7.1.1 Complete identification of the specimen including:name and code number
24、of the coating; pipe diameter; source;production data, including surface preparation of the substrateand depth of anchor pattern, if known; and production runnumber.7.1.2 Name and type of instrument used, and method ofstandardization, and7.1.3 Number of thickness measurements taken, and theaverage,
25、minimum, and maximum value of the measurements.8. Precision and Bias8.1 The repeatability and reproducibility of thickness mea-surements will depend on the instrument design, the operator,and the particular measuring application.8.1.1 RepeatabilityWhen the same instrument is used bythe same operator
26、, duplicate measurements on the same sampleshould agree with each other within 65%.8.1.2 ReproducibilitySeparate operators using differentinstruments on a known thickness standard should obtainaverage results agreeing with each other within 10 % of thethickness standard.9. Keywords9.1 coatings; film
27、; nondestructive; nonmagnetic; pipeline;thicknessASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights
28、, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for re
29、vision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing yo
30、u shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).G12072
