ASTM_D_7946_-_14.pdf

Designation:D794614Standard Test Method forInitial pH(i-pH)-Value of Petroleum Products1This standard is issued under the fixed designation D7946;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This test method covers procedures for the determina-tion of initial pH(i-pH)in new and in-service lubricants.NOTE1In new and used oils,the constituents that may be consideredto have characteristics influencing the i-pH value include organic andinorganic acids,esters,phenolic compounds,lactones,resins,salts ofheavy metals,salts of ammonia and other weak bases,acid salts ofpolybasic acids,and addition agents such as inhibitors and detergents.“Initial”is used to differentiate from aqueous systems.The analysis isterminated after a defined time interval whenever equilibrium conditions,as known for pH measurements in aqueous systems,are not reached(see3.1.1.2)1.2 This test method is used to indicate relative changes thatoccur in oil during use under oxidizing conditions or due tocontamination by blow-by gases of combustion processes ofbiogases regardless of the color or other properties of thein-service lubricants.Although the initial pH is made underdefinite equilibrium conditions,the test method is not intendedto measure an absolute acidic property that can be used topredict performance of oil under service conditions.No generalcorrelation between corrosion of non-ferrous bearing metalsand initial pH value is known.1.3 The values stated in SI units are to be regarded asstandard.No other units of measurement are included in thisstandard.1.4 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:2D1193 Specification for Reagent WaterD4057 Practice for Manual Sampling of Petroleum andPetroleum ProductsD4177 Practice for Automatic Sampling of Petroleum andPetroleum Products3.Terminology3.1 Definitions:3.1.1 initial pH(i-pH),nthe measure of the hydrogen ion(H+)concentration when a fixed sample amount of lubricationoil is dissolved into a fixed volume of solvent and using aspecified detection system.3.1.1.1 DiscussionThis test method expresses the amountof dissociated acidic components as i-pH of a sample in amixture of toluene and propan-2-ol to which a small amount ofwater has been added.3.1.1.2 DiscussionThe measured i-pH is called initialsince the original definition of the pH-scale depends onaqueous solutions.Its application to organic solutions will notgive stable electrode potential for all types of samples.Apotential reading after a defined time is used in those casesinstead.4.Summary of Test Method4.1 The oil sample is dissolved in solvent mixture and thei-pH value is measured using a glass indicating electrode anda reference electrode or a combination electrode.The meterreadings are measured manually or automatically.5.Significance and Use5.1 New and used petroleum products may contain acidicconstituents that are present as additives,degradation productsformed during service,such as oxidation products or compo-nents formed from combustion gases.The i-pH-value is ameasure of the amount of acidic substances and their aciditydefined under the conditions of test.The i-pH-value is used asa measure of lubricant degradation in service.5.2 The corrosiveness of acidic components depends ontheir concentration and acidity.The i-pH-value is a measure ofthe amount of dissociated acidic components with the potentialof corrosiveness towards metals.5.3 Since a variety of oxidation and blow-by productscontribute to the i-pH-value,this test method cannot be used topredict corrosiveness of oil or blends under service conditionsagainst metallic components.No general correlation is knownbetween i-pH-value and the corrosive tendency of blends oroils toward metals.1This test method is under the jurisdiction of ASTM Committee D02 onPetroleum Products,Liquid Fuels,and Lubricants and is the direct responsibility ofSubcommittee D02.06 on Analysis of Lubricants.Current edition approved July 1,2014.Published August 2014.DOI:10.1520/D7946-14.2For 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.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 6.Apparatus6.1 pH-MeterMeter,a voltmeter or a potentiometer,thatwill operate with an accuracy of 60.005 V and a sensitivity of60.002 V over a range of at least