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 year of
2、 last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon(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 applied tothe exte
3、rnal 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 regarded as the standard
4、.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 determine the applica-bility
5、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 base material.3.Significan
6、ce 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 the thickness measurements
7、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 capable of being standardized o
8、ver 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 of dry,nonmagnetic coatings o
9、n 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 during use.5.2 Nonmagnetic stan
10、dards 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 coating to bemeasured.The foil should b
11、e 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 indentation.Foilsare advantageous for standa
12、rdizing on curved surfaces and areoften more readily available than coated standards.NOTE1For 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 instrument will no longer be affected byincrease
13、s 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(1010 grade)substrate,8 mm(0.30 in.)thick.The th
14、ickness standard should be as close aspossible to the expected thickness of the coating to bemeasured.NOTE2If the curvature of the coating to be measured is sufficient topreclude standardization on a flat surface,the standardization should bedone with a standard foil on a substrate with the same cur
15、vature 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 and Linings.Current edition approved July 1,2007.Publ
16、ished 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 ofCommerce,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.Copyright ASTM International Provided by IHS under license with ASTM Li
