ASTM_G_51_-_95_2012.pdf

Designation:G5195(Reapproved 2012)Standard Test Method forMeasuring pH of Soil for Use in Corrosion Testing1This standard is issued under the fixed designation G51;the number immediately following the designation indicates the year of originaladoption or,in the case of revision,the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers a procedure for determining thepH of a soil in corrosion testing.The principle use of the testis to supplement soil resistivity measurements and therebyidentify conditions under which the corrosion of metals in soilmay be accentuated(see G5778(1984).1.2 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.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 of regulatory limitations prior to use.2.Referenced Documents2.1 ASTM Standards:2E177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG57 Test Method for Field Measurement of Soil ResistivityUsing the Wenner Four-Electrode Method3.Significance and Use3.1 Information on pH of soil is used as an aid in evaluatingthe corrosivity of a soil environment.Some metals are moresensitive to the pH of their environment than others,andinformation on the stability of a metal as a function of pH andpotential is available in the literature.34.Apparatus4.1 pH MetersA portable,battery-powered pH meter isnecessary for field measurements.Most instruments can alsofunction as a high-impedance voltmeter.An LCD display ispreferred for its readability in a bright,outdoor environment.4.2 Calomel and Glass Electrodes:4.2.1 Use a saturated calomel reference electrode or itsequivalent in the pH determination.A few crystals of solidpotassium chloride should always be present within the cham-ber surrounding the calomel to assure that the solution issaturated under the conditions of use.The design of theelectrode must permit the formation of a fresh liquid junctionbetween the solution of potassium chloride and the buffer ortest soil for each test and allow traces of soil to be readilyremoved by washing.4.2.2 A glass electrode of rugged construction is required.The performance of the glass electrode is satisfactory if itfurnishes the correct pH value(60.1 pH unit)for standardbuffered solutions.4.2.3 A combination electrode consisting of a saturatedcalomel reference electrode and a glass electrode(4.2.1 and4.2.2)combined as a single electrode is acceptable.However,the requirements outlined above are equally applicable to theelectrodes used in this combination unit.4.3 Subsurface ProbeWhen pH measurements below thesurface of the soil are required,it is necessary to use a probe ofsuitable length which will allow measurements to be made atthe depth of interest.This probe consists of a glass electrode ora combination electrode in a rubber housing at the end of aplastic tube.One type of probe is illustrated in Fig.1.4.4 Soil ThermometerSome pH electrodes have tempera-ture compensation built in as part of the pH electrode,but most1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.10 onCorrosion in Soils.Current edition approved May 1,2012.Published June 2012.Originallyapproved in 1977.Last previous edition approved in 2005 as G5195(2005).DOI:10.1520/G0051-95R12.2For referenced ASTM standards,visit the ASTM website,www.astm.org,orcontact ASTM Customer Service at serviceastm.org.For Annual Book of ASTMStandards volume information,refer to the standards Document Summary page onthe ASTM website.3Pourbaix,M.,Atlas of Electrochemical Equilibria in Aqueous Solutions,Pergamon Press,1966.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 do not(see manufacturers specifications).A thermometer ofrugged construction is required for soil use,and a stainlesssteel sheathed thermometer is preferred.Metal sheathed ther-mometers come in different lengths,and a length appropriatefor the depth of interest should be chosen.5.Reagents and Materials5.1 During the calibration procedure for the pH meter,standard buffered solutions of known pH are necessary.Thesesolutions,or tablets to make up these solutions,can bepurchased from chemical supply companies or pH equipmentmanufacturers.6.Sampling6.1 By the nature of the measurement,pH is determined fora small volume of soil at each reading,and it is important thatat least three measurements at different locations be made anda simple average calculated.The regions of interest,surf