1、Designation: G 200 09Standard Test Method forMeasurement of Oxidation-Reduction Potential (ORP) ofSoil1This standard is issued under the fixed designation G 200; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revi
2、sion. 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 a procedure and related testequipment for measuring oxidation-reduction potential (ORP)of soil samples
3、removed from the ground.1.2 The procedure in Section 9 is appropriate for field andlaboratory measurements.1.3 Accurate measurement of oxidation-reduction potentialaids in the analysis of soil corrosivity and its impact on buriedmetallic structure corrosion rates.1.4 The values stated in inch-pound
4、units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespon
5、sibility 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:2D 1498 Test Method for Oxidation-Reduction Potential ofWaterE 691 Practice for Conducting an
6、Interlaboratory Study toDetermine the Precision of a Test MethodG3 Practice for ConventionsApplicable to ElectrochemicalMeasurements in Corrosion TestingG15 Terminology Relating to Corrosion and CorrosionTestingG57 Test Method for Field Measurement of Soil ResistivityUsing the Wenner Four-Electrode
7、MethodG 187 Test Method for Measurement of Soil ResistivityUsing the Two-Electrode Soil Box Method3. Terminology3.1 The terminology used in this test method, if not specifi-cally defined otherwise, shall be in accordance with Terminol-ogy G15.3.2 Definitions of Terms Specific to This Standard:3.2.1
8、calibration solution, ncommercially available solu-tion with a stable ORP used for calibrating an ORP measuringsystem (meter and probe).3.2.2 ORPabbreviation for oxidation-reduction potential.3.2.3 ORP electrode (probe), ncommercially availablecombination two-element electrode (probe) specifically d
9、e-signed for the measurement of ORP when used in conjunctionwith a compatible ORP meter.3.2.3.1 DiscussionThe combination probe consists of aplatinum electrode and a reference electrode, which are gen-erally silver/silver chloride. For soil measurements, the probemust be sufficiently robust to withs
10、tand the rigors of themeasurement. Regardless, the often fragile probe should beused with caution to avoid damage and maintain measurementreliability.3.2.4 ORP meter, ncommercially available electricalmeter specifically designed for the measurement of ORP withinternal impedance greater than 10 V. Of
11、ten, the meter iscapable of measuring ORP and pH when used in conjunctionwith the appropriate electrode.3.2.4.1 DiscussionStandard voltmeters or multimeterswith internal impedances typically less than 10 V are notsuitable for soil ORP measurements. Pocket style meters wherethe electrode is an integr
12、al part of the meter housing are alsonot suitable.3.2.5 oxidation-reduction potential (soil), nelectrical po-tential measurement to determine the tendency of a soil totransfer electrons between its chemical species. It is themeasured potential of an inert metal electrode (generallyplatinum) with res
13、pect to a reference electrode such as silver/silver chloride.3.2.5.1 DiscussionA soil with a higher, more positivepotential has an increased tendency to acquire electrons and bereduced (aerobic soil conditions). A soil with a lower positiveor negative potential has an increased tendency to lose elec
14、-trons and be oxidized (anaerobic soil conditions). Soil1This 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, 2009. Published July 2009.2For referenced ASTM
15、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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohock
16、en, PA 19428-2959, United States.oxidation-reduction potential is typically reported in units ofmillivolts (mV) or volts (1 volt = 1000 mV). Sign conventionand reference electrodes conform to Practice G3.3.2.6 redox potential, nsynonym for oxidation-reductionpotential.3.2.7 soil sample, nsample of s
17、oil to be tested. Theminimum (typical) sample size is 1 qt.4. Summary of Test Method4.1 The measurement procedure, as described in Section 9of this test method for determining the ORP of a soil sample,aids in determining the corrosivity of that sample.4.2 Soil ORP can be measured in a field or labor
18、atorysetting.4.3 While the primary purpose of this test method ismeasuring soil ORP, it may also be used as a general indicatorof ORP in groundwater. Test Method D 1498 was specificallydeveloped for accurate ORP measurements of aqueoussamples.5. Significance and Use5.1 Soil ORP, in conjunction with
19、other soil characteristicssuch as electrical resistivity (see Test Methods G57 andG 187), is used to predict corrosion tendencies of buriedmetallic structures (for example, pipelines and culverts. TheORP of the soil is one of many factors that influence structureservice life. Its measurement is used
20、 in the design of newburied structures and in the evaluation of existing buriedstructures.5.2 Soil ORP is a time-sensitive measurement. For anaccurate indication of soil corrosivity, the measurement shouldbe made as soon as practicable after removal of the soil samplefrom the ground.5.3 The user of
21、this test method is responsible for determin-ing the significance of reported ORPmeasurements. ORPaloneshould typically not be used in characterizing the corrosivity ofa particular soil. ORP measurements are appropriate whenevaluating oxygen related reactions.5.4 ORPmeasurements can sometimes be qui
22、te variable andnon-reproducible. This is related, in part, to the generalheterogeneity of a given soil. It is also related to the introduc-tion of increased oxygen into the sample after extraction. Theinterpretation of soil ORP should be considered in terms of itsgeneral range rather than as an abso
23、lute measurement.5.5 ORP measurements can be used to determine if aparticular soil has the propensity to support microbiologicallyinfluenced corrosion (MIC) attack. These measurements canalso be used to provide an indication of whether soil conditionswill be aerobic or anaerobic. Appendix X1 provide
24、s referenceguidelines for general interpretation of ORP data.6. Apparatus6.1 The equipment required for the measurement of soilORP, either in the field or in the laboratory, consists of:6.1.1 ORP Meter.6.1.2 Compatible Two-Electrode Combination ORP Elec-trode (Probe)A main probe and a backup probe a
25、re recom-mended.NOTE 1This test method calls for soil ORP measurements to utilize acommercially available combination electrode (inert metal and referencecombined in one probe). Commercially available ORP combinationelectrodes are generally platinum (inert metal) with silver/silver chloride(referenc
26、e) in a 3.5 to 4 M KCl electrolyte.6.1.3 Operating InstructionsFor ORP meter and ORPelectrode.6.1.4 Calibration Solution(s)For verification of measur-ing system accuracy within the range of expected ORP values.Calibration solutions should remain uncontaminated. Theytypically have a published shelf l
27、ife of no more than 1 year andshould not be used once the shelf life is exceeded. Calibrationsolutions can be obtained commercially or may be mixed in thelaboratory using standard pH buffers (4 and 7) and quinhy-drone.NOTE 2Commercially available ORP calibration solution valuesshould be appropriate
28、for the combination electrode (platinum andsilver/silver chloride) used. Calibration kits utilizing pH buffers andquinhydrone solutions are generally used for the platinum and silver/silverchloride combination electrode.6.1.5 Clear Plastic or Polyethylene Bags1 gal (3.785 L)size is typical, or other
29、 convenient means to collect the soilsample and to compress the sample while under test. One cleanand dry bag should be used for each sample. Do not reuse.6.1.6 Squirt Bottle and Soft ToothbrushBottle with goose-neck (or similar) filled with distilled or deionized water andsoft toothbrush (or simila
30、r) for cleaning ORP electrode aftereach measurement. Cleaning procedures should be in accor-dance with the probe manufacturers written instructions andshould in no way damage the probe or otherwise compromisethe ORP measurement.7. Sampling7.1 Generally, collected soil samples to be tested in thelabo
31、ratory shall be placed in an appropriate sealable containeror polyethylene type bag. This allows containers to be identi-fied by location, date/time sample was collected, etc.7.2 Soil samples shall be representative of the area ofinterest. Where the stratum of interest contains a variety of soiltype
32、s, it is desirable to sample each type separately. Soilsamples to be tested in the laboratory shall be allowed to reachroom temperature, approximately 68F (20C), prior to theORP measurement. Field measurements shall reflect the soilstemperature during testing.8. Calibration and Standardization8.1 Tu
33、rn on the ORP meter in accordance with the metermanufacturers written instructions. Allow sufficient warm-up/stabilization time as specified by the manufacturer.8.2 Check the meter “zero” by shorting the input connectionin accordance with the manufacturers instructions. For a BNCtype connection and
34、probe cable, a paper clip between themeter input center connection and outer shield (ground)typically suffices. With the input shorted, adjust the meter asnecessary in accordance with the manufacturers instructionsso it is no greater than 60.5 mV. A meter that cannot be zeroedto within 60.5 mV may b
35、e faulty and should not be used.G2000928.3 Clean the ORP probe with three changes of distilled ordeionized water or by means of a flowing stream of distilled ordeionized water from a wash bottle or other source.8.4 Calibration Procedure using Commercially AvailableCalibration SolutionWith the cleane
36、d ORP probe connectedto the properly operating ORP meter, place the ORP probeelement in one or more calibration solutions and measure theresponses. For non-adjustment type meters, the ORP readingshould be within 30 mV of the stated calibration solutionpotential for platinum and silver/silver chlorid
37、e probe. Formeters that can be adjusted, adjust the reading in accordancewith the manufacturers instructions to the stated potential forthe calibration solution. Once an initial, stable reading isobtained, remove the probe and place in a fresh sample of thesame calibration solution. The second readi
38、ng should differfrom the first by no more than 10 mV. Rinse the ORP probewith distilled or deionized water between readings if more thanone calibration solution is used, that is, solutions with differentORP values.8.5 Calibration Procedure using pH Buffers and Quinhy-drone Calibration SolutionIna4oz
39、(118.4 mL) beaker, pour0.5 oz (14.8 mL) of pH 7 buffer. Using a wood applicator stickadd quinhydrone until the pH 7 buffer is just oversaturated,stirring frequently. A small amount of the quinhydrone mustremain undissolved. In another beaker, repeat this procedureusing a pH buffer of 4. With the cle
40、aned ORP probe connectedto the properly operating ORP meter, put the probe in thebeaker filled with the 7 buffer/quinhydrone mixture, stir theelectrode gently and let it rest against the side of the beaker.Allow to stabilize (60 s), and note the reading. A properlyperforming platinum and silver/silv
41、er chloride ORP combina-tion electrode should be within about plus or minus 15 mVfrom the following values:Temperature and Reading68F (20C) = +96 mV77F (25C) = +90 mV86F (30C) = +83 mVRinse the ORP electrode and pat dry with a soft tissue. Nowput it in the beaker with the 4 buffer/quinhydrone mixtur
42、e, stirthe electrode gently and let it rest against the side of the beaker.Allow to stabilize (60 s), and note the reading. This readingshould be between +170 mV and +185 mV above the readingin the 7 buffer mixture.8.6 The buffer/quinhydrone mixtures should be freshlymade each time the ORP electrode
43、s are calibrated. Do not storethe mixtures or use after2hastheir values can change withtime.9. Procedure9.1 Remove all stones, pebbles, gravel, roots, twigs andother deleterious material from the soil sample that could breakor abrade the ORP probe sense element. Place the suitablesample in a clear p
44、lastic bag.9.2 Adjust the ORP meter, and calibrate and clean the ORPprobe, in accordance with Section 8. The probe should berinsed in distilled or deionized water after removing from thecalibration solution(s).9.3 Carefully insert the ORP probe vertically into the centerof the soil sample so a minim
45、um of 2 in. (5.08 cm) of the probebarrel (lower portion) is covered. There should be a minimumof 2 in. (5.08 cm) of soil around the probe in all directions.Avoid exerting pressure, since the sense element is fragile andmay break.9.4 Squeeze the bagged soil around the probe barrel andsense element to
46、 assure a tight, complete contact between thesense element and the soil. For “soft” (loose) soils, the probeshould be gently pushed in to the soil sample, lightly compact-ing the soil around the probe tip as necessary.9.5 With the probe stationary, observe the meter readingwaiting until it stabilize
47、s or 2 min, whichever occurs first.Certain ORP meters have a stabilization/lock-hold functionthat can be used as appropriate to capture a stable readingbased on meter-specific processing and algorithms. For this testmethod, readings that vary less than 30 mV over a 2 min periodshould be considered s
48、table with the least positive or mostnegative potential recorded.NOTE 3In certain soils (for example, heavy mucks) there can be aconsiderable range in ORP within a given sample from one measurementlocation to the next. In such instances, it is best to “probe” with theelectrode in a few locations wit
49、hin the sample until the least positive ormost negative potential is determined.9.6 Clean the probe with distilled or deionized water includ-ing removing any lodged material from the sensor area.9.7 Repeat Steps 9.3-9.6 two times inserting the probe atdifferent locations within the sample. For each location, oncethe reading has stabilized, read and record the least positive ormost negative potential measured.10. Report10.1 Report the following information for each soil sampletested:10.1.1 Three ORP measurements.10.1.2 Date and time of measurements.10.1.3 Ambi
