1、Designation: G 51 95 (Reapproved 2005)Standard Test Method forMeasuring pH of Soil for Use in Corrosion Testing1This standard is issued under the fixed designation G 51; the number immediately following the designation indicates the year of originaladoption or, in the case of revision, the year of l
2、ast 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 covers a procedure for determining thepH of a soil in corrosion testing. The principle use of the tes
3、tis to supplement soil resistivity measurements and therebyidentify conditions under which the corrosion of metals in soilmay be accentuated (see G 57 78 (1984).1.2 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the us
4、er 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:2E 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 691 Practice for Conducting an Inte
5、rlaboratory Study toDetermine the Precision of a Test MethodG57 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 moresensiti
6、ve 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-imp
7、edance 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
8、 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 rea
9、dilyremoved 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 electrod
10、e 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
11、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 t
12、empera-ture compensation built in as part of the pH electrode, but mostdo 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
13、 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 equ
14、ipmentmanufacturers.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 and1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Meta
15、ls, and is the direct responsibility of Subcommittee G01.10 onCorrosion in Soils.Current edition approved Oct. 1, 2005. Published October 2005. Originallyapproved in 1977. Last previous edition approved in 2000 as G 51 95 (2000).2For referenced ASTM standards, visit the ASTM website, www.astm.org, o
16、rcontact 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, 1966.1Copyright ASTM International, 100 Ba
17、rr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.a simple average calculated. The regions of interest, surface,subsurface, or both, where applicable, must be sampled.7. Calibration and Standardization7.1 Test for LinearityPrior to field use, or periodicallywhen used exte
18、nsively in the field, test the apparatus forlinearity of response. This procedure is as follows:7.1.1 Turn on the instrument, allow to warm up thoroughly,and bring to electrical balance in accordance with the manu-facturers instructions. Before use, clean and rinse the glass andcalomel electrodes in
19、 distilled water.47.1.2 At least two standard buffered pH solutions that spanthe soil pH to be measured are required. From practicalexperience standard solutions of pH 4, 7, and 8 are recom-mended. For the test, the temperature of these solutions shallnot differ from each other by more than 5C. A la
20、boratorythermometer can be used for these measurements.7.1.3 Adjust the temperature compensating dial on the pHmeter to the standard solution temperature.7.1.4 Immerse the electrodes in a small volume of the firstknown standard solution. Now adjust the pH meter to read thisknown pH.7.1.5 Remove the
21、electrodes from the first standard solution,and rinse in distilled water. Immerse the electrodes in thesecond known standard solution and read the pH value. Judgethe system to be operating satisfactorily if the reading obtainedfor the second standard agrees within 60.1 unit of the assignedpH.7.2 Cal
22、ibration of pH MeterCalibrate the pH meter im-mediately before use. If a series of measurements are to bemade, repeat the calibration procedure at intervals of about 30min. Perform the pH meter calibration as follows:7.2.1 Use a standard pH solution in the range of the pH ofthe soil to be tested, if
23、 such information is known beforehand.Otherwise, begin with a standard solution having a pH of 7.Stabilize the temperature of the solution so that it matches thetemperature of the soil to within 10C.7.2.2 Immerse the electrodes in the known standard solutionand calibrate the meter in accordance with
24、 the manufacturersinstructions.8. Procedure8.1 Soil Preparation for pH Determination:8.1.1 Ideally the pH measurement should be made in thefield with the glass electrode contacting the soil at the specificdepth of interest. If the surface soil pH is desired, then the soilcan be broken up if compacte
25、d so as to accept the electrodes.If a subsurface pH is desired, then a boring or an excavationmust be done so that the electrode can be placed in the soil atthe desired depth. The subsurface probe (Fig. 1) is ideal for usewith a boring tool such as hand auger. After boring through thesoil to the dep
26、th of interest, carefully lower the probe into thecavity without further preparation of the soil.8.1.2 Soil samples can be brought to the surface with aboring tool or a post-hole digger, and the measurement made inthe field on the soil thus obtained. This technique is lessdesirable than the probe me
27、thod described in this section.8.1.3 The least desirable pH measurement of soil is thatwhich is based on a soil sample transported to a laboratory forevaluation. However, if this must be done, then make the pHmeasurement as quickly as possible after the soil is taken fromthe field. Place the sample
28、in a clean, airtight, glass containeror plastic bag so that the soil is not in contact with any metal.If the pH measurement is not made within 24 h from the timethe soil sample is taken, then it is recommended that the soilsample be packed in dry ice to retard any change in pH due tochemical or biol
29、ogical reactions. Make the pH measurement onthe soil at room temperature and as received.8.1.3.1 The addition of water to the soil is not recommendedfor any case because some soils are so poorly buffered thatadded moisture will change their pH. However, if a soil isextremely dry with a resistivity e
30、xceeding 106V-cm, a condi-tion not normally encountered, then the pH measurementcannot and should not be made. This situation will manifestitself with a random drifting of the pH meter reading.8.1.3.2 If the soil is frozen, it must be thawed prior tomaking the measurement. Frozen soil manifests itse
31、lf by4Before use, condition new glass electrodes and those that have been stored dryin accordance with the manufacturers recommendations.FIG. 1 Subsurface probeG 51 95 (2005)2random drifting of the pH meter reading and is verified by thesoil temperature measurement.8.2 Determination of pH of Soil:8.
32、2.1 Complete the meter calibration procedure (7.2). Thestandard solution temperature must match the temperature ofthe soil within 10C. Soil temperature can be determined byinserting a metal sheathed thermometer into the soil to thedepth of interest.8.2.2 Clean the electrode surface by washing with d
33、istilledwater.8.2.3 Press the contact area of the glass electrode orcombination electrode, as the case may be, against undisturbedsoil at the location of interest. This step is important, since poorsoil contact or electrode movement can affect stability of themeasurement.8.2.4 The reference electrod
34、e should be placed in contactwith the soil near the glass electrode (this step is not requiredwhen using a combination-type electrode). An electrode sepa-ration of about 30 cm (1 ft) is suggested for surface measure-ments. For subsurface readings, the reference electrode may beplaced on the surface
35、about 30 cm from the bore hole entry.8.2.5 With the electrode(s) in place, set the meter to readpH, allowing 1 or 2 min for equilibrium to be established, thentake the meter reading.8.2.6 After approximately 1 min, repeat the meter reading.In general, the values will agree within 0.2 pH units. If th
36、erange of values is as large as 0.4, then repeat 8.2.3.Iftheproblem persists, check your equipment to verify that it isoperating properly, and check your measurement technique asdescribed in Procedure, Section 8, in this test method. Where asoil is extremely dry, it may not be possible to make a pHm
37、easurement as stated in 8.1.3.1. Where the soil is frozen, itmust be thawed as indicated in 8.1.3.2. Repeat Calibration ofpH Meter (7.2) if equipment malfunction is suspected, whichmay cause erratic pH readings. Finally, if erratic readingspersist, it may be necessary to repeat the measurement at a
38、newlocation in the vicinity of interest.9. Precision and Bias9.1 Interlaboratory Test ProgramAn interlaboratoryround robin was run during the May 1993 ASTM G1 meetinginAtlanta, GA, in which the pH of two soils, randomly selectedfrom the grounds of the hotel, was measured with equipmentbrought to the
39、 meeting by each of the nine participants. Exceptfor the use of only two materials, Practice E 691 was followedfor the design and analysis of the data. Details of the designand analysis of the data are given in the research report.59.2 Test ResultThe precision information given below inunits of pH i
40、s for the comparision of two test results, each ofwhich is an average of three determinations.9.3 Precision:Material A Material BAverage Test Value 4.53 4.2095 % repeatability limit (within lab) 0.27 0.1695 % reproducibility limit (between labs) 0.52 0.22The above terms (repeatability limit and repr
41、oducibilitylimit) are used as specified in Practice E 177. The respectivestandard deviation among test results may be obtained bydividing the above limit values by 2.8.9.4 BiasThe procedure in this test method for measuringpH of soil has no bias because the value of pH is defined onlyin terms of thi
42、s test method.10. Keywords10.1 corrosion of metals in soil; field measurement of pH;measurement of pH; pH of soil; soil pH for corrosion testing;test method for soil pH; underground corrosionASTM International takes no position respecting the validity of any patent rights asserted in connection with
43、 any item mentionedin this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible techni
44、cal committee and must be reviewed every five years andif not revised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideratio
45、n at a meeting of theresponsible technical committee, which you may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harb
46、or 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).5Available from ASTM Headquarters. Request RR: G01-1011.G 51 95 (2005)3
