ASTM G200-09
(Test Method)Standard Test Method for Measurement of Oxidation-Reduction Potential (ORP) of Soil
Standard Test Method for Measurement of Oxidation-Reduction Potential (ORP) of Soil
SIGNIFICANCE AND USE
Soil ORP, in conjunction with other soil characteristics such as electrical resistivity (see Test Methods G 57 and G 187), is used to predict corrosion tendencies of buried metallic structures (for example, pipelines and culverts. The ORP of the soil is one of many factors that influence structure service life. Its measurement is used in the design of new buried structures and in the evaluation of existing buried structures.
Soil ORP is a time-sensitive measurement. For an accurate indication of soil corrosivity, the measurement should be made as soon as practicable after removal of the soil sample from the ground.
The user of this test method is responsible for determining the significance of reported ORP measurements. ORP alone should typically not be used in characterizing the corrosivity of a particular soil. ORP measurements are appropriate when evaluating oxygen related reactions.
ORP measurements can sometimes be quite variable and non-reproducible. This is related, in part, to the general heterogeneity of a given soil. It is also related to the introduction of increased oxygen into the sample after extraction. The interpretation of soil ORP should be considered in terms of its general range rather than as an absolute measurement.
ORP measurements can be used to determine if a particular soil has the propensity to support microbiologically influenced corrosion (MIC) attack. These measurements can also be used to provide an indication of whether soil conditions will be aerobic or anaerobic. Appendix X1 provides reference guidelines for general interpretation of ORP data.
SCOPE
1.1 This test method covers a procedure and related test equipment for measuring oxidation-reduction potential (ORP) of soil samples removed from the ground.
1.2 The procedure in Section 9 is appropriate for field and laboratory measurements.
1.3 Accurate measurement of oxidation-reduction potential aids in the analysis of soil corrosivity and its impact on buried metallic structure corrosion rates.
1.4 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation: G200 − 09
StandardTest Method for
Measurement of Oxidation-Reduction Potential (ORP) of
Soil
This standard is issued under the fixed designation G200; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope G187 Test Method for Measurement of Soil Resistivity
Using the Two-Electrode Soil Box Method
1.1 This test method covers a procedure and related test
equipment for measuring oxidation-reduction potential (ORP)
3. Terminology
of soil samples removed from the ground.
3.1 The terminology used in this test method, if not specifi-
1.2 The procedure in Section 9 is appropriate for field and
cally defined otherwise, shall be in accordance with Terminol-
laboratory measurements.
ogy G15.
1.3 Accurate measurement of oxidation-reduction potential
3.2 Definitions of Terms Specific to This Standard:
aids in the analysis of soil corrosivity and its impact on buried
3.2.1 calibration solution, n—commercially available solu-
metallic structure corrosion rates.
tion with a stable ORP used for calibrating an ORP measuring
1.4 The values stated in inch-pound units are to be regarded
system (meter and probe).
as standard. The values given in parentheses are mathematical
3.2.2 ORP—abbreviation for oxidation-reduction potential.
conversions to SI units that are provided for information only
3.2.3 ORP electrode (probe), n—commercially available
and are not considered standard.
combination two-element electrode (probe) specifically de-
1.5 This standard does not purport to address all of the
signed for the measurement of ORP when used in conjunction
safety concerns, if any, associated with its use. It is the
with a compatible ORP meter.
responsibility of the user of this standard to establish appro-
3.2.3.1 Discussion—The combination probe consists of a
priate safety and health practices and determine the applica-
platinum electrode and a reference electrode, which are gen-
bility of regulatory limitations prior to use.
erally silver/silver chloride. For soil measurements, the probe
must be sufficiently robust to withstand the rigors of the
2. Referenced Documents
2 measurement. Regardless, the often fragile probe should be
2.1 ASTM Standards:
used with caution to avoid damage and maintain measurement
D1498 Test Method for Oxidation-Reduction Potential of
reliability.
Water
3.2.4 ORP meter, n—commercially available electrical me-
E691 Practice for Conducting an Interlaboratory Study to
ter specifically designed for the measurement of ORP with
Determine the Precision of a Test Method
internal impedance greater than 10 Ω. Often, the meter is
G3 Practice for Conventions Applicable to Electrochemical
capable of measuring ORP and pH when used in conjunction
Measurements in Corrosion Testing
with the appropriate electrode.
G15 Terminology Relating to Corrosion and Corrosion Test-
3.2.4.1 Discussion—Standard voltmeters or multimeters
ing (Withdrawn 2010)
G57 Test Method for Field Measurement of Soil Resistivity with internal impedances typically less than 10 Ω are not
suitableforsoilORPmeasurements.Pocketstylemeterswhere
Using the Wenner Four-Electrode Method
the electrode is an integral part of the meter housing are also
not suitable.
This test method is under the jurisdiction of ASTM Committee G01 on
Corrosion of Metals and is the direct responsibility of Subcommittee G01.10 on
3.2.5 oxidation-reduction potential (soil), n—electrical po-
Corrosion in Soils.
tential measurement to determine the tendency of a soil to
Current edition approved May 1, 2009. Published July 2009. DOI: 10.1520/
transfer electrons between its chemical species. It is the
G0200-09.
measured potential of an inert metal electrode (generally
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
platinum) with respect to a reference electrode such as silver/
Standards volume information, refer to the standard’s Document Summary page on
silver chloride.
the ASTM website.
3.2.5.1 Discussion—A soil with a higher, more positive
The last approved version of this historical standard is referenced on
www.astm.org. potential has an increased tendency to acquire electrons and be
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G200 − 09
reduced (aerobic soil conditions). A soil with a lower positive 6.1.1 ORP Meter.
or negative potential has an increased tendency to lose elec- 6.1.2 Compatible Two-Electrode Combination ORP Elec-
trons and be oxidized (anaerobic soil conditions). Soil trode (Probe)—A main probe and a backup probe are recom-
oxidation-reduction potential is typically reported in units of mended.
millivolts (mV) or volts (1 volt = 1000 mV). Sign convention
NOTE 1—This test method calls for soil ORPmeasurements to utilize a
and reference electrodes conform to Practice G3.
commercially available combination electrode (inert metal and reference
combined in one probe). Commercially available ORP combination
3.2.6 redox potential, n—synonym for oxidation-reduction
electrodes are generally platinum (inert metal) with silver/silver chloride
potential.
(reference) in a 3.5 to 4 M KCl electrolyte.
3.2.7 soil sample, n—sample of soil to be tested. The
6.1.3 Operating Instructions—For ORP meter and ORP
minimum (typical) sample size is 1 qt.
electrode.
6.1.4 Calibration Solution(s)—For verification of measur-
4. Summary of Test Method
ing system accuracy within the range of expected ORPvalues.
4.1 The measurement procedure, as described in Section 9
Calibration solutions should remain uncontaminated. They
of this test method for determining the ORP of a soil sample,
typically have a published shelf life of no more than 1 year and
aids in determining the corrosivity of that sample.
should not be used once the shelf life is exceeded. Calibration
4.2 Soil ORP can be measured in a field or laboratory
solutionscanbeobtainedcommerciallyormaybemixedinthe
setting. laboratory using standard pH buffers (4 and 7) and quinhy-
drone.
4.3 While the primary purpose of this test method is
measuring soil ORP, it may also be used as a general indicator
NOTE 2—Commercially available ORP calibration solution values
of ORP in groundwater. Test Method D1498 was specifically should be appropriate for the combination electrode (platinum and
silver/silver chloride) used. Calibration kits utilizing pH buffers and
developed for accurate ORP measurements of aqueous
quinhydronesolutionsaregenerallyusedfortheplatinumandsilver/silver
samples.
chloride combination electrode.
5. Significance and Use 6.1.5 Clear Plastic or Polyethylene Bags—1 gal (3.785 L)
size is typical, or other convenient means to collect the soil
5.1 Soil ORP, in conjunction with other soil characteristics
sampleandtocompressthesamplewhileundertest.Oneclean
such as electrical resistivity (seeTest Methods G57 and G187),
and dry bag should be used for each sample. Do not reuse.
is used to predict corrosion tendencies of buried metallic
6.1.6 Squirt Bottle and Soft Toothbrush—Bottle with goose-
structures (for example, pipelines and culverts.The ORPof the
neck (or similar) filled with distilled or deionized water and
soil is one of many factors that influence structure service life.
soft toothbrush (or similar) for cleaning ORP electrode after
Its measurement is used in the design of new buried structures
each measurement. Cleaning procedures should be in accor-
and in the evaluation of existing buried structures.
dance with the probe manufacturer’s written instructions and
5.2 Soil ORP is a time-sensitive measurement. For an
should in no way damage the probe or otherwise compromise
accurate indication of soil corrosivity, the measurement should
the ORP measurement.
be made as soon as practicable after removal of the soil sample
from the ground. 7. Sampling
5.3 The user of this test method is responsible for determin- 7.1 Generally, collected soil samples to be tested in the
ingthesignificanceofreportedORPmeasurements.ORPalone laboratory shall be placed in an appropriate sealable container
shouldtypicallynotbeusedincharacterizingthecorrosivityof or polyethylene type bag. This allows containers to be identi-
a particular soil. ORP measurements are appropriate when fied by location, date/time sample was collected, etc.
evaluating oxygen related reactions.
7.2 Soil samples shall be representative of the area of
5.4 ORPmeasurementscansometimesbequitevariableand interest.Where the stratum of interest contains a variety of soil
non-reproducible. This is related, in part, to the general types, it is desirable to sample each type separately. Soil
heterogeneity of a given soil. It is also related to the introduc- samples to be tested in the laboratory shall be allowed to reach
tion of increased oxygen into the sample after extraction. The room temperature, approximately 68°F (20°C), prior to the
interpretation of soil ORP should be considered in terms of its ORP measurement. Field measurements shall reflect the soils
general range rather than as an absolute measurement. temperature during testing.
5.5 ORP measurements can be used to determine if a
8. Calibration and Standardization
particular soil has the propensity to support microbiologically
8.1 Turn on the ORP meter in accordance with the meter
influenced corrosion (MIC) attack. These measurements can
manufacturer’s written instructions.Allow sufficient warm-up/
alsobeusedtoprovideanindicationofwhethersoilconditions
stabilization time as specified by the manufacturer.
will be aerobic or anaerobic. Appendix X1 provides reference
guidelines for general interpretation of ORP data.
8.2 Checkthemeter“zero”byshortingtheinputconnection
in accordance with the manufacturer’s instructions. For a BNC
6. Apparatus
type connection and probe cable, a paper clip between the
6.1 The equipment required for the measurement of soil meter input center connection and outer shield (ground)
ORP, either in the field or in the laboratory, consists of: typically suffices. With the input shorted, adjust the meter as
G200 − 09
necessary in accordance with the manufacturer’s instructions or abrade the ORP probe sense element. Place the suitable
so it is no
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